GB2265525A - Method of allocating broadcasting criteria in a network - Google Patents

Abstract

A method of allocating broadcasting criteria to one or more new stations in a network of stations comprises a pseudo- optimum planning method based on an iterative process which controls the number of considered stations and broadcasting criteria combinations and wherein the network is planned to acceptable levels of interference determined by the ambient field strengths.

Description

METHOD OF ALLOCATING BROADCASTING CRITERIA IN A NETWORK The invention relates to methods of allocating broadcasting criteria to one or more new stations in a network such as, for example, a sound broadcasting network, a mobile radio network or a fixed link (microwave) network.

The availability of a "new" spectrum for planning any new network is becoming increasingly rare. For example, the heavy demand for new VHF broadcasting services means that they have to be planned in the existing bands already dedicated to sound broadcasting. This requires a frequency to be revised many times throughout the country and consequently, with repeated use, there will be a risk of mutual inteference between stations either sharing a frequency or close in frequency.

Existing stations, which are within the frequency band being considered or from adjacent bands, consist of all operational UK mainland and continental broadcasting services. The system planner must comply with the associated existing planning problems, called external constraints, and on the other hand, all proposed services form further planning constraints, called internal. These planning constraints at VHF are consistent with the use of CCIR Recommendation 370-5.

The quality for protection is often embodied in the protection margin, as being the extent to which the wanted field strength exceeds the unwanted (interference) field strength. The degree of potential interference can be quantified in terms of the nuisance field, which requires knowledge of the propagation loss and the actual frequency separation, in order to determine the protection ratio.

The required protection ratio (per) is determined from the frequency separation between the proposed and existing services. The protection ratios which are applied to VHf FM stereo sound broadcasting services are taken from CCIR Recommendation 412-4.

The protection margin PM (dB) is the difference between the wanted (protected field strength) and unwanted field strength (nuisance field). Positive protection margins are those in which the wanted field strength exceeds the unwanted field strength. The quality of service is proportional to the magnitude of the PM.

The ambient field strength is the maximum (interference) field strength tolerable at each site. The compatibility impact between any two sites is analyzed by making field strength predictions on a site to site basis. This is referred to as a combinational strength whereby both interference paths (reciprocal paths) are considered.

The nuisance field is calculated as the sum for the unwanted field strength and appropriate protection ratio needed between the proposed and existing services.

In addition to these constraints there are other planning constraints which may apply. For the VHF network these may include interference problems to the adjacent aeronautical radionavigation band (108 to 117.975 MHz) and intermediate frequency (IF) considerations.

One way of planning a network is to use an optimum planning method. Optimum planning considers all the planning possibilities within a network. Such possibilities would be the potential broadcasting criteria assignment combinations available and would describe different levels of network interference.

However, the problem with such an approach is that the planning complexity rapidly increases as additional services are introduced into the network. In general, for a VHf network with 'n' proposed stations and 'F' potential frequencies, there are Fn frequency combinations to be considered. Therefore a proposed network of 50 stations in either 5, 15 or 30 sub-band frequencies gives respectively 9 x 1034, 6 x 1058 and 7 x 1073 total frequency combinations, the latter being typical of practical frequency assignment problems.

In terms of present computing power, it is highly unlikely that large networks could be planned by optimum technique. Further, the use of such extensive computing facilities would be very expensive.

Thus the optimum planning method which considers all potential planning possibilities is only practicable for small network problems and is available as an everyday planning tool.

The invention provides a method of allocating broadcasting criteria in a network using a pseudo-optimum planning method. A pseudo-optimum planning method reduces the number of criteria combinations which need to be considered and can still perform an extensive examination of the network planning problem but without the practical difficulties of the optimum method.

The invention thus provides a method of allocating broadcasting criteria to one or more new stations in a network of stations comprising a pseudo-optimum planning method based on an iterative process which controls the number of considered stations and broadcasting criteria combinations and wherein the network is planned to acceptable levels of interference determined by the ambient field strengths.

