Optimum feedback quantization in an opportunistic beamforming scheme
ABSTRACT In recent years, digital beamforming has evolved into an excellent technology to improve wireless communications over fading channels. Especially in slow fading environments with a sufficient number of users in the system, opportunistic beamforming through multiuser diversity  has offered some advantages over true beamforming methods that rely on full channel feedback and/or robust channel estimation methods. Opportunistic beamforming achieves good throughput with only signal-to-noise ratio (SNR) feedback from the users. The quality of the SNR feedback such as the degree of SNR quantization is essential for opportunistic beamforming because the base station selects the best receiving user based on the SNR measurements sent by the users. In this paper, we develop an optimum SNR quantization method performed by the users and analyze its impact on the system throughput. While keeping the fairness among the users, we show that the opportunistic beamforming gain can still be realized with the help of the proposed quantization method. Theoretical analysis and computer simulation results show the feasibility and effectiveness of the method which provides insights for engineers to implement opportunistic beamforming in practice.
- SourceAvailable from: psu.edu
Conference Proceeding: Exploiting multiuser diversity with only 1-bit feedback[show abstract] [hide abstract]
ABSTRACT: In a system with n users, the sum-rate capacity of the downlink channel grows as log log n, assuming optimal scheduling. However, optimal scheduling requires that the downlink channel state information (CSI) for all users be fully available at the base station. We show that the same capacity growth holds even if the feedback rate from the mobiles to the base station is reduced to one bit. We propose a simple scheduling method to achieve this multiuser capacity and, furthermore, we show that, by a judicious choice of the one-bit quantizer, not only the growth rate, but also most of the capacity of a fully informed system can be preserved.Wireless Communications and Networking Conference, 2005 IEEE; 04/2005
- [show abstract] [hide abstract]
ABSTRACT: Multiuser diversity is a form of diversity inherent in a wireless network, provided by independent time-varying channels across the different users. The diversity benefit is exploited by tracking the channel fluctuations of the users and scheduling transmissions to users when their instantaneous channel quality is near the peak. The diversity gain increases with the dynamic range of the fluctuations and is thus limited in environments with little scattering and/or slow fading. In such environments, we propose the use of multiple transmit antennas to induce large and fast channel fluctuations so that multiuser diversity can still be exploited. The scheme can be interpreted as opportunistic beamforming and we show that true beamforming gains can be achieved when there are sufficient users, even though very limited channel feedback is needed. Furthermore, in a cellular system, the scheme plays an additional role of opportunistic nulling of the interference created on users of adjacent cells. We discuss the design implications of implementing. this scheme in a complete wireless systemIEEE Transactions on Information Theory 07/2002; · 2.62 Impact Factor
Conference Proceeding: How much feedback is multi-user diversity really worth?Communications, 2004 IEEE International Conference on; 07/2004