Doppler frequency determination for mobile wireless devices
A technique for Doppler frequency estimation in Orthogonal Frequency Division Multiplexing (OFDM) systems. A frequency domain approach may be applied to any OFDM because it utilizes pilot subcarriers, and thus does not increase the system overhead. An estimator may be implemented as a relatively low-complexity finite impulse response (FIR) filter bank with coefficients that may be pre-calculated and stored in memory.
1. A method comprising:
receiving a multi-path Orthogonal Frequency Division Multiplexed (OFDM) signal from a remote mobile wireless device;
extracting multiple pilot carriers from the signal;
performing a frequency domain analysis on the extracted pilot carriers to determine a Doppler frequency corresponding to the remote mobile wireless device, wherein the Doppler frequency comprises the ratio of the speed of the remote mobile wireless device to the carrier wavelength, wherein performing a frequency domain analysis on the extracted pilot carriers to determine a Doppler frequency corresponding to the remote mobile wireless device comprises:
generating a plurality of channel estimates corresponding to the extracted pilot carriers, and
performing maximum likelihood estimations
(
min
f
d
T
Λ
k
(
f
d
T
)
=
min
f
d
T
ln
det
(
R
)
+
L
H
H
~
k
2
)
on the plurality of channel estimates, wherein the maximum likelihood estimations utilize
L
=
[
l
1
,
1
0
0
⋯
0
l
2
,
1
l
2
,
2
0
⋯
0
l
3
,
1
l
3
,
2
l
3
,
3
⋰
⋮
⋮
⋮
⋮
⋰
0
l
M
,
1
l
M
,
2
l
M
,
3
⋯
l
M
,
M
]
where entries in matrix L are pre-calculated and stored using a pre-determined set of values of f d T; and
modifying network functionality based, at least in part, on the speed of the remote mobile wireless device as indicated by the Doppler frequency.
2. The method of claim 1 wherein modifying network functionality based, at least in part, on the Doppler frequency comprises initiating a handover based at least in part on motion determined based, at least in part, on the Doppler frequency and physical locations of two or more base stations.
3. The method of claim 1 wherein modifying network functionality based, at least in part, on the Doppler frequency comprises causing transmission characteristics to be modified.
4. The method of claim 1 wherein the values comprise 0 to 0.04 with a step size of 0.001.
5. An apparatus comprising:
an antenna to receive Orthogonal Frequency Division Multiplexed (OFDM) wireless signals from a remote mobile wireless device;
control circuitry coupled with the antenna to extract multiple pilot carriers from the signal, to perform a frequency domain analysis on the extracted pilot carriers to determine a Doppler frequency corresponding to the remote mobile wireless device, wherein the Doppler frequency comprises the ratio of the speed of the remote mobile wireless device to the carrier wavelength, and to modify network functionality based, at least in part, on the speed of the remote mobile wireless device as indicated by the Doppler frequency wherein frequency domain analysis on the extracted pilot carriers to determine a Doppler frequency corresponding to the remote mobile wireless device comprises:
generating a plurality of channel estimates corresponding to the extracted pilot carriers; and
performing maximum likelihood estimations on the plurality of channel estimates utilizing
L
=
[
l
1
,
1
0
0
⋯
0
l
2
,
1
l
2
,
2
0
⋯
0
l
3
,
1
l
3
,
2
l
3
,
3
⋰
⋮
⋮
⋮
⋮
⋰
0
l
M
,
1
l
M
,
2
l
M
,
3
⋯
l
M
,
M
]
where entries in matrix L are pre-calculated and stored using a pre-determined set of values comprising 0 to 0.04 with a step size of 0.001.
6. The apparatus of claim 5 wherein modification of the network functionality based, at least in part, on the Doppler frequency comprises initiating a handover based at least in part on motion determined based, at least in part, on the Doppler frequency and physical locations of two or more base stations.
7. The apparatus of claim 5 wherein modification of the network functionality based, at least in part, on the Doppler frequency comprises causing transmission characteristics to be modified.
8. An agent to control a base station in a wireless communications network comprising control logic to operate on a multi-path Orthogonal Frequency Division Multiplexed (OFDM) signal to extract multiple pilot carriers from the signal, to perform a frequency domain analysis on the extracted pilot carriers to determine a Doppler frequency corresponding to the remote mobile wireless device, and to modify network functionality based, at least in part, on the speed of the remote mobile wireless device as indicated by the Doppler frequency wherein frequency domain analysis on the extracted pilot carriers to determine a Doppler frequency corresponding to the remote mobile wireless device comprises:
generating a plurality of channel estimates corresponding to the extracted pilot carriers; and
performing maximum likelihood estimations on the plurality of channel estimates utilizing
L
=
[
l
1
,
1
0
0
⋯
0
l
2
,
1
l
2
,
2
0
⋯
0
l
3
,
1
l
3
,
2
l
3
,
3
⋰
⋮
⋮
⋮
⋮
⋰
0
l
M
,
1
l
M
,
2
l
M
,
3
⋯
l
M
,
M
]
where entries in matrix L are pre-calculated and stored using a pre-determined set of values wherein the values comprise 0 to 0.04 with a step size of 0.001.
9. The agent of claim 8 wherein modification of the network functionality based, at least in part, on the Doppler frequency comprises initiating a handover based at least in part on motion determined based, at least in part, on the Doppler frequency and physical locations of two or more base stations.
10. The agent of claim 8 wherein modification of the network functionality based, at least in part, on the Doppler frequency comprises causing transmission characteristics to be modified.