Dynamic offset threshold for diversity handover in telecommunications system

Dynamic offset threshold used for diversity handover in telecommunication system

The foregoing and other objectives, features, and advantages of the present invention can be clarified from the special description of the preferred specific embodiments in the accompanying drawings below. The reference text corresponds to all the same parts in the various drawings. The diagram does not need to be scaled, and its focus is on explaining the principle of the present invention.

Figures 1A, 1B, 1C, and 1D show schematic diagrams of various mobile stages of a mobile station in a specific radio proximity network part of a telecommunication system.

Figure 2 shows the relationship between the signal strength and time of the source base station and the destination base station.

FIG. 3 shows a flow of specific example steps executed by the dynamic offset threshold determination unit according to a specific embodiment of the present invention.

Figure 4 shows a schematic diagram of how the critical value of the dynamic deviation of the line cell changes with the direction of entering the cell.

Figure 5A shows the relationship function between the delivery probability and the signal quality of the source cell and the target cell when the mobile station enters the target cell from different directions.

The time difference shown in FIG. 5B for starting the handover sequence is compared with the starting of the handover sequence based on the dynamic offset threshold and the fixed offset threshold.

Figure 6 shows a schematic diagram of a mobile communication system that can benefit from the use of the present invention.

Figure 7 shows a simple functional block diagram of a part of the UMTS terrestrial radio proximity network, including a mobile station (MS), a radio network controller, and a base station.

FIG. 8 shows a schematic diagram of an exemplary RNC node according to a specific embodiment of the present invention.

FIG. 9 shows a schematic diagram of an exemplary base station node according to a specific embodiment of the present invention.

Figure 10 is a schematic diagram of the reporting mode of the present invention. The methods used include short-term periodic measurement reports and other time-triggered measurement reports.

Figure 11 shows a cost chart of soft handover performed at different points in time.

FIG. 12 shows a schematic diagram reflecting the initial part of the handover sequence executed by the base station and the start of another part of the handover sequence and various points of view.

Background of the invention

This patent application is based on and takes precedence over the U.S. Patent Provisional Application Serial No. 60/250,473 filed on December 4, 2000, entitled "DYNAMIC OFFSET THRESHOLD FORDIVERSITY HANDOVER IN TELECOMMUNICATIONSSYSTEM" ), and the U.S. Patent Provisional Application Serial No. 60/250,476 filed on December 4, 2000, with the title "PRELIMINARY PERFORMANCE OFHANDOVER FUNCTIONS IN TELECOMMUNICATIONSSYSTEM", and the serial number of the simultaneous U.S. patent application (Attorney File No.: 2380- 486), the title is "PRELIMINARY PERFORMANCE OF HANDOVER FUNCTIONS INTELECOMMUNICATIONS SYSTEM", which is fully cited here.

1. Field of Invention

The present invention relates to data communication systems, and particularly relates to diversity handover (for example, soft handover) in telecommunication systems such as broadband code division multi-directional proximity telecommunication systems.

2. Relevant skills and other considerations

In a typical cellular radio system, also called a mobile user equipment unit (UE), it communicates with one or more core networks through a radio proximity network (RAN). The mobile station (MS)/user equipment unit (UE) can be a mobile phone ("cellular" phone) and a laptop device with a mobile terminal, for example, portable, pocket, handheld, and computer It can communicate voice and/or data with wireless proximity network.

The geographic area covered by the radio proximity network (RAN) can be divided into cell areas, and each area is served by a base station (also called "B-node" or "node-B" in some networks). The radio provided by the radio base station equipment in a cell line base station covers a geographic area. Each cell has only one unique identification code, which will be broadcast in that cell. The base station communicates with mobile stations within the range of the base station through an air interface (for example, radio frequency). In the radio proximity network, several base stations are usually connected (for example, using terrestrial cables or microwaves) to a radio network controller (RNC). The radio network controller, sometimes referred to as a base station controller (BSC), supervises and coordinates various activities of the base stations connected to it. The radio network controller is generally connected to one or more core networks.

One example of a radio proximity network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Proximity Network (UTRAN). UTRAN is a third-generation system, which in some points is based on the radio proximity technology of the Global System for Mobile Communications (GSM) developed in Europe. UTRAN is basically a wide-band code division multi-directional proximity (W-CDMA) system. The so-called Third Generation Partnership Project (3GPPP) has been committed to more in-depth UTRAN and GSM-style radio proximity network technology.

Those familiar with this technique will find that in W-CDMA technology, a shared frequency band can be used to simultaneously communicate between a mobile station (MS) and multiple base stations. At the receiving station, the signals occupying the shared frequency band can be identified through the use of high-speed spread spectrum CDMA waveform characteristics and virtual noise coding. These high-speed PN codes are used to modulate the signals transmitted from the base station and the mobile station (MS). The transmitter station uses different PN codes (or time offset PN codes) to generate signals that can be demodulated separately at the receiving station. The high-speed PN modulation can also combine several different propagation paths of the transmitting signal to allow the receiving station to generate a receiving signal from a single transmitting station. Therefore, in CDMA, when the cells are connected to each other, the mobile station (MS) does not need to switch frequencies. Therefore, while the original cell continues to serve the original connection branch, the target cell can support another branch connected to the mobile station (MS). Because during the handover period, the mobile station (MS) will always maintain communication through at least one cell, so the call will not be interrupted. Therefore, it is called "soft handover". Contrary to hard handover, the switching operation mode of soft handover is "make-before-break" (make-before-break).

Assume that an mobile station has established a connection branch with a base station (source base station) serving the cell where the mobile station is located (the source cell). May be triggered periodically or using specific events, the mobile station will measure and report to the control node (such as the'Radio Network Controller, [RNC]) the strength of the preselected transmission signal received from each base station (such as the preamble signal) . In the W-CDMA environment, the measurement report sent from the mobile station to the control node includes the cells that already exist in the "active set" (cells that can use diversity handover) and other monitored cells (such as base stations) Signal strength measurement. When the mobile station moves to a target cell that is not in the effective concentration (served by the target base station), the mobile station always hears the preamble signal from the target base station, and includes the target base station in the cell that it sends to the mobile station. In the measurement report of the control node. Finally, the radio proximity network must decide whether to use the soft handover sequence at the destination base station to add a new connection branch to the mobile station (a new branch related to the destination base station).

