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Cog-Fi: A Cognitive Wi-Fi Channel Hopping Architecture for Urban MANETs

Cog-Fi: A Cognitive Wi-Fi Channel Hopping Architecture for Urban MANETs. Sung Chul Choi and Mario Gerla WONS 2012 Presentation. Motivation. Motivation. Network Model. Mobile node. Fixed Interfering source. Network Model. Network node. 8. ch. Interfering source. 3. 5. 1. 4.

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Cog-Fi: A Cognitive Wi-Fi Channel Hopping Architecture for Urban MANETs

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  1. Cog-Fi: A Cognitive Wi-Fi Channel Hopping Architecture for Urban MANETs Sung Chul Choi and Mario Gerla WONS 2012 Presentation

  2. Motivation

  3. Motivation

  4. Network Model Mobile node Fixed Interfering source

  5. Network Model Network node 8 ch Interfering source 3 5 1 4 • Goal: Avoid the channels used by interfering sources using a cognitive multi-channel scheme. 1

  6. Solution Preview • To avoid interfering sources: • Use Cognitive radio technology to sense channel load and discover lightly loaded channels • To maintain P2P network connectivity in spite of unpredictable interferers: • Exploit multi channel diversity: a node can receive on multiple channels via Cognitive Channel Hopping • Guarantee neighbor discovery and rendezvous in a finite # of steps(using the QUORUM set) • Design routing algorithm that accounts for “multichannel links” and Channel Hopping

  7. Cognitive Channel Hopping • Cognitive Channel Hopping (CCH) • Single-radio, channel-hopping solution in which each node picks its channels based on the load sensed on them f f f f f f t t t t t t

  8. CCH: Protocol Operation • A node x periodically triggers Channel Quality Assessment (CQA). • A channel availability vector a = {a1, …, a|C|} is produced. • In this work, ai = 1 - [channel load in i]. • Based on channel availabilities, x picks a channel setQ = {q1, …, qk} from a predefined Quorum list (any two Q-sets have at least one common element) C = {0, 1, 2, … , 11, 12} • It picks the channel set with the highest combined channel quality, defined as: Example list of channel sets, each with size k = 5.

  9. CCH: Protocol Operation • Given Q, x generates two hopping sequences, utx and urx. Mrx Mtx 0 1 3 9 12 0 1 3 9 12 0 1 3 9 12 1 3 9 12 0 Q = {0, 1, 3, 9, 12} 0 1 3 9 12 3 9 12 0 1 k = 5 0 1 3 9 12 9 12 0 1 3 0 1 3 9 12 12 0 1 3 9 … 0 1 3 9 12 0 1 3 9 12 0 1 3 9 12 0 1 3 utx … 0 1 3 9 12 1 3 9 12 0 3 9 12 0 1 9 12 0 urx |utx| = |urx| = k2 = 25

  10. CCH: Channel Rendezvous Property • Claim: A channel rendezvous of a pair of nodes is guaranteed to occur within k2 slots. Mtx(x) Mrx(y) 2 2 2 3 3 3 4 4 4 0 0 0 1 1 1 2 2 2 Qx = {0, 1, 2} Qx = {0, 1, 2} 3 3 3 4 4 4 2 2 2 0 0 0 1 1 1 2 2 2 Qy = {2, 3, 4} Qy = {2, 3, 4} 4 4 4 2 2 2 3 3 3 0 0 0 1 1 1 2 2 2 By the property of a quorum system, there exists at least one common channel. 2 appears in the same column, every row. 2 appears exactly once in each column. … … utx(x) urx(y) … …

  11. CCH: Channel Rendezvous Property • This still holds when two sequences are not in sync. Mtx(x) Mrx(y) 2 2 2 3 3 3 4 4 2 0 0 0 1 1 1 2 2 2 Qx = {0, 1, 2} Qx = {0, 1, 2} 3 3 3 4 4 4 2 3 2 0 0 0 1 1 1 2 2 2 Qy = {2, 3, 4} Qy = {2, 3, 4} 4 4 4 2 2 2 3 4 3 0 0 0 1 1 1 2 2 2 By the property of a quorum system, there exists at least one common channel. 2 appears in the same column, every row. 2 appears exactly once in each column. … … utx(x) urx(y) … …

  12. CCH: Protocol Operation • When x has no packet to transmit, it follows urx(x). • When x has packets to transmit, it follows utx(x) to locate the neighbor. • A channel rendezvous is guaranteed within the length of utx(x), k2. channel quality assessment channel quality assessment slot 0 1 2 3 4 5 6 7 8 9 10 11 12 time tx slot Has packets to send to y. No more packets to send. rx slot

  13. CCH: Protocol Operation • Within a slot, a conventional RTS/CTS-based packet exchange is made. • By default, a slot is 10ms, enough to fit in tens of MAC frames. • Retransmissions occur within a slot and over multiple slots. backoff x RTS DATA y CTS ACK time

  14. CCH: Learning of utx and urx • Learning hopping sequences • Every CCH frame includes information about the hopping sequences that the transmitter is using. • If node x has received a frame from y, it can later use its cache to predict which channel y will be without scanning channels with utx(x). x y

  15. CCH: MAC-level Broadcast ? • Broadcast function is critical in making upper-layer mechanisms to work (e.g., routing). • Not all neighbors are in the same channel as you! 2 1 ? 1 1 4 ? ? 3 2 • Each broadcast frame is kept in a separate buffer and transmitted in the transmitting channel (specified in utx) in the beginning of the slot, for multiple slots.

