CN100386974C - Method of Automatically Updating Noise Floor in Code Division Multiple Access System - Google Patents

Abstract

The present invention relates to a code division multiple access (Code Division Multiple Access, referred to as "CDMA") system, and discloses a method for automatically updating the noise floor in the code division multiple access system, so that the system can set the noise floor more accurately, and the system can be adjusted according to the temperature and other cell interference changes to adaptively update the noise floor, especially when the system is under high load, it can also update the noise floor adaptively, and at the same time provide a strong ability to resist burst interference. In the present invention, the method for automatically updating the floor noise in the CDMA system is not only to obtain the system floor noise according to the uplink interference when the system load is low, but to calculate the floor noise through the uplink interference combined with other relevant parameters, and filter and smooth the calculation results After output.

Description

Method of Automatically Updating Noise Floor in Code Division Multiple Access System

technical field

The present invention relates to a code division multiple access (Code Division Multiple Access, referred to as "CDMA") system, in particular to parameter acquisition related to load control in the CDMA system.

Background technique

Code Division Multiple Access (CDMA) is a mobile communication technology developed on the basis of spread spectrum communication technology. It uses orthogonal codes to distinguish different users, and spreads the data and then transmits them through wireless links. . CDMA technology has the characteristics of high confidentiality, strong anti-interference, high spectrum utilization, simple network planning, large system capacity and flexibility, and has become the mainstream technology for the future development of mobile communications. At present, several third-generation mobile communications (The Third Generation, referred to as "3G") technical standards, including code division multiple access 2000 (Code Division Multiple Access2000, referred to as "CDMA2000"), wideband code division multiple access (Wideband Code Division Multiple Access, referred to as "WCDMA") and time division synchronous code division Multiple access (Time Division Synchronous Code Division Multiple Access, referred to as "TD-SCDMA") is based on the CDMA access method.

Since the spreading codes of each user used by CDMA cannot be guaranteed to be completely orthogonal at the receiving end, the signal sent by one user will cause interference noise to other users, that is, the CDMA system is a self-interference system, and the coverage, capacity and communication quality of the system Interrelated and influence each other. Especially in areas with low traffic density, the transmit power of the base station is large enough compared to the transmit power of the mobile station. Due to the limited transmit power of the mobile station, the network coverage is limited by the uplink, and the cell boundaries of the uplink are limited by Influenced by the uplink load, the size of the cell depends on the traffic carried by the uplink load, and the traffic borne by the cell is determined by the area of the cell, which are cyclically restricted by each other. If an ideal balance point can be found, not only can business requirements be met, but network costs can also be reduced. For example, in the WCDMA system, the transmit power of the mobile station has been defined in the specification. Since the transmit power of the mobile phone is limited, the uplink becomes a limited link covered by the WCDMA system.

In a CDMA system, the load condition of the uplink is measured by the uplink load factor, noise rise, and the like. Uplink load factor (expressed by η _UL ), noise rise (expressed by noise rise), floor noise (expressed by P _N ) and uplink interference (expressed by I _total ) satisfy the relationship of the following formula (1):

$\mathrm{noise\; rise}=\frac{I_{\mathrm{total}}}{P_N}=\frac{1}{1-{\mathrm{\η}}_{\mathrm{UL}}}\·\&Center\; Dot;\&Center\; Dot;$ Formula 1)

Among them, in the CDMA system, the noise floor P _N is used to represent the inherent noise of the current cell through parameter setting; the uplink interference I _total is obtained through physical layer measurement, and in the WCDMA system I _total is the wideband total received power (Received Total Wideband Power, referred to as "RTWP"), in the CDMA2000 system, I _total is the receiving signal strength indicator (Receiving Signal Strength Indicator, referred to as "RSSI"), which includes the actual noise floor of the cell (indicated by P _{N, actual} ) and Noise generated by users in the cell.

The actual noise floor P _N,actual of a cell includes thermal noise and interference from other cells. Among them, the thermal noise changes with the change of temperature, which is a relatively slow change process; the interference of other cells changes with the traffic volume of other cells, because the traffic volume of any cell changes greatly every day , the interference of other cells changes relatively quickly, and the change range is relatively large, which leads to a great change of the uplink actual noise floor P _N,actual in a day.

