ITU-R F 752-2-2006 Diversity techniques for point-to-point fixed wireless systems《点到点固定无线系统的各种技术》.pdf
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1、 Rec. ITU-R F.752-2 1 RECOMMENDATION ITU-R F.752-2*Diversity techniques for point-to-point fixed wireless systems (1992-1994-2006) Scope This Recommendation provides diversity techniques for point-to-point fixed wireless systems. The diversity techniques include those considered in the domain of spa
2、ce, angle, frequency or their combinations. Basic methods for choice of diversity, obtaining or processing the diversity signals are presented in the Annex, which also gives practical diversity effects based on propagation data. Diversity techniques using alternative transmission media or route/site
3、 diversity which may be applied to improve system availability are not handled in this Recommendation. The ITU Radiocommunication Assembly, considering a) that frequency-selective fading may distort and reduce the strength of received signals on line-of-sight and trans-horizon paths and thereby impa
4、ir the performance of a fixed wireless system; b) that the application of diversity techniques is useful in reducing the effects of fading on system performance; c) that the provision of diversity reception is necessary to achieve satisfactory performance on diffraction and trans-horizon paths; d) t
5、hat various techniques for implementing diversity on line-of-sight, diffraction and trans-horizon paths have been studied and are in use; e) that the application of diversity techniques can provide high performance in line-of-sight systems that make efficient use of the radio spectrum; f) that furth
6、er information regarding the use and application of diversity techniques can be found in Recommendations ITU-R P.530 and ITU-R F.1093, recommends 1 that the information presented in Annex 1 should be used when applying diversity techniques to fixed wireless systems (see Note 1). NOTE 1 The ITU-R Han
7、dbook Digital radio-relay systems also contains relevant material on the application of diversity techniques to fixed wireless systems. *This Recommendation should be brought to the attention of Radiocommunication Study Group 3. 2 Rec. ITU-R F.752-2 Annex 1 Diversity techniques for point-to-point fi
8、xed wireless systems 1 Methods of obtaining diversity signals The most common methods are generically described as frequency diversity and space diversity. In frequency diversity, the same information is transmitted over more than one radio channel. In space diversity, the signal reaches the receive
9、r through more than one transmit/receive antenna path. A description of diversity implementation in different systems operating in distinctive propagation regimes requires a more detailed description of space diversity methods. Trans-horizon systems have used diversity on both transmit and receive.
10、They use multiple diversity with full, three-dimensional, flexibility in the placement of antennas, and sometimes use angle diversity in which multiple beams or directivity patterns are formed with a single antenna. Angle diversity provides relatively uncorrelated signals by taking advantage of the
11、variations in the angle of arrival of the scattered energy at the receiver. On line-of-sight paths, space diversity is usually implemented using two antennas at the receiver with a large enough vertical separation to provide two signals in which the impairments due to multipath fading are sufficient
12、ly decorrelated, where the impairments are signal distortion and loss of signal power. Concerns for the performance of digital radios, for which signal distortion is the dominant propagation impairment, have led to the introduction of diversity methods that rely on the non-uniform structure of the i
13、ncident electromagnetic field near the main receiving antenna, instead of large spatial separations, to decorrelate the signal impairments. In these methods, which are called pattern diversity or angle diversity, the diversity signal is derived from a second antenna or beam that has a different dire
14、ctivity pattern or angular beamwidth in the vertical dimension and/or a different boresight elevation angle. These diversity methods, which can be implemented with antennas that are at the same, or nearly the same, height or with multiple feeds within a single antenna, allow diversity to be added to
15、 an existing hop without requiring tower height extensions to obtain path clearance for diversity reception. Although some studies attempt to distinguish between angle and pattern diversity, others use the terms interchangeably. Since the effectiveness of any diversity system depends on the correlat
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