Since the late nineteenth century since Marconi invented the radio, using radio (English RADIO ie radio) transmission of information via radio waves and human life has become increasingly inseparable from the marine, military, radio and television stations to the mobile phone is the scope of transmission of information from the analog information codes, voice, image to all-digital variety of data streams, radio operating band from the long wave, shortwave, FM to microwave, infrared and optical (fiber), the use of communications technology from analog modulation to digital modulation, from a single channel to multi-channel, from the conventional fixed channel to frequency hopping, from a single carrier to multi-carrier, from the frequency division (FDMA) to time division (TDMA) to the code division (CDMA), from narrowband to broadband dozens of 64Kbps Mbps, using the device (technology) from the tubes, transistors, integrated circuits, MCU, DSP and software radio to ... ...
Modulation (ie the information to be transferred and adjusted to match the transmission channel) is a key technology for radio, no modulation, no information is less than the air moving into radio, has no radio. More importantly, advanced modulation in a limited RF bandwidth farther and more reliably, more high-speed data transmission. Modulation is based on analog modulation signal (eg audio signals) or numbers (such as RS232 asynchronous serial data), into analog modulation (FM and AM amplitude modulation such as FM) and digital modulation, a large number of civilian radio and now the first generation of Cellular phones are analog FM, as well as FM radio and so on. Digital modulation into linear amplitude modulation and phase modulation frequency (see 1: P333, below). Digital frequency modulation with FSK (such as low-speed 1200bps radio paging, reference 1: P335), CPFSK (such as digital data radio, reference 1: P336), GMSK (second generation digital mobile phones such as GSM, reference 1: P337), four FM level (high-speed FLEX paging, reference 1: P337). Digital FM modulation voltage-controlled oscillator VCO can be (cf. 1: P251) to achieve, but also with digital FM (cf. 1: P252) to achieve. Digital FM demodulation sub-coherent demodulation (see 1: P253) and non-coherent demodulation (see 1: P266).
1、analog data radio
Data radio wireless data radio is short, and the data transfer application is the earliest remote telemetry data, different from the current wireless microwave radio, wireless Ethernet, GPRS mobile phones and other advanced data transmission equipment, used, and data radio it refers to the transfer of data with remote telemetry stations, our radio management departments to 223 ~ 235M/821 ~
825M/2.4 ~ 2.4835GHz frequency band assigned to other data transmission services (see 2). Remote telemetry data with the use of computers for data processing operations to be born, and the sixties and seventies only the analog FM audio modulation (300 ~ 3400Hz) communication station, so the 101 010 ... ... the data stream through a single frequency (such as FSK for 1 = 1200 Hz, 0 = 1800 Hz) to represent, then the audio signal as analog FM modulation to achieve the early data radio, by its very nature is pre-FSK (or MSK, GMSK) modulation such as two plus FM radio time modulation (reference 3), as shown below:
Schematic diagram of analog data radio
To Jiaxing Blue Wave data radio N88X, for example, its essence is to use microcontroller (232 unpack the data package, radio transceiver control, etc.) and special FSK (or MSK, GMSK) modulation and pre-made chip wireless MODEM, adding Japan's fine analog FM FM Radio (Blue Wave offers fine Japanese Ministry of Information Radio Network Radio N889 modulation as indicated in the certificate FM, http://www.rec198.com).
