Computer Engineering/VLSI Seminar Enhancing Throughput of Multihop Wireless Networks using Multiple Beam Smart Antennas Vivek Jain (Bachelor of Technology (E&C), Indian Institute of Technology at Roorkee, India, 2002) PhD Candidate OBR Center for Distributed and Mobile Computing ECECS Department, University of Cincinnati jainvk@ececs.uc.edu Thesis Title: On-Demand Medium Access with Heterogeneous Antenna Technologies in Multihop Wireless Networks Thesis Advisor: Dr. Dharma P. Agrawal

Outline Introduction Analytical Framework Multihop Wireless Networks Antenna Technologies Medium Access Control Protocols Analytical Framework IEEE 802.11 DCF based Protocols for MBAA ESIF Mechanism AMD for Beamforming Antennas HMAC for MBAA Summary of the Research Work Future Work

Introduction – Wireless Network Infrastructure-based – Devices communicate with central Access Point (AP). Also, referred to as Wireless Local Area Network (LAN). Peer-to-peer – Any two devices can communicate, when in range. Also, referred to as Personal Area Network (PAN) or an Ad hoc Network.

Introduction – Multihop Wireless Network (MWN) Intermediate nodes act as routers or relay nodes Multihop forwarding to ensure network connectivity Extends coverage of single hop wireless networks Multihop wireless networks offer Scalability Reliability Adaptability Easy deployment in rough terrains

Introduction – Mobile Ad hoc Network (MANET) Set of mobile station (MSs) Lack of fixed infrastructure relay nodes Dynamically changing topology Applications Military - Combat Systems, reconnaissance, surveillance Disaster management Medical emergency Virtual navigation Distance education

Introduction – Wireless Mesh Network (WMN) A combination of infrastructure-based and peer-to-peer networks Set of mobile and immobile stations Dynamically changing topology Applications Intelligent transport systems Public safety Public internet access Residential broadband access Distance education

Introduction – Wireless Sensor Network (WSN) Usually a set of small immobile nodes referred as motes Generally static topology Cheap alternative to monitor inaccessible or inhospitable terrains Applications Medical Applications – wireless bio-sensors Nuclear and chemical plants Environmental monitoring Ocean monitoring Battlefields

Introduction – Challenges in MWN Medium access protocols Routing protocols Transport Protocols Cross layer optimization Network capacity utilization Security Network lifetime in WSN Co-existence of several types of MWN Network layer and Medium access layer Smart Antennas and MIMO MANET, WMN, and WSN

Introduction – Antennas 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 E Omnidirectional Communication

Introduction – Multiple Beam Smart Antennas Also referred as Multiple Beam Antenna Array (MBAA) – Exploits spatial bandwidth fully. A node can initiate more than one simultaneous transmissions (or receptions). A E DATA DATA D B F C G

Introduction – Multiple Beamforming Antennas Adaptive array top view (horizontal) Interferer 1 User 1 User 3 User 2 Interferer 2 Interferer 3 2 3 4 6 7 8 10 11 12 5 9 1 Switched array top view (horizontal) Interferer 1 User 1 User 3 User 2 Interferer 2 Interferer 3 top view (horizontal) Interferer 1 User 1 User 3 User 2 Interferer 2 Interferer 3 2 3 4 6 7 8 10 11 12 5 9 1 Switched array Adaptive array Applications Military Networks Cellular Communication Networks Multihop Wireless Networks

Introduction – Antenna System Phased Array Antenna Incident Wave 2 1 3 Greater the number of elements in the array, the larger its directivity 1 2 3 4 5 6 7 4 d 7 5 6 8 Element Linear Equally Spaced Antenna Array 8 Element Equally Spaced Circular Antenna Array

Introduction – Beamforming … … … … Direction of Arrival Estimation Beam Formation As all antenna elements are used for beamforming, a node can either transmit or receive simultaneously, but not both.

Introduction – Medium Access On-Demand or Contention-based Scheduling or Contention-free Channel Allocation Dynamic Pre-defined Topological Change Adaptation Good New Schedules Required Time Synchronization No Yes Energy Utilization Uncontrolled Controlled Concurrent Receptions or Transmissions Local Synchronization Required Inherent On-demand vs. scheduling medium access control protocols

MBAA Model Assumptions A wide azimuth switched-beam smart antenna Antenna array has M elements that forms non-overlapping sectors spanning an angle of 360/M degrees Beam shape is assumed as conical Benefits of nulling or the impact of side-lobe interference are not considered Carrier sense is performed directionally A collision occurs only if a node receives interfering energy in the same beam in which it is actively receiving a packet Range of omnidirectional and directional beam is the same 3 2 4 1 Directional Coverage Area M Omni-directional Coverage Area M-1 The Antenna Model

Analytical Framework Can we develop an analytical framework to: Calculate throughput of on-demand medium access control protocols? Calculate concurrent packet reception capability of medium access control protocols? Calculate upper bounds of throughput for the ideal MAC in a multihop wireless network that can provide as a benchmark to compare with the proposed protocols?