In particular, the invention provides a method of allocating broadcasting criteria to one or more new stations in a network of stations, comprising the steps of: a) calculating the combinational field strengths between each new station and each of the other stations.

b) calculating the combination nuisance field strengths between each new station and each of the other stations; c) calculating the protection margin for each particular combination of broadcasting criteria and discarding those criteria which have negative protection margins; d) determining a set of potential assignments of broadcasting criteria for each new station; and e) using a pseudo-optimum planning method to determine the optimum broadcasting criteria for each new station.

Advantageously the pseudo-optimum planning method comprises the steps of: a) planning the priority of each new station in the network, with stations having the more demanding planning criteria being given highest priority; b) selecting the stations into two or more groups wherein the first group (G1) contains the most critical stations; the second group(G2) the next most critical stations and so on; c) limiting the number of options of potential broadcasting criteria assignments per station in G1 to a predetermined number and calculating the possible criteria combinations; d) discarding those combinations where the predominant nuisance held exceeds the ambient field strength; e) using each of the remaining combinations in turn to impose additional planning constraints in turn to impose additional planning constraints on stations in G2 by the further steps of: f) calculating the nuisance fields between the two groups of stations G1 and G2; g) arranging the potential assignments of the G2 stations to respect those of G1 so that all conflicting planning situations are erased; h) planning G2 by the method of steps c) and d); i. selecting the criteria combination of G1 which maximises the number of G2 combinations; j. using G1 as a set of additional planning constraints on all remaining stations; and k) recording the remaining stations as in step a), reselecting G2 as G1 and a new group as new G2, and repeating steps c) and k) until all stations are assigned broadcasting criteria.

Advantageously the nuisance field strengths for each staiton to station conbination are calculated to determine whether the interference is to be regarded as steady or tropospheric Preferably the nuisance field for tropospheric interference is used unless the nuisance field for steady interference is stronger in which case that is preferably used.

If the predominant interference level for all G2 broadcasting criteria combinations exceeds the ambient field strength or one or more of the stations have exhausted their predetermined number of broadcasting criteria options in satisfying the G1 planning criteria, then there may be no G1 potential assignments which can offer G2 planning solutions at the required ambient field strength.

Preferably, in such cases the one or more problematic G2 stations are replaced by those remaining one or more stations which offer the minimum potential broadcasting criteria. The optimisation is then repeated using the new G2 combination.

Advantageously this process may be repeated as many times as required to find an optimised G2 solution. All unresolved stations are considered for reselection during later iterations.

Preferably the number of potential broadcasting criteria for each new station is restricted to a predetermined figure.

Advantageously, if no solution is found for allocating criteria to a particular station then the number of potential broadcasting criteria considered for that station is increased until a solution is found.

The invention will now be described, by way, of example only, with reference to a hypothetical VHF sound broadcasting network.

The hypothetical network includes the proponed stations shown in Table 1: TABLE 1 Brighton Canterbury (A) Canterbury (B) Clacton Folkestone Hastings (A) Hastings (B) Heathfield Les-Platons Swingate Wrotham The combinational field strengths between proposed and existing services are used to determine a set of potential assignments for each proposal. In so doing, all.frequency combinations are analyzed for the predominant interference levels in terms of the nuisance fields.

Those combinations which still offer tolerable interference levels can then be considered in a pseudo-optimum planning method which uses an iterative technique to plan the proposed network.

A database containing "e" existing services which form all external constraints is called EXISTING. For each existing service we have: a) Name, reference number and country; b) Frequency; c) Location in the form of longitude and latitude; d) Maximum effective radiated power, measured in dB relative to 1 Kw, and polarisation; e) Maximum effective antenna height.

Similiarly, a database called PROPOSED contains i' proposed services (Table 1). Each proposal follows the same format as EXTERNAL except that the frequency is unknown.

In Table 1, co-sited services at both Hastings and Canterbury are required. For the Hastings services, the following information is typical:

Proposed Country No Long Lat ERP Pol Hght Service (dBW) (M) Hastings (A) GB O oE34 50N52 .0 Mixed 114 Hastings Hastings (B) GB O OE34 50N52 .0 Mixed 114 The VHF propagation model that predicts field strengths between any two locations, for land and mixed paths and all climatic conditions, is that described by CCIR Recommendation 370-5.Using the propagation model on a site to site basis, field strength values exceeded at 50 of the locations are determined for 5% and 50% of the time for land and mixed paths. These values are used in the calculation of the nuisance field to determine whether the interference is to be regarded as steady or tropospheric.

