http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:22845 This paper considers maximizing the network-wide minimum supported rate in the downlink of a two-cell system with symmetric channel statistics, where each base station (BS) is endowed with multiple antennas. This is done for different levels of cell cooperation. At one extreme, we consider single cell processing where the BS is oblivious to interference created at the other cell. At the other, we consider full cooperative macroscopic beamforming. In between, we consider coordinated beamforming, which takes account of intercell interference, without full cooperation. Lagrangian duality and large system analysis, where the numbers of antennas at the BS N and of users in each cell K both grow large, with cell loading K/N tending to a finite constant β, are combined to obtain concise expressions for asymptotically optimal beamformers and limiting SINRs, thereby simplifying beamformer design and comparison of the schemes. 2012-11-27T02:30:22.608Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:22825 This paper considers base station (BS) cooperation in the form of coordinated beamforming, focusing on min-max fairness in the power usage subject to target SINR constraints. We show that the optimal beamforming strategies have an interesting nested zero-forcing structure. We then consider the asymptotic regime where the number of antennas at each BS and the number of users in each cell both grow large with their ratio tending to a finite constant. The limiting optimal beamformer structure is characterized in terms of the solution of a convex optimization problem. The dimensionality of this optimization problem is constant1, as opposed to the problem of solving for the exactly optimal beamformer2, and only knowledge of statistics is required to solve it. These asymptotic results provide insights into the average performance, as well as simple but efficient strategies for the finite system case. In particular, the optimal beamforming strategy from the large systems analysis only requires the base stations to have local instantaneous channel state information; the remaining parameters of the beamformer can be calculated using channel statistics which can easily be shared amongst the base stations. 2012-11-21T09:26:07.859Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20067 This paper considers maximizing the network-wide minimum supported rate in the downlink of a two-cell system, where each base station (BS) is endowed with multiple antennas. This is done for different levels of cell cooperation. At one extreme, we consider single cell processing where the BS is oblivious to the interference it is creating at the other cell. At the other extreme, we consider full cooperative macroscopic beamforming. In between, we consider coordinated beamforming, which takes account of inter-cell interference, but does not require full cooperation between the BSs. We combine elements of Lagrangian duality and large system analysis to obtain limiting SINRs and bit-rates, allowing comparison between the considered schemes. The main contributions of the paper are theorems which provide concise formulas for optimal transmit power, beamforming vectors, and achieved signal to interference and noise ratio (SINR) for the considered schemes. The formulas obtained are valid for the limit in which the number of users per cell, K, and the number of antennas per base station, N, tend to infinity, with fixed ratio β = K/N. These theorems also provide expressions for the effective bandwidths occupied by users, and the effective interference caused in the adjacent cell, which allow direct comparisons between the considered schemes. 2012-06-27T10:13:19.820Z ]]>