Chirp%20Spread%20Spectrum%20(CSS)%20PHY%20Submission - PowerPoint PPT Presentation

About This Presentation
Title:

Chirp%20Spread%20Spectrum%20(CSS)%20PHY%20Submission

Description:

CSS proposal utilizes CCA mechanisms of Energy Detection (ED) and Carrier Detection ... The proposer is confident that the CSS proposal would also work well in ... – PowerPoint PPT presentation

Number of Views:51
Avg rating:3.0/5.0
Slides: 51
Provided by: erwin4
Learn more at: https://www.ieee802.org
Category:

less

Transcript and Presenter's Notes

Title: Chirp%20Spread%20Spectrum%20(CSS)%20PHY%20Submission


1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
Chirp Spread Spectrum (CSS) PHY Presentation for
802.15.4a Date Submitted January 04,
2005 Source John Lampe Company Nanotron
Technologies Address Alt-Moabit 61, 10555
Berlin, Germany Voice 49 30 399 954 135, FAX
49 30 399 954 188, E-Mail j.lampe_at_nanotron.com
Re This is in response to the TG4a Call for
Proposals, 04/0380r2 Abstract The Nanotron
Technologies Chirp Spread Spectrum is described
and the detailed response to the Selection
Criteria document is provided Purpose Submitted
as the candidate proposal for TG4a
Alt-PHY 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.
2
Chirp Spread Spectrum (CSS)PHY Presentationfor
802.15.4a
  • by
  • John Lampe, Rainer Hach, Lars Menzer
    Nanotron Technologies GmbHBerlin, Germany
  • www.nanotron.com

3
General Properties of Chirp Signals
  • Simplicity
  • Basically a 2 ary baseband transmission
  • The windowed chirp is a linear frequency sweep
    with a total duration of 1 us

4
Chirp Properties (cont.)
  • Real part of a windowed up-chirp signal with a
    total duration of 1us

5
Chirp Properties (cont.)
  • Figure shows the autocorrelation function (acf)
    and cross-correlation function (ccf) of the
    signal described above
  • Note that the ccf has a constant low value
    (compared to DS sequences).

6
Chirp Properties (cont.)
  • This figure shows the PSD of the signal with a
    power of 10 dBm
  • By padding the signal with zeros the frequency
    resolution has been set to 100 kHz so that the
    plot is similar to what a spectrum analyzer would
    measure.
  • At 12 MHz offset from the center is below -30dBm
    (which is the ETSI requirement for out of band
    emissions)

7
Chirp Properties (cont.)
  • Further processing of the signals Sig A and Sig B
    for symbol detection could be done in coherent
    (real part processing) or non coherent manner
    (envelope filtering).
  • Since the analytical results are well known for
    AWGN channels we will mention these
  • Simulations over other channels will all refer to
    the non coherent system as drawn below.

8
Chirp Properties (cont.)
  • This figure shows the analytical BER values for 2
    ary orthogonal coherent and non coherent
    detection and the corresponding simulation
    results (1E5 symbols) for up down chirp (using
    the chirp signals defined above)
  • The performance loss due to the non-orthogonality
    of up and down chirp is very small.

9
Signal Robustness
  • The proposed CSS PHY is designed to operate in a
    hostile environment
  • Multipath
  • Narrow and broadband intentional and
    unintentional interferers
  • Since a chirp transverses a relatively wide
    bandwidth it has an inherent immunity to narrow
    band interferers
  • Multipath is mitigated with the natural frequency
    diversity of the waveform
  • Broadband interferer effects are reduced by the
    receivers correlator
  • Forward Error Correction (FEC) can further reduce
    interference and multipath effects.
  • Three non-overlapping frequency channels in the
    2.4 GHz ISM band
  • This channelization allows this proposal to
    coexist with other wireless systems such as
    802.11 b, g and even Bluetooth (v1.2 has adaptive
    hopping) via DFS
  • CSS proposal utilizes CCA mechanisms of Energy
    Detection (ED) and Carrier Detection
  • These CCA mechanisms are similar to those used in
    IEEE 802.15.4-2003
  • In addition to the low duty cycle for the
    applications served by this standard sufficient
    arguments were made to convince the IEEE 802
    sponsor ballot community that coexistence was not
    an issue.

