and intolerable. Thus input must be backed off (i.e., level reduced) by >3 dB. This, of course, reduces the EIRP and results in reduced efficiency and reduced information capacity. Consequently, each earth station's uplink power must be carefully coordinated to ensure proper loading of the satellite. The complexity of the problem increases when a large number of earth stations access a transponder, each with varying traffic loads. On the other hand, TDMA allows the transponder's TWT to operate at full power because only one earth-station carrier is providing input to the satellite transponder at any one instant. To summarize, consider the following advantages and disadvantages of FDMA and TDMA. The major advantages of FDMA are as follows: No network timing is required. Channel assignment is simple and straightforward. The major disadvantages of FDMA are as follows: Uplink power levels must be closely coordinated to obtain efficient use of transponder RF output power. Intermodulation difficulties require power back-off as the number of RF carriers increases with inherent loss of efficiency. The major advantages of TDMA are as follows: There is no power sharing and IM product problems do not occur. The system is flexible with respect to user differences in uplink EIRP and data rates. Accesses can be reconfigured for traffic load in almost real time. The major disadvantages of TDMA are as follows: Accurate network timing is required. There is some loss of throughput due to guard times and preambles. Large buffer storage may be required if frame lengths are long. 9.3.5.3 Demand-Assignment Multiple Access (DAMA). The DAMA access method has a pool of single voice channels available for assignment to an earth station on demand. When a call has been completed on the channel, the channel is returned to the idle pool for reassignment. The DAMA system is a subset of FDMA, where each voice channel is assigned its own frequency slot, from 30 to 45 kHz wide. The DAMA access method is useful at earth stations that have traffic 