Essay Childhood Obesity Essay Example for Free

Paper Childhood Obesity Essay Youth Obesity is a medical problem, cause by having abundance body weight just as overabundance of muscle to fat ratio. This is a significant issue for the eventual fate of society particularly since our kids are not getting enough physical exercises on account of innovation and undesirable eating designs. Youngsters who are large are probably going to be stout as grown-ups. Subsequently, this propensities can take our kids to have genuine medical issues, for example, coronary illness, diabetes, stroke, elevated cholesterol, and numerous others medical issues. Nature in which we live is been additionally part of this issue. Youngsters are encircled by unfortunate ads and awful impact from their folks. Refreshments like soft drinks which contains around 400 calories, and undesirable selections of suppers have added to this pestilence cause. Driving our youngsters by giving them instances of how to forestall this sort of issues could be an answer for a superior way of life and future. It is significant that guardians bolster their youngsters by helping them do an eating regimen and physical exercises. In the event that your kid take a gander at you as a genuine case of how to remain sound, they are bound to be and remain dynamic for their own. Rather than leaving them playing computer games, take them to the recreation center and have a fabulous time. Having the option to invest more energy with your children and being a piece of their life, can take them to be better intellectually, yet genuinely. Youth stoutness is been a colossal issue for our general public. Moreover, it is our obligation to help the people in the future by giving them a genuine case of living and love for the individuals who needs the most. Web, www.obesityaction.org, www.healthychildren.org

Girlfight - Overcoming Gender Stereotypes Essay -- Film Movies

Girlfight - Overcoming Gender Stereotypes It's a given that an individual's sex, racial and social roots impact their interest in sports. Specific races and sexual orientations regularly command certain games. African Americans, for instance, will in general rule football and ball, while Caucasians will in general command ice hockey. Similar remains constant for sexual orientation also. Football is a completely male ruled game, while horseback riding, aerobatic and figure skating are substantially more female situated. How and for what reason did these divisions come to fruition? Deciding the starting point of sexual orientation goes past the extent of this paper, anyway one can estimate about how sex orders and generalizations influence one's job in the games field. The film Young lady Fight worked admirably of portraying how one individual managed and defeated sexual orientation generalizations. The film delineates the battle of a secondary school young lady, Diana Guzman, to beat sexual orientation buriers and become a fighter. Her mom having kicked the bucket when she was youthful, she lives with her dad and more youthful sibling, Tiny. The dad powers the child to take boxing exercises since he feels that it is significant that Tiny expertise to shield himself. Anyway Diana can't reveal to her dad that she needs cash to take boxing exercises. Her dad continually bothers her about acting increasingly like a young lady i.e., wearing skirts and giving more thought to her appearance. He doesn't figure it at exceedingly significant that Diana should realize how to safeguard herself too, despite the fact that she clearly lives in a similar perilous neighborhood as her sibling. Truth be told, her dad has very conventional generalizations of male and female. He accepts that the male ought to be the defenderâ€strong, ground-breaking, and prevailing... ... among the principal individuals to break out of these jobs Diana leaves herself open to mock. This can be found in the stressed connections she has with her closest companion and others in her secondary school. In addition, since Diana opposes the sex generalizations she makes some hard memories being acknowledged by the two young men and girlsâ€society doesn't have the foggiest idea how to treat her since she doesn't fit into any of its classifications. Diana is an incredible delineation of the numerous battles of ladies to discover a spot for themselves in sports. On an individual level, resisting cultural generalizations is very troublesome. The buriers that the primary individual must defeat are frequently extraordinary. Anyway once the primary individual separates those buriers, it turns out to be progressively simpler for others to emulate their example. Diana's battle exhibits both how far ladies have come and how far ladies despite everything need to go.

Listening Pathways Bahni Turpin Audiobooks Audiobooks

Listening Pathways Bahni Turpin Audiobooks Audiobooks Bahni Turpin is an American actor and audiobook narrator. She has narrated over a hundred audiobooks,  earning her a place in the Audible Hall of Fame and numerous Audie awards. She was recently named a Golden Voice by AudioFile for her exemplary and prolific career as an audiobook narrator. Shes likely best known for her incredible performance of The Hate U Give by Angie Thomas, which won her an Audie award in 2018. While I can attest to the the brilliance of her narration in that book, its just the tip of the iceberg. Shes brilliant no matter what, whether shes narrating YA romance (The Stars and the Blackness Between Them by Junauda Petrus, The Sun Is Also A Star by Nicola Yoon), a classic of the Harlem Renaissance (Cane by Jean Toomer), or literary fiction (Here Comes the Sun by Nicole Dennis-Benn). If you listen to a lot of audiobooks, you know how useful it is to have a few must-listen narrators in your back pocket. Bahni Turpin is definitely a must-listen for me. If I see her name on an audiobook, I know its going to be an outstanding performance. Ive been known to pick up a book just because she narrates it, and I havent been disappointed yet. If you havent listened to any Bahni Turpin audiobooks and are wondering where to start (there are so many!) use this listening pathway as a guide. Ive highlighted some of my favorites, representing a wide array of genres and styles. These books will give you a good introduction to Turpins talents as a narrator. But I guarantee that you wont want to stop here. Luckily, you dont have to. Start With An Unputdownable YA Novel On the Come Up by Angie Thomas I loved The Hate U Give, but this one really blew me away. Sixteen-year-old Bri just wants to be a rapper, but shes got a lot on her plate, like the fact that her family is suddenly facing homelessness, as well as all the everyday terrors and injustices that pile on top of her as a black teenage girl in America. Theres a reason this book makes such a great introduction to Turpins workâ€"its a book that centers language. Hip-hop is absolutely central, not just to the plot but to Bris identity, her history, her growth. Its a book that was written to be read out loud. Turpin beautifully inhabits teenage Bri, and, as always, nails every other character voice as well. But its her ability to make you really hear, and thus really feel, Bris rhymes, that make this audiobook so extraordinary. Theres a lot of rapping in this novel, and Turpin uses her voice to put it all on the line. All of Bris talent, anger, joy, frustration, energy, and exhaustion comes through loud and clear. Next, Listen To A Brilliant Work Of Historical Fiction The Underground Railroad by Colson Whitehead If youve already read this Pulitzer prizeâ€"winning novel, in which Whitehead brilliantly imagines the Underground Railroad as an actual, physical railroad, thats okayâ€"you can read it again on audio. I promise you wont be sad. Following the journey of Cora as she runs from slavery, this book is a painful read. What Bahni Turpin does is nothing short of astounding. Not only does she inhabit the many accents and dialects of a wide-ranging cast of characters, but somehow, in her voice, she carries the beating heart of the story. This is a book that is hard to read, but that is worth sinking intoâ€"its a book that demands the reader linger, even when lingering is exactly what the reader doesnt want to do. Turpins narration makes that lingering possible. Her voice is so alive and present. She captures the complexity of Coras emotions, making her voice a constant anchor in a story that travels hundreds of miles across hundreds of terrors. Bonus: If you loved  The Underground Railroad, I highly recommend Dread Nation by Justina Ireland. Its a YA novel that takes place in a Civil Warâ€"era America overrun with zombies. Bahni Turpin rocks the narration out of this world. Then Take A Dive Into Some Nonfiction So You Want to Talk About Race by Ijeoma Oluo This is a fantastic, beautifully clear, and accessible book that tackles big questions about systemic racism in America and about how to talk about systemic racism. But I include it here because its also an example of how much great narration can add to an already excellent book. Part of what makes this book so good is its directness. Oluo breaks various issues down into pieces that dont feel overwhelming, but she doesnt simplify. Turpin perfectly captures that particular style in her narration. Its inviting, its personal, its engagingâ€"but shes also got this clear, no-bullshit tone that makes you want to sit up and pay attention. If you, like me, find it hard to get through nonfiction in print, this book is for you. And if youre hesitant to listen to nonfiction on audio, Id recommend this one anywayâ€"its so accessible. Turpin breathes life into the more academic sections (which are already fantastic) and adds another layer of emotion to the personal stories and histories that Oluo recounts. Bonus: If you want to take an even deeper dive into feminist nonfiction, I also recommend Nasty Women by Samhita Mukhopadhyay and The Source of Self Regard by Toni Morrison. Morrison needs no introduction, but it takes a mighty fine narrator to tackle the work of such a literary giant, and Turpin is up to the task. Nasty Women is a collection of essays by a diverse group of women writers on living and fighting in Trump-era America. Turpin brings her usual talents to the audiobook, making these already excellent essays come to life. Finish With A Classic If Beale Street Could Talk by James Baldwin Its always a win-win when a great narrator narrates a classic: if youve never read the book, its a fantastic way to encounter it for the first time. If youve already read it, listening to it on audio is a great way to experience it again. In this novel, Turpin gives life to 19-year old Tish, a young black woman living in New York City in the 1970s. Her boyfriend, Fonny, is imprisoned after being falsely accused of a crime he didnt commit. Tish has just found out shes pregnant, and the book focuses on her family and Fonnys as they try to navigate a deeply racist justice system. Turpins straightforward narration perfectly captures the tone of the novel. Its a painful, heartbreaking book, but a quiet one. Baldwin doesnt hit you over the head with anything. He just illuminates the truths of these characters living their lives in a world that continually tries to erase and imprison them. Turpin beautifully modulates her voice to reflect everything that Tish feelsâ€"her pain, fear, and exh austion, but also her love for Fonny and her family, her determination, her hope. Looking for more Bahni Turpin audiobooks? Shes featured on  these  three lists of awesome narrators (because shes awesome). Sign up for Audiobooks to receive the latest from the audiobooks world. Thank you for signing up! Keep an eye on your inbox.

