Patent Application
20090016309
The present invention relates to an ultra wide band communication system; and more particularly, to a communication apparatus and method that can be used in a sensor network or a low-rate wireless Personal Area Network, and a method thereof.
Conventional modulation and demodulation methods for ultra wide band impulse communication are as follows:
First, the PPM/BPPM, a method used and studied for a long time, changes the position of a basic pulse according to 0 or 1. According to the PPM/BPPM where modulation is performed through temporal offset, a signal arriving earlier than a reference time can be determined as ‘0’ and a signal after the arrival of the signal 0 is determined as ‘1.’ A method using an M-ary orthogonal signal can be applied to the PPM ultra wide band modulation/demodulation method to improve a transmission rate and a signal-to-noise ratio. The BPPM method uses one-digit binary data for pulse phase modulation when the M-ary method is used. In case where a binary data signal is transmitted, the BPPM method becomes the same as the BPSK modulation method. As it can be seen from the above description, it is possible to transmit data twice as much as the conventional PPM and to extend a time period occupied by one pulse because a binary datum is transmitted on a phase basis.
Secondly, the PAM method displays information by changing an output. In 8-ary PAM, three-digit binary data are transmitted by using amplitudes in 8 steps. A special form of the PAM is the OOK method in which ‘1’ is transmitted when there is a pulse and ‘0’ when there is no pulse. The BPSK method displays ‘0’ and ‘1’ according to the phase of a signal. The BPSK is advantages over the PPM in the signal-to-noise ratio by 3 dB; in a transmission capacity by two-folds; and in the time period occupied by a pulse by two-folds. However, in the presence of multipath, there is a problem that the phase is changed. The QPSK is a form extended from the BPSK. Whereas the BPSK identifies a signal with ‘0’ or ‘1,’ the QPSK identifies a signal with two-digit binary data, e.g., ‘00,’ ‘01,’ ‘10’ and ‘11.’ Since the QPSK method transmits two-digit binary data with one waveform, it can transmit data twice as much as the BPSK can.
The DSC method which adopts the Direct Sequence-Code Division Multiple Access (DS-CDMA) without any change has advantages that it can prevent the generation of noise excellently and data from being intercepted in the course.
However, the above-described conventional modulation technologies for realizing ultra wide band impulse communication has shortcoming that they can hardly applied to multipath channels and that they have a limitation in data transmission rates.
It is, therefore, an object of the present invention, which is devised to resolve the problems of the conventional technologies, to provide a communication apparatus and method that can be applied to multipath channels and provide excellent data transmission rates.
It is another object of the present invention to provide a communication apparatus and method whose performance is improved by enhancing error correction ability for correcting errors caused by encoding in a transmitter and a receiver of a communication system.
It is another object of the present invention to provide a communication apparatus and method that can extend a time period used to transmit a pulse by improving link capacity higher than that of conventional technologies, when the same data are to be transmitted in the same time period.
In accordance with one aspect of the present invention, there is provided a transmitter employing multi-coded bi-orthogonal pulse position modulation in an ultra wide band impulse communication apparatus, which includes: a serial-to-parallel converter for converting L-bit serial data to be transmitted into parallel data by performing grouping on the L-bit serial data; a multi-coder for generating a multi-coded symbol by multiplying the parallel data by total L orthogonal codes of length Ns; a bi-orthogonal pulse position modulator for positioning the multi-coded symbol in a predetermined pulse period and performing bi-orthogonal pulse position modulation; and a pulse generator for multiplying an output signal of the bi-orthogonal pulse position modulator by a predetermined pulse and outputting an output signal.
In accordance with one aspect of the present invention, there is provided a modulation method of an ultra wide band impulse communication apparatus, which includes the steps of: a) converting L-bit serial data to be transmitted into parallel data by performing grouping on the L-bit serial data; b) generating a multi-coded symbol by multiplying the parallel data by total L orthogonal codes of length Ns; and c) performing bi-orthogonal pulse position modulation based on symmetrical characteristics of elements of the multi-coded symbol to thereby produce a bi-orthogonal pulse position-modulated signal.
