WO2015115704A1

WO2015115704A1 - Transmission device and method, and reception device and method in optical wireless communication system

Info

Publication number: WO2015115704A1
Application number: PCT/KR2014/005065
Authority: WO
Inventors: 황승훈; 이정호; 정암
Original assignee: 동국대학교 산학협력단
Priority date: 2014-02-03
Filing date: 2014-06-10
Publication date: 2015-08-06
Also published as: KR101509212B1

Abstract

A transmission device, according to one embodiment of the present invention, comprises: a plurality of modulators for generating modulation signals by modulating source signals; a mapper for transmitting a source signal, indicating a symbol mapped to a bitstream, to a modulator corresponding to a subcarrier index mapped to the bitstream among the plurality of modulators, by referring to a mapping table; a bias unit for applying a DC bias such that a modulation signal has a positive value; and an optical transmitter for outputting an optical signal according to the modulation signal having a positive value.

Description

Transmission apparatus and method, reception apparatus and reception method of optical wireless communication system

The present invention relates to a data transmission technology, and more particularly, to a technology for transmitting data in an optical wireless communication system.

Optical wireless communication is a communication method using light in free space, and it has the advantage of enabling high speed data transmission of Gbps level using license free spectrum band, low development cost and easy and quick installation. The optical wireless communication system transmits the intensity modulated signal to the light source according to the instantaneous power of the electrical signal from the transmitting device, and recovers the electrical signal using the current generated by the photodetector at the receiving device. Direct Detection) is used. In particular, the SIM (Subcarrier Intensity Modulation) of the IM / DD technique is an IM technique having a high cost efficiency in using the bandwidth in analog optical communication has the advantage that low bandwidth is required.

In the conventional SIM, as the number of subcarriers used increases, the average transmission power increases because the DC bias required to make the combined signal positive is increased. In general, optical wireless communication systems have a limited average transmission power so as not to harm the human body. This limits the number of subcarriers that can be used with a limited average transmit power.

Accordingly, an object of the present invention is to provide an optical wireless communication system for modulating and transmitting a signal using multiple subcarriers through spatial modulation.

According to one aspect of the invention, a plurality of modulators for generating a modulated signal by modulating the source signal; A mapper for transmitting the source signal representing a symbol mapped to the bit string to a modulator corresponding to a subcarrier index mapped to a bit string among the plurality of modulators with reference to a mapping table; And a bias unit for applying a DC bias such that the modulated signal has a positive value; And an optical transmitter for outputting an optical signal according to the modulated signal having a positive value.

Each modulator may generate a modulated signal through a subcarrier of a frequency band different from that of another modulator.

The modulator generates a first signal by modulating a source signal corresponding to a previous transmission interval according to one of an in-phase (I) channel and a quadrature (Q) channel, and generates a source signal representing the symbol by the I ( The modulated signal may be generated by modulating according to another one of an in-phase channel and a quadrature channel, and synthesizing the first signal and the second signal to generate the modulated signal.

The bias unit may receive the modulated signal from any one of the modulators.

The mapping table may be a table for mapping the bit string, the subcarrier index, and the symbol.

According to another aspect of the invention, an optical detector for receiving an optical signal, and converts the optical signal into a modulated signal; A plurality of demodulators for demodulating the modulated signal to generate a demodulated signal; And a detector for outputting a subcarrier index of a demodulator outputting a normal demodulation signal among the demodulation signals and a bit string corresponding to a symbol represented by the formal demodulation signal with reference to a mapping table.

Each demodulator may generate the demodulated signal by demodulating subcarriers of different frequency bands from other demodulators.

The detector may determine the demodulation signal having the highest similarity as the normal demodulation signal by comparing each demodulation signal with a reference signal.

According to another aspect of the present invention, a method for transmitting a signal by a transmitting device, the method comprising: receiving a bit string; Identifying a subcarrier index and a symbol mapped to a bit string among the plurality of modulators by referring to a mapping table; Generating a modulated signal by modulating a source signal representing the symbol through a modulator corresponding to the subcarrier index among a plurality of modulators; Applying a DC bias such that the modulated signal has a positive value; And outputting an optical signal according to the modulated signal having a positive value.

Each of the modulators may be a modulator that generates a modulated signal through subcarriers of different frequency bands from other modulators.

Generating a modulated signal by modulating a source signal representing the symbol through a modulator corresponding to the subcarrier index among the plurality of modulators corresponds to a previous transmission interval through a modulator corresponding to the subcarrier index among the plurality of modulators. Generating a first signal by modulating a source signal according to one of an in-phase (I) channel and a quadrature (Q) channel; Generating a second signal by modulating a source signal representing the symbol according to another one of the in-phase channel and the quadrature channel; And synthesizing the first signal and the second signal to generate the modulated signal.

