Abstract
In this article, a hybrid multi-user OFDMA scheme which considers different user demands regarding channel access and user-specific imperfect channel quality information (CQI) is analytically described and evaluated. The considered hybrid scheme offers two possible modes to serve the user: firstly, via a non-adaptive mode which applies a discrete Fourier transform precoding to exploit frequency diversity and, thus, does not require any CQI at the transmitter. Secondly, via an adaptive mode which performs an adaptive resource allocation and link adaptation. Since this adaptation to the channel is done based on CQI, the adaptive mode is prone to imperfect CQI which results from estimation errors or time delays. Hence, in case of user-specific imperfect CQI, the question arises which user shall be served adaptively or non-adaptively and which resource shall be allocated to which user such that the system data rate is maximized while fulfilling a certain target bit error rate (BER) and minimum required user data rate. Analytical expressions of the system performance considering imperfect CQI and different user demands are derived. Based on these expressions, algorithms determining which user is served adaptively or non-adaptively subject to the BER and minimum data rate constraints are developed. Simulations show the superiority of the hybrid OFDMA scheme in terms of achievable data rate and user satisfaction compared to conventional pure adaptive and non-adaptive OFDMA schemes in the presence of user-specific imperfect CQI.
Highlights
Orthogonal frequency division multiple access (OFDMA) [1] is regarded as a promising candidate for future mobile radio systems
The SNR threshold problem In order to solve subproblem (19), analytical expressions for the user data rate R (Au/)N and bit error rate (BER) BER(Au/)N for both the adaptive and non-adaptive transmission scheme have to be derived taking into account imperfect channel quality information (CQI) and different user demands assuming that the user serving vector θ is known
This article deals with the analytical description and evaluation of a hybrid multi-user OFDMA transmission scheme with different channel access user demands assuming user-specific imperfect CQI
Summary
Orthogonal frequency division multiple access (OFDMA) [1] is regarded as a promising candidate for future mobile radio systems. SNR threshold calculation modulation scheme selection a user is served adaptively or non-adaptively This decision is based on the system parameters (SP) which are the number Nru of available resource units, the number U of users to be served, the target BER BERT and the user-specific average SNR γu. The SNR threshold problem In order to solve subproblem (19), analytical expressions for the user data rate R (Au/)N and BER BER(Au/)N for both the adaptive and non-adaptive transmission scheme have to be derived taking into account imperfect CQI and different user demands assuming that the user serving vector θ is known. Applying the non-adaptive transmission scheme as described in Section “Adaptive and nonadaptive transmission” leads to an averaging over the Du different SNR conditions of the resource units allocated to a given user.
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