Estimation of a multipath signal in a wireless communication system
Described herein is a method and system for estimating a time-varying multipath communication channel. The system comprises a receiver for receiving a signal comprising a data packet transmitted over the multipath communication channel. The system also comprises a frequency-domain channel estimator that generates a frequency-domain channel estimate based on the received signal. The system further comprises a time-domain channel modeller that receives the frequency-domain channel estimate and generates an estimate of parameters in a time-domain model of the multipath communication channel. The model characterizes the multipath communication channel as a delay line with a plurality of taps, each tap having tap parameters defining a delay, a Doppler and a gain for the tap. The tap parameters are constant over the data packet.
1. A method of estimating a time-varying multipath OFDM communication channel, the method comprising:
receiving a frequency-domain channel estimate of the multipath communication channel, the frequency-domain channel estimate deriving from an OFDM data packet transmitted over the multipath communication channel; and, based on the frequency-domain channel estimate
generating an estimate of tap parameters in a time-domain model of the multipath communication channel, the time-domain model characterising the multipath communication channel as a delay line with a plurality of taps, each tap having tap parameters defining a delay, a Doppler and a complex gain for the tap,
wherein the estimated tap parameters are constant for the duration of the data packet.
2. The method of claim 1 wherein said generating the estimate of tap parameters comprises:
defining a search window for the delay and Doppler tap parameters;
dividing the search window into a plurality of bins;
determining a correlator metric for the respective bins;
identifying one or more peaks in the determined correlator metrics; and
outputting estimates of the delay and Doppler tap parameters based on the identified peaks.
3. The method of claim 1 wherein said generating the estimate of tap parameters comprises:
estimating the delay and Doppler tap parameters for a detected multipath component;
performing a least-squares estimation to generate an estimate of the gain tap parameter for the detected multipath component; and
subtracting the detected multipath component from the channel estimate, using the estimated delay, Doppler and gain tap parameters to quantify the detected multipath component.
4. The method of claim 3 wherein said estimating, least-squares estimation and subtraction are repeated to iteratively remove detected multipath components from the channel estimate.
5. The method of claim 1 further comprising a method of refining an estimate of the time-domain model of the multipath communication channel, said refining comprising:
subtracting all of the plurality of multipath components from the estimate of the multipath communication channel except for a currently-considered multipath component;
generating a refined estimate of the delay tap parameter and the Doppler tap parameter for the currently-considered multipath component; and
performing a least-squares estimation to generate a refined estimate of the gain tap parameter for the currently-considered multipath component.
6. The method of claim 5 wherein said refining is repeated to generate refined estimates for the plurality of multipath components.
7. The method according to claim 1 wherein generating the estimate of tap parameters uses an ambiguity function.
8. The method of claim 7 wherein the ambiguity function is described by the following equation:
A
x
(
τ
,
v
)
≈
1
KL
ⅇ
-
j2π
⌊
K
/
2
⌋
τ
/
T
ⅇ
-
jπ
(
L
-
1
)
vT
d
)
sin
(
π
τ
K
/
T
)
sin
(
π
τ
/
T
)
sin
(
π
vT
d
L
)
sin
(
π
vT
d
)
where A x represents the ambiguity function, τ represents delay, ν represents frequency, K represents the number of subcarriers, L represents the length of the data packet in OFDM symbols, 1/T represents the subcarrier spacing, and T d represents the OFDM symbol duration.
9. The method of claim 1 further comprising:
providing the channel estimate to a radar application for target detection and/or localisation.
10. The method of claim 1 further comprising:
providing the channel estimate to a signal communication processor for channel characterisation and/or processing of the received signal.
11. The method of claim 7 further comprising:
providing the refined estimates to a radar application for target detection and/or localisation.
12. The method of claim 5 further comprising:
providing the refined estimates to a signal communication processor for channel characterisation and/or processing of the received signal.
13. The method of claim 1 further comprising:
characterising a reflective environment of the communication channels based on the time-domain model of the multipath communication channel.
