MXPA99005861A - Establishing a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system - Google Patents

Abstract

The present invention provides a channel selection controller and method for establishing a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, at least two frequency channels being provided over which said wireless link could be established. The channel selection controller comprises:a storage for storing data identifying the at least two frequency channels;a selector for selecting a frequency channel from those listed in said storage;and link acquisition logic for establishing a wireless link on the frequency channel selected by the selector. Further, the selector is responsive to the link acquisition logic being unable to establish said wireless link, to select an alternative frequency channel from those listed in said storage. By this approach, it is possible to increase the number of subscriber terminals that can be supported by the wireless telecommunications system, since if one frequency channel is fully used at the time that a wireless link connecting aparticular subscriber terminal with a central terminal is required, then another frequency channel can be selected for the establishment of that wireless link.

Description

ESTABLISHMENT OF A WIRELESS LINK THAT CONNECTS TO A CENTRAL TERMINAL AND A SUBSCRIBER TERMINAL OF A SYSTEM WIRELESS TELECOMMUNICATIONS The present invention relates generally to wireless telecommunications systems and more particularly to techniques to establish a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system.

BACKGROUND OF THE INVENTION A wireless telecommunications system has been proposed in which a geographical area is divided into cells, each cell having one or more central terminals (CTs) for communication via wireless links with a number of subscriber terminals (STs) in the cell. These wireless links are established by predetermined frequency channels, a frequency channel typically consisting of one frequency to capture signals from a subscriber terminal to the central terminal, and another frequency to output signals from the central terminal to the subscriber terminal. A central terminal may typically have a number of modem shelves, each modem repise operating with a different frequency channel. Due to bandwidth restrictions, it is not practical for each individual subscriber terminal to have its own dedicated frequency channel for communication with the central terminal. Therefore, techniques need to be applied to allow data elements that refer to different communications to pass through the same frequency channel without interfering with each other. In current wireless telecommunications systems, this can be achieved through the use of a "code division multiple access" (CDMA) technique, where a set of orthogonal codes can be applied to the data elements to be transmitted. by means of a particular frequency channel, combining the data elements that are related to different wireless links with different orthogonal codes coming from the set. The signals to which an orthogonal code has been applied can be considered as being transmitted by a corresponding orthogonal channel within a particular frequency channel. Hence, if a set of 16 orthogonal codes is used, 16 orthogonal channels can be created within a single frequency channel, and therefore up to sixteen separate communication signals (corresponding to sixteen separate wireless links) can be transmitted simultaneously through a single frequency channel if different RW codes are applied to each communication signal. Therefore, each modem shelf within the central terminal could support 16 wireless links. Typically, each subscriber terminal will be arranged to always communicate through a particular orthogonal channel with a particular modem shelf of the central terminal, frequently referring to this arrangement as a "fixed assignment" arrangement. As more subscribers subscribe to the wireless telecommunications network, it becomes desirable to support more and more subscriber terminals from each central terminal. There is only a limited number of frequency channels that can be assigned to the wireless telecommunications system, and just as it is desirable for surrounding cells to use different frequency channels in a way that reduces interference, demand can not be met by the mere addition of more modem shelves to each central terminal. Therefore, using the above fixed allocation arrangement, there is a limit as to how many subscriber terminals can be supported from a central terminal. GB-A-2,277,849 describes a technique for connecting a mobile to one of a plurality of base stations within a radio communications network. The mobile after scanning all the channels in its vicinity generates a prioritized list of frequency channels from which the preferred channels are chosen.

BRIEF DESCRIPTION OF THE INVENTION Viewed from a first aspect, the present invention provides a wireless telecommunications em consisting of one or more cells, each cell including one or more central terminals and a plurality of subscriber terminals, one or more central terminals being arranged to provide a plurality of frequency channels by which wireless links can be established by connecting a subscriber terminal with one or more of said central terminals, wherein at least one or more central terminals comprises: means for generating, for a selected subscriber terminal, a list Prioritized frequency channels through which wireless links can be established connecting this subscriber terminal with one or more of the central terminals, the prioritized list identifying a base channel for the subscriber terminal and at least one additional channel coming from of said plurality of frequency channels; a transmitter for transmitting the prioritized list of frequency channels to the subscriber terminal; and wherein the subscriber terminal includes: a receiver to receive the prioritized list of frequency channels; a store to store the prioritized list of frequency channels; the link acquisition logic to search for the establishment of a wireless link in the base frequency channel specified in the prioritized list; a selector responsible for the link acquisition logic that is unable to establish the wireless link, to select an alternative frequency channel from the prioritized list; the link acquisition logic being arranged to seek to establish the wireless link in the alternative frequency channel selected by the selector.

By this method, it is possible to increase the number of subscriber terminals that can be supported by the wireless telecommunications em, since if a frequency channel is fully used at the time the wireless link connecting a particular subscriber terminal with the central terminal is required, then another frequency channel can be selected for the establishment of that wireless link. Previously this would not have been possible, since the subscriber terminal could have been arranged to only communicate with a central terminal using a predefined frequency channel. In the preferred embodiments, the data in said store identifies at least one of said two frequency channels as the preferred frequency channel, and the selector is arranged to select which frequency channel is preferred first. Therefore the subscriber terminal will have a "base" frequency channel which is the preferred channel through which the wireless links are going to be established, the other frequency channels listed in the store will only be used if the frequency channel Base is completely used at the time the wireless link is required. In the preferred embodiments, the subscriber terminal can establish wireless links with a plurality of central terminals forming a service domain, and the subscriber terminal further comprises a receiver for receiving a message from a central terminal of said service domain that identifies the frequency channels for each central terminal in the service domain by which wireless links connecting said central terminals and said subscriber terminals will be established, the store being arranged to store the information received by the receiver. Hence, a plurality of central terminals, which can be used by the subscriber terminal to establish wireless links, can be arranged as a service domain, and the necessary information about the service domain be passed to the subscriber terminal. The provision of more than one central terminal with which a wireless link to a subscriber terminal can be established provides the wireless telecommunications em with an improved fault tolerance. For example, if a particular central terminal has a fault affecting all the modem shelves of the central terminal, then the prior art "fixed allocation" systems, all the subscriber terminals associated with that central terminal will be unable to establish communications until that the fault is corrected. However, in accordance with the preferred embodiments of the present invention, the subscriber terminals will be able to connect to another central terminal, thereby reducing the effect of the failure. Preferably, the link acquisition logic tries for a predetermined time to establish a wireless link in the frequency channel selected by the selector, and if the predetermined time ends without the wireless link having been established, the link acquisition logic requests to the selector that selects an alternative frequency channel from those listed in said store. It will be apparent that some other criteria, other than the conclusion of a predetermined time, could be used to determine that the link acquisition controller has been unable to establish a wireless link through a particular frequency channel. Seen from a second aspect, the present invention provides a subscriber terminal for use in a wireless telecommunications system in accordance with the first aspect of the present invention. In one embodiment, a central terminal can be provided with which the subscriber terminal can establish a wireless link, a plurality of frequency channels being provided by which a wireless link between said subscriber terminal and said central terminal can be established, the store being arranged to store data identifying said plurality of frequency channels. However, preferably, a plurality of central terminals are provided with which the subscriber terminal can establish a wireless link, with each central terminal providing at least one frequency channel by which a wireless link can be established between said subscriber terminal. and said central terminal, the store being arranged to store data identifying at least one of said frequency channels provided by each of the plurality of central terminals. By providing the subscriber terminal with the capability to use more than one central terminal, the tolerance to failure of the wireless telecommunications system is increased, as discussed above.

In the preferred embodiments, the subscriber terminal is located within a sector of a cell of the wireless telecommunications system, the cell having at least one central terminal with an antenna arrangement for providing said sector with a plurality of frequency channels, the store is arranged to store said plurality of frequency channels. Preferably, in response to a user of the subscriber terminal wishing to establish a call, the link acquisition logic attempts to establish a wireless link through the frequency channel selected by the selector, and if the link acquisition logic is incapable. of establishing a wireless link through said frequency channel, the selector is arranged to select an alternative frequency channel from those listed in said store, and the link acquisition logic is arranged to attempt to establish a wireless link for the call on that channel of alternative frequency. Further, in the preferred embodiments, each frequency channel comprises a plurality of orthogonal channels, and the subscriber terminal is arranged to listen in one of the predetermined orthogonal channels of a preferred frequency channel to a signal indicating that an incoming call is directed to the subscriber terminal, identifying the signal whether or not there is an available traffic channel within that preferred frequency channel for handling the incoming call, the link acquisition logic being arranged to establish a wireless link through said preferred frequency channel if the orthogonal traffic channel is available, but if not, the selector is arranged to select an alternative frequency channel, and the link acquisition logic is willing to establish a wireless link through said alternative frequency channel if there is an orthogonal traffic channel available for handling the flame incoming on that alternative frequency channel. In an arrangement as such, the subscriber terminal, upon termination of the incoming call, preferably returns to listen on the predetermined orthogonal channel of the preferred frequency channel. Seen from a third aspect, the present invention provides a central terminal for communicating with a subscriber terminal in accordance with the second aspect of the present invention, the central terminal being arranged to be one of a plurality of central terminals forming a domain of service of a wireless telecommunications system, and comprising: a store to store information about the other central terminals in the service domain; the means being provided for generating it to refer to the store when the prioritized list is generated. Preferably, the central terminal further comprises a receiver for receiving from a service domain controller information about the other central terminals in the service domain, this information being stored in the store. In addition, the store is also arranged, in the preferred embodiments, to store a data bank that identifies each subscriber terminal in the service domain, whether the central terminal is the primary central terminal for that subscriber terminal or that the central terminal is arranged to provide backup service to that subscriber terminal. In the preferred embodiments, the cell has a plurality of central terminals, each of the central terminals providing at least one frequency channel, and each central terminal providing at least one frequency channel different from at least one frequency channel provided by the other central terminals of the cell. Viewed from a fourth aspect, the present invention provides a method for establishing a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, with at least two frequency channels being provided by means of which said wireless link can be established, including the method the steps of: a) generating a prioritized list of at least two frequency channels, in which a frequency channel is identified as the base channel; b) transmit the prioritized list from the central terminal; c) receive the prioritized list in the subscriber terminal; d) store the prioritized list; e) use a selector to select the base frequency channel of the prioritized list in said store; f) establish a wireless link through the frequency channel selected by the selector; and g) if in said step (f) said wireless link can not be established, use the selector to select an alternative frequency channel from which the prioritized list, and the repetitive step (f) using said alternative frequency channel.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the invention will be described hereinafter, by way of example only, with reference to the appended drawings in which like reference numbers are used for similar characteristics and in which: Figure 1 is a view schematic of an example of a wireless telecommunications system in which an example of the present invention is included. Figure 2 is a schematic illustration of an example of a subscriber terminal of the telecommunications system of Figure 1. Figure 3 is a schematic illustration of an example of. a central terminal of | telecommunications system of Figure 1. Figure 3A is a schematic illustration of a modem shelf of a central terminal of the telecommunications system of Figure 1. Figure 4 is an illustration of an example of a frequency plane for the system of FIG. 1. FIGS. 5A and 5B are schematic diagrams illustrating possible configurations for cells for the telecommunications system of FIG. 1. FIG. 6 is a schematic diagram illustrating aspects of a multiplexed code division system for FIG. the telecommunications system of Figure 1.

