ieee dcoss’12
DESCRIPTION
IEEE DCOSS’12. Mitigate Funnel Effect in Sensor Networks with Multi-Interface Relay Nodes. Jorge Mena University of California, Los Angeles Mario Gerla University of California, Los Angeles Vana Kalogeraky Athens University of Economics and Business. 17 de Mayo de 2012. - PowerPoint PPT PresentationTRANSCRIPT
IEEE DCOSS’12Mitigate Funnel Effect in Sensor Networks
with Multi-Interface Relay Nodes
Jorge MenaUniversity of California, Los Angeles
Mario GerlaUniversity of California, Los Angeles
Vana KalogerakyAthens University of Economics and Business
17 de Mayo de 2012
2
Network Research Lab (NRL)
Vehicular Network (VaNet) Traffic congestion modeling and car sensor network
projects WiMax/WiFi testbed that spans the UCLA campus. Network Coding
Cognitive Networks (CogNets) Application, protocol stack and Physical sensing
spectrum allocation research Mobile Health Networks
PAN with UVA/UVB sensors research Radioactive particles sensor research (coming soon)
3
Sensors Networks
Transceivers adapted with a sensor devices (temp, motion, particles, etc.) Disposable, low-cost, low-performance
Sink node Powerful, reusable, resourceful Final destination of all data flows
Sensors establish ad-hoc networks with the goals to sense their surrounding environment and generate update data flows to the sink.
Mica2 sensor
4
The problem we address
Funnel effect problem Sensor networks with high activity may generate large
data flows. Flows from remote areas converge at the region that
surrounds the sink Consuming resources: bandwidth, power Duty cycles conserves energy and saves bandwidth but
may disconnect the network Decreases the number of available paths to sink Available paths consume the little bandwidth Sensors compete for bandwidth and scarse
Intense usage of spectrum resources and energy at the areas that surround the sink due to remote flows.
5
Preliminary view for a solution
If the problem is with resources…
… add more…
… or even more.
6
Relay Node Network
Relay nodes Mobile devices adapted with multiple radio interfaces
and larger power and computational resources They establish overlay networks using orthogonal
(non-interfering) channels on top of the sensor network.
More resources are added since there is no competition for the bandwidth
Using a second interface, a relay may pick up and drop off packets from the sensor network
Solution approach: Use an network of relay nodes that uses orthogonal
channels to provide additional resources to the sensor network that experiences the funnel effect.
7
Problem Statement
Now that we have an idea of what to do, the main question is:
How do we deploy such a network with the minimum number of relay nodes that
mitigate the funnel effect? Our contribution
A placement algorithm Minimum number of relay nodes
8
Network Model
A standard 2-D wireless network n nodes A unidirectional graph G(V,E)
V is the set of vertices (nodes) E is the set of edges (links)
A subset of available channels Cu for each node u from the total set C.
A transmission range r Eucledian distance d(u,v) between two nodes u and v Edge e = (u,v) belongs to E if
d(u,v) < r (the two nodes hear each other) Intersection of Cu and Cv is not empty (there is at least one
common channel)
9
Assumptions
A node u is able to tune its interfaces to any of its channels c in Cu
A sensor has only one interface that is tuned to a common channel c
A relay node has at least two interfaces that may be tuned to any channel in C
Static assignment or some channel assignment algorithm Relay nodes may be potentially connected to several
networks at the same time. SDR, AODV routing for within the intra-net; static routes
for inter-nets. A decision is made at a relay node to accept traffic or
not (policy based through route announcement).
10
Funnel Effect Mitigation – Congested Region Congested Region
A group of nodes characterized by their proximity that experience a high demand of their resources.
A node is considered congested if its local statistics surpass some threshold ETD, packet drops, jitter, etc.
