MXPA98008645A - A method and apparatus for assigning ra channels - Google Patents

Abstract

The present invention relates to a fixed wireless access communications network. The capacity of a fixed wireless access network is limited by the number of radio frequencies and thus the number of available channels. The present invention provides a solution to this problem, at any time that the radio channels are transmitted in one of at least two power levels.

Description

A YAPARATO METHOD TO ASSIGN RADIO CHANNELS Field of the Invention This invention relates to a radio communication system and, in particular, to a method for assigning radio channels in a fixed wireless access system. BACKGROUND OF THE INVENTION Fixed wireless access systems are currently employed for local telecommunication networks, such as the IONIC system. The known systems comprise an antenna and decoding elements, which are placed in the subscriber's premises, for example adjacent to a telephone. The antenna receives the signal and supplies a further signal by wire to a decoder element. Thus, the subscribers are connected to a telecommunications network by a radio link instead of the more traditional method of the copper cable. Such fixed wireless access systems will be able to deliver a wide range of access services from the operator's public telephone service ("POTS"), the integrated digital service network ("ISDN") to broadband data. Radio transmitters and receivers in subscribers' facilities communicate with a base station, which provides cellular coverage over, say, a radius of 5 km. in urban environments. A typical base station will sustain 500 to 2,000 subscribers. Each base station is connected to a standard PSTN network switch via a conventional transmission link / network. When a fixed wireless access telecommunications system is deployed initially, then a base station of a particular capacity will be installed to cover a particular populated area. The base station's capabilities are designed to correspond to the anticipated coverage and capacity requirements. The antennas of the subscribers will be mounted outside, for example, on a chimney, and in the installation they will normally be directed towards the nearest base station (or the best signal strength) or to a repeater antenna (any future reference to the base station it will be taken including a repeater). In order to meet the demand for capacity, within an available frequency band allocation, fixed wireless access systems will divide a geographic area to be covered in cells. Within each cell there is a base station through which the stations of the subscribers communicate, the distance between the cells being determined so that the co-channel interference is maintained at a tolerable level. When the antenna at the subscriber's premises is installed, an optimal direction for the antenna is identified using a monitor equipment. The antenna is then mounted so that it is placed in the optimal direction. There are a number of alternative ways to provide access to the public telephone network, in addition to fixed wireless access systems. One method is to use copper or fiber optic cable. However, this involves digging in the streets in order to lay the wires going to all homes in the service area, which is costly, time consuming and causes noise, dirt, damage to trees and pavements and impairs traffic. After the initial high investment, the telephone company can then only start recovering its invention as new subscribers join the system over a period of time. Other alternatives is cellular radio, such as GSM. This has the advantage that phones are mobile. However, the system operator has to provide continuous coverage along motorized roads, in closed galleries of warehouses, etc. The omni-directional low-altitude antenna used in mobile systems gives little discrimination against multipath interference, and its low height makes it more susceptible to noise. Likewise, when a moving vehicle moves, it suffers from multiple trajectory interference that varies constantly, which produces a variable audio quality. Mobile cellular networks also require costly backhaul networks, which consist of costly switches and a costly master control center, which handles the movement of mobile vehicles from one cell to another. Radio systems based on the rules of mobile vehicles and fixed directional antennas are sometimes used to provide access to the public telephone network. The directional antenna discriminates against some of the interferences of multiple trajectories. However, the system still suffers from the aforementioned disadvantages. For example, an expensive retro-transport network is required and the voice quality is inferior to a copper wire system. Fixed wireless radio access systems comprise a base station that serves a radio cell of up to 15 km. radio (for example). The base station interfaces with the subscriber's system by means of an air interface protocol, designed for this purpose. The base station also interfaces with the public telephone network, for example, this interface can be the ITU G.703 2048 kbit / s, 32 time slots, 32 standard channels, known as El or the North American 24-slot of standard time, known as IT. Typically, each uplink radio channel (i.e., a subscriber antenna to a base station) is matched with a downlink radio channel (i.e., from a base station to a subscriber antenna), to produce a double radio channel. For voice signals, the uplink and downlink channels in a pair usually have the same frequency separation (for example 50 MHz between the uplink and downlink channels) because of this it makes the channel allocation process easy . However, it is possible for the uplink and downlink channels in a pair to have different frequency separations. Often each downlink continuously transmits and is usual for those used downlink carriers, carrying broadcasting information that is continuously transmitted. In the uplink, each subscriber antenna typically only transmits an information packet, when necessary. A carrier is a frequency channel, often with several logical channels, for example ten channels. The base stations are then assigned to radio bearers from the total available, for example 54. As a population of subscribers increases, the capacity of the base station can be increased by increasing the number of bearers assigned to it, for