This invention relates to a method of transmitting information between a plurality of stations in a local area network.
Various methods are known for sharing network communication channels among stations in a local area network (LAN). One widely used method is known as CSMA/CD, (carrier sense multiple access/collision detect). According to this known method, a station wishing to transmit a message listens until the transmission channel is idle before commencing to transmit an information packet. Furthermore, the station continues to listen to the channel after commencing a transmission and if a collision is detected, that is, more than one station has commenced to transmit an information packet, any station which detects such collision terminates its message transmission and transmits a burst of noise (or garble) such that all other stations can be informed of the collision, terminate message transmission, and wait a random time before attempting to commence a further message transmission.
From Patent Abstracts of Japan volume E-690, page 102, abstract of Japanese Published Application No. 63-187746, there is known a wireless communication system wherein a plurality of stations communicate via a repeater installation. A first frequency is used for transmission from the stations to the repeater installation and a second frequency is used for transmissions from the repeater installation to the stations. If the repeater installation detects a collision on the first frequency transmissions, then it immediately informs all stations of such collision using the second frequency, such that the stations can take appropriate action.
Although the CSMA/CD method has proved satisfactory for transmissions over a cable physical medium, it has been found that a problem arises if it is attempted to apply the method to wireless radio transmissions in that small radio signals may be totally masked by larger signals during reception. This phenomenon is known as the "capture effect", and may prevent the detection of collisions in a system such as that disclosed in the aforementioned Japanese patent abstract.