Abstract: Techniques for increasing the capacity of a radio link, using radio signal superimposing in space and frequency and subsequent signal restoration, are described. Each of the transmitting and receiving systems are connected to a plurality of collocated antennas. The signals that are superimposed are recovered by one or a plurality of restorers. The disclosed method of signal processing involves appropriate filtering of signals, then summing them in order to restore the original individual signals and to cancel out all undesired signals received as a result of superimposing. Preferably, the spacing between antennas is optimized so that while the undesired signals are minimized or canceled out, the restored signals are maximized. In simple situations, signal filtering may be reduced to phase adjustment of the signals and the restoration may be done at RF, IF or baseband. In more complex situations, general adaptive filters implemented in baseband may be preferred.

Abstract: The output of an analog modem (12) at a remote cellular station (14) is converted to a digital signal in accordance with G.711 compaction before being applied to a processing chain (36) that results in wireless transmission to a cellular-telephone base station (24). Together with a signal chain (50) at the base station, the remote station's processing chain forms a transparent channel whose output is applied directly to a digital land-line span of the public switched telephone network. Because the G.711 encoding is the same as that conventionally employed for voice communication over a PSTN digital span, the modem's performance is the same in the absence of link errors as that which would result from conventional coupling directly to a PSTN digital link.

Abstract: An improved decision feedback equalizer for use with digital communications. The equalizer includes an error detector, a process controller, a parameter selector and a data buffer for temporarily storing a digital data signal received from a communication channel. The error detector determines whether the equalizer is accurately tracking changes in the communication channel's characteristics or is lost. When the error detector determines that the equalizer is lost, the process controller responsively generates control signals for initiating an optimal retraining/recovery method for the prevailing conditions. In some retraining/recovery methods, data is temporarily stored in the buffer. The stored data is later retrieved and processed once the equalizer is retrained. Retraining is performed using a retraining signal received via the communication channel or, if available, a portion of the data signal which is suitable for retraining, thereby permitting more rapid resumption of data reception.