1、 Rec. ITU-R F.1103-1 1 RECOMMENDATION ITU-R F.1103-1*Basic requirements and technologies for fixed wireless access systems operating in bands below 3 GHz for the provision of wireless subscriber connections in rural areas (Question ITU-R 125/9) (1994-2007) Scope This Recommendation provides basic re
2、quirements and technologies for fixed wireless access (FWA) systems operating in bands below 3 GHz for use for wireless connections in rural areas. The requirements include service aspects as well as performance/availability objectives. The Annexes describe technical and operational information spec
3、ifically required for FWA applications used in rural areas. Vocabulary RCS Radio Concentrator System A wireless system in which the radio resource (e.g. a time slot in the time domain or a frequency channel in the frequency domain) is commonly used by more than one subscriber by applying a multiple
4、access technique. Abbreviations ADPCM Adaptive differential pulse code modulation CDMA Code division multiple access E b) that the equipment for such links should be simple and reliable for reduction of establishment costs, and for ease of maintenance and operation; c) that in the provision of such
5、links, the calling rate allows the use of such methods as fixed wireless access (FWA) systems using point-to-multipoint (P-MP) applications; d) that FWA systems operating in bands below 3 GHz are suitable for the provision of such links and it is necessary to provide technical information on these s
6、ystems for the system designers; e) that in rural areas it is often difficult to implement metallic lines or other cable systems economically, however various telecommunication services provided by metallic lines or other cable systems should, as far as possible, be available also in rural areas; f)
7、 that Recommendation ITU-R F.1490 specifies generic requirements for FWA systems; g) that Recommendation ITU-R F.757 provides basic system requirements and performance objectives for FWA systems using mobile-derived technologies offering telephony and data communication services, recommends 1 that F
8、WA systems used for rural subscriber links should provide services also available by metallic lines. These services may include: 2-wire individual telephone service; payphone service of various kinds; 4-wire service with and without E the capability to carry voiceband data including facsimile and ot
9、her telematic services up to a bit rate of at least 9.6 kbit/s; 2 that, in many cases, the above FWA systems should: carry data at rates up to and including 64 kbit/s; provide, integrated services digital network (ISDN) basic rate access, 2B+D; 3 that giving due regard to economical considerations:
10、3.1 the grade of service (lost call probability) offered by such a system to a subscriber should not normally be worse than 1% and should be calculated employing ITU-T E-series Recommendations (e.g. E.506 and E.541) (see Note 1); 3.2 the error performance and availability objectives should be in acc
11、ordance with Recommendations ITU-R F.697 and ITU-R F.1400; 4 that for the effective use of frequency spectrum, radio concentrators and other digital multiple access techniques are preferred and for detailed technical information on TDMA P-MP systems Annex 1 be referred to (see Note 2); 5 that for eq
12、uipment general characteristics and operational environments, information contained in Annex 2 be referred to as a guide for administrations and system designers; 6 that voice encoding methods employed in digital systems be such that the integration of the system into the switched network is straigh
13、tforward and introduces as few limitations as possible. Rec. ITU-R F.1103-1 3 Recommended encoding methods are 64 kbit/s PCM and 32 kbit/s ADPCM in accordance with ITU-T Recommendations G.711 and G.726, respectively. NOTE 1 Some administrations may adopt other values for the grade of service, e.g. a
14、s much as 5%, depending on local conditions. NOTE 2 Other technologies such as CDMA and orthogonal frequency division multiplex (OFDM) can be found in the Fixed Wireless Access Handbook (Volume 1 of the Land Mobile Handbook). References ITU-R Recommendations Recommendation ITU-R F.382 Radio-frequenc
15、y channel arrangements for fixed wireless systems operating in the 2 and 4 GHz bands Recommendation ITU-R F.697 Error performance and availability objectives for the local-grade portion at each end of an ISDN connection at a bit rate below the primary rate utilizing digital radio-relay systems Recom
16、mendation ITU-R F.701 Radio-frequency channel arrangements for point-to-multipoint radio systems operating in frequency bands in the range 1.350 to 2.690 GHz (1.5, 1.8, 2.0, 2.2, 2.4 and 2.6 GHz) Recommendation ITU-R F.746 Radio-frequency arrangements for fixed service systems Recommendation ITU-R F
17、.757 Basic system requirements and performance objectives for fixed wireless access using mobile-derived technologies offering telephony and data communication services Recommendation ITU-R F.1242 Radio-frequency channel arrangements for digital radio systems operating in the range 1 350 MHz to 1 53