Traditionally, the radio proximity network decides to start a handover sequence at the destination base station according to a soft handover algorithm. In the W-CDMA environment, the soft handover algorithm has various specific events. The first event (Event 1A) is the addition of a radio link, which occurs when the measured and filtered leading signal from the destination base station (not in the effective concentration) exceeds a specific handover threshold. This specific handover critical value, also referred to as the fixed offset critical value here, is the fixed offset of the best (strongest) leading signal in the effective set (for example, the source cell), as proposed in Expression 1. of. The fixed offset is preferably a selected constant. A low fixed offset means that the fixed offset threshold is high, so a high signal strength is necessary to start handover. For high fixed offsets, conversation occurs. Instructions on how to select the fixed offset are provided in the Third Generation Partnership Project Technical Specification 25.331 (Third Generation Partnership Project Technical Specification 25.331).

Expression 1: FixedOffsetThreshold=SignalQuality(BestCell)-FixedOffset

The second event (Event 1B) is the removal of the radio link, which occurs when the measured and filtered leading signal from the destination base station is below the critical value of Expression 1. For the occurrence of these events (such as event 1A and event 1B), usually the leading signal must maintain its strength for a preset trigger time and must decompose a specific hysteresis value into the critical expression. In addition, for new radio link events, the effective set cannot be fully loaded. For a more detailed description of the W-CDMA soft handover algorithm, including other events and conditions, please refer to the Radio Resource Management Strategies proposed by Third Generation Partnership Project, Technical Specification Group RAN, Working Group 2 (WG2) in September 1999. , Obtained in 3G TR 25.922, Ver.0.5.0.

The starting point of the handover sequence can be used to define the cell boundary between two cells. If the cell boundary is too far away from the source base station, the mobile station will lose contact with the source base station before the handover is completed. In this case, the call may unfortunately be lost. In addition, in order to maintain a certain level of signal quality of the mobile station, the source base station and the mobile station must increase transmission power when the mobile station is far away from the source base station. Therefore, it will increase the interference between the current cell and other neighboring cells, which will cause the system capacity to decrease. On the other hand, if the cell boundary is too close to the source base station, but the distance to the destination base station is too far, the destination base station (not the source base station) must start its transmission with high output power .

Using the traditional fixed offset critical value in Expression 1, the point system at which the handover starts is basically the same as the current cell and any cell that is not currently in the effective set. Therefore, it is not possible to control when the handover between two specific cells is started, and most of the handover will start at an undesirable point.

The traditional handover sequence executed by the destination base station involves various activities. It usually starts with allocating resources, then sequentially activates the receivers in the destination base station to make it correlate with the mobile station, and then proceed with the mobile station. L1 synchronization. However, some handover sequence activities, such as L1 synchronization, are quite complicated, cumbersome and time-consuming. This feature of these handover sequence activities will affect the overall network efficiency goals, such as avoiding delays (whether it is call setting delay, channel switching delay, handover delay, etc.). In fact, the common characteristic and main reason for delay in most traffic situations is the time required to perform L1 synchronization in various scenarios, including diversity handover.

Various prior art systems (such as the Erichsen CMS88 and CMS30 TDMA system) use a verification receiver to allow a target cell to synchronize the verification receiver with the mobile station to verify the existence of the mobile station. Essentially, the output of the verification receiver indicates whether the mobile station can be detected in the receiving cell. In this type of system, the handover sequence can be carried out with a positive verification result.

US Patent 6,052,598 uses a series of received signal strength measurements of a mobile unit to infer the time when the mobile unit performs handover according to a fixed offset threshold, and provides an opportunity to allocate wireless resources to the expected mobile unit for the inferred handover.

U.S. Patent No. 5,530,912 provides a delivery zone and pre-delivery zone for delivery to neighboring cells in a cell. When the mobile station falls on the pre-handover zone, a free channel will be reserved in the neighboring cells. Only when the mobile station moves to the handover area will the free channel in the neighboring cell be granted.

Therefore, an object of the present invention is to require a technique to accelerate the time-consuming handover activity and thereby reduce the diversity handover delay.

Invention

A telecommunication system has a source base station and a destination base station, and a handover unit has a dynamic offset threshold determination unit to establish a dynamic offset threshold for starting soft handover. When the dynamic offset threshold of soft handover is exceeded, the initial part of a handover sequence will be initiated at the destination base station. Only by starting the preliminary part of the handover sequence can the handover sequence activities closely related to time (such as L1 uplink synchronization) be made. If it is not completed, it can proceed smoothly before the actual time required for the soft handover. The dynamic offset threshold used to start the handover is based on the probability of the mobile station performing the handover. The probability is the statistical probability that the handover will actually occur, and can be based on the previous handover history data of other mobile stations, the same behavior and the same signal strength.

When the signal strength of the destination base station received at a specific mobile station has a predetermined relationship with a fixed offset threshold (for example, exceeds), another part of the soft handover sequence (for example, the soft handover) is activated. Handover the rest of the sequence).

In a non-limiting exemplary embodiment of the present invention, when the signal strength of the destination base station received at a specific mobile station is not lower than the dynamic offset threshold, the dynamic offset threshold determining unit will start at least the soft handover The preliminary part of the sequence. The dynamic offset threshold is the difference between the signal strength of the source base station received by the specific mobile station and a dynamic offset. The dynamic offset is a function of the fixed offset and the probability of the specific mobile station executing the handover criterion.

The probability of determining the dynamic offset threshold is a function of the signal strength of the destination base station received at a specific mobile station. More preferably, the probability of determining the dynamic offset threshold is a function of the signal strength of the destination base station received at a specific mobile station and the signal strength of the source base station received at the specific mobile station.

In the exemplary configuration of the present invention, the dynamic offset threshold determination unit is located in a control node of the telecommunication system, such as a radio network control (RNC) node. The specific mobile station transmits the measurement report of the signal strength of the destination base station and the source base station received at the specific mobile station to the control node, so that the dynamic offset threshold determining unit determines its dynamic offset threshold.

