1、 Rec. ITU-R F.1761 1 RECOMMENDATION ITU-R F.1761 Characteristics of HF fixed radiocommunication systems (Question ITU-R 158/9) (2006) Scope This Recommendation specifies the typical RF characteristics of fixed radiocommunication systems in the 2-30 MHz range. The ITU Radiocommunication Assembly, con
2、sidering a) the use of fixed and mobile service HF radio communications is a common denominator in achieving interoperable radio communications in multinational efforts; b) there are two types of categories of systems in this band adaptive and non-adaptive; c) that the efficiency of spectrum use in
3、the MF and HF bands shared by the fixed and the mobile services could be improved by the use of frequency adaptive systems in some cases; d) that trials of frequency adaptive systems which have been undertaken during the past 20 years have demonstrated the feasibility of such systems and their impro
4、ved spectrum efficiency compared to operator managed systems; e) that such improved efficiency is attained through: shorter call set-up and improved transmission quality by selection of the most suitable assigned channels; reduced channel occupancy, permitting the same channels to be used by differe
5、nt networks, yet decreasing the probability of harmful interference; minimization of the transmitter power required for each transmission; continued optimization of the emissions owing to the sophistication of the systems; limited simultaneous use of frequencies to the minimum necessary for communic
6、ation requirements, noting a) that additional information on the technical and operational characteristics of HF fixed systems can be found in Report ITU-R F.2061, recommends 1 that the technical and operational characteristics of adaptive and non-adaptive systems described in Annex 1 may be used in
7、 sharing studies when operating between 2-30 MHz. 2 Rec. ITU-R F.1761 Annex 1 Characteristics of HF fixed radiocommunication systems 1 Introduction HF systems have specific attributes that make them a viable solution for many communications requirements. They provide a highly versatile means of comm
8、unications to a broad base of users and the reliable and inexpensive equipment can be easily transported to remote and lightly populated areas. 2 Non-adaptive systems Non-adaptive HF fixed systems are traditional radio systems which require a radio operator to manually establish frequencies. The ope
9、rator must adjust the parameters of the system for maximum performance by monitoring the conditions of the ionosphere, tracking the variable propagation conditions, and selecting the operating conditions (i.e. primarily the frequency) that will allow the signal to propagate best. There is extreme va
10、riability and unpredictability, in the short term, of the HF propagation environment. Propagation in this band is primarily by the sky-wave mode, utilizing refraction of radio waves from the ionosphere, or in some cases by the surface-wave mode. 3 Adaptive systems An adaptive MF/HF system is one whi
11、ch automatically (i.e. without the need for intervention by a radio operator) carries out the functions of establishing radiocommunications links and exchanging of information in a manner that copes with the variations and the high probability of interference inherent to MF/HF frequency bands propag
12、ating through the ionosphere. In addition, adaptive systems are able to monitor spectrum occupancy in a regular manner, and select operating frequencies so as to avoid causing interference to other users more effectively than many non-adaptive systems now in operation. 4 Technical characteristics Fi
13、gure 1 and Tables 1 to 4 contain technical characteristics of representative systems. This information is sufficient for general calculation to assess the compatibility between these systems and systems operating in other services. Required S/N ratio and protection criteria are stated in Recommendat
14、ions ITU-R F.339 and ITU-R F.240 and should be used in compatibility studies between adaptive systems and other systems. Figure 1 indicates SNR requirements to achieve 10-4bit error ratio (BER) in a fading channel for the range of data rates currently used in HF data services. These values were deri
15、ved from measurements of commercial serial-tone modems, and are intended to represent “typical” performance rather than the best available performance. Figure 1 can be used to determine protection criteria for various services: Digital voice technology (for example, MELP) offers a tradeoff in voice
16、quality versus data rate. State-of-the-art voice systems provide excellent voice quality when operating at 2 400 bit/s, but can operate with reduced voice quality at 1 200 and even 600 bit/s. Data broadcasts generally operate at a fixed data rate (for example 600 bit/s). Rec. ITU-R F.1761 3 IP over
17、HF operation operates at a fixed data rate in some networks (for example 6 400 or 8 000 bit/s), while fully adaptive networks continually adjust data rates in response to instantaneous channel conditions. In the latter case, some traffic must be discarded when interference causes reductions in data
18、rate, leading to buffer overflows. FIGURE 1 Example SNR for 1 10-4BER in fading channel*, *SNR (dB) vs. data rate (bit/s) * Two independent equal average power Rayleigh fading paths, with a fixed 2 ms delay between paths, with 1 Hz fading. * Technology for data rates for 2 400 bit/s and below predat
19、es technology for higher data rates. TABLE 1 Example technical characteristics of fixed systems in the 2-30 MHz band Frequency band (MHz) 2-30 Type of emission Analogue/digital System Channel bandwidth (kHz) 2-6 Modulation type Single channel suppressed carrier, telephony and telegraphy Type of oper
20、ation Simplex/duplexType of deployment Star network Typical data rates 2.4-9.6 kbit/s Typical SINAD 12 dB (voice only) 4 Rec. ITU-R F.1761 TABLE 1 (end) Transmitter Tx power (dBW) 22Path length (km) 2 400 Antenna gain (dBi) 6 Antenna height (m) (Relative to ground level) 10-60 Radiation pattern Omni
21、directional/directional Antenna polarization Vertical/horizontal Total loss (dB) 1 Receiver IF filter bandwidth (kHz) 3-7 Sensitivity (dBm) 112 Antenna gain (dBd) 6 Antenna pattern Omnidirectional/directional (30 beamwidth) TABLE 2 Analogue (voice single sideband) Audio output S/N (dB) AWGN (dB) Fad
22、ing (dB) 6 48 48 15 57 62 33 65 73 NOTE Figures in AWGN and fading columns of this Table represent the ratio of signal peak envelope power to the average noise power in a 1 Hz bandwidth. TABLE 3 Digital (Data) Modulation AWGN channel (dB) Fading (dB) 64-QAM 21 30 8-PSK 13 20 NOTE The carrier power t
23、o the average noise power in a 3 kHz bandwidth for probability of bit error 1.0 10-4 AWGN non-fading stable channel condition. Rec. ITU-R F.1761 5 TABLE 4 Example technical characteristics of adaptive fixed systems in the 2-30 MHz band Parameter Mode of operation NVIS (near vertical) Groundwave Skyw
24、ave (oblique) Frequency band (MHz) 2-10 3-30 3-30 Necessary bandwidth (kHz)(1)3 3 3 Transmitter power (dBW) 10-26 0-26 10-40 Transmit attack time delay (ms)(2)25 25 25 Transmit release time delay (ms)(3)10 10 10 Receive AGC attack time delay (ms) Voice Data 30 10 30 10 30 10 Receive AGC release time
25、 delay (ms) Voice Data 900-1 200 35 900-1 200 35 900-1 200 35 Signal-to-noise ratio (dB) High-speed data Analogue voice Digital voice 24 21 8 18 15 3 24 21 8 Transmitting antenna gain (dBi) 0-6 0-3 6-15 Maximum e.i.r.p. (dBW) 10-32 0-29 16-55 Antenna polarization Horizontal Vertical Vertical/ horizo
26、ntal (1)Channel banding can provide a 12 kHz bandwidth. (2)Attack-time delay. The time interval from keying-on a transmitter until the transmitted RF signal amplitude has increased to 90% of its steady-state value. This delay excludes any necessary time for automatic antenna tuning. (3)Release-time delay. The time interval from keying-off a transmitter until the transmitted RF signal amplitude has decreased to 10% of its steady-state value.
