Title of Invention	"A METHOD OF ADAPTIVE INTERPOLATION FILTERING A SIGNAL IN A RECEIVER AND APPARATUS THEREOF"
Abstract	ABSTRACT A METHOD OF ADAPTIVE INTERPOLATION FILTERING A SIGNAL IN A RECEIVER AND AN APPARATUS THEREOF Methods and apparatus that achieve good channel estimation without using unnecessarily complex interpolation filters are described. Adaptive interpolation filtering of a signal in a receiver includes determining at least one correlation function parameter of the chaimel and determining a filter configuration based on the correlation function parameter. The interpolation may be performed in time, where a Doppler frequency shift can serve as the correlation function parameter, or in frequency, where a root mean square or maximum delay spread can serve as the correlation function parameter, or both. A worst case signal-to-noise ratio may be used in determining the filter configuration, or, optionally, the signal-to-noise ratio can be determined in real time. The filter configuration can be determined in real time or selected from one of a plurality of predetermined configurations having different complexities. 27

Title of Invention

"A METHOD OF ADAPTIVE INTERPOLATION FILTERING A SIGNAL IN A RECEIVER AND APPARATUS THEREOF"

Abstract

ABSTRACT A METHOD OF ADAPTIVE INTERPOLATION FILTERING A SIGNAL IN A RECEIVER AND AN APPARATUS THEREOF Methods and apparatus that achieve good channel estimation without using unnecessarily complex interpolation filters are described. Adaptive interpolation filtering of a signal in a receiver includes determining at least one correlation function parameter of the chaimel and determining a filter configuration based on the correlation function parameter. The interpolation may be performed in time, where a Doppler frequency shift can serve as the correlation function parameter, or in frequency, where a root mean square or maximum delay spread can serve as the correlation function parameter, or both. A worst case signal-to-noise ratio may be used in determining the filter configuration, or, optionally, the signal-to-noise ratio can be determined in real time. The filter configuration can be determined in real time or selected from one of a plurality of predetermined configurations having different complexities. 27

