Description SIGNAL TRANSMISSION METHOD OF CTC FOR SATELLITE

MOBILE COMMUNICATION SYSTEM WHICH SIMULTANEOUSLY SUPPORTS BROADCAST SERVICE AND COMMUNICATION SERVICE AND THE CTC

Technical Field

[1] This application claims the benefit of Korean Patent Application No.

10-2007-0116183, filed on November 14, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

[2] The present invention relates to a signal transmission method of a complementary terrestrial component (CTC) for a satellite mobile communication system in order to efficiently provide a broadcast service that is a unidirectional service as well as a communication service that is an interactive service at the same time and to maximize frequency use efficiency, and the CTC.

[3] This work was supported by the IT R&D program of MIC/IITA [2005-S-014-03, Development of satellite IMT-2000+ technology] . Background Art

[4] At present, research and development have been being actively conducted on satellite mobile communication systems using a complementary terrestrial component (CTC) such as a repeater, a complementary ground component (CGC), and an ancillary terrestrial component (ATC) all over the world.

[5] Satellite digital multimedia broadcasting (DMB) systems are now providing services in Korea, and Digital Video Broadcasting - Satellite services to Handhelds (DVB-SH) systems are being studied to provide broadcast services in about 2010 in Europe. In the U.S.A, the Mobile Satellite Ventures ( ¹ MSV) and the Terrestar Networks Inc.('Terrestar') have developed terrestrial-satellite hybrid systems for providing voice and data communications in the downtown area and in the suburbs by using an ATC.

[6] The Korean satellite DMB system is designed to allow vehicles and fixed or portable terminals to receive high-quality audio signals and multimedia signals through the ancillary use of a terrestrial network using a channel gapfiller, together with the use of a satellite, and is optimized for a 2630 - 2655-MHz band for both satellite and terrestrial apparatus. This satellite DMB system includes a feeder link earth station, a broadcasting satellite, 2 types of terrestrial repeaters, and receivers (vehicles, fixed terminals, and portable terminals).

[7] A signal is transmitted to the satellite via the feeder link earth station. At this time, a fixed satellite service (FSS) band, e.g., 14 GHz is used as an uplink. The received

signal is transformed to a 2.6-GHz band signal in the satellite. The 2.6-GHz band signal is amplified using an amplifier of a satellite repeater up to a desired level, and this signal is broadcast over a service area.

[8] A user of the satellite DMB system has to receive a signal via a small-size antenna having low directivity. To this end, a transmission end of the signal has to have a sufficient equivalent isotropically radiated power (EIRP) and thus the satellite has to have a large-size transmission antenna and a high-power repeater. To overcome key problems in 2.6-GHz band signal transmission, e.g., obstacles and shadow areas on a direct path from the satellite, a repeater for retransmitting a satellite signal is added to the satellite DMB system.

[9] The added repeater covers a portion occluded by a obstacle such as a building and can be classified into a direct amplifying repeater and a frequency changing repeater. The direct amplifying repeater merely amplifies a 2.6-GHz band broadcast signal received from the satellite and essentially uses a low-gain amplifier in order to avoid unnecessary emission caused by signal interference between a reception antenna and a transmission antenna. The direct amplifying repeater covers a narrow area up to 500m with respect to a line of sight (LoS). On the other hand, the frequency changing repeater covers a broad area up to 3km with respect to the LoS. The frequency changing repeater transforms a received 2.6-GHz band signal to a different-band signal, i.e., an 11-GHz band signal. In this case, multi-path fading occurs where 2 signals or more are received. The satellite DMB system uses a rake receiver adopting a code division multiplexing (CDM) scheme for stable reception of multi-path fading signals.

[10] The European DVB-SH system uses a satellite for a nationwide coverage and a CGC for an indoor environment and a terrestrial coverage, and aims to provide mobile TV services in a 15-MHz bandwidth of a DVB-H-based S band. Since this DVB-SH system uses a band that is adjacent to a terrestrial international mobile telecommunication (IMT) band of the S band, it can be easily integrated into an IMT terrestrial part and can reuse a network with a terrestrial network, thereby reducing installation cost. A hybrid broadcasting structure with the terrestrial network is under consideration, and a reuse factor of 1 for a CGC cell within a single satellite spot beam and a reuse factor of 3 for the satellite spot beam are also being considered in order to solve signal interference between the satellite and the CGC and to efficiently use frequency. In this case, in France, 9 TV channels can be broadcast for the nationwide coverage through a satellite spot beam and 27 channels can be broadcast for the downtown area and the indoor environment through a terrestrial repeater.

[11] In the U.S.A., the MSV and the Terrestar are developing a geostationary satellite- based satellite mobile communication system for providing a ubiquitous wireless

broadband communication service such as Internet access and voice communication to a personal communication services (PCS) terminal or a cellular terminal in an L band and an S band. By using a hybrid wireless network structure combining a satellite and an ATC, this satellite mobile communication system provides voice services or highspeed packet services through the ATC, i.e., a terrestrial network, in the downtown area or a congested area and provides those services through the satellite in a rural area or the suburbs that cannot be covered by the ATC in the U.S.A. and Canada. The ATC is being developed to use the same interface as used by the satellite, thereby providing a satellite service without increasing the complexity of a terrestrial terminal.

[12] As such, future satellite mobile communication systems for personal portable terminals aim to provide services through a satellite in a rural area or the suburbs where the LoS is guaranteed and to provide the services through a CTC in the downtown area and the indoor environment where a satellite signal is not secured. However, the systems under development are intended to provide a system and a signal transmission method that are efficient for a target service selected between a communication service such as voice and data services and a broadcast service. For future expected communication-broadcasting integrated services, there is a need for a satellite mobile communication system capable of efficiently providing a broadcast service together with a communication service and maximizing frequency use efficiency by improving spectrum use efficiency and a signal transmission method efficient for the satellite mobile communication system. Disclosure of Invention Technical Problem

[13] The present invention provides a signal transmission method of a complementary terrestrial component (CTC) for a satellite mobile communication system in order to efficiently provide a broadcast service together with a communications service and to maximize frequency use efficiency, and the CTC. Technical Solution

[14] According to an aspect of the present invention, there is provided a signal transmission method of a complementary terrestrial component (CTC). The signal transmission method includes, from a transmitter which can use a total frequency band including an uplink and a downlink, receiving communication data through a portion of a communication frequency band of the downlink and broadcast data through a first frequency band that is a portion of a broadcast frequency band of the downlink, allocating the received broadcast data to a second frequency band that is a portion of the same frequency band as the broadcast frequency band, allocating additional data to a third frequency band that is a portion of a remaining frequency band of the same

frequency band as the total frequency band except for the second frequency band, and transmitting the broadcast data and the additional data to at least one terminal.

