Development of Standard Time and Frequency Service using Low Frequency in Korea

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1 Development of Standard Time and Frequency Service using Low Frequency in Korea Center for Time & Frequency Y.K. Lee, D.H. Yu, S.H. Yang, J.K. Lee, S.W. Hwang

2 Contents Introductions LF applications, research goals of Korea LF station, concept of transmission station, current status Study of modulation scheme Modulator and receiver structure, considered code parameters Design of modulator and receiver Simulation scheme, modulator & receiver functions, channel simulator concept

3 LF Applications Low-frequency (LF) signals Frequency band: 30 to 300 khz Propagation: grand wave + sky wave Usage: mainly for standard time and frequency dissemination Existing stations WWVB(USA, 60 khz), JJY(Japan, 40 & 60 khz), DCF77(Germany, 77.5 khz)

4 Korea LF Station Broadcast of Standard Time & Frequency using LF signals What?: Korea Standard Time & Frequency with supplementary information Frequency?: around 65 khz Frequency stability below & timing accuracy under 1 µs Construction of LF test bed station (2015~2019) 500 km Reference station Transmitting station Synchronization with UTC(KRIS)

5 Configuration of the LF Services

Research Goals Phase 1 ( 15~ 19) Phase 2( 20?

design Infra structure implementation Timing system evaluation

station site selection LF system establishment LF broadcasting

6 Research Goals Phase 1 ( 15~ 19) Phase 2( 20?~) Detailed system design Core module implementation Test-bed design Infra structure implementation Timing system evaluation Monitor system implementation LF station design Transmission station site selection LF system establishment LF broadcasting service Implementation of test-bed system Development of application fields Acquirement of next phase budget

7 Concept of Transmission Station Basic design scheme Korea Standard Time

8 First Test Bed Place Monitor St. Test Bed Control St. Verification (Mobile Rx.)

9 Expected Test Bed Place Middle-wave broadcast station place (not yet fixed) Rent about 3 years Antenna height: 132 m Antenna radius: under 110 m

10 Design of Test Bed Antenna Antenna type: umbrella Antenna angle: about 40 degrees Antenna shape Polarization: isotropic TLE length: about 66 m Number of TLE: about 16 Vertical characteristics Horizontal characteristics

11 Current Status Basic specifications (not yet fixed) Carrier frequency: around 65 khz Bandwidth: below 2 khz Power: above 50 kw Data rate: below 200 bps Modulation: BPSK + PN Data format: time code + supplementary information Antenna type: umbrella Modulator and receivers are under developing LF transmitters are ready to contract

12 Study of Modulation Scheme

13 Modulation Method Binary phase shift keying (BPSK) with preamble Chip Rate : 1 khz Effective BW : 1 khz (null-to-null BW of 2 KHz) Preamble (PN sequence) Code Length : 80 chip (80 ms) Data BPSK with spreading Symbol Rate : 100 bps Spreading Code : PN sequence (Processing Gain : 10) Timing boundary preamble BPSK signal with spreading Preamble interval

14 Modulator Structure BSPK with preamble, CRC & PRN Time Code Preamble Time Code Generation CRC Generation Bit Spreading Block Repetition Block Scrambling Spread Code Block MUX BPSK Modulation Added Data Generation CRC Generation Add Tail Bit Convolutional Code Encoding Bit Spreading Block Repetition Block Scrambling Added Data Preamble Example of preamble G = x^7+x^

15 Receiver Structure Receiver structure Rx signal cos 2πf c t sin 2πf c t LPF LPF t=nt c /8 Preamble detector Despreader and BPSK demodulator Demodulated data Preamble detector In-phase samples quadrature samples Preamble code correlator Preamble code correlator ( ) 2 ( ) 2 Peak detector Peak position Complex correlation peak position - Calculations in preamble code correlator - accumulating the samples according to the sign of the replica code - # of calculation : (Preamble code length * 2) additions / sample - sample rate : 8 k-samples/sec (for 1 k-cps and 8 times oversampling)

