1:00, SPCOM-L6.1
HIGH-RATE LINEAR SPACE-TIME CODES
B. HOCHWALD, B. HASSIBI
Multiple-antenna systems that operate at high rates require simple yet effective space-time transmission schemes to handle the large traffic volume in real time. V-BLAST, where every antenna transmits its own independent substream of data, has been shown to have good performance and simple encoding and decoding. Yet its drawbacks include its inability to work with fewer receive antennas than transmit antennas, and its absence of built-in spatial coding. On the other hand, there are many previously-proposed space-time codes that have good fading resistance and simple decoding, but generally poor performance at high data rates or with many antennas. We propose a high-rate coding scheme that can handle any configuration of transmit and receive antennas and that subsumes both V-BLAST and many proposed space-time codes as special cases. The scheme transmits substreams of data in linear combinations over space and time and the codes are designed to optimize the mutual information between the transmitted and received signals. Because of their linear structure, the codes retain the decoding simplicity of V-BLAST, and because of their information-theoretic optimality, they possess many coding advantages

1:20, SPCOM-L6.2
DESIGN OF SPACE-TIME TRELLIS CODES FOR FULL SPATIAL DIVERSITY
Z. SAFAR, K. LIU
Space-time codes have been developed to answer the need for high data rates in future wireless communication systems. In this work, we propose a systematic code construction method that provides full diversity advantage for any number of transmit antennas, any number of encoder states, and any constellation. Our approach is to exploit the properties of the state transitions in the trellis to force the desired structure on the channel symbol difference matrix. The design rules do not specify the space-time codes completely, leaving room for further optimization for coding advantage.

1:40, SPCOM-L6.3
RATE ADAPTIVE SPACE-TIME MODULATION TECHNIQUES FOR COMBATING COCHANNEL INTERFERENCE
Q. YAN, R. BLUM
Space-time coding is a highly effective transmitter technique for combating fading in wireless communications and improving the capacity of wireless networks. However, a recent paper has shown that cochannel interference can degrade performance significantly in cellular systems. In this paper, first we design and demonstrate the interference suppression capability of low rate space-time codes. Optimal 1 b/s/Hz 2-space-time trellis codes with various number of states over $Z_4$ and GF(4) are obtained through global search. Then we propose rate adaptive space-time modulation which can increase the overall throughput. The effectiveness of this proposed method is demonstrated by using 2-space-time codes in an orthogonal frequency division multiplexing (OFDM) system with 2 transmit and 2 receive antennas.

2:00, SPCOM-L6.4
UNION BOUND ON ERROR PROBABILITY OF LINEAR SPACE-TIME BLOCK CODES
S. SANDHU, A. PAULRAJ
Design of practical coding techniques for the multiple antenna wireless channel is a challenging problem. A number of interesting solutions have been proposed recently ranging from block codes to trellis codes for the MIMO (multiple input, multiple output) channel. Here we consider linear block codes for the quasi-static, flat-fading, coherent MIMO channel. A linear code refers to an encoder that is linear with respect to scalar input symbols. We assume maximum likelihood decoding at the receiver. We provide a cohesive framework for analysis of linear codes in terms of a union bound on the conditional probability of symbol error. The error bound is a function of the instantaneous channel realization and does not make any assumptions on channel statistics. We show that the orthogonal block codes in \cite{Tarokh:99} achieve the lowest error bound among all unitary codes and are in fact optimal.

2:20, SPCOM-L6.5
A CLASS OF EFFICIENT-ENCODING GENERALIZED LOW-DENSITY PARITY-CHECK CODES
T. ZHANG, K. PARHI
In this paper, we investigate an efficient encoding approach for generalized low-density (GLD) parity check codes, a generalization of Gallager's low-density parity check (LDPC) codes. We propose a systematic approach to construct approximate upper triangular GLD parity check matrix which defines a class of efficient-encoding GLD codes. It's shown that such GLD codes have equally good performance. By effectively exploiting the structure sharing in the encoding process, we also present a hardware/software codesign for the practical encoder implementation of these efficient-encoding GLD codes.

2:40, SPCOM-L6.6
A SPACE-TIME CODING APPROACH FOR SYSTEMS EMPLOYING FOUR TRANSMIT ANTENNAS
C. PAPADIAS, G. FOSCHINI
We propose a novel transmit diversity scheme for the downlink of communication systems that employ four transmit antennas. The scheme can be seen as a simplified transmission architecture admitting an entire family of space-time codes. It can be also seen as an extension of previously proposed techniques (such as those presented in [1,2,3]) to the case of four transmit antennas with complex input data symbols. Our technique has a number of appealing features, namely, it enables a significant portion of the open-loop channel capacity, it requires simple receiver processing (involving typically 2x2 matrix operations in conjunction with single-user or 2-user decoding) and it admits single-user encoding in an overlay fashion.