As the FM radio and has a large number of popular civil MODEM, low price (such as Nissei ND889 25W radio, costs about 500 yuan, Blue Wave 4800MODEM cost about 200 yuan) is its biggest advantage, but the defect is obvious, the majority of users and professionals are aware, this secondary modulation by the FM radio MODEM plus two plus one pieced together data radio products are: ⑴ rate is low, ⑵ will lose the prefix, ⑶ end noise will appear garbled, ⑷ no other any additional functionality and so on. Blue Wave series of instructions compiled ND88X MODEM send and receive data emphasize the need for strict timing compatible with the radio transceiver is based on the above issues, but from the analog radio transceiver to stop the consistency is not possible accurately to the millisecond, So throw out the garbage and the prefix is inevitable (and intercom call will not throw bad words 300 ms). It should be noted that, with the DSP digital technology, this analog stations plus the MODEM simulation data radio in a foreign country has basically been digitally modulated digital data radio out, although the domestic market - electricity load monitoring system (note : No Power Dispatching and Communication System, Power Dispatching and Communication System demanding to the strength of the power industry, using a fiber-optic communications, and the coexistence of a variety of means of communication), and water conservancy departments still use, is also a major user groups Nissei , but the reason is simple: electricity load, water rainfall / water level data is not much real-time requirements (1200bps, collected several times a day), reliability, less demanding (one does not re-transmission time), load a user control did not have any relationship will not affect the power supply, does not affect the meter reading fee (often around the electricity sector and we do exchange a lot of electricity load control system is to meet the standard first-class appraisal of furnishings, and the fundamental power dispatch communications are two different things).
2、Digital data radio
Just as the first generation of analog FM mobile phone (mobile phones) have a large noise, less functional, able to listen to radio and other shortcomings, the public has for the digital mobile communications GMSK modulation of GSM system replacement, and quickly developed into the third generation of digital spread spectrum modulation techniques increase like the 3G; market small remote telemetry data-transmission areas increased from analog FM radio plus the MODEM simulation of digital radio development for a variety of digital modulation implemented using DSP (such as CPFSK, GMSK, etc.) of digital data radio. Such as Shenzhen Sinosun's WDS2710 CPFSK modulation with digital data radio (Sinosun radio network to provide a certificate of Ministry of Information Industry indicated modulation of CPFSK, http://www.sinosun.cn). As shown below:
Schematic diagram of digital data radio
GMSK digital and cell phone as modem technology, CPFSK data radio is different from the analog FM radio plus the MODEM of the radio core of the baseband signal processing (cf. 1: P215 a "partial response 4.6 technology"). CPFSK with DSP digital signal processing is completed with two Nyguist waveform, the root value and the cosine response Zicheng with roots duobinary filtering the baseband signal processing and soft-decision Viterbi decoding, etc. These are single-chip FSK plus chips are not always possible.
And analog phones to digital phones change, the use of digital modulation data radio to achieve a simulation of digital radio modulation impossible to achieve high-speed (19200bps), high reliability (the prefix is not lost, not garbled), and additional features (such as power meter, field intensity, BERT, network management functionality, intelligent management of the dynamic parameters of the state, see: "American MDS / Japan Nissei / Shenzhen Sinosun digital radio Competition", http://www.sinosun. cn).
DSP-based digital modulation data radio from 2000 to enter the Chinese market, despite the cost price is much higher than analog radio, because of its high-speed, high reliability and long-distance transmission and other obvious advantages and has been in the oil / gas, water / electricity / heating network / gas, rail / transport / security / security / fire protection, street / Earthquakes / weather / environmental, GPS, finance, metallurgy / chemical and industrial process control, automation, data acquisition and control applications, and well received. Can be expected, with the public mobile communication or digital radio abroad market change, the DSP-based digital data radio with the cost prices fall, will replace in the field of remote telemetry MODEM simulation based on the number of FM radio, so we wireless remote telemetry and industrial automation system is more real-time speed, more secure, more flexible and convenient ... ...
References:
1, Xidian University Guoti Yun, LIU Zeng-ji, Xin-Mei Wang, Zhan Road Yong, Professor Yang Qiadeng edited, editor of China National Institute of Communications, People's Post published the Communications Engineering Series "data transmission", October 1998
2, compiled Radio Authority Ministry of Information Industry, People's Post published "People's Republic of radio frequency division rule"
3, People's Republic of China State Bureau of Technical Supervision issued national standards GB/T16611-1996, "data radio universal norms"
