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  1. 1. Research Challenges in Wireless Communications & Networking D. Raychaudhuri WINLAB, Rutgers University Piscataway, NJ 08854 [email_address]
  2. 2. Introduction
  3. 3. Wireless Research: Strategic Themes (near-future) <ul><li>Several fundamental problems need to be solved before the “mobile Internet” can take off: </li></ul><ul><li>Developing PHY/MAC for broadband radios </li></ul><ul><ul><li>~Kbps  Mbps  Gbps, adaptive, robust, QoS,... </li></ul></ul><ul><li>Scaling wireless system capacity </li></ul><ul><ul><li>widespread service implies ~Gbps/Sq-Km </li></ul></ul><ul><li>Designing wireless system-on-chip (SOC) </li></ul><ul><ul><li>low-cost/low-power, integrated CMOS </li></ul></ul><ul><li>Unifying wireless network architectures (WLAN/IP, 2.5G, 3G cellular) & protocols </li></ul><ul><ul><li>multiple radio technologies, faster/simpler standards process </li></ul></ul><ul><li>Creating “useful” mobile information services </li></ul><ul><ul><li>...beyond web browsing on hand-held devices </li></ul></ul>
  4. 4. Wireless Research: Strategic Themes (long-term) <ul><li>Pervasive computing via large-scale sensor networks (connecting people with their physical environment) viable in 5-10 yrs </li></ul><ul><li>Technical challenges: </li></ul><ul><ul><li>self-organizing (ad-hoc) networks </li></ul></ul><ul><ul><li>low-power/low-cost/multipurpose wireless sensors </li></ul></ul><ul><ul><li>scalable network routing and content distribution </li></ul></ul><ul><ul><li>distributed information processing in the network </li></ul></ul><ul><ul><li>end-user interfaces & applications </li></ul></ul><ul><li>Above topics involve wireless, but are also inherently cross-layer or interdisciplinary... </li></ul>
  5. 5. Wireless Product Trends Short-range radio (Bluetooth) Wireless LAN (802.11b) Digital Cellular (2/2.5G) Wireless local loop (WLL) 802.15.3 WPAN, etc. OFDM, mob IP, security, QoS,.. WCDMA, 3G.PP, etc. MIMO/OFDM, ATM/IP, Wireless LAN (802.11x) Integrated Cellular (3G) Public WLAN Broadband Wireless Access (BWA) 3G+ or BWA+?? WPAN (802.15.3.x) Home LAN BWA/3G combo (local access providers) 4G: WLAN/3G/2G (cellular operators) Home network sensor nets, etc. (consumer & verticals) convergence opportunities?? driver technologies potentially disruptive technology areas 2001 2002-03 >2005 OFDM/CDMA, MIMO, diversity, RRM,.. 3G/WLAN IWF, self-org 802.11 low- tier 802.11 UWB, ad-hoc nets
  6. 6. Wireless Research Challenges: Major Areas <ul><li>Wireless research topics can be organized into following major categories </li></ul><ul><ul><li>radio modems: signal processing and hardware </li></ul></ul><ul><ul><li>wireless systems: design and optimization </li></ul></ul><ul><ul><li>mobile networks & protocols </li></ul></ul><ul><li>Many wireless problems of current importance are cross-layer in nature, so that a holistic approach is essential .... </li></ul>
  7. 7. Radio Technology
  8. 8. Radio Technology: Research Topics <ul><li>Selected research topics in the radio/modem area include: </li></ul><ul><ul><li>putting radio modems on “Moore’s Law” </li></ul></ul><ul><ul><li>signal processing innovations (MIMO, adaptive antennas) </li></ul></ul><ul><ul><li>flexible software-defined radios (SDR) </li></ul></ul><ul><ul><li>ultra wideband (UWB) </li></ul></ul><ul><ul><li>integrated wireless system-on-chip (sensors, etc.) </li></ul></ul>
  9. 9. <ul><li>As computing and communications converge, network BW must follow CPU & memory size…. </li></ul>Radio Technology: Moore’s Law applies to wireless! 1990 1995 2000 Year 1 10 100 1000 Mhz 1 10 100 1000 Kbps 1 10 100 1000 Mbps 1 10 100 1000 MB LAN/WAN Switching Local Access CPU Speed Memory Size CPU LAN/WAN Local Access Memory Kbps 1 10 100 1000 Wireless Access Wireless CDPD 3G Mobile 802.11bWLAN, Cable Modem DSL Gbps Router ATM 56K modem Sw Ethernet 802.11a, UWB,.., short-range radio speeds outpacing Moore’s law over last ~5 yrs!
