Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
1997-08-08
2001-05-29
Pham, Chi (Department: 2631)
Pulse or digital communications
Receivers
Interference or noise reduction
Reexamination Certificate
active
06240148
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to spread spectrum communications for mobile communications and wireless Local Area Networks, especially a path-diversity receiving system in which pilot signals are included in information signals.
BACKGROUND OF THE INVENTION
In spread spectrum communications, there must be compensation in signals like processing for errors due to fading in the received signals.
FIG. 5
shows such signals, in which known pilot signals P
1
and P
2
(signals with a plurality of bits, for example, Np bits) are input before and after the predetermined quantity of information signal S(t) (a signal with a plurality of bits). According to these pilot signals, phase errors caused by fading are presumed with respect to the signals between the pilot signals, and compensated. Here, assuming that the pilot signals are (P
1
(k)
i+j·P
1
(k)
q) and (P
2
(k)
i+j·P
2
(k)
q), each information signal symbol is (Di+j·Dq), P
1
(k)
and P
2
(k)
with bits P
1
and P
2
, respectively, being averaged by averaging circuits A
1
and A
2
, and all the pilot signals in the send mode are (1+j·0) (other patterns can be adopted), the average value E of information signal error vectors is expressed by formulas (1) to (5):
E
=
P1i
+
P2i
2
+
j
·
P1q
+
P2q
2
(
1
)
P1i
=
1
N
p
∑
k
=
1
N
p
P1
(
k
)
i
(
2
)
P1q
=
1
N
p
∑
k
=
1
N
p
P1
(
k
)
q
(
3
)
P2i
=
1
N
p
∑
k
=
1
N
p
P2
(
k
)
i
(
4
)
P2q
=
1
N
p
∑
k
=
1
N
p
P2
(
k
)
q
(
5
)
Compensating vector M according to the formulas above is given by a complex conjugate number. P
1
i, P
1
q, P
2
i and P
2
q are the average values of the pilot signal trains, which reduce the influence of noise. The compensation coefficient is calculated by formula (6):
M
=
Mi
+
j
·
Mq
=
P1i
+
P2i
2
-
j
·
P1q
+
P2q
2
(
6
)
Multiplying the value of formula (6) by each information signal symbol, compensates the influence of fading. When Dc stands for the compensated information symbol, it is calculated by formula (7):
Dc=D·M
=(
Di+j·Dq
)(
Mi+j·Mq
)=(
Di·Mi−Dq·Mq
)+
j·
(
Dq·Mi+Di·Mq
) (7)
Assuming the in-phase components and the quadrature components after the compensation of N numbers of paths to be Dci
1
t o DciN and Dcq
1
to DcqN, respectively, the in-phase components Dci and quadrature components Dcq of signals after rake composition are calculated by accumulations of signals in each path as in formulas (8) and (9):
Dci
=
∑
k
=
1
N
Dcik
(
8
)
Dcq
=
∑
k
=
1
N
Dcqk
(
9
)
FIG. 6
shows the phase compensating circuit COR for performing each processing above. In
FIG. 6
, receiving signal Sin undergoes proper timing adjustment and is input to two pilot signal holding circuits SHP
1
and SHP
2
and information signal holding circuit SHS. Each bit P
1
(k) and P
2
(k) of P
1
and P
2
held by SHP
1
and SHP
2
, respectively, is averaged by averaging circuit A
1
and A
2
, respectively, and pilot signals P
1
and P
2
are calculated. Compensation coefficient calculating circuit MC calculates compensation coefficient M according to these pilot signals. Compensation coefficient M is input to multiplication circuit MUL, multiplied by information signal D, and the signal Dck is output after compensation.
FIG. 7
shows a rake processing circuit which also performs phase compensation of a plurality of paths (four paths in
FIG. 7
as an example). First, multipath signals greater than a predetermined level are selected among the input signals by multipath selecting circuit MULSEL. The selected signals are input to compensation circuits COR
1
to COR
4
, arrayed in four phases corresponding to the first to the fourth paths, respectively. Their outputs are then input to accumulating circuit &Sgr; after being appropriately delayed by delaying circuits D
1
to D
4
, respectively. Outputs SCs of &Sgr; correspond to Dci and Dcq above.
SUMMARY OF THE INVENTION
Conventional path-diversity receiving systems store considerably more data in their information holding circuits, and their phase compensating circuits have necessarily been large-size.
The present invention solves the above problem provides a path-diversity system with a small-size phase compensating circuit.
A path-diversity receiving system for spread spectrum communications according to the present invention calculates the compensating coefficient according to the signals of two pilot blocks prior to the information signals, or to the signal of a single pilot block just prior to the information signals, and compensates them by the compensating coefficient.
REFERENCES:
patent: 4313211 (1982-01-01), Leland
patent: 5694388 (1997-12-01), Sawahashi et al.
patent: 5727032 (1998-03-01), Jamal et al.
patent: 5787112 (1998-07-01), Murai
patent: 661831 (1995-07-01), None
patent: WO 91/20142 (1991-12-01), None
Yoshio Honda and Karin Jamal, Channel Estimation Based on Time-Multiplexed Pilot Symbols, Technical Report of IEICE, RCS96-70 (1996-08).
Seiichi Sampei, Rayleigh Fading Compensation Method for 16QAM Modem in Digital Land Mobile Radio System, IEICE B-II, Jan. 1989, pp. 7-15, vol. J72-B-II No. 1.
Adachi Fumiyuki
Sawahashi Mamoru
Shou Guoliang
Zhou Changming
Zhou Xuping
NTT Mobile Communications Network Inc.
Pham Chi
Pillsbury & Winthrop LLP
Tran Khai
LandOfFree
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