10
Support for Interference Ingress
  • Example (w/o FEC)
  • Bandwidth B of the chirp 20 MHz
  • Duration time T of the chirp 1 µs
  • Center frequency of the chirp (ISM band) 2.442
    GHz
  • Processing gain, BT product of the chirp 13 dB
  • Eb/N0 at detector input (BER10-4) 12 dB
  • In-band carrier to interferer ratio (C/I _at_
    BER10-4) 12 - 13 -1 dB
  • Implementation Loss 2 dB

11
Support for Interference Egress
  • Low interference egress
  • IEEE 802.11b receiver
  • More than 30 dB of protection in an adjacent
    channel
  • Almost 60 dB in the alternate channel
  • these numbers are similar for the 802.11g
    receiver

12
Regulatory
  • Devices manufactured in compliance with the CSS
    proposal can be operated under existing
    regulations in all significant regions of the
    world
  • including but not limited to North and South
    America, Europe, Japan, China, Korea, and most
    other areas
  • There are no known limitation to this proposal as
    to indoors or outdoors
  • The CSS proposal would adhere to the following
    worldwide regulations
  • United States Part 15.247 or 15.249
  • Canada DOC RSS-210
  • Europe ETS 300-328
  • Japan ARIB STD T-66

13
Scalability Data Rate
  • Mandatory rate 1 Mb/s
  • Optional rate 267 Kb/s
  • Other possible data rates include 2 Mb/s to allow
    better performance in a burst type, interference
    limited environment or a very low energy
    consumption application
  • Lower data rates achieved by using interleaved
    FEC
  • Lower chirp rates would yield better performance
  • longer range, less retries, etc. in an AWGN
    environment or a multipath limited environment
  • It should be noted that these data rates are only
    discussed here to show scalability, if these
    rates are to be included in the draft standard
    the group must revisit the PHY header such as the
    SFD.

14
Scalability Frequency Bands
  • The proposer is confident that the CSS proposal
    would also work well in other frequency bands
  • Including the 5975 to 7250 MHz band
  • Mentioned in the new FCC operating rules SECOND
    REPORT AND ORDER AND SECOND MEMORANDUM OPINION
    AND ORDER released December 16, 2004

15
Scalability Data Whitener
  • Additionally, the group may consider the use of a
    data whitener, similar to those used by Bluetooth
    and IEEE 802.11 to produce a more noise-like
    spectrum and allow better performance in
    synchronization and ranging.

16
Scalability Power Levels
  • For extremely long ranges the transmit power may
    be allowed to rise to each countrys regulatory
    limit
  • For example the US would allow 30 dBm of output
    power with up to a 6 dB gain antenna
  • The European ETS limits would specify 20 dBm of
    output power with a 0 dB gain antenna
  • Note that even though higher transmit requires
    significantly higher current it doesnt
    significantly degrade battery life since the
    transmitter has a much lower duty cycle than the
    receiver, typically 10 or less of the receive
    duty cycle
  • In this manner the averaged transmitter current
    drain will be less than the averaged receiver
    current drain.

