1、 Rec. ITU-R F.1102-2 1 RECOMMENDATION ITU-R F.1102-2 Characteristics of fixed wireless systems operating in frequency bands above about 17 GHz (Question ITU-R 107/9) (1994-2002-2005) Scope This Recommendation provides characteristics of fixed wireless systems operating in frequency bands above about
2、 17 GHz. The Annex 1 contains possible applications, hop length consideration, basic functions of transmitters and receivers, and other technical/operational characteristics required for the implementation of fixed wireless systems in this frequency range. The ITU Radiocommunication Assembly, consid
3、ering a) that frequency bands above about 17 GHz are allocated to the fixed and other services; b) that the propagation characteristics above about 17 GHz are predominantly governed by precipitation fading and absorption and only suited to short range radio system applications; c) that differing app
4、lications of various administrations may require different radio-frequency channel arrangements; d) that several services with various transmission signal characteristics and capacities may be in simultaneous use in the same frequency band; e) that the various applications may require differing chan
5、nel bandwidths; f) that new applications and network configurations are being used in high density deploy-ment of fixed wireless systems in bands above about 17 GHz, recommends 1 that system design should take into consideration the effects of precipitation outage which critically determines hop len
6、gth; 2 that the frequency bands above about 17 GHz be used for short range applications which will allow equipment to be compact with smaller antennas; 3 that to allow the use of mixed services, whilst achieving spectral economy, the radio-frequency channel arrangements should be based on homogeneou
7、s patterns in accordance with Recommendation ITU-R F.746; 4 that both digital and wideband analogue modulation techniques are applicable; 5 that Annex 1 be referred to for guidance in system design. 2 Rec. ITU-R F.1102-2 Annex 1 Characteristics of fixed wireless systems operating in frequency bands
8、above about 17 GHz 1 Introduction In the frequency bands above about 17 GHz some allocations are provided for the fixed service on a worldwide basis. At these frequencies, outage is due primarily to precipitation fading lasting in excess of 10 s. Hence parameters of particular importance to the impl
9、ementation of such systems are availability and transmitter-to-receiver path length (hop length) that may be achieved. These parameters are considered in this Annex for systems that are typically used in the local network. 2 Application considerations 2.1 Local access/networks The frequency bands ab
10、ove about 17 GHz are being used mainly for short haul links. Compact and highly reliable radio equipment can support voice, data, video, and broadband data transmission. The main applications are: interconnection of LANs; interconnection between LANs (IEEE 802.3/Ethernet and IEEE 802.5/Token Ring) w
11、ith a transmission capacity of the order of 10 Mbit/s; interconnection between LANs (Ethernet including RLANs IEEE 802.11a/IEEE 802.11b/HiperLAN2/HiSWANa) with a transmission capacity of the order of 100 Mbit/s; video transmission; subscriber links; digital primary group or higher speed data links f
12、rom end office to user buildings; cellular phone applications; interconnection between cellular phone exchanges and base stations; relief applications; transportable radio equipment used for backup links when optical fibre systems or other terrestrial circuits have failed; ring closure or point-to-p
13、oint connection in the synchronous digital hierarchy (SDH) access network; high density access networks in, for example, subscriber-based applications. Rec. ITU-R F.1102-2 3 Table 1 categorizes the above applications. TABLE 1 A categorization of applications 2.2 Cost comparison between fibre and rad
14、io links in the access portion An optical fibre system requires construction work continuously along the cable route. On the other hand, radio systems require such work only at the transmitting and receiving stations. For this reason, the greater the distance between locations, the greater the cost
15、for a fibre system will increase. Costs are compared in the following simple model shown in Fig. 1. Physical link configuration Transmission capacity Content of signal Hop length LAN interconnection User to user building Order of 10 Mbit/s Data Several tens of metres to km Subscriber links From end
16、office to user building Analogue or primary rate digital group or higher PDH capacity Data or video Several km to tens of km Inter-cell telephone applications Between cellular system telephone exchange and radio base station 2 Mbit/s up to STM-1 Voice or data Several km to tens of km Transportable e
