Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
  • H04W16/02—Resource partitioning among network components, e.g. reuse partitioning
  • H04W16/06—Hybrid resource partitioning, e.g. channel borrowing

Definitions

• the present invention relates in general to the radio telecommunications field and, in particular, to a method and system for enabling cell load sharing in a mobile-controlled cell selection environment, such as, for example, in a radio packet data system.
• each BTS is assigned to cover a certain geographical service area (cell).
• each BTS is responsible for communicating with all of the MSs that are active in its cell.
• the cell of a BTS e.g., BTS A
• BTS A includes the geographical area in which, out of all of the BTSs in the system, that BTS provides the best radio link quality.
• the border at which an MS changes communication from BTS A to BTS B is called the cell border between cell A and cell B.
• the traffic load generated by the users varies in time. This fact implies that the radio network needs to be over-dimensioned in order to compensate for traffic peaks.
• the existing load is too high to provide adequate service quality to the MSs in those cells, while at the same time, neighboring cells can have surplus capacity.
• This approach which is commonly referred to as "cell-load sharing," is used in conventional cellular speech communication systems (e.g., in the GSM).
• MS-controlled cell selection there are two ways to administer cell selection in cellular radio systems: MS-controlled cell selection; and network-controlled cell selection.
• MS-controlled cell selection it is the MS's responsibility to determine to which
• the MS considers whatever information it has at hand (radio conditions, received signal strengths, service capabilities, and possibly, additional information received in system information messages, etc.) as input(s) to a pre-determined cell selection algorithm.
• the output from the cell selection algorithm denotes the cell to which the MS should connect.
• the network commands the MSs to connect to a certain BTS (cell).
• a necessary condition for network-controlled cell selection is that every MS consistently provides the network with measurement reports. Essentially, the measurement reports inform the network about how the reporting MS perceives the candidate BTSs or cells, in terms of their signal strength and radio link quality.
• the main advantage of network-controlled cell selection is that a relatively intelligent cell selection algorithm can be used.
• the network can use the wealth of information it has available, not only about the radio link conditions, but also about the load in each cell, buffered data packets, quality of service contracts with users, preferred home zones, etc.
• Network-controlled cell selection is used, for example, in the circuit-switched GSM.
• the biggest disadvantages of network-controlled cell selection are the increased complexity for the network involved, and that each MS has to provide measurement reports regularly to the network. Unfortunately, the measurement reports use uplink bandwidth and, therefore, actually decrease the system's capacity.
• the increased complexity results from the network having to administer a locating procedure for each active MS.
• each MS is responsible for its own cell selection procedures.
• the system can use either MS-controlled or network-controlled cell selection.
• MS-controlled cell selection will be the method of choice for the majority of future GPRS networks.
• the pertinent prior art focuses on cell load sharing in systems using network-controlled cell selection approaches. In such systems, the process whereby an active MS selects another cell is always initiated by a cell re-selection (i.e., "handover") command issued from the network.
• the network can identify candidate MSs in a congested cell, and direct these MSs to connect to less congested cells by issuing re-selection commands for dedicated cells (i.e., the less congested cells).
• dedicated cells i.e., the less congested cells
• a method and system are provided for implementing cell load sharing in an MS- controlled cell selection environment, such as, for example, in a radio packet data system, wherein dynamic system information (e.g., SI messages) is used to enable an MS to perceive cell borders that depend on the system load.
• dynamic system information e.g., SI messages
• cell selection parameters in the system information messages are associated with the distribution of the load in various cells. In this way, the MSs (which are responsible for their own cell selection) in overloaded cells can be prompted to select alternative, less loaded cells.
• An important technical advantage of the present invention is that a method is provided for using cell load sharing in a system in which MS-controlled cell selection is also being used.
• Another important technical advantage of the present invention is that it enables systems with only MS-controlled cell selection to also use cell load sharing.
