Jan. 2005 France Telecom doc.: IEEE 802. 15-05-0014-02-004a Submission Slide 1 Project: IEEE P802.15 Working Group for Wireless Personal Area Networks.

Jan. 2005

France Telecom

doc.: IEEE 802. 15-05-0014-02-004a

Submission

Slide 1

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

Submission Title: UWB-IR (Impulse Radio) system proposed for the Low Rate alt-PHY (802.15.4a)Date Submitted: Jan., 2005Source: Benoit Miscopein (1), Patricia Martigne (2), Jean Schwoerer (3)Company: France Telecom R&DAddress: 28 Chemin du Vieux Chêne – BP98 – 38243 Meylan Cedex - France

Voice: (1) +33 4 76 76 44 03, (2) +33 4 76 76 44 23, (3) +33 4 76 76 44 83E-Mail: (1) [email protected], (2) [email protected], (3) [email protected]

Abstract: Complete proposal for 802.15.4a

Purpose: This document is a presentation of a complete proposal for the IEEE 802.15.4 alternate PHY standard

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

Jan. 2005

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Submission

Slide 2

Commonalities with Other Proposals

• Many commonalities exist between proposals, including at least FT, CWC/AetherWire/LETI/STM and Mitsubishi, as all of these share similar views about:

– UWB technology– Bandwidth usage– Ranging approach

• Discussions are under way for future collaborations and merging

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Submission

Slide 3

UWB Technology

• Impulse-radio (IR) based:– Very short pulses Reduced ISI– Robustness against fading– Episodic transmission (for LDR) allowing

long sleep-mode periods and energy saving

• Low-complexity implementation

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Slide 4

Bandwidth Usage

• Flexible use of (multi-)bands up to 7.5 GHz, depending on application and regulatory environment

• Use of TH and/or polarity randomization for smoothing of the spectrum

• Noise-like interference towards existing radio services

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Slide 5

Ranging Approach

• Signal bandwidth 1GHz for very good location accuracy

• Two-way ranging protocol to avoid synchronization between nodes

• Location based on ranging from several nodes on a higher layer

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Submission

Slide 6

Contents

• Structure of the UWB signal• Modulation, coding, multiple access technique• Spectrum aspects• PHY Frame Structure• System dimensioning• The transmitter• The antenna • The receiver• Ranging technique• UWB prototyping• Link Budget

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Submission

Slide 7

Structure of the UWB Signal

"Pure" Impulse radio:

• Very short pulses.Each pulse (a wavelet) is about 1ns wide in time domain <--> 1GHz bandwidth in frequency domain

• Pulses are transmitted within slots of Tc each

pulse-spacing = Tc ± TH

Pulse width = 1ns

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Submission

Slide 8

Modulation and codingBit to symbol mapping :

Binary (low speed mode) or quaternary (high speed) bit to symbol mapping.

Symbol-to-chip mapping :

Each symbol is a sequence of N chips.

Symbols are energy-equivalent.2 (low speed) or 4 (high speed) orthogonal sequences available

OOK (On Off Keying) :

Chips are OOK-modulated

chip = '1' a pulse is transmitted chip = '0' no pulse

Bit-to-Symbol

Symbol-to-Chip

OOK

Binary data from PPDU

Modulated signal

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Submission

Slide 9

Multiple access

Multiple access : TH (Time Hopping).Each Symbol-time (Ts) is divided in N chip-time (Tc).Each chip-time (Tc) is divided in M pulse-time (Tp).

A PN-code selects a pulse-time within the chip-time in which a pulse will be transmitted.Each piconet has its own M-ary N-chip-long PN-code, selected in a set of nearly orthogonal sequences, and shared by all the members-devices.

Within the piconet :Medium sharing is done via CSMA-CA (slotted if operating in beacon mode)

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Submission

Slide 10

Spectrum aspects

Bandwidth :- At least 1GHz bandwidth (-3dB)

Center frequency : 2 options

- 4 GHz in the US and FCC-compliant country.

- 7 GHz to have easier worldwide regulatory compliance.

less potential for (current and future) interference.will cause fewer regulatory issues.

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Submission

Slide 11

Modulation, coding and multiple access

Example : if we choose :- 8 pulse-time of 20 ns each.- Tc = 8*20 = 160 ns chip period.- TH code chip = 8-ary 8-sequence.

- 8 pulses transmitted for 1 symbol.

- 1 symbol = 1 bit (low speed mode).

