h data bit is is partitioned into 528-MHz bands (recall that 500 MHz multiplied by a 24- or 32-chip code. This scheme is is the smallest bandwidth allowed by the FCC for an similar to the Barker code used to multiply data bits in UWB application), as shown in Figure 5.1-32. The bands the 802.11 classic PHY, but unlike 802.11, in this case are assembled into five groups. Group 1 devices are multiple codes are provided to enable simultaneous expected to be introduced first, with more advanced noninterfering use of the bands. Four independent 24- group 2-5 devices providing improved performance. All chip codes are provided, allowing four independent users devices are required to support group 1 bands; the higher of each band or eight total collocated piconets. A rake bands are optional. receiver can be used to separately add the contributions The implementation requires a 128-point inverse FFT of sequences of chips arising from paths with different to create subcarriers spanning slightly more than delays; a decision feedback equalizer is assigned to deal 500MHz of bandwidth. To reduce the computational with interference in the data symbols resulting from demands, QPSK modulation on each subcarrier is used, multipath. Both convolution and block code options are instead of the higher QAM modulations used in 802.11 provided; the codes may be concatenated for improved a/g. Furthermore, for data rates less than 80Mbps, the performance at the cost of computational complexity. subcarrier amplitudes are chosen to be conjugate sym- Link performance at a transmit-receive distance of metric around the carrier. That is, the nth subcarrier at 4 m and data rate of 200 Mbps is summarized in Table 5.1-4. Note that the transmit power, 10 dBm, is 10 dB Table 5.1-4 Link performance, DS-CDMA UWB at 200 mbps. less than the lowest Bluetooth output and about 25 dB less than a typical 802.11 transmitter. The required bit Parameter Value energy over noise, Eb/No, is comparable with what we Data rate have encountered in conventional BPSK or 