sequence little interference by using different orthogonal spreading methods were developed for military applications and codes for each signal: codes whose correlation with each are also used in those cellular telephones that are based other is small or zero. This technique is key to the on code-division multiple access (CDMA) standards. In operation of CDMA cellular phone standards but is not DSSS, the relatively slow data bits (or more generally used in the 802.11 standards. symbols) are multiplied by a much faster pseudo-random The basic symbol rate is 1 Mbps; each symbol consists sequence of chips, and the product of the two is used as of 11 chips, SO the chip rate is 11 Mbps. The spreading the transmitted signal. Recall that the bandwidth of gain, the ratio of the actual bandwidth to that required a signal is determined by the number of symbols per by the underlying data, is thus 11:1 or about 10.4 dB, second transmitted, whether or not those symbols con- meeting the FCC's original minimum requirement of tain useful information. Thus, the bandwidth of a DSSS 10 dB. Because the chip rate is 11 Mbps, one would signal is determined by the chip rate, which in general is expect the bandwidth required to be modestly in excess much larger than the data rate; a DSSS signal can satisfy of 11 MHz. The actual bandwidth of the transmitted the FCC's requirement that the signal be spread. Fur- signal depends on the details of precisely how the signal is ther, the received signal can be multiplied again by the filtered and transmitted; rather than specifying such same sequence to recover the original lower data rate. In implementation-specific aspects, the standard simply spectral terms, multiplying the received wide-bandwidth defines a spectral mask, which provides a limit on how signal by the chip sequence collapses all its energy into much power a compliant transmitter is allowed to radiate a narrower bandwidth occupied by the actual data while at a given distance from the nominal center frequency. simultaneously rando