WO2008069603A1

WO2008069603A1 - Device and method for controlling power

Info

Publication number: WO2008069603A1
Application number: PCT/KR2007/006328
Authority: WO
Inventors: Dae-Ho Kim; Kyung-Yeol Sohn; Youn-Ok Park; Jee-Hwan Ahn
Original assignee: Electronics And Telecommunications Research Institute; Samsung Electronics Co., Ltd.
Priority date: 2006-12-07
Filing date: 2007-12-06
Publication date: 2008-06-12

Abstract

A power controller of a communication system includes a power amplifier, a power controller, and a gain controller. The power amplifier amplifies transmission power of a transmission signal, and the power controller controls a gain of the power amplifier by using a received signal. The gain controller measures a distance between a transmitter having transmitted the received signal and the power controller, and applies a power concentration gain depending on the distance to the transmission signal.

Description

Description DEVICE AND METHOD FOR CONTROLLING POWER

Technical Field

[1] The present invention relates to a terminal of a communication system. More particularly, the present invention relates to an uplink power control method of a terminal in an orthogonal frequency division multiplexing access (OFDMA) system. Background Art

[2] Power control in a communication system is a radio resource managing technique for efficiently using limited frequency resources and is a means for solving the near-far problem.

[3] Transmission power of the terminal is determined by the gain of a power amplifier and a number of subchannels used. Since the terminal uses a single subchannel in a code division multiple access (CDMA) communication system, transmission power of the terminal is determined by the gain of the power amplifier. Therefore, the gain of the power amplifier in the CDMA communication system is performed by an open- loop power control for compensating for the path loss caused by the distance between a base station and a mobile station and a closed-loop power control for compensating for inaccuracy of the open-loop power control. Since the transmission power of the terminal is determined so as to use a subchannel on the boundary area of a cell in the CDMA communication system, the gain of the power amplifier can be controlled within any part of the cell so as to control the power.

[4] The open-loop power control measures the received signal strength, and increases transmission power when the received signal strength is low or reduces a transmission signal and transmits an uplink signal when the received signal strength is high. After the uplink signal is transmitted through the open-loop power control, the terminal performs a closed-loop power control to control transmission power according to the closed- loop power control transmitted by the base station.

[5] Differing from the CDMA system, the terminal has no limit on the number of subchannels used in the orthogonal frequency division multiple access (OFDMA) communication system, and the transmission power of the terminal is designed to be less than that of the base station so as to use a single subchannel on the cell boundary area. Since the terminal can use any number of subchannels from a single subchannel to the entire subchannels, a full loading range (FLR) for the terminal to use the entire subchannels is restricted in consideration of a path loss that increases as the distance between the base station and the mobile station increases and the signal to noise ratio (SNR) needed by the base station per subchannel. In this instance, a power amplifier of the terminal outside the FLR uses the maximum gain. Therefore, since the terminal provided outside the FLR cannot perform power control for increasing the gain of the power amplifier so as to compensate the path loss, the strength of the uplink signal received by the base station is weakened to thus fail to satisfy the required SNR.

[6] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. Disclosure of Invention Technical Problem

[7] The present invention has been made in an effort to provide a power control method and device having the advantage of performing a power control function irrespective of location. Technical Solution

[8] In one aspect of the present invention, a power controller of a communication system includes a power amplifier, a power controller, and a gain controller. The power amplifier amplifies transmission power of a transmission signal, and the power controller controls a gain of the power amplifier by using a received signal. The gain controller measures a distance between a transmitter having transmitted the received signal and the power controller, and applies a power concentration gain caused by the distance to the transmission signal.

[9] In another aspect of the present invention, a transmission power control method by a power controller of a communication system includes measuring a distance between a transmitter having transmitted a received signal and the power controller using the received signal, determining a first gain according to the distance, and amplifying the transmission power by applying the first gain to a transmission signal.

[10] In another aspect of the present invention, a transmission power control method by a power controller of a communication system includes: measuring a distance between a transmitter having transmitted a received signal and a power controller by using the received signal; comparing the measured distance and a threshold distance; determining a first gain according to a comparison result of the measured distance and the threshold distance; applying the first gain to a transmission signal; and applying a second gain that is determined by the received signal strength to the transmission signal to which the first gain is applied, and controlling transmission power of the transmission signal.

