AUTOMATIC CONTROL CHANNEL PLANNING IN ADAPTABLE CHANNEL ALLOCATION SYSTEMS RELATED APPLICATION This application relates to the Norteno Patent Application Na. of Series 08 / 418,682, entitled "Stabil zed Control Channel Planning Using Loosely Couplet, Dedicated Traffic Channels" (Stabilized Planning of Control Channel using Dedicated Traffic Channels of Loose Coupling) and filed on the same date as the present one. BACKGROUND OF THE INVENTION The present invention relates generally to the adaptive assignment of channels in radiocommunication systems and more specifically to automatic control channel planning in systems employing adaptive channel allocation. Several methods have been presented to efficiently use the limited range of frequencies available for radiocommunications. A well-known example is frequency reuse, a technique in which frequency groups are allocated for use in regions of limited geographic coverage known as cells. Cells that contain the same frequency groups are geographically separated to allow users in different cells to simul- taneously use the same frequency without interfering with each other. In this way many thousands of subscribers can
receive service from a system that contains only several hundred frequencies. The design and operation of such a system is described in an article entitled "Advd Mobile Phone Service by Blecher, IEEE Transactions on Vehicular Technology, Volume VT29, No. 2, May, 1980, pages 238-244. The AMPS system is widely known.This system has received from FCC a block of the UHF frequency spectrum subdivided into pairs of narrow frequency bands called channels.There are currently 832 channels of a width of 30 fcHz assigned to mobile communications. Cells in the United States of America A table of the frequencies dedicated to mobile communication in the United States of America is shown in Figure 1. Of the 832 available channels, there are 21 control channels dedicated to each of carrier A and of the carrier B. These 42 control channels provide system information and can not be used for voice traffic, the remaining 790 channels, known as voice channels or of traffic, carry the burden of voice or data communication. Frequency planning is a process by which individual channels are assigned to cells within the network. Currently, the planning is carried out more frequently to prorif ie a fixed frequency plan is
"connected with cables" by each cellular system operator. This is known as fixed channel allocation, or FCA. However, since the interferences and the traffic load vary with time, an FCA has disadvantages in relation to the adaptability of the system. For example, in microwells, picocells, asi. As indoor cellular systems known as PCS, the base stations are located so densely and the environment is so impractical and variable over time (for example the opening of a door changes the conditions of interest), which channel planning becomes almost impossible. Due to the variable nature with the passage of time of the interference, an adaptive scheme can therefore offer significant advantages in regard to this point. The adaptive allocation of channels, or ACA, is a method to dynamically assign frequencies in a cellular system to increase the capacity and adaptability of the system. Under an ACA scheme, more frequencies can be assigned to high traffic cells from less charged cells. In addition, the channels can be assigned in such a way that all the links have a quality s tis cto ia. A common feature of ACA systems is that they assign a chosen channel among a set of channels, which meets some predetermined cavity criteria. However, different schemes
ACA selects channels from the set of channels based on different criteria. The concept of ACA is well known by experts in the field, and its. potential has been described in several pub licitions. For example, "Capacity Improvement by Adaptive Channel Allocation", by Hakan Eriksson, IEEE Global Telecomm. Conf., November 28 - December 1, 1988, pages 1353-1359, illustrates the capacity gains associated with a radio-cellular system where all channels are a common resource shared by all base stations. In the aforementioned report, the mobile measures the quality of the downlink signal, and channels are assigned based on the channel selection with the highest signal to interference ratio (C / l level). B. Riva describes another approach in "Performance Analysis of an Improved Dynamic Channel Allocation Scheme for Cellular Mobile Radio Systems"; (Performance Analysis of an Enhanced System for Dynamic Channel Allocation for Cellular Mobile Radio Systems), 42nd. IEEE Veh. Ten. Conf ,, Denver, 1992, pages 794-797 where the channel is selected based on the achievement of near or slightly better quality than a required C / I humbral. Furuya Y. et al., "Channel Segregation, A Distributed Adaptive Channel Allocation Scheme for Mole Communica ions Systems", (Segregation of
Channels, a Distributed Distributed Channel Allocation Scheme for Mobile Communication Systems), Second Nordic Seminar on Digital Terrestrial Mobile Radio Communication, Stockholm, from October 14 to October 16, 1986, pages 311-315 describe an ACA system where the recent history of link quality is considered as a factor for allocation decisions. In addition, several hybrid systems have been presented where ACA is applied to a small block of sequences in addition to a scheme. FCA. Such an example is presented by Sallberg, K., et al., In "Hybrid Channel Assignment and Reuse Partitioning in a Cellular Mobile Telephone System", (Hybrid Channel Assignment and Rejection Division in Cellular Mobile Telephone System), Proc. IEEE VTC '87, 1 < ? 87, pages 405-411. Apart from increasing system capacity, adaptive channel allocation eliminates the need for system planning. Planning is done by the system itself. This characteristic of ACA is especially attractive when system changes are implemented, when new base stations are added, or when the environment changes, for example due to the construction to demolition of large buildings. The adaptive allocation schemes of channels described above, however, have generally been used only in connection with the allocation of channels of