This means :

=> a bit period of 8*160ns = 1280ns

=> PHY-SAP payload bit rate (Xo) = (1/(1280.10-9))*(1000/1024) = 763 kb/s

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Submission

Slide 12

PHY Frame Structure

Example of a standard PPDU data frame :

PHY Preamble sequence

PHY Header : Frame length

MAC Header : Frame control + Sequence nb + Addressing fields

MAC footer

4 bytes 1 PSDU : 32 bytes (e.g.)

2 1 8 (e.g.) MSDU Data Payload 2

MPDU

The Start of Frame Delimiter is suppressed

it is replaced by a detection of bit-mapping modification (bit-mapping used for the preamble sequence will differ from the one used otherwise)

PPDU = 37 bytes for a 32-bytes standard

PSDU

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Slide 13

Example of system dimensioning (1/5)Example of a standard PPDU data frame

Data frame (37 bytes) ACK

t ACK LIFS

Next data frame

Time for an acknowledged transmission

Calculation of the useful rate for the standard 32-bytes PSDU, using "standard" speed (X0 = 763 kb/s) :

ttransmission = tdata-frame + tACK + tACK-frame + tLIFS = 560,64 µs (considering 8 pulses/symbol, 1 symbol=1 bit, and tACK = 22 symbol-time)

This provides a useful rate of (32*8 bits / 560,64µs)*(1000/1024) = 446 kb/s

…

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Submission

Slide 14

Example of a standard PPDU data frame

For T0 = 1 kb/s (1024 bits/s),

this useful rate of 446 kb/s (corresponding to the transmission of 32 payload bytes i.e. 256 bits) means that the idle time for the system will be tidle = 249 msec approx.

Data frame ACK

t ACK LIFS

ttransmission

Transmission N

Transmission N+1

Transmission N+2

Transmission N+3

1024 bits in 1 sec

tidle

Example of system dimensioning (2/5)

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Submission

Slide 15

Example of a maximum PPDU data frame (127 bytes)

Calculation of the useful rate for the 127-bytes PSDU, using "high speed" mode (X1 = 1526 kb/s) :

In this mode, the mapping is made on 2 bit-symbols instead of being made on 1 bit-symbols for MSDU data payload bits, i.e. for (114 * 8) bits.

PPDU = (5 bytes)std-speed + (114 bytes)high-speed + (13 bytes)std-speed

tdata-frame = 768µs ttransmission = tdata-frame + tACK + tACK-frame + tLIFS = 949,76 µs (considering 8 pulses/symbol, and tACK = 22 symbol-time)

This provides a useful rate of (127*8 bits / 949,76µs)*(1000/1024) = 1045 kb/s

Example of system dimensioning (3/5)

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Submission

Slide 16

For T1 = 500 kb/s (512 000 bits/s),

this useful rate of 1045 kb/s (corresponding to the transmission of 127 payload bytes i.e. 1016 bits) means that the idle time for the system will be tidle = 1 msec approx.

Data frame ACK

t ACK LIFS

ttransmission

Transmission N

Transmission N+1

Transmission N+…

Transmission N+503

512 064 bits in 1 sec

tidle

Example of system dimensioning (4/5)

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doc.: IEEE 802. 15-05-0014-02-004a

Submission

Slide 17

Fixing tidle = 250 µs (minimum required for CSMA-CA)

Example of system dimensioning (5/5)

Data frame ACK

t ACK LIFS

ttransmission

Transmission N

Transmission N+1

Transmission N+…

Transmission N+(x-1)

1 sectidle

Looking for the maximum aggregate channel throughput :

PSDU = 32 octets, std speed – ttransmission = 560,64 µs

– x = 1234 transmitted packets

– Tmax-aggregate = 300 kb/s

PSDU = 127 octets, high speed – ttransmission = 949,76 µs

– x = 834 transmitted packets

– Tmax-aggregate = 825 kb/s

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Submission

Slide 18

Contents

• Structure of the UWB signal• Modulation, coding, multiple access technique• Spectrum aspects• PHY Frame Structure• System dimensioning• The transmitter• The antenna • The receiver• Ranging technique• UWB prototyping• Link Budget

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doc.: IEEE 802. 15-05-0014-02-004a

Submission

Slide 19

The transmitter

Pulse Generator

Clock

F < 100 MHz

Control Logic

BaseBand signal

RF Signal

PSDU Data

• Guide Line : Keep it Simple

– Main Goal : "Low cost & low consumption".