18、0 MHz Recommendation ITU-R F.1243 Radio-frequency channel arrangements for digital radio systems operating in the range 2 290-2 670 MHz Recommendation ITU-R F.1400 Performance and availability requirements and objectives for fixed wireless access to public switched telephone network Recommendation I
19、TU-R F.1401 Considerations for the identification of possible frequency bands for fixed wireless access and related sharing studies ITU-T Recommendations ITU-T Recommendation E.506: Forecasting international traffic ITU-T Recommendation E.541: Overall grade of service for international connections (
20、subscriber-to-subscriber) ITU-T Recommendation G.711: Pulse code modulation (PCM) of voice frequencies ITU-T Recommendation G.726: 40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM) 4 Rec. ITU-R F.1103-1 Annex 1 General characteristics of fixed wireless access systems using TD
21、MA techniques 1 Introduction This Annex provides information on P-MP FWA systems using TDMA. Such systems can also generally operate in a non-concentrating mode such as for pre-assigned low capacity data links. These systems are now widely used to provide a subscriber voice data service primarily in
22、 rural/suburban areas and less frequently in urban locations. 2 General description The basic purpose of these systems is to provide a radio link that will extend services to rural subscribers where cable systems are more costly or severely restricted by terrain or to protect environments. As far as
23、 practicable these services should provide a transmission quality and range of facilities that are normally provided to subscribers in urban areas. Multiple access systems give subscribers access to several circuits, the number n of which is smaller than the number N of subscribers (n N). As this is
24、 a concentrator system, a certain grade of service in respect of attempts to set up calls must be accepted. The grade of service depends on the number n of circuits, the number N of subscribers and the traffic that is originated. A TDMA radio concentrator system (TDMA-RCS) consists of a single trans
25、mitter-receiver unit at the central station and at each subscriber station. The transmitted signal consists of n time slots multiplexed in time, with each capable of providing a telephone channel. Any subscriber station has access to any of the n time slots which are allocated on a demand basis by t
26、he central station. It is possible to introduce repeater stations to extend the service from the exchange to far-distant subscribers. Repeater stations consist of two transmitter-receiver units connected back-to-back through appropriate equipment. Repeaters may serve local subscribers and operate as
27、 two-way RF translators that retransmit the signal into the adjacent radio zones (see Fig. 1), thereby eliminating the need for interconnecting links between cells. In one possible implementation using repeater stations with local switching, the signalling information, the routing requirements, and
28、information on the operational status of the multiple access network are conveyed over supervisory channels which are continuously monitored and, if necessary, updated at all stations. Unutilized subscriber channels or time slots are allocated on demand on a drop and insert basis to the individual s
29、ubscribers via the local switches and the supervisory channels are updated with information on new connections and disconnections. The same channel or time slot can be reused several times along the network due to the local switch facility. No central switch is required. A central station is provide
30、d as a gateway to the public network. Rec. ITU-R F.1103-1 5 FIGURE 1 A possible configuration for a TDMA radio concentrator system for rural subscribers 3 Principles of operation All TDMA P-MP systems use the same transmission principle. Data or digitally encoded speech signals are transmitted from
31、the central station in a time division multiplex (TDM) format, using bit or byte interleaving. Alternatively, the information for the various outlying (subscriber or remote) stations is transmitted sequentially. In the reverse direction, each outlying station is allocated a time slot within which it
32、 transmits its information. Great care must be taken to ensure that the bursts of data arrive at the central station sequentially. This is generally achieved by careful design of the control system and by the provision of absolute delay equalization. Such equalization is either preset or dynamically
33、 adjusted depending on the design objectives for the system. When propagation time variations are short in relation to the baud period of the system, preset equalization is generally adequate. Figures 2 and 3 show a typical system schematic and TDMA frame arrangement, respectively. 6 Rec. ITU-R F.11
