Comparison of Data-driven Link Estimation Methods in Low-power Wireless Networks HONGWEI ZHANG LIFENG SANG ANISH ARORA.

Presentación del tema: "Comparison of Data-driven Link Estimation Methods in Low-power Wireless Networks HONGWEI ZHANG LIFENG SANG ANISH ARORA."— Transcripción de la presentación:

1 Comparison of Data-driven Link Estimation Methods in Low-power Wireless Networks HONGWEI ZHANG LIFENG SANG ANISH ARORA

2 From sensor networks to cyber-physical systems (CPS)  Sensing, networking, and computing tightly coupled with the physical world  Automotive  Alternative energy grid  Industrial monitoring and control  Wireless networks as carriers of mission- critical sensing and control information  Stringent requirements on predictable QoS such as reliability and latency

3 Dynamic wireless links Link estimation becomes a basic element of routing in wireless networks. 5.5 meters (  2 secs) transitional region (unstable & unreliable)

4 Why not beacon-based link estimation?

5 Sampling error due to traffic- induced interference Unicast ETX in different traffic/interference scenarios

6 Sampling error due to temporal link correlation mean reliability of each unicast-physical- transmission minus that of broadcast Errors in estimating unicast ETX via broadcast reliability: estimated unicast ETX minus actual unicast ETX and then divided by actual unicast ETX

7 Two representative methods for estimating ETX  L-NT  uses aggregate unicast feedback {NT i }  represents SPEED, LOF, CARP  L-ETX  uses derived information for individual unicast-physical-transmission  represents four-bit-estimation, EAR, NADV, MintRoute EWMA {NT i }ETX PDR calculation {NT i }{PDR j } EWMA PDR 1/PDR ETX

8 Relative accuracy in L-NT and L-ETX  where P 0 is the failure probability of a unicast-physical- transmission, and W is the window size for calculating PDR j ;  COV[NT i ] > COV[PDR j ] if (which generally holds), thus DE k (L-NT) > DE k (PDR) L-ETX tends to be more accurate than L-NT in estimating link ETX.  DE k (L-ETX)

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13 Testbed based link-level experimentation  We use Mica2 motes that are deployed in a 14  7 grid  Focus on links of the middle row  Interferers randomly distributed in the rest 6 rows, with 7 motes on each row on average; interfering traffic is controlled by the probability d of generating a packet at an arbitrary time

14 Variants of L-NT and L-ETX Variant/stabilized L-NT: L-WNT L-NADV (variant of L-ETX): estimate PER instead of PDR

15 L-NT vs. L-ETX: forwarders used MethodForwarderPercentage(%)Cost ratio L-NT 5 6 7 8 10 0.1 4.14 7.17 21.26 67.33 2.3 1.3 1.5 1.3 1 L-ETX 6 7 8 10 5.91 0.2 5.1 88.79 1.3 1.5 1.3 1

16 Testbed based routing experiments Convergecast routing in a 7  7 grid  A node at one corner as the sink  Other 48 nodes as sources generating packets based on the event traffic trace from “A Line in the Sand” sink

17 L-NT vs. L-ETX: routing performance Event reliability Number of transmissions per packet received Seemingly similar methods may differ significantly in routing behaviors (e.g., stability, optimality, and energy efficiency)

18 Other experimental results  Related data-driven protocols  L-ETX-geo, L-ETX  Periodic traffic, other event traffic load  Sparser network  Random network  Network throughput

19 Concluding remarks  Two seemingly methods L-ETX and L-NT differ significantly in routing performance  Variability of parameters being estimated significantly affects the reliability, stability, latency, and energy efficiency of data-driven link estimation and routing  Future work  Other metrics (e.g., RT oriented)  Opportunistic routing and biased-link-sampling