The present invention relates to a communication system that performs ultra wide band impulse communication, for example, it provides a communication apparatus and method that can be used in a sensor network or a low-rate wireless Personal Area Network. Particularly, the present invention provides a multi-coded bi-orthogonal pulse position modulation/demodulation method in a communication system performing ultra wide band impulse communication, and a communication apparatus and method employing the same.
The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:
Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter. When it is considered that detailed description on prior art may blur the points of the present invention, the description will not be provided herein. Hereinafter, preferred embodiments of the present invention will be described in detail.
To resolve the problems of conventional technologies, the present invention supports coding gain acquisition and diverse transmission rates based on multi-coded bi-orthogonal pulse position modulation and, at the same time, extends a time period occupied by a transmitting pulse. With the technology suggested the present invention, inter-pulse interference caused in an indoor environment due to multipath is reduced, and performance degradation caused in a receiver by interference between pulses can be prevented.
Hereinafter, the technology of the present invention will be described in detail with reference to the accompanying drawings.
Tm: Time period of a pulse
L: The number of bits of data to be transmitted in each data block
Tc: Time period of a multi-coded chip
Ns: Length of a orthogonal multi-code
Ts: Time period of a multi-coded symbol
Referring to
In short, the multi-coded symbols are as follows:
d1=b1c1,1+b2c2,1 . . . +bLcL,1
dNs=b1c1,Ns+b2c2,Ns . . . +bLcL,Ns
Herein, each element of a multi-coded symbol 110 has a value in the range of −L, −L+2, . . . , −1, . . . , +1, L−2, L.
Subsequently, the multi-coded symbols 110 are modulated and transmitted based on the bi-orthogonal pulse position modulation 115. Since the elements of the multi-coded symbol have symmetrical characteristics, the bi-orthogonal pulse position modulation is performed based on the symmetrical characteristics. Herein, (L+1)/2 pulse position periods are needed to perform bi-orthogonal pulse position modulation on the values of the elements in the multi-coded symbol 110. When the value of an element is −L, the pulse is positioned in the first pulse position period. Likewise, when the value of an element is −L+2, the pulse is positioned in the second pulse position period and −L+4, in the third pulse position period; and L, in the (L+1)/2_th pulse position period. As shown above, the multi-coded symbol 110 having a length of Ns is modulated and transmitted in the bi-orthogonal pulse position modulation 115.
Although the present invention takes an embodiment where the L value is an odd number, it can be applied to a case when the L value is an even number. If any, when the L value is an even number, a total of (L/2)+1 pulse position periods are needed and, when the value of an element is 0, the sign of the pulse can be ignored.
Referring to
As shown in
Referring to
Referring to
Particularly, in the multi-coded bi-orthogonal pulse position modulation method of the present invention, the link capacity increases gradually, as the bit number of data transmitted simultaneously increases (L=1, L=3, L=5). This is different from the conventional M-ary BPPM. The high data transmission rate and the increase in the link capacity can be also understood that a time period used to transmit a pulse can be extended when the same data are transmitted during the same time period.
As above, the modulation method of the present invention can reduce interference caused by multipath to thereby enhance performance by extending the maximum pulse transmission period width. Also, since it does not require an additional interference removal in the receiver, it does not require additional costs for reducing complexity and realizing a circuit, and it does not increase power consumption, either.
While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.
Firstly, the technology of the present invention has an advantage that it can improve performance in a transmitter and a receiver by enhancing error-correction ability based on coding gain. Secondly, it can increase link capacity.
Consequently, the technology of the present invention has an advantage that it can reduce inter-pulse interference caused by multipath which occurs frequently in an indoor environment, which is a major operation environment of the wireless Personal Area Network. Also, it has an advantage that, as described with reference to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2004-0088459 | Nov 2004 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR05/00712 | 3/12/2005 | WO | 00 | 4/30/2007 |