16 Considered Code Parameters

17 Design of Basic Time Code Just simple example code

18 Design of Modulator & Receiver

19 Overall Simulation Scheme Modulation part Flexible design to accommodate various modulation methods like AM, PSK, FSK etc. Receiver part Various performance evaluation functions as well as display of time and additional information Channel simulator part Specialized channel modeling to the LF signal characteristics Channel simulator 10MHz Modulator 1 PPS Time code GPS generator Additional information generator Low power transmitter Test Bed Fading Interference Electric noise. Control unit Time display Receiver Rx information Additional information display

Data BPSK with spreading Symbol Rate : 100 bps Spreading Code : PN sequence (Processing Gain : 10)

20 Signal Generator Units Binary phase shift keying (BPSK) with preamble LF System Chip Rate : 1 khz Effective BW : 1 khz (null-to-null BW of 2 KHz) Preamble (PN sequence) Code Length : 80 chip (80 ms) Data BPSK with spreading Symbol Rate : 100 bps Spreading Code : PN sequence (Processing Gain : 10) Modulator Switching system Manual switch Optical switch Ethernet switch xdsl to Ethernet AC-DC Power supply

21 Modulator Functions Main functions Time code generation Synchronization of time and frequency Modulation of time and additional information data Double switching system Time sync. Timing input Delay control resolution Double switching Output timing accuracy : < 50 ns Cesium Reference : 10 MHz, 1 PPS 2 ns Using 3 signal generators

22 Modulator Block Diagram Set Logic-Low Code pattern Logic Low Code Pattern Buffer AM Constant ON/OFF AM Value Carrier frequency: 50 ~ 100 khz with 100 Hz resolution FM: 100 Hz resolution PM: 1 degree resolution AM: 1 % modulation index resolution Bit Input Set Code Rate SYS CLK 1PPS Set Logic-High Code pattern Code TX FIFO Code TX Shift Reg. Code Baud Rate Generator Code TX Shift Reg. Code TX FIFO Logic High Code Pattern Buffer 0 MUX 1 Code AM 0 Value AM 1 Value PM 0 Value PM 1 Value FM 0 Value FM 1 Value MUX MUX MUX Constant PM Value Constant FM Value MUX PM ON/OFF MUX FM ON/OFF MUX adder Integer Fraction Lookup Table adder DAC AMP & Filter SYS CLK 1PPS SYS CLK 1PPS SYS CLK 1PPS

Receiver Functions Main functions LF signal demodulation Display of time and additional information data Received signal monitoring NTP server function LF signal input GNSS, Cesium Ref.

23 Receiver Functions Main functions LF signal demodulation Display of time and additional information data Received signal monitoring NTP server function LF signal input GNSS, Cesium Ref. input Output signals Time/additional information display Channel number: 2 Receiving frequency band: 50 khz ~ 100 khz GNSS signals External reference: 10 MHz and 1PPS Synchronized 10 MHz and 1PPS signals Digitally demodulated signals Basic: just time information Complicated: time + additional information

24 Receiver Block Diagram GPS Signal GPS Receiver 1PPS Time 시각 Comp. 비교 1PPS 시각정보 Time Code NTP NTP Sever 서버 Ethernet SW : 신호처리 & FFT Signal Processing, 제어 Filtering & 필터설정 & Control & 디모듈레이터제어등필터설정신호처러 & 추적 Time 시각 Signal 신호생성 Generation 회로 & 로직 &S/W D/A, PLL, VCO, OCXO, DDS 1PPS 10MHz SYSCLK 100Hz, 10Hz, etc. E.Field/ H.Field Ch.A H.Field Ch.B Dual CH. A/D Data FIFO Filter AM/PM/FM Demodulation Circuit & Logic Demodulated Data Data 데이터 Analysis 해석 S/W & 로직 시각정보 Time & 부가정보 Information data SYS CLK 1PPS ETC. SYS CLK 1PPS ETC. SYS CLK 1PPS ETC. SYS CLK 1PPS ETC. SYS CLK 1PPS ETC.

25 Channel Simulator Main functions LF channel simulation LF signal receiving Received signal logging Delay variation function Antenna

26 Channel Simulation <LF signal generator> <Channel simulator> Transmitting data set up Transmitting frequency, code rate set up Modulation scheme set up Transmitting signals Channel simulation Transmitting code/data Simulated signals <Receiver> Received data verification BER test results evaluation SNR & noise analysis

27 표준이올라가면생활이즐거워집니다! Thanks for your attention!

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