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[0001] 1. Filed of the Invention
[0002] The present invention relates to a method and/or a system and/or a device and/or a computer program product for analyzing a cellular wireless communication network of a first type in order to evaluate whether cell sites of the cellular wireless communication network of the first type are usable as cell sites for a cellular wireless communication network of a second type, and/or for evaluating parameters of the cellular wireless communication network of the second type, such as network performance, network dimensioning, optimization parameters, and the like.
[0003] 2. Description of the Prior Art
[0004] In the last few years, an extension of wireless cellular communication networks all over the world has occurred. There exist several different network system solutions such as the European Global System for Mobile communication (GSM), the US equivalent thereof (GSM1900), North American TDMA (IS-54 or IS136), CDMAOne;(IS-95), Japanese Pacific Digital Cellular PDC, and the like, which are used in these wireless communication networks. Additionally, there is also a constant further development of new network system solutions which are planned to supplement or to replace already existing networks. For example, the 3
[0005] For the implementation of the new network system solutions, it is required to place the necessary communication equipment, such as stationary transceiver network elements and the like, at suitable locations. In other words, it is necessary to design, to found and to construct respective cell sites within the areas which are intended by a network operator to be covered with the new network system solution.
[0006] Due to the amount of already deployed sites in existing wireless communication networks, the high costs for the acquisition of new sites for a new system, and the complex and regulated processes for an acquisition of new sites in particular in urban areas, the implementation of such new network system solutions is difficult. Hence, one attractive and increasingly used option for network operators who already have an existing wireless communication network, such as a 2
[0007] As mentioned above, when a 3G UMTS network is considered as an example, a 3G UMTS Radio Access Systems uses WCDMA technology for the air interface. One characteristic of WCDMA technology is that a frequency reuse factor of 1 is used. This means that the same frequency for communication connections is used in adjacent cells (in contrast thereto, for example, in GSM systems a frequency reuse factor of e.g. 3, 4 or 12 is commonly used, i.e. the same frequency can be used in every third, fourth or 12
[0008] Thus, for the design of a new WCDMA system, in particular when it is planned to reuse existing cell cites of, e.g., a former cellular GSM communication network, an assessment of the interference situation is critical for a selection of the sites. The interference as a communication connection parameter is also essential for an estimation of capacity and quality properties of a network to be planned already in advance, namely for example in the form of a so-called other-to-own cell interference ratio.
[0009] Hitherto, a communication connection condition such as the interference situation in a network to be planned is assessed in two different ways. The first way is to simulate a network behavior with a software based radio network planning/simulating tool. The second way is to perform so-called drive tests in which test engineers drive through the network area and measure the behavior by means of special test equipment.
[0010] The first way provides the possibility to study the new network before it is actually deployed. However, for a usable test result, it is necessary to have an accurate propagation modeling and/or calibration, which can normally be achieved only by performing drive tests. However, a residual error after calibrating remains significant. On the other hand, the drive tests according to the above mentioned second way require a deployment of at least some physical parts of the new network or at least some test transmitters in the intended site locations. This results in high costs for the needed extra equipment and also for the test engineers, and is also time consuming.
[0011] In other words, conventional solutions for evaluating of network conditions and for estimating the capacity and quality of a planned 3G network are based on radio wave propagation predictions, which have the risk of being inaccurate, especially in hot spot areas where propagation conditions are almost impossible to simulate, such as in very dense urban areas, indoor areas or in the vicinity of high-rise buildings like in Manhattan or Hong Kong. Even when small-scale measurements like drive tests are used as a complement, there are still problems. Besides their costs, those drive tests can be normally performed only at a limited number of locations. Additionally, only outside and/or very limited inside measurements can be made. Furthermore, it is not possible to gain a realistic image about the behavior of actual service subscribers, such as usage of mobile/stationary terminals, calling from inside/outside, and the like.
[0012] Thus, the present invention provides an improved method and/or system and/or device and/or computer program product for analyzing an existing wireless communication network in order to evaluate a potential of cell sites of this network for a usage in a wireless communication network of another type than the existing one.
[0013] Furthermore, the present invention provides an improved method and/or system and/or device and/or computer program product which enables a reliable and low cost solution for an analysis of an existing wireless communication network and for a planning of a new wireless communication network in the area of the already existing wireless communication network.
