WO2008038980A1

WO2008038980A1 - Power control method considering handover in communication system having ancillary terrestrial components

Info

Publication number: WO2008038980A1
Application number: PCT/KR2007/004677
Authority: WO
Inventors: Byoung-Gi Kim; Do-Seob Ahn; Kun-Seok Kang; Ho-Jin Lee
Original assignee: Electronics And Telecommunications Research Institute
Priority date: 2006-09-27
Filing date: 2007-09-21
Publication date: 2008-04-03
Also published as: KR20080028717A; EP2070220A1; KR100829860B1

Abstract

Provided is a power control method considering a handover in a communication system having ancillary terrestrial components (ATC). The power control method includes: a) acquiring current location information of a terminal; b) acquiring current transmission power information of the terminal; and c) confirming location of the terminal based on the location information, measuring velocity information of the terminal on a boundary of a ATC cell or a spot beam, and performing a first power control considering a handover based on the current transmission power information and the velocity information by using a receive diversity.

Description

POWER CONTROL METHOD CONSIDERING HANDOVER IN

COMMUNICATION SYSTEM HAVING ANCILLARY

TERRESTRIAL COMPONENTS

Technical Field

[1] The present invention relates to a power control method considering a handover in a communication system having ancillary terrestrial components (ATC); and, more particularly, to a power control method considering a handover that can satisfy a quality of service (QoS) and maintain regular signal-to-interference ratio (SIR) of each user by applying an effective power control and the handover based on location information in a multi-user satellite mobile communication system having ATC.

[2] This work was supported by the Information Technology (IT) research and development program of the Korean Ministry of Information and Communication (MIC) and the Korean Institute for Information Technology Advancement (IITA) [2005-S-014-02, "Development of satellite IMT-2000+ technology"].

[3]

Background Art

[4] An introductory background of ancillary terrestrial components (ATC) is provided in the example of Canada.

[5] A mobile satellite network provides communication services to individuals who live far from the city or live in the country where terrestrial cellular services are not provided.

[6] In 1994, Canada opened a domestic market to foreign mobile satellite companies to promote its domestic satellite industry. Although cellular/PCS services are provided to more than 90% of the Canadian population, they do not cover the entire Canadian territory. Moreover, although most of the foreign mobile satellite companies have provided satellite services for several years, they retain a relatively small number of subscribers than cellular/PCS services which have 1,300 subscribers.

[7] Recently, a next generation mobile satellite is developed and planned in the Canadian satellite industry. The next generation mobile satellite uses multi-beam antennas to increase a spectral efficiency. Also, it can communicate with small size portable terminals and provide digital services superior to the second-generation cellular PCS services. A number of satellite operators petitioned Industry Canada to use spectrum of MSS for the flexibility to develop an Ancillary Terrestrial Component (ATC) to offer mobile service as an integral part of the MSS offerings. The ATC-installed main apparatus uses all MSS spectrums allocated to the predetermined regions. This would expand the service coverage into large cities where the satellite signals are blocked by high-rise buildings and where coverage is non-existent inside buildings. In 2001, the mobile satellite and ATC application were registered to US Federal Communications Commission (FCC) in order to operate as the next generation mobile satellite in a L band (1525~1559MHz/1626.5~1660MHz) and a 2GHz band (1990~2025MHz/2165~2200MHz). The LEO band

(1610~1626.5MHz/2483.5~2500MHz) was said to bring in a similar amount of profits to the amount the L band and the 2GHz band do. In February 2003, the FCC announced regulations which permitted mobile satellite service providers to submit applications for the ATC service in the three bands (L band, 2GHz band and LEO band). In addition, the FCC re-allocated a partial band of 2GHz MSS spectrum 15+15 MHz for the terrestrial fixed service and the mobile service, and maintained 200-2020 MHz and 2180-2200 MHz for the mobile satellite service.

[8] The basic concepts of the satellite mobile communication system having the ATC are described hereinafter. Various technologies and an ATC proposal for increasing spectral efficiency in the same permitted MSS band are proposed. Taking advantage of the geographical fact that services cannot be provided through a particular MSS channel caused by an intra-system interference, Mobile Satellite Ventures (MSV) Canada, an operator of a geostationary orbit MSS, offers the frequency reuse method. The next generation system of the MSV uses numerous small spot beams on surface of the earth. The spot beams can efficiently maintain satellite coverage over an area as wide as 400 Km to 500 Km.

[9] Fig. 1 is a block diagram illustrating a method for reusing frequency in a satellite mobile communication system having ancillary terrestrial components (ATC).

[10] As shown in Fig. 1, the geostationary orbit satellite 10 has enough power to provide communication service with three spot beams 110, 120 and 130. The spot beam 110 having Fl frequency serves rural districts with relatively few populations and low buildings. In contrast, other spot beams 120 and 130 having F2 and F3 frequency respectively use the ATC system in order to cover the downtown area where satellite sig nals are interrupted by crowds and high-rise buildings.