[15] According to another aspect of the present invention, there is provided a signal transmission method of a complementary terrestrial component (CTC). The signal transmission method includes receiving a first frame including communication data and broadcast data from a transmitter through a first carrier of a downlink, allocating the broadcast data to a second frame, allocating additional data to the second frame, and transmitting the second frame to at least one terminal.

[16] According to another aspect of the present invention, there is provided complementary terrestrial component (CTC) including a reception unit, a broadcast data frequency allocation unit, an additional data frequency allocation unit, and a transmission unit. From a transmitter which can use a total frequency band including an uplink and a downlink, the reception unit receives communication data through a portion of a communication frequency band of the downlink and broadcast data through a first frequency band that is a portion of a broadcast frequency band of the downlink. The broadcast data frequency allocation unit allocates the received broadcast data to a second frequency band that is a portion of the same frequency band as the broadcast frequency band. The additional data frequency allocation unit allocates additional data to a third frequency band that is a portion of a remaining frequency band of the same frequency band as the total frequency band except for the second frequency band. The transmission unit transmits the broadcast data and the additional data to at least one terminals.

[17] According to another aspect of the present invention, there is provided a complementary terrestrial component (CTC) including a reception unit, a broadcast data frame allocation unit, an additional data frame allocation unit, and a transmission unit. The reception unit receives a first frame including communication data and broadcast data from a transmitter through a first carrier of a downlink. The broadcast data frame allocation unit allocates the broadcast data to a second frame. The additional data frame allocation unit allocates additional data to the second frame. The transmission unit transmits the second frame to at least one terminal. Advantageous Effects

[18] As described above, according to the present invention, a satellite mobile communication system including a CTC can effectively provide a broadcast service and a communication service at the same time, and frequency use efficiency is maximized by enhancing spectrum use efficiency in signal transmission for each of the broadcast service and the communication service, thereby improving the communication capacity of the satellite mobile communication system.

Description of Drawings

[19] The above and other features and advantages of the present invention will become more apparent by describing in detail embodiments thereof with reference to the attached drawings in which:

[20] FIG. 1 illustrates a satellite mobile communication system according to an embodiment of the present invention;

[21] FIG. 2 illustrates a frequency band serviced by the satellite mobile communication system illustrated in FIG. 1 ;

[22] FIG. 3 illustrates a frequency band allocated by a satellite of the satellite mobile communication system illustrated in FIG. 1 for signal transmission to a complementary terrestrial component (CTC) and a terminal;

[23] FIG. 4 is a flowchart illustrating a signal transmission method of a CTC according to an embodiment of the present invention;

[24] FIG. 5 illustrates a frequency band corresponding to a case where carriers for broadcast data transmitted by a satellite and carriers for broadcast data transmitted by a CTC are the same as each other according to an embodiment of the present invention;

[25] FIG. 6 illustrates a frequency band corresponding to a case where carriers for broadcast data transmitted by a satellite and carriers for broadcast data transmitted by a CTC are different from each other according to an embodiment of the present invention;

[26] FIG. 7 is a constellation diagram illustrating a method of modulating a signal including broadcast data of a satellite in the case illustrated in FIG. 5;

[27] FIG. 8A illustrates a frequency band corresponding to a case where a CTC provides an additional communication service by using communication data carriers of a satellite according to an embodiment of the present invention;

[28] FIG. 8B illustrates a frequency band corresponding to a case where a CTC provides a local broadcast service by using communication data carriers of a satellite according to an embodiment of the present invention;

[29] FIG. 9 is a flowchart illustrating a process of providing a communication service and a local broadcast service in the case illustrated in FIGS. 8 A and 8B;

[30] FIG. 10 illustrates a frequency band corresponding to a case where a CTC uses a frequency band of an uplink for a communication service of a satellite, for a local broadcast service according to an embodiment of the present invention;

[31] FIG. 11 is a flowchart illustrating a signal transmission method of a CTC according to another embodiment of the present invention;

[32] FIG. 12 illustrates a frame structure corresponding to a case where carriers transmitted by a satellite and carriers transmitted by a CTC are different from each other in FIG. 11;

[33] FIG. 13A illustrates a frame structure corresponding to a case where carriers transmitted by a satellite and carriers transmitted by a CTC are the same as each other and the CTC provides an additional communication service in FIG. 11;

[34] FIG. 13B illustrates a frame structure corresponding to a case where carriers transmitted by a satellite and carriers transmitted by a CTC are the same as each other and the CTC provides a local broadcast service in FIG. 11 ;

[35] FIG. 14 is a flowchart illustrating a process of providing a communication service and a local broadcast service in the cases illustrated in FIGS. 13 A and 13B;

[36] FIG. 15 illustrates frame structures corresponding to a case where a satellite mobile communication system is in a half- frequency division duplexing mode in FIG. 11;

[37] FIG. 16 illustrates a CTC that simultaneously supports a broadcast service and a communication service according to an embodiment of the present invention; and

[38] FIG. 17 illustrates a CTC that simultaneously supports a broadcast service and a communication service according to another embodiment of the present invention. Best Mode

[39] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that like reference numerals refer to like elements illustrated in one or more of the drawings. In the following description of the present invention, detailed description of known functions and configurations incorporated herein will be omitted for conciseness and clarity.

[40] In the present invention, a complementary terrestrial component (CTC) simultaneously receives communication data for a communication service that is an interactive service and broadcast data for a broadcast service from a transmitter through different frequency bands of a downlink, i.e., different carriers, or the same frequency bands, i.e., the same carriers, and transmits additional data and the broadcast data to terminals through different frequency bands or the same frequency bands.

[41] Hereinafter, a method of simultaneously supporting a broadcast service and a communication service at a CTC and the CTC will be described in detail with reference to the accompanying drawings.

[42] Signal transmission methods for a mobile communication system having maximum commonality with a terrestrial system can be applied regardless of types of a CTC such as a repeater, a complementary ground component (CGC), and an ancillary terrestrial component (ATC) and regardless of types of an access standard such as orthogonal frequency division modulation/multiplexing access (OFDMA), code division multiple access (CDMA), and time division multiple access (TDMA).

