KR100601155B1 - Methods and systems for dynamic threshold adjustment for handoffs in radio communication sysems - Google Patents

Abstract

A method and system for performing handoff in a wireless communication system using adaptively varying thresholds is described. The adaptive threshold is a function of the quality level of the best source or worst source of the active set. The ramp function can be used over a range of quality values within the adaptive threshold function.

Wireless Communication System, Handoff, Threshold, Source, Ramp Function

Description

Dynamic Threshold Adjustment Method and System for Handoff in Wireless Communication System

The present invention relates generally to wireless communication methods and systems, and more particularly to a system in which a connection can be handed over from one channel or base station to another.

The cellular telephone industry has made remarkable advances in commercial operations in the United States as well as in the rest of the world. Growth in metropolitan areas is far exceeding expectations and rapidly surpassing system capacity. If this continues, the growth effects of the industry will soon reach the minimum market. In addition to meeting these growing capacity demands, innovative approaches are needed to maintain high quality services and avoid price increases.

In cellular systems, typically, a mobile station changes its location to move away from the coverage area of one base station to the coverage area of another base station, for example, to transfer access processing between the mobile station and the base station to another base station. A function for doing so is provided. Since the communicable area associated with a base station is commonly referred to as a "cell", this type of handoff is commonly referred to as an "intercell" handoff. Depending on the quality of the current channel, it may be desirable to transfer the connection from one channel of the base station to another channel supported by this same base station, which is commonly referred to as an "intracell" handoff.

So-called "hard" handoff refers to a handoff performed when there is no significant overlap between transmissions received from the original serving base station and transmissions received from the new target base station. Referring to Figure 1 (a), during hard handoff, mobile station MS typically disconnects its first base station BTS1 and then establishes a connection to its new base station BTS2.

In contrast, a "soft" handoff refers to a handoff when the mobile receives virtually the same information from two (or more) transmission sources for a certain period of time. A scenario of a typical soft handoff is shown in FIG. 1 (b). Here, before starting the soft handoff, the MS is connected to BTS1. During soft handoff, the MS establishes a connection to BTS2 without quitting the connection to BTS1. Each base station in communication with a given mobile station may be referred to as a member of the " active set " of the mobile station. At some point after the connection to BTS2 is established, the connection to BTS1, which is the end of the soft handover process, is released. By overlapping transmissions from BTS1 and BTS2, the mobile station can smoothly switch from receiving information from the first serving base station to receiving information from the new target base station. During soft handoff, the mobile station can also take advantage of the fact that by performing diversity selection / combination on the two received signals, it receives substantially the same information from the two sources to improve the received signal quality.

For simplicity, the above examples of hard and soft handoff have been described with reference to base stations using omni-directional antennas, i.e. each base station transmits a signal that is propagated in 360 degrees in a substantially circular direction. However, as those skilled in the art will appreciate, antenna structures and transmission techniques other than the above may also be used in the wireless communication system. For example, a cell may be subdivided into a number of sectors, such as three sectors where each sector covers 120 degrees, as shown in FIG. Alternatively, the system or cell may use an array antenna structure as shown in FIG. Here, a typical wireless communication system 200 includes a wireless base station 220 using a fixed-beam phased arrangement (not shown). The phased arrangement generates a plurality of fixed narrow beams B ₁ , B ₂ , B ₃ , B _4, etc. extending radially from the base station 220, wherein at least one B ₁ is associated with the MS 210. Used to communicate The beams are preferably overlapped to create a continuous coverage area to serve the wireless communication cell. Although not shown, the phased array may actually consist of three phased array sector antennas.

Naturally, the principles described above with respect to the hard and soft handoffs for the omnidirectional antennas of FIGS. 1A and 1B can be mapped directly to other systems using split and / or array antennas. In the latter type of system, hard and soft handoff may be performed between sectors or beams of the same base station, as well as between sectors or beams connected to different base stations.

Both types of handoffs have their disadvantages and advantages. Soft handoff, on the other hand, provides a robust mechanism for changing the connection from one base station to another. However, because the mobile station is connected to more than one base station during soft handoff, soft handoff requires more system resources than hard handoff. Thus, the advantage of hard handoff is that the demand on system resources is reduced, while the disadvantage is that the call is more likely to be missed compared to soft handoff.

