Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2000-07-18
2004-01-13
Corrielus, Jean B. (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S130000, C455S522000, C455S025000
Reexamination Certificate
active
06678309
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CDMA base station system for controlling the directivity of a plurality of antennas as a whole and transmitting a spread signal to a mobile station system with the transmission power depending on the mobile station system, and more particularly to a CDMA base station system having such transmission directivity characteristics as to reduce interference given to a relatively interference-susceptible mobile station system to a level lower than a conventional level.
2. Description of the Related Art
Efforts are being made to study DS-CDMA systems as radio transmission systems according to the IMT-2000 standardization process. In a radio communication system based on DS-CDMA principles, different spreading codes are assigned to respective mobile station systems. In a CDMA base station system, a received signal is despread using a spreading code assigned to a certain mobile station system for thereby separating the signal destined for the mobile station system from the received signal, and a signal spread using a spreading code assigned to a certain mobile station system is transmitted to the mobile station system.
The radio communication system based on DS-CDMA principles allows a plurality of mobile station systems to share one frequency band by using the above spreading codes. However, since the same frequency band is shared by plural mobile station systems, a spread signal transmitted to and from a certain mobile station system serves as an interference signal for a spread signal transmitted to and from another mobile station system. Therefore, if a multirate service is provided using a DS-CDMA system, then it has been proposed to provide a CDMA base station system with an adaptive antenna array for interference removal. The proposed elimination of interference with an adaptive antenna array will be described below.
The multirate service provided as a DC-CDMA feature is a service which allows the user to obtain a plurality of communication rates. The multirate service can offer voice communications similar to conventional voice communications, and can also transmit high-bit-rate data and image data using a high communication rate.
The adaptive antenna array comprises a plurality of antennas whose overall directivity can be controlled. Specifically, a reception weight or a transmission weight is given to each of the antennas for controlling the directivity upon reception (reception directivity) and the directivity upon transmission (transmission directivity).
In the multirate service, generally, the power level of a signal is greater as the communication rate of the signal is higher. Therefore, when a signal having a relatively high communication rate (high-rate user signal) and a signal having a relatively low communication rate (low-rate user signal) are simultaneously transmitted from a plurality of mobile station systems, the high-rate user signal interferes with the low-rate user signal. To solve this problem, it has been proposed to provide a CDMA base station system with an adaptive antenna array for interference removal upon signal reception. For example, prior proposed attempts are disclosed in “IEICE Trans. Fundamentals, vol. E80-A, no. 12, pp. 2445-2454, December 1997, S. Tanaka, M. Sawahishi, and F. Adachi”, and “IEEE VTC99-Conf. Rec., vol. 1, pp. 243-248, May 1999, S. Tanaka, A. Harada, M. Sawahishi, and F. Adachi”.
For interference removal upon signal reception by the CDMA base station system, the reception weights of the adaptive array antenna are controlled to achieve a reception directivity for preferentially attenuating a reception interference signal having a large power level. For example, if a high-rate user signal and a low-rate user signal are present as interference signals other than a signal that is desired to be received, then the high-rate user signal as an interference signal having a relatively large power level is preferentially attenuated, thus improving signal reception characteristics.
It has also been proposed to improve signal transmission characteristics by controlling the transmission weights of an adaptive antenna array with a CDMA base station system not only for uplink communications from mobile station systems to the CDMA base station system but also for downlink communications from the CDMA base station system to mobile station systems. One proposal is disclosed in “IEICE Technical Report, RCS99-18, May 1999, Harada, Tanaka, Sawahashi, and Adachi”, for example.
Specifically, there has been studied a CDMA base station system for controlling the transmission directivity of an adaptive array antenna using transmission weights based on the reception weights that were obtained for interference removal upon signal reception. The transmission weights based on the reception weights are weights obtained by effecting a calibration process on the reception weights. The calibration process serves to remove effects due to the difference per antenna between the complex amplitude characteristics of an RF receiver and the complex amplitude characteristics of an RF transmitter in the CDMA base station system.
If the transmission directivity of an adaptive array antenna is controlled using transmission weights based on the reception weights, as described above, then since more priority is given to the reduction of interference imposed on a mobile station system (high-rate user) which transmits and sends a high-rate user signal, i.e., a signal having a relatively large power level, than a mobile station system (low-rate user) which transmits and sends a low-rate user signal, i.e., a signal having a relatively small power level, the signal reception characteristics of the low-rate user that is more susceptible to interference than the high-rate user are largely deteriorated.
Stated otherwise, although the transmission directivity of the adaptive array antenna actually needs to be controlled in order to preferentially lower the antenna gain in the direction of the low-rate user for the downlink, it has heretofore been customary to preferentially use the freedom of the adaptive antenna array so as to lower the antenna gain in a multipath direction of the high-rate user signal, for example. Consequently, it is highly difficult to lower interference imposed on the low-rate user. This difficulty manifests itself particularly if many low- and high-rate users are present compared with the freedom of the adaptive antenna array.
One way of determining the reception directivity of the adaptive array antenna with the CDMA base station system has been to employ an MMSE (Minimum Mean Square Errors) control process for determining reception weights in a manner to minimize the power levels of received signals other than a desired received signal. If the desired received signal arrives at the CDMA base station system via a plurality of paths in a multipath environment, then a signal that is received at an earliest time (leading wave) among multipath signals received by the CDMA base station system via the plural paths is selected as a reference signal, and reception weights are determined in order to minimize the power levels of received signals other than the reference signal.
However, the leading wave among the signals received by the CDMA base station system via the plural paths may not necessarily arrive at the CDMA base station system via the path whose power loss is minimum. Accordingly, the determined reception weights may not be optimum.
Specific examples of reception adaptive array antenna devices are revealed in “IEEE Trans. Information Theory, vol. IT-32, no. 2, pp. 195-219, March 1986, J. W. Modestino and V. M. Eyuboglu” and “IEICE Technical Report, A.P97-146, November 1997, Kazuhiko Fukawa”, for example. In the disclosed reception adaptive array antenna devices, the position (time) of a multipath wave selected as a reference signal is fixed in advance, failing to employ reception weights that are optimum at all times.
In the above various conventional arrangements, the po
Corrielus Jean B.
Kokusai Electric Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
CDMA base station system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with CDMA base station system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and CDMA base station system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3202405