Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2000-06-29
2004-04-20
Bocure, Tesfaldet (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S148000
Reexamination Certificate
active
06724808
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital car telephone and cellular phone system (cellular system) using a CDMA (Code Division Multiple Access) communication scheme, and more particularly to a CDMA communication device and a transmission power control method.
2. Description of the Related Art
In recent years, the CDMA communication scheme attracts attention as a communication method for use in mobile communication systems due to its resistance to interference and disturbance. The CDMA communication scheme refers to a communication scheme in which a transmitting side spreads a user signal to be transmitted with a spreading code and then transmits the signal, while a receiving side performs despread with the same code as that used by the transmitting side to obtain the original user signal.
In the CDMA communication scheme, a plurality of transmitting sides perform spread with different spreading codes each having orthogonality, and a receiving side selects a spreading code for use in despread to allow each communication to be specified, thereby making it possible for a plurality of communications to use the same frequency band.
However, since it is difficult to completely maintain the orthogonality among all the spreading codes being used, exact orthogonality is not obtained actually in the respective spreading codes, resulting in a correlational component between one code and another code. The correlational component serves as an interference component for the communication associated with the one code and contributes to deterioration of communication quality. Since the interference component is produced from such a factor, the interference component is increased as the number of the communications is increased.
For this reason, there is a critical risk in that, when signal power from one mobile station is significantly higher than signal power from another mobile station at an antenna of a base station, the base station can not demodulate the signals other than the signal from the mobile station which produces the high received power, of a plurality of signals received at its antenna. The problem is widely known as a near-far problem in the CDMA communication scheme. In the CDMA cellular system, to solve the near-far problem, a TPC (Transmission Power Control) technique is essential in which the signal power from all transmitters at an input of a receiver is controlled to have the same magnitude.
In the transmission power control, a receiver has a preset Eb/N
0
(desired wave power density to noise power density ratio) serving as a reference and the receiver controls transmission power from each transmitter such that an Eb/N
0
obtained from a communication of each transmitter is equal to the Eb/N
0
reference value. More specifically, a downward channel for transmission from a base station to a mobile station includes a transmission power control signal for directing an increase or decrease in transmission power of the mobile station, which data is used by the base station to direct an increase or decrease in current transmission power to each mobile station. On the other hand, an upward channel for transmission from the mobile station to the base station includes a transmission power control signal for directing an increase or decrease in transmission power to the base station, which data is used by the mobile station to direct an increase or decrease in current transmission power to the base station.
In the CDMA cellular system, a rake/diversity reception technique is also essential to high-quality reception under a multipath fading environment.
FIG. 1
is a block diagram showing a configuration of a mobile station in such a cellular system.
The mobile station comprises n antennas
101
1
to
101
n
, transmit/receive amplifier (AMP)
102
, radio unit (TRX)
103
, baseband signal processor (BB)
104
, control unit (MS-CONT)
105
, and terminal interface unit (TERM-INT)
106
.
Antennas
101
1
to
101
n
transmit an upward RF signal amplified at a transmission amplifier in transmit/receive amplifier
102
, and receive a downward RF signal from a base station and output the signal to transmit/receiver amplifier
102
. Diversity reception is achieved by using n antennas
101
1
to
101
n
. Transmit/receive amplifier
102
is provided with a transmission amplifier for amplifying a transmission RF signal and a low noise amplifier for amplifying a reception RF signal, and demultiplexes the RF transmission signal and the RF reception signal for connection to antennas
101
1
to
101
n
. Radio unit
103
converts a transmission signal which has been subjected to baseband spread from digital form to analog form and performs quadrature modulation for conversion to an RF signal, and performs quasi-synchronous detection and converts a signals received from transmit/receive amplifier
102
from analog form to digital form for transmission to baseband signal processing unit
104
.
Baseband signal processing unit
104
performs baseband signal processing such as error correction coding for transmission data, framing, data modulation, spread modulation, despread of a received signal, chip synchronization, error correction decoding, data demultiplexing, diversity handover combination function, reception level measuring function, and the like.
Control unit
105
performs control of the entire mobile station. Terminal interface unit
106
has a function as an adapter for voice and various types of data, as well as a function as an interface to a handset and image/data terminals.
Next,
FIG. 2
shows a configuration of a conventional CDMA communication device provided in baseband signal processing unit
104
.
The conventional CDMA communication device comprises n rake receivers
202
1
to
202
n
, mixer
204
, determinator
205
, n Eb/N
0
measuring units
306
1
to
306
n
, transmission power control information generator
307
, rake receiver control unit
208
, and multipath searcher
209
.
As shown in
FIG. 3
, rake receiver
202
1
includes m finger receivers
50
1
to
50
m
and mixer
70
. Since the configurations of rake receivers
202
2
to
202
n
are similar to that of rake receiver
202
1
, the description thereof is omitted.
Multipath searcher
209
acquires, from received signals
10
1
to
10
n
, reception delay information which is information on delay times among respective paths contained in received signals
10
1
to
10
n
. Rake receiver control unit
208
sets delay times for finger receivers
50
1
to
50
m
in each of rake receivers
202
1
to
202
n
based on the reception delay information acquired at multipath searcher
209
.
Rake receivers
202
1
to
202
n
detects received signals
101
1
to
101
n
, and output demodulated data which is the result of the detection. Specifically, finger receivers
50
1
to
50
m
generate the demodulated data by individually demodulating received signal
10
1
for respective paths, delay the demodulated data using the delay time set by rake receiver control unit
208
, and then output the data to mixer
70
. Mixer
70
combines the demodulated data from finger receivers
50
1
to
50
m
and outputs the combined data.
Mixer
204
combines the demodulated data from rake receivers
202
1
to
202
n
into one signal. Determinator
205
performs decoding with a determination of the signal combined by mixer
204
for output as decoded signal
20
.
Eb/N
0
measuring units
306
1
to
306
n
measure the Eb-N
0
s of the signals from rake receivers
202
1
to
202
n
. Transmission power control information generator
307
sums the Eb/N
0
measured at Eb/N
0
measuring units
306
1
to
306
n
to obtain the measurement result of the Eb/N
0
s, and generates transmission power control information
30
based on the measuring result of the Eb/N
0
s. Transmission power control information
30
is transmitted to the base station which is a transmitter through an upward channel, thereby performing transmission power control.
Next, the operation of the conventional CDMA communication device is de
Bocure Tesfaldet
Ghulamali Qutub
Scully Scott Murphy & Presser
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