Presentation on theme: "IEEE WCNC 2014, Istanbul, Turkey"— Presentation transcript:
1IEEE WCNC 2014, Istanbul, Turkey Effective Transceiver Selection for Mobile Multi-Directional Free-Space-Optical ModulesAbdullah Sevincer and Murat YukselDepartment of Computer Science and EngineeringUniversity of Nevada, RenoProject WebsiteIEEE WCNC 2014, Istanbul, Turkey
2Collaborators & Sponsors FacultyMona Hella Rensselaer Polytechnic InstituteNezih Pala Florida International UniversityStudentsMahmudur Khan (Ph.D.), UNRPrabath Palathingal (M.S.), UNRAlumnusAbdullah Sevincer (Ph.D.), IntelBehrooz Nakhkoob (Ph.D.), RPIMehmet Bilgi (Ph.D.), MicrosoftMichelle Ramirez (B.S.), US Air ForceAcknowledgmentsThis work was supported by the U.S. National Science Foundation under awards and and DARPA under contract W31P4Q-08-C-0080
3MotivationFree-space-optical (FSO) communication has the potential to serve as a complementary technology to RF for the future wireless networking.Multi-element spherical modules covered with multiple highly directional FSO transceivers has been shown to work well to handle mobility for FSO communication.Reducing the modules’ energy consumption becomes a crucial issue for the FSO modules with many transceivers.Need to find an efficient algorithm to reduce power consumption while satisfying throughput performance.
4Wireless Capacity – NOW! Scary trends in mobile wireless demand2+ times increase per year since 2007.“18-fold by 2016!” Cisco, February 2012.“More than 80% is landing on WiFi”, -- excluding iPhone!Opportunistic networking is well accepted by the users!
5Free-Space-Optical (FSO): open spectrum 2.4GHz, 5.8GHz, 60GHz, > 300 GHzFSO usage:point-to-point linksinterconnectsindoor infrared communicationsDoD use of FSO:Satellite communicationsAirForce RIKA; DARPA THOR, ORCL, ORCA: air-to-ground, air-to-air, air-to-satellite802.11a/g,802.16e,Cellular (2G/3G)
6Optical Wireless: Commodity components Digital DataON-OFF Keyed Light PulsesTransmitter(Laser/VCSEL/LED)Receiver(Photo Diode/ Transistor)IrDAs…Lasers…LEDs…VCSELs…Many FSO components are very low cost and available for mass production.
7Optical Wireless: Why?More Secure: Highly directional => low probability of interceptionSmall size and weight: Dense packaging is possibleVery low cost and reliable components, e.g. HBLEDs35-65 cents a piece, and $2-$5 per transceiver package + upto 10 years lifetimeVery low power consumption (100 microwatts for Mbps!)Even lower power for 1-10 Mbps4-5 orders of magnitude improvement over RFHuge spatial reuse => multiple parallel channels for huge bandwidth increases
8FSO Issues/Disadvantages Limited range (no waveguide, unlike fiber optics)Need line-of-sight (LOS)Any obstruction or poor weather (fog, heavy rain/snow) can increase BER in a bursty mannerBigger issue: Need tight LOS alignment:LOS alignment must be maintained with mobility or sway!Effects of relative distance and mobilityReceived powerSpatial profile:~ Gaussian drop offCan we leverage FSO’s benefits while solving the issues?
9FSO Modules: Spherical Designs How to handle mobility under LOS alignment requirement?Mobile FSO =Directionality + Angular Diversity + Electronic SteeringMulti-transceiver spherical FSO designs.Need a distributed protocol for this!ABBidirectional LOSACM/Springer WINET 2009
10FSO Modules: Spherical Designs Need to autonomously manage (electronically steer) multiple data transmissions to leverage spatial reuse.ABC
11FSO Modules: Alignment Protocol LOS Alignment Process:Step 1: Search PhaseStep 2: Data Transfer PhaseGoal: Provide an FSO link with “seamless” alignmentSteer the data transmission among the transceivers as the nodes move with respect to each otherNeed a 3-way handshake among the transceivers to assure a bidirectional alignmentLOSNetwork LayerLink LayerPHYAlignment Protocol
12FSO Modules: Alignment Protocol Alignment Liststo steer transmissions with over multiple alignmentsupdated at every search intervalC121NextHop.InterfaceLocalB.719A.611NextHop.InterfaceLocalB.517A.611A1B121NextHop.InterfaceLocalA.1111C.19721NextHop.InterfaceLocalB.914C.116NextHop.InterfaceLocalB.1111C.116NextHop.InterfaceLocalA.149C.175
13Transceiver Selection Problem Brute force: send search signals at every transceiverWhat happens if there are many transceivers?Too frequent searches (i.e., too many active transceivers)Energy consumptionController scalabilityToo infrequent searchesMay not detect the FSO communication opportunitiesBrute force alignment protocol cannot scale to 100s of transceivers..