All combinations of field strengths between the "i" PROPOSED services and the "yes' EXISTING services are calculated and stored in a data-array called ARRAY-1. Similarly, all combinations of field strengths within the PROPOSED services (i x i) are calculated and stored in a data-array called ARRAY 2.

Using ARRAY 1, which contains all the calculated combinational field strengths between proposed and existing stations, all the nuisance fields are evaluated on a site to site basis.

Each frequency in the band or sub-band is considered as a potential frequency assignment for the proposed service. Each proposed service is considered as a provider and a receiver of interference to each of the existing services. Assuming there are "f" band (sub-band) frequencies, there are "e" site to site calculations for each PROPOSED entry. For each path, the nuisance field is calculated twice, once for each direction. For each of the "F" frequencies the worst case interference is identified. In each instance the worst value is retained. Table 3 illustrates this in the case where eleven frequencies are considered for a proposed Hastings (A) series. The impact of the proposal on existing services is shown in (a) where worst case nuisance fields calculated on each frequency (MHz) are recorded. (b) shows the complementary situation where Hastings (A) is the sufferer of interference.

TABLE 3

a) 48 62 59 65 75 76 58 45 53 65 44 b) 83 78 56 66 72 76 78 83 84 79 66 Freq 100.0 100.1 100.2 100.3 100.4 100.5 100.6 100.7 100.8 100.9 101 (MHz) A set of frequencies, called potential assignments, is determined for each proposed services, which satisfies both the exisitng and proposed planning constraints. Before any decision can be made it is necessary to determine the protection available on each frequency in terms of the protection margins (PM).This involves firstly considering all frequency combinations and satisfying the existing planning criteria before satisfying the proposed criteria.

The PM for a particular frequency combination is the difference between the ambient field strength and the worst case nuisance field strength. If the PM generated is negative the frequency is assumed unusable since the interference exceeds the tolerance threshold. The ambient field strength tolerances for both the existing network and the proposed network are termed S, and S2 respectively.

PM = S - En where En is the nuisance field.

Assuming S, to be 65 dB (,uV/m) and S2 to be 80 dB (uV/M), the worst case PMs for Hastings (A) are shown in Table 4. Hastings (A) is considered as the source of interference in (a) and as the receiver in (b).

TABLE 4

a) 17 3 6 0 -10 11 7 20 12 0 21 b) 100.0 100.1 100.2 100.2 100.3 100.4 100.5 100.6 100.7 100.8 100.9 101 (MHz) Any frequency combination generating a negative PM is ignored.

In this example, in Table 4(a) frequencies 100.4 and 100.5 share this condition. For these frequencies the originating nuisance fields from the proposed station exceed the threshold, St, and therefore these frequencies do not satisfy the existing planning constaints.

Table 4(b) shows the reciprocal case where Hastings (A) is the sufferer of interference from existing services. Negative PMs occur when the nuisance field received at the proposed service exceeds the ambient field strength S2. Frequencies 100.0, 100.7 and 100.8 exhibit negative PMs and are thus unsuitable assignments for Hastings (A). Of those frequencies remaining, the more desirable have the greatest PM's from existing services. Therefore the desirable sequence is, in descending order of PM (100.2, 100.3, 101.0, 100.1, 100.6 and 100.9 MHz).

The planning of the proposed services is based on a pseudo optimum planning algorith which uses an iterative approach whereby in each iteration the proposed services recognised as having the more demanding planning criteria are given highest priority. These services are selected into two groups where the first group, containing the most critical sites, is used to optimise the planning opportunities of the second group.

At the beginning of each iteration, the list of proposed stations is arranged so that those having the minimum available number of potential assignments are placed at the top. When stations share the same number of potential assignments, priority is given to those stations having the least positive set of PMs. This process allows the more critical stations to be grouped.

