Spread spectrum communication system

Details Spread spectrum communication system Spread spectrum communication system

1996-12-26

2001-04-03

Chin, Stephen (Department: 2734)

Pulse or digital communications

Spread spectrum

C375S140000, C375S142000, C375S143000, C370S342000

Reexamination Certificate

active

06212219

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a spread spectrum communication system.
BACKGROUND OF THE INVENTION
Spread spectrum communication systems spread the frequency spectrum of the transmitted signal by modulating the carrier with a spreading signal. This spreading signal is obtained by multiplying pseudonoise (PN) codes by the data being transmitted. The spectrum of the spreading signal approximates that of white noise, so the resulting transmitted signal has a wide bandwidth.
Many different PN codes may be used, and the correlation between these codes is usually limited. Therefore, a spread spectrum system is very secure against eavesdropping, has a high efficiency of frequency, and is very robust to noise. For these reasons, spread spectrum systems are expected to be the primary means of carrying mobile and personal communications and wireless LANs in the future.
For such applications, however, demand is growing for higher data capacities, more efficient use of bandwidth, and faster data transfer than conventional spread spectrum techniques can provide. The present invention extends spread spectrum technology to allow systems with higher rates of data transmission.
The outline of the transmitter of a spread spectrum (SS) communication system using quadrature phase-shift keying (QPSK) modulation is shown in FIG.
26
. In the figure,
102
and
105
are binary phase-shift keying (BPSK) modulators,
107
is a PN code generator (PN.G) for generating PN code sequences, and
108
is a phase shifter for shifting the phase of a carrier wave by &pgr;/2.
Data generated by a data generating portion (DATA
1
)
100
are added to a PN code generated by PN.G
107
in an adder
101
. Data generated by a data generating portion (DATA
2
)
103
are added to a PN code generated by the PN.G
107
. In this case, one complete cycle of PN code is used to encode each bit of the data. The addition performed in adders
101
and
104
is modulo
2
, that is, a PN code is outputted as is when the data bit is
0
, and the PN code is inverted and outputted when the data bit is
1
.
An output of an adder
101
is inputted to a BPSK modulator
102
, and a carrier wave generated by a carrier wave oscillator
109
is modulated by BPSK. An output of an adder
104
is inputted to a BPSK modulator
105
, and a carrier wave is modulated by BPSK, which wave is generated by a carrier wave oscillator
109
and is shifted in phase by &pgr;/2 by a phase shifter
108
. An in-phase component of QPSK modulation (component I, hereinafter) can be obtained from a BPSK modulator
102
, and an quadrature component of QPSK modulation (component Q, hereinafter) can be obtained from a BPSK modulator
105
. These two components of BPSK modulation are added in an adder
106
to create a QPSK modulated signal. The QPSK modulated signal is transmitted from antenna
110
. In this way, a multiplexed spread spectrum QPSK signal is transmitted from the transmitter portion.
The structure of the receiver is not shown. When a spread spectrum multisignal is received, it is divided into components I and Q, and both components of data are demodulated by correlation calculation of the received signal with the same PN code as was used on the transmission side. The data encoded by an inverted PN code causes a negative correlative output, and the data encoded by a noninverted PN code causes a positive correlative output.
SUMMARY OF THE INVENTION
Although a conventional spread spectrum communication system has confidentiality and high efficiency of frequency and is also robust against noise, data transmission capacity is small because an entire cycle of PN code is used to encode each bit of data to be transmitted. Also, the utility efficiency of a frequency is low because the frequency band of transmission is extremely wide due to the spreading of the spectrum.
The object of the present invention is to provide a spread spectrum communication system that improves both the data transmission capacity and the communication speed.
A spread spectrum communication system according to the present invention expresses the data to be sent by the phase difference between the first and the second components.
The present invention transmits the first PN code sequence itself as the first component, transmits an integrated signal of zero or more instances of the second PN code sequence with phase differences as the second component, and defines an information for transmittal by the number of instances of the second PN code corresponding to a cycle of the first PN code sequence.
A spread spectrum communication system according to the present invention performs as follows in order to achieve the above object.
In a spread spectrum communication system for transmitting data by multiplexing a first PN code sequence with a second PN code sequence having the same cycle as the first one, the second PN code sequence is generated by adding the predetermined number of basic PN code sequences shifted in phase, and a transmission information is defined by combinations of the predetermined number of basic PN code sequences for a reference phase of the first PN code sequence.
Also, in a spread spectrum communication system as above, a polarity of the first PN code sequence is controlled according to a predetermined bit of an information to be transmitted.
Further, a polarity of each basic PN code sequence of the second PN code sequence is determined according to a plurality of predetermined bits of information to be transmitted.
Furthermore, the first and the second PN code sequences are generated by a single PN code generating means.
Moreover, each of the first and second PN code sequences are transmitted by carrier waves different from each other.
In the spread spectrum communication system with two components according to the present invention, the first component consists of the first PN code sequence and the second component consists of an addition of a plurality of PN code sequences shifted in phase. An information is defined by shifted phases of the PN code sequences of the second component in comparison with the first component.
With these methods, it is possible to improve the capacity and speed of the data transmission.
Hereinafter an embodiment of the present invention using QPSK modulation is described with reference to the attached drawings.


REFERENCES:
patent: 5063571 (1991-11-01), Vancraeynest
patent: 5144641 (1992-09-01), Akazawa et al.
patent: 5291515 (1994-03-01), Uchida et al.
patent: 5530697 (1996-06-01), Watanable
patent: 5559828 (1996-09-01), Armstrong et al.
patent: 5583884 (1996-12-01), Maruyama et al.
Sasaki et al, “Performance of Differential Parallel Combinatory Spread Spectrum Communication Systems,” Electronics and Communications in Japan, Part 1, vol. 78, No. 10, 1995, pp. 73-84.

Affiliated with

Also associated with

Rating

Spread spectrum communication system does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Spread spectrum communication system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spread spectrum communication system will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2488798