Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-03-22
2003-06-03
Legree, Tracy (Department: 2681)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C375S148000
Reexamination Certificate
active
06574204
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of canceling interference components included in received signals of a base station in a mobile communication system, and more particularly, to a method of canceling interference components included in received signals of a base station in a mobile communication system, which allows user data not to serve as interference components for other user data by subtracting the user data from received signals which are standby for decoding the other user data.
2. Background of the Related Art
Generally, in a mobile communication system based on code division multiple access (CDMA) type, respective mobile terminals transmit transmission data by spreading with its own unique PN sequences so that the data can be transmitted to the closest base station with the same radio frequency shared by other users. That is to say, communication between the base station and a plurality of terminals will be performed with the same radio channel. In the mobile communication system based on CDMA type, the plurality of terminals in the same base station area transmit scrambled data to the base station using the same radio channel. Accordingly, a receiving portion of the base station converts received signals including a plurality of user data into base band signals when the plurality of terminals in the service area of base station receive the user data. The receiving portion despreads the base band signals using the unique PN sequences of the respective terminals to identify, which have been known by the base station, and decodes them to decode them to original data. The process is limited by the interference generated by the other transmitters.
FIG. 1
is a block diagram illustrating a partial configuration of a typical base station receiving portion.
Referring to
FIG. 1
, radio signals transmitted from respective terminals are input to a frequency down processor
10
of the base station through an antenna of the base station and then converted into base band signals. Such base band signals are in parallel input to a plurality of multipliers
21
a
~
21
n
of a composite correlation bank
20
so that the base band signals are respectively multiplied by the unique PN sequences C
1
e
jo1
, C
2
e
jo2
, . . . , C
N
e
joN
of the respective terminals, which have been already known by the base station. Subsequently, spreading values output from the respective multipliers
21
a
~
21
n
are respectively input to a plurality of accumulators
22
a
~
22
n
which are connected to the multipliers
21
a
~
21
n
in series, and then stored as correlation values corresponding to the respective user data for the unit of symbol(or frame).
The respective accumulators
22
a
~
22
n
transmit the user data stored for the unit of symbol(or frame) to the next circuit to decode them to original signals.
The base station receiving portion of
FIG. 1
is supposed on the assumption that all the user data transmitted from the respective terminals have the same transmission rate. In other words, it is noted that such a base station receiving portion is supposed taking account of only mobile communication system which support only voice service. Accordingly, such a base station receiving portion has simple hardware configuration and processes data at relatively high speed because it detects user signals including interference signals. On the other hand, since the base station receiving portion of
FIG. 1
detects the user signals without canceling the interference components, it has a problem that receiving performance is poor, thereby reducing traffic capacity of the overall system.
To solve such a problem, there is suggested a related art base station receiving portion disclosed in “IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS (VOL. 12, NO. 5, JUNE 1994)”, as shown in FIG.
2
.
Referring to
FIG. 2
, data transmitted from respective terminals in a corresponding base station are input to a frequency down processor
100
through an antenna of the base station and converted into base band signals. Subsequently, the base band signals output from the frequency down processor
100
are stored in a memory
200
for the unit of symbol (or frame). The base band signals stored in the memory
200
are input to a plurality of multipliers
310
a
~
310
n
of a composite correlation bank
300
in parallel, so that the base band signals are respectively multiplied by the unique PN sequences C
1
e
jo1
, C
2
e
jo2
, . . . , C
N
e
joN
of the respective terminals, which have been known by the base station, to obtain correlation values. Subsequently, output signals of the respective multipliers
310
a
~
310
n
are respectively input to a plurality of accumulators
320
a
~
320
n
which are connected to the multipliers
310
a
~
310
n
in series, and then stored as correlation values corresponding to the respective user data for the unit of symbol (or frame).
Thereafter, the respective accumulators
320
a
~
320
n
provides correlation values output from the respective multipliers
310
a
~
310
n
to a comparator
400
connected to the respective multipliers
310
a
~
310
n
for the unit of symbol (or frame) in parallel. The comparator
400
compares the correlation values output from the respective accumulators
320
a
~
320
n
with one another to detect one user data having the maximum value. At this time, the detected maximum correlation value is transmitted to the next circuit to be decoded to original data.
Unlike the base station receiving portion of
FIG. 1
, the user data detected to be decoded to original data are to be feedback to the memory
200
and subtracted from the base band signals including a plurality of user data, so that the detected user data do not serve as interference components for other user data during the next despreading step.
In other words, the correlation value having the maximum value, which is output from the comparator
400
, is also input to a multiplier
500
so that the correlation value is multiplied by the unique PN sequences C
1
e
jo1
, C
2
e
jo2
, . . . , C
N
e
joN
of the terminal used for spreading. Signals spread again through the multiplier
500
are provided to a subtracter
600
. The subtracter
600
subtracts only the same spread signal as the input spread signal from the base band signals stored in the memory
200
. Accordingly, the decoded user data are fully canceled from the base band signals stored in the memory
200
.
Subsequently, the base band signals stored in the memory
200
are again input to the plurality of multipliers
310
a
~-
310
n
of the composite correlation bank
300
in parallel, so that the base band signals are respectively multiplied by the unique PN sequences C
1
e
jo1
, C
2
e
jo2
, . . . , C
N
e
joN
of the respective terminals to obtain correlation values having next priority. The output signals of the respective multipliers
310
a
~
310
n
are respectively input to the accumulators
320
a
~
320
n
which are connected to the multipliers
310
a
~
310
n
in series, and then stored as correlation values corresponding to the respective user data for the unit of symbol (or frame).
Then, the respective accumulators
320
a
~
320
n
provides correlation values output from the respective multipliers
310
a
~
310
n
to the comparator
400
connected to the respective multipliers
310
a
~
310
n
for the unit of symbol (or frame) . The comparator
400
compares the correlation values output from the respective accumulators
320
a
~
320
n
with one another to detect one user data having the maximum value. At this time, the detected maximum correlation value is transmitted to the next circuit to be decoded to original data.
As aforementioned, the base station receiving portion of
FIG. 2
performs despreading and decoding operations in the order of the user data having the maximum correlation value until there exists no user data in the memory
200
, and subtracts only the same spread signal as input spread signal from the base band signals stored in the memory
200
in the order of detected user
Fleshner & Kim LLP
Legree Tracy
LG Information & Communications Ltd.
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