The invention relates to the field of telecommunications network and, more particularly, to techniques for improving handoff of a mobile station in a telecommunications network.
A geographical area served by a telecommunications network is divided into cell areas in which radio base stations, also sometimes referred to as base transceiver stations, provide radio coverage to mobile stations (MSs) operating in said cell areas. A MS can be any Personal Digital Assistant (PDA), mobile terminal, mobile telephone that enables mobile station mobile subscribers to communicate voice, data and/or multimedia information over the cellular radio communication network. Each radio base station (BS) may be equipped to service one or more cells.
A MS may be assigned a radio communication channel dedicated for communication between the MS and the cellular network e.g. when receiving or making a phone call. In a cellular radio communication system based on Code Division Multiple Access (CDMA) technology a dedicated radio communication channel need not only to be supported by a single serving cell at each given moment of time, but may on the contrary be supported by several cells using so called macrodiversity which provides increased radio transmission quality.
The CDMA technology is described in Interim Standard-95 (IS-95) published by the Telecommunications Industry Association (TIA). IS-95 is often referred to as second generation (2G) wireless communications and the UTRAN FDD mode (also referred to as Wideband CDMA). The CDMA technology is also the basis for third generation (3G) telecommunications network such as CDMA2000 and CDMA 1X networks. After a couple of revisions, IS-95 was superseded by the IS-2000 standard. This standard was introduced to meet some of the criteria laid out in the International Mobile Telecommunications-2000 (IMT-2000) specification, which is the global standard for 3G wireless communications.
Due to the possibility of using more than one cell to serve a dedicated radio communication channel, these cellular radio communication networks also enables so called soft handover. In order to support handover in networks using CDMA technology, MSs are required to perform measurements on downlink transmissions, i.e. from the cellular network to the MSs. The measurement results are reported back to the cellular network and are used for making a decision on which cell is best suited to serve a MS.
The MS searches for pilots on the current CDMA Frequency Assignment to detect the presence of CDMA Channels and to measure their strengths. When the MS detects a pilot of sufficient strength that is not associated with any of the Forward Traffic Channels assigned to it, it sends a Pilot Strength Measurement Message (PSMM) to a BS. The BS can then assign a Forward Traffic Channel associated with that pilot to the mobile station and direct the MS to perform a handoff.
A similar measurement is also made by a MS in idle mode as the MS roams from a first cell area, for example, to a second cell area. Such a process for selecting a new cell is referred to as a cell re-selection process. In this case the neighbor cell list broadcast on the control channel of the serving BS is specifying which channels to measure on.
Whenever the signal strength between the MS and a target BS increases the MS hands off to the target BS located in a target cell in the list of cells. However, since the neighbor list is often based on the network topology represented by the geographic proximity of cells, a more appropriate target BS may be absent from the neighbor list.
For that reason, even though a MS is provided with a list of neighboring cells, a call may be dropped. For example, a call may be dropped if a strong pilot has been omitted from the cell neighbor list. The MS may detect and report the pilot, but a handoff cannot be granted because the BS is not configured to determine a unique cell based on the pilot report.
Furthermore, a call may also be dropped, if a useless cell takes up room in the neighbor list provided to the MS. This can cause more appropriate cells to which the MS can be handed off to be truncated from a cell neighbor list.
Thus, it would be interesting to determine the appropriate cells in a neighboring list provided to a MS. The invention provides a solution to this problem.
It is a broad aspect of the present invention to provide a method for managing a list of target cells associated to a source cell in a telecommunications network, the method comprising the steps of:
receiving at a radio network manager from a base station controller (BSC), a file containing at least one record associated to the source cell;
determining for each record whether a target cell is missing from the list of target cells;
if the target cell is missing from the list of target cells, the radio network manager identifies the target cell as missing from the list of target cells;
determining for each record whether a target cell is excessive from the list of target cells;
if the target cell is excessive from the list of target cells, the radio network manager removes the target cell; and
sending an updated list of target cells for the source cell from the radio network manager to the BSC.
