Abstract:
For allocating radio resources in a time-division multiple access packet mode radio communication system, each remote station stores transmit authorizations for each time slot of a frame in a table. The packets are stored in a plurality of queues in each remote station. The table is duplicated and one table is read during a frame while the other table is being written.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns packet mode radio communications and more particularly the allocation of uplink radio resources in a radio communication system. 
     2. Description of the Prior Art 
     The problem arises in radio communication systems of allocating uplink radio resources between the various remote stations, in other words, the problem of managing multiple access. The problem does not arise on the downlink, i.e. in the direction from the gateway to the remote stations. For the uplink, i.e. in the direction from the remote stations to the gateway, it is necessary to arbitrate the use of radio resources between the remote stations. 
     There are two solutions to this problem. Firstly, multiple access can be managed by detecting collisions. In a protocol of this kind, the remote stations transmit without any synchronization being required and an information bit is transmitted correctly only if only one remote station transmits at a time. This type of protocol can be validly based only on a shared radio resource that is low in cost because its capacity is greatly increased compared to what is strictly necessary. 
     Access from the remote stations to the common radio resource can also be synchronized by a function which assigns multiple access requests (DAMA—dynamic allocation multiple access). This type of protocol is described by Argagnon C. et al. in “ANIS or providing multimedia services via satellites, though effective use of standards”, IAF&#39;98, Melbourne, for example. 
     U.S. Pat. No. 5,327,432 also addresses the problem of allocating time slots to remote stations of a time-division multiple access radio communication system. The solution proposed in this prior art document is for the gateway to transmit an allocation message which is processed in a remote station by a message-segmenting circuit. This prior art document is more particularly concerned with the time slot allocation protocol. 
     U.S. Pat. No. 5,363,374 describes an anticipatory method of allocating resources. To reduce the time needed to allocate resources, this prior art document proposes transmitting the resource reservation request before the total number of resources required is known. 
     Document EP 0.484.387 describes a method which entails maintaining an up-to-date list in a gateway of remote stations which are currently requesting transmission of packets of a given type and a given length. The gateway determines which remote stations are to be allocated time slots and transmits a frame which indicates the slots allocated for transmitting packets in the next frame. The slots allocated are defined by the respective positions in the frame of the identifiers of the remote stations that will be authorized to transmit. 
     The object of the invention is to improve on the above prior art methods. 
     SUMMARY OF THE INVENTION 
     To be more precise, the invention proposes a method of allocating uplink radio resources in a time-division multiple access packet mode radio communication system comprising at least one gateway and a plurality of remote stations each of which comprises means for storing packets to be transmitted, the method including the steps of: 
     storing packets to be transmitted from a remote station in a plurality of queues, 
     referring to the identifiers of the queues of a remote station in the transmit authorizations for each time slot of a frame, 
     during one frame, transmission by a gateway of transmit authorizations for a next frame which include the identity of a remote station authorized to transmit during said slot and which are written in at least one table in each remote station, and 
     during the next frame, reading of the transmit authorizations in the table by each remote station and transmitting packets stored by each remote station as a function of the transmit authorizations read in this way. 
     The invention also proposes a remote station of a multiple access packet mode radio communication system for implementing the above method. 
     Other features and advantages of the invention will become apparent on reading the following description of one embodiment of the invention which is given by way of example and with reference to the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The single FIGURE of the accompanying drawing is a diagrammatic representation of part of a remote station implementing the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention is described hereinafter with reference to an ATM (asynchronous transfer mode) satellite telecommunication system. The period T of the uplink frame is divided into K time slots and in this example each of the K time slots corresponds to one ATM cell. 
     The invention proposes to provide each remote station with N memories or tables each with K locations corresponding to the K cells that can be transmitted during the period of the uplink frame, where N is an integer not less than two. During a frame period, the remote stations transmit during the K time slots according to the content of one of the memories. The other memory is updated for the next frame, on the basis of requests from the remote stations. 
     The FIGURE is a diagram showing part of a remote station implementing the invention. It shows various queues  1  through  4  of the remote station which contain cells to be transmitted. The outputs of the various queues are routed to a multiplexer  5  which selects cells to be transmitted in accordance with priority rules specific to each system. The mechanism for selecting cells from the various queues and the mechanism for managing queue overflows are not relevant to the invention and are not described further. The cells supplied by the multiplexer are transmitted by the remote station, as symbolized by the transmitter  6 . 
     The remote station further comprises two tables or memories  7  and  8  each of which has K locations. The tables  7  and  8  are read and written alternately, one table being read during a period T while the other one is being written with information received from the gateway. 
     For a given uplink frame T, one table  7  or  8  of each remote station is read synchronously, for example under the control of a frame synchronization signal provided by the gateway. The tables read by the cells contain the transmit authorizations for the remote stations: each of the K lines of the table read during the frame corresponds to one of the K time slots and contains at most one authorization to transmit one cell for one of the remote stations. Reading the lines of the table therefore enables a remote station to determine in which time slot it is authorized to transmit. In the FIGURE, the respective arrows  9  and  10  from the tables  7  and  8  symbolize the fact that transmission of a cell by the transmitter  6  depends on the contents of the tables  7  and  8 . 
     While one table is being read, the other table can be updated under the control of the gateway to indicate the transmit authorizations for the next frame. The table is advantageously updated as a function of requests transmitted by each remote station. 
     The invention ensures that at most one remote station can transmit a cell during a time slot of an uplink frame. 
     It is possible for no transmission authorization to be granted for a given line of the table being read, i.e. for a given time slot. In this case, one option is not to transmit any signal, in which case none of the remote stations transmits cells. Another option is to transmit an empty cell from one of the remote stations. In this case, the line of the table can have a content representative of the absence of authorization to transmit an active cell. The remote station which transmits the empty cell can be chosen either on the basis of the content of the line of the table (which can contain the name of the remote station to transmit an empty cell) or in accordance with a predetermined function, for example, such that the last remote station that transmitted an active cell must transmit an empty cell. 
     Priorities can be managed in accordance with the invention in the remote stations and/or in the gateway. Accordingly, if the various remote stations transmit to the gateway information representative of the priorities of the cells contained in the various queues, the transmit authorizations in the tables can indicate not only the remote station that can transmit but also the queue of the remote station from which the active cell to be transmitted must be taken. 
     Conversely, the invention can also be used in a system in which the remote stations supply to the gateway only an indication representative of the highest priority of the cells in the queue of the remote station. In this case, cells in the next frame are allocated as a function of this highest priority for each of the remote stations and in a given remote station lower priorities are managed locally. 
     Intermediate solutions are clearly possible, depending on the nature of the priority management scheme implemented in a given system. 
     Of course, the present invention is not limited to the examples and embodiments described and shown, and is open to many variants that will suggest themselves to the skilled person. In particular, it is not limited to a TDMA (time-division multiple access) system, but applies to any system in which radio resources must be shared between remote stations. The number of tables or memories is not limited to two, and there can be a greater number of tables or memories. This can be the case in particular if read and write mode synchronization in the tables makes it impossible to read a table in alternate frames. In this case three tables can be provided, which are read and written alternately. The invention is not limited to a system in which each time slot of a frame corresponds to a cell, but applies more generally to time slots comprising more than one cell.