WO2007021155A1

WO2007021155A1 - Apparatus and method for environment adaptation type downlink closed loop control

Info

Publication number: WO2007021155A1
Application number: PCT/KR2006/003250
Authority: WO
Inventors: Byoung-Gi Kim; Kun-Seok Kang; Do-Seob Ahn; Ho-Jin Lee
Original assignee: Electronics And Telecommunications Research Institute
Priority date: 2005-08-19
Filing date: 2006-08-18
Publication date: 2007-02-22

Abstract

Provided are an apparatus and a method for environment adaptation type downlink closed loop control, which control a downlink power employing an efficient power control technique that considers geographical conditions and a type of received data. The apparatus includes a Signal-to-Interference Ratio (SIR) calculator for combining Common Pilot CHannel (CPICH), Dedicated Physical Control CHannel (DPCCH) and Secondary-Common Control Physical CHannel (S-CCPCH) to harmonize with the environment conditions when a signal is received from satellite/base station, and calculating an SIR experienced on corresponding channel, a comparator for comparing the calculated SIR with a target SIR predetermined in an open loop power control, and a Transmit Power Control (TPC) command generator for generating a TPC command based on the comparison result.

Description

APPARATUS AND METHOD FOR ENVIRONMENT ADAPTATION TYPE DOWNLINK CLOSED LOOP CONTROL

Technical Field

[1] The present invention relates to downlink power control in communication systems, and more particularly, to an apparatus and method for environment adaptation type downlink closed loop control, which controls a downlink power employing an efficient power control technique that considers geographical conditions and a type of received data. Background Art

[2] The ultimate goal of the future satellite or mobile communication systems is to offer a variety of communication services anytime, anywhere and to anyone, without regard to a time, a place, and a subject. For the goal, there is proposed a combined structure of Global System for Mobile communication (GSM) and Wideband Code Division Multiple Access (W-CDMA). This proposal is highly acclaimed; and some proposals supporting W-CDMA currently provide terrestrial mobile services in diverse countries by adopting IMT-2000 that offers high quality voice service and multimedia service.

[3] The W-CDMA system having a pilot symbol structure of Satellite-Universal

Mobile Telecommunications Systems (S-UMTS) and Terrestrial-UMTS adoptsasyn- chronization between cells as important feature. It further employs a synchronous demodulation scheme identically in an uplink and a downlink for improvement of link capacitance.

[4] A power control technique of SAT-CDMA system, which is suggested as one of

IMT-2000 satellite transmission standards, makes use of both an uplink/downlink closed loop power control and an uplink open loop power control, like the terrestrial IMT-2000 system of the 3^rd Generation Partnership Project (3GPP).

[5] Generally, the closed loop power control serves to keep a reception power or received signal to noise ratio to be a target value designated by a system. For this, at a receiver, a current reception power or signal to noise ratio is compared with a target value to create and transmit a power control command to a transmitter. At the transmitter, a transmission power is controlled based on the power control command.

[6] The SAT-CDMA system is known as Low Earth Orbit/Geostationary Earth Orbit

(LEO/GEO) mobile satellite system and has a considerably large channel characteristic because a signal delay time between a base station and a terminal reaches dozens to hundreds of msec, compared to a terrestrial system. Therefore, for efficient power control in the SAT-CDMA system, a need has existed for an algorithm capable of controlling a power in advance by predicting a future channel change in consideration of a long delay time.

[7] One of prior arts for solving the problem caused by the delay time within such loop is proposed in U.S. Patent No. 6,493,541, entitled "Transmit Power Control Time Delay Compensation in a Wireless Communications System".

[8] This patent provides a method of estimating a reception power after a delay time within a loop by considering the delay time within the loop until a current power control command is reflected in the reception power, and then generating a power control command based thereon.

[9] However, this patent fails to overcome performance degradation caused by channel change during the delay time within the loop.

[10] Another prior art for overcoming the problem of the prior art as introduced above is disclosed in Korean Patent No. 10-2004-0047907, entitled "Closed Loop Power Control Apparatus and Method in Satellite Mobile Communications System".

[11] This patent teaches a technique of compensating serious performance degradation in view of loop stability, by solving the performance degradation caused by channel change during the delay time within the loop.

[12] However, the two patents have drawbacks as follows. Firstly, they don^vt consider variables of limit value of satellite or base station transmission power in the radio resource management aspect. Secondly, those patents cannot be applied to packet- based communication systems because they provide only voice-based downlink power control technique, without considering geographical conditions.

