Problem: Spectrum Sharing

1. ^ ^ 1 1 Sa Sd ^ X 2 2 optimal (analog,digital) soln pair when digital quality is at its peak Tx Rx optimal analog soln . . . . . . M M best all-digital soln X The 3R’s of Spectrum Management: Reuse, Recycle and ReducePI: D. Tse, co-PI’s: M. Gastpar, A. Parekh, K. Ramchandran, A. Sahai, H. ShelanskiUniversity of California, Berkeley Detecting unused bands • Want to protect primary users by listening before we talk. • How long must we listen? • Issues: • We might be attenuated substantially beyond what is required to decode primary signal. • We probably do not know the codebook for the primary user • We may or may not know what kind of modulation is used • Observations so far: • Energy detector is optimal at very low SNR or if a lot of protection is desired. • Primary user can make the job much easier by incorporating a predictable part. Defining “harmful” interference • Cognitive radio protocols could allocate transmit powers tonodes, but what if someone deviates from his allocation? “I shall not attempt to define [obscenity] and perhaps I could never succeed in doing so. But I know it when I see it …” Supreme Court Justice Stewart in 1964 in “Jackobellis v. Ohio” • Minimalist definition: Interference is harmful when it interferes with the ability of a node to decode what it has the right to decode. We know it when we see it. Tracking down deviants • “No harm, no foul” principle • Two-phase protocol • Victim raises alarm only when it is having trouble decoding messages it should be able to decode. • Pass messages to locate deviant Detector performance • Node behavior • Keep sliding records of received power in the past. • When alarm is raised, use past records to propagate alarm in the rough direction of the deviant Problem: Spectrum Sharing Can multiple heterogeneous wireless systems coexist and share spectrum in a flexible and efficient manner? • Current paradigm: spectrum is carved up • Huge variability in actual usage across all space/time scales • Most bands allocated to a single use, which may or may not have any licensees. • “Unlicensed bands are small and have severe power constraints • Research agenda shifts from spectrum “reduce” to “reuse” and “recycle” • Reduce: traditional spectral efficiency • Reuse: designing systems with sharing in mind • Recycle coexistence with inefficient legacy users Spectrum recycling Interference Game Analog receiver ~ AM/FM/TV broadcast X Transmitter • What impact does technological innovations have on FCC’s property rights and unlicensed regimes ? Data Embedder Digital Upgrader • Can we seamlessly recycle wasteful analog TV/radio spectrum to do digital upgrade? Digital Music/TV Seamless digital upgrade: optimal strategy Analog Decoder • M non-cooperating systems sharing a bandwidth W • Nash equilibrium: each system waterpours over the aggregate interference of other systems • Spread spectrum is always a Nash equilibrium but the price of anarchy can be arbitrarily bad at high SNR. • Question: when do Nash equilibrium with bounded price of anarchy exist? • Have necessary and sufficient condition for existence of orthogonal Nash equilibria with bounded price of anarchy Optimal analog vs. digital quality tradeoffs?  Models: Gaussian source (with memory) Gaussian channel (with memory) Hybrid Transmission  W-Z W G-P X Y S  + + G-P-1 W-Z-1 Digital Decoder Hybrid Encoder Z~N Theorem: There exists a hybrid coded-uncoded system which attains the optimal W-Z: Wyner-Ziv source coding with side-information G-P: Gelfand-Pinsker channel coding with side-information