Differential receiver with frequency offset compensation
View Patent ↗A differential receiver which provides for estimation and tracking of frequency offset, together with compensation for the frequency offset. Estimation and tracking of the frequency offset is undertaken in the phase domain, which reduces computational complexity and allows frequency offset estimation and tracking to be accomplished by sharing already-existing components in the receiver. Compensation for the frequency offset can be performed either in the time domain, before differential detection, or in the phase domain, after demodulation, or can be made programmably selectable, for flexibility.
1. A differential receiver comprising:
an antenna to receive a radio frequency signal, the radio frequency signal encoding a digital data payload;
a converter to
down-convert the radio frequency signal to a baseband signal, and
extract each of (i) an analog in-phase signal and (ii) an analog quadrature phase signal from the baseband signal;
an analog-to-digital converter to respectively convert the analog in-phase signal and the analog quadrature phase signal into a digital in-phase signal and a digital quadrature phase signal;
a detector to obtain a demodulated phase shift keying (PSK) signal based on each of the digital in-phase signal and the digital quadrature phase signal;
a phase extractor to extract a phase based on the demodulated phase shift keying (PSK) signal;
a frequency offset estimation module to, in the phase domain, acquire an estimate of frequency offset contained in the demodulated phase shift keying (PSK) signal based on the phase extracted from the demodulated phase shift keying (PSK) signal; and
a first frequency offset compensation module configured to compensate, in the phase domain, for the frequency offset contained in the demodulated phase shift keying (PSK) signal based on the estimate of frequency offset acquired by the frequency offset estimation module;
a second frequency offset compensation module configured to compensate, in the time domain, for the frequency offset contained in the demodulated phase shift keying (PSK) signal based on the estimate of the frequency offset acquired by the frequency offset estimation module; and
a programmable selector to provide the estimate of the frequency offset acquired by the frequency offset estimation module to either (i) the first frequency offset compensation module or (ii) the second frequency offset compensation module.
2. A differential receiver according to claim 1 , wherein the estimate of frequency offset is acquired by the first frequency offset estimation module according to at least an approximation of the following equation:
2
πΔ
fT
=
ψ
^
=
1
N
∑
n
=
0
N
-
1
{
angle
(
y
(
n
)
)
-
angle
(
y
(
n
-
L
)
)
}
where Δf is the frequency offset, T is time, {circumflex over (ψ)} is the estimate of phase, y(n) is the demodulated phase shift keying (PSK) signal, N is the length of one training block, L represents the distance between two identical samples, and angle (.) indicates the phase extraction operation.
3. A differential receiver according to claim 1 , further comprising a frequency offset tracking module configured to track frequency offset, wherein the estimate of frequency offset is updated based on the tracked frequency offset.
4. A differential receiver according to claim 3 , wherein the frequency offset tracking unit is configured to track the frequency offset in the phase domain.
5. A differential receiver according to claim 4 , wherein the frequency offset tracking unit tracks the frequency offset by measuring a change in an envelope of a demodulated signal.
6. A differential receiver according to claim 5 , wherein the frequency offset tracking unit (i) samples the envelope at points corresponding to maximum and minimum deviations of the envelope, and (ii) tracks the frequency offset by averaging the maximum and minimum deviations.
7. A differential receiver according to claim 5 , wherein the frequency offset tracking unit (i) samples positive and negative phases corresponding to clocked sampling phases for each symbol, and (ii) tracks the frequency offset by summing the positive and negative phases.
8. A differential receiver according to claim 1 , further comprising:
a post-processing arrangement configured to process the compensated, demodulated phase shift keying (PSK) signal so as to obtain the digital data payload.
9. A differential receiver according to claim 8 , wherein the post-processing arrangement comprises a demodulator, a decoder, and a bit-slicer.