In this paper, we propose an eigenmode SNR increasing method for a maximum likelihood(ML) criterion based spacetime linear precoder(ML-STLP). In the proposed method, several ML-STLPs are employed for one frame whereas only one ML-STLP is employed in the conventional method. When over two ML-STLPs are employed, the same MLSTLPs, which have short precoded symbol length, are arranged in parallel. Also, a length of precoded symbol for one frame and a data rate are same between the proposed method and the conventional method. We investigate the effect of the precoded symbol length on the resulting eigenmode SNR and show that the eigenmode SNR increasing can be achieved by selecting the precoded symbol length with higher eigenmode SNR depending on the channel condition. Also, the applicability of the proposed method is demonstrated by a computer simulation.
INTRODUNCTIONIn wireless communication systems, multi-input multi-output (MIMO) systems, which exploits the spatial diversity, is known as a cost-effective solution for high data rate. In the MIMO systems, the space-time linear precoder and decoder, which is a joint processing at the transmitter and receiver sides and decomposes the MIMO channel to the parallel flat fading subchannels i.e., eigenmode, is introduced to achieve performance improvement[1]- [4].Under the assumption that the channel state information is known, various criteria for space-time linear precoder design have been proposed. In various criteria, reducing the probability of error using maximum likelihood (ML) decision rule based criterion minimizes a bit error rate (BER) by maximizing a minimum distance between symbol hypotheses for any modulation scheme [2]. The potential of the space-time linear precoder based on the criterion (ML criterion based space-time linear precoder, i.e., ML-STLP) is determined by a signal-to-noise ratio (SNR) at the output of the eigenmode, i.e., eigenmode SNR. If obtained eigenvalues are high, in proportion, the eigenmode SNRs and a good bit error rate(BER) performance are achieved. However, when only poor eigenvalues are obtained, also the eigenmode SNRs are low, and it is likely to cause poor BER performance.In this paper, we propose an eigenmode SNR increasing method for ML-STLP. In the proposed method, several MLSTLPs are employed for one frame whereas only one ML-STLP is employed in the conventional method. The number of the employed ML-STLP is determined by a channel condition. When over two ML-STLPs are employed, the same ML-STLPs, which have short precoded symbol length, are arranged in parallel. Also, a length of precoded symbol for one frame and a data rate are same between the proposed method and the conventional method. We investigate the effect of the precoded symbol length on the resulting eigenmode SNR by the interlacing inequalities [5], and show that the eigenmode SNR increasing can be achieved by selecting the precoded symbol length with higher eigenmode SNR depending on the channel condition.In the block transmission system, a guard interval is empl...