Browse Prior Art Database

TIMING LOSS DETECTOR FOR ROBUST DATA TRANSMISSION

IP.com Disclosure Number: IPCOM000007171D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2002-Mar-01
Document File: 8 page(s) / 484K

Publishing Venue

Motorola

Related People

Yong-Hwan Lee: AUTHOR

Abstract

Unlike voice communication, data communica- tion, can be seriously affected by a transient chan- nel impairment. In some cases, synchronization between the transmitter and the receiver may not be recovered in the presence of these kinds of impairments without a forced reinitialization proc- ess. Therefore, it is highly desirable for data com- munication equipment to have an efficient synchro- nization loss detector for robust recovery. In this paper, one such detector is proposed for high speed data transceivers with a secondary channel embedded in the main channel. A known sequence multiplexed with the secondary channel data is repeatedly sent through the embedded secondary channel. For continuous watch-dog like operation, the detection is sequentially performed based on a modified up/down counter scheme. The performance of the proposed detector is analytically evaluated in closed form.

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Technical Developments Volume 22 June 1994

TIMING LOSS DETECTOR FOR ROBUST DATA TRANSMISSION

by Yong-Hwan Lee

work nodes, or phase wander and jitter on the dig- ital bit stream [l]. Like other forms oftransient noise, slips cause occasional audible clicks and do not seri- ously hinder voice communications [2]. However, even though the slip rate is regulated acceptably low, a single slip can seriously affect data communica- tion. For example, a slip affects Group 3 facsimile transmission, where a maximum of eight horizon- tal scan lines can be missed [3]. Experimental results on voiceband modems indicate that a single slip causes a long burst of errors over a time period of up to several seconds, depending on the modem type and data rate [4]. In some cases, the modem never recovers from a slip and requires a forced manual reset. Therefore, it is highly desirable for a trans- ceiver to have a detector for robust recovery from a loss of synchronization due to such catastrophic tran- sient impairments.

  High speed data transceivers (or modems) usu- ally have a secondary channel to provide an addi- tional path for servicing other functions, such as net- work management. The secondary channel can be implemented using a frequency division multiplexing method. However, to maximize the use of the chan- nel bandwidth and to reduce the implementation cost, the secondary channel is ohen embedded into the main channel. Using a time division multiplexing (TDM) method, for example, the secondary chan- nel data is synchronously multiplexed into the main channel data before being modulated. The required bandwidth of this embedded secondary channel can

be obtained at a small additional cost of the main channel signal-to-noise ratio (SNR) and can be flex- ibly adjusted without great difftculty.

  The characteristics of a synchronous TDM sig- nal can be used for detecting fatal transient impairments which cause a loss of system synchro- nization. After being multiplexed with the second- ary channel data, a predetermined sync code word (SCW) is repeatedly transmitted through the embedded secondary channel. Each bit ofthe SCW

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ABSTRACT

  Unlike voice communication, data communica- tion, can be seriously affected by a transient chan- nel impairment. In some cases, synchronization between the transmitter and the receiver may not be recovered in the presence of these kinds of impairments without a forced reinitialization proc- ess. Therefore, it is highly desirable for data com- munication equipment to have an efficient synchro- nization loss detector for robust recovery. In this paper, one such detector is proposed for high speed data transceivers with a secondary channel embedded in the main channel. A known sequence multiplexed with the secondary channel data is repeatedly sent through the embedded secondary channel. For continuous watch-dog like operation, the detection is sequentially performed based on a modified up/down counter scheme. The pe...