KR100277034B1 - Method for optimize soft hand-off in cdma wireless communication system - Google Patents

Abstract

The present invention relates to a CDMA network soft handoff optimization method.

The present invention provides a method for establishing a test route, checking a system state, setting and adjusting high frequency parameters, optimizing coverage, receiving power, mobile station transmission power, and Ec / Io parameters to determine whether the criteria are satisfied. If it is not satisfied, return to the step of setting and adjusting the high frequency parameter again, if the criteria are satisfied, setting the handoff route, optimizing the handoff by function, if the softer handoff does not satisfy the function Return to the step of adjusting parameters and optimizing the handoff by function, if the softener handoff satisfies the function, the step of improving coverage and call quality, and investigating whether the parameter can be adjusted, if possible, to improve the coverage and call quality again. Step, and the primary coverage state diagram It comprises the step of reporting the de off bad history and also shaded areas.

The present invention maximizes the advantages of soft handoff while using the same system, while maintaining good sound quality, thus increasing handoff success rate and maximizing capacity.

Description

A method for optimizing soft handoff in code division multiple access mobile communication systems. {METHOD FOR OPTIMIZE SOFT HAND-OFF IN CDMA WIRELESS COMMUNICATION SYSTEM}

The present invention relates to a soft handoff method of a code division multiple access (CDMA) mobile communication system. In particular, a method for optimizing soft handoff by adjusting a parameter and adjusting a slope and beamwidth of a base station antenna is disclosed. It is about.

In general, handoffs made in a code division multiple access mobile communication system include soft handoff, softer handoff, and hard handoff. Among them, soft handoff means that a call transfer from an existing busy base station to another scheduled base station is performed without forcibly disconnecting the existing busy channel. In other words, a handoff required as a mobile station currently serving is moved from a cell serviced by a predetermined base station to a cell serviced by another base station is called a soft handoff.

In this case, the soft handoff is one of the features of the CDMA system in a "make-after-break" format rather than a conventional "break-after-make" format. In other words, the transfer of the call from the existing base station to the scheduled call base station is performed without forced disconnection of the existing busy channel. In the CDMA system, the above-described soft handoff is used to increase the handoff success rate more than the conventional handoff method (hard handoff), and the sound quality is improved.

The biggest reason that the CDMA system can support soft handoff is that the frequency bands of the talk channels are the same. That is, since the frequency bands used by each base station are the same, the same high frequency ultra-short part is used, and a rake receiver is used in the digital part spreading and despreading process. In addition, it is possible to use different spreading codes to distinguish between base stations to be able to access two or more base stations at the same time.

As described above, an important reason for providing soft handoff in a CDMA mobile communication system is that the sound quality is improved by forward diversity due to interference from other cells in the soft handoff period.

A typical soft handoff addition procedure performed in the CDMA mobile communication system is shown in FIG.

Referring to FIG. 1, the soft handoff procedure will be described. When the strength of the pilot included in the neighbor set in the pilot offset list of the mobile station exceeds T_add, the mobile station selects the currently transmitted traffic channel element (TCE). The pilot strength measurement message is transmitted to the transceiver and selector bank (TSB).

The TSB determines whether the support pilot matches the sector pilot offset of the base currently being used to determine the soft handoff, and sends the result to the Call Control File (CCOX) as a handoff request.

The CCOX sends a handoff request to which the call mode is assigned to HM_SOFT to the base station control processor of the target base station to which the corresponding mobile station intends to handoff by referring to its own database.

The base station control processor of the target base station determines the appropriate frequency, frame offset, and TCE for the required handoff and sends a handoff allocation to the CCOX in response.

The CCOX transmits a handoff assignment message to the TSB to indicate whether power control information and information to be communicated with the newly allocated TCE are updated.

If the TSB determines that additional information is needed according to the situation, the TSB requests related information from the CCOX in a call configuration request, and the CCOX loads the information into the call configuration. The TSB also sends a 'soft handoff in Progress Ctl' to the starting base station to indicate that it is in soft handoff. The TSB calculates a path delay and simultaneously transmits a handoff direction through the TCEs of the starting base station and the target base station.

Meanwhile, the CCOX receives information from the TSB that the link is established with the TCE of the target base station.

Upon recognition of the soft handoff procedure performed by the above operation, the mobile station transmits a handoff complete message to the TSB through the traffic channel.

The TSB sends a handoff notification message to inform CCOX that a pilot has been added during the soft handoff process.

The CCOX updates the handoff related statistics and related data after receiving the call notification message from the TSB.