[11] In order to reuse the spot beam 110 having Fl frequency in the ATC system, the distance between the two systems must be sufficient so that there are no interferences with each other. In other words, the idea behind MSV s ATC is that if a terrestrial transmitter and a MSS satellite beam using the same frequency can be distinctive, the ATC can use frequency Fl in region having frequency Fl not used in the MSS satellite beam.

[12] The ATC implementation of a non-geostationary orbit (NGSO) MSS system such as a Globalstar is very complex because the satellite moves rapidly and many MSS satellites are observed at a given time. Even so, like the GSO system, the NGSO MSS system can use multi beam antenna and reuse allocated MSS frequency as the coverage beam of selected satellite antenna.

[13] Recently, a handover and a power control technology are catching attention in the satellite mobile communication system having the ATC.

[14] A handover between the ATC, a cellular and the satellite is disclosed in U.S. patent

No. 6,879,829, which is entitled "SYSTEMS AND METHODS FOR HANDOVER BETWEEN SPACE BASED AND TERRESTRIAL RADIOTERMINAL COMMUNICATIONS, AND FOR MONITORING TERRESTRIALLY REUSED SATELLITE FREQUENCIES AT A RADIOTERMINAL TO REDUCE POTENTIAL INTERFERENCE". In the cited U.S patent, the cellular receives location information by using a global positioning system (GPS) or other technologies and performs a handover by using the location information and threshold value of a received signal.

[15] However, the cited U.S. patent, i.e., U.S. patent No. 6,879,829, only discloses the handover processes between the ATC, the cellular and the satellite. That is, effective power control corresponding to the system is not performed before the handover. Only general power control is adapted and performed. Also, the power control and handover processes in the satellite spot beam or on the boundary of cell are not clearly disclosed. If the power control is performed without considering the handover, the system becomes much less efficient in terms the system capacity. Moreover, when a closed- loop power control and an open-loop power control are performed before the handover, a round-trip delay becomes a problem.

[16] The general power control includes the open-loop power control and the closed- loop power control.

[17] The open-loop power control is a rough power control method on the assumption that path loss of a forward link and a reverse link are the same. Actually, since fading situation of the forward link and the reverse link changes from time to time, an output power control method of the cellular by estimating a received power to a base station based on the magnitude of the received signal is inaccurate. In order to improve this inaccuracy, at every predetermined time the base station notifies the terminal with signal power whether the power of the received signal is too high or too small. Consequently, the cellular can rapidly control the output signal power so that received signal having the same strength is transmitted to the base station. This is the closed- loop power control method.

[18] Precisely, a demodulation unit of the base station compares a measured value of signal-to-interference ratio with a reference value of signal-to-interference at a predetermined interval. Here, the reference value of signal-to-interference ratio is determined by an outer loop power control based on a target frame error rate (FER) value of reverse communication channel assigned by an operator. If the measured value is larger than the reference value, the base station directs the terminal to decrease the output power of terminal to a certain value. If the measured value is smaller than the reference value, the base station directs the terminal to increase the output power of terminal to a certain value. Herein, if the measurement value is larger than the reference value, the terminal transmits signal power stronger than the power the base station needs. This unnecessarily strong signal power negatively affects the quality and communication capacity of other terminals connected to the base station.

[19] In addition, the cited U.S. patent does not disclose an effective power control method among the satellite, the ATC and the cellular after a handover into a predetermined system.

[20] Another power control method after a handover is disclosed in U.S. publication No.

2006/0094352, which is entitled "APPARATUS AND METHODS FOR POWER CONTROL IN SATELLITE COMMUNICATIONS SYSTEMS WITH SATELLITE- LINKED TERRESTRIAL STATIONS". In the cited U.S publication, an effective power control system among a satellite, a terrestrial station and a terminal is provided.

[21] However, the cited U.S. publication, i.e., U.S. publication No. 2006/0094352, discloses a direct power control between the satellite and the terminal in a region where a line of sight (LOS) exists. Although the direct power control method measures the power of a current received signal and compensates the signal power in the next slot or the next frame, the direct power control method is less efficient because of the long round trip delay a signal has to make. When the LOS does not exist, the satellite transmits power control instructions via the terrestrial station. In the regions without the LOS, the satellite provides the power control instructions to the terminal through the ATC indirectly. The indirect power control method performs feedback without considering a total processing time and does not consider the round trip delay.

[22] For the above reasons, the cited U.S. publication discloses the power control method without considering a round trip time.

[23] As described above, the conventional satellite mobile communication system having the ATC discloses only the handover by detecting the received signal and a quality of service (QoS). For example, if transmission signal power of the terminal exceeds a threshold value, and total user interference exceeds a limitation value, and quality of a received satellite signal exceeds a threshold, the handover from the ATC to the satellite is performed although the user can communicate with the ATC continuously.

