Method of reducing the effect of narrowband jammers in radio communication between two stations

DETAILED DESCRIPTION FIG.
1 is a time chart for frequency hops in a radio communication system.
The hop interval T.
sub.
h determines the rate at which new frequencies are generated, e.
g.
by a random number generator.
This means that frequencies are generated every T.
sub.
h -th second.
During the transmitting interval T.
sub.
s communication is in progress at the freqeuncy f.
sub.
1.
During the interval T.
sub.
k, the so-called resetting interval, there is a hop to another freqeuncy f.
sub.
2.
The method described here is applied during the interval T.
sub.
s in the transmitter and receiver units at both communicating stations, while radio communication is silent during the interval T.
sub.
k.
In the frequency hopping system applying the method, the new frequency f.
sub.
2 is not solely determined by a generated random number.
Learned knowledge of the surroundings is also used to affect the selection.
The knowledge collected during operation of the stations is in a state matrix X, illustrated in FIG.
2.
The contents of X can be updated dynamically during the transmitting interval T.
sub.
s and the rate of change is 1/T.
sub.
h.
The state matrix X contains information on presently permitting and prohibited frequencies.
The matrix has three rows and N columns, where N is the number of available frequencies in the frequency hopping system.
In the first row there are the values for the mapping frequencies (see below).
The second row shows the status of a frequency value giving a quality measure calculated with respect to parameters as signal strength and jamming.
The third row contains a time index.
In FIG.
2 there is illustrated an example of a realisation of the X matrix.
Measurement of channel quality may be carried out actively by analysing errors in a received, known bit pattern, or passively by SNR (signal/noise ratio) measurements.
Measurement is carried out in the receiver.
The measurement result is denoted symbolically hereinunder as m.
The measurement results must be available in both transmitter and receiver, and must consequently be transferred to the transmitter