September, 2005 Doc: IEEE 15-05-0551-00-004a Zhen, Li, Kohno (NICT) SlideTG4a1 Project: IEEE P802.15...

TG4a

September, 2005 Doc: IEEE 15-05-0551-00-004a

Zhen, Li, Kohno (NICT) Slide 1

Project: IEEE P802.15 Working Group for Wireless Personal Area Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Networks (WPANs)

Submission Title: [MAC enhancement to support ranging]Date Submitted: [Sept., 2005]Source: [Bin Zhen, Huan-Bang Li, Ryuji Kohno, Company: National

Institute of Information and Communications Technology ]Contact: Bin ZhenVoice:+81 46 847 5445, E-Mail: [email protected]]Abstract: [UWB MAC enhancement ]Purpose: [discussion ]Notice: This document has been prepared to assist the IEEE

P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

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MAC enhancement to support ranging

Bin Zhen, Huan-Bang Li, and Ryuji Kohno

National Institute of Information and Communications Technology (NICT)

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Requirements• Requirements from ranging

– No interruption and corruption• Ranging response should be as fast as possible to reduce error• Hidden nodes

– Ranging need some data communication• E.g. response delay, crystal offset

– Special ranging operation• Leading edge detection of preamble• Accuracy timing

• Requirements on network– Do not break MAC architecture

• MAC should control channel access. PHY do not know frame structure.

– GTS is optional

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Virtual carrier sense• Virtual carrier sense (virtual CS) is provided by MAC

– “Virtual CS is achieved by distributing reservation information announcing the impending use of the media”

– Physical CS is provided by PHY

• The mechanism of virtual CS is network allocation vector (NAV) – the NAV maintains a prediction of future traffic on media based

on duration information announced in RTS/CTS handshake– The NAV can be considered as a counter, which count down to

zero at uniform rate. When the counter is zero, the Virtual CS indicate the media is free

• Easy to be implemented

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Virtual CS in sensor network

• Virtual CS has been simulated and implemented in sensor network – Sensor MAC (over Mote by USC)– EYES project– PAMAS (power aware)

• Virtual CS benefits energy efficiency of sensor node by reducing– packet collision due to hidden node– overhearing when neighbour talks– interleaving during message passing

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Ranging based on virtual CS

• Using virtual carrier to reserve media for ranging and indicate start of ranging– Ranging can be considered as a special

group of long data transmission• Virtual carrier sense is MAC atomic

• Virtual CS– RNG_RTS/RNG_CTS– RNG_INV (ranging by invitation)

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TWR through RNG_RTS/RNG_CTS

Ranging initiator

Ranging responder

RNG_RTS

RNG_CTS

Ranging frame

Ranging data

ACK (if requested)

Ranging Window (Reserved period)

Contention period

Othernodes

NAV(RNG_RTS)

NAV(RNG_CTS)

PHY control periodMAC control period

Handshake period

SIFS SIFS/LIFS

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Frame formatsFrame control

Rng. initiatoraddr.

Rng. responderaddr.

FCSRNG_RTS Rng. duration

Frame control

FCSRNG_CTS

Rng. preambleformat

Rng. duration

Rng. responderaddr.

S S 0-S -S 0 -SS S S SS -S-S

0.5, 1 or 4 (ms)

Ranging frame

synchronization Channel estimation Frame delimiter

Ranging data

Seq. number

Seq. number

Frame control

FCSAddressfield

Seq. number

MHR MSDU

Resp. delay

Relative crystaloffset

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Period divisions• RNG_RTS/RNG_CTS handshake period

– To reserve un-interruptible and collision-free channel access for ranging between pair of nodes

• Other nodes enter power save mode after receiving either of RNG_RTS/RNG_CTS

– To negotiate ranging parameters• Preamble type (short, middle and long)• Duration of ranging window

– To start ranging procedure• enable ranging counting and first-arrival detection• enable PHY channel control

• Ranging window– Between ranging preamble and ACK of ranging data

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Periods division (cont.)• PHY control period

– To measure flying time through ranging frame exchange without MAC awareness.