[24] Also, unlike the terrestrial mobile communication system, a conventional GSO-based satellite mobile communication system offers little advantage because of the long trip delay a signal has to make among the terminal, the satellite and the base station. That is, in the conventional satellite mobile communication system having the ATC, power control method of the terminal served by the ATC is based on a method combined by the open loop power control and the closed power control of the terrestrial system. But, a power control method of the terminal served by the satellite is not disclosed.

[25]

Disclosure of Invention Technical Problem

[26] An embodiment of the present invention is directed to provide a power control method considering a handover that can satisfy quality of service (QoS) and maintain regular signal-to-interference ratio (SIR) of each user by applying an effective power control and the handover based on location information within a multi-user satellite mobile communication system having an ATC.

[27] Other objects and advantages of the present invention can be understood by the following description, and become apparent with reference to the embodiments of the present invention. Also, it is obvious to those skilled in the art of the present invention that the objects and advantages of the present invention can be realized by the means as claimed and combinations thereof.

[28]

Technical Solution

[29] In accordance with an aspect of the present invention, there is provided a power control method in a communication system having ancillary terrestrial components (ATC), including: a) acquiring current location information of a terminal; b) acquiring current transmission power information of the terminal; c) confirming location of the terminal based on the location information, measuring velocity information of the terminal on a boundary of a ATC cell or a spot beam, and performing a first power control considering a handover based on the current transmission power information and the velocity information by using a receive diversity.

[30]

Advantageous Effects

[31] The conventional satellite mobile communication system having an ATC examines a received power and a quality of service (QoS), and performs a handover. In the present invention, however, a terminal performs the steps of: (a) receiving location information about where the terminal exists within an ATC system, a satellite system and a mobile communication system; (b) setting a proper minimum power level and a proper maximum power level of the corresponding system; and (c) using high-level power control method, thereby improving system capacity and power efficiency while decreasing power consumption by the terminal.

[32] When a terminal moves to the edge and/or outside of the coverage area of an ATC, i.e., the terminal is on the boundary of the cell or the beam, the terminal detects such movement by repeating the above steps (a), (b) and (c) and by monitoring location information and velocity information of the terminal. As a result, the present invention performs an effective power control by combining two signals transmitted from two systems and a handover, and provides a seamless communication service to users.

[33] Unlike the terrestrial mobile communication system, the conventional GSO-based satellite mobile communication system has little to gain because of the long round trip time among the terminal, the satellite and the base station. In order to solve the above problem, the present invention adds monitoring equipments to both an open loop power control (OLPC) and a closed loop power control (CLPC) to use information about transmitting power that has not yet been experienced by the receiver over the satellite and ATC channel.

[34]

Brief Description of the Drawings

[35] Fig. 1 is a block diagram illustrating a method for reusing frequency in a satellite mobile communication system having ancillary terrestrial components (ATC).

[36] Fig. 2 is a block diagram illustrating a satellite mobile communication system having an ATC to which the present invention is applied.

[37] Fig. 3 is a diagram showing a motional direction and a magnitude of received signals according to a terminal path and a constantly varying time in the satellite mobile communication system having an ATC in accordance with the present invention.

[38] Fig. 4 is a flowchart illustrating a power control method considering a handover in accordance with an embodiment of the present invention.

[39] Fig. 5 is a detailed flowchart illustrating a power control method when the terminal is located within an ATC cell in accordance with an embodiment of the present invention.

[40] Fig. 6 is a detailed flowchart illustrating a power control method when the terminal is located within a spot beam in accordance with an embodiment of the present invention.

[41] Fig. 7 is a detailed flowchart illustrating a power control method when the terminal is located on the boundary of an ATC cell or a spot beam in accordance with an embodiment of the present invention.

[42] Fig. 8 is a detailed flowchart illustrating a power control method when the terminal does not move on the boundary of an ATC cell or a spot beam in accordance with an embodiment of the present invention.

[43] Fig. 9 is a detailed flowchart illustrating a power control method when the terminal, located on the boundary of an ATC cell or a spot beam, moves from the ATC cell to the spot beam in accordance with an embodiment of the present invention. [44] Fig. 10 is a detailed flowchart illustrating a power control method when the terminal, located on the boundary of an ATC cell or a spot beam, moves from the spot beam to the ATC cell, from one ATC cell to another ATC cell and from one spot beam to another spot beam in accordance with an embodiment of the present invention.

[45]

Best Mode for Carrying Out the Invention

[46] The advantages, features and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter.

[47] Fig. 2 is a block diagram illustrating a satellite mobile communication system having ancillary terrestrial components (ATC) to which the present invention is applied

[48] In a satellite mobile communication system having an ATC, a satellite 10 retaining enough power provides communication service through three spot beams 110, 120 and 130 having frequency Fl, F2 and F3, respectively.

[49] In the regions where satellite signals are interrupted by crowds or high-rise buildings, a spot beam 120 with Fl and another spot beam 130 with F3 are applied. In such regions, mobile satellite service (MSS) bands are reused by installing two ATC systems 140 and 150. In reference to Fig. 2, the two ATC systems 140 and 150 operate with Fl and F2 which are different from F3 of the spot beam 130. Communication services are provided to two ATC systems 140 and 150 through corresponding two ATC antennas 161 and 162, respectively.

