1、STDnITU-R RECMN M-LO39-1-ENGL 1997 4855232 0527444 035 410 Rec. ITU-R M.1039-1 RECOMMENDATION ITU-R M.1039-1 CO-FREQUENCY SHARING BETWEEN STATIONS IN THE MOBILE SERVICE BELOW 1 GE AND FDMA NON-GEOSTATIONARY-SATELLITE ORBIT (NON-GSO) MOBILE EARTH STATIONS (Questions -R 83/8 and -R 84/8) ( 1994- 1997)
2、 Summary In this Recommendation, a statistical calculation method is recommended to be used to evaluate sharing between MESS using FDMA and stations in the mobile service. A dynamic channel assignment technique is described in order to facilitate the sharing. The ITU Radiocommunication Assembly, con
3、sidering a) that the spectrum allocated by the World Administrative Radio Conference for Dealing with Frequency Allocations in Certain Parts of the Spectrum (Malaga-Torremolinos, 1992) (WARC-92) for low-earth orbit (LEO) mobile-satellite services (MSS) below 1 GHz, if shared with mobile services, mu
4、st provide adequate protection from harmful interference; b) large community of travellers. that LEO MSS can provide beneficial radio-based services, including emergency alerting (see Note i), to a NOTE 1 - However, these services will not be identified as safety services as defined by the Radio Reg
5、ulations; c) that the use of LEO enables practical use of frequencies below 1 GHz by space stations; d) 1 GHz can lead to low erlang loading on individual channels; that some coordination and channelisation techniques used in fixed and mobile radio systems in bands below e) sharing between mobile se
6、rvices and low power, low duty cycle mobile-satellite services; that dynamic channel assignment techniques are technically feasible and may provide a means of spectrum f) that the users would operate throughout large geographic areas; g) that the transmission of the MES are short bursts, recommends
7、1 stations in the MSS using FDMA techniques and mobile services in the same frequency band; that the statistical calculation methods described in Annex 1 be used to evaluate sharing between mobile earth 2 that types of dynamic channel assignment techniques such as that described in Annex 2 could be
8、used by non-GSO MSS systems (narrow-band) operating in MSS allocations below 1 GHz in bands to promote compatibility I with terrestrial services. STD-ITU-R RECMN M*1037-L-ENGL 1777 E 4855212 0527Liq5 T51 Rec. ITU-R M.1039-1 411 ANNEX 1 Methods and statistics for determining sharing between MSS earth
9、 station transmitters below 1 GHz and mobile stations 1 Introduction The methods presented in this Annex describe a method to be used to determine if MSS earth station (MES) transmitters can share spectrum with mobile services. The methods described provide a basis for evaluating the effectiveness o
10、f power level limits for MES e.i.r.p. that may be established to allow sharing with mobile services (see Note 1). NOTE 1 -In addition, the uplink transmissions from the MES have an optimum length for sharing with certain terrestrial voice services. It has been indicated this might be up to 500 ms. T
11、he duration of time over which such transmissions would take place is under study (1% in 1-15 min has been suggested). 2 Potential interference from MSS to mobile services Mobile services in the VHF band are typically characterized by frequency modulated voice and data carriers assigned on a periodi
12、c channel grid. Channel spacings used include 12.5 kHz, 15 kHz, 25 kHz and 30 kHz. MSS systems below 1 GHz may use a dynamic channel assignment algorithm which allows the space station to identify those channels not occupied by the mobile stations which are sharing the spectrum. Thus it is expected
13、that there will typically be significant frequency separation (15 kHz or less) between the MSS transmission and the mobile station receiver centre frequency. However, for the purposes of this methodology, the efficiency of the dynamic channel assignment process can not yet be predicted; MSS uplink c
14、hannel selection is therefore assumed to be randomly distributed in 2.5 kiiz (see Note i) steps within the mobile allocation. NOTE 1 - This step size represents practical restrictions on synthesizer implementation with little loss in generality of the analysis. 3 Summary of the methodology Several s
15、teps must be undertaken in order to determine the potential for harmful interference to mobile stations from MES transmitters. The methodology for so doing is outlined in this section. Detailed descriptions of each step are contained in the following sections. 3.1 Coordination contour The first step
16、 is to determine a typical coordination contour around a mobile receiver to be protected. This is described by the range at which an MES transmitter or group of transmitters will produce a pfd in excess of a level determined to be a protection criteria. To perform this calculation one must know the
17、following values: e.i.r.p.,- : maximum e.i.r.p. of the MES (W) B W, : signal bandwidth of the MES transmitter (Hz) Pfdt : PFD considered to be harmful (W/m2) N, : expected maximum simultaneous MES transmitters L(d) : propagation loss as a function of distance. If it can be determined that the coordi
