Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-11-02
2002-09-24
To, Doris H. (Department: 2682)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S206000, C370S208000, C375S140000, C375S142000, C375S143000, C375S150000, C375S152000, C375S146000
Reexamination Certificate
active
06456612
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “Device and Method for Generating Short PN Code in Mobile Communication System” filed in the Korean Industrial Property Office on Nov. 2, 1998 and assigned Ser. No. 98-47240, 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 short PN code generation device and method for a CDMA mobile communication system, and, in particular, to a device and method for generating a short PN code for a high-speed mobile communication system.
2. Description of the Related Art
In general, CDMA (Code Division Multiple Access) mobile communication systems use orthogonal codes, long PN (Pseudo Noise) codes and short PN codes. The short PN codes are used to identify the base stations. For example, the forward link of the IS-95/IS-95A CDMA communication system identifies the base stations by using offsets to short PN codes.
The IS-95/IS-95A forward link uses a short PN code of length 2
15
to identify the base stations. The respective base stations and mobile stations generate the short PN code of length 2
15
in such a manner that while one base station generates the t-th chip of the short PN code, another base station generates a (t+(64*k))-th chip of the short PN code. A “chip” is an individual binary digit in the short PN code. Herein, “(64*k)” will be referred to as an offset. Therefore, the base stations use unique short PN codes each having different offset values to identify themselves. The mobile stations then identify the base stations by searching for the offsets of the short PN codes from the base stations. That is, the mobile stations identify the base stations depending on the offset values of the received short PN codes.
FIG. 1
shows a base station device for spreading a transmission signal using a short PN code of length 2
15
in a conventional CDMA mobile communication system. In.
FIG. 1
, the finally output code unit is a chip. The existing CDMA mobile communication system generates 1.2288M chips per second for the short PN code, and the clock rate of the generated short PN code is equal to a chip rate.
Referring to
FIG. 1
, multipliers
111
and
113
commonly receive an orthogonally spread signal which was multiplied by an orthogonal code (such as a Walsh code). The multiplier
111
multiplies an I-component short PN code by the orthogonally spread signal, and the multiplier
113
multiplies a Q-component short PN code by the orthogonally spread signal. Here, the I-component short PN code and the Q-component short PN code are created so that the base station has a unique offset. A baseband filter
115
filters a baseband signal from the I-channel spread signal output from the multiplier
111
, and a baseband filter
117
filters a baseband signal from the Q-channel spread signal output from the multiplier
113
. A mixer
119
mixes an output of the baseband filter
115
with a carrier cos(2&pgr;f
c
t), and a mixer
121
mixes an output of the baseband filter
117
with a carrier sin(2&pgr;f
c
t). An adder
123
adds an output of the mixer
119
and an output of the mixer
121
.
However, in an IMT-2000 system, which is a third generation mobile communication system introducing a multi-carrier concept, it is expected that the chip rate will increase. With regard to the chip rate, the IS-95 communication system is termed a 1× system, while the IMT
-2000
communication system can be extended up to a 3× system, a 6× system, a 9× system and a 12× system, including the legacy 1× system. In terms of chips per second, the 1× system has a chip rate of 1.2288 Mcps (chips per second), the 3× system has a chip rate of 3×1.2288 Mcps=3.6864 Mcps, the 6× system has a chip rate of 6×1.2288 Mcps=7.3728 Mcps, the 9× system has a chip rate of 9×1.2288 Mcps=11.0592 Mcps, and the 12× system has a chip rate of 12×1.2288 Mcps=14.7456 Mcps. Accordingly, the 1× system operates at the chip rate as that of the existing CDMA mobile communication system, whereas other N× systems operate at a chip rate increased by N times. At this point, in the N× systems, the time period of each chip is decreased by N times. Therefore, if the N× system uses the same offset as in the 1× system, the time period of the offset will be decreased by N times. Accordingly, it is difficult for the mobile station to identify the base stations because it is hard to distinguish whether the short PN code signal is a multipath signal from the existing base station or a short PN code signal from another base station. Thus, it is required to increase the offset by N times. Therefore, if the N× system uses the short PN code having the same period as the short PN code used in the existing 1× system, the number of cases (or the number of offsets) for identifying the base stations is decreased by N times. Accordingly, there is required a short PN code of time period N×2
15
in order to have the same offset number as the existing CDMA mobile communication system.
The above stated short PN code is a PN sequence having a period of 2
k
. The 3× system requires a short PN code of period 3×2
15
. However, there exists no PN sequence having this period. Up to date, a sequence having the 3 random sequence properties and satisfying the PN sequence having this period has not been found (see “Shift Register Sequences” by Solomon W. Golomb).
Therefore, there has been research on a method of generating a PN sequence of period 2
17
, and then using only part of the 2
17
PN sequence in order to obtain the short PN code of period 3×2
15
. Since the short PN codes of period 3×2
15
generated by this method do not have the 3 properties of the random sequences, every effort has been made to reduce the number of hardware gates in generating the I-component short PN code and the Q-component short PN code.
As described above, the short PN code used in the IS-95 system cannot be used in the IMT-2000 mobile communication system due to the decrease in size of the offsets. In addition, when the IMT-2000 communication system uses the same short PN code as the IS-95 system, an increased number of hardware gates are required to generate the short PN code.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a device and method for generating I-component and Q-component short PN codes using a single short PN code generator in a CDMA mobile communication system.
It is another object of the present invention to provide a device and method for generating I-component and Q-component short PN codes by alternately switching a PN code generated from a single short PN code generator in a CDMA mobile communication system.
It is further another object of the present invention to provide a device and method for generating a short PN code that is longer in length than the short PN code used in an IS-95 system to generate I-component and Q-component short PN codes using the generated short PN code in a CDMA mobile communication system.
In accordance with one embodiment of the present invention, there is provided a short PN code generating device in a mobile communication network having a N× CDMA communication system performing spreading at an N× chip rate using a short PN code of chip length N×2
k
and a 1× CDMA communication system performing spreading at a 1× chip rate using a short PN code of chip length 2
k
, wherein the device generates a short PN code such that the N× CDMA communication system can distinguish at least the same number of base stations as the 1× CDMA communication system can distinguish. The device comprises a sequence generator for generating an m-sequence having a chip length longer than the chip length N×2
k
to output an I-component short PN code; and a Q-component short PN code generator for logically operatin
Ahn Jae-Min
Kim Jae-Yoel
Moon Hi Chan
Dilworth & Barrese LLP
Samsung Electronics Co,. Ltd.
To Doris H.
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