KR19990061206A - Soft Handoff Optimization Method in Code Division Multiple Access Networks - Google Patents

Abstract

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

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

Soft Handoff Optimization Method in Code Division Multiple Access Networks

The present invention relates to a method for optimizing soft handoff in a code division multiple access (CDMA) network. More particularly, the present invention relates to a method for optimizing soft handoff by adjusting parameters and adjusting a slope and beam width of a base station antenna.

As is well known to those skilled in the art, soft handoff is one of the features of the CDMA system in the make-after-break format, rather than the 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 use of soft handoff improves the handoff success rate and improves the sound quality.

The biggest reason that CDMA systems can support soft handoff is that the frequency bands of the talk channels are the same. Since the same frequency band is used, the same high frequency ultra-short part is used, and the spreading and despreading processes, which are digital parts, use rake receivers, so that different spreading codes can be used so that two or more base stations can be simultaneously connected.

An important reason for soft handoff is that the sound quality is improved in the soft handoff period due to forward diversity due to interference from other cells.

The additional procedure of soft handoff is explained with reference to FIG.

If 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 transmits a pilot strength measurement message to the Transceiver and Selector Bank (TSB) through the TCE (Traffic Channel Element) currently in communication. .

The TSB determines the soft handoff by comparing the support pilot with the sector pilot offset of the base currently being used and sends the result to the Call COntrol File (CCOX) as a handoff request.

CCOX sends a handoff request to which the call mode is assigned 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 sends 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 depending on the situation, the TSB requests the relevant information from the CCOX in a call configuration request, and the CCOX sends the information to the call configuration.

The TSB notifies the starting base station that it is in soft handoff by sending a 'soft handoff in Progress Ctl'.

The TSB calculates a path delay and simultaneously sends a handoff direction through the TCEs of the starting base station and the target base station.

CCOX receives information from the TSB that a link has been established with the TCE of the target base station.

Upon recognition of performing the handoff procedure, the mobile station forwards the 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.

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

The soft handoff release procedure will be described with reference to FIG.

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 to send a pilot strength measurement message to the TSB when the pilot strength is less than or equal to T_drop after the time expires. send.

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

The mobile station performs the handoff procedure and sends a handoff complete message to the TSB.

The TSB sends a soft handoff complete Ctl (Control) message to the destination base station indicating that the soft handoff is complete and receives an acknowledgment Ctl message in response.

The TSB sends to CCOX a handoff notification message with call_type assigned to soft removal to indicate that the pilot has been released.

The TSB sends a Rel Ctl message requesting channel release to the starting base station and receives a response Ctl message in response.

If there are too many service area overlaps (handoff intervals) 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 handoff areas 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 an optimal soft handoff method through high frequency parameter adjustment and system parameter adjustment in order to solve the above problems.

1 is a soft handoff addition procedure

2 is a soft handoff removal procedure

3 is a flowchart of a soft handoff optimization method according to the present invention.

One preferred embodiment of the present invention for achieving an optimal soft handoff in a CDMA system according to the present invention,

Establishing a test route and verifying system status;

Setting and adjusting high frequency parameters;

Optimizing coverage;

Checking whether the received power, the mobile station transmit power, and the Ec / Io parameters satisfy the criterion, and if not, returning to the step of setting and adjusting the high frequency parameters;

Establishing a handoff route if the criterion is satisfied;

Optimizing handoff for each function;

If the softer handoff does not satisfy the function, returning to adjusting the system parameters and optimizing the functional handoff;

Improving coverage and call quality if the softener handoff satisfies the function;

Checking whether parameter adjustment is possible and returning to the step of improving coverage and call quality if possible; And

And reporting the primary coverage status map, handoff failure history, and shadow map.

In the present invention, it is preferable to present a criterion 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.

When adjusting the system parameter, it is desirable to present a lower limit of T_add so as to prevent an error alarm without extensive filtering.

It is possible to prevent the sound quality from deteriorating before the handoff is performed, and it is preferable to present an upper limit of T_add at a desired handoff rate by the network manager.

It is desirable to present the upper limit of T_drop to prevent the loss of valid pilots.

It is preferable to present a lower limit of T_drop so that the cell size and the weakened pilot can be excluded from the activation set.

It is desirable to provide a region of T_comp to prevent the PSMM from continuously sending a cell that is slightly higher than the strength of the pilot in the activation set or support set.

When different cells are installed in two directions at an urban intersection where sound quality is significantly degraded, it is preferable to present a T_tdrop area to maintain good sound by forcibly maintaining an arc for newly added cells.

In order to decrease the capacity but increase the handoff area, it is preferable to decrease the T_add, T_drop and T_comp values and increase the T_tdrop value.

In order to decrease the handoff area but increase the capacity, it is preferable to increase the T_add, T_drop and T_comp values and lower the T_tdrop value.

It is desirable to adjust the high frequency parameter by adjusting the direction of the antenna.

It is desirable to adjust the high frequency parameter by adjusting the tilt of the antenna,

It is desirable to adjust the overall transmit signal attenuation,

It is desirable to reduce the transmit signal attenuation, increase the antenna tilt for increased coverage,

It is desirable to increase the transmit signal attenuation and decrease the antenna inclination to reduce coverage but improve sound quality.

It is desirable to optimize soft handoff through each combination of parameter adjustments.

In the present invention, the optimal handoff period 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 is related 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 to detect new pilots, so the filtering for 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 forcing a call to the newly added B cell when A and B cells are installed in two directions in the downtown intersection where the 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

When there is a mixture of areas with high signal level with low traffic and 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

When the antenna is located in a high building When the signal level is maintained at the bottom of the building by 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;

Then 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 dB, 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;

At this time, if the function of the soft handoff is not satisfied, the system parameters are adjusted again to perform the function-specific optimization work 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 can be reduced and the sound quality can be improved by quickly removing low-level signals, but the handoff may be more likely to fail in areas where the radio environment is changing rapidly.

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 advantages of soft handoff can be maximized while using the same system, so that the handoff success rate can be increased and the capacity can be maximized while maintaining good sound quality.

Claims (16)

Establishing a test route and verifying system status; Setting and adjusting high frequency parameters; Optimizing coverage; Checking whether the received power, the mobile station transmit power, and the Ec / Io parameters satisfy the criterion, and if not, returning to the step of setting and adjusting the high frequency parameters; Establishing a handoff route if the criterion is satisfied; Optimizing handoff for each function; If the softer handoff does not satisfy the function, returning to adjusting the system parameters and optimizing the functional handoff; Improving coverage and call quality if the softener handoff satisfies the function; Checking whether parameter adjustment is possible and returning to the step of improving coverage and call quality if possible; And And reporting a primary coverage status diagram and handoff failure history and shadow area diagram. 2. The method of claim 1, wherein a criterion is presented such that 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 dB. The method of claim 1, wherein a lower limit of T_add is provided to prevent an error alarm without extensive filtering during system parameter adjustment. 2. The method of claim 1, wherein the sound quality can be prevented from deteriorating prior to performing the handoff, and the network manager suggests an upper limit of T_add at a desired handoff rate. 2. The method of claim 1, wherein an upper limit of T_drop is provided to prevent the loss of valid pilots. 2. The method of claim 1, wherein a lower limit of T_drop is provided to exclude the cell size and the weakened pilot from the activation set. 2. The method of claim 1, wherein the area of T_comp is presented to avoid sending PSMM continuously in cells that are slightly above the strength of the pilot in the activation set or support set. The T_tdrop area is provided to maintain a good sound quality by forcibly holding an arc for a newly added cell when each cell is installed in two directions at an urban intersection where the sound quality is significantly degraded. Softer handoff optimization method. 9. The soft handoff optimization method according to any one of claims 3 to 8, wherein the capacity is decreased but the T_add, T_drop, T_comp values are lowered and the T_tdrop value is raised to increase the handoff area. 9. The soft handoff optimization method according to any one of claims 3 to 8, wherein the handoff area is decreased but the value of T_add, T_drop, T_comp is increased and the value of T_tdrop is decreased to increase the capacity. The method of claim 1 wherein the high frequency parameter is adjusted by adjusting the direction of the antenna. The method of claim 1 wherein the high frequency parameter is adjusted by adjusting the tilt of the antenna. The method of claim 1, wherein the overall transmit signal attenuation is adjusted. 14. The method according to any one of claims 11 to 13, which reduces transmit signal attenuation and raises the antenna slope for increased coverage. The method according to any one of claims 11 to 13, which raises the transmission signal attenuation to reduce coverage but improves sound quality and lowers the antenna slope. 16. The method of claim 14 or 15 wherein the soft handoff is optimized through each parameter adjustment combination.