JPH06511130A - Method and apparatus for performing handoff in a wireless communication system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Method and apparatus for performing handoff in a wireless communication system field of invention TECHNICAL FIELD The present invention relates to communication systems, and more particularly to cellular communication systems. .

Background of the invention Cellular communication systems are well known. Generally, each such communication system is in a relatively wide geographical area via multiple base stations with coverage areas. Provide communication services. Such base stations allow communication units to pass through this area. Hand off the source of the service from one base station to another when This provides virtually uninterrupted connectivity for mobile communication units passing through this area. arranged to provide continuous services.

Communication services within a cellular system consist of communication units and bases that provide the services. is provided by communicating radio frequency (RF) signals to and from the station. Communication unit When the unit moves out of the coverage area of the serving base station, this movement It is detected by signal measurements performed by Knit and transmitted to the serving base station. or detected by signal measurements of the communication unit performed by other nearby base stations. Served. Communication processing is transferred from a service providing base station to a station near the mobile communication unit. The need to handoff to a new (other party) base station is determined by using the measured signal value as a threshold. This can be done on the basis of comparison. (European Telecommunications Standards Association) Glob ETSI) and incorporated herein by reference. al System for Mobile Communications) GSM, as defined in the Publications, is an example of such a system. ) Handing the communication unit from the serving base station to the target base station If it is determined that it needs to be turned off, the communication unit is A communication path must be established with the In the prior art, mobile switching center (M SC: Mobile switching center) Matrix switch or base station controller (BSC: base 5it) Transfer is performed within the matrix switch located in It will be done.

A matrix switch in a cellular system accepts signals from multiple external signaling devices. Handoff is performed depending on the presence or absence of interconnection within the network. For handoffs, the matrix The base switch has mutual connections from both the serving base station and the destination base station. A sequel is given. Matrix switch controller for handoff (e.g., MSC or BSC) disconnects from the original serving cell and , instructs this matrix switch to reconnect to the other cell, or is or the third-party conference function of the cellular infrastructure. conferencing) to bridge the cell for a period of time. a Alternatively, the controller uses a process called ``soft handover.'' , switch to connect to both the destination base station and the serving base station for a predetermined period of time. can be instructed to Soft handover directly controls packet selection. or by a local controller. This may happen on some systems.

Placing a matrix switch on the MSC (or MSC and BSC) Therefore, the relationship between the base station (BS: base 5ite) and the matrix switch is Relatively long signal paths may be required between them. MSC controls multiple ESCs or a BSC controls multiple BSs, or a BS controls multiple sectors. If you are responsible for a relatively large number of purpose limited signal paths with switches and services. It must be installed between the receiving device and the receiving device.

The problem of handoff with matrix switches is that or a different base station system (BSS: base station system) This becomes complicated when performing node-off on a cell that is part of a system. C The destination base station is served by a different BSC than the original serving base station. If service is provided, the end-off must be performed.

Matrix switch and partner channel in ESC of serving base station Both matrix switches in the BSC of the serving base station Because it does not have interconnection with both the base station and the other base station, the MSC handles the dooff is required. On the other hand, the matrix switch in MSC has this Interconnections from all ESCs controlled by the MSC are provided. MSC In order to perform a handoff, the MSC must interconnect to the other cell and commands the MSC matrix switch to disconnect from the serving cell of .

If the other cell station is part of a different cellular system, the handoff is Telephone network (PSTN) intervention may be required. Or a different cell Intersystem handovers are maintained for handoffs between disparate systems. This can be done by dedicated trunk groups. different If two MSCs are involved, these MSCs exchange information regarding the handoff; Request a handoff from a switching system within the PSTN or use a dedicated trunk Groups must be used.

Handoffs based on matrix switches located at the MSC or BSC are However, such configurations require a centralized location or is inefficient due to the distance and number of signal paths in the Therefore, hand-off A method is needed to localize handoffs to the devices directly involved in the operation.