[43] In the following description, a communication service means a software or hardware support for enabling both of devices to communicate required voice and various data with each other. The voice and data is referred to as communication data. A broadcast

service is used as a concept comprehending multicasting as well as broadcasting. The broadcast service is a unidirectional service, and data constituting contents which is information to be transmitted to a reception end through the broadcast service is referred to as broadcast data.

[44] FIG. 1 illustrates a satellite mobile communication system according to an embodiment of the present invention.

[45] Referring to FIG. 1, the satellite mobile communication system includes a satellite, i.e., a geostationary satellite 110, a mobile terminal 120, a satellite gateway 130, and a CTC 140.

[46] The satellite 110 may be one of several GEO satellite groups or only a single satellite including no other satellite. The satellite 110 is composed of a mono-spot or multi-spot beam. An area where a terminal provided with a service from the satellite 110 is located may be a single spot or may be a group of several spots for a roaming user terminal.

[47] The satellite 110 transmits downlink communication data and downlink broadcast data and receives uplink communication data transmitted by the mobile terminal 120.

[48] The mobile terminal 120 communicating with the satellite 110 can execute communication with the satellite 110 by using a wireless communication interface and may be a hand phone and a smart phone having a wireless module mounted thereon. The mobile terminal 120 is connected to a network through the single satellite 110 that is directly connected with the satellite gateway 130 or several satellites.

[49] The satellite gateway 130 is an interface for communication between the satellite 110 and a different system or network. The satellite gateway 130 is a centralized gateway or one gateway of a geographically distributed gateway group according to operator's requirements. Although not shown in FIG. 1, the satellite gateway 130 transmits a signal to a satellite base station and a satellite control station included in a network sub-system. The satellite base station and the satellite control station have the same functions as those of a base station and a control station used in a terrestrial network and may exist inside or outside the satellite gateway 130.

[50] The CTC 140 amplifies and transmits a satellite signal by reusing the same frequency as used by the satellite 110. In other words, the CTC 140 is an option that can be used by a satellite mobile communication system for coverage continuity in a shadow area generated due to buildings or mountains during signal transmission. The CTC 140 may be a repeater, a CGC, or an ATC.

[51] The CTC 140 receives the downlink broadcast data transmitted from the satellite 110 and transmits the received broadcast data and additional data for the mobile terminal 120.

[52] The mobile terminal 120 may perform a vertical handover depending on a state of

communication with the satellite 110 or the CTC 140. The mobile terminal 120 receives the downlink communication data and the downlink broadcast data from the satellite 110 and transmits the uplink communication data to the satellite 110. Or the mobile terminal 120 receives the broadcast data and the additional data from the CTC 140.

[53] The satellite mobile communication system illustrated in FIG. 1 simultaneously provides the broadcast service and the communication service as described above. Operations of the satellite mobile communication system can be divided into an operation of providing the broadcast service and an operation of providing the communication service. Therefore the operations will be described separately.

[54] First, the operation of providing the broadcast service or a multimedia broadcast multicast service (MBMS) will be described. The broadcast service or the MBMS is provided through the satellite 110 and the CTC 140. In a nationwide coverage such as the suburbs or a rural area where a line of sight (LoS) is guaranteed, e.g., in an outdoor area 160 illustrated in FIG. 1, the broadcast service or the MBMS is provided through the satellite 110. In the downtown area or an indoor environment where a satellite signal is not received due to many buildings, e.g., in an urban area 170 illustrated in FIG. 1, the broadcast service or the MBMS is provided through the CTC 140. Since the CTC 140 does not provide voice and data communication services that are interactive services in uplink/downlink, only downlink transmission is to be considered, and the mobile terminal 120 transmits a necessary signal through terrestrial systems 150 if it needs information for the MBMS.

[55] Next, the operation of providing the communication service that is an interactive service for voice and data will be described. In this case, it is almost impossible to provide a communication service to all users within a satellite beam having a large coverage by using a limited frequency resource. Thus, in a system model considered in principle, the communication service is provided to only a few users in an area that cannot be covered by the terrestrial systems 150 within a coverage considered by the terrestrial systems 150, i.e., only a few terminals in the area. The terminals or the terminal 120 in the area that cannot be covered by the terrestrial systems 150 are or is provided with voice and data communication services through the satellite 110, and when they enter the terrestrial coverage 170, they are provided with the voice and data communication services through the terrestrial systems 150 having high transmission efficiency. In other words, a vertical handover occurs. In this case, the terminal 120 has to be able to receive signals from both the satellite 110 and the terrestrial systems 150, i.e., has to have interoperability with the terrestrial systems 150 as well as with the satellite 110. When the satellite 110 and the terrestrial systems 150 use different standards, a chip overhead of the terminal 120 may be large. For this reason, in the

satellite mobile communication system illustrated in FIG. 1, the satellite 110 uses a wireless interface having maximum commonality with that used by the terrestrial systems 150.

[56] The satellite 110 and the terrestrial systems 150 are connected with a network 190 such as a public switched telephone network (PSTN), a public land mobile network (PLMN), a packet switched data network (PSDN), and a world wide web (WWW) through a core network 180 and a base station controller 185, so that they can obtain broadcast data that is data for a broadcast service, i.e., data constituting broadcast contents generated at the network 190. This description can also be applied to communication data that is data for a communication service. However, since the communication service is an interactive service that can be transmitted and received, the communication data not only can be obtained from the network 190 but also can be transmitted to the network 190.

[57] Hereinafter, a description will be made assuming the satellite mobile communication system illustrated in FIG.l.

[58] FIG. 2 illustrates a frequency band serviced by the satellite mobile communication system illustrated in FIG. 1.

[59] Referring to FIG. 2, the frequency band can be divided into a frequency band for a downlink and a frequency band for an uplink and each frequency band includes several frequency carriers. In FIG. 2, a subscript 'd' indicates a downlink, a subscript 'u' indicates an uplink, and a number indicates a carrier order. For example, 'f _dl ' indicates a frequency of a first downlink carrier. If f _dl is the same as f _ul , it means that the satellite mobile communication system operates in a time division duplex (TDD) mode. If f _dl is different from f _ul , it means that the satellite mobile communication system operates in a frequency division duplex (FDD) mode. For example, considering a frequency band for an IMT-2000 satellite part that is highly likely to be reused by an IMT-2000 terrestrial part and portable Internet terminals because of being adjacent to an 1-2-GHz band for the IMT-2000 terrestrial part and a 2.3-GHz band for portable Internet service band and can be easily reused by a terrestrial repeater for providing a terrestrial cellular service, a downlink may correspond to a frequency band of 2170 - 2200 MHz, an uplink may correspond to a frequency band of 1980 - 2020 MHz, and frequencies of carriers can be expressed as f _d] - f _d6 and f _ul - f _u6 on the assumption that a single carrier band has a bandwidth of 5 MHz.

