1、 Rec. ITU-R SM.1046-2 1 RECOMMENDATION ITU-R SM.1046-2 Definition of spectrum use and efficiency of a radio system (Question ITU-R 47/1) (1994-1997-2006) Scope The revision to this Recommendation is giving an alternative for determining the spectrum utilization efficiency (SUE) for various radiocomm
2、unication systems (mobile, point-to-point, etc.) The ITU Radiocommunication Assembly, considering a) that the spectrum is a limited natural resource of great economic and social value; b) that demand for use of the spectrum is increasing rapidly; c) that a number of different factors, such as the us
3、e of different frequency bands for particular radio services, relevant spectrum management methods for networks in those services, the technical characteristics of transmitters, receivers and antennas used in the services, etc., significantly influence spectrum use and efficiency and through their o
4、ptimization, particularly in respect of new or improved technologies, significant economies of spectrum can be achieved; d) that there is a need for defining the degree and efficiency of spectrum use, as a tool for comparison and analysis for assessing the gains achieved with new or improved technol
5、ogies, particularly by administrations in the national long-term planning of spectrum utilization and the development of radiocommunications; e) that comparison of spectrum efficiency between actual radio systems would be very useful, when developing new or improved technologies and assessing perfor
6、mance of existing systems, recommends 1 that, as a basic concept, the composite bandwidth-space-time domain should be used as a measure of spectrum utilization the “spectrum utilization factor”, as illustrated in Annex 1 for transmitting and receiving radio equipment; 2 that the basis for calculatin
7、g spectrum utilization efficiency (SUE), or spectrum efficiency in short, should be the determination of the useful effect obtained by the radio systems through the utilization of the spectrum and the spectrum utilization factor, as illustrated in Annex 1. Some examples of how to use this concept ma
8、y be found in Annex 2; 3 that the basic concept of relative spectrum efficiency as outlined in Annex 1 should be used to compare spectrum efficiencies between radio systems; 4 that any comparison of spectrum efficiencies should be performed only between similar types of radio systems providing ident
9、ical radiocommunication services as explained in 4 of Annex 1; 5 that in determining the spectrum efficiency, the interactions of various radio systems and networks within a particular electromagnetic environment should be considered. 2 Rec. ITU-R SM.1046-2 Annex 1 General criteria for the evaluatio
10、n of spectrum utilization factor and spectrum efficiency 1 Spectrum utilization factor Efficient use of spectrum is achieved by (among other things) the isolation obtained from antenna directivity, geographical spacing, frequency sharing, or orthogonal frequency use and time-sharing or time division
11、 and these considerations reflected in definition of spectrum utilization. Therefore, the measure of spectrum utilization spectrum utilization factor, U, is defined to be the product of the frequency bandwidth, the geometric (geographic) space, and the time denied to other potential users: U = B S T
12、 (1) where: B : frequency bandwidth S : geometric space (usually area) and T : time. The geometric space of interest may also be a volume, a line (e.g. the geostationary orbit), or an angular sector around a point. The amount of space denied depends on the spectral power density. For many applicatio
13、ns, the dimension of time can be ignored, because the service operates continuously. But in some services, for example, broadcast and single channel mobile, the time factor is important to sharing and all three factors should be considered simultaneously, and optimized. The measure of spectrum may b
14、e computed by multiplication of a bandwidth bounding the emission (e.g. occupied bandwidth) and its interference area, or may take into account the actual shape of the power spectrum density of the emission and the antenna radiation characteristics. Traditionally, radio transmitters have been consid
15、ered the users of the spectrum resource. They use the spectrum-space by filling some portion of it with radio power so much power that receivers of other systems cannot operate in certain locations, times and frequencies because of unacceptable interference. Notice that the transmitter denies the sp
16、ace to receivers only. The mere fact that the space contains power in no way prevents another transmitter from emitting power into the same location; that is, the transmitter does not deny operation of another transmitter. Receivers use spectrum-space because they deny it to transmitters. The mere p
17、hysical operation of the receiver interferes with no one (except as it inadvertently acts as a transmitter or power source). Even then the space used physically is relatively small. However, the authorities deny licences to transmitters in an attempt to guarantee interference-free reception. The pro
