What Is SDMA?
SDMA stands for Space-division multiple access, it is a channel access method based on creating parallel spatial pipes (focused signal beams) using advanced antenna technology next to higher capacity pipes through spatial multiplexing and or diversity, by which it is able to offer superior performance in radio multiple access communication systems (where multiple users may need to use the communication media simultaneous.
What Is TDMA?
TDMA stands for Time-division multiple access, it is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium e.g radio frequency channel while using only a part of its channel capacity.
What Is FDMA?
FDMA stands for Frequency division multiple access. It is a channel access method used in some multiple access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividing the bandwidth of the channel into separate non-overlapping frequency sub-channels and allocating each sub-channel to a separate user. Users can send data through a subchannel by modulating it on a carrier wave at the subchannel’s frequency. It is used in satellite communication systems and telephone trunklines.
What Is CDMA?
CDMA stands for Code-division multiple access. It is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies . to permit this without undue interference between the users, CDMA employs spread spectrum technology and a special coding scheme.
Also Read: Difference Between VDSL And G.fast
Difference Between SDMA, TDMA, FDMA And CDMA In Tabular Form
| BASIS OF COMPARISON | SDMA | TDMA | FDMA | CDMA |
| Idea | Segment spaced into cells or sectors. | Segments sending time into disjoint time slots demand driven or fixed patterns. | Segment the frequency band into disjoint sub-bands. | Spread the spectrum using orthogonal codes. |
| Signal Separation | Cell structure, directed antennas. | Synchronization in time domain. | Filtering in the frequency domain. | Code plus special receivers. |
| Cell Capacity | Depends on the cell area. | Limited | Limited | No absolute limit on channel capacity but it is an interference limited system. |
| Terminals | Only one terminal can be active in one cell or one sector. | All terminals are active for short periods of time on same frequency. | Every terminal has its own frequency uninterrupted. | All terminals can be active at the same place at the same moment uninterrupted. |
| Transmission Scheme | Continuous | Discontinuous | Continuous | Continuous |
| Advantages | Very simple & increases performance capacity. | Flexible & established fully digital. | Simple, established, robust. | Flexible, less frequency planning needed, soft handover. |
| Disadvantages | It is inflexible as antennas are typically fixed. | Guard space needed (multipath propagation), synchronization difficulty. | Inflexible, frequencies are a scarce resource. | Complex receivers, needs more complicated power control for senders. |
| What To Note | Only useful in combination with TDMA, FDMA or CDMA. | It is a standard in fixed networks. Also together with FDMA or SDMA used in many mobile networks. | Typically combined with TDMA and SDMA. | Still faces some problems such as higher complexity. It can be integrated with TDMA or FDMA. |