Design of a global network using wimax - Free Essay Example

Sample details Pages: 31 Words: 9192 Downloads: 6 Date added: 2017/06/26 Category Statistics Essay Did you like this example? Introduction Previous Work Previous work that is closely related to this project involves experience with similar software simulation tool to the one that is used for the completion of the practical part of the project. OPNET simulator was used for the set up of a small network and its division into subnets. The project was completed as a lab assignment in the City University laboratories. It was divided into two main lab sessions each of them explained as follows. The aim of first lab session was to demonstrate the need for implementation of switches in the design of the local area networks. Two 16-station LANs were designed, using a hub for the first one; two hubs and a switch for the second one. The main task of the second laboratory was to demonstrate the basics of designing a network, taking into consideration the users, services location of hosts. Don’t waste time! Our writers will create an original "Design of a global network using wimax" essay for you Create order Using OPNET software, the concepts of networking were easily implemented and tested against the criteria set for satisfactory performance of the network model. The visual representation of the obtained results was used for a detailed analysis of the complexity of the network and its services provided to the users. 1 Technical Overview of the WiMAX Standard 1.1 Spectrum of the Standard The IEEE 802.16 standard is initially designed to provide a flexible, cost-effective, standards-based last-mile broadband connectivity to fill in the broadband coverage gaps that are not currently served by the wired solutions such as DSL. The advanced versions of the standard are aiming to create new forms of broadband services both with high speed and mobility. The IEEE 802.16 standard envisages the use of a wide range of frequencies from 2 to 66 GHz. However, the WiMAX Forum has focused on the use of 2 to 10GHz as the operating frequencies. A graphical representation of the WiMAX spectrum bands is listed below. It includes a comparison with other wireless standards; as well as indication of the regions using the listed bands. WiMAX is a technology that supports the delivery of last-mile wireless broadband access as an alternative to cable and DSL. WiMAX provides fixed, nomadic, portable and ultimately mobile wireless broadband connectivity without the need for line-of-sight with a base station. The design of a WiMAX network is based on the following major principles: Spectrum: to be deployed in both licensed and unlicensed spectra. Topology: supports different RAN topologies. Interworking: autonomous RAN architecture that enables faultless incorporation and interworking with Wi-Fi, 3GPP and 3GPP2 networks and existing IP core networks (e.g. DSL, cable, 3G) using IP-based interfaces. IP connectivity: supports a mix of IPv4 and IPv6 network interconnects. Mobility management: opportunity to expand the fixed access to mobility and broadband multimedia services delivery. WiMAX has defined two MAC classification profiles -the ATM and the IP. They have also defined two primary PHY system profiles: 25 MHz-wide channel (in the US) in the 10-66 GHz range. 28 MHz-wide channel (in Europe) in the 10-66 GHz range. IEEE 802.16 standard is designed to develop as a set of air interfaces standards for WMAN based on a universal MAC protocol but using the physical layer specifications, which one dependent on the range of use and the related regulations. The IEEE 802.16 working group designed a flexible MAC layer and associated physical layer for 10-66 GHz. It is more important to recognize certain factors that make some frequencies more suitable for use in WiMAX systems, both fixed and mobile [1new]. 1.1.1 Path Loss The first important factor is the operating frequency and path loss, which may arise from three basic factors: Free space path loss (FSL) It is defined by using the following formula (Equation 1): FSL=10log(4DFC)2 (1) D=distance from transmitter; F=frequency; C=speed of light. The path losses increase with the square of the frequency. For example, the path loss at 2 GHz frequency band is about 12 dB higher than the band at 0.5 GHz. This effect may be compensated with the antenna size. The increase in FSL with the square of the frequency requires the cell sizes at higher frequencies to be smaller in order to maintain link margins. High frequencies such as 5.8 GHz and above are best suited for line of sight environment. In NLOS conditions, a link at 5.8 GHz would support NLOS customer premises equipment at distances less than a kilometre. Loss due to NLOS operations In urban environments, WiMAX systems operate in a NLOS manner, there is a loss in received signals which depends on the reflected signal strengths. Frequencies above 10 GHz are treated separately. In general, lower frequencies such as 800-2000 MHz have better performance for NLOS than the higher bands. Due to the reception of waves reflected from many objects, the signal strength in most NLOS conditions varies sharply. Ground propagation models are required for path loss analysis and as a result additional margin needs to be given for the loss expected. Hence, multiple antenna techniques with spatial diversity are used to improve the margins in NLOS conditions. Loss caused by in-building penetration This kind of loss depends largely on the type of wall and whether the indoor location has windows. They are not very frequency dependent, at least in the zone of consideration of 2 GHz to 4 GHz. In buildings, losses can vary from 2 dB for a room with windows; to 6 dB for a brick wall. An increase up to 10-12 dB can be expected if the indoor areas were built using metal materials. 1.1.2 Doppler Shift and Coherence Time The second important factor is the Doppler Shift. It is an essential consideration for systems meant for mobile use. In the case of mobile WiMAX systems, which are meant to cater to vehicular speeds of up to 120 km/h, the effects of the Doppler shift are only relevant to the higher frequencies. It is given by the following formula (Equation 2): Ds=(VFC)cos (2) Ds=Doppler shift; V=velocity of user; F=frequency; C=speed of light and =angle between the incoming signal and direction of motion. Frequency shifts need to be less than 10% of the subcarrier spacing in order to maintain correct timing between different mobile stations, which may be operating with a base station. Table 1 represents the relationships between Doppler shift with operating frequency and speed. Frequency (MHz) Doppler shift (Hz) Coherence time (ms) Symbol duration (ms) 800 88.9 11.3 0.2 1600 177.8 5.6 0.2 2400 266.7 3.8 0.2 3400 377.8 2.6 0.2 5800 644.4 1.6 0.2 10000 1111.1 0.9 0.2 Table 1. Coherence time in ms is relevant to time synchronisation of mobile stations with the base station (times are in milliseconds) WiMAX is a multicarrier transmission system based on OFDM. The uplinks in WiMAX (both FDD and TDD systems) operate in a TDMA mode. Each subscriber station is assigned its own time slot and the transmission must take place within the slot. Other devices have the right to transmit in the other slots as allotted in the frame of WiMAX. In other words, the coherence of timing between different devices is important, which must operate in synchronisation. The coherence time is defined as 1Ds and it is inversely proportional to the Doppler shift. An indicator of how the motion is affecting the connection between symbols from different devices, a comparison of coherence time and the symbol time in OFDM. Hence, rather than considering a shift in the centre frequency, which is more likely for single-carrier systems, it is more suitable to consider the same shift in time in the subcarriers. Reducing subcarrier spacing would have adversely affected the Doppler spread, whereas increasing the subcarrier spacing would have reduced the delay spread and consequently intersymbol interference and the data rate. 1.2 Architecture In addition to the standard spectrum analysis and factors that are important for the appropriate selection of correct frequencies, the next part of the report presents the ideas of WiMAX network architecture and specifications. 1.2.1 Backhaul Solutions In telecommunications, thebackhaulportion of the network comprises the intermediate links between thecore networks, orbackbone, of the network and the small sub networks at the edge of the entire hierarchical network. Based on principle explained above, one of the architecture models is based on fixed IEEE 802.16 equipment. Independent of the used version, the technology can be employed in a fixed infrastructure as shown in Fig. 2. In this setting, the deployment of point-to-point connections can span tens of kilometres. WiMAX backhauling is defined by the infrastructure between the WiMAX ASN-GW and the base stations. [2 new] The control of the wireless network towards the client devices, as well as the transport traffic to the operator CSN is aggregated by the base stations. Fig. 3 is another example of how the system may be structured. A critical achievement factor in the deployment of the WiMAX systems is the numerous options the service provider can choose from. As the variety of options for the service providers were mentioned, there is time to focus on a topic much more related to the economic point of a network system. In particular, how the network will be develop in terms of cost and charges and they are agreed upon. A list of the important factors is presented as follows: Fixed costof providing a network infrastructure. Non-fixed cost of connection to the network- typically paid by the user in the form of connection cost. Cost of increasingthe networks capacity. Users who want to reschedule their transmission during peak times should not be charged for the growth of the networks capacity. Incremental cost of sending an extra packet. This cost should be very small or equal to zero without congestion, in view of the fact that the bandwidth of a broadband network is in general a shared resource. Social costdefined as the extra delay which occurs to other users by the transmission of data. Figure 4 shows the cost flow of a WiMAX network. WiMAXpoint to multipoint WiMAXmesh Clients WiMAX MS/RS or WiMAX mesh BS Clients WiMAX MS/RS or WiMAX mesh BS + Wi-Fi router WiMAXcell layout Cell dimensioning Number of WiMAX mesh BS in a cluster Wi-FiCell layout Number of AP in a single WiMAX cell Wi-Fi technology options Dual interface boards (WiMAX/Wi-Fi) Average subscribers per square mile Data traffic assumptions for Wi-Fi users and WiMAX SS/RS (utility/demand function) High QoS VoIP connections for Wi-Fi users and WiMAX SS Average number of data connections per square mile / month Backhaul capacity planning WiMAX BS to ISP WiMAX mesh to WiMAX main BS Wi-Fi routers to WiMAX BS Radio capacity planning Channel size Modulation type Frequency reuse FCC limitations Economic considerations CAPEX: WiMAX BS, Wi-Fi routers, spectrum costs, site preparation, site installation, backbone network equipment OPEX: Operation-administration-management costs, site Leases, equipment maintenance, customer acquisition Network revenue pricing model Time unit fees for Internet subscribers and VoIP subscribers (flat rate pricing) On-demand Service (user-based pricing) Charges: access, usage, congestion and QoS Fig. 4 Cost flow diagram for WiMAX networks 1.2.2 Mobile WiMAX Network Solution The second architecture model that is