Pulse or digital communications – Spread spectrum – Frequency hopping
Reexamination Certificate
1999-03-09
2004-03-09
Phu, Phoung (Department: 2631)
Pulse or digital communications
Spread spectrum
Frequency hopping
C375S139000, C375S132000
Reexamination Certificate
active
06704345
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to transmission/reception apparatuses and methods, capable of improving advantages of the CDMA (Code Division Multiple Access) system, etc. in a mobile communication system which is effective in satisfying conditions such as overcoming multi-path fading, improving transmission quality, improving frequency utilization efficiency and storing multi-rate information.
2. Description of the Related Art
Conventionally, access systems such as FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and CDMA are actually used in mobile communications. It is essential for these access systems to overcome multi-path fading, improve the transmission quality, improve the frequency utilization efficiency and store multi-rate information, etc., as described above, and the CDMA system is currently considered to be an effective system meeting these requirements.
The CDMA system is a system in which the transmitting side sends transmission information in frame units after multiplying it by a spreading code and the receiving side extracts the original transmission information by multiplying the received signal by the same spreading code.
FIG. 1
is a block diagram of conventional transmission/reception apparatuses. Here, the transmission/reception apparatuses are a base station and mobile stations (communication terminal apparatuses) of a mobile communication system, which is based on the CDMA system.
In
FIG. 1
, base station
1300
carries out radio communications with a first to third mobile stations
1301
to
1303
. In this example, base station
1300
is provided with a communication circuit with three mobile stations and comprises their respective voice encoders
1310
to
1312
, error correction encoders
1313
to
1315
, modulators
1316
to
1318
, spreaders
1319
to
1321
, adder
1322
, amplifier
1323
, antenna
1324
, matched filters
1325
to
1327
, RAKE combiners
1328
to
1330
, error correction decoders
1331
to
1333
, and voice decoders
1334
to
1336
.
First mobile station
1301
comprises antenna
1340
, matched filter
1341
, RAKE combiner
1342
, error correction decoder
1343
, voice decoder
1344
, voice encoder
1345
, error correction encoder
1346
, modulator
1347
, spreader
1348
, and amplifier
1349
.
Second mobile station
1302
comprises antenna
1350
, matched filter
1351
, RAKE combiner
1352
, error correction decoder
1353
, voice decoder
1354
, voice encoder
1355
, error correction encoder
1356
, modulator
1357
, spreader
1358
, and amplifier
1359
.
Third mobile station
1303
comprises antenna
1360
, matched filter
1361
, RAKE combiner
1362
, error correction decoder
1363
, voice decoder
1364
, voice encoder
1365
, error correction encoder
1366
, modulator
1367
, spreader
1368
, and amplifier
1369
.
In the mobile communication system configured as shown above, the following is an explanation of a case where transmission is carried out from base station
1300
to mobile stations
1301
to
1303
.
First, for first mobile station
1301
, base station
1300
carries out error correction encoding using error correction encoder
1313
on digital data created by voice encoder
1310
, modulates the encoded data with error correction using modulator
1316
and multiplies it by a user-specific spreading code using spreader
1319
.
Likewise, for second mobile station
1302
, base station
1300
processes transmission data using voice encoder
1311
, error correction encoder
1314
, modulator
1317
and spreader
1320
, and for third mobile station
1303
, it processes transmission data using voice encoder
1312
, error correction encoder
1315
, modulator
1318
and spreader
1321
.
Each spread signal is summed up in adder
1322
, amplified in amplifier
1323
and emitted from antenna
1324
.
In first mobile station
1301
, a signal is received by antenna
1340
and only a desired signal is extracted by matched filter
1341
, subjected to path diversity by RAKE combiner
1342
, subjected to error correction decoding to improve the reception quality by error correction decoder
1343
, and voice is reproduced by voice decoder
1344
.
In second mobile station
1302
, only the voice of a desired user is reproduced likewise using antenna
1350
, matched filter
1351
, RAKE combiner
1352
, error correction decoder
1353
and voice decoder
1354
. In third mobile station
1303
, only the voice of a desired user is reproduced likewise using antenna
1360
, matched filter
1361
, RAKE combiner
1362
, error correction decoder
1363
and voice decoder
1364
.
Then, transmission from mobile stations
1301
to
1303
to base station
1300
is explained.
In first mobile station
1301
, digital data created by voice encoder
1345
are subjected to error correction encoding by error correction encoder
1346
, the encoded data with error correction are modulated by modulator
1347
, given user-specific spreading in spreader
1348
, amplified by amplifier
1349
and emitted from antenna
1340
.
In second mobile station
1302
, a signal is emitted likewise through voice encoder
1355
, error correction encoder
1356
, modulator
1357
, spreader
1358
, amplifier
1359
and antenna
1350
. In third mobile station
1303
, a signal is emitted likewise through voice encoder
1365
, error correction encoder
1366
, modulator
1367
, spreader
1368
, amplifier
1369
and antenna
1360
. All these signals are emitted on a same frequency.
Base station
1300
receives signals transmitted from mobile stations through antenna
1324
, extracts only the signal of first mobile station
1301
by matched filter
1325
, carries out path diversity by RAKE combiner
1328
and error correction decoding to improve the reception quality by error correction decoder
1331
, and reproduces voice by voice decoder
1334
.
Likewise, base station
1300
extracts only the signal of second mobile station
1302
by matched filter
1326
, carries out path diversity by RAKE combiner
1329
and error correction decoding to improve the reception quality by error correction decoder
1332
, and reproduces voice by voice decoder
1335
. Furthermore, base station
1300
extracts only the signal of third mobile station
1303
by matched filter
1327
, carries out path diversity by RAKE combiner
1330
and error correction decoding to improve the reception quality by error correction decoder
1333
, and reproduces voice by voice decoder
1336
.
Thus, through CDMA transmissions, signals of mobile stations
1301
to
1303
are spread by different codes and superimposed on a same frequency. In this case, spreading allows a short de-lay time path to be separated, making it possible not only to eliminate influences of multi-path fading through RAKE reception but also to produce path diversity effects, improving the line quality.
Furthermore, the CDMA system can implement a uniform transmission quality for all mobile stations
1301
to
1303
and also allows adjacent cells to use a same frequency, possessing features such as high frequency utilization efficiency and easy multi-rate accommodation.
However, in the conventional transmission/reception apparatus above, carrying out RAKE reception requires accurate detection of fingers, that is, accurate detection of the fading status, delay wave status, etc., which takes considerable time.
Moreover, if at least one of a plurality of mobile stations fails in power control or has noise with great power over a narrow band, its interference may disable communications of all mobile stations within a cell or within peripheral cells.
The number of paths is also variable with time, which may prevent path diversity effects from being always obtained.
Bands available to the system are also restricted due to the chip rate which is the multiplication factor after spreading, limiting its implementation only to bands which are an integer times the bandwidth.
Furthermore, since many mobile stations use a same frequency band simultaneously, the scale of an interference can
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Phu Phoung
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