JPH11112420A - Transmission power control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission power control method in which deviation of power from desired power for transmission power control is reduced due to a control delay when a mobile station moves faster. SOLUTION: A base station sends a transmission power control instruction signal used to control transmission power of a mobile station based on received power of a signal sent from the mobile station together with a transmission signal for each prescribed period. A Doppler frequency estimate section 26 of the mobile station estimates a Doppler frequency due to fading imposed on a received signal based on the transmission power control instruction signal sent from the base station and a rate of change in transmission power, allows a step size decision section 25 to change a rate of change in transmission power based on the Doppler frequency and the transmission power control instruction signal and a transmission power gain control section 27 controls a transmission power of the signal based on the transmission power control instruction signal sent from the base station and the rate of change in the transmission power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to mobile radio communication, and more particularly to a code division multiplex communication system (hereinafter referred to as CDMA).
In the transmission power control method.

[0002]

2. Description of the Related Art Heretofore, literature relating to this kind of CDMA is described in [Andrew J. Viterbi, "CDMA Principles of Spre
ad Spectrum Communication ", Addison Wesley Publishi
ng Company]. In such CDMA, each mobile station shares and uses the same frequency band. Instead, a transmission signal from each mobile station is identified by a spreading code uniquely assigned to each mobile station.

FIG. 3 is an explanatory diagram for explaining a conventional transmission power control method, and shows a configuration on the mobile station side.
In the figure, 11 is a transmitting / receiving antenna, 12 is a high-frequency unit for converting a received signal from a base station into a signal of a spread band, 13
Is a rake receiving section for decoding the output signal of the high frequency section 12 as a base band signal, 14 is a transmission power control bit reproducing section for extracting transmission power control bits sent from the base station at regular intervals, and 15 is transmission power. A transmission power gain control unit for controlling a gain, 16 is a high frequency unit that uses a speech channel signal as a radio band signal, and 17 is a transmission power gain control unit 1.
5 is a variable amplifier that controls the transmission power and emits the output signal of the high-frequency unit 16 by the transmission / reception antenna 11 at the transmission power.

Here, in order for the communication quality of each mobile station to be the same and fair, the received power from the mobile station at the base station must be the same, but the power of the received signal from each mobile station must be the same. There is a fluctuation (fading) accompanying the movement.

Therefore, in the conventional example shown in FIG. 3, the base station notifies the base station of the excess or deficiency of the received power, and the mobile station adjusts the transmission power according to the instruction. In addition,
Such control is referred to as closed-loop transmission power control, and the transmission power control also uses open-loop control in which the mobile station automatically controls power without receiving an instruction from the base station.

Next, the operation of the conventional example will be described. First, the base station observes the reception power of the signal transmitted from the mobile station in a certain section (Tpc [sec]), and if the average power in that section is larger than a desired value, the transmission power of the mobile station is increased. One-bit instruction information (transmission power control bit) that lowers by a certain ratio, and one-bit instruction information (transmission power that raises the transmission power of the mobile station by a certain ratio if smaller than a desired value. The control bit is inserted into the communication channel of the downlink (communication from the base station to the mobile station) at regular intervals (Tpc [sec]) to notify the mobile station.

[0007] After the mobile station demodulates the received signal in the RAKE receiving unit 13, the transmission power control bit reproducing unit 14 extracts the transmission power control bits from the demodulated signal from the RAKE receiving unit 13 at regular intervals and transmits the demodulated signals. Output to power gain control unit 15. Then, if the content of the transmission power control bit is an instruction to increase the transmission power, the transmission power gain control unit 15 increases the transmission power by a fixed rate,
If the instruction is to reduce the transmission power, the variable amplifier 17 is controlled so as to reduce the transmission power by a certain ratio.

[0008]

In the conventional transmission power control method as described above, the mobile station increases or decreases the transmission power (hereinafter, this transmission power increase / decrease ratio is determined by the step size of the transmission power control). ) Is constant irrespective of the time change of the change rate of the received power due to the moving speed or the instantaneous fading. For example, when a larger increase is required, an appropriate increase rate cannot be obtained. When the moving speed is high, there is a problem that the power of the received signal from the mobile station fluctuates rapidly and the error of the received signal at the base station with respect to a desired value increases.

