Method of allocating carrier frequencies for transmission within a transmission network, in particular in tactical network
BACKGROUND OF THE INVENTION 
     1. Field of the invention 
     The present invention concerns a method of allocating carrier frequencies for transmission within a transmission network. 
     The invention applies in particular to microwave tactical transmission networks in which frequency allocation is particularly complex because of the extreme agility which characterizes these networks. 
     2. Description of the Prior Art 
     As a general rule, in such networks frequency allocation must be random to discourage any attempt at prediction by the enemy. One known method for allocating a frequency to a link between a send equipment located at one site of a network and a receive equipment located at another site of the network allocates frequencies at random from a set of carrier frequencies constituting the available frequency resource of the network after removing from this set frequencies that are prohibited for the link in question because of internal constraints of the network due to the proximity of other send or receive equipments at the sites in question and at nearby sites. 
     A drawback of any such method is that in practice it leads to blocking situations in which requests for allocation of frequencies cannot be met. 
     An object of the present invention is to eliminate this drawback. 
     SUMMARY OF THE INVENTION 
     The present invention consists in a method of allocating carrier frequencies for transmission within a transmission network, such as a tactical network, comprising: 
     breaking down the set of carrier frequencies constituting the available frequency resource for said network into batches of unequal size, 
     attributing to any site of the network at the time it enters the network, as indicated by a request for allocation of a frequency for a link between said site and another site referred to hereinafter as the first connection site for the site in question, and previous to such allocation, one of two complementary states such as to obtain complementary states for the site in question and for its first connection site which are retained for subsequent links between the site in question and other sites of the network, and 
     for any link to be set up between two sites of said network, allocating a frequency at random from the largest batch if the sites in question are in complementary states or from a smaller batch if the sites in question are in the identical state. 
     Other objects and features of the invention will emerge from the following description of one embodiment thereof given with reference to the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing a step of a method in accordance with the invention in which the available frequency resource for a network is broken down into batches of unequal size. 
     FIG. 2 is a diagram showing a step of a method in accordance with the invention in which one of two complementary states is assigned to any site of the network. 
     FIG. 3 is a diagram showing constraints internal to the network which lead to the definition of prohibited frequencies. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a diagram showing a typical available frequency resource for a transmission network formed in this case of non-contiguous blocks along the frequency axis, as shown diagrammatically in the first line of the diagram by six blocks B1, B2, B3, B4, B5, B6 of unequal width. 
     The second line of this diagram shows one example of a breakdown of the frequencies of this resource into three unequal size batches A, B and C of decreasing size. 
     For example, batch A could constitute 60% of the resource, batch B 30% and batch C 10%. Other breakdowns are naturally possible. 
     In the example shown in FIG. 1 batch A is formed of blocks B1 and B2 and part of block B3. Batch B is formed of the other part of block B3, blocks B4 and B5 and part of block B6. Batch C is made up of the other part of block B6. Other breakdowns are naturally possible. 
     FIG. 2 is a diagrammatic representation of a fully meshed network with network nodes represented by circles, network users represented by triangles and the numbers associated with each user-node or node-node link representing the order in which the links are opened as the network is deployed, that is to say the order of entry of these nodes or users into the network. 
     The circles and triangles (grouped together under the generic name &#34;sites&#34;) are colored black or white to illustrate the method in accordance with the invention now to be described. 
     Any site at which no link has yet been established is, when it enters the network, that is to say at the time of a request for allocation of a frequency for a link between it and another site, called the first connection site for the site in question, and previously to such allocation: 
     is arbitrarily colored (black or white), if said other site is not already colored itself, said other site being then colored oppositely, 
     or is colored oppositely to said other site if the latter is already colored. 
     Thus (as shown in the figure) as the network is deployed the various sites are colored gradually with two alternating colors to define a set of links of alternating colors (&#34;white-black&#34; or &#34;black-white&#34;). 
     For links of this type a frequency is allocated at random from the largest batch A. 
     A site colored as described above retains the color thus acquired for any subsequent links between it and sites other than the first connection site. It is thus possible that as the network is deployed it is necessary to set up links between sites that are already colored identically. 
     For these &#34;white-white&#34; or &#34;black-black&#34; links, which are statistically less numerous than the &#34;white-black&#34; and &#34;black-white&#34; links, a frequency is allocated at random from the smaller batch B. 
     The random allocation of frequencies is thus tempered by a deterministic initial classification of the frequencies. The resulting semi-random frequency allocation eliminates the blocking situations mentioned above. 
     The provision of a spare batch of frequencies (batch C) enables, as a last resort, attribution of a pair of frequencies to a link for which a frequency could not otherwise be allocated. 
     The random allocation of the pair of frequencies needed for the thus colored link in the batch corresponding to said color is effected after removing the prohibited frequencies from the batch. 
     The FIG. 3 diagram shows the various sources of frequency prohibition. 
     The figure is a diagrammatic representation of send equipments E and receive equipments R at three nearby sites S1, S2, S3. 
     For a link to be set up between a sender at site S1 and a receiver at site S2, for example, the following may be regarded as prohibited frequencies, following verification: 
     a frequency allocated to the sender associated with the receiver in question at site S2, or 
     a frequency allocated to a sender at site S2 other than that associated with the receiver in question, or 
     a frequency allocated to a sender at site S1 other than the sender in question, or 
     a frequency allocated to a sender at a site other than S1 and S2, such as the sender S3. 
     FIG. 3 shows in thick line the link to be set up and in thin line possible interference with the prohibited frequencies.