1,721,002 research outputs found
Space-Time Codes and Concatenated Channel Codes for Wireless Communications
No full textFollowing a brief historical perspective on channel coding, an introduction to space–time block codes is given. The various space–time codes considered are then concatenated with a range of channel codecs, such as convolutional and block-based turbo codes as well as conventional and turbo trellis codes. The associated estimated complexity issues and memory requirements are also considered. These discussions are followed by a performance study of various space–time and channel-coded transceivers. Our aim is first to identify a space–time code/channel code combination constituting a good engineering tradeoff in terms of its effective throughput, bit-error-rate performance, and estimated complexity. Specifically, the issue of bit-to-symbol mapping is addressed in the context of convolutional codes (CCs) and convolutional coding as well as Bose–Chaudhuri–Hocquenghem coding-based turbo codes in conjunction with an attractive unity-rate space–time code and multilevel modulation is detailed. It is concluded that over the nondispersive or narrow-band fading channels, the best performance versus complexity tradeoff is constituted by Alamouti’s twin-antenna block space–time code concatenated with turbo convolutional codes. Further comparisons with space–time trellis codes result in similar conclusions. Keywords—Channel coding, concatenated coding, FEC, history of channel coding, space–time coding, STBC, STTC
Space-Time Trellis and Space-Time Block Coding Versus Adaptive Modulation and Coding Aided OFDM for Wideband Channels
No full textAbstract—The achievable performance of channel coded spacetime trellis (STT) codes and space-time block (STB) codes transmitted over wideband channels is studied in the context of schemes having an effective throughput of 2 bits/symbol (BPS) and 3 BPS. At high implementational complexities, the best performance was typically provided by Alamouti’s unity-rate G2 code in both the 2-BPS and 3-BPS scenarios. However, if a low complexity implementation is sought, the 3-BPS 8PSK space-time trellis code outperfoms the G2 code. The G2 space-time block code is also combined with symbol-by-symbol adaptive orthogonal frequency division multiplex (AOFDM) modems and turbo convolutional channel codecs for enhancing the system’s performance. It was concluded that upon exploiting the diversity effect of the G2 space-time block code, the channel-induced fading effects are mitigated, and therefore, the benefits of adaptive modulation erode. In other words, once the time- and frequency-domain fades of the wideband channel have been counteracted by the diversity-aided G2 code, the benefits of adaptive modulation erode, and hence, it is sufficient to employ fixed-mode modems. Therefore, the low-complexity approach of mitigating the effects of fading can be viewed as employing a single-transmitter, single-receiver-based AOFDM modem. By contrast, it is sufficient to employ fixed-mode OFDM modems when the added complexity of a two-transmitter G2 scheme is affordable
Adaptive Coding and Transmission Paradigms for Wireless Channels
No full textFollowing a brief historical perspective on channel coding the concept of near-instantaneously adaptive wireless transceivers is introduced as a counter-measure of mitigating the channel-quality fluctuations experienced in wireless communications. It is argued that channel coded adaptive modulation schemes can be viewed as a lower complexity alternative of mitigating the channel quality fluctuations of wideband wireless channels in comparison to multiple-transmitter and multiple-receiver based space-time codes. However, provided that the complexity of the latter schemes employing multiple transmitters and receivers is affordable, the performance advantages of adaptive modulation and adaptive channel coding schemes erode, since the channel quality fluctuations of the wireless channel are effectively mitigated
Switching Threshold and Coding-Rate Optimisation for Turbo Convolutional and Turbo BCH Coded Adaptive Modulation
No full textDecision Feedback Equaliser (DFE) aided turbo coded wideband Adaptive Quadrature Amplitude Modulation (AQAM) is capable of accommodating the temporal channel quality variation of fading channels. A procedure is suggested for determining the AQAM switching thresholds and the specific turbo coding rates capable of maintaining the target BER, while aiming for achieving a high effective Bits Per Symbol (BPS) throughput. Subsequently, the performances of both turbo convolutional (TC) and turbo BCH (TBCH) coded fixed and adaptive modulation schemes are characterised and compared when communication over the COST 207 Typical Urban (TU) wideband fading channel. It was found that at a given throughput the set of TBCH coded fixed modulation schemes considered outperforms the corresponding TC counterparts, when using a high latency turbo and channel interleaver. However, both schemes have a similar performance, when applied in conjunction with adaptive modulation
Space-Time Block Coded Adaptive Modulation Aided OFDM
No full textSpace-time block codes provide substantial diversity advantages for multiple transmit antenna systems at a low decoding complexity. In this contribution, we investigate the achievable diversity advantages in the context of adaptive modulation aided turbo coded OFDM. The two-transmitter, one-receiver block space-time coded scheme using no channel coding or gradually increasing rate turbo coding strikes the best trade-off in terms of its overall performance and complexity. Adaptive OFDM performs impressively, when the extra complexity of space-time coding is not affordable, but no adaptive modulation is necessary in conjunction with the more complex multiple transmit and receive antenna associated scenario
Block Turbo Coded Burst-by-Burst Adaptive Radial Basis Function Decision Feedback Equaliser Assisted Modems
No full textA novel adaptive modem scheme is to be presented for transmissions over wideband mobile channels, which employs a Radial Basis Function (RBF) based decision feedback equaliser, in order to mitigate the effects of the dispersive wideband channel. Turbo codes are invoked for improving the bit error rate (BER) and bits per symbol (BPS) performance of the scheme, which is shown to give a significant improvement in terms of mean BPS performance compared to that of the uncoded RBF equaliser assisted adaptive modem
Iterative Decoding of Redundant Residue Number System Codes
No full textTurbo decoded Redundant Residue Number System (RRNS) codes are proposed and their performance is evaluated. An RRNS code is a maximum-minimum distance block code, exhibiting identical distance properties to Reed-Solomon (RS) codes. Hence their error correction capability is given by . We adapt the classic Chase algorithm in order to accept soft inputs and to provide soft outputs. Using the proposed soft input soft output (SISO) Chase algorithm, the turbo decoding of RRNS codes is contrived
Turbo-Coded Adaptive Modulation Versus Space-Time Trellis Codes for Transmission over Dispersive Channels
No full textDecision feedback equalizer (DFE)-aided turbocoded wideband adaptive quadrature amplitude modulation (AQAM) is proposed, which is capable of combating the temporal channel quality variation of fading channels. A procedure is suggested for determining the AQAM switching thresholds and the specific turbo-coding rates capable of maintaining the target bit-error rate while aiming for achieving a highly effective bits per symbol throughput. As a design alternative, we also employ multiple-input/multiple-output DFE-aided space–time trellis codes, which benefit from transmit diversity and hence reduce the temporal channel quality fluctuations. The performance of both systems is characterized and compared when communicating over the COST 207 typical urban wideband fading channel. It was found that the turbo-coded AQAM scheme outperforms the two-transmitter space–time trellis coded system employing two receivers; although, its performance is inferior to the space–time trellis coded arrangement employing three receivers. Index Terms—Coded adaptive modulation, dispersive channels, space–time trellis codes
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