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Thursday, July 28, 2011

High data rate protocols: General aspects

Premises Distributed Network

Recent developments in high data rate protocols studied by cost members have been grouped in five points: Access schemes for WPN’s wireless LAN’s, scheduling, comparison between protocols and wireless ATM.

● Access schemes for wireless personal Networks (WPN):  Some authors propose the use of new efficient algorithms, designed in terms of limiting packet dropping probability for ongoing calls to a selected threshold, while offering high throughput. Other authors develop analytical or software tools that allow a deep study of the performance of the known access schemes.

Broadband Households

[KHZH97] presents two simple Distributed Queuing (DQ) Call Admission Control (CAC) strategies. The first limits of the number of active communications by using centralized control in the BS, while the second uses a time out mechanize to control the maximum number of active connection in a given call. With this capacity gains one roughly two three times greater than in traditional Circuit Switch Systems.

[Mast 975] study the influence of the congestion states on the performance of a system based PRMA, developing an original analytical approach that has been used to confirm the result published by the European RACE project R 2008.

[ SaAg 98] presents the performance of an adaptive Slotted-Aloha DS-CDMA packet random access scheme, maximizing the through out by the use of a MS based algorithm and without the intervention of the B.S.

[RUCO98] Simulates the impact of real channel characterization on a S-ALOHA channel access scheme for different retransmission strategies, and uses spatial diversity and coding to improve system performance.

[RCGO99] Studies and simulates a multiple access scheme based on multe-code DS-CDMA, showing its capacity to support non-homogenous traffic achieving a good QOS.

Wireless LANS: The influence of packet length, number of nodes and lifetime on expected user date rate, on the upper boundary of the HIPER LAN channel access mechanism is studied by [HaCo97], showing that it is very robust under heavy load conditions. It is also shown that data rate for bounded services, can be increased by adding a buffer to the HIPERLAN MAC uses interfact. A mew protocol based on the standard RTS/CTS that is expected to increase through put on a data-per-area basis, compared with HIPERLAN, has been developed by [phOB99a]

● scheduling: several BS controlled scheduling algorithms have been simulated in [RCGO99] and [CoRF99] in a multi-rate multi-code DS-Access (DQRUMA, which offers a high through put white maintaining a low packet delay.

● Comparison between protocols: A comparison between PRMA++ and Adaptive S-ALOHA DS-CDMA is given in [Sa Ag98] showing that while PRMA++ is optimized for voice traffic, It is sensitive to different traffic statistics, and inefficient for integrating different types of traffic. In these circumstances S-ALOHA DS-CDMA outperforms PRMA++.

● Wireless ATM access: Data Link control (DLC) is essential for wireless ATM systems to overcome the incompatibility between ATM design assumption and the characteristics of the physical radio channel. The DLC scheme developed for the ACTS project magic WAND is evaluated in [Mebe99], and the transmission scheme without error control is compared to a scheme with GBN ARQ mechanism that was exhaustively described in [MeBe97] these works allow us to determine for which Services ARQ schemes are beneficial, when considering network services with different maximum delay requirements, HO in wireless ATM is studied in [Tevv98], offering the following requirements: cell sequence preservation, minimal cell loss and HO delay and integration with standard wired large-scale ATM networks [Veo199] proposes  a hybrid type It FEC/ARQ protocol for the Link Layer control (LLC), which uses punctured reed-Solomon codes for a wireless ATM system based on OFDM. 

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