discussed is that of the mobile WiMAX. It is of great interest and use for the simulation project as it explains the principles behind the simulation that has been set. A WiMAX network consists of an ASN in the lowest level and network itself is in fact, quite intuitive. [1 new] An ASN is comprised of a number of BS connected to an access network, where the ASN is connected to the external networks using ASN-GW. The functions of the ASN are represented in Fig. 5 and include a number of BS, access networks, and access gateways. The functions are discussed in details as follows: Establishing of a connection with the MS, including PHY and MAC layer connectivity. Providing handover and roaming services for the MS within the ASN The user should be provided AAA facilities in conjunction with its home network; the ASN is capable of providing proxy AAA services Relay facilities between the ASN and the external networks should also be present Two functional entities are defined in ASN shown in Fig. 6: The base stationconnects to the MS using the WiMAX PHY air interface. The functions of the BS are to maintain the air interface with the MS, providing the DHCP proxy and to maintain its status idle or active. Fig. 6 is an illustration of a typical WiMAX BS. The uplink and downlink traffic scheduling as well as the QoS enforcement are provided by the BS, as the air interface is managed by the BS. The access service network gateway is the second functional entity. The ASN-GW is the point where traffic from all BS is aggregated for interface to external networks. Usually, the ASN-GW is physically a router. Functions such as QoS management, AAA functionalities are also part of the aggregation point responsibilities. ASN-GW may also have control functions over the BS. The alternative architecture embeds those control functions in the BS. Fig. 7 represents the typical ASN functions. If a comparison between WiMAX network architecture and a cellular network model such as GSM was to be done, similarities can easily be identified. The ASN-GW of the WiMAX network serves the functions that are provided by the SGSN; the access network is recognised as BSC in the GSM model, and the air interface is respectively the BST. Further reading and understanding of the GSM model architecture is recommended for the comparison between the two models. Generally, the WiMAX networks are defined to be much more open in building networks and they have greater level of functionalities in its network entities. Three distinct entities comprise a WiMAX network and its application environment: Network access provider entity that operates one or more ASNs. Typically, it is a WiMAX operator that operates ASN in one or more areas. Network service provider provides connectivity and services to NAPs. NSP needs only to connect to other NSPs and expect all services to be delivered through these connections; NSPs provide connectivity to NAPs via CSN. They are also responsible for providing mobility between their own nodes as well as nodes from other NSPs. Application service providers provide services such as HTTP, video streaming, file download, e-mail, etc. Fig. 8 introduces one more entity of the WiMAX network architecture the connectivity service network. The diagram shows that CSNs have AAA servers which are policy functions for QoS. They provide connectivity to external networks such as managed IP networks or the public internet. Policy functions for each device, user and service on the network as well as the security and authentication frameworks are provided by the AAA servers. Authentication at multiple levels is a key feature of the WiMAX network architecture. Additional key features of the mobile WiMAX network architecture include: Both the core and the radio access networks should be based on IP; protocols based on IEEE802.16 and IETF Open interfaces should be defined by fully-defined reference points Support of fixed network, nomadic, or mobile usage with full migration path to mobility A modular network architecture, which can grow based on usage requirements Integration into different types of IP and non-IP networks (for example: ATM, TDM, and others) Network core architecture is not based on support of any particular service, such as voice, data, or video; as a multi-service core network it supports QoS for each service and each connection QoS is based on both policy functions and enforcement The network architecture is relatively flat, which enables a WiMAX service to start with a single ASN; NWG has defined different ASN profiles for this purpose Inter-networking is supported with 3GPP, 3GPP2, Wi-Fi, or wired networks using IETF protocols. 2 WiMAX Layers After the spectrum and network analysis discussions, it is important to look deeper into WiMAX fundamentals. The following chapter has the aim to introduce the two main layers defined in the WiMAX standard, and to explain the related to them topics such as adaptive modulation, QoS, etc. As the WiMAX belongs to the IEEE 802 group, then the bridging or layer-2 concepts should be mentioned. [2] The addressing is based on MAC addresses and the base station is perceived as a bridge. In order to implement all layer 2 functionalities, the device used should be a bridge-not a router. For the identification for nodes addressing is used; as long as the node is recognized by the network, the address is replaced by use of circuits with circuit identifier. The WiMAX physical layer is based on orthogonal frequency division multiplexing. [2new] OFDM is a transmission scheme that enables high-speed data, video, and multimedia communications. It is used by numerous broadband systems DSL, Wi-Fi, DVB-H, MediaFLO and WiMAX. OFDM is an efficient scheme used for high data rate transmission in a non-line-of-sight or multipath radio environment. The MAC layer is based on connection-oriented principle and it is very similar to the ATM transport protocol, which connection uses a context that describes the mapping between the incoming flows and the underlying QoS. A station registers itself to the base station, negotiates the physical layer characteristics and then can communicate bidirectionally. A service flow defines the negotiated QoS for all matching packets (service-specific sub layer). The QoS can be changed dynamically and it supports extremely well data bursts. Everything is negotiated separately for uplink and downlink. 2.1 Physical Layer Details 2.1.1 OFDM Basics OFDM is a multicarrier modulation scheme that is based on the idea of dividing a given high-bit-rate data stream into several parallel lower bit-rate streams. Each of those streams is then modulated on separate carriers, the so called subcarriers or tones. Multicarrier modulation schemes eliminate or minimize ISI by making the symbol time large enough so that the channel induced delays are an insignificant proportion of the symbol duration. For that reason, in high-data-rate systems, in which the symbol duration is relatively small and it is inversely proportional to the data rate, splitting the data stream into many parallel streams increases the symbol duration of each stream. By doing so, the delay spread is only a small fraction of the symbol duration. OFDM is a spectrally efficient version of multicarrier modulation, in which the subscribers are selected in such way that they are orthogonal to one another over the symbol duration. In that way, it avoids the necessity to have no overlapping subcarrier channels to eliminate ISI. The first subcarrier has to have a frequency such that it has an integer number of cycles in a symbol period. The spacing between adjacent subcarriers (subscriber bandwidth Bsc) has to be defined by the following Equation 3: Bsc=BL (3) Where B is the nominal bandwidth, it is also equal to the data rate. L is the number of subcarriers. This relation ensures that all tones are orthogonal to one another over the symbol period. It can be shown that the OFDM signal is equivalent to the inverse discrete Fourier transform of the data sequence block taken L at a time. Therefore, it is very straightforward to implement OFDM transmitters and receivers in discrete time using IFFT and FFT, respectively. In order to completely eliminate the ISI, OFDM introduces guard intervals between the symbols. For the successful elimination, the guard interval should be larger than the expected multipath delay spread. On the other hand, the introduction of the guard interval implies power wastage and decrease in bandwidth efficiency. The amount of power waste depends on the proportion between the OFDM symbol duration and the guard time. Thus, the larger the symbol period, the smaller the power loss and bandwidth efficiency. Large symbol periods also mean more subcarriers. The size of the FFT in an OFDM design should be chosen carefully as a balance between protection against multipath, Doppler shift, and design cost/complexity. For a given bandwidth, selecting a large FFT size would reduce the subcarrier spacing and increase the symbol time. This is the reason why it makes it easier to protect against multipath delay spread. In contrary, the reduced subcarrier spacing makes the system more vulnerable to intercarrier interference owing to Doppler spread in mobile applications. Careful balancing is required to compete the influence of delay and Doppler spread. 2.1.2 Advantages and Disadvantages of OFDM There are several advantages of OFDM over other solutions for high-speed transmission. Reduced computational complexity: OFDM can be easily implemented using FFT/IFFT, where the processing requirements grow only slightly faster than linearly with data rate or bandwidth. The computational complexity of OFDM can be represented the following Equation 4. O(BlogBTm) (4) Where B is the bandwidth and Tm is the delay spread. This complexity is much lower than that of standard equalizer-based system, which complexity is shown by Equation 5: O(B2Tm) (5) Graceful degradation of performance under excess delay: the performance of an OFDM system degrades gracefully as the delay spread exceeds the value designed for. Greater coding and low constellation sizes can be used to provide fallback rates that are significantly more robust against delay spread. In other words, OFDM is well suited for adaptive modulation and coding, which allows the system to make the best of the available channel conditions. This is in contrast with the abrupt degradation owing to error propagation that single-carrier systems experience as the delay spread exceeds the value for which the equalizer is designed. Exploitation of frequency diversity : OFDM facilitates coding and interleaving across subcarriers in the frequency domain, which can provide robustness against burst errors caused by portions of the transmitted spectrum undergoing deep fades. WiMAX defines subcarrier permutations that allow systems to exploit this. Use as a multi-access scheme : OFDM can be used as multi-access scheme, where different tones are partitioned among multiple users. This scheme is also known as OFDMA and is exploited in mobile WiMAX. The ability to provide fine granularity in channel allocation is also offered by the OFDMA. In relatively slow time-varying channels, it is possible to significantly enhance the capacity by adapting the data rate per subscriber according to the SNR of that particular subcarrier. Robust against narrowband interference Suitable for coherent demodulation : it is relatively easy to do pilot-based channel estimation in OFDM system, which renders them suitable for coherent demodulation schemes that are more power efficient. Apart from the advantages that were already described, there are two main disadvantages: There is a problem associated with OFDM signals having a high peak-to-average ratio that causes nonlinearities and clipping distortion. This can lead to power inefficiencies that need to be countered. The second disadvantage is related to OFDM signals which are very susceptible to phase noise and frequency dispersion, and the design must mitigate these imperfections. This also makes it critical to have accurate frequency synchronization. 