Advantageous Effects

[11] According to the exemplary embodiments of the present invention, the terminal's transmission power can be controlled outside the FLR by applying the power concentration gain caused by the distance between the base station and the terminal to the output signal of the modulator. Therefore, the uplink power control can be performed irrespective of the location of the terminal. Brief Description of the Drawings

[12] FIG. 1 shows a block diagram of a power controller of a terminal for an uplink power control in a communication system according to a first exemplary embodiment of the present invention.

[13] FIG. 2 shows a flowchart for an uplink power control method in a communication system according to a first exemplary embodiment of the present invention.

[14] FIG. 3 shows a block diagram of a power controller of a terminal for an uplink power control in a communication system according to a second exemplary embodiment of the present invention.

[15] FIG. 4 shows a power concentration gain according to the distance between the base station and the terminal in a communication system according to an exemplary embodiment of the present invention. Mode for the Invention

[16] In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

[17] Also, the block in the present specification represents a unit for processing a predetermined function or operation, which can be realized by hardware, software, or a combination of hardware and software.

[18] Throughout the entire specification, the terminal represents a mobile station (MS), a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), user equipment (UE), and an access terminal (AT), and includes part or all of the functions of the mobile terminal, the subscriber station, the portable subscriber station, and the user equipment. Also, the base station (BS) represents an access point (AP), a radio access station (RAS), a node B, and a base transceiver station (BTS), and includes part or all of the functions of the access point, the radio access station, the node B, and the base transceiver station.

[19] A power control method and device in a communication system according to an exemplary embodiment of the present invention will now be described with reference to the drawings.

[20] The OFDMA communication system will be exemplified in the exemplary embodiment of the present invention, but the present invention is also applicable to other communication systems using a plurality of subchannels. Also, a power controller for an uplink power control will be exemplified as being provided to the terminal according to an exemplary embodiment of the present invention.

[21] FIG. 1 shows a block diagram of a power controller of a terminal for an uplink power control in a communication system according to a first exemplary embodiment of the present invention.

[22] As shown in FIG. 1, the power controller includes a modulator 100, a gain controller

200, a digital/analog converter (DAC) 300, a power amplifier 400, and a power controller 500.

[23] The modulator 100 modulates a transmission signal to be transmitted to a base station (not shown). The power controller 500 uses a received signal to determine an open-loop power control value and a closed-loop power control value, and controls the gain of the power amplifier 400. Also, the power controller 500 demodulates the received signal and transmits the detected transmission time control signal to the gain controller 200. The gain controller 200 uses the transmission time control signal to sense the distance between the base station (i.e., a transmitter having received the received signal) and the terminal (i.e., a power controller), and applies a power concentration gain following the distance between the base station and the terminal to the modulated transmission signal. The DAC 300 converts the transmission signal modulated by the modulator 100 or the power concentration gain applied transmission signal into an analog signal and transmits the analog signal to the power amplifier 400. The power amplifier 400 amplifies power of the analog transmission signal by applying the open-loop power control value and the closed-loop power control value.

[24] In this instance, the gain controller 200 includes a ranging measurer 210, a power concentration gain table 220, and a digital amplifier 230. The power controller 500 includes an analog/digital converter (ADC) 510, a received signal strength measurer 520, a loop filter 530, a demodulator 540, an adder 550, and a pulse density modulator 560.

[25] In the power controller 500, the ADC 510 converts the analog received signal received from the base station into a digital received signal, and transmits the digital signal to the received signal strength measurer 520 and the demodulator 540. The received signal strength measurer 520 uses the digital received signal to measure the signal's average power, and the loop filter 530 uses the received signal's average power to perform a loop filtering process, and outputs an open-loop power control value to the adder 550. The demodulator 540 demodulates the digital received signal to detect the closed-loop power control signal and the transmission time control signal. The demodulator 540 transmits the detected transmission time control signal to the ranging measurer 210, and outputs the closed- loop power control value caused by the closed- loop power control signal to the adder 550. The adder 550 adds the open-loop power control value and the closed-loop power control value and transmits the addition value to the pulse density modulator 560, and the pulse density modulator 560 modulates the pulse value on the sum of the open-loop power control value and the closed- loop power control value to control the gain of the power amplifier 400.

