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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)
Thesis Title: On-Demand Medium Access with Heterogeneous Antenna Technologies in Multihop Wireless
NetworksThesis Advisor: Dr. Dharma P. Agrawal
Computer Engineering/VLSI Seminar
PhD CandidateOBR Center for Distributed and Mobile Computing
ECECS Department, University of [email protected]
Outline Introduction
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
MANET,WMN,
andWSN
Network layer and Medium
access layerSmart Antennas and
MIMO
Introduction – Antennas
Omnidirectional Antenna – Low Throughput in Wireless Ad hoc networks due to poor spatial reuse.
Omnidirectional Communication
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
DF
G
H
X
Nodes in Silent Zone
E
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).
DATA
DATA
DATA
A
B
C
D
E
F
G
DATADATA
DATA
2
34
6
7
8
10
11
12
5
9
1
Adaptive array Switched array
Introduction – Multiple Beamforming Antennas
top view (horizontal)
Interferer 1
User 1
User 3
User 2 Interferer 2
Interferer 3
Applications
Military NetworksCellular Communication NetworksMultihop Wireless Networks
2
34
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
Adaptive array
top view (horizontal)
Interferer 1
User 1
User 3
User 2 Interferer 2
Interferer 3
Introduction – Antenna System Phased Array Antenna
0 1 2 3 4 5 6 7
d
Incident Wave
8 Element Linear Equally Spaced
Antenna Array
0
1
2
3
4
56
7
8 Element Equally Spaced Circular Antenna Array
Greater the number of elements in the array, the larger its directivity
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
The Antenna Model
1
23
4
M
M-1
Directional Coverage Area
Omni-directional Coverage Area
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
sec/_**},...,,max{
1,min_
21
packetsDurationCommhwww
RxPacketsh
Source Destinationw1 w2 wh
otherwise ;
ioncommunicat ldirectiona 2 ;2
ioncommunicat ionalomnidirect 3 ;3
h
h
h
h
where, h is hop-length
Comm_Duration is communication time taken by a packet on each hop
length-hop effective is h
source of rate generationpacket is
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
Random Backoff after DIFS wait
Beam-based Node-based
Transmission Control Packets (RTS/CTS)
Directional Omnidirectional
All nodes employ IEEE 802.11 DCF with directional virtual carrier mechanism (DVCS).
MMAC-NBMDMAC-NBMDMAC-BB MMAC-BB
Performance Evaluation
1
23
4
8
7
Directional Coverage Area
Omnidirectional Coverage Area
5
6
The Antenna Model
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.
Gains from spatial reuse only are
considered
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.
A
B
C
D
E
G
F
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 – IssuesConcurrent Packet Reception with IEEE 802.11 DCF
Conclusion: Eradicate the backoff after DIFS duration
RTS
RTS
RTS
RTS
RTS
RTS
RTS
RTS
A
B
C
D
E
F
G
DATA
DIFS
DIFS
DIFS
CTSACK
RTS
DIFSC
TS
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
C
A
B
DIFS
DIFS
XRTS
RTS
BADIFS
RTSCTSDATAACKDIFS
C
Use p-persistent
CSMA
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 Removal of contention window based backoff in ESIF does
not affect long-term fairness Both the transmitters get equal opportunity to transmit
A B
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
B
A
C
D
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
A
B
C
D
E
G
F
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 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
E
BA
D
C
BeamformingAdvantages 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
23
4
8
7
Directional Coverage Area
Omnidirectional Coverage Area
5
6
Deafness Problem
Nodes X and Y do not know the busy state of node A and keep transmitting RTSs to A
RTS
RTSB
Y
X
DATAA
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 AlgorithmHybrid 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
SCH
SCH
CTS
Performance Evaluation 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
A
BC
D
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 – 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 With basic access mechanism similar to ESIF, HMAC is able
to deliver optimal performance
A
B
C
D
E
G
F
Performance Evaluation Run-time sender estimation algorithm employed in HMAC
delivers comparable performance to ideal p-persistent mechanism exploited in ESIF
DB
A
E
C
Mesh Network Architecture
Access Point
Wired internet backbone
Wired internet backbone
Wireless Routers
Mobile Users
1
2
5
10
6
8
4
13
149
15 16 1718
19
3
11
7
20
12
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
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.
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
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 controlTwo 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
Source: Benjamin K. Ng and Elvino S. Sousa, “SSSMA for Multi-User MIMO Systems”, IEEE Microwave Magazine, vol. 5 , pp. 61-71 , June 2004
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.
Future Work – MIMO Antennas
Source: http://www.airgonetworks.com/pdf/Farpoint Group 2003-242.1 MIMO Comes of Age.pdf
Outline of Proposed Work
Work completedWork in progressCo-authored
On-Demand Medium Access Control (MAC)
Multihop Wireless Network (MWN)
Antenna Technologies
SS-MQO;RICS
Energy Efficient Reliable
MAC
MIMO MAC
ReliableMAC
Hybrid MACESIF
Unified MAC
MDMAC-BB;MDMAC-NB;MMAC-BB;MMAC-NB
MSC AMD
Single Beam Antenna
Multiple Beam Antenna Array (MBAA)
Omnidirectional AntennaSmart Antenna Multiple Input Multiple Output (MIMO) Antenna
Wireless Mesh Network (WMN)
Wireless Sensor Network (WSN)
Mobile Ad hoc Network (MANET)
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.
Thank You!!!
Questions ???
For more information http://www.ececs.uc.edu/~jainvk