• Still another important technical advantage of the present invention is that in systems that can choose between a network-controlled and MS-controlled cell selection mode (e.g., GPRS), cell load sharing can be used while the system is operating in the MS-controlled cell selection mode.
• a network-controlled and MS-controlled cell selection mode e.g., GPRS
• Yet another important technical advantage of the present invention is that it enables the use of load sharing in radio packet data systems (e.g., GPRS) to increase capacity and avoid congestion, without overloading the uplink with measurement report traffic.
• radio packet data systems e.g., GPRS
• FIGURE 1 is a diagram that illustrates an exemplary system that can be used to implement the present invention
• FIGURE 2 is a diagram that further illustrates how the exemplary system shown in FIGURE 1 can be used to implement the present invention.
• FIGURE 3 is a diagram that illustrates how system information messages can be used to implement a preferred embodiment of the present invention.
• FIGUREs 1 -3 of the drawings like numerals being used for like and corresponding parts of the various drawings.
• a method and system are provided for implementing cell load sharing in a radio packet data system, wherein dynamic system information (e.g., in the form of SI messages) is used to enable an MS to perceive cell borders that depend on the system load.
• dynamic system information e.g., in the form of SI messages
• the network determines the cell borders by including pertinent cell selection parameters in the system information messages.
• the system information messages can be either broadcast to all MSs in the network, or sent dedicated to a selected set of one or more MSs in an overloaded cell.
• the cell selection parameters contain information, for example, about offsets that can be applied to the measured signal strengths, threshold values, cell priorities, etc.
• the cell selection parameters in the system information messages are associated with the distribution of the load in various cells.
• the MSs which are responsible for their own cell selection
• the system information messages can be sent on the broadcast channel, or transmitted dedicated to a selected subset of MSs in the overloaded cell.
• FIGURE 1 is a diagram that illustrates an exemplary system 100 that can be used to implement the present invention.
• System 100 is preferably a system that employs MS-controlled cell selection, and can be a radio packet data system or packet- switched system such as the GPRS .
• the exemplary radio packet data system 100 can be operating in conjunction with a circuit-switched system, such as the GSM, the Digital- Advanced Mobile Phone System (D-AMPS), or any other system capable of supporting a radio packet data system or service.
• System 100 includes a plurality of base stations or BTSs, such as, for example, BTS A ( 102) and neighboring BTS B (104).
• BTS A defines one cell (A)
• BTS B defines a second cell (B).
• SS A SS B
• BSC base station controller
• the system information messages e.g., SI messages in the GSM and GPRS
• FIGURE 2 is illustratively similar to FIGURE 1, except that the scenario depicted in FIGURE 2 has more mobile terminals connected to BTS B 104 than to
• BTS A 102 For example, three mobile terminals (110, 112, 114) have connected to BTS A 102, while seven mobile terminals (116-128) have connected to BTS B 104.
• a sufficient quality of service e.g., QoS in GPRS
• FIGURE 3 is a diagram that illustrates how system information messages can be used to implement a preferred embodiment of the present invention.
• the cell border (108) between cells A and B appears to be shifted towards cell B, and thereby, cell A effectively covers a larger number of the mobile terminals than before.
• An example of a system information message that can be used to convey the above-described offset to one or more mobile terminals in an MS-controlled cell selection environment is a GPRS cell selection parameters information element as defined at Section 11.2.19 of the GSM Technical Specification GSM 04.60, version 6.0.0, June 1998.
• the information element can be delivered to all, or a subset of, the mobile terminals in cell A, either on the Packet Broadcast Control Channel (PBCCH) in cell A, or on one or more Packet Associated Control Channels (P ACCHs) in cell A.
• PBCCH Packet Broadcast Control Channel
• P ACCHs Packet Associated Control Channels
• the information element can contain the 5 bit information element GPRS_RESELECT_OFFSET that defines a bias, or offset, to be used in the "C31/C32" criterion which is used in the GPRS for MS-controlled cell reselection.
• This bias or offset value can be different for different cells and thus can be used to shift the MS-perceived boundary between two cells (e.g., between A and B).
• an offset value of 4 dB can be added to the ranking criterion, C32, of cell B, by setting the five corresponding bits in the system information element described above to "01100" (+4 dB).
