Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1998-03-06
2001-08-21
Chin, Stephen (Department: 2634)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S148000, C375S150000, C375S152000, C327S361000, C327S075000, C708S007000, C708S320000, C370S335000, C370S342000
Reexamination Certificate
active
06278724
ABSTRACT:
The present invention claims priority based on a Japanese patent application, H9-156073, the contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to a signal reception apparatus suitable for use in the DS-CDMA communication system, in particular, to a signal reception apparatus for correcting the phase error of a signal received through each path in the multi-paths environment and performing a RAKE synthesis.
DESCRIPTION OF RELATED ART
In recent years, in the field of wireless communication systems such as mobile wireless communication systems and wireless local area network (LAN), the spread spectrum communication system, in particular, the the Direct Sequence-Code Division Multiple Access (DS-CDMA) communication system has been receiving attention. Generally in a mobile wireless communication system, multiple signals that have been transmitted from the transmitter pass through multiple transmission paths (multi-paths) having different path lengths and reach the receiver. Since these signals are not coherently added at the receiver, so-called multi-fading is generated. However, by employing the rake reception system in the spread spectrum communication system, these multi-paths can be effectively utilized for receiving the multiple signals. The rake reception system in the spread spectrum communication system is referred to as a Radio Activated Keyed Entry (RAKE) reception system throughout the specification.
FIG. 26
a
shows an example of the frame structure of transmission data according to the DS-CDMA communication system. In the example shown in this drawing, each frame has multiple (for example, six) slots. Each of the slots is comprised of a pilot symbol block and an information symbol block. As shown in the drawing, each frame is comprised of pilot symbol blocks P
1
, P
2
, . . . , Pn, and information symbol blocks D
1
D
2
. . . , Dn so that a pilot symbol block and an information symbol block appear alternately. A prescribed number (for example, four symbols) of pilot symbols are arranged in each of the pilot symbol blocks P
1
, P
2
, . . . , Pn. A prescribed symbol sequence is transmitted as the transmission data. Similarly, a prescribed number (for example, 36) of information symbols are arranged in each of the information symbol blocks D
1
, D
2
, . . . , Dn. Before this transmission data is transmitted, the information contained in this transmission data is modulated by, for example, the Quadrature Phase Shift Keying (QPSK) system, and the spread of this transmission data is modulated by the Biphase Shift Keying (BPSK) or QPSK system using prescribed spread codes.
FIG. 26
b
is a block diagram showing the key components of a RAKE receiver for receiving the above-mentioned signals. In this diagram, the high frequency wave receiver
102
converts each of the spread spectrum signals that have been received by the reception antenna
101
into a signal lying in an intermediate frequency band. The distributor
103
divides the converted signal into two signals. The two divided signals are supplied to the multipliers
106
and
107
. The oscillator
104
generates local frequencies. The output of the oscillator
104
is supplied directly to the multiplier
106
and to the multiplier
107
via the phase shift circuit
105
, which shifts the phase of the output by &pgr;/2. The multiplier
106
multiplies the intermediate frequency signal that has been received from the distributor
103
by the output signal of the oscillator
104
. The multiplier
106
then sends the result of the multiplication to the low-pass filter
108
. The low-pass filter
108
outputs an in-phase (I-component) component base band signal Ri. In addition, the multiplier
107
multiplies the intermediate frequency signal that has been received from the distributor
103
by the output signal of the phase shift circuit
105
. The multiplier
107
then sends the result of the multiplication to the low-pass filter
109
. The low-pass filter
109
outputs a quadrature-phase (Q-component) component base band signal Rq. In this way, the quadrature component of the spread spectrum signal that has been received by the reception antenna
101
is detected.
The base band signals Ri and Rq, which have been obtained in this way, are supplied to the complex-type matched filter
110
. The Pseudo Noise (PN) code generation circuit
111
generates a sequence of reference PN codes, and supplies the sequence of reference PN codes to the complex-type matched filter
110
. The complex-type matched filter
110
multiplies the base band signal Ri by a sequence of the I-components of the reference PN codes, and de-spreads the product of the multiplication. Then, the complex-type matched filter
110
outputs the in-phase component Di of the de-spread product of the multiplication to the signal level detector
112
, the frame synchronization circuit
114
, and the phase correction block
115
. Similarly, the complex-type matched filter
110
multiplies the base band signal Rq by a sequence of the Q-components of the reference PN codes, and de-spreads the product of the multiplication. Then, the complex-type matched filter
110
outputs the quadrature-phase component Dq of the de-spread product of the multiplication to the signal level detector
112
, the frame synchronization circuit
114
, and the phase correction block
115
.
The signal level detector
112
calculates the electric (power level of each of the received spread spectrum signals based on the I-component de-spread output Di and the Q-component de-spread output Dq, and sends the result of the calculation for each of the received spread spectrum signals to the multi-paths selector
113
. The multi-paths selector
113
selects multiple (for example, up to four) peaks as the multiple paths in the order of decreasing electric power levels of the received spread spectrum signals from the highest electric power level. The frame synchronization circuit
114
receives from the multi-paths selector
113
information indicating the path that corresponds to the received spread spectrum signal having the maximum electric power level. Then the frame synchronization circuit
114
detects the symbol pattern of the pilot symbol block of the received spread spectrum signal having the maximum electric power level. In this way, the frame synchronization circuit
114
detects the frame timing.
The outputs of the multi-paths selector
113
are supplied to the phase correction block
115
. As will be explained later, the phase correction block
115
corrects the phases of those received spread spectrum signals that correspond to the multiple (for example, up to four) selected paths, and outputs the phase-corrected received spread spectrum signals to the RAKE combiner
116
. The RAKE combiner
116
combines the phase-corrected received spread spectrum signals at a synchronized timing, and the resultant combined signal is supplied to the data decision circuit
117
. The decision circuit
117
judges the data of the combined signal, and demodulates the information contained in the combined signal. In order to detect a synchronized signal, the absolute phase of the received signal needs to be known. The phase correction block
115
detects the amount of phase rotation (error vector) of the received signal of the afore-mentioned pilot symbol (the transmission signal vector of the pilot symbol is known), calculates the correction signal (correction vector) from the error vector, and corrects the phase of the received signal vector.
FIG. 27
a
shows the schematic configuration of the phase correction block
115
. In this diagram, the delay means
120
holds the de-spread signals Di and Dq of the base band signals Ri and Rq that correspond to the information symbol blocks that are supplied from the complex-type matched filter
110
until the calculation of the correction vector is completed, and then outputs the de-spread signals Di and Dq to the RAKE combiner
116
. The pilot symbol phase error extracting-averaging means
130
extracts t
Adachi Fumiyuki
Chen Jie
Qin Xiaoling
Sawahashi Mamoru
Shou Guoliang
Chin Stephen
Pillsbury & Winthrop LLP
Rupert Paul N
Yozan Inc.
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