Full Text	The present invention relates to a method of adaptive interpolation filtering a signal in a receiver and an apparatus thereof. [0001] This application relates to digital communication where the channel is estimated by pilot symbols. In particular, it relates to situations where it is desirable to •: avoid or reduce the use of high-order interpolation filters, because of the required memory and complexity for such filters. It also concerns related situations where it is desirable to estimate channel correlation functions by low-complexity methods. [0002] In wireless communications, the data to be communicated is typically transmitted over a channel whose characteristics vary in time and frequency. That is to say, the amplitude and phase of the channel change from one symbol to the next and from one frequency to the next. How much the channel changes between two symbols ^ in time does essentially depend on two things, namely the duration of a symbol and how fast the actual channel is varying, whereas how much the channel changes between two frequencies depends on how far apart the frequencies are and how frequency selective the channel is. [0003] A common way to estimate a varying channel is to insert knovyn symbols in the transmitted sequence, so-called pilot symbols. The pilot symbols might either be distributed as single symbols, or they might be clustered together to form short sequences of symbols. In systems based on orthogonal frequency division multiplexing (OFDM), it is commonplace to transmit scattered pilot symbols on some of the different carriers to aid in channel estimation. This is for instance the case in digital video broadcasting (DVB), where essentially 1 out of 12 transmitted symbols is a pilot. In ^ DVB, pilots are only transmitted on every third carrier, and on those carriers every fourth symbol is a pilot. [0004] One of the design objectives when determining hov/ close the pilots should be in time and frequency is to get good performance without using too many pilots. That is, there should be enough pilots to allow the channel to be estimated with reasonable complexity and to cause only a small performance loss without wasting bandwidth by transmitting unnecessarily many pilots. The placement of pilots in time is essentially determined by the Nyquist sampling theorem, which implies that the channel must be sampled at a frequency at least twice the highest Doppler i, squency in order to avoid aliasing. For instance, if the Doppler frequency is 50 Hz, then the channel has to be sampled at a sampling frequency, fs, of 100 Hz, i.e., there must be a pilot symbol every 2 U l \ „ w i l l H L WE CLAIM: I 1. A method of adaptive interpolation filtering a signal in a receiver, comprising: determining at least one correlation function parameter of a channel; determining an asymmetric first filter configuration based on the correlation function parameter and optionally a second filter configuration; and performing interpolation filtering on the signal using at least the determined first filter configuration; wherein determining the first filter configuration includes selecting one of a plurality of predetermined configurations having different complexities but having equivalent buffering requirements. i^ 2. The method as claimed in claim 1, wherein determining the asymmetric first filter configuration comprising: determining a signal-to-noise ratio associated with the signal; and determining the asymmetric first filter configuration based on the correlation function parameter and the signal-to-noise ratio. 3. The method as claimed in claim 1, wherein determining the first filter configuration comprises basing the determination on a predetermined threshold signal-to-noise ratio associated with the signal, below which the signal cannot be processed. 4. The method as claimed in claim 1, wherein the at least one correlation function parameter comprises a Doppler fi-equency shift and the performing interpolation filtering comprises performing interpolation in time. 5. The method as claimed in claim 1, wherein determining the second filter configuration comprises: determining a delay spread of the channel; and determining the second filter configuration based on the delay spread; and performing interpolation fihering comprises performing interpolation filtering on the signal in frequency using the determined second filter configuration. 6. The method as claimed in claim 4, wherein the Doppler frequency shift is estimated using at least one of a level crossing rate method and a zero crossing rate method. 22 7. The method as claimed in claim 1, wherein determining the filter configuration comprises selecting one of a plurality of predetermined configurations having different complexities but having the same buffering requirements. 8. The method as claimed in claim 7, wherein: interpolation is performed in time; the at least one correlation fimction parameter is a Doppler frequency shift; each of the plurality of predetermined configurations correspond to the Doppler fi-equency shift; and the complexity of the selected predetermined configuration increases as the Doppler frequency shift increases. ^ ^ 9. The method as claimed in claim 1, wherein performing interpolation filtering comprises interpolating two-dimensionally in both frequency and time. 10. The method as claimed in claim 1, wherein the signal is an orthogonal frequency division multiplexing (OFDM) signal. 11. The method as claimed in claim 1, wherein the signal is a digital video broadcasting (DVB) signal. 12. A method of adaptive interpolation filtering a signal in a receiver, comprising: determining a Doppler frequency shift of a channel; determining a first asymmetric filter configuration based on the Doppler ^ frequency shift; performing interpolation filtering in time on the signal using the determined first filter configuration; determining a delay spread of the channel; determining a second filter configuration based on the delay spread; and performing interpolation filtering on the signal in frequency using the determined second filter configuration; wherein at least one of determining the first filter configuration and determining the second filter configuration includes selecting one of a plurality of predetermined configurations having different complexities but having equivalent buffering requirements. I 23 13. The method as claimed in claim 12, wherein determining a delay spread of the chaimel comprises determining at least one of a maximum delay spread and a root mean square delay spread, the one being selected based on an estimate of the shape of the charmel profile. 14. An apparatus for adaptive interpolation filtering a signal in a receiver, comprising: logic (230) that determines at least one correlation function parameter of a channel; logic (250) that determines an asymmetric first filter configuration based on the correlation function parameter and optionally a second filter configuration; and logic (240) that performs interpolation filtering on the signal using at least the ^ P determined first filter configuration; wherein the logic (250) that determines the first filter configuration selects one of a plurality of predetermined configurations having different complexities but having equivalent buffering requirements. 15. The apparatus as claimed in claim 14, wherein the logic (250) that determines the asymmetric first filter configuration is operatively coupled to logic (235) that determines a signal-to-noise ratio associated with the signal; and wherein the logic (250) determines the asymmetric first filter configuration based on the correlation function parameter and the signal-to-noise ratio. 16. The apparatus as claimed in claim 14, wherein the logic (250) that determines the first filter configuration bases the determination on a predetermined threshold signal-tonoise ratio associated with the signal, below which the signal cannot be processed. 17. The apparatus as claimed in claim 14, wherein the at least one correlation fiinction parameter comprises a Doppler frequency shift and the performing interpolation filtering comprises performing interpolation in time. 18. The apparatus as claimed in claim 14, wherein the logic (250) for determining second filter configuration is operatively coupled to logic (280) that determines a delay spread of the channel; and wherein the logic (250) determines the second filter configuration based on the delay spread; and wherein the logic (240) performs i 24 interpolation filtering on the signal in frequency using the determined second filter configuration. 19. The apparatus as claimed in claim 17, wherein the Doppler frequency shift is estimated using at least one of a level crossing rate method and a zero crossing rate method. 20. The apparatus as claimed in claim 14, wherein the logic (250) that determines the filter configuration selects one of a plurality of predetermined configurations having different complexities but having the same buffering requirements. 21. The apparatus as claimed in claim 20, wherein: interpolation is performed in time; the ^ ^ at least one correlation function parameter is a Doppler frequency shift; each of the plurality of predetermined configurations correspond to the Doppler frequency shift; and the complexity of the selected predetermined configuration increases as the Doppler frequency shift increases. 22. The apparatus as claimed in claim 14, wherein the logic (240) interpolates twodimensionally in both fi^equency and time. 23. The apparatus as claimed in claim 14, wherein the signal is an orthogonal frequency division multiplexing (OFDM) signal. 24. The apparatus as claimed in claim 14, wherein the signal is a digital video j ^ broadcasting (DVB) signal. 25. An apparatus for adaptive interpolation filtering a signal in a receiver, comprising: logic that determines a Doppler frequency shift of a channel; logic (360) that determines a first asymmetric filter configuration based on the Doppler frequency shift; logic (340) that performs interpolation filtering in time on the signal using the determined first filter configuration; logic that determines a delay spread of the channel; logic (380) that determines a second filter configuration based on the delay spread; and 25 logic (350) that performs interpolation filtering on the signal in frequency using the determined second filter configuration; wherein at least one of the logic (360) that determines the first filter configuration and the logic (380) that determines the second filter configuration selects one of a plurality of predetermined configurations having different complexities but having equivalent buffering requirements. 26. The apparatus as claimed in claim 25, wherein determining a delay spread of the charmel comprises determining at least one of a maximum delay spread and a root mean square delay spread, the one being selected based on an estimate of the shape of the channel profile. ^ Dated this the 12* day of June, 2006 MANISHA SINGH NAIR Agent for the Applicant [IN/PA-740] LEX ORBIS Intellectual Property Practice 709/710, Tolstoy House 15-17, Tolstoy Marg New Delhi-110 001 26