[0014] The invention provides a method of analyzing a cellular wireless communication network of a first type, the wireless communication network of the first type comprising a plurality of cells, each cell comprising a transceiver network element for covering the cell and for conducting communications in the cell, wherein each transceiver network element transmits a signal in the wireless communication network of the first type, at least one mobile station located in one cell of the plurality cells and connected to the transceiver network element of the one cell, wherein the mobile station receives and processes the signals from the transceiver network element of the one cell and from transceiver network elements of other cells in range, and at least one network control element controls at least the transceiver network element of the one cell in which the mobile station is located, the method comprising the steps of measuring communication connection condition parameters for the one cell in which the mobile station is located, which communication connection condition parameters are derived from the signals received by the mobile station from the one cell and from a number of the other cells, transmitting the measured communication connection condition parameters to the network control element in the form of mobile measurement reports, processing the mobile measurement reports by using a network analysis functionality associated with the network control element, wherein an indicator related to a predefined communication connection condition of the wireless communication network of the first type is calculated on the basis of information in the mobile measurement reports, and evaluating, on the basis of the indicator, a potential of the one cell for a usage in a wireless communication network of a second type.
[0015] According to one aspect of the invention, the wireless communication network of the first type is a GSM based mobile communication network, wherein the network transceiver element is a base transceiver station element and the network control element is a base station controller, and the wireless communication network of the second type is a 3
[0016] According to further refinements of the method,
[0017] the step of processing the mobile measurement reports further comprises a step of registering the calculated indicator in a statistic, wherein the indicator is assigned to the one cell;
[0018] the measured communication connection condition parameters are received signal levels derived from the signals of the one cell and of the other cells;
[0019] the indicator is a other-to-own interference ratio calculated in accordance with
[0020] wherein i defines the other-to-own interference ratio, RXLEV defines a received signal level, RXLEV
[0021] the other cells to be measured may be determined on the basis of a neighboring cell list;
[0022] the other cells to be measured may be all cells in range for the mobile station;
[0023] each of the mobile measurement reports comprises an identification element for identifying the one cell and identification elements for identifying the signals from the one cell and from the other cells, associated with the measured communication connection condition parameters, wherein the number of the other cells may depend on radio conditions at the time of measurement and/or the location of the mobile station which conducts the measurements for the mobile measurement reports;
[0024] each of the mobile measurement reports comprises selected measured communication connection condition parameters, wherein the selection is based on the strongest measured values for the communication connection condition parameters derived from the signals received by the mobile station from the number of the other cells;
[0025] the step of evaluating the potential of the one cell comprises the steps of determining on the basis of the mobile measurement reports and/or of the indicator whether the one cell fulfills a preset minimum requirement for a usage in the wireless communication network of the second type and indicating on an analysis display whether the one cell is sufficient or insufficient;
[0026] the step of evaluating the potential of the one cell comprises the steps of determining on the basis of the mobile measurement reports and/or of the indicator whether the one cell fulfills a preset minimum requirement for a usage in the wireless communication network of the second type, and, if not, determining and indicating a proposal for optimizing parameters of the one cell so that the preset minimum requirement for a usage in the wireless communication network of the second type can be fulfilled;
[0027] the mobile measurement reports may be obtained for the processing before the network control element, e.g. by using the Abis interface, at the network control element, or after the network control element, e.g. when the network control element forwards the mobile measurement reports to another network element.
[0028] Furthermore, the invention is a system for analyzing a cellular wireless communication network of a first type, the wireless communication network of the first type comprising a plurality of cells, each cell comprising a transceiver network element for covering the cell and for conducting communications in the cell, wherein each transceiver network element transmits a signal in the wireless communication network of the first type, at least one mobile station located in one cell of the plurality cells and connected to the transceiver network element of the one cell, wherein the mobile station receives and processes the signals from the transceiver network element of the one cell and from transceiver network elements of other cells in range, and at least one network control element controls at least the transceiver network element of the one cell in which the mobile station is located, the system comprising measuring means for measuring communication connection condition parameters for the one cell in which the mobile station is located, which communication connection condition parameters are derived from the signals received by the mobile station from the one cell and from a number of the other cells, and for transmitting the measured communication connection condition parameters to the network control element in the form of mobile measurement reports, a processing means for processing the mobile measurement reports by using a network analysis functionality, wherein an indicator related to a predefined communication connection condition of the wireless communication network of the first type is calculated on the basis of information in the mobile measurement reports, and evaluating means for evaluating, on the basis of the indicator, a potential of the one cell for a usage in a wireless communication network of a second type.
