Radio Networks Riccardo Cavallari DEI, Università di Bologna · Riccardo Cavallari DEI,...

Riccardo Cavallari DEI, Università di Bologna

Radio Networks

Radio Networks

Riccardo Cavallari

[email protected]

+39 051 20 93180

Office:

3rd floor, Main Building

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Radio Networks

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Wireless Body Area Networks (WBAN) and

IEEE 802.15.6 Standard


Radio Networks

Outline 1. Introduction

• Definitions and Application Scenarios

• Standardization

2. Physical (PHY) Layer

3. Medium Access Control (MAC) Layer

• Beacon Mode with beacon periods (superframes)

• Non-Beacon Mode with superframes

• Non-Beacon Mode without superframes

5. Coexistence techniques

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Radio Networks

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• Standardization








Radio Networks

Wireless Body Area Networks (WBANs)

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WBAN:

• Collection of nodes placed on, or inside,

the human body (but not limited to).

• Nodes have sensing and/or actuating

and communication capabilities.

Applications:

• Medical: monitoring vital parameters,

hearing aids, cardiac implant, etc.

• Sport/Fitness: rehabilitation, motion capture,

monitoring parameters;

• Entertainment: consumer electronics (audio/video streaming,

interactive gaming), personal item tracking.

WiserBAN EU Project: realizes a miniaturized and ultra-low power RF microsystem, for

medical and multimedia applications.


Radio Networks

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• Standardization

2. Network Topology








Radio Networks

Standard IEEE 802.15.6 (final release, Feb. 2012)

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• Different applications leads to different technical requirements unique standard

IEEE 802.15 Task Group 6 (November 2007):

• Define the Physical (PHY) and Medium Access Control (MAC) Layers for short range,

low complexity, low cost, ultra-low power and high reliable wireless communication in,

on or around the human body.

High level application requirements


Radio Networks

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• Standardization








Radio Networks

Physical (PHY) Layer

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• 3 different PHY

• Modulation @ 2.45GHz

Packet

Component Modulation

Symbol Rate

(ksps)

Spreading

Factor

(S)

Information

Data Rate

(kbps)

PSDU π/2-DBPSK 600 4 121.4

PSDU π/2-DBPSK 600 2 242.9

PSDU π/2-DBPSK 600 1 485.7

PSDU π/4-DQPSK 600 1 971.4

• N° of Channel @ 2.45GHz:

79 Channel of 1MHz Bandwidth

• Min Tx Power:

-10 dBm EIRP

• Receiver Sensitivity @ 2.45GHz:

Frequency Band (MHz)

Information Data Rate

(kbps)

Minimum Sensitivity

(dBm)

2400 – 2483.5

121.4 –92

242.9 –90

485.7 –87

971.4 –83

Narrowband

2483.5 5 50

2360 2400 3100 10600 402 405

420 450

863 870 902 928

958 950

HBC MICS WMTS

Japan Europe

ISM

North America Australia

New Zeland WorldWide Japan

UWB f [ MHz ] ISM


Radio Networks

Data rates

PHY

Frequency band

(MHz), center

frequency

(MHz), or

modulation

Data rate 0 (kb/s)

Data rate 1 (kb/s)

Data rate 2 (kb/s)

Data rate 3 (kb/s)

Data rate 4 (kb/s)

Data rate 5 (kb/s)

Data rate 6 (kb/s)

Data rate 7 (kb/s)

Narrow band

(NB)

402 to 405 75.9 151.8 303.6 455.4 Rsvd Rsvd Rsvd Rsvd

420 to 450 75.9 151.8 187.5 Rsvd Rsvd Rsvd Rsvd Rsvd





2400 to 2483.5 121.4 242.9 485.7 971.4 Rsvd Rsvd Rsvd Rsvd

Ultra wideband (UWB)

Non- coherent 394.8 789.7 1579 3159 6318 12 636 Rsvd Rsvd

Differentially

coherent 487 975 1950 3900 7800 15 600 557 1114

FM 202.5 Rsvd Rsvd Rsvd Rsvd Rsvd Rsvd Rsvd

Human body

communica-

tions (HBC)

21

164

328

656

1312.5

Rsvd

Rsvd

Rsvd

Rsvd


Radio Networks

PHY Protocol Data Unit (PPDU)

PLCP Preamble PLCP Header PSDU

HCSBCH

Parity BitsPHY Header

4 bits 12 bits15 bits 7 bytes 2 bytes

MAC

HeaderFCS

MAC Frame Body

Variable Length: 0 – 255 bytes

RATE LENGTHBURST

MODEReserved

3 bits 8 bits1 bit

Reserved

1 bit

SCRAMBLER

SEED

1 bit 1 bit

•Packet detection

•Time synchronization

•Carrier off-set recovery

• It conveys PHY parameters needed at

the Rx to decode the PSDU:

a) Length and Data Rate of MAC

packet

b) Header check sequence

c) BCH encoder to improve header

robustness

• Physical layer Service Data Unit:

contains the MAC frame


Radio Networks

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• Standardization








Radio Networks

MAC Access Modes and Phases 1/4

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1. Beacon Mode with superframe: beacons at the beginning of each superframe to

establish a common time base for time referenced allocations;

Random Access Phases

CSMA/CA Access Method : • Backoff counter (BC) in the interval [0-CW],

• BC is decremented by one, for each

successive idle CSMA time slot;

• When BC=0, the node obtains a contended

allocation during which the TX occurs.

