KR100330419B1 - Admission Control Based on Cell Load in CDMA System - Google Patents

Abstract

In the mobile communication network, the bandwidth of radio resources is limited. Therefore, in order to provide a service that can satisfy the needs of customers by using the limited resources, it is necessary to manage resources as efficiently as possible. Call admission control method to control. In general, in a CDMA communication system, because the spectrum is shared, the mobile station in the call affects the call quality of other mobile stations with interference. Therefore, in order to guarantee the subscriber's call quality above a certain level, interference should be limited to below a certain level. Therefore, the effective call admission control method in the CDMA system should be flexible in consideration of the load of each cell and at the same time guarantee the call quality required by the subscriber. The present invention for this purpose comprises a first step, when a call acceptance is requested from a mobile station, the base station determining the required power for the call; A second step of the base station adding a total received power and the required power and comparing the result value and a threshold value; And a third step of rejecting the call if the result is greater than a threshold as a result of the comparison of the second step and accepting the call if the result is less than or equal to the threshold. In the present invention, it is possible to adaptively cope with variations in the received power and the cell load.

Description

Call Admission Control Method in Mobile Communication System {Admission Control Based on Cell Load in CDMA System}

The present invention relates to a call admission control method in a direct sequence spreading code division multiple access (DS-CDMA) communication system. More specifically, the present invention relates to call quality in a situation where various kinds of services such as voice and data traffic exist. Call admission control method that dynamically adapts to the load of the cell while ensuring.

In general mobile communication networks, bandwidth, which is a radio resource, is limited, and resources must be managed as efficiently as possible in order to provide a service that can satisfy a customer's demand by using the limited resource. One of the techniques for radio resource management is a call admission control method that controls the acceptance or rejection of a call when each subscriber requests a call. In a direct sequence code division multiple access (DS-CDMA) communication system, capacity is determined by interference from a user in a call at the same time. In order to guarantee call quality, interference must be limited to a certain level, in which case the number of users who can talk simultaneously is not constant but flexible. That is, since the power strengths of the users in the call and the neighboring cells in the target cell belong to the interference, each user has complete power control by the base station. Even if it is done, the number of users who can talk at the same time is flexible. Therefore, there is a need for a call control method that flexibly adapts to the load of the cell. In particular, in a situation where various kinds of traffic exist, this problem is more important because different call quality and transmission rate are required for each traffic type.

There are two factors that determine call quality: call blocking rate and call dropping rate. There is a trade-off between these two factors. That is, as more calls are accepted, the call blocking rate decreases and the call cutting rate increases. In particular, call cutting rate is an important factor in determining call quality. The call admission control method should be designed to accommodate as many users as possible while maintaining the call cutting rate below a certain level. It also needs to be taken into account because different types of traffic require different call qualities.

In order to solve this problem, call admission control or channel allocation method based on interference amount has been considered. Most of them have a problem in that only voice traffic is considered and interference from neighboring cells is not considered.

Accordingly, the present invention has been made to solve the above problems of the prior art, while adaptively coping with the load of a cell in an environment in which various types of traffic such as voice and data traffic exist in a CDMA mobile communication system. It is to provide a call admission control method that can ensure the call quality. In addition, the present invention is to provide a call admission control method for selectively accepting a call request by giving priority to each traffic type.

1 is a flowchart illustrating a call admission control method according to an embodiment of the present invention.

In order to achieve the above object, a call admission control method in a mobile communication system according to the present invention includes: a first step of, when a call acceptance is requested from a mobile station, a base station determining required power for the call; A second step of the base station adding a total received power and the required power and comparing the result value and a threshold value; And a third step of rejecting the call if the result is greater than a threshold and accepting the call if the result is less than or equal to a threshold as a result of the comparison of the second step.

Hereinafter, the call admission control method in a mobile communication system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The present invention provides a call admission control method for adaptively accepting or rejecting a call based on a load of a cell in a CDMA environment requiring different call quality and transmission rate for each traffic type. Here, requesting different call quality means requiring different signal-to-noise ratios for each traffic type, which means that different power is required. Accordingly, in order to maximize system capacity, an appropriate power ratio must be determined for each type of traffic.

In addition, for call admission control to flexibly adapt to the load of the cell, even if the load of the target cell is high, if the load of the neighboring cell is small, relatively many users must be accommodated without deterioration of the call quality. On the other hand, even if the load of the cell of interest is small, if the load of the neighboring cell is high and the interference increases, a relatively small number of users should be accommodated. Finally, when different call blocking rates and call drop rates are required for each traffic type, an appropriate threshold value for the signal-to-noise ratio is set accordingly, and priority is given to each traffic type to selectively accept it.

The power strength and signal-to-noise ratio required by voice traffic are respectively calculated by P _v and The power strength and signal-to-noise ratio required for data traffic are P _d and When the activity factor of each traffic is α _v and α _d , respectively, the signal-to-noise ratio for each traffic is expressed by Equation 1 below.

Here, N _v and N _d represent the number of voice and data subscribers, respectively, and I _k and η _k represent the amount of interference from the outer cell and the background noise of the receiver, respectively. At this time, in order to maximize the capacity of the system, the required power ratio δ as shown in Equation 2 must be satisfied.

Such a power ratio δ can be obtained even in a situation where two or more types of traffic exist. Equation 2 means that the required power of another traffic can be expressed as a constant δ by normalizing the required power for one traffic to '1'. That is, in order to maximize the capacity of the system, it is necessary to satisfy the power ratio shown in Equation 3 for each traffic.

The maximum capacity of a cell is when there is no interference from an external cell and the noise of the receiver. The number of effective users of a data service based on the voice service user is δN _d , and the number of effective users of an external interference amount is L _k = I _k / P When expressed as _k , the maximum capacity of the cell is expressed as in Equation 4 considering the activity coefficient.

Here, the cell load ( X _k ) in the cell _k can be expressed as the ratio of the current effective number of users of the cell to the maximum capacity of the cell, including the external interference amount, using the total received power ( Z _k ) in the base station It is expressed as That is, the total received power at the base station may be used as a parameter representing the cell load.

In general, the amount of interference on the traffic of traffic type i in the base station of cell k is the value of the total received power minus its own signal, so that ) Can be expressed by Equation 6 using the total received power ( Z _k ) and the received power ( P _{k, i} ) received by the subscriber from the base station to which the subscriber belongs.

From Equation 5 and Equation 6 above, the total received power Z _k is the cell load X _k and the signal-to-noise ratio ( You can see that at the same time. Therefore, the call admission control method using the total received power as a parameter can directly and simultaneously control two necessary elements when determining the acceptance / rejection of the call.

A call admission control method according to an embodiment of the present invention will be described in detail with reference to FIG. 1.

When a call is generated, each mobile station selects a base station whose propagation attenuation is minimum as its base station and requests the base station to accept the call (10). At this time, the base station determines the required power ( δ _{j, i} ) already calculated by Equation 3 for the requested call (20). The base station compares the sum of the total received power Z _k and the required power δ _{j, i} with a predetermined threshold Z _{th, i} (30). In this case, the threshold should be set below the value required by the system, and the maximum value ( Z _max ) of this threshold is obtained through the process described below.

The maximum value of the threshold value Z _max can be obtained as follows. First, the required reception power of the reference traffic is normalized to '1'. For other traffic, the value calculated by Equation 3 becomes the required reception power, and the signal-to-noise ratio required for each traffic type is calculated. , The system must satisfy the following equation.

Therefore, the minimum value of the signal-to-noise ratio for satisfying the call quality is when the equation is established in Equation 7, and the total received power Z _{k at} this time becomes the maximum value Z _max of the threshold. Also, the maximum value Z _max of this threshold is always the same regardless of the type of traffic.

On the other hand, in the present invention, by setting different thresholds ( Z _{th, i} ) for each traffic type, priority is given to desired traffic to control call admission. That is, in the case of traffic giving priority, the threshold is set close to the Z _max value, so that the call is accepted more than other traffic. Finally, if the sum of the total received power measured at the call request and the calculated required receive power is less than the threshold set for the traffic, the requested call is accepted (40), otherwise rejected (50).

While the invention has been described above based on the preferred embodiments thereof, these embodiments are intended to illustrate rather than limit the invention. It will be apparent to those skilled in the art that various changes, modifications, or adjustments to the above embodiments can be made without departing from the spirit of the invention. Therefore, the protection scope of the present invention will be limited only by the appended claims, and should be construed as including all such changes, modifications or adjustments.

As described above, according to the present invention, since the base station performs call admission control based on the total received power, call admission control adapted to the cell load is possible. In addition, in the present invention, by assigning different thresholds for each type of traffic, priority can be given to desired traffic to control call requests.

Claims (6)

If a call acceptance is requested from the mobile station, the base station determining a required power for the call; A second step of the base station adding a total received power and the required power and comparing the result value and a threshold value; And And a third step of rejecting the call if the result is greater than a threshold and accepting the call if the result is less than or equal to a threshold as a result of the comparison of the second step. Admission Control Method. The method of claim 1, wherein the required power of the first step is determined according to the traffic type of the call. 3. The method according to claim 2, wherein the required power of the call is expressed as a ratio with respect to the required power of reference traffic. The method of claim 1, wherein the threshold of the second step is determined to have a different value for each type of traffic. 5. The method of claim 4, wherein the first sub-step of determining the total received power to maximize the signal-to-noise ratio for each traffic type as a maximum threshold ( Z _max ), and the threshold of the prioritized traffic is set to a threshold of other traffic. And a second sub-step of setting closer to the maximum threshold so that the prioritized traffic accepts a relatively large number of calls. To the base station, If a call acceptance is requested from the mobile station, determining a required power for the call; A second step of the base station adding a total received power and the required power and comparing the result value and a threshold value; And And a third step of rejecting the call if the result is greater than a threshold and accepting the call if the result is less than or equal to a threshold as a result of the comparison of the second step. A computer-readable recording medium that contains a program for making a program.