[60] FIG. 3 illustrates a frequency band allocated by a satellite of the satellite mobile communication system illustrated in FIG. 1 for signal transmission to a CTC and a terminal.

[61] Referring to FIG. 3, communication data that is data for a communication service and broadcast data that is data for a broadcast service are transmitted through different

carriers. Since the satellite mobile communication system illustrated in FIG. 1 aims to provide both the communication service for voice and data and the broadcast service (or MBMS service), it has to appropriately use the frequency band illustrated in FIG. 2 as illustrated in FIG. 3 in order to simultaneously provide the communication service and the broadcast service.

[62] The communication service is an interactive service and the broadcast service is a unidirectional service. Thus, the satellite 110 allocates frequency bands as illustrated in FIG. 3 for signal transmission to the terminal 120 and the CTC 140. In other words, the satellite 110 allocates downlink carriers f _d] through f^ and uplink carriers f _ul through f uNd for the communication service and allocates the remaining downlink carriers f _dNd+1 through f _dN for the broadcast service. When the satellite mobile communication system is an FDD system, the satellite 110 does not transmit a signal through a frequency band of uplink carriers ^ ₊₁ through f^.

[63] Next, frequency allocation to be performed when the CTC 140 having received the signal transmitted from the satellite 110 provides the broadcast service to the terminal 120 in the urban area 170 will be described. As mentioned with reference to FIG. 1, the CTC 140 considers only downlink transmission, i.e., provides only the broadcast service. In this sense, transmission of communication service contents, such as voice and data, received from the satellite 110 to the terminal 120 in the urban area 170 can be regarded as transmission of an unnecessary signal. Thus, the CTC 140 according to the present invention removes the communication service contents such as voice and data from the signal received from the satellite 110 by performing baseband signal processing on the received signal, and then transmits only broadcast data of broadcast service contents to the terminal 120 in the urban area 170. Since the communication service contents and the broadcast service contents are transmitted through different carriers, the CTC 140 can easily transmit only the broadcast service contents by avoiding receiving carriers carrying the communication service contents such as voice and data.

[64] FIG. 4 is a flowchart illustrating a signal transmission method of a CTC according to an embodiment of the present invention. The flowchart illustrated in FIG. 4 will be described based on the frequency bands illustrated in FIGS. 2 and 3.

[65] Referring to FIG. 4, from a transmitter which can use a total frequency band including f _ul through f _uN for an uplink and f _dl through f _dN for a downlink, the CTC receives communication data that is data for an interactive communication service in a portion of a predetermined communication frequency band f _dl - f _dNd of the downlink and broadcast data that is data for a broadcast service in a portion, i.e., a first frequency band, of a predetermined broadcast frequency band f _d Nd ₊ i - fdN of the downlink in operation S410. The transmitter may be a satellite such as a geostationary satellite.

[66] The CTC allocates the received broadcast data to a portion, i.e., a second frequency band, of the same frequency band as the broadcast frequency band in operation S420 and allocates additional data to a portion, i.e., a third frequency band, of the remaining frequency band of the same frequency band as the total frequency band except for the second frequency band in operation S430. The additional data means data that is added by the CTC to the data received from the satellite by necessity. For example, the additional data may be local broadcast contents that are contents for a local broadcast service that is a broadcast service in an area where the CTC is located.

[67] In operation S440, the CTC transmits the broadcast data and the additional data to at least one terminal according to a result of the allocation.

[68] Detailed examples in which the signal transmission method illustrated in FIG. 4 is used will be described with reference to FIGS. 5 through 10.

[69] First, descriptions will be made separately with reference to FIGS. 5 and 6 for a case where carriers used by a satellite to transmit broadcast data for a broadcast service in a broadcast frequency band and carriers used by a CTC to transmit the broadcast data for the broadcast service in the broadcast frequency band are different and for a case where those carriers are the same.

[70] FIG. 5 illustrates a frequency band corresponding to a case where carriers for broadcast data transmitted by a satellite and carriers for the broadcast data transmitted by a CTC are the same as each other according to an embodiment of the present invention.

[71] Referring to FIG. 5, the CTC, which has received a signal of broadcast data transmitted by the satellite through carriers of a portion f _dNd+1 - f^ _d+Ng of the broadcast frequency band, transmits the broadcast data to a terminal through the same carriers as used by the satellite. In other words, in view of the description made with reference to FIG. 4, the 'second frequency band' allocated for the CTC to transmit received broadcast data to terminals is the same as the 'first frequency band' that is a portion of the broadcast frequency band used to transmit the broadcast data from the satellite to the CTC. The 'second frequency band' and the 'first frequency band' are frequency intervals including carriers ^ ₊₁ through f _dNd+Ng - The 'third frequency band' that is allocated to transmit the additional data to the terminals belongs to the broadcast frequency band f _dNd+1 - f _dN of the CTC, which is the same as the broadcast frequency band f _dNd+1 - f _dN of the satellite, more specifically, the frequency band f _dNd+Ng+ i - W When the CTC receives the broadcast data from the satellite, the additional data may be received together with the broadcast data through at least one carrier of the broadcast frequency band, e.g., the carriers f _dNd+ i through f _dNd+Ng used by the satellite to transmit the broadcast data.

[72] When the satellite does not use all the carriers through f _dN of the broadcast

frequency band allocated for the broadcast service in transmitting the broadcast data, the CTC transmits the additional data to the terminals by using carriers f _dNd+Ng+ i through f _dN that are not used by the satellite from among all the carriers of the broadcast frequency band, i.e., correspond to a frequency interval to which the 'third frequency band' mentioned in relation to FIG. 4 belongs. The additional data may be contents for a local broadcast service, i.e., local broadcast contents, which are created by CTCs in a sector, such as the downtown area, an area, or a country within a single beam of the satellite, specially for the sector. As such, the CTC transmits the additional data such as the local broadcast contents to the terminals by reusing the carriers f _dNd+Ng+ i through f dN that are not used by the satellite, thereby increasing total throughput of the satellite mobile communication system including the CTC.

