NDLI: Precoding for Minimization of Envelope Variations in Multicode DS-CDMA Systems

Content Provider	Springer Nature Link
Author	Ottosson, Tony
Copyright Year	2000
Abstract	A multicode direct-sequence code-division multiple-access system experienceslarge envelope variations as a result of a sum of many independently spreadsignals. However, large envelope variations is problematic because it reducesthe spectral efficiency, the efficiency of the power amplifiers and theperformance. All these effects depend on the non-linear amplifiers thatgenerally are used in handsets. It would of course be possible to use a linearamplifier but then the power efficiency is drastically reduced. In this paperwe analyze the envelope variations of a multicode signal in terms of thecrest factor and find that it increases as the square root of thenumber of used codes. As a consequence it is only possible to use themulticode scheme for a few parallel codes. To reduce the envelope variationsa precoder is introduced. This precoder is a non-linear high-rate block codeespecially designed for the set of spreading codes used. However, the precodercan be made independent of the spreading codes if a user-specific spreadingcode is concatenated with a set of Hadamard or Conference sequences. Theresulting spreadig codes are orthogonal. Also, the precoder is independent ofthe user-specific spreading code, and can thus be used for all users. Afterprecoding the crest factor is significantly reduced and the performance, dueto introduced coding gain, improved. Algorithms for the design of precoderswith both reduced envelope variation and good performance are presented.Furthermore, simulations show that a precoded multicode system outperforms anuncoded multicode system in a single-user as well as in a multiuserenvironment.
Starting Page	57
Ending Page	78
Page Count	22
File Format	PDF
ISSN	09296212
Journal	Wireless Personal Communications
Volume Number	13
Issue Number	1-2
e-ISSN	1572834X
Language	English
Publisher	Kluwer Academic Publishers
Publisher Date	2000-01-01
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Processor Architectures Electronic and Computer Engineering Signal, Image and Speech Processing
Content Type	Text
Resource Type	Article
Subject	Electrical and Electronic Engineering Computer Science Applications

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