[0009]

SUMMARY OF THE INVENTION A transmission power control method according to the present invention is a transmission power control method in a wireless communication system for performing communication between at least one base station and a plurality of mobile stations. The mobile station transmits a transmission power control instruction signal for controlling the transmission power to the mobile station based on the reception power of the signal transmitted from the mobile station together with the transmission signal at regular intervals. Based on the transmitted transmission power control instruction signal and the change rate of the transmission power, the Doppler frequency of the fading received by the received signal is estimated, and based on the estimated Doppler frequency and the transmission power control instruction signal, the change rate of the transmission power is estimated. To change
The transmission power of the signal is controlled based on the transmission power control instruction signal and the change rate of the transmission power.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic principle of the present invention is to appropriately change the step size of transmission power control so as to obtain better fading followability. As such a method of appropriately changing the step size, a speech code such as that described in [LRRabiner / RWSchafer, Translated by Kuki Suzuki, "Digital Signal Processing of Voice", Corona, p.235-238], etc. There is the Jayant method used in adaptive delta modulation in fields such as digitalization.

Here, an outline of transmission power control by this method will be described first. First, an instruction (one-bit information indicating increase or decrease) of transmission power control received from a base station in a certain period (for example, the n-th period) of transmission power control is C (n). If the step size used in the step is S (n) (unit: dB), the instruction C
The step size S (n + 1) for (n) is set by the following equation.

[0012]

## EQU00001 ## When C (n) = C (n-1), S (n + 1) = P.S (n) (P> 1) When C (n) .noteq.C (n-1), S (n + 1) = (1 / Q) · S (n) (Q> 1) where P is a coefficient for increasing the step size S, and Q is a coefficient for decreasing the step size S.

In the above equation, the preferable values of P and Q are not always constant with respect to the manner of fluctuation of the fading, that is, the Doppler frequency. For example, when the Doppler frequency is low and the fading is gradual, even a small step size follows. Therefore, it is sufficient to set P / Q <1, but when the Doppler frequency is high, there is a tendency that the reception level suddenly decreases and then increases rapidly, so that P / Q> 1 is better. The followability is improved.

FIG. 2 shows a simulation result showing a change in standard deviation of a control error due to a change in P and Q. In FIG. 2, the horizontal axis is Fd Tpc (Fd is the maximum Doppler frequency of fading, Tpc is the control cycle of transmission power control, and is 0.5 mec in this example), and the faster the value of Fd Tpc, the faster the fading. Becomes The vertical axis is Do (dB), the standard deviation of the control error generated by the transmission power control in the conventional example, and the standard deviation of the control error when the step size control of the equation (1) is incorporated in the conventional example is D (dB). )), The difference between these two ΔD = D
−Do (dB) (thus, a smaller value of ΔD is more effective than that of the conventional example).

FIG. 2 shows an example of P / Q <1, where P = 1.
2, Q = 2, P / Q> 1, P = 2, Q = 1.2
For comparison, the case of P / Q = 1 (P = Q = 2) is also shown.

As shown in FIG. 2, when the maximum Doppler frequency is low, it is preferable to set P / Q <1.
Also, when the maximum Doppler frequency is high, it is found that setting P / Q> 1 is more preferable. Therefore, in this embodiment, when using the Jayant method for transmission power control, the companding coefficients (coefficients P and Q) are set as appropriate by calculating the maximum Doppler frequency. For estimation of the Doppler frequency, an instruction of the transmission power received from the base station is used to reduce the increase in the scale of the calculation.
This is because this instruction is a series reflecting the fading situation. Then, if the history is traced using the instruction and the step size corresponding to the instruction, fading can be reproduced in the mobile station, and the Doppler frequency estimates the number of intersections with the reference level within a predetermined time as information. ing. The details will be described below.

