Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
1999-11-10
2003-09-30
Pham, Chi (Department: 2631)
Pulse or digital communications
Receivers
Interference or noise reduction
C455S277100, C455S277200
Reexamination Certificate
active
06628733
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diversity receiving device in spread spectrum communications.
2. Description of the Related Art
For a receiving circuit used in a mobile communications device such as a cellular phone, etc., a diversity receiving device adopting a plurality of antennas is frequently used in order to prevent a reception quality from being degraded due to a changing transmission path. The diversity receiving device is used to lower the probability that the quality of a reception signal is degraded when receiving a faded wave. In spread spectrum communications, antenna diversity for selecting the outputs of a plurality of antennas, and path diversity for distinguishing between reception signals according to a time difference thereof, are implemented. With the antenna diversity, wireless receiving units are respectively arranged for a plurality of antennas, and all of receiving systems are continually operated, so that signals of good reception quality are selected and despread.
For the path diversity, its effects are obtained by separating a reception signal with the use of an arrival time difference between electronic waves, which is caused by different transmission paths, and by despreading and combining the separated signals.
FIG. 1
is a block diagram exemplifying the configuration of a conventional CDMA diversity receiving device.
In
FIG. 1
, signals received by two antennas A and B are detected by wireless receiving units
83
-
1
and
83
-
2
. Within the wireless receiving units
83
-
1
and
83
-
2
, the signals received by the antennas A and B are first amplified by variable amplifiers
82
-
1
and
82
-
2
that are controlled by ALC controllers
80
-
1
and
80
-
2
. Mixers
81
-
1
and
81
-
2
convert the RF band signals into baseband signals by multiplying the signals from the variable amplifiers
82
-
1
and
82
-
2
by the cyclic waves which correspond to the signal carrier waves and are output from a local oscillator not shown. The baseband signals are detected by orthogonal-signal-detector
84
-
1
and
84
-
2
. The reason why the wave detectors are represented as the orthogonal-signal-detectors
84
-
1
and
84
-
2
is that both of CDMA signals I and Q received by the antennas A and B are assumed to be detected. Their actual operations are similar to those of a normal detector. They are specifically called orthogonal-signal-detectors, since the CDMA signals I and Q are orthogonal each other. However, if a reception signal is not composed of the signals I and Q, the orthogonal-signal-detectors
84
-
1
and
84
-
2
shown in this figure can be replaced with normal detectors. The ALC controllers
80
-
1
and
80
-
2
perform a control so as to make the outputs from the wireless receiving units
83
-
1
and
83
-
2
constant by using the outputs of the orthogonal-signal-detectors
84
-
1
and
84
-
2
as inputs, and by providing a driving signal to the variable amplifiers
82
-
1
an
82
-
2
.
The reason that the ALC controllers
80
-
1
and
80
-
2
are arranged as described above is to improve conversion accuracy when an analog signal is converted into a digital signal by an A/D converter which is not shown in this figure and is arranged at the stage succeeding the wireless receiving units
83
-
1
and
83
-
2
. Namely, the intensities of the signals received by the antennas A and B vary due to an influence of fading, etc. In A/D conversion, the intensity of a signal to be converted is estimated, and the number of bits of a digital signal after being converted is determined. However, if the intensity of a reception signal is much lower than an estimated value, also the intensities of the signals output from the wireless receiving units
83
-
1
and
83
-
2
become very much low. As a result, a minimum unit used when the intensity of an analog signal is digitized becomes unsuitable, so that an analog signal with a low intensity cannot be digitized with high accuracy. Namely, when an analog signal with a low intensity slightly changes, it is represented as a digital signal with no change. This is because the minimum unit of digitization of an analog value is larger than the amount of this change, which is relatively large for a signal with a low intensity and includes information. That is, digitization noise becomes relatively large for an analog signal with a low intensity, so that a meaningful change of a signal value is not regenerated as a digital signal.
Accordingly, the wireless receiving units
83
-
1
and
83
-
2
detect all of reception signals after amplifying them to signals of a same level under the control of the ALC controller
80
-
1
and
80
-
2
, and transmits the detected signals to a circuit at a succeeding stage. After the detected signals output from the wireless receiving units
83
-
1
and
83
-
2
are converted into digital signals by the A/D converter not shown, they are input to a branch selecting unit
85
. The branch selecting unit
85
selects either of the signals from the antennas A and B, and transmits the selected signal to a matched filter
86
. The branch selecting unit
85
selects either of branches A and B (the system which receives the signals from the antenna A is referred to as a branch A, while the system which receives the signals from the antenna B is referred to as a branch B) with a branch selection instructing signal input from a searcher
87
. The signal output from the branch selecting unit
85
is despread by the matched filter
86
with a despreading code instructed by the searcher
87
, and correlation values at respective timings are calculated. The correlation values obtained by the matched filter
86
are transmitted to the searcher
87
. The searcher
87
determines whether the currently obtained correlation values are either the values from the branch A or those from the branch B based on the contents of the branch selection instructing signal transmitted to the branch selecting unit
85
. If the searcher
87
determines that the currently obtained correlation values are those from the branch A, the correlation values are stored in an antenna A delay profile memory
88
-
1
. If the searcher
87
determines that the correlation values are those from the branch B, the correlation values are stored in an antenna B delay profile memory
88
-
2
.
Then, the searcher
87
respectively reads the correlation values from the antenna A delay profile memory
88
-
1
and the antenna B delay profile memory
882
, and obtains correlation values which are equal to or larger than a predetermined value and their despreading timings. The despreading timings can be easily obtained if the correlation values are stored in time series and the timing of the first correlation value is stored as memory contents. A plurality of the despreading timings thus obtained by the searcher
87
are timing lags delayed by multipath. And, since the matched filter
86
despreads signals with the same despreading code, they are the signals of the same channel. The searcher
87
transmits the despreading code and the despreading timings obtained as described above to a finger allocating unit
90
.
The finger allocating unit
90
allocates the despreading code and the despreading timings, which are transmitted from the searcher
87
, to a plurality of fingers
91
-
1
through
91
-n, and makes the plurality of fingers
91
-
1
through
91
-n perform a despreading process respectively. Each of the fingers
91
-
1
through
91
-n is composed of a sliding correlator and a synchronous-signal-detector, and is intended to despread the received signal with the despreading code allocated by the finger allocating unit
90
at respectively allocated despreading timings, and to detect a transmitted signal. Namely, in a CDMA communication made by a portable terminal, despreading timings may differ due to multipath fading even if signals are of the same channel. Therefore, the searcher
87
selects a plurality of despreading timing candidates from among the correlation values obtained from t
Haga Yoshinobu
Mikami Takushi
Tomiyoshi Norio
Yamano Osamu
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Pham Chi
Tran Khanh Cong
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