Page 473 - Fundamentals of Radar Signal Processing

samples that represent the same range and Doppler resolution cells.

Integration may be applied to the data at three different stages in the
processing chain

1. After coherent demodulation, to the baseband complex-valued (I and Q,
or magnitude and phase) data. Combining complex data samples is
referred to as coherent integration.

2. After envelope detection, to the magnitude (or squared or log magnitude)
data. Combining magnitude samples after the phase information is
discarded is referred to as noncoherent integration.
3. After threshold detection, to the target present/target absent decisions.

This technique is called binary integration.

A system could elect to use none, one, or any combination of these techniques.
Many systems use at least one integration technique, and a combination of either
coherent or noncoherent with post-detection binary integration is also common.
The major cost of integration is the time and energy required to obtain multiple
samples of the same range, Doppler, and/or angle cell (or multiple threshold

detection decisions for that cell); this is time that cannot be spent searching for
targets elsewhere, or tracking already-known targets, or imaging other regions
of interest. Integration also increases the signal processing computational load.
Modern systems vary as to whether this is an issue: the required operations are
simple, but must be performed at a very high rate in many systems.
In coherent integration, complex data samples y are combined to form a
n
new complex variable y:

(6.59)

As shown in Chap. 1, if the SNR of a single sample y is χ the integrated data
1
n
sample y has an SNR χ = Nχ provided that all of the samples add in phase.
1
N
That is, coherent integration attains an integration gain of a factor of N. This is
the signal processing gain G in the radar range equation due to coherent
sp
integration. Detection calculations are then based on the result for a single
sample of target + noise having the improved SNR χ .
N
In noncoherent integration, phase information is discarded. Instead, the
magnitudes or squared magnitudes of the data samples are integrated.
(Sometimes another function of the magnitude, such as the log-magnitude, is
used.) Most classical detection results have been developed for the square law
detector, which bases detection on the quantity