According to an aspect of the present invention, when the dynamic offset threshold determining unit starts at least the preliminary part of the handover sequence, the node where the dynamic offset threshold determining unit is located transmits a message to the destination base station for Initiate at least the preliminary part of the handover sequence at the destination base station.

The present invention can execute the soft handover procedure at a certain point when the execution cost is the lowest, thereby increasing the capacity of the network and reducing the risk of call loss during soft handover.

Schematic description

The foregoing and other objectives, features, and advantages of the present invention can be clarified from the special description of the preferred specific embodiments in the accompanying drawings below. The reference text corresponds to all the same parts in the various drawings. The diagram does not need to be scaled, and its focus is on explaining the principle of the present invention.

Figures 1A, 1B, 1C, and 1D show schematic diagrams of various mobile stages of a mobile station in a specific radio proximity network part of a telecommunication system.

Figure 2 shows the relationship between the signal strength and time of the source base station and the destination base station.

FIG. 3 shows a flow of specific example steps executed by the dynamic offset threshold determination unit according to a specific embodiment of the present invention.

Figure 4 shows a schematic diagram of how the critical value of the dynamic deviation of the line cell changes with the direction of entering the cell.

Figure 5A shows the relationship function between the delivery probability and the signal quality of the source cell and the target cell when the mobile station enters the target cell from different directions.

The time difference shown in FIG. 5B for starting the handover sequence is compared with the starting of the handover sequence based on the dynamic offset threshold and the fixed offset threshold.

Figure 6 shows a schematic diagram of a mobile communication system that can benefit from the use of the present invention.

Figure 7 shows a simple functional block diagram of a part of the UMTS terrestrial radio proximity network, including a mobile station (MS), a radio network controller, and a base station.

FIG. 8 shows a schematic diagram of an exemplary RNC node according to a specific embodiment of the present invention.

FIG. 9 shows a schematic diagram of an exemplary base station node according to a specific embodiment of the present invention.

Figure 10 is a schematic diagram of the reporting mode of the present invention. The methods used include short-term periodic measurement reports and other time-triggered measurement reports.

Figure 11 shows a cost chart of soft handover performed at different points in time.

FIG. 12 shows a schematic diagram reflecting the initial part of the handover sequence executed by the base station and the start of another part of the handover sequence and various points of view.

Detailed description of the invention

In the following description, for the purpose of explanation and not limitation, specific details like special architecture, interface, technology, etc. will be proposed to provide a complete understanding of the present invention. However, those who are familiar with the art will find that the present invention can be implemented in other specific embodiments that are not in these specific details. In other examples, detailed descriptions of well-known devices, circuits, and methods will be omitted so as not to obscure the description of the present invention due to unnecessary details.

The part of the telecommunication system shown in Figure 1A, including the source base station BS _S , Destination base station BS _D , And the control node CN. Source base station BS _S Service cell C ₁ ; Destination base station BS _D Service cell C ₂ . The control node CN controls the source base station BS _S And destination base station BS _D . The control node N has a diversity handover unit 100 responsible for adding and removing connection branches controlled by the control node N. In other words, the diversity handover unit 100 is responsible for which cell (for example, which base station) is to be added to the effective set or which cell is to be deleted from the effective set.

In the time shown in Figure 1A, the mobile station (MS) is on the air interface Iua ₁ Only the source base station BS _S Has a call connection branch CL ₁ . In Figure 1A, the mobile station (MS) is moving in the direction of arrow D and has not yet reached the target cell C ₂ Cell boundaries. Target cell C ₂ The cell boundary is determined by the FixedOffSetThreshold in Figure 1A ₂ The line depicted is related to the fixed offset threshold of Expression 1 (as described above), and represents the position that meets the traditional handover criterion of the mobile station MS (when the mobile station crosses), and the start at the destination base station BS _D The position where the traditional handover sequence of the mobile station MS is performed.

According to the present invention, and as shown in FIG. 1B, when the mobile station MS reaches the FixedOffsetThreshold ₂ Before the line, it started at the destination base station BS _D Perform the preliminary part of the handover sequence related to the mobile station MS. In fact, when the mobile station MS reaches the DynamicOffsetThreshold shown in Figure 1B ₂ At the corresponding position of the line, the preliminary part of the handover sequence is started. As explained later, the preliminary part of the handover sequence contains the destination base station BS _D Set up a receiver to listen to the mobile station MS and the target base station BS _D Perform L1 uplink synchronization of mobile station MS. If the mobile station MS continues to move in the direction of arrow D to cross the FixedOffsetThreshold shown in Figure 1C ₂ Line, at the destination base station BS _D The revised master handover sequence of the mobile station MS will be carried out. The modified main handover sequence includes one or more traditional handover sequence operations that were not executed during the initial part of the handover sequence (for example, the remaining traditional handover sequence operations were not executed). The performance of the modified master handover sequence will cause the establishment of a second connection branch CL with the mobile station (MS) ₂ , The second branch system passes through the destination base station BS _D And tied to the air interface Iua ₂ middle.

As the name suggests, DynamicOffsetThreshold ₂ The line does not stand still, but changes or moves. How to determine DynamicOffsetThreshold will be provided later ₂ Criteria and expressions for line position.

The activation of the preliminary part of the handover sequence is triggered by the dynamic offset threshold determination unit 102 of the diversity handover unit 100. As explained below, the dynamic offset threshold used by the dynamic offset threshold determining unit 102 to start the preliminary part of the handover sequence is based on the probability that the mobile station (MS) will perform soft handoff.

In a non-limiting exemplary embodiment of the present invention, when the signal strength of the target base station received by the specific mobile station is not lower than the dynamic offset threshold, the dynamic offset threshold determining unit will start the initial Handover sequence. The dynamic offset threshold, as shown in Figure 1B, DynamicOffsetThreshold ₂ What the line reflects is the difference between the signal strength of the destination base station received by a specific mobile station and the dynamic offset, as shown in Expression 2.

