KR20040027165A - Variable power controlling method for closed loop of mobile communication system - Google Patents

Abstract

PURPOSE: A variable closed loop power control method of a mobile communication system is provided to reduce interference between systems and increase cell capacity of a CDMA system by more precisely controlling power by variably increasing or decreasing power. CONSTITUTION: When the same power control command is repeated by three times or more(PCMD(t)=PCMD(t-Tp)=PCMD(t-2Tp)), it is determined that a signal-to-interference ratio in a current channel state is far away from a threshold value and power as much as a predetermined 'K' is increased/decreased. Otherwise(PCMD(t)=PCMD(t-Tp)≠PCMD(t-2Tp)), it follows the existing power controlling. If a power control command repeats 1 and -1(PCMD(t)≠PCMD(t-Tp)), it means that the signal-to-interference ratio is near the threshold value, so power as much as 1/K is increased/decreased.

Description

Variable closed loop power control method of mobile communication system {VARIABLE POWER CONTROLLING METHOD FOR CLOSED LOOP OF MOBILE COMMUNICATION SYSTEM}

The present invention relates to a variable closed-loop power control method of a mobile communication system, and more particularly, by performing more precise power control through variable power control increase and decrease in closed loop power control occurring between a mobile station and a base station in a CDMA system. In addition, the present invention relates to a variable closed loop power control method of a mobile communication system that can reduce the interference between systems to increase the cell capacity (user capacity) of the CDMA system determined by the signal-to-interference ratio.

The CDMA system is an interference-limited system in which the performance and capacity of the system are determined by the interference. Because signals transmitted from all mobile stations share the same frequency, internal interference generated in the system plays an important role in determining system capacity and voice quality.

Therefore, the power transmitted from each mobile station must be adjusted to limit the amount of interference with each other. At this time, the power level should be maintained at an appropriate level for satisfactory voice quality.

As the mobile moves, the RF environment continues to change due to slow and fast fading, shadowing, external interference, and others. The purpose of power control is to limit the transmit power while maintaining link quality above a certain level in the forward and reverse links.

In order to maximize capacity in a CDMA system, each terminal's signal must be received at the base station with a minimum signal-to-noise ratio. If the transmission power of the terminal is low, the call quality is lowered. If the terminal is high, the call quality of the terminal is improved, but the call quality of other subscribers is worsened because it greatly interferes with other terminals using the same channel.

Therefore, in order for all subscribers to maintain good call quality and maximize the capacity, the receiving power of each terminal received by the base station is the same, and each terminal transmit power should be controlled so that the size has a minimum signal-to-interference ratio. This is also necessary to solve the near-far problem of CDMA systems.

In order to minimize the near-end interference problem, the CDMA system makes the power levels of the received signals of all mobile stations at the base station the same. At this time, the target value of the received signal power level is a minimum value that can satisfy the performance evaluation values (eg, BER, FER, dropped-call, and coverage) defined by the user. To do this, the mobile station in proximity to the base station must keep its transmission power low compared to the mobile station far from the base station.

In the CDMA system, power control is divided into open-loop power control and closed-loop power control. The open loop is mainly for compensation according to the distance between the mobile station and the base station. Measure the total receive power of the specified base station total CDMA channel. At this time, since the entire power is monitored without using the demodulated signal, the estimation time can be quickly estimated without knowing the synchronization time, base station name, and path loss.

However, in the mobile station and the base station, the paths of the opposite channels are different due to the difference between the forwarding (base station → mobile station) and the reverse (mobile station → base station) channels even though the same mobile station and the base station communicate with each other due to mismatches in the transceiver, different frequency bands, and communication between the same mobile station and the base station. Loss cannot be predicted accurately. To correct this error, each mobile station or base station issues periodic low-speed power control commands to the opposite channel compared to the reference signal-to-interference ratio, and the other base station and mobile station adjust the output accordingly. . This method is called closed-loop power control (used only in reverse in IS-95, but in advanced IS-2000 and WCDMA, closed-loop power control was introduced in both reverse and forward).

