Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Reexamination Certificate
2000-09-06
2003-09-02
Le, Thanh Cong (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
C455S561000, C375S349000
Reexamination Certificate
active
06615030
ABSTRACT:
This application claims a priority based on Japanese Patent Application No. 2000-032343 filed on Feb. 9, 2000, the entire contents of which are incorporated herein by reference for all purposes.
BACKGROUND OF THE INVENTION
The present invention relates to a mobile communication system and a radio base station apparatus, in which communication with a plurality of radio mobile station apparatuses is carried out using the code division multiple access method, and, in particular, relates to a mobile communication system and a radio base station apparatus, in which interference noise components contained in a target demodulation signal due to signals of other radio mobile station apparatuses are subject to suppression processing to obtain a signal that has been subjected to demodulation processing and that signal is transmitted toward a wired transmission path, thereby improving channel usage efficiency.
A wireless communication system using the code division multiple access method possesses suitable characteristics for mobile communication, such as resistiveness to mutual interference with another system, resistiveness to multi-path, easiness of hand-off, superiority in privacy protection, and the like. However, differently from other multiple access methods, in the communication system using the code division multiple access method, a plurality of users existing within a same base station cell carry out communication using a same frequency and a same frequency band at the same time, and accordingly, the system also has a problem of channel usage efficiency. This problem is caused as follows. Namely, interference is generated when, in the presence of the near-and-far problem, a strong signal of a user closer to a base station covers other weak communication signals. Or, interference by other stations is caused by unnecessary transmission power of a certain station itself. Such interference brings decrease of channel usage efficiency.
Countermeasures against decrease of channel usage efficiency include utilization of broad-band gain obtained by using broad-band signal transmission, use of a code series having low cross-correlation, adoption of power control for solving the near-and-far problem, and the like. In particular, power control not only suppresses unnecessary transmission power of a certain station itself leading its transmission power to the necessity minimum so as to suppressing interference by other stations to the minimum, but also is effective for solving the near-and-far problem.
However, even if these countermeasures are employed, it is difficult to prevent degradation of communication quality that accompanies increase of cross-correlation interference (degradation of signal-to-noise ratio) caused by increase of the number of users carrying out simultaneous communication.
As a measure for solving the above-mentioned problem, effective is an interference cancel technique that removes interference generated by other channels, and various types of interference cancel techniques have been examined. Interference by another user can be estimated in a receiver, and it is possible to perform processing for removing the interference. Among these interference cancel methods, there has been proposed a multi-user receiving method utilizing information on a plurality of user signals that are objects of demodulation. An interference cancel apparatus utilizing this method performs demodulation processing for a plurality of user signals that are objects of demodulation, performing respread processing and synthesizing processing on the demodulated signal to generate a replica signal, subtraction processing with the received multi-wave signal to perform demodulation processing, so as to suppress the interference components. Here, the interference cancel processing is performed in a cascaded multi-stage configuration, so that the interference component suppressing effect is increased.
FIG. 11
is a block diagram showing a configuration of an interference canceler unit according to the conventional technique. In the following, the conventional technique will be described referring to the drawing. In
FIG. 11
, the reference numeral
111
refers to an interference cancel processing part,
112
to a reverse spread processing/respread processing part,
113
to a synthesizing processing part,
114
to a subtraction processing part, and
115
-
1
-
115
-n to demodulation processing parts.
As shown in
FIG. 11
, the interference canceler unit according to the conventional technique comprises: the interference cancel processing part
111
for performing interference cancel processing on a multi-wave signal into which a plurality of received spread spectrum signals are synthesized; and a plurality of demodulation processing parts
115
-
1
-
115
-n for performing demodulation processing such as correlating detection and synchronous detection on the signal subjected to the interference cancellation. The interference cancel processing part
111
comprises: a plurality of reverse spread processing/respread processing parts
112
for performing reverse spread processing and respread processing on a received signal; synthesizing processing parts
113
for synthesizing signals subjected to the respread processing; and subtraction processing parts
114
for subtracting the synthesized signal from received signal. The interference cancel processing part
111
is constructed such that the processing by those processing parts is repeated in a plurality of stages. The interference cancel processing part
111
can process received signals of users #
1
-#n, and the demodulation processing parts
115
-
1
-
115
-n perform the demodulation processing on the received signals of the users #
1
-#n, respectively.
Since the interference canceler unit according to the conventional technique has the above-described structure, the scale of the interference canceler unit and the quantity of processed signals become enormous. Further, in the case of a radio base station apparatus that should receive many users, the scale of the apparatus becomes unrealistically large when it is to be constructed to include an interference canceler unit that performs the interference cancel processing for all user signals.
As known information on this type of interference cancel, may be mentioned, for example, Japanese Non-examined Patent Laid-Open Nos. 10-51353, 10-190494, etc.
SUMMARY OF THE INVENTION
A mobile communication system using the above-described code division multiple access can not help increase of cross-correlation interference due to increase of the number of users in communication at the same time. Thus, interference cancel technique is indispensable. Among the interference cancel methods, the interference canceler method of multi-user receiving type utilizes information on a plurality of user signals that are objects of demodulation, and thus, requires a signal processing part including a plurality of correlators and respread circuits for suppressing cross-correlation interference components. This signal processing part for suppressing the cross-correlation interference components is constructed in multiple stages so as to improve the effect of suppressing the cross-correlation interference components, and accordingly, the scale of the apparatus becomes large. Further, the interference canceler system of the multi-user receiving type performs signal processing utilizing the user signals that are objects of demodulation. Accordingly, it is necessary to suitably manage and control each of the received signals. As a result, a communication system using thus-mentioned interference cancel method has such a problem that it becomes large in the scale of a base station apparatus and in the scale of signal processing, thus increasing costs.
An object of the present invention is to solve such problem in a mobile communication system using the above-mentioned code division multiple access method that the apparatus scale becomes larger as the number of received users becomes larger, in developing an interference can
Ishida Yuuji
Nakahara Naruhito
Niida Sumaru
Saito Joichi
Suzuki Toshinori
Cong Le Thanh
Tran Tuan
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