A New Equalizer Structure for Fast Start-Up Digital Communications

In order to meet the needs of the rapidly growing computer and data processing industries, a number of high-speed data sets have been developed in recent years for voiceband telephone channels. Most of these data sets use transversal filters 1 for precise automatic equalization. The transversal equalizer consists of a tapped delay line with variable tap gains. During a start-up period prior to data transmission, the tap gains are adjusted automatically to minimize the peak distortion 1 or the mean-square error 2,3 - 4 of the received pulses. The time required to adjust the tap gains to nearly their optimum settings is usually called the settling time of the equalizer. Most automatic equalizers have settling times of a few seconds. The start-up time of the system can be longer because there are usually other operations to be performed in the start-up period (operations such as synchronization, carrier recovery, and so forth). Recently, much attention has been focused on the possible use of the high-speed data sets in private-line multiparty polling systems (such as airline reservation systems, on-line banking systems, and so forth). Such systems are generally real-time information retrieval systems where the inquiry and response are short (the message lengths are usually less than 1000 bits 5 ). With a 4800 b / s data set, it takes only 0.208 second to transmit a message of 1000 bits. Consequently the actual transmission time can be much less than the start-up time of the system (which can be five seconds).