Contention between nodes: allocations are non-recurring time intervals valid per instance

of access.

EAP (Exclusive Access Phase): for high priority traffic.

RAP (Random Access Phase): for regular traffic.

Slotted Aloha Access Method: • Contention Probability (CP) properly set;

• z =random in the interval [0-1];

• If z≤CP the node obtains a contended

allocation in the current Aloha slot, during

which the TX occurs .


Radio Networks

CSMA/CA access illustration

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RAP1

Data

arrives

Tf

Slot = CSMA slot SIFS = pSIFS

F1 = frame transaction initiated by node 1 in a contended allocation (e.g., a data type frame and an I-Ack frame with pSIFS in between)

Tf = time required to complete F1 GTn = nominal guard time

Slo

t

CW = CWmin = 8;

backoff counter is set

to 3 over [1, CW] and

unlocked.

SIF

S

Slo

tS

lot F1

Backoff

counter (= 0)

Contention fails 1st time.

CW is not changed;

backoff counter is reset to

5 over [1, CW] and locked.

CAP

Slo

t

Backoff

counter (= 5)

is unlocked

Slo

tS

lot

No enough time is

left; backoff counter

(= 2) is locked.

Slo

t

Tf Tf

RAP2

Slo

tS

lot F1

Contention fails 2nd

time.

CW = 16 (doubled);

backoff counter is reset

to 8 over [1,CW] and

locked

Backoff

counter (= 2)

is unlocked.

Slo

tS

lot

Backoff

counter (= 8)

is unlocked

Backoff

counter (= 0)

Slo

tS

lot

Slo

tS

lot

Slo

t F1

Backoff

counter (= 0)

Slo

t

Contention succeeds.

CW is reset to CWmin;

backoff counter is reset to 2

over [1, CW] and locked

Backoff counter decrements

Tf

SIF

S

SIF

S

SIF

S

Priority User Priority Traffic designation CWmin CWmax

Lowest

Highest

0 Background (BK) 16 64

1 Best effort (BE) 16 32

2 Excellent effort (EE) 8 32

3 Controlled load (CL) 8 16

4 Video (VI) 4 16

5 Voice (VO) 4 8

6 Medical data or network

control

2 8

7 Emergency or medical event

report

1 4


Radio Networks

Slotted Aloha access illustration

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RAP1

F1 = frame transaction initiated by node 1 in a contended allocation (e.g., a management type frame and an I-Ack frame with pSIFS in between)

CAP RAP2

Aloha

slot

Aloha

slot

Aloha

slot

Aloha

slot

Aloha

slot

Aloha

slot

Aloha

slot

Aloha

slot

CP = CPmax = 1/2.

Node 1 does not

obtain a

contended

allocation.

CP =1/2.

Node 1 obtains a

contended allocation

and sends a frame

which then fails.

F1

CP = 1/2 (unchanged).

Node 1 obtains a


and sends a frame

which then fails again.

F1

CP = 1/4 (halved).

Node 1 does not

obtain a

contended

allocation.

CP = 1/4.

Node 1 does

not obtain a

contended

allocation.

CP = 1/4.

Node 1 does

not obtain a

contended

allocation.

CP = 1/4.

Node 1 obtains a


and sends a frame

which then succeeds.

F1

CP is reset to CPmax.

Node 1 does not

obtain a

contended

allocation.

Priority User Priority Traffic designation CPmax CPmin

Lowest

Highest

0 Background (BK) 1/8 1/16

1 Best effort (BE) 1/8 3/32

2 Excellent effort (EE) 1/4 3/32

3 Controlled load (CL) 1/4 1/8

4 Video (VI) 3/8 1/8

5 Voice (VO) 3/8 3/16

6 Medical data or network

control

1/2 3/16

7 Emergency or medical event

report

1 1/4

z = rand[0,1]

z ≤ CP to transmit


Radio Networks


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Managed Access Phase

Beacon period (superframe) n Beacon period (superframe) n+1

Allocation

interval

Allocation

interval

Allocation

interval

...

Beacon period (superframe) …

7 8 9 7 8 9 7 8 9

Beacon period (superframe) n Beacon period (superframe) n+1

...

