Narrow-band PHY Proposal for 802.15.4g Doc # P802.15-09-0118-01-004g Project: IEEE P802.15 Working...

Narrow-band PHY Proposal for 802.15.4g

Doc # P802.15-09-0118-01-004g

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: [Narrow Band PHY Proposal for 802.15.4g]Date Submitted: [10 March 2009]Source: [Cristina Seibert] Company [Silver Spring Networks] [Benjamin A. Rolfe] Company [Blind Creek Associates] [George Flammer] Company [Silver Spring Networks]Address [] Voice:[]E-Mail: [cseibert @ silverspringnet.com] [ben @ blindcreek.com] [gflammer @ silverspringnet.com]

Re: []

Abstract: Preliminary Proposal for a Narrow Band PHY for 802.15.4g

Purpose: Technical Proposal

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.


Doc # P802.15-09-0118-01-004g April 19, 2023

Slide 2


Smart Utility Networks(SUN)

Preliminary Technical Features Summary


Doc # P802.15-09-0118-01-004g April 19, 2023

Slide 3

PHY Overview Contents

• Key Characteristics of SUN• General PHY Features• Key PHY Techniques

– Hopping and Modulation– Data Whitening

• PHY Processing Aspects– Data Transfer– PHY Frame (PPDU)

• PHY Channel Plan• MAC Support• Conclusions


Doc # P802.15-09-0118-01-004g April 19, 2023

Slide 4

Key Characteristics of SUN

Some of the characteristics of the W-SUN include:• Low data rate: over the air data rates of 40kb/s up to 1 Mb/s• High resilience and adaptability in the presence of interference

and good coexistence properties with both like systems and non SUN systems.

• Enhanced IP support (> 1500 octet payload)• Ubiquity• Very high reliability and availability• Dynamic scaling to very large aggregate networks• Peer to Peer, minimal infrastructure-dependent operation

MAC

PHY


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Slide 5

General PHY Features• Frequency Hopping Spread Spectrum:

– Individual channels at nominal < 250 KHz, 20 dB down from peak

– 300 KHz channel spacing– Channel plan across multiple bands

• Simple PHY frame – Support for 2047 octet payload (802.1 MTU)– w/32-bit CRC on PHY payload (802 standard generator)

• Nominal (base)100kbps data rate, alternate rates possible

• Simple FSK modulation• Data whitening of payload bits


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Slide 6

Hopping and Modulation

• FHSS:– A method of transmitting radio signals

– Carrier tunes to various channels

– Channel pseudorandom sequence known to both transmitter and receiver.

• FSK:– A frequency modulation scheme

– Digital information is transmitted through discrete frequency changes of a carrier wave.

– MFSK is a spectrally efficient form of FSK.


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Slide 7

Data whitening

• Whitens payload data (PSDU/MPDU) to avoid long series of 1’s and 0’s.

• 8-bit scrambler (255 bit sequence)

– taps at bits [8,4,3,2]

• Scrambler re-seeded periodically

D

CLK

OD

CLK

OD

CLK

OD

CLK

OD

CLK

OD

CLK

OD

CLK

O

21 3 4 5 6 7

D

CLK

O

8


Doc # P802.15-09-0118-01-004g April 19, 2023

Slide 8

PHY Processing Aspects

• The physical layer (PHY) provides the on-air interface between communicating nodes. Its header is sent “in the clear” and its payload (the MAC/DLL data) is scrambled by the PHY Layer.

• The major functions of the PHY layer is the recovery of bit timing, determination of start-of-frame, recovery of the scrambling seed, and length of the PHY frame, and performing a 32-bit cyclic-redundancy-check against the unscrambled MAC/DLL data field.

• The PHY layer then processes the incoming stream for length bytes, calculating the CRC-32. If the CRC-32 matches that received, the PHY layer passes the frame to the MAC/DLL for subsequent processing.


