MODERN DATA TRANSMISSION RADIO MODEMS..
SERDYUKOV Petr Nikolaevich, Doctor of Technical Sciences
ZORIN Vasily Ivanovich, Doctor of Electrical Engineering
BELCHIKOV Anatoly Vladimirovich, Candidate of Technical Sciences
LAVRENTYEV Alexey Igorevich
MODERN DATA TRANSMISSION RADIO MODEMS.
BRIEF OVERVIEW
Currently, radio modems have been developed and manufactured that are used to transmit digital information in the following systems:
- monitoring oil and gas fields;
- security and fire alarms;
- ensuring the safety of premises and persons;
- environmental monitoring;
- remote control;
- telemetry;
- automated control, for example, in railway transport;
- positioning (GPS, GLONASS);
- VHF radio communications used by operational search and rescue operations entities, etc.
Domestic radio modems
A summary table of the main characteristics of domestically produced radio modems is given in Table 1.
Table 1. Characteristics of domestically produced radio modems
Dashes in Table 1 indicate that there is no data or this feature is not implemented in the device.
The table shows that the radio modems have the following characteristics:
- the operating frequency range of the transceivers of most radio modems: 146 — 174 MHz, 440 — 470 MHz;
- the transmitter power varies from 10 mW to 10 W;
- modification types: FSK, MSK, GMSK;
- data transfer rates vary from 1200 bit/s to 19200 bit/s;
- some modems use parity control and error-correcting codes that correct one error and detect two errors;
- protocols used: transparent, packet.
Some modems have several modifications depending on the place and method of their use. According to their design, radio modems are produced:
- as complete units, including the modem itself and the transceiver;
- in separate design of the transmitting and receiving parts of the radio modem;
- in the form of an attachment to a radio station, connected to the microphone and telephone inputs of the radio station;
- in the form of a module made on a separate board, which is connected between the computer and the radio station.
Foreign radio modems
A summary table of the description of foreign-made radio modems is given in Table 2.
Table 2. Characteristics of foreign-made radio modems
Obviously, the main parameters of these modems are similar to domestic ones. The only special feature is the extended frequency range in which they operate. All modems use frequency modulation with reception on a frequency detector. Most modems have a transparent protocol, although there is also a packet mode. Information on the use of noise-resistant codes is not provided.
Single-chip modems for radio communication systems
Some radio modems are built on the basis of single-chip FX series microcircuits. A summary table of the characteristics of these microcircuits is given in Table 3.
Table 3. Single-Crystal Radio Modems
| Name | Modulation Type | Transmission Rate | Supply Voltage | Application |
| FX469 | MSK | 1200, 2400, 4800 bps | Up to 5 V | General purpose devices |
| FX589 | GMSK | 4 – 40 Kbps | Up to 5 V | General purpose devices |
| FX909 | GMSK | 4800 – 19200 bps | Up to 5 V | Packet radio |
| FX919 | 4-level FSK | 2400, 4800, 9600 bps | Up to 5 V | Packet radio |
| FX929 | 4-level FSK | 2400, 4800, 9600 bps | Up to 5 V | Packet radio |
| FX939 | GMSK | 2400, 4800, 9600 bps | Up to 3 V | Packet radio |
| FX949 | GMSK | ________ | Before 3 V | Packet radio |
| FX959 | GMSK | 4000, 16000 bps | Up to 3 V | General purpose devices |
As can be seen from the table, modems implemented on these chips have a data transfer rate from 1200 to 19200 bit/s, the main type of modulation is GMSK, the modems use packet and transparent protocols.
The main characteristics of mobile radio modems can be borrowed from the descriptions of the equipment of modern professional mobile radio communication systems. Table 4 shows the main characteristics of such modems.
Table 4. Characteristics of modern professional mobile radio communication systems
| Characteristic | EDACS | TETRA | APCO 25 | Tetrapol | IDEN |
| Possible operating frequency range, MHz | 138 – 174; 403 – 423; 450 – 470; 806 – 870 |
theoretically 150 – 900 | 138 – 174; 406 – 512; 746 – 869 |
70 – 520 | 805 – 821; 855 – 866 |
| Spacing between frequency channels, kHz | 25; 12.5 (data transfer) | 25 | 12.5; 6.25 |
12.5 | 25 |
| View modulation | FM | p /4-DQPSK | C4FM(12.5 kHz) CQPSK (6.25 kHz) |
GMSK (BT = 0, 25) | M16-QAM |
| Channel data transfer rate, bit/s | 9600 | 7200 (28800 – when transmitting 4 channels on one frequency) | 9600 | 8000 | 9600 (up to 32 k when transmitting data in packet mode) |
| Possibility of data encryption | standard proprietary end-to-end encryption algorithm | 1. standard algorithms; 2. end-to-end encryption |
4 levels of information security |
|
no information |
| Channel coding | no information | block coding; convolutional coding; interleaving; scrambling |
block coding; trellis coding; interleaving | convolutional coding; interleaving; scrambling; differential coding | no information available |
Conclusions
1. The analysis shows that there is currently a fairly wide range of radio modems for various applications.
2. For data transmission in mobile communication systems, it is advisable to use frequency modulation with an index of 0.5 and Gaussian premodulation filtering (GMSK). The coherent method of receiving this signal has the best noise immunity.
Literature
1. http://irz.ru/
2. http://uralfactories.ru/
3. http://rateos.ru/
4. http://glorient.ru/
5. http://mdc.ede.ru/
6. http://intecs.ru/
7. Ovchinnikov A.M., Vorobyov S.V., Sergeev S.I. Open standards of digital trunking communication. Series of publications “Communications and Business”, M. ICSTI – International Center for Scientific and Technical Information, “Mobile Communications”, 2000 – 166 p.
8. Serdyukov P.N., Grishankov B.T., Afrikanov S.A., Shadchnev V.Ya. Comparative analysis of noise immunity and spectral efficiency of signals in equipment of APCO 25, TETRA, TETRAPOL standards. First Russian TETRA Congress 2002. Proceedings, pp. 40 – 48.