Apparatus and method for transmitting data in low-frequency band in human body communication system, and the human body communication system

1. An apparatus for transmitting data in a low frequency band in a human body communication system, the apparatus comprising:

a preamble generator for generating a preamble signal;

a header generator for generating packet header information;

a data generator for generating data;

a serial-to-parallel converter for converting the data transferred from the data generator to symbols through a serial-to-parallel conversion;

an orthogonal modulator for mapping the symbols transferred from the serial-to-parallel converter to one of sequences orthogonal to each other;

a multiplexer for time-divisionally selecting signals output from the preamble generator, the header generator, and the orthogonal modulator; and

a frequency shifter for shifting an output of the multiplexer to a particular frequency.

2. The apparatus of claim 1 , further comprising:

a Start Frame Delimiter (SFD) generator for generating an SFD notifying a start point of header information in a transmitted packet including preambles, the SFD, a header, and data; and

a pilot generator for generating a pilot, which enables a synchronization process when data is received.

3. The apparatus of claim 2 , wherein an output rate of each of the sequences is adjusted to the orthogonal modulator, so as to make transmission bands at a final output port coincide with each other, when a packet including the preambles, the SFD, the header, pilots, and the data is transmitted.

4. The apparatus of claim 2 , wherein the preamble from the preamble generator is repeated one or more times and is then transmitted, the SFD from the SFD generator is transmitted, a header generated by the header generator is transmitted, and the data generated by the data generator is then transmitted with pilots inserted in the data at a predetermined period, the pilots being generated by the pilot generator.

5. The apparatus of claim 1 , wherein the frequency shifter shifts the output of the multiplexer to a particular frequency by using a frequency shift sequence.

6. The apparatus of claim 5 , wherein the frequency shift sequence used by the frequency shifter is a sequence including alternately repeating 0s and 1s.

7. The apparatus of claim 1 , wherein a transmission bandwidth of the apparatus is variably controlled by a data rate C, a length 2 L2 of the orthogonal modulator, and N of the serial-to-parallel converter, which is an N:1 serial-to-parallel converter.

8. The apparatus of claim 1 , wherein the frequency shifter sets a central frequency to a multiple of an output rate (C·2 L2 )/N, which is obtained by multiplying the output rate (C·2 L2 )/N by a natural number.

9. A human body communication system for performing a non-contact communication using an electric field around a human body, the human body communication system comprising:

a transmission circuit for transmitting data, which is generated according to a packet format defined by a MAC transmission/reception processor, using a particular frequency;

an electrode for outputting an output from the transmission circuit to an outside;

an Analog Front End (AFE) circuit for receiving a signal from the electrode, amplifying the signal and removing noise from the signal;

a received signal strength measurement unit for measuring a strength of a received signal;

a proximity sensor for outputting a proximity sensor value according to detection of a proximity of a human body;

a multiplexer for selectively outputting signals from the proximity sensor and the received signal strength measurement unit;

a reception circuit for processing signals from the multiplexer and an analog-to-digital converter; and

a Micro Controller Unit (MCU) for determining, by using the RSSI value or a proximity sensor value, whether the electrode is in a non-contact state, and outputting a control signal based on a result of the determination.

10. The human body communication system of claim 9 , wherein the measured strength of the received signal is used as a basis for selection of at least one of a sequential code, a data rate, a spreading factor, a gain, a filter bandwidth, a frequency selection, and a gain control of the Analog Front End (AFE) circuit.

11. The human body communication system of claim 9 , further comprising:

a host interface unit interconnecting the Micro Controller Unit (MCU) and the modem; and

a MAC transmission/reception processor defining a packet format for transmission and reception of data.

12. The human body communication system of claim 9 , wherein the transmission circuit comprises:

a preamble generator for generating a preamble signal;

a header generator for generating packet header information;

a data generator for generating data;

a serial-to-parallel converter for converting the data transferred from the data generator to symbols through a serial-to-parallel conversion;

an orthogonal modulator for mapping the symbols transferred from the serial-to-parallel converter to one of sequences orthogonal to each other;

a multiplexer for time-divisionally selecting signals output from the preamble generator, the header generator, and the orthogonal modulator; and

a frequency shifter for shifting an output of the multiplexer to a particular frequency.

13. The human body communication system of claim 9 , further comprising:

a comparator for comparing a magnitude of a signal from the Analog Front End (AFE) circuit and converting the signal to a digital signal according to the magnitude of the signal,

wherein the received signal strength measurement unit measures a strength of a signal from the comparator.

14. The human body communication system of claim 9 , further comprising:

an analog-to-digital converter for converting a signal from the Analog Front End (AFE) circuit to a digital signal according to a magnitude of the signal from the Analog Front End (AFE) circuit,

wherein the received signal strength measurement unit measures a strength of a signal from the analog-to-digital converter.

15. The human body communication system of claim 14 , wherein the received signal strength measurement unit measures the strength of the signal from the analog-to-digital converter and performs an automatic gain control based on the measured strength.

16. A method of transmitting data in a low frequency band in a human body communication system, the method comprising:

generating preamble signals, packet header information, and data;

converting the generated data to symbols through a serial-to-parallel conversion;

mapping the symbols to one of sequences orthogonal to each other;

time-divisionally selecting the preamble signals, the packet header information, and the mapped symbols; and

shifting the selected signals, information, and symbols to a particular frequency.

17. The method of claim 16 , wherein shifting of the selected signals, information, and symbols to the particular frequency uses a frequency shift sequence.

18. The method of claim 16 , further comprising:

generating a Start Frame Delimiter (SFD) notifying a start point of header information in a transmitted packet including preambles, the SFD, a header, and data; and

generating a pilot, which enables a synchronization process when data is received.

19. The method of claim 16 , wherein, in shifting of the selected signals, information, and symbols to the particular frequency, a central frequency is set to a multiple of an output rate (C·2 L2 )/N of the orthogonal modulator, which is obtained by multiplying the output rate (C· 2 L2 )/N of the orthogonal modulator by a natural number.