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Details
Inventors: Munday, Peter J.; Massey, Nicholas R.; Harmer, David; Jeffries, James M.;
Assignee: Racal Research Limited (GB2)
Primary Examiner: Sotomayor; John B.
Assistant Examiner:
Attorney, Agent or Firm: Larson and Taylor

A frequency hopping radio communications system has a plurality of radios each incorporating a transmitter and a receiver. When a radio is not transmitting or receiving, a switch switches it into a mode in which it monitors the signal strength in each of the available hop channels so as to assess the level of interference, and selects a subset of the total number of channels, those having the lowest interference level. The identities of this subset of channels are stored in a store. When the radio is to transmit a message, it first transmits the identities of the subset of channels stored in the store--using the full number of hop channels (the information being transmitted with sufficient redundancy to overcome likely interference). The receiving radios receive the identities of the subset of channels. The transmitting radio then transmits, pseudo-randomly, on this subset only and each of the receivers receives on this subset only. In this way, transmission and reception takes place only on the channels where the interference is low.

DETAILED DESCRIPTION What is claimed is: 1.
A radio communications system in which each of a plurality of transmission means is capable of transmitting transmissions on each of a predetermined set of channel frequencies and each of a plurality of receiving means is associated with a respective one of the transmission means and is capable of receiving said transmissions at the respective channel frequencies, comprising assessment means associated with each receiving means for monitoring the received signal strength at each of the channel frequencies in the said set when the receiving means is not receiving said transmissions, whereby to determine a subset of the said set which subset consists of those channel frequencies carrying reduced signal strength in the absence of any said transmission, first control means associated with each transmission means for controlling the transmission means to transmit the identities of the channels in the said subset determined by the associated receiving means, second control means associated with each receiving means and responsive to the receipt by the receiving means of the transmitted identities to control the receiving means to be operative to receive the transmissions only at channel frequencies in the subset, and means responsive to a message to be transmitted by each transmission means to cause that transmission means to transmit the said message using only channel frequencies in the subset at which the associated receiving means is operative to receive transmissions.
2.
A system according to claim 1, including synchronisation means for synchronising the transmission means and the receiving means so as to produce synchronisation between the channel frequencies at which each transmission means is transmitting and the channel frequencies at which each receiving means is operating.
3.
A system according to claim 1, including randomising means associated with each transmission means and with each receiving means for pseudo-randomly selecting the channel frequencies from the said set and the channel frequencies from the said subset


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