Post on 01-Apr-2015
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) benoit.miscopein@francetelecom.com, (2) patricia.martigne@francetelecom.com, (3) jean.schwoerer@francetelecom.com
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
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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)
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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.
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
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
…
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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)
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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)
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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)
Jan. 2005
France Telecom
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
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)
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
Slide 20
Antenna characteristics
• Frequency band: [3-10] GHz
• Printed antenna 24x20 mm²
• Omnidirectional radiation
Matching2 4 106 8 GHz
SWR
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
Slide 23
The receiver
x2 Lowpass filter Threshold
Bandpass filter
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
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
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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.
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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.
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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.
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
Slide 30
Proposed ranging techniqueA
Request
ACK
Channel Sounding Frame
Z
Tw
T>Tg
B
Tw
ACK
Request
Tw
ACK
Request
N
t
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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)
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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}
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
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)
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
Slide 38
PHY prototyping
• The TX control logic is implemented on a 10 kGate FPGA – Modulation,
– Frame building,
– Multiple access
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
Submission
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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
Jan. 2005
France Telecom
doc.: IEEE 802. 15-05-0014-02-004a
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.