Interference management in networks

Abstract

In a radio network comprising nodes, and links therebetween, representing the network as a graph, the graph preserving angles between the nodes, assigning minimum and maximum power transmission levels, where minimum power levels are highest power levels that do not interfere with neighboring links when the neighboring links are transmitting at the maximum power levels; using the angles, identifying mutually interfering links at the maximum power levels; and assigning a first link to a first group and then assigning further links to a same group if they do not interfere and different groups if they do interfere until all links are assigned. The groups may be separate time slots or separate frequencies.

Description

[0001] INTERFERENCE MANAGEMENT IN NETWORKS

[0002] RELATED APPLICATION / S

[0003] This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 529,820, filed on July 31, 2023, the contents of which are incorporated herein by reference in their entirety.

[0004] FIELD AND BACKGROUND OF THE INVENTION

[0005] The present invention, in some embodiments thereof, relates to interference management in radio networks and, more particularly, but not exclusively, to apparatus, a system and a method for setting up and dynamically adjusting transmission parameters in a multiple link radio network to manage interference between the links.

[0006] Radio networks with multiple high capacity directional links are used in the backbone connections between cellular base stations and for numerous other purposes. Multiple links in different directions may share adjacent transmitters on towers and like transmission infrastructure.

[0007] A network with multiple links and which uses the same frequency on several links may have interference power much greater than the noise power, and the interference power may impinge on the capacity of the network.

[0008] In such cases, the SIR (Signal-Interference Ratio) is significantly larger than the SNR (Signal-Noise Ratio) and thus the noise may be regarded as negligible.

[0009] To date the problem is solved in a static manner by assigning different non-interfering frequencies to links that show interference issues, so that interference is reduced below the noise power. The problem is that more frequencies require use a broader band which can lead to greater costs and more complex management than a narrow band

[0010] SUMMARY OF THE INVENTION

[0011] The present invention uses a directed graph as a method of mapping the interference between links in a communication system. The directed graph provides a basis for algorithmically solving the interference issue on a dynamic basis, and thus to provide dynamic linking. Bandwidth or transmission power and frequencies may be assigned between links on the basis that priority is assigned in time slots to different links as needed and the priority links are allowed maximum power, other interfering links being limited to powers that do not interfere with the priority links. A greedy algorithm may be used to assign transmission power levels between the links to achieve a highest overall transmission capacity. Given the interference information provided by the directed graph and minimization of interference by allocating transmission power in timeslots, distinctive frequencies may be assigned to the links in an iterative process so that links may transmit with minimal power while minimizing interference.

[0012] According to an aspect of some embodiments of the present invention there is provided, in a radio network comprising a plurality of nodes, each node having at least one link to another node and at least some of the nodes having a plurality of links to other nodes, a method which comprises: representing the network in a graph, the graph preserving angles between the nodes; assigning minimum and maximum power transmission levels, the minimum power levels being highest power levels that do not interfere with neighboring links when the neighboring links are transmitting at the maximum power levels; using the angles, identifying mutually interfering links at the maximum power levels; and assigning a first link to a first group and then assigning further links to a same group if they do not interfere and different groups if they do interfere until all links are assigned.

[0013] In embodiments, the first and different groups are different time slots, such that links assigned to a current time slot transmit at respective maximum power transmission levels and the links not assigned to the current time slot transmit at respective minimum transmission levels.

[0014] In embodiments, the assigning maximum and minimum power levels further comprises assigning to each respective link an intermediate power level for each time slot based on which neighboring link is scheduled to be transmitting at full power during that time slot.

[0015] In embodiments the first and different groups are frequencies, and optionally, at least some of the links are bidirectional links.

[0016] According to a second aspect of the present invention there is provided a radio network comprising a plurality of nodes, each node having at least one link to another node and at least some of the nodes having a plurality of links to other nodes, and a method comprising: calculating for pairs of links maximal and minimal power levels at which one node may transmit without causing interference with the other; from the pairs of power levels calculating respective capacities for the radio network; plotting the network capacities against respective power levels; finding a maximum, and using the power levels corresponding to the maximum.