[73] Since the CTC merely performs amplification in broadcast data processing without performing baseband signal processing, it can be easily installed. In addition, the satellite and the CTC form a single frequency network, the terminal can obtain a diversity gain by receiving a signal of broadcast data from the satellite and a signal of broadcast data from the CTC through the same carrier. Since a single carrier (or subcarrier) is used to transmit a single piece of broadcast data, the satellite mobile communication system including the CTC and the satellite can have high spectrum use efficiency.

[74] However, according to this signal transmission method, since the satellite and the

CTC form a single frequency network, the broadcast data signal received from the satellite and the broadcast data signal received from the CTC may interfere with each other if these signals are not synchronized with each other. As a result, synchronization between those signals is an issue in the signal transmission method.

[75] FIG. 6 illustrates a frequency band corresponding to a case where carriers for broadcast data transmitted by the satellite and carriers for the broadcast data transmitted by the CTC are different from each other according to an embodiment of the present invention.

[76] Referring to FIG. 6, the CTC, which has received a signal of broadcast data transmitted by the satellite through carriers through f _dNd+Ng of the broadcast frequency band, transmits the broadcast data to a terminal through carriers f _dNd+Ng+ i through f _dNd+2Ng that are different from the carriers f _dNd+1 through f _dNd+Ng - In other words, in view of the description made with reference to FIG. 4, the 'second frequency band' allocated for the CTC to transmit received broadcast data to terminals is a band fdNd ₊ Ng ₊ i - f _dNd+2N g which belongs to the same frequency band as the remaining frequency band of the broadcast frequency band f _dNd+1 - f _dN except for a portion, i.e., the 'first frequency band' f _dN d ₊ i - fdNd ₊ Ng, of the broadcast frequency band used to transmit the broadcast data from the satellite to the CTC. The 'third frequency band' that is allocated to transmit

the additional data to the terminals belongs to the broadcast frequency band f _dNd+2Ng+ i - f dN except for the same frequency band as the first frequency band f _dNd+1 - f _dNd+Ng and the second frequency band f _dNd+Ng+ i - f _dNd+2Ng from among the same frequency band as the broadcast frequency band f _dN d ₊ i - W

[77] In this case, the satellite and the CTC do not form a single frequency network. Thus, it is not necessary to synchronize a broadcast data signal received from the satellite with a broadcast data signal received from the CTC and the CTC can flexibly perform baseband signal processing for transmission of the broadcast data signal received from the satellite to the terminals.

[78] In other words, when the satellite and the CTC form a single frequency network as illustrated in FIG. 5, it is possible to prevent interference between the broadcast data signal from the CTC and the broadcast data signal from the satellite only when the CTC transmits the broadcast data signal from the satellite to the terminals. On the other hand, when the CTC transmits the broadcast data to the terminals by using different carriers than used by the satellite to transmit the broadcast data, interference does not occur between the broadcast data signal from the satellite and the broadcast data signal from the CTC even if those broadcast data signals have different contents because the terminal receive different carriers.

[79] Referring to FIG. 6, after receiving the broadcast data signal from the satellite through a carrier transmitted from the satellite, the CTC performs baseband signal processing on the received broadcast data signal and then transmits the processed broadcast data signal to the terminals through a different carrier. In general, the CTC transmits a signal to the terminals in a better transmission channel condition than in a transmission channel condition the satellite transmits a signal to the terminals because the signal transmitted from the satellite to the terminals undergoes much path loss due to a long distance between the satellite and the terminals. Thus, considering that a signal from the CTC (or CTC signal) can contain a larger amount of information than that of a signal from the satellite (or satellite signal), local broadcast contents for a local broadcast service are added to broadcast data received from the satellite as illustrated in FIG. 6 for transmission from the CTC to the terminals, thereby improving spectrum use efficiency. The amount of information provided by the CTC for a terminal is larger than that provided by the satellite.

[80] Thus, the CTC can improve its data throughput by performing higher-level modulation on the broadcast data and the additional data destined to the terminals than modulation used by the satellite for the broadcast data. For example, when the satellite modulates a signal by using quadrature phase shift keying (QPSK) and then transmits the signal to the CTC and the CTC modulates a signal by using 16-quadrature amplitude modulation (QAM) and transmits the signal to the terminals due to a good

channel condition, the CTC can also transmit local broadcast contents whose amount is 3 times that of broadcast data included in the signal received from the satellite in addition to the received broadcast data on the assumption that each carrier of the satellite and each carrier of the CTC have the same bandwidth.

[81] Like in FIG. 5, in FIG. 6, the terminals can obtain a diversity gain by receiving a satellite signal and a CTC signal at the same time. However, in FIG. 6, unlike in FIG. 5, the CTC requires a device for converting a carrier carrying the satellite signal into a different carrier for transmission to the terminals and each terminal has to have a structure of a receiver capable of receiving both the carrier carrying the satellite signal and a carrier carrying the CTC signal. As a result, a receiver having a more complex structure than in FIG. 5 is required.

[82] FIG. 7 is a constellation diagram illustrating a method of modulating a signal including broadcast data of a satellite in the case illustrated in FIG. 5.

[83] When a CTC also transmits additional data to a terminal, together with broadcast data for a broadcast service, by using a carrier used by the satellite to transmit the broadcast data, interference between a signal of the broadcast data and a signal of the additional data occurs in the terminal, resulting in degradation of the reception performance of the terminal. Thus, the CTC transmits the broadcast data received from the satellite to the terminal without adding the additional data to the broadcast data. In this case, the CTC cannot exploit an advantage of its higher data throughput than that of the satellite. Considering this point, it is desirable to use a hierarchical modulation method in order to improve spectrum use efficiency like in FIG. 5. FIG. 7 suggests the hierarchical modulation method.

[84] Referring to FIG. 7, constellations for broadcast data transmitted from the satellite, i.e., global contents, and constellations for broadcast data added by the CTC, i.e., local contents, are illustrated.

[85] In FIG. 7, the satellite transmits additional data used by the CTC, e.g., local broadcast contents, as well as broadcast data for its broadcast service. Since the satellite has to transmit a larger amount of data than in FIG. 5 to the CTC and the terminal, it uses a high-level modulation method used in the CTC. When the satellite applies the high-level modulation method used in the CTC on its broadcast data for transmission, a terminal capable of receiving only broadcast data modulated by an original modulation method of the satellite cannot receive the high-level modulated broadcast data in an area where a CTC signal cannot be received. For this reason, the hierarchical modulation method as illustrated in FIG. 7 is used. In other words, the satellite uses a higher-level modulation method than the original modulation method illustrated in FIG. 5, but transmits a signal of its broadcast data using constellations used in the original modulation method and transmits a signal of local broadcast contents for

the CTC using constellations of the high-level modulation method.