34、03-1 In general, the connection of P-MP systems to the network is effected at the central station and it is preferable that the P-MP system appears to be transparent to the network without any constraints imposed by the use of TDMA. Furthermore, the use of a conventional interface allows the central
35、 station to be placed at some distance from the connection point to the network, as the link to this point can be made by conventional radio or cable systems. Normally, the regenerated signal received at each outlying station is used to provide timing information for the outlying station. Synchroniz
36、ation information for the burst mode transmissions is obtained from the supervisory bits received from the central station. Hence each burst contains preamble information and consequently bursts with long frame periods are desirable for efficient use of the system. However, this approach can lead to
37、 overall delays that are unacceptable in a public switched network, consequently the relationship between transmission efficiency and permitted system delay must be carefully considered. FIGURE 2 A typical configuration of a P-MP TDMA fixed wireless system Rec. ITU-R F.1103-1 7 FIGURE 3 TS arrangeme
38、nt in a TDMA system using TDD and FDD 8 Rec. ITU-R F.1103-1 Annex 2 Supplementary information on technical and operational aspects of FWA systems used in rural areas 1 General It is necessary to reduce to a minimum the cost of establishing the infrastructure required for systems used in rural areas.
39、 This infrastructure includes, in particular: the provision of adequate access roads; the provision of housing for the equipment, and if necessary, maintenance facilities such as accommodation for maintenance personnel; the provision of accommodation for power supplies, together with fuel tanks, if
40、necessary; the provision of antenna supports, etc. In existing fixed wireless systems, the cost for this infrastructure has often occupied a very high proportion of the expenditure. It may be noted, that in certain cases (when crossing marshy land, deserts, mountainous regions or foreign territory)
41、the use of trans-horizon radio-relay systems working in a relatively low frequency band may be advantageous, since this will avoid the provision of stations remote from important centres of population without necessitating a large installation. In these cases solid-state components might not be suit
42、able for the transmitter power-amplifier. While it is generally difficult to forecast the long-term requirements of traffic demands for trunk links or access links in rural areas, the choice of system capacity is an economic optimum based on such forecasts. An initial installation of equipment will
43、be uneconomic if its final capacity exceeds future requirements. On the other hand, replacement of an initially installed smaller system, when its capacity becomes inadequate, should only be necessary after several years growth. A higher capacity system will then be justified, and the initial equipm
44、ent can be recovered for use on another light-traffic link. Moreover, considering the broadband demand in the future, scalable systems are desirable. 2 Frequency band consideration It is outside the scope of this Recommendation to identify any preferred frequency bands below 3 GHz for FWA systems us
45、ed in rural areas. The information in Table 1 of Recommendation ITU-R F.746 would be useful for system designers for their consideration on the choice of the frequency band as well as the RF channel arrangements. Also, Recommendation ITU-R F.1401 provides considerations for the identification of pos
46、sible frequency bands for FWA and related sharing studies. 3 Antennas The antennas at the subscriber stations should be sturdy and with a small surface area exposed to the wind. When considering the difficulties of access to remote sites, the need for reliability is paramount. Yagi antennas, if well
47、 constructed, are a good solution at frequencies up to about 1.5 GHz. At higher frequencies, other types of antenna such as a helix or a dipole array with a reflector may be used, depending on the gain required and the frequency used. Horn antennas have Rec. ITU-R F.1103-1 9 proved to be a good comp
48、romise between gain, reliability and cost at frequencies at or above 1.5 GHz. The use of the same antenna for transmission and reception is generally more economical for FDD systems, but in such cases a larger frequency separation must be adopted to avoid blocking the receiver (e.g. 3% to 5% of the
49、mean frequency). However, technical difficulties might arise from the adoption of too large a frequency separation because of the bandwidth limitation of some antennas. For TDD systems, the same antenna is used for both transmission and reception so that it can apply the simpler and more economical antenna configuration. In a multiple access system, the antenna(s) at the central station (where all the subscribers in the service area are concentrated) should be chosen so that their radiation characteristics are as closely matched as possible to the geo
