Multiplex communications – Resonant transfer techniques
Reexamination Certificate
1999-03-23
2003-04-01
Chin, Wellington (Department: 2664)
Multiplex communications
Resonant transfer techniques
C370S441000
Reexamination Certificate
active
06542478
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application entitled DEVICE AND METHOD FOR GENERATING PN SEQUENCE IN CDMA COMMUNICATION SYSTEM earlier filed in the Korean Industrial Property Office on Mar. 23, 1998, and there duly assigned Ser. No. 98-10395.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a Code Division Multiple Access System (CDMA), and more particularly, to a device and method for generating a PN (PseudoNoise) sequence by orthogonal code hopping.
2. Description of the Related Art
Generally, symbols of an orthogonal or biorthogonal code are hopped according to a predetermined hopping pattern in each of a plurality of transmitters in an asynchronous CDMA base station to generate a PN sequence. Asynchronous base stations can use PN sequences to allow a mobile station to identify them. A plurality of slots (e.g., 16 slots) are assigned to one frame. A period of hopped orthogonal Gold code is sent in each slot. Since the orthogonal Gold code hopping patterns are different in the plurality of slots, the mobile station can identify a corresponding base station. If the mobile station can detect the starting point of one frame, it can discriminate a base station from others by determining the offset of the orthogonal Gold code in each slot from the frame starting point. The PN sequence may be used for spread spectrum or scrambling in the case where a different orthogonal code is used for channel identification. A particular receiver may simultaneously receive signals from a corresponding transmitter as well as from transmitters communicating with other receivers. If the plurality of signals, which contain data symbols to be despread, share the same PN sequence and the same orthogonal code (e.g., Walsh code) for channel identification, the receiver will be able to simultaneously despread the signals but fail to recover the intended data symbols. In the case of a periodic PN sequence, data symbols cannot periodically be recovered.
FIGS. 1A and 1B
are schematic views of conventional PN sequence generators based on orthogonal code hopping and orthogonal Gold code hopping, respectively.
FIGS. 1C and 1D
are schematic views of conventional PN sequence generators based on biorthogonal code hopping and biorthogonal Gold code hopping, respectively.
FIGS. 2A and 2B
illustrate a case where a receiver simultaneously receives the same orthogonal or biorthogonal code from different transmitters using PN sequence generators, based on possibly different hopping patterns, and cannot discriminate between data symbols through despreading. When an orthogonal code other than a PN sequence is used for distinguishing a communication channel in a transmitter, only data symbols using the same channel identifying orthogonal code avoid discrimination since collision occurs when the orthogonal code for generating a PN sequence and the orthogonal code for channelization of two received signals are the same. As illustrated in
FIGS. 2A and 2B
, a PN sequence PN
A
of a transmitter A
210
and a PN sequence PN
B
of a transmitter B
260
are generated from the same orthogonal code, however, each uses a different hopping pattern. In
FIG. 2B
, though an orthogonal code OC
3
is simultaneously received from the transmitters A
210
and B
260
(See FIG.
2
A), only the data symbol using a channel identifying orthogonal spreading code W
2
in the orthogonal code OC
3
is lost due to symbol collision. That is, all of the coincident symbols in the respective PN sequences which are identical cannot be recovered (i.e., OC
3
). If the strengths of the signals received from the respective transmitters A
210
and B
260
are equal, they cannot be discriminated. If one is far stronger than the other, the stronger signal can be discriminated.
Orthogonal or biorthogonal codes for use in PN sequence generation include, but are not restricted to Walsh codes, Hardamard codes, Gold codes, and the like.
Referring to
FIG. 1A
, reference numeral
110
denotes a PN sequence generator, constructed in accordance with the prior art, based on orthogonal code hopping. Reference numerals
120
,
130
, and
140
are orthogonal symbol generators to generate orthogonal codes. A selector
150
selectively outputs orthogonal symbols generated from each of the respective orthogonal symbol generators
120
to
140
according to an orthogonal symbol hopping pattern provided by hopping pattern generator
160
. The selector
150
outputs a PN sequence from the selected symbols. The orthogonal symbol hopping pattern generator
160
generates an orthogonal code hopping pattern under a predetermined rule. It is to be noted here that like reference numerals denote the same components in the drawings.
FIG. 1B
is a schematic view of PN sequence generator based on orthogonal Gold code hopping. In
FIG. 1B
, the orthogonal symbol hopping pattern generator
160
determines an initial value for an m-sequence (with a period of 2n−1) generator
163
. An initial value register
162
stores the determined initial value. Another m-sequence generator
167
with a period of 2n−1 generates an m-sequence having an initial value with no relation to the initial value stored in initial value register
162
. This second generated initial value is stored in an initial value register
166
. A Gold sequence is generated by exclusive-ORing the outputs of the two m-sequence generators
163
and
167
by an exclusive-OR gate
164
. To change the Gold sequence to an orthogonal Gold code, the operations of the m-sequence generators
163
and
167
are stopped for one clock period if the status value, which is the initial stored value of the m-sequence generator
167
, of the m-sequence generator
167
is equal to a predetermined reference value as determined by comparator
169
. Each m sequence generator generates (2n−1) m-sequences in one period. (2n−1) sequences are also produced by adding the output values of the two m-sequence generators symbol by symbol. To obtain 2″ orthogonal Gold sequences from the (2n−1) sequences, a zero is inserted in a predetermined position of the (2n−1) sequences where the status value, (i.e., initial value of the m-sequence generator) is identical to a reference value. Zero is inserted in the same position in the next period because the m-sequence generator generates period m-sequences. The reference value can be determined depending on where zero is to be inserted in an orthogonal Gold code sequence, and the insertion position can be predefined freely. Whenever the values are equal, a switch
168
normally connected to the output of the exclusive-OR gate
164
is switched to select a zero value for insertion into the Gold sequence. Otherwise, when the values are not equal, the m-sequence generators
163
and
167
are operated again.
FIG. 1C
is a schematic view of a conventional PN sequence generator based on biorthogonal code hopping, modified from the PN sequence generator based on orthogonal code hopping. If there are 32 orthogonal symbol generators, each orthogonal symbol generator periodically generates a corresponding orthogonal sequence. For example, the hopping pattern of the orthogonal symbol hopping pattern generator
160
is 1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32. The biorthogonal symbol hopping pattern generator
170
generates one additional bit to the hopping pattern generated by generator
160
. This one bit may be MSB or LSB and indicates a sign. By passing the additional bit through the XOR gate
190
, not 64 PN sequences are generated instead of 32. Given orthogonal codes of the same length provided as input to hopping pattern generators
160
and
170
, the output of a biorthogonal symbol hopping pattern generator
170
is twice as long as the orthogonal symbol hopping pattern generator
160
output. The output of the biorthogonal symbol hopping pattern generator
170
p
Chin Wellington
Dilworth & Barrese LLP
Pham Brenda
Samsung Electronics Co,. Ltd.
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