– Pulses are generated in baseband.

– No mixer, no VCO but pulse shaping.

– Simple control logic and "reasonable" clock frequency (Crystal)

Pulse shaper

PA (option)

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Slide 20

Antenna characteristics

• Frequency band: [3-10] GHz

• Printed antenna 24x20 mm²

• Omnidirectional radiation

Matching2 4 106 8 GHz

SWR

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Slide 21

Antenna frequency response

• Antenna gain

– @ 3 GHz: Gant= 4 to 5 dB

– @ 6 GHz: Gant= 3 dB

• Considering the losses in the printed antenna, we set Gant= 3 dB in the link budget

3 GHz

6 GHz

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Slide 22

The receiver

One major guideline : Keep It Simple

• Energy detection technique rather than coherent receiver, for relaxed synchronization constraints.

• Threshold detection (no A/D conversion).C The threshold is set by the demodulation block at each symbol

time, if needed.

• Synchronization fully re-acquired for each new packet received (=> no very accurate timebase needed).

Low cost, low complexity

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Submission

Slide 23

The receiver

x2 Lowpass filter Threshold

Bandpass filter

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Slide 24

Packet Acquisition & Synchronization

No sliding correlation.

• PHY preamble sequence of 4 bytes with special bit mapping (all chips are set to 1).

Maximize the preamble energy.

• Every signal peak exceeding the treshold is acquired.• Triggers shall match arrival times defined by TH-Code.

Cost-effective synchronization.

• Synchronization is fully re-acquired for each new packet

No need to maintain accurate timebase between packets.

Jan. 2005

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Submission

Slide 25

Packet Acquisition & Synchronization

• The synchronization algorithm detects the threshold crossings and updates a assumption matrix, which can also be viewed as a tree exploration

i Detected edge for t_pos(i)

i No edge detection for t_pos(i)

?

2

3

43

4

Δ1,2

Δ2,3

Δ3,4

Δ2,3 Δ3,4

? = 1

Time base origin determination

Δi,j = Known time offset between the pulses appearance, with respect to the TH code.

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Submission

Slide 26

Packet acquisition & Synchronization

• The threshold level is set to detect a number of crossings consistent with the expectations.

• For any tested Channel Model, the synchronization is properly acquired (during the Synch preamble)

• Measured accuracy is around several tens of ps.

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Submission

Slide 27

Performance simulations

• Simulations done with a C++ simulator

• only BER simulations performed, each data point averages 10 channel realizations.

• One operating piconet simulations for CM1, CM2, CM3 and CM5

• CM1 realizations do not provide any error in the simulated range

• Range are computed with a 20xlog(D) relation.

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Submission

Slide 28

Proposed ranging technique

• Ranging capability based on the TOA/TWR technique

• Ranging capabilities with fine precision : system with an 1 GHz bandwidth, leading to an expected ranging accuracy of 30 cm.

• Based on the synchronization acquisition algorithm, aiming at detecting the direct path

– The synchronization acquisition looks efficient, even in difficult environments (CM4)

– Direct path detection is likely to be possible, thanks to a long synchronization preamble (15 dB can theoretically be compensated), if the RF front-end sensibility enables this detection

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Submission

Slide 29

Proposed ranging technique

• Not yet fully tested.• Acquisition of a common time reference, thanks to 2

successive steps between initiator and responder– Short packets exchange (to get a first range measurement) – Responder device sends a Channel Sounding Frame (CSF)

afterwards, to refine the measurement (first path selection), at initiator side.

• Can also be used for mutualized measurements, where the differents initiators can use the same CSF (e.g. inscription of a new device in the piconet), for free

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Submission

Slide 30

Proposed ranging techniqueA

Request

ACK

Channel Sounding Frame

Z

Tw

T>Tg

B

Tw

ACK

Request

Tw

ACK

Request

N

t

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Submission

Slide 31

Energy Detection

• uses exactly the same algorithm as synchronization,• processes 1 byte of data instead of the 4-byte-packet

synchronization preamble (which is twice more energetic than data)

About 9 dB less efficient than packet synchronization.

Consistent with ED requirements for IEEE 802.15.4 (at most 10 dB above sensivity)

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Submission

Slide 32

Clear Channel Assessment

• Introduction of a new value for the PhyCCAMode to allow a channel virtual listening operation (VLO) PhyCCAMode = 4

• The CCA is made by Energy Detection (ED)

• In beaconed or non beaconed systems, an active listening is processed at each Backoff period to get potentially addressed packets.

