Balancing Uplink and Downlink under Asymmetric Traffic Environments Using Distributed Receive Antennas

Illsoo SOHN  Byong Ok LEE  Kwang Bok LEE  

IEICE TRANSACTIONS on Communications   Vol.E91-B   No.10   pp.3141-3148
Publication Date: 2008/10/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e91-b.10.3141
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Next-Generation Mobile Multimedia Communications)
TDD,  asymmetric traffic,  crossed-slot interference,  distributed antenna system,  WCDMA,  IEEE802.16e,  WiBro,  

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Recently, multimedia services are increasing with the widespread use of various wireless applications such as web browsers, real-time video, and interactive games, which results in traffic asymmetry between the uplink and downlink. Hence, time division duplex (TDD) systems which provide advantages in efficient bandwidth utilization under asymmetric traffic environments have become one of the most important issues in future mobile cellular systems. It is known that two types of intercell interference, referred to as crossed-slot interference, additionally arise in TDD systems; the performances of the uplink and downlink transmissions are degraded by BS-to-BS crossed-slot interference and MS-to-MS crossed-slot interference, respectively. The resulting performance unbalance between the uplink and downlink makes network deployment severely inefficient. Previous works have proposed intelligent time slot allocation algorithms to mitigate the crossed-slot interference problem. However, they require centralized control, which causes large signaling overhead in the network. In this paper, we propose to change the shape of the cellular structure itself. The conventional cellular structure is easily transformed into the proposed cellular structure with distributed receive antennas (DRAs). We set up statistical Markov chain traffic model and analyze the bit error performances of the conventional cellular structure and proposed cellular structure under asymmetric traffic environments. Numerical results show that the uplink and downlink performances of the proposed cellular structure become balanced with the proper number of DRAs and thus the proposed cellular structure is notably cost-effective in network deployment compared to the conventional cellular structure. As a result, extending the conventional cellular structure into the proposed cellular structure with DRAs is a remarkably cost-effective solution to support asymmetric traffic environments in future mobile cellular systems.