Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2000-03-01
2004-01-27
Chin, Stephen (Department: 2734)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S144000, C375S148000, C375S150000, C375S267000, C375S343000, C375S347000, C375S351000, C370S320000, C370S335000, C370S437000, C370S462000, C455S065000, C455S134000, C455S137000, C455S226200, C455S226300, C455S275000, C455S277200
Reexamination Certificate
active
06683906
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to radio communication apparatuses, and more particularly to a radio communication apparatus which subjects each signal which is received via a multi-path and demodulated, to a Hadamard transform at each finger, by use of an M-ary quadrature coding scheme, obtains correlation values of the codes, combines correlation values output from the fingers which obtain valid correlation values, and demodulates a received signal based on a maximum correlation value of the combined correlation values.
The code division multiple access (CDMA) system is regarded as a mobile communication system of the next generation, and in the United States, a standardized system (N-CDMA) called IS-95 is already reduced to practice. In addition, there is a possibility of the CDMA system being applied to a semi-fixed mobile communication system called wireless local loop (WLL) as a means of infra-structure. Such a system proposed by Qualcomm of the United States is a CDMA system using a chip rate of 1.2288 Mcs, wherein a synchronous detection system using an extrapolated pilot signal is employed for the down-line, and an asynchronous detection system using the M-ary orthogonal modulation is employed for the up-line. In the asynchronous detection system, an amplitude signal is converted into power so as to eliminate a phase error caused by fading or the like, and the communication quality or bit error rate (BER) is improved by employing the RAKE reception technique. The present invention, as will be described later, is suited for application to this kind of radio communication apparatus.
2. Description of the Related Art
FIGS. 1 through 7
and
FIGS. 8A through 8C
are diagrams for explaining the prior art, more particularly, the standardized system IS-95.
FIG. 1
is a system block diagram showing a transmitter part of a mobile station, and
FIG. 2
is a diagram showing a signal sequence of the transmitter part. Signals (A) through (E) shown in
FIG. 2
are the signals (A) through (E) shown in FIG.
1
.
An input information signal is subjected to a cyclic coding in a CRC operation unit
11
, and is converted into an error correction code in a convolutional encoder (ENC)
12
. This error correction code is subjected to an identical symbol repeating process in a symbol repeating unit
13
, so as to unify the input signals in the range of 1.2 kbps to 9.6 kbps to the signal (A) of 9.6 kbps. The signal (A) is further subjected to a buffering process in an interleaver
14
. A signal sequence (B) of 28.8 kbps is read from the interleaver
14
and input to an M-ary (64) orthogonal modulator
15
.
The 64-ary orthogonal modulator
15
converts the 6-bit input data to a corresponding 64-bit Walsh code (C), that is, spreads the input data by 64/6 times. For example, the 6-bit input data “000000” is converted into a 64-bit Walsh code “00000000 . . . 00000000”, and the 6-bit input data “000001” is converted into a 64-bit Walsh code “01010101 . . . 01010101”. Such Walsh codes (C) are finally output from the 64-ary orthogonal modulator
15
as a signal (D) of 307.2 kcps.
A multiplier
17
multiplies to the signal (D) a PN code (user code or long code) LCD which is generated for each user by a long code generator
16
. As a result, a spread code sequence (E) of 1.2288 Mcps is output from the multiplier
17
and is supplied to a multiplier
20
1
provided for the I-channel and a multiplier
20
2
provided for the Q-channel. The multiplier
20
1
multiplies to the spread code sequence (E) a PN code (short code) SCD for identifying the base station, which is generated from a short code generator
18
and is received via a shifter
19
. On the other hand, the multiplier
20
2
multiplies to the spread code sequence (E) the PN code SCD which is generated from the short code generator
18
.