17
Scalability Backward Compatibility
  • Due to some of the similarities with DSSS it is
    possible to implement this proposal in a manner
    that will allow backward compatibility with the
    802.15.4 2.4 GHz standard
  • The transmitter changes are relatively
    straightforward
  • Changes to the receiver would include either dual
    correlators or a superset of CSS and DSSS
    correlators
  • It is anticipated that this backward
    compatibility could be achieved via mode
    switching versus a dynamic change on-the-fly
    technique
  • left up to the implementer
  • This backward compatibility would be a
    significant advantage to the marketplace by
    allowing these devices to communicate with
    existing 802.15.4 infrastructure and eliminating
    customer confusion

18
Mobility Values
  • Communication
  • No system inherent restrictions are seen for this
    proposal
  • The processing gain of chirp signals is extremely
    robust against frequency offsets such as those
    caused by the Doppler effect due to high relative
    speed vrel between two devices
  • Such situations also occur when one device is
    mounted on a rotating machine
  • The limits will be determined by other, general
    processing modules (AGC, symbol
    synchronization,...)
  • Ranging
  • The ranging scheme proposed in this document
    relies on the exchange of two hardware
    acknowledged data packets
  • One for each direction between two nodes
  • We assume that the longest time in this procedure
    is the turnaround time tturn between the two
    nodes which will be determined by the respective
    uC performance. During this time the change of
    distance should stay below the accuracy da
    required by the application.
  • For da 1m
  • tturn 10 ms this yields
  • vrel ltlt 100m/s

19
MAC Enhancements and Modifications
  • There are no anticipated changes to the 15.4 MAC
    to support the proposed Alt-PHY. Three channels
    are called for with this proposal and it is
    recommended that the mechanism of channel bands
    from the proposed methods of TG4b be used to
    support the new channels. There will be an
    addition to the PHY-SAP primitive to include the
    choice of data rate to be used for the next
    packet. This is a new field.
  • Ranging calls for new PHY-PIB primitives that are
    expected to be developed by the Ranging
    subcommittee.

20
Channel Models
  • Since this proposal refers to the 2.4GHz ISM
    band, only channel models with complete parameter
    set covering this frequency range can be
    considered
  • At the time being these are LOS Residential (CM1)
    and NLOS Residential (CM2).
  • The 100 realizations for each channel model were
    bandpass filtered with -15MHz around 2.437GHz
    which corresponds to the second of the three
    sub-bands proposed.
  • The filtered impulse responses were down
    converted to complex baseband.
  • The magnitudes over time are shown in the
    following plots
  • Furthermore some graphs of the function H_tilde
    as described and required in the SCD are shown
  • For now we assume that the neighbor sub-bands
    will not differ significantly from the center
    sub-band and that we restrict simulations on the
    center sub-band
  • The SCD requirements on the payload size to be
    simulated seem to be somewhat inconsistent. At
    some point 10 packets with 32 bytes are mentioned
    which would be a total of 2560 bits. On the other
    hand a PER of 1 is required which mean
    simulating more than 100 packets or 25600 bits.
  • Since the delay spread and thus the time in which
    subsequent symbols can influence each other of
    all given channel impulse responses are well
    below the symbol duration of 1us suggested by
    this proposal we believe that we get the best
    results when we simulate a large number of
    independent transmissions of symbols.
  • Assuming an equal probability of error for all
    bits of a packet we can give the relationship
    between the BER and PER by
    With N being the number of payload
    bits.
  • Thus we can calculate the BER which is required
    for any PER
  • For PER1 and N256 we get BER3.9258E-5

21
Channel Model 1
22
Channel Model 2
23
Size and Form Factor
  • The implementation of the CSS proposal will be
    much less than SD Memory at the onset
  • following the form factors of Bluetooth and IEEE
    802.15.4/ZigBee
  • The implementation of this device into a single
    chip is relatively straightforward
  • As evidenced in the Unit Manufacturing
    Complexity slides

24
PHY SAP Payload Bit Rate Data Throughput
  • The PPDU is composed of several components as
    shown in the figure below
  • The following figure shows in greater detail, the
    component parts of each PPDU.