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Slide 9

Data Transfer

Calculate FCS(CRC-32)

Scrambler(PSDU Only)

Generate PHR

Scrambled PSDU + FCS

PHR + Scrambled PSDU

+ FCS

Preamble + PHR + Scrambled PSDU +

FCSPSDU + FCS

SHR Insertion

RF

RFCalculate FCS

(CRC-32)De-Scrambler(PSDU Only)

Data Detection Synchronization

PSDU

PSDU

MA

C (P

HY

-SA

P)


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Slide 10

PHY Frame (PPDU)

Octets: 7 2 1 2 variable 4

Bits: 56 16 8 4 1 11 32

Preamble SFD Scrambler Seed RFU

EXT

Length (PSDU) CRC-32

SHR PHR PHY Payload FCS

– Support for 2047 octet payload (802.1 MTU)– IEEE CRC-32 on PHY frame

Structure of PPDU


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Slide 11

PHY Channel Plan

• Large number of narrow band channels across multiple bands• Hop-able across all bands implemented• At least one band from:

– 779-787 MHz (China)– 840 to 956 MHz

• 868–868.6 MHz (e.g. Europe, China, others)• 902–928 MHz (e.g., Americas, China, others)• 950-956 MHz (Japan)• 865.6-867.6, 840.5-844.5

– 2400–2483.5 MHz (worldwide)• Other bands available?


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Slide 12

PHY Channel PlanIncrease channels per page to support more channels

Band # Chans

902–928 MHz 85

2400–2483.5 MHz 277

950-956 MHz 19

840.5-844.5 12

865.6- 867.6 5

868.0-868.6 1


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Slide 13

PHY Channel PlanExample: 902–928 MHz Chan n: 902.3+(n*0.3) where n=0 to 84

0: 902.30 1: 902.60 2: 902.90 3: 903.20 4: 903.50 5: 903.80 6: 904.10 7: 904.40 8: 904.70 9: 905.00

10: 905.3011: 905.6012: 905.9013: 906.2014: 906.5015: 906.8016: 907.1017: 907.4018: 907.7019: 908.00

.

.

.

63: 921.2064: 921.5065: 921.8066: 922.1067: 922.4068: 922.7069: 923.0070: 923.3071: 923.6072: 923.90

75: 924.8076: 925.1077: 925.4078: 925.7079: 926.0080: 926.3081: 926.6082: 926.9083: 927.2084: 827.50


Doc # P802.15-09-0118-01-004g April 19, 2023

Slide 14

MAC Support

• Meet regulatory requirements for channel occupancy – E.g. max on channel 0.4 seconds

• Visit each channel in sequence before re-visiting– OK to skip channel (black-listing)

• Reliability support– Packet acknowledgment – Packet retransmission


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Slide 15

Conclusions

• Proposal consistent with scope of approved SUN PAR– Support millions of users at low data rates– Robust and available– Low cost and ubiquitous– Operation in unlicensed spectrum

• Applications supported by this proposal are consistent with those proposed by utilities and manufacturers during PAR approval process and in tutorials

• Some references: – 15-08-0199-00-wng0-the-smart-grid.ppt– 15-08-0455-00-0000-utility-view-of-nan-drivers-and-

requirements.pdf


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Part 2Background:

Narrow Band PHY ProposalFeature Rational


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General Tradeoffs - FHSS

• + Many channels => frequency diversity benefit => good coexistence and interference mitigation

• + Narrow channels => long symbol time => low ISI, low processing requirements

• + Narrow channels => minimal frequency selective fading => no need for expensive equalizers => low cost and simplicity

• + Low PAPR => inexpensive power amplifiers => low cost and simplicity

• + Does not rely on high precision on clocks and filters => low cost

• + Proven actual deployments on the scale of millions of units• SSN, Coronis/France Telecom, Elster, CellNet/Hunt, GE, Eka

• - high bandwidth overhead for high bit rates transmission


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Narrow Band Channels

• Supports 100kbps with simple modulation• Allows large number of channels

– 84 in 900MHz, 277 in 2.4GHz – Can meet “Frequency Hopper” regulations (FCC, others)– Channel diversity advantages for interference mitigation– Lots of channels good for network capacity– Spectrum scavenging

• Utilization of channels across multiple bands– Some that may be under-used now

• Adjacent channel rejection (simple inexpensive approach)– Established Low-IF receivers with image ~100KHz – 300KHz spacing parks the next channel’s energy away from the

image– Lots of flexibility for designer/implementation


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Channel Diversity Advantage

Current 802.15.4 PHY Channels per band: – 902MHz 10 Channels– 2.4GHz 16 Channels

NB PHY:– 902MHz 84 Channels– 2.4GHz 277 Channels


Doc # P802.15-09-0118-01-004g Channel Diversity• Random Channel Access (1,10,84 channels)• Independent access probability (no channel

correlation• 1% Duty Cycle average (all nodes)