In order to measure the uplink load of the system more accurately, so that the load control algorithm can perform more accurate control, it is required to set the noise floor _PN to be relatively accurate, that is, to be as close as possible to the actual noise floor _PN,actual of the current cell, otherwise it will cause The measured η _UL , noise rise and the like have relatively large deviations, thus bringing relatively large errors to the uplink load control algorithm using these parameters. For example, when there is no user in the current cell, the corresponding load factor should be 0. If the set noise floor P _N is -105 decibel milliseconds (dBm), the actual floor noise P _{N, actual} is -102dBm. The difference between the noise floor P _N of the cell and the actual noise floor P _{N,actual of the cell} is 3dB, that is, the difference is 2 times. At this time, according to the formula (1), it will be calculated that the current load factor η _UL is 0.5, and the noise rise is 3dB. The measured η _UL and noise rise have relatively large deviations, and the uplink load control algorithm using these parameters lead to larger errors.

The method for updating the noise floor in the CDMA system of solution 1 of the prior art is based on manual operation. This solution requires the operator to select a time when there are no users or few users in the cell to measure the uplink interference I _total , and use a certain average value of the measured values as the currently set noise floor P _N .

Solution 1 of the prior art requires manual control, and operation and maintenance are very inconvenient. Therefore, in order to facilitate operation and maintenance, the update of the noise floor in the existing CDMA system can also be performed automatically.

The method for updating the noise floor in the CDMA system of solution 2 of the prior art can be performed automatically. This solution requires the system to monitor the number of equivalent users of each cell in real time. If the number of equivalent users of a certain cell and its adjacent cells is found to be relatively low, it will start updating the noise floor of the cell to reduce the uplink interference for a period of time. The measured value of I _total is filtered as the updated noise floor P _N .

It can be seen that both the prior art scheme 1 and the prior art scheme 2 need to measure the uplink interference I _total when the system load is light to obtain the noise floor P _N . This is mainly because in this case, the current noise floor _PN is approximately equal to the current uplink interference I _total .

In practical application, the above solution has the following problems: the noise floor P _N set by the existing technical solution is inaccurate and cannot truly reflect the noise floor of the current cell.

The main reason for this situation is that the existing technical solutions all choose to measure when the system load is light, and do not consider the situation when the system load is high, so the interference of other cells to the current cell is not included in the current cell noise floor P _N , and when the system load is high, interference from other cells to the current cell cannot be ignored, resulting in an inaccurate set noise floor P _N ; in addition, the existing technical solutions do not consider temperature changes, namely The change of the noise floor _PN caused by the temperature change is also not considered, so the noise floor set by using the existing technical solution cannot truly reflect the noise floor of the current cell.

Contents of the invention

In view of this, the main purpose of the present invention is to provide a method for automatically updating the noise floor in a code division multiple access system, so that the system can set the noise floor more accurately, and the system can adaptively update the noise floor according to changes in temperature and other cell interferences. Noise, especially when the system is under high load, the noise floor can also be updated adaptively, while providing strong anti-burst interference capability.

To achieve the above object, the invention provides a method for automatically updating noise floor in a code division multiple access system, comprising the following steps:

The CDMA system of A initializes the noise floor;

B receives the measurement report of uplink interference and calculates the noise floor at the current moment;

C inputs the noise floor at the current moment calculated in step B into a low-pass filter for smoothing;

When D needs to update the noise floor, the output of the low-pass filter is used to update the noise floor; the steps B, C, and D are executed cyclically.

Wherein, in the step B, the noise floor at the current moment is calculated according to the uplink interference, the adjacent cell interference factor and the signal-to-noise ratio of the chip required for user demodulation.

In addition, the method for obtaining the chip signal-to-noise ratio required for demodulation by the user includes: setting parameters, or calculating the user's uplink signal-to-interference ratio.

In addition, the low-pass filter is an alpha filter.

In addition, the low-pass filter is a linear smoothing filter.

