Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1999-05-10
2003-07-08
Patel, Ajit (Department: 2664)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S509000
Reexamination Certificate
active
06590891
ABSTRACT:
The invention relates to the field of data processing systems for the exchange of data or messages between extensions or stations of one or more networks.
These systems are sometimes provided with relay stations provided with a network number and comprising, inter alia, a clock which defines a local reference time, a module intended to transmit/receive messages on a frequency which varies according to a selected time-division scheme (the schemes may vary from one station to the next) defined relative to the local reference time, and a control module which forms the messages to be transmitted and processes the messages received in order, e.g. to relay them towards other stations.
Some systems include relay stations of this type referred to as “variable frequency” relay stations, intended, inter alia, to relay messages towards other stations which may or may not be relay stations. Relay stations of this kind may be, e.g. access points (or bridges) of a wire network for the exchange of messages between stations of the wire network and mobile stations of a radio network. In this example, each relay station can communicate with several “non-relay” stations with which it forms a cell. A network can therefore be broken down into several cells which communicate by means of their respective relay stations.
As a result of the fact that the relay stations have personal non-synchronised clocks, they have the disadvantage that they are independent of one another, as, whether their respective time-division evolution schemes are identical or not, some of them may lag behind, with the result that the frequency on which one of the relay stations is transmitting at a given moment is not the frequency on which another relay station is receiving at this same moment.
This means that transmission between different cells is impossible as there has been no frequency tuning between these cells. This impossibility will last, on average, all the longer the greater the number of relays required for transmission, given that there must be frequency tuning at each relay.
The aim of the invention is therefore to provide a data transmission system and a corresponding process which do not have the aforementioned disadvantage.
To this end, it proposes a system of the type described in the introduction, in which:
on the one hand, the control module of each relay station brought into a selected state is adapted to form synchronisation messages including its network number and information relating to this selected state and intended at least for certain other relay stations, at least one of the relay stations, referred to hereinafter as the “master station”, having a control module permanently verifying this selected criterion, and,
on the other hand, each relay station (both the master station and the other stations referred to hereinafter as “slave stations”) includes a synchronisation module capable, upon receiving a synchronisation message containing the same network number as its own, of extracting the status information therefrom in order to bring its relay station into the selected state.
According to another feature of the invention, the information relating to the said selected state contained in the synchronisation messages includes at least information relating to a common reference time and to a common frequency and, inter alia, representative of the time-division scheme of this common frequency.
In this case, each synchronisation module is adapted to extract the information relating to the common frequency and to the common reference time from a synchronisation message received by the transmitting/receiving module associated therewith in the relay station, then, on the one hand, to adjust the local reference time defined by the local clock to the common reference time and, on the other hand, to provide the transmitting/receiving module with the information relating to the common frequency. The relay station is then considered to be in the selected state, on the one hand, when its local reference time is the common reference time and, on the other hand, when its transmitting/receiving module is ready to transmit/receive messages on the common frequency varying according to the time-division scheme of the latter.
By definition, the term synchronised station shall refer to a station brought into the selected state, i.e. a station which has been synchronised with the common reference time received from a synchronising station which may be a master station or a slave station which has just been synchronised and which relays (or broadcasts) the initial synchronisation message. In other words, a master station is necessarily a synchronising station, while a slave station can only be considered to be a synchronising station once it has been synchronised.
In this manner, by virtue of a synchronising station according to the invention, several cells independent of one another can be converted into one super cell forming a global network in which the messages can pass through from one cell to the next (or possibly from a segment of a first network to a segment of a second network).
These can be radio network segments (or cells) or radio and wire network segments, the formats of which are preferably selected, in the case of radio networks, from at least the formats of the “HIPERLAN” standard and IEEE standard 802.11 and, in the case of wire networks, from at least the ISO standards for the IEEE standards 802.3, 802.5 and 802.14.
The HIPERLAN format is described, inter alia, in the publications of the European Telecommunications Standards Institute (ETSI) and, more particularly, in “Technical Standard ETS-300-652”.
In the case of IEEE standard 802.11, the invention allows for the synchronisation of the access points (“Access Point AP”), such that they can use the radio interface as a distribution system (“Distribution System DS”) in order to communicate with one another. Extended radio networks (“Extended Service Set ESS”) using solely radio interfaces can therefore be obtained by virtue of the invention.
The system is moreover particularly suitable for networks referred to as “frequency-hop” networks or “direct-sequence spectrum spreading” networks, well known to the person skilled in the art.
According to yet another feature of the invention, the master (or synchronising) and slave relay stations are preferably connected together, i.e. there is a path between two arbitrary stations formed by stations within radio range.
The common frequency, its time-division evolution scheme and the common reference time are preferably the local parameters of the synchronising (or master) station. However, these could of course be partially or completely different parameters.
The information contained in the synchronisation message and relating to the common frequency advantageously comprises the list of frequencies and the respective durations of these frequencies or an identifier for the list of frequencies in its evolution scheme and the respective durations of these frequencies.
According to yet another feature of the invention, each synchronising station can place in the synchronisation message an identifier intended to signal to the slave relay stations and possibly to other recipient synchronising stations the type of message it is transmitting thereto, i.e. the fact that it is a synchronisation message. In order to make use of this information, each transmitting/receiving module is capable of detecting the presence of the identifier, such that only the synchronisation messages containing it are transmitted directly to the synchronisation module for the extraction of the information they contain.
In one particularly advantageous embodiment, the transmitting/receiving modules of at least the slave relay stations are adapted to be adjusted successively to the different frequencies provided by their respective time-division evolution schemes for predetermined periods so as to be able to pick up any synchronisation message from the synchronising station (master or synchronised slave station).
These operations for successive
Jacquet Philippe
Muhlethaler Paul
Inria Institut National de Recherche en Informatique et en Autom
Patel Ajit
Rabin & Berdo P.C.
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