Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W24/00—Supervisory, monitoring or testing arrangements
  • H04W24/10—Scheduling measurement reports ; Arrangements for measurement reports
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/0005—Control or signalling for completing the hand-off
  • H04W36/0083—Determination of parameters used for hand-off, e.g. generation or modification of neighbour cell lists
  • H04W36/0085—Hand-off measurements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/0005—Control or signalling for completing the hand-off
  • H04W36/0055—Transmission or use of information for re-establishing the radio link
  • H04W36/0058—Transmission of hand-off measurement information, e.g. measurement reports

Definitions

• the present invention relates in general to the mobile telephony field and, in particular, to a method for use in improving measurement reporting in a mobile communications system.
• AFA Automatic Frequency Allocation
• each cell in the network monitors the signal strength on all (or a subset of all) frequencies available to the operator.
• the signal strength measured on each frequency is utilized to estimate the interference that would be generated if that frequency were to be used. If any non-allocated frequency has a lower estimated interference than that of an allocated frequency, a frequency switch is made. Thus, the allocated frequencies with the highest interference are replaced by the frequencies with the lowest estimated interference.
• the AFA algorithm repeats this procedure (iteratively) until no further improvement (in terms of the carrier-to- interference ratio or C/I) can be obtained.
• One technique that can be used is to measure the downlink interference at the base station that defines the cell. However, since this measurement is being made at only one point (e.g., where the measurement receiver's antenna is located), this lone reading is wholly inadequate from a testing and operational standpoint.
• Another technique that can be used is to place interference measurement equipment at a number of different, fixed locations in a cell. Consequently, the downlink interference in the cell could be measured at all of those locations.
• this approach requires the purchase of a substantial amount of measurement equipment, which is quite costly to install and maintain. In fact, this added cost would outweigh the potential benefits that could be derived from making the downlink interference measurements at the numerous locations in the cell.
• the measurement equipment should be located where the majority of the cell traffic occurs, but the network operator typically does not have such knowledge beforehand.
• the downlink measurements are required to be performed by the mobile terminals.
• the mobile terminals typically conduct the downlink measurements while operating in the idle mode, but the transfer of all of the terminals' measurement results to the base station should be accomplished in a manner so as to occupy as little of the system's resources (e.g., allotted frequency spectrum) as possible.
• existing cellular communications systems e.g., GSM
• signal strength measurements collected by a mobile terminal while operating in the idle mode are utilized by the mobile terminal only during the idle mode.
• measurements collected by the mobile terminal while operating in the active mode are transferred (reported) to the network during the active phase of the connection.
• a problem with the existing systems is that the measurements collected by the mobile terminals in the idle mode are not reported to the network at all.
• the active mode measurement data is to be used for purposes other than handover control and power regulation, because conflicting requirements can be placed on the data to be collected.
• the handover control function requires the use of downlink signal strength measurement data from the neighboring cells that are immediately adjacent to the serving cell.
• the frequency allocation control function requires the use of downlink signal strength measurement data from distant neighbors. Such a conflict in the use of the downlink signal strength measurement data can lead to compromises in defining which cells to measure, which decreases the performance of both functions.
• An additional but related problem is that a mobile terminal operating in the active mode does not have as much time to perform measurements as a mobile terminal operating in the idle mode.
• an object of the present invention to enable mobile terminals to transfer measurement information to the network without increasing the air interface load or reducing system performance.
• the foregoing and other objects are obtained by a method which enables a mobile terminal to switch over from the idle mode (powered on and waiting to set up for a call) to the active mode (call connected), and start sending measurement information to the network as soon as a dedicated traffic channel is assigned.
• the measurement data is transferred to the network on the slow associated control channel.
• the first report of measurement information which is transferred to the network during the first available slow associated control channel period, contains data that the mobile terminal obtained while it was waiting in the idle mode. Subsequently, the mobile terminal transfers measurement information to the network based on the data obtained in the active mode.
• FIGURE 1 is a block diagram of an exemplary mobile communications system that can be used to implement the present invention.