[13]

Disclosure of Invention Technical Problem

[14] It is, therefore, an object of the present invention to provide an apparatus and method for an environment adaptation type downlink closed loop control, which is capable of effectively controlling a downlink power using a novel power control technique that considers geographical conditions and a type of received data.

[15] The other objectives and advantages of the invention will be understood by the following description and will also be appreciated by the embodiments of the invention more clearly. Further, the objectives and advantages of the invention will readily be seen that they can be realized by the means and its combination specified in the claims.

[16]

Technical Solution

[17] In accordance with one aspect of the present invention, there is provided an apparatus for environment adaptation type downlink closed loop power control, including: an SIR calculator for combining CPICH, DPCCH and S-CCPCH to harmonize with the environment conditions when a signal is received from satellite/ base station, and calculating an SIR experienced on corresponding channel; a comparator for comparing the calculated SIR with a target SIR predetermined in an open loop power control; and a TPC command generator for generating a TPC command based on the comparison result.

[18] In accordance with another aspect of the present invention, there is provided a method for environment adaptation type downlink closed loop power control, including the steps of: (a) measuring an interference of CPICH and DPCCH received signal to calculate an interference of received signal every frame period; (b) calculating a Rician factor; (c) comparing the calculated Rician factor with a threshold to judge a current location as a rural area if the calculated Rician factor is greater than the threshold and the current location as a downtown area if the calculated Rician is not greater than the threshold; (d) combining CPICH, DPCCH and S-CCPCH depending on a type of received data in the judged area and calculating an SIR experienced on the corresponding channel; and (e) determining an uplink transmission power based on the calculated SIR.

[19]

Advantageous Effects

[20] As described above and below, the present invention has an advantage in that it can control a downlink power by making the most of finite transmission power so that desired services can be offered to harmonize with an area while minimizing internal beam interference and mutual beam interference, in the downlink power control that transmits a signal and a TPC command from the user terminal to the base station such as satellite or central office. This can be accomplished by controlling the downlink power accordingly by means of judging a current area (rural or downtown) through of calculation of reception Rician factor K and determining a type (voice or packet) of data received in a corresponding area.

[21]

Brief Description of the Drawings

[22] The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:

[23] Fig. 1 is a block diagram illustrating a configuration of a mobile communication system to which the present invention is applied;

[24] Fig. 2 exemplifies a detailed circuit diagram of the mobile communication system to which the present invention is applied; [25] Fig. 3 depicts a timing diagram for describing a relative timing relationship of pilot channels used in the present invention;

[26] Fig. 4 is a flowchart illustrating a method for environment adaptation type downlink closed power control in accordance with an embodiment of the present invention;

[27] Fig. 5 is a view illustrating a frame structure of DPCH channel used in the present invention;

[28] Fig. 6 is a view exemplifying a frame structure of CPICH channel used in the present invention; and

[29] Fig. 7 is a view exemplifying a frame structure of S-CCPCH channel used in the present invention.

[30]

Best Mode for Carrying Out the Invention

[31] The above-mentioned objectives, features, and advantages will be more apparent by the following detailed description associated with the accompanying drawings; and thus, the invention will be readily conceived by those skilled in the art to which the invention pertains. Further, in the following description, well-known arts will not be described in detail if it seems that they could obscure the invention in unnecessary detail. Hereinafter, a preferred embodiment of the present invention will be set forth in detail with reference to the accompanying drawings.

[32] Fig. 1 is a block diagram illustrating a configuration of a mobile communication system to which the present invention is applied.

[33] As shown therein, the mobile communication system to which the present invention is applied includes a satellite /base station 10 and a terminal 20. The satellite/base station 10 compensates a roundtrip delay time between the satellite and the base station, and decodes a Transmit Power Control (TPC) command provided from the terminal 20 to judge whether to raise or lower a power based on the decoded TPC command. It then determines a transmission power to be sent through its antenna and transmits a signal to the terminal 20 according to the determined transmission power. At the terminal 20, when the signal is received from the satellite/base station 10, attenuation experienced on channel, namely, a current Signal-to-Interference Ratio (SIR) is calculated by combining Common Pilot CHannel (CPICH), Dedicated Physical Control CHannel (DPCCH) and Secondary-Common Control Physical CHannel (S-CCPCH) to harmonize with environment conditions. Thereafter, the calculated SIR is compared with a target SIR set in an open loop power control to predict a power to be received after the roundtrip delay time in advance and then send it to the satellite/ base station 10.

