Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Patent
1995-12-01
1999-06-22
Olms, Douglas W.
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
370441, 370320, 370342, H04B 7212, H04B 7216, H04J 300
Patent
active
059149477
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates generally to a mobile radio communication system such as an automobile telephone system, a portable telephone system, a cordless telephone system or a radio LAN system, and more particularly to a mobile radio communication system adopting a spread spectrum communication method.
BACKGROUND ART
Recently, attention has been paid to a spread spectrum communication method which is advantageous in preventing interference or jamming, as one of communication methods applicable to a mobile radio communication system.
With the spread spectrum communication method, a code division multiple access (CDMA) system is realized. For example, in a transmission-side apparatus, digitized voice data and image data (base band signals) are subjected to modulation by a digital modulation method such as a PSK or FSK modulation method. Then, the modulated transmission data is spectrum-spread by using spread codes such as pseudo-noise codes and converted to a wide-band signal. The wide-band signal is then converted to a radio frequency signal and transmitted. On the other hand, in a reception-side apparatus, the received radio frequency signal is frequency-converted to an intermediate frequency signal or a base band frequency signal. Then, the frequency-converted signal is inversely spread by using the same codes as the spread codes used in the transmission-side apparatus. Thereafter, digital demodulation is performed by a digital demodulation method such as a PSK or FSK demodulation method. Thus, the reception data is reproduced. By varying the spread codes, a plurality of transmission/reception apparatuses can be used simultaneously with the same frequency.
In this type of CDMA system, a so-called "near-far problem" occurs due to the distance between a base station and a mobile station. Specifically, this problem occurs when a plurality of mobile stations simultaneously perform communication with the same frequency. In this case, the power of electric waves transmitted from the mobile station located near the base station is greater than the power of electric waves transmitted from the mobile station located far from the base station. As a result, the base station cannot receive the radio waves from the far mobile station, owing to the high-power radio waves from the near mobile station. Consequently, radio connection control between the base station and the far mobile station cannot be performed, or the quality in communication is degraded.
In the prior art, in order to solve this problem, the following technique has been proposed. That is, the intensity of a received electric field is measured in the mobile station or the base station. On the basis of the measured result, the transmission power of the mobile station is controlled by an open-loop control method or a closed-loop control method. Irrespective of the distance between the base station and the mobile stations the base station can receive at all times the electric waves from the mobile station at a constant reception power.
In the open-loop transmission power control methods the electric field intensity (received electric field intensity) of the constant-power radio frequency signal transmitted from the base station is measured in the mobile station. Based on the measured value, the mobile station determines the transmission power of itself. Specifically, when the received electric field intensity of the radio frequency signal coming from the base station is low, it is determined that the distance between the base station and the mobile station is large, and the transmission power is set at a high value. On the other hands when the received electric field intensity of the radio frequency signal coming from the base station is highs it is determined that the distance between the base station and the mobile station is small, and the transmission power is set at a low value.
On the other hands in the closed-loop transmission power control methods the electric field intensity (received electric field intensity) of a constant
REFERENCES:
patent: 5170412 (1992-12-01), Massey
patent: 5260967 (1993-11-01), Schilling
patent: 5373502 (1994-12-01), Turban
PCT/ISA/210.
Kabushiki Kaisha Toshiba
Olms Douglas W.
Vincent David R
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