WO2005050992A1

WO2005050992A1 - Intelligent broadcasting system for providing broadcasting services with multi-level quality

Info

Publication number: WO2005050992A1
Application number: PCT/KR2004/003005
Authority: WO
Inventors: Byeong Yong Lim; In Soo Yoon
Original assignee: Miwagi Inc.
Priority date: 2003-11-19
Filing date: 2004-11-19
Publication date: 2005-06-02

Abstract

The present invention relates to a method and apparatus for providing a user with a multi-level quality service in a broadcast servicing system. A broadcast servicing system for providing a multi-level quality service according to the present invention comprises a multi-level video encoder, a multi-level audio encoder, a data encoder, a multiplexer, an encryptor, a user quality management system, a user quality authorization system, an encryption key generator, a multi-level video decoder, a multi-level audio decoder, a data decoder, a demultiplexer, a decryptor, an access quality control system, a smartcard, a degrader, and a demultiplexer between channels.

Description

INTELLIGENT BROADCASTING SYSTEM FOR PROVIDING BROADCASTING SERVICES WITH MULTI-LEVEL QUALITY

Technical Field The present invention relates to a broadcasting service system, and more particularly, to a broadcasting system which provides a user with a piece of broadcast content with two or more quality levels and provides the user with broadcast content of an authorized quality according to a right authorized to the user.

Background Art Conventionally, due to an inherent broadcast characteristic in which broadcast data ofthe same quality reach all users indiscriminately through a single medium called a radio wave that propagates through the air, when broadcast equipment is installed, forwarding costs do not increase even though the number of users increases. Furthermore, in the case of analog broadcasting, there is no room for the introduction of the concept of differentiated broadcasting service quality. Even in digital broadcasting, although service quality is lowered, the cost for a broadcast network cannot be reduced. As such, a system for providing users with a piece of broadcast content with different quality levels and demanding differentiated payments to the users has not been provided thus far. Also, in the case of sky wave television broadcasting or sky wave radio broadcasting, financial resources for broadcasting have increased through advertising revenues or uniform television subscription fees. Furthermore, pay-per-view broadcasting such as satellite television or CATV (Community Antenna Television), an additional set-top box for receiving broadcast data has to be used, and a conditional access system (CAS) for controlling the forwarding of broadcast data, which corresponds to a given channel, to a user's television receiver according to a fee that is paid by the user has to be installed in the set-top box. That is, in the prior art, one source data is forwarded through one channel, and the conditional access system controls whether or not to allow a user to receive broadcast data by channel. As such, conventional broadcasting services have merely a simple billing system in which a television subscription fee is simply imposed to a user based on the content a user is allowed to see and hear, i.e., whether or not the user sees and hears through a specific channel. If a broadcasting service having a variety of quality levels is to be provided for the same content by utilizing this technology, however, it is required that a high-quality channel and a low-quality channel be provided separately. This inevitably results in the consumption of valuable frequency resources. With the development of wireless communication technology, even in the field of broadcasting, digital ground wave broadcast technologies such as satellite digital broadcasting or FfDTV as well as existing analog broadcasting have become commercialized. Furthermore, a ground wave or satellite digital multimedia broadcasting (DMB) technology for serving mobile users through a portable device has been developed. Satellite DMB broadcasting has been rapidly rising as next- generation multimedia technology such as IMT-2000. It is thus expected that a broadcasting service can be provided through a device which is integrated into a dedicated broadcast receiving apparatus, a mobile phone, a PDA and the like. That is, it is expected that a variety of devices such as mobile phones and PDAs as well as conventional television sets or radios can serve as broadcast receivers, and the area of the broadcasting services will significantly expand. More particularly, in the case of DMB, since a limited frequency spectrum is used, radio frequencies are important resources and are also applied to mobile devices. Accordingly, the quality of service provided to a user is an important factor in such an actual broadcasting service. Under the present circumstances, there is an urgent need for a method and apparatus in which a piece of broadcast content is serviced to a user at a variety of quality levels, and payment is demanded accordingly, while efficiently using broadcast channels (i.e., almost no additional investment in a network). A conventional wired Internet broadcasting service uses a method of forwarding differentiated data to a user. However, although conventional wired Internet broadcasting services also have the property of 1 : multi user communication, it is fundamentally different in its technical construction from a wireless broadcasting service in which a number of users are serviced while sharing a radio wave as a single transmission medium. That is, in the case of a wired Internet broadcasting service, while broadcast content is forwarded from a forwarding apparatus to a subscriber, forwarding networks are sequentially diverged. After the broadcast content reaches the subscriber's terminal, the subscriber uses a dedicated subscriber network. On the contrary, in a wireless broadcasting service, subscribers share common limited transmission means called a radio wave from a forwarding apparatus up to the last subscriber terminal. In other words, a conventional wired Internet broadcast employs a method in which data of the highest quality is transmitted in such a manner that data of a higher priority is first forwarded, considering available bandwidth on a transmission line from a broadcast content transmission apparatus to a user terminal or the processing capability of a receiving device. Consequently, although quality received by users varies, this method is not an intentional and managed service differentiation method. Furthermore, in order to improve the service quality, there is a problem in that forwarding and processing ability have to be enhanced through additional investment in a subscriber network, and an access network between a subscriber network and a main network, etc. so that data of a lower priority can be forwarded. Moreover, if an access network for multimedia and broadcasting, such as an ADSL network, is not constructed in a terminal, a common Internet access service has only the characteristics of a 1 :1 communication service. As such, in order to enhance the service quality, a service provider has to improve the transmission ability through additional investment in the entire network including the subscriber network or the access network as well as the main network. Therefore, this method corresponds to a structure in which necessary investment has to be made only when the intention of a subscriber who wants to receive a high quality service with payment of a subscription fee has been confirmed. In this case, once the investment has been made to such a user so that the forwarding apparatus and receiving apparatus technically receive a high quality service, it is not necessary to provide a low quality service while intentionally limiting a possible high quality service. As a result, this structure has a transmission/reception structure in which data of a low resolution can or cannot be forwarded selectively through some lines. However, a digital TV broadcasting service or a DMB broadcasting service is different in its network structure from that of Internet. Thus, since all subscribers who receive the same source data share the same transmission network, it is impossible to adopt the aforementioned method. In some cases, there is a case where an access service network configuration is the same as the above, but an Internet broadcasting service provider who uses such a network differentiates an information use fee, while providing services of a high quality and a low quality through the same network. In this case, however, since separate content is provided through separate channels, this method employs a method in which a separate transmission line is used. Accordingly, this method has a structure in which the burden for a transmission line or transmission equipment of a main network and an access network grows heavier. A radio wave broadcasting service uses one public medium called a radio wave within space. In this case, since transmission lines or transmission equipment cannot be differentiated, a forwarding method and the structure of a receiver have to be managed and/or controlled. From the standpoint of a receiver for a digital broadcasting service, in order to meet a customer's need to use content of a low quality at a low cost, the above method can be used sometimes even when an expensive receiver is used. More particularly, in the case of a portable broadcasting service, if it is intended to lower the entry barrier to the portable broadcasting service by utilizing devices having a limited motion picture processing ability, such as conventional mobile phones, camcorders or digital cameras, there is no reason to purchase content of a high quality at a high cost. In this case, there is a need for a method for utilizing a conventional display device or power supply unit by connecting only an inexpensive receiving module excluding a separate display device or power supply unit. Meanwhile, from the standpoint of a broadcasting service provider, it is not guaranteed that an external receiver can be used together with a device having a limited motion picture processing ability. In this connection, it is possible to practice a low fee system only when a receiver, which is owned by a user who has selected a low-quality service, is managed and/or controlled so that it cannot be used to receive a high quality service. In a DMB service in which a wireless section is used as a transmission medium and investment is not made in a network in proportion to increases in the number of subscribers, if services of a variety of quality levels can be provided only with the same investment in a network without using additional bandwidth, and this service providing structure can solve anxieties of a broadcasting service provider and can be managed and/or controlled to implement a service differentiation policy in a safe manner, it is possible to mitigate the barrier of subscription and increase the number of subscribers by differentiating payments depending on differentiated quality levels. Accordingly, there is an urgent need for a method and apparatus in which broadcasting services of various quality levels can be provided to users, while broadcasting is performed up to a receiving terminal as the same data. Currently, in a broadcast set-top box, a conditional access system (CAS) controls the reception of subscribers. An integral factor of the CAS is cryptography. Generally, in the case of an analog mode, cryptography techniques employing a scrambler have been used, and in the case of a digital mode, cryptography techniques using an encryption key have been used. Furthermore, a decryptor on a receiver side includes a decryption algorithm for decrypting a received signal. In the process of such cryptography, a secure processor that generates a decryption key, which is required by a decryptor, plays an important role. This secure processor is also called a conditional access device or a CAS chip. This conditional access device can be provided as a part of a smart card in a detachable manner, or can be attached as a part of the hardware of a receiver. Source data are usually scrambled using an 8-byte encryption key. A decryption key corresponding to the encryption key is called a control word. The control word is encrypted as 128 bytes by means of a RSA key, and is then transferred to a receiver or a smart card of the receiver. The control word is changed every few minutes. Furthermore, the control word itself is the same to every receiver, but is different by channel or program. A control word encrypted in accordance with RSA is called an entitlement control message (ECM). ECM is a control word, which is encrypted as a password specific to an individual conditional access system. Thus, an additional ECM decryption key for decrypting the control word has to be transferred. That is, a decryption key capable of decrypting a decryption key being a password decryptor is an ECM decryption key. This ECM decryption key is periodically changed in such a manner that a message is sent to a conditional access system, usually after one month elapses. Frequently, in order to enhance security, an ECM decryption key can be transferred to a conditional access system more often. However, when an ECM decryption key is sent every month, a decryption key, which is different by conditional access system, is sent, and is thus individually addressed. As such, a message, which entitles a user a reception right, is called an entitlement management message (EMM). A subscriber authorization system on a sender side receives an authorization request from a subscriber management system that stores the identification number of a smart card, a user profile and the like to generate an EMM, and transmits the generated EMM to a conditional access system through digital multiplexing. That is, an EMM is different by subscriber in principle. An EMM can be sent to all subscribers who are located in a given region. A conditional access system can find an ECM decryption key, which is addressed to itself, by using a built-in algorithm. The built-in algorithm is thoroughly protected. The ECM decryption key can be changed more often, if needed. Accordingly, if a conditional access system decrypts an EMM to find an ECM decryption key being a RSA key, the found ECM decryption key can be used to find a decryption key or descrambler by decrypting the ECM for approximately one month. Basically, a reception right in a wired broadcasting service exists in a conditional access system. If the conditional access system is constructed in the form of a smart card, a user can see and hear broadcasts through any receiver only by inserting the smart card. However, in order for the conditional access system to be used in a given receiver, that is, in order to assign a subscription right by receiver, it is required that a serial number be recorded into the receiver so that it can be used to drive the conditional access system. That is, the conditional access system includes an algorithm for extracting a decryption key. However, thus limit of subscriptions according to the prior art is controlled by the channel or program. Further, in order to provide the same broadcast content with a variety of quality levels, this system has lots of problems due to the broadcast bandwidth used. That is, the conventional technology limits only whether or not to allow a user to receive broadcast data.

Brief Description ofthe Drawings FIG. 1 shows a configuration showing the interconnection between a broadcast apparatus and a broadcast receiving apparatus. FIGS. 2a and 2b are block diagrams shown to explain a method of providing multiple quality levels of service in a broadcasting service according to an embodiment ofthe present invention. FIG. 3 is a table shown to explain a multi-level encoding process. FIGS. 4a and 4b are block diagrams of a broadcasting system that limits the level of service quality of broadcast data provided to a user by controlling the encryptor and the decryptor according to an embodiment ofthe present invention. FIGS. 5a and 5b are views showing a data machining process according to the embodiment of FIG. 4. FIGS. 6a and 6b are block diagrams of a broadcasting system that limits the service quality level of broadcast data, which is provided to a user, according to a demultiplexing control policy according to an embodiment ofthe present invention. FIGS. 7a and 7b are views illustrating a data machining process according to the embodiment of FIG. 6. FIGS. 8a and 8b are block diagrams of a broadcasting system that limits service quality levels of broadcast data, which are provided to a user according to a demultiplexing control policy according to an embodiment ofthe present invention. FIG. 9 is a conceptual diagram illustrating a data machining process in a broadcasting system that limits the service quality level of broadcast data provided to a user, by using basic data and displacement data according to an embodiment of the present invention. FIG. 10 is a conceptual diagram illustrating a data machining process in a broadcasting system that limits the service quality level of broadcast data, which are provided to a user, by using data by quality level according to an embodiment of the present invention. FIG. 11a is a conceptual diagram illustrating a data machining process in a broadcasting system that limits the service quality level of broadcast data, which are provided to a user, by using a quality degrader in a receiving apparatus according to an embodiment ofthe present invention. FIG. l ib is a block diagram of a broadcast receiving apparatus that limits a service quality level of broadcast data provided to a user by using a quality degrader according to an embodiment of the present invention. FIG. l ie is a block diagram of a broadcast receiving apparatus for limiting the illegal use of a broadcast receiving apparatus by a user according to an embodiment of the present invention. FIG. l id is a block diagram of a broadcast receiving apparatus for limiting the illegal use of a broadcast receiving apparatus 1130 by a user according to another embodiment ofthe present invention. FIGS. 12a and 12b are block diagrams of a broadcasting system that adopts a limit of a service quality level of broadcast data by transmission channel according to an embodiment ofthe present invention.

Disclosure of Invention Technical Questions The present invention is conceived to meet a new need in wired/wireless broadcasting services. An object of the present invention is to provide a method and apparatus for servicing multiple quality levels of broadcast to a user in a wireless broadcasting service. Another object of the present invention is to provide a method and apparatus in which when source data are video data, the service quality level provided to a user is classified based on the number of pixels, the number of colors, the number of frames per second and a compression rate of video data, when the source data are audio data, a service quality level provided to a user is classified based on the number of samples per second, the number of bits per second and a compression rate of audio data, and when the source data are data, a service quality level provided to a user is classified based on the type of information, whereby users are differently billed based on the above information. A further object of the present invention is to allow a subscriber to access one quality level of broadcast data among a plurality of quality levels by overcoming simple limitations on allowances or inability of reception ofthe broadcast data. A still further object of the present invention is to provide a multiple quality levels of service in which differentiated prices are applied to users even in the same program channel in a broadcasting service and to construct a variety of billing systems suitable for the characteristics of a given user. A still further object of the present invention is to effectively preclude a user from having access to an unauthorized level of service quality through a combination of a multi-level decryption key, a decoding control policy and a demultiplexing control policy, or through the use of a controllable quality degrader, which can be arbitrarily manipulated by the user. Through this, according to the present invention, a broadcasting service provider can maximize profits for a short time, and revenue can be increased by inducing customers who use a low quality level of service to use a high quality level of service for a long time. A still further object of the present invention is to allow an individual user to reduce their cost burden by practicing an economic fee system corresponding to differentiated quality levels. A still further object of the present invention is to provide a content protection method in which a user is prevented to access content of an unauthorized level of service quality by using a method such as a multi-level encryption key, a decoding control policy, a demultiplexing control policy, a quality degrader and the like.

Technical Solutions The simplest embodiment, which can be considered to accomplish the above objects, is a method in which data having different levels of quality by channel for one broadcast data is broadcast, and access to a given channel is limited by user, as in the prior art. For example, full color of 18 frames can be broadcast through channel 1 , full color of 9 frames can be broadcast through channel 2, and black and white color of 9 frames can be broadcast through channel 3. Furthermore, a conditional access system (CAS) controls access to each channel by user. According to the present embodiment, since the conventional CAS, etc. can be used almost as it is, there is an advantage in that a system can be easily implemented. However, there is a disadvantage in that a channel can be wasted because broadcast channels corresponding to the number of quality levels, which have to be supported, have to be used. More particularly, in a wireless environment, an efficient use of a radio frequency bandwidth is very important. Thus, this embodiment has many problems. In order to accomplish the above objects, a method for providing multiple quality levels of service in a wireless broadcasting service according to the present invention includes a transmission apparatus for compressing, multiplexing and encrypting video, audio and data signals, and a broadcast receiving apparatus for decrypting and demultiplexing data received in wireless, and decoding the data into the video, audio and data signals. The transmission apparatus includes a video encoder for compressing a video signal, an audio encoder for compressing an audio signal, a data encoder for producing a data signal in the form necessary for transmission, a multiplexer for multiplexing the signals, an encryptor for encrypting a signal, a transmitter for transmitting a wireless signal, a user quality management system for managing information on a user and managing billing depending on the level of service quality of a user, and a user quality authorization system for using service information received from the user quality management system to generate a multi-level decryption key, a demultiplexing control policy and a decoding control policy, and then transferring them to a receiving apparatus in wireless or over a telephone channel. A sender side transmits broadcast data that are constructed to be replayed as a plurality of quality levels for the same piece of broadcast content. A receiver side receives the broadcast data, and allows a user to replay only data of a given quality level, which is authorized to the user. In this time, the user quality authorization system distributes an access quality control policy (data), which indicates what level of service quality is authorized to a user according to the rights of the user, to the receiver side through a broadcast control channel. Furthermore, the access quality control policy can be distributed off-line, can be set to a give level of service quality when a receiver is fabricated, or can be distributed from the user quality authorization system depending on the communication mode (on-demand mode). The access quality control policy is data on the quality level with which a user can access broadcast data. The access quality control policy will be described in detail later. It is to be noted that the user quality management system and the user quality authorization system according to the present invention are distinguished from the prior art in which only determination as to whether or not to allow a user to receive broadcast data can be made simply for a broadcast channel due to the technical structure of the sender side or receiver side. In the prior art, a piece of broadcast content can be received as only one quality level. Accordingly, a system for determining only whether or not to allow a user to receive broadcast data is used. On the contrary, the user quality management system and the user quality authorization system of the present invention are adapted to determine which one of a plurality of reception quality levels of broadcast data that are provided to a receiver or a user through a broadcast network and can be received by the receiver would be allowed for a user to access. The broadcast receiving apparatus includes a receiver for receiving a wireless signal, a decryptor for decrypting an encrypted signal, a demultiplexer for demultiplexing audio and data signals, a video decoder for decoding a video signal, an audio decoder for decoding an audio signal, a data decoder for decoding a data signal, and an access quality control system for allowing a user to access a desired one of two or more service quality levels, which are provided from the sender side, for the same content. The access quality control system of the present invention has a function different from the authorization function of a conventional conditional access system in which it is just simply determined whether a user or receiver has a right to receive a broadcast through a broadcast channel in a case where broadcast data of only one quality level can be received due to the technical structures of the sender side or receiver side. The access quality control system also determines which one of a plurality of reception quality levels for the same source data would be allowed for a user to access. That is, the access quality control system according to the present invention stores information on determination as to which one of a plurality of quality levels associated with one broadcast data would be allowed for a subscriber to access. It is thus different from the conventional conditional access system for determining only whether or not to allow a user to access broadcast data. - Furthermore, according to an aspect of the present invention, a broadcast receiving apparatus can be constructed in the form of a smart card from which a portion or all of a conditional access system or an access quality control system can be easily detached. According to another aspect of the present invention, a broadcast apparatus can include a multi-level encoder for encoding one source data into multiple quality levels to generate a plurality of multi-level encoded data, a multiplexer for multiplexing the multi-level encoded data to generate multiplexed data, and a transmitter for broadcasting the multiplexed data. According to still another aspect of the present invention, a broadcast apparatus can include a multi-level encoder for encoding one source data into multiple quality levels to generate a plurality of multi-level encoded data, and a transmitter for broadcasting the multi-level encoded data through different broadcast channels. According to another aspect of the present invention, a broadcast receiving apparatus can include a receiver for receiving broadcast data containing a plurality of multi-level encoded data, an access quality control system for controlling a data replayer according to an access quality control policy, which indicates which quality level of broadcast data in association with the broadcast data would be allowed for a user to access, and a data replayer for reproducing broadcast data of a given quality level, which is authorized to the user, by using the multi-level encoded data, based on the access level control information. According to still another aspect of the present invention, a broadcast receiving apparatus can include a channel demultiplexer for receiving multi-level encoded data, which is broadcast through different broadcast channels, and demultiplexing the multilevel encoded data among the channels to restore original source data. Multi-level encoding will be described in detail later. According to an aspect of the present invention, an intelligent broadcasting system can include a broadcast receiving apparatus having a degrader for degrading broadcast data as broadcast data of a predetermined quality, and a user quality management system for demanding payment at a given low price for a user who receives broadcast data of a low quality, by using the broadcast receiving apparatus. According to still another aspect of the present invention, a broadcast receiving apparatus can include a receiver for receiving broadcast data, and a quality degrader for degrading the broadcast data as broadcast data of a predetermined quality level. According to the present invention, a broadcast receiving apparatus can further include a serial number comparison unit for comparing the serial number of a low quality level dedicated receiving apparatus and the serial number of a conditional access system for use in the receiving apparatus, and allowing replay of the broadcast data only when the two serial numbers coincide with each other. According to the present embodiment, if a broadcast receiving apparatus which is adapted to replay broadcast data as only data of a predetermined quality level compatible with the fee paid by a subscriber, is used, it degrades the quality of received broadcast data as a predetermined quality level, so that the subscriber can access only broadcast data of a quality corresponding to the fee. According to still another aspect of the present invention, a broadcast receiving apparatus can include a receiver for receiving broadcast data, an access quality control system for controlling a quality degrader according to an access quality control policy, which indicates which one of two or more receiving quality levels associated with the broadcast data would be allowed for a user to access, and the quality degrader for degrading the broadcast data as broadcast data of a given quality level, which is authorized to the user, under the control of the access quality control system. The access quality control system can determine whether or not to operate the quality degrader as to the broadcast data. Furthermore, the quality degrader can degrade the broadcast data by using a plurality of degradation modes, and the access quality control system can control the quality degrader about one of the plurality of degradation modes that will be performed by the quality degrader. According to another aspect of the present invention, in a broadcasting service for differentiating receiving quality levels, it is possible to prevent illegal reception of broadcast data of a high quality level only with a low fee by means of an authorization quality level comparison unit that enhances security through the use of a serial number of a broadcast receiving apparatus According to still another aspect of the present invention, a broadcast receiving apparatus allows a user to access broadcast content through at least one of a plurality of quality levels associated with a piece of broadcast content. To this end, the broadcast receiving apparatus includes an input unit for allowing a user to select one of a plurality of quality level modes. Furthermore, information on the selection of the user can be transferred to a user quality management system on the sender side so that it can be used as basic information for billing, etc.

Best Mode for Carrying Out the Invention Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a configuration showing the interconnection between a broadcast apparatus and a broadcast receiving apparatus. A broadcast apparatus 101 broadcasts broadcast data to a broadcast receiving apparatus 102 through a broadcast network 103. Then, the broadcast receiving apparatus 102 provides a user with the received broadcast data by playing the same. The broadcast network 103 may be a wired/wireless broadcast network or an analog/digital method. The broadcast receiving apparatus 102 includes variety of devices such as dedicated reception terminals for satellite DMB, mobile phones, PDAs, or the like a capable of receiving broadcast data, besides conventional receiving apparatus such as televisions or radios. FIGS. 2a and 2b are block diagrams shown to explain a method of providing multiple quality levels of service in a broadcasting service according to an embodiment of the present invention. A broadcasting system according to the present invention comprises a broadcast apparatus 210 and a broadcast receiving apparatus 220. The broadcast apparatus 210 comprises multi-level encoders 211, 212, and 213, a multiplexer 214, an encryptor 215, and a transmitter 216, a user quality management system 217, a user quality authorization system 218 and an encryption key player 219. The multi-level encoders 211, 212, and 213 encode source data into multiple levels to generate multi-level encoded data. The multi-level encoders 21 1, 212, and 213 are at least one selected from a group consisting of a multi-level video encoder 211, a multi-level audio encoder 212 and a data encoder 213. For example, in case of audio broadcast, only the multi-level audio encoder 212 is included. In case of moving picture broadcast, the multi-level video encoder 21 land the multi-level audio encoder 212 may be included. The multi-level audio encoder 212 encodes not only voice data but also all the audio data. FIG. 2 shows an event including the multi-level video encoder 21 1, the multi-level audio encoder 212 and the data encoder 213 for convenient explanations. The multi-level video encoder 21 1 serves to encode video signals into multi- levels. The service quality of video signal is determined based on the number of pixels, the number of colors to be used, the number of frames per second and a compression rate of video data. The multi-level video encoder 211 encodes video signals into multi-levels by considering the service quality like above. Multi-level coding means that broadcast data are coded while being divided according to a plurality of service quality levels. A coding method can include a method of encoding broadcast data into basic data and displacement data, and a method of encoding broadcast data into data of plural quality levels. The method of encoding the broadcast data into data of the plural quality levels means that one source broadcast content is generated (encoded) into broadcast data of two or more quality levels. For example, in the case of audio data, 6-bit sampled source audio data are encoded into audio data of three quality levels including 16-bit sampled, 12-bit sampled and 8-bit sampled audio data. An example of the method of encoding audio data into data of plural quality levels may include a method in which the audio data are encoded into multiple quality levels such as a basic pixel number, a double pixel number, a triple pixel number, etc. in the case of three levels of service quality, and is then transmitted. In the number of colors used, service quality can be classified into 8 bits, 16 bits and 24 bits per pixel. In the number of frames per second, coding of a frame unit such as I, P and B is possible if a compression algorithm such as MPEG is used. It is thus possible to separate service quality levels through the use of the compression algorithm. Even when there is no separation between frames such as motion JPEG, replayed frames can be arbitrarily grouped depending on the number of frames replayed. Therefore, it can be used in multiple quality level encoding for which the present invention has sought. In a compression rate of a screen, multi-level encoding is possible, such as basic picture quality, medium picture quality and high picture quality. In this case, data of each of the quality levels can be replayed as data of corresponding quality level on the receiver side. The method of encoding broadcast data into the basic data and the displacement data will be described in detail later with reference to FIG. 3. The multi-level audio encoder 212 serves to transmit audio signals by compressing the same. The service quality of audio signal is determined based on the number of samples per second, the number of bits per sample and a compression rate of audio. A multi-level audio encoder 212 encodes an audio signal into multiple quality levels considering this service quality level, and then transmits the encoded audio signal. For example, in the case of three levels of service quality, the audio signal can be encoded into multiple quality levels, such as audio of below 8kHz, audio from 8kHz to 22kHz, audio from 22kHz to 44kHz in the number of samples per second. The data encoder 213 serves to compress a data signal or multiply the data signal by application. Information used in the data encoder 213 can include information such as captions and hypertext for implementing interactive TV broadcasting. Even the data encoder 213 can encode service quality levels by application with them being classified. The multiplexer 214 multiplies multi-level encoded data received from the multi-level video encoder 211, the multi-level audio encoder 212 and the data encoder 213 and transmits the same to the encryptor 215. The encryptor 215 encrypts data and transmits the encrypted data. An encryption mode may include DES (Data Encryption Standard), AES (Advanced Encryption Standard), RSA or simple scrambling. An encryption key for encryption can be assigned from an encryption key player 219, which is controlled by a subscriber authentication system and/or a user quality authorization system 218. The user quality management system 217 manages information relating to the receiving quality for one source data, which is authorized to a user in association with the user's identifier, and performs billing depending on quality level. The user quality management system 217 manages a user identifier, which becomes a basis for billing and a subject for distribution, such as a serial number of a broadcast receiving apparatus, a serial number of a conditional access system, personal information of a user or the like, in association with the quality level applied to a user, and performs billing depending on the quality level in cooperation with a user quality authorization system. The user quality management system 217 can grant service quality levels, which are composed of several combinations depending on characteristics such as channel and time. For example, it is possible to select and use a service quality desired by a user by granting a service quality composed of a combination such as (basic pixel number, 24-bit color) or (double pixel number, 8-bit color) for one channel. Moreover, if a user requests a service quality level in an on-demand form and updates the user quality management system, the user quality management system 217 can grant the service quality requested by the user to the user, or the user can arbitrarily select a desired service quality level, record the selected service quality level, and then periodically transfer this information to the user quality management system. If bi-directional access is impossible, a user can access a web page of a broadcasting service provider through the Internet and then log in the web page for user authentication, or the user can request service over the telephone. Next, the user can set settings regarding a desired service quality level. This setting is input to the user quality management system 217. For example, if data of a high quality, a middle quality and a low quality are provided for a piece of broadcast content, a user can select the middle quality and thus enjoy broadcast content at a low price. Furthermore, a user can select a high quality level in return for higher cost, and thus enjoy broadcast content of high quality. In response to this, an access quality control system 230 of a broadcast receiving apparatus (or user terminal) 220 performs a control operation according to user access control rights, which indicate which one of two or more service quality levels, which can be received by channel, is authorized to a user, i.e., an access quality control policy. This control operation can be performed according to an access quality control policy, which is distributed in real time by the user quality authorization system 218, or can be performed by referring to a stored access quality control policy. The access quality control system 230 includes an access quality control policy storage unit 229. The access quality control policy storage unit 229 has a memory device for storing quality level information, which is granted by channel, such as RAM or EEPROM. The access quality control policy can be ranked and then stored as numerical information such as 1, 2 and 3. A control processor 228 controls a decryptor 222, a demultiplexer 223 and decoders 224, 225 and 226 based on an access quality control policy stored in the access quality control policy storage unit 229, thereby limiting the quality of broadcast data provided to a user. Furthermore, the control processor 228 can limit the quality level of broadcast data provided to a user by using the stored access quality control policy, according to the channel selected by a user. A user can select a high quality level for a channel what the user frequently sees, and a low quality level for a channel that the user rarely sees. The access quality control policy storage unit 229 stores an access right to broadcast data as an access quality control policy. If the user quality authorization system distributes an access quality control policy in real time, the access quality control system 230 can use an access quality control policy that has been just received without the need to maintain an additional access quality control policy storage unit 229 for storing the access quality control policy. Furthermore, it can be considered that a memory for temporarily storing an access quality control policy that has been received in real time corresponds to the access quality control policy storage unit 229 according to the present invention. Furthermore, according to another embodiment of the present invention, the access quality control system 230 can maintain an additional clock (not shown) and store an access quality control policy every hour. It is thus possible to limit the quality of broadcast data provided to a user according to the current time. It is also possible to limit the quality of broadcast data, which is provided to a user, through a combination of channel and time. For example, referring to FIG. 2c, if an access quality control policy shown in FIG. 2c is transferred from the user quality authorization system to the access quality control system, or stored in the access quality control system 230, a subscriber who employs the broadcast receiving apparatus ofthe present invention can be provided with broadcast data of a high quality (quality 1) from 7 to 10 p.m., while being provided with broadcast data of a low quality (quality 3) for channel 1. Thus, a subscription fee can be properly imposed to the subscriber accordingly. A subscriber who usually has access to broadcast data in the above time zone has an advantage in that he or she can pay the fee corresponding to data of high quality only for that particular time zone. Even in the case of a channel, a subscriber who is interested in a given channel can pay a fee corresponding to data of high quality only for that channel. In FIG. 2c, since a subscriber has great interest in channels 3 and 4, channels 3 and 4 can be accessed through data of high quality (quality 1) all day long. Furthermore, according to another embodiment of the present invention, the access quality control system 230 records a user's access quality control policy for all broadcast data into the access quality control policy storage unit 229 in a batch and same manner. For example, if the collective selection of "high quality" for all receivable broadcast data rather than those receivable by each broadcast channel is stored in the access quality control policy storage unit 229, a user can access the broadcast data of all channels at the high quality level. The user quality authorization system 218 serves to receive service quality level information, which is granted to a user, from the user quality management system 217, generate an access quality control policy necessary for the user (one of a multi-level decryption key, a decoding control policy and a demultiplexing control policy, or a combination of two or more of them), and distribute the generated access quality control policy to the user in wireless mode or over a telephone channel. If the generated access quality control policy is distributed to the broadcast receiving apparatus 220 in wireless mode, the multi-level decryption key, the decoding control policy, the demultiplexing control policy and the like can be distributed in an encrypted manner by means of an encryptor such as a public key algorithm and a decryptor. For instance, they can be distributed in an encrypted manner using an encryption scheme and an encryption channel which are implemented in a user authorization system. In this case, although a third party tries to illegally modify a broadcast receiving apparatus, it is difficult to know the password and the encryption mode. Furthermore, although a broadcast receiving apparatus is illegally modified, illegal use can be easily prevented through a change of password or encryption mode by a broadcasting service provider. A decoding control policy is data on to what degree a decoding function will be allowed for a given broadcast receiving apparatus. A demultiplexing control policy is data on to what degree a demultiplexing function will be allowed for a given broadcast receiving apparatus. That is, those data are data, which are necessary to control a decoder or a demultiplexer so that a user can access broadcast data of a given quality level. This will be described in detail later. If a service quality level composed of a combination is authorized, a multi-level decryption key, a decoding control policy and a demultiplexing control policy are distributed with them being combined. The multi-level decryption key, the decoding control policy and the demultiplexing control policy can be distributed off-line. A transmitter 216 broadcasts broadcast data that have been encrypted by the encryptor 215. The broadcast receiving apparatus 220 comprises a receiver 221, a decryptor 222, a demultiplexer 223, multi-level decoders 224, 225, and 226, a smart card 227 and an access quality control system 230. The receiver 221 receives broadcast data. The decryptor 220 decrypts the encrypted data received by the receiver 221, by using the decryption key given from a decryption key generator. The demultiplexer 223 demultiplexes the signals decrypted by the decryptor 222 into signals necessary to the multi-level video decoder 224, the multi-level audio decoder 225 and the data decoder 226. The access quality control system 230 controls the decryptor 222, the demultiplexer 223 or the decoders 224, 225 and 226 according to the multi-level decryption key, the demultiplexing control policy or the decoding control policy, which is received from the user quality authorization system 218 of the broadcast apparatus

210. Furthermore, when a device (broadcast receiving apparatus) is generated, a decryption key, a demultiplexing control policy and a decoding control policy can be built in the device in hardware or software. Thus, the access quality control system 230 can limit service quality depending on the device. Moreover, the access quality control system 230 can be constructed in the form of a smart card that can be detached. The access quality control system 230 can include the control processor 228, and the access quality control policy storage unit 229, if needed. In the access quality control system, the control processor is an indispensable component. However, if the access quality control system performs a received user quality control policy in real time, it may not include an additional access quality control policy storage unit. Accordingly, the access quality control policy storage unit is an optional component in the access quality control system. The control processor 228 controls the demultiplexer, the decoder, the decryptor and so on based on the input of the user quality authorization system 218 or the smart card 227. Hereinafter, the operation of the components shown in FIG. 2 will be described in detail. Multimedia data that will be transmitted from the broadcast apparatus 210 are encoded into streams of multiple quality levels through the multi-level video encoder

211, the multi-level audio encoder 212 or the data encoder 213. The user quality authorization system 218 can generate and distribute a demultiplexing policy and a decoding policy, and assign an encryption-generating key to each of the multi-level quality streams according to an encryption policy. The generated multi-level quality streams are encrypted through the encryptor 215, and are then multiplexed through the multiplexer 214 for transmission. Meanwhile, the generated multi-level quality streams can be first multiplexed by means of the multiplexer 214 and then encrypted by means of the encryptor 215. In order words, the order of the multiplexer 214 and the encryptor 215 can be changed. Furthermore, one of the multiplexer 214 and the encryptor 215 or both of them can be omitted within a range of technical spirits of the present invention. The construction in the broadcast receiving apparatus 220 is symmetrical to that in the broadcast apparatus 210. The demultiplexer 223 of the broadcast receiving apparatus 220 demultiplexes the encrypted video, audio and data streams corresponding to their respective service quality levels. The access quality control system 230 uses a demultiplexing policy, a decoding policy, a multi-level decryption key or the like, which corresponds to a service quality level for which a user has subscribed, which is received from the user quality authorization system 218 ofthe transmission apparatus 210, or an access quality control policy off-line to control the demultiplexer 223, the decoders 224, 225 and 226, and the decryptor 222 so that they are compatible with each service quality level. For example, the access quality control policy can be distributed by being stored in a smart card or a receiver, which is distributed off-line, so that the access quality control system 230 can receive the access quality control policy through the smart card or the receiver. In this case, the control processor 228 of the access quality control system can be constructed by modifying the secure processor ofthe conditional access system. In the case of an on-demand mode service, the user terminal 220 transmits an electronic serial number (ESN) or a telephone number of a personal mobile phone, or a corresponding service number to the user quality authorization system 218. The user quality authorization system 218 confirms the service quality level authorized to a user by referring to the user quality management system 217, generates an access quality control policy regarding video, audio and data streams, which correspond to the authorized service quality level, and then transfers the generated access quality control policy to the control processor 228 ofthe access quality control system. If this control operation is performed in real time, the access quality control level system does not have an additional access quality control policy storage unit. In the case of on-demand mode service, if a user sees and hears advertising at a predetermined time in association with broadcast, etc., the service can be provided in such a manner that a decryption key or a service policy is provided free or at a discounted price. In the case of an off-line service, a user can receive a corresponding service quality level only for an authorized service period by purchasing a smart card or receiver in which an access quality control policy is stored or dedicated hardware or software in which a service quality level is set. Even in the case of an off-line service, if a user sees and hears advertising at a predetermined time in association with advertising, etc., the service can be provided in such a manner that a decryption key or a service policy is provided free or at a discounted price. It is to be noted that the method of providing multiple quality levels of service in the broadcasting service, which has been described with reference to FIG. 2, is illustrative, and the connection configuration between the function blocks, implementation algorithm and the like shown in FIG. 2 can be modified. It will be also evident to those skilled in the art that the above modification falls within the scope ofthe present invention. FIG. 3 is a table shown to explain a multi-level encoding process, which is performed by the multi-level video encoder 211. A method of multiplexing/encoding source broadcast data into basic data and displacement data will be first described. In this method, if one source broadcast data are to be provided to a user as a plurality of quality levels (for example, quality 1, quality 2 and the quality 3), in order to replay data of each quality level, only basic data are employed, or a combination of basic data and at least one displacement data is employed. An exemplary method in which broadcast date is multiplexed/encoded into basic data and displacement data will be described with reference to FIG. 3. One source video data shown in FIG. 3 have 8*8 pixels. In this time, basic data are composed of video data having 2*2 pixels. If only information corresponding to pixels indicated by "A" in FIG. 3 is included, video data having 2*2 pixels become basic data. In order to support 4*4 pixels, being a higher quality level, data that are necessary to support the data of 4*4 pixels while not being included in the basic data become first displacement data. In FIG. 3, data corresponding to pixels indicated by "B" become the first displacement data. Accordingly, only the first displacement data do not become the video data having 4*4 pixels, but only when the basic data and the first displacement data are combined, the video data having 4*4 pixels are obtained. For video data having 8*8 pixels, being the next higher quality level, data that are necessary to support data of 8*8 pixels while not being included in basic data and first displacement data become second displacement data. Data corresponding to pixels indicated by "C" in FIG. 3 become the second displacement data. Accordingly, if the source video data are encoded into multiple levels according to the present embodiment, it is divided into the basic data, the first displacement data and the second displacement data, thus producing data. A broadcast receiving apparatus can generate only basic data according to an authority granted to a user (support 2*2 pixels), or can support 4*4 pixels by decoding the basic data and the first displacement data through the multi-level video decoder. It is also possible to support 8*8 pixels by decoding the basic data, the first displacement data and the second displacement data through the multi-level video decoder. According to this embodiment, since the size of a total of data, which are generated through a multi-level encoding process, is substantially similar to or the same as those of original source video data, there is an advantage in that a broadcasting service of multiple quality levels for the same content can be provided while using transmission bandwidth as it is. In this embodiment, basic data and displacement data do not include overlapping data. However, in another embodiment of the present invention, they can include overlapping data. For example, for convenience of implementation of the present invention, the system can be constructed so that basic data and displacement data include overlapping data. The method of multiplexing/encoding data with plural quality levels will now be described. In this embodiment, if video data of a low quality, a middle quality and a high quality are supported, the video data of the low quality include data corresponding to pixels indicated by "A" for supporting 2*2 pixels. The video data of the middle quality are to support 4*4 pixels, and include data corresponding to pixels indicated by "A" and "B". The video data of the high quality are to support 8*8 pixels, and include data corresponding to pixels indicated by "A", "B" and "C". In this embodiment, there is an advantage in that a plurality of data need not to be re-combined so as to generate data of a given quality level in the broadcast receiving apparatus. Only the multi-level encoding method using the displacement data has been described in the case of a resolution of video data with reference to FIG. 3. This can be applied to other quality scale of video data or audio data, and other data in the same manner. FIGS. 4a and 4b are block diagrams of a broadcasting system that limits the level of service quality of broadcast data provided to a user by controlling the encryptor and the decryptor according to an embodiment ofthe present invention. In a transmission apparatus 410, streams of multiple quality levels, which are generated from a multi-level video encoder 411, a multi-level audio encoder 412 or a data encoder 413, pass through encryptors 414 to 420. A user quality authorization system 424 allocates an encryption-generating key to each of the multiple quality level streams. The encrypted multiple quality level streams are multiplexed by means of a multiplexer 421, and are then transmitted. The user quality authorization system 424 generates decryption keys of video, audio and data streams, which correspond to the service quality level for which a user has subscribed, and then transfers them to a control processor of a broadcast receiving apparatus 430, i.e., a multi-level decryption key player 444. The user quality authorization system distributes an access quality control policy in such a manner that only encryption keys compatible with authorized quality levels, which are stored in the user quality management system, among the plurality of the decryption keys, are transmitted to a receiver part. In most cases, the user quality authorization system distributes a decryption key of entitlement control message (ECM) only within a range necessary to replay an authorized quality level to a user. The receiver side can store the encryption keys in the access quality control policy storage unit and control the multi-level decryption key player. In the case where the decryption key is controlled in real time, the receiver side can store an entitlement management message (EMM) or a control word in a temporary storage unit of the access quality control system only within a range necessary to replay the authorized quality level, and then distribute it to a user. - A demultiplexer 432 of the broadcast receiving apparatus 430 demultiplexes the encrypted video, audio and data streams, which correspond to the respective service quality levels. An access quality control system 445 can be assigned with decryption keys corresponding to the service quality levels for which a user has subscribed through the user quality authorization system 424 of the transmission apparatus 410, or decryption keys off-line through a smart card 443, which has been purchased by the user, and then transfer the decryption keys to decryptors 433 to 439 corresponding to the respective service quality levels. At this time, the access quality control system 445 includes a multi-level decryption key generator 444 as a main component. The decryptors 433 to 439 decrypt the video, audio and data streams only when they receive the decryption keys from the access quality control system 445, and then transfer them to a multi-level video decoder 440, a multi-level audio decoder 441 and a data decoder 442. In other words, according to this embodiment, the decryptors are disposed in the broadcast receiving apparatus 430, and are then controlled according to the access quality control policy, so that a user can access only broadcast data of a given quality level. FIGS. 5a and 5b are views showing a data machining process according to the embodiment of FIG. 4. One source data 510 are encoded into basic data 511 and displacement data 512 and 513 with multiple levels by means of the multi-level encoders 411, 412 and 413. It is to be noted that the number ofthe displacement data shown in FIG. 5 is illustrative, but the number of the displacement data can vary according to an embodiment. According to another embodiment of the present invention, one source data 510 can be encoded into data of plural quality levels with multiple quality levels by means of the multi-level encoders 411, 412 and 413. The multi-level encoded data 511, 512 and 513 are encrypted by means of the encryptors 414 to 420. The encrypted data 514 to 516 are then multiplexed by the multiplexer 421, and is then transmitted as a broadcast signal 518 through the transmitter 422. A receiver 431 of the broadcast receiving apparatus 430 receives the broadcast signal 518. The received broadcast signal 518 is converted into multiplexed data 519, which can be processed by the demultiplexer 432. The demultiplexer 432 demultiplexes the multiplexed data 519. Data 520 to 522, which are generated as a result of the demultiplexing, are the same as the encrypted data 514 to 516 before being demultiplexed by the multiplexer 421 in the transmission apparatus 410. The encrypted data 520 to 522 are decrypted through the decryptors 433 to 439. In this time, the decryptors 433 to 439 are controlled by the access quality control system 445. If data of 4*4 pixels are to be granted to a user, it is required that a decryption key be provided to only the decryptor 1 433 and the decryptor 2 434, but the decryption key be not provided to the decryptor 3 435. Then, the multi-level video decoder 440 can provide data of 2*2 pixels and data of 4*4 pixels, but cannot provide data of 8*8 pixels. That is, although encrypted data 1 520 can be decrypted into the basic data 523 and encrypted data 2 521 can be decrypted into displacement data 1 524, encrypted data 3 522 cannot be decrypted into displacement data 2 525. Accordingly, the access quality control system 445 can properly control the quality level of data, which are provided to a user, according to the authority of the user. This can be applied to a case where a plurality of quality levels of data are provided in the same manner. FIGS. 6a and 6b are block diagrams of a broadcasting system that limits the service quality level of broadcast data, which is provided to a user, according to a demultiplexing control policy according to an embodiment ofthe present invention. In a transmission apparatus 610, video, audio and data signals are encoded through a multi-level video encoder 611, a multi-level audio encoder 612 and a data encoder 613, multiplexed through a multiplexer 614, and then transferred to an encryptor 615. A user quality authorization system 618 generates a demultiplexing control policy, which can demultiplex video, audio and data streams corresponding to a service quality level of a user, and then transfers it to an access quality control system 630 of a broadcast receiving apparatus 620. The encryptor 615 encrypts the multiplexed multimedia streams, and then transmits them to a transmitter 616. The transmitter 616 broadcasts the encrypted multimedia streams. In the broadcast receiving apparatus 620, a decryptor 622 decrypts the encrypted multimedia streams, which are received through a receiver 621, according to a decryption key. A demultiplexer 623 demultiplexes the decrypted multimedia streams into video, audio and data streams according to the demultiplexing control policy, which is received through the access quality control system 630, and then transfers them to multi-level video, audio and data decoders 624 to 626. In this time, streams corresponding to unauthorized service quality levels are precluded by the demultiplexer 623. The demultiplexing control policy is data indicating how demultiplexing can be performed in the broadcast receiving apparatus 620. For example, the demultiplexing control policy is data indicating that all multiplexed data of basic data, displacement data 1 and displacement data 2 must be demultiplexed, or that only the basic data have to be demultiplexed. The demultiplexing control policy can also include a limit on the service quality level for data, which have not been encoded with multiple levels or not grouped into service quality levels in the transmission apparatus 610. For instance, although the transmission apparatus 610 has transmitted frames that are not grouped, the demultiplexer 623 can transmit only the number of authorized frames per second to the decoders 624, 625 and 626 if the number of the frames per second is limited in the demultiplexing control policy. Furthermore, although the transmission apparatus 610 has transmitted ungrouped replayed pixels, the demultiplexer 623 can transfer only authorized pixels per frame to the decoders 624, 625 and 626 if the number of pixels per frame is limited in the demultiplexing control policy. In other words, according to this embodiment, the demultiplexer 623 is disposed in the broadcast receiving apparatus 620, and thus controlled according to the access authority of a user, so that the user can access only broadcast data of a given quality level. FIGS. 7a and 7b are views illustrating a data machining process according to the embodiment of FIG. 6. One source data 710 are encoded into basic data 711 and displacement data 712 and 713 with multiple levels through the multi-level encoders 611, 612 and 613. It is, however, to be noted that the number of displacement data shown in FIG. 7 are illustrative, but the number of the displacement data can vary, if needed. According to another embodiment of the present invention, one source data 710 can be encoded into data of plural quality levels with multiple levels through the multi-level encoders 611, 612 and 613. The multi-level encoded data 711, 712 and 713 are then demultiplexed through the multiplexer 614. The multiplexed data 714 are then encrypted through the encryptor 615, and the encrypted data 715 are broadcast as a broadcast signal 716 by means ofthe transmitter 616. The receiver 621 of the broadcast receiving apparatus 620 receives the broadcast signal 716. The received broadcast signal 716 is decrypted by the decryptor 622. The decrypted data 718 is identical to the multiplexed data 714 of the transmission apparatus 610. The multiplexed data 718 is demultiplxed by the demultiplexer 718. In this time, the demultiplexer 623 is controlled by the access quality control system 630. If data of 4*4 pixels are to be granted to a user, the demultiplexer 623 demultiplexes multiplexed data 718 into only basic data 719 and displacement data 1 720, but does not generate displacement data 2 721. Thus, the decoders decode the basic data 719 into video data of 2*2 pixels and provide the generated video data to a user, or decode the basic data 719 and displacement data 1 720 into video data of 4*4 pixels and provide the generated video data to the user. However, since displacement data 2 721 are not provided, video data of 8*8 pixels, which can be provided only when displacement data 2 721 exist, cannot be provided to the user. Accordingly, the access quality control system 630 can properly limit the quality level of a user, which is provided to the user, according to the authority of the user. This can be applied to a case where data of a plurality of quality levels are provided in the same manner. FIGS. 8a and 8b are block diagrams of a broadcasting system that limits service quality levels of broadcast data, which are provided to a user according to a demultiplexing control policy according to an embodiment ofthe present invention. In a transmission apparatus 810, video, audio and data signals are encoded through a multi-level video encoder 811, a multi-level audio encoder 812 and a data encoder 813, and are then transferred to a multiplexer 814. A user quality authorization system 818 generates a decoding control policy, which can decode video, audio and data streams corresponding to a service quality level of each user, and then transfers it to an access quality control system 830 of a broadcast receiving apparatus 820. An encryptor 815 encrypts the multiplexed multimedia streams and then transfers them to a transmitter 816. The transmitter 816 broadcasts the encrypted data. In the broadcast receiving apparatus 820, a decryptor 822 decrypts the encrypted multimedia streams that are received through the receiver 821 according to a decryption key. A demultiplexer 823 demultiplexes the decrypted multimedia streams into video, audio and data, and then transfers them to multi-level video, audio and data decoders 824 to 826. The multi-level video, audio and data decoders 824 to 826 decode only portions corresponding to an authorized service quality level according to the decoding control policy, which is received from the access quality control system 830. The decoding control policy is data indicating how decoding can be performed in the broadcast receiving apparatus 820. For example, the decoding control policy can be data, which indicate whether or not to allow all of basic data, displacement data 1 and displacement data 2 to be decoded with multiple quality levels, or to allow only basic data to be decoded. The decoding control policy includes a limit of service quality levels for data, which are not encoded with multiple levels or grouped into a service quality level in the transmission apparatus 810. For instance, although the transmission apparatus ha sent ungrouped frames, the decoders 824 to 826 can replay only the number of authorized frames per second if the number ofthe frames per second is limited in the decoding control policy. Furthermore, although the transmission apparatus 811 has transmitted ungrouped regenerated pixels, the decoders 824 to 826 can regenerate only authorized pixels per frame if the number of pixels per frame is limited in the decoding control policy. The decoders 824 to 826 are controlled by the access quality control system 830. If data of 4*4 pixels are to be granted to a user, the multi-level video decoder 824 decodes the basic data and displacement data 1 to generate the data of 4*4 pixels. In this case, however, since decoding including displacement data 2 is not authorized, the multi-level video decoder 824 cannot generate data of 8*8 pixels. In order to generate the data of 8*8 pixels, the multi-level video decoder 824 must be provided with an according direction from the access quality control system 830. Accordingly, the access quality control system 830 can properly limit the quality level of data, which are provided to a user, according to an authority ofthe user. This can be applied to a case where data of a plurality of quality levels are provided in the same manner. It has been described in the above that the access quality control system 830 controls the decryptor, the demultiplexer and the multi-level decoders to limit data, which can be received by a user, with reference to FIGS. 4 to 8. However, a method in which the access quality control system controls a predetermined combination of the decryptor, the demultiplexer and the multi-level decoder is possible. For example, the access quality control system can limit the quality of data provided to a user by controlling the decryptor and the demultiplexer at the same time. FIG. 9 is a conceptual diagram illustrating a data machining process in a broadcasting system that limits the service quality level of broadcast data provided to a user, by using basic data and displacement data according to an embodiment of the present invention. Source broadcast data 901 are encoded into basic data and displacement data with multiple levels by means of multi-level encoders. The multi-level encoded data 902, 903 and 904 are then broadcast through a transmission apparatus. In this time, as described above with reference to the aforementioned embodiments, an encryption or multiplexing process can be performed. The multi-level encoded data 902 to 904 are received by a receiving apparatus. Only some of the multi-level encoded data can be replayed by a user through the access quality control system of the receiving apparatus. In this time, some of the decoded data can be selected by the access quality control system. The access quality control system performs a control operation according to an access quality control policy, which indicates which quality level in association with the broadcast data would be allowed for a user to access. A data replayer uses the multi-level encoded data to generate broadcast data of an authorized quality level under the control of the access quality control system. The data replayer can be constructed by using at least one combinations of the decryptor, the demultiplexer and the multi-level decoders, which have been described in the above embodiments. FIG. 9 shows a case where the access quality control system combines only the basic data 902 and displacement data 1 903. In this case, the receiving apparatus combines the basic data 902 and displacement data 1 903, and then provides them to a user. According to another embodiment of the present invention, the access quality control system can store the access quality control policy by channel or hour as to which quality level in association with the broadcast data would be allowed for a subscriber to access, and control the data replayer according to the access quality control policy. The access quality control system limits the quality level of broadcast data, which are provided to a user, according to the stored access quality control policy by channel and the channel selected by the user. Furthermore, the access quality control system maintains an additional clock and stores the access quality control policy every hour. It is thus possible to limit the quality level of broadcast data, which are provided to a user, according to the current time. Furthermore, the quality level of broadcast data provided to a user can be controlled through a combination ofthe channel and time. In this embodiment, consumption of bandwidth can be minimized, and illegal use of a third party can be reduced. Furthermore, if an encryptor and a decryptor are used, although a third party illegally modifies a broadcast receiving apparatus, it is difficult to know the password and encryption mode. Although a broadcast receiving apparatus is modified, illegal use of a third party can be easily prevented by changing the password or encryption mode by means of a broadcasting service provider. According to another embodiment of the present invention, a user can select a reception quality level for the same broadcast data in real time. Information, which allows access to broadcast data of a plurality of quality levels, is stored in the access quality control policy that is stored in the access quality control system in association with the broadcast data. Furthermore, the data replayer includes a user input unit for allowing a user to input broadcast data having one of a plurality of quality levels. If the user selects broadcast data of a given quality level, the data replayer generates broadcast data of the selected quality level and then provides it to the user. For instance, a service quality level composed of a combination (basic pixel, 24-bit color) or (double pixel, 8-bit color) for one broadcast data (for example, a given drama) can be granted to a user so that the user can select the desired service quality level. In this embodiment, it is possible to provide services of various quality levels to a user even with the same billing. FIG. 10 is a conceptual diagram illustrating a data machining process in a broadcasting system that limits the service quality level of broadcast data, which are provided to a user, by using data by quality level according to an embodiment of the present invention. Source broadcast data 1001 are multiplexed and then encoded into data of plural quality levels through multi-level encoders. The multi-level encoded data 1002, 1003 and 1004 are broadcast through a transmission apparatus. As described in the above embodiments, encryption or multiplexing can be performed. The multi-level encoded data 1002 to 1004 are received by a receiving apparatus.

Only some of the multi-level encoded data are decoded by means of the access quality control system of the receiving apparatus. In this time, some of the decoded data can be selected by the access quality control system. FIG. 10 shows a case where the access quality control system allows only the middle quality data 1006 to be decoded. In this case, the receiving apparatus decodes the middle quality level data 1006, and then provides it to a user. FIG. 11a is a conceptual diagram illustrating a data machining process in a broadcasting system that limits the service quality level of broadcast data, which are provided to a user, by using a quality degrader in a receiving apparatus according to an embodiment ofthe present invention. In the aforementioned embodiments, the method in which one source broadcast data are encoded into multiple levels, and some of the multi-level encoded data are provided to a user has been described. Multi-level encoding means that source data are encoded according to service quality levels. The multi-level encoding method can include a method of encoding source data into basic data and displacement data, and a method of encoding source data into data of plural quality levels. Also, a plurality of multi-level encoded data can include partially overlapping data. In this embodiment, it will be described a method in which a transmission apparatus 1104 performs broadcasting in the same manner as a typical broadcast transmission apparatus, but a receiving apparatus 1105 limits the quality level of data, which are provided to a user, through a quality degrader 1106. This embodiment can be applied to even a case where a transmission apparatus does not perform a multi-level encoding process. In this embodiment, however, a case where the transmission apparatus does not perform a multi-level encoding process will be described, but this can be applied to a case where the transmission apparatus performs the multi-level encoding process. For example, if video data of 1024*768 pixels are received but only 512*384 pixels are granted to a user of the broadcast receiving apparatus, the broadcast receiving apparatus degrades the video data of 1024*768 pixels into a resolution of 512*384 pixels, and then provides it to the user. In this degradation method, some ofthe whole pixel data, which are broadcast, is transmitted. In the same manner, even in the case of color, if 256 color is supported using 8 bits so as to represent color, only 16 colors can be supported using only 4 bits. This quality degradation method can employ a variety of well-known methods. In this embodiment, although it has been described a method of degrading a quality of received broadcast data in the case of a resolution of video data, this method can be applied to other quality scale of video data or audio data, and other data in the same manner. In the broadcast apparatus, common encoders or multi-level encoders encode broadcast data. A multiplexer multiplexes the broadcast data, and then broadcasts them. Also, upon broadcasting, the broadcast data can be encrypted and then broadcast. In the broadcast receiving apparatus, the broadcast data are received through a receiver. The broadcast data are then demultiplexed by a demultiplexer, and is then decoded through a decoder. The degrader 1106 degrades the broadcast data received as data of a predetermined quality level, and provides the degraded data to a user. In this embodiment, the broadcast apparatus includes a user quality management system for storing user information, which indicates which one of two or more broadcast quality levels associated with one source data is allowed to a user of intelligent broadcasting service in a broadcast apparatus on the transmission side, and managing billing depending on the service quality level provided to the user. That is, the user quality management system stores data relating to quality level and billing information depending on the quality level among a user identifier corresponding to each user of the intelligent broadcasting service and two or more broadcast quality levels associated with one broadcast data, in association with the user identifier. A broadcasting service provider can store information about which broadcast quality level is granted to a user based on this user information. The information can be managed by channel, hour or program. Furthermore, the user quality management system can perform billing depending on the broadcast quality level provided to a user based on the stored user information. This billing process can be also performed by the user quality management system. According to an embodiment of the present invention, the broadcast receiving apparatus can be fabricated by adding the degrader in software or hardware so that only data of a given quality level regarding one source data can be replayed. In this embodiment, since the broadcast receiving apparatus degrades broadcast data that are received as data of a given quality level, a user who uses the broadcast receiving apparatus of the present invention can receive the broadcast data of only the given quality level. Furthermore, the present embodiment can be applied to all broadcast data, which are broadcast through a multi-level encoding method or other common method. In the case of multi-level encoded broadcast data, only a predetermined quality level can be replayed in the receiving apparatus. In the case where the broadcast data are broadcast by means of a common method, the broadcast data can be set so that they are graded with a predetermined quality level. In another embodiment, the access quality control system can control which one of a plurality of quality levels associated with the broadcast data would be allowed for a user to access. This embodiment does not include this access quality control system. According to this embodiment, a method in which the broadcast receiving apparatus can access broadcast data of a high quality (broadcast data broadcast by the broadcast transmission apparatus) is limited, and the quality level of broadcast data to which a subscriber can have access is decided depending on which broadcast receiving apparatus is provided to the subscriber. Therefore, it facilitates its implementation and embodiment. The degrader can be constructed by using respective components of the broadcast receiving apparatus including a digital analog converter and a display control logic, as well as the above-described decryptor, the decoder and the demultiplexer. According to another embodiment of the present invention, the broadcast apparatus can further include a serial number comparison unit for comparing a serial number, which is an identifier ofthe broadcast receiving apparatus, and a serial number, which is an identifier of the conditional access system, and only when the two serial numbers coincide with a pair of previously stored serial numbers, authorizing replay of the broadcast data. A predetermined conditional access system (CAS) can further include a serial number comparison unit that operates according to an electronic serial number (ESN), which is uniquely assigned to the receiving apparatus, so that the serial number comparison unit operates only in the receiving apparatus including the degrader, but does not operate in other receiving apparatus. The serial number comparison unit compares an ESN of the receiving apparatus and a serial number of the conditional access system, and if it is determined that they are not a predetermined ESN that is authorized to the conditional access system, generates a decryption key, and does not allow replay of the broadcast data. In quality level differentiation broadcast according to the present invention, even if the conditional access system is attached to a receiver as well as when the conditional access system is detachably provided in the form of a smart card, a user who has requested data of a low quality level at a low price can illegally attach the conditional access system, which is adapted to be used only for a low quality level (degradation)-dedicated receiving apparatus, to a common receiving apparatus, and then easily receive data of a high quality level. It is thus required that a conditional access system, which has to be used at a low price, be used only in a degradation (low quality)-dedicated receiving apparatus, through a combination of a serial number of the conditional access system and an ESN. In this embodiment, an ESN is recorded in a ROM, etc. in the form of firmware of which the rewriting or deletion is impossible so as to enhance security. In the above embodiment, if the conditional access system is not included, a serial number of a degrader, an access quality control system, etc. can be used instead of a serial number ofthe conditional access system. According to another embodiment of the present invention, the broadcast apparatus can include a receiver, a degrader and a serial number comparison unit except for the conditional access system. The serial number comparison unit stores a serial number of the receiving apparatus or a serial number of the degrader in a medium on which the rewriting or deletion is impossible. In another embodiment of the present invention, the broadcast apparatus can further include an access quality control system for controlling whether or not to drive the degrader or a driving mode. The receiving apparatus itself has the ability to replay data of a common quality level or a plurality of quality levels, as well as data of a given degraded quality level. In this case, broadcast data, which are received according to an access quality control policy indicating which one of two or more quality levels associated with one source data (broadcast data) would be allowed for a user to access, can be degraded to data of a quality level that is allowed to the user, or not degraded. The access quality control policy can be stored when the receiving apparatus is sold, and modified off-line, if needed, or the user quality authorization system on a sender side can frequently distribute an access quality control policy for a user through broadcast control channels to the access quality control system of the receiving apparatus. Furthermore, the access quality control system can perform a control operation by referring to the access quality control policy stored in the access quality control policy storage unit, or according to an access quality control policy that is distributed in real time. Accordingly, the control processor is an indispensable component of the access quality control system, but the access authorization information storage unit is not an indispensable component ofthe access quality control system. According to another embodiment of the present invention, the access quality control system can receive the access quality control policy through communication with a predetermined management server. Each broadcast receiving apparatus is operated under the control of the management server. Accordingly, a manager of the management server or the management server can perform billing suitable for a user of each of the broadcast receiving apparatus according to the access quality control policy. In this time, each broadcast receiving apparatus can employ an ESN (Electronic Serial Number), which is uniquely assigned to the broadcast receiving apparatus. That is, a broadcasting service provider stores an ESN ofthe broadcast receiving apparatus, which is distributed to a user, a serial number of the conditional access system, and user (subscriber) information in the management server, and performs billing for a corresponding user through an ESN received from the broadcast receiving apparatus, the serial number ofthe conditional access system and the like. According to the prior art, the conditional access system (CAS) for providing only a specific channel to a user is used. In other words, the user is given with only a right to see or not to see predetermined broadcast data. However, according to this embodiment, a user can access or see and hear broadcast data of a quality level corresponding to a price that the user chooses to pay, according to billing. The access quality control system, the user quality authorization system of the transmission apparatus, and the user quality management system can use the same components as those described in the aforementioned embodiments. According to another embodiment of the present invention, information, which indicates which one of two or more broadcast quality levels associated with one source data is granted to a user of an intelligent broadcasting service, can be stored in a broadcast apparatus on the sender side. The broadcast apparatus includes a user quality management system for managing billing depending on the service quality level provided to a user. That is, the user quality management system can store data relating to the quality level and billing information depending on the quality level among a user identifier corresponding to each user of the intelligent broadcasting service and two or more broadcast quality levels associated with one broadcast data in association with the user identifier. A broadcasting service provider can maintain information about which broadcast quality level can be granted to a user, based on this user information. The information can be managed by channel, hour or program. Furthermore, the user quality management system can perform billing depending on a broadcast quality level provided to a user based on the stored user information. This billing process can be also performed by the user quality management system. A broadcasting service provider can also perform billing depending on a broadcast quality level provided a user, based on the user information stored in the user quality management system. This billing process can be also performed by the user quality management system. FIG. l ib is a block diagram of a broadcast receiving apparatus that limits a service quality level of broadcast data provided to a user by using a quality degrader according to an embodiment ofthe present invention. In this embodiment, a receiver l l l l receives broadcast data. The broadcast data can include multi-level encoded broadcast data, but can also include broadcast data which are not multi-level encoded, as in a common broadcast transmission apparatus. If the common broadcast transmission apparatus is used, it is advantageous in that the conventional broadcast transmission apparatus can be used as it is. An access quality control system 1116 controls a quality degrader 1112, and stores an access quality control policy 1115 indicating which one of two or more quality levels associated with broadcast data would be allowed for a user to access. A control processor 1114 controls the quality degrader 1112 by referring to the access quality control policy 1115, so that the quality degrader 1112 can perform a quality degradation operation according to the access quality control policy 1115. If a control processor does not operate in real time, the access quality control policy storage unit 1115 may not be used. The quality degrader 1112 degrades broadcast data that are received through the receiver l l l l into broadcast data of a given quality level, which is granted to a user, according to an access quality control policy. For example, in the case where the access quality control policy is set to support only a resolution of 512*384 pixels, the received broadcast data can be degraded into video data of 512*384 pixels if the received broadcast data are video data of 1024*768 pixels. Meanwhile, in the case where the quality level is set to the middle quality level in the access quality control policy, the video data of 1024*768 pixels can be degraded into video data of 512*384 pixels if data corresponding to the middle quality level have 512*384 pixels. According to another embodiment of the present invention, the access quality control policy 1115 can be information indicating whether or not to operate the quality degrader regarding broadcast data and how the quality degrader will be operated in what mode. The control processor 1114 controls whether or not to operate the quality degrader 1112 according to the access quality control policy 1115. In the case of this embodiment, the quality degrader 1112 is not operated for a subscriber who pays a fee for broadcast data of a high quality level and then provides broadcast data of a high quality level, but is operated for a subscriber who pays a fee for broadcast data of a low quality level and then provides degraded broadcast data. In this embodiment, the degraded broadcast quality levels can be plural in nature, and can be a predetermined quality. According to another embodiment of the present invention, an access quality control policy 1115 can be information indicating which one of a plurality of quality level degradation modes will be performed. Furthermore^", the quality degrader 1112 supports a plurality of the quality degradation modes. For example, the quality degrader 1112 can support degradation of video data and degradation of audio data. The access quality control policy 1115 can store information indicating which degradation method will be used. The control processor 1114 controls the quality degrader 1112 by referring to the access quality control policy 1115, and performs a corresponding degradation operation. The access quality control policy 1115, which is applied to the access quality control system 1116, can be stored when a receiver is sold, and can be modified off-line, if needed. Also, the user quality authorization system on the sender side can frequently distribute an access authorization policy suitable for a user to the access quality control system ofthe receiving apparatus through the broadcast control channel. Also, the access quality control policy can be distributed through communication with a predetermined management server (e.g., a user quality authorization system in the above embodiment). Moreover, in the case of an on-demand service mode, a user can adjust the quality level of accessible broadcast data in real time according to a fee paid by the user, in such a manner that the user has access to a user quality management system online and then requests broadcast data of a desired quality level. Furthermore, a predetermined decryption key can be stored in a control processor attached to a smart card 1113 or a receiver off-line. The decryption key is then distributed to a user, and the user can access broadcast data of a desired quality level. Furthermore, if received broadcast data are multiplexed data, the broadcast receiving apparatus 1110 includes a demultiplexer for demultiplexing the multiplexed data. In this embodiment, it is possible to efficiently use a broadcast channel by multiplexing and broadcasting broadcast data. Also, if the broadcast receiving apparatus 1 110 includes the quality degrader 1112, this construction can be applied to a case where received broadcast data are multi-level encoded broadcast data. A user input unit 1117 allows a user to input a desired one of a plurality of quality levels, which are granted to the user, so as to access broadcast data. For example, if the type of the quality levels granted to the user is three, the user can select one of the three quality levels. Plural combinations can be possible by using broadcast data of accessible and grantable quality levels as data size and controlling the number of pixels in video data and the number of bits in audio data within the data size. For example, one user can set video to a high quality level and audio to a low quality level within a range of 1Mbps. Another user can set video to a low quality level and audio to a high quality level. In this embodiment, it is advantageous in that the width of selection is widened by allowing a user to select the quality level within accessible bandwidth. According to another embodiment of the present invention, a user can control the accessible quality level in an on-demand mode through the user input unit 1 117, while having access to broadcast data. Data input by the user are transmitted to a predetermined server through a wireless or wired communication network. Thus, the user can control the access quality control policy 1115 by adjusting the accessible quality level. Thereafter, a service provider demands payments for the user based on the adjusted quality level. It is to be noted that the user input unit can be applied to other embodiments of the present invention. According to another embodiment of the present invention, there is provided a broadcast receiving apparatus (low quality-dedicated broadcast receiver) for degrading received broadcast data into a predetermined quality level. In this embodiment, since the broadcast receiving apparatus degrades broadcast data of a given quality level, a user who uses the broadcast receiving apparatus of the present invention can receive the broadcast data of only the given quality level. Thus, this embodiment can be applied to all broadcast data, which are broadcast through a multi-level encoding method or a common method. In the case of broadcast data broadcast by means of the multi-level encoding method, the receiving apparatus can replay the broadcast data only with a predetermined quality level. In the case of broadcast data broadcast by means of the common method, the broadcast data are degraded to a predetermined quality level. In another embodiment, the access quality control system stores information on determination as to which one of a plurality of quality levels associated with the broadcast data would be allowed for a user to access. In this embodiment, however, the access quality control system is not included. In this embodiment, a method in which the broadcast receiving apparatus can access broadcast data of a high quality level (broadcast data broadcast by the broadcast transmission apparatus) is limited, and the quality level of broadcast data to which a subscriber can have access is decided depending on which broadcast receiving apparatus is distributed to the subscriber. Accordingly, its implementation is very easy. In the case where a low quality level (degradation)-dedicated receiving apparatus and a common receiving apparatus, which can access broadcast data of a high quality level, are separately provided, if an ESN of the low quality-dedicated receiving apparatus can be illegally copied to the common receiving apparatus which can receive broadcast data of a high quality level, a problem can arise. In other words, in the present invention, although a user sees and hears broadcast data in association with an ESN of a broadcast receiving apparatus, if an ESN of a low quality level receiver is copied to a high quality level receiver, and a conditional access system (CAS), etc. is mounted to the low quality level receiver, an unauthorized user can access broadcast data of the high quality level, while paying a low fee for the low quality level. Furthermore, in a case where there exists a broadcast receiving apparatus, which has been previously provided before a receiver having the access quality control system of the present invention is provided, there is no method for performing a degradation command if a conditional access system which has obtained a subscription right at a low fee is transferred and coupled to the existing receiver. Thus, there may be a blind point in that broadcast data can be normally received. Currently, since almost all receivers have the same receiving quality level, there is no problem in that an illegal copy of an ESN is used for the purpose of unduly paying a lessened subscription fee. As in the present invention, however, where quality differentiation is performed, a severe problem can occur. Hereinafter, a method of solving this problem will be described. FIG. l ie is a block diagram of a broadcast receiving apparatus for limiting the illegal use of a broadcast receiving apparatus by a user according to an embodiment of the present invention. In this embodiment, the broadcast receiving apparatus is classified depending on its type, and an ESN of the broadcast receiving apparatus is classified depending on the type of the receiving apparatus. In this state, only when the type of the broadcast receiving apparatus and the type of the ESN coincide with each other, the broadcast receiving apparatus normally operates. A service provider classifies ESNs of receiving apparatuses (broadcast receiving apparatus 1120) according to their types so that this information can be used by a receiving apparatus verification system 1127. Only when the type of the ESN of the receiving apparatus and the type of an actual receiving apparatus coincide with each other, reception is granted. In other words, it is determined whether the receiving apparatus verification system 1127 included in the broadcast receiving apparatus 1120 has the same access authority as that ofthe ESN ofthe broadcast receiving apparatus. The receiving apparatus verification system 1127 can enhance its security by using an ESN, which is uniquely assigned to the broadcast receiving apparatus 1120. The ESN is stored in an ESN storage unit 1123 such as a memory; An ESN reader 1124 reads an ESN to identify the broadcast receiving apparatus 1120 by referring to the ESN storage unit 1123. An ESN-quality storage unit 1122 groups ESNs and stores quality data of broadcast data, which are authorized to a user by grouped ESN. For example, if an ESN begins with 0, it refers to a receiving apparatus not having a service quality limit. If an ESN begins with 1, it refers to a receiving apparatus that can access broadcast data of a high quality level and has to comply with a service quality level limit policy. If an ESN begins with 2, it refers to a receiving apparatus that can access broadcast data of a middle quality level and has to comply with a service quality level limit policy. If an ESN begins with 3, it refers to a receiving apparatus that can access only broadcast data access of a low quality level. Information about them is stored in the ESN quality level storage unit 1122. Quality level data of broadcast data, which can be replayed in the broadcast receiving apparatus 1120, are stored in an access quality control policy storage unit 1126. An authorization quality level comparison unit 1125 compares the read ESN and the quality level data stored in the access quality control policy storage unit 1126 with quality level data by ESN, which is stored in the ESN quality level storage unit 1122, and controls the quality degrader 1121 as the lowest service quality level to limit replay of broadcast data. In this time, control of the quality degrader 1121 can be performed through a control processor (not shown). The receiving apparatus verification system 1127 determines the given quality level authorized to itself, and determines whether the ESN of the quality level is the same as or lower than data of the ESN quality level storage unit 1122. If it is determined that they are the same, normal service can be provided. If it is determined that they are not the same, service cannot be provided. For example, "high quality" is stored in the access quality control policy stored in the receiving apparatus verification system 1127. If the ESN of the broadcast receiving apparatus begins with 3, a service quality level, which has been authorized through the receiving apparatus verification system 1127, is higher than a service quality level that has been authorized to a terminal through the ESN. It can be thus considered that the ESN has been copied. The receiving apparatus verification system 1127 controls the degrader and the like so that received broadcast data cannot be replayed. It is thus possible to prevent illegal subscription through illegal copy of an ESN. Even in the case of a low quality level (degradation)-dedicated receiving apparatus not having the access quality control system, if an ESN is illegally copied, the same effects can be obtained through the above method. In this case, however, since the access control information storage unit ofthe access quality control system does not exist, the authorization quality level comparison unit determines whether broadcast data have been replayed by comparing the ESN quality level storage unit 1122 and the ESN. FIG. 1 Id is a block diagram of a broadcast receiving apparatus for limiting the illegal use of a broadcast receiving apparatus 1130 by a user according to another embodiment ofthe present invention. In this embodiment, if the broadcast receiving apparatus 1130 receives an access quality control policy, it feedbacks the received access quality control policy to a user quality management system or a user quality authorization system on the sender side. If there is no feedback, or if the feedback information results do not coincide with information registered in the user quality management system, the user quality authorization system prevents service based on the assumption that the broadcast receiving apparatus 1130 receives all data of a high quality level. An ESN reader 1134 reads an ESN to identify a broadcast receiving apparatus with reference to an ESN storage unit 1133. An access quality control policy storage unit 1136 stores the quality data of the broadcast data of which the replay is authorized in the broadcast receiving apparatus. A feedback communication unit 1132 transmits the read ESN, the ID number of the conditional access system (CAS) and the quality data stored in the access quality control policy storage unit 1136, to a predetermined server. In the same manner as the system that has already been serviced, if the ESN of the broadcast receiving apparatus 1130 cannot be classified depending on its type, the type of the broadcast receiving apparatus depending on the ESN is stored in a user quality management system (not shown) or a predetermined server. A receiving apparatus verification system 1137 of the broadcast receiving apparatus 1130 transfers the ESN and the type of actual broadcast receiving apparatus to the user quality management system (not shown) through a feedback communication unit 1132. Only when the information stored in the user quality management system and the received information coincide with each other, reception or replay of broadcast data is allowed. Through this, illegal copying of an ESN can be effectively prevented, and the existing receiving apparatus verification system can be maintained as it is. Thus, there is an advantage in that multiple quality levels of service can be added without changing an existing system. For example, if the fact that a broadcast receiving apparatus having an ESN of 123456 is a middle quality level is stored, whereas a broadcast receiving apparatus having an ESN of 123456 is a high quality level is stored in feedback information that has been received from the receiving apparatus verification system 1137 ofthe broadcast receiving apparatus 1130, the user quality management system on the sender side performs billing of a high quality level to the user of the broadcast receiving apparatus. According to another embodiment of the present invention, if an access quality control policy of the receiving apparatus verification system of the broadcast receiving apparatus does not coincide with a user access quality control policy received from the user quality management system on the sender side, the receiving apparatus verification system does not replay broadcast data or can modify the access quality control policy stored therein into the received access quality control policy. It is to be noted that the above-described method of limiting the illegal use of a broadcast receiving apparatus by a user can be applied to other embodiments of the present invention. According to another embodiment of the present invention, the receiving apparatus can include a user input unit for allowing a user to input one of a plurality of quality levels for broadcast data. It is thus possible to apply various degradation methods of different degradation modes. If a user selects broadcast data of one quality level, a data replayer generates the broadcast data of the selected quality level, and then provides the generated broadcast data to the user. FIGS. 12a and 12b are block diagrams of a broadcasting system that adopts a limit of a service quality level of broadcast data by transmission channel according to an embodiment ofthe present invention. According to this embodiment, one of broadcast data is encoded into multiple levels to generate a plurality of multi-level encoded data. The multi-level encoded data are then broadcast through different broadcast channels. In a transmission apparatus 1200, streams of multiple quality levels, which are generated through a video encoder 1201, an audio encoder 1202 and a data encoder 1203, are allocated to transmission channels according to a service quality level. The streams of the multiple quality levels are then transmitted to the respective channels through multiplexers 1204 to 1206, encryptors 1207 to 1209, and transmission channels 1210 to 1213. A user quality authorization system 1215 serves to allocate encryption- generating keys to the encryptors 1207 to 1209 by transmission channels. The user quality authorization system 1215 can generate decryption keys of video, audio and data streams, which correspond to service quality levels for which each user subscribes, and transfers them to a control processor 1232 of a broadcast receiving apparatus 1220. In the broadcast receiving apparatus 1220, signals received by transmission channels are decrypted through reception channels 1221 to 1223, and then pass through decryptors 1224 to 1226. An access quality control system 1234 is provided with decryption keys corresponding to service quality levels for which a user subscribes through the user quality authorization system 1215 of the transmission apparatus 1200, or transfers the decryption keys that are received off-line to the decryptors 1224 to 1226 corresponding to the respective service quality levels. The decryptors 1224 to 1226 of the transmission channels decrypt the video, audio and data streams only when the decryption keys are received from the access quality control system 1234, and then transfer them to a multi-level video decoder 1228, an audio decoder 1229 and a data decoder 1230 through a demultiplexer 1227. A user who uses a basic quality level can use only a basic transmission channel, and can also additionally use a transmission channel 2 and a transmission channel 3 in order to improve the service quality level ofthe user. In this embodiment, it has been described that the access quality control system

1234 controls the decryptors to limit data, which are accessible by a user. However, a method in which the access quality control system controls one of the decryptors, the demultiplexer and the multi-level decoders, or a combination thereof is possible. For example, the decryptors and the demultiplexers can be controlled at the same time to limit the quality level of data which are provided to a user. The present invention has been described on the basis of a wireless broadcasting service, and has a construction suitable for the wireless broadcasting service. It is, however, to be understood that the construction of the present invention can be applied to a wired Internet broadcasting service in the same manner. The embodiments of the present invention include computer readable media including program instructions to implement various operations embodied by a computer. The media may also include, alone or in combination with the program instructions, data files, data structures, tables, and the like. The media and program instructions may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well known and available to those having skill in the computer software arts. Examples of computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROM disks; magneto-optical media such as floptical disks; and hardware devices that are specially configured to store and perform program instructions, such as read- only memory devices (ROM) and random access memory (RAM). The media may also be a transmission medium such as optical or metallic lines, wave guides, etc. including a carrier wave transmitting signals specifying the program instructions, data structures, etc. Examples of program instructions include both machine code, such as generated by a compiler, and files containing higher level code that may be executed by the computer using an interpreter. The hardware elements above may be configured to act as at least one software modules for implementing the operations of this invention.

Industrial Applicability According to the present invention, there is provided a method of providing a multiple quality levels of service to a user in a wireless broadcasting service. Furthermore, the method of providing multiple quality levels of service in accordance with the present invention has an effect in that access of a user to a service quality level, which is not authorized to the user, can be effectively prohibited through the use of a multi-level encryption key. Furthermore, the method of providing multiple quality levels of service in accordance with the present invention has an effect in that access of a user to a service quality level, which is not authorized to the user, can be effectively prohibited at a data receiver level through a combination of an encryption key and a demultiplexing control policy. Moreover, according to the present invention, a subscriber can be controlled to access one of broadcast data of a desired one of a plurality of quality levels, by overcoming only simple limitations on allowance or inability of reception of the broadcast data. Furthermore, the method of providing multiple quality levels of service according to the present invention has an effect in that access of a user to a service quality level, which is not authorized to the user, can be effectively prevented in a data receiver level by using a combination of an encryption key and a decoding control policy. Furthermore, according to the present invention, multiple quality levels of service that adopt differentiated fees can be provided to each user according to a given quality level even in the same program channel in a wireless broadcasting service.

