Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
2001-10-05
2004-06-29
Phu, Phoung (Department: 2631)
Pulse or digital communications
Receivers
Interference or noise reduction
C375S346000, C375S285000, C455S296000
Reexamination Certificate
active
06757346
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to code division multiplex radio equipment with an interference canceler.
2. Description of the Related Art
As a next-generation digital mobile communications method, a radio access method using a code division multiple access (CDMA) method is being examined and put into practical use. The CDMA method is a multiple access method using a spectrum diffusion communications method. In the CDMA method, a plurality of channels or user's transmission data are multiplexed by a code and are transmitted through a transmission line, such as a radio circuit and the like. The CDMA method is an interference restriction type system where system capacity is restricted by interference due to the incomplete orthogonality of a code between users, and an interference elimination technology is useful for the increase of system capacity.
FIG. 1
shows the basic configuration of a multi-stage type parallel interference canceler.
The interference canceler shown in
FIG. 1
is particularly applied to a base station in a CDMA communications system. Receiving signals are transmitted to interference replica generation units
1
a
-
1
to
1
a
-
n
provided for each user. The interference replica generation units
1
a
-
1
to
1
a
-
n
generate both the interference replica signal and symbol replica signal of the signal received from each user. The receiving signal is inputted to a delayer
2
a
, is delayed by a time required for the interference replica generation units
1
a
-
1
to
1
a
-
n
to generate both the interference replica signal and symbol replica signal, and is inputted to an interference elimination unit
3
a
. The interference elimination unit
3
a
eliminates interference components by subtracting the interference replica signals transmitted from each interference replica generation units
1
a
-
1
to
1
a
-
n
from the receiving signal that passes through the delayer
2
a
in the interference elimination unit
3
a
. Since the interference replica generation units
1
a
-
1
to
1
a
-
n
are provided in relation to each of all users that are accommodated in a base station, the interference elimination unit
3
a
obtains a signal by eliminating all signals transmitted by each user from the receiving signal as interference components.
This process is performed in several stages (two stages in FIG.
1
). Specifically, the signal obtained by the interference elimination unit
3
a
are further inputted to each of the interference replica generation units
1
b
-
1
to
1
b
-
n
, and an interference signal component corresponding to each user is extracted from the signal outputted from the interference elimination unit
3
a
. The signal outputted from the interference elimination unit
3
a
is inputted to a delayer
2
b
, is delayed by a time required for the interference replica generation units
1
b
-
1
to
1
b
-
n
to generate both the interference replica signal and symbol replica signal and is inputted to an interference elimination unit
3
b
. The interference elimination unit
3
b
eliminates the interference replica signals outputted from the interference replica generation units
1
b
-
1
to
1
b
-
n
from the signal from the delayer
2
b
. The interference replica generation units
1
a
-
1
to
1
a
-
n
generate a symbol replica signal and input it to corresponding interference replica generation units
1
b
-
1
to
1
b
-
n
in a subsequent stage. A symbol replica signal from a previous stage is inputted to the interference replica generation units
1
b
-
1
to
1
b
-
n
, and a new symbol replica signal is generated by combining the symbol replica signal from a previous stage with the signal from each user that is extracted from the signal from the interference elimination unit
3
a
. Thus the generated symbol replica signal is inputted to receivers
4
-
1
to
4
-
n
provided for each user. Furthermore, the signal from the interference elimination unit
3
b
is also inputted to each of the receivers
4
-
1
to
4
-
n
, and each of the receivers
4
-
1
to
4
-
n
demodulates and receives the signal transmitted from each user.
The configuration of the interference canceler shown in
FIG. 1
is for a base station and a receiver receives both the interference replica signal obtained by eliminating all receiving signals from each user as interference components and the symbol replica signal obtained by demodulating a signal from each user. Theoretically, it is all right if signals other than a signal from a target user are eliminated and the user signal is demodulated from the remaining signal after interference elimination. However, since in a base station, signals from all users must be received, the configuration becomes very lengthy if a circuit is configured based on the principle described above. Therefore, the system is configured so that both an interference replica signal obtained by eliminating all signals from all users from a receiving signal and a symbol replica signal, which is the demodulation signal of a receiving signal from each user can be received. It is also all right if only the symbol replica signal, which is the demodulation signal of a receiving signal from each user, is received. However, in that case, when an interference replica signal is generated, in reality the interference replica signal gains slight power due to fading and the like, and becomes a definite signal, although the power of the interference replica signal is ideally “0”. The circuit shown in
FIG. 1
is configured utilizing the fact that a receiving characteristic is improved if this interference replica signal is used to demodulate a user signal along with a symbol replica signal.
FIG. 2
shows the configuration of the interference replica generation unit shown in FIG.
1
.
The interference replica generation unit is provided with a plurality of fingers to perform RAKE-combination. Each finger includes an inverse diffusion unit
5
and a channel estimation unit
6
. A receiving signal is inputted to a searcher
12
. The searcher
12
extracts a timing signal for multiplying the receiving signal by an inverse diffusion code, and, the inverse diffusion unit
5
demodulates the receiving signal based on this timing. After the channel estimation unit
6
estimates the channel of the demodulated signal, a combination unit
7
combines the demodulated signal for each finger at a maximum ratio and inputs the signal to a judgment unit
8
. After being temporarily judged in the judgment unit
8
, the receiving signal is branched into the same number of signals as the number of the fingers. The branched receiving signals after the temporary judgment are inputted to the same number of delay restoration units
9
as the number of the fingers. The timing signal detected by the searcher
12
is inputted to the delay restoration units
9
, and each of the delay restoration units
9
provides a delay to the branched signal. Thus, a signal delay corresponding to each multi-path possessed when the receiving signal is inputted to the finger, is restored. A re-diffusion unit
10
restores the signal after the temporary judgment, to which a delay is given, to a diffusion/modulation signal. A combination unit
11
combines the re-diffusion signals from each finger into an interference replica signal. The output signal of each delay restoration unit
9
is transmitted to an interference replica generation unit in a subsequent stage or a receiver as a symbol replica signal.
FIG. 3
shows the configuration in the case where an interference canceler is not introduced in radio base-station equipment.
The flow of a receiving signal is as follows. First, when an antenna
20
receives a signal, the frequency converter
22
of a transmitting/receiving panel
21
converts the receiving signal from an RF frequency to a baseband frequency. Then, A/D converters
24
-
1
and
24
-
2
convert the receiving signal from an analog signal to a digital signal. Quadrature demodulators
26
-
1
and
26
-
2
quadrature-demodulate this digital signal,
Asano Yoshihiko
Minowa Morihiko
Nakamura Tadashi
Saito Tamio
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Phu Phoung
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