Multiplex communications – Duplex – Transmit/receive interaction control
Reexamination Certificate
1998-12-04
2003-09-02
Kizou, Hassan (Department: 2662)
Multiplex communications
Duplex
Transmit/receive interaction control
C370S288000, C370S342000, C375S285000, C375S346000
Reexamination Certificate
active
06614766
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an interference canceller, and more particularly to an interference canceller suitable for a cellular DS/CDMA (Direct Sequence Code Division Multiple Access) mobile communication system or the like.
In a cellular CD/CDMA mobile communication system, an interference occurs which results from an interference and noise from another mobile station due to correlation between spread codes caused by asynchronism with mobile stations. Such an interference serves as a factor which degrades the channel capacity and the transmission quality of the mobile communication system. Hence, it is desired to precisely eliminate such an interference from a received signal.
2. Description of the Related Art
FIG. 1
shows a conventional multistage type interference canceller. Each of the stages in the multistage type interference canceller is made up of interference canceller units
81
and a combiner
82
. The stages thus configured are cascaded.
FIG. 1
shows the multistage type interference canceller having the first stage through the mth stage. Data symbol receivers
83
are provided in the mth stage, which is the final stage.
The interference canceller units
81
and the final stage are provided in parallel for the respective users' channels. The suffix of the reference number
81
indicating the interference canceller units
81
includes a stage number and a user number corresponding to the user channel (ICU
1
,
1
, ICU
1
,k, ICU
2
,
1
, ICU
2
,k . . . ).
In the first stage, a received signal R
0
is input to the interference canceller units ICU
1
,
1
-ICU
1
,k corresponding to the users' channels, which output interface replica signals S
1
,
1
-S
1
,k and interference residual signals d
1
,
1
-d
1
,k. The combiner
82
combines the interference residual signals d
1
,
1
-d
1
,k corresponding to the users' channels. The combined interference residual signals d
1
,
1
-d
1
,k are subtracted from the received signal R
0
, so that a resultant error signal e
1
of the first stage is obtained.
In the second stage, the interference canceller units ICU
2
,
1
-ICU
2
,k are supplied with the error signal e
1
from the combiner
82
of the first stage and the interference replica signals S
1
,l-S
1
,k from the interference canceller units ICU
1
,
1
-ICU
1
,k of the first stage. Then, the interference canceller units ICU
2
,
1
-ICU
2
,k respectively output interference replica signals S
2
,
1
-S
2
,k and interference residual signals d
2
,
1
-d
2
,k. The combiner
82
combines the interference residual signals d
2
,
1
-d
2
,k corresponding to the users' channels. The combined interference residual signals d
2
,
1
-d
2
,k are subtracted from the error signal e
1
of the first stage. Hence, an error signal e
2
of the second stage is obtained.
In the mth stage, which is the final stage, the receivers ReCm,
1
-ReCm,k are supplied with an error signal em-
1
and interference replica signals Sm-
1
,
1
-Sm-
1
,k of the previous stage, and perform an interference eliminating process using the supplied signals, so that data symbols can be decoded. By sequentially repeating the interference eliminating process, the error signal is gradually reduced, and interference replica signals can be obtained from which signals interference between the users can be eliminated.
FIG. 2
shows a conventional interference canceller unit, which includes despread processing parts
91
, a despreader
91
-
1
, an adder
91
-
2
, a multiplier
91
-
3
, a channel estimation circuit
91
-
4
, a combiner
92
, a decision part
93
, spread processing parts
94
, a multiplier
94
-
1
, an adder
94
-
2
, a respreader
94
-
3
, and a combiner
95
.
The despread processing parts
91
and the spread processing parts
94
are respectively provided to received delayed waves, that is, multipaths. The structure shown in
FIG. 2
is configured so as to handle three paths. In
FIG. 2
, signals corresponding to the respective paths are given a suffix “i” (In
FIG. 2
, i=1-3). The signals corresponding to the paths are referred to RAKE fingers.
The despread processing part
91
is supplied with the error signal ej-
1
of the previous stage and the interference replica signals Sj-
1
,
1
-Sj-
1
,k (these signals of the first stage are zeros). The despreader
91
-
1
receives the error signal ej-
1
from the previous stage (the received signal R
0
in the first stage) and performs a despread operation thereon using the spread code. A suffice “j” indicates the stage identification number.
The adder
91
-
2
adds the despread signal and the interference replica signals Sj-
1
,
2
-Sj-
1
,k (which are zeros in the first stage), and creates a resultant receive symbol R
1
of the first path. The channel estimation circuit
91
-
4
receives the receive symbol R
1
, and estimates channels of paths (the characteristics of transmission paths) using pilot symbols shown in FIG.
3
B. Thus, channel estimate values &xgr;i{circumflex over ( )} are obtained for the respective paths.
The despread signal Ri is multiplied by a complex number &xgr;i{circumflex over ( )} * of the channel estimate &xgr;i{circumflex over ( )} by the multiplier. Hence, a received symbol can be obtained from which a phase error due to influence of the transmission paths has been eliminated.
The output signals of the multipliers
91
-
3
related to the respective paths are diversity-combined (maximal ratio combining) by the combiner
92
. A resulting receive symbol &Sgr;Ri &xgr;i{circumflex over ( )} * obtained by the maximal ratio combining is compared with the decision part
93
, so that a data symbol can provisionally be decided.
The signals generated and output by the respread processing parts
91
are called interference replica generation signals. The interference replica generation signals are converted into interference replica signals and interference residual signals, which are then transferred to the next stage.
The provisionally decided symbol Zs{circumflex over ( )} output by the decision part
93
branches into signals corresponding to the paths. In each of the spread processing parts
94
, the multiplier
94
-
1
multiplies the provisionally decided symbol Zs{circumflex over ( )} by the channel estimation value &xgr;i{circumflex over ( )}. Hence, the provisionally decided data symbol is decomposed into the signals corresponding to the respective paths, which are output to the next stage as interference replica signals Sj,
1
-Sj,k.
The adders
94
-
2
of the spread processing parts
94
respectively add the interference replica signals Sj,i-Sj,k that are output by the multipliers
94
-
1
and correspond to the paths and the interference replica signals Sj-
1
,
1
-Sj-
1
,k supplied from the previous stage. Then, the adders
94
-
2
respectively output the differences between the interference replica signals Sj,i-Sj,k of this stage and the interference replica signals Sj-
1
,i-Sj-
1
,k. The output signals of the adders
94
-
2
of the spread processing parts
94
are spread using a spread code in the respective respreaders
94
-
3
. The respread output signals of the respreaders
94
-
3
corresponding to the respective paths are combined by the combiner
95
. The output signals of the combiners
95
of the interference canceller units provided for the respective users' channels are output to the combiner
82
shown in
FIG. 1
as interference residual signals dj,
1
-dj,k.
FIG. 3A
shows a conventional final-stage receiver provided in the final stage of the multistage type interference canceller, and
FIG. 3B
shows a frame format. The final-stage receiver labeled
100
in
FIG. 3A
includes despread processing parts
101
, a combiner
102
and a decoder
103
.
The despread processing parts
101
of the final-stage receiver
100
are supplied with the error signal em-
1
from the interference replica generation unit of the previous stage and the interference replica signals Sm-
1
,
1
-Sm-
1
,k, and perform the same process as that of the aforementioned desp
Kobayakawa Shuji
Seki Hiroyuki
Tanaka Yoshinori
Toda Takeshi
Fujitsu Limited
Kizou Hassan
Rosenman & Colin
Tsegaye Saba
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