example, 3, 6 or 18 carriers. As already mentioned, fixed wireless access systems divide a geographical area to be covered in cells. For initial planning and design purposes, these cells are usually represented as hexagons, each cell having a base station (in the center of the hexagon) with which a plurality of subscribers within the cell (hexagon) communicate. When detailed cell planning is performed, the ideal hexagonal array may start in failure due to site restrictions or for propagation reasons of the radio. The number of subscriber stations which can be supported within each cell is limited by the available number of carrier frequencies and the number of channels per frequency. Base stations are expensive and require an extensive effort to obtain planning permission for their erection. In some areas, the appropriate sites of the base station are not available. One problem in the design of the fixed wireless access system is to have as few base stations as possible, while supporting as many subscriber stations as possible. This helps to reduce the cost per subscriber in a fixed wireless access system. An initial problem is to increase the ability to carry traffic from base stations, while, at the same time, it maintains interference levels within acceptable limits. This is named as trying to optimize or increase the carrier's relationship to the level of interference. By increasing the traffic capacity, the number of missed or blocked calls is reduced and the quality of the call can be improved. (A missed call is a call attempt that -fails.) The cells are typically grouped into clusters, as shown in Figure 1. In this example, a cluster of seven cells is shown and for a system of 6 carriers, each cell in the cluster can use a different group of 6 frequencies from the total available (for example 54). Within each cluster 7 x 6 = 42 frequencies are each used once. This leaves 12 channels to be occupied, if required. Within the cluster, all the channels are orthogonal, that is, separated by the time of emission and / or the frequency and, therefore, there will be no co-channel interference within this isolated cluster. Figure 2 shows how a larger geographic area can be covered by reusing frequencies. In Figure 2, each frequency is used twice, once in each cluster. Co-channel interference can occur between cells, using the same frequencies and needs that will be saved against cell planning. When the capacity of a cell or cluster of them is exhausted, one possibility is to form sectors in each cell. This involves using directional antennas at the base station, rather than omnidirectional antennas. The interval 3602 around the base station is divided into a number of sectors and the carriers are assigned to each sector. In this way, more carriers can be added, while keeping the interference low only by using certain frequencies in certain directions or sectors. For example, up to 12 carriers per cell can be added, giving a total of 18 carriers and thus tripling the capacity of each cell (as shown in Figure 3). With 18 carriers per cell, the number of cells in a cluster drops to three, as shown in Figure 3. This is because all 54 frequencies are fully used in the cluster and will be reused in other clusters. The known approaches to seek to increase system capacity include frequency planning, which involves carefully planning reuse patterns and creating sector designs in order to reduce the likelihood of interference. However, this method is complex and difficult and there will still be the possibility of unwanted reflections of multiple trajectories that can cause excessive interference. Frequency planning is also costly and time consuming and decreases the deployment regime. Some of the difficulties with frequency planning include that it depends on having a good ground basis and a good prediction tool. Object of the Invention The present invention seeks to pre a method and apparatus for assigning radio channels in a fixed wireless access system, which overcomes or at least mitigates one or more of the aforementioned problems. It seeks to increase the ability to carry traffic from base stations, while, at the same time, keeps interference levels at a minimum. SUMMARY OF THE INVENTION According to a first aspect of the present invention, a method of assigning a radio channel in a fixed wireless access network is pred, this network comprises: (i) a base station; (ii) a plurality of subscriber stations; and in that the base station and the subscriber stations are adapted so that communication between the base station and the subscriber stations is achieved in use, with the use of one of a number of radio channels, each radio channel has a different frequency; and in that each radio channel is transmitted in one of at least two power levels, this method comprises the step of: assigning a radio channel for use in the communication between one of the subscriber stations and the base station, of according to the distance of the subscriber station from the base station, so that, in use, the channel frequencies of the transmitted channels at relatively low power nodes can be used again to establish communication between a subscriber and a second base station, at a distance closer to the first base station than would otherwise be possible. A corresponding apparatus for the assignment of the radio channel in a fixed wireless access network is also provided, this network comprises: (i) a base station; (ii) a plurality of subscriber stations; and in that the base station and the subscriber stations are adapted so that communication between the base station and the subscriber stations is achieved in use, with the use of one of a number of radio channels, each radio channel has a different frequency; and in that each radio channel is transmitted in one of at least two power levels, this apparatus comprises: a dispatcher, arranged to assign a radio channel for use in communication between one of the subscriber's stations and the base station , in accordance with the distance of the subscriber station from the base station, so that in use, the channel frequencies of the channels transmitted at relatively low power levels, can be used again to establish communication between a subscriber and a second base station at a distance closer to the base station than the one that would otherwise be possible.

