KR19980082570A - Reverse Link Subscriber Load Condition Additional Method in Digital Cellular System - Google Patents

Abstract

end. TECHNICAL FIELD [0002]

Cell Optimization and Performance Evaluation of Base Station in Digital Cellular System

I. Technical Problems to be Solved by the Invention:

A method of calculating a noise source for realizing a virtual subscriber environment the same as the environment in which the subscriber is actually talking.

All. The point of the solution of the invention:

In a method for adding a reverse link subscriber load condition in a digital cellular system, the gain (noise figure) of a base station receive attenuator is controlled to be attenuated to make a virtual subscriber load state.

la. An important use of the invention:

Cell Optimization and Performance Evaluation of Base Station in Digital Cellular System

Description

Reverse Link Subscriber Load Condition Additional Method in Digital Cellular System

The present invention relates to a communication system, and more particularly, to a method for cell optimization in a digital cellular system and a performance verification of a base station transceiver subsystem (BTS).

The ultimate goal of the Code Division Multiple Access (CDMA) system is to improve call capacity, call mobility, and call quality. The performance of each condition varies depending on the type and size of the noise, and this phenomenon is characteristic of the CDMA system. The noise type includes noise caused by the subscriber. Since each subscriber acts as a noise to each other, the call quality decreases as the number of subscribers increases. Therefore, it is required to design a cell in order to satisfy a desired call quality at a maximum capacity of a subscriber, and cell optimization is performed for this purpose. In such a background, it is natural that the maximum test environment should be established during the field test. However, establishing a multi-cell environment as an actual subscriber makes field testing practically impossible. Even if it is possible, it is a waste of manpower and test terminals. From this point of view, it is desirable to create a virtual subscriber environment implemented in the same system as the environment in which the subscriber is actually talking.

It is therefore an object of the present invention to provide a method for adding a reverse link subscriber load condition in a digital cellular system.

It is another object of the present invention to provide a method for adding a reverse link subscriber load condition to implement a virtual subscriber environment that is the same as the environment in which an actual subscriber is talking.

It is a further object of the present invention to provide a method for reducing the time, manpower, and equipment cost of implementing a test environment for cell optimization.

According to another aspect of the present invention, there is provided a method of adding a reverse link subscriber load condition in a digital cellular system, the method comprising: controlling a gain (noise figure) of a base station reception attenuator to be attenuated so as to establish a virtual subscriber load state; .

1 is a view for explaining a noise source adding method according to an embodiment of the present invention;

FIG. 2 is a graph showing measured results before and after noise source injection analyzed by a spectrum analyzer 6 connected to the downstream end of the LNA 4 shown in FIG. 1; FIG.

3 is a view for explaining a noise source adding method according to another embodiment of the present invention.

4A to 4C are diagrams showing the states of the thermal noise and the tone signal, in which FIG. 4A shows a state measured by the spectrum analyzer 16 of FIG. 3 when a tone signal is applied, (C) shows a state measured by the spectrum analyzer 16 of FIG. 3 when the attenuation of the gain of the attenuator 12 is controlled; and FIG. 11 (c) shows a state of the attenuator 12 of FIG.

5 (a) to 5 (c) are diagrams showing the increments of noise by y in FIG. 4 (a) to (c) in a state in which a virtual subscriber, that is, other subscriber noise N _OU is loaded.

6 is a diagram for explaining a reception attenuation (Rx Attenuation) structure in a CDMA system;

Figure 7 is one embodiment in the value of the subscriber number (N) by the received power _{Prx (N, E b / N} O) as determined by the following equation.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be noted that the same elements among the drawings are denoted by the same reference numerals whenever possible. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

In the embodiment of the present invention, a virtual subscriber required for establishing a full load environment is adjusted in the system in order to solve difficulties in supply and demand such as manpower and terminals generated in establishing a full load environment in a field test. The virtual subscriber becomes another subscriber noise source.

1 is a diagram illustrating a method of adding a reverse subscriber load condition according to an embodiment of the present invention, and shows an RF stage of a base station. 1 includes an antenna 3, a directional coupler 4, a BPF (Band Pass Filter) 6, an LNA (Low Noise Amplifier), an attenuator 12, and an XCVR have. 1, in the embodiment of the present invention, as a method of adding a load condition of a reverse link subscriber for establishing a full load environment, a directional coupler 2 at an RF (Radio Frequency) And apply the other subscriber noise sources. The other subscriber noise source becomes a virtual subscriber load. The other subscriber noise source applied to the directional coupler 2 is applied to the XCVR 10 through the BPF (Band Pass Filter) 6 and the LNA 8. Meanwhile, a spectrum analyzer 16 is connected to a node between the LNA 8 and the XCVR 10 in order to measure the increment of other subscriber noise sources applied in the other subscriber noise generators 2. The spectral analyzer 16 must be connected to the rear end of the LNA because the other subscriber noise sources are smaller than the system noise generated in the base station. That is, it is intended to measure the noise increment after amplifying the other subscriber noise sources through the LNA 8.