2.1.3 OFDMA: Sub channelization Sub channels are formed by the division of available subcarriers into groups. [3new] Fixed WiMAX based on the OFDM-PHY allows a limited form of sub channelization in the uplink only. There are 16 defined sub channels, where 1,2,4,8 or all sets can be assigned to a subscriber station in the uplink. Uplink sub channelization in fixed WiMAX allows SSs to transmit using only a fraction (as low as 1/16) of the bandwidth allocated to it by the BS. The scheme used allows link budget improvements and can be used to improve range performance and/or improve battery life of SSs. A typical 1/16 sub channelization factor provides a 12 dB link budget enhancement. In contrast, mobile WiMAX uses OFDMA-PHY and it allows sub channelization in both the uplink and downlink. Sub channels effectively form the minimum frequency resource-unit, which is allocated by the BS. Therefore, different users may be allocated different sub channels as this is multiple-access mechanism. It is also known as orthogonal frequency division multiple access, which gives mobile WiMAX PHY its name. Sub channels may be formed using wither contiguous subcarriers or subcarriers pseudo-randomly distributed across the frequency spectrum. More frequency diversity is achieved by using distributed sub carriers, which is particularly useful for mobile applications. WiMAX defines several sub channelization schemes based on distributed carriers for both the uplink and downlink. One of them is partial usage of subcarriers, which is mandatory for all mobile WiMAX implementations. The second sub channelization scheme is based on contiguous subcarriers and is also known as adaptive modulation and coding. Although the frequency diversity is lost, band AMC allows system designers to exploit multiuser diversity, allocating sub channels to users based on their frequency response. Multiuser diversity can provide significant gains in overall system capacity, if the system strives to provide each user with a sub channel that maximizes its received SINR. Generally, the contiguous sub channels are more suited for fixed and low-mobility applications. Fig. 9 shows a typical sub carrier structure. FIGURE 9 + explanation 2.1.4 Frame Structure Mobile WiMAX used to support Time Division Duplex only but recently full and half-duplex Frequency Division Duplex support has been added. [4 new] It is mainly because of local restrictions in some areas. A major disadvantage of the TDD is that it needs to be synchronised over the whole system. On the other hand, there are several reasons why TDD usage is preferred. One of them is that the ratio of DL/UL data rates can be adjusted freely. It is in contrast with the FDD where the ratio is always constant and in most cases symmetric. Channel reciprocity is assured by using TDD, which gives better support of link adaptation, MIMO and other closed loop advanced antenna technologies. Whereas FDD requires a pair channel, but TDD can share one for both DL/UL traffic. Additionally, from economical point of view, FDD transceivers are more complex and therefore more expensive to manufacture. For the simulation project that has been set up, FDD mode was used and for this purpose the next part of this chapter explains the FDD frame structure in relation to relaying. For information purposes TDD frame structure is also discussed. 2.1.4.1 Frame Format for FDD The FDD mode does not provide guard times and parallel transmissions in DL and UL. [5new] The BS always sets up the master frame, in other words, it generates the timing schedule for the next period. The process begins with synchronisation pilots, a broadcast channel and a random/contention access channel; a few regular frames follow, but this very much depends on the technology used. Some of the frames are reserved for the second hop(s) by the BS, which are later used in the responsibility of the relay(s). A term called stealth relaying is used when the BS does not even distinguish between relays and ordinary SSs. It is preferable to use centrally and relay-aware BS controlled resource allocation for further systems. Interleaved multihop frames are incorporated by modern multihop systems, where frames for the first and second hops alternate in time and they are all controlled by the BS. The smallest granularity resource unit is a chunk, 100 chunks form a basic frame. Symbols, on the other hand, are used for signalling and synchronization, but they are out of focus here. They are shown in grey in Fig. 10(a) and the only impact here is the overhead-resources not available for data throughput. DL and UL transmissions happen simultaneously in the same frame raster. There are 3 ways of integrating relaying (the frames used for the second hop or beyond: Time Domain Relaying: resources for hop1 and hop2 are separated in time (sequentially) Frequency Domain Relaying: recourses for hop1 and hop2 are separated in frequency (neighbour band) OFDMA Domain Relaying: recourses for hop1 and hop2 are separated in frequency (sub channels) As OFDMA was already introduces as topic earlier, it is important to describe what its advantages are over OFDM relaying. First one is that the resources can be subdivided in a finer granularity than it is possible using OFDM only. Fig. 10(b) shows that first-hop transmissions are always treated the same way. They only occupy the required resources for their traffic and there is not waste due to completely assigned but incompletely filled frames. In the UL several SSs share the full bandwidth and each of them transmits on a subset of sub channels, with a guard band between them. The BS or RN coordinates the orthogonal interference-free use of these sub channels by the SSs. OFDMA subdivision in the DL is also available, where the BS and RN send on distinct sub channels, but using sufficient guard band. Even if the side band power is below the signal level, this can cause serious interference trouble at the SS when receiving the useful signal from a far dist ant BS and the interference from the RN nearby. In this case, interference mitigation strategies in the BS are helpful. This also leads to proper association decisions for intra-cell handover. The handover concept is introduced later in the report and the fundamental principles are discussed in details. 2.1.4.2 TDD Frame Structure Mobile WiMAX TDD mode allows the DL and UL transmissions to share the same transmission medium. [6new] Fig. 11 shows the typical structure of TDD frame. Transmission and reception cannot occur simultaneously, due to the prohibitively complex filtering, which is essential for the separation of UL and DL. Something more, in order to avoid interference between the signals transmitted from the BS and other SSs, time gaps such as the transmit/receive transition gap or receive/transmit transition gap are needed. The TTG allows sufficient time for the BS to switch from transmit to receive mode. RTG provides time for the BS to switch from receiving to transmitting. Parameters that form the size of the time gaps are: cell radius, the transceiver turnaround time and other implementation constraints. 2.1.5 Adaptive Modulation and Coding in WiMAX It is inevitable to mention the modulation and coding techniques that are employed by the WiMAX standard. Their principles are important as later in the report; those modulations are used for the simulation purposes and are base on the discussion how the SSs can be connected to the BSs and what effect the modulation and coding have on the connectivity. WiMAX supports a variety of modulation and coding schemes. [3 new]This allows the scheme to change on a burst-by-burst basis per link, depending on channel conditions. The SS can provide feedback on the DL channel quality to the BS by using channel quality feedback indicator. For the UL, the BS can easily estimate the channel quality, based on the received signal quality. The BS scheduler can take into account the channel quality for each users UL and DL and assign a modulation and coding technique that maximizes the throughput for the available SNR. Adaptive modulation and coding increases the overall system capacity, as it allows real-time trade-off between throughput and robustness on each link. Table 2 lists various modulation and coding scheme used by WiMAX. In the DL, QPSK, 16 QAM, and 64 QAM are mandatory for both fixed and mobile WiMAX. 64 QAM is optional in the UL. FEC coding using conventional codes is mandatory as well. Conventional codes are combined with an outer Reed-Solomon code in the downlink for OFDM-PHY. Turbo codes and low-density parity check codes are optionally supported at a variety of code rates as well. There are 52 combinations of modulation and coding techniques that are defined in WiMAX as burst profiles. Downlink Uplink Modulation BPSK, QPSK, 16 QAM, 64 QAM; BPSK optional for OFDMA-PHY BPSK, QPSK, 16 QAM; 64 QAM optional Coding Mandatory: convolution codes at rate , 2/3, , 5/6 Mandatory: convolution codes at rate , 2/3, , 5/6 Optional: convolution turbo codes at rate , 2/3, , 5/6; repetition codes at rate ,1/3, 1/6, LDPC, RS-Codes for OFDM-PHY Optional: convolution turbo codes at rate 1/2., 2/3, , 5/6; repetition codes at rate , 1/3, 1/6, LDPC Table 2. Modulation and Coding supported by WiMAX. 2.2 MAC Layer Details The second important layer of the WiMAX standard is the MAC medium access control. In general, the 802.16 MAC is designed to support multipoint-to-multipoint architecture, where a centrally located BS handles multiple independent sectors simultaneously. [7 new] On the downlink, data to SSs are multiplexed in TDM fashion. On the contrary, the uplink is shared between SSs in TDMA fashion. IEEE standard 802.16 defines 2 general service-specific convergence sub-layers for mapping services to and from 802.16 MAC connections. The first one is the ATM convergence sub-layer, which is defined for ATM services. The second one is the packet convergence layer, defined for mapping packet services such as IPv4, IPv6, Ethernet, and virtual local area network. There are 3 primary tasks of the sub-layer: To classify service data units to the correct MAC connection Preserve or enable QoS Enable bandwidth allocation Depending on the type of service, the mapping takes a range of forms. Additionally to the basic convergence sub-layer tasks, the layers can also perform more complicated functions payload header suppression and reconstruction to enhance air link efficiency. As it was already mentioned, the 802.16 MAC is connection-oriented and all services, including inherently connectionless services, are mapped to a connection. Thus, it provides a mechanism for requesting bandwidth, associating QoS and traffic parameters, transporting and routing data to the appropriate convergence sub-layer; as well as all other actions associated with the contractual terms of service. Connections are referenced with 16-bit connection identifiers and may require continuously granted bandwidth or bandwidth on demand. Every SS has a standard 48-bit MAC address, which serves mainly as an equipment identifier. The primary addresses used during operation are the CIDs. Three management connections are assigned to the SS when entered the network. These connections reflect the three different management connections in each direction: Basic connection- used for the transfer of short, time-critical MAC and radio link control massages. Primary management connection- used to transfer short longer, more delay-tolerated messages (e.g. those used for authentication and connection setup). Secondary management connection- used for the transfer of standards-based management messages, such as DHCP, TFTP, and SNMP. Apart from the management connections, transport connections for the contracted services are also allocated to the SSs. Transport connections are unidirectional and facilitate different DL and UL QoS and traffic parameters; they are typically assigned to services in pairs. Additional connections for other purposes may also be reserved by MAC: Contention-based initial access Broadcast transmissions in the DL, as well as for signalling broadcast connection-based polling of SS bandwidth needs Multicast, rather than broadcast, connection-based polling. SSs may be instructed to join multicast polling groups associated with these multicast polling connections. 