Receiver-Initiated Channel Hopping(RICH)

Makis Tzamaloukas (jamal@cse.ucsc.edu)Computer and Communications Research Group (CCRG)

http://www.cse.ucsc.edu/research/ccrg

Computer Engineering DepartmentJack Baskin School of Engineering

University of CaliforniaSanta Cruz, CA 95064

February 9th, UCSC A. E. Tzamaloukas2

Presentation Outline

Introduction Physical Layer Motivation Polling Issues RICH

RICH-SP RICH-DP

Throughput Analysis Delay Analysis Simulations Conclusions

February 9th, UCSC A. E. Tzamaloukas3

Physical Layer - Unlicensed RF

FCC regulations require the use of frequency hopping (FH) or direct sequence (DS) spread spectrum modulation to operate in an ISM band

Multiple users can share the available bandwidth at the same time at a minimal increase of complexity and cost

February 9th, UCSC A. E. Tzamaloukas4

Physical Layer - FHSS

Frequency Hopping Spread Spectrum (FHSS)time

hopt1 t2 t3 t4 t5 t6 t7 t8 t9

h1

h2

h3

h4

h5

h6

h7

h8

h9

In the USA the:915 MHz band has 52 FH channels2.4 GHz band has 79 FH channels5.8 GHz band has 125 FH channels

On the right, two pairs of nodes exchange DATA packets by following a unique hopping pattern

February 9th, UCSC A. E. Tzamaloukas5

Physical Layer - FHSS

Hopping sequence: The pattern with which nodes use the channels

Advantages: robustness against multi-path propagation, minimize hidden node terminal problems, increased security, not prone to fading, capable to capture a packet even when multiple packets overlap

Most commercially available ISM radios are FH

February 9th, UCSC A. E. Tzamaloukas6

Motivation

The receiver of a data packet is the point of interest Recast the collision avoidance dialogues so that the receiver,

sender or both can have control of the dialogue Provide correct floor acquisition without carrier sensing and

code assignment Be applicable to multi-channel frequency-hopping or direct-

sequence spread-spectrum radios

February 9th, UCSC A. E. Tzamaloukas7

Polling Issues

When to poll: whether or not the polling rate is independent of the data rate at polling nodes independent polling data-driven polling

To whom: whether the poll is sent to a particular neighbor or to all neighbors; for dense networks a schedule may have to be provided to the poll recipients

How: whether the polling packet asks for permission to transmit as well

February 9th, UCSC A. E. Tzamaloukas8

RICH Characteristics

Dwell time should be long enough to transmit a pair of MAC addresses, a CRC and framing bits

Use synchronous frequency hopping to ensure that all radios hop to different frequency hops at the same time

Nodes do not need carrier sensing or code assignment

Commercially available radios can be used

February 9th, UCSC A. E. Tzamaloukas9

RICH-SP

h1

h2

h3

h4

t1 t3t2 t4 t5 t6hop

time

All the nodes follow a common channel-hopping sequence. If a node receives an RTR then it sends its data to the polling node over the same channel hop; all the other nodes hop to the next channel hop.

RTR DATA

RTR silence

DATACTSRTR

RTR backoff

RTR

February 9th, UCSC A. E. Tzamaloukas10

RICH-DP

The key difference from RICH-SP is that now an RTR is an invitation to receive and transmit; therefore, two data packets can be exchanged in the same busy period

h1

h2

h3

h4

t1 t3t2 t4 t5 t6hop

timet6

RTR silence

DATACTSRTR

RTR backoff

RTR

RTR DATA DATA

February 9th, UCSC A. E. Tzamaloukas11

Throughput Analysis Model

ad-hoc network of N nodes multiple channels, error-free the size of an RTR and CTS is less than one slot; the size for a data

packet is derived from a geometric pdf the turn-around time is considered to be part of the duration of control

and data packet a polled node receiving an RTR always has a data packet to send the probability that the packet is addressed to the polling node is 1/N Analysis is based on a model first introduced by Sousa and Silvester

[Trans. On Communications - March 1988]