It is another broad aspect of the present invention to provide a radio network manager for managing the list of target cells associated to the source cell, the radio network manager comprising:
an input/output (I/O) unit for receiving a file containing at least one record associated to the source cell from a base station controller (BSC);
a processor for:
determining for each record whether a target cell is missing from the list of target cells;
identifying the target cell as missing from the list of target cells, if the target cell is missing from the list of target cells;
determining for each record whether a target cell is excessive from the list of target cells;
removing the target cell, if the target cell is excessive from the list of target cells; and
sends from the I/O unit an updated list of target cells to the BSC.
The foregoing and other aspects, features, and advantages of the invention will be apparent from the following more particular detailed description as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques. In order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.
Reference is now made to
The network 200 is divided in cells. A partial view of the network 200 is provided in
Reference is now made to
The BSC 100 comprises an input/output (I/O) unit 102 for receiving information from the network 200 and for sending information to the network 200 and ultimately the PSTN or the Internet, a processor 104 for operating the BSC 100, a database 105 for storing information that can be accessed by the processor 104. The database 105 stores a cell configuration 108 of a part of the network consisting of cells for which the BSC 100 controls the BSs. The cell configuration 108 is a listing of all BSs, their communication channels and the associated pilots.
The BSC 100 stores the performance measurements made by MSs in the network 200 in a Performance Measurements (PM) storage 106. Performance measurements are provided by the MSs e.g. MS 10 on a radio link (signaling connection 305). After receiving performance measurements, the processor 104 of BSC 100 adds information in the PM 106. An example of the performance measurements stored in PM 106 is provided in table 206 of
The RNM 110 comprises an input/output (I/O) unit 111 for receiving messages from the network 200 and for sending messages to the network 200, a processor 113 for operating the RNM 110, a database 118 that can be accessed by the processor for storing files of call flows in the network 200 such as table 206 that may be sent from the BSC 100 to the RNM 110. The table 206 can be sent to the RNM 110 based on the File Transfer Protocol (FTP). The processor 113 analyzes received files from different BSCs in the network 200 and also analyzes stored data at the database 118. The database 118 stores a cell configuration 128. The cell configuration 128 is a listing of identifiers of all BSs, their communication channels identifiers and associated Pilot_PN identifiers. The databases 105 and 118 may be any persistent memory such as a file system, a Read-Only Memory (ROM) or a Structured Query Language (SQL) database. The processors 104 and 113 can be hardware, software, or any combination thereof. The RNM 110 further manages a neighbor list (NL 122) of target cells for each cell associated to the BSC 100 in network 200 and updates the NL107 stored at the BSC 100 by transmitting updated data on the link 310.
Since a MS can be served by a first cell before handing off to a second cell, it can be understood that the first cell is the reference cell and the second cell the target cell. Thus following the handoff of the MS from the first cell to the second cell, the first cell which is the reference cell becomes a target cell and the second cell becomes the reference cell.
Reference is now made to
At step 404, the BSC 110 receives messages consisting of Origination messages, Page response messages, and call failure messages. The messages comprises among other things information consisting of Pilot Strength Measurement Messages (PSMMs) for informing the serving BSC 100 of a significant change in the strength of a detectable pilot.
At step 408, the BSC 100 processes measurements received from the MS 10, adds related information and stores the combination of measurements and measurements information in table 206 at the PM 106 (step 410).Then, for each LogCallAttribute 212, the BSC in table 206 adds a timestamp 207 for indicating the time of reception of the LogCallAttribute 212, a Call Connection Reference (CCR) 208 for identifying a call in which the MS 10 is involved, the identity 209 of the MS 10 such as a International Mobile Station Identity (IMSI) and a Source CCID 211 for identifying the assigned communication channel. A LogCallAttribute 212 is one of a LogCallEvent and a LogCallError. The LogCallEvent identifies the events occurring during a call for a particular MS such as the MS 10 when the MS originates a call (Origination message), responds to a page request (Page response message), and a handoff processing (processed PSMM 300). On the other hand, the LogCallError identifies when a call attempt ended with an error. At the end of any call attempt where an error has occurred, the current error code value, the data from the last processed PSMM record 300 before the call attempt is ended with an error and the pilot active set (not shown) at the time of the call drop are logged.
