Performance analysis of channel codes in multiple antenna OFDM systems

Multiple antenna techniques are used to increase the robustness and performance of wireless networks. Multiple antenna techniques can achieve diversity and increase bandwidth efficiency when specially designed channel codes are used at the scheme’s transmitter. These channel codes can be designed in the space, time and frequency domain. These specially designed channel codes in the space and time domain are actually designed for flat fading channels and in frequency selective fading channel, their performance may be degraded. To counteract this possible performance degradation in frequency selective fading channel, two main approaches can be applied to mitigate the effect of the symbol interference due to the frequency selective fading channel. These approaches are multichannel equalisation and orthogonal frequency division multiplexing (OFDM). In this thesis, a multichannel equalisation technique and OFDM were applied to channel codes specially designed for multiple antenna systems. An optimum receiver was proposed for super-orthogonal space-time trellis codes in a multichannel equalised frequency selective environment. Although the proposed receiver had increased complexity, the diversity order is still the same as compared to the code in a flat fading channel. To take advantage of the multipath diversity possible in a frequency selective fading channel, super-orthogonal block codes were employed in an OFDM environment. A new kind of super-orthogonal block code was proposed in this thesis. Super-orthogonal space-frequency trellis-coded OFDM was proposed to take advantage of not only the possible multipath diversity but also the spatial diversity for coded OFDM schemes. Based on simulation results in this thesis, the proposed coded OFDM scheme performs better than all other coded OFDM schemes (i.e. space time trellis-coded OFDM, space-time block coded OFDM, space-frequency block coded OFDM and super-orthogonal space-time trellis-coded OFDM). A simplified channel estimation algorithm was proposed for two of the coded OFDM schemes, which form a broad-based classification of coded OFDM schemes, i.e. trelliscoded schemes and block-coded schemes. Finally in this thesis performance analysis using the Gauss Chebychev quadrature technique as a way of validating simulation results was done for super-orthogonal block coded OFDM schemes when channel state information is known and when it is estimated. The results obtained show that results obtained via simulation and analysis are asymptotic and therefore the proposed analysis technique can be use to obtain error rate values for different SNR region instead of time consuming simulation.Thesis (PhD)--University of Pretoria, 2012.Electrical, Electronic and Computer Engineeringunrestricte

Generalized union bound for space-time codes

Abstract⎯Gallager’s second bounding technique, also known as the generalized union bound, is employed to derive a new upper bound on the error probability of space-time codes with maximum-likelihood (ML) decoding on quasi-static Rayleigh fading channels. The new bound is distinguished by two characteristics: unlike the classical union bound, the new bound is rapidly convergent and is only a few decibels away from simulation results; compared to Gallager’s first bound, it has better computational efficiency and numerical stability. Hence, the new bound is a useful tool for performance analysis and computer search of good space-time codes. Moreover, the correlation between fading coefficients is easily accommodated by the new bound. The application of the new bound to convolutional coding on block fading channels is also demonstrated, and an improved version is derived for the bit error probability of maximum a posteriori probability (MAP) decoding. 1 Index Terms⎯Gallager bounds, optimization, space-time coding, union bound, weight spectrum. I

Generalized Union Bound for Space–Time Codes

Abstract—Gallager’s second bounding technique, also known as the generalized union bound, is employed to derive a new upper bound on the error probability of space–time codes (STCs) with maximum-likelihood (ML) decoding on quasi-static Rayleigh fading channels. The new bound is distinguished by two characteristics: unlike the classical union bound, the new bound is rapidly convergent and is only a few decibels away from simulation results; and compared with Gallager’s first bound, it has better computational efficiency and numerical stability. Hence, the new bound is a useful tool for performance analysis and computer search of good STCs. Moreover, the correlation between fading coefficients is easily accommodated by the new bound. The application of the new bound to convolutional coding on block-fading channels is also demonstrated, and an improved version is derived for the bit-error probability of maximum a posteriori probability decoding. Index Terms—Gallager bounds, optimization, space–time coding, union bound, weight spectrum