Performance Analysis of Multiantenna Wimax Systems over Frequency-Selective Fading Channels

Abstract

A multicell WiMax system which supports orthogonal frequency division multiplexing (OFDM) and antenna arrays at the base stations is considered in this paper as conforming to the IEEE 802.16-2004 standard. Focusing on the uplink, we propose an analytical framework to assess the average error probability of the system over time-dispersive (or, equivalently, frequency selective) and space-dispersive (due to the antenna array) Rayleigh fading channels. The proposed method takes into account the effects of the correlation of the channel gains over the space-frequency domain, the power-angle structure of the inter-cell interference, the array processing at the base station and the interleaving scheme. , which prescribes the employment of OFDM modulation and supports antenna array technology. The pushing demand for broadband systems makes WiMax one of the most promising technologies for the near future in wireless communications. The system is expected to operate in heterogeneous propagation environments as applications range from the provisioning of wireless services in rural areas to intensive and real-time applications on notebooks and other mobile devices. Thereby, a thorough analysis of its performance under realistic and different propagation environments is mandatory.Several works have recently focused on the evaluation of the error rate of bit-interleaved coded OFDM systems over frequency selective fading channels [3]- [5]. To simplify the performance evaluation, the concept of effective signal-to-noise ratio (SNR) has been introduced in [3] as the SNR of an equivalent additive white Gaussian noise (AWGN) channel which would yield the same error probability as that of the considered frequency-selective channel. The effective SNR can be used to adapt modulation and coding to the instantaneous channel conditions (and the service requirements) or to assess the average error rate for a given transmission mode [4]. Average and outage system performances have also been derived in [5] for multiantenna combining techniques in Nakagami-fading propagation environments, while the effects of non-stationary intercell interference on the performance of multiantenna WiMax systems have been studied in [6] [7].

Analytic framework for performance evaluation of multi-antenna WIMAX systems over fading channel

“…We consider an hexagonal cell layout as in [5] where the transmission from the single-antenna subscriber station SS 0 to the -antenna base station BS 0 is impaired by the out-of-cell interferers {SS } =1 . The bit sequence { }, to be transmitted by SS 0 , is coded, bit-interleaved and mapped onto the sequence of complex symbols { }.…”

“…As in [5], we select as error event the codeword that corresponds to the worst con guration of error bits; such a con guration needs to be evaluated for the speci c code and interleaver, as done in [5] for the IEEE 802.16-d standard.…”

“…The effective SNR can be used to adapt modulation and coding modes or to assess the average error rate for a given transmission mode [4]. Going one step further, in [5] a uni ed framework has been proposed to analytically assess the bit error rate (BER) of a multi-antenna WiMax system over space-time dispersive Rayleigh fading environments with spatially correlated intercell interference. The error rate is expressed as a function of the effective signal to interference plus noise ratio (SINR), rede ned with respect to [4] so as to jointly account for the correlation of the inter-cell interference over the antennas and the correlation of the channel gains over both the antennas and the subcarriers.…”

“…The analysis in [5] accounts for a single transmission mode: BPSK modulation and convolutional code (CC). However, the pushing demand for high data rate applications makes mandatory the employment of more ef cient transmission modes.…”

“…In particular, WiMax prescribes M-QAM and concatenated coding schemes made by an inner CC and an outer Reed-Solomon (RS) code. In this paper, we extend the framework [5] to account for the whole set of standard-compliant transmission modes. The BER is rst evaluated at the CC output by adapting the concept of effective SINR to M-QAM based on a set partitioning of the modulation mapping [6].…”