If a method of adding a reverse subscriber load condition according to an embodiment of the present invention is implemented as shown in FIG. 1, a tester can calculate a full load field in an actual field by using a noise value generated in an actual field, Can create a virtual other subscriber load. This is because the noise source is supplied at the RF stage having the same or similar signal characteristics as those of the actual field environment.

FIG. 2 shows the results measured by the spectral analyzer 16 connected to the downstream end of the LNA 8, before and after the injection of the atlas indenter noise source. The state is the result measured before other subscriber noise sources are injected. At this time, it can be seen that only system noise (hereinafter referred to as thermal noise N _th or background noise) is measured. ② The state is the result measured after the noise source injection. At this time, it can be seen that the thermal noise N _th component is added to the other subscriber noise N _ou components. The other subscriber noise N _ou component is the noise increment caused by the injected other subscriber noise source. Therefore, the criterion for the noise increment can be defined as the thermal noise N _th component. If the thermal noise N _th component is taken as a noise increment criterion, it is possible to know the increment of other subscriber noise sources. That is, it is possible to measure the size of other subscriber noise sources. As a result, if the reference thermal noise N _th is kept constant, a constant subscriber state required by the tester can be created using the other subscriber generator 2 shown in FIG.

Unfortunately, under the actual field environment, the thermal noise N _th component is constantly changing with time. As a result, the other subscriber noise sources that are loaded can not be kept constant at all times.

Also, the thermal noise N _th component under the actual field environment differs from sector to sector. This also causes the other subscriber noise sources to be loaded to be unstable at all times. Hereinafter, the content of the fact that the thermal noise N _th component differs from sector to sector under an actual field environment will be described in more detail. One cell is composed of, for example, three sectors, and each sector has two reception paths (RX paths) composed of A and B. [ Therefore, a cell in which a base station is located has a total of six reception paths. However, the important fact here is that thermal noise (background noise) N _th is different for each sector. As a result, it is concluded that the number of other subscriber noise generators 2, such as the one shown in FIG. 1, is required in view of the fact that the size of the other subscriber noise is determined based on the thermal noise N _th . Otherwise, six receive attenuators are required for each one of the noise generators. In the test of a multi-cell environment, that is, when the surrounding cells for one cell are about 6 cells, in order to implement the noise source through the equipment, the equipment is set up in 7 cells at the same time, Field optimization must be performed. Therefore, this method has the burden of building and testing both manpower and equipment at the same time.

In another embodiment of the present invention, a virtual subscriber load condition is set through receiving attenuation adjustment in order to reduce the above-mentioned burden generated in establishing a full load environment in a field test. Another embodiment of the present invention for setting a virtual subscriber load condition through reception attenuation adjustment will be described below.

3 is a view for explaining a noise source adding method according to another embodiment of the present invention. The configuration of FIG. 3 is similar to that of FIG. 1, except that the other subscriber noise generator 2 shown in FIG. 1 is removed and a tone signal generator 20 is newly provided and the spectrum analyzer 16 connected to the rear end of the LNA 8 of FIG. 1 is connected to the XCVR module 10, that is, the rear end of the AGC 14 is different from the configuration of FIG. The RX attenuation within the CDMA system occurs at the LNA 8 shown in FIG. 3 and at the attenuator 12 and AGC 14, which belong to the XCVR module 10. The dual receive attenuation adjustment, that is, the gain adjustable gain of the received signal, is the attenuator 12 in the XCVR module 10. In another embodiment of the present invention, the receive attenuation adjustment is performed using the receive attenuator 12. If the receiver attenuator 12 is used to adjust the reception attenuation, the spectrum analyzer 16 must be connected to the rear end of the attenuator 12 in order to measure the result. However, since the receiving attenuator 12 is located at the front end of the AGC 14 in the XCVR module 10, the spectrum analyzer 16 can not be connected to the output terminal of the receiving attenuator 12 in the XCVR module 10. Therefore, in another embodiment of the present invention, the spectrum analyzer 16 is connected to the rear end of the AGC 10. When the spectrum analyzer 16 is connected to the rear end of the AGC 10, the signal strength of the output terminal of the XCVR module 10 is controlled by the function of the AGC (Automatic Gain Control) 14 in the XCVR (Tranceiver) It becomes constant. In another embodiment of the present invention, the load condition of other subscribers is set using the fact that the signal strength of the output terminal of the XCVR module 10 is always constant regardless of the gain adjustment of the attenuator 12.

