Error detection/correction and fault detection/recovery – Pulse or data error handling – Error/fault detection technique
Reexamination Certificate
2000-04-28
2003-12-23
Chung, Phung M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Error/fault detection technique
C380S046000, C375S346000, C375S367000, C714S746000, C714S780000
Reexamination Certificate
active
06668352
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “Distortion Compensating Device and Method in a Multi-code Mobile Communication System” filed in the Korean Industrial Property Office on Apr. 28, 1999 and assigned Serial No. 99-15222, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a multi-code mobile communication system, and in particular, to a device and method for compensating for signal distortion produced during multi-code transmission in a CDMA (Code Division Multiple Access) mobile communication system.
2. Description of the Related Art
The most challenging issue in the rapidly developing mobile communication industry is efficient use of limited radio frequency bandwidth. High speed transmission using multi-codes is one of the methods of efficiently providing radio multi-media service without increasing bandwidth. Multi-code transmission is the process of converting high rate data to a plurality of parallel low rate data streams, assigning an orthogonal code, and, thus, a code channel, to each parallel code channel which transmits each of the converted parallel low rate data streams, and combining the orthogonally spread code channels for transmission.
FIG. 1
is a block diagram of a typical transmitter in a multi-code using mobile communication system. The transmitter transmits data using four orthogonal codes. A transmitter
10
provides a signal to a specific receiver, or subscriber, and is one of a plurality of transmitters that are identical in structure.
Referring to
FIG. 1
, the transmitter
10
is comprised of a serial-to-parallel converter (SPC)
101
, five multipliers
102
to
105
and
107
, an adder
106
, and an amplifier
108
. The SPC
101
converts input serial user bit stream b
1
(t) into four parallel symbol bit streams b
11
(t) to b
14
(t). The multiplier
102
orthogonally spreads symbol bit stream b
11
(t) with orthogonal code W
11
(t) by multiplication. The multiplier
103
orthogonally spreads symbol bit stream b
12
(t) with orthogonal code W
12
(t) by multiplication. The multiplier
104
orthogonally spread symbol bit stream b
13
(t) with orthogonal code W
13
(t) by multiplication. The multiplier
105
orthogonally spreads symbol bit stream b
14
(t) with orthogonal code W
14
(t) by multiplication. The adder
106
sums the spread symbols bits received from the multipliers
102
to
105
on a bit basis. The multiplier
107
PN-spreads the output of the adder
106
with a first PN code PN
1
(t) by multiplication. The amplifier
108
amplifies the PN-spread signal received from the multiplier
107
, for transmission.
As described above, the conventional transmitter converts a signal to a specific subscriber into a parallel signal, spreads each parallel signal with a different orthogonal code, sums the spread signals, spreads the sum with a predetermined PN code, and amplifies the PN-spread signal. The spreading of different orthogonal codes is considered multi-code communication.
Signals output from transmitters #
1
to #k can be considered summed in the transmission channel as indicated by reference numeral
11
. During propagation in the transmission channel, which may be the atmosphere, the signal is combined with AWGN (Additive White Gaussian Noise).
FIG. 2
is a block diagram of a conventional receiver corresponding to the conventional transmitter using multi-codes. While a plurality of receivers #
1
to #k are shown, a receiver
20
for a specific subscriber will be described as representative of them all since they are identical in structure.
Referring to
FIG. 2
, the receiver
20
is comprised of multipliers
201
to
209
, accumulators
210
to
213
, deciders
214
to
217
, and a parallel-to-serial converter (PSC)
218
. The multiplier
201
PN-despreads an input signal r(t) with its own PN code PN
1
(t) by multiplication. The multipliers
202
to
205
multiply the PN-despread signal by a conjugate signal &bgr;
1
e
j&phgr;
for channel compensation. The multipliers
206
to
209
orthogonally demodulate the channel-compensated signals received from the multipliers
202
to
205
with corresponding orthogonal codes W
11
(t) to W
14
(t) by multiplication. The orthogonal codes are the same as those used in the transmitter
10
of FIG.
1
. The accumulators
210
to
213
accumulate the despread signals received from the multipliers
206
to
209
in symbol units. The deciders
214
to
217
decide symbol bits from the outputs of the accumulators
210
to
213
and output the decision results. The PSC
218
converts the symbols received in parallel according to the decision results of the decider
214
to
217
to serial symbol bits and outputs a symbol bit sequence b
1
(t). The PSC
218
is the counterpart of the SPC
101
of FIG.
1
.
The receiver
20
PN-despreads an input signal, separates the PN-despread signal. into as many signals as the number of the multi-codes used, in the above example, four signals, multiplies each of the signals with an orthogonal code for orthogonal demodulation, accumulates the orthogonally demodulated signals in symbol units, and then decides symbol bits. Then, the decided signals are converted to a serial signal, which are the symbol bits obtained in the receiver
20
.
A signal spread by multi-codes passes through a transmitter amplifier with an increased peak-to-average power ratio, relative to a signal spread by a single code. In general, the high power amplifier (HPA) used as the transmitter amplifier in a multi-code system shows a non-linear characteristic. Therefore, the nature of the HPA causes signal distortion when its saturation point is set too high. That's why the saturation point of the transmitter amplifier is decreased to reduce signal distortion in a transmitter. However, a decrease in the saturation point leads to a corresponding decrease of amplification efficiency. In view of the importance of power consumption to the performance of a mobile station, the above transmitter amplifier is not suitable for a mobile station since it increases power consumption.
Accordingly, there is a need for a receiver that compensates for the signal distortion generated when a signal passes through a transmitter amplifier with a high saturation point in order to prevent deterioration of BER (Bit Error Rate) performance. The high probability of errors in the distorted signal during propagation in the atmosphere reinforces the need for an error compensating device in the receiver.
SUMMARY OF THE INVENTION
It is therefore, an object of the present invention to provide a device and method for effectively compensating for the distortion of an input signal caused by an HPA in a multi-code mobile communication system.
It is another object of the present invention to provide a device and method for correcting errors of a parallel code channel by checking the parity of the code channel with parity data received on a redundancy channel.
Briefly, these and other objects are achieved by providing a receiving device in a multi-code mobile transmission system. In the novel multi-code mobile communication system, user data is transmitted on a plurality of parallel data channels and parity data generated from the user data is transmitted on a redundancy channel. An energy calculator of the receiving device calculates the energy of each symbol output by deciders and indicates the symbol with the smallest energy. A parity checker determines whether errors have been generated by checking the parity of symbol data, and a sign inverter inverts the sign of the symbol with the smallest energy (as indicated by the energy calculator), if it is determined that errors have been generated. Thus, errors are corrected.
REFERENCES:
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patent: 5841806 (1998-11-01), Gilhousen et al.
patent: 5943361 (1999-08-01), Gilhousen et al.
patent: 6094465 (2000-07-01), Stein et al.
patent: 6163566 (2000-12-01), Sh
Chung Phung M.
Dilworth & Barrese LLP
Samsung Electronics Co,. Ltd.
Whittington Anthony T.
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