[26] In the gain controller 200, the ranging measurer 210 uses the transmission time control signal to control the terminal's transmission time so as to receive the transmission signal within the demodulation reference time. That is, when the base station receiver fails to receive the transmission signal within the demodulation reference time for allowing demodulation, the demodulation cannot be performed, and when the receiving time becomes far longer than the demodulation reference time, performance by the channel estimator is worsened, reducing demodulation performance. Therefore, the ranging measurer 210 performs a ranging process for controlling the transmission time so as to receive the transmission signal within the demodulation reference time. Through the ranging process, the terminal can know distance information between the base station and the terminal. The power concentration gain table 220 stores a power concentration gain caused by the distance between the base station and the terminal as a table format. The digital amplifier 230 applies the power concentration gain corresponding to the distance measured by the ranging measurer 210 to the transmission signal transmitted by the modulator 100 to control the terminal's transmission power.

[27] The terminal located in the FLR controls the gain of the power amplifier 400 according to the open-loop power control value and the closed-loop power control value to control the transmission power since the gain of the power amplifier 400 is not the maximum value. However, since the gain of the power amplifier 400 is fixed with the maximum value so as to compensate for the path loss, the terminal located outside the FLR uses the gain controller 200 to apply the power concentration gain depending on the distance between the base station and the terminal, and thereby controls the terminal's transmission power. In this instance, additional power for applying the power concentration gain is generated by controlling the number of subchannels used by the terminal. The power concentration gain is set to be increased as the distance becomes farther.

[28] In the case of not using the power concentration gain, the terminal's transmission power is determined by the gain of the power amplifier 400 and the number of subchannels as expressed in Equation 1. [29] (Equation 1)

^[30] Tx _ power (dBm) = P₁ (PA_Gam ) + P₂ (N_SCH )

[31] Herein, Tx_power(dBm) is the terminal's transmission power, Pi(PA_Gai_n) is the gain of the power amplifier 400, N_SCH is the number of subchannels used by the transmission signal, and P₂(N_SCH) is power determined by the number (N_SCH) of subchannels.

[32] In this instance, since the gain of the power amplifier 400 of the terminal located outside the FLR is fixed with the maximum value, the number of subchannels used by the terminal is reduced and the power increase residual corresponding to the reduced number of the subchannels is used as the power concentration gain in the first exemplary embodiment of the present invention. Therefore, the terminal's transmission power in the case of using the power concentration gain is expressed in Equation 2.

[33] (Equation 2)

^[34^] Tx _power(dBm) = P₁ (PA₀J + g(d)'P₂(N_SCH)

[35] Herein, Pi(PA_Gai_n) is the gain of the power amplifier 400, g(d) is the power concentration gain caused by the distance (d) between the terminal and the base station, N scH is the number of subchannels used by the transmission signal, and P₂(N_SCH) is power determined by the number (N_SCH) of subchannels that are allocated in consideration of the limit of the transmission power of the terminal outside the FLR.

[36] In detail, transmission power when the open-loop power control and the closed-loop power control are performed in the communication system is expressed in Equation 3.

[37] (Equation 3)

^[38] Tx_power(dBm) = -mean _rx _ power (dBm)

-Power Offset

+g(d>P(N_scu)

+

Closed Loop Correction(dB)

[39] Herein, mean_rx_power is the received signal strength, and PowerOffset is a predetermined constant that is set to use the maximum transmission output when the terminal's received signal strength has the minimum value. ∑Closed Loop Correction(dB) is the closed-loop power control value, g(d) is a power concentration gain caused by the distance (d) between the terminal and the base station, N_SCH is the number of subchannels used by the transmission signal, and P(N_SCH) is power determined according to the number (N_SCH) of subchannels. In Equation 2, - mean_rx_power - PowerOffset corresponds to the open-loop power control value, and the (-) sign in front of mean_rx_power represents the function of the open-loop power control value, which is for increasing the transmission power when the receiving power strength is weak and reducing the transmission power when the receiving power strength is strong. The closed-loop power control value compensates for the error caused by inaccuracy of the open-loop power control by increasing the gain of the power amplifier 400.