The following example illustrates how the given set of proposed services (hypothetical) in Table 5 are sorted into priority. As previously seen, Hastings (A) and Hastings (B) from the first two recorded entries in the unsorted list. Their associated worst case PMs are also given. The list continues with Las-Platons, Folkestone, Wrotham.

Sorting begins by identifying the station(s) with the least number of potential assignments. The more problematic stations offering the minimum number of frequency options now appear at the top of the sorted list. A second consideration is then given to those stations with shared frequency options such as Les-Platons, Canterbury (A) and Canterbury (B), each with three options, and Wrothan and Folkestone, each with four, where priority is given to the station with the lowest set of PM's. The stations are then arranged as shown in Table 6.

TABLE 5

Hastings (A) 2 24 14 2 1 14 Hastings (B) 2 24 14 2 1 14 Les-Platons 6 2 0 FoZkestone 3 2 2 4 Brighton 7 9 10 8 1 6 3 Swingate 4 2 5 14 1 C lacton 6 Heathfield O 1 Canterbury (A 6 5 3 Canterbury (B 6 5 3 Wrotham 8 1 3 5 100.0 100.2 100.4 100.6 10.8 101.0 100.1 100.3 100.5 100.7 100.9 Frequency (MHz) TABLE 6

Clacton 6 Heathfietd 0 2 0 Les Platoons 6 Canterbury (A) 6 5 3 Canterbury (B) 6 5 3 Folkestone 3 2 2 4 Wrotham 8 1 3 5 Swingate 4 2 5 14 1 Hastings (A) 2 24 14 2 1 14 Hastings (B) Brighton 7 9 10 8 1 6 3 100.0 100.2 100.4 100.6 100.8 101.0 100.1 100.3 100.5 100.7 100.9 Frequency (MHz) For the initial iteration the top ten station entries from the ordered list (Table 6) are placed into two groups of five, where the first group (G1), comprising the top five stations, is used to optimise the planning possibilities within the second group (G2).At this stage, each of the G1 stations are confined to only three of their possible potential assignments - those retaining the most positive PMs - while G2 stations have no restriction on their assignment options. After optimisation, group G1 stations are then withdrawn from the remaining station list for the prevailing iterations. Group G1 stations then form additional planning constraints to all the remaining stations.

The next iteration sees the previous optimised group G2 chosen as the new G1 group, G11, where it is now used to optimise a new G2 group, G21. First though, all the remaining stations are reordered in planning priority as previously described.

For the first iteration with the example, Groups G1 and G2 are shown in Table 7 and 8.

TABLE 7 GrouD G1 Clacton 100.3 (Max number of frequency Heathfield 100.5, 100.0 options per G1 service Les-Platons 100.3 100.7, 101.0 is 3) Canterbury (A) 100.2, 100.9, 101.0 Canterbury (B) 100.2, 100.9, 101.0 (Freq in MHz) TABLE 8 GrouD G2 Folkestone 100.8, 100.2, 100.4, 100.6 Wrotham 100.0, 101.0. 100.3, 100.6 Swingate 100.7, 100.5, 100.3, 100.4, 100.8 Hastings (A) 100.2, 100.3, 101.0, 100.1, 100.6, 100.9 Hastings (B) 100.2, 100.3, 101.0, 100.1, 100.6, 100.9 (Frequency in MHz) Group G1 permits a maximum of 35 = 243 potential ways of assigning frequencies exclusively to its proposed services - these are called frequency combinations. For each, the relevant field strengths from ARRAY 2 are extracted and used to determine the combinational nuisance fields existing between G1 stations.

For each of the frequency combinations, the predominant nuisance field is compared against the ambient field strength S2. Combinations where the ambient field strength is exceeded are not considered further. Those remaining are then used to optimise group G2.

In the example there are a total of 1 x 2 x 3 x 3 x 3 = possible frequency combinations. The sequence is shown in Table 9.

The frequency combinations which are assumed to satisfy the ambient field strength S2 = 80 dB (,uv/m) for group G1 are shown with a against the number.