The BSC 100 stores a record similar as the table 301 of
The BSC 100 performs steps 404 to 410 until the predetermined CLK 125 is reached (step 412) or until a maximal file size for a measurement file is reached (step 414). If the first value is below or equal to the first threshold value for CLK 125 (step 412), the BSC 100 determines whether the second threshold value for the maximal file size is below or equal the maximal file size (step 414). When, at step 412, the processor 104 determines that the first threshold value for CLK 125 is above the predetermined threshold or when at step 414 processor 104 determines that the second value for a maximal file size is above the second threshold value, the BSC 110 sends the content of the PM 106 consisting of the latest measurement file similar as the table 206 to the RNM 110 (step 416). The RNM 110 stores the latest measurement file received from the BSC 100 in the PM 116 (step 418) and processes the measurement files (step 420) when the CLK 125 is reached.
The RNM 110 is then able to determine missing target cells (step 424) and excessive target neighbors cells (step 428) from merged NL 308. The RNM 110 also sorts the recommended neighbor list (NL) 123 (step 430) and reduces the number of recommended target cells to a defined number of maximum target neighbor cells (step 431) before sending an updated NL 124 to BSC 100.
More particularly, the RNM 110 uses the recommended neighbor list (NL) 123 and builds the updated list NL 124. The NL 124 contains a neighbor list for each cell of each BSC associated to the RNM 110. The neighbor list for BSC 110 is NL 124. The updated NL 124 is a subset of NL 123 without the missing counters 227, 228 and 229, Calls 231 and Adds 232. The unknown target cells in the recommended NL are replaced automatically by the RNM 110 or by other means involving the RNM 110 in the updated NL 124 with the most probable target cell id matching the unknown target cell Pilot_PN in the vicinity of a source cell. At step 432, the RNM 110 sends an updated NL 124 to the BSC 100. Following this, the BSC 100 updates the NL 107 with NL 124.
Missing Neighbors in Neighbor Cell List
Reference is now made to
Before determining missing neighbors target cells, the RNM 110 analyzes each LogCallAttributes 212 (step 500). A first way for determining a missing neighbor is when a call fails for a MS due to an error that indicates an RF failure (step 510) and the MS re-originates the call after a short period of time from a missing pilot of a missing neighbor cell and the missing pilot was not reported in the PSMM data For example, if the MS 10 is located in cell 205, which is considered to be the source cell and is currently on a call with another party (not shown) and a radio (RF) failure occurs then the MS 10 re-originates the call after a short predetermined period of time from a pilot of another cell such as pilot 325 of cell 210 by sending either an Origination Message or a Page Response Message to the BS 2, the pilot 325 of cell 210 may be considered missing.
If at step 522, the pilot 325 from which the call was originated is not a member of the active set 214 at the time of the call drop and is not reported in the last processed PSMM 300 record before the call attempt is ended with an RF failure error (step 524), the processor of the RNM 110 identified the pilot 325 as missing. Also, to avoid false detection, verification is made at the RNM 110 to ensure that the initiating pilot is not a member of the neighbor cell list of any member in the active set at the time of the call drop (not shown). The RNM 110 compares the first LogCallAttribute 212 of the stored failure IMSI and the LogCallAttribute 212 after failure of event type Origination or Page Response (LogCallEvent 212) of the next CCR for the same IMSI. If the initiating pilot found in the LogCallAttribute 212 after failure is reported missing, the missing pilot is added to the recommended NL 123 of each member of the active set 214 of the stored failure IMSI. At step 526, a first missing counter 227, which tracks the number of times a missing pilot is not reported in a PSMM while an RF failure occurred in a source cell, is incremented. In particular, the RNM 110 increments the first missing counter 227 for each source cell member of the active set 214. If the pilot 325 has been reported in the PSMM data or if the pilot 325 is a member of the active set 214 there is no action performed by the RNM 110 (step 599).
