ication is possible [22] for (3.2) For this Shannon limit, we have M = 1.44 X PG. (3.3) Direct-Sequence Spread-Spectrum CDMA in High-Density Networks This theoretical Shannon limit shows that spread-spectrum A-CDMA sys- tems can have more users per cell than traditional systems, which are lim- ited by the number of dimensions, such as non-overlapping frequency bands (FDMA) or time slots (TDMA). Of course, with practical coded A-CDMA radios in a cell, it may be difficult to accommodate this many users in a sin- gle cell. FDMA and TDMA systems, however, use up to 20 percent of this theoretical capacity to ensure the practical isolation between non-interfer- ing channels. 3.5.1 Data versus Voice Applications For data applications, the bit error probabilities are typically less than 10-5, and consequently the threshold of tolerable interference shown in Figure 3.4 may be lower than that in digital voice applications, resulting in fewer CDMA channels. Another way to increase CDMA capacity for voice appli- cations is to use voice activation circuits that cut off radio transmit power when there is no voice activity. Since the average voice activity factor is 35 percent, using such circuits in a CDMA system dramatically lowers the noise floor or allows proportionally more active voice channels. Owing to the higher tolerance to error and the option of voice activation, the spread-spectrum CDMA's capacity advantage is greater with digital voice systems than with data networks. 3.5.2 Power Control For an interference-limited CDMA system, each active mobile transmitter produces some level of interference in receivers of other mobile radio sig- nals at the cell site. Therefore, mobile radios should not transmit any more power than is necessary for satisfactory performance. Power control of mobile radios would ensure that for a fixed number of active radios, the interference caused by each radio is minimal and approximately equal. Another benefit of power control is that the life of usable battery time is extended for mobile s