We investigate the effect of fading correlation and branch gain imbalance on the Shannon capacity of diversity systems in conjunction with adaptive transmission techniques. This capacity provides the theoretical upper bound for the spectral efficiency of adaptive transmission schemes. We obtain closed-form expressions for this capacity for Rayleigh fading channels under four adaptation policies: optimal power and rate adaptation (opra), optimal rate adaptation with constant power (ora), truncated channel inversion with fixed rate (tifr), and complete channel inversion with fixed rate (cifr). We give numerical examples illustrating the main trends and offer comparisons on the behavior of opra, ora, tifr, and cifr under variation of different parameters. 1.
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"There are numerous published papers based on study of channel capacity evaluation. In , the capacity of Rayleigh fading channels under four adaptation policies and multibranch system with variable correlation is investigated. The capacity of Rayleigh fading channels under different adaptive transmission and different diversity combining techniques is also studied in , . "
" addresses ergodic capacity with multi-user diversity, while ,  analyze capacity under different diversity combining schemes. Capacity under diversity combining in the presence of spatial correlation and channel estimation error are analyzed in – and  respectively. "
[Show abstract][Hide abstract] ABSTRACT: Asymptotic comparisons of ergodic channel capacity at high and low
signal-to-noise ratios (SNRs) are provided for several adaptive transmission
schemes over fading channels with general distributions, including optimal
power and rate adaptation, rate adaptation only, channel inversion and its
variants. Analysis of the high-SNR pre-log constants of the ergodic capacity
reveals the existence of constant capacity difference gaps among the schemes
with a pre-log constant of ?1. Closed-form expressions for these high-SNR
capacity difference gaps are derived, which are proportional to the SNR loss
between these schemes in dB scale. The largest one of these gaps is found to be
between the optimal power and rate adaptation scheme and the channel inversion
scheme. Based on these expressions it is shown that the presence of space
diversity or multi-user diversity makes channel inversion arbitrarily close to
achieving optimal capacity at high SNR with sufficiently large number of
antennas or users. A low-SNR analysis also reveals that the presence of fading
provably always improves capacity at sufficiently low SNR, compared to the
additive white Gaussian noise (AWGN) case. Numerical results are shown to
corroborate our analytical results.
Preview · Article · Apr 2011 · IEEE Transactions on Information Theory
"Capacity analysis of multipath fading channels becomes an important and fundamental issue in the design and study of new generations of wireless communication systems due to scarce radio spectrum available and to the rapidly growing demand for wireless services. Accordingly there has been many papers dealing with the channel capacity of Rayleigh, Nakagami, Rician, and generalized gamma fading channels      . In , a novel closed-form expression for achieving average channel capacity of a generalized selection combining RAKE receiver in Rayleigh fading is derived. "
[Show abstract][Hide abstract] ABSTRACT: In this paper, closed-form expressions for the capacities per unit bandwidth for Rayleigh fading channels with equal gain combining (EGC) diversity case are derived for power and rate adaptation, constant transmit power, channel inversion with fixed rate, and truncated channel inversion adaptation policies. Channel inversion policies provide the highest capacity over the other adaptation policies with EGC diversity. The constant transmit power policy provides the lowest capacity as compared to the other policies.
Full-text · Article · Apr 2009 · AEU - International Journal of Electronics and Communications