Space-frequency Trellis Codes Research Articles

Differential Quasi-Orthogonal Space-Frequency Trellis Codes

Two rate-one differential quasi-orthogonal space-frequency trellis codes (DQOSFTCs) for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) channels are proposed. The DQOSFTCs are systematically constructed within an OFDM symbol period, by combining unitary quasi-orthogonal trellis codes and differential modulation over the frequency domain (DF-QOSFTC) or time domain (DT-QOSFTCs). Besides multipath diversity, our DQOSFTCs achieve high-coding gain and simple decoding when the channel state information is not available at both the transmitter and the receiver. Simulation results show that our proposed codes significantly outperform the existing differential space-frequency trellis codes.

Differential space-frequency trellis codes

A new differential space-frequency trellis coding (DSFTC) scheme is proposed for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The transmitter differentially encodes the message drawn from a set of unitary matrices following a trellis encoding rule. At the receiver, where no channel state information (CSI) is available, differential decoding and soft-input Viterbi algorithms are employed in the decoding process. The proposed codes can achieve full rate, 1 symbol/subcarrier, and full spatial diversity. Simulation results show that the proposed codes provide significant improvements over differential space-frequency block codes (DSFBC) due to increased coding gains

Improved Design Criterion for Space-Frequency Trellis Codes over MIMO-OFDM Systems

In this paper, we discuss the design problem and the robustness of space-frequency trellis codes (SFTCs) for multiple input multiple output, orthogonal frequency division multiplexing (MIMO-OFDM) systems. We find that the channel constructed by the consecutive subcarriers of an OFDM block is a correlated fading channel with the regular correlation function of the number and time delay of the multipaths. By introducing the first-order auto-regressive model, we decompose the correlated fading channel into two independent components: a slow fading channel and a fast fading channel. Therefore, the design problem of SFTCs is converted into the joint design in both slow fading and fast fading channels. We present an improved design criterion for SFTCs. We also show that the SFTCs designed according to our criterion are robust against the multipath time delays. Simulation results are provided to confirm our theoretic analysis.

On the Code and Interleaver Design of Broadband OFDM Systems

In this letter, we study the performance of space-frequency-coded orthogonal frequency-division modulation systems over multiple-input multiple-output frequency-selective channels. The diversity and coding advantages are derived in terms of the minimum Hamming distance and the minimum squared product distance of the code as well as the relative frequency locations (tones) where a pair of codewords with the minimum Hamming distance differ. These relationships between performance and well-defined code parameters provide new insight to code construction and interleaving design. In addition, we propose a block interleaver that yields nearly optimal coding advantage for space-frequency trellis codes.