[86] For example, if the satellite can perform modulation on its broadcast data by using

QPSK for transmission and the CTC can perform data processing by using 16-QAM in FIG. 5, the satellite transmits a signal of its broadcast data and a signal of local broadcast contents for the CTC after performing 16-QAM instead of QPSK. At this time, the satellite transmits its broadcast data by using 4 constellations of QPSK as illustrated in FIG. 7 in order to obtain the same effect as when the satellite uses QPSK as illustrated in FIG. 5. The satellite also transmits local broadcast contents added by the CTC by using a constellation of 16-QAM, and thus the CTC can perform data processing by using 16-QAM. By using this hierarchical modulation method, the satellite mobile communication system can improve spectrum use efficiency in an urban area where the CTC is located when compared to the case illustrated in FIG. 5.

[87] Considering that the satellite simultaneously transmits a signal of communication data and a signal of broadcast data through a communication data carrier and a voice data carrier, but the CTC transmits only the broadcast data to a terminal without transmitting the communication data, i.e., the CTC does not use the communication data carrier of the satellite, as illustrated in FIG. 2, spectrum use efficiency can be improved by the effective usage of the communication data carrier by the CTC.

[88] FIGS. 8A and 8B illustrate cases where the CTC provide different services by using a communication data carrier of the satellite. In view of the description made with reference to FIG. 4, the 'second frequency band' is the same frequency band as the first frequency band f _dNd+1 - f _dN and the 'third frequency band' belongs to the same frequency band as the communication frequency band f _dl - f _dNd .

[89] First, a situation where services are provided as illustrated in FIGS. 8A and 8B will be described with reference to FIG. 1. In the coverage 170 of the terrestrial systems 150, when an available frequency capacity of the terrestrial systems 150 is saturated due to excessive frequency use of the terrestrial systems 150 or the terrestrial systems 150 do not operate due to a disaster, the CTC 140 provides communication data such as voice and data, i.e., a communication service, or transmits local broadcast contents. In this case, since the CTC 140 transmits a signal for the communication data or the local broadcast contents to the terminal 120 through a carrier, e.g., a carrier of a communication data signal of the satellite 110, a transmission signal of the CTC 140 interferes with a transmission signal of the satellite 110. As a result, the terminal 120 which can receive both the transmission signals experiences degradation in the performance of receiving the transmission signal of the satellite 110.

[90] Thus, the CTC 140 has to provide the communication service or a local broadcast service for transmitting the local broadcast contents to only a terminal that cannot receive the transmission signal of the satellite 110 in a coverage where the CTC 140 is

located within the coverage 170 of the terrestrial systems 150, such as an urban area. Thus, the core network 180 uses information about the strength of a satellite signal and the strength of a CTC signal in a position of each terminal and thus, if the satellite signal is weak in a position of a terminal, the core network 180 may allocate a channel of a communication data carrier of the satellite to the terminal. The use state of a frequency band will be described separately with reference to FIGS. 8A and 8B according to a type of a service provided by the CTC to a terminal by using the communication data carrier of the satellite.

[91] FIG. 8 A illustrates a frequency band corresponding to a case where the CTC provides an additional communication service by using the communication data carrier of the satellite according to an embodiment of the present invention.

[92] Referring to FIG. 8A, the CTC provides an additional communication service in addition to a communication service provided by the satellite by using communication data carriers f _dl - f _dNd that are available for transmission of communication data of the satellite. In this case, communication data carriers f _ul - f^ that are available for transmission of communication data by a terminal in an uplink for the satellite are also used to provide the additional communication service in an uplink for the CTC. When the CTC transmits and receives additional data such as voice and data for the additional communication service, it complies with an existing voice and data communication protocol provided by the terrestrial systems 150.

[93] FIG. 8B illustrates a frequency band corresponding to a case where the CTC provides a local broadcast service by using the communication data carrier of the satellite according to an embodiment of the present invention;

[94] Referring to FIG. 8B, if there is a terminal requesting local broadcast contents that are contents for a local broadcast service for a particular area from among several terminals receiving a weak satellite signal, the CTC provides additional data such as the local broadcast contents to the terminal through a communication channel allocated to the terminal by using the communication data carriers f _dl - f _dNd that are available for transmission of the communication data of the satellite. In this case, the communication data carriers f _ul - f _uNd that are available for transmission of communication data by a terminal in an uplink for the satellite are also used to transmit control information for the local broadcast service in an uplink for the CTC. Such usage is different from an existing method where broadcast data is simultaneously transmitted to all terminals by using carriers of broadcast data for a broadcast service.

[95] FIG. 9 is a flowchart illustrating a process of providing a communication service and a local broadcast service in the case illustrated in FIGS. 8 A and 8B.

[96] Referring to FIG. 9, it is determined whether the CTC transmits a signal by using the same carriers as voice and data communication carriers used by the satellite in

operation S910. If so, it is estimated whether the strength of a satellite signal is weak or strong at a terminal that is to receive the signal from the CTC in operation S920. If the strength of the satellite signal is weak, the CTC can transmit the signal by using the same carriers as the voice and data communication carriers used by the satellite. At this time, the CTC determines whether to provide an additional (voice and data) communication service or a local broadcast service in operation S930 and allocates a channel for a corresponding service.

[97] When the CTC is to provide the additional communication service, the CTC allocates a channel for the additional communication service to the frequency band f _dl - f^ of the downlink for the communication service provided by the satellite and the frequency band f _ul - f _uNd of the uplink for the communication service provided by the satellite in operation S941. When the CTC is to provide the local broadcast service, the CTC allocates a channel for the local broadcast service to the frequency band f _dl - f _dNd of the downlink and allocates a channel for the control information for the local broadcast service to the frequency band f _ul - f^ of the uplink in operation S942.

[98] FIG. 10 illustrates a frequency band corresponding to a case where the CTC uses a frequency band of an uplink for a communication service of a satellite, for a local broadcast service according to an embodiment of the present invention.

[99] Referring to FIG. 10, the CTC also transmits local broadcast contents that are different from broadcast data for a broadcast service transmitted from the satellite to a terminal by a method of broadcasting through carriers used by the satellite for the voice and data communication service, especially uplink carriers f _u] through f _uNd . In light of the description made with reference to FIG. 4, the 'second frequency band' is the same frequency band as the first frequency band f _dNd+] - f _dN , and the 'third frequency band' belongs to the same frequency band as the frequency band f _ul - f _uNd of the uplink for the communication service provided by the satellite. Here, 'additional data' indicates local broadcast contents.