Summary of the invention A method and apparatus for performing handoff in a cellular communication system includes at least two bridging two cells, including providing a switch at each point in the signal path It is characterized by The method further includes communication from the serving cell to the destination cell. Determining that a system handoff is indicated and A switch in the signal path to the serving cell that bridges the and identifying the group. Finally, the method uses bridging switches to including handoff.

The device for such a method of performing handoffs has at least two service areas. including providing a switch at each signal distribution point to bridge the Such a system Intra-system handoffs involve switches bridging the serving cell and the destination cell. Based on the information contained in the means of constructing and requesting that handoffs occur within the Initiated from the serving base station.

Brief description of the drawing FIG. 1 shows a block diagram of a cellular communication system according to one embodiment of the invention.

FIG. 2 shows a conventional matrix switch.

FIG. 3 shows a switch according to the present invention, with a switch at each line branch point. 1 shows a block diagram of a communication unit.

FIG. 5 shows a handoff flowchart according to a preferred embodiment of the present invention.

Detailed description of the preferred embodiment Conceptually, a solution to the problem of localizing handoffs is to - A switch is placed at each signal distribution point that bridges the area. This space The switch may be located in a BS serving multiple sectors, or A famous transcoder (transmission code) that serves multiple BSSs. Transmission Coder). This kind of belief By placing the switch at the signal distribution point, the system can be Handoff is achieved through the lowest level of the system. Low-level handoff behavior By entrusting the signal to the signal branch point, the call can be blocked (handover). (call blocking) and increase system capacity. let Also, delegating handoffs to lower-level branch points is not available at a branch point (e.g. MSC>) but is not available at a lower level branch point (e.g. Performs handoff decisions based on signal quality information available at the base station (e.g., base station). can be made to run.

FIG. 1 shows a cellular communication system, designated by reference numeral (10), according to one embodiment of the present invention. Showing the stem. This system (lO) has MSC#1~j (10,11). included. Each MSC of MSC #1-j (e.g., MSC #1) encoder #lk (12, 13). Transcoder #1~k (1 2, 13) (for example, transcoder #1) is BSC #1 −m(15,16). Each BSC of B5C81-m (e.g. , BSC #1) controls BSSs 1 to n (18, 19). BSS 1- Each BS of n (18, 19) (for example, BSS1 (18)) has multiple sectors. (Cells) Provide communication services within (22-24).

In FIG. 2, in the preferred embodiment, MSC(10,12).

Transcoder (12-14), ESC (15-17) and BS (18-21) ) shows the switching means (34) contained within. This switching means (switch) It may be a switch (matrix switch) or a packet switch.

The switch (34) can connect any two external connections (as is well known in the art). A path can be provided (within the switch (34)) between ~q). switch( 34) is a packet switch, the route is the header in the transmitted packet. or based on the external fn (Fast Packet Switching) Created. If the switch (34) is a matrix switch, the line path is created under the control of an external processor. Each MSC (10°11),) Nskog (12-14), BSC (is-17) and BS (18-21) By providing a switch (34) within the system (10), the lowest possible level within the system (10) is Allows handoffs to occur at the bell. Various requirements within the system (10) Packet switching and circuit switching are performed on the same system (10 ) may exist simultaneously within different levels.

By forcing the handoff to occur at the lowest possible level in the system, two or Placing a switch (34) at each branch point with a larger service area thereby reducing interconnect wiring for specific functions within such systems (10). . By placing a switch (34) at each branch point, the lowest level possible. trunking (relaying), thereby improving overall system efficiency. can be done. In addition, by placing the switch at such a branch point, the hand If the off-controller (call controller) is also located at the branch point, this Control traffic can be limited to branch points.

FIG. 5 shows a handoff flowchart according to a preferred embodiment of the present invention. Book In understanding the invention, reference will be made to this flowchart as appropriate.

As an example, the communication unit (50 in FIG. 3) is It exchanges communication signals with a public switched telephone network (PSTN) subscriber (not shown). call During configuration, switch (34) in BS (18) is connected between terminal 1 and terminal p+3. Commanded to establish signal path. Switch in call controller (BSC15) switch (34) is instructed to establish a call path between terminal 1 and terminal p+2. Ru.