Beacon period (superframe) n+m

1 2Allocation

interval

1 2Allocation

interval

Access to the channel is managed by the hub

• Scheduled Access Method:

1-periodic scheduled allocation: one or

more allocation intervals, of the same

temporal length, are granted to the

node in every superframe. Suitable for

high duty cycle periodic or quasi-

periodic traffic. (e.g., streaming)

m-periodic scheduled allocation: one or

more allocation intervals, of the same

temporal length, are granted to the

node every m>1 superframe. Suitable

for low duty cycle periodic or quasi-

periodic traffic. (e.g., status signals)


Radio Networks


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• Improvised Access Methods:

for on-demand contention-free frame exchange outside scheduled allocations

Hub

transmits

Node 1

transmits

Data(B-

Ack)

B-A

ck+

Po

ll

Data(I-Ack)

Po

ll

Data(L-

Ack)

Data(B-

Ack)

B-A

ck+

Po

ll

Scheduled uplink

allocation interval

Data(I-Ack)

I-Ack

Data(I-Ack)

I-Ack

I-A

ck+

Po

ll

Data(I-Ack)

I-Ack P

oll

Data(I-Ack)

I-Ack

Scheduled downlink

allocation interval

Post

Data(L-

Ack)

Po

ll

Immediate Future Immediate Future

Polled

allocation

interval

Polled

Allocation interval

Polled

Allocation

interval

ImmediateImmediate Immediatea) Polling Access: the hub grants to

the node one or more non-

reoccuring time intervals for

initiating one or more frame

transactions by the node

uplink! Suitable for “ordinary”,

“unexpected” or “extra” traffic.

E.g., error signaling.

Hub

transmits

Node 1

transmits

Data(L-

Ack)

Data(B-

Ack)

B-A

ck

Scheduled uplink

allocation interval

Post

Data(I-Ack)

I-Ack

Data(I-Ack)

Post

I-Ack

Scheduled downlink

allocation interval

Post

Data(I-Ack)

Data(I-Ack)

Data(L-Ack)

Data(B-

Ack)

B-A

ck

Post

Data(L-Ack)

Data(B-

Ack)

B-A

ck

Post Post

Posted

allocation interval

Posted

allocation interval

Immediate ImmediateFuture Immediate Immediate Immediate

I-Ack

Data(I-Ack)

I-Ack

I-Ack

a) Posting Access: the hub grants to

itself one or more non-reoccuring

time intervals for initiating one or

more frame transactions

downlink! Suitable for

“unexpected” or “extra” traffic. E.g.,

BAN management information.


Radio Networks

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Outline

1. Introduction


• Standardization








Radio Networks


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2. Non-Beacon Mode with superframes:

no beacons but superframe and

allocation slots are established

because the channel access involves

time referencing. Only MAP.

3. Non-Beacon Mode without superframes:

no beacons; superframe and allocation

slots are not established because the

allocation involves no time referencing.

• Unscheduled Access Method:

A hub may provide unscheduled reoccuring polled or posted allocations, nodes

may use CSMA/CA to obtain a contended allocation.


Radio Networks

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Outline

1. Introduction


• Standardization








Radio Networks

Coexistence with other BANs

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• Coexistence Techniques:

a) Beacon Shifting: in order to mitigate potential beacon collisions and

schedule allocation conflicts the hub transmits its beacons at different time

offset, according to a particular beacon shifting sequence, not being used

by other neighbor hubs.

b) Channel Hopping: the hub changes its operating channel periodically

according to a particular channel hopping sequence, not being used by

other neighbor hubs. The node shall hop to the same channel to remain

connected with its hub.


Radio Networks

References

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1. 15-08-0644-09-0006-tg6-technical-requirements-document, November 2008.

2. Kwak K.S, Ameen M.A, Kwak D, Lee C, Lee H; “A Study on proposed IEEE

802.15 WBAN MAC protocols”, ISCIT December 2009.

3. Massè F, Penders J; “Quality-of-Service in BAN: PER reduction and its trade-offs”;

International conference on BSN July 2010.

4. 15-08-0780-11-0006-tg6-channel-model, September 2010.

5. 15-08-0034-15-0006-ieee-802-15-6-regulation-subcommittee-report, May 2010.

6. IEEE Standard for Local and metropolitan area networks - Part 15.6: Wireless

Body Area Networks," IEEE Std 802.15.6-2012 , vol., no., pp.1,271, Feb. 29 2012.

7. Reichmann A; “Standardization of Body Area Networks”; COMCAS January 2010.


Radio Networks

Radio Networks

Riccardo Cavallari

[email protected]

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Radio Networks Riccardo Cavallari DEI, Università di Bologna · Riccardo Cavallari DEI,...

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