[34] More specifically, the satellite/base station 10 is provided with a delay compensator 11 for compensating a delay time during a roundtrip delay time between the satellite and the base station, a TPC decoder 12 for decoding the TPC command sent from the terminal 20, a transmission power decider 13 for deciding a transmission power based on the decoded TPC command, and a downlink transmitter 14 for transmitting a signal to the terminal 20 according to the transmission power decided by the transmission decider 13.

[35] In the meantime, an apparatus for environment adaptation type downlink closed power control or a power control apparatus (or the terminal) of the present invention includes an SIR calculator 21, a comparator 22, and a TPC generator 23. Specifically, at the SIR calculator 21, when the signal is received from the satellite/base station 10, attenuation experienced on channel, that is, a current SIR is calculated by combining CPICH, DPCCH and S-CCPCH to comply with the environment conditions (area and data). At the comparator 22, the calculated SIR is compared with a target SIR set in an open loop power control. At the TPC generator 23, a TPC command is issued based on the comparison result at the comparator 22.

[36] To be more specific, it is preferably that the TPC generator 23, if the calculated SIR is not greater than the target SIR, produces a TPC command to increase a power by a difference therebetween and, if the calculated SIR is greater than the target SIR, issues a TPC command to decrease the power by the difference.

[37] Fig. 2 exemplifies a detailed circuit diagram of the mobile communication system to which the present invention is applied.

[38] As shown in Fig. 2, there are CPICH, DPCH, S-CCPCH, etc. as pilot channels used in the present invention. The apparatus for environment adaptation type downlink closed power control or the terminal 20 according to the present invention measures a reception power of corresponding channel based on an area and a type of received data.

[39] Fig. 3 depicts a timing diagram for describing a relative timing relationship of pilot channels used in the present invention.

[40] As depicted in Fig. 3, h dpch(i) , h s-ccph(i) and h cpich(i) denote channel gains experienced during a given length between the satellite and the base station for ith slot, respectively. Here, the length of slot is given by 10 ms.

[41] Fig. 4 is a flowchart illustrating a method for environment adaptation type downlink closed power control in accordance with an embodiment of the present invention.

[42] First of all, the present invention is implemented in such a way that smooth communication service can be offered by making the most of finite transmission power of satellite or base station through establishment of the following four environments that consider the finite transmission power and geographical conditions.

[43] 1. Channels used in the power control upon receipt of packet-based service in the rural area: CPICH and DPCCH (1.2)

[44] 2. Channels used in the power control upon receipt of packet-based service in the downtown area: DPCCH, CPICH and S-CCPCH (1.4)

[45] 3. Channel used in the power control upon receipt of voice-based service in the rural area: DPCCH (0.2)

[46] 4. Channels used in the power control upon receipt of voice-based service in the downtown area: CPICH and DPCCH (1.2)

[47] When a normalized reception power of CPICH channel is 1, pilot reception powers of DPCCH and S-CCPCH are all 0.2. Therefore, a parenthesized value implies a sum of reception powers of required channels for prediction of SIR.

[48] The background of the channel selection in each case as defined above is as follows. That is, since the packet-based communication requires a higher SIR, namely, a lower Frame Error Rate (FER), compared to the voice-based communication, it is designed in such a manner that the channel selection is made to be advantageous to the packet-based communication in the downtown area in which the transmission power of satellite or base station can be lowered by elevating the reception SIR of terminal.

[49] And also, the rural area is less in users than the downtown area. Therefore, although a more power is utilized in the rural area to elevate the transmission power of the satellite or base station, interference that affects other users is relatively little in the rural area, compared to the downtown area. Thus, using the channels according to the above priority can acquire more superior performance, in light of both the efficient use of the finite transmission power that the satellite or base station substantially has and the complexity of channel prediction.

[50] Now, description will be given on the method for environment adaptation type downlink closed power control in accordance with the embodiment of the present invention hereinafter.

[51] First of all, at steps S401 and S402, when a downlink signal is received, interference of DPCH received signal is measured at a predetermined time interval to calculate interference of received signal every frame period by using the following equation:

[52]

[53]

Eq. (1)

[54] [55] wherein d(t), g(t), p(t) and s(t) denote a DPCH reception complex symbol, a channel gain, a transmission power, and a pilot symbol of DPCCH, respectively.