  16. Solution: Cog-Fi Architecture • Cog-Fi is a cross-layer architecture with these modules: IP CH-LQSR CH-LQSR • Make a routing decision. Routing channel load, link rate, BER CCH • Coordinate channel access. • Store and maintain channel status. MAC SNR/BER 802.11 PHY • Regular 802.11 PHY. PHY

  17. CH-LQSR: Motivation • Conventionalon demand routing protocols like AODV and DSR are not well-suited. • Problem 1: Not all hops are equal. S T

  18. CH-LQSR: Motivation • Conventional, hop-count based routing protocols like AODV and DSR are not well-suited. • Problem 1: Not all hops are equal. 1 18Mbps 54Mbps T S 18Mbps 11Mbps 2

  19. CH-LQSR: Motivation • Conventional, hop-count based routing protocols like AODV and DSR are not well-suited. • Problem 2: Broadcast does not occur simultaneously. S T

  20. CH-LQSR: Motivation • Conventional, hop-count based routing protocols like AODV and DSR are not well-suited. • Problem 1: Not all hops are equal. • Use the channel load and link rates to quantifying the quality of each hop, and factor this in when computing routes. • Problem 2: Broadcast does not occur simultaneously. • Modify Route Discovery procedure.

  21. CH-LQSR: ETTCH Metric e v u • Extend ETX and ETT [4, 5]. • p: prob. that the packet transmission is not successful: p = 1 – (1 – pf) · (1 – pr) • s(m): prob. that the packet is delivered at m-th attempt. s(m) = pm – 1 · (1 – p) • The expected transmission count (ETX) of link e = (u, v) is: • Factoring in the link bandwidth and packet size, one can define the expected transmission time (ETT) of e as: • c: channel index • Sd: data packet size • B: bandwidth (data rate) of the channel B, the bandwidth, is computed by taking the channel load and link rates into account. pfand pr, the forward and backward packet error probabilities, are computed based on the link BER reported from the PHY module.

  22. CH-LQSR: ETTCH Metric e v u • (cont'd. from the previous slide) • The multi-channel ETT of e, ETT(e), is: which is the avg. of ETTc(e) values over the channels in the channel set the receiver v is using. • Finally, Channel Hopping ETT of a path P is:

  23. CH-LQSR: Protocol Operation • Extension of DSR • Route Discovery involving RREQ/RREP. • Once a route is discovered, source routing is used. A B How do I reach T? S C D E Here I am! T

  24. CH-LQSR: Protocol Operation • Extension of DSR • Route Discovery involving RREQ/RREP RREQ(T) RREQ(T) RREQ(T) RREQ(T) RREQ(T) RREQ(T) Path: S Path: S-A-B ETTCH: 0.032 Path: S-A ETTCH: 0.012 Path: S-D ETTCH: 0.011 Path: S-A-B-C ETTCH: 0.076 Path: S A B S C D E RouteCache(E) RouteCache(E) ETTCH ETTCH path path src src dest dest T S-A-B-C S-D 0.076 0.011 T T S S

  25. Cog-Fi: Evaluation Setup • QualNet 4.5 • CCH: implemented as a full-fledged MAC protocol. • CH-LQSR: implemented as a full-fledged routing protocol. • Channel environment • 13 orthogonal channels in the 5-GHz band. • Interfering source: (x, y, tx_power, channel, active_%). • CCH parameters • Use RBAR for rate adaptation [8], using 802.11a rates. • Channel set size k = 5. • Channel switching delay: 80µs. • Slot size: 10ms. • CQA Period: 3 seconds.

  26. Cog-Fi: Evaluation Setup • List of schemes compared for evaluation [COG] for single-radio nodes CONTROL Symbol Description CCH+CH-LQSR Our Cog-Fi solution. CCH+DSR CCH with DSR. CCH+AODV CCH with AODV. time scanning communication control interference 802.11a Single-channel 802.11a, routed using DSR. COG A conventional cog radio scheme, with DSR. RH+DSR Random hopping and DSR.

  27. Cog-Fi: 25-node (5x5) Grid Topology • 5 saturated 1500-byte CBR streams for 5 random node pairs. 1 … 2 40m … 2 3 7 5 … … … … 8 4

  28. Cog-Fi: 100-node (10x10) Grid • 5 saturated 1500-byte CBR streams for 5 random node pairs. 1 … 2 30m … 2 3 7 5 … … … … 8 4

  29. Summary • Goal: Devise a multi-channel multi-hop mechanism with the following requirements. • Interfering sources should be avoided • A CCH node employs a cognitive radio-like channel sensing to identify lightly loaded channels. • The network connectivity must be maintained. • Exploit multi channel diversity: a node can receiver on multiple channels via Cognitive Channel Hopping • Guarantee neighbor discovery and rendezvous in a finite # of steps(using the QUORUM set) • Performance is further improved by CH-LQSR, ie by using a link metric that factors in channel load and link rates.

  30. Thank You!

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