Communications: directive radio wave systems and devices (e.g. – With particular circuit – For correlation
Patent
1993-02-10
1995-02-14
Sotomayor, John B.
Communications: directive radio wave systems and devices (e.g.,
With particular circuit
For correlation
342134, 342145, 342202, G01S 1330
Patent
active
053899326
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
BACKGROUND OF THE INVENTION
The present invention relates to a pulse compression control system using a double modulation applied to a radar transmission pulse, a synchronous pulse for communication or the like and utilization of a code sequence having low side lobes in an autocorrelation function.
By transmitting modulated pulses by a code sequence having a length of N, an autocorrelation of which designates a sharp peak value at one point and by receiving and demodulating this pulse and obtaining the autocorrelation, a compression of 1/N in the pulse width and an expansion of N times in an amplitude can be carried out. Therefore, when this art is applied to radar by transmitting the pulse at low peak electric power, receiving the reflected pulse, and compressing the pulse, the resolution can increase. Also, by applying to various information transmissions, a correct synchronous point can be detected.
PRIOR ART
It is known that the code sequence having sufficiently low side lobes compared with the main peak value of the autocorrelation function, for example, is a Barker code. For example, a pulse having a width of T is phase modulated by the Barker code "1110010", which is constituted by 7 bits in which one bit length is T/7. Namely, a code "1" is phase modulated to a carrier phase of 0.degree. and a code "0" is phase modulated to a phase of 180.degree., and then a coded phase modulated pulse is obtained. The coded modulated pulse is transmitted as a radar pulse.
The coded phase modulated pulse is reflected from a target article or the like, receives the reflected pulse, and is phase synchronously detected to obtain the detection output +1, +1, +1, -1, -1, +1, -1 in a term T, if, for example, the signal having a carrier phase of 0.degree. is +1, and the signal having a carrier phase of 180.degree. is -1. The detected output signal itself or the inverted detected signal is added at a certain timing, and then the output signal having an amplitude level of 7 can be obtained once. In the other case, amplitudes are 0 or -1. Accordingly, by utilizing the output signal having the amplitude of 7, if using a transmission pulse having a pulse width of T, the resolution is the same as when using the transmission pulse having a pulse width of T/7 can be obtained.
It has been found that there are approximately 9 Barker codes having only side lobes of 0 or .+-.1 between N=2 and N=6084, namely, in the case of N=2 there are 2, in the case of N=3 there is 1, in the case of N=4 there are 2, in the case of N=5 there is 1, in the case of N=7 there is the above-mentioned 1, in the case of N=11 there is 1, and in the case of N=13 there is 1.
Further an M sequence (Maximal length sequence) is known as a code sequence that is applied to a coded pulse radar. For example, in the case where period L is 7, the M sequences include a code sequence of "1110100" besides the above Barker code sequence. Also, in the case where L=15, for example, the code sequences "111100010011010" and "111101011001000" have been known. Further in the case of L=31, six code sequences have been found.
As mentioned above, few code sequences wherein the autocorrelation function thereof has a sharp peak at one point exist in the Barker sequences or the M sequences, therefore, the coded pulse radar using an identical code sequence is made to have large interference and it is difficult for the coded pulse radar to operate in an excessively dense environment.
In the case where the system is applied in a multi-access communication system or the like, since code sequences by which a synchronous pulse is modulated are few, it is difficult to increase the number of subscribers utilizing the system.
SUMMARY OF THE INVENTION
An object of the present invention is to increase the kinds of usable code sequences by allowing a certain amount of side lobe in a pulse compression system using code sequences having a sharp peak at one point in an autocorrelation function thereof and having low side lobes.
A pulse compression control system of the pres
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Komata Asao
Ota Eikichi
Fujitsu Limited
Sotomayor John B.
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