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Browse Prior Art Database

CYCLIC DIVERSITY RECEIVER

IP.com Disclosure Number: IPCOM000009902D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-26
Document File: 2 page(s) / 105K

Publishing Venue

Motorola

Related People

Louay M. A. Jalloul: AUTHOR [+2]

Abstract

A new diversity receiver is shown for improving the COMA forward link modem performance. The diversity gain of the receiver is quantified using computer simulations in a flat Rayleigh fading channel. The new proposed diversity receiver structure is simple to implement. The achievable gains in link performance, relative to no diversity, range from 3 to 9dB wjth 2 and 4 antennas, respectively.

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MOTOROLA

Technical Developments

CYCLIC DIVERSITY RECEIVER

by Louay M. A. Jalloul and Kamyar Rohani

ABSTRACT

A new diversity receiver is shown for improving the COMA forward link modem performance. The diversity gain of the receiver is quantified using computer simulations in a flat Rayleigh fading channel. The new proposed diversity receiver structure is simple to implement. The achievable gains in link performance, relative to no diversity, range from 3 to 9dB wjth 2 and 4 antennas, respectively.

INTRODUCTION

The second generation (IS95NB) COMA forward link performs poorly in slow flat Rayleigh fading channels. The mobile subscriber requires in excess of 20dB Eb/Nt to meet 1% frame error rate (FER) in a slow (e.g. less than 3kmph at 800MHz) Rayleigh fading channel. This poor performance occurs since jnterleaving and coding cannot cope with the long fade duration [I ]. Thus, the range and capacity of the system will be reduced if this condition persists. Diversity techniques are typically used to combat such severe fading. Maximal ratio combing (MRC) and selection diversity are well known techniques that combat fading [2]. However, all these types of diversity techniques require some RF processing and additional circuitry for each diversity path before demodulation.

The diversity scheme shown here is simple to implement. It requires two or more antennas but uses only the ex.isting circuitry for demodulation.

DIVERSITY RECEIVER

The new scheme is called cyclic diversity receiver (CDR). The mobile receiver uses 2 (or more) antennas in receiving the base station transrnitted signal. A single RF front end is used and is shared by the two antennas. The MS receiver periodicalJy selects one antenna and then the other as

Motorola. Inc. 2000

shown in Figure 1. In this configuration two antennas are used and the switching period is 1.25msec. The gain in the link perfonnance is obtained due to the fact that coded symbols input to the decoder are less correlated than in the single antenna case. The correlation between the symbols that are input to the ...