  10. 10. Radio Technology: Modem Evolution QPSK/GMSK Equalized QPSK/QAM/ GMSK,.. Multicarrier Modulation (OFDM, etc.) Spread Spectrum (CDMA) Multiple antenna spatial processing (MIMO, etc.) Wideband CDMA (w/ interference canc. & multiuser det) IS-136, etc. DVB, 802.11a, etc.. US HDTV, WLL, 802.11b IS-95 4G and next-gen WLL ~10-100 Mbps depending on cell size & mobility ~5-10 bps/Hz achievable with QAM UMTS/IMT-2000 ~2 Mbps depending on cell size ~0.5 bps/Hz typical for proposed systems (works at vehicular mobility speeds) Time/Frequency processing Time/Frequency + spatial processing UWB WPAN and WLAN ~100-500 Mbps no allocated spectrum no RF carrier short-range, high-data rate Pulsed communication
  11. 11. Example opportunistic transmission scenario: : vehicular user passes by an “Infostation” Short-range radio channels W z d trajectory Offset w
  12. 12. Initial results show that channel is well-behaved for distance ~5m  100’s of Mbps readily achieved with various modem techniques Data from Domazetovic & Greenstein [2001] Short-range radio channel
  13. 13. Radio Technology: UWB Source: J. Foerster, Intel Research, 2001 Pragmatic bit-rate comparison between UWB and 802.11x options “ sweet spot” for use as nx100 Mbps WPAN UWB appropriate for energy-efficient radio links, typically short-range Also has potential hardware complexity advantages...
  14. 14. Radio Technology: Hardware Innovations <ul><li>As wireless modems become faster and more ubiquitous, key hardware innovations urgently needed: </li></ul><ul><ul><li>compact RF components, including MEMS </li></ul></ul><ul><ul><li>mixed signal design & testing </li></ul></ul><ul><ul><li>silicon integration and packaging </li></ul></ul><ul><ul><li>UWB radio architecture </li></ul></ul><ul><ul><li>software-defined radio @ 10-100 Mbps </li></ul></ul><ul><ul><li>integrated wireless sensors (low-power) </li></ul></ul>
  15. 15. Wireless Systems
  16. 16. Wireless Systems: Research Topics <ul><li>Designing and optimizing wireless systems via radio resource management (power control, interference avoidance, scheduling, etc.) </li></ul><ul><li>Selected research topics in the wireless systems area include: </li></ul><ul><ul><li>scaling cellular system capacity </li></ul></ul><ul><ul><li>scaling ad-hoc network capacity & throughput per user </li></ul></ul><ul><ul><li>radio resource management for 3G and ad-hoc nets </li></ul></ul><ul><ul><li>interference avoidance </li></ul></ul><ul><ul><li>spectrum sharing in unlicensed bands </li></ul></ul>
  17. 17. <ul><li>Rapidly increasing use of untethered data devices implies that wireless access network capacity (bps/sq-Km) will soon have to scale to “gigabit” levels... </li></ul>Wireless Systems: Increasing the scale of networks Internet Wireless Access Networks Mobile Comm Devices Fixed PC/WS Mobile PDA/PIA Semi-mobile Laptop, etc. Growing proportion of all computing devices --> 50% +? Telecom Network Sensors/ low-tier data Example : ~10,000 devices/sq-Km @1 Mbps peak and 0.1 Mbps avg implies system capacity ~Gbps/sq-Km