FIG. 1 is an explanatory diagram for explaining a transmission power control method according to one embodiment of the present invention, and shows a configuration on the mobile station side. In the figure, 21 is a transmitting / receiving antenna, 22 is a high frequency unit for converting a received signal from a base station into a signal in a spread band, and 23 is a base for an output signal of the high frequency unit 22.
A RAKE receiver for decoding as a band signal, 24
A transmission power control bit regeneration unit that receives an output signal of the AKE receiving unit 23 and extracts transmission power control bits sent from the base station at regular intervals, and the transmission power control bits are transmitted by the step size determination unit 25 and It is input to the Doppler frequency estimator 26.

Reference numeral 25 denotes a step size determining unit for determining a step size based on the time series of transmission power control bits and the estimated Doppler frequency, and 26 denotes a step size based on the past value of the step size and the time series of transmission power control bits. The Doppler frequency estimator 27 for calculating the Doppler frequency estimation value includes a transmission power control bit output from the transmission power control bit reproducing unit 24 and a step size determining unit 25.
, A transmission power gain control unit that sets a transmission power gain based on the step size output from, a high frequency unit that uses a speech channel signal as a radio band signal, 29 a transmission power controlled by a transmission power gain control unit 27, With the transmission power, the output signal of the high frequency unit 28 is transmitted to the transmission / reception antenna 2.
1 is a variable amplifier that fires.

Next, the operation of this embodiment will be described. First, the high-frequency unit 22 converts a received signal received by the transmitting / receiving antenna 21 into a signal in a spread band,
The E receiving section 23 decodes the output signal of the high frequency section 22 as a baseband signal. Then, based on the demodulated signal decoded by the rake receiving unit 23, the transmission power control bit reproducing unit 24 reproduces the transmission power control bit transmitted from the base station at regular intervals Tpc [sec].

The step size determining unit 25 determines a step size from the estimated Doppler frequency Festimate estimated by the Doppler frequency estimating unit 26 and the transmission power control bits extracted by the transmission power control bit reproducing unit 24.

Here, the determination of the step size by the step size determination section 25 will be described. First, the transmission power control bit input in the n-th control cycle is represented by C (n).
(For convenience, the transmission power is increased by −1, and the transmission power is decreased by +1), the transmission power control bit input one cycle before is C (n−1), and the currently used step size is S
If (n) (unit: dB), a new step size S (n + 1) for C (n) is set by the following equation.

[0022]

## EQU00002 ## When C (n) = C (n-1), S (n + 1) = P.S (n) When C (n) .noteq.C (n-1), S (n + 1) ) = (1 / Q) · S (n)

At this time, the companding coefficients P and Q are
Tables Ptable (Festimate) and Q created in advance to find the best P and Q for each frequency using
Determined from table (Festimate).

For example, if the simulation results shown in FIG. 2 are used, if Festimate ≦ 0.009, P = 1.2, Q = 2 0.009 ≦ Festimate ≦ 0.012, P = Q = 2 0.012 ≦ Festimate, P = 2. Set Q = 1.2.

In the Doppler frequency estimating section 26,
First, from the time series of the transmission power control bits and the step size generated before the current transmission power control cycle, the past T
A fading value F (-i) at a time in units of a transmission power control cycle for reproducing est [sec] is reproduced by the following equation.

[0026]

(Equation 3)

Here, j = 0 is the time when the reception of the transmission power control bit has started, S (i) is the step size determined at time i, and C (i) is the transmission power control bit received at time i. , D are control delays until the transmission power control bit corresponding to the transmission in S (i) is received by the mobile station.

Next, the average value Fav of F (-i) during the past Test [sec] is calculated. That is, the transmission power control period Td
And L = Test / Td F (-i) (i = 1 to L) are used. Then, the average value Tav of the time when F (i) continues to exceed this value is calculated. Since this value indicates the most characteristic increase or decrease of the received power at the observation time,
Considering the dominant fading frequency in that section, the Doppler frequency estimation value Festimate is estimated by the following equation.