TABLE 9 No. Clacton HeathPleld Les-Platons Canterbury (A) Canterbury ( 1 100.3 100.5 100.3 100.2 1d0.2 2 100.3 100.5 100.3 100.2 100.9 3* 100.3 100.5 100.3 100.2 101.0 4* 100.3 100.5 100.3 100.9 100.2 5 100.3 100.5 100.3 100.9 100.9 6 100.3 100.5 100.3 100.9 101.0 7 100.3 100.5 100.3 101.0 100.2 52 100.3 100.0 101.0 101.0 100.2 53* 100.3 100.0 101.0 101.0 100.9 54 100.3 100.0 101.0 101.0 101.0 (Freq in MHz) Each of the possible frequency combinations which satisfy the ambient field strength S2 (shown by "*") is used in turn to impose additional planning constraints on G2 stations. Again, the required field strengths are extracted from ARRAY 2 so that the nuisance fields can be calculated between the two groups of stations.All the G2 potential assignments are then made to respect those of G1 so that all conflicting planning situations are erased. Group 2 is now planned in the same way G1 was. The frequency combination for Gi which maximises the number of G2 combinations is said to be the optimum for the group. This then becomes a set of additional planning constraints to all those remaining stations.

The remaining stations are now reordered in planning priority as before and Group G2 is reselected as G11. while a new group G2 is selected for G21. The process is then repeated for the new groups.

Using the four G1 frequency combinations number 3, 4, 52 and 53 from Table 9, and assuming that both the Canterbury services in G1 interfere with the G2 services at Hastings and Folkestone if the frequency separations are less than 200 and 100 KHz respectively, the four possible G2 situations are shown in Tables 10-13. Frequencies shown in MHz).

TABLE 10 Group 2 for G1 potential assignment 3.

Folkestone 100.8 100.4 100.6 Wrotham 100.0 101.0 100.6 Swingate 100.7 100.5 100.4 Hastings (A) 100.6 Hastings (B) 100.6 TABLE 11 Group 2 for G1 potential assignment 4.

Folkestone 100.4 100.6 Wrotham 100.0 101.0 100.3 Swingate 100.7 100.5 100.4 Hastings (A) 100.6 Hastings (B) 100.6 TABLE 12 Group 2 for G1 potential assignment 52.

Folkestone 100.2 100.4 100.6 Wrotham 100.0 101.0 100.3 Swingate 100.7 100.5 100.4 Hastings (A) 100.2 100.3 100.1 Hastings (B) 100.2 100.3 100.1 TABLE 17 Group G2 for G1 potential assignment 53.

Folkestone 100.8 100.2 100.4 Wrotham 100.0 101.0 100.3 Swingate 100.7 100.5 100.4 Hastings (A) 100.2 100.3 100.1 Hastings (B) 100.2 100.3 100.1 Group G2 also permits a maximum of 35 = 243 potential ways of assigning frequencies exclusively to its proposed stations. However, taking account of the G1 planning constraints, the totals may be restricted by the available number of frequency options (Tables 10 and 11). The maximum totals after respecting the G1 frequency combinations 3, 4, 52 and 53 and 27, 18, 243 and 243 respectively.

However, by taking into account the G2 planning constraints, these are further restricted to 18, 9, 156 and 147. The G1 frequency combination which maximises the number for G2 is thus No. 52, which produces 156 possible ways of planning G2 stations at the required network planning criteria. The Gi combination now becomes a set of additional planning constraints for all the remaining services, while the optimised group G2, with its 156 frequency combinations, is reconsidered in the next iteration.

Problems may occur if there are either no G2 potential assignments found or if multiple G2 solutions exist. In the second case, the problem is solved by using the least spectrum demanding G1 assignment.

Possible reasons for the first type of problem are that the predominant interference level for all G2 frequency combinations exceeds the ambient field strength S2, or one or several of the services have exhausted their three frequency options in satisfying G1 planning criteria. In such cases, the problematic G2 services are predicted and replaced with the remaining services offering the minimum potential frequencies. The optimisation is repeated using the new G2 combination. This process may be further repeated as many times as required to find an optimised G2 solution. All unresolved services are considered for reselection during later iterations.

