CDMA modulation method and device therefor

Details CDMA modulation method and device therefor CDMA modulation method and device therefor

2002-05-10

2004-12-21

Pascal, Robert (Department: 2817)

Modulators

Phase shift keying modulator or quadrature amplitude modulator

C375S146000

Reexamination Certificate

active

06833770

ABSTRACT:

This application is the U.S. national phase of international application PCT/JP00/08293 filed Nov. 24, 2000, which designated the U.S.
TECHNICAL FIELD
The present invention relates to a spread modulating method and an apparatus using the method in a spread spectrum communications system and a CDMA (Code Division Multiple Access) system, in particular relating to a CDMA spread modulating method and an apparatus using the method for implementing complex QPSK (Quadrature Phase Shift Keying) spread modulation.
BACKGROUND ART
Spread spectrum communication and CDMA (Code Division Multiple Access) systems using spread spectrum communication technologies are characterized by having strong resistance to multipath fading, capability of enhancing the data rate, excellent communication quality, high efficiency in frequency usage and the like, so that they are attracting the attention as the next-generation mobile communications system and multimedia mobile communications.
In the spread spectrum communication, the signal to be transmitted is spread into a signal having a bandwidth much wider than that of the original signal on the transmission side and is transmitted. On the reception side, the spectrum-spread signal is reverted back into the signal having the original signal bandwidth. The above features are obtained by this feature.
FIG. 7
is a block diagram showing a transmitter in a conventional spectrum spread communications system. Information
100
to be transmitted is processed through a primary modulator
101
into a data signal D(t) such as a data signal which has been modulated by BPSK (Binary Phase Shift Keying), QPSK(Quadrature Phase Shift Keying) or the like. The data signal D(t) is secondarily modulated by a secondary modulator
102
based on a spread spectrum code C(t) generated from a spreading code generator
103
. AnM-sequence, Goldcode, Hadamard code and other codes can be used as the spreading code C(t). The CDMA system makes distinctions between users, cells, data channels, etc., based on the spreading code C(t) generated from spreading code generator
103
. Thereafter, at a multiplier
104
, the secondary modulated waveform is multiplied by the carrier wave generated from radio carrier wave generator
105
so that it is transformed into a radio frequency wave. The thus transformed carrier wave (baseband transmission signal) is amplified by an amplifier
106
and sent out from antenna
107
.
Similarly to the primary modulation there are some techniques such as BPSK, QPSK as the technique for secondary modulation(spread modulation).
FIG. 8
is a block diagram showing one example of a conventional secondary modulator. In this secondary modulator, as shown in
FIG. 8
, data Di and data Dq which are independent from each other on the in-phase channel (ICH) and quadrature channel (QCH) are operated by multipliers
110
and
111
using independent spreading codes Ci and Cq. By this operation, Di·Ci and Dq·Cq are obtained as spread signals
112
and
113
, respectively. This technique is called a dual-channel QPSK method, which is effective in transmitting independent data streams in parallel. The spread modulation is described in detail in the following literature:
Literature 1: pp. 471-478 in ‘Spread spectrum communications system’ written by Mitsuo Yokoyama, published from Kagaku Gijutsu Shuppan-sha.
Next, a complex QPSK spread modulating technique which is more complicated will be described.
FIG. 9
is a block diagram showing another example of a secondary modulator for implementing the complex QPSK spread modulation. Here, complex data (Di, Dq) is complex-spread in a complex QPSK processor
121
by complex spreading codes (Si. Sq) so as to produce ICH spread signal Ai and QCH spread signal Aq. This complex QPSK modulation is represented by the following equation (1):