Switches (34) in transcoder (12) and MSC (10) (not shown) ) is similarly constructed.

During communication, the communication unit (50) moves from cell 22 to cell 23. like this The need for handoff within the system (10) is based on comparing the measured signal value with a threshold value. It can be partially determined by In GSM, the communication unit (5 in Figure 4) The scanning unit (scanner) (43) in 0) checks the signal quality of control signals of surrounding cells. Measure the signal quality factor (signal strength, etc.) 1OO), and this measurement value is used by the call controller (BSC) for handoff decisions. 15) (101). In other systems, the base station (18 or 19) A scanning unit (28) disposed in the cells (22 to 27) around the service providing cell Measure the signal quality factor of the communication unit (5o) (100) and use this measurement value as the call controller. Transfer to the controller (BSC15).

Upon receiving the signal quality measurements, the BSC (15) includes the forwarded signal quality measurements. Based on this, the need for handoff and the handoff partner are determined. handoff Having determined the need for The communication unit (50) is commanded to hand off to the other party. Also, BSC (15) is a construction means (36) (e.g. a lookup table or an algorithm). by referring to the serving cell (22) and the partner cell (22) The lowest level signal branch serving both BS (23) is connected to BS (18). It is determined that the switch (34) has been placed. When this judgment is made, the BSC (15) is achieved by cutting the signal path between terminal 1 and terminal p+3. 104) and via terminals 1 and p+2. commanding the switch (34) at the BS (18) to re-establish the audio path; Ru.

As the communication unit advances via cell 23 to cell 24, the process repeats and the call The controller (BSC15) cuts the path via terminals 1 and p+2, and Switch in BS (18) to re-establish the path via terminal 1 and p+l. command to the switch (34). In such a case, ESC(15) becomes BSC(15) By referring to the construction means (36) in the BS (18), configure the switch in the BS (18). It is again identified as the lowest level switch (34).

When the communication unit (50) advances to the cell 25, the BSC (15) 6), the lowest level branching point in the signal distribution system is the BSC ( 15). Judging like this , the controller (35) in the ESC (15) controls the signal between terminal 1 and terminal p+2. to disconnect the signal path and re-establish the signal path via terminals 1 and p+1. , commands the switch (34) in the BSC (15). In addition, BSC (15) is 1, the other party's BS (19) to establish a signal path between terminal l and terminal p+3. command to the switch (34) inside.

After leaving the cell 25, the communication unit (50) is controlled by the B5C16 Upon entering the cell (not shown), the serving BSC (15) configures the construction means (36). By referring to the switch (34) in the transcoder (12) (not shown) (24) provides services to both the serving cell (24) and the partner cell (24). It is determined that this is the lowest level branching point. Judging in this way, service provision B The SC (15) sends the communication unit (50) to the transcoder (12) on the other side. sends a request to the transcoder (12) requesting to hand off to the transcoder (12);

As yet another example, the first communication unit (50 in FIG. 3) within cell 22 an access request requesting access to the second communication unit (51) in 23; Send to the serving BSC (15). BSC(15) is conventional paging method is used to identify the communication unit (51) on the other side as being in the cell 23. Separate. Both the first communication unit (50) and the second communication unit (51) Upon determining the location, the BSC (15), according to a preferred embodiment of the invention, Referring to (36), the lowest level branch point serving both cells is B5. It is determined that the switch (34) is located at 18. Judging like this, The call controller (BSC15) sends a command to this switch (34) to , establishes an audio path between terminal p+3 and terminal p+2. Also, BSC (15) transmits an access permission to the first communication unit on the first frequency (fl), and The access permission is transmitted to the second communication unit (51) on the wave number (f2). 1st letter The communication unit (50) and the first communication unit (51) are tuned to the appropriate frequency. Then, they start exchanging communication signals on their respective frequencies.

During the communication, the second communication unit goes from cell 23 to cell 24 . Communication Uniso) (5 The movement of 1) is carried out by the communication unit (51), and is carried out by the communication unit (51). ) is detected by the signal strength measurement of the control transmission of the ESC via the BS (18). (15).