18、nation contour is small enough as compared to the expected movements of mobile stations and MESS, then no further calculations are required. If the coordination contour is too large for this determination to be made, the following steps must be executed. STDWITU-R RECMN R-LO37-1-ENGL 1777 4855212 05
19、2744b 778 412 Rec. ITU-R M.1039-1 3.2 Calculation of threshold exceedance Probability Probabilistic techniques are used to determine the percentage of time that the protection pfd will be exceeded at a particular mobile station receiver. If this “exceedance probability” is low enough, exceeding the
20、protection level is not considered to be harmful interference. 3.2.1 Geographic area for the calculation The first step is to determine an area over which transmissions from MESS will contribute significantly to the statistics of received pfd at the mobile receiver. If too large an area is used, the
21、 subsequently calculated exceedance probability is likely to be understated. This area is typically described by a radius corresponding to the protection contour described above. 3.2.2 Single transmitter pfd probability density function Given an area over which the calculation is to be performed, on
22、e then calculates a discrete probability density function (see Note 1) for the expected values of pfd at a mobile receiver. This is a two-step process, beginning with theestablishment of a random variable describing the probability distribution of MES to mobile receiver range. The probability of a p
23、articular pfd is then evaluated as that associated with the range which, in combinations with the MES e.i.r.p., propagation model and potential filter isolation, produces that pfd. NOTE 1 - The probability density function (PDF) for a random variable defines the probability weight for each of the va
24、lues that the random variable can take on. The integral of the probability density function is unity. If one constructs a new function for each of the values that the random variable can take on by integrating the probability density function from minus infinity to that random variable value, one ha
25、s created the cumulative distribution function. 3.2.3 Multi-carrier pfd probability density function The resulting probability density function of pfd applies when a single MES transmitter is activated. The probability density functions for pfd associated with two or more MES transmitters are derive
26、d from the single carrier probability density function using a convolutional method described in 5 7. 3.2.4 Probability that MES transmitters are activated The resulting pfd distributions must be conditioned by the actual probability that one or more MES transmitters are active within the area of th
27、e receiver to be protected. These probabilities are traffic level dependant and are typically described by the Poisson distribution. This portion of the calculation is dependant on the type of access scheme chosen for the MSS system, however the maximum transmission probabilities have been bounded b
28、y assuming very efficient use of available channels by the MSS operator. 3.2.5 Exceedance probability Actual exceedance probability depends on the share of MSS system traffic originating within the protection contour of the mobile receiver. Typically the ratio of MSS space station coverage area to t
29、he area described by the protection contour is 0.1% or less. Because the actual distribution of system traffic cannot be determined in advance of system operation, the method described for calculation of exceedance probability shows how to make this factor a parameter. This will facilitate understan
30、ding of the impact of expected traffic levels on the potential for harmful interference to a mobile station. 3.2.6 Exceedance probability versus actual interference The calculated exceedance probability actually overstates the potential for harmful interference for the following reasons: - it assume
31、s that each mobile link is always active, either transmitting or receiving; - it assumes that each mobile receiver is operating at its maximum range (minimum performance threshold) with no additional link margin; however power control may be employed in some systems, eliminating this effect; STD-ITU
32、-R RECMN M-3037-3-ENGL 1997 4855232 0529447 824 D Rec. ITU-R M.1039-1 413 - it discounts the fact that dynamic channel assignment techniques used by MSS systems will avoid active receiver frequencies; many MES transmissions will be short bursts which may not open squelch on many receivers and may no
33、t be audible if they occur during talker activity on speech channels, however if the channel is used for data or signalling performance it may be degraded no matter how short the burst. - 4 Reference propagation model For purposes of evaluating the potential of interference from LEO MSS uplink trans