[50] The workings of communication among the terminal, the satellite mobile communication system and the ATC system in the satellite mobile communication system having an ATC will be described fully hereinafter.

[51] A terminal 172 receives location information within a spot beam 110 having Fl, and transmits data to a satellite 10 through an up-link 184 of the MMS bands.

[52] Then, the satellite 10 transmits the data to a fixed terrestrial station 20 through a down-link 181 of a feeder link. After processing the data, the satellite 10 receives the data from the fixed terrestrial station 20 through an up-link 181 of the feeder link. Then, the satellite 10 transmits the data to the corresponding terminal 172 through a down-link 184 of the MSS bands.

[53] If a first terminal 171 needs to communicate with a second terminal 173, the first terminal 171 receives the location information and transmits the location information to an ATC base station 161 in an ATC cell 140 by reusing Fl 192 of MSS bands uplink. Then, the ATC base station 161 transmits the data to an ATC controller 50, and the ATC controller 50 transmits the data to a gateway 30 through a public switched data network/public data network (PSDN/PDN) 40 of a wired network. Also, the fixed terrestrial station 20 transmits the data to the satellite 10 through the up-link 181 of the feeder link, and the satellite 10 transmits the data to the second terminal 173 located in the spot beam 120.

[54] Then, the second terminal 173 transmits data to the first terminal 171 in the ATC cell

140 of the spot beam 130 through a reverse process of the above process.

[55] Fig. 3 is a diagram showing a motional direction and a magnitude of received signals according to a terminal path and a constantly varying time in the satellite mobile communication system having an ATC in accordance with the present invention.

[56] A spot beam 130 uses frequency F3 of the MSS bands, and two ATC cells 140 and

150 reuse frequencies Fl and F2 of the MSS bands, respectively.

[57] A graph 300 shows the magnitude of received signals in relation to time when the terminal moves in a certain direction 301.

[58] Handover and power control can be classified into six categories. The first one is when the power control operates in a spot beam 130. The second one is when the handover and the power control operate from a spot beam 130 to an ATC cell 140 or 150. The third one is when the power control is performed within an ATC cell 140 or 150. The fourth one is when the handover and the power control are performed from the first ATC cell 140 to the second ATC cell 150. The fifth one is when the handover and the power control are performed from the ATC cell 140 or 150 to the spot beam 130. The sixth one is when the handover and the power control are performed from the first spot beam 130 to the second spot beam 120.

[59] Here, a first received signal 340 is a power transmitted from the first ATC base station 161 in the first ATC cell 140 and is received according to the motion direction 301 of the terminal. A second received signal 350 is a power transmitted from the second ATC base station 162 in the second ATC cell 150 and is received according to the motion direction 301 of the terminal. A third received signal 360 is a power transmitted from the spot beams 120 and 130 and is received according to the motion direction 301 of the terminal. Particularly, high-level handover and power control are required in boundary regions of the cell or the spot beam such as 310, 320 and 330.

[60] In reference to Fig. 4, effective power control based on the location information of the terminal in the satellite mobile communication system having an ATC will be described fully hereinafter.

[61] Fig. 4 is a flowchart illustrating a power control method considering a handover in accordance with an embodiment of the present invention.

[62] At step S401, the terminal receives its location information and velocity information via GPS or various technologies at a moment when the terminal starts to transmit data.

[63] At step S402, the terminal acquires transmission power information such as a minimum power P and a maximum power P from the search table in which location information is stored. [64] The location information is examined at step S403. If the terminal is within the ATC cell, a power control within the ATC cell is performed at step S404. [65] If the terminal is located in the spot beam, a power control within the spot beam is performed at step S405. [66] If the terminal is located on the boundary of the ATC cell or spot beam, a power control and a handover on the boundary of the ATC cell or the spot beam are performed at step S406. [67] Fig. 5 is a detailed flowchart illustrating a power control method S404 when the terminal is located within the ATC cell in accordance with an embodiment of the present invention.

[68] If the terminal is within the ATC cell, the terminal acquires a target signal- to-interference ratio (SIR) based on an open-loop power control and a compensation algorithm of a round- trip delay at step S501. [69] The target SIR and a current SIR and the determination value for the next transmission power are described hereunder. [70] First, an average power of received signal is measured based on the following Eq. 1 of Friis. [71] .₂

G_tG_rλ

' 16^d²L

Eq. 1 [72] In Eq. 1, P is a transmission power; G is an antenna gain of an ATC; G is a antenna t t r gain of the terminal; 1 is a wavelength; d is a distance between the terminal and the ATC; and L [=101og (d/d )ⁿ] is a loss from the distance. The value of n is between 3 and 4 when the terminal is located in the ATC cell, and between 2 and 3 when the terminal is located in the spot beam.

