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Interference-Aware Fair Rate Control in Wireless Sensor Networks (IFRC)

Interference-Aware Fair Rate Control in Wireless Sensor Networks (IFRC)

Sumit Rangwala

Ramakrishna Gummadi, Ramesh Govindan, Konstantinos Psounis

Wireless network of N nodes

Data transmission over multiple hops to a single node

“Design a distributed algorithm to dynamically allocate fair and efficient rate to each flow”

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Neighbor

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- Nodes measured vibrations and transmitted it to a central node
- Over multiple hops

- Preconfigured rates for each flow
- Led to congestion
- More than an hour to receive 10 min of vibration data in a 15 node network

- Led to congestion

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- CSMA MAC (without RTS/CTS)
- Link-layer retransmissions
- Routing Tree
- One flow originating per node

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Assumptions consistent with current practice in sensornets

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- Goal
- Max-min allocation

- Wireless Networks
- Transmission rate from a node to its neighbor depends on neighborhood traffic
- Flows affecting this transmission rate are not merely flows traversing a node.

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B

Flows that affect each others' rate may not traverse a common link or node

- Transmission rate along 16 →14
- Dependent on traffic on various other links
- 20 → 16, 21 → 16, 14 → 12
- 17 →14, 13 →11, 12 →10

- Dependent on traffic on various other links

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- Transmission rate along 16 →14
- Dependent on traffic on various other links
- 20 → 16 (a) , 21 → 16 (b), 14 → 12 (c)
- 17 →14 (d), 13 →11 (e), 12 →10 (f)

- Dependent on traffic on various other links

- Transmission rate along 16 →14
- Dependent on traffic on various other links
- 20 → 16 (a) , 21 → 16 (b), 14 → 12 (c)
- 17 →14 (d), 13 →11 (e), 12 →10 (f)

- Dependent on traffic on various other links

- Transmission rate along 16 →14
- Dependent on traffic on various other links
- 20 → 16 (a) , 21 → 16 (b), 14 → 12 (c)
- 17 →14, 13 →11, 12 →10

- Dependent on traffic on various other links

Child/Parent

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- The rate of flows traversing 16 →14 (flows from 20, 21, and 16)
- … is affected by rate of:
- Flows originating from 17, 14, 13, 12,
- As well as 15, 18, 19

- … is affected by rate of:

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Interfering links

l1 interferes with a link l2 if transmission along l1 prevents

- initiation of a transmission along l2 or
- successful reception of a transmission along l2.
Potential interferer

Node n1 is a potential interferer of node n2 if

- flow originating from node n1 uses a link that interferes with the link n2 → parent(n2).

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Child/Parent

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For CSMAand many-to-one traffic

potential interferer (ni) includes

- neighbors of ni
- neighbors of parent(ni)
- Descendents of all the above nodes

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- Congestion Detection
- Based on avg. queue length

- Congestion Sharing
- To all the potential interferers

- Rate Adaptation
- AIMD

rlocal (rate of flow from this node)

Forwarding Traffic

Queue at each node

Packet transmitted until queue is empty (with retransmission)

IFRC adapts rate of flow originating at a node,

not the rate of flows traversing the node

- Congestion Detection
- Based on queue length calculated as
qavg = wq * qinst + (1- wq) * qavg

- Thresholding

- Based on queue length calculated as
- Rate Adaptation
- Every 1/rate sec (Additive Increase)
rate= rate + δ/ rate

- On local congestion (Multiplicative Decrease)
rate= rate/2

- Every 1/rate sec (Additive Increase)

- Each node piggybacks on every transmitted packet
- Its own rate (rlocal) and its congestion state
- Rate and congestion state of its most congested child

Rule 1:

Local rate of a node should not be greater than that of its parent

(rlocal <rparent)

Rule 2:

For any congested neighbor or congested child of a neighbor

Local rate should not be greater than the rate of the congested node

(rlocal <rcongested node)

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Child/Parent

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These rules are sufficient to signal all potential interferers

