Channel selection in a frequency hopping radio set is controlled by a pseudo-random number generator, the pseudo-random number being used to address an N bit memory (3) which is used to identify each of n available channels from N equipped channels. When a preselected number of the n channels have been identified by the psuedo-random number generator a latch (4) is enabled to store the channel number for selection purposes. Various scrambling methods are employed so that the channels on which one network of radio sets is operating is not readily identifiable from the channels on which another network of radio sets is operating.
A protection mechanism includes means for taking an input binary value and generating a unique key value as well as performing the reverse operation of taking a key value and generating an input binary value. The mechanism includes a scrambler which includes an array having a number of multibit container locations for storing a unique sequence of random numbers. The scrambler forms another binary value by rearranging the bits of the input binary value as a function of the random number values in addition to altering the states of such bits as a function of the random number values and the numeric bit position values of sources of the input binary bits. The resulting binary value is applied to an alphanumeric encoder which converts the binary value into a series of alphanumeric characters containing a valid key value.
A method and apparatus for the selection of random values from a set of N non-sequential values includes software in ROM and RAM for information pool storage. Coupled to the ROM and RAM, a microprocessor sorts the values from smallest to largest, initializes local variables, processes a current value from a first value of the set, and compares the difference to a current information pool entry difference. A range increment is incremented if the difference equals the current information pool entry difference and a new information pool entry is created if the difference does not. The information pool is stored and random values are selected by generating a pseudo random number, constraining the pseudo random number between one and N, indexing into the information pool using the pseudo random number to create a pool entry index and generating the random value using a selected pool entry first value.
A physical channel assignment method prevents the same logical channels from being always adjacent to each other on a frequency axis so that any interference between the adjacent channels can be averaged. By using the values of first pseudo-noise codes as the channel numbers and assigning the physical channels (f1 to f7) to the first logical channel (#1); obtaining second pseudo-noise codes whose phases are shifted from those of the first pseudo-noise codes; and using the values of the second pseudo-noise codes as the channel numbers and assigning the physical channels (f1 to f7) to the second logical channel(#2), the first and second logical channels (#1, #2) can be prevented from being always adjacent to each other on the frequency axis.
In order to establish communications in a conference network of transmitter-receiver stations, each station establishes a frequency-jumping standby law while a calling station transmits a frequency-diversity call sequence on said standby law and the other stations are listening in accordance with said standby law. Furthermore, each station establishes a second frequency law which is synchronous with the standby law but the stair-steps of which are of longer duration. At the end of a call sequence, the calling station and the stations which have detected this sequence are put in the listening state over a time interval t.sub.1 at the corresponding possible traffic frequency of the second frequency law. Each station which has detected a signal then transmits a jamming signal over a time interval t.sub.2 at the aforementioned traffic frequency and the stations which have not detected any signal extend the listening period by the same time interval t.sub.2. Non-reception of a signal during the time interval t.sub.2 makes it possible to establish a communication at the corresponding frequency.
A communication station such as a hand held telephone quickly identifies a desired carrier signal or time slot of a carrier signal and synchronizes itself in time and frequency to that carrier or slot. Synchronization is achieved even when frequency and time reference signals in the communication station are offset, e.g., due to drift, with respect to the carrier signal or slot by averaging successions of signal measurements that occur at times when corresponding signal values are expected. In one method, a plurality of measurements of the received signal taken at a group of predetermined time points where corresponding values are expected are averaged together, in order to enhance the signal to noise ratio. Averaging is carried out several times using different groups of time points, the groups corresponding to respective, different expected clock frequency errors. The results of the averaging steps are used in determining a best hypothesis for the received signal. Dynamic programming is used to test synchronization hypotheses based on different hypotheses of timing drift rate and to discriminate between different hypotheses of timing and timing drift rate in order to maximize sums of correlations.
