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

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

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

4. 4 Recap: Constraints in Capacity Analysis  transmission successful if there are no other transmitters within a distance (1+  )r of the receiver Interference constraint r a single half-duplex transceiver at each node Radio interface constraint receiver sender r (1+  )r

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

6. 6 Improving Wireless Mesh Capacity  transmission successful if there are no other transmitters within a distance (1+  )r of the receiver Interference constraint r a single half-duplex transceiver at each node Radio interface constraint rate*distance capacity: Reduce LIncrease W Approx. optimal Multiple transceivers Reduce interf. area

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

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

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

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

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

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

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

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

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

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

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

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

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

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

21. Spectrum Allocation Chart 21

22. Unlicensed Spectrum r Opportunity: unlicensed spectrum is large and has low utilization m 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) 22

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

24. Zigbee 802.11a Others Unlicensed Spectrum 1.Operate below noise-level Limits range Wideband Existing Solutions

25. Zigbee 802.11a Others Unlicensed Spectrum 1.Operate below noise-level Limits range 2. Pick a contiguous unoccupied band Limits throughput Wideband Existing Solutions

26. Zigbee 802.11a Others Unlicensed Spectrum 1.Operate below noise-level Limits range 2. Pick a contiguous unoccupied band Limits throughput Wideband Sacrifice Throughput or Range! Existing Solutions

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

28. Research Issues r How to detect available frequency bands? r How to operate across chunks of non- contiguous frequencies? r 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. Cognition: How to detect occupied bands? Unlicensed  Can’t assume known narrowband devices Typical solution: Power threshold Ideal Threshold Narrowband Power in dBm Baseband Frequencies (MHz) Faraway 802.11

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

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

33. Adaptive Sensing 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 Unlicensed devices typically react to interference Carrier sense in 802.11, TCP backoff, etc.

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. Narrowband ReactionDetection Metric 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 Autorate: Will use lower modulation, increasing packet size Duration of narrowband power Look for statistically significant change in metric using standard tests (e.g. t-test)

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

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

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

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

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

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

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

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

47. 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. 48 RRC Statement in UMTS r Given the large overhead to set up radio resources, UMTS implements RRC state machine on mobile devices for data connection ChannelRadio Power IDLENot allocated Almost zero CELL_FAC H Shared, Low Speed Low CELL_DCHDedicated, High Speed High Courtesy: Erran Li.

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

50. 50 RRC Effects on Device/Network FACH and DCH Wasted Radio Energy34% Wasted Channel Occupation Time33%

51. 51 Case Study: Pandora Streaming Problem: High resource overhead of periodic audience measurements (every 1 min) Recommendation: Delay transfers and batch them with delay-sensitive transfers Problem: High resource overhead of periodic audience measurements (every 1 min) Recommendation: Delay transfers and batch them with delay-sensitive transfers

52. 52 Case Study: Fox News Problem: Scattered bursts due to scrolling Recommendation: Group transfers of small thumbnail images in one burst Problem: Scattered bursts due to scrolling Recommendation: Group transfers of small thumbnail images in one burst

53. 53 Case Study: BBC News Scattered bursts of delayed FIN/RST Packets Problem: Scattered bursts of delayed FIN/RST packets Recommendation: Close a connection immediately if possible, or within tail time Problem: Scattered bursts of delayed FIN/RST packets Recommendation: Close a connection immediately if possible, or within tail time

54. 54 Case Study: Google Search Search three key words. ARO computes energy consumption for three phases I: Input phase S: Search phase T: Tail Phase UL Packets DL Packets Bursts RRC States Usr Input Problem: High resource overhead of query suggestions and instant search Recommendation: Balance between functionality and resource when battery is low Problem: High resource overhead of query suggestions and instant search Recommendation: Balance between functionality and resource when battery is low

55. 55 RRC State Transitions in LTE

56. 56 RRC State Transitions in LTE RRC_IDLE No radio resource allocated Low power state: 11.36mW average power Promotion delay from RRC_IDLE to RRC_CONNECTED: 260ms

57. RRC state transitions in LTE RRC_CONNECTED Radio resource allocated Power state is a function of data rate: 1060mW is the base power consumption Up to 3300mW transmitting at full speed 57 Cellular Networks and Mobile Computing (COMS 6998- 11) Courtesy: Junxian Huang et al.

58. RRC state transitions in LTE Continuous Reception Send/receive a packet Promote to RRC_CONNECTED Send/receive a packet Promote to RRC_CONNECTED Reset Ttail 58 Cellular Networks and Mobile Computing (COMS 6998- 11) Courtesy: Junxian Huang et al.

59. RRC state transitions in LTE Ttail stops Demote to RRC_IDLE DRX Ttail expires 59 Cellular Networks and Mobile Computing (COMS 6998- 11) Courtesy: Junxian Huang et al.