Figures 7 A and 7B are schematic diagrams illustrating the steps of signal transmission processing for the telecommunications system of Figure 1. Figures 8 A and 8 B are schematic diagrams illustrating the steps of signal reception processing. for the telecommunications system of Figure 1. Figures 9 A and 9B are diagrams illustrating ascending and descending delivery methods when the system is fully charged. Figure 10 illustrates the CDMA channel hierarchy according to preferred embodiments of the present invention. Figure 11 is a schematic diagram illustrating the ascending and descending communication paths for the wireless telecommunications system. Figure 12 is a schematic diagram illustrating the formation of a downward signal transmitted by the central terminal. Figures 13 A and 13 B illustrate the structure of the information tables sent by the ascending and descending trajectories. Figures 14 A and 14 B illustrate the high frame structure for the descending and ascending trajectories. Figures 15A and 15B illustrate typical downstream and upstream channel structures that could occur in a loaded system according to preferred embodiments of the present invention.

Figure 16 illustrates how the available traffic channels are classified into preferred embodiments of the present invention. Figure 17 illustrates the elements used by the central terminal to perform interference limitation. Figure 18 illustrates possible antenna configurations that can be used in a wireless telecommunications system in accordance with the preferred embodiment of the present invention; and Figures 19 A and 19 B illustrate how channel switching is facilitated in preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 is a schematic overview of an example of a wireless telecommunications system. The telecommunications system includes one or more service areas 12, 14 and 16, each of which is served by a respective central terminal (CT) 10 which establishes a radio link with subscriber terminals (ST) 20 within the mentioned area. The area that is covered by a central terminal 10 may vary. For example, in a rural area with low subscriber density, a service area 12 could cover an area with a radius of 15-20 km. A service area 14 in an urban environment where there is a high density of subscriber terminals 20 could only cover an area with a radius in the order of 100m. In a suburban area with an intermediate density of subscriber terminals, a service area 16 could cover an area with a radius of the order of 1 km. It will be appreciated that the area covered by a particular central terminal 10 can be chosen to adjust the local requirements of expected or actual density of subscribers, local geographic considerations, etc., and is not limited to the examples illustrated in Figure 1. More , coverage does not need to be, and typically will not be circular in scope due to antenna design considerations, geographic factors, constructions and so on, which will affect the distribution of transmitted signals. The central terminals 10 for respective service areas 12, 14, 16 can be connected to each other by means of links 13, 15 and 17 interacting, for example, with a public switched telephone network 18 (PSTN). The links may include conventional telecommunications technology using copper wires, optical fibers, satellites, microwaves, etc. The wireless telecommunications system of Figure 1 is based on providing fixed microwave links between subscriber terminals 20 at fixed locations within a service area (eg, 12, 14, 16) and central terminal 10 for that area of service. service. Each subscriber terminal 20 may be provided with a permanent fixed access link to its central terminal 10, but in preferred embodiments access based on demand is provided, so that the number of subscribers that can be supported exceeds the number of subscribers. wireless links available. The way in which access based on demand is implemented will be described in detail later.

