Matched pulse shaping filter
View Patent ↗A communications receiver receives a signal which has not been filtered by a matched pulse shaping filter. In the receiver, a circuit element processes the received signal and as a part of that process introduces additional linear distortion into the processed received signal. A matched filter, coupled to the circuit element, generates a fully matched filtered signal compensated for the distortion intrinsic to the received signal pulse shape and the distortion introduced by the circuit element.
1. A high definition television receiver in accordance with the ATSC standard, for receiving a television signal, comprising:
a receiver front end, generating a pulse signal which has riot been filtered by a matched pulse shaping filter;
a carrier tracking loop, coupled to the receiver front end, for translating the pulse signal to baseband and introducing additional linear distortion into the baseband pulse signal;
a matched pulse shaping filter, coupled to the carrier tracking loop, for generating a fully matched filtered pulse signal compensated for the distortion intrinsic to the shape of the signal pulse from the receiver front end and the distortion introduced by the carrier tracking loop; and
a receiver back end, coupled to the matched filter, for producing an image represented by a video component of the television signal and a sound represented by an audio component of the television signal.
2. The receiver of claim 1 wherein:
the pulse signal from the receiver front end is a near baseband signal having positive and negative frequency spectral images, each having a limited bandwidth and exhibiting a skirt on the low frequency band edge; and
the carrier tracking loop translates the positive and negative frequency spectral images to baseband such that the skirts overlap near DC, producing the additional distortion near DC and no additional distortion elsewhere.
3. The receiver of claim 2 wherein:
the pulse signal from the receiver front end exhibits a square-root raised cosine frequency characteristic;
the baseband pulse signal exhibits a distorted square-root raised cosine frequency characteristic near DC and a square-root raised cosine frequency characteristic elsewhere; and
the matched filter exhibits a modified square-root raised cosine response characteristic near DC, modified to compensate for the distortion near DC, and a square-root raised cosine response characteristic elsewhere.
4. The receiver of claim 2 wherein:
the additional distortion near DC is a peak; and
the matched filter exhibits a corresponding trough near DC.
5. The receiver of claim 2 wherein:
the signal from the receiver front end further includes a pilot tone having respective positive and negative frequency images located at frequencies within the low frequency skirts of the positive and negative frequency spectral images of the near baseband signal; and
the carrier tracking loop translates the positive and negative frequency spectral images such that the positive and negative pilot tone images are translated to DC.
6. The receiver of claim 3 where the matched pulse shaping filter frequency response S(f) is of the type:
S
(
f
)
=
{
K
for
β
2
T
≤
f
≤
(
2
-
β
)
2
T
K
2
cos
(
π
T
f
2
β
)
for
0
≤
f
≤
β
2
T
K
*
cos
(
π
T
[
f
-
(
2
-
β
)
2
T
]
2
β
for
(
2
-
β
)
2
T
≤
f
≤
(
2
+
β
)
2
T
where f is the frequency in Hertz, β is the roll-off parameter 0≦β≦1, K is a constant, T=1/B and B is the passband bandwidth of the received signal in Hz.