System and method for probing a channel in a communication system
View Patent ↗A system and method for probing a channel by a base station in a communication system is provided. The channel probing includes performing pre-probing for selecting a subchannel, adjusting a subcarrier distance of a probing signal according to frequency selectivity indicative of frequency-domain channel selectivity based on a time channel correlation of each of a plurality of users and performing main-probing for transmitting the probing signal on the selected subchannel.
1. A method for probing a channel by a base station in a communication system, the method comprising:
performing pre-probing for adjusting a subcarrier distance of a probing signal and selecting a subchannel for the probing signal according to a channel status of frequency domain; and
performing main-probing for transmitting the probing signal on the selected subchannel,
wherein the subcarrier distance is a distance in frequency between adjacent subcarriers on which probing signals are transmitted.
2. The method of claim 1 , further comprising determining, by each of a plurality of users, a time channel correlation by estimating a channel correlation in a time domain using a downlink common pilot signal and reporting the estimated channel correlation to the base station.
3. The method of claim 1 , further comprising determining, by each of a plurality of users, a frequency selectivity of each user by estimating a frequency selectivity in a frequency domain using a downlink common pilot signal and reporting the estimated frequency selectivity to the base station.
4. The method of claim 1 , wherein the performing of the pre-probing comprises:
transmitting, by each of a plurality of users, a pre-probing signal satisfying
P
k
p
(
dl
+
k
,
t
)
=
c
p
(
l
,
t
)
at intervals of a predetermined distance d (≧K) on a subcarrier over a full band;
estimating, by the base station, the pre-probing signal; and
finding a subchannel set S k satisfying S k ={{circumflex over (m)} k |γ k ({circumflex over (m)} k ,t)≧α k } having a Signal-to-Noise Ratio (SNR) higher than a particular threshold α k ,
wherein c p (l,t) denotes an l th signal of a pilot sequence at a time t, a superscript p denotes a pre-probing step, {circumflex over (m)} k denotes a subchannel which is an element of the subchannel set S k , γ k ({circumflex over (m)} k ,t) denotes an instantaneous SNR of an arbitrary user k at time t, estimated in an m k th subchannel, K denotes a total number of users, k denotes an index allocated to a user, the distance d is measured in frequency, and t denotes time.
5. The method of claim 4 , wherein the particular threshold α k is determined by adjusting a threshold control parameter β satisfying α k =(1−β)(max{γ k (m,t)})+β(min{γ k (m,t)}), 0≦β≦1, where γ k (m,t) denotes an instantaneous SNR of an arbitrary user k at time t, estimated in an m th subchannel.
6. The method of claim 5 , wherein the estimated instantaneous SNR γ k (m,t) satisfies γ k (m,t)=|{tilde over (H)} k (m,t)| 2 γ o and wherein when a channel gain of an n th subcarrier of a user k at time t is denoted by H k (n,t), {tilde over (H)} k (m,t) denotes a channel gain in an m th subchannel, obtained by averaging channel gains of all subcarriers, and γ o denotes an average SNR.
7. The method of claim 1 , wherein the performing of the main-probing comprises:
transmitting a main-probing signal satisfying
P
k
m
(
m
^
k
N
+
l
,
t
)
=
c
p
(
l
,
t
)
exp
(
-
j2π
n
(
k
-
1
)
μ
)
,
m
^
k
∈
S
k
on a subchannel {circumflex over (m)} k in a subchannel set S k , selected in the pre-probing,
wherein c p (l,t) denotes an l th signal of a pilot sequence at a time t, superscript m denotes a main-probing step, μ denotes a pilot phase-shift value of an uplink, k (1≦k≦μ) denotes an index allocated to a user that simultaneously transmits a probing sequence in the same subcarrier, N denotes a number of subcarriers per subchannel, and n is a subcarrier.
8. The method of claim 1 , wherein a period T 1 of the pre-probing is determined as a value satisfying
T
^
1
=
arg
max
T
1
{
R
k
(
T
1
)
≤
δ
1
}
,
wherein δ 1 denotes a correlation threshold, and is determined based on a time channel correlation of each of a plurality of users, reported to the base 1 station, and R k (T 1 ) is a correlation of the period T 1 .
