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A Cross Layer MAC with Explicit Synchronization through Intelligent Feedback for Multiple Beam Antennas
Vivek Jain, Anurag Gupta Dharma P.
AgrawalECECS DepartmentUniversity of Cincinnati
{jainvk, guptaag, dpa}@ececs.uc.edu
Dhananjay Lal
Research and Technology Center
Robert Bosch CorporationDhananjay.Lal@RTC.Bosch.com
Outline
Introduction Multiple Beam Antennas MAC Protocol Design Issues The ESIF Protocol Performance Evaluation Conclusions
Introduction
A B
C
DF
G
H
X
Nodes in Silent Zone
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”.
Introduction Multiple Beam Antenna – 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
Multiple Beam Antennas - Types
top view (horizontal)
Interferer 1
User 1
2
34
6
7
8
10
11
12
5User 3
9
User 2 Interferer 2
Interferer 3
1
Switched array
User 1
Interferer 1
top view (horizontal)
User 3
User 2
Interferer 3
Interferer 2
Adaptive array
Applications
Military networksCellular Communication NetworksWireless Local Area Networks
Multiple Beam Antennas - Beam Forming
Therefore, a node can either transmit or receive simultaneously but not both.
… …
Direction of Arrival Estimation Beam Formation
IEEE 802.11 DCF
TimeRTSDIFS
SIFS
DIFS RTS
Defer access
aSlotTime
RandomBackoff
Source
Destination ACK
Other
CTS
SIFS Data
SIFS
NAV (RTS)
NAV (CTS)
NAV (Data)
Physical Carrier Sensing
Virtual Carrier Sensing
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.
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 – 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
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.
Control packet (RIF/CIF/SCH) format
Performance Evaluation
1
23
4
8
7
Directional Coverage Area
Omnidirectional Coverage Area
5
6
The Antenna Model
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
Gains from spatial reuse only are
considered
ESIF – Basic Operation
Simulation ParametersParameter 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 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
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
Thank You!!!
Questions ???
Performance Evaluation Deafness and route coupling do not affect omni-protocols,
but directional protocols experience performance degradation at higher loads.
A 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.
A
B
C
D
Performance EvaluationD
H
I
J
C
G
B
FA
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 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
A B
C
D
E
Performance Evaluation
Energy expended in random and compete-5 topologies
Multiple beam omni-directional protocols expend more energy due to omni-directional transmission of control messages.
IEEE – Packet Formats
Frame control field for control messages
IEEE 802.11
Type value(b3 b2)
Typedescription
Subtype value(b7 b6 b5 b4)
Subtypedescription
01 Control 1011 Request To Send (RTS)
01 Control 1100 Clear To Send (CTS)
01 Control 0000–1001 Reserved
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