2.2.1 MAC PDU Construction and Transmission As it was already discussed, the MAC sub-layer is independent of the higher-layer protocol and performs such operations as scheduling, [3 new] ARQ, bandwidth allocations, modulation and code rate selection. The SDUs arriving from the higher-layer to the sub-layer are assembled to create the MAC PDU, which is the basic payload unit handled by the MAC and PHY layers. Multiple SDUs can be carried on a single MAC PDU, or a single SDU can be fragmented to be carried over multiple MAC PDUs; this is entirely based on the size of the payload. When an SDU is fragmented, the position of each fragment within the SDU is labelled by a sequence number. The usage of the sequence number is to ease assembling of the SDU from its fragments in the correct order at the receiver MAC layer. Multiple MAC PDUs destined to the same receiver can be concatenated and carried over a single transmission opportunity or data region. This is purely done to use the PHY resources more efficiently. This is shown in Fig. 12. For non-ARQ-enabled connections, each fragment of the SDU is transmitted in sequence. For ARQ-enabled connections, the SDU is first divided into fixed length ARQ blocks. Each ARQ block has its own block sequence number. ARQ BLOCK-SIZE parameter is used by the BS for each CID to specify the length of the block. The length of the SDU should be integral multiple of the ARQ BLOCK-SIZE, if it is not the last ARQ block is padded. Once the SDU is portioned into ARQ blocks, the partitioning remains until all the ARQ blocks have been received and acknowledged by the receiver. After the partitioning, the SDU is assembled into MAC PDUs in a normal fashion as it is shown in Fig. 12. For ARQ-enabled connections, the fragmentation and packing sub head er contains the BSN of the first ARQ block following the sub header. The ARQ feedback from the receiver comes in the form of ACK indicating successful reception of the ARQ blocks. The feedback is sent either as a stand-alone MAC PDU or piggybacked on the payload of a regular MAC PDU. ARQ feedback can be two types: Selective:indicates that the ARQ block has been received without errors Cumulative:indicates that all blocks with sequence number less than or equal to the BSN have been received without error. Each MAC PDU consists of a header followed by a payload and cyclic redundancy check. The CRC is based on IEEE 802.3 and is calculated on the entire MAC PDU; the header and the payload. Two types of PDUs (Fig. 13) are introduced, and each of them has different header structure: Generic PDU- used to carry data and MAC-layer signalling massages. It starts with a generic header, which structure is shown on Fig.13, and then followed by a payload and a CRC. The different information elements in the header of a generic MAC PDU are shown in Table 3. Bandwidth PDU- used by the SS to inform the BS that more bandwidth is needed in the UL, due to pending data transmission. This type of PDU consists of bandwidth-request header, and there is no payload or CRC. The header information elements are shown in Table 4. Field Length (bits) Description HT 1 Header type (set to 0 for such header) EC 1 Encryption control (0= payload not encrypted; 1= payload encrypted) Type 6 Type ESF 1 Extended sub header field (1 = ES present; 0 = ES not present) CI 1 CRC indicator (1 = CRC included; 0 = CRC not included) EKS 2 Encryption key sequence (index of the traffic encryption key and the initialization vector used to encrypt the payload) Rsv 1 Reserved LEN 11 Length of MAC PDU in bytes, including the header CID 16 Connection identifier on which the payload is to be sent HCS 8 Header check sequence Table 3, Generic MAC header fields Field Length (bits) Description HT 1 Header type (set to 1 for such header) EC 1 Encryption control (set to 0 for such header) Type 3 Type BR 19 bandwidth request (the number of bytes for uplink bandwidth request by the SS for the given CID) CID 16 Connection identifier HCS 8 Header check sequence Table 4. Bandwidth request MAC header fields Once a MAC PDU is constructed, it is handed over to the scheduler, which schedules the MAC PDU over the PHY resources available. The scheduler checks the service flow ID and the CID of the MAC PDU, which allows it to gauge its QoS requirements. Based on the QoS requirements of the MAC PDUs belonging to different CIDs and service flow Ids, the scheduler determines the optimum PHY resource allocation for all the MAC PDUs, on a frame-by-frame basis. 2.2.2 DL and UL MAP WiMAX MAC supports both TDD and FDD modes. [7 new] In FDD, both continuous and burst downlinks are supported. Continuous downlinks allow for certain robustness improvement techniques for example interleaving. Burst downlinks allow the use of more complex robustness and capacity enhancement techniques, e.g. subscriber level adaptive burst profiling and advanced antenna systems. The MAC builds the DL sub frame, starting with a frame control section. The frame control section contains the DL-MAP and UL-MAP messages. They indicate PHY transitions on the downlink; bandwidth allocations and burst profiles on the uplink. The DL-MAP is applicable to the current frame and is always at least 2 FEC blocks long. In both TDD and FDD modes, the UL-MAP provides allocations starting no later than the next downlink frame. If the processing times and the round trip delays are observed, then the UL-MAP may allocate starting in the current frame. The minimum time between receipt and applicability of the UL-Map for an FDD system is shown in Fig. 14 2.2.3 Authentication, Registration and Security Another important factor of the MAC protocol is that it manages procedures such as authentication, registration and security. Each of the SS holds two certificates: factory installed X.509 digital certificate and certificate of manufacturer. Those certificates are sent from the SS to the BS in the Authorization Request and Authentication Information messages. The certificates establish a link between the 48 bit MAC address of the SS and its public RSA key. The network is able to identify the SS using the certificates, and afterwards it can check the authorization of the SS. If the SS is authorized to join the network, BS will respond with an Authorization Reply containing an Authorization Key. The Authorization Key is encrypted with the SSs public key and used to secure further transactions. When the authorization is successful, the SS will be registered with the network. This will establish the secondary management connection of the SS and determine capabilities related to connection setup and MAC operation. The version of IP used on the secondary management connection is also determined during registration. WiMAXs privacy protocol is based on the Privacy Key Management protocol. It is based on the DOCSIS BPI+ specification, but has been modified to fit seamlessly into the MAC protocol. It accommodates stronger cryptographic methods, such as the Advanced Encryption Standard. PKM is build around the concept of security associations. SA is a set of cryptographic methods and the associated keying material. It contains the information about which algorithms to apply, which key to use, and so on. Every SS establishes at least one SA during initialization. Apart from the basic and primary management connections, all other connections are mapped to an SA either at connection setup time or dynamically during operation. For the traffic encryption, the PKM uses the Data Encryption Standard, running in the cipher block chaining more with 56-bit keys. The CBC initialization vector depends on the frame counter and differs from the frame to frame. To reduce the number of computationally intensive public key operations during normal operation, the transmission encryption keys are exchanged using 3DES with a key exchange key derived from the authorization key. The PKM protocol messages are authenticated using the Hashed Message Authentication Code protocol with SHA-1. Message authentication in essential MAC functions, such as the connection setup, is provided by the PKM protocol. 2.2.4 Services and Parameters The last part of the MAC layer is the services and their parameters. It is an essential part of the standard implementation and this part of the chapter lists all QoS that are provided by the WiMAX family. Scheduler is the one that controls the scheduling services for the standard and handles the mechanisms supported by the MAC to transport data. [9 new] Each connection is associated with a single data service. Data services are associated with a set of QoS parameters that define their behaviour. Two data parameters are used for the management of the parameters: dynamics service addition and dynamic service change. Five different services are supported: unsolicited grant services, real-time polling services, extended real-time polling services non-real-time polling services, and best effort. Table 5 lists the application and specification for each of those services. [10 new] QoS Category Applications QoS Specifications UGS VoIP Maximum sustained rate Maximum latency tolerance Jitter tolerance rtPS Streaming audio and video Minimum reserved rate Maximum sustained rate Maximum latency Traffic priority ertPS Voice with activity detection (VoIP) Minimum reserved rate Maximum sustained rate Maximum latency tolerance Jitter tolerance Traffic priority nrtPS File transfer protocol Minimum reserved rate Maximum sustained rate Traffic priority BE Data transfer, web browsing, etc. Maximum sustained rate Traffic priority Table 5. Mobile WiMAX applications and QoS UGS- supports real-time data streams. Each stream is of fixed-size data packets issued at periodic time intervals. It is particularly useful for applications such as VoIP without silence suspension. Mandatory service flow parameters are: maximum sustained rate, maximum latency tolerance, jitter tolerance and request/transmission policy. If the policy is present, the minimum reserved traffic rate parameter will be the same value as the maximum sustained traffic rate parameter. rtPS- supports real-time data streams, each of which is issued at periodic intervals. It is useful for MPEG videos and consists of variable-size data packets. Compulsory parameters are: minimum reserved rate, maximum sustained rate, maximum latency, traffic priority, and again request/traffic policy. ertPS- it is a combination of USG and rtPS. [4new] ertPS is designed to support VoIP with activity detection, which means that when there is a silence period in the communication, the bandwidth can be saved by downsizing the packets length. The maximum sustained traffic rate, which defines the default size of the allocations, may be changed with ertPS. nrtPS- used for delay-tolerant data streams, which consist of variable data packets. Minimum data rate is required as it used the FTP. Flow parameters are: minimum reserved rate, maximum sustained rate, traffic priority, and request/transmission policy. BE is used to support data streams for which no minimum service level is required and therefore may be handled on a space-available basis. Associated parameters are: maximum sustained rate, traffic priority, and request/transmission policy. 