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: email@example.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.
Introduction to Chirp Spread Spectrum (CSS) Technology presented by Zbigniew Ianelli Nanotron Technologies GmbH Berlin, Germany www.nanotron.com
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
The basic Chirp signal Chirp pulse: Sinc pulse (baseband): Sinc pulse (RF band):
Properties of signal forms in the air and baseband interfaces
Chirp pulses for the RF channel:
High robustness (BT>>1)
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)
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.
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
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
Due to the high BT product, chirp pulses are very resistant against disturbances.
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.
CSS needs no synchronization; a wireless connection can be established very quickly.
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.
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
2000 km/h is equivalent to 1243 miles/hour
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.
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
Some Applications and Measurements of Chirp Spread Spectrum (CSS) Technology presented by John Lampe Nanotron Technologies GmbH Berlin, Germany www.nanotron.com
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
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
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
Need for Standardization Ole Ploug R&D Manager Central Controls R&D Refrigeration and Air Conditioning www.danfoss.com