traffic, and not control channels. Consequently, even though each base station has access to all traffic channels, the assignment of control channels has typically remained a fixed assignment in which each base station employs a certain predetermined control channel or certain control channels predetermined Since the control channels are not assigned in an adaptive manner, the operator must plan these channels geographically, that is, which base obtains which control channel to minimize the amount of inter-channel interference observed in the control channels. Therefore, the advantages of increasing the capacity and adaptability achieved in the ACA traffic channel assignment have not been achieved, in general terms, in relation to the assignment of control channels. Because the control channels have been set for each base station, changes in channel allocation require a costly reconfiguration of the system. However, the operator will not actually have to plan the system only if both the traffic channels and the control channels are assigned automatically. A partial solution to the problems of the fixed assignment of control channels can be provided by means of a system that directly incorporates the assignment of control channels in a conventional ACA scheme. However,
assignments of traffic channels in routines ACA is based on some criteria such as interfrequency example, velocity of < channel, previous channel performance, etc., while the criteria for measuring quality are quite different for the control channels. For example, there is no speed of é; < ito of previous performance for control channels since (1) a control channel can not be successful, and (2) the performance of different control channels can not be compared because this will require the alternative use of each of the control channels. control to obtain an average measurement of performance. This is undesirable since the assignment of control channels must remain reasonably stable. Another problem with the corpora tion of control channels directly in a conventional ACA routine is that the transmission in the control channels is discontinuous and irregular, particularly in the uplink from the mobile to the base, because the numerous mobile stations transmit signals from control over a range of different distances and different power levels. Therefore, the measurements of these discontinuous control signals do not provide a reliable indication to support for ACA decisions. Therefore, the incorporation of control channels directly into a conventional ACA routine is not a desirable solution to
problem presented by the lack of a mechanism to adaptively assign control channels. There is a need in the industry, therefore, for a system and method of automatic planning of control channels in ACA systems that provide reliability and adaptability of systems in the allocation of control channels. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method and apparatus that allows a system employing an adaptive channel assignment < ACA > To assign traffic or voice channels, also automatically plan the control channels. The method can assign control channels using any existing ACA scheme, for example, in AMFS or ADC systems, currently used by an operator for traffic channel assignment. In accordance with exemplary embodiments of the invention, a radio communication system employs a block of control channels in the frequency spectrum to transmit control information between base stations and mobile stations. The system also uses a set of traffic channels to transmit information such as voice information between bases and mobiles. Each base in the cellular system has access to all traffic channels
and to all control channels. Included in the set of traffic channels is a block of dedicated traffic channels, each of which is related to or connected to a particular control channel in the block of control channels. The particular pairing of frequencies of dedicated traffic channel and its associated control channel is the same when these frequencies are rejected. When one of the dedicated traffic channels is reassigned to another base station in accordance with the ACA decision, the associated control channel is reassigned to the same base station. Because the frequency pairing is the same when frequencies are rejected, there is a high correlation between quality in the coupled channels. Accordingly, by an adaptive allocation of the traffic channels dedicated to base stations using an ACA routine, the coupled control channels are assigned in an adaptive manner as well, without directly incorporating the control channels into an ACA routine. The invention thus provides numerous advantages compared to previous radiocommunication systems. For example, both traffic channels and control channels are assigned in an adaptive manner to completely free an operator from the need to plan the system. The benefit of not having to associate in a fixed way control channels with base stations, and the