February 9th, UCSC A. E. Tzamaloukas12

N=16

N=20

N=20

N=4

N=4N=8

N=8N=16

0

1

2

3

4

THR

OU

GH

PU

T I N

MIN

I PA

CK

ETS

per

SLO

T

0.2 0.4 0.6 0.8 1PROBABILITY OF TRANSMISSION IN A SLOT p

THROUGHPUT FOR L=10

--- MACA-CT

--- RICH-SP

Fixed packet length

Throughput analysis results

Throughput vs. probability of transmission. Results for RICH-SP are compared against MACA-CT [Joa-Ng and Lu - INFOCOM 1999]

L=10

L=10

L=100

L=100

L=2

L=2

0

1

2

3

4

5

THR

OU

GH

PU

T IN

MIN

IPA

CK

ETS

per

SLO

T

0.2 0.4 0.6 0.8 1PROBABILITY OF TRANSMISSION IN A SLOT p

THROUGHPUT FOR N=12

--- RICH-SP

--- MACA-CT

Fixed number of nodes

February 9th, UCSC A. E. Tzamaloukas13

Throughput analysis results

Throughput vs. probability of transmission. The packet length is fixed equal to 10 hops and the number of nodes in the network is a parameter. Results for RICH-DP are compared against RICH-SP.

N=8

N=12

N=8

N=12

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

THRO

UGHP

UT IN

MIN

IPAC

KETS

per

SLO

T

0.2 0.4 0.6 0.8 1PROBABILITY OF TRANSMISSION IN A SLOT p

THROUGHPUT FOR L=10RICH-SP

RICH-DP

February 9th, UCSC A. E. Tzamaloukas14

Delay analysis results

L=2

L=10

L=2 L=2

L=10 L=10

10

20

30

40

50

NORM

ALIZ

ED S

YSTE

M DE

LAY

0 0.2 0.4 0.6 0.8PROBABILITY OF TRANSMISSION IN A SLOT p

DELAY FOR N=12MACA-CTRICH-SPRICH-DP

L=10 L=10

L=2

L=10

L=2L=210

20

30

40

50

ACTU

AL S

YSTE

M DE

LAY

0 0.1 0.2 0.3 0.4 0.5 0.6PROBABILITY OF TRANSMISSION IN A SLOT p

DELAY FOR N=12MACA-CT

RICH-SPRICH-DP

Normalized delay Actual delay

February 9th, UCSC A. E. Tzamaloukas15

Network Topologies

BaseN1

N2

B1 B2

N1

N1

N1N1

(a) (b)

(c)

Base

February 9th, UCSC A. E. Tzamaloukas16

Simulated Radio Model

Radio features– 2.4GHz FHSS, no capture,

no power control– 80 channels, 1Mbps each– 120us dwell time– half-duplex operation– RICH MAC protocol– omni-directional antenna

February 9th, UCSC A. E. Tzamaloukas17

Simulation Results

RICH-DP (Simulation)

RICH-SP (Analysis)

RICH-DP (Analysis)

MACA-CT (Analysis)MACA-CT (Simulation)

RICH-SP (Simulation)

0

1

2

3

4

5

THRO

UGHP

UT IN

MIN

IPAC

KETS

per

SLO

T

0.2 0.4 0.6 0.8PROBABILITY OF TRANSMISSION IN A SLOT p

THROUGHPUT FOR N=12

Topology (c)

Analysis

Topology (b)

Topology (a)

0

0.5

1

1.5

2

2.5

THRO

UGHP

UT IN

MIN

IPAC

KETS

per

SLO

T

0.2 0.4 0.6 0.8 1PROBABILITY OF TRANSMISSION IN A SLOT p

THROUGHPUT FOR N=8

February 9th, UCSC A. E. Tzamaloukas18

Simulation Results

aggregate data rate < available bandwidth

February 9th, UCSC A. E. Tzamaloukas19

Simulation Results

aggregate data rate > available bandwidth

February 9th, UCSC A. E. Tzamaloukas20

Simulation Results

Comparison

February 9th, UCSC A. E. Tzamaloukas21

Conclusions

By reversing the collision avoidance handshake we improved the performance of MAC protocols for ad-hoc networks

RICH protocols achieve correct floor acquisition without carrier sensing or code assignment

RICH outperforms any other multi-channel collision avoidance MAC protocol to date in terms of throughput and delay

Extensive simulations verified our analytical results