Vivek Jain, Anurag Gupta Dharma P. Agrawal IEEE 802.11 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, dpa}@ececs.uc.edu Research and Technology Center Robert Bosch Corporation Dhananjay.Lal@RTC.Bosch.com

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

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

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

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

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

IEEE 802.11 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

IEEE 802.11 DCF for Multiple Beam Antennas All nodes employ IEEE 802.11 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

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

Performance Evaluation B 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.

Performance Evaluation B 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.

Performance Evaluation B C D E G F Performance Evaluation Concurrent packet reception at node D Concurrent packet transmission by node D

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

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

Follow Up: IEEE Globecom 2005, St. Louis, Nov. 27-Dec.2. Conclusions Concurrent packet reception in multiple beam antennas is highly improbable with IEEE 802.11 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,"

Questions ??? Thank You!!!

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

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

Performance Evaluation D 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.

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

Performance Evaluation B C D E Performance Evaluation Concurrent packet reception at any node Concurrent packet transmission by any node

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

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