This will be described in more detail with reference to FIGS. 3 and 4. FIG. 4A to 4C are diagrams showing the states of the thermal noise and the tone signal. FIG. 4A shows a state measured by the spectrum analyzer 16 of FIG. 3 when a tone signal is applied, 12 shows the state at the output terminal of the attenuator 12 when attenuation is controlled, and FIG. 3 (c) shows the state measured by the spectrum analyzer 16 of FIG. 3 when attenuating the gain of the attenuator 12 is attenuated.

When the tone signal generated in the tone signal generator 20 of FIG. 3 is applied to the spectrum analyzer 16 through the directional coupler 4, the BPF 6, the LNA 8, the reception attenuator 12 of the XCVR module 10 and the AGC 14, A result similar to a) will appear. Referring to FIG. 4 (a), the spectrum analyzer 16 shows a tone signal 30 having a certain size of thermal noise N _th and a Slev size. Then, if the tester attenuates the gain of the attenuator 12, the amplitude of the tone signal 30 at the rear end of the attenuator 12 will be reduced by x larger than the initial size as shown in FIG. 4 (b). However, the tone signal reduced by x size is automatically gain-controlled by the AGC 14 and again the Slev-sized tone signal 30 appears as shown in FIG. 4 (c). Therefore, even if the gain attenuation is adjusted for the attenuator 12, the magnitude of the tone signal appearing in the spectrum analyzer 16 becomes equal to Slev as shown in FIG. 4 (c). But also look at the size of the thermal noise N _th in the 4 (b), can be seen that it is increased by greater than the y _th of the thermal noise N in (a) of FIG. This is because AGC 14 adjusts the amplitude of the thermal noise N _th as well as the tone signal in response to the attenuation adjustment of the receiving attenuator 12. In this case, SNR a (SNR) of (SNR) _out1 and in Figure 4 (c) SNR (Signal to Noise Ratio) of (b) of Figure 4 _out2 is the same as that is, (SNR) _out1 = (SNR) _out2 . That is, the noise increment by y is (SNR) _out1 = (SNR) _out2 . The noise increment by y is a state in which the subscriber other than the virtual subscriber N _OU is loaded. Therefore, the states of (a), (b) and (c) of FIG. 4 are shown as (a), (b) and (c) of FIG. Referring to (c) of FIG. 5, an increment of noise by y is expressed in a state that a virtual subscriber, that is, other subscriber noise N _OU is loaded.

Hereinafter, a description of the state in which the virtual subscriber is loaded will be described later with reference to the reception attenuation structure inside the CDMA system.

FIG. 6 is a diagram for explaining a reception attenuation (Rx attenuation) structure in a CDMA system. The receive attenuation (Rx Attenuation) exists at LNA 8, receive attenuator 12, and AGC 14. In this reception attenuation structure, the normal (SNR) _out of the input signal S _i and the input noise N _i is expressed by the following equation (1).

[Equation 1]

Here, S _i = input signal

N _i = input noise

F ₁ = Noise Figure of LNA 8: Schedule

F ₂ = noise figure of receiver attenuator 12: variable

F ₃ = Noise figure value of AGC 14: constant

G ₁ = gain of LNA 8: schedule

G ₂ = gain of receiver attenuator 12: variable

G ₃ = gain of AGC 14: variable

If other subscriber noise N _OU is included in the input noise Ni in Equation (1), Ni becomes N _th (thermal noise) + N _OU (other subscriber noise). In this case, (SNR) _out is expressed by Equation (2).

&Quot; (2) "

N _ou : other subscriber noises

N _th : thermal noise

In such a state equation (2), for adjusting the (noise figure of the F2 or receive attenuators 12), receiving the gain G2 of the attenuator 12 (SNR) _out of (SNR) when "represented as shown in equation (3) _out.

&Quot; (3) "

Where G ' ₂ = gain adjusted by receive attenuation

F ' ₂ = noise figure value changed by receive attenuation

Therefore, if the gain G2 of the attenuator 12 (or the noise figure F2 of the attenuator 12) is adjusted to satisfy the following equation (4), the virtual subscriber is in a loaded state.

&Quot; (4) "

(SNR) _out = (SNR) ' _out

When the (SNR) _out, (SNR) _'out shown in Equation 1 to Equation 4 corresponds to Figure 4, and the (SNR) _out corresponds to the (SNR) _out2 shown in (c) of Figure 4, the ( SNR) ' _out corresponds to (SNR) _out1 shown in (b) of FIG.