Octets 4 1 1 Variable (up to 256)
Preamble SFD Frame length (8 bits) PHY payload
SHR SHR PHR PSDU
25
PHY SAP Payload Bit Rate Data Throughput (cont)
  • The SFD structure has different values for, and
    determines, the effective data rate for PHR and
    PSDU
  • The Preamble is 32 bits in duration (a bit time
    is 1 us)
  • In this proposal, the PHR field is used to
    describe the length of the PSDU that may be up to
    256 octets in length
  • In addition to the structure of each frame, the
    following shows the structure and values for
    frames including overhead not in the information
    carrying frame

26
PHY SAP Payload Bit Rate Data Throughput (cont)
  • The figures show the structure, as defined in the
    IEEE Standard 802.15.4 and the SCD
  • cases of acknowledged transmissions as used in
    section 3.2.1 values and for unacknowledged
    transmissions.
  • For this proposal, the value of Tack and SIFS are
    retained from the IEEE Standard 802.15.4 and are
    each 192 microseconds
  • The value of LIFS is also shown as 192
    microseconds.
  • Additional revisions of this proposal may show a
    different value as the authors discuss the need
    for longer LIFS values with members of TG4b
  • The values of SIFS and LIFS have a MAC dependency
    above the value of 192uS required for PHY turn
    around
  • SIFS has a value of 192us (12 symbols) in the
    current standard and LIFS has a value of 40
    symbols.

27
Simultaneous Operating Piconets
  • Separating Piconets by frequency division
  • This CSS proposal includes a mechanism for FDMA
    by including the three frequency bands used by
    802.11 b, g and also 802.15.3
  • It is believed that the use of these bands will
    provide sufficient orthogonality
  • The chirp signal defined earlier has a rolloff
    factor of 0.25 which in conjunction with the
    space between the adjacent frequency bands allows
    filtering out of band emissions easily and
    inexpensively.

28
Signal Acquisition
  • The signal acquisition is basically determined by
    the structure and duration of the preamble
  • In contrast to always on systems like DECT or
    GSM
  • Low duty rate systems must be able to acquire a
    signal without any prior knowledge about that
    signals level or timing
  • While the IEEE 802.15.4-2003 uses a preamble
    duration of 32 symbols (128 µs at 2.4 GHz) other
    commercially available transceiver chips (e.g.
    nanoNET TRX from Nanotron) use 30 symbols at
    1MS/s (i.e. 30µs).
  • For consistency with IEEE 802.15.4-2003 this CSS
    proposal is based upon a preamble of 32 symbols
    which at 1MS/s turns out as 32 µs
  • Existing implementations demonstrate that
    modules, which might be required to be adjusted
    for reception (Gain Control, Frequency Control,
    Peak Value Estimation, etc.), can be setup in
    such a time duration
  • The probability of missing a packet is then
    simply determined by the probability that the SFD
    is received correctly
  • As shown before, the BER required for a PER of
    1, is BER3.9258E-5

29
Clear Channel Assessment
  • A combination of symbol detection (SD) and energy
    detection (ED) has proven to be useful in
    practice. The duration of the preamble can be
    used as upper bound for the duration for both
    detection mechanism. By providing access to the
    threshold for ED the system allows the
    application to adjust its behavior (false alarm
    vs. miss probability) according to its needs.

30
System Performance
  • Simulation over 100 channel impulse responses (as
    required in the SCD) were performed for channel
    model 1 and channel model 2.
  • No bit errors could be observed on channel model
    1 (simulated range was 10 to 2000m). This is not
    really surprising because this model has a very
    moderate increase of attenuation over range
    (n1.79)
  • The results for channel model 2 are displayed
    below. The parameter n4.48 indicates a very high
    attenuation for higher ranges. The results were
    interpreted as BER and PER respectively and for
    convenience were plotted twice (linear and log y
    scale).