The resulting capacity to adapt to small changes in the environment, such as new buildings and large constructions, or changes in infrastructure, for example the addition of more base stations in "places of high movement", is of essential importance. This represents a significant advantage in comparison with other systems that use ACA only in traffic channels. Another advantage of the present invention is that it operates by assigning the traffic channels based on measurements of the traffic channels. These measurements are signif icantly more reliable and easier to determine than measurements of the control channels. The invention also offers the benefit of ACA that the system adapts to traffic conditions. Peak traffic conditions can be accommodated by temporarily allocating a greater number of traffic channels in a restricted area. For control channels, this adaptation to a uniform traffic is generally a minor concern. However, the present invention allows the use of more than one control channel in a base when required due to the traffic conditions. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the present invention will be more readily understood when reading
the following detailed description in combination with the drawings in which: Figure 1 is an illustration of the spectrum of frequencies assigned in accordance with the North American standard IS-54Bj; Figure 2 is a diagram of an exemplary network of radiocommunication; Figure 3 is a schematic diagram of an exemplary base and mobile station; Figure 4 is a diagram of traffic and control channels in a frequency spectrum in accordance with an exemplary embodiment of the invention; Figure 5 is a diagram of allocation of traffic channels when no dedicated traffic is in use; and Figure 6 is a mapping diagram of traffic channels when a dedicated traffic channel is in use. DETAILED DESCRIPTION Before describing the details of the present invention, an example of the construction of a cellular radio mobile system in which the present invention can be employed will be described. While the construction shown represents a digital system, those skilled in the art will note that it is also possible to increase the present invention in others.
types of systems such as for example analog systems or in a reasonable way. Figure 2 is a schematic diagram illustrating 10 cells, Cl to CIO, in a cellular mobile radio telephone system. Normally, methods in accordance with the present invention will be implemented in a cellular mobile radio system comprising much more than ten cells. For the purposes of this discussion, the system represented here is considered as an isolated part of a larger system that has been fragmented. For each Cl to CIO cell, there is a respective base station DI to DIO. Figure 2 illustrates base stations located in the vicinity of cell centers and have omnidirectional antennas. The base stations of adjacent cells can, however, be co-located in the. closeness of cell boundaries and have recirculating antennas. Figure 2 also illustrates ten mobile stations MI to MIO, which can be moved within a cell and from one cell to another cell. The method according to the present invention can be implemented in a cellular mobile radio system comprising many more mobile stations than ten. Normally, there are many more mobile stations than this base ion. A mobile switching center MSC, in accordance with what is illustrated in figure 2, is connected to the ten stations
of the base illustrated, for example, by means of cables or by other means such as, for example, radio links. The mobile switching center is also connected by cables or other means, for example, to a public switched telephony network or to a similar fixed network with ISDN capability. Not all the connections of the mobile switching center to the base stations and the connections to the fixed network are illustrated in Figure 2 in order to simplify the illustration. An exemplary base station 110 and a mobile 120 are illustrated in Figure 3. The base station includes a control and processing unit 130 which is connected to the MSC 140 which in turn connects to the public switched telephone network (not I polished). The base station 110 for a cell includes a plurality of traffic or voice channels handled by a traffic channel transceiver 150 controlled by the control and processing unit 130. Also, each base station includes a control channel transceiver 1¿0 that can handle more than one control channel. The transceiver lí >0 of the control channel is controlled by the control and processing unit 130. The control channel transceiver 160 outputs control information in the control channel of the base station or cell to mobiles that are in this channel of control. He
The traffic channel transceiver emits the traffic to speech channels which may also include control channel location information, digital. When the mobile 120 enters the idle mode first, it periodically scans the control channels of the base stations such as the base station 110 to determine which cell to connect to. The mobile 120 receives the absolute and relative information emitted in a control channel such as its traffic channel and control transceiver 170. Then, the processing unit 180 evaluates the received control channel information that includes the characteristics of the candidate cells and determines on which cell the mobile should connect. The received control channel information not only includes absolute information as to the cell with which it is associated, but it may also contain relative information as to other cells near the cell with which the control channel is associated. These adjacent cells are periodically scanned while monitoring the primary control channel to determine if a more suitable candidate exists. In the radio communication system described above, the frequency spectrum in accordance with an exemplary embodiment of the present invention is divided into two parts, a part for the control channels and a part for the control channels.
