CHAPTER 5.2 Short-range wireless applications and technologies Packet fragmentation The two interference-avoiding methods described above are applicable primarily for action by the Bluetooth network. One method that the Wi-Fi network can employ to improve throughput is packet fragmentation. By fragmenting data packets and sending more, but shorter transmission frames, each transmission will have a lower probability of collision with a Bluetooth packet. Although reducing frame size increases the percentage of overhead bits in the transmission, when interference is heavy the overall effect may be higher throughput than if fragmentation was not used. Increasing bit rate for a constant packet length will also result in a shorter transmitted frame and less exposure to interference. The methods mentioned above for reducing in- terference presume no coordination between the two different types of collocated wireless networks. How- ever, devices are now being produced, in laptop and notebook computers for example, that include both Wi-Fi and Bluetooth, sometimes even in the same chipset. In this case collaboration is possible in the device software to prevent inter-network collisions. AMPLITUDE 1 0 ­ 1 ­1 ­0.5 0 0.5 1 TIME Figure 5.2-27 UWB monopulse. Differing from conventional radio communication systems, which use up conversion and down conversion to pass information signals between baseband and band- pass frequency channels where wireless propagation occurs, UWB signal generation and detection use base- band techniques. An example of a UWB ``carrier'' is a Gaussian monopulse, shown in Figure 5.2-27. Its power spectrum is shown in Figure 5.2-28. If the time scale in Figure 5.2-27 is in nanoseconds, then the width of the pulse is 0.5 nanoseconds and the 3 dB bandwidth of the power spectrum is approximately 3.2 GHz with maxi- mum power density at 2 GHz. In order to pass information over a UWB communi-