1 is a flowchart showing a schematic process of a conventional closed loop power control method. As shown in FIG. 1, a mobile station (or a base station) demodulates a received signal to extract a power control bit and transmits the power control bit according to the power control bit. Turns the power up or down in 1dB steps. Also, depending on whether the signal-to-interference ratio is greater than or less than the reference value, a power control bit is inserted to raise the transmit power if the value is greater than the reference value, and if the value is less than the reference value, the transmit power is brought down. Inserts a power control bit to transmit a signal to a base station (or mobile station).

Generally, fading occurs due to the Doppler effect caused by the movement of a mobile station in a cellular environment. In particular, a large influence on the error rate of the mobile station and the base station is fast fading (referred to as railway fading), and closed-loop power control is intended to compensate for the difference between the fading of the forward and reverse links and the effects of the fast fading.

In general, the characteristics of a fading channel may be regarded as a condensed channel in which errors occur in one symbol and contiguously occur. That is, if the current state of power reception is higher than the reference value, the power should be lowered. If such a command is repeated, the signal is transmitted higher than the power to be transmitted by the mobile terminal, so the power is rapidly reduced to suit this situation. To be required.

However, the current system has a fixed limit of 1 dB that can be increased or decreased by one power control. That is, such a fixed size power control has a problem that it is difficult to quickly adapt to the environment of the aggregation channel.

Accordingly, the present invention was created to solve the above-mentioned conventional problems, and performs more precise power control through variable power control increase and decrease in closed loop power control occurring between a mobile station and a base station in a CDMA system. Accordingly, an object of the present invention is to provide a variable closed loop power control method of a mobile communication system that can reduce the interference between systems to increase the cell capacity (user capacity) of the CDMA system determined by the signal-to-interference ratio.

According to the present invention for achieving the above object, when the mobile station (or base station) demodulates a received signal and extracts a power control bit to control transmission power, the same power control command is repeated three or more times (PCMD (t)). = PCMD (t-Tp) = PCMD (t-2Tp)), increasing or decreasing the transmission power by a predetermined K; If the same power control command is repeated twice or less (PCMD (t) = PCMD (t-Tp) ≠ PCMD (t-2Tp)), increasing or decreasing the transmission power in 1 dB increments; If the power control command is repeated 1, -1 (PCMD (t) ≠ PCMD (t-Tp)), it comprises a step of increasing or decreasing the transmission power by 1 / K.

1 is a flow chart showing a schematic process of a conventional closed loop power control method.

Figure 2 is a flow chart showing a schematic process of a conventional closed loop power control method according to the present invention.

In the fading channels where the error occurs in series, the present invention can quickly reduce the power control target by reducing more than the same amount if the previously received power control command was 'decreased' and the next received command was also 'decreased'. If the power control command is different from the previous command, the signal strength is changing in the vicinity of the threshold of the current signal-to-interference ratio. In this case, a smaller amount of increase and decrease is used to quickly approach the power control target value. It is about a method.

As described above, in order to reach the target value of power control more quickly by using the conventional aggregated channel characteristic, it is preferable to divide the power control step into various types. In other words, it can be seen that the gain is large in terms of accuracy of power control by controlling the power control bits of increasing and decreasing power from one bit to multiple bits and corresponding to the difference. However, since the power control bit is transmitted to the talk channel between the mobile station and the base station, the capacity of the channel is reduced, and since it is already determined to use one bit in the IS-2000 and WCDMA standards, the possibility of implementation is impractical.

Therefore, the present invention is to determine the amount of increase and decrease of the power control according to the previous power control command by using one bit, can be expressed as shown in the following equation (1).

P (t) = P (t-Tp) + K * PCMD in dB

Where P (t) = transmit power,

Tp = power control cycle,

PCMD = power control command (+1 or -1),

K = constant increase and decrease constant,

That is, in the conventional system, the power control period Tp generally has a period of 800 Hz or 1600 Hz, and the PCMD is -1 when the base station or the mobile station compares the signal-to-interference ratio, and is -1 when the base station or the mobile station is larger than a predetermined threshold, and +1, It is a value sent from the mobile station or base station of the other party, and the increase and decrease constant K value does not change.

