Space Division Multiple Access is used to allocating a separated space to users in wireless networks. In this system, the base station has no information on the position of the mobile units within the cell and radiates the signal in all directions within the cell in order to provide radio coverage. A MAC algorithm could now decide which base station is best, taking into account which frequencies, time slots or codes are still available. It is a combination of one or more schemes. The basis for the SDMA algorithm is formed by cells and sectorized antennas which constitute the infrastructure implementing space division multiplexing.

TDMA: Time division multiple access offers a much more flexible scheme, which comprises all technologies that allocate certain time slots for communication, i.e., controlling TDM. If we tune into a certain frequency that is not necessary, i.e. the receiver can stay at the same frequency the whole time. Using only one frequency, and thus very simple receivers and transmitters, many different algorithms exist to control medium access. As already, mentioned, listening to different frequencies at the same time is quite difficult, but listening to many channels separated in time at the same frequency is simple. Almost all MAC schemes for wired networks work according to this principle, e.g., Ethernet, Token Ring, ATM etc. The synchronization between sender and receiver has to be achieved in the time domain. It can be done by using a fixed pattern similar to FDMA techniques, i.e., allocating a certain time slot for a channel, or by using a dynamic allocation scheme. Dynamic allocation schemes require an identification for each transmission as this is the case for typical wired MAC schemes (e.g., sender address) or the transmission has to be announced beforehand. MAC addresses are quite often used as identification. This enables a receiver in a broadcast medium to recognize if it really is the intended receiver of a message. Fixed schemes do not need identification, but are not as flexible considering varying bandwidth requirements.

FDMA: Frequency division multiple access (FDMA) comprises all algorithms allocatingfrequencies to transmission channels according to the frequency divisionmultiplexing (FDM). Channels can be assigned to the same frequency at all times, i.e., pure FDMA,or change frequencies according to a certain pattern, i.e. FDMA combined withTDMA. FDM is often used for simultaneous access to the medium bybase station and mobile station in cellular networks. Here the two partners typicallyestablish a duplex channel, i.e. a channel that allows for simultaneoustransmission in both directions. The two directions, mobile station to base stationand vice versa are now separated using different frequencies. This scheme is then called frequency division duplex (FDD).

The two frequencies are also known as uplink, i.e., from mobile station to base station or from ground control to satellite, and as downlink, i.e., from base station to mobile station or from satellite to ground control. All uplinks use the band between 890.2 and 915 MHz, all downlinks use 935.2 to 960 MHz. According to FDMA, the base station, shown on the right side, allocates a certain frequency for up- and downlink to establish a duplex channel with a mobile phone. Up- and downlink have a fixed relation. If the uplink frequency is fu = 890 MHz + n·0.2 MHz, the downlink frequency is fd = fu + 45 MHz, i.e fd = 935 MHz + n·0.2 MHz for a certain channel n. The base station selects the channel. Each channel (uplink and downlink) has a bandwidth of 200 kHz.

CDMA: Code Division Multiple Access takes an entirely different approach from TDMA. CDMA, after digitizing data, spreads it outover the entire available bandwidth. Multiple calls are overlaidon each other on the channel,with each assigned a unique sequence code. CDMA is a form of spread spectrum, which simply means that data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range.

In CDMA, each phone's data has a unique code.

All of the users transmit in the same wide-band chunk of spectrum. Each user's signal is spread over the entire bandwidth by a unique spreading code. At the receiver, that same unique code is used to recover the signal. Because CDMA systems need to put an accurate time-stamp on each piece of a signal, it references the GPS system for this information. Between eight and 10 separate calls can be carried in the same channel space as one analog AMPS call.