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An efficient algorithm for optimum joint downlink beamforming and power control

: Schubert, M.; Boche, H.


Institute of Electrical and Electronics Engineers -IEEE-:
IEEE 55th Vehicular Technology Conference, VTC Spring 2002. Vol.4 : May 6 - 9, 2002, Birmingham, Alabama
Piscataway: IEEE Operations Center, 2002
ISBN: 0-7803-7484-3
Vehicular Technology Conference (VTC) <55, 2002, Birmingham>
Fraunhofer HHI ()
antenna arrays; array signal processing; broadcast channels; cellular radio; covariance matrices; encoding; interference suppression; optimisation; power control; radio links; radiofrequency interference; telecommunication control; transmitting antennas; efficient algorithm; optimum joint downlink beamforming; optimum power control; frequency flat multi-antenna broadcast channel; system throughput; power constraint; throughput; receivers; data rates; transmission power minimization; spatial covariance channel information; maximal eigenvalue; interference balancing; successive interference cancellation; coupling matrix; costa pre-coding; closed-form solution

We address the problem of joint downlink beamforming and power control in a frequency flat multi-antenna broadcast channel. In this context, a common optimization strategy is to maximize the system throughput under a certain power constraint. This, however, does not guarantee a fair sharing of throughput among the users, which is required in case that the receivers cannot cooperate. Thus, we propose a different approach, which always assumes optimally balanced data rates. If the problem is feasible, i.e., desired target rates can be reached, spare degrees of freedom can be used in order to minimize the total transmission power. This strategy can even be applied if only spatial covariance channel information is available. The authors have developed a theoretical framework based upon uplink/downlink duality, feasibility considerations, and bounds on the maximal eigenvalue of the resulting coupling matrix. An overview of the results is given and they are discussed in the context of existing literature. Finally, a theoretical benchmark is provided for the case of perfect channel knowledge. Then, beamforming can be combined with Costa (1983) pre-coding, as proposed by Caire and Shamai (see 36th Asilomar Conf. on Signals, Systems and Computers Asilomar Pacific Grove, CA, Nov. 2001). This leads to a closed-form solution of the problem.