1、RECOMMENDATION ITU-R F.755-2“ POINT-TO-MULTIPOINT SYSTEMS IN THE FIXED SERVICE (Question ITU-R 125/9) (1992-1994-1999) The ITU Radiocommunication Assembly, considering a) that there are different applications, services and deployment scenarios which require various point-to-multipoint (P-MP) system
2、configurations; b) that different P-MP systems in the fixed service (FS) are used in various frequency bands depending on the services transported and the deployment scenario envisaged; c) that minimization of interference and optimization of spectrum usage can be achieved by proper emission control
3、, appropriate access techniques and efficient modulation; d) systems; e) the central station and directive antennas at the terminal station, andor repeater station; f) path length and location (rural, suburban, urban, etc.); g) h) interference criteria and sharing criteria with other services, that
4、P-MP systems can provide comparable performance and availability objectives with those used for wired that P-MP systems commonly use omnidirectional or sectorized antennas or multiple antenna configurations at that various applications are suited to different parts of the spectrum dependent upon cap
5、acity, area coverage, that P-MP systems are suitable for high density deployment; that operating characteristics of P-MP systems are required in order to determine appropriate intra-service recommends that for time division multiple access (TDMA) P-MP systems used as radio concentrators, Recommendat
6、ion 1 ITU-R F.756 should be referred to; 2 that for radio-frequency channel arrangements for analogue and digital P-MP radio systems operating in frequency bands in the range 1427-2 690 MHz, Recommendations ITU-R F.701, ITU-R F.1098, ITU-R F.1242 and ITU-R F. 1243 should be referred to; 3 descriptio
7、n of a particular implementation; 4 5 information on various systems; 6 can be made to Recommendation ITU-R F.697; that for single channel or multichannel multipoint video distribution services, Annex 1 can be referred to for a that for packet radio systems, Annex 2 can be referred to for some speci
8、fic examples; that for TDMA systems for data transmission, primarily in urban areas, Annex 3 can be referred to for that for some requirements for P-MP systems used in the local grade portion of an ISDN connection, reference * This Recommendation should be brought to the attention of Radiocommunicat
9、ion Study Groups 3 (Working Party 35) and 7 (Working Party 7D), and Joint Rapporteur Group 7D-9D. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTDmITU-R RECMN F.755-2-ENGL 3999 = 4855232 053b395 TbU II 106 Rec. ITU-R F.755-2 7 prima
10、ry rate, reference can be made to the access section of the national portion of Recommendation ITU-R F. 1 189; 8 that Annex 4 can be referred to for applications of frequency division multiple access (FDMA) P-MP systems operating in the frequency bands 3.4-3.6 GHz, 3.6-3.8 GHz, 10.15-10.3 GHz paired
11、 with 10.5-10.65 GHz, 26/28 GHz and 32 GHz; 9 10 bands 26 and 28 GHz, Annex 1 and Annex 2 of Recommendation ITU-R F.748 can be referred to. that for performance requirements of P-MP systems which provide to the end-user a connection at or above the that Annex 5 can be referred to for technical and o
12、perational aspects in the 25-32 GHz frequency range; that for radio-frequency (RF) channel arrangements for digital P-MP radio systems operating in the frequency ANNEX 1 An example of single-channel and multichannel multipoint distribution services 1 System description The multipoint distribution se
13、rvice provides, for one-way P-MP transmission, at approximately 2 GHz, up to four channels of voice, video and data signals to geographically distributed communities of interest. These signals may be used for entertainment, business, social or community purposes. A typical multipoint distribution se
14、rvice system consists of an omnidirectional transmit antenna and a combiner to combine the output of each transmitter at the transmitting site, a directional receive antenna, down converter and a video receiver at each receive location. The transmit site is generally limited in output power, typical
15、ly 200 W e.i.r.p., and normally drives an antenna with either an omnidirectional or a cardioid radiation pattern with gains of 10 to 16 dBi. In some instances pairs of back-to-back cardioid antennas are driven by a single transmitter. The received signal is changed by the down converter from the tra
16、nsmission frequency to an unused channel frequency compatible with the video receiver. In the case of multichannel multipoint distribution services, a narrow-band channel (125 kHz bandwidth) is provided for an audio response to the transmitter site. A typical frequency plan for a four-channel multip
17、oint distribution service operating in the 2.5 GHz band with a maximum transmit bandwidth of 6 MHz is given below: Transmit frequencies fn = fo - 128 + 24 n + 12 n fn = fo - 146 + 24 m + 12 n form = 1, 3, 5, 7 form =2,4,6 Response frequencies JZ = fo + 89.9375 + 0.125 nz + n where: fo : frequency of