14. The method of claim 1 further comprising determining the frequency domain estimate, said determining comprising:
estimating data from the data packet; and
using the data as pilot symbols to obtain the frequency domain estimate from a signal received over the multipath communication channel.
15. A computer program product comprising machine-readable program code recorded on a non-transitory machine-readable recording medium, for controlling the operation of a data processing apparatus on which the program code executes to perform the method of claim 1 .
16. The method of claim 1 , further comprising generating the frequency-domain channel estimate based on feedback from decoder decisions.
17. A non-transitory computer readable medium including instructions for:
receiving a frequency-domain channel estimate of the multipath OFDM communication channel, the frequency-domain channel estimate deriving from an OFDM data packet transmitted over the multipath communication channel; and, based on the frequency-domain channel estimate
generating an estimate of tap parameters in a time-domain model of the multipath communication channel, the time-domain model characterising the multipath communication channel as a delay line with a plurality of taps, each tap having tap parameters defining a delay, a Doppler and a gain for the tap,
wherein the estimated tap parameters are constant for the duration of the data packet.
18. The non-transitory computer readable medium of claim 17 further including instructions for:
defining a search window for the delay and Doppler tap parameters;
dividing the search window into a plurality of bins;
determining a correlator metric for the respective bins;
identifying one or more peaks in the determined correlator metrics; and
outputting estimates of the delay and Doppler tap parameters based on the identified peaks.
19. The non-transitory computer readable medium of claim 17 further including instructions for:
estimating a delay and Doppler tap parameter for a detected multipath component;
performing a least-squares estimation to generate an estimate of the gain tap parameter for the detected tap; and
subtracting the detected multipath component from the channel estimate, using the estimated delay, Doppler and gain tap parameters to quantify the detected multipath component.
20. The non-transitory computer readable medium of claim 19 further including instructions for:
repeating the estimating, least-squares estimation and subtraction to iteratively remove respective multipath components from the channel estimate.
21. The non-transitory computer readable medium of claim 17 further including instructions for:
subtracting all of the plurality of multipath components from the estimate of the multipath communication channel except for a currently-considered multipath component;
generating a refined estimate of the delay tap parameter and the Doppler tap parameter for the currently-considered multipath component; and
performing a least-squares estimation to generate a refined estimate of the gain tap parameter for the currently-considered multipath component.
22. The non-transitory computer readable medium of claim 21 further including instructions for:
repeating the steps of subtracting, generating a refined estimate and performing a least-squares estimate as defined in claim 16 to generate refined estimates for the plurality of multipath components.
23. The non-transitory computer readable medium of claim 17 further including instructions for generating the frequency-domain channel estimate based on feedback from decoder decisions.
24. A system for estimating a time-varying multipath communication channel, the system comprising:
a receiver for receiving a signal comprising an OFDM data packet transmitted over the multipath communication channel;
a frequency-domain channel estimator that generates a frequency-domain channel estimate based on the received signal; and
a time-domain channel modeller that receives the frequency-domain channel estimate and generates an estimate of tap parameters in a time-domain model of the multipath communication channel, the model characterising the multipath communication channel as a delay line with a plurality of taps, each tap having tap parameters defining a delay, a Doppler and a gain for the tap,
wherein the estimated tap parameters are constant over the duration of the data packet.
25. The system of claim 24 wherein the frequency-domain channel estimator is configured to generate the frequency-domain channel estimate based on feedback from decoder decisions.
26. An apparatus for estimating a time-varying multipath communication channel based on a signal comprising a plurality of multipath components, the signal associated with an OFDM data packet, and based on a frequency-domain channel estimate deriving from the data packet, the apparatus comprising:
a time-domain channel modeller that receives the frequency-domain channel estimate and generates an estimate of tap parameters in a time-domain model of the multipath communication channel, the model characterising the multipath components according to the tap parameters, the tap parameters defining a delay, a Doppler and a gain for the multipath components, wherein the estimated tap parameters are constant over the duration of the data packet.
27. The apparatus of claim 26 wherein the frequency-domain channel estimate is generated based on feedback from decoder decisions.