Cyclic Equalization--A New Rapidly Converging Equalization Technique for Synchronous Data Communication

The effective data throughput in polling systems is, to a large degree, dependent on the start-up time of the data modems that are used in the network. Many of these systems operate at high speed and transmit data blocks of comparatively short duration. At 4800 b/s, a 1000-bit block is transmitted in about 200 ms, and to achieve a reasonable overall efficiency, the time needed to condition the modem for transmission (start-up) should be short in comparison to the time required to transmit an average block. This becomes increasingly difficult with 369 higher modem speeds. Prior to the transmission of the actual data, timing and carrier information must be recovered very accurately, and the adaptive equalizer that is necessary to cope with the linear channel distortion at such high speeds must be trained. The time required to adjust the equalizer represents the bulk of the modem start-up time; it is thus important to study in detail the problems associated with fast equalizer start-up. The most common structure of such an equalizer consists of a transversal filter with a set of controlled gain coefficients that are spaced at the symbol interval T. and the start-up problem is to find an initial set of "reasonably good" values for these coefficients in a very short time. The purpose of this paper is to present a practical method for doing this. We first provide some background and discuss some factors that affect equalizer start-up. This leads to the principle of cyclic equalization that is discussed in Section III.