Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1999-02-23
2003-05-20
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Repeater
C370S337000, C370S347000
Reexamination Certificate
active
06567385
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a communication system implementing time division multiple access in which a number of terminal stations communicate with a central node and wherein information is sent in the form of bursts from the terminal stations towards the central node. The invention also relates to a method of communicating information, from a number of terminal stations to a central node, using time division multiple access.
The invention still further relates to a method of rearranging the transmission positions for bursts of information sent from a number of terminal stations in a point-to-multipoint system implementing time division multiple access depending on the transmission demand of the terminal stations.
STATE OF THE ART
In point-to-multipoint radio communication networks information is communicated between a central node (a radio node) and a number of terminal stations, also called radio terminals. Each radio terminal in turn continuously communicates with a user station arranged next to the terminal and the radio node continuously communicates with a transmission network. For communication from the radio node to the radio terminals, i.e. for downlink communication, the transmission is continuous and all terminals have got access to all the information, i.e. information is broadcasted. However, for communication from the terminals to the radio node, i.e. uplink communication, time division multiple access is implemented which means that the radio terminals communicating with the radio node share a common communication resource within which each radio terminal is assigned a time period during a frame, (the communication channel is divided into a number of frames), during which it is allowed to send a burst of information.
Thus information is sent in both directions between the transmission network and the users. During steady state operation, i.e. during normal operation, the radio terminals transmit regularly with a constant time interval, a frame, in which each terminal is assigned a given capacity and a given starting position so that the total capacity can be used as efficiently as possible which means that the bursts from the respective terminals are packed as densely as possible within the frame. However, the amount of data may vary from terminal to terminal which means that the bursts which are sent do not have to have a constant length in relation to each other. During the time period it takes to send a frame, all the active radio terminals must be allowed to send information at their predetermined time positions. The radio node comprises scheduling means which is used to determine these time positions.
In a point-to-multipoint access network it often occurs that the transmission demand, e.g. the amount of information that needs to be sent from terminals varies, or terminals may be disconnected as well as new terminals may be connected etc. It is then important that such changes can be handled in such a manner that the transmissions channels still can be used in an efficient way. This is done through rearranging the frame or by defragmentation of the frame. In order to provide for defragmentation, the time positions for sending bursts from the respective terminals have to be changed for example in order to enable the sending of information from a new connected terminal, i.e. that a time interval has to be made available to such terminal. The displacement of the transmission positions for the terminals must be handled in such a way that the new terminal is allowed to transmit information or that a terminal needing to send more information is enabled to do so etc. In a system not permitting reconfiguration of the transmission positions of the bursts from the respective terminals, buffering means provided in the radio node as well as in the radio terminal would only have to store the information corresponding to the number of information bits arriving during a frame. This however means, for example, that if a terminal is disconnected, there is a risk that the capacity of the channel might not be fully used.
However, a number of systems are known which permit the displacement of the transmission positions.
FIG. 1A
schematically illustrates bursts from a terminal, here denoted terminal T, which are sent in a first, early, position within the frame and the sending positions for which are changed to a later position within the frame. It should be noted that information or data continuously arrives to the terminal from the user station as well as data continuously is sent out from the radio node to the transmission network. Furthermore each burst contains the same amount of information and the information is buffered in buffering means BT in terminal T as well as in the radio node. As can be seen from
FIG. 1A
in frames N−1 and N, bursts B
N−1
, B
N
are sent at a first position within the respective frame whereas in frames N+1 and N+2 burst B
N+1
, B
N+2
are sent at a new, later position within the frames. This means that between frame N and frame N+1 the buffering means of the radio terminal has to store more information and the radio node has to send out prestored information.
This means that the total filling degree in the buffering means (terminal and node) is constant within the system but that data has been redistributed from the node to the terminal buffering means. This is graphically illustrated in
FIGS. 1B and 1C
respectively. In
FIG. 1B
the amount of data in the buffering means of the radio terminal is illustrated as it changes with time, i.e. from the sending of frames N−1 to N+2. Data in the buffering means of the radio terminal D
BT
during steady state operation maximally reaches a given value and as a burst is sent during frame N−1, the data in the buffering means of the terminal station is sent out. Thereafter, during the rest of the frame, data is collected until the sending of a further burst in frame N. However, since a displacement from an early position within the frame to a later position within the frame takes place during the time that passes between the sending of frame N to frame N+1, the data in the buffering means of the radio terminal is substantially doubled until a burst is sent out at the later position as illustrated with a burst B
N+1
in frame N+1. Then, again, a steady state operation is reinstated which however requires a larger buffer in the radio terminal. In
FIG. 1C
the corresponding situation for the buffering means of the radio node is illustrated and the amount of data in the node buffer D
BN
is illustrated as a function of time. As can be seen from
FIG. 1C
, the opposite situation occurs in the node buffering means and it will be realized that the sum of the data in the buffers in the radio node and in the terminal respectively, illustrated through X and Y respectively in
FIGS. 1B
and
1
C, before and after the displacement, is the same, which means that the delay in the point-to-multipoint communication system will be the same but data has been redistributed to the buffering means of the radio terminal from the radio node. Thus, the same amount of data is sent every time but the sending is set out once which means that a larger delay is produced and large buffering means are required.
In order to allow the defragmentation of a channel it must also be possible to displace bursts from a later position to an earlier position within a frame. This is described with reference to
FIGS. 2A-2C
corresponding to
FIGS. 1A-1C
but with the difference that the change produced in frame N+1 is that bursts are sent at an earlier position. As can be seen from
FIG. 2B
it is a prerequisite by that the terminal has prestored data if it is to be able to send two bursts of the same size within a short period of time It is supposed that the amount of data is equal in each burst. There must also be free capacity in the buffering means of the node in order to be able to handle a fast filling up of the buffering means since two burs
George Keith M.
Nguyen Chau
Telefonaktiebolaget LM Ericsson (publ)
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