60. 60 Summary r App developers may not be aware of interactions with underlying network radio resource management r A good topic to think about as a part of your project

61. 61 Outline r Admin. and recap r Improve mesh capacity r Radio resource management for energy management r Intro to networks

62. 62 Summary: Wireless Link Layer r The basic services of the link layer m framing, link reliability, etc m link access: interference, quality of service (and fairness) control, link state management r Guided by network layer m transmit to which neighbor at what quality B A S E F H J D C G I K M N L

63. 63 Network Layer Services r Transport packets from source to dest r Network layer protocol in host and router Basic functions: r Control plane m compute routing from sources to destinations r Data plane: forwarding m move packets from input interface to appropriate output interface(s) B A S1S1 E D2D2 S2S2 J D1D1 C G I K M N L

64. 64 Network Layer: API r API (provided to upper layer) m transmit( info, src, dest, …); r A key decision in network layer design is how to represent destinations? m we refer to how applications specify destinations as the addressing scheme m the supported addressing scheme(s) can have profound impacts on usability, flexibility, and scalability

65. Discussion: How to Specify a Destination? 65 B A S E F H J D C G I K M N L

66. Two Basic Approaches for Identifying Destinations r Locators m Encode locations on network topology r Identifiers (ID) m independent of network topology 66 A E D CB F

67. Addressing Scheme: Sensornet Example r Destination: message to a sensor (e.g., who detected fire) m // id. m // loc m // prop. 67 B A S E D F J D C G I K M N L

68. Addressing Scheme: Printer r How may we specify the destination as the color printer on the 2 nd floor of AKW m Internet domain name: lw2c.cs.yale.edu m Internet protocol (IP) address: 128.36.231.8 m [building = AKW; floor=2; entity = printer; quality = color] 68

69. 69 Addressing Scheme: Telephone r Very first scheme: connection by operators to business m ID or locator?

70. 70 Addressing Scheme: Telephone r The telephone numbering scheme: m invented in 1888 by Almon Strowger, an undertaker : “No longer will my competitor steal all my business just because his wife is a BELL operator.”

71. Addressing Scheme: Telephone r E.164: Maximum 15 digits r Hierarchical addressing scheme: country code + national destination (area) code (optional) + subscriber number m e.g., +1-203-432-6400 r Why hierarchical addressing scheme? m 203-432 uniquely determines the switch upon which the telephone is attached to 71 B A S E D F J D C G I K M N L

72. 72 IP Addressing r Also a hierarchical locator addressing scheme m network part (high order bits) m host part (low order bits) r What’s a network? ( from IP address perspective) m device interfaces with same network part of IP address m link layer can reach each other 223.1.1.1 223.1.1.3 223.1.1.4 223.1.2.2 223.1.2.1 223.1.2.6 223.1.3.2 223.1.3.1 223.1.3.27 223.1.1.2 223.1.7.0 223.1.7.1 223.1.8.0 223.1.8.1 223.1.9.1 223.1.9.2

73. Summary r Evolution of telephone addressing scheme m Identifier (business type) m Identifier (person) m Locator (hierarchical phone #, Internet IP address) m Nowadays: identifier (person again w/ mobile phones) 73

74. Basic Network Layer Model 74 A E D C B F Each node is a network attachment point (e.g., router, base station), to which hosts/user equipment attaches User device identified by addressing scheme locator: identifies attachment point identifier: independent of location

75. 75 Routing in IP/Telephone Networks r Represent network as a graph r Determine a path to each destination on the graph r Key problems m Location management E.g., due to user mobility (roaming), attached point changes m Routing under mobility and wireless channels A E D CB F 2 2 1 3 1 1 2 5 3 5

76. Outline r Admin. r Location management m cellular networks 76

77. 77 BSC Radio Subsystem BSC Setting: GSM (Circuit Switching Domain) MS (mobile station) BSC (base station controller) BTS (base transceiver station) MSC (mobile switching center) GMSC (gateway MSC) fixed network MSC GMSC Network & Switching Subsystem and Operation Subsystem MS BTS

78. 78 Routing in Cellular Networks r Issues in cellular networks: m Location management: a phone # is mostly an identifier, to route a call to a phone #, how to find the current attachment point (BTS) of the phone? m Handoff: a user may move during a phone call, how to not drop the call?

79. 79 Two Primitives for Cellular Location Management r Mobile station: reports to the network of the cell it is in m called update m uses the uplink channel r Network: queries different cells to locate a mobile station m called paging m uses the downlink channel

80. 80 Performance of the Two Primitives r A city with 3M users r During busy hour (11 am - noon) r Update only m total # update messages: 25.84 millions m on average each user visited > 8 cells r Paging only m call arrival rate: 1433 calls/sec m total # paging transactions: 5.2 millions

81. Discussion r A user receives one call for ~5 cells (25M vs 5M) visited, thus may not need to update after every switching of cell r However, if no update at all, then paging cost can be high—may need to page the MS at every cell m Q: how do you page? 81

82. 82 Location Management Through Location Areas (LA) r A hybrid of paging and update r Used in the current cellular networks r Partitions the cells into location areas (LA) m e.g., around 10 cells in diameter in current systems r Each cell (BTS) periodically announces its LA id r If a mobile station arrives at a new location area, it updates the base station about its presence r When locating a MS, the network pages the cells in an LA

83. 83 How to Decide the LAs: A Simple Model r Assume the cells are given  Cell i has on average N i users in it during one unit time; each user receives calls per unit time  There are N ij users move from cell i to cell j in a unit of time Cell 1 Cell 2 N1N1 N2N2 N 12 N 21

84. 84 How to Decide the LAs: A Simple Scenario r Separate LAs for cells 1 and 2 m #update: m #paging: r Merge cells 1 and 2 into a single LA m #update: m #paging: Cell 1 Cell 2 N1N1 N2N2 N 12 N 21 N 12 + N 21 (N 1 + N 2 ) 0 2 (N 1 + N 2 )

85. Cost Comparison where C_update is relative cost of update to pgaing, assuming paging cost per cell is 1 85 At the same mobility, if call arrival rate is high, more likely separate At the same call arrival rate, if higher mobility, more likely to merge MergeSeparate

86. 86 Basic Location Management Practice in GSM r Base stations announce LA r Visiting network MSC maintains visitor location register (VLR) r If a MS moves to a new LA, it reports its location to visiting MSC r A global home location register (HLR) database for each carrier m MSC/VLR notifies HLR that it currently has MS

87. 87 BSC Radio Subsystem BSC GSM MS (mobile station) BSC (base station controller) BTS (base transceiver station) MSC (mobile switching center) GMSC (gateway MSC) fixed network MSC GMSC Network & Switching Subsystem and Operation Subsystem MS BTS VLR HLR

88. GSM Location Update: Example 88

89. GSM Location Update: Example 89

90. GSM Location Update: Example 90

91. GSM Location Update: RR Connection Setup 91

92. GSM Location Update: Update 92

93. GSM Location Update: Update 93

94. GSM Location Update: Update 94

95. GSM Location Update : Authenticate Subscriber 95

96. GSM Location Update: Enable Ciphering 96

97. GSM Location Update: RR Connection Release 97

98. Extension: From GSM to GPRS to 3G UMTS 98

99. Extension: From GSM to GPRS to 3G UMTS r Issue: it is anticipated that users will make more connections in data network m Same mobility but higher lambda => smaller location area 99

100. UMTS Location Update 100

101. 101 Summary r The LA/RA/UTRANA design considers m call pattern: when (how often) does a mobile station receive a call m mobility model: how does a mobile station move r Issues of LA based approaches m Users roaming in LA borders may generate a lot of updates

102. 102 Distributed Location Management Schemes r Timer based A MS sends an update after some given time T r Movement based A MS sends an update after it has visited N different cells r Distance based A MS sends an update after it has moved away for D distance (need ability to measure distance) r Profile based A MS predicts its mobility model and updates the network when necessary

103. 103 Timer-based Location Management  A MS sends an update after some given timer T r The network pages the MS upon a call request at all cells which the MS can potentially arrive during T m cells reachable from last update cell, e.g., within distance v max * T, where v max is the maximum speed r Question: how to determine T?

104. 104 Timer-based Location Management r Assume time between call arrivals is T call r Cell radius is d cell r Total bandwidth cost: Take derivative and set it to 0 to derive the optimal value:

105. 105 Summary: Location Management r Two primitives of location management in cellular networks m update (a proactive approach) m paging (a reactive approach) r Hybrid update/paging tradeoff m The location area (LA) approach m Distributed approaches timer based movement based distance based profile based

106. Remaining Issue: Handoff r A MS may be in a call during mobility r Issue: m the signal to/from the current serving base station (e.g., Node B in 3G) may gradually degrade as the MS moves away m the signal to/from the next base station may become better, but the signal strength is hard to know, if the MS is not actively communicating w/ the next base station 106

107. WCDMA Soft Handoff r An MS communicates with multiple Node Bs m Downlink: multiple base stations send to the MS and the MS combines the received signals m Uplink: multiple base stations receive data from the MS and forward to a RNC to combine The combing RNC is called the serving RNC 107

108. Serving RNC and Drift RNC 108 RNC1: Serving RNC RNC1: Serving RNC RNC2: Drift RNC Serving RNC handoff

109. UMTS Serving RNC Handoff r Serving RNC r Drift RNC 109

110. Backup Slides 110