Any type of access method, such as frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), or a combination thereof Both hard and soft handoffs may be used in a wireless communication system. For purposes of explanation rather than limitation, the foregoing description primarily describes the techniques according to the invention in the form of conventional techniques and CDMA systems, but those skilled in the art will appreciate that the techniques of the invention may be used in systems using any access method as well. will be. In a wireless communication system using CDMA access technology, a mobile station can be simultaneously connected to one or more sectors belonging to one or more base stations. As mentioned above, the sector that the mobile station uses for communication is referred to as " active aggregation. &Quot; For example, consider the system shown in FIG. 4 with cells C1 and C2 each having sectors S1 ... S6. Assume that A, B, and E each represent an active set of sectors C1-S2, C1-S2, and C2-S5, that is, mobile station 400, to which mobile station 400 is connected.

Due to the movement (and possibly other influences) of the mobile station 400, the quality of each connection changes over time. Quality here refers to one or more certain types of measurements, such as received signal strength or downlink signal to interference ratio. In order to adjust to the time variation of the connection quality, the mobile station 400 is provided with a set of sectors whose transmission is monitored in relation to its received signal quality. This set is called the measurement set. By periodically evaluating the quality of the sectors in the measurement set, mobile station 400 identifies the sector set suitable for the elements of the active set referred to as the candidate set. If the elements of the current active set and the elements of the candidate set are different from each other, the mobile station 400 sends a measurement report to a system such as a radio network controller (RNC) (not shown). The measurement report includes information related to the transmission quality received from the sector of the candidate set. Next, the RNC determines whether to perform hard handover or soft handover, ie which sectors are added to and / or deleted from the active set. The RNC also performs handoff by requesting the establishment and release of radio and network resources for connecting between the mobile station and the associated base station. After the handoff is made, the contents of the active set are updated at the mobile station (and RNC).

However, based on the measurements reported to the system by the mobile station, there are various techniques for evaluating whether a handoff is desired and if so what type of handoff is desired. Some of these techniques use fixed thresholds, while others use dynamic thresholds. For example, US Pat. No. 5,422,933 describes a method and system for handing off ongoing communication from a serving cell of a cellular communication system to an adjacent cell. Dynamic thresholds are calculated to achieve handover according to various operating conditions. The current mobile minimum attenuation level, the minimum allowable attenuation level of the serving cell and the neighboring cell, and the RF signal strength of the mobile unit in the neighboring cell and the serving cell are used to calculate the dynamic threshold.

Another example can be found in US Pat. No. 5,483,699, which describes a method and system for handoff an ongoing communication from a transport cell of a cellular communication system to an adjacent cell. The dynamic threshold is calculated to achieve handoff based on the minimum attenuation level of the mobile unit and the minimum level allowed by the neighboring cell, and the like. However, the latter two systems have the disadvantage that the determination of the dynamic threshold is more complicated due to the number of cases considered, and there is no facility for handling soft handoff.

More recently, plans have been described for the CDMA system known as CDMA 2000. In CDMA 200 data, there is a description of the dynamic threshold used for soft handoff. According to the above description, when the measured quality level exceeds a predetermined statistical threshold T1, a forward pilot channel is added to the candidate set. The candidate set includes the sectors that are evaluated more often and the test against the second dynamic threshold T2 is performed. The dynamic threshold T2 is calculated using the sum of the received signal quality measurements for all pilot channels in the active set. However, this approach is only provided on the forward link (i.e., downlink) and is also more complex and requires two-step (i.e., statistical and dynamic thresholds) to add sectors to and delete sectors from the active set. There is a limit to the need for the evaluation process.
US-5577022 discloses a technique for investigating and verifying a pilot signal of its own base station whose signal strength received at a predetermined position is sufficient to support communication. In particular, a pilot investigation technique is implemented that reduces the occurrence of "false alarms" that occur in the false measurement at the mobile station for base station pilot signal strength. This can be done by inserting the changing base station type of the term "pre-candidate set" where the base station is allocated from an adjacent set. The pre-candidate set includes a set of states that are considered Markov chain pre-candidate sets. Qualifying a base station from an adjacent set is first assigned to state # 1, and then transferred to another pre-candidate state depending on the result of the decolation / integral operation.
GB-2313740 includes a threshold adjustment means for dynamically changing a threshold value during a call in progress, the link quality is monitored and compared to a selected threshold value to determine when a handover occurs and to which neighboring cell a handover occurs. A handover management method for a cellular wireless network of the type is disclosed.

