Page 415 - Fundamentals of Radar Signal Processing

Another novel technique applies a pulse-to-pulse phase code similar to the

LFM-like P3 and P4 codes discussed in Chap 4. Correlating with specific
elements of the code on receive can emphasize a particular range foldover
region at the expense of the others. These two techniques are discussed in Zrni
(2008).

5.5.4 Ambiguity Resolution
Several techniques exist to resolve range and Doppler ambiguities when

multiple-PRF data is available. Consider range ambiguity resolution first. Once
a PRF is selected, it establishes an unambiguous range R = c/2PRF. A target at
ua
an actual range R > R will be detected at an apparent range R that satisfies
ua
t
a

(5.124)

for some integer k. Equivalently

(5.125)

where the notation ((·)) denotes modulo x. Normalize the range measurements
x
to the range bin spacing ΔR, for example, n = R /ΔR; then
a
a

(5.126)

The basic approach to resolving range ambiguities relies on multiple PRFs.

Suppose that there are N range bins in the unambiguous range interval on PRF i;
i
thus, R = N ΔR. Note that the unambiguous range is different for each PRF.
uai
i
For simplicity, assume that the range bin spacing is the same in each PRF. Then

(5.127)

The set of equations in Eq. (5.127) is called a set of congruences.
The set of congruences can be solved using the Chinese remainder
theorem (CRT) (Trunk and Brockett, 1993). The CRT states that given a set of r
relatively prime integers N , N ,…, N and the set of congruences in Eq.
1
0
r–1
(5.127), there exists a unique solution (modulo N = N N … N ) for n given
t
1
0
r –1
by the equations