The invention also relates to a fixed network of wireless access communications, which comprises: (i) a base station; (ii) a plurality of subscriber stations, in which the base station and the subscriber stations are adapted so that communication between the base station and the subscriber stations is achieved in use, with the use of one of a number of subscribers. Radio channels, each radio channel has a different frequency; and in which each radio channel is transmitted to one of at least two power levels; (iii) an allocator, arranged to assign a radio channel for use in communications between one of the subscriber stations and the base station, according to the distance to the subscriber's station from the base station, so that in use , sanal fresuensias of the sanales transmitted at relatively low potency levels can be used again to stabilize the somunization between a subscript and a second base stasis, at a distance closer to the first base stasis than would otherwise be possible. Advantageously, by transmitting the channels at different power levels, the coverage area for different channels is varied. This provides the advantage that channel frequencies, for channels that have a low power level, can be reused in a geographical area closer to the base station than would otherwise be possible without causing significant co-channel interference. Also, because the system is used are a fixed system of wireless access communications, where the subscriber's antennas are directed, the interference is also reduced and this enables the capacity to be increased to a great extent than would otherwise be the case. possible. For example, this provides the advantage that for subscribers located in a region that is encompassed by two adjacent cells, the antenna can be directed to one of the two base stations, to reduce interference from the second base station. Another important advantage is that the planning of frequency is redused and replaced by a process that can occur after the installation. This process involves power that balances the carriers for optimal capacity. Frequency planning can be expensive and time consuming, decreasing the deployment regime. This method allows greater capacity and greater deployment. Advantageously, the subscriber stations each comprise a subscriber antenna with at least one mobile antenna beam. In this way, subscribers located in the external regions of a cell, where only high power channels are available, the number of available channels can be increased by re-directing the antenna towards the base station in an adjacent cell. Preferably, at least one subscriber station comprises two or more directional antennas. The antennas are each directed towards a different base station, so the number of available channels is increased allowing communication to be established using any of the antennas. This also has the advantage that the installation of the subscriber antennas is simplified due to the shorter time needed to identify a preferred base station and the antenna direction for a single antenna. Preferably, the radio channels are downlink radio channels. This provides the advantage that the layering can be increased in the dessending channel only. For example, if the subscribers have access to the Internet, they send a request, small in size, in the assent line, as long as they have great informational sanctities in the outgoing link (for example, network pages). In this type of situation, greater sapsity in the dessending line is required than for the ascending line. Also, because the uplink channels are limited by the interference to a greater extent than the downlink channels, it is advantageous that the radio sanals are sandal of the downlink radio.

It is also preferred that the radio channel frequency assignment method further comprises the steps of: (i) transmitting packet data on the allocated channel; (ü) check the transmitted data for errors; and (iii) retransmit any transmitted data where errors were detected. This provides the advantage that when the packet data is communicated, then the sapsity can be increased, while the transmission is allowed to go off if there are errors in the transmission of the packet data. BRIEF DESCRIPTION OF THE DRAWINGS In order that the present invention be more fully understood and show only the same can be taken to taste, it will now refer, in the form of an example only, to the Figures as shown in the sheets. of accompanying drawings, in which: Figure 1 shows a cluster of seven cells, which are represented as hexagons; Figure 2 shows two clusters of seven selves, where each frequency is reused twice, once in each cluster; Figure 3a shows a total display of 6 carriers, with a cluster size of 7, using 42 frequencies of the total available of 52; Figure 3b shows the unfolding of Figure 3a after each cell has been divided into sectors, adding 12 carriers per cell, giving a total of 18 carriers and tripling the capacity of each cell. The number of cells per cluster is now 3; Figure 4 is a schematic diagram of a station with carriers of three frequencies; Figure 5 is a schematic diagram of two adjacent cells; Figure 6 illustrates how the asymmetry formed in the bearer relations at the interference level for uplink and downlink channels arises; Figure 7 also illustrates how the asymmetry formed in the carrier relationships at the interference level for the uplink and downlink channels arises; and Figure 8 shows a priority list of available channels. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, in the form of an example, the best way considered by the inventors to carry out the invention will be described. In the following description, numerous specific details are pointed out in order to provide a complete understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention can be put into practice by several specifics. The term "sector" is used to refer to a geographical area around a base station, within which the sub-subscriber stations are allowed to communicate with the base station. Similarly, an "uplink" channel is a channel through which signals are transmitted from a subscriber to the base station. A "downlink" channel is a channel by means of which the signals are transmitted from the base station to a subscriber station. By reducing the potency to which a carrier is transmitted, the coverage area (or sector) for that carrier is redused, as is the interference caused to a more distant terminal in a reuse cell. For example, Figure 4 shows a cell 40 with a base station 41. In this cell, the lower frequency F3 carriers are transmitted at the highest power, so that those carriers are available to the subspiers solved elsewhere in the cell 40. The sector for F3 carriers is then the total cell. The higher frequency carriers Fl are transmitted at the lower power and are only available to the subscribers placed within the area 42 in the cell, ie, near the base station. Similarly, the carriers at intermediate frequencies F2 are transmitted at an intermediate power and are available to subscribers between the base station and the limit 43. It is also possible for the carriers F3 to be carriers of higher frequency and that the carriers Fl be of minor frequency. Any suitable arrangement of frequencies between the sectors can be used. In an example, the channel assignment method involves using a priority list of available channels. As illustrated in Figure 8, a number of carriers 81, I to N, are available, where the carriers have different power levels 82. These carriers are arranged according to their power level, with those of the power lowest being assigned to the highest priority. The sanal allocation method then implicitly essoger the highest priority available sanal. It is also possible to inspect the saliency of this sanal essogido, for example, by taking the sonorous vigilance of the sanal de lasse dessendente or making test calls. The first sanal is the highest priority and the sual has an aseptable salinity is then essogido. Subscribers close to the base station (within the limit 42) have carriers of any of the available frequencies, while subscribers between the boundary 43 and the edge of the cell have fewer available carriers.

Because the power level for the internal sector 42 is reduced, the carrier frequencies in this sector can be reused in a geographical area closer to the base station than would otherwise be possible, without causing significant channels. After the installation of the communication system, the power levels of the channels are adjusted to improve capacity, as described. This adjustment is carried out by the device or in the base station itself or elsewhere in the communication network. For example, the control can be performed from a central location, such as a management center of the communications network. Any suitable apparatus can be used, as is known to a person skilled in the art. A channel allocation method is then used, which involves choosing an available channel with the lowest available power level and providing an adequate output or bearer relationship at the interference level. This step involves searching all available channels and can be carried out by a device inside the base station or elsewhere in the communication network. Any adesuado apparatus can be used to examine the method, as it is sonosido by a person expert in the matter. A channel that provides an adequate quality is one that allows the information to be transmitted without the introduction of a certain number of the level or error rate. This method allows the number of channels available to the most disadvantaged users in the system (those for which the fewest channels are available) to be maximized. A problem with this type of system, if used with a mobile phone system, is that as a mobile station travels through a cell, it also passes between sectors and this affects the number of channels available to it at any location. When in the internal sestor of a cell, the mobile subscriber can be assigned a channel of some freshness and then, if the subscriber moves in the next sector, this frequency may no longer be available. To maintain the comunisasión, the mobile subssriptor needs to "deliver" between sanales suando it moves between sestores and this is insonveniente and unnecessarily complex. Figure 5 shows two adjacent cells 51, 52, each cell being somewhat similar to the one shown in Figure 4. For both selves, internal sestor 53, 54 has sanalities transmitted at the lowest power level and channel frequencies for the internal sector 53 are reused by the internal sector of the adjacent cell 54. For the external sectors of cell 51, the frequencies F3 and F4 are used (these may be frequency ranges) as shown, and for cell 52, the frequencies for the external sectors are inverted, as shown. This ensures that for a subscriber located in the region of overlap between the two cells 55, the probability of the co-channel interference is reduced. For example, for the signals of the subscriber 56 from the cell 51 it will be in a frequency interval F2 as long as the signal from the cell 52 will be in the frequency range F3. It is not essential to use the exact arrangement of frequencies or intervals of frequencies for the external ses- sors, as shown in Figure 5. Other arrangements can be used that also reduce the co-channel interferensia. Because in the fixed systems of wireless access, the subscriptor stations are equipped with diressional antennas, the so-sanales interferensia is further reduced. For example, if the subscriber 56 in Figure 5 has a directional antenna, it can be directed to the base station 57 so that the interference of the signals associated with the base station 58 is reduced. As already mentioned, the Cersanos subscribers to the base station (within the internal sector) have carriers of any of the available frequencies, in as much the subssiptores in the most external sestor (for example between the limit 43 and the edge of the selda) have more beams available carriers. means