Can Opportunistic Wireless Communication Systems operate at ultra low power and deliver Quality of Service? "Future Telecommunications: Regulated or Self-Organized?“Jean-Paul LinnartzSenior Technology Director, Philips Research
Outline • Paradigms governing Radio Communication • Noise limitations • Interference Limitations • Power Limitations • Examples • Interference cancellation • Receive power-limited systems • Heterogeneous traffic in ISM bands • Concluding Observation
1904 – 2008 Radio Communication, a field with tremendous innovation 1904: Marconi proudly communicated across the Atlantic Ocean. 2008: we proudly invent new wireless systems that cover a few meters • .
Body Sensors will accompany us from the baby cradle to the elderly care home Many electronic devices will incorporate body sensors Baby - Toddler - Child - Teen - Young Adult - Parent – Mid Aged Adult - Senior 4
The ambient Information superhighwayToward an homogeneous communication infrastructure The dream: One network connects 1010 people and 1012 sensor nodes. The reality: an explosion of different, incompatible and mutually interfering standards 1 Global network 103 MANs 106 Macrocells 106 LANs 107 WLAN nodes 108 access links 109 personal trusted devices 109 PANs 1011 Sensor nodes 1993 5
Bitrates span many orders of magnitude Our wireless systems need to connect sensors @ a few bits/minute up to real-time gaming and medical imaging @ multi-gigabits/sec Ultra low power • Interference mitigation • Speed race 10k 100k 1M 10M 100M 1G 10G WirelessData Rate (bit/s) 6
Exponential Growth of Communication Traffic The pace of innovation in the semiconductor market follows Moore’s law. Communication was believed to grow slower because of limited spectrum availability. Nonetheless the total traffic carried by radio transmission has grown with exponents much higher than those of semiconductor chips.
Exponential law on radio connectivity • Exponent consists of a number of terms: • Higher carrier frequencies • Denser reuse • More efficient signal handling • More efficient traffic assignment per channel • Each term has a succession of technologies that provided growth in innovation waves: • FM radio allowed denser reuse • Cellular telephone optimized reuse according to interference constraints • Diversity • CDMA telephone allowed reduction of fade margins • Directional antenna’s • Digitization of speech • Multi-user communication and Interference cancellation • MIMO • Trunking • Random Access protocols, ALOHA • Cognitive radio
Paradigm shifts Noise-Limited Channel-Limited Interference-Limited Battery power Limited Diversity Channel equalizers Rake Receiver OFDM Doppler Compensation Transatlantic Morse FM – CDMA – cellular – MIMO - Cognitive radio Adaptive front ends Pulsed UWB, Wake-up radio 9
The battle against nature / culture • “Civilizations initially learn how to handle nature, later their biggest concern is how organize their culture” • The key challenge in interference-limited radio systems is to avoid noise enhancement • What comes after the era of the interference-limited paradigm?
70’s and 80’s: Spectrum is very scarce but broadcast networks were planned using a noise-limited paradigm Interference protection of cable networks against radio pirates, Scheeren, P.; Arnbak, J. Communications Magazine, IEEE, Volume 25, Issue 4, Apr 1987 Page 7 - 17
Noise enhancements • The noise-enhancement is the main reason why the signal processing community had so much success in applying their concepts in wireless communication
Broadcast Planning Field stength Distance Interference Limited Cell planning. Adjacent channel occupancy was a major concern. Noise-limited CCIR planning Curves
Observation: Cellular reuse is not effective for data Queueing delay for packet transmission in a cellular packet-switched system versus traffic carried per cell. Various reuse patterns. Cosine Group Xiangyu Wang 01-06-2005 4
Spectrum Agile/Cognitive Radios • Spectrum allocated, but much of it is unused (“white space”) • Agile radios harness white space • 10xmore access to spectrum Source: Shared spectrum company funded by NSF
What is Cognitive Radio? radio systems that learn about the utilization of the radio spectrum, by itself and from others collaboratively, and • adaptively adjust their operating • behavior • in order to achieve high throughput, • reliability, … • through autonomous and distributed interference handling
0.3 0.25 0.2 0.15 0.1 0.05 0 Tx 2 Rx 1 2 1 0 0 -1 -1 -2 -2 0.4 0.3 0.2 0.1 0 2 1 2 1 0 0 -1 -1 -2 -2 Example: Interference in MAC protocols Homogenous arrival rate • Ready to Send - Clear to Send (RTS - CTS) is a virtual carrier sense mechanism. • Practical implementations, e.g. 802.11e, have performance issues • Too conservative in reserving radio resources (Conditional) capture probability • Intermediate Result • a priori (__) and a posteriori (..) capture probability for potential interferers. Non-homogenous arrival rate Credit: Chin Keong Ho, TU/e
Coexistance of low power sensor nodes and high power WLAN • WLAN signals are much stronger that Zigbee Signals • WLAN transmitters can rapidly access the channel when idle • WLAN traffic blocks all BSN traffic, unless special precautions are taken • Cross-standard Cooperative protocols: • A fake WLAN handshake can silence all WLAN traffic for a short period.
