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Showing papers by "Codex Corporation published in 1975"


Patent
23 Jul 1975
TL;DR: In this article, a high speed QAM data communications receiver of the type adapted to receive bursts of signals having a bandwidth B Hz and sent at a predetermined rate of 1/T signals per second over a channel, wherein the receiver includes an automatic adaptive equalizer having taps spaced equally apart, tap coefficient circuitry for repeatedly multiplying the output of each tap by a respective tap coefficient, and adjustment circuitry for adjusting the tap coefficients, and output circuitry responsive to the equalizer for providing output signals at times kT + τ, k = 0, 1,..., where τ
Abstract: In a high speed QAM data communications receiver of the type adapted to receive bursts of signals having a bandwidth B Hz and sent at a predetermined rate of 1/T signals per second over a channel, wherein the receiver includes an automatic adaptive equalizer having taps spaced equally apart, tap coefficient circuitry for repeatedly multiplying the output of each tap by a respective tap coefficient, and adjustment circuitry for adjusting the tap coefficients, and output circuitry responsive to the equalizer for providing output signals at times kT + τ, k = 0, 1, . . . , where τ is a timing epoch, that improvement wherein the taps are spaced apart by T/n seconds, where n is greater than TB, and control circuitry is provided for early actuation of the adjustment circuitry to begin adjustment of the tap coefficients and hence training of the equalizer regardless of the initial value of the timing epoch, whereby the data capacity of the receiver is increased by reduction of the time required for set up of the receiver.

65 citations


Patent
23 Jul 1975
TL;DR: In this paper, an early segment of each burst of signals is used to adapt the equalizer in a decision-directed mode, and when the adaptation is completed the system switches to its normal higher rate of data transmission.
Abstract: Initial Adjustment of a receiver having an automatic adaptive equalizer in a modem communication system is accomplished by employing a data transmission rate lower than normal for an early segment of each burst of signals. At this lower rate, accurate reception is possible without complete adaptation of the equalizer. These same (early segment) signals are used to adapt the equalizer in a decision-directed mode. When the adaptation is completed the system switches to its normal higher rate of data transmission.

59 citations


Journal ArticleDOI
TL;DR: A TDM interrupt scheme appears to be the most efficient way to identify requests and process control signals in a dynamic allocation system, but introduces a problem of interference between simultaneous signals.
Abstract: The features and limitations of time- and frequencydivision miltiplexed (TDM and FDM) systems for providing interactive services on broad-band communication networks are considered. We find that TDM systems make efficient use of bandwidth for digital signal rates below 10 kbits/s while FDM systems are efficient for analog signals and digital signal rates above 1 kbit/s. Although TDM and FDM systems can employ static allocation in which fixed channels are assigned to subscribers, dynamic allocation increases the efficiency of bandwidth usage by an order of magnitude. A TDM interrupt scheme appears to be the most efficient way to identify requests and process control signals in a dynamic allocation system, but introduces a problem of interference between simultaneous signals (not present with a polling technique for request identification).

7 citations