18、 the centre of band = 2 595 MHz rn : group number = 1,2, 3, . . ., 7 n : group number = 1,2, 3,4. The system design approach for the multipoint distribution service was selected to allow randomly sited transmitters to reuse optimally the same or adjacent channel as often as possible and provide a re
19、asonable size of protected area surrounding each transmit site. This approach required trading off high transmit power against the availability of high gain receive antennas and limiting service to only those receive sites that have line-of-sight paths to the transmit site. COPYRIGHT International T
20、elecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesAn example of the technical characteristics of a typical 2.5 GHz P-MP system used for multipoint distribution services is shown in Table i. TABLE 1 Antenna gain (dBi) (relative to Transmitter power (dBW) omnidire
21、ctional) Receiver I Transmitter I 13 Antenna gain (dBi) 20 10 Noise figure (dB) 8 I Modulation I VSB/AM I Antenna characteristics I Rec. ITU-R F.699 Signal type TV Camerhnterference (dB) (unfaded) 45 9.1 I I e.i.r.p. (dBW) I 23 I Typical receiver antenna height (m) 2 Interference considerations 2.1
22、Protected area In the multipoint distribution service, receivers are protectec from harmfu interference if they are located within the protected area around their associated transmit station. The protected area is defined by the maximum distance from the transmitter at which a reliable signal is pro
23、vided. This maximum distance in the worst propagation area of the North American continent is 25 km for a transmit site with an e.i.r.p. of 200 W and a down converter having a 10 dB noise figure. A reliable signal for this purpose is defined to be a signal sufficient to provide a 23 dB or better sig
24、nal-to-noise ratio for 99.9% of the time. For stations using a directional transmit antenna, the protection distance Db from the transmitter can be calculated by the following relationship: (Grnus - G) - 20 Db = Dbmax 10 where: Dbmci,r: G, : G: distance in the direction of maximum antenna gain (km)
25、maximum antenna gain (dBi) antenna gain in the direction of interest (dBi) For either directional or non-directional antennas, the maximum protection distance, assuming a standard receive height of 9 m, is further limited to the radio horizon. 2.2 Co-channel interference Frequency reuse in an area i
26、s controlled by ensuring that the carrier-to-interference ratio C/I owing to Co-channel interference is greater than 45 dB. This CII offers reasonable protection from harmful interference to receivers in this service while not unnecessarily restricting the ability of new stations to provide a servic
27、e to unserved areas. The achievement of this CI1 in actual systems relies upon the angular and cross-polarization discrimination charac- teristics of the receive antenna. The specific antenna used as a reference is instrumental in determining the amount of frequency reuse in a given area. The charac
28、teristics of a typical 0.6 m (2 ft) parabolic antenna were selected for the purpose of making such CI1 calculations. In certain cases where the actual receive antenna has better performance characteristics, that antenna is used when performing CI1 calculations. COPYRIGHT International Telecommunicat
29、ions Union/ITU RadiocommunicationsLicensed by Information Handling Services STD-ITU-R RECMN F.755-2-ENGL 1999 II 4855232 053b377 833 U 108 Rec. ITU-R F.755-2 2.3 Adjacent-channel interference Adjacent-channel interference is controlled by imposing conditions on both the multipoint distribution servi
30、ce transmit and receive sites. An objective of O dB C/Z was chosen for this condition. In order to help achieve this condition in a practical manner, multipoint distribution service stations serving the same area are encouraged to Co-locate transmit antennas as close as physically possible (0.5 km,
31、or less separation) and to transmit on orthogonal polarization, but with signals of equal power. Further study is required as to the effects of propagation on polarization stability in the 2 GHz band. 2.4 Sharing considerations The vertical pattern for the typical omnidirectional transmit antenna us
32、ed in 2.5 GHz P-MP system is shown in Fig. 1. Figure 1 and Table 1 are appropriate to use in determining sharing considerations with other services. FIGURE 1 Typical transmit antenna pattern in the vertical plane 1 0.9 0.8 0.7 0.6 3 .? 0.5 c 0 n 2 0.4 0.3 0.2 o. 1 O Horizontal m -5-4-3-2-1 O 12 3 4
33、5 6 7 8 9 IO O 1 2 3 4 5- v 6= 7 8 9 10 12 14 16 a? Elevation angle (degrees) 0755-01 COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services - STD-ITU-R RECMN F.755-2-ENGL 1999 4855212 053b196 77T Rec. ITU-R F.755-2 1 o9 ANNEX 2 Examples of
