On Bandwidth Efficient Modulation for High-Data-Rate Wireless LAN Systems
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On Bandwidth Efficient Modulation for High-Data-Rate Wireless LAN Systems John D. Terry Nokia Research Center, 6000 Connection Drive, Irving, TX 75039, USA Email: [email protected]
Juha Heiskala Nokia Research Center, 6000 Connection Drive, Irving, TX 75039, USA Email: [email protected]
Victor Stolpman Southern Methodist University, 3145 Dyer Street, Dallas, TX 75275-0338, USA Email: [email protected]
Majid Fozunbal Georgia Institute of Technology, Atlanta, GA 30332, USA Email: [email protected] Received 3 October 2001 and in revised form 25 March 2002 We address the problem of high-data-rate orthogonal frequency division multiplexed (OFDM) systems under restrictive bandwidth constraints. Based on recent theoretic results, multiple-input multiple-output (MIMO) configurations are best suited for this problem. In this paper, we examine several MIMO configurations suitable for high rate transmission. In all scenarios considered, perfect channel state information (CSI) is assumed at the receiver. In constrast, availability of CSI at the transmitter is addressed separately. We show that powerful space-time codes can be developed by combining some simple well-known techniques. In fact, we show that for certain configurations, these space-time MIMO configurations are near optimum in terms of outage capacity as compared to previously published codes. Performance evaluation of these techniques is demonstrated within the IEEE 802.11a framework via Monte Carlo simulations. Keywords and phrases: OFDM, WLAN, MIMO, antenna diversity, space-time block codes, TCM.
1.
INTRODUCTION
Currently, the IEEE 802.11a standard offers data rates ranging from 6 Mbit/s to 54 Mbit/s. However, there is a growing interest for a 100 Mbit/s mode of operation for the IEEE standard. Unfortunately, to achieve such a rate within the IEEE 802.11a framework requires the system to operate at a spectral efficiency better than 6 bit/s/Hz. The spectral efficiency problem is further complicated by the fact that 20% of the available bandwidth is used for the cyclic prefix to mitigate the effects of frequency selective fading. From a system design perspective, the complexity associated with this mode of operation should not be much greater than that for the 54 Mbit/s mode of the standard. These stringent requirements constitute a very interesting research problem. Recent information theoretic results [1] suggest that there is a tremendous capacity potential for wireless communication systems using antenna diversity. Foschini and
Gans [1] and others [2, 3] noted that orthogonal frequency division multiplexed (OFDM) systems are particularly well suited for antenna diversity techniques. Hence, it is expected that multiple element antenna arrays will play an increasingly important role in emerging wireless LAN networks. Indeed, when used in conjunction with appropriately designed signal processing algorithms, these arrays can dramatically enhance performance. In systems where channel state information (CSI) is not known to the transmitter, space-time
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