Accordingly, there is a need to develop an improved technique for efficiently utilizing system resources at different operating conditions by determining when a handoff is appropriate and which handoff type is appropriate.

The above and other problems, disadvantages, and limitations with conventional handoff techniques are that adaptive thresholds may be used for the various thresholds used to evaluate the desirability of both soft handoff and hard handoff. It is overcome according to the invention which can be provided. According to an embodiment, the soft handoff threshold for adding, deleting, and replacing elements of the active set varies with the quality level for the best or worst element of the current active set. Likewise, the threshold value used to determine when hard handoff is desired may also vary depending on the quality level of the active aggregation element.

The present invention provides many advantages over conventional techniques for performing handoff, including: (1) flexible control of both hard and soft handoff, and (2) channel quality at the same time. (3) reduction of the average number of sectors (or other types of sources, such as beams) to which the mobile stations are simultaneously connected, (4) adaptive to the maximum and minimum thresholds Providing a mechanism to control the relative soft handoff and the number of hard handoffs by selecting the slope of the threshold function, (5) reducing the likelihood of call dropping compared to conventional techniques using higher fixed handoff thresholds, and (6 Reduction of user-to-user interference compared to conventional techniques that use lower fixed thresholds to allow the active set to contain a relatively large number of sectors.

The above and other objects, features, and advantages of the present invention are readily understood by reading the following detailed description in conjunction with the drawings.

1 (a) is a diagram illustrating hard handoff.

1 (b) shows a soft handoff.

2 shows a base station using a sector antenna;

3 shows a base station using an array antenna;

4 shows two cells of six sectors in communication with a mobile station.

5 illustrates a portion of a typical mobile station structure.

6 is a graph illustrating various handoff algorithm conditions for adding, deleting, and replacing sectors in accordance with an embodiment of the present invention.

7 is a graph illustrating algorithm conditions for hard handoff in accordance with an embodiment of the present invention.

8 is a graph showing a variable additional threshold in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION Hereinafter, specific details such as certain circuits, circuit components, techniques, etc. will be described in order to provide an overall understanding of the present invention for purposes of illustration and not limitation. However, those skilled in the art will appreciate that the present invention may be practiced in other embodiments that depart from the above specific details. In other instances, specific descriptions of well-known methods, devices, and circuits are omitted in order not to unnecessarily obscure the description of the present invention.

Before giving a detailed description of the present invention, a partial example of a mobile station configuration that can operate to perform the signal quality measurement described above is shown in FIG. Although the block diagram is simplified to show only the components related to the measurement of downlink signal strength, those skilled in the art will be familiar with other important functional blocks associated with mobile stations. In FIG. 5, incoming radio signals are received by transmitter / receiver (TRX) 500. By the microprocessor controller 530, timing is synchronized to the received symbol sequence. The strength of the received signal is measured by the signal strength measuring unit 520, and then the value is transmitted to the microprocessor controller 530. In addition, the bit error rate (BER) of the received signal may be determined according to the received signal quality indication reflected by block 540. The measurement of the received signal quality relates in particular to determining when intracell handoff is desired. Those skilled in the art will appreciate that other quality measures, such as signal to interference ratio, may be used in the handoff algorithm. The mobile station will also have input and output devices such as a keypad and display 535 as well as a microphone and speaker unit (not shown) that allow information to be exchanged between the mobile station and the base station.