[0017] In the method the finding a maximum may involve curve fitting between calculated capacities, or alternatively finding a capacity analytically where the curve fitting indicates a maximum. The method may consist of repeating the plotting in an area around the found maximum to find a new maximum.

[0018] As in the above, at least some of the links may be bidirectional links.

[0019] According to a third aspect of the present embodiments, in a radio network comprising a plurality of nodes, each node having at least one link to another node and at least some of the nodes having a plurality of links to other nodes, a method may involve: setting the entire network to a single frequency; setting each link in succession to a new frequency, and calculating a resulting increase in network capacity; finding the link with the greatest increase in capacity and assigning the new frequency to the link with the greatest increase in capacity; continuing to assign new frequencies on the basis of the greatest increase in capacity until all available frequencies are allocated or until a respective greatest increase in capacity falls below a predetermined minimum.

[0020] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0021] Implementation of the method and / or system of embodiments of the invention can involve performing or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of embodiments of the method and / or system of the invention, several selected tasks could be implemented by hardware, by software or by firmware or by a combination thereof using an operating system.

[0022] For example, hardware for performing selected tasks according to embodiments of the invention could be implemented as a chip or a circuit. As software, selected tasks according to embodiments of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In an exemplary embodiment of the invention, one or more tasks according to exemplary embodiments of method and / or system as described herein are performed by a data processor, such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes a volatile memory for storing instructions and / or data and / or a non-volatile storage, for example, a magnetic hard-disk and / or removable media, for storing instructions and / or data.

[0023] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0024] Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

[0025] In the drawings:

[0026] FIG. 1 is a simplified diagram illustrating an arrangement of communication links being represented as a directed graph in accordance with embodiments of the present invention;

[0027] FIGs. 2, 3, 4, 5, 6 and 7 are simplified diagrams illustrating a process of identifying interference between links on the directed graph of Fig. 1 in accordance with embodiments of the present invention;

[0028] FIG. 8 illustrates a partial solution in which several links in the directed graph of Fig. 1 are divided between two time slots so that some links are dominant in each time slot and interference is reduced;

[0029] FIG. 9 illustrates a full solution for the links in the directed graph of Fig. 1 according to embodiments of the present invention;

[0030] FIG. 10 is a simplified directed graph showing two links and an angle in between and explaining how to calculate powers at which the dominant and non-dominant links may transmit without mutually interfering;

[0031] FIGs. 11, 12, 13, 14, 15, 16 and 17 illustrate stages of a procedure according to the present embodiments for determining a power level to use for the maximum power in Fig. 10, which power level gives optimal transmission capacity for the links as a whole bearing in mind that nondominant links in each time slot are transmitting at a minimal power level;

[0032] FIG. 18 is a simplified flow chart illustrating the procedure represented by Figs. 11 - 17;

[0033] FIGs. 19, 20 and 21 illustrate the use of a greedy algorithm for adding a minimal number of non interfering frequencies to a directed graph according to embodiments of the present invention;

[0034] FIG. 22 illustrates routing assignment carried out using a directed graph according to embodiments of the present invention and avoiding interference; and FIG. 23 is a flow chart illustrating a simplified method according to an embodiment of the present invention of assigning links on a directed graph to a minimal number of groups that allows interference to be minimized; and

[0035] FIG. 24 is a simplified diagram illustrating a process of finding a maximal capacity under non-interfering conditions, according to embodiments of the present invention.

[0036] DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0037] The present invention, in some embodiments thereof, relates to interference management in radio networks and, more particularly, but not exclusively, to apparatus, a system and a method for setting up and dynamically adjusting transmission parameters in a multiple link radio network to manage interference between the links.