The procedure for releasing the soft handoff added by the foregoing is performed by the bar shown in FIG.

Referring to the soft handoff release procedure with reference to FIG. 2, if the strength of the pilot included in the active set in the pilot offset list of the mobile station falls below T_drop, the mobile station starts the handoff timer and continues after the time expires. When the pilot strength is less than or equal to T_drop, a pilot strength measurement message is sent to the TSB.

The TSB determines that the pilot has been removed and sends a handoff direction message to the mobile station.

The mobile station performs a handoff procedure and sends a handoff complete message to the TSB, which sends a soft handoff complete Ctl (Control) message to the target base station indicating that the soft handoff is complete and receives an acknowledgment Ctl message in response. . The TSB also sends to the CCOX a handoff notification message with call_type assigned to soft removal to indicate that the pilot has been released. In addition, the TSB sends a Rel Ctl message requesting channel release to a starting base station and receives a response Ctl message in response.

If there are too many service area overlaps (handoff periods) between neighboring cells, the capacity of the corresponding base station is reduced due to inter-cell interference, so the best performance can be obtained only by optimizing the handoff area between neighboring stations. To optimize the handoff area, it can be divided into adjustment by high frequency parameter and adjustment by system parameter. However, no specific method for obtaining an appropriate handoff area has yet been proposed.

Accordingly, an object of the present invention is to provide a method for performing an optimal soft handoff through high frequency parameter adjustment and system parameter adjustment in order to solve the above problems.

The present invention for achieving the above object is a soft handoff method performed in the code division multiple access mobile communication system including a plurality of base stations by the mobile station to move between the cells served by different base stations Setting a test route, checking a system state, and setting high frequency parameters to optimize coverage; and whether received power, mobile station transmit power, and Ec / Io parameters corresponding to the set high frequency parameters satisfy the criteria. Optimizing the soft handoff for each function by adjusting the set high frequency parameters if not satisfied, and setting a route for soft handoff if the criterion is satisfied according to the set and adjusted high frequency parameters. , Soft according to the above optimization Adjusting a system parameter such that the soft handoff satisfies a function if the handoff does not satisfy a function; and a first coverage state diagram corresponding to the high frequency parameter and the system parameter set to satisfy the function of the soft handoff. We propose a soft handoff method for a code division multiple access mobile communication system including reporting a soft handoff failure history and a shadow map.

1 is a diagram illustrating a typical soft handoff addition procedure performed in a code division multiple access mobile communication system.

2 illustrates a typical soft handoff removal procedure performed in a code division multiple access mobile communication system.

3 is a control flowchart illustrating a soft handoff optimization method performed in a code division multiple access mobile communication system according to an embodiment of the present invention.

Hereinafter, an embodiment according to the present invention will be described with reference to the accompanying drawings.

First of all, in the present invention, it is preferable to present a criterion so that the received power is greater than -91 dBm, the mobile station transmit power is less than +10 dBm, and the Ec / Io is greater than -14 dBm. It is desirable to present the lower limit of T_add to prevent error alarms without extensive filtering. Secondly, it is desirable to prevent the sound quality from deteriorating prior to performing the handoff, and it is desirable to provide an upper limit of T_add at a desired handoff rate by the network manager, and an upper limit of T_drop to prevent the loss of a valid pilot. It is preferable. Third, it is desirable to provide a lower limit of T_drop so that three sized and weakened pilots can be excluded from the activation set, preventing the PSMM from continuing to send a cell that is slightly higher than the strength of the pilots in the activation set or support set. It is desirable to raise the area of T_comp so that it can be done. Fourthly, if different cells are installed in two directions at downtown intersections where the sound quality is significantly degraded, it is better to suggest the area of T_tdrop to maintain good sound quality by forcing a call to newly added cells. desirable. Fifth, it is preferable to decrease the T_add, T_drop and T_comp values to increase the handoff area, but to increase the T_tdrop value to increase the handoff area. Sixth, to increase the capacity, the T_add and T_drop is reduced. , It is preferable to increase the value of T_comp and decrease the value of T_Tdrop. Seventh, it is desirable to adjust the high frequency parameter by adjusting the direction of the antenna, and eighth, it is desirable to adjust the high frequency parameter by adjusting the tilt of the antenna, and ninth, to adjust the overall transmission signal attenuation. Preferably, the tenth, it is desirable to reduce the transmit signal attenuation for increased coverage and to raise the antenna tilt, and eleventh, to increase the transmit signal attenuation to reduce coverage but improve sound quality, and to lower the antenna tilt. And finally, it is desirable to optimize soft handoff through each parameter adjustment combination.