Expression 2: DynamicOffset=FixedOffset+(K*Probability(Handover))

In Expression 2, K is a constant. The constant K in Expression 2 is used to determine the importance of the probability function to the overall offset, and to map the probability to an appropriate value.

Next, the dynamic offset used in Expression 2 is a function of the handover criterion and the probability of the specific mobile station to achieve the handover criterion, as shown in Expression 3.

Expression 3: DynamicOffsetThreshold=SignalQuality(SourceCell)-DynamicOffset

According to one mode of the present invention, a method for determining the probability of handover is to make the probability of handover toward a target cell a function of the signal quality measured from the target cell, as shown in Expression 4 (for example).

Expression 4: P(H(SQ(x)))=N _max /N _SQ(X)

In Expression 4, P(H(SQ(x))) is the probability that a specific signal quality (for example, signal quality (x)) will result in handover (H); N _m a _x Is the number of users who have reached the highest signal quality; and N _SQ(X) It is the number of users who have reached a certain signal quality (for example, signal quality (x)). The highest signal quality is the highest signal quality measured by any user from the target cell (for example, from the target base station), and can be from previous measurement reports related to the signal strength of the target base station (for example, from all users) To confirm. Therefore, by observing the signal quality of a group of users from the target cell, the system can know how many users have reached a specific signal quality. Therefore, the diversity handover unit 100 will continue to track and store in the memory to achieve the highest signal quality (N _max ) And the number of users reaching each signal quality level. Using this information, the dynamic offset threshold determination unit 102 can determine how many users reach a higher signal quality level at any signal quality level.

Therefore, the diversity handover unit 100 determines the signal quality when the mobile station reaches the turning point. The turning point is the place where (1) the mobile station (MS) performs handover, and (2) the mobile station (MS) does not perform handover at an equal probability before the mobile station (MS) enters a cell. After passing this turning point, most users will continue to move toward the target cell and finally deliver.

However, in some cases, the signal quality of the target cell used in the model of Expression 4 may not be sufficient to determine the probability of delivery. If the mobile station has a good radio connection with the source base station and the destination base station before reaching the turning point (for example, on a large hill where two base stations can be seen), the mobile station from the destination base station The signal strength will be higher. However, this high level may still be far lower than the signal quality of the source base station, so the handover will not start. In this regard, refer to Figure 2, which is a diagram of the relationship between signal quality and time. The example of signal quality from the source base station and the destination base station is shown. The signal quality of the destination base station is particularly high, but Still not enough to trigger a soft handover. Later, at the point where the handover is finally performed, the signal strength of the destination base station is quite low, but compared with the source base station, it is still high enough to start the handover sequence. In these situations, the probability function cannot be used because all users have reached the maximum signal quality of the target base station before the turning point and the probability function is always 1.

With reference to the foregoing, the better probability function mode is related to the signal quality of the source base station and the signal quality of the destination base station. The relationship R between the two signal qualities can be defined by Expression 5.

Expression 5: R=(SignalQuality(Destination Cell))/(SignalQuality(SourceCell))

The high signal quality of the target cell does not mean that the relationship is high. Therefore, the problems found when only observing the signal quality of the target cells can be solved. Compared with the source cell, when the quality of the signal measured from the target cell increases, the relationship will increase. It is sufficient to track the relationship until the signal quality from the target cell is as good as the signal quality from the source cell, that is, the relationship is 1.

The probability of delivery to a target cell according to this second preferred mode is shown in Expression 6.

Expression 6: P(H(R(x)))=N _max /NR(x)

In Expression 6, P(H(R(x))) is the probability of passing (H); N _max It is the number of users whose relationship R is 1; and NR(x) is the number of users who have reached the specific relationship R(x).

The specific exemplary basic steps performed by the system diversity handover unit 100 shown in FIG. 3, including its dynamic offset threshold determination unit 102, are in accordance with a specific embodiment of the present invention. Step 3-1 describes that the diversity handover unit 100 obtains base stations that are not in the effective set (for example, the destination base station BS _D ) Signal quality measurement. Of course, the diversity handover unit 100 will, and most likely, receive the signal quality measurement of the base station in the effective concentration, but the purpose of this activity is to determine whether to add a new base station to the effective concentration, which means The signal quality of qualified base stations must be obtained through measurement. Reference opinions on the signal quality measurement report time will be provided later.

In step 3-2, the diversity handover unit 100 checks whether a preliminary handover procedure flag has been set, which is referred to as "flag" for short. At first, it will be assumed that the initial handover procedure flag is not set, and then step 3-3 will be executed.

Step 3-3 is the first step of the dynamic offset critical value determining unit 102. The basic steps of the dynamic offset critical value determining unit 102 are the part framed by the dashed line 102 in FIG. 3. In step 3-3, the dynamic offset threshold determination unit 102 checks whether the handover probability exceeds a preset percentage (for example, 50%, which means that the mobile station (MS) has crossed the turning point). As mentioned earlier, the handover probability is a function of the signal strength of the destination base station (as explained in Expression 4 above). In addition, as another example, the handover probability is a function of the signal strength of the destination base station and a function of the signal strength of the source base station (as explained in Expression 5 above). In any event, as in part of step 3-3, the dynamic offset threshold determination unit 102 checks the stored information about the leading signal that has reached the qualified base station measured by the mobile station (MS). Signal strength statistics of previous mobile station instances, and based on a preset basis (such as expression 4 or expression 5), the probability of soft handover to the qualified base station is determined for the mobile station (MS) currently reporting.

If the handover probability of the mobile station (MS) currently being reported is not greater than the preset percentage (for example, 50%), the execution of the dynamic offset threshold determination unit 102 will end, as reflected in step 3-10. On the other hand, if the handover probability of the currently reporting mobile station (MS) is greater than the preset percentage, the dynamic offset threshold determination unit 102 will execute steps 3-4 to 3-6, and also step 3. -7 to step 3-9.