that sub-subscribers away from the base station are at a disadvantage in terms of the number of sanal available. However, the number of sanal available for these sub-subscribers is increased by having available channels from any adjacent base station. For example, subscriber 56 may increase the number of available channels using those of any sector 59 or 60. Subscriber stations may be equipped with two or more directional antennas, one directed towards a different base station. By doing , the subscribers, such as that at 56 in Figure 5, have access to more channels, because they can use channels from more than that base station. is done by changing the subscriber antenna used. Alternatively, a subscriber antenna system may be used in which an antenna assembly is used, which has two or more antenna beams. It is also possible to use a subscriber system with a mobile antenna beam, for example, using a Rotman lens beam former, using a rotary antenna assembly or using several antennas each with a beam width less than 3602. , which are arranged to cover the 3602. When using a directional antenna, takes time to install, because the antenna has to be directed in a way that makes possible the communication of the desired quality that will be achieved with a preferred base station . often involves monitoring the site itself using special equipment and is time consuming and expensive. By using several antennas that together give a substantial cover in all directions, installation process is greatly simplified. For example, four directional antennas can be used and arranged to provide effectively omni-directional coverage around the subscriber set. A particular embodiment may comprise four antennas of 1202, arranged at 902 with each other, providing coverage of 3602, with some degrees of overlap. The antenna assembly is simply installed (for example on the top of the tesho) without being specially directed and then the communications system is able to "steer" the antenna of the subscripter by using the antenna beam to be used after installation. process of direction can be controlled by an Operations, Administration and Maintenance Center ("OAM") in the network of communisations or alternatively it can be controlled by an apparatus wi the subscrict system itself. Mobile antenna hases can also be used in way. In another modality, the sapsidad of the sanales of dessending line is only increased by varying the levels of potensia of these sanales, as it was dessribió previously. is especially advantageous for situations where more layering in the downlink channels is required compared to the uplink channels. For example, Internet access by a subscrict involves the transmission of relatively large amounts of data on downlink channels (such as network pages) while uplink channels are used to send relatively small requests. from the subscriber to the base station. In type of situation and when the packet data is transmitted, it is possible to use channels having a lower carrier ratio at the interference level than that acceptable for a voice channel. is because an error detection method can be used to initiate the retransmission of data that is not transmitted accurately enough. For example, an automatic transmission request system ("ARQ") can be used. means that the capacity of the communications system can be further increased, using channels of different levels of power in combination are a method of detesting error, to allow signals to be transmitted using channels of a lower carrier ratio to the interference level, where possible. Likewise, there is an asymmetry formed in the bearer relations at the interference level for the uplink and downlink channels, which can be exploited. That is, for downlink channels in the type of the communication system illustrated in any of Figures 1 to 5, there is less interference to the corresponding uplink channels. Because there is less interference in the downlink channels in the worst case, the capacity of these channels can be "extended", using the method of different power levels, as described above. Figure 6 illustrates how the asymmetry formed in the carrier ratios at the interference level for the upstream and downstream channels arises. Considered an uplink channel of the subscriber 61 to the base station 60. For this sanal, the interferensia can come from several other subscribers 64, 65 in other selves who are using similar or similar fresal sanales. Once the base station receives these signals of similar frequency, they can not easily tell which subscrption station they come from. However, for a desalting link, such that from the base 60 to subscript 62, interferensia is only experienced by other subscribers in the same "line of sight" 63 from the base station 60 as the subscriter 62 This is because the antenna assemblies of the subscript in a fixed security system are diressional, while for the same base station, the antenna array is typically omni-directional in substantial form. Figure 7 also illustrates how the asymmetry formed in carrier ratios at the interference level for uplink and downlink channels arises. For the base station 71, there are up to 6 uplink interference sources 72, but for the sub-sink 73 there is only 1 downlink interferensia source. The orthogonal polarizations for the different sanales can be used to reduce the interference. For fixed radio access systems, subsystem antennas are usually located outside of the worst obstrusions and polarization mixtures. This has made use of the orthogonal polarization of some value to improve the average rejection of the carrier at the level of interference. This method can also be used in conjunction with the proposed ideas. A range of aplishesions are ensuered within the scope of the invention. They include situations where it is required to assign channels in a fixed wireless access communication system for either or both of the uplink and downlink channels. For example, for access to the Internet and for the transmission of package data.