Slotted Aloha Slotted Aloha throughput with N=50, a=0.01 and p=0.03

CSMA CSMA throughput with N=50, a=0.01, p=0.03 and f =0.03

Concurrent Packet Reception Bounds Percentage of CPR for asynchronous on-demand receiver-initiated protocols

Concurrent Packet Reception Bounds Percentage of CPR for asynchronous on-demand transmitter-initiated protocols

Throughput Bounds – Ideal MAC Destination Source w1 w2 wh where, h is hop-length Comm_Duration is communication time taken by a packet on each hop Also,

IEEE 802.11 DCF for MBAA Does the existing IEEE 802.11 DCF based MAC protocols for single beamforming antennas yield optimal results for MBAA also? If not, then what are the features that are needed in a protocol to leverage the benefits of MBAA?

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.

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 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.

ESIF Can we have an on-demand medium access protocol that can yield nearly optimal results in multihop wireless networks with MBAA? If yes, then Is the protocol synchronous or asynchronous or a hybrid of both? Does the protocol support differentiated service classes?

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 – 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 – Basic Operation

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

Concurrent Packet Reception Bounds Percentage of CPR for IEEE 802.11 over four and eight beam antennas Percentage of CPR for ESIF over four and eight beam antennas

QoS over ESIF Mechanism Multilevel Queue Organization in each beam of the sender in SS-MQO Multilevel Sender Queue (MSQ) at the receiver in RICS

Performance Evaluation B A D C Performance Evaluation Each node generate class 0, class 1 and class 2 packets with probabilities 0.2, 0.3 and 0.5, respectively, while they are selected with respective probabilities of 0.5, 0.3 and 0.2 Prioritized flow selection is enforced more strictly in RICS as QoS parameters are applied at two ends – sender and receiver

Directional Coverage Area Omnidirectional Coverage Area Beamforming Advantages Longer Range Better connectivity and lower end-to-end delay Spatial Reuse Increased capacity and throughput Limitations Deafness and hidden terminal problems Node is unaware of ongoing communication in the neighborhood regions where it not currently beam-formed 1 2 3 4 8 7 Directional Coverage Area Omnidirectional Coverage Area 5 6

Deafness Problem X RTS A B DATA RTS Y Nodes X and Y do not know the busy state of node A and keep transmitting RTSs to A

Deafness – Consequences At transmitter Increases retransmission attempts after doubling contention window for every unsuccessful attempt At receiver Can increase collisions due to interference with active RTS or data receptions Overall Network Reduces throughput and increases end-to-end latency

Deafness – Proposed Solutions (Single Beam Antennas) Omni-directional transmission of control messages Asymmetry in gain of directional and omni-directional nodes leads to deafness Circular sweeping of control messages Increases end-to-end delay due to sweeping

Deafness – Proposed Solutions (Multiple Beam Antennas) Proactive approach A node transmits control messages in all free beams Reactive approach A node transmits control messages in all beams that are free and have potential transmitters

Proposed Algorithm Hybrid Approach Uses DVCS mechanism to dynamically maintain two parameters for every beam isRTSReceived: Set to true when a node receives a RTS intended for itself isCTSReceived: Set to true when a node receives a CTS not intended for itself Transmit control messages in all unblocked beams whose isRTSReceived is set to true Transmit control messages in all unblocked beams if isCTSReceived is true for the beam engaged in actual data communication SCH CTS

Performance Evaluation B D Throughput obtained in MMAC-NB is low due to collisions occurring at node D from transmissions by nodes A and B The topology has no effect on ESIF as control messages are sent only in routes with potential transmitters

HMAC Can we have a medium access control protocol that can support both omnidirectional and beamforming antennas including MBAA? If yes, then Is the new protocol backward compatible with IEEE 802.11 DCF? Does this protocol reach ideal throughput upper bounds? Can we have cost-effective mesh network architecture?

HMAC - Features Can we have a medium access control protocol that can support both omnidirectional and beamforming antennas including MBAA? If yes, then Is the new protocol backward compatible with IEEE 802.11 DCF? Does this protocol reach ideal throughput upper bounds? Can we have cost-effective mesh network architecture?

HMAC – Enhancements over ESIF Employs Algorithm for Mitigating Deafness while transmitting control packets Exploits a Run-time Sender Estimation Algorithm Does not rely on neighbor feedback Maintains same packet formats for control messages as in IEEE 802.11 DCF and is thus compatible with it Simpler implementation as compared to ESIF

HMAC/IEEE Frame control field for control messages (RTS/CTS) HMAC – Packet Formats HMAC/IEEE RTS packet format HMAC SCH packet format for RTS HMAC/IEEE CTS and ACK packet format HMAC SCH packet format for CTS HMAC/IEEE Frame control field for control messages (RTS/CTS)

Performance Evaluation B C D E G F Performance Evaluation With basic access mechanism similar to ESIF, HMAC is able to deliver optimal performance

Performance Evaluation D B A E C Performance Evaluation Run-time sender estimation algorithm employed in HMAC delivers comparable performance to ideal p-persistent mechanism exploited in ESIF

