| Popis: |
Much work has been done on design of efficient coded modulation schemes since the publication of [Ungerboeck, 1982] for trellis coded modulation and [Imai & Hirakawa, 1977] for block coded modulation. Recently, increasing interest in digital mobile radio and indoor wireless systems has led to the consideration of coded modulation designs for combating fading channels. In this research, it is intended to present results of an investigation of the construction of Reed Solomon coded MPSK modulation which is robust for the Gaussian channel and a Rayleigh fading channel. Two approaches have been applied to Reed Solomon coded modulation. First, a Reed Solomon code was combined with MPSK signal set using Gray code mapping; this was called Reed Solomon coded modulation not based on set partitioning. This approach was the baseline scheme which would be compared with the proposed approach, namely Reed Solomon coded modulation based on set partitioning. The second approach to coded MPSK with M = 2m was multilevel Reed Solomon coding. In this case, each of the m bits defining an MPSK symbol was coded and decoded by different Reed Solomon codecs. The set partitioning principle was applied to define subsets with distances Deltai,-, (i = 1 to m) that were nondecreasing with i. Each of the m bits defined a subset and was decoded in multistage decoding schemes. The novel idea here was that in the receiver, we used a rotated 2m+1-PSK detector if the transmitter used a 2m-PSK modulator. The designs of Reed Solomon coded modulation schemes for the Gaussian channel and a Rayleigh fading channel (i.e. choice of the code configurations which were suitable for this channel) have been studied. The performance of Reed Solomon coded modulation based on set partitioning was compared with Reed Solomon coded modulation not based on set-partitioning, then with multilevel Reed Solomon coded modulation using Gray mapping and finally with coded modulation schemes using binary codes, Reed Muller codes. It has been shown that over the Gaussian channel and a Rayleigh fading channel, Reed Solomon coded modulation based on set partitioning is better than several alternatives, such as schemes not based on set partitioning, multistage Reed Solomon coded modulation based on Gray mapping and Reed Muller coded modulation. It was found that good codes for a Rayleigh fading channel have configurations in which all component codes have the same minimum Hamming distance because the fading phase is uniformly distributed random process. Therefore, by matching configurations of component codes with the channel characteristics, it was shown that Reed Solomon coded modulation based on set partitioning was robust for the Gaussian and a Rayleigh fading channel. Reed Solomon coded modulation schemes were applied to Orthogonal Frequency Division Multiplexing (OFDM) transmissions. The main disadvantage of OFDM systems is that they have high Peak-to-Mean Envelope Power Ratio (PMEPR). A scheme for reducing the PMEPR of OFDM systems was investigated. Multiphase complementary code pairs of length 2 are proposed to reduce the PMEPR of MPSK and QAM OFDM. Concatenated codes with Reed Solomon coded modulation as an inner code and an RS(511, 443) code as an outer code are proposed as coding schemes for OFDM systems. |