(Di+jDq)·(Si+jSq)=(Di·Si−Dq·Sq)+j(Di·Sq+Dq·Si) =Ai+jAq  (1)
where j is an imaginary unit.
In order to produce the terms on the right side of equation (1), a complex QPSK processor
121
implements the operation between complex data (Di, Dq) and complex spreading codes (Si, Sq) by multipliers
122
,
123
,
124
and
125
. As a result, (Di·Si), (Dq·Sq), (Di·Sq) and (Dq·Si) in equation (1) are obtained. Then, the results are summed (subtracted) in adders
126
and
127
, taking into account the signs in equation (1).
The W-CDMA (Wideband-CDMA) as a next-generation mobile communications scheme implements spread modulation using two kinds of spreading codes. Specifically, a long code having a markedly long symbol period and short code having a short symbol period are used in combination so as to implement spreading and scrambling. The roles of spread demodulation and spreading codes in the W-CDMA are described in detail in the following literatures:
Literature 2: ‘Next Generation Mobile Radio Access for Multimedia transmission: W-CDMA’ Sawahashi and Adachi, Technical Report of IEICE, SST-98-41, 1998-12;
Literature 3: ‘Mobile Radio Access Based on Wideband Coherent DS-CDMA’, Ohno, Sawahashi, Doi, Higashi, NTT DoCoMo Technical Journal, Vol.4No3.
Next, a spread modulating method using two kinds of spreading codes, or of the combination of the double-spreading using (Ci, Cq) in FIG.
8
and the complex QPSK modulation using (Si, Sq) in
FIG. 9
will be described. Specifically, data signals (Di, Dq) are subjected first to the double-spreading using the spreading codes (Ci, Cq), and then subjected to the complex QPSK modulation using the spreading codes (Si,Sq). This complex QPSK modulation is represented by equation (2).
(Di·C+JDq·Cq)·(Si+JSq)=(Di·Ci·Si−Dq·Cq·Sq)+j (Di·Ci·Sq+Dq·Cq·Si)=Ai+jAq  (2)
FIG. 10
is a block diagram showing another example of a secondary modulator for implementing this complex QPSK spread modulating method. In the secondary modulator for implementing this complex QPSK modulation shown in
FIG. 10
, the data signals (Di, Dq) and spreading codes (Ci, Cq) are double-spread through multipliers
110
and
111
. In a complex QPSK processor
121
, the signals
112
and
113
having undergone double-spreading are subjected to the complex QPSK spread modulation with the other spreading codes (Si, Sq) and the result is supplied to adder/subtractors
126
and
127
for addition (subtraction).
That is, complex QPSK processor
121
, in order to produce the right side terms in equation (2), implements operations between complex data (Di·Ci, Dq·Cq) and complex spreading codes (Si, Sq) using multipliers
122
,
123
,
124
and
125
. From these operations, the terms (Di·Ci·Si), (Dq·Cq·Sq), (Di·Ci·Sq) and (Dq·Cq·Si) in equation (2) are determined.
Here, when the spreading rate (chip rate) of the spreading codes (Ci, Cq) is equal to that of the other spreading codes (Si, Sq), the spreading codes (Si, Sq) provide a scrambling function, so that the spreading codes (Si, Sq) are also called scramble codes.
The data signal (Di, Dq) in
FIG. 10
are independent from each other as already mentioned. For example. Di may be allotted for information data to be transmitted and Dq may be allotted for a control signal. In some cases, the information data Di and control data Dq may be adjusted as to their amplitude ratio by a gain factor G, dependent on their signal importance.
FIG. 11
is a block diagram showing a secondary modulator in which control signal Dq is adjusted by a gain factor G.
This secondary modulator, as shown in
FIG. 11
, the quadrature channel data signal Dq is weighted by a multiplier
131
based on the signal of gain factor G generated from a gain factor controller
136
. The data signal weighted with the gain factor G, or the data signal (Di, G·Dq) and the spreading codes (Ci, Cq) are double-spread by multipliers
110
and
111
, in the same manner as that shown in FIG.
10
. Then, the resultant signals are subjected to complex QPSK spread modulation with the other spreading codes (Si, Sq) by means of QPSK processor
121
and adders
126
and
127
.
The signals Ai and Ag having undergone

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