1. Vivek Jain, Anurag Gupta Dharma P. Agrawal
IEEE DCF Based MAC Protocols for Multiple Beam Antennas and their Limitations
Vivek Jain, Anurag Gupta Dharma P. Agrawal
Dhananjay Lal
ECECS Department
University of Cincinnati
{jainvk, guptaag,
Research and Technology Center
Robert Bosch Corporation

2. Outline Introduction Multiple Beam Antennas IEEE 802.11 DCF
Proposed Variants
Performance Evaluation
Concurrent Packet Reception Bounds
Protocol Guidelines
Conclusions

3. Introduction
Omnidirectional Antenna – Low Throughput in Wireless Ad hoc networks due to poor spatial reuse A B C D E F G H
Directional Communication
Directional Antenna – Better Spatial reuse. But a node still unable to fully utilize “spatial bandwidth”. A B C D F G H X
Nodes in Silent Zone
Omnidirectional Communication

4. Introduction Multiple Beam Antenna – Exploits spatial bandwidth fully
A node can initiate more than one simultaneous transmissions (or receptions). A E
DATA
DATA D B F C G

5. Multiple Beam Antennas - Types
User 1
Interferer 1
top view (horizontal)
User 3
User 2
Interferer 3
Interferer 2
Adaptive array
top view (horizontal)
Interferer 1
User 1 2 3 4 6 7 8 10 11 12 5
User 3 9
User 2
Interferer 2
Interferer 3 1
Switched array
Applications
Military networks
Cellular Communication Networks
Wireless Local Area Networks

6. Multiple Beam Antennas - Beam Forming
… …
Direction of Arrival Estimation
Beam Formation
Therefore, a node can either transmit or receive simultaneously but not both.

7. IEEE DCF
De-facto medium access control for wireless LAN and ad hoc networks
Originally designed for omnidirectional communication, its virtual carrier sensing (VCS) mechanism is enhanced for directional communication to include directional of arrival also.
Physical Carrier Sensing
DIFS
SIFS
RTS
Data
Time
Source
SIFS
SIFS
CTS
ACK
Destination
DIFS
NAV (RTS)
RTS
Other
NAV (CTS)
aSlotTime
NAV (Data)
Virtual Carrier Sensing
Defer access
RandomBackoff

8. IEEE 802.11 DCF for Multiple Beam Antennas
All nodes employ IEEE DCF with directional virtual carrier mechanism (DVCS).
Transmission Control Packets (RTS/CTS)
Directional
Omnidirectional
MDMAC-BB
MDMAC-NB
MMAC-BB
MMAC-NB
Beam-based
Node-based
Random Backoff after DIFS wait

9. Performance Evaluation
Packet generation at each source node is modeled as Poisson process with specified mean arrival rate
Each packet has a fixed size of 2000 bytes and is transmitted at a rate of 2Mbps
Each node has maximum buffer of 30 packets
Each packet has a lifetime of 30 packet durations
Each simulation is run for 100 seconds. 1 2 3 4 8 7
Directional Coverage Area
Omnidirectional Coverage Area 5 6
Gains from spatial reuse only are considered
The Antenna Model

10. Performance EvaluationB A C D
Performance Evaluation
Omnidirectional protocols are able to achieve concurrent data communications between node pairs A-B and C-D.
Directional protocols on the other hand suffer from deafness problem while omni-directional antenna from poor spatial reuse.

11. Performance EvaluationB C D E G F
Performance Evaluation
None of the protocols are able to extract throughput of more than 33% of the maximum possible value
This implies only one route is active on an average and hence concurrent packet reception is not occurring at node D.

12. Performance EvaluationB C D E G F
Performance Evaluation
Concurrent packet reception at node D
Concurrent packet transmission by node D

13. Concurrent Packet Reception Bounds
N neighbors transmitting with probability p under saturation state

14. Protocol Guidelines
Transmit control packets in beams with transmitting nodes – suppress deafness
Common backoff timer for all beams – support concurrent packet transmission
Employ local synchronization – support concurrent packet reception
Employ hot-potato type of buffering, i.e., successive CPR and CPT cycles – minimize delay

15. Follow Up: IEEE Globecom 2005, St. Louis, Nov. 27-Dec.2.
Conclusions
Concurrent packet reception in multiple beam antennas is highly improbable with IEEE DCF based protocols
Asynchronous protocols are not suited for multiple beam antennas
A new MAC protocol based on the formulated guidelines is required.
Follow Up: IEEE Globecom 2005, St. Louis, Nov. 27-Dec.2.
V. Jain, A. Gupta, D. Lal, and D. P. Agrawal, "A Cross Layer MAC with Explicit Synchronization through Intelligent Feedback for Multiple Beam Antennas,"

16. Questions ???
Thank You!!!

17. Performance EvaluationB C D
Performance Evaluation
Deafness and route coupling do not affect omni-protocols, but directional protocols experience performance degradation at higher loads.

18. Performance EvaluationB C D
Performance Evaluation
Omnidirectional protocols overwhelms node C leading to data loss when the packet lifetime expires.

19. Performance EvaluationD H I J C G B F A E
Gains from omnidirectional communication of control packets at medium loads
Directional protocols perform better at higher loads because of better spatial reuse.

20. Performance EvaluationB C D E
Performance Evaluation
Node-based backoff protocols for multiple beam antennas achieve maximum throughput due to gains from concurrent packet transmissions

21. Performance EvaluationB C D E
Performance Evaluation
Concurrent packet reception at any node
Concurrent packet transmission by any node

22. Performance Evaluation
Multiple beam omni-directional protocols expend more energy due to omni-directional transmission of control messages.
Energy expended in random and compete-5 topologies

23. Concurrent Packet Reception Bounds in Saturated State
The probability that a node receives data in b beams concurrently is given by
P(b,N) is the probability that b out of N neighbors transmit in a slot concurrently and is given as
Q(b,M) is the probability of arranging b nodes in M beams such that CPR can happen, is given as
Thus the total probability of concurrent packet reception by a node is then given by