In step 3-4, the dynamic offset critical value determining unit 102 calculates the DynamicOffset of Expression 2. The dynamic offset threshold determination unit 102 will continue to calculate the DynamicOffsetThreshold of Expression 3. Next, after the DynamicOffsetThreshold of the target cell is calculated, in step 3-6, the dynamic offset threshold determination unit 102 determines that the mobile station (MS) is to be transferred from the target base station BS _D Whether the received measurement and filtered preamble signal exceeds the DynamicOffsetThreshold. If the DynamicOffsetThreshold is exceeded, in step 3-7, the dynamic offset threshold determination unit 102 will execute its preliminary handover procedure.

In the execution of the preliminary handover procedure in step 3-7, the dynamic offset threshold determination unit 102 will transmit the preliminary handover start information 110 to the destination base station BS _D ,As shown in Figure 1. The initial delivery of the initial information 110 will refer to the destination base station BS _D The required information is transmitted to the destination base station BS _D , In order to perform the preliminary part of the handover sequence of the mobile station (MS) and authorize the target base station BS _D Start the preliminary part of its handover sequence. The destination base station BS _D The information needed to perform the preliminary part of the handover sequence includes the mixing code and the identity of the mobile station (MS) [the mixing code can be used as the identity of the identity].

The information needed to perform the preliminary part of the handover sequence will be included in the revised radio link setting information. The modified radio link setting information includes a flag to inform the destination base station that the initial or remaining part of the handover sequence is to be executed.

After the diversity handover unit 100 executes its preliminary handover procedure, it will set the pre-procedure flag in step 3-8. After starting the preliminary part of the handover sequence, the destination base station BS _D A timer is set to determine whether the mobile station (MS) has crossed the DynamicOffsetThreshold and whether it has crossed the FixedOffsetThreshold. If the destination base station BS _D If the set timer has expired, the destination base station BS _D It is assumed that the mobile station (MS) returns (changes direction instead of towards the destination base station BS) _D Forward), or the call has ended, and the steps in the preliminary part of the handover sequence have been cancelled. Therefore, in order to reflect that the destination base station BS may be cancelled _D In the preliminary part of the handover sequence performed, in step 3-9, the dynamic offset threshold determination unit 102 sets a timer. After the timer is set, the dynamic offset threshold determination unit 102 will end the execution actions related to the measurement report of the reporting mobile station (MS).

After receiving the measurement report of step 3-1, if the diversity handover unit 100 determines in step 3-2 that the preliminary handover procedure flag has been set, then step 3-11 will be executed. In step 3-11, it will be determined whether the reporting mobile station (MS) has crossed the FixedOffsetThreshold, and whether it is ready for the destination base station BS _D Perform a modified handover sequence (for example, the rest of the traditional handover sequence that is not included in the preliminary part of the handover sequence). If the reporting mobile station has moved to the base station BS suitable for the purpose _D When the modified handover sequence is executed, the diversity handover unit 100 will execute the modified handover initiation procedure in step 3-12. The activity in the modified handover initiation procedure executed by the diversity handover unit 100 is to transmit the handover initiation information to the destination base station BS _D , The handover start information 112 shown in FIG. 1C. When receiving the handover start information 112, the destination base station BS _D Then the modified handover sequence will be executed. The destination base station BS _D The information required to perform the modified handover sequence includes the mobile station's mixing code and the mobile station (MS) identity, as mentioned above. The various points of view of the revised handover sequence will be discussed below with reference to FIG. 12.

If it is determined in step 3-11 that the other parts of the handover sequence cannot be executed, step 3-13 will check whether the timer (set in step 3-9) has expired. If the timer set in step 3-9 has expired, the dynamic offset threshold determination unit 102 will find the destination base station BS _D It is considered that the reporting mobile station (MS) no longer needs to hand over or is stopped, so the steps included in the preliminary part of the handover sequence of the reporting mobile station (MS) are cancelled. So know the destination base station BS _D After the initial part of the handover sequence has been cancelled, the dynamic offset threshold determination unit 102 will again consider that the initial part of the handover sequence of the mobile station that is reporting has not been executed, so it will be cleared in step 3-14 Flag for the initial delivery procedure. After the flag is cleared in step 3-14, or if it is determined in step 3-13 that the timer has not expired, the dynamic offset threshold determination unit 102 will end its processing according to the current measurement report (such as step 3- 10).

When the signal quality measurement report of the qualified base station is received, the steps in Figure 3 will be executed. It should be understood that, for a specific mobile station (MS), the qualified destination base station BS added by the mobile stations listening and connection branches _D There are several, so there will be more than one destination base station BS _D Perform the steps in Figure 3.

It can be understood from the foregoing that, according to the present invention, the dynamic offset threshold determines the starting point of the handover process, especially the starting point of the preliminary part of the handover process. Interestingly, the dynamic offset threshold will be different between different cell pairs. Depending on the probability of handover from the source base station to the destination base station, the dynamic offset threshold between two specific cell pairs will be different. For illustration, the two mobile stations shown in Figure 4, MS ₁ With MS ₂ , Is changing from a different cell C ₁ With C ₃ Target cell BS _D move. First Action Station (MS ₁ ) With service cell C ₁ Base station BS ₁ Has a first connection branch, and a second mobile station (MS ₂ ) With service cell C ₃ Base station BS ₃ There is a first connection branch. Two mobile MS ₁ With MS ₂ Arrow D ₁ With D ₂ Target cell represented by BS _D Move, so it may be delivered to the target cell BS _D . However, from cell C ₁ Mobile station (MS ₁ ) Dynamic offset threshold _2-1 (DynamicOffsetThreshold _2-1 ) The position of the line is the same as that from cell C ₃ Mobile station (MS ₂ ) Dynamic offset threshold _2-2 (DynamicOffsetThreshold _2-2 ) The position of the line is different. In other words, from cell C ₁ Mobile station (MS ₁ ) Dynamic offset threshold _2-1 (DynamicOffsetThreshold _2-1 ) The radius of the line (larger) is the same as that from cell C ₃ Mobile station (MS ₂ ) Dynamic offset threshold _2-2 (DynamicOffsetThreshold _2-2 ) The radius of the line is different. Therefore, according to the present invention, when approaching a target cell (such as a target base station), the DynamicOffsetThreshold will change depending on which direction it enters from.