• the receiving mobile terminals perceive the cell border between cell A and cell B (108 in this example) as shifted by 4 dB relative to the equal-signal-strength border (106).
• the corresponding system information element in cell B i.e., the element controlling the cell border between cell A and cell
• the SI 3 Rest Octets information element is a type 5 information element that contains a "CELL-RESELECT-OFFSET" information field.
• the CELL-RESELECT- OFFSET is a bias or offset value (in dB) that is included in the so-called "C2" criterion for a cell. This bias or offset value can be different for different cells and thus can be used to shift the MS-perceived boundary between two cells (e.g., between A and B).
• a CELL-RESELECT-OFFSET value of 4 dB can be added as an offset in the C2 criterion for cell A, by transmitting the corresponding bit pattern in the CELL_RESELECT_OFFSET information element in the System Information 3 Rest Octets transmitted on the BCCH in cell A.
• this exemplary scenario assumes that the CELL_RESELECT_OFFSET field in the System Information 3 Rest Octets transmitted on the BCCH in cell B corresponds to a 0 dB bias or offset in cell B.
• the offset caused by the cell parameters in the transmitted system information messages causes the mobile terminals in cell B which are close to the border of cell A (e.g., mobile terminals 116 and 118) to rank cell A as a "better" cell to be connected to than cell B. Therefore, these two mobile terminals effect a change (e.g., via a conventional handover procedure) from cell B to cell A.
• the result is that the load (mobile terminal traffic) is moved from cell B to cell A in such a way that a sufficient quality of service can be offered to the users in both cell
• the present invention increases the cellular system's ability to maintain a sufficient quality of service during periods of local congestion in the network.
• a pertinent load can be related to (1) the total number of users in a cell, (2) the total number of active users in a cell, (3) the ratio of the total number of active users in a cell to the number of channels in the cell, (4) the ratio of the total number of queued data packets in a cell to the number of channels in the cell, (5) a measure of the QoS that can be offered in a cell (e.g., bandwidth per user, fraction of QoS contracts to users that can be fulfilled, etc.), and so on.
• a measure of the QoS that can be offered in a cell e.g., bandwidth per user, fraction of QoS contracts to users that can be fulfilled, etc.
• the cell boundary shifts that can result are not limited to boundaries between so-called macro-cells, but could include boundaries between disparate types of cells, such as, for example, micro-cells and macro-cells, pico-cells and micro-cells, etc.
• the system information in all cells in a defined network area is dynamic information. Using this dynamic information at any given time, the network can (with any given temporary load distribution) optimize the quality of service offered to the packet data service users in the whole area.
• the system information (to be broadcast or transmitted from the network) can be made dependent on the number of mobile terminals in each cell, the number of scheduled data packets in each cell, by the users' perceived quality of service in each cell, the packet delays in each cell, and so on.
• a network algorithm e.g., being executed by a processor at a base station controller, BSC, or a mobile services switching center, MSC
• BSC base station controller
• MSC mobile services switching center
• the present invention has been described above in the exemplary context of a GSM packet data service (e.g., GPRS), the present invention can be applied to any cellular radio system that can use system information as input to an MS- controlled cell selection algorithm. Furthermore, the present invention can be applied to any cellular radio system that can operate in an MS-controlled cell selection mode.
• a system can include, for example, GPRS in GSM, GPRS in D-AMPS, an IS-95 system, cellular radio satellite systems, as well as the Universal Mobile Telephone System (UMTS), and both present and future spread spectrum and Wideband Code Division Multiple Access (WCDMA) systems.
• UMTS Universal Mobile Telephone System
• WCDMA Wideband Code Division Multiple Access

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

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Cited By (14)

Citations (3)

• 1999
  • 1999-09-14 CN CN 99811174 patent/CN1319316A/zh active Pending
  • 1999-09-14 EP EP99952844A patent/EP1116402A1/de not_active Withdrawn
  • 1999-09-14 CA CA002344498A patent/CA2344498A1/en not_active Abandoned
  • 1999-09-14 BR BR9913997-9A patent/BR9913997A/pt not_active IP Right Cessation
  • 1999-09-14 AU AU64908/99A patent/AU6490899A/en not_active Abandoned
  • 1999-09-14 WO PCT/SE1999/001606 patent/WO2000018164A1/en not_active Application Discontinuation

Patent Citations (3)

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