Full Text

The present invention relates to a method of adaptive interpolation filtering a signal in a receiver
and an apparatus thereof.
[0001] This application relates to digital communication where the channel is
estimated by pilot symbols. In particular, it relates to situations where it is desirable to
•: avoid or reduce the use of high-order interpolation filters, because of the required
memory and complexity for such filters. It also concerns related situations where it is
desirable to estimate channel correlation functions by low-complexity methods.
[0002] In wireless communications, the data to be communicated is typically
transmitted over a channel whose characteristics vary in time and frequency. That is to
say, the amplitude and phase of the channel change from one symbol to the next and
from one frequency to the next. How much the channel changes between two symbols
^ in time does essentially depend on two things, namely the duration of a symbol and
how fast the actual channel is varying, whereas how much the channel changes
between two frequencies depends on how far apart the frequencies are and how
frequency selective the channel is.
[0003] A common way to estimate a varying channel is to insert knovyn symbols in the
transmitted sequence, so-called pilot symbols. The pilot symbols might either be
distributed as single symbols, or they might be clustered together to form short
sequences of symbols. In systems based on orthogonal frequency division multiplexing
(OFDM), it is commonplace to transmit scattered pilot symbols on some of the different
carriers to aid in channel estimation. This is for instance the case in digital video
broadcasting (DVB), where essentially 1 out of 12 transmitted symbols is a pilot. In
^ DVB, pilots are only transmitted on every third carrier, and on those carriers every
fourth symbol is a pilot.
[0004] One of the design objectives when determining hov/ close the pilots should be
in time and frequency is to get good performance without using too many pilots. That
is, there should be enough pilots to allow the channel to be estimated with reasonable
complexity and to cause only a small performance loss without wasting bandwidth by
transmitting unnecessarily many pilots. The placement of pilots in time is essentially
determined by the Nyquist sampling theorem, which implies that the channel must be
sampled at a frequency at least twice the highest Doppler i, squency in order to avoid
aliasing. For instance, if the Doppler frequency is 50 Hz, then the channel has to be
sampled at a sampling frequency, fs, of 100 Hz, i.e., there must be a pilot symbol every
2