Doc # P802.15-09-0118-01-004g Channel Diversity• Random Channel Access (1,10,84 channels)• Independent access probability (no channel



Doc # P802.15-09-0118-01-004g Channel Diversity• Random Channel Access (1,16,277 Channels)• Independent access probability (no channel



Doc # P802.15-09-0118-01-004g

PHY Frame

Octets: 7 2 1 2 variable 4

Bits: 56 16 8 4 1 11 32

Preamble SFD Scrambler Seed(Channel ID)

RFU

EXT

Length (PSDU) CRC-32

SHR PHR PHY Payload FCS

• Scrambler seed in PHY header– So it can be changed– Allows flexibility in implementation at upper layers

• Length to support 2047 octets for IP– Necessitates 32-bit CRC

Structure of PPDU


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FSK Modulation• FSK is simple, cheap, proven

– Proven technology/Low cost solution (low complexity)– Many low cost implementations available – Constant envelope – Allows non-coherent generation / demodulation or coherent

implementations– Allows for a limiter discriminator detector (simple, cheap)– Minimal filtering requirements

• 25kHz frequency deviation (±3kHz)– modulation index 0.5 (MSK), has spectral advantages – constant phase modulation – ±3kHz tolerance simplifies implementation (more options)

• Easy low cost implementation

fdev +

fdev -

TX-Data Bit

Carrier

Modulator RF


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Error DetectionDepend on detection and retry

• Environment typically interference limited• Long burst errors more likely than random bit or short

burst errors• FEC trade-off

More bits at low bit rate => more time on air =>higher probability of interference

• Retry + channel diversity + low duty cycle– Diversity increases prob. of success on retry– Diversity reduces interference (< prob of error)– Low duty cycle reduces probability of interference


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Part 3Background:

Data Whitening


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Agenda

• Problem Statement• Existing implementations• Receiver designs• Demodulator designs• Problems with demodulators• Whitening effect• Problems with whitening approaches• Various solutions• Benefits of preferred solution


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Problem Statement• Long runs of 1s or 0s will occur in data (payloads)• Whitened data aids in

– bit timing recovery and tracking– Minimize DC bias

• Common technique (everyone does it?)– 802.11, 802.15.1, 802.15.3, …– FHSS, DSSS, OFDM– FSK/GFSK, QPSK, DBPSK, DQPSK n-QAM …

• Interference limited application scenarios need minimal bandwidth consumption (e.g., as opposed to Manchester encoding)

• Arbitrary data can ‘unscramble’ in fixed scrambler• Low or no on-air overhead


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What’s Typical

• 802.15.1 (Bluetooth) – Fixed ‘seed’– 7-bit LFSR {4,7}– Fixed initialization

• 802.15.3 – four seeds– Each a 15-bit sequence– 4 different seed values– Seed ID in PHY header

• 802.11 – Variable seed sent as part of header– FHSS, DSSS and OFDM use scramblers, 7-bits, taps {4,7}– FHSS, DSSS use fixed seed values– OFDM sends seed value in PHY header SERVICE field:

• Pseudo-random non-zero seed set by sender


Doc # P802.15-09-0118-01-004g

Many receiver designs


Doc # P802.15-09-0118-01-004g

Many demodulator designs

• Differential– Foster-Seeley

– Slope– Ratio– Quadrature

• Phase Lock Loop

Foster-Seeley


Doc # P802.15-09-0118-01-004g FM demodulation

The received signal is delayed and mixed with the original signal giving difference signal output representing the frequency/phase modulation in the incoming signal.

This is differential detection, and the circuit is widely known as a discriminator.

To recover the data, the bit-timing must be recovered and a decision taken on whether the signal represents a “1” or a “0.” The data recovery is done by some method of “data slicing,” followed by a timing-recovery circuit. The data recovery mechanism is critical, as the output of the analog discriminator can sit on a varying DC level.

These schemes are well-proven but have a drawback - the need to deal with DC drift in the demodulated output – which is exacerbated by zero-IF receiver designs.


