Title :
Optimal Beamforming Schemes and its Capacity Behavior for Downlink Distributed Antenna Systems
Author :
Sang-Rim Lee ; Sung-Hyun Moon ; Han-Bae Kong ; Inkyu Lee
Author_Institution :
Sch. of Electr. Eng., Korea Univ., Seoul, South Korea
Abstract :
In this paper, we investigate the outage and ergodic capacity of downlink distributed antenna systems (DAS) where each distributed antenna unit (DAU) has multiple antennas with per-DAU power constraint. We first derive the optimal beamforming vector in a closed form by applying a matrix minor condition to relax the positive semi-definite constraint. We observe that our derived solution has a form of maximum ratio transmission per each DAU with full power. Based on the derived optimal beamforming, the outage and ergodic capacity under Rayleigh fading channels are analyzed. To this end, we show that a distribution of the received signal-to-noise ratio is characterized as a Gamma distribution by approximating a sum of non-identical independent Nakagami-m random variables as a single Nakagami-m random variable based on the moment matching method. Then, we present an accurate formula of the outage and ergodic capacity in a closed form which matches well with the simulation results. Furthermore, we derive an upper bound of an achievable average rate of DAS with limited feedback. We then propose a new feedback bit allocation algorithm to maximize the derived metric. Simulation results confirm the accuracy of the derived outage and ergodic capacity expressions and the efficiency of the proposed bit allocation method.
Keywords :
Nakagami channels; Rayleigh channels; antennas; array signal processing; gamma distribution; matrix algebra; radiofrequency interference; statistical mechanics; DAS; Gamma distribution; Rayleigh fading channel; capacity behavior; distributed antenna unit; downlink distributed antenna system; ergodic capacity; feedback bit allocation algorithm; matrix minor condition; maximum ratio transmission; moment matching method; nonidentical independent Nakagami-m random variables; optimal beamforming vector scheme; outage capacity; per-DAU power constraint; positive semidefinite constraint; received signal-to-noise ratio; Distributed antenna systems; beamforming; limited feedback;
Journal_Title :
Wireless Communications, IEEE Transactions on
DOI :
10.1109/TWC.2013.041613.111987