In the present invention, the optimum soft handoff interval can be set by adjusting the high frequency parameter and the system parameter.

According to the present invention, it is possible to solve the problem by providing an optimization method of minimizing the soft handoff area while maintaining a good sound quality by using two traffic channels at the same time during the soft handoff.

The present invention largely includes an optimization scheme by adjusting parameter values, and the contents of the slope and beam width of the base station antenna. The optimization method by adjusting the parameter value relates to the change of the handoff area by adjusting the values of T_add, T_comp, T_drop, and T_tdrop.

If the handoff area is too wide, there is a waste of power, and if the handoff area is too narrow, the advantages of soft handoff are reduced: good sound quality due to diversity and high handoff success rate.

In the optimization method, coverage optimization must be performed first.

In general, coverage is defined as mobile station receive power, mobile station Ec / Io, and mobile station transmit power. Initial coverage optimization should be mostly adjusted by high frequency parameters.

The quantitative interpretation of the handoff-related parameters must first minimize the time required for detecting new pilots, so filtering on pilots in neighboring sets should be minimized. Therefore, the lower limit of T_add must be high enough to prevent error alarms without extensive filtering.

The upper limit for T_add should be able to prevent the sound quality from deteriorating prior to performing the handoff, and is determined according to the handoff rate desired by the network manager.

The upper limit for T_drop should be able to prevent the loss of valid pilots, and the lower limit should be set so that cell size and weakened pilots can be correctly excluded from the active set.

T_comp is set to prevent the pilot strength measurement message from being sent in a cell that is slightly higher than the pilot strength in the active set or the support set.

T_tdrop is used to maintain good sound quality by forcibly maintaining a call for newly added B cells when A and B cells are installed in two directions at downtown intersections where sound quality is significantly degraded.

In principle, the high frequency parameters should not be adjusted. This is because the optimization of the high frequency parameter can be more complicated because even a small adjustment has a large effect on the coverage.

In general, among the high frequency parameters, only the transmit signal attenuation and the slope of the antenna are adjusted. If the transmit signal attenuation value is increased or the tilt of the antenna is increased, the coverage is increased.

In describing the application of the present invention,

▶ Optimization by adjusting high frequency parameter

-Antenna orientation

Since adjustment of this parameter acts as a factor that greatly changes the design coverage, the adjustment should be made under the following specific circumstances.

If the building is located in front of the installed antenna and interferes with the progress of radio waves

When interference occurs in areas where traveling waves are separated by media with small propagation loss such as rivers.

When radio wave loss is affected by a large medium such as a park with many forests

· There are mixed traffic areas with low signal level and high traffic level with low traffic level.

-Antenna tilt adjustment

In principle, this parameter should be used when the coverage cannot be met by the transmission output.

When adjusting the soft handoff area

When there is no antenna inclination on curved terrain and when it acts as an interference signal to other base stations

If the antenna is located in a tall building, frequent signal levels are maintained at the bottom of the building due to antenna gain.

Integrated Transmission Signal Attenuation

This parameter is the most frequently adjusted parameter and can be adjusted remotely at the base station modulator or directly at the base station.

Use to adjust the handoff area or change the coverage.

The greater the overall transmit signal attenuation, the wider the coverage.

▶ Optimization by system parameter

When reducing the handoff area, the values of T_add, T_drop, and T_comp are raised and T_tdrop is lowered.

When increasing the handoff area, the T_add, T_drop and T_comp values are lowered and the T_tdrop value is raised.

Too large a handoff region reduces capacity due to interference, and too narrow a handoff success rate, so setting an appropriate handoff region is the most important of the optimizations.

Referring to Figure 3 the operation of the present invention,

Initially set up a test route and check the system status;

Adjust and adjust the high frequency parameters. In particular, the beamwidth of the sector antenna is set at this time.

This process optimizes coverage;

If the received power is greater than -91 dBm, the mobile station transmit power is less than +10 dBm, and Ec / Io is greater than -14 dBm, the radio frequency parameter is reset;

If the criterion is satisfied, a route of handoff is established;

After that, the optimization of handoff by function is performed;

In this case, if the function of the soft handoff is not satisfied, the system parameters are adjusted again to perform the function optimization again.

Coverage and call quality are improved if the function of the soft handoff is satisfied;

Then check if the parameter is adjustable and if possible improve coverage and call quality again;

If the parameter is not adjustable, it is optimized, so it operates as a step of reporting the primary coverage status diagram, the handoff failure history, and the shadow area diagram.

