IEEE 802'15 PHY Proposal

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
Proposed Code Sequences for IEEE 802.15.4a
Alt-PHY Date Submitted Jan 2005 Source
Francois Chin, Sam Kwok, Xiaoming Peng, Kannan,
Yong- Huat Chew, Chin-Choy Chai, Hongyi Fu,
Manjeet, Tung-Chong Wong, T.T. Tjhung, Zhongding
Lei, Rahim Company Institute for Infocomm
Research, Singapore Address 21 Heng Mui Keng
Terrace, Singapore 119613 Voice 65-68745687
FAX [phone] E-Mail chinfrancois_at_i2r.a-
star.edu.sg Re Response to the call for
proposal of IEEE 802.15.4a, Doc Number
15-04-0380-02-004a Abstract I2Rs Proposal to
IEEE 802.15.4a Task Group Purpose For
presentation and consideration by the
IEEE802.15.4a committee 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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Proposed Code Sequences, Modulation Coding
for IEEE 802.15.4a Alt-PHY

• Francois Chin
• Institute for Infocomm Research
• Singapore

3
Proposal Motivation

• To satisfy IEEE 802.15.4a technical requirements,
  low power consumption is crucial
• Conventional coherent UWB system based on
  correlator in the receiver can provide fairly
  good performance, but at the expense of
  implementation complexity, and consequently power
  consumption and system cost
• To meet low power and low cost requirement, UWB
  system with OOK (On-Off Keying) modulation and
  noncoherent detection is proposed
• In the proposed UWB OOK system, the signal
  demodulation is performed by simply integrating
  signal energy, thus omitting signal / pulse
  generator, significantly relieve the strict
  synchronization requirement and greatly simplify
  transceiver structure with the minimal power and
  cost demand
• However, some challenges of such OOK system are
  threshold setting, simultaneous operating
  piconets (SOP) timing boundaries estimation
• This proposal contains techniques that will
  overcome such limitation, and improve the overall
  system performance of the UWB OOK system

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Proposed System Parameters
Proposed chip rate of 11 MHz is a common
denominator in the clock rate of 11a/b/g, MB-OFDM
and DS-UWB
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UWB Pulse Spectrum

• 1.5 ns rectified cosine shape
• 1400 MHz 10-dB bandwidth
• Centre frequency 4 GHz

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Modulation Coding
Binary data From PPDU
Scrambling 1,-1 Sequence
0,1 Sequence
Bit-to- Symbol
Chip Repetition
Symbol- to-Chip
Pulse Generator
Chip Scrambler
0,1,-1 Sequence

• Bit to symbol mapping
• group every 4 bits into a symbol
• Symbol-to-chip mapping
• Each symbol is mapped to a 32-chip 0,1
  sequence, according to Gray Coded Code Position
  Modulation (CPM)
• Chip Repetition (11 Mcps)
• Factor of K5 corresponds to 275 kbps (Mandatory
  Mode)
• Chip Scrambling (11 Mcps)
• the K x 32-chip 0,1 sequence is mutliplied
  with random scrambing 1,-1 sequence
• this is to avoid spectral spikes
• Pulse Generator (11 x 12 132 MHz)
• Chips are repetited and Ternary -modulated
• chip 1' ? 12 ve pulse are transmitted _at_
  132 MHz
• chip -1' ? 12 -ve pulse are transmitted _at_
  132 MHz
• chip '0' ? no pulse

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Multiple access

• Multiple access within piconet same as 15.4.
• Multiple access across piconets CDMA.
• Different Piconet uses different Base Sequence

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Base Sequence Set

• 31-chip M-Sequence set
• Only one sequence and one fixed band (no hopping)
  will be used by all devices in a piconet
• Logical channels for support of multiple piconets
• 6 sequences 6 logical channels (e.g.
  overlapping piconets)
• The same base sequence will be used to construct
  the symbol-to-chip mapping table

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Symbol-to-Chip Mapping Gray Coded Code Position
Modulation (CPM)
To obtain 32-chip per symbol, cyclic shift the
Base Sequence first, then extend 1-chip
Base Sequence 1
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Properties of M-Sequences

• Cyclic auto-correlation of any antipodal sequence
  gives peak value of 31 and sidelobe value of -1
  throughout
• Cyclic correlation of any antipodal sequence with
  its corresponding uni-podal sequence give peak
  value of 16 and correlation with other 15
  uni-podal sequences with give zero sidelobe
  throughout
• i.e. Each transmit OOK sequence will give a peak
  correlator output at a correlator with its
  corresponding antipodal sequence ZERO at other
  15 correlators

11
Cyclic Extended Chip

• To avoid / reduce inter-symbol interference in
  channels with excess delay spread
• To ensure zero inter-chip interference in
  receiver correlator output

12
Synchronisation Preamble
Correlator output for synchronisation

• Code sequences has excellent autocorrelation
  properties
• Preamble is constructed by repeating Sequence
  0000

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The transmitter

• 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)

PSDU Data
Clock F 132MHz
Control Logic
BaseBand signal
Pulse shaper
PA (option)
Pulse Generator
RF Signal
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The receiver
Fc5.5MHz
Soft Despread
BPF
( )2
LPF
ADC

• Energy detection technique rather than coherent
  receiver, for relaxed synchronization constraints
• Soft chip values gives best results
• Oversampling sequence correlation is used to
  recovery chip timing recovery
• Synchronization fully re-acquired for each new
  packet received (gt no very accurate timebase
  needed)
• Low cost, low complexity

22 MHz Sample Rate
15
Frame Format
2
1
0/4/8
2
n
Octets
Data Payload
Frame Cont.
MAC Sublayer
Seq.
Address
CRC
MHR
MSDU
MFR
Data 32 (n23)
TBD
1
1
For ACK 5 (n0)
Octets
PHY Layer
Frame Length
Preamble
SFD
MPDU
SHR
PHR
PSDU
PPDU