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The difference between DMR and dPMR system of digital two way radio

Date:Jan 26, 2021

The difference between framework agreements


The protocol layered structure of DMR is as follows:

1


The layered structure of the DPMR protocol is as follows:

2


The difference between MA and FDMA


TDMA: Time Division MultipleAccess. Time division multiple access is to divide time into periodic frames (Frame). Each frame is then divided into several time slots to send signals to the base station. Under the condition of meeting timing and synchronization, the base station can receive the signals in each time slot. The signal of the mobile terminal is not mixed. At the same time, the signals sent by the base station to multiple mobile terminals are arranged in a predetermined time slot for transmission in order. As long as each mobile terminal receives in the designated time slot, the signals sent to it can be distinguished among the combined signals And receive it.


FDMA: (Frequency DivisionMultiple Access/Address), there are many different technologies that can be used to achieve channel sharing. The channel frequency band is divided into a number of narrower disjoint frequency bands (called sub-bands), and each sub-band is allocated to a user dedicated (called address). This technology is called "frequency division multiple access" technology. Frequency division multiplexing (FDM) refers to a technology in which the carrier bandwidth is divided into multiple sub-channels of different frequency bands, and each sub-channel can transmit one signal in parallel. Under frequency division multiplexing technology, multiple users can share a physical communication channel. This process is frequency division multiple access (FDMA).


FDMA analog transmission is the least efficient network, which is mainly reflected in the fact that the analog channel can only be used by one user at a time, making the bandwidth not fully utilized.


The basic difference between TDMA (Time Division Multiple Access) and FDMA (Frequency Division Multiple Access) lies in the definition of a channel and how it is used (accessed). In FDMA, a specific bandwidth (for example: 6.25kHz) at a specific frequency (for example: 150.000MHz) is used to define a channel. Basically, channels have been allocated in this way for decades. TDMA applies the same principle to bandwidth and frequency, but the signal is divided into time periods, and different time periods allow the ability to obtain additional data transmission within the same frequency band.


In a channel with a bandwidth of 25kHz, TDMA has better utilization. For example, 2 to 3 users can occupy the same bandwidth as a FDMA channel user, but a TDMA technology with a bandwidth of 12.5kHz can pass better The utilization rate can achieve the effect brought by two newly developed FDMA technologies with 6.25kHz bandwidth such as dPMR.


Both TDMA and FDMA technologies achieve the same 6.25kHz narrowband capability through different methods. The difference is that the FDMA system is the "real" 6.25kHz channel, while the TDMA system provides the effect of'equal to' the 6.25kHz channel through different periods of time in the 12.5kHz bandwidth. 12.5kHz is considered the current narrowband standard channel spacing. From this perspective, both systems have reached the so-called "double capacity". The difference is that the FDMA system always doubles the capacity no matter with or without basic users. For TDMA, the doubled capacity can only be achieved when the repeater synchronizes the time period and two users access the same repeater in the same geographic area at the same time.


Theoretically speaking, under the same conditions and the same transmission power, the narrow frequency channel in the FDMA system has a better coverage than the 12.5kHz bandwidth channel of the TDMA system. This is because the noise floor of any receiver is directly proportional to the filter bandwidth, so the smaller the bandwidth, the smaller the signal that can be received. In real-world use, various factors, such as terrain, base station antenna height, and surrounding buildings, all affect the coverage. Therefore, without a specific comparison test, one system cannot be claimed to be better than another. It can be claimed that when compared with an analog FM signal, the digital signal is easily better than the analog signal at the edge of the communication range, thus providing more reliable audio in a larger total area, even if the coverage is similar to the analog FM signal. The signal is the same.