gh the appropriate processor. For instance, if a certain spread spectrum processor has an input S/N of 12 dB and an output S/N of 20 dB, then its processing gain is 8 dB. bandwidth bit rate in Hz (18.5) More commonly, processing gain is given in a decibel value; then spread bandwidth in Hz Gp(dB) = 10 log (18.6) information bit rate 8 AM for "toll-quality" telephony. CELLULAR AND PCS RADIO SYSTEMS Example. A certain cellular system voice channel information rate is 9.6 kbps and the RF spread bandwidth is 9.6 MHz. What is the processing gain? Gp(dB) = 10 log(9.6 X 106) - 10 log 9600 - 69.8 - 39.8 (dB) = 30 dB It has been pointed out by Steele (Ref. 2) that the power control problem held back the implementation of CDMA for cellular application. If the standard deviation of the received power from each mobile at the base station is not controlled to an accuracy of approximately 11 dB relative to the target receive power, the number of users supported by the system can be significantly reduced. Other problems to be overcome were syn- chronization and sufficient codes available for a large number of mobile users (Ref. 2; see also Ref. 14). Qualcomm, a North American company, has a CDMA design that overcomes these problems and has fielded a cellular system based on CDMA. It operates at the top of the AMPS band using 1.23 MHz for each uplink and downlink. This is the equivalent of 41 AMPS channels (i.e., 30 kHz X 41 = 1.23 MHz) deriving up to 62 CDMA channels (plus one pilot channel and one synchronization channel) or some 50% capacity increase. The Qualcomm system also operates in the 1.7 to 1.8-GHz band (Ref. 2). EIA/TIA IS-95 is based on the Qualcomm system. Its processing gain, when using the 9600-bps information rate, is 1.23 X 106/9600 or about 21 dB. 18.6.4.1 Correlation: Key Concept in Direct Sequence Spread Spectrum. In direct sequence (DS) spread spectrum systems, the chip rate is equivalent to the code generator clock rate. Simplistically, a chip can be considered an element of RF energy with a certain recogn