• FIGURE 2 is a diagram that illustrates the downlink and uplink frame formats for a cellular communications system using a time division multiple access (TDMA) scheme, in accordance with the preferred embodiment of the present invention.
• TDMA time division multiple access
• FIGS 1-2 of the drawings like numerals being used for like and corresponding parts of the various drawings.
• the mobile terminal when a GSM mobile terminal first connects to the network, the mobile terminal has no prior knowledge about the timing of the slow associated control channel (SACCH) period. As such, GSM mobile terminals are frequently connected to their network near the middle of a SACCH period, and the measurements performed during the remainder of this period are thus incomplete.
• SACCH slow associated control channel
• mobile terminals operating in accordance with the present invention advantageously make use of the first complete SACCH period to provide useful measurement data to the network.
• the mobile terminal when an active connection is first set up between a mobile terminal and network base station, the mobile terminal starts sending measurement reports to the network as soon as a dedicated channel is assigned.
• the measurement information is transferred to the network on the slow associated control channel.
• the first measurement report which is transferred to the network during the first complete slow associated control channel period on the dedicated channel, contains measurement data that the mobile terminal obtained while it was waiting in the idle mode.
• the mobile terminal transfers measurement information based on data obtained in the active mode.
• FIGURE 1 is a block diagram of an exemplary mobile communications system 10 that can be used to implement the present invention.
• the exemplary system (10) shown is the cellular GSM, but this example is for illustrative purposes only, and the invention is not intended to be limited to any particular mobile communications system.
• the inventive concept can also be applied to cover other telecommunications fields, such as, for example, satellite communications wherein a mobile terminal first makes an active connection on the uplink in a satellite communications system.
• Cellular system 10 can include a plurality of mobile terminals (exemplified by the one mobile terminal 12 shown), which communicate with a Base Transceiver Station (BTS) antenna 14 via a radio air interface.
• BTS Base Transceiver Station
• BTS antenna 14 defines the coverage of one cell in the mobile network of system 10.
• a plurality of BTSs (not explicitly shown) including BTS 14 is controlled by a Base Station Controller (BSC) 16, which controls such functions as handovers and channel assignments in the cellular network.
• BSC Base Station Controller
• a plurality of BSCs (not explicitly shown) are connected to a Mobile Services Switching Center (MSC) 18, which controls calls to and from other telephony and data communications systems (not explicitly shown), such as, for example, a Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN), Public Land Mobile Network (PLMN), Public Data
• PSTN Public Switched Telephone Network
• ISDN Integrated Services Digital Network
• PLMN Public Land Mobile Network
• MSC Gateway MSC
• VLR Visitor Location Register
• HLR Home Location Register
• HLR 22 contains subscriber information, such as supplementary services and authentication parameters, and information about the location of the subscriber's mobile terminal (e.g., in which MSC area the mobile terminal currently resides).
• subscriber information such as supplementary services and authentication parameters, and information about the location of the subscriber's mobile terminal (e.g., in which MSC area the mobile terminal currently resides).
• signal strength measurements are made in both the idle mode (e g , while the mobile terminal is switched on and moving around) and the active mode
• the initial cell selection is made when mobile terminal 12 is first "powered on”
• mobile terminal 12 scans all radio frequencies allocated to the GSM, and calculates the average signal strength level for each of those frequencies
• the mobile terminal tunes to the strongest (highest average level) carrier and determines whether it is a Broadcast Control Channel (BCCH) earner
• BCCH Broadcast Control Channel
• the mobile terminal determines this by searching for the frequency correction burst, which is sent in time slot "0" on the BCCH carrier If the strongest earner is
• the mobile terminal (12) While in the idle mode, the mobile terminal (12) stays in a "sleep" mode, except when it is scheduled to listen for paging messages (or decode the BCCH information)
• all system information messages conveyed on the BCCH are read at least once every thirty seconds, in order to monitor changes in cell parameters (e g , the cell might have become barred in the meantime)
• the mobile terminal (12) While listening to its own paging group for paging messages, the mobile terminal (12) takes measurement samples on certain frequencies allocated to predefined neighboring cells In the GSM, the mobile terminal is required to take at least five measurement samples for each predefined neighboring cell
• the network transmits (e g , via BTS antenna 14) a BCCH Allocation (BA) list on the BCCH, which informs mobile terminal 12 about which BCCH carriers it is to monitor (the predefined neighboring cells) for cell re-selection purposes
• BSIC Base Station Identity Code
• TDMA scheme in accordance with the preferred embodiment of the present invention
• the exemplary frame formats shown in FIGURE 2 are described with respect to the standard GSM protocol, but the invention is not intended to be so limited