Referring to the operation according to the application of the present invention,

As system parameters change,

As the value of T_add decreases, the handoff area increases and the capacity decreases.

Increasing the T_add value decreases the handoff area and increases the capacity.

When decreasing the T_drop value, the handoff area increases and the capacity decreases.

Increasing the T_drop value decreases the handoff area and increases the capacity.

As the value of T_comp decreases, the handoff area increases and the capacity decreases.

When increasing the T_comp value, the handoff area decreases and the capacity increases.

When the T_tdrop value is lowered, the handoff area is reduced and can be improved in terms of sound quality by quickly removing low level signals. In areas where the radio environment is changing rapidly, handoffs are more likely to fail.

When increasing the T_tdrop value, the handoff area increases and the low level signal is held for a long time, which is bad in terms of sound quality and capacity, but can increase the handoff success rate.

According to high frequency parameter change

Increasing the transmit signal attenuation reduces coverage and reduces interference, resulting in better sound quality.

Lowering the transmit signal attenuation increases coverage and increases interference, resulting in poorer sound quality.

Increasing the antenna tilt increases coverage.

Coverage is reduced when the antenna tilts down.

According to the present invention operating as described above, the soft handoff success rate is high and the capacity can be maximized while maintaining the good sound quality while maximizing the advantages of the soft handoff while using the same system.

Claims (14)

A soft handoff method performed in a code division multiple access mobile communication system including a plurality of base stations by moving a mobile station between cells served by different base stations, Setting up a test route, checking the system status and setting high frequency parameters to optimize coverage; Determining whether the received power, the mobile station transmit power, and the Ec / Io parameter corresponding to the set high frequency parameters satisfy the criterion if not satisfied, and adjusting the set high frequency parameters; Optimizing soft handoff for each function by setting a route for soft handoff when the criterion is satisfied in response to the set and adjusted high frequency parameters; Adjusting a system parameter such that the soft handoff satisfies the function if the soft handoff according to the optimization does not satisfy the function; And reporting a primary coverage state diagram, a softener handoff failure history, and a shadow area diagram corresponding to the high frequency parameter and the system parameter set such that the soft handoff satisfies the function. Soft handoff method in mobile communication system. The method of claim 1, wherein the criterion is And said criterion is presented such that the received power is greater than -91 dBm, the mobile station transmit power is less than +10 dBm, and the Ec / Io is greater than -14 dB. The method of claim 1, A soft handoff method of a code division multiple access mobile communication system, characterized in that a lower limit of T_add is presented to prevent an error alarm without extensive filtering during system parameter adjustment. The method of claim 1, A soft handoff method of a code division multiple access mobile communication system, characterized in that the network manager proposes an upper limit of T_add at a desired handoff rate to prevent the sound quality from deteriorating prior to the soft handoff. The method of claim 1, A soft handoff method of a code division multiple access mobile communication system characterized by providing an upper limit of T_drop to prevent the loss of a valid pilot. The method of claim 1, A soft handoff method of a code division multiple access mobile communication system, characterized by a lower limit of T_drop, which can exclude a cell size and a weakened pilot from an activation set. The method of claim 1, A method of soft handoff in a code division multiple access mobile communication system characterized by presenting a region of T_comp so as to prevent the PSMM from continuously sending a cell that is slightly higher than the pilot strength in the activation set or the support set. The method of claim 1, When different cells are installed, each of which significantly degrades the sound quality, the T_tdrop area is suggested to maintain a good sound quality by forcing a call to be added to the newly added cell. Soft handoff method. The method according to any one of claims 3 to 8, A method for soft handoff in a code division multiple access mobile communication system comprising increasing T_Add, T_drop and T_comp and lowering T_tdrop to increase capacity in adjusting the system parameters. The method according to any one of claims 3 to 8, A soft handoff method of a code division multiple access mobile communication system, characterized in that the T_Add, T_drop and T_comp values are lowered and the T_tdrop value is raised to increase the handoff area in adjusting the system parameters. The method of claim 1, And adjusting the direction of the antenna to adjust the high frequency parameter. The method of claim 1. And adjusting the inclination of the antenna to adjust the high frequency parameter. The method according to any one of claims 11 to 12, A soft handoff method of a code division multiple access mobile communication system characterized by reducing the transmission signal attenuation and increasing the antenna slope to increase the coverage. The method according to any one of claims 11 to 12, And softening the transmission signal so that the coverage is reduced but the sound quality is improved, and the antenna slope is lowered.

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