In FIG. 4, it is necessary to know how many subscribers the signal is reduced by x based on the gain (or noise index) control of the attenuator 12 so that the magnitude y of the increased noise shown in FIG. 4 (c) The subscriber load status value of the subscriber can be known.

The received power according to the number of subscribers is calculated. The total received power P _{total_RX} received at the base station is _obtained by the following equation (1).

&Quot; (5) "

In Equation (5), it should be understood that all values except the number of subscribers N are known values. In FIG. 7, E _b / N _o is 6, 7, 8, 9, and 9, respectively, where F is 0.65, S is 0.85, v is 0.45, Rb is 9600 pb, W is 1.23 MHz, N _th W is -113 dBm / (N, E _b / N _O ) of the number of subscribers (N), which is obtained by Equation (5), in the case of 10, 11, 12, And in the following Table 1 indicates the increment of the total received power P _{total_RX} thermal noise N _th preparation of a base station receiver according to the number of subscribers on a call, as determined by Equation 1, N.

[Table 1]

N Increase thermal noise-free received power N Increase thermal noise-free received power One 0.062 dB 7 0.999 dB 2 0.205 dB 8 1.176 dB 3 0.353 dB 9 1.362 dB 4 0.505 dB 10 1.555 dB 5 0.664 dB 11 1.758 dB 6 0.828 dB 12 1.97 dB

As shown in FIG. 7 and Table 1, the increment of the total received power P _{total_RX} against the thermal noise N _th for the number of subscribers can be known.

Therefore, assuming that the size x of the signal shown in FIG. 4B is 1.97 dB shown in Table 1, the y value shown in FIG. 4C (that is, the other subscriber noise N _ou ) is the noise value for 12 subscribers as shown in Table 1.

Thermal noise N _th contrast increment for the total received power P _{total_RX} for the subscriber number as shown in Table 1 can get the x value for the number of the desired subscriber, The test can be obtained by the equation (5). The x value is adjusted by the gain (or noise figure) control of the attenuator 12 of FIG. As a result, another embodiment of the present invention adjusts the gain (or noise figure) of the base station receive attenuator 12 to create as many virtual subscribers as desired.

While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. Therefore, the scope of the present invention should not be limited by the described embodiments but should be determined by the equivalents of the claims and the claims.

As described above, the present invention has the following effects.

First of all, you can do a full load field test. In a fixed base station, the service area is very important to favor call mobility. As the number of subscribers increases, the boundaries of the reverse link decrease, and consequently, a cell optimization test in a full load state is indispensable. The ultimate goal of the CDMA system is call capacity, call mobility, and call quality. Even when the maximum number of subscribers is loaded, the call quality should be maintained and the call should not be interrupted during the move. Therefore, it is possible to construct an environment in which call capacity, call mobility and call quality can be coexisted by noise injection by the OUNS described above.

Second, call capacity in various cell environments can be accurately calculated within the system. The number of terminals required for one-sector capacity testing is approximately 80. The number of necessary terminals in the capacity test in a multi-cell environment can be roughly estimated as the number of necessary terminals in one sector system. Therefore, since the number of terminals required in the cell capacity test is implemented internally, the number of required terminals is drastically reduced.

Claims (6)

A reverse link subscriber load condition addition method in a digital cellular system, Wherein the gain of the base station receive attenuator is controlled to be attenuated so that a virtual subscriber is loaded. The subscriber load condition adding method according to claim 1, wherein the number of subscribers in a state that the virtual subscriber is loaded is obtained by using a predetermined calculation formula for calculating received power. The apparatus of claim 1, wherein the subscriber-loaded state is formed by a condition that a signal-to-noise ratio at an output terminal of the attenuator is equal to a signal-to-noise ratio at an output terminal of an automatic gain control circuit connected to a rear end of the attenuator Wherein the subscriber load condition further comprises: A reverse link subscriber load condition addition method in a digital cellular system, Wherein a noise index of the base station receiving attenuator is controlled to be attenuated so that a virtual subscriber is loaded. The subscriber load condition adding method according to claim 4, wherein the number of subscribers in a state that the subscriber is loaded is obtained using a predetermined calculation formula for calculating received power. 5. The automatic gain control circuit according to claim 4, wherein the subscriber-loaded state is formed by a condition that a signal-to-noise ratio at an output terminal of the attenuator is equal to a signal-to-noise ratio at an output terminal of the automatic gain control circuit connected to the rear end of the receiving attenuator Wherein the subscriber load condition further comprises: