INTERACTIVE COMMUNICATION SYSTEM COMPRISING USERS CONNECTED IN GROUPS

Abstract: The invention relates to a communication system comprising a transmission medium, users connected in groups to the transmission medium through a convergence point, and a main station designed to receive data transmitted by the users over the transmission medium. The access to the transmission medium is limited for one and the same group of users at any given moment. According to the invention, the main station comprises means for assigning to the users access rights to the transmission medium by taking into account their membership of a group of users.

Description: Interactive communication system comprising users connected in groups. The invention relates to a communication system comprising a communication medium between a main station and at least one convergence point for serving a group of users, said convergence point having a certain transmission capacity on the transmission medium. The invention also relates to a main station and a user terminal designed for use in such a system. The invention applies in particular to SMATV (Satellite Master Antenna Television) systems. The problem which arises in this type of system is the following: the convergence point is provided with transmission means on the transmission medium which have a given capacity such that at any given moment the access to the transmission means is limited for the users of one and the same group. For example, the technical report TR 101 201 Nl.1.1 published in October 1997 by ETSI describes an interactive SMATV distribution system. In such a system, a group of users share the same transmitter and the same transmission antenna for transmitting requests to the main station of the communication system. Since the transmitter is capable of transmitting on one carrier only at any given moment, this means that only one user can transmit at any given moment. Management means are accordingly necessary for managing the access of the users of a same group to the transmission medium. The solution proposed in said document is shown diagrammatically in Fig. 1. It consists in joining together a satellite transmission network 1 and a cable network 2: the convergence point 3 is formed by a satellite antenna 4 connected to an interactive satellite terminal 5 which in its turn is connected to a central station 6 of a cable network 2. The central station 6 of the cable network 2 is a cable network head in the sense of recommendation ETS 300 800 of ETSI. It serves the final users 7 and provides the interface with the satellite transmission network 1. It is seen as one single user by the satellite transmission network, and the final users remain unknown to the satellite transmission network. This solution involves the following problem: the central station 6 is a cable network head in the sense of recommendation ETS 300 800. It accordingly involves a comparatively expensive equipment. The cost of this equipment is shared among the users of the network 2. This solution is thus only viable financially if the network 2 comprises a sufficiently great number of users. The invention has for its object to provide an effective and less expensive solution for small groups of users. This object is achieved with a system, a main station, and a user terminal as claimed in Claims 1, 5, and 7 of the present patent application. It is the main station which governs the path between the convergence point and the users in a communication system according to the invention. The main station assigns the reservations on the transmission medium directly, taking into account the fact that the access to the transmission medium is limited for one and the same group of users. In the case of an interactive satellite transmission system, for example, the main station assigns to the users speaking time intervals on a carrier, making sure not to assign the same time interval on different carriers to different users of one and the same user group. This solution is advantageous financially for the following reasons: - the management of the reservations is shifted to the main station of the communication system so that no management device for these reservations is necessary anymore at the level of the convergence point, - no specialized, non-standard material is used (from an industrial point of view, the development and production of the specialized, non-standard material used in comparatively small quantities is very expensive). In a first embodiment of the invention, the main station is provided with tables which can be manually programmed by an administrator of the communication system so as to contain the configuration of the communication system, in particular information on the membership of the users of a user group. In another advantageous embodiment, the users of a user group are each provided with an identifier which renders it possible to identify the user and the group to which he belongs, and they comprise transmission means for transmitting said identifier to the main station when they establish connection with the communication system. This identifier is formed, for example, by the physical address (MAC address) of the terminal, formatted in two parts, a first part identifying the convergence point and a second part identifying the terminal. This physical address is transmitted in the address field of the connection-establishing messages emitted by the users when they make connection with the system. This solution renders possible an automatic learning process of the main station on the basis of the addresses of the users which make connection with the communication system. No manual configuration operation is accordingly necessary in this case. The invention also relates to a method of assigning reservations as defined in Claim 9 and an identification method for users as defined in Claim 10. The invention will be better understood and further details will become apparent from the following description with reference to the annexed drawings which are given by way of non-limitative example and in which: - Fig. 1 shows a system as described in the prior art, - Figs. 2 and 3 show communication systems according to the invention, - Fig. 4 shows the format of a physical address of a user terminal according to the invention, - Fig. 5 shows the format of a connection message sent by a user terminal to the main station, and - Fig. 6 shows a method of assigning reservations on to the transmission medium by a main station according to the invention. Fig. 