[0029] According to on aspect of the present invention, the wireless communication network of the first type is a GSM based mobile communication network, wherein the network transceiver element is a base transceiver station element and the network control element is a base station controller, and the wireless communication network of the second type is a
[0030] According to further refinements of the system
[0031] the processing means for processing the mobile measurement reports further comprises a counter element which registers the calculated indicator in a statistic, wherein the indicator is assigned to the one cell;
[0032] the measured communication connection condition parameters are received signal levels derived from the signals of the one cell and of the other cells;
[0033] the indicator is a other-to-own interference ratio calculated in accordance with
[0034] wherein i defines the other-to-own interference ratio, RXLEV defines a received signal level, RXLEV
[0035] the other cells to be measured may be determined on the basis of a neighboring cell list;
[0036] the other cells to be measured my be all cells in range for the mobile station;
[0037] each of the mobile measurement reports comprises an identification element for identifying the one cell and identification elements for identifying the signals from the one cell and from the other cells, associated with the measured communication connection condition parameters, wherein the number of the other cells may depend on radio conditions at the time of measurement and/or the location of the mobile station which conducts the measurements for the mobile measurement reports;
[0038] each of the mobile measurement reports comprises selected measured communication connection condition parameters, wherein the selection is based on the strongest measured values for the communication connection condition parameters derived from the signals received by the mobile station from the number of the other cells;
[0039] the evaluating means for evaluating the potential of the one cell determines on the basis of the mobile measurement reports and/or of the indicator whether the one cell fulfills a preset minimum requirement for a usage in the wireless communication network of the second type and indicates on an analysis display whether the one cell is sufficient or insufficient;
[0040] the evaluating means for evaluating the potential of the one cell determines on the basis of the mobile measurement reports and/or of the indicator whether the one cell fulfills a preset minimum requirement for a usage in the wireless communication network of the second type and, if not, to determine and to indicate a proposal for optimizing parameters of the one cell so that the preset minimum requirement for a usage in the wireless communication network of the second type can be fulfilled;
[0041] the mobile measurement reports may be obtained for the processing before the network control element, e.g. by using the Abis interface, at the network control element, or after the network control element, e.g. when the network control element forwards the mobile measurement reports to another network element.
[0042] Moreover, these object are achieved, for example, by a corresponding device for analyzing a cellular wireless communication network of a first type, the wireless communication network of the first type comprising a plurality of cells, each cell comprising a transceiver network element for covering the cell and for conducting communications in the cell, wherein each transceiver network element transmits a signal in the wireless communication network of the first type, at least one mobile station located in one cell of the plurality cells and connected to the transceiver network element of the one cell, wherein the mobile station receives and processes the signals from the transceiver network element of the one cell and from transceiver network elements of other cells in range, and at least one network control element controls at least the transceiver network element of the one cell in which the mobile station is located, the device comprising a processing means for processing mobile measurement reports comprising communication connection condition parameters measured for the one cell, in which the mobile station is located, and derived from the signals received by the mobile station from the one cell and from a number of the other cells, wherein the processing means processes the mobile measurement reports by using a network analysis functionality, wherein an indicator related to a predefined communication connection condition of the wireless communication network of the first type is calculated on the basis of information in the mobile measurement reports, and evaluating means for evaluating, on the basis of the indicator, a potential of the one cell for a usage in a wireless communication network of a second type.
[0043] Furthermore, the invention is a corresponding computer program product usable for a data processing unit, comprising software code portions for performing an analysis of a cellular wireless communication network of a first type, the wireless communication network of the first type comprising a plurality of cells, each cell comprising a transceiver network element for covering the cell and for conducting communications in the cell, wherein each transceiver network element transmits a signal in the wireless communication network of the first type, at least one mobile station located in one cell of said plurality cells and connected to the transceiver network element of the one cell, wherein said mobile station receives and processes the signals from the transceiver network element of the one cell and from transceiver network elements of other cells in range, and at least one network control element controls at least the transceiver network element of the one cell in which said mobile station is located, the product, when running on the data processing unit, measuring communication connection condition parameters for the one cell in which the mobile station is located, which communication connection condition parameters are derived from the signals received by the mobile station from the one cell and from a number of the other cells, transmits the measured communication connection condition parameters to the network control element in the form of mobile measurement reports, process the mobile measurement reports by using a network analysis functionality associated with the network control element, wherein an indicator related to a predefined communication connection condition of the wireless communication network of the first type is calculated on the basis of information in the mobile measurement reports, and evaluate, on the basis of the indicator, a potential of the one cell for a usage in a wireless communication network of a second type.
