1. Practical aspects of FHSS-based ISM band wireless telemetry system development
10th International PhD Workshop on Systems
and Control
Hluboka, Czech Republic
Valentin Vasilevskiy,
PhD Student, OmSTU
Student member, IEEE
Victor Antropov,
R&D Engineer
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 ( 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. International Telecommunication Union ISM bands, Frequency range [Hz]
Main idea
We can use Industrial, Scientific and Medical (ISM) band for the CWTS operation to eliminate the need of licensing
International Telecommunication Union ISM bands, Frequency range [Hz]
6.765–6.795 MHz
13.553– MHz
26.957– MHz
40.66–40.70 MHz
433.05– MHz
902–928 MHz
2.400–2.500 GHz
5.725–5.875 GHz
24–24.25 GHz
61–61.5 GHz
122–123 GHz
244–246 GHz

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 RU , «Radio system of information reception and processing for centralized security system…»
FHSS System
Works in ISM band ( 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. Phase (for coherent systems only)
Synchronization
Synchronization
Frequency
Phase (for coherent systems only)
Time
Symbol timing
Frame timing

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 RU
(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
10th International PhD Workshop on Systems
and Control
Hluboka, Czech Republic
Valentin Vasilevskiy,
PhD Student, OmSTU
Student member, IEEE
Victor Antropov,
R&D Engineer
Radioengineering Department,
Omsk State Technical University,
Russia