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- 1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: Introduction to Chirp Spread Spectrum (CSS) Technology Date Submitted: November 11, 2003 Source: John Lampe, Zbigniew Ianelli Company: Nanotron Technologies Address: Alt-Moabit 61, 10555 Berlin, Germany Voice : +49 30 399 954 135 , FAX: +49 30 399 954 188, E-Mail: j.lampe@nanotron.com Re: Discussion of interesting RF technology Abstract: Tutorial Presentation on CSS for IEEE 802 – part 1 Purpose: November Plenary Tutorial #4 . Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.
- 2. Introduction to Chirp Spread Spectrum (CSS) Technology presented by Zbigniew Ianelli Nanotron Technologies GmbH Berlin, Germany www.nanotron.com
- 3. Contents A brief history of Chirp pulses Characteristics of Chirp pulses The basic Chirp signal Properties of signal forms Scalable technology How to code using CSS Key Properties of CSS
- 4. A brief history of Chirp pulses Used by whales and dolphins Patent for radar applications in 1944 by Prof. Hoffmann Further developed by Sidney Darlington (Lifetime IEEE Fellow) in 1947 („Pulse Compression Radar“) Patented by Canon for data transmission in fiber optic systems Chirp Spread Spectrum for commercial wireless data transmission is investigated since 1997
- 5. Characteristics of Chirp pulses A chirp pulse is a frequency modulated pulse. Its duration is T; within this time the frequency is changing in a monotonic manner from a lower value to a higher one („Up-Chirp“) or reverse („Down-Chirp“). The difference between these two frequencies is a good approximation for the bandwidth B of the chirp pulse. Up-Chirp in the time domain (roll-off factor 0.25) Spectrum of the chirp pulse with bandwidth B and a roll-off factor of 0.25 B S(f) f
- 6. The basic Chirp signal Chirp pulse: Sinc pulse (baseband): Sinc pulse (RF band):
- 7. Properties of signal forms in the air and baseband interfaces Chirp pulses for the RF channel: High robustness (BT>>1) Wideband signal Constant envelope of the RF waveform Constant, uniform PSD (Power Spectral Density) well controlled spectrum in very simple way Sinc pulses in the baseband: High speed (B δ=1) Easy signal processing (threshold detector)
- 8. Scalable Technology Frequency spreading: Basic information theory tells us that CSS benefits when the bandwidth B of the Chirp pulse is much higher than the data rate R: B >> R Time spreading: The data rate can scale independently of the BT product. The duration T of the Chirp pulse can be chosen freely. A signal with a very high BT product can be achieved, which transforms into a very robust signal in the channel.
- 9. Scalable Technology (continued) Excellent range – data rate scalability: Preferred for system where range and/or data rate requirement varies rapidly. Especially promising for wideband or ultra wideband system where available frequency bandwidth B is much higher than the data rate R
- 10. How to code using CSS Modulation techniques: On-Off-Keying (OOK), for example: Up-Chirp = „1“; Null = „0“ allows 2 independent coexisting networks Superposed Chirps (4 possible states): Null/Up-Chirp/Down-Chirp/ Superposition of Up- and Down-Chirp allows one network with double the data rate t f 1 0 1 0 0 1 f LO f HI Chirp pulse OOK with Null and Up-Chirp
- 11. Key Properties of CSS High robustness: Due to the high BT product, chirp pulses are very resistant against disturbances. Multipath resistant: Due to the broadband chirp pulse, CSS is very immune against multipath fading; CSS can even take advantage of RF echoes. Low power consumption: CSS allows the designer to choose an analog implementation, which often consumes much less power. Low latency: CSS needs no synchronization; a wireless connection can be established very quickly.