Figure 2 illustrates an example of a configuration for a subscriber terminal 20 for the telecommunications system of Figure 1. Figure 2 includes a schematic representation of customer premises 22. A customer radio unit 24 (CRU) is mounted through the client's property. The customer radio unit 24 includes a flat panel antenna or the like 23. The customer radio unit is mounted at a location by the customer's property, or by a pole, etc., and in such an orientation that the antenna flat panel 23 within the customer radio unit 24 faces at address 26 of the central terminal 10 for the service area in which the customer's radio unit 24 is located. The customer radio unit 24 is connected through a descent line 28 to a power supply unit 30 (PSU) within the client's property. The power supply unit 30 is connected to the local power supply to supply power to the customer radio unit 24 and a network terminal unit 32 (NTU). The customer radio unit 24 is also connected through the power supply unit 30 to the network terminal unit 32, which in turn is connected to the telecommunications equipment in the customer's premises, for example to one or more telephones 34, fax machines 36 and computers 38. The telecommunications equipment is represented as being inside a single building of the client. However, this need not be the case, since the subscriber terminal 20 preferably supports either a single line or a double line, so that two subscriber lines could be supported by a single subscriber terminal 20. The terminal of Subscriber 20 may also be arranged to support analog and digital telecommunications, for example analog communications at 16, 32 or 64 kbit / sec or digital communications in accordance with the ISDN BRA standard. Figure 3 is a schematic illustration of an example of a central terminal of the telecommunications system of Figure 1. The common equipment shelf 40 consists of a number of equipment shelves 42, 44, 46, including an RF combiner and a shelf for power amplifier 42 (RFC), a power supply shelf 44 (PS) and a number of modem shelves 46 (MS) (in this example 4). The combiner shelf RF (42) allows the modem shelves 46 to operate in parallel. If "n" modem shelves are provided, then the combiner shelf RF (42) combines and amplifies the energy of "n" transmission signals, each signal being transmitted from one of the respective "n" modem shelves, and amplifies and part the "n" signals received so that the separated signals can pass through the respective modem shelves. The power supply ledge 44 provides a connection to the local power supply and fuses it for the different components in the common equipment rack 40. A bidirectional connection extends between the ledge 42 of the RF combiner and the main center terminal antenna 52. , as an omnidirectional antenna, mounted by a central terminal mast 50. This example of a central terminal 10 is connected through a point-to-point microwave link to a location where an interface is made to the telephone network 18 switched to the public, shown schematically in figure 1. As mentioned above , other types of connections (e.g., copper wires or optical fibers) can be used to link the central terminal 10 to the telephone network 18 switched to the public. In this example the modem shelves are connected through lines 47 to a microwave terminal 48 (MT). A microwave link 49 extends from the microwave terminal 48 to a point-to-point microwave antenna 54 mounted via the pole 50 for a host connection to the public switched telephone network 18. A personal computer, workstation or the like can be provided as a site controller 56 (SC) to support the terminal 'central 10. The site controller 56 may be connected to each modem shelf of the central terminal 10 through, for example, RS232 connections (55). The site controller 56 can then provide support functions such as fault location, alarms and status and the configuration of the central terminal . A site controller 46 will typically support a single central terminal 10, although a plurality of site controllers 56 could be linked to support a plurality of central terminals 10. As an alternative to the RS232 connections (55), which extend to a controller from site 56, data connections as a link X.25 (57) (shown with dotted lines in Figure 3) could instead be provided from a pad 228 to a switch node 60 of a handler element 58 (EM). A handler element 58 can support a number of distributed central terminals 10 connected by respective connections to the switching node 60. The handler element 58 allows a potentially large number (eg, up to, or more than 1000) of central terminals 10 to be integrated within of a management network. The operating element 58 is based around a powerful work station 62 and may include a number of 64 computer terminals for network engineers and control personnel. Figure 3A illustrates various parts of a modem shelf 46. An RF unit transmitting / receiving (RFU- implemented for example by a card in the modem shelf) 66 generates the RF signals of modulated transmission at medium energy levels and recovers and amplifies the baseband RF signals for the subscriber terminals. The RF unit 66 is connected to an analog card 68 (AN) that performs AD / DA, baseband filtering and vector summing of 15 signals transmitted from the modem cards (MCs) 70. The analog unit 68 is connected to a number of 70 modem cards (typically 1-8). The modem cards perform the baseband signal processing of the signals transmitted and received to / from the subscriber terminals 20. This may include half speed and propagation convolution code x 16 with "code division multiplexed access" (CDMA) ) by means of the transmitted signals, and recovery of synchronization, propagation and correction of error by the received signals. Each modem card 70 in the present example has two modems, and in preferred embodiments there are eight modem cards per shelf, and thus sixteen modems per shelf. However, in order to incorporate redundancy so that a modem can be substituted in a subscriber link when a failure occurs, only 15 modems through a single modem ledge 46 are generally used. The sixteenth modem is then used as a backup that can be turned on if a failure of one of the other 15 modems occurs. The modem cards 70 are connected to the tributary unit 74 (TU) which terminates the connection to the public switched telephone host network (for example, through one of the lines 47) and handles the signaling of information of telephony to the subscriber terminals through one of 15 of the 16 modems. The wireless telecommunications between a central terminal 10 and the subscriber terminals 20 could operate by several frequencies. Figure 4 illustrates a possible example of the frequencies that could be used. In the present example, the wireless telecommunication system is designed to operate in the 1.5-2.5GHz band. In particular, the present example is designed to operate in the band defined by ITU-R (CCIR), Recommendation F.701 (2025-2110 MHz, 2200-2290 MHz). Figure 4 illustrates the frequencies used for the signal ascending from the subscriber terminals 20 to the central terminal 10 and for the signal descending from the central terminal 10 to the subscriber terminals 20. It will be noted that 12 radio channels amounting and 12 that descend each of 3.5MHz are provided centered around 2155MHz. The spacing between the transmission reception channels exceeds the minimum required spacing of 70MHz. In the present example, each modem shelf supports 1 frequency channel (i.e. a frequency that is higher than the corresponding decreasing frequency). Currently, in a wireless telecommunications system as described above, the CDMA encoding is used to support up to 15 subscriber links through a frequency channel (a subscriber link through each modem). Hence, if a central terminal has 4 modem shelves, it can support 60 subscriber links (15 x 4) (that is, 60 STs can be connected to a CT). However, it is becoming desirable that more than 60 STs are supported from a central terminal, and, in preferred embodiments of the present invention, improvements to the CDMA coding technique are provided to increase the number of subscriber links that can be supported. by a central terminal. Both the CDMA encoding, and the improvements made to the CDMA encoding according to preferred embodiments, will be described in more detail later. Typically the radio traffic of a particular central terminal 10 will extend within the area covered by a central terminal 10 neighborly. To avoid, or at least reduce the interference problems caused by adjacent areas, only a limited number of the available frequencies will be used by any given central terminal 10. Figure 5A illustrates a cellular-type arrangement of the frequencies to mitigate interference problems between adjacent central terminals. In the arrangement illustrated in Figure 5A, the shaded lines for the cells 76 illustrate a set of frequencies (FS) for the cells. Selecting three sets of frequencies (for example, where FS1 = F1, F4, F7, F10); FS2 = F2, F5, F8, F11; FS3 = F3, F6, F9, F12), and provided that the immediately adjacent cells do not use the same set of frequencies (see, for example, the arrangement shown in Figure 5A), it is possible to provide an arrangement of assignment cells fixed omnidirectional where interference between nearby cells can be reduced. The transmitter power of each central terminal 10 is preferably set so that the transmissions do not extend as far as the nearest cell that is using the same set of frequencies. Therefore, according to the arrangement illustrated in Figure 5A, each central terminal 10 can use the four frequency pairs (for the up and down signal, respectively) within its cell, each modem shelf in the central terminal 10 being associated with a respective RF channel (channel frequency pair). Figure 5B illustrates a cell-type arrangement that uses sectioned cells to mitigate problems between adjacent central terminals. As with Figure 5A, the different type of shaded lines in Figure 5B illustrates different frequency sets. As in Figure 5A, Figure 5B represents three frequency sets (for example, where FS1 = F1, F4, F7, F10, FS2 = F2, F5, F8, FU, FS3 = F3, F6, F9, F12) . However, in Figure 5B the cells are sectorized using a sectorized central terminal 13 (ST) which includes three central terminals 10, one for each sector S1, S2 and S3, with the transmissions for each of the three central terminals 10 being directed to the appropriate sector between S1.S2 and S3. This allows the number of subscribers per cell to increase threefold, while permanent fixed access is still provided for each subscriber terminal 20. Arrangements like those in Figures 5A and 5B can help to cause interference, but in order to ensure that cells operating on the same frequency do not inadvertently decode the data of others, a repeating pattern of seven cells is used in such a way that for a cell operating on a given frequency, all six adjacent cells operating through the The same frequency is assigned a unique code of random pseudo noise (PN). The use of PN codes will be discussed in more detail later. The use of different PN codes prevents neighborhood cells that work by the same frequency from inadvertently decoding the data of the others. As mentioned above, CDMA techniques can be used in a fixed allocation arrangement (i.e., one in which each ST is assigned to a particular modem by a modem shelf) to allow each channel frequency to support 15 subscriber links . Figure 6 gives a schematic overview of coding and CDMA coding. In order to encode a CDMA signal, baseband signals, for example user signals for each respective subscriber link, are encoded at 80-80N within a baseband signal of 160k symbols / sec where each symbol represents 2 bits of data (see, for example, the signal represented in 81). This signal is then propagated by a factor of 16 using a propagation function 82-82N to generate signals at an effective chip rate of 2.56M symbols / sec at 3.5MHz. The propagation function involves applying a PN code (which is specified by a CT basis) to the signal, and also applying a Rademacher-Walsh (RW) code that ensures that the signals to respective subscriber terminals will be orthogonal to each other. Once this propagation function has been applied, the signals for respective subscriber links are then combined in step 84 and converted to radio frequency (RF) to give multiple user channel signals (eg 85) for transmission from the transmitting antenna 86. During the transmission, a transmitted signal will be subject to sources of interference 88, including external interference 89 and interference of t other channels 90. Accordingly, at the time that the CDMA signal is received at the receiving antenna 91, the channel signals of Multiple user can be distorted as shown at 93. In order to decode the signals for a given subscriber link from the received multiple user channel, a Walsh correlator 94- 94N uses the same RW and PN codes that were used for the coding of each subscriber link to extract a signal (eg, as represented at 95) for the respective received baseband signal 96-96N. It will be noted that the received signal will include some residual noise. However, unwanted noise can be removed using a low pass filter and signal processing. The key to CDMA is the application of RW codes, these being a mathematical set of sequences that have the function of "orthonormality". In other words, if any RW code is multiplied by any other code RW, the results are 0. A set of 16 RW codes that can be used is illustrated in table 1 below: RWO RW1 RW2 RW3 RW4 RW5 RW6 RW7 RW8 RW9 RW10 RW11 RW12 RW13 RW14 RW15 TABLE 1 The above set of RW codes are orthogonal codes that allow multiple user signals to be transmitted and received by the same frequency at the same time. Once the bitstream is orthogonally isolated using the RW codes, the signals for the respective subscriber links do not interfere with each other. Because the RW codes are orthogonal, when they are perfectly aligned all codes have a cross-correlation of 0, thus making it possible to decode a signal while canceling the interference of users operating by other RW codes. In preferred embodiments of the present invention, it is desired to provide the central terminal with the ability to support more than 15 subscriber links per channel frequency, and to achieve this the previous set of 16 RW codes has been improved. In order to maintain compatibility with current products using the 16 RW codes, it was desirable that any improvement should retain the same set of 16 RW codes. The way in which the improvements have been implemented provides flexibility in how the frequency channels are configured, with certain configurations allowing a larger number of subscriber links to be supported, but at a lower raw bit rate . In preferred embodiments, a channel can be selected to operate at the following raw bit rates: 160 kb / s full speed (F1) 80 kb / s medium speed (H1, H2) 40 kb / s speed of a quarter (Q1 , Q2, Q3, Q4) 10 kb / s low speed (L1, L2, L3, L4), for acquisition in elevation. In preferred embodiments, the mode in which these pipelines are provided differs for the downlink (CT to ST) and upstream (ST to CT) communication paths. This is because it has been noted that different performance requirements exist for descending and ascending trajectories. By descending all the signals emanate from a single source, say the central terminal, and therefore the signals will be synchronized. However, by the upward path, the signals will emanate from a number of independent STs, and therefore the signals will not be synchronized. Given the above considerations, in preferred embodiments, by the total upward trajectory speed (160 kb / s) the operation is implemented using the basic set of RW codes discussed at the beginning, but the average and one-quarter speeds are achieved through the use of "superimposed codes" which consist of high speed RW code symbol patterns that are transmitted for each intermediate speed data symbol. For half-speed operation, two superimposed 2-bit codes are provided, while for quarter-speed operation, four codes are provided by four-bit stations. When a signal is generated for transmission, one of the superimposed codes, where appropriate, is applied to the signal in addition to the appropriate RW code. When the signal is received, then in the CDMA demodulator the incoming signal is multiplied by the PN, RW codes by means of stations of the channel. The correlator integration period is set to equal the length of the superimposed code. Overlapping codes are extensively used to provide variable speed upstream traffic channels. The superimposed codes will also be used to implement downstream control channels, these control channels will be described in more detail later. However, as mentioned at the beginning, a different method is used to provide flexible channels through the downstream traffic channel courses. Downstream traffic channels will operate at high speed, in 160 kb / s mode with lower data rates of 80 and 40 kb / s being supported "multiplexing time division" (TDM) the available bandwidth. In preferred embodiments, the time slot bit numbering TDM will follow the CCITT convention G.732 with bits transmitted in the bit 1 sequence, bit 2 bit 8. The bit orientation is specified per channel as being the most significant bit first (MSB), the least significant bit first (LSB) or N / A. The provision of a hybrid CDMA / TDM method for downstream traffic channels retains the benefits of CDMA access, ie the interference is reduced when traffic is reduced. In addition, the use of TDM ensures that the CDMA signal is limited to a 256 constellation of "quadrature amplitude modulation" (QAM) which reduces the dynamic scale requirements of the receiver. The QAM constellations will be familiar to those skilled in the art. Through upstream channels, the pure CDMA method using overlapping codes eliminates the need to synchronize the STs time to a TDM reference frame. This has the advantage of eliminating TDM delays and "guard time" between TDM frames. Another benefit is reduced peak power management requirements in the ST RF transmitter chain which would otherwise be necessary when transmitting TDM data that is disrupting. The very dynamic scale requirement is restricted to the CT receiver. The manner in which the transmitted and received signals are processed in accordance with preferred embodiments in the present invention will be described with reference to FIGS. 7 and 8. FIG. 7A is a schematic diagram illustrating the steps of signal transmission processing as they are configured in a subscriber terminal 20 in the telecommunications system of Fig. 1. In Fig. 7A, an analogous signal from a telephone is passed through an interface as a two-wire interface 102 to a hybrid processing circuit 104. and then through an encoder-decoder 106 to produce a digital signal within which a raised channel including control information is inserted into 108. If the subscriber terminal supports a number of telephones or other telecommunications equipment, then the elements 102, 104 and 106 may be repeated for each piece of telecommunications equipment. At the output of the high-insertion circuit 108, the signal will have a bit rate of either 160, 80 or 40 Kbits / s, depending on which channel has been selected for signal transmission. The resulting signal is then processed by a convoy encoder 110 to produce two signals with the same bit rate as the input signal (collectively, these signals will have a symbol rate of 160, 80 or 40 KS / s). Next, the signals are passed to a propagator 111 where, if a reduced bit rate channel has been chosen, an appropriate superimposed code provided by the superimposed code generator 113 is applied to the signals. At the output of propagator 111, the signals will be at 160 KS / s regardless of the bit rate of the input signal because the superimposed code will have increased the symbol rate by the necessary amount. The signal output from the propagator 111 is passed to a propagator 116 where the Rademacher-Walsh and PN codes are applied to the signals by a code generator RW (112) and a PN code generator (114), respectively. The resulting signals, at 2.56 MC / s (2.56 mega chips per second, where a chip is the smallest data element in a propagated sequence) are passed through a converter 118 from digital to analog. The digital-to-analog converter 118 forms the digital samples into an analogous waveform and provides a baseband power control stage. The signals are then passed to a low pass filter 120 to be modulated in a modulator 112. The signal modulated from the modulator 122 is mixed with a signal generated by a voltage controlled oscillator 126 that responds to a synthesizer 160. The output of the mixer 128 is then amplified in a low noise amplifier 130 before being passed through a band pass filter 132. The output of the bandpass filter 132 is further amplified in an additional low noise amplifier 134., before being passed to the power control circuitry 136. The output of the power control circuitry is further amplified in an energy amplifier 138 before being passed through an additional bandpass filter 140 and it is transmitted from the transmission antenna 142. Figure 7B is a schematic diagram illustrating the steps of signal transmission processing as configured in a central terminal 10 in the telecommunications system of Figure 1. As will be evident, the terminal The central station is configured to perform signal transmission processing similar to the subscriber terminal 20 illustrated in FIG. 7A, but does not include the elements 100, 102, 104, and 106 associated with the telecommunications equipment. In addition, the central terminal includes a TDM encoder (105) to perform time division multiplexing where required. The central terminal will have a network interface by which incoming calls destined for a subscriber terminal are received. When an incoming call is received, the central terminal will contact the subscriber's terminal to which the call is directed and will provide an adequate channel through which the incoming call can be established with the subscriber's terminal (in preferred embodiments, this is done using the call control channel discussed in more detail later). The channel established for the call will determine the time slot to be used for call data passed from the CT to the ST and the TDM encoder (115) will be supplied with this information. Hence, when the data of the incoming call is passed from the network interface to the TDM encoder (105) via line 103, the TDM encoder will apply a suitable TDM encoding to allow the data to be inserted in the time slot. adequate Thereafter, the processing of the signal is the same as the equivalent processing performed in the ST and described with reference to Figure 7A, the superimposed code generator produces a single superimposed code of value "1" so that the output The signal from the propagator 111 is the same as the signal input to the propagator 1 1 1. As mentioned at the beginning, in preferred embodiments, the superimposed codes, rather than the TDM, are used to implement downstream control channels, and the data relating to such channels are passed from a demand allocation engine (to be discussed in more detail later) via line 107 through switch 109 to the high-insertion circuit 108, sub thereby passing the TDM encoder (105).

