intentional emitters like computers or personal digi- a WPAN standard. We first examine the direct-sequence tal assistants. The restrictions are more stringent in the CDMA proposal, based on 802.15-03 334/r3 due to 1- to 3-GHz region to protect cellular telephony and Welborn et al., with some updates from /0137 r0. This global position satellite navigation. Finally, like the proposal divides the available bandwidth into two original requirements on the ISM band, UWB users are chunks, a low band and a high band, avoiding the 5-GHz required to spread their signals over at least 500 MHz UNII region to minimize interference with existing and within the allowed band. projected unlicensed products (Figure 5.1-29). The radio The wide bandwidth available for a UWB signal means can operate using either the low band only, the high band that the peak data rate can be very high indeed. However, only, or both bands, achieving data rates of 450, 900, or the limited total power implies that the range of trans- 1350 Mbps, respectively. Alternatively, the dual-band mission is not very large. As with any transmission operating mode can be used to support full-duplex method, UWB range can be extended at the cost of re- communications, in which the radio can transmit in one duced data rate by using more complex coding methods band and simultaneously receive in the other. to allow a tiny signal to be extracted from the noise. The transmissions use Hermitian pulses, the nomen- The resulting trade-off between range and rate is shown clature referring to the pulse shape and consequent in Figure 5.1-28. Here a full band transmission is one that spectrum (Figure 5.1-30). The high band pulse is shown; exploits the whole 7-GHz bandwidth available under the a longer pulse is used for the low band. FCC specs, whereas a subband transmission uses only the The modulation techniques used are either BPSK or minimum 500-MHz bandwidth. It is clear that a subband a variant of the biphase keying: M-ary biorthogonal approach can deliver 100 Mbps at a f