34、mitters to mobile stations (MS) or base stations (BS) in the VHF frequency band a reference link model is given. Further study is required to evaluate an appropriate propagation model for other frequency bands below 1 GHz. The predicted propagation loss is a function of transmitterheceiver separatio
35、n distance. Recommendation ITU-R P.529 states that the received field strength for VHF frequencies can be modelled, to first order as: where: P : transmitted power (W) ht : transmitting antenna height (m) h, : receiving antenna height (m) d : separation (km) h : wavelength (m). Converting this expre
36、ssion from a field strength to a power flux-density from that transmitter incident at a distance d: For the purpose of evaluation the potential of interference from a LEO MSS transmitter to a mobile station, an ntenn L height product of the order of 10 m should be used. This accounts for the fact th
37、at LEO MSS transmitters are likely to be hand held or vehicle mounted, rather than tower mounted. For the case of base stations in the mobile service, a larger product should be used as appropriate. In the case of airborne receivers or MSS transmitters, larger products should also be used. 5 Probabi
38、lity of multiple MES transmissions As noted in 0 3.1, the potential for interference will be dependant on the expected number of simultaneous MES transmitters which can contribute to the aggregate pfd incident at the mobile service receiver. Random access protocols (see Note i) allow for occasional
39、multiple simultaneous transmissions on the same frequency and as such represent the upper limiting case on the potential for aggregate interference to a mobile station receiver. The probability of simulta- neous transmitters is evaluated using the Poisson distribution: -e An n! Pa(.) = - -* where: n
40、 : number of simultaneous transmitters A : average transmissions per unit time. NOTE 1 -Many random access protocols are referred to as “ALOHA” protocols, a specific type of random access -I protocol. STD*ITU-R RECMN M=L037-3-ENGL 3777 4855232 0527q48 7b0 n O 1 2 3 4 5 6 414 Rec. ITU-R M.1039-1 Pa (
41、n) Ca (n) (1) 1 - Ca (n) 0.670320 0.670320 0.329680 0.268128 0.938448 0.061552 0.053626 0.992074 0.007926 0.007150 0.999224 0.000776 O.OOO7 15 0.999939 0.000061 O.oooO57 0.999996 0.000004 0.000004 1.000000 0.000000 The particular type of random access protocol chosen will determine the appropriate v
42、alue of A. The use of slotted random access protocols allows the highest value of carried traffic, a theoretical maximum of 36.8%; practical upper bounds are around 30%. This is double the value of traffic and value of A as compared to a simple un-slotted technique. Systems must be designed to opera
43、te within the throughput constraint of the random access protocol to maintain their quality of service. Thus while short periods of traffic loading in excess of the stability values may be seen, it is reasonable to assume that systems will need to operate below these values in order to retain their
44、users. A value of A = 0.4 in the expression for the Poisson distribution yields practically realisable peak loading levels for the slotted random access protocol. Table 1 demonstrates the probability of O, 1, 2, ., 6 simultaneous transmitters for a value of A = 0.4. One can see from this table that
45、the probabiliy of more than four simultaneous transmitters is O.oooO1. Thus an appropriate value for Nt is 4, however, consideration may be given to using other values. TABLE 1 Representative MES transmission probabilities The aggregate pfd incident at a mobile service receiver from a number of MES
46、transmitters of equal power at a given distance can be expressed as: 6 Evaluation of single carrier pfd probability distribution The single carrier pfd probability distribution is evaluated from two basic assertions: that the propagation loss between the MES and the mobile service receiver is depend
47、ant upon distance and that the probability distribution of all possible separations is known. For the former, refer to P 4 for the propagation loss model. For the latter, a uniform density of MES (tenninals/m2) is used. More complicated distributions could be used but they would implicitly assume th
48、at some feature of the mobile service receiver, an uncorrelated phenomenon with respect to the placement of MESS, had some influence on the MES distribution. STDmITU-R RECMN M-LU37-L-ENGL 1797 M 4855232 0529447 bT7 Rec. ITU-R M.1039-1 415 It is straightforward to demonstrate that a uniform density o
49、f MES produces a unit ramp Probability density function for the random variable describing the separation between the MESS and the mobile service receiver. This discrete probability density function is constructed in the following manner: ! .e o i -150 M d - 160 O 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 %m%$ Transmitter(s)-receiver separation (km) STD-ITU-R RECMN M-1037-1-ENGL 1777 W 4855212 0527Li52 171 418 Rec. ITU-R M.1039-1 From Fig. 1, a protection criteria of - 140 dB(W/m2/4 kHz) would be exceeded by: - - - - Thus the coordination contour would be defined as 35 km for a protecti