18、tection may be in space (separation distance, coordination distance), in frequency (guardbands) or even in time (in the United States of America, some MF broadcasting stations are limited to daylight operation). This denial constitutes “use” of the space by the receiver. The radioastronomy bands are
19、 a familiar example of the recognition of receiver use of the spectrum space. One way to incorporate these facts into a unit of measure of spectrum space is to partition the resource into two spaces the transmitter space and receiver space and define dual units to measure the usage of each space. Wh
20、ere simplicity is most important, the two units can be recombined into a single measure for system use. Rec. ITU-R SM.1046-2 3 Further information concerning the general approach to calculate the spectrum utilization factor may be found in Chapter 6 of the National Spectrum Management Handbook (Gene
21、va, 1995). 2 Spectrum utilization efficiency (SUE) According to the definition of SUE (or spectrum efficiency as a shortened term) of a radiocommunication system, it can be expressed by a complex criterion: SUE = M, U = M, B S T (2) where: M: useful effect obtained with the aid of the communication
22、system in question U: spectrum utilization factor for that system. If necessary, the complex spectrum efficiency indicator may be reduced to a simple indicator: the ratio of useful effect to spectrum utilization factor: TSBMUMSUE= (2) 3 Relative spectrum efficiency (RSE) The concept of relative RSE
23、can be used effectively to compare the spectrum efficiencies of two similar types of radio systems providing the same service. RSE is defined as the ratio of two spectrum efficiencies, one of which may be the efficiency of a system used as a standard of comparison. Hence, RSE = SUEa/ SUEstd(3) where
24、: RSE : relative spectrum efficiency (ratio of SUEs) SUEstd : SUE of a “standard” system SUEa : SUE of an actual system. The likely candidates for a standard system are: the most theoretically efficient system, a system which can be easily defined and understood, a system which is widely used a de f
25、acto industry standard. The RSE will be a positive number with values ranging between zero and infinity. If the standard system is chosen to be the most theoretically efficient system, the RSE will typically range between zero and one. As an example, the most theoretically efficient system may be ch
26、aracterized according to the principles of information theory. The communication capacity of a communication channel on which a subscriber or a listener receives a wanted communication is determined by the relation: C0= F0ln (1 + 0) 4 Rec. ITU-R SM.1046-2 where: F0: bandwidth of the wanted communica
27、tion 0 : signal/noise ratio at the receiver output. If the signal/noise ratio at the receiver input is equal to the protection ratio sand the bandwidth of the communication channel over which the signals are transmitted is equal to Fm, then the communication capacity is Cp= Fmln (1 + s). It must exc
28、eed or at least be equal to the communication capacity of the channel over which the subscriber receives a wanted communication, i.e. Cp C0. Hence the minimum possible value of the protection ratio sat which the subscriber will receive a communication with a signal/noise ratio equal to 0is defined a
29、s: s= (1 + 0)F0 /Fm 1 (4) The major advantage of directly computing the RSE is that it will often be much easier than computing the SUEs. Since the systems provide the same service, they will usually have many factors (sometimes even physical components) in common. This means that many factors will
30、“cancel out” in the calculation before they need to be actually calculated. Often this will greatly reduce the complexity of the calculation. Some examples of RSE calculations are presented in Annex 2 below and in Chapter 6 of the National Spectrum Management Handbook (Geneva, 1995). 4 Comparison of
31、 spectrum efficiencies As described in previous sections, values for SUE could be computed for several different systems and could indeed be compared to obtain the relative efficiencies of the systems. Such comparisons, however, will have to be conducted with caution. For example, the SUEs computed
32、for a land mobile radio system and a radar system are very different. The information transfer rate, the receivers and transmitters in these two systems are so different that the two SUEs are not commensurate. It would not be particularly useful to try to compare them. Hence, the comparison of spect
33、rum efficiency should be only done between similar types of systems and which provide identical radiocommunication services. It would be beneficial to conduct the comparison of the spectrum efficiency or utilization of the same system over time to see if there is any improvement in the specific area
