Distance ADaptive (DAD) Broadcasting for Ad Hoc Networks
Dec 21, 2015
Copyright: S. Krishnamurthy, UCR
The Paper X. Chen, M. Faloutsos & S.V.
Krishnamurthy, “Distance Adaptive Broadcasting for Ad Hoc Networks”, in IEEE MILCOM 2002.
Copyright: S. Krishnamurthy, UCR
Objective To find a good way to perform
effective broadcasting in an ad hoc network such that: Fewer number of rebroadcasts are
needed. Achieve a higher coverage Achieve power efficiency Result in a fewer number of collisions
Copyright: S. Krishnamurthy, UCR
Our Approach Only outmost nodes rebroadcast
Outmost nodes are more likely to reach new nodes
We achieve a reduction in contention Each node identifies the outmost nodes
within its range based on some neighborhood information that is exchanged.
Copyright: S. Krishnamurthy, UCR
Roadmap Description of problem Metrics of Interest Previous work Our approach Results and Discussion Future work
Copyright: S. Krishnamurthy, UCR
Broadcasting in Ad hoc network
Definition A session in which information is to reach all
nodes. Multiple rebroadcasts (local) would be needed
Objective Perform broadcasting in an efficient way so as
to use fewer rebroadcasts while maintaining the requisite coverage
Copyright: S. Krishnamurthy, UCR
Metrics and parameters Metrics
Coverage – fraction of nodes reached Broadcast Efficiency Broadcast Latency or Duration
Parameters Mobility -- speed Node density
Copyright: S. Krishnamurthy, UCR
Previous work Flooding Expanding Ring Search –
application specific. S.Y.Ni, Broadcasting storm problem
Probabilistic Scheme wherein a node re-broadcasts a received packet with a certain probability.
Copyright: S. Krishnamurthy, UCR
General probabilistic broadcast (GEN)
Parameter k as the target rebroadcast size
When node receives a packet, it randomly generates a number n that is between 0 and its neighborhood size
If n < k, it will rebroadcast, otherwise it discards the packet.
The protocol attempts to have ‘k’ new rebroadcasts for every broadcast.
Copyright: S. Krishnamurthy, UCR
Broadcasting and outmost nodes
Not every node is needed to rebroadcast
It’s more efficient to let the outmost nodes rebroadcast
Outmost nodes span the desired area more quickly
E.g. outmost nodes 4,5,6,7,8 rebroadcast, it is not necessary for nodes 1,2,3 to rebroadcast.
Copyright: S. Krishnamurthy, UCR
Our approach Using power level to decide outmost
nodes Distance ADaptive: based on local
information, a node decides certain number of outmost nodes that are to rebroadcast.
Two variants DAD-NUM, DAD-PER
Copyright: S. Krishnamurthy, UCR
DAD-NUM• Fixed number of outmost nodes performing
rebroadcast• Node keeps a neighbor table to records the received
power level from each neighbor.• This table is sorted to decide the threshold power
level that identifies the outmost nodes• Include this threshold in the broadcast packet • When the packet is received, the receiver compares
the threshold in the packet and the received power strength to decide whether it should rebroadcast
Copyright: S. Krishnamurthy, UCR
DAD-NUM State diagram
Init_state
Pkt_recv.Set timer Pkt_Gen
Finished
Receiveda packet
Time out
If receiving power is less than threshold power in packet, ignore packet.
Time out
Find threshold power and putit in packet, broadcast packet.
Copyright: S. Krishnamurthy, UCR
DAD-PER Only difference from DAD-NUM:
• A fixed percentage of total neighboring nodes performing rebroadcast
Not good for topologies wherein node density is small or variant.
Copyright: S. Krishnamurthy, UCR
Simulation results System Setup
• Glomosim 2.0• 802.11 MAC CSMA/CA• Hello Message: every 5 seconds• Network topology in 3000m x 3000m• Transmission radius 223m• Result is average on 200 random topologies
Copyright: S. Krishnamurthy, UCR
Broadcast efficiency DAD-NUM has the
highest efficiency DAD-PER is better
than GEN when the rebroadcast size is small.
Copyright: S. Krishnamurthy, UCR
Coverage Bars represent the
improvement in coverage of DAD-NUM over GEN.
DAD-NUM can achieve up to a 20% increase in coverage.
Copyright: S. Krishnamurthy, UCR
Efficiency v.s. Coverage DAD-NUM can
achieve a better Coverage than GEN while attaining a higher broadcast efficiency.