[73] Then, the target SIR is predicted by measuring a frame error rate (FER)/bit error rate

(BER), and the SIR of the current received signal is determined based on the following Eq. 2.

Eq. 2 [75] In Eq. 2, d(t) is a data symbol; g(t) is a channel gain; p(t) is a transmission power; and s(t) is a pilot symbol which is already known. [76] The next transmission power determination value based on the open-loop power control and the compensation algorithm of the round-trip delay is expressed as the following Eq. 3.

^[77] P_1x it + 1) = TOSx(P_{1x mm} , min(^ _max , max(0, P_1x (?) - |ΔP(f)|(l - exp(f / τ)))))

Eq. 3

[78] Here, t is a predetermined interval reporting to the base station, and generally 20 ms; and DP(t) is expressed as the following Eq. 4.

^[79] ΔP(r) = SIR_taiRet - SIR(t) - RTD_comvemat1on (t)

Eq. 4

[80] HHeerree,, RTD compensation (t) is the compensation algorithm of the round-trip delay and expressed as the following Eq. 5.

[81]

^RTD compensation (0 = PynomtoM) + PynomtoM ^{~ RTD})

Eq. 5

[82] Then, a closed-loop power control and the compensation algorithm of the round-trip delay are simultaneously performed based on the target SIR at step S502. Here, the next transmission power determination value is expressed as the following Eq. 6.

^[83] P_b (t + 1) = mm(P_{b raax} , max(P_fc __mm , P_fc (0 + PCC x sιgn(AP(ή)))

Eq. 6 [84] In Eq. 6, a power control command (PCC) is acquired by performing an algorithm expressed as the following Eq. 7.

[85] If lcurrent SIR(t)l < target SIR AND SIR(t)<0, PCC=SmallStepSize

[86] If lcurrent SIR(t)l < target SIR AND SIR(t)>0, PCC=-SmallStepSize

[87] If lcurrent SIR(t)l > target SIR AND SIR(t)<0, PCC=LargeStepSize

[88] If lcurrent SIR(t)l > target SIR AND SIR(t)>0, PCC=-LargeStepSize

[89] Eq. 7

[90] Meanwhile the closed-loop power control and the compensation algorithm of the round-trip delay are performed at step S502, the BER and a quality of service (QoS) are compared with threshold values at step S503. If the BER and the QoS are smaller than the threshold values, operation range of the current transmission power and the location of the terminal are examined at step S504. [91] If the current transmission power of the terminal is between the minimum power P nun and the maximum power P max of the ATC cell, i.e., if the current transmission power of the terminal is within the operation range of the transmission power of the ATC cell, a new target SIR is acquired based on the open-loop power control and the compensation algorithm of the round- trip delay at step S501. However, if the current transmission power of the terminal is beyond the operation range of the transmission power of the ATC cell, go to step S403. Herein, the terminal receives the location information, moves into the corresponding system, and performs other appropriate power control procedures.

[92] If the BER and the QoS are larger than the threshold values at step S503, the closed- loop power control and the compensation algorithm of the round- trip delay are performed continuously at step S502.

[93] Fig. 6 is a detailed flowchart illustrating a power control method S405 when the terminal is located within a spot beam in accordance with an embodiment of the present invention.

[94] Unlike the ATC and terrestrial system, the GSO-based system has the round-trip time longer than 0.5 sec, which results in a heavy overhead for the system operation. Therefore, initial information, e.g., the target SIR and an initial transmission power of the terminal, are acquired based on the closed-loop power control for minimizing system complexity while the open-loop power control is adapted for power control after the initial state.

[95] First, the terminal is located in the spot beam based on the location information at step S403, the target SIR is acquired based on the closed-loop power control and the compensation algorithm of the round-trip delay expressed as the following Eq. 8 at step S601.

^[96] P_1x (t + \) = max(i^>_ _mm , min(4 _max , max(0, P_1x (t) -ACK(I- exp(f / r)))))

Eq. 8

[97] Herein, ACK variable is substituted by the Eq. 4 when the satellite sends an ACK answer signal to the terminal. If the terminal does not receive the ACK answer signal, the terminal monotonously increases the transmission power until it receives the ACK answer signal.

[98] That is, in reference to Fig. 2, when the terminal 172 transmits a preamble signal to a satellite 10 in order to acquire the initial transmission power and the target SIR, the satellite 10 transmits the preamble signal of the terminal to the fixed terrestrial station 20 through the down-link 181 of the feeder link. Then, the fixed terrestrial station 20 calculates the initial transmission power and the target SIR of the terminal 172, and transmits the acquired information to the satellite 10 through the up-link 181 of the feeder link to transmit the acquired information to the terminal 172. Then, the satellite 10 transmits the initial transmission power and the target SIR to the terminal 172 through the down-link 184 of the MSS bands.