3 Handovers The aim of the next chapter is to introduce the term handovers and to explain their importance for the WiMAX standard features. Handovers are very vital part of a wireless technology.[11new] When an SS moves between different BSs, the connection should also move and in order to do so a seamless handover should be performed. By the term seamlessness, it defines the necessity to maintain current session, QoS and service level agreements during and after the handover. In other words, the seamless handover should not be noticeable by the user; however, this very much depends on the kind of services the user is requiring. With real-time applications, such as videoconferencing or streaming media, s slight decrease of the connection may be observed. In contrast, while a user is browsing a website or transfers files, they will most probably not notice any change in their connection. There are two crucial factors related to the handover procedure: the latency and the packet loss. They have to be as small as possible to make the handover seamless. Several reasons why and when a handover should be initiated are listed below: SS current position and velocity high velocity may lead to different handover decisions Link quality in case a BS is overloaded, the network can decide to relocate some of the SSs Conserving battery power for battery saving purposes, an SS may chose to switch to a closer station and be energy efficient Context and requirements if an SS requires different type of service, it may be necessary to change BS. Handovers have a significant effect on the performance of channel allocation algorithms. At high traffic loads, the majority of forced call terminations are as a result of the lack of channels available for handover rather than to interference. This is a major problem in microcellular systems, where the rate of handovers is considerably higher than that in normal cellular systems. There are a number of solutions to reduce the performance penalty caused by handovers. One of them is to reserve some channels solely for handovers, generally referred to as cut-off priority or guard channel schemes. However, this solution reduces the maximum amount of carried traffic or system capacity and hence yields increased new call blocking. Algorithms that give higher priority to requests for handovers than to new calls are called Handover prioritization schemes. Guard channel schemes are therefore a type of handover prioritization arrangement. Another type of handover prioritization is constituted by handover queuing schemes. Normally, when an allocation request for handoff is rejected, the call is forcibly terminated. By allowing handover allocation requests to be queued temporarily, the forced termination probability can be reduced. The simplest handover queuing schemes use a First-In First-Out (FIFO) queuing regime. A non-pre-emptive priority handover queuing scheme in which handover requests in the queue that are the most urgent ones are served first. A further alternative to help reduce the probability of handover failure is to allow allocation requests for new calls to be queued. New call allocation requests can be queued more readily than handovers because they are less sensitive to delay. Handover queuing reduces the forced termination probability owing to handover failures but increase the new call blocking probability. New call queuing reduces the new call blocking probability and also increases the carried teletraffic. This is because the new calls are not immediately blocked but queued, and in most cases they receive an allocation later. Handovers have a significant effect on the performance of channel allocation algorithms. At high traffic loads, the majority of forced call terminations are as a result of the lack of channels available for handover rather than to interference. This is a major problem in microcellular systems, where the rate of handovers is considerably higher than that in normal cellular systems. There are a number of solutions to reduce the performance penalty caused by handovers. One of them is to reserve some channels solely for handovers, generally referred to as cut-off priority or guard channel schemes. However, this solution reduces the maximum amount of carried traffic or system capacity and hence yields increased new call blocking. Algorithms that give higher priority to requests for handovers than to new calls are called Handover prioritization schemes. Guard channel schemes are therefore a type of handover prioritization arrangement. Another type of handover prioritization is constituted by handover queuing schemes. Normally, when an allocation request for handoff is rejected, the call is forcibly terminated. By allowing handover allocation requests to be queued temporarily, the forced termination probability can be reduced. The simplest handover queuing schemes use a First-In First-Out (FIFO) queuing regime. A non-pre-emptive priority handover queuing scheme in which handover requests in the queue that are the most urgent ones are served first. A further alternative to help reduce the probability of handover failure is to allow allocation requests for new calls to be queued. New call allocation requests can be queued more readily than handovers because they are less sensitive to delay. Handover queuing reduces the forced termination probability owing to handover failures but increase the new call blocking probability. New call queuing reduces the new call blocking probability and also increases the carried teletraffic. This is because the new calls are not immediately blocked but queued, and in most cases they receive an allocation later. There are two main types of handovers: horizontal (handovers within the same technology) and vertical (handovers between different network access technologies). Horizontal handovers- are Layer-2 handovers and are also referred to as micro-mobility. In this case only the BS is changed and the IP-information is kept the unchanged. This kind of handover causes small latency and low packet loss Vertical handovers- Layer-3 handovers and are also referred as macro-mobility. It changes the IP-connection point, and as a result the IP information is changed as well. As a result, significant latency and packet loss are observed. 3.1 Handover Types WiMAX specification supports three types of handovers: Hard Handover, Fast Base Station Switching, and Macro Diversity Handover.[4new] HHO is compulsory, whereas the other two are optional. The WiMAX forum has been working on the enhancement of the HHO techniques to achieve handovers in less than 50 milliseconds. 3.1.1 Hard Handover HHO is a procedure that changes the serving BS using a break-before-make approach. Effectively, this means that the connection to the old BS is broken before the new BS is connected to the SS. Using this approach, excess signalling traffic is avoided during the handover procedure, however, the time before the connection is again in normal operation may be longer. While the SS is connected to a BS, it listens to the link-layer messages for another BS, which periodically broadcasts neighbour advertisement messages. The advertising messages are used for network identification and recognition of the services that are provided. Facts about the signal quality from a neighbouring BS are included in the messages. In case a better BS is not found, the SS stores the information that has been received for future handovers. Fig. 15 illustrates a typical scenario of HHO, when a moving user reaches the point where the signal level is of better quality with another BS. A further decision criterion has to be set up to avoid constant handover back and forth between BSs. 3.1.2 Macro Diversity Handover When MDHO is supported by MS and by BS, the Diversity Set (or in some cases it is called Active Set) is maintained by SS and BS. Diversity set is a list of the BSs, which are involved in the handover procedure. Diversity set is defined for each of SSs in network. SS communicates with all BSs in the diversity set (Fig. 16). For downlink in MDHO, two or more BSs transmit data to SS such that diversity combining can be performed at the SS. For uplink in MDHO, MS transmission is received by multiple BSs where selection diversity of the received information is performed. The BS, which can receive communication among SSs and other BSs, but the level of signal strength is not sufficient is noted as Neighbour BS. While the SS is moving towards the neighbouring BS, at some moment the signal from the neighbouring BS becomes strong enough and the BS can be included in the active set. The factor that is used to measure the inclusion/exclusion of the BS is the long term CINR. There are two ways that the SS uses to monitor DL control information and broadcast messages: It listens only to the anchor BS for burst allocation information of other BSs in the active set Listens to all BSs in the active set. By listening to all active set BSs, a DL/UL-MAP message from any BS may include information for other BSs. The MDHO is started when the SS decides to receive/transmit from multiple BSs at the same time. For DL traffic, two or more BSs transmit the data to the SS, which performs diversity combining. For the UL traffic, the traffic generated by the SS is received by all BSs in the active set and selection diversity is then performed. Interestingly, the MDHO requires all BSs to communicate on synchronised basis, because of the frames sent by the BSs at a certain time frame have to be received by the SS within the specific prefix interval. The BSs frame structure have to be synchronised and the frequency assignments to have the same values. Furthermore, the same set of CIDs and MAC/PHY PDUs sent to the SS have to be generated by the BSs. The encryption information and network entry exchanged information have to be shared between the SS and the BSs as well. 3.1.3 Fast Base Station Switching In FBSS, the SS and BS diversity set is maintained similar as in MDHO. SS continuously monitors the base stations in the diversity set and defines an Anchor BS. Anchor BS is only one base station of the diversity set that MS communicates with for all uplink and downlink traffic including management messages (Fig. 17). This is the BS where SS is registered, synchronized, performs ranging and there is monitored downlink channel for control information. The anchor BS can be changed from frame to frame depending on BS selection method, which means each frame can be sent via different BS in diversity set. Generally, the requirements for the FBSS are the same as the ones of MDHO without the demand for the same CIDs and MAC/PHY PDUs.

