Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-09-15
2003-02-18
Olms, Douglas (Department: 2661)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C455S522000
Reexamination Certificate
active
06522639
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CDMA/TDD-based transmission/reception apparatus carrying out open-loop transmit power control and its transmit power control method.
2. Description of the Related Art
A CDMA (Code Division Multiple Access) system is one of multiple access systems by which a plurality of stations in a radio transmission system such as car telephones and cellular telephones carry out communications on a same frequency band simultaneously and transmits information signals with their spectrum spread over a band wide enough compared to the original bandwidth, having the features of achieving highly efficient use of frequencies and accommodating many users.
However, it has a near-far problem when each mobile station transmits a signal by the same power on the CDMA system and a desired transmission station is far and a non-desired transmission station (interference station) is near. The near-far problem is the reception power of a signal transmitted from the interference station becomes greater than the reception power of a signal transmitted from the desired transmission station, failing to suppress mutual correlation between spreading codes with a processing gain alone, which leads to make communications impossible.
Therefore, a cellular system using the CDMA system requires transmit power control according to the conditions of each channel on the uplink. It also requires transmit power control for compensating against instantaneous fluctuations of received signal power as fading which is a cause of deterioration of the line quality in terrestrial mobile communication.
Here, there are cases where a TDD (Time Division Duplex) is used as a duplex system for this multiple access communication system. The TDD system is a system carrying out communications by time-sharing a same radio frequency for transmission and reception, and since it uses a same frequency band for transmission and reception its frequency correlation of fading fluctuations between a transmission signal and reception signal is 1.
Furthermore, if the period of switching between transmission and reception is short enough, time correlation in the condition of the channel of mutual fading fluctuations, etc. is high, and therefore mobile stations can perform open-loop transmit power control that controls transmission power based on received signal power effectively.
If the base station has a plurality of antennas, there are cases where transmission diversity is used which selects the most suitable transmission antenna based on received signal power of those antennas. Using transmission diversity eliminates the necessity of space diversity at mobile stations making it possible to reduce the size of those mobile stations.
The following is an explanation of a base station and mobile station of a CDMA/TDD-based radio transmission system which carries out conventional open-loop transmit power control and uses transmission diversity, using the attached drawings.
FIG. 1
is a block diagram showing a configuration of a conventional base station. The base station apparatus shown in
FIG. 1
comprises modulation section
11
that modulates transmission data, spreading section
12
that multiplies the modulated signal by spreading code A and spreads it, antenna control section
13
that switches transmission antennas, antennas
14
and
15
that transmit/receive signals, despreading section
16
that multiplies the received signal by spreading code B and despreads it, demodulation section
17
that demodulates the despread signal and antenna selection section
18
that measures the level of the received signal from the demodulation result and selects a transmission antenna.
The transmission data are modulated by modulation section
11
and spread with spreading code A by spreading section
12
. Then, the spread signal is transmitted from either antenna
14
or antenna
15
controlled by transmission antenna control section
13
.
The signal received by antenna
14
and antenna
15
is despread by despreading section
16
with spreading code B. The despread signal is demodulated by demodulation section
17
with received data extracted and the demodulation result input to transmission antenna selection section
18
as the antenna selection information. Then, transmission antenna selection section
18
compares the levels of the received signals at the two antennas based on the demodulation result and the antenna that received the larger level is selected as the antenna for transmitting data in the next slot and the signal showing the selection result is output to transmission antenna control section
13
.
FIG. 2
is a block diagram showing a configuration of a conventional mobile station. The mobile station shown in
FIG. 2
comprises antenna
21
that transmits/receives signals, despreading section
22
that multiplies the received signal by spreading code A and despreads it, demodulation section
23
that demodulates the despread signal, received signal power measuring section
24
that measures the level of the received signal from the demodulation result, modulation section
25
that modulates transmission data, spreading section
26
that multiplies the modulated signal by spreading code B and spreads it and transmit power control section
27
that performs transmit power control based on received signal power.
The signal received by antenna
21
is despread by despreading section
22
with spreading code A, demodulated by demodulation section
23
with the received data extracted and the demodulation result input to received signal power measuring section
24
. Received signal power measuring section
24
measures received signal power from the demodulation result and the measurement result is input to transmit power control section
27
. Transmit power control section
27
calculates a transmission power value from the transmission power value of the base station, target received signal power value at the base station and measurement result.
The transmission data are modulated by modulation section
25
, spread by spreading section
26
with spreading code B, and with power amplified by transmit power control section
27
based on the calculated transmission power value, transmitted from antenna
21
.
Thus, in the conventional radio transmission system the base station transmits signals by selecting one antenna from a plurality of antennas and the mobile station carries out open-loop transmit power control based on received signal power.
However, in the conventional radio transmission system above, the mobile station carries out transmit power control only targeted at the antenna through which the base station transmitted signals and if signals are received by a plurality of antennas at the base station, transmission power is not controlled for the antennas that did not transmit signals and transmission power is not enough controlled for all of reception antennas, causing a problem of causing transmit power control errors.
SUMMARY OF THE INVENTION
It is an objective of the present invention to reduce transmit power control errors to a small level when the base station performs reception through a plurality of antennas.
The present invention achieves the objective above by the base station spreading the transmission data distributed by the number of transmission antennas with mutually different spreading codes, then transmitting them in parallel from a plurality of transmission antennas, and by the mobile station despreading the each of received signals transmitted the plurality of transmission antennas, measuring and combining received signal power and controlling transmission power based on the combined received signal power.
REFERENCES:
patent: 5652748 (1997-07-01), Jolma et al.
patent: 5652764 (1997-07-01), Kanzaki et al.
patent: 5786791 (1998-07-01), Bruckert
patent: 5859875 (1999-01-01), Kato et al.
patent: 5872775 (1999-02-01), Saints et al.
patent: 5873028 (1999-02-01), Nakano et al.
patent: 5881057 (1999-03-01), Komatsu
patent: 5886987 (1999-03-0
Hiramatsu Katsuhiko
Kitade Takashi
Miya Kazuyuki
Olms Douglas
Stevens Davis Miller & Mosher LLP
Vanderpuye Ken
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