Design considerations in multi-carrier code division multiple access
Date
1998
Authors
Marchildon, Guy Denis
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Abstract
A recently proposed multiple access scheme that combines the advantages of Orthogonal Frequency Division Multiplexing and Code Division Multiple Access has shown to have potential for application in the mobile radio environment. The purpose of this thesis is to investigate several design aspects of this scheme, which is called Multi-Carrier Code Division Multiple Access (MC-CDMA). The scheme is evaluated for the downlink (basestation to mobile reciever) of a single cell system using a typical bad urban mobile radio channel. The important system parameters are selected based on design requirements of high flexibility, good bit error rate performance, low crest factor, and low complexity. The investigation includes the selection of spreading codes, as well as the code length and the number of subcarriers. Following sections detail the interleaver design and the channel estimation technique chosen for the system simulations.
With the system design parameters selected an investigation into detection schemes is made. Conventional detection for MC-CDMA is performed by equalization in the frequency domain followed by a hard decision. Several detection schemes are compared through Monte Carlo simulations. Multi-user detection and maximum likelihood detection are then evaluĀated.
The issue of high crest factor is considered in conjuction with the frequency distribution of the transmitted MC-CDMA signal. Crest factor is a critical issue in multi-carrier system in that high crest factor limits the system to the use of expensive amplifiers. Methods of reducing the crest factor for different detection schemes are investigated taking account of their effects on the frequency distribution. These methods are based on the use of phase rotations of the signal components. The issues addressed in this thesis provide groundwork for future development in the application of MC-CDMA in the mobile radio environment.