34、packet radio systems 1 Introduction This Annex describes packet radio technology and systems. Packet radio techniques are now being successfully used in a number of countries. 2 System application Packet radio systems function most effectively when the data traffic they must handle is in the form of
35、 bursts. Systems operated below 1 GHz normally carry low data rates up to 9.6 kbit/s. Above 1 GHz, higher data rates can be used. For example, a packet radio network can provide the interconnection means in a computer communications network. Communications may be between host computers and end user
36、terminals, and between end terminals. In addition, such systems are often installed in rural areas, where the cost of adding new cables between the customers node and the nearest network facility can be prohibitive. In other cases, a chronic shortage of copper loops makes such systems attractive in
37、urban areas. 3 System description The basic concept in packet radio is that the data are transmitted in packets. Systems employing TDMA and carrier sensed multiple access (CSMA) have been designed. These systems allow simultaneous access to one radio channel by either a CSMA or a TDMA protocol, and
38、both permit individual stations to act as store and forward repeaters to handle traffic locations farther from the central site. Alternatively, two frequency duplex regenerative repeaters can be used to provide additional flexibility in system design. Packet switching conveys with it superior error
39、control techniques and a CRC-16 check sum can be appended to each block of data (reference ITU-T X.25 standards). To achieve very low bit-error ratios (BERS) (better than 1 x lo-“) on transmission of large blocks of data, more than one CRC-16 check sum can be used in the block. In P-MP data transmis
40、sion systems, it has been observed that block retransmission techniques are superior to forward error correction (FEC). Since packet data systems do not operate in real time because of padding delays, special techniques can be used to keep the overall delay to a minimum, such as commencing transmiss
41、ion before the complete packet is received and using high network transmission rates such as 4.8 to 9.6 kbit/s. Clearly, not being “real time” offers significant benefits in spectrum conservation, since data are sent at the highest possible speed on the network even though the destination is a low s
42、peed device. In one TDMA system configuration, network management is conducted by a unit called a station. Such a station has a number of radios in its subset and it determines the overall link connectivity of the network. In environments composed of fixed and possibly mobile units, each radio colle
43、cts possible link connections, stores the information in memory, and sends it to the station. Using these data, the station establishes a final connectivity network. Network architecture can be varied to include configurations without stations or a broadcast configuration. 4 Efficiency and modulatio
44、n methods CSMA systems have the advantage of being able to use standard land mobile radio transceivers employing frequency modulation. This provides the capability to carry up to 9.6 kbits of data and achieve a BER of 1 x at receive carrier levels of -107 dBm. Measurements have shown that, in a well
45、 designed CSMA system, up to 40% of the channel capacity can be used. Typical channel capacities in a CSMA operating between 130 and 960 MHz are given in Table 2. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN FW755-2-
46、ENGL 3999 4855232 053bL99 606 110 Rec. ITU-R F.755-2 TABLE 2 Average message characters 60 60 60 60 60 60 CSMA channel capacity Average delay (SI 30 16 0.26 20 28 0.24 10 52 0.23 5 100 0.23 2.5 240 0.23 1 400 0.22 Messagedminute Maximum luser number of users per message At some point, as the number
47、of messages/minute/user increases (for example, at 30 messages/minute/user) the traffic may no longer be considered as being in the form of bursts and another type of system may be more appropriate. The use of direct sequence spread spectrum modulation with minimum shift keying (MSK) of the carrier
48、frequency has been proposed for a TDMA system in the 2 GHz band. This technique can minimize interference to other systems using the same frequency and frequency bands while enabling the packet radio to reject interference and function satisfactorily with a lower signal-to-interference ratio than an
49、 analogue receiver. However, spread spectrum equipment is generally more complex and costly than analogue receivers. 5 Summary Packet radio systems employing CSMA and TDMA techniques have demonstrated their ability to provide high performance and efficient transmission of data traffic. ANNEX 3 P-MP systems utilizing TDMA techniques for data transmission in urban areas 1 Introduction The general principles of P-MP systems using TDMA are discussed in Annex 1 of Recommendation ITU-R F.756. Considerable development has taken place in recent years in the use of this techniq
