A Novel Detection Algorithm Using the Sorted QR Decomposition Based on Log-Likelihood Ratio in V-BLAST Systems

Abstract

In this paper, we propose a novel detection algorithm using Log-Likelihood Ratio (LLR) to detect signals in V-BLAST systems. This algorithm utilizes the sorted QR decomposition (SQRD) of the channel matrix, and applies LLR to determine the order of detection. Simulation results show that the proposed algorithm provides a better performance than the conventional SQRD with a few additional computations. Approximately, the average BER performance of our algorithm is better than that of the conventional SQRD algorithm by 6dB for BPSK and by 2dB for QPSK respectively at 10 −3 target BER. I. INTRODUCTIONUsing multiple antennas at the transmitter and the receiver, we can obtain high spectral efficiency with the help of the layered space-time (LST) codes [1]. The simplified version of LST codes is known as V-BLAST (Vertical Bell Lab. Layered Space-Time). In order to detect LST codes at the receiver, several detection algorithms were proposed in [2]- [6]. Especially, ZF-OSIC (Zero-forcing Ordered Successive Interference Cancelation) was introduce in [2]. As a similar approach, the LLR based ZF-OSIC was proposed in [3], and was widely adopted. It decides the order of detection by LLR with aid of the SNR as well as the instantaneous noise. Although these two approaches provide reasonable BER performance at the receiver, the computational efforts which are required to resolve the transmitted signals are quite high. This is because OSIC based detector needs the pseudoinversion of the channel matrix repeatedly until it finds all the transmitted symbols [6]. To reduce this complexity, [6] was devised to use the sorted QR decomposition (SQRD) by sorting the detection sequence based on SNR followed by exchanging the columns of the channel matrix. However, it showed some performance degradation in comparison with that of ZF-OSIC due to the non-optimal sorting processes.In this paper, we propose a new detection algorithm for V-BLAST which is applying SQRD of the channel matrix by LLR to determine the order of detection. Like LLRbased ZF-OSIC of [3], the proposed scheme outperforms the conventional SQRD algorithm with just small amount of

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