Claims (12)

1. CLAIMS 1. A method for assigning radio channels in a fixed wireless access network, this network comprises: (i) a base station; (ii) a plurality of subscriber stations; and in that the base station and the subscriber stations are adapted so that communication between the base station and the subscriber stations is achieved in use, with the use of one of a number of radio channels, each radio channel has a different frequency; and in that each radio channel is transmitted in one of at least two power levels, this method comprises the step of: assigning a radio channel for use in the communication between one of the subscriber stations and the base station, of according to the distance of the subscriber station from the base station, so that, in use, the channel frequencies of the channels transmitted to relatively low power nodes can be used again to establish communication between a subscriber and a second base station, at a distance more sersana to the first base station, than that which would be possible otherwise.
2. 2. A method of allocating a radio sanal, as claimed in claim 1, this method also assumes the step of assigning the radio sanal of agreement are the power levels of the available radio channels.
3. 3. A method of assigning a radio channel, as claimed in claim 1, wherein this method further comprises the step of allocating the radio sanal by sourcing an available radio channel with the lowest power level.
4. 4. A method of allocating a radio channel, as claimed in claim 2, in which this method also assumes assigning the radio sanal by using an available radio sanal is a carrier rejection at the interference level above a predetermined value.
5. 5. A method of allocating a radio channel, as claimed in claim 1, wherein the subscriber stations of the communication network are placed within a cell, comprising a geographic area around the base station and the communication network further comprises a second cell adjacent to the first cell; a second base station, located inside the second cell; and a plurality of second subscriber stations, located within the second cell and in which the second base station and the second subscriber stations are adapted so that communication between the second base station and the second subscriber stations is achieved. in use, with the use of one of a number of second radio channels, each second radio channel has a different frequency; and wherein each second radio channel is transmitted to one of at least two power levels and in which the radio channels transmitting at the lowest power have substantially the same frequencies in each cell.
6. 6. A method of allocating radio sanal, as claimed in claim 5, in which the radio sanales, which transmit to the highest potency, have substantially different frequencies in each cell.
7. 7. A method for allocating a radio sanal frequency, as claimed in claim 1, in which at least one subscripter station suffers a subscripter antenna with less one mobile antenna beam.
8. 8. A method for allocating a radio channel freshness, as claimed in claim 1, in which, if less than one subscriptor state, comprises two or more directional antennas.
9. 9. A method for assigning a radio channel frequency, as claimed in claim 1, wherein the radio channels are downlink radio channels.
10. 10. A method for assigning a radio channel frequency, as claimed in claim 1, which further comprises the steps of: (i) transmitting packet data on the allocated channel; (ii) check the data transmitted in the errors; (iii) retransmit any transmitted data in which errors are detected.
11. 11. An apparatus for assigning a radio channel in a fixed wireless access communication network, this network comprises: (i) a base station; (ii) a plurality of subscriber stations; and wherein the base station and the subscriber stations are adapted so that communication between the base station and the subscriber stations is achieved in use, with the use of one of a number of radio channels, each channel of radio has a different frequency; and in which radio sanal is transmitted in one of at least two power levels, this apparatus comprises: a dispatcher, arranged to assign a radio channel for use in communication between one of the subscriber stations and the base station , according to the distance of the subscriber station from the base station, so that in use, the channel frequencies of the channels transmitted at relatively low power levels, can be used again to establish the communication between a subscriber and a second base station at a distance closer to the base station than it would otherwise be possible.
12. 12. A network of fixed communications, of wireless asseso, sual somprende: (i) a base station; (ii) a plurality of subscriptor stations; and in which base stasis and subscriptor stasis are adapted so that somunisation between the base station and the subscriber stations is achieved in use, with the use of one of a number of radio channels, each radio channel has a different frequency; and in which each radio channel is transmitted in one of at least two power levels; (iii) an allocator, arranged to assign a radio channel for use in communication between one of the subscriber's stations and the base station, according to the distance of the subscriber's station from the base station, so that in use, the channel frequencies of the channels transmitted at relatively low power levels can be used again to establish communication between a subscripter and a second base station at a distance closer to the base station than the base station. what would otherwise be possible.