  18. 18. <ul><li>Consider first the scaling limits of existing and emerging wireless network standards... </li></ul><ul><li>2G cellular/PCS: </li></ul><ul><ul><li>cell size ~ 3-5 Km, avail BW ~ 5 Mhz, spectral eff ~ 0.2-0.3 bps/Hz </li></ul></ul><ul><ul><li>max capacity ~ 100 Kbps avg, 1 Mbps peak (with packet MAC) per sq-Km </li></ul></ul><ul><ul><li>off by 3 orders-of-magnitude! </li></ul></ul><ul><li>3G Cellular/PCS: </li></ul><ul><ul><li>cell size ~ 3-5 Km, avail BW ~ 25 Mhz, spectral eff ~ 0.3-0.5 bps/Hz </li></ul></ul><ul><ul><li>max capacity ~ 1 Mbps avg, 10 Mbps peak (with packet MAC) per sq-Km </li></ul></ul><ul><ul><li>still off by 2 orders-of-magnitude! </li></ul></ul><ul><li>Wireless LAN (802.11x, Hiperlan): </li></ul><ul><ul><li>cell size ~ 0.1-0.5 Km, avail BW ~ 100 Mhz, spectral eff ~ 0.2-0.3 bps/Hz </li></ul></ul><ul><ul><li>max capacity ~ 100 Mbps avg, 1 Gbps peak per sq-Km </li></ul></ul><ul><ul><li>correct order-of-magnitude, but too many access points & limited mobility </li></ul></ul>Wireless Systems: Increasing the scale of networks
  19. 19. Wireless Systems: Architecture Evolution Mobile/Wired Network GW Cellular Macrocell (~5-10 Km radius) Custom wireless protocol Standard IP, ATM, etc. 2G/2.5G/3G radio access (single standard) Gigabit Metro Area Network (w/ integrated mobility support) BTS AP/ mini-BTS WLAN+ or “4G” or new radio access (multiple standards) Standard IP + M interface Regulated spectrum, static freq co-ord Unregulated spectrum, dynamic freq coordination Faster radio PHY’s with high interference rejection & bps/Hz efficiency IP end-users 2G/3G end-users Mbps/Km2 Gbps/Km2 Current Wireless Network Scalable Heterogeneous Pico/Micro/Macrocellular Wireless Network Model Static provisioning Dynamic provisioning/ QoS Radio Microcell (~0.5-1 Km radius) Location-aware information services, mcast, cache, etc. WAP services. etc. High-speed radio hot spot Radio macrocell WPAN WLAN Microcell (~100m radius) IP end-users
  20. 20. Wireless Systems: RRM Model for Cellular systems <ul><li>Multiple cell scenario with desired and interfering signals </li></ul><ul><li>Algorithms for allocation of bit-rate, base station, channel, tx schedule, power </li></ul><ul><li>Common theme: reduce interference, transmit when the channel is “good” </li></ul>Source: Prof. R. Yates, Rutgers U BS k BS 1
  21. 21. Wireless Systems: RRM in 3G – adaptive incremental redundancy example Source: Dr. L. Razoumov, Rutgers U
  22. 22. <ul><li>Scaling of wireless services will need new spectrum (~Ghz) particularly for new high-speed data services </li></ul><ul><li>Need to rethink traditional approach to spectrum regulation </li></ul><ul><ul><li>More unlicensed spectrum (e.g. 5 Ghz U-NII) </li></ul></ul><ul><ul><li>Market mechanisms other than one-time spectrum auctions? </li></ul></ul><ul><ul><li>Spectrum etiquette procedures for coexistence of QoS-based wireless services (beyond “LBT”) </li></ul></ul><ul><ul><li>Incentives for efficient utilization of spectrum resources? </li></ul></ul><ul><ul><li>Relationship to property rights? </li></ul></ul>Wireless Systems: Efficient Spectrum Use
  23. 23. <ul><li>Spectrum etiquette procedure a key issue for U-NII scenario </li></ul><ul><li>“ CSCC” approach proposed as possible solution... </li></ul><ul><ul><li>Coordination channel using simple standard protocol at edge of band </li></ul></ul><ul><ul><li>Semantics of higher layer coordination protocol TBD... </li></ul></ul><ul><ul><li>Support arbitrary spectrum policies based on user priority, cost bids, etc. </li></ul></ul>Wireless Systems: Efficient Spectrum Use Common Spectrum Coord Channel (CSCC) Channel: #1 #2 #3 #4 #5 #6 #N ..... .... .... Packet service Streaming service A Streaming service B Periodic announcements incl..: Service type, User #, Channel #, service params, Priority, Cost/Price Bids, etc.
