Digital walkie-talkies are getting more and more attention with the market demand and the demand for walkie-talkies. The Digital Mobile Radio Standard (DMR) is a digital radio standard specially developed by the European Telecommunications Standards Institute (ETSI) for professional mobile radio (PMR) users. Approved in 2005.

 

Main advantage

 DMR systems have many advantages over traditional analog systems and other digital systems. In short, the DMR digital system brings the following advantages:

 

• Existing licensed channel capacity doubled

 One of the main advantages of DMR is the ability to support two simultaneous and independent calls over a single 12.5 kHz channel via TDMA. According to the DMR standard, TDMA reserves a 12.5 kHz channel width and divides it into two alternating time slots A and B (as shown in Figure 1 below), each time slot acting as a separate communication path. In Fig. 1, walkie-talkies 1 and 3 talk on time slot 1; walkie-talkies 2 and 4 talk on time slot 2.

 

• Backward compatible with traditional analog systems

It is important for licensees to retain existing licenses to ensure backward compatibility with their legacy radio or external systems such as on-site contractors. Since the DMR uses a 12.5 kHz channel, the required spectrum compatibility is built in.

 

• Efficient use of infrastructure equipment

 Another advantage of the DMRTDMA approach is that two communication channels are obtained with one repeater, one antenna and one simple duplexer. Compared to the FDMA solution, dual-slot TDMA achieves an efficiency of 6.25 kHz while minimizing the investment in repeaters and combined equipment. The equipment requirements for the two methods for a simple system are shown in Figure 6 below.

 

• Longer battery life and greater efficiency

 Battery life has always been one of the biggest challenges for mobile devices. In the past, there was limited choice to increase the talk time for one charge. However, dual-slot TDMA provides a good solution. Since a single call uses only one of two time slots, only half of the transmitter capacity is required. The transmitter is idle for half of the time, that is, it is an unused time slot "round" at any time.

 

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