Joint Frequency and Delay Correlation

[FDOUT, FREQ_AXIS] = FDCORR(A,B,FRANGE)
FDCORR Joint frequency and delay correlation
Performs an efficient circular cross correlation between two vectors over all possible frequency offsets (Dopplers) between -pi and pi where 2pi is the sampling rate.
A: vector representing received signal sampled at FS = 2pi
B: vector representing correlation code sampled at FS = 2pi
FRANGE: Two element vector from lowest to highest frequency to search over within a frequency range from -pi to pi.
For Example [-pi/10 pi/10]. Omitting FRANGE will default to [-pi pi].
FDOUT: 2D Correlation surface vs delay and frequency offset FREQ_AXIS: Frequency values aligned to frequency axis (-pi to pi)

With no output arguments FDCORR will plot the surface correlation magnitude vs frequency and delay offset in the
current figure window.

Vector "A" represents a received signal that has been encoded with a correlation code (such as GPS and CDMA applications) or a training sequence. It has an unknown frequency offset due to Doppler offsets and frequency offsets in the receiver, and an unknown delay shift relative to the start of the code sequence represented by vector "B". FDCORR will efficiently find the correlation between the received sequence and reference code over frequency and delay offsets.

Vectors A and B are interchangable.

fd_corr_demo.m is included in the zip file to demonstrate use.