34、 under study. It should also be noted that although spectrum efficiency is an important factor, because it allows the maximum amount of service to be derived from the radio spectrum, it is not the only factor to be considered. Other factors to be included in the selection of a technology or a system
35、 include the cost, the availability of equipment, the compatibility with existing equipment and techniques, the reliability of the system, and operational factors. Rec. ITU-R SM.1046-2 5 Annex 2 Examples 1 Spectrum use by land mobile radio systems 1.1 Spectrum efficiency of an indoor pico-cellular r
36、adio system In the case of an indoor pico-cellular system in the frequency band between 900 MHz and 60 GHz, the spectrum efficiency can also be derived using equation (2). From this equation, the spectrum efficiency of an indoor pico-cellular radio system may be defined as: Erlangs / (bandwidth area
37、) (5) where erlangs is the total voice traffic carried by the pico-cellular system, bandwidth is the total amount of spectrum used by the system and area is the total service area covered by the system. Since the pico-cellular system is to be implemented in a high-rise building, the total floor area
38、 is used in the calculation of spectrum efficiency. The number of channels required per cell can then be calculated based on the Erlang B Tables for a given number of users on the floor and traffic per user. 1.1.1 Pico-cellular system covering a building In order to calculate the total bandwidth req
39、uired for the whole building, the vertical re-use distance in terms of the number of floors is required. This parameter is dependent on the floor losses and is different for different types of buildings. The total number of half duplex channels required for the building can then be calculated and is
40、 equal to: 2 No. of channels per cell No. of cells per floor No. of floors of separation The factor 2 is needed here to reflect the number of channels needed for two-way communications. The spectrum efficiency, SUEbuilding, of the system providing coverage in the building can then be calculated usin
41、g equation (5): areafloortotalbandwidthchannelchannelsofNo.TotalbuildingentiretheincarriedtrafficTotal=buildingSUE (6) Example: In this indoor system operating at 900 MHz Bandwidth of a (half duplex) channel 25 kHz No. of channels per cell 10 No. of cells per floor 4 No. of floors of separation 3 To
42、tal No. of channels required 120 At a grade of service of 0.5%, the traffic carried on one floor = Tf= 16 E or 2 Tfdue to both base and mobile stations. areafloortotal025.0120floorsofNo.16=buildingSUE (7) 6 Rec. ITU-R SM.1046-2 If the floor is 25 m by 55 m, SUEbuilding= 3 880 E/MHz/km2. 1.1.2 Pico-c
43、ellular system covering a down-town area Similarly, the bandwidth required for the whole down-town area may also be calculated if the horizontal re-use distance is known. Again, this parameter is dependent on the building material and the propagation loss of a signal into and out of a building. This
44、 re-use distance directly affects the number of buildings that can be placed in a cluster (or interference group). In this case, the total number of half duplex channels required in the down-town area is equal to: 2 No. of channels per building No. of buildings per cluster Again the factor 2 is need
45、ed here to reflect the number of channels needed for two-way communications. The spectrum efficiency, SUEarea, of the system providing coverage to the entire down-town area can then be calculated using equation (5): areaservicetotalbandwidthchannelchannelsofNo.TotalareaentiretheincarriedtrafficTotal
46、=areaSUE (8) Here, the total service area is the total floor area of the buildings covered by the pico-cellular system. Example: In this indoor system operating at 900 MHz No. of channels per building 120 No. of buildings per cluster 4 Bandwidth of a (half duplex) channel 25 kHz Total No. of channel
47、s required 480 2E/MHz/km970areafloortotal025.04120buildingsofNo.floorsofNo.16=areaSUE (9) NOTE 1 Additional information may be found in: CHAN, G. and HACHEM, H. September, 1991 Spectrum efficiency of a pico-cell system in an indoor environment. Canadian Conference on Electrical and Computer Engineer
48、ing, Quebec City, Canada. HATFIELD, D.N. August, 1977 Measures of spectral efficiency in land mobile radio. IEEE Trans. Electromag. Compt., Vol. EMC-19, 3, 266-268. 1.2 RSE of land mobile radio systems RSE values of land mobile radio systems using different types of modulation were compared in the r
49、elation to the most theoretically efficient system (see Annex 1, 3 and equation (4). For the sake of simplicity and to obtain finite analytical expressions, calculations were made for the simplest models of a network in the form of an ideal rectangular lattice and propagation conditions typical for the UHF frequency band. However, the general laws will be the same for more complex models of real networks with more sophisticated propagation models. The network model is made up of squares of equal dimensions with the