Accordingly, it is possible to construct a variety of billing systems suitable for each user. Also, according to the present invention, access of a user to a service quality level, which is not authorized to the user, can be effectively prevented by using a combination of a multi-level decryption key, a decoding control policy, a demultiplexing control policy, etc. Furthermore, according to the present invention, a low price system can be applied to a user who receives data of a low quality level, through the use of a receiver having a degrader for degrading broadcast data into a predetermined quality level and a user management system for separately managing the receiver. Moreover, according to the present invention, access of a user to a service quality level, which is not authorized to the user, can be effectively prevented by using a combination of the serial number of a receiver having a degrader and the serial number .... . *\ - of a conditional access system that imposes a low price. Furthermore, according to the present invention, receiving quality can be controlled through a conditional access authorization system for controlling whether or not to operate a degrader. If an existing broadcast receiving apparatus exists or a differentiated service by broadcast receiving apparatus is provided, illegal use can be prevented and security can be improved, by using serial number information of the broadcast receiving apparatus. Accordingly, a broadcasting service provider can maximize profits, and customers who use a low-quality level service can be induced to use a high-quality level service, for a short time. As a result, profits can be increased for a long time. In a broadcasting service, this profit increase can be accomplished without additional investment, unlike a communication service. Furthermore, television subscription fees and advertising rates can be increased due to an increased number of subscribers. Meanwhile, from the standpoint of a user, each user can reduce the burden of receiving broadcast data since the user can receive a low fee system corresponding to a differentiated quality level. Moreover, since total profits increase without further investment, service cost portions that have to be paid per person can be significantly reduced. Accordingly, there is an advantage in that even a user who uses a high- quality level of service can pay a significantly lower subscription fee. Also, from a viewpoint of the receiver, in the case of a portable broadcasting service, there is no reason to purchase content of a high quality level at a high price although an external receiver is attached to a device having a limited motion picture processing ability, such as a mobile phone, a camcorder or a digital camera. On the contrary, from a standpoint of broadcasting service providers, they cannot practice an inexpensive billing system because it is not guaranteed that an external receiver can be connected to only a device having a limited motion picture processing ability. Therefore, there is a need for a method of solving anxieties of such broadcasting service providers and safely implementing demultiplexing and decoding policies of the broadcasting service provider. The present invention can meet those needs of the broadcasting service provider and the user in a safe manner. Although the present invention has been described in connection with the embodiment of the present invention illustrated in the accompanying drawings, it is not limited thereto since it will be apparent to those skilled in the art that various substitutions, modifications and changes may be made thereto without departing from the scope and spirit ofthe invention.

Claims

1. An intelligent broadcasting system, comprising: a broadcast apparatus; and a broadcast receiving apparatus, wherein the broadcast apparatus comprises: a multi-level encoder for encoding one source data into multiple levels to generate a plurality of multi-level encoded data, a multiplexer for multiplexing the multi-level encoded data to generate multiplexed data, an encryptor for encrypting the multiplexed data according to a predetermined mode to generate encrypted data, and a transmitter for broadcasting the encrypted data; and wherein the broadcast receiving apparatus comprises: a receiver for receiving the broadcasted encrypted data, a decryptor for decrypting the received encrypted data to generate the multiplexed data; a demultiplexer for demultiplexing the generated multiplexed data to generate the multi-level encoded data, and a multi-level decoder for decoding the multi-level encoded data.

2. The intelligent broadcasting system as claimed in claim 1, wherein the broadcast receiving apparatus further comprises an access quality control system for controlling at least one of the decryptor, the demultiplexer and the multi-level decoder according to an access quality control policy for a user of the broadcast receiving apparatus, to allow replay of the source data as at least one of two or more reception quality levels associated with the source data.

3. A broadcast apparatus for an intelligent broadcasting service, comprising: a multi-level encoder for encoding one source data into multiple levels to generate a plurality of multi-level encoded data; a multiplexer for multiplexing the multi-level encoded data to generate multiplexed data; and a transmitter for broadcasting the multiplexed data.

4. The broadcast apparatus as claimed in claim 3, further comprising an encryptor for encrypting the multi-level encoded data or the multiplexed data according to a predetermined mode.

5. The broadcast apparatus as claimed in claim 4, further comprising a user quality authorization system for distributing an access quality control policy that allows replay of the source data as at least one of two or more reception quality levels associated with the source data.

6. The broadcast apparatus as claimed in claim 3, further comprising a user quality authorization system for distributing an access quality control policy that allows replay of the source data as at least one of two or more reception quality levels associated with the source data.

7. The broadcast apparatus as claimed in claim 6, wherein the access quality control policy is a combination of at least one of a decoding control policy and a demultiplexing control policy.

8. The broadcast apparatus as claimed in claim 3, wherein the multi-level encoder encodes the source data into basic data and at least one displacement data.

9. The broadcast apparatus as claimed in claim 3, wherein the multi-level encoder encodes the source data into two or more data where a quality ofthe data is different.

10. The broadcast apparatus as claimed in claim 9, wherein the quality ofthe data is a combination of at least one of the number of pixels, the number of colors, the number of frames per second and a compression rate of video data, in case that the source data are video data.

11. The broadcast apparatus as claimed in claim 9, wherein the quality ofthe data is a combination of at least one of the number of samples per second, the number of bits per sample and a compression rate of audio data, in case that the source data are audio data.

12. The broadcast apparatus as claimed in claim 3, further comprising a user quality management system for maintaining user information indicating which one of two or more broadcast quality levels associated with the source data is granted to a user of the intelligent broadcasting service, and managing billing depending on the service quality level that is provided to the user.

13. A broadcast apparatus for an intelligent broadcasting service, comprising: a multi-level encoder for encoding one source data into multiple levels to generate a plurality of multi-level encoded data; and a transmitter for broadcasting the multi-level encoded data through different broadcast channels.

14. The broadcast apparatus as claimed in claim 13, wherein the multi-level encoder encodes the source data into basic data and at least one displacement data.

15. A broadcast receiving apparatus for an intelligent broadcasting service, comprising: a receiver for receiving broadcast data including a plurality of data for which one source data are encoded into multiple levels; an access quality control system for controlling a data replayer according to an access quality control policy that indicates which one of two or more reception quality levels associated with the broadcast data is allowed for a user to access; and the data replayer for generating broadcast data of a given quality level authorized to the user from the multi-level encoded data, and providing the generated broadcast data to the user according to the access quality control policy.

16. The broadcast receiving apparatus as claimed in claim 15, wherein the data replayer comprises: a demultiplexer for demultiplexing the broadcast data to generate the multi-level encoded data; and a multi-level decoder for decoding the multi-level encoded data.

17. The broadcast receiving apparatus as claimed in claim 15, wherein the access quality control system controls at least one of the demultiplexer and the multi-level decoder according to the access quality control policy so that broadcast data of a quality level authorized to the user can be generated.

18. The broadcast receiving apparatus as claimed in claim 16, wherein the broadcast data are encrypted data, and the data replayer further comprises a decryptor for decrypting the encrypted data.

19. The broadcast receiving apparatus as claimed in claim 18, wherein the access quality control system controls at least one of the decryptor, the demultiplexer and the multi-level decoder according to the access quality control policy so that broadcast data of a quality level authorized to a user can be generated.

20. The broadcast receiving apparatus as claimed in claim 15, wherein the access quality control system controls the data replayer according to the access quality control policy by channel or hour as to which quality level in association with the broadcast data is allowed for the user to access.

21. The broadcast receiving apparatus as claimed in claim 15, wherein the access quality control policy includes information on allowance of access to broadcast data of plural quality levels among the two or more reception quality levels associated with the broadcast data, the data replayer further comprises a user input unit for receiving a selection of quality level in order to access to the broadcast data from the user, broadcast data ofthe selected quality level are generated and provided.

22. A broadcast receiving apparatus for an intelligent broadcasting service, comprising: a channel demultiplexer for combining data received through a plurality of different broadcast channels as a plurality of data in which one source data are encoded into multiple levels, to demultiplex the one source data.

23. An intelligent broadcasting system for an intelligent broadcasting service, comprising: a broadcast apparatus; and a broadcast receiving apparatus, wherein the broadcast apparatus comprises a user quality management system for maintaining a user identifier corresponding to a user of the intelligent broadcasting service and data of a given quality level, which is used by the user, among two or more broadcast quality levels associated with one broadcast data in association with the user identifier, and for managing billing depending on the quality level used by the user; and the broadcast receiving apparatus comprises: a receiver for receiving the broadcast data; and a quality degrader for degrading the broadcast data into broadcast data of a predetermined quality level.

24. - A broadcast receiving apparatus for an intelligent broadcasting service, comprising: a receiver for receiving broadcast data; and a quality degrader for degrading the broadcast data into broadcast data of a predetermined quality level.

25. The broadcast receiving apparatus as claimed in claim 24, further comprising: a conditional access system for controlling subscription of a predetermined broadcast channel; and a serial number comparison unit for comparing a serial number, which is an identifier of the broadcast receiving apparatus, and a serial number, which is an identifier of the conditional access system, and only in case that the two serial numbers are a pair of previously stored serial numbers, allowing replay ofthe broadcast data.

26. A broadcast receiving apparatus for an intelligent broadcasting service, comprising: a receiver for receiving broadcast data; an access quality control system for controlling a quality degrader according to an access quality control policy, which indicates which one of two or more reception quality levels associated with the broadcast data is allowed for a user to access; and the quality degrader for degrading the broadcast data into broadcast data of a given quality level, which are granted to the user, under the control ofthe access quality control system.

27. The broadcast receiving apparatus as claimed in claim 26, wherein the access quality control system controls whether to operate the quality degrader according to the access quality control policy as to the broadcast data.

28. The broadcast receiving apparatus as claimed in claim 26, wherein the quality degrader degrades the broadcast data by employing a plurality of degradation modes, and the access quality control system controls whether to operate the quality degrader according to which one ofthe plurality of the degradation modes regarding the broadcast data.

29. The broadcast receiving apparatus as claimed in claim 26, wherein the access quality control system receives the access quality control policy by communicating with a predetermined management server, and controls the quality degrader based on the received access quality control policy.

30. The broadcast receiving apparatus as claimed in claim 26, wherein the broadcast data are multiplexed data, and the apparatus further comprises a demultiplexer for demultiplexing the multiplexed data.

31. The broadcast receiving apparatus as claimed in claim 26, wherein the access quality control policy includes information, which allows the user to access broadcast data of two or more quality levels, with respect to whether to operate the quality degrader and which degradation mode will be performed among a plurality of the degradation modes, the receiver further comprises a user input unit for receiving a selection of quality level in order to access the broadcast data, and broadcast data ofthe selected quality level are generated and provided.

32. A broadcast receiving apparatus for an intelligent broadcasting service, comprising: a receiver for receiving broadcast data in which one source data is encoded into basic data and at least one displacement data; and a data replayer for decoding at least one of the basic data and the displacement data to generate broadcast data of a quality level that is authorized to a user.

33. A broadcast receiving apparatus for an intelligent broadcasting service, comprising: an ESN reader for reading an ESN to identify a broadcast receiving apparatus; an ESN quality level storage unit for grouping the ESNs and storing quality level data of broadcast data, which are authorized to a user, by grouped ESN; an access quality control policy storage unit for storing the quality data of the broadcast data of which the replay is authorized in the broadcast receiving apparatus; and an authorization quality level comparison unit for comparing the read ESN and the quality level data stored in the access quality control policy storage unit with quality level data by ESN, which are stored in the ESN quality level storage unit, and in case that it is determined that the read ESN and the quality data are in discord with the quality data by ESN, limiting the replay ofthe broadcast data.

34. A broadcast receiving apparatus for an intelligent broadcasting service, comprising: an ESN reader for reading an ESN to identify a broadcast receiving apparatus; an access quality control policy storage unit for storing quality level data of broadcast data of which replay is authorized in the broadcast receiving apparatus; and a feedback communication unit for transmitting the read ESN and the quality data stored in the access quality control policy storage unit to a predetermined server.

35. An intelligent broadcasting system, comprising: a broadcast apparatus for encoding one source data into multiple levels to generate broadcast data, and broadcasting the generated broadcast data; and a broadcast receiving apparatus for receiving the broadcast data and allowing only a user who is authorized by a predetermined access quality control system to replay the broadcast data of a predetermined quality level.