1. Designing MAC protocols for ad hoc wireless network
-Yanlin Peng
11/18/2018
©CSL

2. Introduction
In ad hoc networks all wireless devices within a range discover each other and communicate in peer-to-peer fashion without involving central access points
Multi-hop connectivity is one of the most prominent features
The current version of IEEE MAC protocol does not function well in multi-hop ad hoc networks
Performance suffers as the number of devices grows, and a large ad-hoc network quickly becomes difficult to manage
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3. Goals Classify MAC layer protocols for ad hoc networks
Provide design guidelines for ad hoc network MAC layer protocols
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4. Protocol list
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5. Key features Channel separation and access Topology Power
Transmission initiation
Traffic load and scalability
Range
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6. Channel Separation and Access
How to use the available medium efficiently
Physical layers
Radio frequency(RF) signal
Still the main method for data transmission
Ultra wide band radio(UWB)
Promising?
Acoustic communication
Single channel or multiple channel?
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7. Single Channel
All the nodes share the medium for all their control and data transmissions
Collisions are an inherent attribute and back-off mechanism is required
Hidden node problem
Important protocol: BTMA, MACA,FAMA
CSMA, MACA, MACAW, FAMA, RIMA-SP, DPC/ALP, MACA-BI, MARCH
All of these protocols except CSMA based on RTS/CTS handshake and carrier sensing to avoid hidden node problem.
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8. Single Channel FAMA Noise c FAMA-NPS FAMA-NCSB C
FAMA-NPS
FAMA-NCS
FAMA
Sense carrier before sending an RTS
Dominative CTS
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9. Single Channel MARCH Reduce control signaling
proposes a single RTS on the first hop of the path, while only CTS is required for every subsequent hop
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10. Multiple Channel Generalized separation
BTMA,DBTMA,PAMA,DCAPC,GRID-B
TDMA (Time Division Multiple Access)
FPRP,CATA,SRMA/PA, Markowski, ADAPT, D-PRMA
FDMA (Frequency Division Multiple Access)
MCSMA
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11. Multiple Channel CDMA(Code Division Multiple Access)
Use orthogonal codes to spread signals
One code is one channel
MC MAC
Use one code for control and N codes for data
Dynamically allocates multiple codes for high rate packets
IEEE
FHSS and DSSS
Did not use orthogonal codes
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12. Multiple Channel SDMA(Space Division Multiple Access)
Use directional antennas to access the full spectrum
Lal
Receiver init an omni-directional RTR
Neighbors reply by using a directional RTS (DRTS)
Receiver replies to the accepted senders with a Directional CTS (DCTS) to complete the handshake
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13. Multiple Channel Hybrid MMAC PRMA, HIPERLAN, HRMA Bluetooth
using smart antennas to establish a multi-hop link between the source and the destination through the RTS/CTS handshake
Hybrid
PRMA, HIPERLAN, HRMA
Use both TDMA and FDMA
Bluetooth
CDMA and TDMA
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14. Summary
RTS/CTS handshake is the basic solution for hidden node problem.
Carrier sensing is the basic solution for collision avoidance.
Multiple-channel protocols allow for more users than single-channel protocol. However, multiple-channel need more complex management.
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15. Topology Features Single-hop flat topology Multi-hop flat topology
Changing frequently
Single-hop flat topology
Multi-hop flat topology
Clustered topology
Centralized topology
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16. Single-hop flat topology
CSMA, MSC, FAMA, MACA-BI, RIMA-SP, IEEE
Limited capability and performance in dense or highly loaded network
High power consumption and lack of flexibility
More suitable for wired networks or smaller scale and lower throughput wireless networks
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17. Multi-hop flat topology
PAMAS
MCSMA
Frequency channel reuse
GRID-B
pre-defined geographic area
DCA-PC, DCA/APL, Lal,
MMAC
Establish multi-hop links using directional antennas
MARCH
Hearing control signaling from the previous hop
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18. Clustered topology
Emulate infrastructure wireless networks by electing a clustered head working as a base station
Cluster head burdens more than nodes
VBS
Simple mechanism for choosing a cluster head randomly
periodically send “hello” messages
join the cluster of the lowest IP address
Nodes with lower IP address suffer from more resource use
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19. Clustered topology WCA elects cluster heads based on a weight function
weight parameters
the distance from neighbors
the time as a cluster head (battery power available)
Mobility
Connectivity
supports mobile nodes by allowing handovers for nodes moving from one cluster to another
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20. Clustered topology Jin, GPC Bluetooth HIPERLAN
electing a cluster head according to battery power only
simpler but less generalized approach than WCA
Bluetooth
In the form of piconets of one master and up to seven slavers
The only protocol statically assigning a master
HIPERLAN
forwarders and p-supporters share the duties of a cluster head
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21. Centralized topology BTMA, MACAW, PRMA
Ad hoc networks generally do not adopt a centralized topology
However, these protocols provide valuable concepts, such as a busy tone channel and time slot reservation that are extendable to ad hoc networks
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22. Summary
a multi-hop flat topology or a clustered topology are more suitable to ensure scalability in ad hoc networks
In homogeneous networks, a multiple-hop flat topology is more appropriate
In heterogeneous networks, a clustered topology allows the high-power nodes to become cluster heads and handle most of the overhead control messaging
For example, a heterogeneous network consisting of WLAN and GSM or 3G
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23. Power Transmit power control Sleep mode
Control the transmit power so that it is just enough to reach the intended receiver.