17、quipment for relief operations (see Note 1) Backup for optical fibre links Analogue or primary rate digital group or higher PDH capacity or SDH Voice, data or video Several km to tens of km SDH access network ADMs ring closure/interconnection or tributary extension SDH hierarchy Virtual containers (
18、Vc) Several km to tens of km High density subscriber-based access Direct access to subscriber Up to STM-1 Data and voice Fraction of a km up to a few km Vertically-connected wireless link From user building to subscriber Order of 100 Mbit/s Data and video Several tens of m ADM: Add/drop multiplexer
19、PDH: Plesiochronous digital hierarchy STM-1: Synchronous transfer mode 1 NOTE 1 See Recommendation ITU-R F.1105. 4 Rec. ITU-R F.1102-2 1102-01FIGURE 1Assumed modelRadio equipment cost: R1Radio installation cost: R2E/O, O/E cost: F1Optical fibre cost: F2E/O, O/E E/O, O/ENumber ofsubscribers: NDistanc
20、e: DBase station User buildingFibre (overhead) installation cost: F3Cost R for introducing a radio system is given by: R = (R1 + R2) N Cost F for introducing an optical fibre system is given by: F = F1 N + (F2 + F3) N D Figure 2 shows the result of cost comparison. According to Fig. 2, with the same
21、 number of subscribers, any increase in distance decreases the cost of radio with respect to that for a fibre system. Further, with the same distance, radio systems are advantageous when the number of subscribers is small. Moreover, the applicable area for radio expands sharply when the distance bec
22、omes greater. 1102-02FIGURE 2Results of cost comparison between fibre and radioHighRadio equipmentpriceEffective area whereradio is suitableStandardLowEffective areawhere optical fibreis suitableNumberofsubscribersDistance (km)Area where theapplicability ofradio is difficultRec. ITU-R F.1102-2 5 If
23、only cost is taken into consideration, the greater the distance, the more the applicable area of radio will expand. However, it is necessary to take into account the fact that the propagation distance of radio systems using frequency bands above about 17 GHz is limited by rain attenuation. The provi
24、sion of multiple-hop short-range links would therefore tip the balance towards the favour of fibre systems, but generally within the local loop multiple-hop systems are rare. In practice a mixture of fibre and radio would be used depending on which system is the most cost effective and practical for
25、 that particular part of the application. 2.3 Rapid deployment One of the characteristics of radio systems is the speed at which they can be commissioned. Fibre systems require installation of fibres between the locations where communications are to be implemented, resulting in a long construction p
26、eriod until lines can be placed in service. In particular, the construction period increases sharply when optical fibre is laid underground when compared to pole-mounted installation. Further, there may be cases when fibre installation is impossible because of inability to obtain the right of way. T
27、he use of radio links to facilitate cable television system installation in such situations is a known implementation of this property. However, the lead-in time for radio systems is very short since it requires installation only at the locations where communications are to be implemented. This make
28、s it possible to open circuits within a few hours. Although link planning, licensing and site clearance procedures increase the lead-in time in practice, the lead-in time is still likely to be significantly shorter than that for a fibre link. In radio systems, it is necessary to confirm the line-of-
29、sight condition. Studies concerning computer-based line of sight confirmation preparing databases of geographical features and buildings are being made, and a quick antenna alignment procedure may be helpful. The relative ease of redeploying radio equipment is one of its attractive characteristics.
30、Transportable radio systems are more suitable for rapid communications relief during times of disaster, link and fibre failures and the like. 3 Hop length considerations No universal hop length/frequency characteristic can be constructed, however the following parameters contribute to the availabili
31、ty objectives on hop length: Free space specific attenuation: A0(dB/km) Frequency dependent, from Recommendation ITU-R P.525. O2and H2O specific gaseous absorption attenuation: A(dB/km) Frequency dependent in the relevant frequency ranges from Recommendation ITU-R P.676. Antenna isotropic gain: Gi (
32、dB) Constant depending on geometrical size of antennas, with no theoretical upper bound, but practically limited, to allow feasible boresight alignment, by field operability of 6 Rec. ITU-R F.1102-2 the 3 dB main beam angle width (normally not narrower than 1). This leads to a practical limit of G 4
