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Imperfect Channel Knowledge Based Ergodic Channel Capacity of Transmit Beamforming

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  • Communication
  • Design

Abstract

Imperfect Channel Knowledge Based Ergodic Channel Capacity of Transmit Beamforming Imperfect Channel Knowledge Based Ergodic Channel Capacity of Transmit Beamforming Du Yang, Lie-Liang Yang and Lajos Hanzo School of ECS, University of Southampton, SO17 1BJ, UK Tel: +44-23-8059 3364; Fax: +44-23-8059 4508 E-mail: dy05r,lly,[email protected]; http://www-mobile.ecs.soton.ac.uk Abstract—1 In this treatise, we have derived the lower ergodic channel capacity bound of a closed-loop transmit beamforming system scheme, when considering the effects of channel estimation errors, transmit beamforming vector quantization errors, the ef- fective capacity loss caused by pilot symbols and that imposed by the channel information feedback bits. We intend to answer the question “whether the potential capacity improvement achieved by using a closed-loop design and an increased number of transmit antennas will be completely eroded by the imperfections of the channel information acquisition and signalling?”. Based on our investigations, we found that the capacity improvements predicted are indeed achievable for slowly fading channels, but erode for realtively rapidly fading channels. An improved closed- loop transmit beamforming scheme is proposed for rapidly fading channels. Index Terms—Closed-loop transmit beamforming, ergodic ca- pacity, imperfect channel knowledge, pilot-assisted channel esti- mation I. INTRODUCTION In a single-user point-to-point communication scenario as- sociated with perfect Channel State Information at both the Receiver (CSIR) and the transmitter (CSIT), the achievable ergodic channel capacity (characterized in terms of bit/s/Hz) can be substantially increased compared to having no CSIT, especially when having more transmit antennas than receive antennas [1], [2]. This is achieved by exploiting the CSIT with the aid of sophisticated transmit pre-processing tech- niques [3]–[5], However, having perfect CSIT at our disposal is not realistic, especially at high Doppler fr

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