Browse Prior Art Database

ADAPTIVE MODULATIONS FOR MIMO SYSTEMS

IP.com Disclosure Number: IPCOM000021895D
Original Publication Date: 2004-Feb-16
Included in the Prior Art Database: 2004-Feb-16
Document File: 5 page(s) / 314K

Publishing Venue

Motorola

Related People

F. Kharrat: AUTHOR [+3]

Abstract

This article proposes an efficient scheme based on adaptive modulation in a multiple antenna context to provide high data rates with acceptable performance and reasonable complexity. The selection of the appropriate modulation is done through the derivation of an accurate upper-bound on the error probability of the related MIMO system.

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Adaptive Modulations for MIMO systems

by F. Kharrat, S. Fontenelle and J.J. Boutros

Abstract

This article proposes an efficient scheme based on adaptive modulation in a multiple antenna context to provide high data rates with acceptable performance and reasonable complexity. The selection of the appropriate modulation is done through the derivation of an accurate upper-bound on the error probability of the related MIMO system.

Problems to be solved

Future wireless systems require considerably high data rates and transmission reliability. In a conventional communication system employing one antenna at each side (Single Input Single Output), the achievable capacity is directly limited by the transmit power and the available spectrum bandwidth. The use of SISO architecture for high data rates wireless systems require the use of high order modulations (less robust and more complex) or higher power devices. Communication systems employing multiple antennas at both the transmitter (Tx) and the receiver (Rx) sides (Multiple Input Multiple Output) have been suggested to cope with these limitations, by transmitting simultaneously distinct data streams on each Tx antenna and exploiting the Rx antennas to separate the different streams. The channel capacity achieved by such systems has been shown to increase proportionally to the minimum number of antennas at Tx and Rx, provided that propagation conditions are favourable and ML detection is performed.

However, high speed wireless data transmission requires robust and spectrally efficient communication techniques for fading channels. Most current systems that employ spatial multiplexing do not assume any channel knowledge at Tx and hence do not adapt the data rate of the transmission. These non-adaptive methods require a fixed link margin to maintain acceptable performance when the channel quality is poor, and are thus designed for the worst case channel conditions, resulting in insufficient utilisation of the full channel capacity. When channel information, even limited, is available at Tx, it may be used to improve the overall throughput of the system. Adapting transmit characteristics to the signal fading allows the channel to be used more efficiently since power and rate can be allocated to take advantage of favourable channel conditions. The basic idea behind adaptive transmission is to maintain a constant Eb/No ratio by varying the transmitted power level, symbol transmission rate, constellation size, coding rate/scheme or any combination of these parameters. Without sacrificing the Frame Error Rate, these schemes provide high average spectral efficiency by transmitting at high data rates under favourable channel conditions and reducing throughput as channel degrades.

A natural question is consequently how to use channel knowledge at Tx to design efficient adaptive schemes in a MIMO context and provide high data rates with acceptable performance. The purpose of this article is to provide a powerful...