Therefore, the two mobile stations MS shown in Figure 4 ₁ With MS ₂ The probability function used is different, so the position of the turning point of each mobile station MS is also different. For example, referring to Figure 5A, two mobile stations MS are shown ₁ With MS ₂ The two possible handover probabilities are a function of the relationship between the signal quality of the source base station and the destination base station. When the relationship between the signal quality of the source base station and the destination base station increases, handover may occur, so the difference between the FixedOffsetThreshold and the DynamicOffsetThreshold will also increase.

Figure 5B compares the time difference in starting the handover sequence according to the critical value represented by the dynamic offset critical value and the fixed offset critical value. In addition, the case 1 shown in Fig. 5B is shown in Fig. 4 (for example, a mobile station (MS ₁ )) and Case 2 in Figure 4 (e.g. mobile station (MS ₂ )) dynamic offset critical value.

The initial part of the handover sequence includes steps in the destination base station BS _D Activate the receiver of the mobile station (MS), and at the destination base station BS _D Perform L1 synchronization of the mobile station (MS). No matter whether the receiver is activated or the synchronization operation is activated, it will not cause any additional radio interference. However, the pre-allocation of hardware resources required to perform the preliminary part of the handover sequence still has a cost problem. Therefore, it is important that when the initial part of the handover sequence is started, the mobile station (MS) and the destination base station BS _D Must be close enough to make the destination base station BS _D The mobile station (MS) can be detected. Otherwise, when performing the initial part of the handover sequence, it will be at the destination base station BS _D A lot of hardware resources are wasted. The choice of the constant K in Expression 2 must be high enough so that the initial part of the handover sequence will not start too late, but it must be low enough so that it will not start too early due to these factors.

With reference to the above, for example, in step 3-1, the mobile station (MS) generated information about the destination base station BS _D The signal quality measurement report of will be forwarded to the control node. In general W-CDMA, when an event is triggered, for example, when the destination base station BS _D When the signal quality of is higher than the specific threshold required for handover, the measurement report will be sent from the mobile station (MS) to the control node. If an event is used to trigger a measurement report, the previous measurement signal quality level at the mobile station (MS) must be tracked, and when the handover event is triggered, these records must be forwarded to the control node CN. As for the alternative, regular measurement reports are also transmitted from the mobile station (MS) to the control node CN. This periodic measurement report contains more signal transmissions. Then there is a change of using only periodic measurements in a short period of time in order to collect the necessary statistics from several mobile stations (MS), as shown in Figure 10. Later, you can use periodic measurements to collect new statistics. In this way, the probability function can be adapted to the current traffic conditions, but it will not use too much signal transmission. It is very important that this method can be applied to the current traffic conditions, because the network operator does not need to manually adjust the control node and the base station.

In the exemplary configuration of the present invention, the dynamic offset threshold determination unit is located in a control node of the telecommunication system, such as a radio network control (RNC) node. The specific mobile station will send a measurement report of the signal strength of the destination base station received at the specific mobile station to the control node, so that the dynamic offset threshold determination unit can make predictions.

The present invention can execute the soft handover procedure at a certain point when the execution cost is the lowest, thereby increasing the capacity of the network and reducing the risk of call loss during soft handover. The cost of execution can be expressed by a combination of radio resources used, hardware resources used, and the proportion of lost calls. Fig. 11 shows a schematic diagram of the execution cost function of the handover program executed at different time points. If the mobile station (MS) suddenly changes direction or terminates the call, the resources already set for the mobile station (MS) will be wasted. In order to minimize the waste of resources in such events, the handover procedure can be divided into smaller continuous actions, each of which is triggered by its critical value. Then, when the probability of handover increases, users can continue to set more and more resources.

Therefore, the present invention does not predict when a fixed threshold handover of a mobile station (MS) will occur, but can provide a dynamic offset threshold for starting soft handover. When the dynamic offset threshold of soft handover is exceeded, the initial part of the handover sequence will be initiated at the destination base station. Only by starting the preliminary part of the handover sequence can the handover sequence activities closely related to time (such as L1 uplink synchronization) be made. If it is not completed, it can proceed smoothly before the actual time required for the soft handover. The dynamic offset threshold for starting a handover is based on the probability of the mobile station performing a handover. The probability is the statistical probability that the handover will actually occur, and can be based on the previous handover history data of other mobile stations, the same behavior and the same signal strength.

Together with the other graphs in Fig. 3, Fig. 12 shows a schematic diagram of the initial part of the handover sequence and the start of the remaining (other) parts of the handover sequence and various viewpoints. In particular, FIG. 12 shows examples of basic actions related to the mobile station (MS), the destination base station, and the control node, as well as specific signal transmission and other transmissions between these entities.

Action 12-1 of FIG. 12 is to transmit the measurement report from the mobile station (MS) to the control node CN. Of course, the transmission of the measurement report will pass through the base station, such as the source base station or another base station in the effective concentration. When the control node receives the measurement report, the control node evaluates the measurement result in the measurement report, as shown in action 12-2. The evaluation of action 12-2 includes several steps in Figure 3. One of the steps involved is step 3-1. Obtain the signal strength measurement result of the destination base station from the mobile station (MS) (the destination base station is not in the effective concentration). In addition, action 12-2 includes steps 3-3 to 3-6 in Figure 3, which include determining the handover probability (step 3-3) and calculating the DynamicOffset of Expression 2 (step 3-4) and calculating the expression 3 DynamicOffsetThreshold (steps 3-5).

If it is determined in step 3-6 (included in action 12-2) that the measured signal quality of the destination base station received by the mobile station (MS) exceeds the DynamicOffsetThreshold, the initial handover procedure of the control node (step 3-7). The preliminary part of the handover sequence is basically represented by the upper dashed block in FIG. 12. The execution of the preliminary handover procedure of the control node includes action 12-3 (uplink resource allocation) and action 12-4 (transmitting uplink radio link configuration request information from the control node to the destination base station), And (after the uplink radio link is successfully set) receive UE detection information (action 12-8). Examples of the types of resources allocated include radio resources for traffic functions (for example, coding, resources for handling permissions and congestion) and hardware resources (for example, receiver (RX) cards allocated to users, [possibly] shared resources Permissions and congestion processing [for example, similar processor use cases]).

