Netro Corporation

P-com, Inc.

Stuart M Feeney

Eliezer Pasternak

Gideon Ben-Efraim

The present invention provides an efficient point-to-multipoint microwave ATM network including a base station (BS) broadcasting a continuous transmission with a sector antenna. The system uses time division multiplex (TDM) for downstream transmission and time division multiple access (TDMA) for upstream transmission. The downstream transmission consists of ATM cells encapsulated in MAC protocol data units (PDUs) for forward error correction (FEC) and synchronization. Small Subscriber Terminals (STs), including Subscriber Radio Units (SRUs), receive the broadcast and pass it to a Subscriber Access System (SAS) that drops the ATM cells addressed only to them. To allow strong FEC protection and to maintain the same symbol rate as the downstream transmission without sacrificing bandwidth, a modified trellis code modulation technique, which incorporates Reed Solomon coding, is used during upstream transmission.

Wireless ATM metropolitan area network

An automatic frequency control circuit measures the deviation in frequency of a selected signal from a reference frequency and when the deviation exceeds a selected threshold which is variable, steps the frequency of the selected signal back to the proper frequency. The selected signal is typically an intermediate frequency (IF) signal in a radio receiver. For detection of frequency deviation, an exclusive OR (EX-OR) circuit receives a reference signal having a frequency proportional to a desired IF carrier frequency and an input signal having a frequency proportional to an actual IF frequency. A divider coupled to a voltage controlled oscillator (VCO) used in demodulation of the IF signal provides the input signal. An output signal of the EX-OR circuit includes a component with a frequency proportional to the difference between the actual and desired IF frequencies. A low pass filter isolates that component, and a charge pump generates a control voltage proportional to the frequency of that component. A comparison of the control voltage and the threshold determines whether the actual IF frequency should be changed.

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Cupertino, CA, United States of America

Stuart M Feeney