An Examination Of Post Event Information ( Pei ) - 1545 Words

Another form of Post-event information (PEI) is conformity, in the event that an individual witnesses a crime committed there is always the potential that there are co-witnesses that also witnessed the crime, while an increase in witnesses may hold some positives there is the potential for conformity. Conformity takes place when one witnesses’ memories of a past event become more like another person’s described memories of the same event (Kieckhaefer, J.M. Wright, D.B., 2015, pg. 462). Co-witnesses often alter their memory reports to coincide with other witnesses’ reports (Goodwin K.A. et al., 2013, pg. 91). If a co-witness is a friend or family then an individual is even more likely to conform to their views than they would be if the co-witness was a stranger. Kieckhaefer and Wright also found evidence that another factor that increases a witnesses memory conformity is if the co-witness is likable(Kieckhaefer, J.M. Wright, D.B., 2015, pg. 463). There have been multiple studies conducted where researchers use confederates, research helpers used to feed unknowing participants information, to determine whether or not participants will conform to the confederate’s reports (Goodwin, K.A. et al., 2013, pg. 91). Furthermore, witnesses are more likely to alter their views when they are motivated to avoid deviating from the group. Therefore, if a group of other individuals pressure a witness they are likely to alter their experience to fit with others (Goodwin, K.A. et al.,Show MoreRelatedEyewitness Testimony : An Important Area Of Research2072 Words   |  9 Pagesepisodic memories are memories of past events that are situated in a specific time and place (Thorley, 2013). Furthermore, having participant’s study and recollect stimuli such as word lists, stories, and mock crimes can help assess episodic memory. Furthermore, eyewitness testimony is an important area of research in cognitive psychology and human memory. Juries tend to pay close attention to eyewitness testimony and generally find it a reliable source of information (Simply Psychology, 2009). HoweverRead MoreThe Influence of Lifestyle and Money Attitude on Purchase Decisions: the Moderating Effect of Marketing Stimulation and Personal Value11754 Words   |  48 PagesRESEARCH AND TECHNOLOGY ISSUE 2, VOLUME 2 (APRIL 2012) ISSN: 2249-9954 1. Introduction Following the changes that take place over time, people’s materialistic demands and desire for materialistic enjoyment have increased continuously in our modern information and technologically advanced era. Lifestyle has become an important variable in the drawing up of marketing strategies. Each product has a different intended market and, hence, differentiation through market segmentation is necessary in order toRead MoreAccounting Information System Chapter 1137115 Words   |  549 PagesCHAPTER 1 ACCOUNTING INFORMATION SYSTEMS: AN OVERVIEW SUGGESTED ANSWERS TO DISCUSSION QUESTIONS 1.1 The value of information is the difference between the benefits realized from using that information and the costs of producing it. Would you, or any organization, ever produce information if its expected costs exceeded its benefits? If so, provide some examples. If not, why not? Most organizations produce information only if its value exceeds its cost. However, there are two situationsRead MoreSucess Factors in Merger and Acquisition38351 Words   |  154 PagesSà ¶derholm and Professor Ralf Mà ¼ller for their initial guidance by commenting on our research proposal and providing us with some industry contacts. We would like to thank all interviewees and respondents who contributed their valuable time and useful information to this study. Last but not least, our classmates are entitled a ‘thank you’ for challenging our research study and providing us with valuable suggestions. Umeà ¥, January 2008. ABSTRACT Mergers and acquisitions (MA) in the corporate world

The baby boomer in the midst of the economic crisis Free Essays

Most of the baby boomer generation were imbibed with the stereotype perception on the facets of work, employment and success. In a typical scenario, that â€Å"best† schedule would connote that a baby boomer would go to work on a regular schedule, 8-5, working from Monday to Friday schedule. Most of the time would be spent in the office, taking a daily commute to and from the office, with some time being taken by overtime, some work to be done on the weekends, and some other tasks to be accomplished at home. We will write a custom essay sample on The baby boomer in the midst of the economic crisis or any similar topic only for you Order Now Success was also easily defined, with the person attaining the highest position in the corporate ladder becoming the epitome of that standard of success (Brad Harrington, Douglas Hall 98). Many of the people, baby boomer and others, believe that the current recession is about to end and that more prosperous times are about to return are, what observers state, is sadly suffering from a near sighted view of the present economic crisis. In reality, since the peaking of the 2005 United States housing crisis, the continuing barrage of the sub-prime financial crisis in 2007,and the resulting economic slowdown in the American economy in December of the same year, its has been observed that the United States economy, and to a certain degree the global market, has entered into an era of prolonged adjustments, with expected periods of growth, but the severe economic restructuring currently being put in place is believed to continue for the next years. What is believed to be the main driver of these developments is the baby boomer generation. It is assumed that the previously mentioned financial crisis is also contributory to the current financial morass, but the imperative reasons is that what is considered as the largest demographic in the history of mankind, the baby boomer generation born after the Second World War, has overreached its spending power (Professor Rodrigue Tremblay). What is seen to be the immediate effect of this development is that there must be a realization that the exhaustion of the spending power of the baby boomer generation is irreversible. In this regard, the solutions cannot be found overnight; the remedy will be decades of readjusting of corporate spending, reduced spending and increased savings, and liquidating massive mountains of debt. The ramifications of this development will be seen to reverberate through the entire economic structure, as seen in the downturn of the automobile industry, and the increases in the health care sector, as the baby boomer continue to age (Tremblay). What is considered as a significant public policy issue is the potential load that a society that is reaching its twilight years will place on the nation’s health provider system and the government expenditures. The â€Å"2030† issue is about addressing the challenge that by that time, there will be adequate and an efficacious system will be in place in three decades time, when the elderly sector in society will be double the present population. By the year 2030, it is expected that many of the baby boomer generation will be between the ages of 66 to 84 years, and they will comprise 61 million individuals. Apart from these, the number of the older baby boomers, will be more than 9 million by 2030 (James Knickman, Emily Snell). The present structure of the long term care sector is constructed around the provision of the service by private providers, which can be categorized as non-profit and some for profit outfits. When the available resources increase, the development of new services can accelerate at a faster pace. Inversely, when available resources decrease, it is also expected that the capacity of the sector will diminish. Taking the example of home health care as a point of reference, the growth in the yearly expenditure rate increase went from ten percent in the period of the 1980’s reaching into the 1990’s, plummeting to a negative three percent in just two years, from 1998 to 1999 (Knickman, Snell). The Congressional Budget Office (CBO), in a 1999 report, calculates that expenditures related to long term care needs was approximately $120 billion in 2000, more than half (59 percent) addressed by the private sector. The balance of the expenditures were covered by individual expenses, with the private long term sector just covering one percent of the long term health care expenditures. In the conservative estimation of the CBO, the total amount for long term health care will rise an average of 2. 6 percent above inflationary levels annually over a span of three decades, totaling more than $150 billion in 2010, close to $200 billion in 2020, and a colossal $ 230 billion by the year 2030 (Knickman, Snell). In the composition of the Federal budgetary outlay, three government dominate the bulk of Federal spending; Medicaid, Medicare and Social Security. Federal outlays for these programs in 2004 reached more than $960 billion, exclusive of receipt offsetting of Medicare premiums. In total, these three programs totaled more than 40 percent of the entire Federal budget. It is be noted that the Federal government is contemplating on implementing sweeping changes in the mechanism of the Social Security system. The changes in the Social Security structure is inclusive of proposals to divert a portion of their tax payments to private investment tools (United States Congressional Budget Office 9). One piece of advice that the boomers might give serious contemplation to is the fact that there exists now a need to increase levels of savings rather than increased spending. All the events the last few years have sent a clear signal to the aging sector to turn to savings and restrain spending binges; but these acts of saving on the part of the boomers would mean a decrease in the levels of consumption and reduced spending, so that they can liquidate their liabilities, and that will increase the personal net income of the boomers. But what does that spell for the economy, if the largest spending sector considers more saving and reducing their consumption? It will translate to a comprehensive deceleration in economic growth and some excruciating adjustments in broad sectors in the economy (Tremblay) . In this light, it is expected that the effects of the current financial crisis hounding the global economies will be magnified and increase in its intensity, and the magnified effects of the crisis will continue to be felt in the decades to come. The economic doldrums will not be continuous, as there will be some short lived gains and increases, but will quickly return to the state of economic stagnation. To cite an example, in the last decade, Japan suffered a period of stagnation induced by the elderly demographic buffeted the nation’s economy for the entire nineties. Even to this day, Japan is still trying to finds its way out of the economic morass it suffered during that time (Tremblay). Many of the countries whose population practices a very high standard of savings patterns will be able to export much of that capital to other countries. During the baseline year for model simulations, 1997, it was seen that many industrial states were exporting more than $60 billion in net investments to some low and middle level nations, amounting to 1. 