Multiple Access in RF communications refers to the techniques used to allow multiple users or devices to share the same frequency spectrum or channel simultaneously. It is essential in environments where numerous devices need to communicate without causing interference with each other. The core idea is to divide the available resources, whether they be time, frequency, code, or space, so that each user can transmit and receive data without collisions or degradation in performance.
Multiple access can be confused with duplexing, but they serve different purposes. Duplexing is concerned with managing bidirectional communication between two endpoints, typically by separating the transmit and receive channels in either time (TDDTDD: A wireless communication technique that uses a single frequency band for both transmitting and receiving operations but separates these operations in time. In a TDD system, upstream (transmission from user equipment to base station) and downstream (transmission from base station to user equipment)…) or frequency (FDDFDD: A communication technology that uses separate frequency bands for transmitting and receiving operations. This technique enables simultaneous bi-directional communication by allocating one frequency band for upstream (transmission from the user equipment to the base station) and another distinct…). In contrast, multiple access focuses on managing the communication between multiple users or devices over a shared medium. Put simply, Duplexing is used to manage the direction (downlink vs uplink), where Multiple Access manages multiple users sharing the downlink/uplink simultaneously.
| Name | Full Name | Description |
|---|---|---|
| CDMA | Code-Division Multiple Access | Code-Division Multiple Access (CDMA) is a digital cellular technology that utilises spread spectrum techniques. Unlike competing systems, such as GSM, that use time-division multiplexing, CDMA does not assign a specific frequency to each user. Instead, every channel utilises the full available... |
| CP-OFDMA | Cyclic-Prefix Orthogonal Frequency Division Multiple Access | Cyclic-Prefix Orthogonal Frequency Division Multiple Access (CP-OFDMA) is a digital multi-carrier modulation scheme utilised in wireless communications to prevent intersymbol interference (ISI). This technique employs a cyclic prefix to preserve the orthogonality of transmitted signals, thus... |
| CSMA-CA | Carrier Sense Multiple Access with Collision Avoidance | Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is a network protocol for carrier transmission. This protocol is used in wireless networks to avoid collisions caused by the simultaneous transmission of data packets. In CSMA/CA, before a device transmits data, it first checks... |
| FDMA | Frequency Division Multiple Access | Frequency Division Multiple Access (FDMA) is a channel access method used in telecommunications. It divides the frequency band into multiple distinct channels, each assigned to an individual user. This enables multiple users to transmit data simultaneously without interference. FDMA is primarily... |
| OFDMA | Orthogonal Frequency-Division Multiple Access | Orthogonal Frequency-Division Multiple Access (OFDMA) is a multi-user version of the popular digital modulation scheme known as Orthogonal Frequency Division Multiplexing (OFDM). It is an advanced modulation technique used in telecommunications, allowing for the simultaneous transmission of multiple... |
| PDMA | Pattern-Division Multiple Access | Pattern-Division Multiple Access (PDMA) represents an advanced communication technology that allows multiple users to share a common frequency band. It achieves this by assigning unique spreading codes to each user, thus preventing interference between signals. In PDMA, the entire frequency... |
| SC-FDMA | Single-Carrier Frequency Division Multiple Access, LP-OFDMA | Single-Carrier Frequency Division Multiple Access (SC-FDMA) is a frequency division multiple access scheme that has gained popularity, particularly in long-term evolution (LTE) uplink communication. It is a method that allows multiple users to share a common communication channel by dividing the... |
| SDMA | Space-Division Multiple Access | Space-Division Multiple Access (SDMA) is a method of wireless communication that separates signals based on the physical space they occupy. It is a channel access method based on creating parallel spatial pipes (focused signal beams) using advanced antenna technology next to higher capacity pipes... |
| TDMA | Time-Division Multiple Access | Time-Division Multiple Access (TDMA) is a channel access method utilised in shared medium networks such as early cellular networks (2G GSM). This method allows several users to share the same frequency band by dividing the signal into different time slots. Each user is allocated a unique time slot... |
| WDMA | Wavelength-Division Multiple Access | Wavelength-Division Multiple Access (WDMA) is a technology utilised in fibre-optic communications. This technology enables multiple data streams to be transmitted simultaneously over a single optical fibre. Each data stream is assigned a unique wavelength of light, effectively creating multiple... |