Mesh Network Architecture Wired internet backbone Access Point 1 Wireless Routers 3 12 2 11 4 7 5 6 13 8 14 20 9 10 19 18 17 15 16 Mobile Users

Summary – Analytical Framework Evaluated the performance of slotted Aloha and basic CSMA Slotted Aloha gives better throughput than basic CSMA at lower loads At heavier loads, CSMA gives better performance Asynchronous on-demand protocols like CSMA gives stable results for MBAA at higher loads However, as number of beams increases, throughput per beam in CSMA falls due to synchronization losses Developed analytical framework for calculating concurrent packet reception capability of asynchronous protocols Throughput in CSMA can be enhanced by using localized synchronization and properly adjusting transmission probability p of nodes such that Np>2, where N is the number of contending nodes. Calculated throughput upper bounds for an ideal MAC

Summary – IEEE 802.11 DCF Based MAC Protocols for MBAA Concurrent packet reception in multiple beam antennas is highly improbable with IEEE 802.11 DCF based protocols Asynchronous protocols thus cannot leverage the benefits of MBAA A new MAC protocol based on the formulated guidelines is required.

Summary – ESIF 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 Two protocols, SS-MQO and RICS to support QoS over ESIF mechanism, are proposed recently.

Summary – HMAC HMAC is the first attempt to allow coexistence of mesh and ad hoc networks with heterogeneous antenna technologies HMAC is backward compatible with IEEE 802.11 DCF Exploits Algorithms for Mitigating Deafness and Run-time Sender Estimation to achieve optimal performance

Future Work – MIMO Antennas Single-user MIMO Spectral efficiency is increased by supporting multiple data streams over spatial channels. Spatial diversity is exploited to enhance the detection performance. Multi-user MIMO MIMO channel is evenly divided and allocated to multiple users. Each user channel has access to the space domain over entire transmission channel and frequency bandwidth. Source: Benjamin K. Ng and Elvino S. Sousa, “SSSMA for Multi-User MIMO Systems”, IEEE Microwave Magazine, vol. 5 , pp. 61-71 , June 2004

Future Work – MIMO Antennas Source: http://www.airgonetworks.com/pdf/Farpoint Group 2003-242.1 MIMO Comes of Age.pdf

Outline of Proposed Work Multihop Wireless Network (MWN) Unified MAC Wireless Mesh Network (WMN) Wireless Sensor Network (WSN) Mobile Ad hoc Network (MANET) MSC MDMAC-BB; MDMAC-NB; MMAC-BB; MMAC-NB Hybrid MAC MIMO MAC Reliable MAC On-Demand Medium Access Control (MAC) SS-MQO; RICS ESIF Energy Efficient Reliable MAC AMD Single Beam Antenna Multiple Beam Antenna Array (MBAA) Omnidirectional Antenna Smart Antenna Multiple Input Multiple Output (MIMO) Antenna Work completed Work in progress Co-authored Antenna Technologies

Publications Dhananjay Lal, Vivek Jain, Qing-An Zeng, Dharma P. Agrawal, “Performance Evaluation of Medium Access Control for Multiple Beam Antenna Nodes in a Wireless LAN,” in IEEE Transactions on Parallel and Distributed Systems, Vol.15, No. 12, pp. 1117-1129, 2004. Vivek Jain, Nagesh S. Nandiraju, and Dharma P. Agrawal, “Mode Selection Criteria in Mobile Ad hoc Networks using Heterogeneous Antenna Technologies,” in Proceedings of OPNETWORK 2005, Aug 2005. Vivek Jain, Anurag Gupta, Dhananjay Lal, and Dharma P. Agrawal, “IEEE 802.11 DCF Based MAC Protocols for Multiple Beam Antennas and Their Limitations,” in Proceedings of IEEE MASS, Nov. 2005. Vivek Jain, Anurag Gupta, Dhananjay Lal, and Dharma P. Agrawal, “A Cross Layer MAC with Explicit Synchronization through Intelligent Feedback for Multiple Beam Antennas,” in Proceedings of IEEE GlobeCom, Nov. 2005. Vivek Jain and Dharma P. Agrawal, “Mitigating Deafness in Beamforming Antennas,” in Proceedings of IEEE Sarnoff Symposium, March 2006. Ratnabali Biswas, Vivek Jain, Chittabrata Ghosh, and Dharma P. Agrawal, “On-Demand Reliable Medium Access in Sensor Networks,” in IEEE WoWMoM 2006 (accepted). Anurag Gupta, Vivek Jain, and Dharma P. Agrawal, “Differentiated Service Classes Over Multiple Beam Antennas,” manuscript submitted. Vivek Jain and Dharma P. Agrawal, “Concurrent Receptions with On-Demand Medium Access Protocols for Multiple Beam Antennas,” manuscript submitted. Vivek Jain, Anurag Gupta, and Dharma P. Agrawal, “On Medium Access in Multihop Wireless Networks with Heterogeneous Antenna Technologies,” manuscript submitted.

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