[0038] Generally, backbone networks are made up of multiple links that share towers or frequencies. The links sharing a frequency and being sufficiently close, including sharing a tower, may interfere with one another unless their frequencies and / or transmission powers are carefully managed. More particularly, links may interrupt each other over a distance as long as their signals share the same frequency and the loss due to the distance is not enough to decrease the interference gain below the noise level. Thus the question arises as to whether there is an optimal way to manage a link such that maximum capacity can be obtained without causing interference between the links.

[0039] A network which uses the same frequency on several links might have interference power which is much greater than the noise power, and thus the best way to manage capacity is to manage the interference.

[0040] Thus, the SIR (Signal-Interference Ratio) is significantly larger than the SNR (Signal-Noise Ratio) and thus we say the noise is negligible.

[0041] In the present embodiments, the problem may be modelled using a graph where the transmitters and receivers are the nodes and the links and interference are represented by the edges.

[0042] The graph allows for interference and provides a view of where the interference is coming from and how much interference there is for any given link, and the graphs may give information about interference patterns, and resulting path loss.

[0043] It is then possible to select some of the links as priority links. A priority link may be defined as a link that is allowed to interfere for any given time slot, other potentially interfering links being limited to a minimal power level so that they do not cause interference to the priority link. The selection of priority links may be carried out dynamically and the priority may be enforced by running the priority link at full power and reducing the power at any interfering link so that there is no meaningful interference, meaning that the interference is bound by a pre-calculated value. Alternatively, non-interfering frequencies may be assigned to the potentially interfering links.

[0044] In general, the power level assigned to a link is not arbitrary. The full signal has to be accurately decoded at the receiving end and there is a certain power drop per given distance. Hence there is an intrinsic constraint on the power levels used for transmission.

[0045] Accordingly, in one embodiment, transmission is divided into time slots and potentially interfering links are grouped together. The potentially interfering links in the group are then assigned different time slots to be the priority link, so that every link gets a share of priority. In embodiments, the capacity needed on different links may be used to apply differential levels of high priority time slots, but more particularly the embodiments may ensure that a time schedule assigns links to slots so that no two mutually interfering links are both given priority in the same timeslot.

[0046] In embodiments, a spare timeslot may be given to non-priority links in rotation .

[0047] In embodiments, a transmitter may have a sequence of say five timeslots. Any given link obtains priority over one or some of the five timeslots, at which time it is allowed to transmit at maximum.

[0048] At this point, it is possible to use interpolation to find an optimal allowed interference across the network so that the capacity across the network is optimal.

[0049] Likewise, frequency slots may be assigned to the links, so that neighboring links may not have interfering frequencies.

[0050] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and / or methods set forth in the following description and / or illustrated in the drawings and / or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

[0051] Referring now to the drawings, Figure 1 is a simplified diagram illustrating a graph of a network 10, including nodes 12, 14, 16, 18, 20 and 22 and corresponding links indicated by arrows and connecting links bidirectionally in a network according to embodiments of the present invention. The view is a graph, so distances are not preserved. In the case of interference, angles are relevant, as will be discussed in greater detail below, and thus angles are preserved in the graph. It is to be noted that not all nodes are connected directly. Thus, node 12 is connected only to nodes 14 and 20. Node 20 is connected only to nodes 12, 14 and 22, and node 18 is connected only to node 16. Reference is now made to Fig. 2, which illustrates the graph of Fig. 1 and shows a first stage in identifying interference in the network. The connection between nodes 12 and 16 via 14 is considered, and first we look at the down link from 12 to 14.

[0052] As shown in Fig. 3, the link 12→ 14 makes an oblique angle with the link 14→ 16. Accordingly, the link 12→ 14 is marked as liable to interfere with link 14→ 6 if power enters at higher than a minimum power level Pmin. Pminis a power level determined for the links below which mutual interference between the links does not occur, and thus any link transmitting at below that level does not cause interference with other links.

[0053] Referring now to Fig. 4 the two links 14→ 16 and 16→ 18 are considered. Again, the angle is oblique and the two links meet at the same antenna 16. Accordingly they are marked as mutually interfering as long as the power level is above a given Pmin.