Sending the uplink radio link setting request (action 12-4) from the control node to the destination base station will cause two basic actions at the destination base station. The two basic actions include the initial part of the handover sequence executed by the destination base station. The first action is to turn on the confirmation receiver of the destination base station to listen to the mobile station where soft handover will occur in advance (action 12-5). The second action is to perform the uplink synchronization procedure between the mobile station and the destination base station (action 12-7). The uplink synchronization procedure involves the newly activated receiver at the destination base station receiving passive transmissions from the mobile station (action 12-6). The uplink synchronization procedure includes measuring or determining the time position of the mobile station. Determining the time position of the mobile station is quite complicated and time-consuming, but according to the present invention, it is performed at a less important time. The various viewpoints of uplink synchronization and the details of the synchronization searcher used to determine the time position of general mobile stations can be obtained from the following US patent application, which is incorporated herein by reference: US Patent Application Serial No. 09/452,105, The title is "Synchronization of Diversity Handover Destination Base Station"; and US Patent Application Serial No. 09/070,778, titled "Search Window Delay Tracking In Code DivisionMultiple Access Communication System".

Assuming that the destination base station can complete the uplink synchronization related to the mobile station, an MS detection information (for example, UE detection information) will be transmitted from the destination base station to the control node, as shown in action 12-8. At this point, the control node will execute the flag and timer setting steps of steps 3-8 and 3-9 in FIG. 3.

The reception of the uplink radio link setting request information in action 12-4 will start a timer at the destination base station. If the destination base station cannot detect the mobile station before the timer expires (using the verified receiver from action 12-5), the resources set for the receiver and the mobile station will be removed. If the signal quality between the mobile station and the destination base station never exceeds the FixedOffsetThreshold of Expression 1 (for example, if the mobile station changes direction or terminates the call before entering the destination cell), this type of timing The device can also be used to remove these resources.

When the measured signal quality of the target base station received by the mobile station (MS) exceeds the FixedOffsetThreshold of Expression 1, it will be determined that the mobile station (MS) has actually entered the delivery area of the target cell. The system shown in Figure 12, such as action 12-9, transmits the measurement report from the action to the control node. The measurement report transmission of action 12-9 is followed by the measurement report transmission of 12-1 and is independent of each other. For example, action 12-10, the measurement report will be evaluated to determine whether the handover sequence has been completed. The evaluation of action 12-10 in FIG. 12 involves step 3-1, step 3-2, and step 3-11 in FIG. 3. In particular, in the following discussion, it will be assumed that when the measurement report is performed in actions 12-9, the measured signal strength of the signal quality of the target base station received by the mobile station (MS) exceeds the FixedOffsetThreshold ( See step 3-11).

When the signal quality of the destination base station received by the mobile station (MS) exceeds the FixedOffsetThreshold of Expression 1, the remaining part of the handover sequence will be executed. Since the preliminary part of the handover sequence (as described above) has been performed, the time position of the mobile station (MS) can be known from the uplink L1 synchronization procedure of the preliminary part of the handover sequence. Therefore, the actual handover of the mobile station can now be performed, and the destination base station does not need to spend precious time on performing the time-consuming L1 uplink synchronization work.

The rest of the handover sequence is basically shown by the dashed block at the bottom of FIG. 12. Such as action 12-11, downlink resources will be allocated at the control node. Examples of such downlink resources include radio resources for traffic functions (for example, coding, resources for processing permissions and congestion); hardware resources (transmitter (TX) cards allocated to users, [possibly] shared resources License and congestion processing [similar to processor usage]); DL transmission resources (reserved transmission channels for user data). Downlink radio link setting request information will be transmitted from the control node to the destination base station, such as action (action 12-12). Receiving the downlink radio link setting request information at the destination base station will cause the destination base station to perform a radio link setting operation. The RL setting includes the resource allocation and organization required by the radio link, similar to an RX card. The radio connection management algorithm will also be executed at the destination base station. After successfully setting the radio link, the destination base station will send a radio link setting response message to the control node, as shown in actions 12-14.

After knowing that the radio link between the destination base station and the mobile station (MS) has been successfully set, the control node will send an active set update message to the mobile station (MS), as shown in actions 12-15. The effective set update information of actions 12-15 can basically instruct the mobile station (MS) to put the destination base station into the effective set, so as to establish a connection branch through the destination base station. Assuming that the destination base station uses AAL2 to transmit user data, the destination base station (such as actions 12-16) will internally establish an AAL2 connection through the destination base station to process the new connection branch. For the destination base station that uses other protocols for user data transmission, another appropriate connection will be established at the base station. Action 12-17 is the information from the destination base station, which is used to confirm that the destination base station has in fact established its internal (for example, AAL2) connection.

When receiving the first user data (as sent in action 12-18), the destination base station will turn on the mobile station (MS) transmitter in action 12-19. After the transmitter is turned on, the target base station and the mobile station (MS) will perform a power boost operation (action 12-20), which can determine the power level required for the base station to transmit. After determining the appropriate transmission potential of the base station, the downlink synchronization procedure of action 12-21 will be performed between the target base station and the mobile station (MS). After successfully completing the downlink synchronization procedure, the mobile station (MS) will send a valid set update completion message (such as action 12-22) to the control node. The destination base station will send a radio link restoration instruction to the control node in action 12-23.

Therefore, it can be clearly found from the foregoing description, especially from FIG. 12, that the present invention will start the initial part of the handover sequence of a specific mobile station at the destination base station, and then start the handover of the specific mobile station at the destination base station. The other part of the sequence (for example, the rest of the handover sequence). The initial part of the handover sequence involves operations between the destination base station and a specific mobile station, and its time requirements are greater than the operations performed during the rest of the handover sequence. In particular, in the example shown, the preliminary part of the handover sequence includes the L1 uplink radio synchronization of the specific mobile station.

