What are the differences and similarities between multiple access, duplexing, and multiplexing techniques in telecommunications?
• How do FDMA, TDMA, and CDMA compare in terms of bandwidth efficiency, interference, and complexity?
• What are the advantages and disadvantages of FDD and TDD for duplexing?
• How can FDM and TDM be combined to achieve higher data rates and better quality of service?
Multiple access is a technique used in telecommunications to allow multiple users to share a single communication channel. There are several different multiple access techniques, each with its own advantages and disadvantages.
- Frequency division multiple access (FDMA): In FDMA, the available bandwidth is divided into multiple frequency bands, each of which is assigned to a different user. This is the oldest and simplest form of multiple access, and it is still used in many applications, such as radio and television broadcasting.
- Time division multiple access (TDMA): In TDMA, the available time is divided into multiple time slots, each of which is assigned to a different user. This allows multiple users to share the same frequency band, but they can only transmit during their assigned time slot. TDMA is used in many cellular phone systems, such as GSM and IS-136.
- Code division multiple access (CDMA): In CDMA, all users transmit on the same frequency band at the same time. However, each user is assigned a unique code that is used to distinguish their signal from the signals of other users. CDMA is used in many cellular phone systems, such as CDMA2000 and WCDMA.
Duplexing is a technique used in telecommunications to allow communication to flow in both directions over a single communication channel. There are two main types of duplexing:
- Frequency division duplexing (FDD): In FDD, two different frequency bands are used for communication in the two directions. For example, in a cellular phone system, the uplink (from the phone to the base station) might use a different frequency band than the downlink (from the base station to the phone). Users transmit and receive simultaneously on different frequency bands. FDD is commonly used in cellular networks like LTE (Long-Term Evolution).
- Time division duplexing (TDD): In TDD, the same frequency band is used for communication in both directions, but the two directions are separated in time. For example, in a TDD cellular phone system, the uplink might use the first half of a time slot, and the downlink might use the second half of the time slot.
TDD is a duplexing technique that allows a device to transmit and receive data over the same frequency, but at different time intervals.
The device alternates between transmission and reception, using time slots for each. TDD is often used in WiMAX and some 4G and 5G networks.
Multiplexing is a technique used in telecommunications to combine multiple signals into a single signal for transmission over a communication channel. There are two main types of multiplexing:
- Frequency division multiplexing (FDM): In FDM, multiple signals are combined by assigning each signal to a different frequency band. This is the same technique that is used in FDMA.
- Time division multiplexing (TDM): In TDM, multiple signals are combined by interleaving them in time. This is the same technique that is used in TDMA.