[0054] Reference is now made to Fig. 5. Links 12→ 14 and 14→ 16 are marked as mutually interfering as already discussed. Link 14→ 16 was marked as interfering with 16→ 18 in Fig. 4 but here 16^18 is constrained to transmit at lower than Pminand thus there is no interference.

[0055] The next link considered is the link 22→ 16. The angle is approximately a right angle and thus there is no issue with interference.

[0056] Referring to Fig. 6, link 12→ 20 and link 14→ 20 are considered. The angle between them is acute. This is a situation where terminal 14 appears as a hidden terminal to the 12→ 20 link and there is interference.

[0057] Fig. 7 illustrates the completed graph where the rounded arrows indicate all the links that suffer from interference. Note that the 18→ 16 and 16→ 14 links are added as being of obtuse angle.

[0058] Reference is now made to Fig. 8 which shows the next part of the procedure. After the mutually interfering links are identified they may then be assigned either non-interfering frequencies or non-interfering time slots. A greedy algorithm is used to assign the time slots. An initial link is applied with a time slot (or frequency) and neighboring links that interfere are applied with a different time slot (or frequency). Thus link 12→ 20 is arbitrarily given slot 1. Then link 14 →20, which is a mutually interfering link is automatically given slot 2.

[0059] Figure 9 shows the completed graph. Link 12→ 14 is assigned slot 1 as it is compatible with 12→ 20. Link 14→ 16 is not compatible and so is assigned slot 2. Link 16→ 18 is not compatible with 14→ 16 and thus receives slot 1.

[0060] In the above example, two slots were sufficient to cover the entire network, however more complex networks, with more interference, may only be solved with more timeslots. However, the above is not sufficient to give the network the maximum possible capacity. This is because, as mentioned, there are minimum levels of transmission that do not cause interference, so all links are free to transmit at all time slots on that minimal power, but can transmit at maximal power only if mutually interfering links are on minimal power, so as shown in Fig. 10, the process also tries to find suitable transmission levels for maximum and minimum power levels. It will be clear that the maximum network capacity need not coincide with setting the highest possible powers on priority links, since the minimum power for the non-priority links will be lower. The question is, is there an optimum?

[0061] That is to say, more interference allowed translates to less capacity on priority links but more capacity on the non-priority links.

[0062] As shown in Fig. 10, we want to calculate the maximum power Pj(e)when an interfering link transmits at a selected Pmin during a given timeslot. e interferes on the priority edge eYin the current tick. d - distance between source of interference. a - AoA (angle of arrival) between interfering transmitter and target receiver.

[0063] If e transmits in power Ptthen the signal strength entering the interfered receiver is

[0064] Set Pr= Pminwe get

[0065] In such circumstances the two links do not interfere. Now the question is, can we use this information to obtain an improved capacity?

[0066] Referring now to Fig. 11, in order to find levels for such an optimum, we may first find the worst SINR possible (xm). That is, when all links transmit at full power. The optimal value is obviously somewhere between 0 and xm. The line 0→ xmis divided into working segments.

[0067] Referring now to Fig. 12, we then define a function f that sums the capacity in a network for a given power attribution P.

[0068] We may then find an allowed interference factor x such that f becomes maximum and the point is plotted.

[0069] The plotted points are then joined by curve fitting as shown in Fig. 13, to arrive at curve 130.

[0070] In Fig. 14, maximums 140 are obtained from the curve.

[0071] Referring now to Fig. 15, the interpolation is only an approximation to the real function. Therefore, we analytically or by test, evaluate the value of / 150 at the maximum points 140. As shown in Fig. 16, we then choose the one maximum among all the points after the curve maxima have been corrected for the actual f value. In Fig. 16 the highest maximum has been corrected downwards, leaving the point 160 as the highest actual point.

[0072] Referring now to Fig. 17, for more precision we can repeat the interpolation for a segment around the chosen points in recursion. Thus, the interpolation is repeated between the lines X0 and XI which themselves select a small region around the chosen point 160. The repeated interpolation may give a new maximum point - here point 170.

