Yongmei Dai

A Comparative Study of QRD-M Detection and Sphere Decoding for MIMO-OFDM Systems

We present a comparative study of two tree search based detection algorithms, namely, the M-algorithm combined with QR decomposition (QRD-M) and the sphere decoding (SD) algorithms, for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. First, we show that nodes ordering before and during the tree search are important for both algorithms. With appropriate ordering, QRD-M can improve detection performance significantly and SD can reduce decoding complexity substantially. Then we compare the implementation complexity of the two algorithms, in terms of the number of nodes required to search or the required number of multiplications to achieve maximum likelihood detection performance. It is interesting to show that the average complexity of SD is lower than that of QRD-M, whereas the worst case complexity of SD is much higher than that of QRD-M

Pseudo-Inverse MMSE Based QRD-M Algorithm for MIMO OFDM

We propose a pseudo-inverse minimum mean squared error (MMSE) based QR decomposition (QRD) M-algorithm (QRD-M) for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The proposed algorithm can effectively mitigate the detrimental effect of MIMO channel ill-conditions on the bit error rate (BER) performance. As a result, the number of retained branches (M value) can be reduced to half of the original QRD-M algorithm in Kyeong Jin Kim and R.A. Iltis (2002) in order to achieve the same performance for both the uncoded and coded systems. The detection complexity is therefore greatly reduced

A low complexity near ML V-BLAST algorithm

A low complexity MIMO detection scheme is proposed to achieve near optimal maximum likelihood (ML) detection performance. The scheme is especially efficient in high data rate packet transmission systems, such as wireless LAN based hotspots, fixed broadband wireless access systems, or 4G cellular based hotspots etc. The complexity of the optimal performance achieving scheme is significantly lower than that of the ML detection and the state of art technologies.

Ordered array processing for space-time coded systems

The zero-forcing interference suppression and cancellation scheme proposed by Tarokh et al., in 1999, for grouped space time coded system suffers performance loss due to limited diversity gains for the first detected antenna groups, and power allocation was suggested to overcome this problem. In this letter, we propose an ordered detection algorithm which compensates the diversity loss by always detecting the group with the strongest post-nulling signal-to-noise ratio. Compared with the power allocation scheme, our proposed scheme is more robust to varying channel conditions and when used with iterative interference cancellation, a performance gain of 2.4 dB can be obtained at a frame-error rate rate of 10/sup -2/.

A list sphere decoder based turbo receiver for groupwise space time trellis coded (GSTTC) systems

A list sphere decoder (LSD) based turbo receiver is introduced for groupwise space time trellis coded (GSTTC) systems. It can approach the single-user bound by iteratively exchanging soft information between the LSD and the soft-input soft-output (SISO) maximum a posteriori (MAP) space time trellis (STT) decoder. The LSD approximates the SISO maximum likelihood (ML) channel detector using only a subset of hypotheses, and thus greatly reduces the computational complexity. Simulation results show that good FER and BER performances as well as fast convergence can be achieved with a very small list for simple STT codes with a small number of states. For more powerful codes with more states, a large list is required. Compared with the linear minimum mean square error (LMMSE) turbo receiver, the proposed receiver is more flexible and converges faster. Its performance can always be improved by increasing the list size, but at the cost of increased complexity. For higher order modulation, the performance gain is larger.

Performance comparison between coded V-BLAST and GSTTC MIMO-OFDM systems

A performance comparison between convolutional coded vertical Bell-lab layered space time (V-BLAST) and groupwise space time trellis coded (GSTTC) multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems is presented in this paper. Both systems have the same data rate and employ receivers with comparable complexity, which are zero-forcing, minimum mean square error (MMSE) and list sphere decoder (LSD) based turbo receivers. Simulation results show that V-BLAST significantly outperform the GSTTC systems when MMSE or LSD based turbo receiver is applied, while GSTTC perform similarly to or better than the V-BLAST systems when zero-forcing detection algorithm is applied.

Near optimal list MIMO detection

A list MIMO detection scheme is proposed to achieve near optimal maximum likelihood detection performance. The scheme is especially efficient in high data rate packet transmission systems, such as wireless LAN based hotspots, fixed broadband wireless access systems, 4G cellular based hotspots etc. The complexity of the optimal performance achieving scheme is significantly lower than that of the ML detection and the state of art technologies

Iterative interference cancellation and ordered array processing for groupwise space time trellis coded (GSTTC) systems

In this paper, an iterative interference cancellation (IIC) scheme is proposed for the ordered zero-forcing (ZF) algorithm to regain the signal energies lost during the interference suppression (IS) process in groupwise space lime trellis coded (GSTTC) systems. Both hard decision and soft decision based IIC are studied. With hard decision based IIC, significant improvement over the ordered ZF algorithm is achieved and a performance comparable to that of the complex ordered maximum SNR (MaxSNR) algorithm is reached. With soft decision IIC, the proposed scheme can even outperform the ordered MaxSNR algorithm and provides a better performance-complexity tradeoff in systems with large number of antennas and simple space time trellis codes.