– PHY generates ranging frame directly• No data payload

• MAC control period– To send ranging data through normal data communication from

responder to initiator– MAC generate MAC header (MHR) and MAC service data unit

(MSDU)– Ranging data includes

• Response delay: between the end of injected ranging frame and the start of outgoing ranging frame

• Relative crystal offset estimate

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MSC of TWR using RNG_RTS/RNG/CTS

Ranging originator Ranging responder

Higher layer MAC PHY PHY MAC Higher layer

TWR requestRNG_RTS

RNG_CTS

TWR indication

TWR response

ranging ready (rep.)ranging ready (ini.)Ranging frame

Ranging frame Response delay (T2)

Round-trip delay T1

Response delay (T2),Crystal offset

ACK (if requested)

TWR confirm

Media reservation duration; Ranging frame;Leading edge detection; Counter

d= c*(T1-T2)/2

TWR indication

TWR end state

Re

serve

d

pe

riod

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Channel access• RNG_RTS/RNG_CTS handshake

– Normal CSMA with backoff before transmission

• Ranging window– Both initiator and responder have no carrier

sense during the ranging window• All intervals between packets are SIFS

– Other nodes sense a busy channel virtually or physically during the whole window

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Recovery procedure• RNG_RTS/RNG_CTS handshake error

– Failure of receiving RNG_CTS response trig retransmission of RNG_RTS

• Ranging must be finished within ranging window– No retransmission mechanism in the ranging window – Failure of receiving the expected response means the

early end of ranging• Ranging frame, ranging data packet and ACK• The receiver of the destined node will cancel the next

transmission

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Before ranging operation• Ranging initiator and responder must join the

same piconet, so that both of them know each other– Address

• Device address/associate short address – Node capability information

• power source, security, FFD/RFD, receiver idle– Ranging attributes

• Ranging window• Ranging support, coherent/non-coherent receiver, or

short/middle/long preamble– Security parameters

• Encryption and authentication

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TWR through RNG_INV

Ranging initiator

Ranging responder

RNG_INV

Ranging frameRanging data

ACK(if requested)

SIFS

Ranging Window (Reserved period)

Contention period

Othernodes NAV(RNG_BINV)

PHY control period

MAC control period

Handshake period

SIFS/LIFS

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Protocol description

• Normal CSMA and backoff before transmission of RNG_INV from responder

• RNG_INV is impliedly acknowledged by ranging frame– Initiator sends ranging frame after SIFS if channel is sensed idle– Failure of receiving ranging frame from initiator trigs re-

transmission of RNG_INV with backoff

• Operations in the ranging window is the same as those in TWR through RNG_RTS/RNG_CTS

RNG_INV

Frame control

Rng. initiatoraddr.

Rng. responderaddr.

FCSRng. duration

Rng. preambleformat

Seq. number

MHR MSDU

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MSC of TWR using RNG_INVRanging originator Ranging responder

Higher layer MAC PHY PHY MAC Higher layer

TWR requestRNG_INV

TWR indication

TWR response ranging ready (rep.)

ranging ready (ini.)Ranging frame

Ranging frame Response delay (T2)

Round-trip delay T1

Response delay (T1),Crystal offset

ACK (if requested)

TWR confirm

Media reservation duration; Ranging frame;Leading edge detection; Counter

d= c*(T1-T2)/2

TWR indication

TWR end state

Re

serve

d

pe

riod

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Performance• Both RTS/CTS and BI are original proposed to

solve hidden nodes issue– They can be used to reserve channel because of

collision free property– Applying them to ranging can be considered as a

special case• Sender or receiver initiated ranging

– RNG_INV suppresses RNG_RTS part of RNG_RTS/RNG_CTS handshake.