U l \ „ w i l l H L
WE CLAIM:
I
1. A method of adaptive interpolation filtering a signal in a receiver, comprising:
determining at least one correlation function parameter of a channel;
determining an asymmetric first filter configuration based on the correlation
function parameter and optionally a second filter configuration; and
performing interpolation filtering on the signal using at least the determined
first filter configuration;
wherein determining the first filter configuration includes selecting one of a
plurality of predetermined configurations having different complexities but having
equivalent buffering requirements.
i^ 2. The method as claimed in claim 1, wherein determining the asymmetric first filter
configuration comprising:
determining a signal-to-noise ratio associated with the signal; and
determining the asymmetric first filter configuration based on the correlation
function parameter and the signal-to-noise ratio.
3. The method as claimed in claim 1, wherein determining the first filter configuration
comprises basing the determination on a predetermined threshold signal-to-noise ratio
associated with the signal, below which the signal cannot be processed.
4. The method as claimed in claim 1, wherein the at least one correlation function
parameter comprises a Doppler fi-equency shift and the performing interpolation
filtering comprises performing interpolation in time.
5. The method as claimed in claim 1, wherein determining the second filter
configuration comprises: determining a delay spread of the channel; and determining
the second filter configuration based on the delay spread; and performing
interpolation fihering comprises performing interpolation filtering on the signal in
frequency using the determined second filter configuration.
6. The method as claimed in claim 4, wherein the Doppler frequency shift is estimated
using at least one of a level crossing rate method and a zero crossing rate method.
22
7. The method as claimed in claim 1, wherein determining the filter configuration
comprises selecting one of a plurality of predetermined configurations having
different complexities but having the same buffering requirements.
8. The method as claimed in claim 7, wherein:
interpolation is performed in time;
the at least one correlation fimction parameter is a Doppler frequency shift;
each of the plurality of predetermined configurations correspond to the
Doppler fi-equency shift; and
the complexity of the selected predetermined configuration increases as the
Doppler frequency shift increases.
^ ^ 9. The method as claimed in claim 1, wherein performing interpolation filtering
comprises interpolating two-dimensionally in both frequency and time.
10. The method as claimed in claim 1, wherein the signal is an orthogonal frequency
division multiplexing (OFDM) signal.
11. The method as claimed in claim 1, wherein the signal is a digital video broadcasting
(DVB) signal.
12. A method of adaptive interpolation filtering a signal in a receiver, comprising:
determining a Doppler frequency shift of a channel;
determining a first asymmetric filter configuration based on the Doppler
^ frequency shift;
performing interpolation filtering in time on the signal using the determined
first filter configuration;
determining a delay spread of the channel;
determining a second filter configuration based on the delay spread; and
performing interpolation filtering on the signal in frequency using the determined
second filter configuration;
wherein at least one of determining the first filter configuration and
determining the second filter configuration includes selecting one of a plurality of
predetermined configurations having different complexities but having equivalent
buffering requirements. I
23
13. The method as claimed in claim 12, wherein determining a delay spread of the
chaimel comprises determining at least one of a maximum delay spread and a root
mean square delay spread, the one being selected based on an estimate of the shape of
the charmel profile.
14. An apparatus for adaptive interpolation filtering a signal in a receiver, comprising:
logic (230) that determines at least one correlation function parameter of a
channel;
logic (250) that determines an asymmetric first filter configuration based on
the correlation function parameter and optionally a second filter configuration; and
logic (240) that performs interpolation filtering on the signal using at least the
^ P determined first filter configuration;
wherein the logic (250) that determines the first filter configuration selects one
of a plurality of predetermined configurations having different complexities but
having equivalent buffering requirements.
15. The apparatus as claimed in claim 14, wherein the logic (250) that determines the
asymmetric first filter configuration is operatively coupled to logic (235) that
determines a signal-to-noise ratio associated with the signal; and wherein the logic
(250) determines the asymmetric first filter configuration based on the correlation
function parameter and the signal-to-noise ratio.
16. The apparatus as claimed in claim 14, wherein the logic (250) that determines the first
filter configuration bases the determination on a predetermined threshold signal-tonoise
ratio associated with the signal, below which the signal cannot be processed.
17. The apparatus as claimed in claim 14, wherein the at least one correlation fiinction
parameter comprises a Doppler frequency shift and the performing interpolation
filtering comprises performing interpolation in time.
18. The apparatus as claimed in claim 14, wherein the logic (250) for determining second
filter configuration is operatively coupled to logic (280) that determines a delay
spread of the channel; and wherein the logic (250) determines the second filter
configuration based on the delay spread; and wherein the logic (240) performs
i
24
interpolation filtering on the signal in frequency using the determined second filter
configuration.
19. The apparatus as claimed in claim 17, wherein the Doppler frequency shift is
estimated using at least one of a level crossing rate method and a zero crossing rate
method.
20. The apparatus as claimed in claim 14, wherein the logic (250) that determines the
filter configuration selects one of a plurality of predetermined configurations having
different complexities but having the same buffering requirements.
21. The apparatus as claimed in claim 20, wherein: interpolation is performed in time; the
^ ^ at least one correlation function parameter is a Doppler frequency shift; each of the
plurality of predetermined configurations correspond to the Doppler frequency shift;
and the complexity of the selected predetermined configuration increases as the
Doppler frequency shift increases.
22. The apparatus as claimed in claim 14, wherein the logic (240) interpolates twodimensionally
in both fi^equency and time.
23. The apparatus as claimed in claim 14, wherein the signal is an orthogonal frequency
division multiplexing (OFDM) signal.
24. The apparatus as claimed in claim 14, wherein the signal is a digital video
j ^ broadcasting (DVB) signal.
25. An apparatus for adaptive interpolation filtering a signal in a receiver, comprising:
logic that determines a Doppler frequency shift of a channel;
logic (360) that determines a first asymmetric filter configuration based on the
Doppler frequency shift;
logic (340) that performs interpolation filtering in time on the signal using the
determined first filter configuration;
logic that determines a delay spread of the channel;
logic (380) that determines a second filter configuration based on the delay
spread; and
25
logic (350) that performs interpolation filtering on the signal in frequency
using the determined second filter configuration;
wherein at least one of the logic (360) that determines the first filter
configuration and the logic (380) that determines the second filter configuration
selects one of a plurality of predetermined configurations having different
complexities but having equivalent buffering requirements.
26. The apparatus as claimed in claim 25, wherein determining a delay spread of the
charmel comprises determining at least one of a maximum delay spread and a root
mean square delay spread, the one being selected based on an estimate of the shape of
the channel profile.
^ Dated this the 12* day of June, 2006
MANISHA SINGH NAIR
Agent for the Applicant [IN/PA-740]
LEX ORBIS
Intellectual Property Practice
709/710, Tolstoy House
15-17, Tolstoy Marg
New Delhi-110 001
26