The processing of the signal is then the same as the equivalent processing performed in the ST, with the superimposed code generator providing superimposed codes suitable for the propagator 111. The superimposed code generator will be controlled so as to produce the desired superimposed code, in preferred embodiments. , this control comes from the DA engine (to be discussed in more detail later). Figure 8A is a schematic diagram illustrating the signal reception processing steps as configured in a subscriber terminal 20 in the telecommunications system of Figure 1. In Figure 8A, the signals received in the receiving antenna 150 are they pass through a band pass filter 152 before being amplified in a low noise amplifier 154. The output of the amplifier 154 is then passed through an additional bandpass filter 156 before being further amplified by an additional low noise amplifier 158. The output of the amplifier 158 is then passed to a mixer 164 where it is mixed with a signal generated by a controlled voltage oscillator 162 which responds to a synthesizer 160. The output of the mixer 164 is then passed through the L / Q modulator (166) and a low pass filter 168 before being passed to an analog-to-digital converter 170. The digital output of the converter 170 A / D at 2.56 MC / s is then passed to a correlator 178, to which the same Rademacher-Walsh and PN codes used during the transmission are applied by a generator 172 of RW code (corresponding to the generator code RW 112) and a PN code generator 174 (corresponding to a PN 114 code generator), respectively. The output of the correlator 178, at 160 KS / s, is then applied to the correlator 179, wherein no superimposed code used in the transmission step to encode the signal is applied to the signal by the superimposed code generator 181. The elements 170 , 172, 174, 178, 179 and 181 form a CDMA demodulator. The output of the CDMA demodulator (in the correlator 179) is then at a rate of either 160, 80 or 40 KS / s, depending on the superimposed code applied by the correlator 179. The output of the correlator 179 is then applied to a decoder 180. Viterbi. The output of the Viterbi decoder 180 is then passed to a raised extractor 182 to extract the information from the raised channel. If the signal refers to call data, then the output from the overhead extractor 182 is then passed through the TDM decoder 183 to extract the call data from the particular time slot into which it is inserted by the CT TDM encoder ( 105). Then, the call data is passed through a codee 184 and a hybrid circuit 188 to an interface such as a two-wire interface 190, where the resulting analog signals are passed to a telephone 192. As mentioned at the beginning in In relation to the ST transmission processing steps, the elements 184, 188, 190 may be repeated for each piece of telecommunications equipment 192 in the ST. If the data output by the raised extraction circuit 182 is data via a downstream control channel, then instead of passing that data to a piece of telecommunications equipment, a control logic 185 is passed through the switch 187. of call, where that data is interpreted by the ST. At the subscriber terminal 20, an automatic gain control stage is incorporated in the IF stage. The control signal is derived from the digital portion of the CDMA receiver using the output of a signal quality estimator. Figure 8B illustrates the signal reception processing steps as configured in a central terminal 10 in the telecommunications system of Figure 1. As will be evident from the figure, the steps of signal processing between the RX antenna (150) and the raised extraction circuit 182 are like those within the ST discussed in connection with Figure 8A. Nevertheless, in the case of the CT, the call data output from the high extraction circuit is passed through the line 189 to the network interface within the CT, although the control channel data is passed through the switch 191 to the motor DA (380) for processing. The DA engine is discussed in more detail later. The superimposed codes and the channeling planes are selected to ensure a signal orthogonality ie, in a suitably synchronized system, the contribution of all channels except the channel being demodulated add up to zero by the correlator integration period. In addition, the ascending energy is controlled to maintain a constant energy per bit. The exception to this is a low speed which will be transmitted to the same energy as a fourth speed signal. Table 2 below illustrates the superimposed codes used for full, half and quarter speed operations: TABLE 2 In preferred embodiments, a 10 kb / s acquisition mode is provided which uses concatenated overlays to form an acquisition overlay; this is illustrated in table 3 below: TABLE 3 Figures 9A and 9B are diagrams illustrating the ascending and descending delivery methods, respectively, when the system is fully loaded, and illustrates the difference between the use of overlapping codes illustrated in Figure 9A and the use of TDM as illustrated in FIG. Figure 9B. When overlapping codes are used, an RW code is split in the RW space domain to allow up to four subchannels to operate at the same time. In contrast, when using TDM, an RW code is split in the time domain, to allow up to four signals to be sent using an RW code, but at different times during the 125 us frame. As illustrated in Figures 9A and 9B, the last two codes RW, RW14 and RW15 are not used for data traffic in preferred modes, because they are reserved for call control and acquisition functions; this will be described in more detail later. The CDMA channel hierarchy is as illustrated in figure 10. Using this hierarchy, the following CDMA channels are possible: F1 H1 + H2 H1 + Q3 + Q4 H2 + Q1 + Q2 Q1 + Q2 + Q3 + Q4 Having described how CDMA codes are driven to allow flexible pipelines to be achieved, where bit rates can be reduced to allow more subscriber links to be managed per channel frequency, an overview of how the connection paths will be provided ascending and descending are established with reference to figures 11 and 12.

Figure 11 is a block diagram of downlink and uplink communication path between the central terminal 10 and the subscriber terminal 20. A downlink communication path is established from the transmitter 200 in the central terminal 10 to the receiver 202 at the subscriber terminal 20. An uplink communication path is established from the transmitter 204 at the subscriber terminal 20 to the receiver 206 at the central terminal 10, once the downlink and uplink paths have been established in the wireless telecommunication system 1, telephone communication can occur between a subscriber terminal user 208, 210 and a user receiving the service through central terminal 10 on a downlink signal 212 and a rising signal 214. The descending signal 212 is transmitted by the transmitter 200 of the central terminal 10 and is received by the rec eptor 202 of the subscriber terminal 20. The up signal 214 is transmitted by the transmitter 204 of the subscriber terminal 20 and is received by the receiver 206 of the central terminal 10. The receiver 206 and the transmitter 200 in the central terminal 10 they synchronize with each other with respect to time and phase, and align in the information boundaries. In order to establish the downlink communication path, the receiver 202 in the subscriber terminal 20 must be synchronized with the transmitter 200 in the central terminal 10. The synchronization occurs through the development of an acquisition mode function and an override function. tracking mode in the downlink signal 212. Initially, the transmitter 200 of the central terminal 10 transmits the downlink signal 212. FIG. 12 shows the contents in the downlink signal 212. An information signal in frame 212 is combined with a downlink code. superposition 217 where appropriate, and the resulting signal 219 is combined with a code sequence signal 216 for the central terminal 10 to produce the downlink 212. The code sequence signal 216 is derived from a combination of a signal from 220 pseudo-random noise code and one Code signal 222 Rademacher-Walsh. The downlink signal 212 is received at the receiver 212 of the subscriber terminal 20. The receiver 202 compares its phase and its code sequence with a phase and code sequence within the code sequence signal 216 of the downlink signal 212. The central terminal 10 is considered to have a master code sequence and the subscriber terminal 20 is considered to have a slave code sequence. The receiver 212 incrementally adjusts to the phase of its slave code sequence to recognize a coupling to the master code sequence and place the receiver 202 of the subscriber terminal 20 in phase with the transmitter 200 of the central terminal 10. The sequence The slave code of the receiver 212 is not initially synchronized with the master code sequence of the transmitter 200 and the central terminal 10 due to the path delay between the central terminal 10 and the subscriber terminal 20. Said path delay is caused by the separation geographic between the subscriber terminal 20 and the central terminal 10 and other environmental and technical factors that affect the wireless transmission.