• the invention can also be applied to any other type of cellular communications system that utilizes a TDMA scheme and mobile-assisted measurement procedures, such as, for example, the Advanced Mobile Phone Service (AMPS), Digital-AMPS (D-AMPS), Personal Digital Cellular (PDC) System, Personal Communications System (PCS), etc
• AMPS Advanced Mobile Phone Service
• D-AMPS Digital-AMPS
• PDC Personal Digital Cellular
• PCS Personal Communications System
• the mobile terminal 12 (and other mobile terminals in the system) make, at a minimum, signal strength and quality measurements for its own cell, and at least signal strength measurements for neighboring cells while in the idle mode
• the mobile terminal averages these measurements and stores the measurement information and averages in a local memory location
• the MSC 18 initiates a call by sending a set up message to the mobile terminal (12) If the mobile terminal can handle the call, it sends a call confirmed message back to the MSC
• the MSC (18) then initiates a procedure to assign a dedicated traffic (e g , speech) channel to the mobile terminal (12)
• the BSC 16 selects an unused traffic channel and sends a Channel Activation message to the BTS 14, which responds by sending a Channel Activation Acknowledge message back to the BSC 16
• the BSC 16 then sends an
• this new traffic channel which is to be dedicated for use by this particular mobile terminal (12), typically includes a dedicated traffic channel (TCH), a slow associated control channel or
• a SACCH is a data channel associated with either a particular TCH or SDCCH and that continuously carries information.
• a FACCH is also associated with a particular TCH and works in the "burst-stealing" mode to replace speech or data traffic with signalling information.
• the mobile terminal transfers the stored measurement data (collected earlier while in the idle mode) to the network immediately during the next complete SACCH period (denoted by 102) on the dedicated traffic channel.
• the GSM format typically utilizes a duration of four SACCH time slots to completely transfer measurement data.
• the invention is not intended to be so limited and can utilize more or less time slots than the four SACCH time slot duration shown (i.e., systems other than the GSM may use different time slot durations).
• the mobile terminal (12) then begins to make measurements for reporting in the active mode.
• the mobile terminal 12 receives and measures the signal strength for its serving cell.
• the mobile terminal transmits the active mode signal strength measurement for its serving cell on the SACCH.
• the mobile terminal measures signal strength for at least one of the neighboring cells and stores that information for a subsequent transmission. The active mode measurements are continued thereafter for the duration of the call.
• the measurements made by mobile terminals in the idle mode can be used for automatic frequency planning.
• AFA is an automated frequency planning technique that utilizes an iterative algorithm to automatically and frequently reconfigure a network's cell plan (to minimize radio interference) and gradually improve the quality of the radio environment.
• the uplink and downlink signal strengths for all available frequencies are monitored for each cell in the network.
• the measured signal strength on each frequency is used to estimate the interference generated if that frequency were to be used. If any non-allocated frequency has a lower estimated interference than an allocated frequency, the network switches over from the allocated to the non-allocated frequency.
• the allocated frequencies with the highest interference are replaced by the frequencies having the lowest measured signal strength, and so on until no additional improvement in performance can be made.
• the uplink measurements are made at the base stations, but the downlink measurements can now be made by the mobile terminals in the idle mode, which provides ample time to make an appropriate number of measurements.
• the mobile terminals can be ordered to make idle mode measurements in accordance with a specific procedure. For example, in the GSM, a list similar to the BA list of frequencies to be measured is broadcast to the mobile terminals. The mobile terminals can note those frequencies and make the required measurements while waiting in the idle mode. Alternatively, the idle mode measurement frequencies can be relayed to the mobile terminals by being "piggy-backed" on various signalling messages, such as, for example, one or more Location Updating messages.
• the invention makes it possible to detect the allocation of a "bad" BCCH. For example, if one or more mobile terminals are unable to decode the BSIC for a particular allocated BCCH, and the measured signal strengths are high for that BCCH, then the BCCH frequency can be assumed to have high interference and not suitable for use. Also, if the mobile terminals decode a BSIC for a BCCH other than the one anticipated, a problem with the BSIC allocation is indicated.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)

Applications Claiming Priority (3)

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• 1998
  • 1998-06-02 AU AU80462/98A patent/AU8046298A/en not_active Abandoned
  • 1998-06-02 WO PCT/SE1998/001043 patent/WO1998057512A1/en not_active Application Discontinuation
  • 1998-06-02 EP EP98928736A patent/EP0988762A1/en not_active Withdrawn
  • 1998-06-02 CA CA002293645A patent/CA2293645A1/en not_active Abandoned
  • 1998-06-02 CN CN98806129A patent/CN1260940A/zh active Pending

Non-Patent Citations (1)

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