Whisper Of Radio - CUHK

Whisper of RadioSpectrum Sharing in Cognitive Radio NetworksWei ZhangSchool of Electrical Engineering and TelecommunicationsThe University of New South WalesW. Zhang, Whisper of Radio, November 13, 2008. – p.1/39

Warm-up QuestionsQuestion 1: What are we doing in wirelesscommunications?W. Zhang, Whisper of Radio, November 13, 2008. – p.2/39

Olympic GameFaster, Higher, Stronger.W. Zhang, Whisper of Radio, November 13, 2008. – p.3/39

Warm-up QuestionsQuestion 2: What have we done in wirelesscommunications?W. Zhang, Whisper of Radio, November 13, 2008. – p.4/39

All Roads Lead to RomeWireless Communication is an “air travel”. What we have done isequivalent to increase passenger throughput.W. Zhang, Whisper of Radio, November 13, 2008. – p.5/39

All Roads Lead to RomeWireless Communication is an “air travel”. What we have done isequivalent to increase passenger throughput.add more airports - MIMOW. Zhang, Whisper of Radio, November 13, 2008. – p.5/39

All Roads Lead to RomeWireless Communication is an “air travel”. What we have done isequivalent to increase passenger throughput.add more airports - MIMObroaden runway to allow giant airplane (A340) - UWBW. Zhang, Whisper of Radio, November 13, 2008. – p.5/39

All Roads Lead to RomeWireless Communication is an “air travel”. What we have done isequivalent to increase passenger throughput.add more airports - MIMObroaden runway to allow giant airplane (A340) - UWBadd more lanes in runway - OFDMW. Zhang, Whisper of Radio, November 13, 2008. – p.5/39

All Roads Lead to RomeWireless Communication is an “air travel”. What we have done isequivalent to increase passenger throughput.add more airports - MIMObroaden runway to allow giant airplane (A340) - UWBadd more lanes in runway - OFDMborrow military airports - Cognitive RadioW. Zhang, Whisper of Radio, November 13, 2008. – p.5/39

OutlineIntroduction to Cognitive RadioResearch ChallengesWhispering RadioMultihop RelayingPerformance ResultsSummary & DiscussionW. Zhang, Whisper of Radio, November 13, 2008. – p.6/39

Spectrum ScarcityRadio spectrum is a limited resource, most has been exclusively allocated tolicensed systems and users.source: http://www.ntia.doc.gov/osmhome/allochrt.htmlW. Zhang, Whisper of Radio, November 13, 2008. – p.7/39

Spectrum Under-utilizationMost of the spectrum is largely under-utilized in vast temporal and geographicdimensions.M. A. McHenry, “NSF spectrum occupancy measurements project summary,” SharedSpectrum Company Report, Aug. 2005.W. Zhang, Whisper of Radio, November 13, 2008. – p.8/39

Cognitive RadioCognitive radio (CR) technology refers to a new type of radio that isaware of the environment in real time;self-adjustable to adapt to any corresponding variations, such asfrequency band, power, coding and modulation.CR is able to solve the conflicts between spectrum scarcity and spectrumunder-utilization by opportunistically accessing the licensed spectrum.W. Zhang, Whisper of Radio, November 13, 2008. – p.9/39

Cognitive Radio“Radio etiquette is the set of RF bands, air interfaces, protocols, and spatialand temporal patterns that moderate the use of radio spectrum. CR extendsthe software radio with radio-domain model-based reasoning about suchetiquettes.”J. Mitola and G. Q. Maguire, “Cognitive radio: Making software radios more personal,”IEEE Pers. Commun., vol. 6, pp. 13–18, Aug. 1999.W. Zhang, Whisper of Radio, November 13, 2008. – p.10/39

Cognitive Radio“Cognitive radio is an intelligent wireless communication system that is awareof its surrounding environment . and adapts its internal states to statisticalvariations by making corresponding changes in certain operating parameters(e.g., transmit power, carrier frequency, and modulation strategy) in real time,with two primary objectives in mind:Highly reliable communications whenever and wherever needed; andEfficient utilization of the radio spectrum.S. Haykin, “Cognitive radio: brain-empowered wireless communications,” IEEE J. Sel.Areas Commun., vol. 23, pp. 201–220, Feb. 2005.W. Zhang, Whisper of Radio, November 13, 2008. – p.11/39