31
System Performance
32
System Performance
33
System Performance
34
TOA Estimation for Ranging
Noise and Jitter of Band-Limited Pulse Given a
band-limited pulse with noise su we want to
estimate how the jitter (timing error) st with
which the passing of the rising edge of the pulse
through a given threshold can be detected is
effected by the bandwidth B.
35
Symmetrical Double-Sided Two-Way Ranging (SDS
TWR)
Tround ... round trip time Treply ... reply
time Tprpp ... propagation of pulse
Double-Sided Each node executes a round trip
measurement. Symmetrical Reply Times of both
nodes are identical (TreplyA TreplyB). Results
of both round trip measurements are used to
calculate the distance.
36
Ranging - Effect of Time Base Offset Errors
Assuming offset errors eA, eB of the timebases
of node A and B we get
On the condition that the two nodes have almost
equal behavior, we can assume
This has the effect that timebase offsets are
canceled out
Calculations show that for 40ppm crystals and 20
us max difference between TroundA and TroundB
and between TreplyA and TreplyB an accuracy
below 1 ns can easily be reached!
37
Influence of Symmetry Error Calculation of an
SDS TWR Example System
  • Example System EtA 40 ppm, EtB 40 ppm
    (worst case combination selected)

d ?d (?Treply 20 ns) ?d (?Treply 200 ns) ?d (?Treply 2 µs) ?d (?Treply 20 µs) ?d (?Treply 200 µs)
10 cm 0.012 cm 0.12 cm 1.2 cm 12 cm 120 cm
1 m 0.012 cm 0.12 cm 1.2 cm 12 cm 120 cm
10 m 0.05 cm 0.12 cm 1.2 cm 12 cm 120 cm
100 m 0.4 cm 0.4 cm 1.2 cm 12 cm 120 cm
1 km 4 cm 4 cm 4 cm 12 cm 120 cm
10 km 40 cm 40 cm 40 cm 40 cm 120 cm
  • Conclusion Even 20 µs Symmetry Error allows
    excellent accuracy of distance ! Symmetry Error
    below 2 µs can be guaranteed in real
    implementations !

38
Principle of Dithering and Averaging
  • Dithering
  • Averaging

39
Simulation of a SDS TWR System
Example system Simulates SDS TWR Dithering
Averaging Crystal Errors 40 ppm Single shot
measurements _at_ 1 MBit/s data rate
(DATA-ACK) Transmit Jitter 4 ns
(systematic/pseudo RN-Sequence) Pulse detection
resolution 4 ns Pulses averaged per packet
32 Symmetry error 4 µs (average) Distance 100
m Results of Distance Error ?d ?dWC lt 50
cm ?dRMS lt 20 cm (ideal channel without noise)
40
Link Budget
  • footnotes
  • 1 Rx noise figure in addition the proposer can
    select other values for special purpose (e.g. 15
    dB for lower cost lower performance system)
  • 2 The minimum Rx sensitivity level is defined
    as the minimum required average Rx power for a
    received symbol in AWGN, and should include
    effects of code rate and modulation.

41
Sensitivity
  • The sensitivity to which this CSS proposal refers
    is based upon non-coherent detection
  • It is understood that coherent detection will
    allow 2 - 3 dB better sensitivity but at the cost
    of higher complexity (higher cost?) and poorer
    performance in some multipath limited
    environments
  • The sensitivity for the 1 Mb/s mandatory data
    rate is -92 dBm for a 1 PER in an AWGN
    environment with a front end NF of 7 dB
  • The sensitivity for the optional 267 kb/s data
    rate is -97 dBm for a 1 PER in an AWGN
    environment with a front end NF of 7 dB

42
Power Management Modes
  • Power management aspects of this proposal are
    consistent with the modes identified in the IEEE
    802.15.4 2003 standard
  • There are no modes lacking nor added
  • Once again, attention is called to the 1 Mbit/s
    basic rate of this proposal and resulting shorter
    on times for operation

