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Link/Network Layer: MIMO, Cognitive Radio; Energy Management of Radio Resource Control (RRC)

Link/Network Layer: MIMO, Cognitive Radio; Energy Management of Radio Resource Control (RRC). Y. Richard Yang 11 /15/2012. Outline. Admin. and recap Improve mesh capacity Reduce L (infrastructure “ blackholes ” , mobility for delay tolerant networks) MIMO: Use multiple antennas

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Link/Network Layer: MIMO, Cognitive Radio; Energy Management of Radio Resource Control (RRC)

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  1. Link/Network Layer:MIMO, Cognitive Radio; Energy Management of Radio Resource Control (RRC) Y. Richard Yang 11/15/2012

  2. Outline • Admin. and recap • Improve mesh capacity • Reduce L (infrastructure “blackholes”, mobility for delay tolerant networks) • MIMO: Use multiple antennas • Cognitive radio: use more spectrum • Radio resource management for energy management of mobile devices

  3. Admin. • Project meeting slots to be posted on classesv2

  4. receiver r (1+D)r sender Recap: Constraints in Capacity Analysis Radio interface constraint Interference constraint • a single half-duplex transceiver at each node • transmissionsuccessful if there areno other transmitterswithin a distance (1+D)rof the receiver

  5. Recap: Capacity Bound Note: Let L be the average (direct-line) distance for all T end-to-end bits. rate*distance capacity:

  6. Improving Wireless Mesh Capacity Radio interface constraint Interference constraint • a single half-duplex transceiver at each node • transmissionsuccessful if there areno other transmitterswithin a distance (1+D)rof the receiver Reduce L Increase W Approx.optimal rate*distance capacity: Multipletransceivers Reduceinterf. area

  7. Outline • Admin. and recap • Improve mesh capacity • Reduce L (infrastructure “blackholes”, mobility for delay tolerant networks) • MIMO: Use multiple antennas

  8. Multiple Input Multiple Output (MIMO) • 4x4 MIMO • http://www.quantenna.com/qac-2300rdk.html • LTE • Kindle Fire HD

  9. 1 1 2 2 MIMO Basics Solve two variables from two equations.

  10. Using MIMO for more Concurrency: Motivation No Transmission in current 802.11n Assume tx1 is sending to rx1 Can tx2 transmit in 802.11 using carrier sensing?

  11. MIMO Benefit: Concurrency using Interference Nulling tx2: for every symbol q, transmits q on first antenna and aq on second antenna. interference at rx1: if tx2 picks NO interference at rx1.

  12. Problem • rx2 hears p from tx1 • Can rx2 decode?

  13. Decoding at rx2: Observation • for different symbols p from tx1, the received signal at rx2 moves along a 1-d vector Perp. Of tx1 space • rx2 can estimate channels h12, h13 from preamble

  14. Decoding at rx2: Removing tx1 signal by Projection • rx2 projects received signal orthogonal to projection space

  15. Decoding at rx2: Projection Details - rx2 picks w2 and w3:to compute projection space

  16. Decoding at rx2: Projection Details => Summary: MIMO allows concurrency w/ interference nulling.

  17. Problem of Only Nulling If only nulling, tx3 cannot transmit nulling Assume both tx1 and tx2 are transmitting.

  18. Solution: MIMO using Interference Alignment Key idea: rx2 ignores interference from tx1 by projection. If tx3 aligns tx3 -> rx2 interference along the same direction as that oftx1 -> rx2, then rx2 can remove it too. nulling Assume both tx1 and tx2 are transmitting.

  19. MIMO with Nulling and Alignment tx3 picks ’, ’, ’ rx2 sees: Because rx2 projects to orthogonal to , no interference from tx3 to rx2

  20. Outline • Admin. and recap • Improve mesh capacity • Reduce L (infrastructure “blackholes”, mobility for delay tolerant networks) • MIMO: Use multiple antennas • Cognitive radio: use unlicensed spectrum

  21. Spectrum Allocation Chart

  22. Unlicensed Spectrum • Opportunity: unlicensed spectrum is large and has low utilization • US unlicensed freq: • 2.400-2.4835 G • 902-928 M • 5.800-5.925G • 5.15-5.25 G (200 mw) • 5.25-5.35 (1 w) • 5.725-5.825 (4w)

  23. 802.11a Zigbee Problem of Using Unlicenced • Unlicensed spectrum may have occupants and is fragmented • Requirement: Coexistence with dynamic and unknown narrowband devices in the unlicensed spectrum Unlicensed Spectrum Others

  24. Wideband 802.11a Zigbee Existing Solutions • Operate below noise-level Limits range Unlicensed Spectrum Others

  25. 802.11a Zigbee Existing Solutions • Operate below noise-level Limits range 2. Pick a contiguous unoccupied band Limits throughput Wideband Unlicensed Spectrum Others

  26. 802.11a Zigbee Existing Solutions • Operate below noise-level Limits range 2. Pick a contiguous unoccupied band Limits throughput Wideband Sacrifice Throughput or Range! Unlicensed Spectrum Others

  27. 802.11a Zigbee Swift: Cognitive Aggregation • Cognition: Detect unoccupied bands • Aggregation: Weave all unoccupied bands into one link Wideband Unlicensed Spectrum Others

  28. Research Issues • How to detect available frequency bands? • How to operate across chunks of non-contiguous frequencies? • How do sender and receiver establish communication when their perceived available frequency bands differ?

