ansmitted in each transmission time slot. Information is encoded via pulse position or pulse amplitude modulation (PPM, PAM). The spreading effect of time hopping, together with the short pulse duration, results in a transmitted signal spread across an ultra-wide bandwidth. Table 4-8: Benefits of Common Spread Spectrum Techniques Frequency Hopping Direct sequence Simple to design and manufacture Higher data speeds Cheaper to implement Increased range Higher density of overlapping Throughput is interference-tolerant up to networks a threshold level Gradual degradation of throughput with interference Radio Communication Basics Spread Spectrum in Wireless Networks - Pros and Cons The advantages of spread spectrum techniques, such as resistance to interference and eavesdropping and the ability to accommodate multiple users in the same frequency band, make this an ideal technology for wireless network applications (Table 4-8). Although the good interference performance is achieved at the cost of relatively inefficient bandwidth usage, the available radio spectrum, such as the 2.4 GHz ISM band, still permits data rates of up to 11 Mbps using these techniques. Since speed and range are important factors in wireless networking applications, DSSS is the more widely used of the two techniques although, because of its simpler and cheaper implementation, FHSS is used for lower rate, shorter-range systems like Bluetooth and the now largely defunct HomeRF. Wireless Multiplexing and Multiple Access Techniques Introduction Multiplexing techniques aim to increase transmission efficiency by transmitting multiple signals or data streams on a single medium. The resulting increased capacity can be used either to deliver a higher data rate to a single user, or to allow multiple users to access the medium simultaneously without interference. User access to the bandwidth can be separated by a numbers of means: in time (TDMA), in frequency (FDMA or OFDMA), in space (SDMA) or by assigning users unique codes (CDMA). These methods will be d