Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Reexamination Certificate
2000-09-07
2004-03-09
Than, Cong Van (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
C455S164200, C455S165100, C455S192100, C375S147000, C375S148000
Reexamination Certificate
active
06704552
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile communication apparatus. In particular it relates to a mobile communication apparatus with an automatic frequency controller suitable to apply to a code division multiple access (CDMA) communication system.
2. Description of the Related Art
Spread spectrum communication systems such as code division multiple access (CDMA) communication systems are now attracting a great deal of attention for use in mobile communications because they obtain favorable receiving properties in communications susceptible to multi-path interference, since those systems have high resistance to both interference and disturbance. In a conventional spread spectrum communication system, it is strictly required that a reference clock frequency, i.e., an operation frequency, of both transmitter and receiver coincide with one another. However, an oscillator that satisfies such a high accuracy demand is expensive, and thus, has been considered unsuitable for use in mobile communication terminals because they must be sold at a relatively lower price. Therefore, a conventional CDMA mobile communication terminal generally performs automatic frequency control (AFC) that automatically matches an operation frequency of a receiver with a frequency of a received signal.
A conventional CDMA receiver calculates a difference between a frequency of a received signal and an operation frequency of a receiver using only a receiving channel for receiving information data and controlling the operation frequency so as to compensate for the difference.
In
FIG. 1
, the conventional CDMA receiver comprises a radio communication unit
10
which obtains analog I and Q signals from a received signal received by an antenna (not shown), an A/D converter
21
which converts analog I and Q signals to digital I and Q signals, a signal processor
20
which processes the digital I and Q signals to output a digital frequency control signal for controlling an operation frequency of the CDMA receiver, a D/A converter
28
which converts the digital frequency control signal to an analog frequency control signal, and a low-path filter
29
which shapes a waveform of the analog frequency control signal and supplies the resulting signal to the radio communication unit
10
.
In the radio communication unit
10
, an amplifier
11
amplifies the received signal from an antenna (not shown). A voltage control oscillator
12
enables its oscillating frequency to be controlled according to a voltage of the analog frequency control signal from the low-pass filter
29
. A phase shifter
13
shifts an output signal from the voltage control oscillator
12
by &pgr;/2. A multiplier
14
multiplies the amplified received signal from the amplifier
11
by the output signal from the voltage control oscillator
12
. A multiplier
15
multiplies the amplified received signal from the amplifier
11
by an output signal from the phase shifter
13
. Low-path filters
16
and
17
shape waveforms of output signals from the multipliers
14
and
15
to output analog I and Q signals, respectively.
The A/D converter
21
converts the analog I and Q signals from the radio communication unit
10
to digital I and Q signals.
In the signal processor
20
, each of finger units
22
1
to
22
n
despreads the digital I and Q signals from the A/D converter
21
with a predetermined spread code and outputs a despread signal. In addition, each of the finger units
22
1
to
22
n
extracts a pilot signal from the despread signal and converts all the symbols in the pilot signal to those in the same quadrant, then outputs the converted signal. A rake receiver
23
synthesizes the despread signals in the same phase and outputs the synthesized signal. A delay profile calculator
24
calculates an arrival phase of the received signal by each of a plurality of estimated multi-path delays and a reception level in each arrival phase based on the digital I and Q signals from the A/D converter
21
and outputs the results as a delay profile of an object receiving channel. A path controller
25
determines a despread timing when each of the finger units
202
1
to
202
n
despreads the digital I and Q signals according to the delay profile supplied from the delay profile calculator
24
and supplies an instruction signal indicative of the despread timing to each of the finger units
22
1
to
22
n
.
An automatic frequency control (AFC) unit
26
calculates a difference between a frequency of a received signal and an oscillating frequency of the voltage control oscillator
12
so as to output a frequency difference signal as a digital frequency control signal. The calculation is based on signals output from the finger units
22
1
to
21
n
, wherein all the symbols in the pilot signal are converted to those in the same quadrant at this time. A channel assignment controller
27
notifies the delay profile calculator
24
and the finger units
22
1
to
22
n
of a receiving channel. The D/A converter
28
converts the digital frequency control signal output from the AFC unit
26
to an analog frequency control signal. The low-path filter
29
shapes the waveform of the analog frequency control signal output from the D/A converter
28
to supply the shaped analog frequency control signal to the voltage control oscillator
12
.
Next, an operation of the conventional CDMA receiver will be discussed with reference to FIG.
1
.
The radio communication unit
10
samples both I and Q signals from a received signal received at an antenna (not shown) and supplies those sampled I and Q signals to the signal processor
20
via the A/D converter
21
.
On the other hand, the channel assignment controller
27
notifies the delay profile calculator
24
and the finger units
22
1
to
22
2
of information indicative of the receiving channel for the CDMA receiver, e.g., a predetermined spread code for despreading against the received signal of the receiving channel.
Notified of the information indicative of the receiving channel, the delay profile calculator
24
calculates a correlated power value between the received signal from the radio communication unit
10
and a known transmission replica, and outputs the result as a delay profile of the receiving channel. The delay profile denotes an arrival phase of the received signal by each of the estimated multi-path delays and a receiving level for each arrival phase. The path controller
25
selects one of despread timings in a favorable receiving state from the delay profile of the receiving channel and directs the despread timing to the finger units
22
1
to
22
n
respectively. Each of the finger units
22
1
to
22
n
despreads and demodulates the received signal of the receiving channel notified from the channel assignment controller
27
at the despread timing directed from the path controller
25
, then extracts the pilot signal from the despread and demodulated signal and converts all the symbols in the pilot signal to those in the same quadrant, then outputs the converted signal to the AFC unit
26
.
The AFC unit
26
multiplies a conjugate complex number of a symbol by a complex number of the next symbol so as to calculate a phase difference per symbol time, then divides the result by a symbol time. This results in calculating a frequency difference corresponding to each finger unit, wherein the symbols are received from the finger units
22
1
to
22
2
and converted to those in the same quadrant. The AFC unit
26
then synthesizes the frequency differences and outputs the synthesized value to the D/A converter
28
as the digital frequency control signal. The output signal from the AFC unit
26
is converted from digital to analog in the D/A converter
28
and the waveform thereof is shaped in the low-path filter
29
. The shaped signal from the low-pass filter
29
is used for controlling the oscillating frequency of the voltage control oscillator
12
. Consequently, the oscillation frequency of the voltage control oscillator
12
is controlled so as
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