Patent Application
20140133520
The present invention relates to the technical field of communication systems and more particularly this invention relates to tactical radio communication that uses psedurandom sequence to generate non overlapping parallel frequency patterns that enable multiple radios to communicate in parallel while they hop their carrier frequencies.
In tactical radio communication, security is a key concern which is achieved using frequency hopping.
Prior art patents look to the synchronization, frequency hopping and solving the problem of interference between participating stations. U.S. Pat. Nos. 4,998,290 and 7,233,770 B2 are typical in this respect.
From applicants' view point, prior art work does present the idea of generating non-overlapping parallel frequency hopping patterns which allow multiple communications to take place simultaneously while communication security is provided using frequency hopping.
The object of the present invention is to develop a strategy that generates non-overlapping parallel frequency hopping patterns which allows the tactical radios to communicate in parallel. For this purpose, both time division multiplexing and frequency division multiplexing are used. Any number of radios that are communicating with each other form a net. All the radios in a net use the same set of frequencies for communication and the number of radios in a net can differ. For example, there can be only two radios in a net, one transmitter and one receiver or five radios in a net, one transmitter and four receivers, all using same set of frequencies. The total time that is allowed for communication in one time frame is divided between the number of radios making a net (R), so that each radio gets its turn for transmitting data. If R number of radios are present in a net and T is the total time for communication, then time given to a single radio (ST) in a net for the transmission of data is:
ST=T/R
In accordance with the present invention, an example that considers a network consisting of thirty radios is taken. Thirty radios can cause a maximum of fifteen simultaneous communications (since two radios are necessary to carry out communication). The frequencies at which the radios communicate is decided by psedurandom (PN) sequence. The example presented here shows three different time frames, and the number of hopping frequencies (H) assigned to each net in a given time frame is 8.
Subsets of bits from psedurandom sequence are used to generate a frequency and then these frequencies are assigned to the set of radios in a pattern that guarantees that there is never a frequency conflict. The frequencies are assigned in this pattern: all radios of net 1 are assigned some f1 frequency, all radios of net2 are using f2 frequency for communication, all radios of net 3 are given f3 frequency for communication. Then after first hop, first set of radios are communicating at f2 frequency, second set of radios are using f3 frequency, third set of radios are using f4 frequency and so on. In this way, a unique frequency is used by each communicating set of radios and it becomes possible for multiple set of radios to communicate simultaneously.
The features and objectives of the present invention are further explained by the following detailed description of preferred embodiments and from the drawings.
Referring to
All nets are given time T for communication. This time T is equally divided between the number of radios present in a net. For a net having 3 radios, T/3 time will be given to a single radio for transmission and for the rest of 2T/3 time units it will be receiving data from the other two radios. Moreover each radio has a radio-identifier (RI) number associated with it. The radios of a net become transmitters in the ascending order of their RI, that is the radio with the smallest RI transmits first. In the next time frame, this whole process repeats again. A radio that enters in a net in rx mode sits at a fixed frequency and synchronizes with its tx radio.
Referring to
radio-14, radio-22 & radio-29 are not taking part in communication in the first time frame. Let us consider the net consisting of radio-1, radio-3 and radio-12, where 1,3 and 12 are the RI's of the respective radios. During request frame, radio-1 sends a request signal in the first time slot of request frame to radio-3 and radio-12, radio-3 sends request signal in the third time slot of request frame to radio-1 and radio-12 and radio-12 sends a request signal (in the twelfth time slot of request frame) to radio-1 and radio-3. Then during acknowledge frame radio-1, radio-3 and radio-12 send acknowledge signals (in the first, third and twelfth time slot of acknowledge frame) to radio-3 & radio-12, radio-1 & radio-12 and radio-1 & radio-3 respectively, thus establishing a net. The radios become transmitter in the ascending order of their RI's, hence radio-1 becomes the transmitter first, then radio-3 and finally radio-12. Radio-1 first transmits for T/3 time units to radio-3 and radio-12, then radio-3 transmits for the next T/3 time units and finally radio-12 transmits data to radio-3 and radio-1.
Referring to
Referring to
Referring to
A network having C number of radios can carry out a maximum of C/2 communications as two radios are necessary for the transfer of information. Keeping that in mind, the example case consisting of thirty radios can carry out a maximum of fifteen communications. This means that in order to allow all the radios to communicate simultaneously while avoiding frequency conflict, maximum fifteen unique frequencies are needed. Although the example under consideration needs eight unique frequencies because there are eight nets, but it is possible that in the next time frame fifteen nets are formed so, in order to be sure that there is never a frequency collision always C/2 unique frequencies are generated.
Referring to
Frequency column of TABLE 1 shows a set of predefined frequencies, which are used for communication. The selection of a particular frequency is made by frequency index Q. Once 4096 frequecies have been produced, then the process of generating frequencies ends.
Referring to
The frequencies are assigned to the communicating set of radios in the order shown by TABLE 2:
When radio-1, radio-3 & radio-12 are using frequency f1 for communication, then radio-2, radio-4, radio-8, radio-10, radio-11 & radio-18 are using frequency f2 and at the same time radio-5, radio-15 & radio-26 are using frequency f3 and all are communicating simultaneously. After first hop, radio-1, radio-3 & radio-12 are using frequency f2; radio-2, radio-4, radio-8, radio-10, radio-11 & radio-18 are using frequency f3; radio-5, radio-15 & radio-26 are using frequency f4 and so on. Hence there is always a unique frequency for each set of communicating radios.
Since index number Q is generated by taking mod so, possibility of repetition exists. This can pose serious problem as unique frequency for communication can not be guaranteed and frequency collision may occur. If some frequency f3 is repeating then the problem created by repetition of frequency is shown by TABLE 3.
The problem of frequency collision is shown by second and third rows of column3, where net 1 and net 2 both happen to be using same frequency for communication due to which data received will be erreneous. In order to make sure that there is always a unique frequency for each communicating set of radios, a New Frequency Array is developed that guarantees that no consecutive fifteen frequencies are repeating (for the example, thirty radios are used so, maximum fifteen communications can take place and hence fifteen unique frequencies are needed).
Referring to
Hence a newly generated Frequency Array is obtained, which guarantees that consecutive fifteen frequencies are unique. So, the frequency array of
The frequencies assigned by TABLE 2 are for the first time frame. In order to understand how frequencies are assigned in the next time frames refer to
TABLE 4 shows the assignment of frequencies in the second time frame.
New nets are established between the radios in the next time frame. For instance, radio-1, radio-3 and radio-12 were communicating in the first time frame but in second time frame radio-1 and radio-22 are communicating, radio-3 and radio-2 form a net and radio-12 is communicating with radio-16. In the same way TABLE 5 shows the assignment of frequencies in the third time frame.
In this way frequencies are assigned to the communicating pair of radios. We have a total of 3630 frequencies, after which they will start repeating.
The embodiment described relates to a system with thirty radios. However, this invention is not limited to thirty radios, it is possible to have more or less than thirty radios. The necessary condition for the working of this algorithm is, if a network consists of C radios, then a frequency array having C/2 unique frequencies should be produced, i-e any consecutive C/2 frequencies in the array should not be repeating.