[0029]

## EQU4 ## Festimate = (1/4). (1 / Tav)

In the equation (4), the coefficient of 1/4 is
Assuming that the cycle of rising continues is about half of the time of continuing falling, the cycle of this fluctuation is 2Tav, and the fading frequency is approximated to (1/2) of the cycle of the change in the received power caused by this, so that 2Festimate = This is based on the relationship of 1/2 Tav.

Then, in the transmission power gain control section 27,
The variable amplifier 29 is controlled so that the transmission power becomes Pout as shown in the following equation.

[0032]

(Equation 5) Here, Po is the initial transmission power. By performing such control, in the example of the simulation result shown in FIG. 2, control close to transmission power control that takes the smallest value of ΔD according to Fd Tpc becomes possible.

[0033]

As described above, according to the present invention, a base station transmits a transmission power control instruction signal for controlling transmission power to a mobile station based on the reception power of a signal transmitted from the mobile station. Is transmitted at regular intervals together with the transmission signal, and the mobile station estimates the Doppler frequency of fading received by the received signal based on the transmission power control instruction signal transmitted from the base station and the change rate of the transmission power. Since the change rate of the transmission power is changed based on the Doppler frequency and the transmission power control instruction signal, and the transmission power of the signal is controlled based on the transmission power control instruction signal and the change rate of the transmission power, If the deviation of the transmission power control from the desired power can be reduced according to the moving speed of the mobile station, it is possible to provide more fair communication quality to a large number of users. With a cormorant effect.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a transmission power control method according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a simulation result representing a change in a standard deviation of a control error due to a change in P and Q.

FIG. 3 is an explanatory diagram for explaining a conventional transmission power control method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 transmission / reception antenna 12 high frequency unit (reception) 13 rake reception unit 14 transmission power control bit reproduction unit 15 transmission power gain control unit 16 high frequency unit (transmission) 17 variable amplifier 21 transmission / reception antenna 22 high frequency unit (reception) 23 rake reception unit 24 transmission Power control bit reproduction unit 25 step size determination unit 26 Doppler frequency estimation unit 27 transmission power gain control unit 28 high frequency unit (transmission) 29 variable amplifier

Claims (3)

[Claims] 1. A transmission power control method in a wireless communication system for performing communication between at least one base station and a plurality of mobile stations, wherein the base station performs the control based on the reception power of a signal transmitted from the mobile station. Transmitting a transmission power control instruction signal for controlling the transmission power to the mobile station together with the transmission signal at regular intervals, wherein the mobile station changes the transmission power control instruction signal and the transmission power transmitted from the base station. Estimating the Doppler frequency of fading received by the received signal based on the rate, based on the estimated Doppler frequency and the transmission power control instruction signal, change the change rate of the transmission power, the transmission power control instruction signal and A transmission power control method, wherein the transmission power of a signal is controlled based on the change rate of the transmission power. 2. A transmission power control method in a wireless communication system for performing communication between at least one base station and a plurality of mobile stations, wherein the base station is configured to perform communication based on a received power of a signal transmitted from the mobile station. Transmitting a transmission power control instruction signal for controlling the transmission power to the mobile station together with the transmission signal at regular intervals, wherein the mobile station changes the transmission power control instruction signal and the transmission power transmitted from the base station. Estimating the Doppler frequency of fading received by the received signal based on the rate, when the transmission power control instruction signal from the base station is the same as the transmission power control instruction signal one cycle before, the first change rate of the transmission power When the transmission power control instruction signal from the base station is different from the transmission power control instruction signal one cycle before, the transmission power change rate is reduced by the second ratio, The first ratio and the second ratio are changed based on the estimated Doppler frequency and the transmission power control instruction signal. Based on the transmission power control instruction signal and the transmission power change rate, a signal A transmission power control method comprising controlling transmission power. 3. A method for estimating the Doppler frequency, comprising: calculating a reproduction value of fading based on a product sum of a transmission power control instruction signal transmitted from the base station and a transmission power change rate; and averaging the fading reproduction value. 3. The transmission power control method according to claim 1, wherein an average value of a time during which the reproduction value of the fading continues to exceed the value is calculated, and estimation is performed based on the average value.