  24. 24. Wireless Systems: Efficient Spectrum Use Example of CSCC etiquette used for “dynamic pricing” based spectrum allocation: channel CSCC channel Price Bid $.07/hr f n f n f n f n Price Bid $.09/hr A B B contends for f n A raises bid on f n … e-cash exchange ? A A B User ID Service Type Price Bid $.05/hr A wins contention ( B records & reports transaction!)
  25. 25. Mobile Networks
  26. 26. Mobile Networks: Some Research Topics <ul><li>Selected research topics in the mobile networks area include: </li></ul><ul><ul><li>new MAC protocols: 802.11x, 803.15.x, sensor nets </li></ul></ul><ul><ul><li>“ 4G” network architectures </li></ul></ul><ul><ul><li>mobility protocols: beyond mobile IP </li></ul></ul><ul><ul><li>new architectures (WLAN hot-spots, Infostations, ..) </li></ul></ul><ul><ul><li>self-organizing wireless networks (sensors, etc.) </li></ul></ul><ul><ul><li>ad-hoc network routing </li></ul></ul><ul><ul><li>multicasting and mobile content delivery </li></ul></ul><ul><ul><li>wireless network security </li></ul></ul>
  27. 27. Mobile Networks: “4G” Protocol Evolution WPAN radio Today’s Wireless Systems The Future Low-tier services IP 802.11 Radio Ethernet Mobile Service Middleware IP WLAN Services 3G/4G Radio WLAN radio WPAN/low- tier radio 2.5G/3G Radio GSM/ GPRS 2.5G/3G Services 3G Access Network PSTN IP WPAN network layer (e.g. Bluetooth) Generic Radio Access Network Radio-specific vertically integrated systems with complex intetworking gateways Security QoS VPN Content Delivery 4G Services Radio Independent modular system architecture for heterogeneous networks uniform radio API’s generic network API uniform service API (Internet+) Unified IP-based mobile network incl support for multihop, mcast, etc, service feature modules
  28. 28. Mobile Networks: Protocols beyond mobile IP Radio Access Network 1 Global Internet Mobile IP overlay network radio bridge/ router (forwarding node) access point <ul><li>Mobile IP provides a permanent IP address </li></ul><ul><li>for users moving between wireless AP’s </li></ul><ul><li>Desired RAN features for ad-hoc WLAN, </li></ul><ul><li>sensor nets, 4G: </li></ul><ul><li>handoff support (micro-mobility) </li></ul><ul><li>discovery and self-organization </li></ul><ul><li>ad-hoc routing, integrated with MAC </li></ul><ul><li>peer-to-peer modes </li></ul><ul><li>multicast, QoS, security, etc. </li></ul><ul><li> closer layer 2/3 coupling needed </li></ul>IP extensions or generalized L2 MAC??