[0044] Moreover, the invention is a method of analyzing a cellular wireless communication network of a first type, the wireless communication network of the first type comprising a plurality of cells, each cell comprising a transceiver network element for covering the cell and for conducting communications in the cell, wherein each transceiver network element transmits a signal in the wireless communication network of the first type, at least one mobile station located in one cell of the plurality cells and connected to the transceiver network element of the one cell, wherein the mobile station receives and processes the signals from the transceiver network element of the one cell and from transceiver network elements of other cells in range, and at least one network control element controlling at least the transceiver network element of the one cell in which the mobile station is located, the method comprising the steps of measuring communication connection condition parameters for the one cell in which the mobile station is located, which communication connection condition parameters are derived from the signals received by the mobile station from the one cell and from a number of the other cells, transmitting the measured communication connection condition parameters to the network control element in the form of mobile measurement reports, storing the mobile measurement reports in a storage device, transferring, after completion of the storing step, a set of the stored mobile measurement reports to a network analysis functionality, wherein an indicator related to a predefined communication connection condition of the wireless communication network of the first type is calculated on the basis of information in the mobile measurement reports, and a potential on of the one cell for a usage in a wireless communication network of a second type is evaluated the basis of the indicator.
[0045] Furthermore, the invention is a system for analyzing a cellular wireless communication network of a first type, the wireless communication network of the first type comprising a plurality of cells, each cell comprising a transceiver network element for covering the cell and for conducting communications in the cell, wherein each transceiver network element transmits a signal in the wireless communication network of the first type, at least one mobile station located in one cell of the plurality cells and connected to the transceiver network element of said one cell, wherein the mobile station receives and processes the signals from the transceiver network element of the one cell and from transceiver network elements of other cells in range, and at least one network control element controlling at least the transceiver network element of the one cell in which the mobile station is located, the system comprising measuring means for measuring communication connection condition parameters for the one cell in which the mobile station is located, which communication connection condition parameters are derived from the signals received by the mobile station from the one cell and from a number of the other cells, and for transmitting the measured communication connection condition parameters to the network control element in the form of mobile measurement reports, a storage for storing the mobile measurement reports in a storage device, and means for transferring, after completion of the storing step, a set of the stored mobile measurement reports to a network analysis functionality, wherein an indicator related to a predefined communication connection condition of the wireless communication network of the first type is calculated on the basis of information in the mobile measurement reports, and a potential on of the one cell for a usage in a wireless communication network of a second type is evaluated the basis of the indicator.
[0046] By virtue of the present invention, the following advantages can be achieved:
[0047] A network operator planning to deploy a new communication network in the area of an already existing communication network is able to obtain measured data about the actual network environment from users of the already existing communication network and to consider them in an network evaluation and planning process. In other words, a large amount of live data is collected in short time and the collected data directly corresponds to an actual user distribution within the cell area. The obtained realistic data leads to accurate and realistic end results in the network evaluation and planning process.
[0048] The live data measured from the actual users of the already existing communication network comprise information which can not or at least is very difficult to obtain or predicted in connection with the conventional network planning and evaluation. For example, the data comprise, at least implicitly, information about where (i.e. whether inside or outside or from moving or stationary locations) calls are most often made in the existing communication network, e.g. by processing the information about from which cell/BTS (indoor or outdoor, and the like) the measurement results are obtained. In particular knowledge about a possible indoor usage of subscriber terminals is, for example, a relevant factor for an estimation of, e.g., a later WCDMA usage pattern. Thus, network planning can be performed more efficiently since the behavior of users of the existing communication network (e.g. GSM) is, in comparison to that what can be achieved with a drive test, a more accurate basis for an estimation of the behavior of users of the communication network to be planned.
