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12 - Cellular OFDMA-TDD

Published online by Cambridge University Press:  02 September 2009

Harald Haas
Affiliation:
Universität Bremen
Stephen McLaughlin
Affiliation:
University of Edinburgh
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Summary

Motivation and problems

High peak data rate transmission, network self-organisation and universal frequency reuse are considered important features for future cellular, ad hoc, multi-hop and hybrid wireless networks (Prehofer and Bettstetter, 2005). OFDMA is viewed as a promising modulation/multiple-access technique for providing very high data-rates and flexible resource allocation while at the same time enabling low complexity receivers (Stimming et al., 2005). Time-division duplexing (TDD) supports traffic asymmetry very well which is inherent to packet data services. Moreover, TDD offers channel reciprocity which is exploited in this research in a novel fashion for medium access and subchannel allocation. The problems that arise from TDD are the requirement for time synchronisation and additional interference scenarios. This is particularly important as OFDMA performs poorly under conditions of universal frequency reuse because of the high CCI. Figure. 12.1 illustrates the CCI problem in a cellular network using TDD with frequency reuse of one. The figure shows two adjacent BSs (base stations), namely BS1 and BS2 with a MS (mobile station) associated with each BS, namely MS1 and MS2. MS1 is transmitting data to BS1. Consequently, MS1 causes interference to MS2, since MS2 is in receiving mode. Similarly, BS2 causes interference to BS1. Due to the potentially small spatial separation between transmitter and ‘victim’ receiver and the low path loss between BSs due to line-of-sight conditions, in a full frequency reuse network, CCI poses a major challenge on the MAC protocol design and channel assignment procedure.

Type
Chapter
Information
Next Generation Mobile Access Technologies
Implementing TDD
, pp. 336 - 376
Publisher: Cambridge University Press
Print publication year: 2008

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