A message exchange protocol with high priority on control packets determine this region and forms a cluster with a well-defined boundary (its Convex Hull)
11
Funnel Effect Mitigation – Basic Intuition Two remote sensor nodes, S1 and S2 may
be connected by a relay node R provided that it is placed within the intersection of the sensors’ ranges:
r < d(S1,S2) ≤ 2r
12
FEM – Relay Placement
Given a congested region and our basic intuition, cover the region with relays
In a circular-manner, cover the convex hull until all the edge nodes are connected to at least one relay node
Repeat with the inner ring of relay nodes
Stop when the inner-most ring is connected to the sink.
13
Placement Condition
To approach the minimal number of relay nodes, we use the placement condition:
The geographical location of a new relay node is that which covers the largest amount number of elements and it is closest to the sink
14
Placement Condition
Node proximity:The minimum allowed proximity distance for two nodes to be covered by one relay is r√(3)
This guarantees that a relay node is placed at a location at least r/2 units closer to the sink from the midpoint of the segment of two nodes being covered
extent is the parameter that controls up to what node proximity the new relay will cover.
15
Node Extent
d(S1,S2) ≤ r × extent < 2r
16
Placement Theory
Theorem 1If the point c (slide 18) lies within the
placement area, then it is the only geographical location that satisfies the
placement condition. Corollary 1
If the point c lies outside the placement area, then the closest point a or b to c
has the best placement.
17
Three Scenarios (First)
18
Three Scenarios (Second)
19
Three Scenarios (Third)
20
The Placement Algorithm Input: Congested region C, sink, extent Output: List R of relay node placements
R = 0 if all elements in C are covered, return R C’ = Convex Hull(C) Sort C’ so we can visit each element in clock-wise order (make a ring) for each element e in C’ not covered:
if e reaches the sink, mark it as covered and continue the loop find the simple best placement p for e and mark it as covered for each e’ in C’ after e that is not covered:
if d(e,e’) > r x extent, break this loop find the best placement q for the triangle (e,e’,sink) and mark
e’ as covered R = R U Closest(sink,{p,q})
return Algorithm1(R, extent, sink)
21
The Placement Algorithm
22
Algorithm Analysis
The complexity time to calculate the Convex Hull of a set C of size m is O(mlog(h)), for h being the number of elements in the hull.
Sorting C’ takes O(hlog(h)) The nested loops visit every single element in the hull (h)
exactly one time, so it’s linear Since m>h, the dominating factor is the repeated
calculations of the convex hull Due to the placement condition, for every recursive call,
the algorithm advances at least r/2 units closer into the sink. rC’ is the radius of first Convex Hull. There are rC’/r/2 =
2rC’/r number of recursive calls (constant) So the overall complexity is dominated by O(mlog(h))
23
Experiment Settings
Simulation QualNet 5.0 1000m by 1200m flat terrain with
Rayleigh fading model (forrest, debris) 40 sensors, 1 sink, 7 feeding sensors WiFi 2Mbps Tx rate, 200m Tx range, 32-
Byte packet size at 4/sec (local traffic) Foreign sensors simulate the rest of the
network by generating packets of size 1KB at a rate of 2/sec.
24
Metrics Observed
Throughput observed per node E2E Delay observed per node Jitter of the data flow
inter-packet arrival gap of two consecutive packets sent from the same source.
25
Naïve Placement Strategy
26
Results (Number of Relays)
Placement Constraint:
Our strategy tries to maximize the coverage of nodes by choosing the location that covers the most elements in the convex hull AND is the closest to the sink.
27
Results (Avg. Throughput)
Funnel Effect.
Without relays, we observe little throughput, mostly from the nodes inside the Congested Region. As a consequence, the foreign nodes starve.
28
Results (Avg. E2E Delay)
With relays the network stabilizes.
29
Results (Jitter Observed)
The relay network improves the availability of data due to the addition of new path resources.
30
Conclusions
Placement condition guarantees minimum number of relay nodes used 43% less relays used
O(mlog(h)) algorithm Improves observed throughput and delivery
ratio It stabilized the transmission delay
Less oscillations of data flows Decreases the jitter, making packets more
readily available
31