USR – 3380 Next Generation of wireless communication: some questions concerning reliability. Laurent Clavier (laurent.clavier@telecom-lille.fr) STM Workshop - July 2016 USR – CNRS 3380
First I would like to thanks several people who contributed to these reflexions: Gareth, Ido, Nourddine , Malcolm, François… and many others. And a special thanks to Tomoko … and Yoko. STM Workshop - July 2016 USR – CNRS 3380
Connected things… Where are we going? STM Workshop - July 2016 USR – CNRS 3380
IoT and M2M … Forecasts – 50 billions of connected objects (5.10 10 ) in 2020 1000 billions (10 12 ) ( depending on the studies ). If each object is powered by an AA battery (~15 kJ), we need 0,75 peta Joules (0,75 10 15 or 750 thousand billions of Joules)… 15 peta Joules it means one 1GW nuclear reactor during ~9 days 180 days …. So what? STM Workshop - July 2016 USR – CNRS 3380
Let’s have a closer look… Performing some measurements STM Workshop - July 2016 USR – CNRS 3380
STM Workshop - July 2016 USR – CNRS 3380
NODE Sensor Microcontroller Data Storage – External Memory Communication Low-Power Transceiver MEASUREMENT PLATFORM Differential Amplifiers Data Storage – External Microcontroller Memory Serial Port to PC STM Workshop - July 2016 USR – CNRS 3380
Classification of the energy measurements 50 Current (mA) 45 40 35 30 25 20 15 10 5 0 4.74 4.76 4.78 4.8 4.82 4.84 4.86 Time (seconds) STM Workshop - July 2016 USR – CNRS 3380
Energy versus interference In addition to the energy measurement, we also make some interference measures characterized by the RSSI The X-MAX protocol allows to try 3 successive transmissions Our approach allows • to take into account the energy consumed by retransmission • to take into account the listening periods • to take into account the lost ACKs • … STM Workshop - July 2016 USR – CNRS 3380
Energy versus interference In an anechoïc chamber, introducing interferers (all with IEEE802.15.4 – 1, 2 or 3 interferers, highly actives) Energy used per packet (mJ) RSSI (dBm) STM Workshop - July 2016 USR – CNRS 3380
Energy versus interference In an anechoïc chamber, introducing interferers (all with IEEE802.15.4 – 1, 2 or 3 interferers, highly actives) Energy used per packet (mJ) No interferer High probability of success Low level of energy needed per packet RSSI (dBm) STM Workshop - July 2016 USR – CNRS 3380
Energy versus interference In an anechoïc chamber, introducing interferers (all with IEEE802.15.4 – 1, 2 or 3 interferers, highly actives) Energy used per packet (mJ) 2 to 3 interferers Increase of lost packets (1) 1 transmission red (2) 2 black (3) 3 green (4) Lost packets blue Increase in consumption RSSI (dBm) STM Workshop - July 2016 USR – CNRS 3380
Energy versus interference In a laboratory, introducing interferers (all with IEEE802.15.4 – 1, 2 or 3 interferers, highly actives) Energy used per packet (mJ) Real radio channel, uncontrolled sources of interference RSSI (dBm) STM Workshop - July 2016 USR – CNRS 3380
Reliability of a transmission for a given level of interference STM Workshop - July 2016 USR – CNRS 3380
Mean consumption per packet for a given level of interference (transmitter) STM Workshop - July 2016 USR – CNRS 3380
Lifetime of a Zigbee node Anechoïc chamber Laboratory STM Workshop - July 2016 USR – CNRS 3380
Agenda Some questions concerning reliability. • The problem • Radio channel • Interference STM Workshop - July 2016 USR – CNRS 3380
Agenda • The problem • Radio channel • Interference STM Workshop - July 2016 USR – CNRS 3380
What is the question? An environment STM Workshop - July 2016 USR – CNRS 3380
What is the question? To be monitored STM Workshop - July 2016 USR – CNRS 3380
What is the question? Nodes communicate to gather the information… STM Workshop - July 2016 USR – CNRS 3380
Let’s have a look on one single receiver Interference 𝒛 𝒖 = 𝒊 𝒖 ∗ 𝒚 𝒖 + 𝒋(𝒖) + 𝒐(𝒖) Thermal noise Received signal Transmitted signal Radio channel impulse response STM Workshop - July 2016 USR – CNRS 3380