  29. Aggregating Non-Contiguous Bands • Leverage OFDM • Divides frequency band into multiple sub-bands that can be treated independently • Transmitter: Puts power and data only in OFDM bands not occupied by narrowband devices • Receiver: Extracts data only from OFDM bands used by transmitter Frequency band

  30. Ideal Threshold Cognition: How to detect occupied bands? • Unlicensed  Can’t assume known narrowband devices • Typical solution: Power threshold Narrowband Power in dBm Faraway 802.11 Baseband Frequencies (MHz)

  31. Ideal Threshold Cognition: How to detect occupied bands? • Unlicensed  Can’t assume known narrowband devices • Typical solution: Power threshold Narrowband Power in dBm Faraway 802.11 Baseband Frequencies (MHz) Problem: No Single Threshold Works Across All Locations

  32. Ideal Threshold Cognition: How to detect occupied bands? Unlicensed  Can’t assume known narrowband devices Typical solution: Power threshold Narrowband Power in dBm Nearby 802.11 Faraway 802.11 Baseband Frequencies (MHz)

  33. Adaptive Sensing • Unlicensed devices typically react to interference • Carrier sense in 802.11, TCP backoff, etc. Intuitively: • Poke the narrowband device, putting power in ambiguous bands • If the narrowband device reacts, back away Reasonable for unlicensed spectrum, which operates as best-effort

  34. Continuously sense the medium when not sending a packet Detect appearance of narrowband device when narrowband power exceeds noise level Detect reaction from changes in narrowband power profile Adaptive Sensing: Alg

  35. Carrier Sense (e.g.,802.11): Will not transmit when sensing a SWIFT packet Probability of narrowband power immediately after a SWIFT packet Back-off (e.g., TCP, MAC): Will send less often Inter-arrivals of narrowband power Duration of narrowband power Autorate:Will use lower modulation, increasing packet size Look for statistically significant change in metric using standard tests (e.g. t-test)

  36. Adaptive Sensing in Action • Start with a conservative choice of bands • Keep tightening as long as narrowband is unaffected Conservative Threshold

  37. Adaptive Sensing in Action • Start with a conservative choice of bands • Keep tightening as long as narrowband is unaffected Wideband

  38. Adaptive Sensing in Action Wideband Metric Estimate Normal Behavior Time

  39. Adaptive Sensing in Action Tighten Wideband Sense Metric Test: Same as Normal Time

  40. Adaptive Sensing in Action Tighten Wideband Sense Metric Test: Different from Normal Time

  41. Adaptive Sensing in Action Loosen Wideband Sense Metric Test: Same as Normal Time

  42. Wideband Throughput and Range • Baseline that operates below the noise of 802.11

  43. Wideband Throughput and Range

  44. Other Work • Cognitive Radios • 802.22, KNOWS, CORVUS, DIMSUMNet etc. • Wideband systems • Intel, Chandrakasan et al., Mishra et al., Sodini et al.

  45. Outline • Admin. and recap • Improve mesh capacity • Radio resource management for energy management

  46. Many link layers use a hybrid approach Mobile device uses random access to request radio resource The device holds the radio resource during a session RACH (request signaling channel) SDCCH (request call setup) AGCH (assign signaling channel) SDCCH (assign TCH) Recall: GSM Logical Channels and Request call setup from an MS BTS MS SDCCH message exchange Communication

  47. Radio Resource Control Setup for Data in 3G + RRC connection setup: ~ 1sec Radio Bearer Setup: ~ 1 sec Figure source: HSDPA/HSUPA for UMTS: High Speed Radio Access for Mobile Communications. John Wiley and Sons, Inc., 2006. Source: Erran Li.

  48. RRC State Management in UMTS • Given the large overhead to set up radio resources, UMTS implements RRC state machine on mobile devices for data connection Courtesy: Erran Li.

  49. RRC of a Large Commercial 3G Net DCH Tail: 5 sec FACH Tail: 12 sec Tail Time: waiting inactivity timers to expire DCH: High Power State (high throughput and power consumption) FACH: Low Power State (low throughput and power consumption) IDLE: No radio resource allocated Promo Delay: 2 Sec

  50. RRC Effects on Device/Network

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