s in the matrix. In the uplink, every six information bits are mapped to one of the 64 bit rows of the Hadamard matrix. The 64 bits in the row are substituted for the original 6 bits and the 64 bits are modulated on to the radio carrier using QPSK modulation. This is an inverse fast Hadamard transform. The base station applies a fast Hadamard transform on every 64 received bits. Ideally only one of the resultant FHT coefficients will be nonzero. The nonzero value determines the row number that in turn determines the 6 bits originally sent. In other words, the process exploits the property of 'sequency' implicit in the Hadamard matrix. Elegantly, the IFHT/FHT delivers some useful spreading gain (64/6 = 10.75 dB). It is also error tolerant. Given that the Hamming distance between each Hadamard code is 32, up to 15 bits can be errored per block of 64 without corrupting the 64 bits actually sent. The only slight snag is that all users are cosharing the 64 codes and have to be separated from each other by unique scrambling codes (-1s and + 1s running at the same rate as the data). The spreading codes deliver sensitivity, the scrambling codes deliver selectivity, the pilot and synchronisation codes deliver stability. In the downlink, each row in the Hadamard matrix can be used to carry a unique channel to a unique user. Theoretically, this means 62 channels per 1.25 MHz of channel bandwidth (taking out the pilot and synchronisation channel). Every single information bit is replaced with the entire 64 bits of the users code (a 64/1 expansion). A data rate of 19.2 kbps therefore is spread to an outbound data rate of 1.2888 Mbps occupying a 1.25-MHz channel. As with the uplink, a scrambling code that is unique to the base station is also applied to provide base station to base station selectivity (actually a single code 'pseudonoise' sequence off set in time for each base station). Later evolutions of IS95 have increased the matrix to 128 rather than 64 but the same principles apply. Either way, the CDMA multiplexing or c