  29. 29. Mobile Networks: 3G/WLAN interworking Techniques for seamless service: - Authentication, global roaming - Security issues - Dynamic handoff - End-to-end QoS control - Network management - Service level agreements Bluetooth<-> 3G IWF WLAN<->3G IWF Bluetooth UWB, Bluetooth<->WLAN IWF WLAN, HiperLAN, UWB, Cellular/2.5G,3G 3G/WLAN interworking Unified Mgmt Layer Protocol stacks PHY link net IWF1 IWF2 BT WLAN 3G Multiple devices with various radio interfaces
  30. 30. <ul><li>Mobile user passes through hot-spot (Infostation) in sec during which ~MB files are downloaded/uploaded </li></ul><ul><ul><li>Requires modifications to conventional WLAN MAC, incl fast synch, pre-authentication, etc. </li></ul></ul><ul><ul><li>Motivates 2-tier arch with ~10m service zone (for high-speed data transfer) and ~50m access control zone </li></ul></ul>Transit time ~sec Infostations access point Data cache ~100 MB/s Fast transfer Low-speed control channel (for synch & service setup) Service Zone Access Control Zone Total transit time ~10sec Mobile Networks: Hot-Spot MAC
  31. 31. <ul><li>802.11a MAC can be used for opportunistic service </li></ul><ul><ul><li>Pre-authenticate user in low-bit rate mode (~50m range) </li></ul></ul><ul><ul><li>Mobile terminal waits for modem to reach max 54 Mbps (~10m range) </li></ul></ul><ul><ul><li>High priority access mode used for Infostations access </li></ul></ul>Mobile Networks: Hot-Spot MAC AP Beacon IS Control packet Terminal enters WLAN coverage area Mobile requests advance authentication ........ Authentication message exchange PIFS normal channel activity .. IS transfer request* PIFS Infostations file transfer* Terminal enters max PHY speed zone ACK A1 A2 A3 Priority Access initiated *RTS/CTS msgs not shown time
  32. 32. <ul><li>UWB potentially well-suited for sensor networks </li></ul><ul><ul><li>Bit-rate readily traded off against range </li></ul></ul><ul><ul><li>Energy efficient modulation </li></ul></ul><ul><ul><li>Robust to interference </li></ul></ul><ul><ul><li>Multiple radio links supported by single UWB RF </li></ul></ul><ul><ul><li>Low cost silicon for integrated sensor device </li></ul></ul>Mobile Networks: UWB Sensors S1 S2 S3 UWB (R13, code 13) UWB (R12, code 12) UWB (R23, code 23)
  33. 33. <ul><li>Potential MAC/link layer based on DS/CDMA UWB PHY: </li></ul><ul><ul><li>Continuous beacon for synchronization & sensor ID broadcast </li></ul></ul><ul><ul><li>Low bit-rate, high-spreading gain common link establishment channel with a single code used in random access mode </li></ul></ul><ul><ul><li>Handshake protocol for setting achievable link bit-rate with dedicated code </li></ul></ul>Mobile Networks: UWB Sensor MAC S1 S2 Beacon S1 Beacon S2 S1 S2 Link establishment signal (S1,S2, C12) Link ACK (S1,S2, C12) Control Code A Code B Common code Rate adaptation, ARQ
  34. 34. <ul><li>Ad-hoc network ideas proposed for tactical and sensor scenarios, with potential applications to WLAN/4G: </li></ul><ul><ul><li>flat network model with multi-hop routing radios </li></ul></ul><ul><ul><li>on-demand routing protocols (DSR, AODV, etc.) designed for high node mobility (...fairly mature topic) </li></ul></ul><ul><ul><li>enhancements via MAC clustering, energy-efficient routing, .. </li></ul></ul><ul><ul><li>application-level data aggregation (diffusion routing, XML,..) </li></ul></ul><ul><ul><li>geographically constrained routing </li></ul></ul>Mobile Networks: Ad-hoc Networks SN MAC cluster (optional) radio links for multi-hop routing <ul><li>Active problem areas: </li></ul><ul><li>Scaling of capacity </li></ul><ul><li>Dynamic behavior </li></ul><ul><li>Energy efficiency </li></ul><ul><li>MAC/routing interactions </li></ul><ul><li>QoS routing </li></ul><ul><li>Geo routing </li></ul><ul><li>Security of ad-hoc nodes </li></ul><ul><li>Integration with WLAN, etc. </li></ul>