According to still another aspect of the present invention, there is provided a method of receiving a signal by a receiving device, comprising: receiving an optical signal; Converting the optical signal into a modulated signal; Demodulating the modulated signal through a plurality of demodulators to generate a demodulated signal; And outputting a subcarrier index of a demodulator outputting a normal demodulation signal among the demodulation signals and a bit string corresponding to a symbol represented by the formal demodulation signal with reference to a mapping table.

Each demodulator may be a demodulator for generating the demodulated signal by demodulating subcarriers of different frequency bands from other demodulators.

The step of outputting a subcarrier index of a demodulator outputting a normal demodulation signal among the demodulation signals and a bit string corresponding to a symbol represented by the formal demodulation signal with reference to the mapping table may include comparing the demodulation signal with a reference signal for similarity. Determining a highest demodulation signal as the normal demodulation signal; And a subcarrier index of the demodulator outputting the normal demodulation signal and a bit string corresponding to a symbol indicated by the formal demodulation signal with reference to the mapping table.

As described above, according to the present invention, by using only one subcarrier of a plurality of subcarriers for signal transmission, data can be transmitted at high speed without increasing DC bias.

1 illustrates an optical wireless communication system in accordance with an embodiment of the present invention.

2 is a diagram illustrating a transmitting device according to an embodiment of the present invention.

3 is a diagram illustrating a mapping table used by a transmitting apparatus according to an embodiment of the present invention.

4 is a block diagram illustrating a receiving apparatus according to an embodiment of the present invention.

5 is a diagram illustrating an example of a frequency band allocated to a modulator and a demodulator included in a transmitter and a receiver according to an embodiment of the present invention.

6 is a diagram illustrating another example of a frequency band allocated to a modulator and a demodulator included in a transmitter and a receiver according to an embodiment of the present invention.

7 is a flowchart illustrating a process of transmitting a signal by a transmitting device according to an embodiment of the present invention.

8 is a flowchart illustrating a process of receiving a signal by a receiving device according to an embodiment of the present invention.

9 is a constellation diagram for obtaining time diversity at the same transmission rate as BPSK when QPSK is applied to a modulator of a transmission apparatus according to an embodiment of the present invention.

The present invention may be variously modified and have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail with reference to the accompanying drawings. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Also, in the present specification, when one component is referred to as "transmitting a signal" to another component, the one component may be directly connected to the other component to transmit a signal, but there is a specially opposite description. It is to be understood that unless otherwise, the signal may be transmitted in the intermediary with another component.

1 is a diagram illustrating an optical wireless communication system according to an embodiment of the present invention.

Referring to FIG. 1, an optical wireless communication system according to an embodiment of the present invention includes a transmitting device 110 and a receiving device 120.

The transmitting device 110 receives a bit stream from another device to which the transmission device 110 is connected, generates a modulated signal by modulating the bit string, and receives an optical signal obtained by modulating the intensity according to the instantaneous power of the modulated signal. Make a call to device 120. In this case, the transmitting apparatus generates a modulated signal including a plurality of subcarriers using a mapping table corresponding to the number of subcarriers used for modulation. 2, the modulation signal generation process using the mapping table will be described in detail.

The receiving device 120 receives an optical signal from the transmitting device 110, converts the received optical signal into an electrical signal including a plurality of subcarriers, demodulates each subcarrier, and extracts a symbol string by referring to a mapping table. Convert to A demodulation process of the reception device 120 will be described in detail later with reference to FIG. 4.

2 is a diagram illustrating a transmitting apparatus according to an embodiment of the present invention, and FIG. 3 is a diagram illustrating a mapping table used by a transmitting apparatus according to an embodiment of the present invention.

Referring to FIG. 2, the transmitting device 110 includes a mapper 210, a first modulator 220, a second modulator 230, a third modulator 240 and a fourth modulator 250, and a DC bias 260. And an optical transmitter 270. In this case, in FIG. 2, the modulation is performed using four modulators, but the number of modulators may be changed according to an implementation method.