[100] In this case, the CTC uses uplink carriers used by the satellite for the voice and data communication service as downlink carriers for transmission of the local broadcast contents to a terminal. In this case, at the terminal, no interference occurs because different carriers are used for a downlink signal including voice and data transmitted from the satellite and a signal including the local broadcast contents transmitted from the CTC.

[101] However, at the satellite, i.e., a receiver of the satellite, interference exists between an uplink signal of the terminal including the communication data for the communication service and a downlink signal of the CTC including the local broadcast contents and thus the performance of receiving the communication data may degrade. In spite of this shortcoming, since communication service performance desired by the

satellite can be maintained by using a complex interference canceling technique such as a multi-user detector, the degradation in the communication data reception performance at the satellite is not a big issue in the implementation of the satellite mobile communication system.

[102] So far, transmission of communication data and broadcast data by using different carriers has been described with reference to FIGS. 2 through 10. Hereinafter, a method of transmitting data of different types by using the same carrier and a corresponding frame structure will be described. Mode for Invention

[103] FIG. 11 is a flowchart illustrating a signal transmission method of a CTC according to another embodiment of the present invention.

[104] Referring to FIG. 11, the CTC receives a first frame including communication data that is data for an interactive communication service and broadcast data that is data for a broadcast service through a first carrier of a downlink from a transmitter such as a satellite in operation S1110. The CTC allocates the broadcast data to a second frame in operation Sl 120, allocates additional data to the second frame in operation Sl 130, and transmits the second frame to at least one terminal in operation S 1140, thereby supporting the broadcast service and the communication service at the same time.

[105] A frame structure illustrated in FIG. 12 can be used when the satellite mobile communication system uses full FDD.

[106] FIG. 12 illustrates a frame structure corresponding to a case where carriers transmitted by the satellite and carriers transmitted by the CTC are different from each other in FIG. 11.

[107] Referring to FIG. 12, the satellite transmits a first frame 1210 including communication data such as voice and data and broadcast data through a first carrier f _dl of a downlink. Since the quality of service (QoS) of the communication data is more important than that of the broadcast data in terms of latency, the satellite transmits the communication data prior to the broadcast data by the first frame 1210. The first frame 1210 is a downlink frame of the satellite, and an uplink frame 1220 of the satellite is composed of only communication data such as voice and data. After receiving the first frame 1210, the CTC transmits a second frame 1230 that is a downlink frame including the broadcast data received from the satellite and additional data such as local broadcast contents through a second carrier f _dl . that is different from the first carrier f _dl .

[108] Since different carriers are used for the satellite and the CTC, there is no interference between a signal of the satellite and a signal of the CTC. Thus, the satellite mobile communication system can perform flexible content transmission by using the satellite and the CTC. However, because of the use of FDD, asymmetry between an uplink and a downlink caused by communication data for a communication service that is an in-

teractive service and broadcast data of an downlink for a broadcast service that is a unidirectional service cannot be effectively considered in the satellite mobile communication system. Moreover, since different carriers (or sub-carriers) are used by the satellite and the CTC to transmit the same broadcast data, the spectrum use efficiency of the satellite mobile communication system degrades and the complexity of a receiver of a terminal for obtaining diversity in receiving the broadcast data of the satellite and the broadcast data of the CTC also increases. However, advantageously, in this case, synchronization between the satellite and the CTC is not required as in FIG. 6.

[109] FIGS. 13A and 13B illustrate frame structures corresponding to cases where carriers transmitted by the satellite and carriers transmitted by the CTC are the same as each other in FIG. 11.

[110] FIG. 13A illustrates a frame structure corresponding to a case where the carriers transmitted by the satellite and the carriers transmitted by the CTC are the same as each other and the CTC provides an additional communication service in FIG. 11.

[I l l] FIG. 13B illustrates a frame structure corresponding to a case where the carriers transmitted by the satellite and the carriers transmitted by the CTC are the same as each other and the CTC provides a local broadcast service in FIG. 11.

[112] To avoid a repetitive description between FIGS. 13A and 13B, a description will be collectively made with reference to FIGS. 13A and 13B.

[113] Referring to FIGS. 13A and 13B, first frames 1310a and 1310b that are downlink frames of the satellite have the same structure as the first frame 1210 illustrated in FIG. 12 and uplink frames 1320a and 1320b of the satellite have the same structure as the uplink frame 1220 of the satellite illustrated in FIG. 12.

[114] The CTC allocates broadcast data to a temporal position 1332a or 1332b of a second frame 1330a or 1330b that is to be transmitted through the first carrier f _dl of the satellite. The temporal positon 1332a or 1332 b is the same as a temporal position at which the broadcast data is to be transmitted in the first frame 1310a or 1310b of the satellite. The CTC then allocates voice and data for an additional communication service or local broadcast contents for a local broadcast service to the second frame 1330a or 1330b. At this time, the CTC removes communication data such as voice and data transmitted from the satellite and then allocates additional data to the second frame 1330a or 1330b at the same temporal position 1331a or 1331b as temporal position for the communication data in the first frame 1310a or 1310b. FIG. 13A illustrates a frame structure corresponding to a case where the additional data is voice and data for an additional communication service and FIG. 13B illustrates a frame structure corresponding to a case where the additional data is local broadcast contents for a local broadcast service.

[115] Here, since the additional data interferes with or is interfered with by the communication data of the satellite, transmission of the additional data by the CTC can be assumed to be executed by a method of communication instead of broadcasting. Under this assumption, the additional communication service or the local broadcast service is not provided to all terminals within a coverage of the CTC. Instead, after channels for the communication service of the satellite are searched for, from among which a channel that is also available to the CTC is allocated to only terminals that cannot receive a satellite signal and the additional communication service (a supplementary communication service of the CTC) or the local broadcast service is provided through the channel.

[116] In this case, since the CTC uses a broadcast data carrier used by the satellite, broadcast data can be transmitted through a single carrier. A terminal can obtain diversity by receiving a satellite signal and a CTC signal by using a simple receiver. Furthermore, the CTC effectively transmits additional data through a carrier used by the satellite, thereby improving the spectrum use efficiency of the satellite mobile communication system.

[117] However, in spite of those advantages, synchronization between the satellite signal and the CTC signal is required to avoid interference between the two signals in the case of the frame structures illustrated in FIGS. 13A and 13B.