The method of the invention permits the planning of large networks, which has previously been impossible to carry out using traditional methods, and allows a superior utilisation of the frequency spectrum. The method of the invention can be further reused to superimpose different networks with the same frequency band, for example, giving better spectrum reuse throughout the country. It is therefore suitable for adding stations to a permanent plan or for planning restricted services, such as low power special event radio with a short life expectancy. The huge reduction in time spent on planning networks is also significant to the system planner.

The method of the invention is suitable for planning VHF and other sound broadcasting services, microwave radio systems, mobile radio networks and other broadcasting networks where the use of site to site analysis to predict interference levels is a valid method of analysis.

Claims (15)

1. A method of allocating broadcasting criteria to one or more new stations in a network of stations comprising a pseudo-optimum planning method based on an iterative process which controls the number of considered stations and broadcasting criteria combinations and wherein the network is planned to acceptable levels of interference determiined by the ambient field strengths.

2. A method of allocating broadcasting criteria to one or more new stations in a network of stations, comprising the steps of: a) calculating the combinational field strengths between each new station and each of the other stations; b) calculating the combination nuisance field strengths between each new station and each of the other stations; c) calculating the protection margin for each particular combination of broadcasting criteria and discarding those criteria which have negative protection margins; d) determining a set of potential assignments of broadcasting criteria for each new station; and e) using a pseudo-optimum planning method to determine the optimum broadcasting criteria for each new station.

3. A method according to Claim 2 wherein the pseudo-optimum planning method comprises the steps of: a) planning the priority of each new station in the network, with stations having the more demanding planning criteria being given highest priority; b) selecting the stations into two or more groups wherein the first group (G1) contains the most critical stations, the second group (G2) the next most critical stations and so on; c) limiting the number of options of potential broadcasting criteria assignments per station in Gi to a predetermined number and calculating the possible criteria combinations; d) discarding those combinations where the predominant nuisance field exceeds the ambient field strength; e) using each of the remaining combinations in turn to impose additional planning constraints on stations in G2 by the further steps of: f) calculating the nuisance fields between the two groups of stations G1 and G2; g) arranging the potential assignments of the G2 stations to respect those of G1 so that all conflicting planning situations are erased; h) planning G2 by the method of steps c) and d); i. selecting the criteria combination of G1 which maximises the number of G2 combinations; j. using G1 as a set of additional planning constraints on all remaining stations; and k) reordering the remaining stations as in step a), reselecting G2 as G1 and a new group as new G2, and repeating steps c) to k) until all stations are assigned broadcasting criteria.

4. A method according to claim 3 wherein, if there ar no G1 potential assignments which can offer G2 planning solutions at the required ambient field strength, the one or more problematic G2 stations are replaced by those remaining one or more stations which offer the minimum potential broadcasting criteria and the optimisation is repeated using the new G2 combination.

5. A method according to claim 4 wherein the steps are repeated as many times as required to find an optimised G2 solution.

6. A method according to claim 4 or claim 5 wherein all unresolved stations are considered for reselection during later iterations.

7. A method according to any one of claims 2 to 6 wherein the nuisance field strengths for each station to station combination are calculated to determine whether the interference is to be regarded as steady or tropospheric.

8. A method according to claim 7 wherein the nuisance field value for the stronger of the steady or tropospheric interferences is used.

9. A method according to any one of claims 2 to 8 wherein the number of potential broadcasting criteria for each new station is restricted to a predetermined figure.

10. A method according to claim 9 wherein, if no solution is found for allocating criteria to a particular station then the numbers of potential broadcasting criteria considered for that station is increased until a solution is found.

11. A method according to any one of the preceding claims wherein the network is a sound broadcasting network.

12. A method according to claim 11 wherein the network is a VHF sound broadcasting network.

13. A method according to any one of claims 1 to 10 wherein the network is a mobile radio network.

14. A method according to any one of claims 1 to 10 wherein the network is a fixed link microwave network.

15. A method of allocating broadcasting criteria to one or more new stations in a network of stations as hereinbefore described with reference to the example.