A Cross Layer MAC with Explicit Synchronization through Intelligent Feedback for Multiple Beam Antennas 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 MAC Protocol Design Issues The ESIF Protocol Performance Evaluation 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

MAC – Issues Concurrent Packet Reception with IEEE 802.11 DCF DIFS E RTS RTS RTS DATA ACK CTS DIFS D B F RTS RTS RTS RTS CTS RTS C G Conclusion: Eradicate the backoff after DIFS duration

MAC Issues – Backoff Removal Multiple transmitters, located in the same beam of common receiver, always get the same receiver schedule and thus initiate communication at the same time - collision A node with very high data generation rate will overwhelm its receiver, without giving latter a chance to forward this traffic - fairness issue All classes of service get same priority – QoS issue Use p-persistent CSMA DIFS A RTS X RTS B C DIFS A B C DIFS DIFS CTS ACK RTS DATA Hold the transmitting node

ESIF – Assumptions Nodes are equipped with multiple switched beam antenna array and can precisely calculate the Angle of Arrival (AoA) of the received signal All nodes form non-overlapping multiple beams with equal gain so as to collectively span entire space Beam shape is assumed as conical and benefits of nulling or the impact of side-lobe interference are not considered A node can either transmit or receive data on multiple beams at the same time but not both The channel is symmetric.

ESIF – ENAV Every node maintains an ENAV: The beam a neighbor falls within Neighbor’s schedule - the duration until this neighbor is engaged in communication elsewhere Whether a neighbor’s schedule requires maintaining silence in the entire beam Number of data packets outbound for the neighbor The p-persistent probability to use when talking to this neighbor

ESIF – Cross Layer Data Management Using network layer information along with ENAV a node determines: Whether a beam contains an active route The number of potential transmitters in each beam Until what time the node needs to maintain silence in a particular beam Each node has a store-and-forward buffer for relaying data packets Available buffer is used dynamically to form different queues for each beam - prevents head-of-the-line blocking

ESIF – Design ESIF piggybacks feedback onto control messages; RTS with Intelligent Feedback (RIF), and CTS with Intelligent Feedback (CIF), Schedule Update with Intelligent Feedback (SCH) SCH identifier allows a neighbor to adjudge whether to defer transmission for only this node or for the entire beam buffer-threshold to control priorities between receiver and transmitter modes Reception gets priority as long as the buffer size remains under the threshold If a node cannot actually initiate transmitter mode, the receiver still gets the priority Priority switch solves problems of an overwhelmed receiver. This also provides a mechanism to control the contribution of a node to end-to-end delays

ESIF – Control Message Packet Format Control packet (RIF/CIF/SCH) format Type field in Frame Control is used to identify a control message as RIF, CIF or SCH Duration holds the estimated time of communication that the other nodes must backoff for; Priority contains the priority of this request, and p is the persistent probability which the other nodes should use when talking to this node.

Performance Evaluation Generation of packets is modeled as a Poisson process with the equal mean arrival time IEEE 802.11 DCF based protocols are used for omnidirectional antenna (Omni), single beam directional antenna (Directional-NB) and MBAA (MMAC-NB), directional (Directional) and multiple-beam (Multibeam) Directional-NB, MMAC-NB and ESIF protocols involve DVCS ESIF is implemented with a buffer-threshold value of 1 1 2 3 4 8 7 Directional Coverage Area Omnidirectional Coverage Area 5 6 Gains from spatial reuse only are considered The Antenna Model

ESIF – Basic Operation

Simulation Parameters Value Data rate 2 Mbps Data packet size 2000 bytes Control Packet size 45 bytes ACK size 38 bytes DIFS duration 50 microseconds SIFS duration 10 microseconds Short retry limit 7 Long retry limit 4 Sensing power 0.07 mW Reception power 1.45 mW Transmission power 1.75 mW Total beams 8 Simulation Time 100 seconds Buffer 30 packets Packet Lifetime 30 Packet Durations

Performance Evaluation B Removal of contention window based backoff in ESIF does not affect long-term fairness Both the transmitters get equal opportunity to transmit

Performance Evaluation B A C D Performance Evaluation ESIF enhances throughput by the priority switch between transmission and reception modes ESIF is able to achieve concurrent data communications between node pairs A-B and C-D

Performance Evaluation B C D E G F Performance Evaluation ESIF is able to achieve CPR at common intermediate node D Dynamic priority switch ensures data packets just received are transmitted (concurrently) in the next cycle, thus, maximizing throughput and minimizing delay

Conclusions ESIF is the first attempt to achieve concurrent packet reception with on-demand protocols for MBAA ESIF removes the contention window based random backoff in IEEE 802.11 DCF based protocols and uses embedded feedback to synchronize neighboring nodes Allows nodes to receive or transmit multiple packets simultaneously in different beams Cross layer information is used to guarantee long-term fairness ESIF is a hybrid of synchronous and asynchronous on-demand medium access control

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. ESIF extracts the highest throughput among all protocols by using a proportional p value for p-persistent CSMA.

Performance Evaluation D H I J C G B F A E Directional protocols perform better at higher loads because of better spatial reuse. ESIF takes advantage of CPR and CPT to achieve optimal performance

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 On-demand protocols does not yields optimal results for Complete-k topologies due to synchronization losses

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

Frame control field for control messages IEEE – Packet Formats Frame control field for control messages IEEE 802.11 Type value (b3 b2) Type description Subtype value (b7 b6 b5 b4) Subtype description 01 Control 1011 Request To Send (RTS) 1100 Clear To Send (CTS) 0000–1001 Reserved