2 shows a communication system according to the invention. This system comprises two transmission media 9 and 10. The transmission medium 9 is a distribution medium which renders it possible for a main station 11 to distribute data to users Tj (i = 0, 1, 2, 3, 4). The transmission medium 10 constitutes a return path which renders it possible for the users Tj to transmit requests to the main station 11. The main station 11 is provided with an access point 14 for the transmission medium 10. The users T; (i = 1, 2, 3, 4) are part of a user group 15 which is connected to the transmission medium 10 via a convergence point 16. The user To is an individual user. He is connected to the transmission medium by means of an individual access point 17. The invention relates to all communication systems of the type as shown in Fig. 2 in which a convergence point 16 has a transmission capacity over a transmission medium 10 which is limited such that at any given moment the access to the transmission medium 10 is limited for the users of one and the same group. The transmission medium 10 is formed, for example, by radio wave links or satellite links. According to the invention, the main station 11 assigns to the users Tj reservations on the transmission medium in dependence on their membership of a user group. To achieve this in a preferred embodiment of the invention, each user is given an identifier which renders it possible to identify the user and the group to which he belongs. This identifier is then transmitted to the main station by the user when making connection with the transmission system. This identifier is formed, for example, by the physical address of the terminal T, which is transmitted in each connection request sent by a terminal to the main station 11. A particular physical address format is used for this: the physical addresses are formatted in at least two parts, one part identifying the convergence point and the other part identifying the terminal. In a first embodiment, all addresses of the terminals are formed by stringing together a first address part Al stored in the convergence point or in the access point of the terminal and a second address part A2 stored in the terminal. In a second embodiment, two distinct physical addresses may be applied to the terminal depending on its mode of connection (individual or collective) to the transmission medium. To achieve this, a physical address part A2 and a complete physical address A3 are stored in the terminal. If the terminal is connected in the individual mode, the terminal is assigned the physical address A3, which is fully stored in the terminal. If the terminal is connected in the collective mode, a physical address formed by stringing together the physical address part stored in the terminal (A2) and the physical address part stored in the convergence point (Al) is assigned to the terminal. The individual or collective mode of connection of the terminal (and thus the address to be used, A3 or Al and A2 joined together) is indicated by a status variable S which is stored in the terminal and whose value is defined during the installation of the terminal. This second mode of realization renders it possible to have more addresses available for groups of terminals. Upon the reception of connection requests, the main station 11 registers the physical address of the connected terminals in a table. The main station 11 traverses this table for assigning reservations to terminals of the communication system in order to determine the membership of the relevant terminals of a group of terminals. Fig. 3 shows an example of an interactive SMATV distribution system according to the invention. In such a system, the main station 11 distributes data and control information to the user terminals Tj via a satellite 20. These users T; transmit data and requests to the main station 11 by means of this same satellite 20. The following description will exclusively relate to those operating principles of an interactive satellite transmission system which are necessary for understanding the invention. More details can be found, for example, in the technical report TR 101 201 VI.1.1 of ETSI. For communicating with the main station, the terminals of an interactive satellite transmission system access the transmission medium by an access mechanism, for example a TDMA (Time Division Multiple Access) mechanism combined with a frequency division FDMA (Frequency Division Multiple Access). Each carrier is for this purpose subdivided into time intervals with which different access modes are associated. The following are used in particular: - time intervals which are accessible in a contention mode and to which all the terminals have free access, with the risk of collisions (a classical collision-resolving algorithm is used for resolving any collisions which may occur). These contention time intervals are particularly used by the terminals for making connection with the communication system. - time intervals which are accessible upon reservation and which are dynamically granted by the main station 11 upon a request from the terminals. The requests are transmitted, for example, in the contention time intervals, or following payload data in time intervals previously granted by the main station. The following problem arises when the terminals are connected to transmission media by means of a transmitter and a collective antenna: the transmitter is capable of transmitting and receiving only one carrier at any given moment. The main station accordingly must not grant the same time interval on different carriers to users of one and the same group. To solve this problem, a specific addressing format is used for the terminals of the communication system. In practice, each terminal of a communication system as represented in Fig. 3 is provided with a 48-bit address (referred to as MAC address) which is fixedly coded in each terminal or which is provided by an external source. For example, one might choose to assign to these MAC addresses the format shown in Fig. 4: - the two bits of highest order (bO and bl) are reserved for ensuring the compatibility with the addresses defined in accordance with the IEEE 802.2 standard. According to the 802.2 standard, the physical address of a terminal is coded in 48 bits. The bit of highest order (bO) indicates that it is an individual address or a group address (the use of a group address in the destination address field of a frame renders it possible for several terminals to receive the same