  35. 35. <ul><li>Hierarchical, self-organizing network currently under consideration, based on: </li></ul><ul><ul><li>3 service tiers (cellular, WLAN, personal area) </li></ul></ul><ul><ul><li>BS’s, AP’s, FN’s (forwarding radio nodes), user devices </li></ul></ul><ul><ul><li>automatic discovery and power mgmt protocols </li></ul></ul><ul><ul><li>hierarchical, ad-hoc multihop routing and spatial MAC </li></ul></ul>Mobile Networks: Hierarchical Ad-Hoc Net Internet Forwarding node low-tier (e.g. sensor) user nodes Access Point FN AP BTS 3G cell personal-area pico-cell WLAN micro-cell
  36. 36. <ul><li>Research issues which arise in connection with information delivery over wireless nets: </li></ul><ul><ul><li>Qos with heterogeneous & time-varying radios </li></ul></ul><ul><ul><li>transport layer problems (TCP timeouts, etc.) </li></ul></ul><ul><ul><li>need for services such as reliable multicast </li></ul></ul><ul><ul><li>information “pull” model vs. multicasting model </li></ul></ul><ul><ul><li>opportunistic services (hot-spots, caching,..) </li></ul></ul><ul><ul><li>delivery of the “right information” at the “right time and place” (location/content aware) </li></ul></ul><ul><ul><li>media scaling to match radio and terminal capabilities </li></ul></ul><ul><ul><li>sensor network & pervasive computing software models </li></ul></ul>Mobile Networks: Higher Layers
  37. 37. <ul><li>New real-time, context- and location-aware information delivery paradigms under consideration ... </li></ul><ul><li>Content multicasting based on XML investigated as possible option for delivering relevant info to mobiles. </li></ul>Mobile Networks: Content Multicast SX SX Content Provider Semantic Router A Semantic Router B Interest profile Mobile interest profile contains: (user, location, terminal capability,..) content multicast User XML Descriptor
  38. 38. <ul><li>A flexible, open-architecture mobile/ad-hoc sensor network testbed recently established at WINLAB </li></ul><ul><ul><li>open-source Linux routers and AP’s (commercial hardware) </li></ul></ul><ul><ul><li>Linux and embedded OS forwarding and sensor nodes (custom) </li></ul></ul><ul><ul><li>radio link and global network monitoring/visualization tools </li></ul></ul>Mobile Networks: Experimental Research PC-based Linux router Router network with arbirtrary topology AP Compute & storage servers Management stations Radio Monitor Forwarding Node/AP (custom) Sensor Node (custom) 802.11b PDA 802.11b Linux PC Commercial 802.11
  39. 39. Wireless Research: Multidisciplinary Research Topics <ul><li>In conclusion, we mention some wireless-related multidisciplinary research topics: </li></ul><ul><ul><li>spectrum regulation principles (...economics, policy) </li></ul></ul><ul><ul><li>integrated wireless sensors (...materials, semiconductor) </li></ul></ul><ul><ul><li>software models for pervasive computing (..CE, CS) </li></ul></ul><ul><ul><li>dynamics of large-scale ad-hoc sensor nets (...math, control) </li></ul></ul><ul><ul><li>security in ad-hoc sensor networks (...CS) </li></ul></ul><ul><ul><li>new applications of sensors: environmental, medical, public safety, etc. (..CS, domain experts from various disciplines) </li></ul></ul><ul><ul><li>robotics (..mechanical, controls) </li></ul></ul>