Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2002-11-27
2004-03-30
Tran, Khai (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S150000, C370S242000
Reexamination Certificate
active
06714582
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a code division multiple access communication system and code division multiple access transmitting apparatus. More particularly, the invention relates to a code division multiple access communication system and code division multiple access transmitting apparatus in which interference noise can be reduced.
In a CDMA (Code Division Multiple Access) mobile communications system, a base station spread-spectrum modulates control information and user information of each user by employing different spreading code sequences, multiplexes the modulated information and transmits the same. Each mobile station in the system sends and receives information upon spreading and despreading the information using a spreading code sequence specified by the base station.
FIG. 37
is a block diagram of a CDMA transmitter in a base station that encodes, multiplexes and transmits the transmit data of a control channel and of a plurality of user channels. In the Figure, numerals
11
1
to
11
n
denote spread-spectrum modulators of respective control and user channels, each having a frame generator
21
, a serial/parallel converter (S/P converter)
22
for converting frame data to parallel data, and a spreading circuit
23
.
The frame generator
21
includes a transmission data generator
21
a
for generating serial transmit data D
1
, a control-data generator
21
b
for generating control data CNDT such as a pilot, and a framing circuit
21
c
for forming the serial data D
1
into a block every prescribed number of bits and inserting the control data CNDT before and after every block to thereby form frames. The pilot signal allows a receiver to recognize the amount of phase rotation caused by transmission so that the data may be subjected to a phase rotation by an equivalent amount in the opposite direction.
The S/P converter
22
alternately distributes the frame data (the control data and transmit data) one bit at a time to convert the frame data to two sequences D
I
, D
Q
, namely I-component (in-phase component) data and Q-component (quadrature-component) data. The spreading circuit
23
includes a pn sequence generator
23
a
for generating a noise code (pn sequence) specific to the base station, a channel code generator
23
b
for generating a channel code specific to the control channel or user channel, an EXOR circuit
23
c
for outputting a spreading code C
1
by taking the EXOR (exclusive-OR) between the noise code and the channel code, and EXOR circuits
23
d
,
23
e
for performing spread-spectrum modulation by taking the exclusive-ORs between the data D
I
and D
Q
(symbols) of the two sequences, and the spreading code C
1
.
Reference characters
12
i
denote a combiner for outputting an I-component code-multiplexed signal &Sgr;V
I
by combining the I-component spread-spectrum modulated signals V
I
output by the spread-spectrum modulators
11
1
~
11
n
of the user channels;
12
q
a combiner for outputting a Q-component code-multiplexed signal &Sgr;V
Q
by combining the Q-component spread-spectrum modulated signals V
Q
output by the spread-spectrum modulators
11
1
~
11
n
;
13
i
,
13
q
FIR-type chip shaping filters for limiting the bands of the code-multiplexed signals &Sgr;V
I
, &Sgr;V
Q
;
14
i
,
14
q
DA converters for DA-converting the outputs of the filters
13
i
,
13
q
;
15
a quadrature modulator for applying QPSK quadrature modulation to the code-multiplexed signals &Sgr;V
I
, &Sgr;V
Q
of the I and Q components and outputting the modulated signal;
16
a transmit circuit for converting the frequency of the output signal of the quadrature modulator to a radio frequency, amplifying the high frequency and transmitting the result; and
17
an antenna.
FIG. 38
is a block diagram of a CDMA receiver in a mobile station. A radio unit
31
converts a high-frequency signal received by the antenna to baseband signals by applying a frequency conversion (RF→IF conversion). An orthogonality detector
32
detects orthogonality of the baseband signals and outputs in-phase component (I-phase component) data and quadrature component (Q-component) data. In the orthogonality detector
32
, reference characters
32
a
denote a receive-carrier generator;
32
b
a phase shifter for shifting the phase of the receive carrier by &pgr;/2; and
32
c
,
32
d
multipliers for multiplying the baseband signals by the receive carrier and outputting the I-component signal and the Q-component signal. Low-pass filters (LPF)
33
a
,
33
b
limit the bands of these output signals and AD converters
35
a
,
35
b
convert the I- and Q-component signals to digital signals and input the digital signals to a despreading circuit
41
.
The despreading circuit
41
subjects the input I- and Q-component signals to despread processing using a code identical with the spreading code and outputs a reference signal (pilot signal) and an information signal. A phase compensator (channel estimation unit)
42
averages the voltages of the I- and Q-components of the pilot signal over a prescribed number of slots and outputs channel estimation signals It, Qt. A synchronous detector
43
restores the phases of despread information signals I′, Q′ to the original phases based upon a phase difference &thgr; between a pilot signal contained in a receive signal and an already existing pilot signal. More specifically, the channel estimation signals It, Qt are cosine and sine components of the phase difference &thgr;, and therefore the synchronous detector
43
demodulates the receive information signal (I,Q) (performs synchronous detection) by applying phase rotation processing to the receive information signal (I′,Q′) in accordance with the following equation using the channel estimation signal (It,Qt).
(
I
Q
)
=
(
I
t
Q
t
-
Q
t
I
t
)
(
I
′
Q
′
)
An error correction decoder
44
decodes the original transmit data by using the signal that enters from the synchronous detector
43
and outputs the decoded data.
In the above-described mobile wireless communication system, a base station usually cannot use a fixed directivity pattern for communication with mobile stations; it communicates using a non-directional antenna. However, not only is transmission by a non-directional antenna poor in power efficiency because radio waves are emanated also in directions in which a targeted mobile station is not present, but such transmission also degrades communication quality by subjecting mobile stations other than the targeted mobile station to interference. For this reason, practice has been to equally divide the 360° circumference of the base station so as to split the cell into a plurality of sectors (sector-shaped zones), and use a directional antenna in each sector, thereby mitigating interference.
FIG. 39
is a schematic structural view of a transceiver in a code division multiple access communication system for a case where a cell has been divided into sectors, and
FIG. 40
is a flowchart of transceive processing. These illustrate an example of a case where user data signals Data
1
, Data
2
are transmitted from a single base station BS to mobile stations MS
1
, MS
2
in two sectors neighboring each other. Sectors Sec
1
, Sec
2
in the base station BS have transceive antennas ANT
1
, ANT
2
possessing separate directivities and, by virtue of the antenna directivities, take charge of the sending and receiving of signals to and from coverage areas (sectors) that are geographically independent of each other.
The user data signals Data
1
, Data
2
undergo encoding processing, for error correction or the like, in channel coders CH-cod
1
, CH-cod
2
in respective ones of the sectors Sec
1
, Sec
2
, and the processed signals are input to spreading circuits SC
1
, SC
2
. Encoded data Cdata
1
, Cdata
2
is spread-spectrum modulated in the spreading circuits SC
1
, SC
2
by mutually different spreading-code sequences PN
1
, PN
2
generated by spreading-code generators
Aoki Nobuhisa
Nakamura Takaharu
Obuchi Kazuhisa
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Tran Khai
LandOfFree
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