traffic channels. Figure 4 shows a set 50 of N control channels F_cl to F_cN. With the AfPS and IS-54 systems, for example, a block of 21. frequencies located in a located part of the frequency spectrum can be set aside for such control channels. way that mobiles know where to scan in the frequency spectrum to detect control channels. In accordance with other schemes, the control channels can be placed in channels that are not adjacent to each other and can be located by mobile stations using various mechanisms, for example, by location information transmitted in traffic channels. Those skilled in the art will note that the present invention can be applied to any system in which control channels are employed. Figure 4 also shows sets 60 and 70 of N + M channels used for traffic, including a set 60 of N dedicated traffic channels F_dtl to F_dtN. For example, a block 60 of 21 dedicated traffic channels may be specified somewhere in the channel space, such as adjacent to block 50, even though this particular arrangement is not required. Finally, Figure 4 shows a set 70 of M ordinary traffic channels F_tl to F_tM. Unlike conventional systems, the control channels in accordance with the exemplary modalities of the
invention can be employed by any base station, and no fixed assignment of control channels is made a priori. On the contrary, each control channel is connected or associated with one of the dedicated traffic channels, shown in Figure 4, which results in N pairs of dedicated traffic control channels, F_ci / F_dti, where i is within from a range of 1 to N. The method of assigning frequencies as well as the division of frequencies used for control channels, dedicated traffic channels, and ordinary traffic channels can be the same in all base stations of the cellular system. In addition, the particular frequency matching of each dedicated traffic channel and its associated control channel may be the same in all base stations of the system. Traffic channels, including dedicated traffic channels, can be incorporated directly into an ACA scheme, so they are assigned to base stations in accordance with changing interference conditions, for example. The ACA scheme used for the traffic channels is preferably a distributed scheme, that is, the ACA method uses local information and is carried out in the base stations or in the MSC. When a dedicated traffic channel, for example F_dtl, is reassigned within a block or due to an ACA optimization decision,
the coupled control channel, in this example F_cl, will also be reassigned to the same base station. The invention therefore provides the automatic planning of the control channels through a method of coupling each control channel with a dedicated, associated traffic channel. Such reassignment of a dedicated traffic channel may occur, for example, due to an unacceptably high level of inter-channel interference from a base station that transmits on the same dedicated traffic channel frequency. Because the neighboring neighbor base station employs the same dedicated traffic channel pair and associated control channel, it is also likely that unacceptably high interference on the frequency of the control channel will occur. In other words, because all the control channels in all the bases are coupled in the same way with the dedicated traffic channels in the traffic block 60, ei < There is a great correlation between the level of quality and interference in the coupled channels. Accordingly, it will also be desirable to use the control channel coupled to an assigned dedicated traffic channel, because the dedicated traffic channel has been chosen, for example, because of its low level of interference. Accordingly, the optimization of the dedicated traffic channels in block 60 pair
means of the ACA scheme will automatically optimize the control channels in block 50. In addition, basing the channel allocation decisions on measurements of traffic channels in ez that based on measurements of the control channels, increases the confidence of the system. Since the transmission in the control channels is discontinuous and irregular, par- ticularly in the uplink of the mobile to the base, the measurements of the traffic channels provide a more reliable indication on which ACA decisions can be based. In accordance with an exemplary embodiment, the invention can reduce the occurrence of changes in the assignment of control channels by controlling the selection of dedicated traffic channels by the base station. For example, the use of the dedicated traffic channels in block 60 may be restricted from the way a base only the number of dedicated traffic channels of block 60 as it requires control channels. In most cases, only one control channel per base is required, and therefore one base employs only one of the dedicated traffic channels in block 60. Therefore, if none of the dedicated traffic channels are found in use in a particular base station, the ACA 80 scheme can select only the N channels of
dedicated traffic as a whole, as shown in figure 5. On the other hand, if a dedicated traffic channel is already in use at a particular base station, the ACA scheme can select from only block 70 of M traffic channels ordinary, instead of dedicated traffic channels, as shown in Figure 5. However, during fixed traffic conditions, additional control channels can be assigned to the base station based on which dedicated traffic channels show a low interference level, and the base can then employ additional coupled dedicated traffic channels. The base also typically uses additional traffic channels of the frequency spectrum that are not in the dedicated traffic block 60. Due to the restriction presented above regarding the number of dedicated traffic channels that can be used by a base station in particular, the invention can provide a high refusal factor for dedicated traffic channels of about N, the number of control channels. N is 21, for example, in the IB-54 system and 12 in the BSM system, and may be chosen sufficiently large to ensure an acceptable level of shared channel interference. Because the effective reject factor of the dedicated traffic channels in block 60 is relatively large,
