CDMA transmitter and method generating combined high-rate and low-rate CDMA signals

摘要

A wideband code division multiple access (CDMA) communication system overlayed on an IS-95 network generates two or more digital bit streams from a group of wideband digital data streams, each digital bit stream spread to form a CDMA component signal. Each CDMA component signal is combined with a corresponding IS-95 digital bit stream to form a composite CDMA signal, allowing a base station to share transmitter subsystems between the wideband and IS-95 systems. For up to three carrier frequencies, up to three composite CDMA signals are employed. A digital bit stream for a group of summed user conversations in the IS-95 system modulates a respective RF carrier frequency to generate a low-power RF signal. The CDMA component signals of the wideband CDMA system are generated so each has a chip rate identical to the chip rate of the digital bit streams of the IS-95 system. The baseband digital data streams for all wideband user conversations are summed digitally for each targeted RF carrier frequency to produce the composite wideband digital signal for each targeted frequency. In one application, each composite wideband digital signal, each at the IS-95 chip rate, is then used to modulate a carrier frequency which is either the same, or has approximately the same frequency and phase as the carrier frequency used in the IS-95 system. Three low-power RF signals are produced in the wideband system, each having the same spectral characteristics as the corresponding low-power RF signals generated in the IS-95 system. These low-power RF signals at the same frequency are combined into a single signal provided to the amplifier and antenna subsystem of a base station transmitter. In another application, each composite digital signal is digitally combined with a respective IS-95 digital bit stream prior to modulation by respective RF carrier. Therefore, signal combining between the IS-95 and wideband CDMA portions of a base station system is accomplished either digitally or with RF signals prior to amplification, thereby allowing the IS-95 system and wideband CDMA system portions of the base station to share RF filters, amplifiers and antennas of the base station transmitters.