A second way for determining a missing pilot in a neighbor list is when a missing pilot is reported in the PSMM data and subsequently an RF failure occurs. At step 510, the RNM 110 determines that a call error due to an RF failure occurred, but the MS 10 does not re-originate the call before the time limit (step 520). Before the call failure, if a missing pilot (identified with a CCID 213 of zero) is reported in the last processed PSMM 300 record of a LogCallError 212 (step 530) and if the missing pilot strength is above or equal to a predetermined threshold (step 532), the missing pilot is added to the recommended NL 123 of each member of the active set of the stored failure IMSI. At step 534, a second missing counter 228, which tracks the number of times a missing pilot is reported in the PSMM data and a RF failure occurred in a source cell is incremented. If there is no missing pilot in the PSMM data or if the missing pilot is below the predetermined threshold, no action is performed by the RNM 110 (step 599).
A third way for determining a missing pilot in a neighbor list is when a missing pilot is reported in the PSMM data and no RF failure occurs. At step 510, the RNM 110 determines that no call error due to an RF failure occurred. However, at step 512, the RNM 110 detects a missing pilot in the process PSMM record 300 of a LogCallEvent 212 of event type Handoff processing for a CCR without RF failure. Thus, if the number of pilots in the pending active set 214 is one (step 514), and if a predetermined parameter allows to constantly have the first two strongest pilots to be in the active set without having the second pilot verified to meet strength criteria (step 516), the RNM 110 increments a third counter 229 which tracks the number of times a missing pilot is reported in PSMM data and no failures occurs in a source cell (step 518). The missing pilot is added to the recommended NL 123 of the reference pilot 215, if the counter 229 is above or equal to a predetermined threshold. In table 301 of
When the active set 214 comprises one or more pilots, the neighbor lists of all active set members 214 are combined into one neighbor list, which consist in a merged neighbor list of target cells 308. The reference pilot may add a pilot from this list that is not in its own neighbor list.
Reference is now made to
Excessive Neighbors in Neighbor Cell List
Reference is now made to
After removing the neighbor cells without been involved in any calls the RNM 110 sets a threshold for the maximum call that will not be supported by all neighbors when determining the recommended NL 124 (step 612). Generally, the maximum number of unsupported calls represents not more than 1% or 2% or in the more conservative case 0% of the total number of calls that used the source as a reference pilot. The maximum percentage of unsupported calls is a predetermined parameter.
In a particular case, if the maximum number of unsupported calls is equal to zero for the neighbor list (step 614), the RNM 110 determines that all the target cells with at least one calls 231 of the merged NL 308 are not excessive for a source cell (step 690). Otherwise, the RNM 110 processes the merged NL 308 of target cells starting with the target cell having less Call 231 (step 624). In the case of merged NL 308 the RNM 110 starts with target cell 245. The RNM 110 further determines for a target cell in the NL 308 whether the counter Calls 231 is above or equal the threshold for call not supported (step 616). If the counter Calls 231 for a target cell is above or equal to the threshold, the RNM 110 determines that the target cell and the target not evaluated in the merge NL 308 are not excessive (step 690). Otherwise, the RNM 110 processes the HO events 221 in which the target cell was added (618). At step 620, the RNM 110 determines a set of rules for removing the target cell and if these rules are satisfied the target cell is added to the excessive NL 306 (step 622) and the next target cell is evaluated. Otherwise, the target cell is considered not excessive and added in the recommended NL 123 (step 690) and the next target cell is evaluated. Reference is now made to
When the RNM 110 determines that a target cell is not excessive, at step 690, the RNM 110 determines if the target cell is present in the current neighbor cell list of the source cell (step 692). The RNM 110 then determines if the target cell is already a neighbor cell of the source. If it is not the case, the processor 113 determines that the target cell is a missing target cell and adds the cell to the source recommended NL 123 (step 694). If it is the case, the RNM 110 keeps the target cell as an existing neighbor cell in the source recommended NL 123 (696).
It can also be understood that some messages and therefore some parameters sent between network elements of the network 200 are omitted for clarity reasons. The network 200 shown in
For example, the network 200 shown in
While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various alterations may be made therein without departing from the scope of the invention.