The mapper 210 receives a bit string from another device, and transmits a source signal indicating a bit to be modulated to one of the first modulator 220 to the fourth modulator 250 with reference to the mapping table. That is, the mapper 210 divides the bit stream into subcarrier subblocks and symbol subblocks, determines a subcarrier to transmit the corresponding bit stream according to bits of the subcarrier subblock, and selects a source signal to be modulated according to the bits of the symbol subblock. Decide The mapper 210 transmits a source signal determined according to the symbol subblock to a modulator corresponding to the subcarrier determined according to the subcarrier subblock. In this case, the number of bits included in the subcarrier subblock and the number of bits included in the symbol subblock may be specified in advance. That is, the number of bits included in the subcarrier subblock is log ₂ (the number of modulators), and the number of bits included in the symbol subblock may be preset according to a modulation scheme performed by each modulator (for example, BPSK 1 bit, QPSK is 2 bits, etc.)

For example, with reference to FIG. 3, when the number of each modulator is four, each modulator uses the BPSK modulation scheme, and the mapper 210 receives the bit string "000", the mapper 210 is set to "000". The first bit and the second bit "00" may be set as a subcarrier subblock, and the third bit "0" may be set as a symbol subblock. The mapper 210 determines that the subcarrier index matching "00" of the subcarrier subblock is "1" with reference to the mapping table. Also, the mapper 210 refers to the mapping table and checks that the symbol matching “0” of the symbol subblock is “-1”. Thereafter, the mapper 210 transmits the source signal according to the symbol "-1" to the first modulator 220 corresponding to the subcarrier index "1". In this case, it is assumed that the

subcarrier indexes

1, 2, 3, and 4 correspond to the first modulator 220, the second modulator 230, the third modulator 240, and the fourth modulator 250, respectively.

For another example, when receiving the bit string "011", the mapper 210 sets the first bit of "011" and the second bit "01" as a subcarrier subblock, and the third bit "1". "Can be set as a symbol subblock. The mapper 210 determines that the subcarrier index matching "01" of the subcarrier subblock is "2" with reference to the mapping table. In addition, the mapper 210 refers to the mapping table and confirms that the symbol matching "1" in the symbol subblock is "1". Thereafter, the mapper 210 transmits the source signal according to the symbol "1" to the second modulator 230 corresponding to the subcarrier index "2".

As described above, the mapper 210 conceptually sets a modulator to modulate a symbol and a symbol to be modulated according to each subblock of each bit string. However, in an actual implementation method, the mapper 210 modulates a symbol according to the subcarrier index and the symbol matched to the input bit stream using a matching table that matches the bit string and the subcarrier index and the symbol corresponding to each bit string as shown in FIG. 3. A modulator may be determined and a process of transmitting a source signal according to a symbol to a corresponding modulator may be performed, and a conceptual process such as dividing a sub block may not be performed.

The first modulator 220 to the fourth modulator 250 generate a subcarrier by modulating the source signal. In this case, the first modulator 220 to the fourth modulator 250 generate subcarriers of different frequency bands. This will be described in detail later with reference to FIGS. 5 and 6.

The bias unit 260 applies a DC bias to the modulation signal generated by one of the first modulator 220 to the fourth modulator 250 so that the corresponding signal is all positive. The bias unit 260 transmits the modulated signal converted into a positive value to the optical transmitter 270.

The optical transmitter 270 transmits an optical signal whose intensity is modulated according to the instantaneous power of the modulated signal received from the bias unit 260.

Therefore, the transmitting device 110 according to an embodiment of the present invention can transmit data at high speed without increasing the DC bias by using only one subcarrier of a plurality of subcarriers for signal transmission.

Referring to FIG. 4, the receiver 120 according to an exemplary embodiment of the present invention may include a photo detector 410, a first demodulator 420, a second demodulator 430, a third demodulator 440, and a fourth demodulator. 450 and detector 460.

The photo detector 410 receives an optical signal transmitted from the transmitting device 110, converts the optical signal into a modulated signal that is an electrical signal, and transmits the modulated signal to the first demodulator 420 to the fourth demodulator 450. do.

The first demodulator 420 to the fourth demodulator 450 generate demodulated signals from the modulated signal through a bandpass filter (BPF) and RF synchronization detection. In this case, the first demodulator 420 to the fourth demodulator 450 are demodulators that generate demodulated signals for modulated signals corresponding to four preset frequency bands. Therefore, only one of each modulator is a demodulation signal in a normal form, and the rest outputs a demodulation signal in an abnormal form. That is, the modulated signal is a signal corresponding to any one of four frequency bands, and may be converted into a demodulated signal having a normal form by passing through one BPF of each demodulator.

The detector 460 receives a demodulation signal from the first demodulator 420 to the fourth demodulator 450. The detector 460 detects a demodulation signal of a normal form (hereinafter, referred to as a normal demodulation signal) among demodulation signals received from each demodulator. For example, the detector 460 may detect a demodulation signal having the highest coherence between the reference signal received separately from the demodulation signal and each demodulation signal as a normal demodulation signal. The detector 460 refers to a mapping table and outputs a bit string mapped to a subcarrier index of a demodulator that outputs a demodulated signal of a normal form and a symbol represented by the normal demodulated signal.

