The principle of time-division multiplexing (TDM) consists in sequentially allocating a common frequency channel for transmitting the signals of each information channel in a multichannel system. In foreign sources, the term Time Division Multiple Access (TDMA) is used to describe this principle.
TDMA — time-division multiple access. This is a method of using radio frequencies in which several subscribers share the same frequency slot, with each subscriber using different time slots for transmission. The TDMA principle is applied in standards such as GSM, EGSM, D-AMPS, and PDC (Japanese standard).
A synonym for this technology is TDD (time division duplex — time-division of channels).
Advantages of TDMA technology:
• Improves communication quality. The use of digital voice transmission technologies allows accurate reproduction of human speech even at low radio signal levels, ensuring high-quality audio transmission throughout the coverage area.
• Increases spectral efficiency and saves frequency resources. By organizing two logical information channels within a single physical radio channel, the need for frequency resources is reduced by half.
• Integrates voice and data transmission in a single radio station. By creating two information channels on one radio channel, one can be used for voice transmission and the other for data transfer.
• Significantly extends battery life. When using only one time slot, the radio transmits only 50% of the time compared to a conventional analog radio, which saves about 40% of battery capacity and extends its service life.
Challenges of TDMA technology:
As with frequency-division multiple access (FDMA), there are mutual interferences, mainly due to two reasons. The first is that linear distortions caused by limited bandwidth and the non-ideal amplitude-frequency and phase-frequency characteristics of any real-world communication system impair the pulse nature of signals. In time-division transmission, this leads to pulses from one channel overlapping with those of other channels. In other words, inter-channel crosstalk or intersymbol interference occurs. Additionally, interference can result from imperfect synchronization of clock pulses between the transmitting and receiving sides.
Although theoretically both time and frequency division offer the same efficiency in using the frequency spectrum, TDMA systems are generally less efficient than FDMA systems in this regard. However, systems with time division have a clear advantage in that the different transmission times of signals from different channels eliminate crosstalk caused by nonlinear distortions. Moreover, time-division equipment is simpler than frequency-division systems, where a duplex filter (duplexer) is required to separate forward and reverse channels.
Related articles:
FDMA,
GSM standard,
EGSM, DMR standard, CDMA