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Problems with demodulators

• DC coupled demodulators

• AC coupled demodulators can ‘droop’ toward a rail if extended sequences of ones or zeros are received


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Solution = Whiten data

• Scrambling or whitening makes long sequential runs of ones or zeros statistically unlikely….

• … increasing the average frequency of edge transitions….

• …making tracking bit synchronization easier…

• … and keeps AC-coupled demodulators average signal within the hysteresis zone


Doc # P802.15-09-0118-01-004g

Problems with Scramblers• Data is not always white and there exist

data patterns which can ‘unscramble’ the scrambler resulting in undesired long runs of ones or zeros

• This is rare.

• This is fatal.


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Whitening Solution #1(Manchester encoding)

• Manchester encoding introduces a level transition for each bit, converting sequential zeros or ones into an alternating waveform running at twice the data rate.• This means that the worst-case bandwidth required for Manchester (or 802.3) encoding will be twice that required for the data rate in the absence of encoding• Doubling the BW will result in a range reduction… Next option…


Doc # P802.15-09-0118-01-004g

Scrambler

24

1

LENGTH[6]

2

3

5D

CLK

Q24

1

2

3

5D

CLK

Q

24

1

LENGTH[7]

TAP[0] TAP[7]

24

1

24

12

41LENGTH[1]

24

1 2

3

5D

CLK

Q

24

1

24

1

2

3

5D

CLK

Q

TAP[1] TAP[6]

24

1

Generic scrambler circuitry constructed from programmable shift register.

The Taps can be pre-loaded with arbitrary ‘seeds’ which will produce different output streams based given identical input streams.


Doc # P802.15-09-0118-01-004g

Scrambler Solution #1(try before sending)

24

1

LENGTH[6]

2

3

5D

CLK

Q24

1

2

3

5D

CLK

Q

24

1

LENGTH[7]

TAP[0] TAP[7]

24

1

24

12

41LENGTH[1]

24

1 2

3

5D

CLK

Q

24

1

24

1

2

3

5D

CLK

Q

TAP[1] TAP[6]

24

1

24

1

LENGTH[6]

2

3

5D

CLK

Q24

1

2

3

5D

CLK

Q

24

1

LENGTH[7]

TAP[0] TAP[7]

24

1

24

12

41LENGTH[1]

24

1 2

3

5D

CLK

Q

24

1

24

1

2

3

5D

CLK

Q

TAP[1] TAP[6]

24

1

Use multiple seeds:

If data breaks one, less likely to break the other

Like 15.3 (4 seeds)

Many methods:

Guess and adjust

A-priori knowledge


Doc # P802.15-09-0118-01-004g

Scrambler Solution #2

24

1

LENGTH[6]

2

3

5D

CLK

Q24

1

2

3

5D

CLK

Q

24

1

LENGTH[7]

TAP[0] TAP[7]

24

1

24

12

41LENGTH[1]

24

1 2

3

5D

CLK

Q

24

1

24

1

2

3

5D

CLK

Q

TAP[1] TAP[6]

24

1

In a FHSS system, change the ‘seed’ every channel and if the packet is not received on a particular channel…

Just take the hit – knowing that the next channel will scramble differently and will statistically be incredibly unlikely to be non-receivable.


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Additional Benefits of #2

• Provides orthogonally for geographically overlapping networks.

• Provides an ‘extra long’ start word - moving from 16 bits to 24 bits dramatically decreases the packet false starts

• Provides some protection from ‘replay’ attacks

• Provides protection from ‘spurious reception’


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No extra byte needed

If the benefits of the separate ‘scramble seed’ are not required, transmitting the seed becomes superfluous.

Such applications can eliminate the costs by:– Shortening the preamble by one byte– Setting the first start byte identically to the preamble

byte– There is no need to ever change the scrambler seed


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Conclusion(s)• Whitening has been shown to be necessary• Scrambling has been shown to be low cost

whitening implementation• Static scrambler seeds have been used to some

success (802.11, etc.)• Dynamic seeding of has multiple benefits at

same cost(s)

Proposal: include dynamic seedfor 802.15.4g scrambler.

Narrow-band PHY Proposal for 802.15.4g Doc # P802.15-09-0118-01-004g Project: IEEE P802.15 Working...

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