Browse Prior Art Database

MINIMUM DISTANCE CHANNEL QUALITY METRIC

IP.com Disclosure Number: IPCOM000006987D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-14
Document File: 2 page(s) / 125K

Publishing Venue

Motorola

Related People

Gus Vos: AUTHOR [+3]

Abstract

A critical hmction of a mobile RF packet modem in a multi-cellular environment is to maximize its performance by using the most appropriate (clos- est) base station. In a multi-cellular environment, many different base stations may be necessary to give appropriate coverage and performance to a par- ticular area. The mobile RF packet modem that oper- ates in this domain must be capable ofselecting the base station that yields the best performance. The best performance is gained when the RF link between the base station and the mobile terminal is the strongest. The mobile terminal requires a metric that is related to the quality of the incoming RF signal to decide whether the current RF link is good enough and to keep listening to the current base station or to leave and roam for a better RF link. The opera- tion ofthe invention is to generate the required chan- nel quality metric for the mobile RF modem.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 2

MO-LA INC. Technical Developments Volume20 October 1993

MINIMUM DISTANCE CHANNEL QUALITY METRIC

by Gus Vos, Hayward Cho and Bruce Colford

INTRODUCTION

  A critical hmction of a mobile RF packet modem in a multi-cellular environment is to maximize its performance by using the most appropriate (clos- est) base station. In a multi-cellular environment, many different base stations may be necessary to give appropriate coverage and performance to a par- ticular area. The mobile RF packet modem that oper- ates in this domain must be capable ofselecting the base station that yields the best performance. The best performance is gained when the RF link between the base station and the mobile terminal is the strongest. The mobile terminal requires a metric that is related to the quality of the incoming RF signal to decide whether the current RF link is good enough and to keep listening to the current base station or to leave and roam for a better RF link. The opera- tion ofthe invention is to generate the required chan- nel quality metric for the mobile RF modem.

  Often in a wireless data system the channel can not reliably transmit digital information without a forward error correcting mechanism. For example: The MDC protocol has a rate % convolutional decoder with a constraint length of 7 as a forward error correcting mechanism. Currently all MDC products use a (minimum distance) maximum likely hood decoding algorithm. If this technique is used to decode the data, as opposed to say the Viterbi decoder, then the invention can be utilized. The invention is a small modification to the maximum likely hood decoder that will enable it to produce a reliable channel quality metric.

  The invention is to use the number of bits the maximum likely hood decoder corrects in a data block as the channel quality metric. The number of bits corrected can be easily calculated when using a maximum likely hood decoder. With a maximum likely hood decoder, in general, the error vector is obtained using the calculated syndrome of the error pattern. With every linear code there is a maximum

6

number of bits that can be corrected by the code. If less than the maximum number of bits have been corrupted in the received,code word then the error vector is the difference between the received code word and the transmitted code word. The estimated decoded code word is obtained by adding the received code word to the error vector. The number of bits that are corrected is the number of ones in the error vector. Thus, the number of ones in the error vector is a great measure of the channel quality for that code word.

  If more than the maximum number of correcta- ble bits are corrupted in the received code word, the error vector may have no meaning and the number of ones in the error vector will not correspond to the number of bits wrong in the received word. This situ...