When the mobile receives a list of channel numbers and / or codes in a mobile assisted handover (MAHO) command, it measures the received signal quality associated with each of the channels. Once the mobile station has made the required measurements, it reports them to the system, which then evaluates the various sectors using a handoff algorithm. An example of how the active set changes over time based on using the handoff algorithm for the measurement is presented in FIG. 6. In FIG. 6, it is assumed initially that only one sector A (eg, as shown in FIG. 4) belongs to the active set. In the example above, the measurement set includes all sectors of the active set and both sectors adjacent to the active set. Since only sector A in this example is an element of the active set, the measurement set consists of sectors C1-S1 (= A), C2-S2 (= B), and C1-S6 (= C).

In the above example, the handoff algorithm indicates that different handoff operations will occur according to the conditions stated below:

Sector addition: Sector X is added to the current active set if its quality Q _x satisfies the following conditions:

Q _x > Q _best -add_th

Here, Q _best represents the quality of the sector having the highest quality in the active set, and add_th is a threshold value. For example, referring to FIG. 6, sector B is added to the active set at the moment marked 'add B' because the difference between its quality level and the quality level received from sector A becomes add_th. Note that after the 'add B' time, sectors D (C1-S3) are added to the measurement set because they are adjacent to sector B.

2. Sector Deletion: Sector X is deleted from the current active set if its quality Q _x meets the following conditions:

Q _x <Q _best -delete_th

Here, delete_th represents a deletion threshold value. An example where this condition occurs can be found at the moment indicated by 'C removal' in FIG. 6, in which case sector C is active since the difference between its received quality level and sector B's quality level exceeds delete_th. It is removed from the assembly.

3. Sector Replacement: Sector X replaces the sector with the worst quality of the active set if the active set is full and the following conditions persist:

Q _x > Q _worst + replace_th

Here, replace_th represents a threshold used for sector replacement. In FIG. 6, if the maximum number of sectors in the active set is two, sector C should replace sector A at the moment indicated by 'replace A with C' in FIG. 6. The operation described in the handoff algorithm for adding, deleting, or replacing sectors occurs as a soft handoff in the above example if the hard handoff threshold is not exceeded if the hard handoff occurs first.

4. Perform Hard Handover: If the quality Q _x of sector X satisfies the following condition, a hard handover from the current active set to the new sector is performed:

Q _x > Q _best + hho_th

Here, hho_th represents a hard handover, i.e., a threshold used to remove all connections of the current active set and establish a new connection to sector X. In this regard, it should be noted that mobile stations are not universally capable of continuously measuring all sector qualities in the measurement set, nor are they likely to continuously transmit measurement reports to the network. Instead, the mobile station measures the sector quality in the measurement set at a given moment, thereby performing the measurement periodically, as indicated by the vertical band in FIG. If the quality of the measured sectors increases more slowly, sector replacement (if the active set is full) or sector addition (if the active set is not full) is performed. In this case, i.e., if the quality of the measured sector is slowly increasing, the quality of the sector may never exceed the hard handoff threshold associated with the best active aggregate sector quality.

On the other hand, the sector quality of the measured sector may increase very quickly. This may occur if the mobile station measures certain sectors of poor quality, for example due to a shadowing effect caused by a building or other obstacle. If the mobile station moves out of the shielded area, the mobile station may have a direct line of sight with the base station of the measured sector. This causes a rapid quality increase for the measurement sector.

The latter overview is shown in FIG. 7. Here, the active set of mobile stations includes sectors A and B after the "add B" time. However, the quality of sector C is kept relatively low so that sector C does not replace the worst sector of the active set nor is it added to the active set. Next, as can be seen in the figure, the measured quality of sector C increases very quickly at the time when hard handover to sector C is performed.

The typical handoff technique described above has several advantages over the techniques described in the Background section of this application, such as being a simple one-step procedure, easy to implement, and more flexible as it can be used for soft and hard handoff. On the other hand, there is a limit to using a fixed threshold. However, using a fixed threshold means that the handoff algorithm cannot adjust to changes in the transmission quality of different channels, resulting in inefficient processing of radio and network resources. For example, if a fixed handoff threshold is set very tightly and the sectors in the measurement set must have relatively good quality before being added to the active set, then the mobile station does not identify any sector that would be good enough for the active set. This means that the handoff algorithm unnecessarily increases the chance of missed calls. Optionally, if the threshold is set more loosely, making it more likely that sectors will be added to the active aggregation, the mobile station is more likely to be connected to a larger number of sectors, and therefore more systems than are actually needed to maintain the connection. Allocate resources (e.g., short codes). Also, if the thresholds for soft handoff (delete_th, replace_th) and the threshold for hard handoff (hho_th) are set to fixed values, the system cannot adjust the ratio of soft handoff to hard handoff.                 