[99] In reference to Fig. 6, the open-loop power control and the compensation algorithm of the round-trip delay are performed at step S602. [100] Meanwhile the closed- loop power control and the compensation algorithm of the round-trip delay are performed at step S602, the BER and the QoS are compared with threshold values at step S603. If the BER and the QoS are smaller than the threshold values, operation range of the current transmission power and the location of the terminal are examined at step S604.

[101] If the current transmission power of the terminal is between the minimum power P mm and the maximum power P of the spot beam, i.e., if the current transmission power max of the terminal is within the operation range of the transmission power of the spot beam, the target SIR is acquired based on the closed- loop power control and the compensation algorithm of the round- trip delay at step S601. However, if the current transmission power of the terminal is beyond the operation range of the transmission power of the spot beam, go to step S403. Then, the terminal receives the location information and moves into the corresponding system, and performs other appropriate power control procedure.

[102] If the BER and the QoS are larger than the threshold values at step S603, the open- loop power control and the compensation algorithm of the round- trip delay are performed continuously at step S602.

[103] Fig. 7 is a detailed flowchart illustrating a power control method S406 when the terminal is located on the boundary of an ATC cell or a spot beam in accordance with an embodiment of the present invention.

[104] First, receiver diversity is applied to increase the SIR of the received signal at step S701.

[105] Then, appropriate power control and handover are performed accordingly when: (a) the terminal does not move at step S702; (b) the terminal moves from the ATC cell to the spot beam at step S703; (c) the terminal moves the spot beam to the ATC cell at step S704; (d) the terminal moves from one ATC cell to another ATC cell at step S705; and (e) the terminal moves from one spot beam to another spot beam at step S706.

[106] Fig. 8 is a detailed flowchart illustrating a power control method S702 when the terminal does not move on the boundary of an ATC cell or a spot beam in accordance with an embodiment of the present invention.

[107] The terminal receives its location information and the velocity information. When the terminal does not move on the boundary of the ATC cell or the spot beam at step S 801, based on a broadcasting channel (BCH) at step S 802, the terminal recognizes two systems which transmit large powers. Herein, the receive diversity is used to increase the signal-to-interference ratio (SIR).

[108] Firstly, if the terminal receives power from both one ATC cell and the other ATC cell by measuring an average power of the received signals at step S 803, a power control method, which is the one performed at step S404 in Fig. 5 when the terminal is within the ATC cell, is performed.

[109] Secondly, if the terminal receives power both from one spot beam and the other spot beam at step S 805, a power control method, which is the one performed at S405 in Fig. 6 when the terminal is within the spot beam, is performed.

[110] Thirdly, if the terminal receives power both from the ATC cell and the spot beam at step S 804, appropriate location information and the target SIR based on the open-loop power control and the compensation algorithm of the round-trip delay are acquired by setting a timer at step S806. Thereafter, the power control based on the closed-loop power control and the compensation algorithm of the round-trip delay are performed at step S807. Also, if at step S8O8 the time indicated by the said timer is less than the operation time, the target SIR is acquired based on the closed-loop power control and the compensation algorithm of the round-trip delay at step S809. Thereafter, the open- loop power control and compensation algorithm of the round-trip delay are performed at step S810. Herein, if the time indicated by the said timer is less than the operation time and if the location information and the velocity information of the terminal are correct at step S811, go to the step S806 and repeat the above steps.

[I l l] In order to equally control power transmitted to both the ATC cell and the spot beam, the closed-loop power control and the open-loop power control are alternated for the constant time.

[112] If the time indicated by the said timer is more than the operation time at steps S 808 and S811, go to the step S403. Then, the terminal receives the location information and moves into the corresponding system, and appropriate power control procedure is performed.

[113] Fig. 9 is a detailed flowchart illustrating a power control method S703 when the terminal, located on the boundary of an ATC cell or a spot beam, moves from the ATC cell to the spot beam in accordance with an embodiment of the present invention.

[114] The terminal receives its location information and the velocity information. If the terminal is located on the boundary of the ATC cell or the spot beam and moves S702, and if the terminal moves from the ATC cell to the spot beam at step S901, the terminal performs the handover based on the open-loop power control and the compensation algorithm of the round-trip delay at step S902. Here, the terminal has already acquired the target SIR based on the receiving diversity at step S701. Also, the target SIR is acquired based on measuring the average power by combining powers of the ATC cell and the spot beam by using the receiving diversity.

[115] While the power control is performed at step S902, the BER and the QoS are compared with threshold values at step S903. If the BER and the QoS are smaller than the threshold values, operation range of the current transmission power and the location of the terminal are examined at step S904. [116] Herein, a minimum power and a maximum power of the ATC cell are P and P mm cell

, and a minimum power and a maximum power of the spot beam are P and max cell mm beam

P , respectively. In addition, operation range of the transmission power in the max beam

ATC cell and operation range of the transmission power in the spot beam are partially overlapped. If the current transmission power of the terminal is between a first power P having a large value among P and P , and a second power P having a mm mm cell min beam max small value among P and P , i.e., if the current transmission power of the max cell max beam terminal is within the operation range of the transmission power of the ATC cell and spot beam, a new target SIR is acquired based on the close-loop power control and the compensation algorithm of the round- trip delay at step S905. And move to step S902 wherein the power control is performed based on the open-loop power control and the compensation algorithm of the round-trip delay.

