Practical aspects of FHSS-based ISM band wireless telemetry system development

1. Practical aspects of FHSS-based ISM band wireless telemetry system development Valentin Vasilevskiy, PhD Student, OmSTU Student member, IEEE Victor Antropov, R&D Engineer 10th International PhD Workshop on Systems and Control Hluboka, Czech Republic Radioengineering Department, Omsk State Technical University, Russia

2. Introduction to centralized wireless telemetry systems (CWTS) Applications: burglar alarms, fire alarms, power utility meters, leak detectors, environmental monitoring, temperature control, etc. Topology: star, consists of a base station and independent numerous telemetry object devices uplink Simplified structure of a wireless telemetry system with a centrally located base station downlink

3. Limitations and advantages of conventional CWTS: • Require license for frequency band usage (costs money/usually suitable for government structures only) • Require high transmitter power to provide good operating distance (15..25 km)(results in big current drain, not for battery powered applications) • Low interference level in a frequency band • High speed transmission is possible (the more bandwidth we have the more bits per second we can transfer) • Two-way operation (high reliability, low response time)

4. Main idea • We can use Industrial, Scientific and Medical (ISM) band for the CWTS operation to eliminate the need of licensing

5. Problems • The maximum transmitter power is limited to 10 dBm (10 mW) • Impossible to compensate multipath fading inherent to single frequency transmission • Impossible to achieve long range with conventional equipment • Very high level of in-band interference • car alarm remote controls • radiocontrolled toys, etc)

6. Conventional analogs in 433 MHz Band • Hundreds of meters operating range (AT86RF211 – Atmel, ASTRX1 – AMI Semiconductor, SRWF-501F433 – Tangray infotech, …) • Up to 5 km operating range (XE1205 – Xemics, RC12x0 – Radiocrafts, СС10xx – Chipcon, …)

7. Example of CWTS ISM band implementation based on conventional devices (Russia, Omsk)

8. Solution • Frequency-Hopping Spread Spectrum (FHSS) • Eliminates multipath fading • Resistance to narrowband interference • Low speed (50 bit/second) • Raises Bit Energy to Noise Level (Eb/No) • One-way system (no downlink) • Use an advantage of proper base station location, highly raised base station receiver high-gain antenna and high selectivity A/DSP.

9. Closest analog LONTA 202, Patent RU2231458, «Radio system of information reception and processing for centralized security system…» • FHSS System • Works in ISM band (433.92 MHz ±0,2%) • Transmitter power up to 10 mW • Operating range up to 20 km (city service)

10. Design considerations • Synchronization • Data rate • Spectrum efficiency • Energy efficiency

11. Synchronization

12. Wideband receiver (LONTA 202) • FFT as a set of narrowband filters

13. Data rate , • Digital communication system error probability is dependent on Eb/N0 ratio: where Eb – bit energy, N0 - noise power spectral density, S – signal power, N – noise power, W – bandwidth, R – data rate.

14. Low data rate raises Eb/N0 ratio • Telemetry systems often do not require high data rate (remote sensing, temperature measurements, burglar alarm system, etc). • LONTA 202 FHSS wireless security system uses 50 bps data rate

15. Spectrum efficiency • The FHSS system performance is strongly dependent on a spectrum efficiency of the signal during one hop. • The less signal bandwidth during a hop the less probability of collisions between different object transmitters. • Shape filters can be used (Gaussian, raised cosine) to reduce signal effective bandwidth. • Low modulation indexes

16. Amplitude-Frequency Modulation (Lonta-202, Patent RU2231458)

17. Energy efficiency • Arbitrary envelope modulation type requires linear amplifiers in transmitters • Constant envelope modulation type allows usage of energy effective D-class nonlinear amplifiers

18. Proposed system • Plurality of transmitters and a wideband quadrature receiver (robust frequency and time synchronization recovery)

19. One channel of the wideband quadrature receiver • Complex mixer • Cascaded Digital Down Converters, Finite Impulse Responce filter (Overall adjacent channel rejection not less than 90 dB) • Simplified Quadrature FM-Discriminator

20. Spectrum and energy efficiency • Gaussian Frequency Shift Keying (GFSK) ____Patent RU2231458 (LONTA-202), Datarate = 50 bps ____Proposed system, Datarate = 50 bps, GFSK BT=0.5, Frequency deviation = 25 Hz

21. Simulation results, BER (Bit Error Rate) dependency on Eb/N0 ratio

22. Conclusions I • The proposed FHSS-based wireless telemetry system provides robust operation in an ISM band with high operating distance. This task was achieved by means of: - choice of spectral effective modulation technique with high level of power efficiency - providing narrowband highly selective level of filtering - providing robust algorithm of demodulation - defining trade-off between baud rate of the system and spectrum width

23. Conclusions II • Advantages of the proposed system: - no frequency or symbol synchronization scheme is needed as long as all possible signal positions are used to recover the message - effective in the ISM band with high level of interference - improved BER compared to closest analogues - increased number of the telemetry objects - FPGA-oriented algorithm

24. Practical aspects of FHSS-based ISM band wireless telemetry system development Valentin Vasilevskiy, PhD Student, OmSTU Student member, IEEE Victor Antropov, R&D Engineer 10th International PhD Workshop on Systems and Control Hluboka, Czech Republic Radioengineering Department, Omsk State Technical University, Russia