After acquiring and starting the tracking in the central terminal , the master code sequence of the code sequence signal 216 in the downlink signal 212, the receiver 202 enters a frame alignment mode to establish the downlink communication path. The receiver 202 analyzes the frame information within that of the frame information signal 218 of the downlink signal 212 to identify a start of the frame position for the downlink signal 212. Although the receiver 202 does not know at what point in the downstream signal information stream 212 has received the information, the receiver 212 must seek the start of the frame position in order to be able to process the information received from the transmitter 200 of the central terminal 10. Once the receiver 202 has identified another start of the the frame position, the downlink communication path has been established from the transmitter 200 of the central terminal 10 to the receiver 202 of the subscriber terminal 20. The structure of the information radio frames sent in the downlink and uplink paths they will be described with reference to figures 13 and 14. In figures 13 and 14, the following terms are used: Bn Uti charge l of client, 1 x 32 to 2 x 64 kb / s Dn Signaling channel, 2 to 16 kb / s OH Top radio channel - 16 kb / s Traffic mode - 10 kb / s Acquisition / reservation mode Both figures 13A and 13B show a 125us sub frame format, which is repeated in a total radio frame, a frame typically lasts 4 milliseconds (ms). Figure 13A illustrates the radio frame structures that are used in the preferred embodiments for the downward trajectory. The subframe (i) in Figure 13A shows the radio frame structure used for the low speed, 10 kb / s, acquisition mode (Ln-D) during which only the upper channel is transmitted. The subframe (i) in Figure 13A shows the radio frame structure used for the call control channel operating at a quarter speed, 40 kb / s, mode (Qn-D), while the subframe (iii) ) of Figure 13A illustrates the radio frame structure used for traffic channels operating at full speed, 160 kb / s, mode (F1-D). Similarly, the subframe (i) of FIG. 13B shows the radio frame structure used for the upstream path when operating at low speed acquisition or a call control mode (Ln-U). Subframes (ii) to (iv) show the radio frame structure used for traffic channels when operating at a quarter speed mode (Qn-U), medium speed mode (Hn-U), and mode total speed (F1-U), respectively. Now considering the upper channel in more detail, Figures 14A and 14B show the upper frame structure employed for various information speeds. The upper channel may include a number of fields, a frame alignment word (FAW), a code synchronization signal (CS), a power control signal (PC), a maintenance operations channel signal (OMC) , a mixed WTO / D (HDLC) channel (OMC / D) signal, and a channel identifier byte (Ch.lD), and some unused fields. The word box alignment identifies the start of the box position for its corresponding information box. The code synchronization signal provides information for the control synchronization of the transmitter 204 at the subscriber terminal 20 to the receiver 206 at the central terminal 10. The power control signal provides information for controlling the transmission energy of the transmitter 204 in the subscriber terminal 20. The operations and maintenance channel signal provides status information regarding the downlink and uplink communication paths and a path from the central terminal to the subscriber terminal where the communication protocol also extends. operates on the modem shelf between the shelf controller and the modem cards. The OMC / D signal is a combination of the OMC signal and a signaling signal (D), while the Ch. ID signal is used to identify only one RW channel, said Ch. ID signal is used by the subscriber terminal to ensure that the correct channel has been acquired. In the preferred embodiments, the subscriber terminal will receive the downstream traffic channel information at a rate of 160 kb / s. Depending on the speed of channel B, the ST will be located in an appropriate part of the radio head. The following TDM representations are created: TABLE 4 In the previous table, the scheme used to identify a channel is the following. The speed code "F1" indicates the total speed, 160 kb / s, "D" indicates that the channel is a downstream channel, and "Tn / t" indicates that the channel is the multiple time division between the STs, "n "indicates the selected traffic time segment. All the STs that operate in a traffic channel will receive the channel-D channel information at the speed of 16 kb / s. The D-channel protocol includes an address field to specify which ST is used to process the content of the message. The channel structure was illustrated above in Figures 9A and 9B. In the preferred embodiments, the channel structure is flexible but comprises: - At least one link acquisition channel (LAC) - At least one call control channel (CCC) -Typically priority traffic channels (PTC) -1 to 13 traffic channels (TC) The manner in which the pipeline is provided ensures that the above fixed signage provisions using the set of 16 RW codes described above are still supported, as well as the demand for access services that are available when a system is used according to the preferred embodiment. Figures 15A and 15B illustrate typical downstream and upstream structures that may occur in a loaded system according to the preferred embodiments of the present invention. As illustrated in Figure 15A, in the downward path, some signals can be found at 160 kb / s using a total RW channel. An example of such signals may be those sent in the fixed establishment links to products that do not support the CDMA pulses provided by the systems according to the preferred embodiments of the present invention, as illustrated by RW1 and RW2 in Figure 15A . Alternatively, a user may have authority to use an entire RW channel, for example when sending a fax, as illustrated by RW12 in Figure 15A. As illustrated by RW5 through RW11, the TDM can be used in the downstream traffic channels to allow more than one CT to ST communication to be carried out on the same RW channel during each frame. In addition, as illustrated by RW3 and RW4, in the preferred embodiments certain channels can be secured to limit the interference of other nearby cells, as will be described in more detail below. Similar pipelines can be achieved for the ascending paths, but as illustrated in Figure 15B, the overlapping codes are used in place of the TDM to allow more than one ST to CT communication to be carried out on the same RW channel during each frame. (as shown in Figure 15B for RW5 to RW11). It should be noted that, in both Figures 15A and 15B, the channels RW14 and RW15 are reserved as a call control channel and a link acquisition channel, respectively, and the overlapping codes are used in said channels, without taking into account if the trajectory is an ascending or descending trajectory. Said two channels will be described in more detail below. The acquisition / network entry will be carried out through the link acquisition channel (LAC). After power-on, a ST will automatically attempt the downward acquisition of the LAC on a predetermined "home" RF channel. The LAC downstream channel (ie, RW15 in the preferred modes) will operate at 10 kb / s, total single user power. The descending acquisition will be simultaneous for all the STs. Each CT modem shelf will maintain a database that contains the serial numbers within the STs that could possibly be supported by the CT. The status of each ST will be registered with higher level states in the following way: free cold call_in_course Transition states will also be defined. An ST is considered cold if it has just been supplied, the CT has lost control communications with the ST or the CT has completed a cycle. With the LAC, the CT issues individual ST serial numbers and offers an invitation to acquire the uplink signal LAC. The cold ascending acquisition will be carried out in the low speed link acquisition channel. The CT will invite the specific STs to cold start through a control channel. Assuming that an ascending channel is available, the appropriate acquisition overlay will be selected, and acquisition will begin. The "fast" firing of the descending RW channel can be supported at speeds other than Ln-D. Fast refers to that a coherent demodulation is maintained, and only convolutional decoding and the frame synchronization procedures need to be repeated.

In the acquisition, the control information will be exchanged. The ST will be authorized and a short ST-identifier (between 12 and 16 bits) will be placed and used for the subsequent emissions. The ascending ST will operate long enough for the upstream signal to receive the parameters by the ST in terms of code phase and transmission power. These parameters will be used by the ST for subsequent hot start acquisitions and will also be maintained by the TC to allow the CT to force a cold ST for warm start. Upon successfully completing the network entry, the ST will be placed in the free state and instructed to stop the uplink communications and transfer to the call control channel (CCC) (RW14 in the preferred modes). The time taken for the network entry can be monitored and the following techniques can be used to reduce the network entry time if desired: (i) Prioritize, so that network access is first offered to them GOS users high (Degree of Service). (ii) Convert the traffic channels to LACs. (iii) In the case of a CT restart, invite the STs to attempt the warm upward start. A reduction in the network input time of a factor of 4 can be achieved. Said mechanism will need to be safeguarded against the possible deterioration of the parameters of warm upward start, that is, it can only be allowed as long as the related RF CT parameters do not have been modified. The CT will need to issue an ID to allow a ST to validate that the warm upward parameters were valid for that TC. (iv) Restart ST, the TC will save the copies of the warm start parameters of ST, so that a cold ST can have warm start parameters loaded in the acquisition invitation and then be instructed at warm start. After the network entry, all the STs listen to the CCC. Said channel issues the administration and call control information through a HDLC channel of 32 kb / s. In order to maintain communication management, the TC interrogates each ST in sequence. Each interrogation comprises an invitation to issue for a ST issued to acquire the ascending CCC followed by an information management exchange (authorization, ST alarm update, warm start parameters, ascending radio development information, etc.). Administration may fail due to any of the following reasons: (i) The ST has reduced energy or has been reduced. An EM alarm can be indicated if the above persists and the database so that the ST should be marked as cold. Immediately after, follow the network entry procedure. (ii) The ST is making a call or in the procedure of making a call. You can suspend the interrogation cycle and the management communications made in the appropriate traffic channel. When the administration interrogation fails, it must be followed by a number of rapid interrogations until the ST responds or is cold. The CCC is required to transmit all copies of the invitations to acquire the LAC, so that an ST can be forced to acquire the ascending LAC.

