What is the minimum number of clusters needed to support at least 20000 simultaneous users given the above cellular structure of each cluster. Define FDMA, TDMA, FHMA, CDMA, SSMA and SDMA, clarifying their characteristics, advantages and disadvantages as multiple access techniques. FDMA is the frequency division multiple access. It assigns individual channels to individual users on-demand. For the period of a call, only a single user uses the channel.
Several users share a single carrier frequency using non-overlapping time slots.
Battery consumption is lower than that in FDMA, since the transmission is not continuous. During the times when transmission is idle, the transmitter can be turned off. Handoff is simpler, since the mobile unit is able to listen to the base stations during the idle time slots. TDMA may incorporate priorities by allocating different number of time slots per user. Spread spectrum techniques, by contrast, use bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth.