CN1138372C - A method of call admission control in CDMA communication system - Google Patents

Abstract

The invention discloses a method for call admission control in a CDMA communication system. For a call request, the invention checks the load of the forward link and the load of the reverse link. Whether the request moment exceeds the threshold is used to determine whether to accept the call, and if it exceeds the threshold, the call is rejected. If the threshold is not exceeded, the call attempt request is accepted. Therefore, the method for call admission control provided by the present invention can accurately adapt to the real operating environment of the system and has high efficiency.

Description

A method of call admission control in CDMA communication system

The invention relates to a method for call admission control in a CDMA communication system.

In the current CDMA communication system, there are two common methods of call admission control, one is the forward capacity control method of the number of calls, and the other is the forward overload control method. For the forward capacity control method of the number of calls, the method controls the cell capacity according to the number of established calls being served in the cell. According to this method, if the influence of factors such as the power output of the cell and the propagation environment are considered, the threshold value of the fixed service permission, that is, the number of calls, is obtained through experiments. Whenever the base station receives a call attempt request from a mobile station in the cell, the base station compares the total number of calls being served in the sector to the call admission threshold. If the total number of calls is less than the call admission threshold, the call is dispatched, and if the total number of calls is greater than or equal to the call admission threshold, the call attempt is queued, or the call is rejected. In the above method, due to the different propagation environments among the cells, the maximum number of calls that can be accessed in different cells is different, and the call permission threshold is also different. Moreover, due to the mutual interference between the forward base stations, the number of user calls that can be served in the cell is not absolute, and it changes with the change of the transmit power of the surrounding base stations. Therefore, the call permission threshold based on the number of calls is used as the cell call criterion The basis for access control judgment cannot truly reflect the ability of the base station to actually access calls.

In a CDMA cellular system, each base station has a maximum allowable forward transmit power limit. That is to say, all the power allowed at any one time must be equally divided among all forward traffic signals transmitted from the base station. If the number of simultaneous service links of the base station is allowed to increase without limitation, the forward traffic The power of the incoming signal will eventually become too weak to guarantee error-free reception for existing users, and again the signal quality keeps deteriorating. Therefore, for the forward overload control method, the method uses forward overload to control the overall forward power requirement of the base station according to the power budget of the power amplifier of the given base station. This method adopts a "blind blocking" scheme. Once the forward power of the base station reaches a low threshold, such as 85%, even if there is enough power to adapt to a given user request, the request of a new user to establish a call is blocked. Moreover, this method tends to operate conservatively, underutilizes the available base station power by 2-3 dB, and fails to fully consider the interference between adjacent base stations.

As mentioned above, the common disadvantage of the above two methods is that the call admission control of the system cannot accurately adapt to the real operating environment of the system, and the efficiency is not high.

In view of the above problems, the purpose of the present invention is to provide a method for call admission control in a CDMA communication system that can accurately adapt to the real operating environment of the system and has high efficiency.

In order to achieve the above object, the technical solution adopted in the present invention is: a method for call admission control in a CDMA communication system, the method comprising the following steps: (1) the base station receives the call request; (2) the call admission control unit performs a counter To call admission judgment, if the reverse admission control allows the call to enter, then perform step (3), otherwise, perform step (8); (3) the load detection unit of the base station calculates the forward interference indicator value of the cell area; ( 4) The admission control unit of the base station compares the forward interference indicator value calculated by the load detection unit with the forward admission threshold value, if it is less than the threshold value, then perform step (5), otherwise, perform step (8); ( 5) the call admission control unit checks whether there is an available idle extension code that meets the request rate, if so, execute step (6) otherwise execute step (8); (6) call admission control unit checks whether there is an idle baseband The processing unit, if there is, executes step (7) otherwise executes step (8); (7) the call admission control unit carries out the processing of allowing the call to enter, and returns to the step (1) after processing and waits for the next call to be processed; 8) The call control unit performs the processing operation of rejecting the call, and returns to the step (1) to wait for processing the next call after the processing is completed.

The above-mentioned forward access threshold is: ηS _upp , where η is an adjustment factor, which is different for service types or priorities, and 0<η≤1, and S _upp is the maximum transmit power of the base station.

It can be known from the technical scheme adopted by the present invention above: since data service becomes a wider service in the CDMA wireless communication system, the forward and reverse services are asymmetrical, and the forward load is usually much greater than the reverse load. Therefore, the present invention, for a call request, Through the inspection of the reverse link load and the inspection of the forward link load, the call is accessed under the condition that the previous reverse link load allows the call admission, so that the method for the call admission control provided by the present invention can accurately Adapt to the real operating environment of the system and have high efficiency.

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a model diagram of a cellular area system of the present invention;

Fig. 2 is a model diagram of 19 cellular areas;

Fig. 3 is a flowchart of the call admission control of the present invention.

Firstly, the principle of the present invention will be described through the typical application environment of the present invention.

Refer to Figures 1 and 2. It can be seen from FIG. 1 that the base station subsystem 112 communicates wirelessly with five example mobile stations 120a-120e through the antenna 110, and the base station subsystem 112 communicates with the mobile switching center 114 through optical fibers or cables. The mobile stations 120a-120e periodically report their measured total interference power received on the forward link, and the base station subsystem 112 can also estimate the distance of each mobile station 120a-120e from the base station based on the propagation delay of the signal.

During normal operation of the system described above, mobile stations 120a-120e communicate with base stations to initiate calls, set up calls, or send or receive various overhead messages to and from the base stations. In the measurement report message sent by the mobile station 120a-120e to the base station, the total interference power received by the mobile station 120a-120e can be carried, and the base station carries the total received power information according to the received information sent by each mobile station 120a-120e in the cell area The forward link load of the cell is estimated based on the time delay calculated from the distance of each mobile station 120a-120e to the base station.

并认为对所有j≠1时， $S_{R1i}>S_{\mathrm{Rji},}$ 用户应当总是与收到信号强度最大的基站通信。现在，假定任意小区或扇区的总传输功率的一部分1-β分给导引信号，以及任意公共信息(诸如伪随机码初始向量或寻呼数据)将传至所有用户。留下的部分β才定位给此小区或扇区内基站自己的所有k_u个用户。这样，第i个用户收到发射功率的一部分 其中Φ_i满足条件，基站1中用户i接收到的干扰功率加平均噪声(用

表示)为： $I_{0_{\mathrm{li}}}W=\underset{j=l}{\overset{J}{\mathrm{\&Sigma;}}}{S}_{R_{\mathrm{ji}}}+N_{0}W$ 这个值比实际值略为高一点，因为在

中功率的很小部分 不应包括在内。Figure 2 is a model diagram of a 19-cell area. For the cellular area shown in Figure 2, it is assumed that user i is controlled by base station 1 and receives interference signals from J base stations. Let the total power received by user i from base station j be

And consider that for all j≠1, $S_{R1i}>S_{\mathrm{Rji},}$ Users should always communicate with the base station with the highest received signal strength. Now, assume that a fraction 1-β of the total transmission power of any cell or sector is allocated to the pilot signal, and that any common information (such as a pseudo-random code initialization vector or paging data) will be communicated to all users. The remaining part β is positioned to all k _u users of the base station in this cell or sector. In this way, the i-th user receives a part of the transmit power where Φ _i satisfies the condition, The interference power received by user i in base station 1 plus the average noise (using

Expressed as: $I_{0_{\mathrm{li}}}W=\underset{j=l}{\overset{J}{\mathrm{\&Sigma;}}}{S}_{R_{\mathrm{the\; ji}}}+N_{0}W$ This value is slightly higher than the actual value, because in the

small fraction of medium power should not be included.

等于第j基站总发射功率和对数正态分布衰耗的乘积，为： $S_{R_{\mathrm{ji}}}=S_j\&CenterDot;d_{\mathrm{ji}}^{-m}10^{-{\mathrm{\&xi;}}_{\mathrm{ji}}/10}$ d_ji是第j个基站到第i个用户的距离，而ζ_ji是相应的对数正态分量，均值为0，标准方差σ＝8dB，幂次选m＝4，将(2)式代入(1)式，得到： $I_{0_{\mathrm{li}}}W=\underset{j=1}{\overset{J}{\mathrm{\&Sigma;}}}{S}_j\&CenterDot;d_{\mathrm{ji}}^{-m}10^{-{\mathrm{\&xi;}}_{\mathrm{ji}}/10}+N_{0}W$ The power of the jth base station received by user i

Equal to the product of the total transmit power of the jth base station and the lognormal distribution attenuation, which is: $S_{R_{\mathrm{the\; ji}}}=S_j\&Center\; Dot;d_{\mathrm{the\; ji}}^{-m}10^{-{\mathrm{\&xi;}}_{\mathrm{the\; ji}}/10}$ d _ji is the distance from the j-th base station to the i-th user, and ζ _ji is the corresponding logarithmic normal component, the mean value is 0, the standard deviation σ=8dB, and the power is selected as m=4, and the formula (2) is substituted into (1) formula, get: $I_{0_{\mathrm{li}}}W=\underset{j=1}{\overset{J}{\mathrm{\&Sigma;}}}{S}_j\&Center\; Dot;d_{\mathrm{the\; ji}}^{-m}10^{-{\mathrm{\&xi;}}_{\mathrm{the\; ji}}/10}+N_{0}W$

Typically, background noise (mainly thermal noise) is negligible compared to the total signal power received from all base stations (including signals from all users). Because the base station transmit power is not as limited as the mobile station transmitter, the N ₀ W term can be removed from the above formula.

上限的取得是在本小区基站和所有邻近基站都以最大功率S_upp发射时，用户手机端测得的总干扰功率，即： ${\left(I_{0_{\mathrm{li}}}W\right)}_{\mathrm{upp}}=\underset{j=l}{\overset{J}{\mathrm{\&Sigma;}}}{S}_{\mathrm{upp}}\&CenterDot;d_{\mathrm{ji}}^{-m}10^{-{\mathrm{\&xi;}}_{\mathrm{ji}}/10}$

The upper limit is obtained when the base station of the cell and all adjacent base stations are transmitting at the maximum power S _upp , the total interference power measured by the mobile phone of the user, namely: ${\left(I_{0_{\mathrm{li}}}W\right)}_{\mathrm{upp}}=\underset{j=l}{\overset{J}{\mathrm{\&Sigma;}}}{S}_{\mathrm{upp}}\&CenterDot;d_{\mathrm{the\; ji}}^{-m}10^{-{\mathrm{\&xi;}}_{\mathrm{the\; ji}}/10}$

与距离与对数正态分布变量都均有关，其分布难以简单分析。但是，此分布可以直接用蒙特一卡洛(Monte Carlo)仿真来获得。假设一个给定用户只能收到以其所在小区同心的两个同心圆环内基站的发射功率，如图2所示。这样，J＝19，它包括了给定的基站，第一环内的6个基站及第二环内的12个基站，变量 与i用户的位置有关，此用户是假定在空间内均匀分布的。这样，此分布将是此小区内所有位置的平均值，将干扰与最大发射功率之比

作为前向干扰的归一化因子，即： ${\mathrm{\&lambda;}}_d={\left(I_{0_{\mathrm{li}}}W\right)}_{\mathrm{upp}}/S_{\mathrm{upp}}$ $=\underset{j=1}{\overset{J}{\mathrm{\&Sigma;}}}{d}_{\mathrm{ji}}^{-m}10^{-{\mathrm{\&xi;}}_{\mathrm{ji}}/10}$

It is related to both distance and lognormal distribution variables, and its distribution is difficult to analyze simply. However, this distribution can be directly obtained by Monte Carlo simulation. Assume that a given user can only receive the transmit power of base stations in two concentric rings concentric with the cell where the user is located, as shown in Figure 2. Like this, J=19, it has included given base station, 6 base stations in the first ring and 12 base stations in the second ring, variable Relates to the location of user i, which is assumed to be uniformly distributed in space. In this way, this distribution will be the average value of all locations in this cell, the ratio of the interference to the maximum transmit power

As a normalization factor for forward interference, that is: ${\mathrm{\&lambda;}}_d={\left(I_{0_{\mathrm{li}}}W\right)}_{\mathrm{upp}}/S_{\mathrm{upp}}$ $=\underset{j=1}{\overset{J}{\mathrm{\&Sigma;}}}{d}_{\mathrm{the\; ji}}^{-m}10^{-{\mathrm{\&xi;}}_{\mathrm{the\; ji}}/10}$

作归一化处理，归一化因子λ与用户i到基站的距离d相关，然后对所有用户作统计平均，得到： $I_{0}W=\stackrel{\&OverBar;}{\left(I_{0_i}w\right)/{\mathrm{\&lambda;}}_i}$ $=\frac{1}{K}(\underset{i=1}{\overset{K}{\mathrm{\&Sigma;}}}\left(I_{0_i}W\right)/{\mathrm{\&lambda;}}_i)$ 其中，K为小区中已经服务的用户数。When determining the forward interference indicator value I ₀ W, it is assumed that in the actual communication process, the total interference power plus the average noise received by user i of the target cell is right

For normalization processing, the normalization factor λ is related to the distance d from user i to the base station, and then statistically average all users to obtain: $I_{0}W=\stackrel{\&OverBar;}{\left(I_{0_i}w\right)/{\mathrm{\&lambda;}}_i}$ $=\frac{1}{K}(\underset{i=1}{\overset{K}{\mathrm{\&Sigma;}}}\left(I_{0_i}W\right)/{\mathrm{\&lambda;}}_i)$ Wherein, K is the number of served users in the cell.

Considering the influence of fading and burst interference, take the measurement values of N points in an observation window T, and use the statistical average of these values as the forward interference indicator value I ₀ W, $I_{0}W={\mathrm{E.}}_N{\mathrm{E.}}_K(\left(I_{0_i}W\right)/{\mathrm{\&lambda;}}_i)$ $=\frac{1}{N}\frac{1}{K}\left(\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}(\underset{i=1}{\overset{K}{\mathrm{\&Sigma;}}}\left(I_{0_i}W\right)/{\mathrm{\&lambda;}}_i{)}_j\right)$

Since this value is the statistical average of the forward link receiving interference reported by all mobile stations in the cell, it more comprehensively reflects the impact of the base station of the cell and all surrounding cell base stations on the forward link of the cell and is used as the forward load level The basis for judging is a very ideal choice.

上限的取得是在 取得最大值 的时候，也就是所有基站都以最大功率S_upp发射。这样，可定义ηS_upp(0＜η≤1)为前向准入控制门限，η为调整因子，针对业务类型或优先级而不同。当某一小区有新的业务请求时，先根据小区内所有的移动台上报的干扰计算小区的前向干扰指示值I₀W，当该值大于呼叫准入门限时，说明小区内的干扰很严重，不与准入；否则，准入。或者可以根据定义的不同门限阈值，当手机上报的干扰均值处在不同的门限时分配不同的业务数据速率。Next, determine the threshold value of the call admission control. by formula $I_{0}W=\stackrel{\&OverBar;}{\left(I_{0_i}W\right)/{\mathrm{\&lambda;}}_i}$ $=\frac{1}{K}(\underset{i=l}{\overset{K}{\mathrm{\&Sigma;}}}\left(I_{0_i}W\right)/{\mathrm{\&lambda;}}_i)$ can get: $\left(I_{0_i}W\right)/{\mathrm{\&lambda;}}_i=\frac{I_{0_i}W}{{\left(I_{0_i}W\right)}_{\mathrm{upp}}}{S}_{\mathrm{upp}},$ Ideally,

The upper limit is achieved at get the maximum When , that is, all base stations transmit with the maximum power S _upp . In this way, ηS _upp (0<η≤1) can be defined as the forward admission control threshold, and η is an adjustment factor, which is different for service types or priorities. When a certain cell has a new service request, first calculate the forward interference indicator value I ₀ W of the cell according to the interference reported by all mobile stations in the cell. When the value is greater than the call admission threshold, it means that the interference in the cell is very serious , not with access; otherwise, access. Alternatively, different service data rates may be assigned when the average interference value reported by the mobile phone is at different thresholds according to different defined thresholds.

Specifically, the present invention is realized like this, with reference to Fig. 3: at first, base station receives a call request in step S1; Call admission control unit carries out reverse call admission control in step S2, if reverse admission control algorithm Allow the call to enter, then execute step S3, otherwise, execute step S8 to do the processing of rejecting the call; in step S3, the load detection unit of the base station calculates the forward interference indicator value of the cellular area, and this value identifies the forward link Load condition: In step S4, the admission control unit of the base station compares the forward interference indication value calculated by the load detection unit with the forward admission threshold threshold value, if it is less than the threshold threshold value, then execute step S5, otherwise, execute step S8 to do Reject the processing of this call; Call admission control unit checks whether there is an idle extension code that meets the request rate at step S5, when there is no idle extension code that meets the request rate at step S5 place, control unit executes step S8 and does rejection The processing of this calling, when there is available idle extension code at step S5, whether there is an idle baseband processing unit in step S6 check of call admission control unit; When all baseband processing units are all currently used at step S6 place, control The unit executes step S8 to reject the call, and when there is an available baseband processing unit in step S6, the call admission control unit allows the call to enter in step S7, and returns to the beginning to wait for the next call request. In step S8, the control unit returns to the beginning after processing the operation of rejecting the call, and waits for the arrival of the next call request.

Claims (2)

1, a method for call admission control in a CDMA communication system, is characterized in that: the method comprises the following steps: (1) base station receives call request; (2) call admission control unit carries out reverse call admission judgment, if Reverse admission control allows the call to enter, then perform step (3), otherwise, perform step (8); (3) the load detection unit of the base station calculates the forward interference indicator value of the cell area; (4) the admission control of the base station The unit compares the forward interference indication value calculated by the load detection unit with the forward admission threshold value, if it is less than the threshold value, then perform step (5), otherwise, perform step (8); (5) call admission control unit Check whether there is an available idle spreading code that meets the request rate, if yes, execute step (6) otherwise execute step (8); (6) call admission control unit checks whether there is an idle baseband processing unit, if yes, execute Step (7) otherwise execute step (8); (7) call the admission control unit to allow the processing of the call to enter, return to the step (1) after processing and wait for the next call to be processed; (8) call the control unit to reject The processing operation of the call returns to the step (1) after processing and waits for the next call to be processed. 2. The method for call admission control in a CDMA communication system according to claim 1, characterized in that: the forward admission threshold threshold is: ηS _upp , Wherein, η is an adjustment factor, which is different for service types or priorities, and 0<η≤1, and S _upp is the maximum transmit power of the base station.