Performance Evaluation of Space-Time and Harq Diversity in MIMO HSDPA

Performance Evaluation of Space-Time and Harq Diversity in MIMO HSDPA

Walid Hakimi (Sys’Com Laboratory,National School of Engineering, Tunis, Tunisia) and Ammar Mahmoud (Sys’Com Laboratory, National School of Engineering, Tunis, Tunisia)
DOI: 10.4018/jmcmc.2012070105
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Abstract

Multi-antenna techniques can be used to achieve improved system performance, including improved system capacity (more users per cell) and improved coverage (possibility for larger cells), as well as improved service provisioning, for example, higher per-user data rates. This study provides an overview of space-time diversity technique using Alamouti codes applied to the 3G evolution. The delays introduced by HARQ retransmission decrease the performance of the HSDPA system. Multi-antenna techniques are specifically applied to HSDPA to avoid HARQ retransmissions. The authors demonstrate that space-time Rake detector in MIMO 2x2 based on Alamouti code without HARQ process could give better performances than MIMO 2x1 taking into account the HARQ context. In the case of MIMO 2x2,they also observed that the limit of retransmissions affects the system performance and efficiency. Using the generalized Alamouti coding technique in MIMO 4x4 with Multipath Parallel Interference Canceller (MPIC) detector, we achieve notable improvement of performance under the same channel and signal to-Noise Ratio (SNR) conditions.
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2. Mimo Hsdpa Transmitter Model

To support MIMO transmission, the High Speed-Downlink Shared Channel (HS-DSCH) is modified to support up to two antennas. Data are treated in the same manner like in the case of Single Input antenna (Base Station side) and Single antenna Output (Mobile Station side). Only the modified part is spreading and scrambling (Figure 1).

Figure 1.

HARQ retransmission scheme for MIMO NTxNR HSDPA system with Alamouti code or Quasi-STBC code

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