Joint Power Control and Blind Beamforming over Wireless Networks: A Cross Layer Approach
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Joint Power Control and Blind Beamforming over Wireless Networks: A Cross Layer Approach Zhu Han Department of Electrical and Computer Engineering and Institute for Systems Research, University of Maryland, College Park, MD 20742, USA Email: [email protected]
Farrokh R. Farrokhi Department of Electrical and Computer Engineering and Institute for Systems Research, University of Maryland, College Park, MD 20742, USA Email: [email protected]
K. J. Ray Liu Department of Electrical and Computer Engineering and Institute for Systems Research, University of Maryland, College Park, MD 20742, USA Email: [email protected] Received 6 January 2003; Revised 9 September 2003 Traditional joint power control and beamforming achieve the targeted signal-to-interference-noise ratio (SINR) at the receivers by assuming the knowledge of the measurements of channel parameters and SINR. Blind beamforming is an effective technique for beamforming and channel estimation without the need of training sequences, thus not consuming extra bandwidth. In this paper, we propose a novel joint power control and blind beamforming algorithm that reformulates the power control problem in such a way that it does not need any prior knowledge and additional measurements in the physical layer. In contrast to the traditional schemes that optimize SINR and, as a result, minimize bit error rate (BER), our proposed algorithm achieves the desired BER by adjusting a quantity available from blind beamforming. By sending this quantity to the transmitter through a feedback channel, the transmit power is iteratively updated in a distributed manner in the wireless networks with cochannel interferences (CCIS). Our proposed algorithm is more robust to estimation errors. We have shown in both analysis and simulation that our algorithm converges to the desired solution. In addition, a Cramer-Rao lower bound (CRB) is derived to compare with the performance of our proposed joint power control and blind beamforming system. Keywords and phrases: array signal processing, power control, distributed control, direction of arrival estimation.
1.
INTRODUCTION
Over the past few decades, wireless communications and networking have witnessed an unprecedented growth, and have become pervasive much sooner than anyone could have imagined. One of the major challenges for the system design is the limited available radio frequency spectrum. Channel reuse is a common method to increase the wireless system capacity by reusing the same channel beyond some distance. However this introduces cochannel interference (CCI) that degrades the link quality. Two promising approaches to combat CCI are power control and antenna array processing. Power control is one direct approach toward minimizing CCI. The transmit powers are constantly adjusted. They are increased if the signal-to-interference-noise-ratios
(SINRs) at the receivers are low and are decreased if the SINRs are high. Such a process improves the quality of weak links and reduces the unnecessary transmit powers. Antenna array processing
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