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Published byRudolf Banks Modified over 9 years ago
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The 3R’s of Spectrum Management: Reuse, Recycle and Reduce PI: D. Tse, co-PI’s: M. Gastpar, A. Parekh, K. Ramchandran, A. Sahai, H. Shelanski University of California, Berkeley 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 What impact does technological innovations have on FCC’s property rights and unlicensed regimes ? 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. Detector performance 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 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. 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 Analog receiver X ^ X Transmitter Data Embedder AM/FM/TV broadcast Digital Music/TV Digital Upgrader X Spectrum recycling Can we seamlessly recycle wasteful analog TV/radio spectrum to do digital upgrade? ~ Optimal analog vs. digital quality tradeoffs? best all-digital soln optimal analog soln optimal (analog,digital) soln pair when digital quality is at its peak Theorem: There exists a hybrid coded-uncoded system which attains the optimal Models: Gaussian source (with memory) Gaussian channel (with memory) Interference Game 1 2 M 1 2 M TxRx............ 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 Seamless digital upgrade: optimal strategy W-Z -1 G-P -1 ^ SdSd + W-Z G-P S W YX + Z~N Hybrid Transmission ^ SaSa Digital Decoder Analog Decoder Hybrid Encoder W-Z: Wyner-Ziv source coding with side-information G-P: Gelfand-Pinsker channel coding with side-information
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