Cognitive RadioMore specifically, the CR technology will enable the users to:Determine which portions of the spectrum is available and detect thepresence of licensed users when a user operates in a licensed band(spectrum sensing);Select the best available channel (spectrum management);Coordinate access to this channel with other users (spectrum sharing);andVacate the channel when a licensed user is detected (spectrum mobility).I. F. Akyildiz, et. al., “Next generation/dynamic spectrum access/cognitive radio wirelessnetworks: a survey,” Computer Networks, vol. 50, pp. 2127–2159, 2006.W. Zhang, Whisper of Radio, November 13, 2008. – p.12/39

Application: WRANWirelessMICTV TransmitterWRANBase StationWRANRepeaterWirelessMIC: WRAN Base StationTypical 33kmMax. 100km: CPEConsists of one base station (BS) and at least 512 simultaneously associatedconsumer premise equipments. Typical range of the system is 33 km. UtilizesUHF/VHF TV bands between 54 and 862 MHz.W. Zhang, Whisper of Radio, November 13, 2008. – p.13/39

OutlineIntroduction to Cognitive RadioResearch ChallengesWhispering RadioMultihop RelayingPerformance ResultsSummary & DiscussionW. Zhang, Whisper of Radio, November 13, 2008. – p.14/39

Challenge: Spectrum SensingPrimary RxSpectrum SensingPrimary TxPrimary SystemSecondaryUserSecondaryReceiverCognitive Radio SystemSpectrum sensing should detect the spectrum holes reliably and instantly.Hidden terminal problem. Cooperative spectrum sensing.W. Zhang, Whisper of Radio, November 13, 2008. – p.15/39

Challenge: RRMAllocate resources efficiently for potentially large available bands andpotentially huge number of usersAvoid interference to primary users (top priority accessing resources):Re-allocate resources upon detection of licensed users. How to guaranteeQoS?Co-exist with other non-licensed systems, e.g. resourcescompetition/lending/borrowingW. Zhang, Whisper of Radio, November 13, 2008. – p.16/39

Other Potential ChallengesSynchronization and channel estimation issues aroused fromhuge number of users, extremely wide band, collaboration with peersNew signaling schemes are required for the dynamic radio resourceCircuit-wise issuesoscillator design capable of hopping on a large set of differentfrequency bandsADC design capable of handling the potentially large dynamic range.W. Zhang, Whisper of Radio, November 13, 2008. – p.17/39

Our ContributionsCooperative Spectrum SensingCooperative Communications for CRInterference ManagementWhispering Radio6 Journal papers published and submitted3 US patents pendingW. Zhang, Whisper of Radio, November 13, 2008. – p.18/39

OutlineIntroduction to Cognitive RadioResearch ChallengesWhispering RadioMultihop RelayingPerformance ResultsSummary & DiscussionW. Zhang, Whisper of Radio, November 13, 2008. – p.19/39

Grey SpectrumThe spectrum of licensed channels can be classified as:White space – the spectrum where PU is inactive.Grey space – the spectrum where PU is in operation with low power.Black space – the spectrum where PU is in operation with high power.To exploit the grey spectrum, cognitive users (CU) should “speak”as loudly as possible to its desired listeners;as softly as possible not to annoy others, especially “supervisors”.W. Zhang, Whisper of Radio, November 13, 2008. – p.20/39

Speak, Whisper or Mute?P1 : the minimum Tx power of the CU which can reach its desired users.P2 : the maximum Tx power of CU which does not “annoy” the PU.Speak, Whisper or Mute?When PU is idle, CUs can freely access the “white space”. – Speak Mode.When PU is working and P1 P2 , CUs can only speak with a volume inthe range of [P1 , P2 ]. – Whisper Mode.When PU is working and P1 P2 , CUs keep silence. – Mute Mode.W. Zhang, Whisper of Radio, November 13, 2008. – p.21/39

Signal ModeliPItdirdtrrPSAssume Rayleigh block fading channels. The prob. µ of successfully receivinga packet isµ, h Θ(R N ) iRSI0Pr{SINR Θ} Pr{ Θ} EI exp RI N0RSΘ1·exp( ).(1)PdItrPS d α/Nα0{z tr} 1 ΘP (d ) Sir {z},µSNR,µSIRW. Zhang, Whisper of Radio, November 13, 2008. – p.22/39