Thus, according to an embodiment of the present invention, the thresholds such as add_th, delete_th, replace_th and hho_th used to determine hard and soft handoff are all, for example, the best sector Q _{best in the} active set during the observation time t. And can be dynamically adjusted based on the quality of the current sector for each of the _worst and Q _worst sectors. Thus, according to this embodiment, the threshold is a function f_ (.) For the following variables:

add_th = f _add (Q _best , t)

delete_th = f _delete (Q _best , t)

replace_th = f _replace (Q _worst , t)

hho_th = f _hho (Q _best , t)

The calculations for each of the dynamic thresholds reflect the current transmission situation, that is, the active set can be reduced to a few (or maybe one sector) sectors if the transmission situation is good, and in the event of a worsening transmission situation. Will increase. In addition, the calculations for each of the dynamic thresholds are relatively easy to calculate because they rely only on the quality of one sector of the active set, that is, Q _best or Q _worst and some other fixed system parameters. In the embodiments of the present invention described below, the complexity of the handoff algorithm according to the present invention is further reduced by using linear adaptive threshold functions within different intervals.

According to the examples provided herein, the thresholds add_th, delete_th, replace_th, and hho_th are ramp functions. Although useful because of low computational complexity, those skilled in the art will appreciate that the threshold may be implemented using any function, linear or nonlinear, other than a ramp function that allows adjustments to changes in quality conditions in the wireless channel. will be. However, in the following, a brief description is given of a typical threshold function where the threshold is a ramp function over a predetermined range of quality values, each of which remains constant high and constant low outside of this range. A description of a typical threshold function of add_th is provided in FIG. 8. Since add_th is a function of Q _best, the graph shows the change in the value for add_th on the basis of the current quality of Q _best. If the quality of Q _best is lower than Q _{add_low} , add_th has the highest value (max_add_th). Within the range between Q _{add_low} and Q _{add_high} , the value of add_th is determined according to ramp function 700. It will be appreciated that while the ramp function 700 has a negative slope, other threshold functions may use a function having a positive slope. If the quality of Q _best is _greater than or equal to Q _{add_high} , add_th is set to the lowest value min_add_th.

Hereinafter, specific, still illustrative and descriptive threshold functions are mathematically described for add_th, delete_th, replace_th, and hho_th. In this equation, the unit of sector quality, threshold, and all other values described below is assumed to be dB. Other assumptions above for the threshold function are as follows:                 

xxx_slope is the slope of the ramp function when xxx_slope> 0 (xxx = add, delete, rep, or hho);

max_xxx_th is greater than min_xxx_th; And

Q _{xxx_high} is greater than Q _{xxx_low}

Variable addition threshold function

If Q _best <Q _{add_low} , add_th = max_add_th;

If Q _{add_low} <= Q _best <= Q _{add_high} ,

add_th = max_add_th-add_slope * (Q _best -Q _{add_low} );

If Q _best > Q _{add_high} , add_th = min_add_th;

Here, Q _{add_low} , Q _{add_high} , min_add_th, max_add_th and add_slope are set to fixed values.

Variable delete threshold function

If Q _best <Q _{delete_low} , delete_th = max_delete_th;

If Q _{delete_low} <= Q _best <= Q _{delete_high} ,

delete_th = max_delete_th-delete_slope * (Q _best -Q _{delete_low} );

If Q _best > Q _{delete_high} , delete_th = min_delete_th;

Here, Q _{delete_low} , Q _{delete_high} , min_delete_th, max_delete_th, and delete_slope are set to fixed values.

