Analysis of OFDMA resource allocation with limited feedback

Radio link adaptation, multiple antenna techniques, relaying methods and dynamic radio resource assignment are among the key methods used to improve the performance of wireless communication networks. Opportunistic resource block (RB) allocation in downlink orthogonal frequency division multiple access (OFDMA) with limited feedback is considered. The spectral efficiency analysis of multiuser OFDMA with imperfect feedback path, multiple antenna methods and relaying methods is a particular focus. The analysis is derived for best-M feedback methods and for a RB-wise signal-to-noise ratio (SNR) quantization based feedback strategy. Practical resource fair round robin (RR) allocation is assumed at the RB assignment, i.e., each user gets the same portion of the available RBs. The fading of each RB is modelled to be independent and identically distributed (IID). This assumption enabled a communication theoretic approach for the performance evaluation of OFDMA systems The event probabilities related to the considered OFDMA systems are presented so that the feedback bit error probability (BEP) is a parameter in the expressions. The performance expressions are derived for the BEP in the case of binary phase-shift keying (BPSK) modulation and single antenna methods. Asymptotic BEP behavior is considered for the best-M feedback methods when the mean SNR tends to infinity. The system outage capacity and the average system spectral efficiency are investigated in the case of multiple antenna schemes. Antenna selection and space-time block coding (STBC) are considered in multiple antenna schemes when each RB is allocated exclusively to a single user. Simple OFDMA-spatial division multiple access (SDMA) schemes are also analyzed when zero forcing (ZF) detection is assumed at the receiver. Relay enhanced dynamic OFDMA with single and multiple antennas at each end is considered for fixed infrastructure amplify-and-forward (AF) relaying methods. The average spectral efficiency has been derived for the best-M and RB-wise one bit feedback schemes, antenna selection and STBC methods. The best choice for a combination of multiple antenna scheme and feedback strategy depends on several system parameters. The proposed analytical tools enable easy evaluation of the performance of the investigated schemes with different system parameters. The fundamental properties of the combinations of feedback and multiple antenna schemes are extensively studied through numerical examples. The results also demonstrate that the analytical results with idealized IID fading assumption are close to those obtained via simulations in a practical frequency selective channel when RBs are selected properly. Dynamic RB allocation is attractive for practical OFDMA systems since significant performance gain over random allocation can be achieved with a practical allocation principle, very low feedback overhead and an imperfect feedback channel.