- 12. Mobility Properties of CSS Resistance against Doppler effect: The Doppler effect causes a frequency shift of the chirp pulse, which introduces a negligible shift of the baseband signal on the time axis. Example: Bandwidth of the chirp 80 MHz Duration of the chirp 1 µs Center frequency of the chirp (ISM band) 2.442 GHz Relative speed between transmitter and receiver 2000 km/h Frequency shift due to Doppler effect 4.52 kHz Equivalent shift of the message on the time axis 56.5 ps Note: 2000 km/h is equivalent to 1243 miles/hour
- 13. Coexistence Properties of CSS Immune to in-band interferer: Scalable processing gain (determined by BT product of the chirp) enables selection of appropriate immunity level against in-band interferences. Example: Bandwidth B of the chirp 64 MHz Duration time T of the chirp 1 µs Center frequency of the chirp (ISM band) 2.442 GHz Processing gain, BT product of the chirp 18 dB E b /N 0 at detector input (BER=0.001) 14 dB In-band carrier to interferer ratio (C/I @ BER=0.001) -4 dB
- 14. Some Applications and Measurements of Chirp Spread Spectrum (CSS) Technology presented by John Lampe Nanotron Technologies GmbH Berlin, Germany www.nanotron.com
- 15. Applications requiring mobility faster than 11 mph, such as: Tire pressure Assets in vehicles (in-car communications) Drive-by Drop boxes Drive-by AMR Toll booths Applications requiring robustness or fewer retransmissions in multipath environments, such as: Industrial mission-critical Airplanes Ships / engine rooms Gaming New WINA alliance one example of this need Applications requiring ranging accuracy better than 0.5 meters, such as: Asset tracking (active RFID) Personnel tracking Motion detection Automatic network installation New Applications / Global Markets
- 16. Applications desiring extended range, such as: Meter Reading Building Automation And other longer-range applications where repeaters are not practical Enhanced Applications / Markets
- 17. Evaluation Board Includes: RF IC SAW filter Optimized balun for asymmetrical antenna operation Crystals
- 18. Outdoor testing with CSS Test environment: Straße des 17. Juni - Siegessäule
- 19. Comparing CSS to DECT Outdoors
- 20. d=23 m, P out = -15 dBm = 32 µW, G=1,5 dB, BER = 10 -3 d=15 m, P out = -15 dBm = 32 µW, G=1,5 dB, BER = 10 -3 Result: d = 23 m with P out = -15 dBm Calculated: d = 50 m with P out = +10 dBm, = 3 Indoor testing with CSS
- 21. Indoor testing with CSS d=5 m, P out = -30 dBm= 1 µW, G = 1,5 dB, BER = 10 -4 d=26 m, P out = 8 dBm = 6,3 mW, G = 1,5 dB, BER = 10 -3 CSS transmits 1Mbps with P out = 1 µW over 5m and with 6,3mW over 26m Load-bearing Walls
- 22. Outdoor Link-Budget Link budget without cable losses or antenna-gain, best case: LB best = 103 dB Outdoor free space propagation: distance ~ link-budget with = 2.1 … 2.3 But: Outdoor propagation is not always free space propagation, due to e.g. hills, trees, houses, … Therefore: Measurements have to be done! d = 940 m
- 23. Testing CSS on Hahneberg, Berlin-Spandau 4626 ±10 m 3404±10 m 739±10 m Ref P1 P2 P3 P4 940±10 m
- 24. Outdoor testing with CSS 4626 ±10 m P out = 24 dBm = 250 mW 3404±10 m 739±10 m P out = 7 dBm = 5 mW Ref P1 P2 P3 P4 940±10 m P out = 9 dBm = 7.9 mW
- 25. Outdoor testing with CSS Measurement Challenge: Teufelsberg 6483 m distance 7.7 dBm output power 18 dB antenna gain No FEC BER 10E-3
- 26. CSS Outdoor Test Summary G ant = 1 dB P out = 9 dBm, d = 940 m P out = 7 dBm, d = 740 m P out = 26 dBm, d = 6.4 km P out = 30 dBm, d = 9.8 km 6400 m 26 dBm = 400 mW 9800 m 940 m 740 m Range @ BER=10 -3 30 dBm = 1 W 9 dBm = 7.9 mW 7 dBm = 5 mW Output Power @ antenna
- 27. Need for Standardization Ole Ploug R&D Manager Central Controls R&D Refrigeration and Air Conditioning www.danfoss.com
- 28. Summary Introduced CSS technology Explained behavior and benefits Suggested some additional applications that can be satisfied Shown test results that demonstrate some of CSS’ capabilities Shown one customer’s application requirements
- 29. Conclusions CSS has qualities of both spread spectrum and UWB. CSS enhances robustness and range CSS adds mobility CSS can be implemented with today’s technologies CSS is a global solution
Editor's Notes
- #7: Here is the same spectra represented in two extremely different ways. The sinc pulse is also used in some UWB implementations, so there are some similarities.
- #8: Benefits of constant power: 1. Cheaper to implement. 2. Lower human exposure.
- #16: CSS is appropriate for global markets because it operates well in global bands, such as 2.4. Robustness – latency intolerant
- #18: Used for some of the measurements
- #19: Page In the heart of Berlin. Cars, fences and street lamps in the trees along the street.
- #20: Page Output power is about 13 dBir. Only two measurement points because we have no BER measurement – these are finished consumer products. 10 -3 (first cracks in voice transmitted), then complete loss of voice transmission. Dect is also 2.4 GHz. Output power is 22 – 24 dBm Result – CSS has 2.5 times longer range
- #21: Page European office. Hall walls are stronger, inner walls are lighter. G = antenna gain (asymmetric rod antenna) Blue = Tx, Red = Rx. Locations not cherry-picked.
- #23: Page -93 dBm input sensitivity, +10 dBm output power = 103 dB link budget 2 is the perfect free space value. We used 2.1 as a conservative estimate.
- #24: Page Rod antennas were used for P1 and P4, directional antennas (18 dBi antenna gain) for P2 and P3. P2 is next to a railroad station with a 900 MHz / 1.8 GHz GSM base station. P3 is on top of a shopping center with two computer stores and a cell phone store. Ref is about 3 miles from Tegel international airport. There were many disturbers – ground radar from the airport, etc.
- #25: Page At P1, we varied the height of the Rx from 1.5 – 5 meters, saw no difference. P2 output power was approximately the same as P3, perhaps a bit lower. P3 had Bluetooth disturbers from the stores below.
- #26: This is the old eavesdropping site in Berlin during the cold war, now an airport radar location.
- #27: Page Measurements indicate that with 30 dBm output power, CSS can reach 9.8 km.
- #28: Page