Variable replacement threshold function

If Q _worst <Q _{rep_low} , replace_th = minax_replace_th;

If Q _{rep_low} <= Q _worst <= Q _{rep_high} ,

replace_th = min_replace_th-replace_slope * (Q _{rep_low} -Q _worst );

If Q _worst > Q _{rep_high} , replace_th = max_replace_th;

Here, Q _{rep_low} , Q _{rep_high} , min_rep_th, max_rep_th and rep_slope are set to fixed values.

Variable hard handoff threshold

If Q _best <Q _{hho_low} , hho_th = max_hho_th;

If Q _{hho_low} dB <= Q _best <= Q _{hho_high} ,

hho_th = max_hho_th-hho_slope * (Q _best -Q _{hho_low} );

If Q _best > Q _{hho_high} , hho_th = min_hho_th;

Here, Q _{hho_low} , Q _{hho_high} , min_hho_th, max_hho_th and hho_slope are set to fixed values.

By dynamically adjusting the various handoff thresholds in this way, as the quality of transmission from the best sector increases, fewer sectors are added to the active set, thus saving system resources. Conversely, as the transmission quality from the best sector is degraded, more sectors are added to the active set, so that the overall connection quality can be maintained at a desirable level. In addition, the higher the transmission quality from the best sector, the higher the chance of hard handoff, which also contributes to the efficient use of system resources.

Accordingly, the present invention is evaluated to provide a number of advantages over conventional techniques for performing handoff, including: (1) flexible control of both hard and soft handoff, (2) At the same time, the calculation of less complex thresholds that are virtually dynamic to change with channel quality changes, (3) reduction in the average number of sectors (or other types of sources, such as beams) that mobile stations are simultaneously connected to, (4) minimum and maximum Provides a mechanism to control the relative number of soft handoffs and hard handoffs by selecting the slope of the threshold and the adaptive threshold function, and (5) possibility of missed calls compared to conventional techniques using higher fixed handoff thresholds Reduction, and (6) conventional techniques that utilize a lower fixed threshold so that the active set contains a relatively large number of sectors; Reduced interference between users in comparison.

The above described embodiments are to be considered in all respects as illustrative and not restrictive. For example, although the above embodiment does not refer to multiple frequency bands, those skilled in the art will appreciate that the present invention may be used in a system that uses multiple frequency bands, and thus intrafrequency or interfrequency band handoff, for communication. You will know that. Accordingly, the invention is susceptible to many variations in specific implementations that may be obtained from the description contained herein by one of ordinary skill in the art. All such changes and modifications are considered to be within the scope and spirit of the invention as defined by the following claims.

Claims (24)