Upstream acquisition procedure of traffic channel The basic procurement procedure of the lateral ST is as follows; (i) Turn on the ascending circuit (receiver) at a speed of 10 kb / s and select the appropriate traffic channel RW and superimposed codes. Acquisition of ascending CT is limited to achieving frame alignment. (ii) The ascending PC / CS channel will be decoded to create a busy / free indication. If the PC / CS reports busy, then it means that another ST is using that traffic channel and the ST aborts the acquisition procedure. (iii) Turn on the uplink signal at a rate of 10 kb / s, and select the appropriate RW traffic channel and overlapping codes. Allow the ST transmitter to be at a nominal total speed energy level minus 18 dB. Although the PC / CS reports free, the ST will continue its fast ascending code search, passing the ascending energy level by +2 dB at the end of each search. The rising signal must acquire a nominal total speed energy minus 6 dB. Upstream acquisition is aborted if the maximum transmission level is reached and the PC / CS continues to report free. (iv) PC / CS reports busy. At this point the ST may have genuinely acquired the traffic channel, or instead may be observing that the PC / SC is busy because another ST has acquired the traffic channel. The ST sends an authentication request and responds with its ST-identifier. The CT guarantees upward access to return the ST-identifier. The ST aborts the acquisition procedure if the returned ST-identifier is not recognized (that is, it is not the ST-identifier that was sent). Said authentication procedure is arbitrary between the two STs that contend for the exit access and also prevents the STs from acquiring the TCs that have been reserved from the entry access.

Incoming call A number of TCs will be reserved for incoming calls, and the incoming call processing is as follows: (i) Verify the CT database - if the ST is in the current call status, the call will be denies. (ii) Verify that an ascending CT of the required bandwidth is available. If there is a bandwidth then a TC is reserved. (iii) An incoming call setup message is issued through the CCC to inform the ST of the incoming call and specify the TC on which the call is received. If the TC is not available but the TC is part of a service domain, then the incoming call reception message is sent with a null TC, otherwise the call is rejected. The service domains will be described in more detail later. The incoming call reception message is repeated a number of times. (iv) The ST tries the upward acquisition. The ST hears the downward signal and continues to attempt upward acquisition until the CT sends a message to the ST to return the ST to the CCC. The ST also runs a counter to return it to the CCC in case an incoming call is not completed. (v) In the successful ascending acquisition, the CT gives authenticity to the ST. (vi) In the direction of speed originates from the CT modem. A command is measured by the PC / CS to turn the signal down to the required bandwidth. The ST returns to the speed start command via the ascending PC / SC. The link is now of the required bandwidth.

Outgoing call Outgoing calls are supported by allowing slotted random access to TC up signals. The processing of the outgoing call is as follows: (i) The public CT "free list" of available traffic channels and priority traffic channels with their respective bandwidths. These lists are published periodically (in the preferred modalities, every 500 ms) and are used to mark the ascending access slots. (ii) An off-hook condition is detected by the ST. The ST initiates a call set-up counter. (iii) The ST waits for the following free list that will be received at the CCC. If the free list is empty, the outgoing call is blocked. The ST will generate a congestion tone. (iv) If the free list has available channels, the ST randomly selects a channel from the free list. The algorithm that the ST uses to select a channel will need to be specified in the free list. For example, it may be necessary for the ST to always select from a channel pool of minimum bandwidth so that the bandwidth channels remain available for high GOS users. Alternatively, the ST can select any channel independently of the bandwidth for minimum blocking. In the preferred modes, the STs will not select the low band amplitude channels and negotiate the rate increase. (v) The ST attempts the ascending acquisition in the specified TC, said procedure having been described previously. If the acquisition is successful then the outgoing call is processed. Otherwise, the ST returns to the CCC and waits for the next free list available. To avoid a number of STs attempting respectively to acquire the same TC, and to block each other, an appropriate protocol can be employed to govern the way in which the individual STs will act upon receiving the free list. (vi) The ST may not be able to acquire a TC for the time in which the call establishment counter expires. The ST can in such cases stop trying the outgoing access and generate the congestion tone.

Outgoing priority call It is recognized that the random access protocol used to establish normal outgoing calls can lead to blocking. In the preferred embodiments, access to a priority traffic channel is allowed, which is not blocked to a large extent. The priority call is complicated because the ST must: (i) Capture and decode the dialed digits. (I) The digits are regenerated when a blocking condition occurs. (iii) Allow transparent network access in a non-blocking condition. (iv) Classify all outgoing calls as priority or normal, so that normal calls are discarded in favor of priority calls. The priority call procedure in the preferred modalities is as follows: (i) The TC will publish directory numbers (DNs) for an emergency service number in the CCC. (ii) The ST will attempt upstream access according to the normal algorithms. If the outgoing access is successful then the client can dial as normal. All the marked digits are checked against the list of Emergency DN, so calls can be classified as normal or priority in the CT. (iii) If the congestion tone returns, the customer can dial the emergency number on the ST. If the ST detects an emergency DN sequence then upward access is attempted through the priority traffic channel (PCT). (iv) In the acquisition of the PTC, the ST is based on the digit sequence marked for the CT to mark in the PSTN. (v) The CT converts the PTC to a TC and embeds another TC to convert it to PTC, discarding a normal call in progress if necessary.

Interference limit (background size) In a large-scale cell deployment, optimal capacity is achieved by keeping radio traffic to a minimum while maintaining an acceptable degree of service. The lowest possible radio traffic results in improved "vehicle to interference" ratios (C / l) for users within the cell of interest and for co-channel users in nearby cells. The C / I ratio is a measure (usually expressed in dB) of how the previous high interference of the transmitted signal needs to be decoded effectively. In the preferred embodiments, the central terminal is provided with the commercial traffic capacity for C / l, thus enabling less-rigid network planning to be carried out. Said feature can be carried out by a system using the CDMA as in the preferred embodiments of the present invention, and it is a benefit that the CDMA offers through the TDMA and FDMA systems. In the preferred embodiments, the CT will control the number of traffic channels to minimize access noise. The TCs are classified as: (i) Busy - carrier traffic; (ii) Access, incoming (access_input), reserved for incoming access; (iii) Access, outgoing (outbound access) - reserved for outbound access - so that the TCs appear in the free list; (iv) Priority - reserved for outgoing priority access - so that the TCs appear in the free list. (v) Free - available for any purpose; and (vi) Blocked - not available due to limiting interference. Such a classification scheme is illustrated in Figure 16. The TC will place the traffic based on the following: (i) The TC will monitor the times of establishment of incoming and outgoing calls and will convert the access of TCs from the free TCs to achieve a required degree of service. (ii) When a call is established, a TC access is converted to a busy TC. If a free TC is available, it will be converted to a new TC access. If there are no free TCs then the TC access is lost until the call is cut off. (iii) When the call is cut off, the busy TC becomes a free TC. If a previous call establishment results in a lost TC access then the occupied TC becomes again a TC access. (iv) When the PTC is accessed, a new PTC is created by converting a free, Access or Busy TC (normal call). (v) The CT shall monitor the soft down and uphill error counts of busy CT in an attempt to establish link quality. If the CT registers a soft error count below the average and the long call set-up times are being recorded, a locked TC can be converted to a free TC. Conversely, if the CT records a higher than average soft error count, a free or access TC can be converted to a blocked TC. Figure 17 illustrates how the central terminal performs the above interference limiting function. When the incoming call information arrives at a central terminal modem 320, the encoder 325 codes the information for transmission on the wireless link 300 to the subscriber terminal 20. At the subscriber terminal 20, the decoder 326 decodes the information, and passes the decoded user information through line 328 to the subscriber's telecommunications equipment. As the decoder 326 decodes the information, it is possible to establish an estimate of bit error rate (BER) associated with the signal transmission on the wireless link 300, which can be passed to the multiplexer 332 to be combined with other signals, such as those of a call control function 336 or online user information 338, before going to a decoder 334. At this point, the BER estimate is decoded and passed through the OMC channel on the wireless link 310 to the decoder 340 within the mode at the central terminal 320. Once decoded by the decoder 340, the signal passes to the multiplexer 345, where the BER estimate of the subscriber terminal is detected and passed through the line 355 to the function of dynamic fundo size 360. In addition, as in the subscriber terminal 20, the decoder 340 in the mold in the central terminal 320 can be established an error rate estimate of bit 35 0 associated with the signal transmission on the wireless link 310. Said estimate of BER 350 also passes through the line 355 to the dynamic background size function 360. The dynamic background size function 360 is provided on the shelf of CT modem 302, and receives the BER estimate of each of the modems of said ledge indicated by the lines that enter the bottom of the function of the dynamic background size 360. In addition to the BER estimates, the Service grade "GOS" is obtained from two sources. First, at each subscriber terminal 20, the call control function 336 will observe the ease of being able to establish traffic channels to transmit and receive information, and from the previous one a GOS estimate can be provided to the multiplexer 332 to be decoded. by the encoder 334 for subsequent transmission with the wireless link 310 to the central terminal modem 320. At this point, the GOS estimate is decoded by the decoder 340, passes through the multiplexer 345, and then the GOS estimate goes to through line 355 of the dynamic background size function 360. Additionally, the incoming call information to the central terminal, other than the call information of the subscriber terminal 20 connected to the central terminal, is provided through the concentrated network interface 390 towards the DA 380 engine. The DA 380 engine includes a call control function, similar to the call control function ada 336 at each of the subscriber terminals 20, for each of the modems on the modem shelf. At this point, in a similar form to the call control function 336 at the subscriber terminals 20, the call control functions in the DA 380 engine can also provide GOS estimates for incoming calls, and said GOS estimates pass. through line 395 to the dynamic background size function 360. In the establishment, the 370 administration systems in the element manager will have connected to the central terminal, and will have provided the dynamic background size function 360 in the modem ledge with the information identifying a BER target, a GOS target and a background size limit (that is, the number of channels that can be used for information traffic). The dynamic background size function 360 then compares said administration system information with the actual BER, Real GOS, and the actual background size information it receives. A suitable algorithm can be provided in the dynamic background size function 360 to determine, based on said information, whether the background size is suitable. For example, if the actual bit error rate exceeds the target SEE provided by the management system 370, then the dynamic backfill function 360 may be arranged to send a request for the size of the fund to the demand allocation engine 380 The demand allocation engine 380 provides a modem that can send signals through lines 400 to each of the modems on the CT modem shelf. If the dynamic background size function 360 has required the DA 380 engine to perform a background size, then the DA 380 engine can disable one or more of the modems, thereby causing interference, and therefore that the real BER is reduced. In addition to being used to limit the interference, the DA engine is also responsible, in the preferred embodiments, for providing the coders 325 with instructions by which series of superimposed codes or how many TDM slots are to be used for the signals to be transmitted to STs. The dynamic background size function can store the BER and GOS information received in storage 365, and periodically can pass said information to the administration system 370 for analysis. In addition, if the system is not able to achieve the target BER or GOS with the assigned background size, the dynamic background size function can be arranged to place an alarm in the administration system. The reception of said alarm will indicate to the personnel using the administration system that manual intervention may be required to remedy the situation, that is, through the provision of other central terminal hardware to support the STs. The CDMA approach used in the preferred modes shows the property that the removal of any of the orthogonal channels (by disabling the modem) will improve the resistance of the other channels to interference. At this point, a suitable approach for the demand allocation engine 380, to receive the background size request of the dynamic size function 360, is to disable the modem that has the least traffic passing through it.