There will be few intracellular transfers of dedicated traffic channels. The opportunity in which a link in the dedicated traffic channel will be reassigned out of a block 60 will also be very infrequent because the dedicated traffic channels generally have a lower shared channel interference than the ordinary traffic channels. The high rejection factor can therefore provide a stable selection of the dedicated traffic channels, that is, most of the time, the same channel of dedicated traffic is chosen. Therefore, the assignments of the control channels, which are coupled to the dedicated traffic channels, are relatively fixed, and are reassigned, generally, for example, only when the system is reconfigured, or in the case in which an additional control channel is required locally. In such cases, the traffic channel can inform all users of the current control channel where to find the new control channel. In general terms, it is desirable that the number of control channels N be relatively large in such a way as to ensure low interference of shared channel. Ordinary traffic channels, on the other hand, may have a much lower cash rejection under heavy traffic conditions in an ACA scheme. For example, in the worst case, all the bases assign all the traffic channels, in
In this case, the rejection factor is only 1. Therefore, since N for the control channels is generally greater than the minimum required rejection factor of the system for all channels including ordinary traffic channels, an additional advantage of The present invention is that dedicated traffic channels can be easily allocated due to their inherently low shared channel interference, that is, because the number of dedicated traffic channels allocated to each cell is limited. In the case of an intercell transfer where the user in the dedicated traffic channel moves to another cell, or in the case in which the user of the dedicated traffic channel hangs up, another user who currently uses a Ordinary traffic channel served by the base can take the place of the user who has left the dedicated traffic block, since at least one control channel will be available per base. This dedicated traffic channel will have a higher probability with a higher performance than the ordinary traffic channel since it has a rejection factor of o. If there are no other users in the cell to which the dedicated traffic channel can be transferred, a fictitious user can be entered. At any time, a control channel must be present in a cell, for example, to
issue cell information, even if temporarily no user is served by this database. When no traffic channel is in use, even a dedicated traffic channel, it is not clear which control channel to assign for this purpose. Therefore, a fictitious user can be introduced. This allows the system to have a channel ready in case it is required. The channel assigned to the fictitious user does not have to be active, but is preferably treated by the ACA routine as a channel to be assigned when a new real user becomes active. As soon as a call is made, the fictitious user becomes a real user. During the time in which there are no users, the environment may change. The ACA scheme can still anticipate this by continuous channel aionitoreo. Each time you can select the best dedicated traffic channel that will be used if a call is required. However, insofar as no call comes in, this process can also be considered as serving a fictitious user. The foregoing description focuses on the features of the present invention. Those skilled in the art will readily appreciate that the present invention can be applied to any ACA scheme, i.e. an adaptive channel assignment based on any selection scheme by quality criteria. Even when these modalities
For example, a fixed set of frequencies assigned to control channel use (for example, the 21 control channels allocated for AMPS and IS-54), will be recognized by those skilled in the art, who will recognize that the present invention can also be applied to systems in the which the frequencies of control channels are not fixed. For example, the digital control channel (DCC) scheme in IS-136 allows the assignment of a digital control channel anywhere in the spectrum. However, since each carrier supporting a DCC also supports two traffic channels in the TDMA scheme 15-136 of three intervals, one of these traffic channels can be coupled to the DCC on the shared carrier. Furthermore, while illustrative embodiments have been described in terms of mobile stations and cellular systems generally, it will be understood that the present invention is applicable to any type of remote device without cable (e.g., PCS, PDA, modems, data terminals, units portable) and any type of system (for example, satellite transmission system, hybrid satellite and ground-based transmission system, indoor system, etc.). The exemplary embodiments described above have the purpose of polishing in all aspects the present invention but not restoring it. Therefore, the
The present invention can be made with many variations in terms of its detailed implementation which can be derived from the description contained herein by a person skilled in the art. All of these variations and modifications are considered within the scope and spirit of the present invention in accordance with that defined in the appended remarks.