[0073] Calculations for the maximum and reduced power levels are done in the planning stage., that is prior to actual use, and a table of allowed power levels for each of a sequence of time slots is predefined, thus:

[0074] Table 1 - Exemplary power levels for a sequence of four timeslots or ticks

[0075] Each link ends up with a table of signal strength for each time slot. While the network is live the links only switch powers used according to the relevant table.

[0076] Hidden nodes or hidden channels are potential sources of mutual interference as noted elsewhere herein, and are taken into account when assigning time slots.

[0077] The power calculations may provide a perspective as to the cost of using the same frequency for nearby links. We may then simulate a benefit on each link for switching the channel used to a different frequency.

[0078] Referring now to Fig. 18, which is a simplified flow chart, an algorithm for frequency assignment is based on this benefit.

[0079] - Start with a single frequency for the entire network - 180 and Fig. 19

[0080] - Calculate network-wide benefit for each link by switching each link one by one to a new frequency - 182.

[0081] - Choose greedily the link with the best benefit - 184

[0082] - Move the link to use the new frequency - 186

[0083] We thus end up with two frequencies used, 200 and 202 as shown in Fig. 20.

[0084] We repeat 188 this depending on the requirement:

[0085] - Until max frequencies are reached, or until benefits fall under a certain threshold. The benefit calculations may be designed so that greedy-type algorithms are optimal. As shown in Fig. 21, the benefit of adding a new frequency, say at link 210 is the amount of extra power we can run all the links at when link 210 is on a new (and thus not interfering) frequency, as opposed to the loss of power due to link 210 sharing frequencies with other mutually interfering links.

[0086] Referring now to Fig. 22, a routing approach may be taken between two terminal nodes 220 and 222. The route passes through intermediate nodes 224 226, 228 and 230 but does not pass through node 232. However node 232 provides hidden terminal, or hidden node, interference to node 228 and hence one of the two links entering 228 is given a different frequency.

[0087] In the routing approach the benefit is the difference in distances between the shortest path and P - which is a random path through all available links.

[0088] We can combine the two benefits using multiplication.

[0089] Reference is now made to Fig. 23, which illustrates a procedure for finding interfering links and assigning them into groups to minimize interference as discussed above with Figs 1- 9.

[0090] Given a radio network of the kind shown in Fig. 1, where nodes have bidirectional links to one or more other nodes - 230, we may represent the network as a graph - 232. In particular, the graph may preserve angles between the nodes.

[0091] We may assign minimum and maximum power transmission levels. These are pairs of power levels where minimum power levels are the highest power levels that do not cause mutual interference with neighboring links when the neighboring links are transmitting at a corresponding maximum power level - 234.

[0092] Then, using the graph and in particular the angles, we identify mutually interfering links at the chosen maximum power levels -236.

[0093] Now we have categorized the links in the graph to mutually interfering and non-interfering. We may assign a first link to a first group and then assign further links to a same group if they do not interfere and different groups if they do interfere, for example using a greedy algorithm, until all links in the network are assigned one way or the other. In some cases, it may be possible to assign all links with just two groups, in other cases three, four or more groups may be required.

[0094] The different groups may be different time slots so that mutually interfering groups do not transmit at mutually interfering frequencies during the same time slot, except in a way that bounds the interference between them. Instead, links assigned to the current time slot may transmit at respective maximum power transmission levels, while those not assigned to the current time slot transmit at respective minimum transmission levels, so as to use available capacity without interfering. The minimum power levels may differ for different links for different time slots. Thus, a given link may be a hidden source at an acute angle compared to a main link during one time slot and may be a source of minor interference from an obtuse angle compared to the main link during a second time slot. Such a source is known as a hidden node or hidden terminal. Thus, different power levels may apply.

[0095] The first and later groups may be different frequencies.