• This reduces turn-around overhead and improves channel and power efficiency

• UWB channel is not suitable to transmit short data due to long synchronization time

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Analyzed system parameters• Real system of TWR

– Data rate: 1Mbps– Ranging frame: 250 byte (1ms)– MAC command frame: 25 bytes (0.1ms)– Piconet range: 60m

• Normalized parameters– propagation delay= 1e-4; (0.2μs)– Normalized handshake= 0.1;

• 2% hidden traffics• Non-persistence ranging operation• 2^n backoff if channel is sensed busy

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Performance criteria• Normalized throughput• Good ranging latency

– time delay to the first trial after last good ranging– Latency= (2^number_of_transmission-1)*

backoff_unit-1• Ranging trial per good ranging• Power consumption per good ranging

– CSMA_power= ranging_trials* transmission_probability*range_frame

– Handshake_power = ranging_trials* transmission_probability*handshake_frame + ranging frame

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Network throughput

Single hop10

-210

010

20

0.2

0.4

0.6

0.8

1

offered load

no

rmal

ized

th

rou

gh

pu

t

RNG-BICSMA-npRNG-RTS/CTSCSMA-np-hd

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Power consumption per good ranging

10-3

10-2

10-1

100

101

0.5

1

1.5

2

offered load

po

wer


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Ranging trials per good ranging

10-2

10-1

100

101

102

100

101

102

offered load

tra

ns

mis

sio

ns


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Delay per good ranging

10-2

10-1

100

101

10-2

100

102

offered load

de

lay


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Security consideration• Separated ranging request, ranging operation

and ranging data transmission– Handshake and ranging data are controlled by MAC– TWR is controlled by PHY

• No information payload in ranging frame

• Only MAC security mechanism is OK– Authentication before ranging handshake

• Ranging information can be used for verification of the claimed position

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Complexity analysis• IEEE 802.15.4 already define GTS in a

superframe– Data transmission in CAP must be finished

before start of GTS– Data transmission in GTS must be finished

before end of GTS slot

• NAV computing is already available– Not much increased complexity in device

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TDOA ranging modes

Key:Sync PulseLocation PulseTDOA backhaul

Mode 2 - Active

controller

reference node

Key:Sync PulseLocation PulsePosition Report

Mode 1 - Passive

controller

reference node

SOI SOI

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Applying virtual CS to TDOA• Reference nodes must be precise clock-wise synchronized• The basis of TDOA is OWR

– Only PHY control period in the ranging window– No ranging data

• Before ranging, SOI must join same piconet with reference nodes

Group RNG_INV for mode 1

Frame control

Ref. node1 addr.

FCSRng. duration

Rng. preambleformat

Seq. number

MHR MSDU

Ref. node2 addr.

Ref. node3 addr.

RNG_INV for mode 2

Frame control

SOIaddr.

FCSRng. duration

Rng. preambleformat

Seq. number

MHR MSDU

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TDOA mode 1• Mobile node knows position• SOI reserve channel using group RNG_INV• TDOA mode 1 can be separated into 3 SWR which send ranging

frame with defined interval (SIFS)– Only the invited reference nodes send ranging frames– SOI knows the defined interval between ranging frames before ranging

Reference node

SOIRNG_INV

Ranging preamble

SIFS

Ranging window(PHY control period)

Handshake period

SIFS/LIFS

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TDOA mode 2• Network knows position• One of the reference nodes sends RNG_INV

– Master reference node

RNG_INV

Ranging preamble

SIFS

Contention period

Handshake period

SIFS/LIFS

Reference node

SOI

Ranging window(PHY control period)

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Conclusions• Virtual CS can be used to support ranging

– Separate of TOA/TDOA measurement and ranging calculation• Ranging data is managed by MAC• Ranging preamble is controlled by PHY• Ranging data can be protected by MAC security mechanism

– Sender/receiver initiated ranging• RNG_INV is better due to less handshake

• Support both TWR and SDS-TWR• Benefits

– Little disadvantage by introducing handshake mechanism– Separated ranging operation and communication operation

• Backward compactable with 15.4 MAC

– Can be used in both beacon and non-beacon network

September, 2005 Doc: IEEE 15-05-0551-00-004a Zhen, Li, Kohno (NICT) SlideTG4a1 Project: IEEE P802.15...

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