ice to host) transfers. Data payload size When interference causes PER to rise, reducing packet size can improve throughput by reducing uncorrectable errors. RF channel selection Wireless USB's MB-OFDM radio provides multiple alternative channels which can be used by a host if supported by all devices in the cluster. Host schedule control Allowing isochronous data transfers to temporarily use channel time allocated for asynchronous transfers, in order to retransmit failed isochronous data packets. Dynamic bandwidth Host control of the spectral shaping capabilities of control the MB-OFDM UWB radio, described in the following section. In wireless USB, the host and other devices can maintain statistical information on packet error rate and on link indicators such as received signal strength (RSSI) and link quality (LQI). The latter indicator measures the error in the received modulation of successfully decoded symbols. The main RF link controls available in wireless USB are described in Table 4-20. Transmit power control and RF channel selection are also included in the network optimisation measures introduced in the 802.11k extension to the Wi-Fi networking standard, covered in Chapter 6. Ultra Wideband Radio Introduction Ultra Wideband wireless communication systems are based on impulse radar technology that was developed for military applications by the Chapter Four USA and USSR in the 1960s. Impulse radar or radio transmits extremely short electromagnetic pulses, typically less than 1 ns (nanosecond) in length, with no underlying carrier signal. Such short pulses result in an effective bandwidth of the transmission that may be from 500 MHz up to several GHz. In 2002 the FCC in the USA opened 7.5 GHz of radio spectrum for UWB applications, from 3.1 to 10.6 GHz, and adopted a definition of UWB as any intentional transmission in which the bandwidth to -3 dB points was at least 20% of the mean frequency of the transmission, with a minimum bandwidth of 500 MHz. Since UWB transmissions cover a wide swath of the radio 