A method of controlling the elements of a source active set in communication with a mobile station simultaneously, A first threshold add_th that determines when to add a source to the active set, Providing a plurality of thresholds for controlling elements of the active set comprising a second threshold delete_th that determines when to delete a source from the active set; A method for controlling a source active set element comprising controlling the elements of the active set based on the plurality of threshold values. Providing the plurality of thresholds includes: Providing a third threshold hho_th that determines when to perform a hard handoff from one or more current elements of the active set to another source, And changing a value of at least one of the plurality of thresholds as a function of a quality level (Q _best , Q _worst ) associated with the elements of the active set. Claim 2 was abandoned when the setup registration fee was paid. The method of claim 1, The providing of the plurality of thresholds further includes providing a fourth threshold value replace_th for determining when to replace an element of the active set with another source. . Claim 3 was abandoned when the setup registration fee was paid. The method according to claim 1 or 2, Wherein said at least one of said plurality of thresholds is said first threshold value that varies with a non-constant function for a quality level (Q _best ) of a source having the highest quality level in said active set. How to control set elements. Claim 4 was abandoned when the registration fee was paid. The method of claim 3, wherein And wherein the non-constant function comprises a ramp function between the maximum and minimum values of the first threshold. Claim 5 was abandoned upon payment of a set-up fee. The method according to claim 1 or 2, Wherein said at least one of said plurality of thresholds is said second threshold value that varies with a non-constant function for a quality level (Q _best ) of a source having the highest quality level in said active set. How to control set elements. Claim 6 was abandoned when the registration fee was paid. The method of claim 5, And wherein the non-constant function comprises a ramp function between the maximum and minimum values of the second threshold. Claim 7 was abandoned upon payment of a set-up fee. The method of claim 2, Wherein said at least one of said plurality of thresholds is said fourth threshold value that varies with a non-constant function for a quality level (Q _worst ) of a source having the worst quality level of said active set. How to control set elements. Claim 8 was abandoned when the registration fee was paid. The method of claim 7, wherein And wherein the non-constant function comprises a ramp function between the maximum and minimum values of the fourth threshold value. Claim 9 was abandoned upon payment of a set-up fee. The method according to claim 1 or 2, Wherein said at least one of said plurality of thresholds is said third threshold value that varies with a non-constant function for a quality level (Q _best ) of a source having the highest quality level of said active set. How to control set elements. Claim 10 was abandoned upon payment of a setup registration fee. The method of claim 9, And wherein the non-constant function comprises a ramp function between the maximum and minimum values of the third threshold value. _A receiver for receiving signal quality measurements (Q _A , Q _B , Q _C ) reported by the mobile station, and As a processor, A first threshold value add_th that determines when to add a source to a source active set that simultaneously communicates with the mobile station; And a processor for determining if a handoff is desired for the mobile station based on the signal quality measurement and a plurality of thresholds including a second threshold value delete_th that determines when to delete a source from the active set. A wireless communication system control node, The plurality of thresholds further includes a third threshold hho_th that determines when to perform a hard handoff from one or more current elements of the active set to another source, And the plurality of thresholds includes an adaptive threshold whose value varies in accordance with a quality level (Q _best , Q _worst ) associated with a transmission source in the mobile station active set. Claim 12 was abandoned upon payment of a registration fee. The method of claim 11, The plurality of adaptive thresholds includes one or more adaptive thresholds that vary according to a quality level (Q _best ) of a non-constant function of a source having the highest quality level in the active set. System control node. Claim 13 was abandoned upon payment of a registration fee. The method of claim 12, And the non-constant function comprises a ramp function between the maximum and minimum values of the one or more adaptive thresholds. Claim 14 was abandoned when the registration fee was paid. The method of claim 11, And said transmitting source is one of a cell, a base station, a sector antenna, and a beam connected to the antenna array. Claim 15 was abandoned upon payment of a registration fee. The method of claim 11, And the plurality of adaptive thresholds comprises a fourth threshold (replace_th) that determines when to replace an element of the active set with another source. Claim 16 was abandoned upon payment of a setup registration fee. The method of claim 11, And the control node is a switching node. A system for controlling a source active aggregation element in communication with a mobile station simultaneously, First threshold means for determining when to add a source to the active set, A plurality of threshold means comprising a second threshold means for determining when to delete a source from the active set, and Means for controlling the elements of the active set based on values of the plurality of threshold means; The plurality of threshold means further comprises third threshold means for determining when to perform a hard handoff from one or more current elements of the active set to another source, And the system further comprises means for changing a value of at least one of the plurality of threshold means as a function of quality levels (Qbest, Qworst) associated with the elements of the active set. Claim 18 was abandoned upon payment of a set-up fee. The method of claim 17, And the plurality of threshold means further comprises fourth threshold means for determining when to replace an element of the active set with another source of transmission. Claim 19 was abandoned upon payment of a registration fee. The method of claim 17, The value of at least one of the plurality of threshold means is a value of the first threshold means that varies according to a non-constant function for a quality level (Q _best ) of a source having the highest quality level in the active set. Control system. Claim 20 was abandoned upon payment of a registration fee. The method of claim 19, And the non-constant function comprises a ramp function between the maximum and minimum values of the first threshold. Claim 21 was abandoned upon payment of a registration fee. The method of claim 17, The value of at least one of the plurality of threshold means is a value of the second threshold means that varies according to a non-constant function for a quality level (Q _best ) of a source having the highest quality level in the active set. Control system. Claim 22 was abandoned upon payment of a registration fee. The method of claim 21, And the non-constant function comprises a ramp function between the maximum and minimum values of the second threshold. delete delete

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