• In PhyCCAMode = 4– Signal detection and acquisition

– Decode the framelength byte, the ACKrequest bit and the adress fields to arm a VLO timer, including the Tack_max, if the packet is not addressed to the device

– In this case, any PLME-CCA.request leads to a PLME-CCA.confirm{BUSY}, during this time

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Submission

Slide 33

Clear Channel Assessment

Detection of a "competing" packet, by reading Framelength, ACKreq and address fields

Set a VLO vector = Framelength+Tack_max+ACKlength (if needed)

PLME-CCA-request BUSY

t

PLME-CCA-request

ED measure

Slot

Backoff period

ACK

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Submission

Slide 34

Clear Channel Assessment

• Introduction of the VLO is valuable to lower the collision risks and the power consumption as TRX is shut down during VLO

• The ED is performed by the signal acquisition block : can discriminate

– Clear channel

– Intrapiconet activity : PLME-CCA.confirm{BUSY}

– Interpiconet interference : PLME-CCA.confirm{IDLE}

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Slide 35

Summary of 802.15.4 MAC Modifications

aBaseSlotDuration 240 symbol time instead of 60

aBackoffPeriod 80 symbol time instead of 20

CCAmode Mode 4 (with VLO enabled) added

Frame Type subfield 000 Beacon

001 Data (low speed)

010 ACK

011 MAC Command

100 Data (high speed)

101 Data (optionnal very high speed)

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Slide 36

PHY prototyping

• Besides simulations, we also developed a working prototype for such a PHY layer.

• The main guideline was the use of COTS components, amenable to high density integration

• We developed a full TX plateform, compliant with our proposal

• The RX processing is partially taken in charge by a Digital Sampling Oscilloscope, on which our C++ receiver code is run

– Enveloppe detector

– Synchronization acquisition

– Demodulation

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Slide 37

PHY prototyping

• The pulse generation is based on high speed logic, and the doublet is formed by a Wilkinson power coupler

• Features: – 600 ps, – 400 mVpp, – Bw = 3.5 GHz

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Slide 38

PHY prototyping

• The TX control logic is implemented on a 10 kGate FPGA – Modulation,

– Frame building,

– Multiple access

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Slide 39

PHY prototyping

• Results– Meets the spectral bandwidth and raw bit rate

specifications, and integrated TX is proven feasable

– Synchronization acquisition and demodulation operate in "real life"

– On the RX side, we are testing an enveloppe detector, whose simulations are consistent with our sensibility expectations

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Submission

Slide 40

Parameter Value (optional) Value

peak payload bit rate (Rb) X0 = 763 kb/s X1 = 1526 Kb/s

Average Tx power ( TP ) -11.5 dBm -11.5 dBm

Tx antenna gain ( TG ) 3 dBi 3 dBi

maxmin' fff c : geometric center frequency of

waveform ( minf and maxf are the -10 dB edges of the

waveform spectrum)

4 GHz 4 GHz

Path loss at 1 meter ( )/4(log20 '101 cfL c )

8103c m/s

44.5 dB 44.5 dB

Path loss at d m ( )(log20 102 dL ) 29.54 dB at d=30 meters

20 dB at d=10 meters

Rx antenna gain ( RG ) 3 dBi 3 dBi

Rx power ( 21 LLGGPP RTTR (dB)) - 79.5 dBm - 70 dBm

Average noise power per bit ( )(log*10174 10 bRN )

-115.2 dBm - 112,2 dBm

Rx Noise Figure ( FN ) 7 dB 7 dB

Average noise power per bit ( FN NNP ) - 108.2 dBm - 105,2dBm

Minimum Eb/N0 (S) 12 dB 15 dB

Implementation Loss (I) 5 dB 5 dB

Link Margin ( ISPPM NR ) 11.6 dB 15.2 dB

Proposed Min. Rx Sensitivity Level - 91.1 dBm - 85.2 dBm

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Submission

Slide 41

Meets the 802.15.4a objectives

• We presented a system, optimized for :– Energy– Cost– Technical complexity

• Early simulations tend to prove the validity of such a PHY layer

• The proof of concept of the prototype highlights very interesting features concerning the ability to define a low cost system

– use of a reasonable frequency clock (50 MHz)– 8 chips are transmitted per binary symbol, for redundancy

and hence robustness : very simple coding technique.