In addition, the step B uses a counter to count the measurement report of the uplink interference, and the step D clears the counter when the count value reaches the bottom noise update cycle count value and updates it with the output of the low-pass filter the noise floor.

In addition, in the step D, the updating of the noise floor is triggered at a preset specific moment.

By comparison, it can be found that the main difference between the technical solution of the present invention and the prior art is that the method for automatically updating the floor noise in the CDMA system of the present invention does not only obtain the system floor noise according to the uplink interference I _total when the system load is low, but It calculates the noise floor by combining the uplink interference I _total with other relevant parameters, and outputs the calculation result after filtering and smoothing.

The difference in this technical solution has brought more obvious beneficial effects, that is, firstly, since the solution of the present invention does not need to be carried out when the system load is low, the floor noise of the system can be calculated at any time, so it is effectively avoided. The existing technology can only update the floor noise when the system load is relatively light, and the updated floor noise cannot match the system floor noise at high loads; secondly, because the present invention also performs filtering and smoothing processing on the floor noise , thus avoiding the influence of sudden interference, making the set noise floor more accurate; third, since the scheme of the present invention can update the floor noise automatically and adaptively, the set noise floor will adapt to the change of the real noise floor of the system Tracking ensures that the noise floor set at any time can more truly reflect the real noise floor of the system at that time; finally, with the solution of the present invention, since the system noise floor can be set more accurately, the calculation of parameters is more accurate, ensuring that the uplink The accuracy of the load control algorithm will greatly improve the performance of the whole system.

Description of drawings

Fig. 1 is a flowchart of a method for automatically updating the noise floor in a CDMA system according to a preferred embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings.

First, the basic principle of the present invention will be explained. The present invention calculates the noise floor at the time of reporting the uplink interference measurement according to the uplink interference and other easily obtained parameter values, then filters the calculation result to resist burst interference, and updates the noise floor with the filtered output value at a specific moment. In this way, there is no need to limit the noise floor update only when the system load is low. The updated noise floor value takes into account the interference of other cells, and since the system can update the noise floor adaptively, the real-time updated noise floor also reflects the temperature The change of the noise floor caused by the change of load and load, and because the filter is used to smooth the noise floor at each measurement reporting time, it can also provide strong anti-burst interference capability.

In order to illustrate the solution of the present invention more clearly, the solution of the present invention will be described in detail below in conjunction with the accompanying drawings.

The flow of the method for automatically updating the noise floor in a CDMA system according to a preferred embodiment of the present invention is shown in FIG. 1 .

First enter step 110, the system initializes the noise floor. Wherein, the initialized noise floor value P′ _N can be obtained by measurement through an existing technical solution, or it can be an estimated value.

Then enter step 120, after the system receives the measurement report of the uplink interference I _total , it adds one to the noise floor update counter. Wherein, the measurement report of the uplink interference I _total is provided by the physical layer. In a preferred embodiment of the present invention, the noise floor update counter is used to count the measurement reports of the uplink interference I _total .

Then enter step 130, calculate the noise floor according to the uplink interference I _total and input the calculation result into the filter. Among them, the filter is a low-pass filter, which can be implemented in many ways, and is used to smooth the noise floor, resist sudden interference, and effectively avoid the impact of sudden interference on the update accuracy of the noise floor. In a preferred embodiment of the present invention, adopt the α filter with good low-pass characteristic, its transfer function is y (n)=α · x (n)+(1-α) · y (n-1) , where y(n) is the output of the filter at sampling point n, and x(n) is the input of the filter at sampling point n. In another preferred embodiment of the present invention, the same purpose can be achieved by using a linear smoothing filter instead of an alpha filter. It should be noted that, in a preferred embodiment of the present invention, the method of calculating the noise floor according to the uplink interference I _total is performed according to the following formula (2).

$P_N=I_{\mathrm{total}}\&Center\; Dot;[1-(1+{\stackrel{\‾}{f}}_{\mathrm{UL}})\underset{j=1}{\overset{N}{\mathrm{\Σ}}}\frac{1}{1+\frac{1}{({\mathrm{E.}}_c/N_o{)}_j}}]\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;$ Formula (2)

Formula (2) can be obtained according to the existing literature. The acquisition of formula (2) will be described in detail below.