Upon determining the need for handoff, the call controller (BSC 15) is handed off to the handoff partner cell (24) on another channel (f3). command to the communication unit (51). In addition, the call controller (BSC15 ) cuts the signal path between terminal p+3 and terminal p+2, and disconnects the signal path between terminals p+3 and p+2. The matrix switch (34) is commanded to re-establish the signal path to and from +1. command.

As yet another example, following the example above, the second communication unit (51) The process may proceed to cell 25 from there. As mentioned above, such a move (51) detected by the signal strength measurement carried out by the service provider E. Transferred to SC (15).

At this time, the BSC (15) determines that handoff to cell 25 is appropriate. do. In the preferred embodiment, to perform a handoff from cell 24 to cell 25, The identity of the switch is determined with reference to the construction means (36) in the BSC (15). Ru.

Referring to the construction means (36), the call controller (BSC15) The matrix switch (34) in 5) serves two service areas (24, 2 5) is the lowest level matrix switch bridging.

When this judgment is made, the controller (35) in the BSC (15) The switch (34) is commanded to establish a line path between terminal p+3 and terminal l. command. The controller (35) also constructs a route between p+2 and p+1. The matrix switch (34) in B5Cl3 is commanded to final stage and Then, the controller (35) constructs a path between terminals l and p+3. Command the matrix switch in B51Q.

The communication unit (51) is serviced by another BSC (16 in Figure 1). The process continues when the user advances into another service area. Communication unit (5 1) measures the signal value again as a means of detecting the handoff partner. service The service providing BSC (15) provides both services by referring to the construction means (36). The lowest level signal branch point (transcoder (1 2))). Identifying the lowest level branch point between ESC(15,16) , the serving BSC (15) forwards the handoff request to the transcoder (12). send

Upon receiving the handoff request, the MSC (10) issues a routing request. request) in the transcoder (12) (not shown) and the BSC (16) of the other party's base station (not shown). On the contrary, The handoff partner BSC (16) sends the transfer command to the BSC (16) and the handoff partner. Opponent 9! ! It is transmitted to a switch (34) (not shown) of the BS (not shown).

Figure 3

Claims (10)

[Claims] 1. A method for performing handoff in a cellular communication system, the method comprising: A switch at each point in the signal path bridging at least two cells stage; A handoff of the communication unit from the serving cell to the other cell is instructed. stage of determining whether the serving cell and the other cell are to be bridged identifying a switch in the signal path to the service providing cell; and handing off via the switch; How to do it. 2. measures the signal quality factor and provides an indication based at least in part on the measured value; further comprising the step of determining the need for a handoff and the directed party. A method according to claim 1, characterized in that: 3. the step of transferring the measured value to a call controller of the serving cell; 3. The method according to claim 2, further comprising: 4. Based on the identity of the indicated party and the serving cell, the call controller The method may further include the step of separating the bridging points by means of a controller. The method according to claim 3, characterized in that: 5. Based on the identification of the partner cell and the serving cell, the bridge referencing a look-up table for the identification of the target point. 5. A method according to claim 4, characterized in that: 6. further comprising measuring a signal quality factor of neighboring cells by the communication unit. 3. The method according to claim 2, comprising: 7. The signal quality of the communication unit is determined by cells surrounding the serving cell. The method according to claim 2, further comprising the step of measuring the ratio. Law. 8. A method for performing handoff in a cellular communication system, the method comprising: A switch at each signal distribution point serving at least two service areas. Step of establishing a cell; handoff of communication processing from the serving cell to the other party's cell Step of determining what has been instructed; identifying the switch; sending a handoff request to the common switch; and handing off the communication processing via the common switch; A method characterized by comprising: 9. further comprising the step of determining a base station having at least two cells as a signal distribution point; 9. The method of claim 8, comprising: 10. A transcoder that transcodes signals from at least two base station systems. The method further includes the step of determining the coder as a signal distribution point. 9. The method according to claim 8.