Adaptive M-QAM Modulation for MIMO Systems
Abstract
Adaptive modulation substantially increases the throughput of a wireless network by adjusting the modulation index to the channel conditions. It was shown that adaptive power and rate M-QAM system can give a power gain of almost 20dB relative to non-adaptive transmission for CDMA systems. A review of adaptive modulation for broadband system was presented. Multiple-input multiple-output (MIMO) links exploit the spatial dimension and antenna arrays at both ends of a link to transmit multiple parallel streams in the same time and frequency channel. The result is an extraordinary bandwidth-efficient approach to wireless communication, especially in rich multi-path environments. V-BLAST is a simple and widely considered architecture for open-loop (OL) MIMO systems. In this paper we propose algorithms for implementing adaptive M-QAM modulation for both OL- and CL-MIMO systems. The goal is to maximize the throughput subject to a target BER constraint. For OL-MIMO the algorithm proposed finds the number of transmit antennas and the modulation index to be used for all streams. For CL-MIMO, we propose a new rate maximization scheme that, on the average, has 20% throughput improvement over OL-MIMO. We also modify the water-filling and MMSE solutions to accommodate adaptive modulation and BER constraints. We use the flat Rayleigh-fading channel model for our simulations, and assume perfect channel estimation. This paper is organized as follows: The OL- and CL-MIMO strategies are discussed in Section II. The adaptive M-QAM scheme is discussed in Section III. In Section IV we introduce our adaptive modulation implementations and propose a new rate maximization scheme for CL-MIMO that takes into account the BER threshold.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2005
- Accession Number
- ADA447442
Entities
People
- Mehmet Fatih Demirkol
- Ramkumar Gowrishankar
Organizations
- University of Hawaiʻi at Mānoa