Those skilled in the art know that there is another way to express the uplink load factor η _UL , as shown in the following formula (3).

${\mathrm{\η}}_{\mathrm{UL}}=(1+{\stackrel{\‾}{f}}_{\mathrm{UL}})\&Center\; Dot;\underset{j}{\mathrm{\Σ}}\frac{1}{1+\frac{W/R_i}{({\mathrm{E.}}_b/N_o{)}_j}}=(1+{\stackrel{\‾}{f}}_{\mathrm{UL}})\·\underset{j}{\mathrm{\Σ}}\frac{1}{1+\frac{1}{({\mathrm{E.}}_c/N_o{)}_j}}\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;$ Formula (3)

in, is the uplink average adjacent cell interference factor, R _i is the service rate of user i, (E _b /N _o ) _j is the bit signal-to-noise ratio required for demodulation of user j, (E _c /N _o ) _j is the demodulation rate of user j Adjust the chip signal-to-noise ratio required, W is the chip rate of the CDMA system. For a detailed description of formula (3), please refer to "WCDMA Technology and System"[1]; (E _c /N _o ) _j can be calculated by the user's uplink signal-to-interference ratio (Signal to Interference Ratio, referred to as "SIR"), specifically For the calculation method, refer to "UMTS Wireless Network Planning and Optimization" [2], or obtain it through parameter setting, or calculate it according to the method provided in [3] with application number 200410081076.8.

Those skilled in the art can easily obtain formula (2) from formula (1) and formula (3) mentioned above.

Then enter step 140, judge whether the counter value is equal to the floor noise update cycle count value, if yes, enter step 150, otherwise return to step 120. Among them, the count value of the update period of the noise floor can be set by the system in advance according to the needs. If the update of the noise floor is required to be faster, a smaller count value can be set, otherwise, a larger count value can be set.

In step 150, the counter is set to zero, and the current noise floor is updated with the current filter output, and then step 120 is entered. Among them, after setting the counter to zero, enter the next floor noise update period. Those skilled in the art can understand that the output of the filter is the result of smoothing several previous sampling points at this time, so the burst interference that may occur at a certain sampling point can be effectively eliminated, so that the output of the filter is closer to The real noise floor of the current cell.

Through the cyclic execution of the above steps, the self-adaptive and automatic update of the system noise floor can be realized.

It should be noted that, in the above-mentioned preferred embodiments of the present invention, the system noise floor is updated periodically according to the count value of the counter. Those of ordinary skill in the art can understand that other methods can be used to determine when to update the system noise floor . For example, time trigger can be used to start updating the system noise floor at certain specific times, or it can be manually set to decide when to update. This does not affect the essence of the present invention.

Although the present invention has been illustrated and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein, and without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (7)

1. A method for automatically updating background noise in a CDMA system, comprising the steps of:

a, initializing the bottom noise by the CDMA system;

b, receiving a measurement report of uplink interference and calculating bottom noise at the current moment;

c, inputting the bottom noise at the current moment calculated in the step B into a low-pass filter for smoothing;

d, when the bottom noise needs to be updated, updating the bottom noise by the output of the low-pass filter; and,

the step B, C, D is performed in a loop.

2. The method according to claim 1, wherein in step B, the bottom noise at the current time is calculated according to the uplink interference, the interference factor in the neighboring cell, and the signal-to-noise ratio of the chip required for user demodulation.

3. The method of claim 2 wherein the step of obtaining the chip snr required for demodulation by the user comprises: the uplink signal interference ratio is obtained through parameter setting or through the calculation of the uplink signal interference ratio of the user.

4. The method of claim 1 wherein the low pass filter is an alpha filter.

5. The method of claim 1 wherein the low pass filter is a linear smoothing filter.

6. The method of claim 1, wherein step B employs a counter to count the measurement report of the uplink interference, and step D clears the counter when the count value reaches a bottom noise update period count value and updates the bottom noise with the output of the low pass filter.

7. The method of claim 1, wherein in step D, the updating of the bottom noise is triggered at a predetermined time.