RF channel ignition In the preferred modalities, it has been observed that if an ST allows operating from more than one CT / RF channel modem shelf then the following benefits can be achieved: (i) Fault tolerance - if a fault occurs CT modem shelf subsystem an ST can turn on an alternate frequency for service. (ii) Call blocking - a denied ST service of a CT ledge may select to turn on an alternative frequency for service. (iii) Traffic load balancing - the element manager can, based on the call blocking statistics, select the movement of the STs between the CT shelves. (iv) Frequency diversity - in the presence of selective channel fading (slow multipath) an ST can operate on the frequency channel that offers superior signal strength and lower soft error count. RF channel ignition is only possible where there are two or more co-localized CT shelves serving the same geographic area in different RF frequency channels within the same RF band. A deployment that meets these criteria can be configured as a "service domain". Possible deployment scenarios are illustrated in Figure 18. Figure 18 (i) shows an arrangement where the obnidirectional antennas are used to provide the total cell with four frequency channels, i.e. F1, F4, F7, F10. Figure (ii) shows an arrangement where the sectioned antennas are used to provide six separate sectors in a cell, each sector being covered by two frequency channels. Figure 18 (iii) shows an alternative arrangement where three sectioned antennas are used to divide the cell into the three sectors, each sector being covered by a separate frequency channel, and then an obnidirectional antenna is used to provide an "umbrella" cover "for the total cell, said cover using a frequency channel different from the three frequency channels used by the sectioned antennas. In order for the system to work effectively, the STs must be able to turn on the channels quickly, and the rapid channel start-up requires the synchronization of the CT ledge to be provided at the following levels: (i) CDMA PN code. This code preserves the ascending code phase in the RF channels during warm start; and (ii) RF vehicle frequency. This frequency eliminates the need for the coarse frequency to seek a downstream RF channel ignition. In the installation, an ST will be programmed with an RF channel and a PN code, these codes specify the initial domestic channel of the ST. The manner in which channel ignition is facilitated in the preferred embodiments will be described with reference to Figures 19A and 19B. A service domain controller 400 is preferably provided to act as an interference between the exchange connected to the service domain controller in the path 405 and a terminal number and exchanges 10 connected to the service domain controller in the paths 410. The central terminals connected to the service domain controller form a "service domain" of terminal and exchanges that can be used by a subscriber terminal 20 for the control of communications. In the preferred embodiments, the service domain controller is used to provide each CT 10 with adequate information about the other CTs in the service domain. Each TC may then issue a "service domain" message comprising an RF frequency list and CT identifiers that form a service domain to be used by the CTs for the subsequent RF firing functions. The ST then stores that information for future reference when a link is established with one of the CTs. It is preferable for each TC to issue the service domain message, since an ST can be listed in any of the CTs at the time the message is issued. Each CT database contains one entry for each ST located in the service domain. Each database entry describes how the TC observes its relationship with the ST and can be marked as: (i) Primary service provider - the TC is the domestic channel of the STs. All management communication with a ST is done through your domestic CT. (I) Provision of security service - the TC provides a service to the ST. (iii) Available for security service - the TC will provide the service to the ST if required. It should be noted that the ST does not need to turn on a completely different CT, from its place it can light a different CT ledge (and therefore a different RF frequency channel) in the same CT. However, in the preferred embodiments, the ST will typically fire with a different CT, although some errors experienced by a CT ledge may also affect other ledges within the same CT, and therefore for fault tolerance (described in more detail below), it is preferable for the ST to light a separate CT. The consistency of the database on CT shelves is preferably supported by the service domain controller.400. The database consistency needs to be in real time, so that an ST that enters the network can immediately have full access to the service domain (the service domain message is issued to all STs, and thus a new ST will wait for access through the total service domain). Incoming access using security CTs requires that some function be provided to issue duplicate incoming call security messages to all CTs that make up a service domain. Preferably, the above is controlled by the service domain controller 400, which sends the incoming call setup messages to each TC operating in the service domain. All CTs will place the access access traffic channels and will delay the incoming call establishment message through the call control channel. If the upstream access is successful, a TC will respond to the service domain controller with an accepted call message, the other CTs will respond with the call setup messages with failure. Outbound access through a security CT is similar to normal outbound access. Another job that can be carried out by the service domain controller is to help the element manager 58 in the reconfiguration of the equipment in the case of a failure. For example, if a CT is taken out of commission because of a failure, a different CT can be put "online", and the service domain controller can provide the new CT with the necessary information about the other CTs in the service domain. Figure 19B illustrates said elements of the subscriber terminal used to implement the RF channel ignition. The radio subsystem 420, which incorporates the transmit and receive signal processing steps, will pass any information received in the call control channel on line 425 to the message decoder 430. If the decoder 430 determines that the information in the call control channel it forms a service domain message, then it passes through the line 435 to the channel selection controller 440, wherein the information within the service domain message is stored in the storage 445. Similarly, if the message decoder identifies the information as "a free list", identifying the available traffic channels at a particular RF frequency, then that information is passed to the call control function 336 and the controller selects the channel 440 through path 450. The call control function 336 stores the free list in storage 445 for the us or subsequent by the call control function 336 and the channel selection controller 440. If the message decoder 430 determines that the information forms an incoming call set-up message, then that information is supplied on line 455 for the function call control 336 and the channel selection controller 440 for processing. The incoming call setup message typically specifies a TC on the current frequency channel that should be used to access the incoming call, and the channel selection controller will attempt to establish a link on said TC. The channel selection controller will instruct in such cases the radio subsystem 420 on line 465 to use the current frequency channel to establish the required link. On the other hand, if the traffic channel specified in the call setup message is "null" the channel selection controller has the option of changing the RF frequency using the information stored in the storage 445 about the other CTs in the service domain. To allow the controller that the selection controller 440 receives the information about the state of links, a link operation status signal may be supplied through line 470 from the radio subsystem. This signal will give an indication of the radio link quality, and may be a simple "OK" or "fail" indication, or alternatively may include extra information such as the BER values for the link. Said information can be used by the channel selection controller to determine whether or not a particular frequency channel should be used. To allow the call control function to specify a specific access_output channel for outgoing calls, a line 460 is provided between the call control function 336 and the channel selection controller.440. The call control function 336 may select an output access channel from the free list in the storage 445 and instruct the channel selection controller through the line 460 to attempt the acquisition of said channel. The following examples indicate how the structure described above can be used to carry out the channel ignition in particular circumstances.

RF channel ignition for fault tolerance If an RF channel suffers complete loss of the downlink signal, the following procedure takes place in the preferred modes: (i) The ST will attempt to reacquire the downlink signal for a period of 20 seconds. (ii) If the acquisition fails, the channel selection controller 440 of the ST will select the next available channel of the service domain information in storage 445 and will try to acquire the downstream signal. Said procedure will be repeated until the downward signal is acquired. (iii) Once the security RF channel is located, the ST "will wait" on the call control channel and may subsequently be in the granted traffic access. (iv) If the CT failure persists, EM 58 may use the service domain controller 400 to reconfigure the service domain so that the operating CT shelves become primary service providers for the "depleted" STs background. " A failure that does not result in the complete loss of the downstream signal will not result in the "mass" RF channel turning on. Ind, a failure can result in excessive or total call blocking, as described below.

Switching on the RF channel for call blocking If the incoming access traffic channels are blocked, the following procedure is used in the preferred modes: (i) The call set-up message sent through the call control channel will specify a TC in which to access the call. (ii) In the event that incoming access is blocked, the TC will specify a null TC. The channel selection controller 440 of the ST will in these cases change to the next RF channel from the service domain information in the storage 445 and monitor the call control channel. (iii) If the ST receives a call setup message with a valid TC, then the call is processed as normal. (iv) When the call is cut, the downward signal ST preferably changes back to home CT. If the outgoing access traffic channels are blocked, the following procedure is used in the preferred modes. (i) The ST regis a hanging. The free list in the storage 445 is verified and if a traffic channel is available then the call control function 336 secures an online channel request 460 to the channel selection controller 440 and normal upstream access is attempted. (ii) If the free list does not show available access_out channels in the current frequency channel, then the channel selection controller will be used to change the ST to the next RF channel in the service domain, where the ST will wait by the following free list. (iii) When the ST finds a free list with an available access_out channel, then the upstream access is attempted and the call is processed as normal. (iv) When the call is cut off, the downward signal ST preferably changes back to the domestic CT.