[118] FIG. 14 is a flowchart illustrating a process of providing a communication service and a local broadcast service in the cases illustrated in FIGS. 13 A and 13B.

[119] Referring to FIG. 14, the CTC determines whether the satellite mobile communication system including the CTC transmits communication data and broadcast data by using the same carrier in operation S 1410. If so, the CTC determines whether the same carrier as used by the satellite for a communication service is used in operation S 1420. If so, it is estimated whether the strength of a satellite signal is strong at a terminal in operation S 1430. If the strength of the satellite signal is estimated as weak, the CTC determines whether an additional (voice and data) communication service or a local broadcast service is to be provided in operation S 1440 and allocates a channel for a corresponding service.

[120] If the CTC provides the additional communication service, the CTC allocates a channel for the additional communication service to a downlink for a communication service provided by the satellite and an uplink for the communication service provided by the satellite in operation S 1451. If the CTC provides the local broadcast service, the CTC allocates a channel for a local broadcast service to a downlink and a channel for control information for the local broadcast service to an uplink in operation S 1452.

[121] FIG. 15 illustrates frame structures corresponding to a case where a satellite mobile communication system is in a half- FDD mode in FIG. 11.

[122] Referring to FIG. 15, frame structures in a downlink and an uplink for a case where the satellite mobile communication system is in a half- FDD mode are illustrated. Basically, the satellite mobile communication system is FDD system, but transmits a signal of a satellite and a signal of a CTC by using time division multiplexing access (TDMA).

[123] In other words, referring to FIG. 15 together with FIG. 11, a predetermined downlink signal transmission interval 1501 is divided into a satellite signal transmission interval

1502 and a CTC signal transmission interval 1503 and the satellite initially transmits a first frame 1510 including communication data and broadcast data through a downlink carrier, i.e., the first carrier f _d] . The CTC receives the first frame 1510 during the satellite signal transmission interval 1502 that is a specific period of time within the downlink signal transmission interval 1501. The satellite then stops signal transmission at the end of the satellite signal transmission interval 1502.

[124] The CTC having received the satellite signal during the satellite signal transmission interval 1502 removes communication data of the satellite signal and transmits only the broadcast data to a terminal at a moment at which the satellite stops signal transmission. In other words, the CTC allocates the broadcast data to a time interval

1503 following the satellite signal transmission interval 1502 within the downlink signal transmission interval 1501 in order to transmit the broadcast data to the terminal.

[125] Since the data capacity of the CTC signal is larger than that of the satellite signal, the CTC can transmit the broadcast data of the satellite to the terminal during a shorter interval 1521 than a time interval 1511 during which the satellite transmits the broadcast data. If the data capacity of the CTC signal is larger than the amount of broadcast data received by the CTC from the satellite, the CTC additionally allocates local broadcast contents to a time interval 1522 following the interval 1521 to which the broadcast data is allocated within the downlink signal transmission interval 1501 in order to transmit the local broadcast contents to the terminal.

[126] In the uplink, only the communication data may be transmitted by the terminal.

Because the satellite mobile communication system is an FDD system, spectrum inefficiency may be caused by the non-use of the remaining intervals 1532 and 1540 except for an interval 1531 allocated to the communication data.

[127] Referring to FIG. 15, the satellite and the CTC transmit data during different time intervals while using the same carrier, thereby obtaining diversity like when different carriers are used for transmission. Moreover, since broadcast data is transmitted by using the same carrier, high spectrum efficiency can be obtained in the satellite mobile communication system and the terminal can use a simple- structure receiver.

[128] However, in this case too, synchronization has to be made between the satellite and the CTC in order to accurately match a moment at which the satellite stops signal

transmission with a moment at which the CTC transmits a signal. [129] FIG. 16 illustrates a CTC 1600 that simultaneously supports a broadcast service and a communication service according to an embodiment of the present invention. [130] Referring to FIG. 16, the CTC 1600 includes a reception unit 1610, a broadcast data frequency allocation unit 1620, an additional data frequency allocation unit 1630, and a transmission unit 1640. [131] From a transmitter which can use a total frequency band including an uplink and a downlink, the reception unit 1610 receives communication data in a portion of a communication frequency band of the downlink and broadcast data in a first frequency band that is a portion of a broadcast frequency band of the downlink. The reception unit 1610 may be a common receiver having antenna capable of receiving a signal of the transmitter. [132] The broadcast data frequency allocation unit 1620 allocates the received broadcast data to a second frequency band that is a portion of the same frequency band as the broadcast frequency band. [133] The additional data frequency allocation unit 1630 allocates additional data to a third frequency band that is a portion of the remaining frequency band of the same frequency band as the total frequency band except for the second frequency band. The additional data may be local broadcast contents that are contents for a local broadcast service. [134] The transmission unit 1640 transmits the broadcast data and the additional data to at least one terminals. [135] Details about a method of allocating the broadcast data and the additional data at the

CTC 1600 refer to the descriptions made with reference to FIGS. 4 through 10. [136] FIG. 17 illustrates a CTC 1700 that simultaneously supports a broadcast service and a communication service according to another embodiment of the present invention. [137] Referring to FIG. 17, the CTC 1700 includes a reception unit 1710, a broadcast data frame allocation unit 1720, an additional data frame allocation unit 1730, and a transmission unit 1740. [138] The reception unit 1710 receives a first frame including communication data and broadcast data through a first carrier of a downlink from a transmitter. The reception unit 1710 may be a common receiver having antenna capable of receiving a signal of the transmitter. [139] The broadcast data frame allocation unit 1720 allocates the broadcast data to a second frame. Such allocation means temporally allocating the broadcast data to the second frame that secures a predetermined time interval. [140] The additional data frame allocation unit 1730 allocates additional data to the second frame. The additional data may be local broadcast contents that are contents for a local

broadcast service.

[141] The transmission unit 1740 transmits the second frame to at least one terminal.

[142] Details about a method of allocating the broadcast data and the additional data at the CTC 1700 refer to the descriptions made with reference to FIGS. 11 through 15.

[143] The present invention can be embodied as a computer-readable code on a computer- readable recording medium. The computer-readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of computer-readable recording media include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves. The computer-readable recording medium can also be distributed over network of coupled computer systems so that the computer- readable code is stored and executed in a decentralized fashion.

[144] While the present invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. Accordingly, the disclosed embodiments should be considered in a descriptive sense not in a restrictive sense. The scope of the present invention will be defined by the appended claims, and differences within the scope should be construed to be included in the present invention.