Low Complexity Transmit Antenna Selection with Power Balancing in Ofdm Systems

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Low Complexity Transmit Antenna Selection with Power Balancing in OFDM Systems Ki-Hong Park, Student Member, IEEE, Young-Chai Ko, Senior Member, IEEE, and Mohamed-Slim Alouini, Fellow, IEEE

Abstract—In this paper, we consider multi-carrier systems with multiple transmit antennas under the power balancing constraint, which is defined as the constraint that the power on each antenna should be limited under a certain level due to the linearity of the power amplifier of the RF chain. Applying transmit antenna selection and fixed-power variable-rate transmission per subcarrier as a function of channel variations, we propose an implementation-friendly antenna selection method which offers a reduced complexity in comparison with the optimal antenna selection scheme. More specifically, in order to solve the subcarrier imbalance across the antennas, we operate a two-step reallocation procedure to minimize the loss of spectral efficiency. We also provide an analytic lower bound on the spectral efficiency for the proposed scheme. From selected numerical results, we show that our suboptimal scheme offers almost the same spectral efficiency as the optimal one. Index Terms—Transmit antenna selection, orthogonal frequency division multiplexing, power balancing constraint, adaptive modulation.


I. I NTRODUCTION HE design of the transmitter or receiver with multiple antennas is an important problem since it has a major impact on the performance of wireless communication systems. In order to obtain considerable improvements, perfect channel state information should be used at the transmitter. However, in practice, the limitation on the feedback overhead and the need of calibrations for channel reciprocity lead to the development of transmit diversity systems with partial channel knowledge [1]. Transmit antenna selection (TAS) can significantly reduce the feedback load since only the information of the selected antenna should be known at the transmitter [2]. On another front, state-of-the-art wireless systems have been developed and deployed with orthogonal frequency division multiplexing (OFDM) to obtain high spectral efficiency

Manuscript received May 1, 2010; accepted August 2, 2010. The associate editor coordinating the review of this paper and approving it for publication was C. Tellambura. This is an expanded version of work that was presented at the IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC’09), Perugia, Italy, in June 2009. K.-H. Park and Y.-C. Ko are with the Department of Electronics and Computer Engineering, Korea University, Seoul, Korea (e-mail: {grn552; koyc}@korea.ac.kr). M.-S. Alouini was with the Electrical and Computer Engineering Program of TAMU-Qatar, Doha, Qatar. He is currently with the Division of Physical Science and Engineering, KAUST, Thuwal, Makkah Province, Saudi Arabia (e-mail: mohamed.alouini@kaust.edu.sa). This research was supported in part by the MKE (The Ministry of Knowledge Economy), Korea, under the ITRC (Information Technology Research Center) support program, supervised by the NIPA (National IT Industry Promotion Agency) (NIPA-2010-(C1090-1011-0011)), and funded in part by QNRF (The Qatar National Research Fund; a member of QF). Digital Object Identifier 10.1109/TWC.2010.09.100736

and robustness against intersymbol interference (ISI) caused by multipath propagation [3]. High peak-to-average power ratio (PAPR) has been the main drawback of OFDM systems since the transmit signals of subcarriers which are overlapped constructively in the time domain may make the power amplifier of the RF chain operate in its non-linear region. Accordingly, this often leads to an undesirable and inefficient performance degradation [4]. The issue becomes more problematic in the case the system involves multiple antennas, especially when TAS is used. For instance, when the antennas are...
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