[56] Next, it is confirmed at step S403 whether a CPICH received signal is existed or not. [57] If the confirmation result shows that there is the received signal, interference of the CPICH received signal is measured at a predetermined time interval to calculate interference of received signal every frame period at step S404. But, if there is no received signal, the process of the present invention goes to step S405, without computing the interference of received signal. As mentioned above, the interference of received signal is computed by using Eq. (1) above.

[58] Thereafter, at step S405, a Rician factor K is calculated by using the following probability density function to acquire geographical information.

[59] [60]

r < 0

Eq. (2)

[61]

[62] wherein

; and r, C and β represent a desired signal component, a direct wave component, and a mean square of desired component, respectively.

[63] Subsequently, the calculated Rician factor γ is compared with a threshold at step S406. [64] If the comparison result indicates that the calculated Rician factor is greater than the threshold, the process decides the current location as the rural area and then proceeds to step S407. Otherwise, if the Rician factor is not greater than the threshold, the process decides the current location as the downtown area and then goes to step S413. The threshold used herein can be properly adjusted to harmonize with system conditions.

[65] And then, if the current location is the rural area, a type of received data is confirmed at step S407.

[66] If it is confirmed at step S407 that the type of received data indicates the packet- based service, it corresponds to the above "Case 1"; and thus SIR is calculated by making a combination of interferences of received signals using reception powers experienced on DPCCH and CPICH channels and then an uplink transmission power to be sent to the satellite/base station is determined at steps S408 and S409.

[67] The combination of interferences of received signals implies αSIR DPCCH + βSIR CPICH , wherein α and β ¹ are variables satisfying the relationship r- that αSIR DPCCH + β ' SIR CPICH =

1.

[68] Otherwise, if it is confirmed at step S407 that the type of received data indicates the voice-based service as shown in step S411, it comes under the above "Case 3"; and thus SIR is calculated using reception power experienced in DPCCH channel through Eq. (3) below and then an uplink transmission power to be sent to the satellite/base station is determined at steps S409 and S410.

[69] Meanwhile, if the current location is the downtown area, a type of received data is confirmed at step S413.

[70] If it is confirmed at step S413 that the type of received data indicates the packet- based service, it falls under the above "Case 4", requiring both the highest reception SIR and the lowest RER simultaneously; and then it is further confirmed whether or not S-CCPCH channel signal was received to elevate the reception SIR at step S414.

[71] If it is confirmed at step S414 that the S-CCPCH channel signal was received, SIR is calculated by making a combination of interferences of received signals using reception powers experienced on DPCCH, CPICH and S-CCPCH channels through Eq. (3) below at steps S415 and S417 and then the process goes to step S410. But, if the S-CCPCH channel signal was not received, SIR is calculated by making a combination of interferences of received signals using reception powers experienced on DPCCH and CPICH channels through Eq. (3) below at steps S416 and S417 and then the process goes to step S410.

[72] The combination of interferences of received signals implies αSIR DPCCH + β ' SIR CPICH

+ γSIR , wherein α, β and γ are certain variables satisfying the relationship that αSIR DPCCH + β ' SIR CPICH + γ ' SIR DPCCH = 1.

[73] [74]

Eq. (3) [75] [76] wherein α i , g i and P commom denote an orthogonal factor, a channel gain and a pilot component of CPICH channel, respectively.

[77] If it is confirmed at step S413 that the type of received data indicates the voice- based service, the process of the invention proceeds to step S408 to perform the following steps, like the packet-based service in the rural area.

[78] Fig. 5 is a view illustrating a frame structure of DPCH channel used in the present invention.

[79] As shown in Fig. 5, an SIR estimation is conducted by using a pilot symbol, which a DPCCH control channel and a DPDCH data channel are time division-multiplexed and then transmitted for SIR prediction estimation. Based on the estimated SIR, a data symbol of DPDCH channel is compensated. It is structured that a chip rate is set as 3.84 Mcps and each slot has 2560 chips, one frame being consisted of 15 slots.

[80] Fig. 6 is a view exemplifying a frame structure of CPICH channel used in the present invention.

