Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1998-09-30
2001-04-24
Le, Amanda T. (Department: 2734)
Pulse or digital communications
Spread spectrum
Direct sequence
C370S206000
Reexamination Certificate
active
06222873
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an orthogonal complex spreading method for a multichannel and an apparatus thereof, and in particular, to an improved orthogonal complex spreading method for a multichannel and an apparatus thereof which are capable of decreasing a peak power-to-average power ratio by introducing an orthogonal complex spreading structure and spreading the same using a spreading code, implementing a structure capable of spreading complex output signals using a spreading code by adapting a permutated orthogonal complex spreading structure for a complex-type multichannel input signal with respect to the summed values, and decreasing a phase dependency of an interference based on a multipath component (when there is one chip difference) of a self signal, which is a problem that is not overcome by a permutated complex spreading modulation method, by a combination of an orthogonal Hadamard sequence.
2. Description of the Conventional Art
Generally, in the mobile communication system, it is known that a linear distortion and non-linear distortion affect power amplifier. The statistical characteristic of a peak power-to-average power ratio has a predetermined interrelationship for a non-linear distortion.
The third non-linear distortion which is one of the factors affecting the power amplifier causes an inter-modulation product problem in an adjacent frequency channel. The above-described inter-modulation product problem is generated due to a high peak amplitude for thereby increasing an adjacent channel power (ACP), so that there is a predetermined limit for selecting an amplifier. In particular, the CDMA (Code Division Multiple Access) system requires a very strict condition with respect to a linearity of a power amplifier. Therefore, the above-described condition is a very important factor.
In accordance with IS-97 and IS-98, the FCC stipulates a condition on the adjacent channel power (ACP). In order to satisfy the above-described condition, a bias of a RF power amplifier should be limited.
According to the current IMT-2000 system standard recommendation, a plurality of CDMA channels are recommended. In the case that a plurality of channels are provided, the peak power-to-average power ratio is considered as an important factor for thereby increasing efficiency of the modulation method.
The IMT-2000 which is known as the third generation mobile communication system has a great attention from people as the next generation communication system following the digital cellular system, personal communication system, etc. The IMT-2000 will be commercially available as one of the next generation wireless communication system which has a high capacity and better performance for thereby introducing various services and international loaming services, etc.
Many countries propose various IMT-2000 systems which require high data transmission rates adapted for an internet service or an electronic commercial activity. This is directly related to the power efficiency of a RF amplifier.
The CDMA based IMT-2000 system modulation method introduced by many countries is classified into a pilot channel method and a pilot symbol method. Of which, the former is directed to the ETRI 1.0 version introduced in Korea and is directed to CDMA ONE introduced in North America, and the latter is directed to the NTT-DOCOMO and ARIB introduced in Japan and is directed to the FMA2 proposal in a reverse direction introduced in Europe.
Since the pilot symbol method has a single channel effect based on the power efficiency, it is superior compared to the pilot channel method which is a multichannel method. However since the accuracy of the channel estimation is determined by the power control, the above description does not have its logical ground.
FIG. 1
illustrates a conventional complex spreading method based on a CDMA ONE method. As shown therein, the signals from a fundamental channel, a supplemental channel, and a control channel are multiplied by a Walsh code by each multiplier of a multiplication unit
20
through a signal mapping unit
10
. The signals which are multiplied by a pilot signal and the Walsh signal and then spread are multiplied by channel gains A
0
, A
1
, A
2
and A
3
by a channel gain multiplication unit
30
.
In a summing unit
40
, the pilot signal multiplied by the channel gain A
0
and the fundamental channel signal multiplied by the channel gain A
1
are summed by a first adder for thereby obtaining an identical phase information, and the supplemental channel signal multiplied by the channel gain A
2
and the control channel signal multiplied by the channel gain A
3
are summed by a second adder for thereby obtaining an orthogonal phase information.
The thusly obtained in-phase information and quadrature-phase information are multiplied by a PN1 code and PN2 code by a spreading unit
50
, and the identical phase information multiplied by the PN2 code is subtracted from the identical phase information multiplied by the PN1 code and is outputted as an I channel signal, and the quadrature-phase information multiplied by the PN1 code and the in-phase information multiplied by the PN2 code are summed and are outputted through a delay unit as a Q channel signal.
The CDMA ONE is implemented using a complex spreading method. The pilot channel and the fundamental channel spread to a Walsh code
1
are summed for thereby forming an in-phase information, and the supplemental channel spread to the Walsh code
2
and the control channel spread to a Walsh code
3
are summed for thereby forming an quadrature-phase information. In addition, the in-phase information and quadrature-phase information are complex-spread by PN codes.
FIG. 2A
is a view illustrating a conventional CDMA ONE method, and
FIG. 2B
is a view illustrating a maximum eye-opening point after the actual shaping filter of FIG.
2
A.
As shown therein, in the CDMA ONE, the left and right information, namely, the in-phase information (I channel) and the upper and lower information, namely, the quadrature-phase information (Q channel) pass through the actual pulse shaping filter for thereby causing a peak power, and in the ETRI version 1.0 shown in
FIGS. 3A and 3B
, a peak power may occur in the transverse direction for thereby causing deterioration.
In view of the crest factor and the statistical distribution of the power amplitude, in the CDMA ONE, the peak power is generated in vertical direction, so that the irregularity problem of the spreading code and an inter-interference problem occur.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an orthogonal complex spreading method for a multichannel and an apparatus thereof overcome the aforementioned problems encountered in the conventional art.
The CDMA system requires a strict condition for a linearity of a power amplifier, so that the peak power-to-average power ratio is important. In particular, the characteristic of the IMT-2000 system is determined based on the efficiency of the modulation method since multiple channels are provided, and the peak power-to-average power ratio is adapted as an important factor.
It is another object of the present invention to provide an orthogonal complex spreading method for a multichannel and an apparatus thereof which have an excellent power efficiency compared to the CDMA-ONE introduced in U.S.A. and the W-CDMA introduced in Japan and Europe and is capable of resolving a power unbalance problem of an in-phase channel and a quadrature-phase channel as well as the complex spreading method.
It is still another object of the present invention to provide an orthogonal complex spreading method for a multichannel and an apparatus thereof which is capable of stably maintaining a low peak power-to-average power ratio.
It is still another object of the present invention to provide an orthogonal complex spreading method for a multichannel and an apparatus thereof in which a spreading operation is implemented by multiplying a predetermined channel
Bang Seung Chan
Han Ki Chul
Kim Jung Im
Kim Tae Joong
Shim Jae Ryong
Electronics and Telecommunications Research Institute
Jacobson Price Holman & Stern PLLC
Le Amanda T.
LandOfFree
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