[0096] Reference is now made to Fig. 24, which is a simplified flow chart showing a method of finding an optimal capacity for the network over different maximum-minimum power level pairs.

[0097] In the network -242- it is possible to calculate - 244- for pairs of links, maximal and minimal power levels at which one node may transmit without causing interference with the other. Based on each pair it is possible to calculate a capacity for the network, which may then be plotted -246- say as maximum power against capacity. Curve fitting 248 - may allow a maximum to be found -250. Then the network may be operated at the power levels corresponding to the maximum.

[0098] The maximum found may then be analytically or empirically confirmed. The area immediately around the maximum found may be reiterated any number of times to refine the result.

[0099] General

[0100] As used herein the term “about” refers to ± 10%.

[0101] The terms "comprises", "comprising", 'includes", "including", “having” and their conjugates mean "including but not limited to".

[0102] The term “consisting of* means “including and limited to".

[0103] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise.

[0104] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment and the present description is to be construed as if such embodiments are explicitly set forth herein. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or may be suitable as a modification for any other described embodiment of the invention and the present description is to be construed as if such separate embodiments, subcombinations and modified embodiments are explicitly set forth herein. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

[0105] It is the intent of the applicants) that all publications, patents and patent applications referred to in this specification are to be incorporated in their entirety by reference into the specification, as if each individual publication, patent or patent application was specifically and individually noted when referenced that it is to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting. In addition, any priority documents) of this application is / are hereby incorporated herein by reference in its / their entirety.

Claims

WHAT IS CLAIMED IS:

1. In a radio network comprising a plurality of nodes, each node having at least one link to another node and at least some of said nodes having a plurality of links to other nodes, a method comprising: representing said network in a graph, said graph preserving angles between said nodes; assigning minimum and maximum power transmission levels, said minimum power levels being highest power levels that do not interfere with neighboring links when said neighboring links are transmitting at said maximum power levels; using said angles, identifying mutually interfering links at said maximum power levels; and assigning a first link to a first group and then assigning further links to a same group if they do not interfere and different groups if they do interfere until all links are assigned.

2. The method of claim 1, wherein said first and different groups are different time slots, such that links assigned to a current time slot transmit at respective maximum power transmission levels and said links not assigned to said current time slot transmit at respective minimum transmission levels.

3. The method of claim 2, wherein said assigning maximum and minimum power levels further comprises assigning to each respective link an intermediate power level for each time slot based on which neighboring link is scheduled to be transmitting at full power during that time slot.

4. The method of claim 1, wherein said first and different groups are frequencies.

5. The method of any one of the preceding claims, wherein at least some of said links are bidirectional links.

6. In a radio network comprising a plurality of nodes, each node having at least one link to another node and at least some of said nodes having a plurality of links to other nodes, a method comprising: calculating for pairs of links maximal and minimal power levels at which one node may transmit without causing interference with the other;from said pairs of power levels calculating respective capacities for said radio network; plotting said network capacities against respective power levels; finding a maximum, and using the power levels corresponding to said maximum.

7. The method of claim 6, wherein said finding a maximum comprises curve fitting between calculated capacities.

8. The method of claim 7, wherein said finding a maximum comprises finding a capacity analytically where said curve fitting indicates a maximum.

9. The method of any one of claims 6 to 8, comprising repeating said plotting in an area around said found maximum to find a new maximum.

10. The method of any one of claims 6 to 9, wherein at least some of said links are bidirectional links.

11. In a radio network comprising a plurality of nodes, each node having at least one link to another node and at least some of said nodes having a plurality of links to other nodes, a method comprising: setting said entire network to a single frequency; setting each link in succession to a new frequency, and calculating a resulting increase in network capacity; finding the link with the greatest increase in capacity and assigning the new frequency to said link with the greatest increase in capacity; continuing to assign new frequencies on the basis of the greatest increase in capacity until all available frequencies are allocated or until a respective greatest increase in capacity falls below a predetermined minimum.

12. The method of claim 11, wherein at least some of said links are bidirectional links.

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