frame). The next bit (bl) serves to define the nature of the addresses, local or global. The local addresses are administered by the responsible manager of a given network and have a significance only in this network, while the global addresses (also called universal addresses) are unique at planet level and are administered by the IEEE, who assign them to various manufacturers. To ensure the compatibility with the addresses defined by the IEEE 802.2 standard, the choice made here is accordingly bO = bl = 1 (local group address in accordance with the IEEE 802.2 standard). - the next twenty bits (b2-b21) are used for identifying the convergence point, - the next six bits (b22-b27) are used for identifying the manufacturer of the terminal, - the last twenty bits (b28-b47) are used for identifying the terminal. In a first embodiment, one part Al of the address of 22 bits length is stored in each access point and in each convergence point (i.e. in the equipment which connects the antenna to the terminal and which ensures in particular the functions of frequency translation), and one part A2 of the address of 26 bits length is stored in each terminal which is connected to this convergence point. In a second embodiment, a part Al of the address of 22 bits length is stored in each convergence point, and the following are stored in each terminal: - a complete address of 48 bits which is an individual universal address (bO = bl = 0) and which is used when the terminal is connected to transmission media in the individual mode, a part A2 of the address of 26 bits length which corresponds to the two last groups of six and twenty bits, respectively, and which is used when the terminal is connected in the collective mode. In this case this address part is stringed together with the address part of 22 bits stored in the convergence point so as to form a 48-bit address which constitutes the physical address of the terminal. In this second embodiment, it is indicated by a status variable S stored in the terminal which address should be used, the value of said variable being defined during the installation of the terminal. These two embodiments are compatible in one and the same communication system. The terminals achieve connection to the transmission system through the transmission of connection messages in time intervals which are competitively accessible. These connection messages are diagrammatically shown in Fig. 5. They comprise more in particular an address field FI which contains the physical address of the terminal and a data field F2 which contains the characteristics of the required connection (the data rate required, the type of service, ...). The main station, which receives these connection messages, thus automatically gets to know the groups of terminals. The main station 11 assigns to the users reservations on the transmission media, taking into account their membership of a user group such that one and the same time interval is not granted to users of a same group on different carriers. An example of the method according to the invention of granting reservations is shown in Fig. 6. This method renders it possible to grant n; reservations to each of the n terminals Tj which are connected to the communication system. In the example described here, each reservation is formed by a pair (time interval / carrier). The main station carries out the following steps for each terminal T J : step 100: it searches among the terminals T 1; ..., T^ (i.e. among the terminals to which it has already granted reservations) those which belong to the same group as the terminal Tj. This group is referred to as group G R in the following description. If at least one of the terminals Ti, ..., TM belongs to the group G K (arrow Y in the Figure), the method proceeds to step 110. If not (arrow N in the Figure), it proceeds to step 120. - step 110: the main station grants n; reservations to the terminal Tj. The time intervals S j (T,) (with j = 1, ..., n for these reservations are chosen such that they are different from the time intervals of the reservations already granted to the terminals of the group G R . This operation is diagrammatically represented in the Figure by the following mathematical expression: - step 120: the main station assigns n; access rights to the terminal Tj in any manner. In an advantageous embodiment, the users which are part of a user group comprise listening-in means for listening in to the assignments made by the main station to the other users of their group, and control means for blocking the use of a time interval which is accessible in a contention mode if the main station has granted this same time interval (on another carrier) to another user of the same group. Said listening-in means consist in that an analysis is made of the signaling information transmitted by the main station 11, which information gives the structure of the upcoming frames for each carrier. The listening-in facility may be limited to a given number of carriers if the main station comprises means for assigning carriers chosen from among a sub-set of carriers to the users of a same group, as well as means for transmitting to the users of a group the list of the carriers liable to be relevant to them, i.e. the list of the carriers to be listened in to. The embodiments described above do not render it possible to avoid that two users of a same group access a same contention time interval if this time interval has not been granted to a terminal of the same group by the main station. In another advantageous embodiment, this collision risk is limited by the introduction of a power measurement device before the transmission. The determination of a power threshold value which is considered normal for one single transmission and a comparison of the power level with this threshold value renders it possible to determine whether several users are trying to transmit data in the same time interval and to block the transmission if this is the case. An example has been described in which the terminals access the transmission medium by a multiple access mechanism on the basis of time division, combined with a frequency allocation. This example is by no means restrictive. For example, the invention is also applicable if the multiple access mechanism to the transmission medium is a CDMA (Code Division Multiple Access) mechanism. In the example described, the transmission media 9 and 10 are both formed by satellite links. The broadcasting media and the return path, however, may be of different types.