Copyright: S. Krishnamurthy, UCR
Latency DAD-NUM takes a
short time to complete the broadcast session than GEN
Improvement can be up to 21%
Copyright: S. Krishnamurthy, UCR
Conclusion and future work
Conclusion DAD is better than GEN with regards to:
• Coverage• Efficiency• Latency
Future work Apply DAD to in power-heterogeneous
ad hoc networks.
Copyright: S. Krishnamurthy, UCR
The Paper S.Agarwal, S.V.Krishnamurthy,
R.H.Katz and S.Dao, “Distributed Power Control in Ad-hoc Wireless Networks”, IEEE PIMRC 2001.
Copyright: S. Krishnamurthy, UCR
The IEEE 802.11 MAC
A B
CRTS
CTS
D
•RTS – CTS – DATA – ACK
•Solves the hidden and exposed terminal problem in most cases.
E
Copyright: S. Krishnamurthy, UCR
Why is Power Control Hard? No centralized controller as in
cellular networks. Distributed decisions on what power
to use.
Copyright: S. Krishnamurthy, UCR
Benefits Energy Conservation Frequency Re-use – more number of
simultaneous transmissions possible – translates into an increase in the network capacity.
Copyright: S. Krishnamurthy, UCR
Transmission Range Models Typically models assume a circular
range – 250 meters is the transmission range – within this range, data can be decoded.
Interference range – larger than the transmission range – data cannot be decoded – only the interference can be sensed.
Copyright: S. Krishnamurthy, UCR
Clustering Elect clusterheads for a group of
nodes. The clusterhead is responsible for
the transmit power for each node within its cluster.
Imposing a cellular infrastructure onto an ad hoc framework.
Refer to paper for reference.
Copyright: S. Krishnamurthy, UCR
Power Control Extensions to the IEEE 802.11 MAC Ten Quantized Power Levels The levels vary linearly the
difference between levels is about a tenth of the maximum power level.
Implement a power control loop between a communicating pair.
Copyright: S. Krishnamurthy, UCR
Modifications to control messages RTS/CTS messages modified to include a
new field. When a node receives the RTS message it
measures received signal strength (There is usually what is called a Received Signal Strength Indicator or RSSI in hardware).
The receiver indicates the ratio of the received strength to the minimum acceptable strength in the CTS header.
Copyright: S. Krishnamurthy, UCR
The Power Loop Closed The transmitter (the originator of data)
then does a similar computation with the received CTS message.
It then includes a similar ratio in the header of the DATA message.
So both the transmitter and the receiver are now aware of the power situation on the link – how well are we doing!
Copyright: S. Krishnamurthy, UCR
Basic Idea Increase power if the power requirements
are not satisfied – packet loss. Decrease power if power requirements
are satisfied Maintain table for each neighbor – to
know the power level to be used in order to communicate with that neighbor.
Copyright: S. Krishnamurthy, UCR
Nuances A single power measurement will not
suffice. One would need to dampen fluctuations. Once a power level is chosen, ten
transmissions at that level (a heuristic parameter).
The power control loop is only used for unicast transmissions – routing updates etc. that are broadcast do not use this.
For further details – read paper.
Copyright: S. Krishnamurthy, UCR
Sample Simulation Results Simulations were done in ns 2.0 Various mobility models were
considered. TCP Throughput (actually goodput –
does not take into account duplicates) is the metric of interest.
Copyright: S. Krishnamurthy, UCR
Sample Simulation Results• Througput improvement is due to an increase in capacity – higher frequency re-use.
Copyright: S. Krishnamurthy, UCR
Sample Simulation Results (Cont).
• Decrease in overall energy consumption (on average).
Copyright: S. Krishnamurthy, UCR
Why can performance be worse ?
•Node 3 is receiving Data from Node 4
Node 2 does not know about the data transferThe high power CTS collides with the Data at Node 3
•Node 1 establishes a high power link
1 2
RTS
CTS
3
Data 4
Copyright: S. Krishnamurthy, UCR
Power Control leads to Asymmetry There is an inherent asymmetry
resulting from power control. Simply changing power levels can
lead to unfairness – and collisions and can in some scenarios degrade performance.
Copyright: S. Krishnamurthy, UCR
Problems at the routing layer Traditional routing protocols may no
longer be used. Uni-directional links are formed. How
can they be used ? Neighbor discovery a challenge.
Copyright: S. Krishnamurthy, UCR
Interesting topics for projects Few papers try to do power control Paper by Monks in INFOCOM 2001 Paper by Jung and Vaidya – Mobicom 2002. However, no capacity increase, use highest
power for transmission of control signals. We will see these in next class. Open area – tough problems – but
opportunities.