Intelligent Antenna Sharing in Wireless Networks Aggelos Bletsas aggelos@media.mit.edu Viral Communications Group MIT Media Lab - Fall 2004

Wireless = Broadcast (it makes it hard… it makes it challenging…) Direct Multi-hop Cooperative (~100 years old) (~35 years old) (~today…) “Wireless Broadcast Advantage” Antenna Sharing: exploits observation of a common “property” across different users (antennas) in space… “Property”= data, time, location… Our contribution: distributed and adaptive cooperative algorithms, applicable in practice…

Instantaneous wireless channel conditions matter (not only average)… Tx Rx d Closer is not always better [Goud Jr et. al 2004]… fading is not always harmful (MIMO results)… Instantaneous wireless channel conditions matter (not only average)… Algorithms should adapt to wireless propagation “instantaneously” (within channel coherence time) - no need for topology estimation…

Diversity (including repetition)… wasteful, does not scale… Cooperative diversity: complex space-time coding… receiver hardware might be non linear (superposition does not apply)… Opportunistic Relaying: pick “best” relay (“best” relay = best end-2-end path) no communication among relays needed (distributed, “real time” solution)

Method of distributed timers = opportunistic relaying Mapping channel conditions to time! RTS CTS Harmonic mean Exploiting RTS/CTS packets of MAC and reciprocity… best path = relay that expires first… Collision probability depends on λ (user defined)…

Performance increases with number of relays… Outage vs SNR 2 relays 7 relays Performance increases with number of relays… Need for less transmission power… (less interference = scalability) Better performance SEP vs SNR

Picking best relay leads to higher capacity compared to picking a set of relays, for fixed total transmission power!

Implementation of opportunistic relaying using low cost, embedded radios… Relays Rx/display Tx

Antenna sharing for cooperative time keeping End-2-End Error Diameter of network Distributed Synchronization – server free, scalable Scalable = larger network, better performance

Antenna sharing for cooperative position estimation Estimate your location relatively to neighbors with “good” signal paths (high SNR measurements). Prior art found in protein structure determination (“molecular distance geometry problem”)… More on this in separate lecture…

Intelligent Antenna Sharing in Wireless Networks Practical, Adaptive to the environment Algorithms. Distributed Algorithms. No need for network topology knowledge. Algorithm could be implemented to non-linear receivers. “See Around Corners” ability… Antenna Sharing is extended to efficient network timing/positioning.