One of the non-limiting exemplary configurations of the present invention is shown in Universal Mobile Telecommunications (UMTS) 10 as shown in FIG. 6. The representative, connection-oriented, external core network shown in Cloud 12 can be the Public Switched Telephone Network (PSTN) and/or Integrated Services Digital Network (ISDN). The representative, non-connection-oriented, external core network shown in Cloud 14 may be the Internet. Both core networks are coupled to their corresponding service nodes 16. The PSDN/ISDN connection-oriented network 12 is connected to a connection-oriented service node shown by a mobile switching center (MSC) node 18 that provides circuit switching services. The non-connection-oriented network 14 of the Internet is connected to a general packet radio service (GPRS) node 20 that provides packet switching services, sometimes referred to as a serving GPRS service node (SGSN). .

Each core network service node 18 and 20 is connected to a UMTS terrestrial radio proximity network (UTRAN) 24 through a radio proximity network (RAN) interface called an Iu interface. The UTRAN 24 includes one or more radio network controllers (RNC) 26. For simplicity, UTRAN 24 in Figure 6 only shows two RNC nodes, RNC 26 ₁ With RNC 26 ₂ . For the sake of simplicity, only one of the RNC nodes 26 shows the time position estimator 100 of the present invention in FIG. 6. Each RNC node 26 is connected to multiple base stations (BS) 28. For example, and for the sake of simplicity, each RNC node 26 only displays two connected base station nodes. Regarding this, RNC 26 ₁ Service base station 28 _1-1 And base station 28 _1-2 , While RNC 26 ₂ Service base station 28 _2-1 And base station 28 _2-2 . It can be found that each RNC can serve a different number of base stations, and each RNC does not need to serve the same number of base stations. In addition, FIG. 6 shows that the RNC can be connected to one or more other RNC mobile stations (MS) in the URAN 24 through the Iur interface. For example, the mobile station (MS) 30 shown in FIG. 6 will be connected via radio or air interface. 32 communicates with one or more base stations (BS) 28. Each radio interface 32 is respectively an Iu interface, an Iub interface, and an Iur interface as shown by a dotted line in FIG. 6.

Preferably, the radio proximity is based on wide-frequency code division multi-directional proximity (WCDMA) using CDMA spread spectrum coding to configure different radio channels. Of course, other proximity methods can be used. WCDMA provides broadband multimedia services and other high-speed transmission rate requirements, as well as robust features like diversity handover and RAKE receivers to ensure high quality. Each user mobile station (MS) or equipment unit (UE) 30 will be assigned its own mixing code so that the base station 28 can recognize the transmission of a specific mobile station (MS) and allow the mobile station (MS) to Identify the transmission of the base station belonging to the mobile station (MS) from all other transmissions and noise in the same area.

FIG. 7 shows a general view of the nodes of the mobile station (MS) 30 and similar radio network controller 26 and base station 28. The mobile station (MS) 30 in FIG. 7 includes a data processing and control unit 31 for controlling various operations required by the mobile station (MS). The data processing and control unit 31 of the mobile station (MS) provides control signals and data to a radio transceiver 33 connected to an antenna 35.

The exemplary radio network controller 26 and base station 28 shown in FIG. 7 are radio network nodes, which respectively include a corresponding data processing and control unit 36 and 37 for executing the RNC 26 and the user equipment unit (UE) 30 Various radio and data processing operations required for communication between. The data processing and control unit 36 of the RNC includes the diversity handover unit 100 of the present invention and the dynamic offset critical value determination unit 102 of the present invention. Part of the equipment controlled by the data processing and control unit 37 of the base station includes a plurality of radio transceivers 38 connected to one or more antennas 39.

FIG. 8 shows a detailed schematic diagram of an exemplary non-restricted RNC node 26 in the present invention. The RNC node 26 in FIG. 8 is a switching node with a switch 120. The switch 120 is used to connect other components in the RNC node 26 with each other. Such other components include expansion terminal 122 ₁ To 122 _n , And an expansion terminal 124. Expansion terminal 122 ₁ To 122 _n The basic function of is used to connect the RNC node 26 to the base station 28 served by the RNC node 26; the expansion terminal 124 is used to connect the RNC node 26 to the core network via the Iu interface.

Other components of the RNC node 26 also include a diversity handover unit 126; an ALT unit 128; a codec 130; a timing unit 132; a data service application unit 134; and a main processor 140. Those familiar with the art will generally find the functions of these components. It should be noted that the ALT unit 128 is a unit for providing multiplexing and demultiplexing and (optionally) queuing different cell protocols. In an example of the present invention, the diversity handover unit 100 and its dynamic offset threshold determination unit 102 are located in the diversity handover unit 126. One or more functions in the dynamic offset threshold determination unit 102 may be performed by the main processor 140.

The system shown in FIG. 9 is not a limitation, and is a detailed schematic diagram of an exemplary base station (BS) node 28 according to a specific embodiment of the present invention. Similar to the RNC node 26, the base station (BS) node 28 in FIG. 9 is a switching node with a switch 220, which is used to interconnect other constituent elements in the base station (BS) node 28. Such other components include the expansion terminal 222; the ALT unit 228; the BS main processor 240, and the interface circuit board 242.

The expansion terminal 222 connects the base station (BS) node 28 to the radio network controller (RNC) node 26, and therefore includes an Iub interface. Like the radio network controller (RNC) node 26, the ALT unit 228 is used to provide multiplexing and de-multiplexing and (optionally) a unit for queuing different cellular protocols.

During this preliminary period, the base station will only receive data, and there will be no transmission. The data is sent from the receiver circuit board to the main processor for processing. When performing UL synchronization, a message is sent to the RNC. Therefore, the antenna 39, the amplifier and filter 280, the receiving circuit board 270, the interface 240, and the expansion terminal 222 are involved. The difference in the rest of the handover sequence is that it will be transmitted to the MS, which means that the transmitter circuit board 260 is also involved.

The present invention has been described with reference to the most practical and preferred specific embodiments. It should be understood that the present invention is not limited to the specific embodiments disclosed. On the contrary, it is intended to cover the spirit and scope of the appended patent application. Various modifications and equivalent configurations.