9. The method of claim 1 , wherein a period T 2 of the main-probing is determined as a value satisfying
T
^
2
=
arg
max
T
2
{
R
k
(
T
2
)
≤
δ
2
}
,
wherein δ 2 denotes a correlation threshold, and is determined based on a time channel correlation of each user, reported to the base station, and R k (T 2 ) is a correlation of the period T 2 .
10. A system for probing a channel in a communication system, the system comprising:
a base station for performing pre-probing for adjusting a subcarrier distance of a probing signal and selecting a subchannel for the probing signal according to a channel status of frequency domain, and for performing main-probing for transmitting the probing signal on the selected subchannel,
wherein the subcarrier distance is a distance in frequency between adjacent subcarriers on which probing signals are transmitted.
11. The system of claim 10 , wherein each of a plurality of users estimates a channel correlation in a time domain using a downlink common pilot signal and reports the estimated channel correlation to the base station.
12. The system of claim 10 , wherein each of a plurality of users estimates a frequency selectivity in a frequency domain using a downlink common pilot signal, and reports the estimated frequency selectivity to the base station.
13. The system of claim 10 , wherein each of multiple users transmits a pre-probing signal satisfying
P
k
p
(
dl
+
k
,
t
)
=
c
p
(
l
,
t
)
at intervals of a predetermined distance d (≧K) on a subcarrier over a full band, and the base station estimates the pre-probing signal and finds a subchannel set S k satisfying S k ={{circumflex over (m)} k |γ k ({circumflex over (m)} k ,t)≧α k } having a Signal-to-Noise Ratio (SNR) higher than a particular threshold α k , wherein c p (l,t) denotes an l th signal of a pilot sequence at time t, a superscript p denotes a pre-probing step, {circumflex over (m)} k denotes a subchannel which is an element of the subchannel set S k , γ k ({circumflex over (m)} k ,t) denotes an instantaneous SNR of an arbitrary user k at time t, estimated in an m k th subchannel, K denotes a total number of users, k denotes an index allocated to a user, the distance d is measured in frequency, and t denotes time.
14. The system of claim 13 , wherein the particular threshold α k is determined by adjusting a threshold control parameter β satisfying α k =(1−β)(max{γ k (m,t)})+β(min{γ k (m,t)}), 0≦β≦1, where γ k (m,t) denotes an instantaneous SNR of an arbitrary user k at time t, estimated in an m th subchannel.
15. The system of claim 14 , wherein the estimated instantaneous SNR γ k (m,t) satisfies γ k (m,t)=|{tilde over (H)} k (m,t)| 2 γ o , wherein when a channel gain of an n th subcarrier of a user k at time t is denoted by H k (n,t), {tilde over (H)} k (m,t) denotes a channel gain in an m th subchannel, obtained by averaging channel gains of all subcarriers, and γ o denotes an average SNR.
16. The system of claim 10 , wherein the base station transmits a main-probing signal satisfying
P
k
m
(
m
^
k
N
+
l
,
t
)
=
c
p
(
l
,
t
)
exp
(
-
j2π
n
(
k
-
1
)
μ
)
,
m
^
k
∈
S
k
on a subchannel {circumflex over (m)} k in a subchannel set S k , selected in the pre-probing, wherein c p (l,t) denotes an l h signal of a pilot sequence at a time t, a superscript m denotes a main-probing step, μ denotes a pilot phase-shift value of an uplink, k (1≦k≦μ) denotes an index allocated to a user that simultaneously transmits a probing sequence in the same subcarrier, N denotes a number of subcarriers per subchannel, and n is a subcarrier.
17. The system of claim 10 , wherein a period T 1 of the pre-probing is determined as a value satisfying
T
^
1
=
arg
max
T
1
{
R
k
(
T
1
)
≤
δ
1
}
,
wherein δ 1 denotes a correlation threshold and is determined based on a time channel correlation of each of a plurality of users, reported to the base station, and R k (T 1 ) is a correlation of the period T 1 .
18. The system of claim 10 , wherein a period T 2 of the main-probing is determined as a value satisfying
T
^
2
=
arg
max
T
2
{
R
k
(
T
2
)
≤
δ
2
}
,
wherein δ 2 denotes a correlation threshold and is determined based on a time channel correlation of each user, reported to the base station, and R k (T 2 ) is a correlation of the period T 2 .