In contrast, the power control method according to the present invention can be represented by Equation 2 below.

P (t) = P (t-Tp) + ΔK * PCMD (t) in dB

Where P (t) = transmit power,

Tp = power control cycle,

PCMD (t) = power control command (+1 or -1),

ΔK = K: (PCMD (t) = PCMD (t-Tp) = PCMD (t-2Tp))

= 1: (PCMD (t) = PCMD (t-Tp) ≠ PCMD (t-2Tp))

= 1 / K: (PCMD (t) ≠ PCMD (t-Tp))

At this time, K is larger than one.

When the power control command is repeated three or more times in Equation 2, it is determined that the signal-to-interference ratio in the current channel state is far from the threshold, and the power is increased or decreased by a predetermined K. Otherwise, follow the existing power control. In addition, if the power control command repeats 1 and -1, it means that the signal-to-interference ratio is near the threshold, and thus increases or decreases the power by 1 / K.

In the above algorithm, K should be tested in the real system to find the most efficient value. In general, if the K value is large, the response to the memory of the channel is faster, so that the power reaches the target quickly. When this response exceeds a certain value range, excessive compensation occurs, and a larger power gain beyond the target power occurs. Therefore, K may be out of the target value, so K must find a suitable value through a test.

Next, FIG. 2 is a flowchart showing a schematic process of a conventional closed loop power control method according to the present invention. As shown in FIG. 2, a process of detecting a power control bit and performing transmission power control according thereto is similar, but transmitting It can be seen that the power increase / decrease range is adjusted differently according to the repetition period of the transmission control command.

That is, if the same power control command is repeated three or more times (PCMD (t) = PCMD (t-Tp) = PCMD (t-2Tp)), it is determined that the signal-to-interference ratio in the current channel state is far from the threshold. , Increase or decrease power by predetermined K. Otherwise (PCMD (t) = PCMD (t-Tp) ≠ PCMD (t-2Tp)) follows the existing power control.

Also, if the power control command repeats 1, -1 (PCMD (t) ≠ PCMD (t-Tp)), it means that the signal-to-interference ratio is near the threshold, so that the power is increased by 1 / K. It is.

Accordingly, the present invention has the effect of maintaining the signal-to-interference ratio more firmly with respect to the fading environment which is a general wireless cellular environment than the conventional power control method.

As described above, the variable closed loop power control method of the present invention provides a more precise power control through variable power control increase and decrease in closed loop power control occurring between a mobile station and a base station in a CDMA system. It is effective to reduce the interference between the cell capacity of the CDMA system.

Claims (2)

In the mobile station (or base station) demodulating the received signal to extract the power control bits to control the transmission power, If the same power control command is repeated three or more times by Equation 1 (PCMD (t) = PCMD (t-Tp) = PCMD (t-2Tp)), increasing or decreasing the transmission power by a predetermined K; If the same power control command is repeated twice or less (PCMD (t) = PCMD (t-Tp) ≠ PCMD (t-2Tp)), increasing or decreasing the transmission power in 1 dB increments; If the power control command is repeated 1, -1 (PCMD (t) ≠ PCMD (t-Tp)), the step of increasing or decreasing the transmission power by 1 / K comprising a step of the mobile communication system Variable closed loop power control method. (Equation 1) P (t) = P (t-Tp) + ΔK * PCMD (t) in dB Where P (t) = transmit power, Tp = power control cycle, PCMD (t) = power control command (+1 or -1), ΔK = K: (PCMD (t) = PCMD (t-Tp) = PCMD (t-2Tp)) = 1: (PCMD (t) = PCMD (t-Tp) ≠ PCMD (t-2Tp)) = 1 / K: (PCMD (t) ≠ PCMD (t-Tp)) Where K is greater than one. 2. The method of claim 1, wherein if the power control command is repeated three or more times, it is determined that the signal-to-interference ratio in the current channel state is far from a threshold value. A variable closed loop power control method for a mobile communication system, characterized in that it is determined to be near a threshold.