Documents:

3379-delnp-2006-abstract.pdf

3379-delnp-2006-Claims-(02-04-2014).pdf

3379-delnp-2006-Claims-(02-08-2013).pdf

3379-delnp-2006-claims.pdf

3379-delnp-2006-Correspondence Others-(02-04-2014).pdf

3379-delnp-2006-Correspondence Others-(20-05-2013).pdf

3379-delnp-2006-Correspondence Others-(29-11-2013).pdf

3379-delnp-2006-Correspondence-Others-(02-08-2013).pdf

3379-delnp-2006-Correspondence-Others-(05-10-2012).pdf

3379-delnp-2006-Correspondence-Others-(08-07-2013).pdf

3379-delnp-2006-correspondence-others.pdf

3379-delnp-2006-description (complete).pdf

3379-delnp-2006-drawings.pdf

3379-delnp-2006-form-1.pdf

3379-delnp-2006-Form-2-(02-08-2013).pdf

3379-delnp-2006-form-2.pdf

3379-delnp-2006-form-26.pdf

3379-delnp-2006-Form-3-(02-04-2014).pdf

3379-delnp-2006-Form-3-(05-10-2012).pdf

3379-delnp-2006-Form-3-(20-05-2013).pdf

3379-delnp-2006-Form-3-(29-11-2013).pdf

3379-delnp-2006-form-3.pdf

3379-delnp-2006-form-5.pdf

3379-delnp-2006-GPA-(02-04-2014).pdf

3379-delnp-2006-pct-210.pdf

3379-delnp-2006-pct-304.pdf

3379-delnp-2006-pct-409.pdf

3379-delnp-2006-pct-416.pdf

3379-delnp-2006-Petition-137-(02-08-2013).pdf

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Patent Number

260171

Indian Patent Application Number

3379/DELNP/2006

PG Journal Number

14/2014

Publication Date

04-Apr-2014

Grant Date

02-Apr-2014

Date of Filing

12-Jun-2006

Name of Patentee

TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

Applicant Address

S-164 83 STOCKHOLM, SWEDEN

Inventors:

#	Inventor's Name	Inventor's Address
1	WILHELMSSON, LEIF	LYFTVAGEN 5, S-240 10 DALBY (SE)
2	ANDERSSON, LENNART	ANNIES VAG 6, S-266 97 HJARNARP (SE)
3	BERNHARDSSON, BO	SPJUTGRANDEN 5, S-224 75 LUND (SE)

PCT International Classification Number

H04L 25/02

PCT International Application Number

PCT/EP2004/012797

PCT International Filing date

2004-11-11

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/519,261	2003-11-13	U.S.A.
2	10/920,928	2004-08-18	U.S.A.