Two problems ( a ) The radio channel… Reflected paths Source: x(t) Destination: y(t) Distance Shadowing – large scale fading Multipath – small scale fading; inter symbol interference 𝑧 𝑢 = 𝑏 0 𝑦 𝑢 − 𝑢 0 + 𝑏 1 𝑦 𝑢 − 𝑢 1 + ⋯ + 𝑏 𝑜 𝑦 𝑢 − 𝑢 𝑜 = ℎ 𝑢 ∗ 𝑦 𝑢 What is a good model for h(t) ? STM Workshop - July 2016 USR – CNRS 3380
Two problems ( b ) Interference… Source: x(t) Destination: y(t) 𝑜 𝑗 𝑢 = ℎ 𝑗 𝑢 ∗ 𝑦 𝑗 𝑢 𝑗=1 What is a good model for i(t) ? STM Workshop - July 2016 USR – CNRS 3380
Two problems ( b ) Interference… Another way to address the problem is to consider that interference is a signal Source: x(t) Destination: y(t) 𝒁 = 𝑰. 𝒀 + 𝑶 Distributed MIMO – Massive MIMO STM Workshop - July 2016 USR – CNRS 3380
We keep on the simple antenna receiver. ( a ) Channel modeling issues ( b ) Interference modeling issues Source: x(t) Destination: y(t) 𝑧 𝑢 = ℎ 𝑢 ∗ 𝑦 𝑢 + 𝑗(𝑢) + 𝑜(𝑢) STM Workshop - July 2016 USR – CNRS 3380
Agenda • The problem • Radio channel • Interference STM Workshop - July 2016 USR – CNRS 3380
Agenda • The problem • Radio channel (statistical model) • Background / Previous works • Measurements and new approach • Some results • Space evolution… • Interference STM Workshop - July 2016 USR – CNRS 3380
The channel as a linear transformation y(t) x(t) Channel 𝑧 𝑢 = 𝑃 𝑢𝑢 𝑦 𝑢 = 𝑦 𝑡 𝐿 1 𝑢, 𝑡 𝑒𝑡 We introduce t such that 𝐿 1 𝑢, 𝑢 − τ = ℎ(𝑢, τ) and we take 𝑡 = 𝑢 − τ : 𝑧 𝑢 = 𝑦 𝑢 − 𝜐 ℎ 𝑢, 𝜐 𝑒𝜐 Impulse response So… to be known, traditionally: • We work with second order statistics • The signal resolution is much less than the multipath resolution STM Workshop - July 2016 USR – CNRS 3380
Impulse response – check your glasses... 1 0.8 Multipaths Amplitude 0.6 0.4 0.2 0 0 0.2 0.4 0.6 0.8 1 t STM Workshop - July 2016 USR – CNRS 3380
Symbol duration T>>1 1 Amplitude 0.5 0 -T 0 T 2T t STM Workshop - July 2016 USR – CNRS 3380
The impact of the previous Symbol duration T>>1 symbol at the sampling instant is very low. 1 Symbol 1 Amplitude 0.5 0 -T 0 T 2T t BUT we want higher data rates… so we increase the bandwidth. STM Workshop - July 2016 USR – CNRS 3380
When sampling at 3T for recovering Symbol duration T<<1 the 4 th symbol, inter-symbol interference arises due to those late paths that carries the 1 st symbol. 1 Amplitude 0.5 0 -T 0 T 2T 3T t STM Workshop - July 2016 USR – CNRS 3380
Modelling the channel as a linear filter Measured Response 0.2 Bandwidth 2GHz y(t) x(t) h(t) Central frequency 58 GHz 0.1 0 0 50 100 Impulse responses Delay (ns) N 1 t t t Peak detection h k k 0.2 k 0 Four random variables / vectors: 0.1 number of paths, delays, 0 amplitudes, phases 40 80 0 Delay (ns) STM Workshop - July 2016 USR – CNRS 3380
Delays Turin (Modified Poisson) Suzuki, Hashemi ( D -k) Saleh et Valenzuela (Two Poisson) [ Used by IEEE 802.15.3a ] Other approaches found in literature : Weibull, Non stationary Poisson, -stable processes. STM Workshop - July 2016 USR – CNRS 3380
Continuous D -K model (Turin) Mean arrival rate K.l(t) Discrete D -K (Suzuki, Hashemi) l(t) 1 delay D Saleh Valuenzela 0.5 Based on clusters and… two Poisson 0 0 20 40 60 STM Workshop - July 2016 USR – CNRS 3380
Delays Turin (Modified Poisson) Suzuki, Hashemi ( D -k) Saleh et Valenzuela (Two Poisson) [ Used by IEEE 802.15.3a ] Other approaches found in literature : Weibull, Non stationary Poisson, -stable processes. Amplitudes/Phases Rayleigh, Rice, Nakagami … Gamma, lognormal, … Delay and amplitude modeling are difficult Data pre-processing is complex Besides those statistical models rely on second order statistics STM Workshop - July 2016 USR – CNRS 3380
Checking the WSSUS property… US: Uncorrelated Scatterers Paths that arrive at different time are not correlated. (Stationary in frequency domain) WSSUS hypothesis WSS: Wide Sense Stationary In a given area, second order statistical properties do not change. Correlation between two measures at different times t 1 and t 2 (or different locations d 1 and d 2 ) only depends on differences D t = t 2 -t 1 (or D d = d 2 -d 1 ). STM Workshop - July 2016 USR – CNRS 3380
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