[81] As shown therein, this channel is utilized in a downlink physical layer with a fixed symbol rate of 30 kbps and has a symbol pattern known by all of the satellite/base station and the terminal.

[82] Accordingly, this channel can be very advantageously used for channel prediction.

Namely, the present invention provides a technique that can estimate a channel by transmitting a pilot symbol in predefined pattern known by the transmitter and the receiver for estimation of SIR channel variation rate.

[83] In addition, the CPICH channel is sent, without conducting the power control at the transmitter; and therefore, the channel is a very useful one, in case of recovering data experienced on channel and also estimating frequency offset at the receiver.

[84] Fig. 7 is a view exemplifying a frame structure of S-CCPCH channel used in the present invention.

[85] As shown in Fig. 7, the present invention provides a technique of estimating channel change using a pilot symbol of S-CCPCH for SIR estimation. The background that adopts the channel in the present invention is because it is similar to a data rate of DPCH and also can perform the power control in the same manner.

[86] The method of the present invention as mentioned above may be implemented by a software program and stored in a computer-readable storage medium such as CD- ROM, RAM, ROM, floppy disk, hard disk, optical magnetic disk, etc. This process may be readily carried out by those skilled in the art; and therefore, details of thereof are omitted here.

[87] While the present invention has been described with respect to certain preferred em- bodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.

Claims

[1] An apparatus for environment adaptation type downlink closed loop power control, comprising: a Signal-to-Interference Ratio (SIR) calculating means for combining Common Pilot CHannel (CPICH), Dedicated Physical Control CHannel (DPCCH) and Secondary-Common Control Physical CHannel (S-CCPCH) to harmonize with the environment conditions when a signal is received from satellite/base station, and calculating an SIR experienced on corresponding channel; a comparing means for comparing the calculated SIR with a target SIR predetermined in an open loop power control; and a Transmit Power Control (TPC) command generating means for generating a TPC command based on the comparison result.

[2] The apparatus for environment adaptation type downlink closed loop power control as recited in claim 1, wherein the SIR calculating means harmonizes with the environment conditions in such a way that the CPICH and the DPCCH are combined if the received signal is packet data in a rural area; the DPCCH, the CPICH and the S-CCPCH are combined if the signal is packet data in a downtown area; the DPCCH is combined if the received signal is voice data in the rural area; and the CPICH and the DPCCH are combined if the signal is voice data in the downtown area.

[3] The apparatus for environment adaptation type downlink closed loop power control as recited in claim 1, wherein the TPC generating means generates a TPC command to increase a power by a difference between the calculated SIR and the target SIR if the calculated SIR is not greater than the target SIR, and a TPC command to decrease a power by the difference if the calculated SIR is greater than the target SIR.

[4] A method for environment adaptation type downlink closed loop power control, comprising the steps of:

(a) measuring an interference of CPICH and DPCCH received signal to calculate an interference of received signal every frame period;

(b) calculating a Rician factor;

(c) comparing the calculated Rician factor with a threshold to judge a current location as a rural area if the calculated Rician factor is greater than the threshold and the current location as a downtown area if the calculated Rician is not greater than the threshold;

(d) combining CPICH, DPCCH and S-CCPCH depending on a type of received data in the judged area and calculating an SIR experienced on the corresponding channel; and

(e) determining an uplink transmission power based on the calculated SIR.

[5] The method for environment adaptation type downlink closed loop power control as recited in claim 4, wherein said step (d) calculates the SIR by combining the CPICH with the DPCCH if the received signal is packet data in a rural area; the DPCCH, the CPICH and the S-CCPCH if the signal is packet data in a downtown area; the DPCCH if the received signal is voice data in the rural area; and the CPICH with the DPCCH if the signal is voice data in the downtown area.

[6] The method for environment adaptation type downlink closed loop power control as recited in claim 4, wherein said step (a) calculates the interference of the received signal as follows:

wherein d(t), g(t), p(t) and s(t) denote a DPCH reception complex symbol, a channel gain, a transmission power, and a pilot symbol of DPCCH, respectively.

[7] The method for environment adaptation type downlink closed loop power control as recited in claim 6, wherein said step (b) calculates the Rician factor K by using the following probability density function:

wherein

[8] The method for environment adaptation type downlink closed loop power control as recited in claim 7, wherein said step (d) computes the SIR by:

wherei

ndicate an orthogonal factor, a channel gain and a pilot component of CPICH channel, respectively.