A Simple Differential Modulation Scheme for Quasi-Orthogonal Space-Time Block Codes with Partial Transmit Diversity
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Research Article A Simple Differential Modulation Scheme for Quasi-Orthogonal Space-Time Block Codes with Partial Transmit Diversity Lingyang Song1 and Alister G. Burr2 1 UniK,
University of Oslo, P.O. Box 70, 2007 Kjeller, Norway of Electronics, University of York, Heslington, York YO10 5DD, UK
2 Department
Received 21 August 2006; Revised 20 November 2006; Accepted 12 February 2007 Recommended by David Gesbert We report a simple differential modulation scheme for quasi-orthogonal space-time block codes. A new class of quasi-orthogonal coding structures that can provide partial transmit diversity is presented for various numbers of transmit antennas. Differential encoding and decoding can be simplified for differential Alamouti-like codes by grouping the signals in the transmitted matrix and decoupling the detection of data symbols, respectively. The new scheme can achieve constant amplitude of transmitted signals, and avoid signal constellation expansion; in addition it has a linear signal detector with very low complexity. Simulation results show that these partial-diversity codes can provide very useful results at low SNR for current communication systems. Extension to more than four transmit antennas is also considered. Copyright © 2007 L. Song and A. G. Burr. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
Transmit diversity techniques that can provide effective robustness over fading channels have been extensively investigated in recent years [1–13]. Orthogonal space-time block codes (O-STBCs) were reported in [1, 2], aiming at achieving maximum diversity gain. Later, in order to satisfy the high data rate requirement, a family of quasi-orthogonal spacetime block codes (QO-STBCs) has been proposed in [3], which can obtain full rate but partial diversity by mapping the input data to one fixed constellation, and simulation results suggest that these codes can provide very useful results at low SNR. At high SNR, they perform worse than OSTBC due to the reduced diversity. Recently, improved quasiorthogonal space-time block codes for four transmit antennas were reported in [4, 5], which can provide both full rate and full diversity. However, this is achieved at the cost of significant signal constellation expansion and thus further increase in the computational complexity. All the above work assumes that the channel can be readily tracked at the transmitter or receiver. In order to combat the environment with poor channel information, [6, 7] differential orthogonal space-time block codes (D-O-STBCs)
and [8–10] differential space-time modulation (DSTM) were developed based on the orthogonal properties of the transmission matrices. However, the transmission rate is still low for more than two transmit antennas. Recently, several full-rate, full-diversity differential QO-STBC (D-QO-STBC) schemes have been investigated in [11–13], yieldi
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