The modulator and demodulator of the transmitter 110 and the receiver 120 described above with reference to FIGS. 1 to 4 generate or demodulate a subcarrier of a preset frequency band.

Hereinafter, the setting form of the frequency band of each modulator will be described in detail.

5 is a diagram illustrating an example of a frequency band allocated to a modulator and a demodulator included in a transmitter and a receiver according to an embodiment of the present invention, and FIG. 6 is a transmitter and a receiver according to an embodiment of the present invention. FIG. Is a diagram illustrating another example of a frequency band allocated to a modulator and a demodulator included in a receiver.

Referring to FIG. 5, f ₁ to f _n are frequency bands of subcarriers assigned to each modulator and demodulator. That is, f ₁ is a frequency band allocated to the first modulator and the demodulator, and f _n is a frequency band allocated to the nth modulator and demodulator. In this case, a guard band, which is a frequency band not allocated to any modulator or demodulator, may be located between each frequency band.

In addition, according to an implementation method, each frequency band may be set to be orthogonal to neighboring frequency bands as shown in FIG. 6.

Accordingly, the transmission device 110 and the reception device 120 according to an embodiment of the present invention can reduce the possibility of an error occurring in the modulation and demodulation process even if continuous transmission of the bit string occurs.

Referring to FIG. 7, in operation 710, the transmitting apparatus receives a bit string from another device.

In operation 720, the transmitting apparatus identifies a subcarrier index and a symbol mapped to a bit string by referring to a mapping table.

In operation 730, the transmitting apparatus modulates the source signal according to the symbol into a modulated signal which is a subcarrier of a frequency band corresponding to a subcarrier index among predetermined subcarriers.

In step 740, the transmitting device applies a DC bias to the modulated signal to convert the modulated signal to a positive value.

In operation 750, the transmitting device transmits an optical signal whose intensity is modulated according to the instantaneous power of the modulated signal.

In step 810, the receiving device receives an optical signal from the transmitting device.

In operation 820, the receiving apparatus converts the optical signal into a modulated signal that is an electrical signal.

In operation 830, the receiving apparatus demodulates the modulated signal through a plurality of demodulators to generate a demodulated signal. At this time, each demodulator is a demodulator designed to modulate subcarriers in a different frequency domain than other demodulators.

In operation 840, the receiving apparatus checks a normal demodulated signal among demodulated signals demodulated through each demodulator. For example, the receiver may detect a demodulation signal having the highest coherence between the reference signal and the demodulation signal input separately from the demodulation signal of each demodulator as a normal demodulation signal.

In operation 850, the receiving apparatus outputs a bit string mapped to a symbol represented by the subcarrier index and the normal demodulation signal corresponding to the demodulator outputting the normal demodulation signal with reference to the mapping table.

Referring to FIG. 9, when a modulator of a transmitting device defines a time interval in which a single source signal is transmitted among consecutively received source signals as a transmission interval, a previous transmission interval for transmitting a bit according to the source signal in the current transmission interval Use bits according to the source signal of. That is, the modulator modulates the source signal of the current transmission interval according to the Q (Quadrature) axis, modulates the source signal of the previous transmission interval according to the I (Inphase) axis, and combines the two signals to generate a modulated signal. In this case, the mapper 210 of the transmitting device may separately transmit the source signal of the previous section when transmitting the source signal of the current transmission section to one of the modulators.

For example, each modulator of the transmitting device applies a QPSK in the first transmission period T1 to modulate the source signal representing the first bit d1 along the I (Inphase) axis and the source signal representing the second bit d2 to Q ( Quadrature) generates a modulated signal obtained by combining two signals modulated on each axis and modulated according to each axis. In this case, the transmitted signal may correspond to one of four signal points on the QPSK signal constellation according to the bits of d1 and d2. Next, the modulator transmits the modulated signal by performing QPSK modulation on the source signal according to bit d2 transmitted in the transmission period T1 together with the bit d3 to transmit bit d3 in the second transmission period T2. That is, the modulator modulates the source signal corresponding to bit d2 of the previous transmission interval along the I axis, modulates the source signal according to the newly transmitted bit d3 along the Q axis, and combines the two signals to generate a modulated signal. The modulator similarly modulates the source signal according to bit d3 transmitted from T2 along the I axis and modulates the source signal according to the new bit d4 along the Q axis in the third transmission section T3 to generate a modulated signal. . The signal transmitted in each transmission section is a signal in which two bits are modulated, but one of the two bits has already been transmitted in the previous transmission section. There is no difference in transmission speed. However, by transmitting the same bit in different transmission intervals, a diversity effect can be obtained in a receiving device in time.