14Transceiver Selection Problem Recap goals:Discover opportunities to establish LOS with neighborsMaintain the existing linksInsights:Movements of neighbors project to spatially correlated (or close) transceiversSignificant number of transceivers are not relevant
15Transceiver Selection Discover: need to exploreSend search from as many transceivers as possibleMaintain: need to exploitSend search only from the transceivers close to the ones where an alignment already existsSingle Mode: discover and maintain at the same time-scaleTwo Mode: discover at larger time-scalesHow to keep the network throughput high (FSO links stay on) via minimal search messaging overhead?
16Simulation Setup ns-2 simulations of TCP traffic Parameter NameDefault ValueNumber of nodes 49Number of flows 49x48Visibility 6 kmNumber of interfaces 8, 16, 24Mobility 1 m/sSimulation time 3000 sTransmission range & separation of nodes 30 mArea 210 x 210 mNode radius 20 cmDivergence angle 0.5 radianPhoto detector diameter 5 cmLED diameter 0.5 cmns-2 simulations of TCP trafficCompare throughput for single vs. two mode operations..Discovery0.03, 0.15, 0.3, 0.5, 4, and 8 secondsMaintenance0.03, 0.15, and 0.3 secondsSearch from the previous and next (+/- 1 )transceivers
17Order of magnitude fewer searches in the two-mode alignment ResultsOrder of magnitude fewer searches in the two-mode alignment
18Similar throughput with 10 times fewer search messages ResultsSimilar throughput with 10 times fewer search messages
19Similar throughput with 10 times fewer search messages ResultsSimilar throughput with 10 times fewer search messages
20Summary and Future Work Messaging overhead of LOS alignment protocol can be controlled with simple tricks10 fold savings are possible by a two-mode designImmediate future work:Discovery could be improved: use randomizationMore study of the mobility rateLonger term future work:A theoretical framework to formulate the tradeoffsApplicability to directional RF antennas
22Seems Inescapable by the Internet Wireless nodes will soon dominate the Internet.Currently ~1B nodes, including wireline.Urgent response to the exploding wireless demand is a necessity.
23What is RF and FSOCellular is Full: wireless airwaves are full”, CNN, Feb 21, 2012.
24Dense Deployment: No Help Beyond a Point As we add more RF nodes, per-node throughput diminishesDense deployment of many omni-directional antennas increases interferencesqrt(N) as N increases (Gupta, Kumar, 2000)Can become linear with hierarchical cooperative MIMO imposing constraints on topology and mobility pattern (Ozgur et al., 2006)None is able to totally eliminate the scaling problemThe RF spectrum is getting saturated.. We need alternative communication spectrum resources for opportunistic usage.
25Opportunistic Wireless Channel Characteristics Complements always-on, lower-rate, higher coverage wireless.Available CapacityOptical wireless opportunistic channelRF opportunistic channelBasic RF channelDelay-tolerant applications (e.g. , FTP, Video-on-demand)Basic RF channel (e.g. 2G, 3G, 4G/WiMAX)Real-time, interactive applications (e.g. chat, VoIP)TimeThis talk will consider a specific PHY technology, free-space-optics (FSO), that could be useful in this context, and its implications on higher-layer protocols.
26FSO Modules: Alignment Protocol Send “search” frames periodicallyneed an “alignment timer”Receive data frames only after alignment is establishedmight still get wrong or erroneous frames – leave them to the higher layersDiscardDiscardRecv(SYN | SYN_ACK |DATA)Recv(ACK, j)Recv(ACK | DATA)Not AlignedSending SYNRecv(SYN, i)SendingSYN_ACKTarget Node = iStartRecv(ACK, i)Alignment TimerTimeoutRecv(SYN_ACK, i)Recv(SYN, i)SendingACKTarget Node = iAlignedTarget Node = iProcessDataRecv(DATA, i)Recv(SYN_ACK |ACK)Recv(DATA, j)Recv(DATA, i)Recv(SYN | SYN_ACK | ACK)Recv(DATA, j)DiscardDiscardState diagram of LOS alignment protocol
27FSO Prototype: Transceiver Picture of transceivers.3-D optical antenna design.
29LiteratureMultiple elements/transceivers in FSO communication in interconnects which communicate over very short distances. Focus: Mechanical steering or beam steering Optical flow assignment has not been considered to manage multiple different data flows among transceivers during an on going transmissionThe main issues:interference (or cross-talk) between adjacent transceivers due to finite divergence of the light beamMisalignment due to vibration.M. Naruse and S. Yamamoto and M. Ishikawa. Real-time active alignment demonstration for free-space optical interconnections. IEEE Photonics Technology Letters, 13:1257–1259, November Bisaillon and D. F. Brosseau and T. Yamamoto and M. Mony and E. Bernier and D. Goodwill and D. V. Plant and A. G. Kirk. Free-space optical link with spatial redundancy for misalignment tolerance. IEEE Photonics Technology Letters, 14:242–244, February Canon,