Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-12-27
2003-05-27
Vo, Don N. (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S148000
Reexamination Certificate
active
06570908
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “Device and Method for Compensating for Distortion in Multi-code Mobile Communication System” filed in the Korean Industrial Property Office on Dec. 27, 1998 and assigned Serial No. 98-59044, 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 a distortion occurring during multi-code transmission in a CDMA (Code Division Multiple Access) mobile communication system.
2. Description of the Related Art
The most challenging issue to the rapidly developed mobile communication industry is efficient use of limited radio frequency bands. High rate transmission using a multi-code is one of methods for efficiently accommodating future radio multi-services without increasing the spreading band width of the limited radio frequency. The multi-code transmission is a scheme of converting high rate data to several parallel low rate data, assigning an orthogonal code to each parallel code channel on which to transmit the converted parallel low rate data, and then combining the low rate data, prior to transmission.
FIG. 1
illustrates the structure of a typical transmitter in a multi-code mobile communication system. Referring to
FIG. 1
, four different orthogonal codes are used for data transmission. Since each subscriber uses the same transmitter in structure, a transmitter
111
for transmitting a signal to a specific subscriber will be described by way of example.
In
FIG. 1
, the transmitter
111
is comprised of a serial-to-parallel converter (SPC)
121
, five multipliers
131
to
134
and
151
, an adder
141
, and an amplifier
161
. The SPC
121
converts input serial user information bits b
1
(t) to parallel four information bits b
11
to b
14
. The multiplier
131
orthogonally spreads the information bit b
11
by multiplying the information bit b
11
by a first orthogonal code a
11
. The multiplier
132
orthogonally spreads the information bit b
12
by multiplying the information bit b
12
by a second orthogonal code a
12
. The multiplier
133
orthogonally spreads the information bit b
13
by multiplying the information bit b
13
by a third orthogonal code a
13
. The multiplier
134
orthogonally spreads the information bit b
14
by multiplying the information bit b
14
by a fourth orthogonal code a
14
. The adder
141
sums the spread information bits received from the multipliers
131
to
134
bit by bit. The multiplier
151
PN-spreads the output of the adder
141
by multiplying the output of the adder
141
by a first PN code PN
1
. The amplifier
161
amplifies the PN-spread signal received from the multiplier
151
.
As described above, the typical transmitter converts a signal provided by a specific user to parallel signals, spreads each parallel signal with a different orthogonal code, sums the orthogonally spread signals, spreads the sum with a predetermined PN code, and amplifies the PN-spread signal, prior to transmission. Spreading the parallel signals with different orthogonal codes can be referred to as use of a multi-code.
Meanwhile, signals output from transmitters
111
to
11
N in the above procedure are added in the air and then transmitted to a base station. From
FIG. 1
, it is noted that AWGN (Additive White Gaussian Noise) is added to the transmission signals of the transmitters
111
to
11
N during transmission.
FIG. 2
illustrates the structure of typical receivers
211
to
21
N corresponding to the transmitters
111
to
11
N using the multi-code scheme. While the plurality of receivers
211
to
21
N are shown in
FIG. 2
, the following description will be conducted on the receiver
211
of a specific user because they are the same in structure.
Referring to
FIG. 2
, the receiver
211
includes five multipliers
221
and
231
to
234
, accumulators
251
to
254
, deciders
261
to
264
, and a parallel-to-serial converter (PSC)
271
. The multiplier
221
PN-despreads an input signal r(t) by multiplying the input signal r(t) by its unique PN code PN
1
(t). The multipliers
231
to
234
multiply the PN-despread signal by a conjugate signal &bgr;
1
e
j&phgr;
for channel compensation. Multipliers
241
to
244
multiply channel-compensated signals received from the corresponding multipliers
231
to
234
by corresponding orthogonal codes a
11
(t) to a
14
(t), for orthogonal demodulation. The mutually different orthogonal codes are the same as used in the transmitter
111
. The accumulators
251
to
254
accumulate the despread signals received from the multipliers
241
to
244
in symbol units. The deciders
261
to
264
subject information bits of the outputs of the corresponding accumulators
251
to
254
to a decision. The PSC
271
converts serial information bits based on the decision results, received from the deciders
261
to
264
, to a serial information bit sequence b
1
(t). The PSC
271
corresponds to the SPC
121
of the transmitter
111
.
As shown in
FIG. 2
, each of the receivers
211
to
21
N PN-despreads an input signal and divides the PN-despread signal into four signals as many as the codes used. Then, it multiplies each of the four signals by an orthogonal code, for orthogonal demodulation, accumulates the orthogonally demodulated signal, and subjects information bits of the accumulated signal to a decision. The decided signal is converted to a serial signal, which is information bits obtained in the receiver.
A signal passes th rough a transmitter amplifier with an increased average peak to power ratio in the multi-code transmission scheme, as compared to a single code transmission scheme. In general, a high power amplifier (HPA) corresponding to the transmitter amplifier exhibits non-linear characteristics. Therefore, if the saturation point of the HPA is set to a high level, the non-linear characteristics produces a distortion signal. To reduce the distortion, a transmitter drops the saturation point of its amplifier. The resulting decrease of efficiency of the amplifier, however, causes another problem. Furthermore, considering that power consumption is a dominant factor which determines the performance of a terminal, the above transmitter amplifier cannot be used for the terminal because it increases the power consumption.
A signal is distorted while passing through a transmitter amplifier with a high saturation point and a receiver experiences a low bit error rate (BER) performance. Therefore, the distorted signal should be compensated. In addition, since the distorted signal is likely to have errors during transmission in the air, the receiver is to be provided with an error correcting device.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a device and method for efficiently compensating for the HPA-caused distortion of a received signal in a multi-code mobile communication system.
It is another object of the present invention to provide a device and method for outputting a received signal whose distortion is compensated for using a Euclidean distance in a multi-code mobile communication system.
It is a further object of the present invention to provide a device and method for removing another user signal acting as an interference signal in a multi-code mobile communication system.
These and other objects are achieved by providing a device for compensating for the distortion of an input signal for a receiving device in a multi-code mobile communication system. In the distortion compensating device, each of at least two receivers has a pattern generator for generating pattern signals from symbol data, and a regenerator for spreading the symbol data and pattern signals. Here, each symbol is decided by a multi-code from the input signal. An interference canceler removes a signal output from the other of the two receivers from the input signal of a specific receiver. A distortion compensator receives
Dilworth & Barrese LLP
Samsung Electronics Co,. Ltd.
Vo Don N.
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