Quality of Service in the Radio Spectrum • The WLAN in ISM band concept triggered an explosion of activities in wireless connectivity • Increasingly large portions of the spectra will be used by multiple coexisting systems, applying cognitive radio concepts But, ... it becomes increasing difficult obtain medical-grade wireless connectivity • The allocation of dedicated bands is not favored • Dedicated solutions are economically not viable, as alternative mass-market solutions follow rapid innovation and steep price erosion • The IT departments choose for IT–friendly solutions, i.e., IEEE 802.11a/b/g/n WLAN, which has minimal QoS quarantees
Can Opportunistic Wireless Communication Systems deliver Quality of Service? Cognitive, opportunistic radio nodes operate in shared bands with many potential interferers, • Belonging to same or to different networks • Use the same channel, partially overlapping or neighboring channels • Using the same, a different or even an known standard • Use similar or widely different traffic properties • Use similar or widely different communication ranges and power levels • Operate using a distributed or coordinated management • Friendly, cooperative, civilized, selfish, non-cooperative, malicious How can one guarantee Quality of service?
Can Opportunistic Wireless Communication Systems operate at ultra low power? Cognitive, opportunistic radio may consume large amounts of power • Operation in an interference-limited regime, hence requirements to RF receivers may lead to high power consumption • Monitoring of the radio channel (power levels, extracting cyclostationary statistical properties ) • Determining a smart strategy, requires gathering information
Listening consumes more power than talking Shannon: Eb/N0 “communication theory is TX power centric” Stand-bye, hibernating or sleeping Amplifying and filtering incoming signals Detecting an incoming signal Synchronizing Channel estimation Digitizing analog signals Checking addressing Cancelling interference … New RX power centric paradigms are needed for system design 22
Low power receiver design challenge PR= PLNA + PMix + PFil PLNA PMix PFil 23 A/D LNA Mixer Filter 23 What is the best circuit power allocation in order to achieve the highest information throughput (bits) per Joule of energy consumed in the receiver ?
Throughput per Joule that a receiver can achieve while consuming a certain circuit power CIR = -10dB Throughput (bit/s) per Joule Continuous circuit power assigned to receiver, optimally distributed over various stages 24 Credit: Johan van den Heuvel, TU/e
Conclusion Future Telecommunications: Self-Organizing, thus highly regulated
Can Opportunistic Wireless Communication Systems operate at Ultra Low Power and deliver Quality of Service? • Historically, radio spectrum has been seen as a scarce resource that was sparsely used. However, the opening up of the ISM bands for unlicensed WLAN communication suddenly triggered a tremendous industrial growth. Moreover, recently developed cognitive radio concepts allow an opportunistic way of accessing the spectrum, with great liberty in frequency bands, modulation schemes, and multiple-access methods. In this presentation, these developments are discussed in the context of other trends. Wireless systems are increasingly used for life and mission critical applications while unlicensed and cognitive radio approach cannot fulfill QoS requirements. Further, as we deploy very dense radio networks operating only over short ranges, the receiver circuit power rather than the transmit amplifier power consumption dominates the battery life time of portable radio nodes. It challenges the traditional Eb/N0 optimization, which was the leading paradigm since Shannon in 1948.