What is TDMA? How does the 2-slot radio work?

- Apr 18, 2019-

Two-way radio is about to achieve the biggest leap since its invention

Transistors - the transition from analog to digital. Digital radio offers many advantages over analog radio, including improved voice

A wider range of quality, better privacy, advanced call control features, easy integration with data systems and more.


We are now at the beginning of a massive migration of professional digital broadcasting.

application. Therefore, it is necessary to increase the spectral efficiency. Therefore, it is necessary to divide a channel that can only make one call at a time into two channels.


There is a technique to achieve "split" of the channel, allowing multiple accesses on a single channel. 


Time division multiple access (abbreviation: TDMA) is a way to implement shared radio communication. It allows multiple users to use the same frequency in different time slots. Users transmit quickly, one after the other, and each user uses their own time slot. This allows multiple users to share the same transmission medium.


TDMA mode shared communication channel is "in turn": only one transmitter is assigned a channel at a time. Of course there must be some kind of agreement to determine who has the transfer rights, time, frequency and duration. A simple example is that a two-way radio user uses the word "over" to indicate the termination of a transport stream and release the communication channel for transmission by other users.

TDMA-2-time-slot-structure

More formal arrangements are often required, especially when each user is assigned a very short but repetitive engagement. The entire time period can be divided into designated "time slots", and each transmitter is assigned a different time slot for transmission. This scheme requires synchronization of all radio transmitters, plus a "supervisor" to allocate time slots because new transmitters want to enter the channel to track vacant time slots. Some "overhead" space must be provided to allow for transitions between transmitter time slots; the better the synchronization, the less time lost for these transition periods. Time multiplexing also means that the data stream from a given transmitter is not contiguous, but bursty. In order to represent a continuous conversation, the digitized information acquired during the time period between transmissions must be time-compressed, transmitted in bursts, and then spread in the receiver to form a transparent continuous message.


The analogy of the panel discussion is sometimes used to illustrate the nature of TDMA. Participants interrupted or screamed "TDMA violations." GSM digital mobile phone standard uses TDMA; each channel simultaneously makes 8 telephone calls in a repeating transmission sequence of 8 time slots.

TDMA-2-time-slot-structure

The component selection of a TDMA system must include careful consideration of bandwidth and settling time; long time constants of components with insufficient bandwidth can cause the signal to "seep" the time slots of neighboring users.


TDMA advantages: strong anti-interference ability, high frequency band utilization, large system capacity; reduced base station complexity, small intermodulation interference; simple handover; system needs precise timing and synchronization. 


The two-way radio transmitted by TDMA does not need to use the repeater. The two sets of two-way radios can communicate simultaneously at the same frequency point, which greatly saves the cost and steps for users to apply for new frequency points. For industries with high timeliness requirements, such as security properties, hotel supermarkets and other industries, timeliness is guaranteed and efficiency is much improved!