[117] However, if the current transmission power of the terminal is out of the operation range, i.e., from P mm to P max of the transmission power of the larger value of the ATC cell and the spot beam, go to the step S403. Then, the terminal receives the location information and moves into the corresponding system, and appropriate power control procedure is performed.

[118] If the BER and the QoS are larger than the threshold values at step S903, the open- loop power control and the compensation algorithm of the round- trip delay are performed continuously at step S902.

[119] If the terminal does not move from the ATC cell to the spot beam, the power control procedure in Fig. 10 is performed.

[120] Fig. 10 is a detailed flowchart illustrating a power control method when the terminal, located on the boundary of an ATC cell or a spot beam, moves from the spot beam to the ATC cell, from one ATC cell to another ATC cell and from one spot beam to another spot beam in accordance with an embodiment of the present invention.

[121] Based on the location information and the velocity information the terminal receives, if the terminal is located on the boundary of the ATC cell or the spot beam and moves at step S702, and if the terminal moves from the spot beam to the ATC cell at step SlOl, the terminal performs the handover based on the closed-loop power control and the compensation algorithm of the round- trip delay at step S 102. Herein, the terminal has already acquired the target SIR based on the receive diversity at step S701.

[122] While the power control is performed at step S 102, the BER and the QoS are compared with predetermined values at step S 103. If the BER and the QoS are smaller than threshold values, operation range of the current transmission power and the location of the terminal are examined at step S 104.

[123] If the current transmission power of the terminal is between a first power P min having a large value among the minimum power of the ATC cell and the minimum power of the spot beam, and a second power P having a small value among the maximum max power of the ATC cell and the maximum power of the spot beam, i.e., if the current transmission power of the terminal is within the operation range of the transmission power of the ATC cell and spot beam, a new target SIR is acquired based on the open- loop power control and the compensation algorithm of the round-trip delay at step S 105. Thereafter, go to step S 102 wherein power control is performed based on the closed-loop power control and the compensation algorithm of the round-trip delay. [124] However, if the current transmission power of the terminal is beyond the operation range, i.e., the transmission power of the ATC cell or the spot beam from P to P , mm max go to the step S403. Then, the terminal receives the location information and moves into the corresponding system, and appropriate power control procedure is performed.

[125] If the BER and the QoS are larger than the threshold values at step S 103, the closed- loop power control and the compensation algorithm of the round- trip delay are performed continuously at step S 102.

[126] If the terminal is not a stop state S702 and moves from one ATC cell to another ATC cell at step S 106, a power control method, which is the one performed at step S404 in Fig. 5 when the terminal is within the ATC cell, is performed.

[127] On the other hand, if the terminal is not a stop state S702 and moves from one spot beam to another spot beam, a power control method, which is the one performed in at step S405 in Fig. 6 when the terminal is within the spot beam, is performed.

[128] During the above process, the terminal monitors its location information and the velocity information in real time, and the appropriate power control and the handover are performed based on the location information and the velocity information.

[129] The above described method according to the present invention can be embodied as a program and be stored on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be read by the computer system. The computer readable recording medium includes a read-only memory (ROM), a random-access memory (RAM), a CD-ROM, a floppy disk, a hard disk and an optical magnetic disk.

[130] The present application contains subject matter related to Korean Patent Application No. 2006-0094398, filed in the Korean Intellectual Property Office on September 27, 2006, the entire contents of which are incorporated herein by reference.

[131] While the present invention has been described with respect to certain preferred embodiments, 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] A power control method in a communication system having ancillary terrestrial components (ATC), comprising: a) acquiring current location information of a terminal; b) acquiring current transmission power information of the terminal; and c) confirming location of the terminal based on the location information, measuring velocity information of the terminal on a boundary of a ATC cell or a spot beam, and performing a first power control considering a handover based on the current transmission power information and the velocity information by using a receive diversity.

[2] The power control method of claim 1, further comprising performing a second power control based on the current transmission power information in the ATC cell or the spot beam.

[3] The power control method of claim 2, wherein the step d) includes: dl) confirming location of the terminal based on the location information; d2) when the terminal is within the ATC cell, performing a power control within the ATC cell based on the current transmission power information; and d3) when the terminal is within the spot beam, performing a power control within the spot beam based on the current transmission power information.