Claims: CLAIMS: 1. A communication system comprising a transmission medium between a main station and at least one convergence point for serving a group of users, said convergence point having a certain transmission capacity on the transmission medium, characterized in that the main station comprises means for assigning to the users reservations on to the transmission medium by taking into account their membership of a group of users and the transmission capacity of the convergence point. 2. A communication system as claimed in Claim 1, characterized in that the users of a group of users are provided with an identifier which renders it possible to identify the user and the group to which he belongs, and in that they comprise transmission means for transmitting said identifier to the main station when they make connection with the communication system. 3. A communication system as claimed in Claim 1, characterized in that said transmission medium comprises satellite links and said convergence point comprises a collective antenna which is connected to a satellite transmitter, said satellite transmitter being connected to said users. 4. A communication system as claimed in Claim 1, characterized in that, said transmission medium being designed to be shared in time and in frequency al least, said reservations correspond at least to a transmission frequency for a given time. 5. A main station suitable for communicating through a transmission medium with at least one convergence point which serves a group of users and having a certain transmission capacity on the transmission medium, characterized in that said station comprises means for assigning to the users reservations on to the transmission medium by taking into account their membership of a group of users and the transmission capacity of the convergence point. 6. A main station as claimed in Claim 5, characterized in that, the users of a group being provided with an identifier which renders it possible to identify the user and the group to which he belongs, said station comprises means for memorizing the identifiers of the users which make connection with the communication system and means for determining from said identifier the membership of a user of a group. 7. A user terminal suitable for being part of a group of user terminals which access a transmission medium through a convergence point for communicating with a main station, characterized in that said terminal comprises at least memory means for storing a first part of the identifier which identifies said user, means for obtaining a second part of the identifier identifying said convergence point, means for joining together said first and second part of the identifier for forming an identifier for said user, and transmission means for transmitting said identifier to the main station when making connection with the communication system. 8. A user terminal as claimed in Claim 7, characterized in that said identifier constitutes a physical address of the terminal which is transmitted to the main station in a connection message to the communication system. 9. A method of assigning reservations which is designed to be used in a main station of a communication system for assigning to the users reservation on a transmission medium, characterized in that it comprises: - a step of verifying whether the user belongs to a group of users connected to the transmission medium through a convergence point having a certain transmission capacity on the transmission medium, - a step of assigning reservations which takes into account the membership of the users of a group of users and the transmission capacity of the convergence point. 10. A method of identifying users in a communication system which comprises users connected to a transmission medium through a convergence point, characterized in that it consists in the assignment at least to said users of an identifier formatted in two parts, a first part identifying the convergence point and a second part identifying the user.

Inventors: ANSEAUME BERTRAND, BRAJAL AMERICO, ANSEAUME, BERTRAND, BRAJAL, AMERICO
Applicants: ANSEAUME BERTRAND, BRAJAL AMERICO, KONINKL PHILIPS ELECTRONICS NV, ANSEAUME, BERTRAND, BRAJAL, AMERICO, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 1999
Main classification: H04N7
IPC codes: H04B7, H04H1, H04J3, H04N7