[0049] Communication connection parameters in the existing communication network can be achieved by performing live measurements in order to determine, for example, the amount of interference which is received in a cell from neighboring cells. This information is usable to estimate the interference situation, which would be given by a one to one site reuse in the new system. Furthermore, it is possible to identify the most significant contributors to interference. On the basis of this identification and of information concerning the present site deployment in the existing network, detailed recommendations for an optimum deployment strategy for the new network to be planned can be given. Hence, an improved optimization during the planning of the new communication network can be provided.
[0050] Thus, one benefit of the invention is that instead of propagation predictions (with or without complementation by drive tests) the network operator obtains directly measured information, which is also measured at the locations where cellular service users in reality need the services. Furthermore, the invention provides a new way to evaluate suitability of each site of a network of a first type (e.g. GSM) to the deployment on co-sited cell of a network of a second type (e.g. WCDMA). In other words, the invention allows a more accurate form of capacity estimation from existing network deployment and provides an improved pre-launch analysis of the network based on existing network design. In comparison to an evaluation according to the prior art, which is based on computer prediction simulations and/or drive tests, which does not give reliable or overall picture of an actual network situation, the present invention improves the accuracy of the network evaluation process, for example, in areas where a WCDMA is planned on top of GSM and GSM network traffic situation and where interference conditions need to be taken into account. As site acquisition is a challenging process in urban areas due to various regulations and property ownership situation, the present invention is in particular useful in cases where re-using of sites is considered as a preferred solution when building up the new network. The invention helps to reliable identify possible co-location places or sites in this process and saves costs and time.
[0051] The above and still further objects, features and advantages of the invention will become more apparent upon referring to the description and the accompanying drawings.
[0052]
[0053]
[0054]
[0055]
[0056]
[0057] A best mode of carrying out the invention is illustrated in connection with
[0058] In
[0059] According to a preferred embodiment, the wireless communication network of the first type is of a GSM type. The GSM network comprises a plurality of cells A, B, C, D, E, F, G, . . . , wherein each cell comprises a respective base transceiver station (BTS) as a transceiver network element
[0060] In the example shown in
[0061] The BTS
[0062] Connected to the BSC
[0063] It is to be noted that the dashed shown elements (
[0064] In
[0065] The MMRs received from the mobile station
[0066] Furthermore, it is to be noted that in the network analysis system (as well as in the network analysis method described below) a plurality of mobile stations
[0067] In
[0068] According to the method, in a step S
[0069] In step S
[0070] wherein i defines the other-to-own interference ratio in the cell A, RXLEV defines received signal levels measured and transmitted by the mobile station (for example RSSI), RXLEV
[0071] The calculated indicator i can then be registered in a statistic of the network analysis functionality
[0072] When the indicator(s) i is/are calculated, in step S
[0073] It is to be noted that interaction between GSM and WCDMA and interference conditions are commonly known as well as formulas to determine a specific WCDMA capacity and factors in connection with GSM conditions. There are several possible formulas that can be used to transform the reported power levels to some indicator value which describes how good one particular cell would be from reusing it for WCDMA point of view. Furthermore, there are several formulas which use the calculated indicators for the evaluation for a reuse situation in a WCDMA network. One example for such a formula is a WCDMA downlink capacity:
[0074] wherein η
[0075] For the evaluation of the WCDMA communication condition, in the present case of the WCDMA downlink capacity, the calculated and above described other-to-own-cell interference ratio i represents an important factor. This other-to-own-cell interference ratio i depends, for example, on the isolation of the respective cell, i.e. the physical location of the cell in the network and antenna tilting of the BTS, as well as on the location of the user (mobile station) in the cell (when the user is closer to the BTS, i is lower). As described above, i can be determined from live measurements in the existing GSM network. Hence, the presented method provides the advantage that real measurement results can be used instead of predicted or assumed factors, such as path loss and the like. Furthermore, the measurements represent an actual user distribution in the GSM network which is substantially closer to a user distribution in the planned WCDMA network than an estimated one.