So far I looked at the center of the embodiment for the present invention. Many embodiments other than the above-described embodiments are within the claims of the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

Claims

A plurality of modulators for generating a modulated signal by modulating the source signal;

A mapper for transmitting the source signal representing a symbol mapped to the bit string to a modulator corresponding to a subcarrier index mapped to a bit string among the plurality of modulators with reference to a mapping table; And

A bias unit for applying a DC bias such that the modulated signal has a positive value; And

An optical transmitter for outputting an optical signal according to the modulated signal having a positive value

Transmission device comprising a.
According to claim 1,

And each modulator generates a modulated signal through a subcarrier of a different frequency band from another modulator.
The method of claim 2,

And the bias unit receives the modulated signal from any one of the modulators.
The method of claim 2,

The modulator,

Generating a first signal by modulating a source signal corresponding to a previous transmission interval according to one of an in-phase (I) channel and a quadrature (Q) channel,

Generating a second signal by modulating a source signal representing the symbol according to another one of the in-phase (I) channel and the quadrature (Q) channel,

Generating the modulated signal by combining the first signal and the second signal

A transmitting device, characterized in that.
According to claim 1,

And the mapping table is a table for mapping the bit string, subcarrier index, and symbol.
An optical detector for receiving an optical signal and converting the optical signal into a modulated signal;

A plurality of demodulators for demodulating the modulated signal to generate a demodulated signal; And

A detector for outputting a subcarrier index of a demodulator outputting a normal demodulation signal among the demodulation signals and a bit string corresponding to a symbol represented by the formal demodulation signal with reference to a mapping table;

Receiving device comprising a.
The method of claim 6,

Each demodulator demodulates subcarriers of different frequency bands from other demodulators to generate the demodulated signal.
The method of claim 6,

And the mapping table is a table for mapping the bit string, the subcarrier index, and the symbol.
The method of claim 6,

And the detector compares each demodulation signal with a reference signal to determine a demodulation signal having the highest similarity as the normal demodulation signal.
In the method for transmitting a signal,

Receiving a bit string;

Identifying a subcarrier index and a symbol mapped to a bit string among the plurality of modulators by referring to a mapping table;

Generating a modulated signal by modulating a source signal representing the symbol through a modulator corresponding to the subcarrier index among a plurality of modulators;

Applying a DC bias such that the modulated signal has a positive value; And

Outputting an optical signal according to the modulated signal having a positive value;

Transmission method comprising a.
The method of claim 10,

And each modulator is a modulator for generating a modulated signal through subcarriers of different frequency bands from other modulators.
The method of claim 11, wherein

Generating a modulated signal by modulating a source signal representing the symbol through a modulator corresponding to the subcarrier index of the plurality of modulators,

Generating a first signal by modulating a source signal corresponding to a previous transmission interval according to any one of an in-phase (I) channel and a quadrature (Q) channel through a modulator corresponding to the subcarrier index among the plurality of modulators ;

Generating a second signal by modulating a source signal representing the symbol according to another one of the in-phase channel and the quadrature channel; And

Synthesizing the first signal and the second signal to generate the modulated signal;

Transmission method comprising a.
The method of claim 10,

And the mapping table is a table for mapping the bit string, subcarrier index, and symbol.
In the method for receiving a signal,

Receiving an optical signal;

Converting the optical signal into a modulated signal;

Demodulating the modulated signal through a plurality of demodulators to generate a demodulated signal; And

Outputting a subcarrier index of a demodulator outputting a normal demodulation signal among the demodulation signals and a bit string corresponding to a symbol represented by the formal demodulation signal with reference to a mapping table;

Receiving method comprising a.
The method of claim 14,

Each demodulator is a demodulator for generating the demodulated signal by demodulating subcarriers of different frequency bands from other demodulators.
The method of claim 14,

And the mapping table is a table for mapping the bit string, subcarrier index, and symbol.
The method of claim 15,

The method may further include outputting a subcarrier index of a demodulator outputting a normal demodulation signal and a bit string corresponding to a symbol represented by the formal demodulation signal with reference to the mapping table.

Comparing each demodulation signal with a reference signal to determine a demodulation signal having the highest similarity as the normal demodulation signal; And

Referring to the mapping table, outputting a subcarrier index of the demodulator outputting the normal demodulation signal and a bit string corresponding to a symbol represented by the formal demodulation signal;

Receiving method comprising a.