A Cross Layer MAC with Explicit Synchronization through Intelligent Feedback for Multiple Beam Antennas Vivek Jain, Anurag Gupta Dharma P. Agrawal ECECS.

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 [email protected]

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