Unipolar space-time codes with reduced decoding complexity for TH-UWB with PPM
In this paper, we consider the problem of space-time (ST) coding with unipolar pulse position modulations (PPM) and propose a novel ST code that satisfies a large number of construction constraints rendering it superior to the existing PPM encoding schemes. In particular, the proposed 2 times 2 code...
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| Format: | article |
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2009
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| Online Access: | http://hdl.handle.net/10725/3080 http://dx.doi.org/10.1109/TWC.2009.080684 http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5288944 |
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| Summary: | In this paper, we consider the problem of space-time (ST) coding with unipolar pulse position modulations (PPM) and propose a novel ST code that satisfies a large number of construction constraints rendering it superior to the existing PPM encoding schemes. In particular, the proposed 2 times 2 code achieves a full transmit diversity order while transmitting at a rate of 1 PPM-symbol per channel use. The proposed scheme can be associated with M-ary PPM constellations for all even values of M without introducing any constellation expansion. This renders the proposed scheme suitable for low cost carrier-less ultra-wideband (UWB) systems where information must be conveyed only by the time delays of the modulated sub-nanosecond pulses without introducing any amplitude amplifications or phase rotations. Finally, the proposed scheme can be associated with a reduced complexity optimal maximum-likelihood (ML) decoder that takes the structure of the proposed code into consideration in order to simplify the decoding procedure. We also propose a simple diversity-preserving suboptimal decoder that requires approximately half the number of multiplications compared to the ML decoder. Possible extensions to transmitters equipped with three antennas are also discussed in situations where a certain number of feedback bits is available. |
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