An output of the multiplier
20
1
is passed through a filter
22
1
and a digital-to-analog (D/A) converter
23
1
and converted into an analog signal before being supplied to a quadrature phase shift keying (QPSK) modulator
24
. An output of the multiplier
20
2
is passed through a ½ chip delay unit
21
, a filter
22
2
and a D/A converter
23
2
and converted into an analog signal before being supplied to the QPSK modulator
24
. Since the ½ chip delay unit
21
provides a ½ chip shift between the I-channel and the Q-channel, an output of the QPSK modulator
24
becomes an offset QPSK (OQPSK) modulated signal. By this OQPSK modulation, no phase change of &pgr; occurs, and the phase change becomes &pgr;/2 at the maximum. For this reason, even under an extreme band limitation, the signal envelope only dips slightly, and no zero-point occurs. An OQPSK modulated signal output from the QPSK modulator
24
is converted into a radio frequency signal in a transmitting radio frequency (RF) unit (Tx)
25
and is transmitted to the base station via an antenna A
0
.
FIG. 3
is a system block diagram showing a receiver part (reverse link demodulator part) of the base station. In addition,
FIG. 4
is a diagram for explaining a service area of the base station, and
FIG. 5
is a diagram for explaining asynchronous detection. Further,
FIG. 6
is a system block diagram showing fingers forming the receiver part, and
FIG. 7
is a diagram showing a signal sequence of the receiver part.
As shown in
FIG. 4
, 1 cell is divided into 3 sectors, and 2 reception (diversity) antennas are provided with respect to 1 sector. A maximum number of antennas capable of simultaneously communicating with a mobile station MS which is located at an arbitrary position is 4, namely, A
11
, A
12
, A
21
and A
22
, in this particular case. Hence, 4 corresponding antennas A
1
through A
4
are shown in FIG.
3
.
In
FIG. 3
, the received signals from the antennas A
1
through A
4
are amplified and converted into intermediate frequency signals IF in corresponding receiving RF units (Rx)
31
1
through
31
4
, and demodulated into orthogonal demodulated data (I
1
, Q
1
) through (I
4
, Q
4
) in corresponding QPSK demodulators (DEM)
32
1
through
32
4
. The orthogonal demodulated data (I
1
, Q
1
) through (I
4
, Q
4
) are selected by a signal selector
33
which operates under the control of a searcher
40
, and input to fingers
34
1
through
34
4
. In this state, the received wave is not necessarily supplied constantly to each finger, and each finger operates under conditions, such as antenna selection and delay time PN
offset
, which are specified by the searcher. Hence, various combinations are actually permitted for the connection of the QPSK demodulators
32
1
through
32
4
and the fingers
34
1
through
34
4
.
FIG. 6
shows the construction of the fingers
34
1
through
34
4
. In a despreader
41
of the finger
34
1
, the input demodulated data I
1
, Q
1
are respectively despread by a correlator
42
based on the short code PN
offset
(PNI
1
, PNQ
1
) supplied from the searcher
40
. The short codes PNI
1
, PNQ
1
correspond to the short code SCD of the transmitter end, and PNI
1
is phase (chip) synchronized to the demodulated data I
1
while PNQ
1
is phase (chip) synchronized to the demodulated data Q
1
.
Further, output data I
1
, Q
1
of the correlator
40
are despread by corresponding multipliers
43
1
and
43
2
based on a long code LCD corresponding to the user code LCD of the transmitting end. In addition, an adder
44
1
adds 4 consecutive despread codes I
1
from the multipliers
43
1
, and an adder
44
2
adds 4 consecutive despread codes Q
1
from the multiplier
43
2
. If no chip error occurs during the transmission, output data I
1
, Q
1
(A) of the adders
44
1
and
44
2
correspond to the output Walsh code of the 64-ary orthogonal modulator
15
of the transmitting end. Actually, however, the output data I
1
, Q
1
(A) of the adders
44
1
and
44
2
do not necessarily correspond to the output Walsh code of the 64-ary orthogonal modulator
15
due to the chip error or the like introduced during the transmission.
The output data
Chin Stephen
Ha Dac V.
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