[40] That is, when the terminal is located within the FLR in the communication system, the power concentration gain (g(d)) is fixed with the value of 1 so that the power control is performed in a like manner of the case in which no power concentration gain is used. When the terminal is located outside the FLR, the power control can be performed outside the FLR by increasing the power density per subchannel by using the power concentration gain (g(d)) that is variable according to the distance between the base station and the terminal.

[41] FIG. 2 shows a flowchart for an uplink power control method in a communication system according to a first exemplary embodiment of the present invention.

[42] The terminal uses the received signal to measure the distance between the base station and the terminal (SlOO), and compares the distance between the base station and the terminal and the FLR (S200).

[43] When the distance between the base station and the terminal is less than the FLR, the gain controller 200 applies the power concentration gain (PCG=I), which is determined to not change the per- subchannel power of the transmission signal, to the transmission signal transmitted by the modulator 100 (S300).

[44] However, when the distance therebetween is greater than the FLR, the gain controller

200 applies the power concentration gain (PCG>1) caused by the distance between the base station and the terminal to the transmission signal transmitted by the modulator 100 to amplify the transmission signal (S500). The transmission power per subchannel of the transmission signal is increased by the power concentration gain (PCG>1).

[45] The power controller 500 increases the gain of the power amplifier 400 according to the sum of the open-loop power control value and the closed- loop power control value (S400), and the power amplifier 400 amplifies the analog signal transmitted by the DAC 300 according to the increased gain to control the transmission power.

[46] Accordingly, when the terminal is located within the FLR, the terminal uses the fixed power concentration gain (PCG=I) to control the transmission power according to the gain of the power amplifier 400 in a like manner of the case in which no power concentration gain is used.

[47] When the terminal is located outside the FLR, the gain of the power amplifier 400 is fixed with the maximum value, and hence, the terminal controls the transmission power by using the power concentration gain (PCG>1) that is variable according to the distance between the base station and the terminal.

[48] FIG. 3 shows a block diagram of a power controller of a terminal for an uplink power control in a communication system according to a second exemplary embodiment of the present invention.

[49] As shown in FIG. 3, the power controller includes a modulator 100, a gain controller

200', a digital/analog converter (DAC) 300, a power amplifier 400, and a power controller 500.

[50] As shown in FIG. 3, the power controller is similar to the power controller according to the first exemplary embodiment shown in FIG. 1 except for the gain controller 200'. In detail, the gain controller 200 of FIG. 1 includes a digital amplifier 230 for applying a power concentration gain to the digital output signal transmitted by the modulator 100, and the gain controller 200' of FIG. 3 includes an analog amplifier 230' for applying a power concentration gain to the analog output signal transmitted by the DAC 300. Therefore, the method for controlling the transmission power by using the digital amplifier 230 of FIG. 1 is not much different from the method for controlling the transmission power by using the analog amplifier 230' of FIG. 3, and the terminal may have the structure of either one of the first and second exemplary embodiments depending on the advantages, drawbacks, and ease of hardware realization.

[51] FIG. 4 shows a power concentration gain according to the distance between the base station and the terminal in a communication system according to an exemplary embodiment of the present invention.

[52] As shown in FIG. 4, the horizontal axis is the distance between the base station and the terminal, and the vertical axis is the power concentration gain (PCG) [dB]. The power concentration gain is acquired by considering a path loss model of the frequency used in the mobile communication system, the terminal's maximum transmission power, the SNR for each modulation method required by the base station, transmit and receive antenna gains, and the distance between a base station and a terminal, and is stored in the power concentration gain table 220.

[53] For example, FIG. 4 is a graph indicating the power concentration gain caused by the terminal's distance that is simulated by using the Stanford University Interim (SUI)-A path loss model in the 2.3 GHz bandwidth. In the simulation, the maximum transmission power of the terminal is 23dBm, the gain of the base station antenna is 17 dB, and the modulation schemes are QPSK and 16QAM. The FLR for the QPSK and 16QAM modulation schemes are respectively 500m and 380m. In this instance, when the distance between the base station and the terminal is 800m, which is outside the FLR, as shown in FIG. 4, the power concentration gain for the QPSK modulation is 17dB and the power concentration gain for the 16 QAM modulation is 1OdB. That is, the optimized power concentration gain is determined according to the distance between the base station and the terminal, is stored in a table, and can be used to control the transmission power of the terminal located outside the FLR.