[4] The power control method of claim 3, wherein the step d2) includes: d2-l) measuring an average power of received signals; d2-2) acquiring a target signal-to-interference ratio (SIR) based on an open-loop power control and a compensation algorithm of a round trip delay; d2-3) performing the power control based on a closed-loop power control and the compensation algorithm of the round trip delay by using the target SIR; d2-4) comparing a bit error rate (BER) and a quality of service (QoS) with threshold values; d2-5) when the BER and the QoS are smaller than the threshold values, examining an operation range of the current transmission power and the location of the terminal; and d2-6) when the current transmission power of the terminal is between a minimum power P and a maximum power P of the ATC cell, acquiring a mm max new target SIR based on the open-loop power control and the compensation algorithm of the round trip delay and performing the power control based on the closed- loop power control and the compensation algorithm of the round trip delay by using the new target SIR.

[5] The power control method of claim 3, wherein the step d3) includes: d3-l) measuring an average power of received signals; d3-2) acquiring a target signal-to-interference ratio (SIR) based on a closed-loop power control and a compensation algorithm of a round trip delay; d3-3) performing the power control based on an open-loop power control and the compensation algorithm of the round trip delay by using the target SIR; d3-4) comparing a bit error rate (BER) and a quality of service (QoS) with threshold values; d3-5) when the BER and the QoS are smaller than the threshold values, examining an operation range of the current transmission power and the location of the terminal; and d3-6) when the current transmission power of the terminal is between a mini mum power P and a maximum power P of the spot beam, acquiring a new mm max target SIR based on the closed-loop power control and the compensation algorithm of the round trip delay and performing the power control based on the open-loop power control and the compensation algorithm of the round trip delay by using the new target SIR.

[6] The power control method of claim 3, wherein in the step c) the power control considering the handover includes: cl) not moving on a boundary of the ATC cell or the spot beam; c2) moving from the ATC cell to the spot beam; c3) moving from the spot beam to the ATC cell; c4) moving from a first ATC cell to a second ATC cell; and c5) moving from a first spot beam to a second spot beam.

[7] The power control method of claim 6, wherein the step cl) includes: cl-1) measuring the velocity information of the terminal; c 1-2) when the terminal does not move, detecting two systems sending a largest power signal and a second largest power signal to the terminal; c 1-3) measuring an average power of received signals; c 1-4) if the terminal receives signals transmitted from the first ATC cell and the second ATC cell, performing the step d2); c 1-5) if the terminal receives signals transmitted from the first spot beam and the second spot beam, performing the step d3); c 1-6) if the terminal receives signals transmitted from the ATC cell and the spot beam, setting a timer; and c 1-7) acquiring a target SIR based on an open-loop power control and a compensation algorithm of a round trip delay and performing a power control based on a closed- loop power control and the compensation algorithm of the round trip delay, and acquiring the target SIR based on the closed-loop power control and the compensation algorithm of the round trip delay and performing the power control based on the open-loop power control and the compensation algorithm of the round trip delay for executing the timer.

[8] The power control method of claim 6, wherein the step c2) includes: c2-l) measuring an average power of received signals by combining signals transmitted from the ATC cell and the spot beam by using a receive diversity; c2-2) acquiring a target SIR; c2-3) performing a power control and a handover based on a open-loop power control and a compensation algorithm of a round trip delay by using the target

SIR; c2-4) comparing a bit error rate (BER) and a quality of service (QoS) with threshold values; c2-5) when the BER and the QoS are smaller than the threshold values, examining an operation range of the current transmission power and the location of the terminal; and c2-6) when the current transmission power of the terminal is between a first power having a large value among a minimum power of the ATC cell and a minimum power of the spot beam, and a second power having a small value among a maximum power of the ATC cell and a maximum power of the spot beam, acquiring a new target SIR based on a closed- loop power control and the compensation algorithm of the round trip delay and performing the power control based on the open-loop power control and the compensation algorithm of the round trip delay by using the new target SIR.

[9] The power control method of claim 6, wherein the step c3) includes: c3-l) measuring an average power of received signals by combining signals transmitted from the ATC cell and the spot beam by using a receive diversity; c3-2) acquiring a target SIR; c3-3) performing a power control and a handover based on a closed-loop power control and a compensation algorithm of a round trip delay by using the target

SIR; c3-4) comparing a bit error rate (BER) and a quality of service (QoS) with threshold values; c3-5) when the BER and the QoS are smaller than the threshold values, examining an operation range of the current transmission power and the location of the terminal; and c3-6) when the current transmission power of the terminal is between a first power having a large value among a minimum power of the ATC cell and a minimum power of the spot beam, and a second power having a small value among a maximum power of the ATC cell and a maximum power of the spot beam, acquiring a new target SIR based on an open-loop power control and the compensation algorithm of the round trip delay and performing the power control based on the closed- loop power control and the compensation algorithm of the round trip delay by using the new target SIR.

[10] The power control method of claim 6, wherein the step c4) includes: c4-l) measuring an average power of received signals by combining signals transmitted from the first ATC cell and the second ATC cell by using a receiving diversity; and c4-2) performing the step d2).

[11] The power control method of claim 6, wherein the step c5) includes: c5-l) measuring an average power of received signals by combining signals transmitted from the first spot beam and the second spot beam by using a receiving diversity; and c5-2) performing the step d3).