Reliable TransmissionDefinition 1: The transmission of a CU is reliable if the successful prob. of theCU satisfies Pr{SINR Θc } ǫc .LpPUTxPpCRTxPURxuvCRRxdPcProposition 1: In the one hop CRN, for given QoS Θc and εc , the transmissionof CU is reliable iff its transmit power Pc satisfiesPc P1where P1 is given byΘcP1 log(1/εc ) PpN0 αu dα ,(2)W. Zhang, Whisper of Radio, November 13, 2008. – p.23/39

Transparent TransmissionDefinition 2: The transmission of a CU is transparent to a PU if thesuccessful prob. of the PU satisfies Pr{SINR Θp } ǫp .LpPUTxPpCRTxPURxuvCRRxdPcProposition 2: In the one hop CRN, for given QoS Θp and εp , the transmissionof CU is transparent to the active PUs iff its transmit power Pc satisfiesPc P2where P2 is given byP2 vLp α exp( Θ Lα ·p pεp Θ pN0)Pp εpPp(3)W. Zhang, Whisper of Radio, November 13, 2008. – p.24/39

Whispering RadioRemember whisper mode? P1 P2 . The distance d is the key to keep whispermode.Theorem 1: In the one hop CRN, TX could reliably and directly reach RX overa single hop while being transparent to PU iff the distance d is smaller thanDmaxpM u( 1 M 2 sin2 φ M u cos φ)Dmax ,(4)1 M2 1αlog(1/ε)P2cwhere M Pand φ is the angle between the CTx-CRx and·ΘcpPTx-CRx.Hint of proof : Substituting P1 into P1 P2 and using some geometry knowledge.W. Zhang, Whisper of Radio, November 13, 2008. – p.25/39

Black to GreyWhat if the whispering radio communications cannot be established betweenthe cognitive transmitter and receiver due to the long distance? In the case,spectrum is black to the CUs.Keep quiet? Spectrum inefficiency.Option: Keep whispering, but through relay nodes.Why: Since P2 is a constant (see Eq. (3)). The only option to guaranteeP1 P2 is to reduce P1 (see Eq. (2)) by shortening the distance d.W. Zhang, Whisper of Radio, November 13, 2008. – p.26/39

OutlineIntroduction to Cognitive RadioResearch ChallengesWhispering RadioMultihop RelayingPerformance ResultsSummary & DiscussionW. Zhang, Whisper of Radio, November 13, 2008. – p.27/39

Multihop Relay NetworkPUdLpPNPUsLssv2u3u2v3LddLcx1CUsΨd1sd2CU 1CU dd3d4CU 2CU 3d5CU 4CRNThe cognitive relay nodes are distributed in a homogeneous Poisson pointprocess with intensity λ. The length of the i-th hop is di .W. Zhang, Whisper of Radio, November 13, 2008. – p.28/39

MultihopIn the routing, the transmitter per hop attempts to find a relay node inside thesector Ψ such that the hop length di satisfies di Di,max (rf. Theorem 1).Di,maxCUiΨW. Zhang, Whisper of Radio, November 13, 2008. – p.29/39

Routing AlgorithmsNearest Neighbor Routing (NNR)Find the nearest node as relay in the sector Ψ within the distance Di,max .Hop distance is shorter, so the channel is more reliable, but need manyhops.Furthest Neighbor Routing (FNR)Find the Furthest node as relay in the sector Ψ within the distance Di,max .Less hops but each hop distance is long compared to NNR.W. Zhang, Whisper of Radio, November 13, 2008. – p.30/39

Multihop ReliabilityDefinition 4: Multihop reliability is the probability that a packet could besuccessfully delivered from the source to the destination.Over a route Rj , the end-to-end (e2e) reliability is the product of reliabilities(success probabilities) at each hop, i.e.,YµR j µi ,(5)i Rjwhere i Rj is the index of the node that belongs to route Rj andµi Pr{SINRi Θc }. Rj is the number of hops in route j.W. Zhang, Whisper of Radio, November 13, 2008. – p.31/39