Queue Threshold

Network size and topology

Avg. depth of the tree

Queue Threshold

- Additive Increase
- δ = rate of increase

- Analytically characterize δ to ensure stability

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4th Floor

- Platform
- Tmote Sky
- TinyOS 1.1.15

- Setup
- 40 node testbed
- Network diameter = 8 hops

- Static routing tree
- Depth of the Tree = 9 hops
- Link quality varied from 66% to 96%

- 40 node testbed
- Each experiment was conducted for an hour

Base Station

Base Station

Average goodput as well as the instantaneous goodput is fair

IFRC achieves 80% of the optimal fair rate

IFRC achieves 60% of the optimal fair rate

IFRC achieves 60-80% of the optimal fair rate

Max Buffer Size = 64

Not a single drop due to queue overflow

- IFRC works without modification
- Sending rate = weight* rlocalpkts/sec

w = 1

w = 2

w = 1

IFRC assigns rate proportional to node weight

- Two base stations rooted at 1 and 41
- Nodes get rates that are fair across trees

- IFRC is efficient
- Node 4,5 and 6 get greater (but equal) rates
- Their flows don’t traverse the most congested region.

- Node 4,5 and 6 get greater (but equal) rates

- Analysis of set of flows that share congestion at a node
- Potential interferers

- Design and implementation of low-overhead rate control mechanism
- Analysis of IFRC’s steady-state behavior
- Provide guidelines for parameters selection

- For more Information
- http://enl.usc.edu/~srangwal/projects/ifrc.html

- Code
- Tinyos contrib
- tinyos-1.x/contrib/usc-ifrc

- ENL public CVS
- http://enl.usc.edu/cgi-bin/viewcvs/viewcvs.cgi/ifrc

- Tinyos contrib

Backup Slides

- fiflow originating from node i
- Fiflows routed through node I
- At each node i, define Ғito be the union of Fi and all sets Fj
- where j is either a neighbor of i, or a neighbor of i’s parent. These flows are flows from i’s potential interferers.

- Allocate to each flow in Ғia fair and efficient share of the nominal bandwidth B. Denote by fl,ithe rate allocated at node i to flow l.
- Repeat this calculation for each node.
- Assign to flthe minimum of fl,i over all nodes i.

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Child/Parent

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Sensornets

Graceful, fair, degradation under load [Hull et al. (Fusion), Wan et al. (CODA)]

Centralized rate allocation [Sankarasubramaniam et al. (ESRT), Ee et al.]

AIMD-based rate adaptation without congestion sharing [Woo et al.]

Wireless ad-hoc networks

Congestion sharing heuristics for any-to-any communication [Xu et al. (NRED)]

Unlike prior work, we precisely identify the set of potential interferers

These heuristics don’t precisely identify the set of potential interferers

- Based on queue length calculated as EWMA
qavg = wq * qinst + (1- wq) * qavg

- Multiple thresholds
- Lower threshold L
- Upper thresholds U(k) = U(k-1) + I/2k-1
- U(0) = U

Local Congestion

L

U

U + I

U + 3I/2

Local Congestion

- Slow start
- Starts with rate = rinit
- Every 1/ ratesec
- rate= rate + Φ

- Slow start ends when
- node itself get congested
- constrained by other nodes to reduce its rate
- Congestion sharing

every 1/ri sec

ri = ri+δ/ri

ri = ri /2

ri = ri /2

ri = ri /2

L

U

U + I

U + 3I/2

every 1/ri sec

ri = ri+δ/ri

ri remains unchanged

Rate adaptation with changing queue size

- Maintains rbase station, like rlocal of any other node, to share congestion across nodes
- Follows the same algorithm for rate adaptation with one exception
- Decreases rbase stationonly when a child of base station is congested.
- It does not decreases its rate when any other neighbor is congested or any child of a neighbor is congested.

- Decreases rbase stationonly when a child of base station is congested.

- Additive increase
- Constraint on ε
- U0 and U1 based on [Floyd et al.]
- Rule of thumb for Fj
- (n = size of network)

Max Queue Length

IFRC achieves 60-80% of the optimal fair rate

Nodes join

Nodes leave

- Special case of weighted fairness
- nodes with no data to send ≡ weight = 0

Base Stations