GPC, DCA-PC, DPC/ALP, Lal, MMAC
Sleep mode
Sleep while idle to reduce power consumption due to overhearing irrelevant transmission
PAMAS, HIPERLAN, Blutooth
Potential drawback: powering up consume more power
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24. Power Battery level awareness Reduced control overhead
Adjusting node behavior according battery power levels
Useful in power-heterogeneous network
DPC/ALP, Jin, GPC, WCA
Reduced control overhead
Reduced overhead of control messages
MARCH
Savings for particular settings
Unaware of any power issues
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25. Summary
The different power-saving mechanisms in this section actually conserves power depending on the application type.
A multi-purpose protocol should include as many of these mechanisms as possible to ensure its power efficiency in different application scenarios.
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26. Transmission initiation
Sender-initiated protocols and receiver-initiated protocols
Dependent on the potential application areas of that protocol
Sender initiated
Receiver initiated
MACA-BI, RIMA-SP, RICH-DP, Lal
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27. Summary
A sender-initiated protocol is more suitable for generalized networks
For some specialized networks, such as sensor networks, receiver-initiated protocols can yields better network performance
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28. Traffic load and scalability
Highly loaded networks
RICH-DP, Lal (receiver-initiated)
Lal, MMAC (space multiple access)
PS-DCC (changing sending probability)
GRID-B and ADAPT (Multiple access of channel or slot)
TDMA protocols
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29. Traffic load and scalability
Dense networks
Promote perform by power control
GPC, DCA-PC, Lal, MMAC, GRID-B, MCSMA
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30. Traffic load and scalability
Voice and real-time traffic
Priority and reservation
PRMA
Allows voice nodes to reserve slots for subsequent frames
SRMA/PA
Allows voice nodes to preempt data nodes
VBS
ensure a certain bandwidth allocation, which makes them suitable for supporting real-time traffic
Markowski
Hard real-time nodes preempt soft real-time nodes that also preempt non-real-time nodes
PRMA Can work well within a clustered topology of ad hoc network.
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31. Summary
Multiple-channel protocols and power-efficient protocols exhibit better performance for high-load and high-density networks.
TDMA and reservation-based protocols perform best for networks dominated by voice and real-time traffic.
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32. Range
In wireless network, a more appropriate measure of offered traffic is bit-meters/second. That is also called spatial capacity.
S = B/A
S: spatial capacity
A: transmission coverage area
B: aggregate throughput of all coexisting transmissions in A
I.e., a network able to transmit a bit 100 meters, may not be able to transmit the sane bit 200 meters.
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33. Range
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34. Summary
There are tradeoffs between increasing the range and achieving a high spatial capacity
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35. Guide
Support multiple channels in order to separate control from data and reduce the probability of collisions
Adopt a multi-hop topology to ensure scalability
The protocol should also support a flat mode and a clustered mode depending on application requirements
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36. Guide
Be power-aware, control transmission, power, and support sleep mode
sender-initiated
the optimal range for a generalized protocol should be in the short to medium range, because in a long-range network control becomes more difficult and collisions more frequent
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37. My observations Quality of service
This article referred to differentiated service when talking about voice and real-time traffic, but did not emphasize quality of service
Qualify of service consists of many aspects, such as throughput, latency boundary
Differentiated service is more and more important and cannot be neglected. For example, in DSRC, differentiated service is indispensable, since packets for security apparently have the highest priority
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38. My observations (cont.)
Ad hoc networks with speedy nodes, such as DSRC
Multiple channels and limited directions
Helps from other sensors, such as speedometer
Power is relatively plenty with the support of car inverters
Absolute priority needed (for safety messages)
Relatively steady topology considering relative speed
Predicable moving
Heterogeneous wireless networks are possible, such as , GSM, CDMA, GPS
Predicable moving (if cars accelerate or change directions, other sensors can tell this to wireless LAN)
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39. Vehicle-to-vehicle Safety Messaging in DSRC
DSRC is 75 MHz of spectrum at 5.9 GHz allocated by the FCC (Federal Communication Commission)
DSRC will support safety-critical communications as well as other Intelligent Transportation System applications based on a technology
DSRC will have six service channels and one control channel
This paper design a protocol to send safety messages from vehicle to vehicle in the control channel
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40. Vehicle-to-vehicle Safety Messaging in DSRC
Features
Most safety messages produced by a vehicle are useful to many vehicles
Safety messages was updated periodically
QoS consideration
reception probability and channel busy time
Protocol
based on the repetition ideas
implemented in two layers, the MAC layer and MAC extension layer
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41. Vehicle-to-vehicle Safety Messaging in DSRC
MAC extension layer
lies between the Logical Link Control layer (IEEE 802.2) and the MAC layer.
Schedule safety messages
Six protocols based on the same MAC extension layer.
Asynchronous and
synchronous
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42. My observation Multiple channels and Medium range
Multi-hop or clustered topology
Power is not the primarily concerned feature
Sender initialized
Low latency needed
Broadcast is appropriate for safety messages
No feedback or detection mechanisms for receipt
The collision probability will increase when the highway is jammed
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