1. Intelligent Antenna Sharing in Wireless Networks
Aggelos Bletsas
Viral Communications Group
MIT Media Lab - Fall 2004

2. 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…

3. 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…

4. 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)

5. 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)…

6. 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

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

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

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

10. 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…

11. 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.