[54] The power concentration gain has been described as being stored in the power concentration gain table 220 in the first and second exemplary embodiments of the present invention, but can also be calculated through the power concentration gain operation according to the distance measured by the ranging measurer 210.

[55] While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[56] The exemplary embodiments of the present invention may be realized by not only the above described method and device, but also by a program for realizing the functions corresponding to the configurations of the exemplary embodiments of the present invention or by a medium having recorded the program, which will be easily realized by a person of an ordinary skill in the art.

Claims

[1] A power controller of a communication system comprising: a power amplifier for amplifying transmission power of a transmission signal; a power controller for controlling a gain of the power amplifier by using a received signal; and a gain controller for measuring a distance between a transmitter having transmitted the received signal and the power controller, and applying a power concentration gain caused by the distance to the transmission signal.

[2] The power controller of claim 1, wherein when the distance is less than a full loading range for the power controller to use subchannels, the gain controller sets the power concentration gain so that per subchannel power of the transmission signal may not be changed by the applied power concentration gain.

[3] The power controller of claim 1, wherein when the distance is greater than a full loading range for the power controller to use subchannels, the gain controller sets the power concentration gain so that per subchannel power of the transmission signal may be increased by the applied power concentration gain.

[4] The power controller of claim 1, further comprising: a modulator for modulating the transmission signal before transmitting the transmission signal to the power amplifier; and a digital/analog converter for converting an input signal into an analog signal, wherein the gain controller includes a digital amplifier for applying the power concentration gain to the transmission signal modulated by the modulator to control transmission power of the power controller and transmitting the transmission power controlled transmission signal to the digital/analog converter.

[5] The power controller of claim 1, further comprising: a modulator for modulating the transmission signal before transmitting the transmission signal to the power amplifier; and a digital/analog converter for converting the modulated transmission signal into an analog signal, wherein the gain controller includes an analog amplifier for controlling transmission power of the power controller by applying the power concentration gain to the analog signal output by the digital/analog converter.

[6] The power controller of claim 1, wherein the power controller determines an open-loop power control value and a closed- loop power control value by using the received signal and increases the gain of the power amplifier.

[7] The power controller of claim 1, wherein the power concentration gain is determined by residual power following the number of subchannels used by the transmission signal.

[8] The power controller of claim 1, wherein: the power controller detects a transmission time control signal so that the transmission signal may be provided to the transmitter within a demodulation reference time; and the gain controller senses the distance by using the transmission time control signal.

[9] A transmission power control method by a power controller of a communication system comprising: measuring a distance between a transmitter having transmitted a received signal and the power controller using the received signal; determining a first gain according to the distance; and amplifying the transmission power by applying the first gain to a transmission signal.

[10] The transmission power control method of claim 9, further comprising: determining a second gain by using the received signal; and amplifying the transmission power by using the second gain.

[11] The transmission power control method of claim 10, wherein the determining of the second gain further comprises determining the second gain according to the sum of an open-loop power control value and a closed-loop power control value calculated by using the received signal.

[12] A transmission power control method by a power controller of a communication system comprising: measuring a distance between a transmitter having transmitted a received signal and a power controller by using the received signal; comparing the measured distance and a threshold distance; determining a first gain according to a comparison result of the measured distance and the threshold distance; applying the first gain to a transmission signal; and applying a second gain that is determined by the received signal strength to the transmission signal to which the first gain is applied, and controlling transmission power of the transmission signal.

[13] The transmission power control method of claim 12, wherein when the measured distance is less than the threshold distance, the first gain is set to be a value in which power per subchannel of the transmission signal is not changed by the first gain, and when the measured distance is greater than the threshold distance, the first gain is set to be a value in which power per subchannel of the transmission signal is increased by the first gain.

[14] The transmission power control method of claim 13, further comprising: when the measured distance is greater than the threshold distance, reducing the number of subchannels of the transmission signal, and determining the first gain according to residual power according to the reduced number of subchannels and the measured distance.

[15] The transmission power control method of claim 12, wherein the threshold distance is a distance for the power controller to use the subchannels.