1 percent of the gross domestic product of the nations that receive these outflows of capital. In that year, only nations in East Asia region were seen to be net exporters of capital. But in the year 2015, the recipients of the outflows of the industrial nations will be the ones exporting capital, and the industrial nations currently exporting the capital will be the ones importing the capital (World Bank 40). In the years not covered by the data released by the Congressional Budget Office (CBO), the continued aging of the baby boomers, compounded with increasing costs related to health care, will create a significant shift in the financial situation of the Unite States. It is expected that in the next three decades, the population of Americans at or over the age of 65 will jump 100 percent, while the number of people that are under the age of 65 will only increase by 15 percent. What is more alarming is the rate for the increase for health care expenditures is expected to outstrip the pace of economic growth during the same period. If the costs continue at a pace of 2. 5 percent, the Federal government will increase its budgetary allocations for Medicare and Medicaid, from 4. 2 percent at present more than 11 percent by the year 2030 (Congressional 10). Budgetary allocations for Social Security is expected to increase in the next thirty years by an average of 40 percent under the operation of the present laws. The share of the allocations for Social Security will rise from the 4. 2 figure at present to at least 6 percent in 2030. By comparison, the revenue projections for Social Security is expected to be static during the period, hovering at around 5 percent of gross domestic product (GDP). All combined, these pressures will exert significant amounts of stress on the budget that growth in the economy is unlikely to fully satiate (Congressional 11). Works Cited Harrington, Brad, Hall, Douglas T. Career Management and work life integration: using self assessment to navigate contemporary careers. Los Angeles, USA: Sage Publications 2007. Knickman, James R. , Snell, Emily K. â€Å"The 2030 Problem: Caring for Aging Baby Boomers†. Health Research and Education Trust 2002 August, 37(4), pp. 849-884 http://www. ncbi. nlm. nih. gov/pmc/articles/PMC1464018/ Tremblay, Rodrigue. â€Å"The Great Baby-Boomers Economic Stagnation of 2007-2017†. http://www. globalresearch. ca/index. php? context=vaaid=14268 United States Congressional Budget Office. The US Budget and Economic Outlook 2006- 2015. P. O. Box 416, Old Chelsea Station New York NY: Cosimo, Inc. 2005 World Bank. Global economic prospects and the Developing countries, Volume 13. 1818 H Street, NW, Washington, DC: World Bank Publications 2003. How to cite The baby boomer in the midst of the economic crisis, Papers

Sociology of Consumption

In these chapters, John Crammer examines the consumption patterns existing in Japan. His main argument is that by studying them, researchers can better understand the social life of a country, the formation of people’s identities and values, or micro-economics of households (Clammer, 2008, p. 1). Advertising We will write a custom essay sample on Sociology of Consumption specifically for you for only $16.05 $11/page Learn More In the author’s opinion, the discussion of consumption patterns is particularly important for the study of the Japanese culture that differs in many ways from Western cultures. He focuses on such aspects as social stratification, teenager’s behavior, values of Japanese customers, and the relations between consumption and urbanization. John Crammer believes that the mass consumption in Japan began to grow in the sixties. At that time, the country began to transform itself from an industrialist society into a con sumerist one (Clammer, 2008, p. 2). The scholar points out that the consumption in this country is not a mere transfer of good and commodities; more likely it is status competition (Clammer, 2008, p. 6). In other words, buyers want to show that they have achieved success. Thus, consumption is closely linked to the construction of self-identify. Nevertheless, the Japanese society is also very stratified and people try to adhere to their social roles. For instance, a person, who looks for a job, is more likely to be dressed in a certain way (Clammer, 2008, p. 11). As a rule, such a person does not want to emphasize his/her wealth because such behavior is not usually approved by the society. Thus, people’s buying habits are affected not only by his/her desire to acquire status in the eyes of ones peers or friends. Secondly, according to this author, consumption is important for establishing or maintaining relations between people. For instance, Japanese teenagers view shopping as a way of reinforcing friendship; it is a part of their peer culture (Clammer, 2008, p. 14). This issue should be overlooked by people who study the culture of Japan. It should be taken into account that Japanese people are less individualistic, and collective values or interests may be of greater importance for them. This is why peers usually go to department stores together.Advertising Looking for essay on social sciences? Let's see if we can help you! Get your first paper with 15% OFF Learn More Additionally, John Crammer points out consumption patterns can tell much about gift-giving in Japan. As a rule, Japanese people regard gift-giving as one of their obligations which are required by the etiquette (Clammer, 2008, p. 18). For instance, people who occupy a lower position in the workplace hierarchy, often give presents to people who are their superiors (Clammer, 2008, p. 17). They are signs of recognition. On the whole, gifts are not used to create bonds betwe en people; one of their roles is to highlight the distance existing between people. For instance, female employees give their make co-workers chocolates (Clammer, 2008, p. 17). Such a gift indicates that there are only formal relations between two people. Such behavior may exist in other cultures, but in Japan it is more widespread. Apart from that, the author does not agree with the opinion that the Japanese middle-class is homogeneous and prosperous. Many of these people do not feel that their employment is secured; therefore, the consumption patterns of Japanese middle-income people differ significantly. Their goals and priorities may not coincide. However, one should note that Japanese customers attach more importance the quality of the product, rather than its price (Clammer, 2008, p. 24). Cheapness is not one of the qualities that appeals to Japanese buyers. Furthermore, they believe that companies should not offer only goods or services. These organizations have to act as c orporate citizens that pay attention to the interests of the community. So, Japanese society sets higher performance standards for businesses. Thus, consumption patterns can throw light on the cultural values of Japanese people and their behavior. Furthermore, in his book, John Clammer (2008) examines the connection between consumer culture and urbanization. According to the author, consumption is important for avoiding the economic downfall of many urban regions. For instance, in Japan the inner-cities do not turn into ghettos; they are more likely to become the concentration of very large stores, offices, or cinemas (Clammer, 2008, p. 28). Additionally, one should take into consideration that Japanese people give more preference to collectivity, rather than individualism. Therefore, the residents of urban areas are more inclined to form groups or associations. Thus, their leisure and consumption are affected by this collectivity. They are not as isolated from one another as many American or European consumers are. This is one of the distinctions that people should be aware of.Advertising We will write a custom essay sample on Sociology of Consumption specifically for you for only $16.05 $11/page Learn More Overall, these examples suggest consumption pattern in Japan can be viewed as indicators as social and cultural life. They can give the reaches insights into the values and goals of a certain nation. First of all, one can mention that Japanese people see consumption as a way of attaining status in the community. They normally place emphasis on the quality of the products and the corporate social responsibility of companies. Secondly, buying is an organized and collective activity. Reference List Clammer, J. (2008). Contemporary Urban Japan: A Sociology of Consumption. New York: John Wiley Sons. This essay on Sociology of Consumption was written and submitted by user Tess M. to help you with your own studies. You are free to use it for research and reference purposes in order to write your own paper; however, you must cite it accordingly. You can donate your paper here.