33、4 dBi. Transmit power: PT(dBm) Related to the available technology for RF carrier generation/amplification and to the linearity requirement of the modulation format. Bit error ratio (BER) threshold: PTh(dBm) Relative to the relevant BER at which the availability objective is defined. This parameter
34、is related to the receiver noise figure, the transmitted bit rate and the carrier-to-noise performance of the modulation format. Rain attenuation for the objective time percentage: R%(dB) Estimated on the basis of rain-rate intensity for the relevant unavailability time percentage through the method
35、 reported in Recommendations ITU-R P.530 and ITU-R P.838, using statistics obtained from Recommendation ITU-R P.837. The above parameters may be subdivided into two blocks (see Note 1): A fixed, implementation dependent, constant “hop gain” (HG): HG = 2Gi + PTh + PTmmmmmmdB (1) A rain-rate/frequency
36、 dependent “hop attenuation” (HA%) for a given time percentage over the length l (km) of the hop as foreseen by Recommendation ITU-R P.530: HA%= R%+ (A0+ A) lmmmmmmdB (2) Using the above approach, graphs like those reported in Figs. 3, 4 and 5 (computed as an example for the climatic zones B, G and
37、K with frequency and percentage of unavailability (U%) as parameters) may be derived, from which the maximum hop length for the given implementation/ frequency/climatic zone/objective time-percentage may be obtained. NOTE 1 Since, in general, radio systems above about 17 GHz are supplied with integr
38、al antennas, in these assumptions feeder losses are neglected; in the case of feeder connection between equipment and antenna, the feeder losses will decrease the hop gain (HG). 4 Digital radio implementations The application requirements, spectrum availability, propagation conditions and available
39、technology above about 17 GHz result in equipment implementations that differ substantially from those that predominate below about 17 GHz. Nevertheless, there is no abrupt transition but a gradual one starting from the band 13 GHz. The predominant distinctive characteristics of digital radio applic
40、ations above about 17 GHz are: a wide range of transmission capacities; partitioning of equipment into an outdoor unit consisting of radio front-end attached to antenna, and an indoor unit containing the baseband sub-assemblies and in many cases the Rec. ITU-R F.1102-2 7 IF sub-assemblies as well. T
41、his virtually avoids waveguide feeder losses which could be prohibitive and provides great equipment mounting flexibility through low-loss inter-connection at baseband and/or IF; new applications trending towards higher order modulations and higher technical spectral efficiencies. 1102-0312 36 471 5
42、 8129131014151617181920140.0 160.0 180.0 200.00.010.020.030.040.0Hop gain, HG (dB)FIGURE 3Critical hop length vs. hop gain for climatic zone B, horizontal polarizationCriticalhop lenght,L(km)Curve f (GHz) U % Curve f (GHz) U %1 18 0.1 11 38 0.12 18 0.03 12 38 0.033 18 0.01 13 38 0.014 18 0.003 14 38
43、 0.0035 18 0.001 15 38 0.0016 28 0.1 16 55 0.17 28 0.03 17 55 0.038 28 0.01 18 55 0.019 28 0.003 19 55 0.00310 28 0.001 20 55 0.001U: unavailability (%)8 Rec. ITU-R F.1102-2 1102-041263117548129131020191615181714200.0180.0160.0140.00.010.020.030.040.0Hop gain, HG (dB)FIGURE 4Critical hop length vs.
44、hop gain for climatic zone G, horizontal polarizationCriticalhop lenght,L(km)Curve f (GHz) U % Curve f (GHz) U %1 18 0.1 11 38 0.12 18 0.03 12 38 0.033 18 0.01 13 38 0.014 18 0.001 14 38 0.0015 18 0.003 15 38 0.0036 28 0.1 16 55 0.17 28 0.03 17 55 0.038 28 0.01 18 55 0.019 28 0.001 19 55 0.00110 28
45、0.003 20 55 0.003U: unavailability (%)Rec. ITU-R F.1102-2 9 1102-051263117458129131610141718151920140.0 160.0 180.0 200.040.030.020.010.00.0Hop gain, HG (dB)FIGURE 5Critical hop length vs. hop gain for climatic zone K, horizontal polarizationCriticalhoplenght,L(km)Curve f (GHz) U % Curve f (GHz) U %
46、1 18 0.1 11 38 0.12 18 0.03 12 38 0.033 18 0.01 13 38 0.014 18 0.001 14 38 0.0015 18 0.003 15 38 0.0036 28 0.1 16 55 0.17 28 0.03 17 55 0.038 28 0.01 18 55 0.019 28 0.001 19 55 0.00110 28 0.003 20 55 0.003U: unavailability (%)4.1 Design trade-offs Design trade-offs are rather complex due to the mult
47、iple interdependencies. However, to simplify the task, the trade-off criteria can be subdivided in various ways, depending on specific optimization goals. For example, it is meaningful to distinguish between service quality and user friendliness criteria, as exemplified in Table 2. 10 Rec. ITU-R F.1
48、102-2 TABLE 2 These trade-off criteria can be rearranged, as needed. For example, for a selected combination of transmission capacity and performance, the primary service quality trade-off is between system gain and spectral efficiency. If enhancement options are available, such as error correction, the trade-off criteria sub-set expands and increases design flexibility. Some additional design trade-off criteria may belong to both categories. For example, MTBF affects both service quality and user friendliness. In