Change of RF channel for the traffic load balance The traffic load balance, in the preferred modes, is provided by the static configuration through EM 58. The call blocking and the establishment time statistics can be distributed to the EM where an operator can decide the movement of one ST to another RF channel.

Change of RF channel for frequency diversity. The frequency diversity, in the preferred embodiments, is provided with the static configuration through EM 58. The radio link statistics can be distributed to the EM where an operator can decide the movement of one ST to another RF channel. Although a particular embodiment has been described herein, it will be appreciated that the invention is not limited thereto and that various modifications and additions may be made thereto within the scope of the invention. For example, various combinations of the features of the following dependent claims may be made with the features of the independent claims without departing from the scope of the present invention.

Claims (29)

NOVELTY OF THE INVENTION CLAIMS

1. - A wireless telecommunications system comprising one or more cells, each cell comprising one or more central terminals and a plurality of subscriber terminals, one or more central terminals arranged to provide a plurality of frequency channels in which the wireless links are they can be established by connecting a subscriber terminal with one or more central terminals, characterized in that at least one or more of the central terminations comprises: means for generating for a selected subscriber terminal a prioritized list of frequency channels in which the wireless links connecting the subscriber terminal with one or more central terminals, the prioritized list identifying a domestic channel for the subscriber terminal and at least one other channel of said plurality of frequency channels; a transmitter for transmitting the prioritized list of frequency channels to the subscriber terminal; and characterized in that the subscriber terminal comprises: a receiver for receiving the prioritized list of frequency channels; a storage to store the prioritized list of frequency channels; the acquisition of a logical link to search for the establishment of a wireless link to a domestic frequency channel specified in the prioritized list; a selector that responds to the logical link acquisition that is unable to establish the wireless link, to select an alternative frequency channel from the prioritized list; the logical link acquisition available to look for the establishment of the wireless link in the alternative frequency channel selected by the selector.

2. A wireless telecommunications system according to claim 1, further characterized in that one or more central terminals are arranged to provide a plurality of frequency channels in at least one sector of the cell in which the wireless links can be established connecting a subscriber terminal with at least one sector with one or more central terminals.

3. A wireless telecommunications system according to claim 2, further characterized in that the cell has at least one central terminal with an antenna arrangement for providing said sector with a plurality of frequency channels.

4. A wireless telecommunications system according to any of the preceding claims, further characterized in that the cell has a plurality of central terminals, each central terminal providing at least one frequency channel, and each central terminal providing at least one channel of different frequency in at least one frequency channel provided by the other central terminals of the cell.

5. A wireless telecommunications system according to any of the preceding claims, further characterized in that the subscriber terminal can establish wireless links with a plurality of central terminals that form a service domain, the prioritized list identifying the frequency channels for each central terminal in the service domain in which the wireless links connect said central terminals and the subscriber terminal can be established.

6. A wireless telecommunications system according to any of the preceding claims, further characterized in that the logical link acquisition tries for a predetermined time to establish a wireless link in the frequency channel, and if the predetermined time elapses without having been Once the wireless link is established, the logical link acquisition asks the selector to select an alternative frequency channel from the prioritized list.

7. A wireless telecommunications system according to any of the preceding claims, further characterized in that each frequency channel comprises a plurality of octagonal channels, and the subscriber terminal is arranged to be heard on a predetermined channel of the orthogonal channels of the domestic frequency channel for a signal indicating a free list, the free list identifying the orthogonal channels available within the frequency channel for call control in the case of an outgoing call, the logical link acquisition being arranged to establish a wireless link in said domestic frequency channel if the free list identifies that an orthogonal channel is available , but if not, the selector is arranged to select an alternative frequency channel from the prioritized list, and the logical link acquisition to establish a wireless link on said alternative frequency channel if a free list associated with the alternative frequency channel identifies an orthogonal traffic channel available e for control of the outgoing call in the alternative frequency channel.

8. A wireless telecommunications system according to any of the preceding claims, further characterized in that each frequency channel comprises a plurality of orthogonal channels, and the subscriber terminal is arranged to be heard in a predetermined channel of the channel's orthogonal channels of domestic frequency for a signal indicating that an incoming call is routed to the subscriber terminal, the signal identifying whether or not the orthogonal traffic channel is available in the domestic frequency channel for control of the incoming call, the acquisition of logical link being arranged to establish a wireless link in said home frequency channel if an orthogonal traffic channel is available, but if not, the selector is arranged to select an alternative frequency channel from the prioritized list, and the logical link acquisition is you have to establish a wireless link in said alternative frequency channel if there is an orthogonal traffic channel available for control of the incoming call in the alternative frequency channel.

9. A wireless telecommunications system according to claim 8, further characterized in that, at the end of the incoming call, the subscriber terminal returns to the listening position in the predetermined orthogonal channel of the domestic frequency channel.

10. - A wireless communication system according to any of the preceding claims further characterized in that at least one or more central terminals are arranged to be part of a plurality of central terminals forming a service domain of a wireless telecommunications system, and comprises a storage to store information about the other central terminals in the service domain, the means to generate being arranged to refer to the storage when the prioritized list is generated.

11. A wireless telecommunications system according to claim 10, further characterized in that at least one of the central terminals further comprises a receiver for receiving from the service domain controller information about the other central terminals in the service of domain, such information stored in storage.

12. A wireless telecommunications system according to claim 11, further characterized in that the storage is also arranged to store a database that is identified for each subscriber terminal in the service domain, with the central terminal being the central terminal primary for the subscriber terminal, or that the central terminal is arranged to provide a security service to said subscriber terminal.

13. A central terminal for use in a wireless telecommunications system according to any of the preceding claims, comprising: means for generating a selected subscriber terminal a prioritized list of frequency channels in which wireless links can be established which connect the subscriber terminal with the central terminal; and a transmitter for transmitting the prioritized list of frequency channels to the selected subscriber terminal.

14. A subscriber terminal for use in a wireless telecommunications system according to any of claims 1 to 12, containing: a receiver to receive the prioritized list of frequency channels; a storage to store the prioritized list; the acquisition of a logical link to search for the establishment of a wireless link in the domestic frequency channel as specified in the prioritized list; a selector that responds to the logical link acquisition, being unable to establish the wireless link to select an alternative frequency channel from the prioritized list; the logical link acquisition being arranged to look for the establishment of the wireless link in the alternate frequency channel selected by the selector.

15. A method of establishing a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, at least two frequency channels being provided where the wireless link can be established, the method comprising the steps of : (a) generate a prioritized list of at least two frequency channels, in which a frequency channel is identified as a domestic channel; (b) transmit the prioritized list from the central terminal; (c) receive the prioritized list at the subscriber terminal; (d) store the prioritized list; (e) using a selector to select the domestic frequency channel from the prioritized list in said storage; (f) establishing a wireless link in the frequency channel selected by the selector; (g) if in said step (f), said wireless link can not be established, use the selector to select an alternative frequency channel from the prioritized list, and repeat step (f) using said alternative frequency channel.

16. A method according to claim 15, further characterized in that the subscriber terminal can establish wireless links with a plurality of central terminals forming a service domain, and the method further comprises the steps of: identifying the frequency channels for each central terminal in the service domain in which the wireless links connecting said central terminals and said subscriber terminal can be established; and employing said step (a) to generate the prioritized list of said frequency channels.

17. A method according to claim 15 or claim 16, further characterized in that said step (f) is attempted for a predetermined time to establish a wireless link in the frequency channel selected by the selector, and if the time default passes without the wireless link having been established, said step (g) is carried out to select an alternative frequency channel for those stored.

18. A wireless telecommunications system according to claim 17, further characterized in that a channel selection controller is provided with each of the subscriber terminals in at least one sector.

19. A wireless telecommunications system according to any of claims 15 to 18, further characterized in that the cell has a plurality of central terminals, each central terminal providing at least one frequency channel and each central terminal providing at least one channel of frequency different from at least one frequency channel provided by the other central terminals of the cell.

20. - A method of establishing a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, at least providing two frequency channels in which said wireless link can be established, the method containing the steps : a) store the data identifying at least two frequency channels; b) cooling a selector to select a frequency channel from those listed in said storage; c) establish a wireless link in the frequency channel selected by the selector; b) if in said step c), said wireless link can not be established, repeat said step d) to select an alternative frequency channel, and repeat step c) using said alternative frequency channel.

21. - A method according to claim 20, further characterized in that said data identify one of said two frequency channels as a preferred frequency channel, during a first repetition of said b), as the selector is arranged to select the preferred frequency channel.

22. - A method according to claim 20 or claim 21, further characterized in that the subscriber terminal can establish wireless links with a plurality of central terminals forming a service domain, and the method further comprises the steps of: receiving a message from a central terminal of said service domain that identifies the frequency channels for each central terminal in the service domain in which the wireless links connecting said central terminals and said subscriber terminal can be established; and employing said step a) to store the information received by the receiver.

23. - A method according to any of claims 20 to 22, further characterized in that the step c) is attempted for a predetermined time to establish a wireless link in the frequency channel selected by the selector, and if the predetermined time passes without the wireless link having been established, said step d) is carried out to select an alternative frequency channel from those stored.

24. - A channel selection controller according to claim 1, substantially as described above with reference to the accompanying drawings.

25. - A subscriber terminal according to claim 5, substantially as previously described with reference to the attached drawings.

26. - A central terminal according to claim 12, substantially as before with reference to the accompanying drawings.

27. - A wireless telecommunications system according to claim 15, substantially as previously described with reference to the accompanying drawings.

28. - A wireless telecommunications system according to claim 17, substantially as previously described with reference to the accompanying drawings.

29. - A method of establishing a wireless link according to claim 20, substantially as previously described with reference to the accompanying drawings.