Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-05-26
2002-03-19
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S441000, C375S140000, C375S150000, C375S152000
Reexamination Certificate
active
06359875
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CDMA (Code Division Multiple Access) receiving apparatus which receives and demodulates a direct sequence CDMA signal produced through QPSK (Quadrature Phase Shift Keying) spreading modulation.
In the DS-CDMA (Direct Sequence CDMA) method, as a modulating method, the BPSK (Binary Phase Shift Keying) method, or the QPSK method is selected. When the QPSK method is used, an in-phase signal and a quadrature signal undergo spreading modulation using different spreading codes, and are combined in a transmitting apparatus. The thus-produced signal is transmitted from the transmitting apparatus. A CDMA receiving apparatus demodulates the received signal into the in-phase signal and the quadrature signal, and despreading processing is performed on the in-phase signal and the quadrature signal using despreading codes which are caused to be in synchronization with the spreading codes, respectively. Reduction of the cost of such a CDMA receiving apparatus is demanded.
2. Descriptions of the Relate Art
FIG. 1
illustrates a CDMA receiving apparatus in the related art, and shows part of the CDMA receiving apparatus which uses the above-mentioned QPSK spreading modulation. As shown in
FIG. 1
, the CDMA receiving apparatus includes an antenna
51
, a high-frequency amplifier
52
, a bandpass filter
53
, demodulators
54
,
55
, a carrier wave generator
56
, a phase shifter (&pgr;/2)
57
for shifting the phase of a signal input thereto by &pgr;/2, A-D converters (A-D)
58
and
59
, despreading portions
60
,
61
,
62
and
63
, adders
64
,
65
, a fading compensating portion
66
and a determining and outputting portion
67
.
The direct sequence CDMA signal, transmitted from a transmitting apparatus, obtained through the QPSK spreading modulation is input to the CDMA receiving apparatus through the antenna
51
. The high-frequency amplifier
52
amplifies the thus-input signal. The bandpass filter
53
removes unnecessary frequency band components from the amplified signal. The carrier wave from the carrier wave generating portion
56
is input to the demodulator
54
directly and to the demodulator
55
via the phase shifter
57
which shifts the phase of the carrier wave by &pgr;/2, and, thus, coherent detection is performed through the demodulators
54
and
55
on the signal output from the bandpass filter
53
. The thus-obtained signals are a demodulated in-phase signal and a demodulated quadrature signal, and are converted into digital signals through the A-D converters
58
,
59
, respectively. Then, the thus-obtained signals are input to the despreading portions
60
,
61
,
62
and
63
. The despreading codes Ci, Cq, which are in synchronization with the spreading codes used in the transmitting apparatus as mentioned above, are input to the despreading portions
60
,
61
,
62
and
63
. Thus, despreading processing is performed on the signals output from the A-D converters
58
and
59
. The thus-obtained signals are added as shown in FIG.
1
through the adders
64
and
65
. Thus, the in-phase signal and the quadrature signal are obtained. The in-phase signal and the quadrature signal are then input to the fading compensating portion
66
and the fluctuations of the signals occurring due to the fading in the propagation path are compensated. Then, determination processing is performed on the thus-obtained signals through the determining and outputting portion
67
. Then, the received signal is output from the determining and outputting portion
67
.
FIG. 2
illustrates a spreading QPSK modulating portion, and shows an arrangement of a portion for performing digital processing so as to obtain the direct sequence CDMA signal through QPSK modulation. Di and Dq represent an in-phase transmission information symbol and a quadrature transmission information symbol, respectively. Ci and Cq represent a spreading code for the in-phase signal and a spreading code for the quadrature signal, respectively. Si and Sq represent the in-phase signal and the quadrature signal obtained through spreading modulation, respectively. The in-phase transmission information symbol Di, the quadrature transmission information symbol Dq, and the spreading codes Ci and Cq for the in-phase signal and for the quadrature signal are input to exclusive OR circuits
71
,
72
,
73
and
74
. Then, through level converting portions
75
,
76
,
77
and
78
, for example, “0” is converted into “1” and “1” is converted into “−1”. Then, the thus-obtained signals are added through adders
79
and
80
. Then, the in-phase signal Si and the quadrature signal Sq are output. The transmitting apparatus forms a QPSK-modulated signal from the in-phase signal Si and the quadrature signal Sq, and transmits the QPSK-modulated signal.
FIG. 3
illustrates a general arrangement of a matched filter. Such a matched filter can be applied to a portion for the synchronization of the despreading codes and to each of the despreading portions
60
,
61
,
62
and
63
shown in FIG. l. The arrangement of
FIG. 3
includes one-chip-time delaying elements (D)
81
-
1
through
81
-n, multipliers
82
-
0
through
82
-n, and an adder
83
. To this arrangement, a signal S is input. Further, to the multipliers
82
-
0
through
82
-n, the despreading codes C
0
through C
n
are input, respectively.
When the matched filter comprising the above-described arrangement is applied to each of the despreading portions as mentioned above, the delaying elements
81
-
1
through
81
-n form shift registers for shifting the input signal S every one chip time. The input signal S, the output signals of the shift registers and the despreading codes C
0
through C
n
are input to the multipliers
82
-
0
through
82
-n, respectively, as shown in FIG.
3
. The signals output from the multipliers
82
-
0
through
82
-n are added through the adder
83
. The output signal of the adder
83
is a despread and demodulated output signal for one symbol.
FIG. 4
shows a general arrangement of a sliding correlator. The sliding correlator can be applied to each of the despreading portions
60
,
61
,
62
and
63
shown in FIG.
1
. The arrangement shown in
FIG. 4
includes a multiplier
91
, an adder
92
, a one-chip-time delaying element (D)
93
, and a switch
94
which is closed by a control signal SB, the period of which is the symbol period.
When the sliding correlator is applied to each of the despreading portions as mentioned above, the input signal S and the despreading code C are input to the multiplier
91
which performs multiplication thereof. The multiplication output signal output from the multiplier
91
and the addition output signal output from the adder
92
, which has been delayed by the time for one chip through the delaying element
93
, are input to the adder
92
which performs addition thereof. Thus, integration is performed during the period for one symbol. When the switch
94
is closed by the control signal SB, the despread demodulated output signal for one symbol can be obtained.
When the QPSK modulation method is applied to the direct sequence CDMA method, the spreading QPSK modulating portion in the transmitting apparatus can be embodied by, for example, using the arrangement shown in FIG.
2
. In this case, by treating the operation (Di+jDq).(Ci+jCq) performed by the exclusive OR circuits
71
,
72
,
73
and
74
shown in
FIG. 2
as multiplication of the complex spreading series, despreading can be performed by complex multiplication using the complex conjugate values of the complex despreading code series. However, when despreading is performed by the complex multiplication, because a multiplier is needed, the circuit scale is large, and/or, an amount of data processing for performing the calculation is large.
SUMMARY OF THE INVENTION
An object of the present invention is to reduce the circuit scale of the despreading portions or to reduce the amount of calculation performed by the despreading portions.
A CDMA receiving apparatus
Fukumasa Hidenobu
Hamada Hajime
Matsuyama Koji
Oishi Yasuyuki
Chin Wellington
Rosenman & Colin LLP
Tran Maikhanh
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