[0076] Furthermore, it is possible by using the method of the invention to determine/calculate further WCDMA related communication condition parameters in a similar manner. For example, a downlink cell throughput can be determined when additional parameters are known. These parameters are the downlink E
[0077] The WCDMA related communication condition parameters which are determined on the basis of the measured GSM parameters can be used for an evaluation and planning of a WCDMA based network in the sites of the existing GSM network. An example of such an evaluation and planning process is shown in
[0078] According to
[0079] As a further option, the network analysis functionality
[0080] In step S
[0081] On the basis of the optimization proposals derived in step S
[0082] Hence, the proposed network analysis of an existing GSM network on the basis of live measured mobile station measurements in order to evaluate the potential for reusing sites thereof in a WCDMA network to be planned is useful, for example, in a selection of the existing GSM sites that are suitable for WCDMA co-siting with given coverage and/or throughput requirements, for soft handover rate estimations which feeds into RNC dimensioning and parameter settings, for WCDMA BTS hardware dimensioning in order to support traffic in the WCDMA network, for WCDMA neighboring cell list creation in intra-frequency and inter-system cases when using the given GSM sites. Besides this, the WCDMA deployment analysis and optimization processes described above are also applicable in the following cases:
[0083] proposal of soft handover parameters per cell to obtain x % soft handover overhead;
[0084] evaluation of coverage reason inter-system handover rates when using the given GSM sites;
[0085] determination of lowest number of sites to provide x % coverage for, e.g., WCDMA 64 kbps;
[0086] determination of highest throughput by using all or a part of the given GSM sites.
[0087] In other words, the measured GSM communication condition parameters can be processed to find optimal WCDMA network deployment scenarios and network setting parameters. By using measurements of neighboring/adjacent cells by the mobile stations in the existing GSM network, it is possible to define an amount of interference, which is received in a cell from other cells. This information is used, for example, to estimate the interference situation, which would be given by a one to one site reuse in the new UMTS system and by doing so support the decision whether a site is possible to be reused to deploy a new UMTS network. Additionally, parameters of the UMTS based network, such as network performance, network dimensioning, optimization parameters, and the like, are derivable from the measured GSM communication condition parameters.
[0088] In
[0089] According to
[0090] The network analysis functionality
[0091] Furthermore, as mentioned above, the proposed network analysis can be implemented in the form of software/firmware. That means that a computer program product usable for a data processing unit, for example, in a operation support system (OSS) is provided. In this case, it is obvious that the involved network elements, i.e. in particular the network control element or BSC
[0092] According to a further example, as mentioned above, in
[0093] As a further example, the mobile measurement reports used for the analysis can be recovered from the Abis interface between the BTS and the BSC. The MMRs described above are commonly sent on this Abis interface and can be recovered therefrom without the need that the MMRs are sent to the network analysis functionality in a special way. In other words, the MMRs can be collected, for the further processing, as described above, i.e. from the BSC, or before the BSC, e.g., from the Abis interface. Also, the MMRs can be collected after the BSC, e.g., when the BSC forwards the MMRs to another (not shown) network element, such as the MSC. It is obvious, that in such a case, i.e. when the MMRs are obtained before or after the BSC, the network analysis functionality may be located separately from the BSC.
[0094] It is to be noted that there are various other ways to collect measurement reports from the mobile stations or to keep track of performance parameters (such as i) for each cell. Additionally, the invention is not limited to the other-to-own-cell interference ratio i as the only WCDMA related performance indicator. For example, the number of connections a cell is having may be considered, which relates to the required resources in a 3G network. Also, soft handover overhead (SHO), which is expected in the 3G network and which is an important performance indicator in the 3G network, may be considered, which SHO should be within reasonable limits, such as, for example, 20% to 30% in a macrocellular environment. Here, a number of sufficiently strong signals is converted into an estimation of “useful” soft handover connections in the 3G network, from which in turn the SHO can be derived. It is obvious that there are several other possibilities which are obvious for persons skilled in the art, so that the actual indicator selection is not of particular relevance.
[0095] Moreover, even though the above described embodiments are related to the case where a WCDMA based 3G UMTS network is planned to replace and/or to complement an existing GSM network, it is obvious for a person skilled in the art that the proposed network analysis is applicable also for other network solutions, such as the ones described above, or for network solutions to be developed in the future.
[0096] As described above, a method, system, device and computer program product are provided for analyzing a cellular wireless communication network of a first type. For analyzing the cellular wireless communication network of the first type, communication connection condition parameters for one cell A are measured, which communication connection condition parameters are derived from signals received by a mobile station
[0097] It should be understood that the above description and accompanying figures are merely intended to illustrate the present invention by way of example only. The described embodiments of the present invention may thus vary within the scope of the attached claims.