43
Power Consumption
  • The typical DSSS receivers, used by 802.15.4, are
    very similar to the envisioned CSS receiver
  • The two major differences are the modulator and
    demodulator
  • The modulator of the CSS is much simpler than the
    DSSS however since the major power consumption is
    the transmitter and the difference is negligible
  • The power consumption for a 10 dBm transmitter
    should be 198 mW or less
  • The receiver for the CSS is remarkably similar to
    that of the DSSS with the major difference being
    the correlator
  • The correlator for the CSS uses a frequency
    dispersive mechanism while the DSSS uses a chip
    additive correlator
  • The difference in power consumptions between
    these correlators is negligible so the power
    consumption for a 6 dB NF receiver should be 40
    mW or less
  • The power consumed during the CCA is basically
    similar to the receiver power consumption
  • All of the receiver circuits are being used
    during the CCA (correlator is used for the
    carrier detect function)

44
Power Consumption (cont.)
  • Power save mode is used most of the time for this
    device and has the lowest power consumption
  • Typical power consumptions for 802.15.4 devices
    are 3 µW or less
  • Energy per bit is the power consumption divided
    by the bit rate
  • The energy per bit for the 10 dBm transmitter is
    less than 0.2 µJ
  • The energy per bit for the receiver is 40 nJ
  • As an example, the energy consumed during an
    exchange of a 32 octet PDU between two devices
    (including the transmission of the PDU, the tack,
    and the ack) would be 70.6 µJ for the sender
    device while the receiving device consumed 33.2
    µJ
  • As a reference point it should be noted that
    according to the Duracell web site, a Duracell AA
    alkaline cell contains more than 12,000 Joules of
    energy.

45
Antenna Practicality
  • The antenna for this CSS proposal is a standard
    2.4 GHz antenna such as widely used for 802.11b,g
    devices and Bluetooth devices. These antennas
    are very well characterized, widely available,
    and extremely low cost. Additionally there are a
    multitude of antennas appropriate for widely
    different applications. The size for these
    antennae is consistent with the SCD requirement.

46
Time To Market
  • No regulatory hurdles
  • No research barriers no unknown blocks, CSS
    chips are available in the market
  • Normal design and product cycles will apply
  • Can be manufactured in CMOS

47
Unit Manufacturing Complexity
  • Target processRF-CMOS, 0.18 µm feature size

Pos. Block description Estimated Area Unit
1 Receiver with high-end LNA 2.00 mm²
2 Transmitter, Pout 10 dBm 1.85 mm²
3 Digitally Controlled Oscillator miscellaneous blocks 0.62 mm²
4 Digital and MAC support 0.60 mm²
5 Digital Dispersive Delay Line (DDDL) for selected maximum chirp duration 0.32 mm²
6 Chirp generator for selected maximum chirp duration 0.08 mm²
7 Occupied chip area for all major blocks required to build complete transceiver chip utilizing CSS technology 5.47 mm²
48
Unit Manufacturing Complexity
  • Target processRF-CMOS, 0.13 µm feature size

Pos. Block description Estimated Area Unit
1 Receiver with high-end LNA 1.90 mm²
2 Transmitter, Pout 10 dBm 1.71 mm²
3 Digitally Controlled Oscillator miscellaneous blocks 0.59 mm²
4 Digital and MAC support 0.38 mm²
5 Digital Dispersive Delay Line (DDDL) for selected maximum chirp duration 0.21 mm²
6 Chirp generator for selected maximum chirp duration 0.06 mm²
7 Occupied chip area for all major blocks required to build complete transceiver chip utilizing CSS technology 4.85 mm²
49
Summary
  • Chirp Spread Spectrum (CSS) is simple, elegant,
    efficient
  • Combines DSSS and UWB strengths
  • Adds precise location-awareness
  • Robustness multipath, interferers, correlation,
    FEC, 3 channels, CCA
  • Can be implemented with todays technologies
  • Low-complexity
  • Low-cost
  • Low power consumption
  • Globally certifiable
  • Scalability with many options for the future
  • Backward compatible with 802.15.4-2003
  • Mobility enhanced
  • No MAC changes (minimal for ranging)
  • Size and Form Factor meets or exceeds
    requirements
  • Excellent throughput
  • SOPs FD channels
  • Signal Acquisition excellent
  • Link Budget and Sensitivity excellent
  • Power Management and Consumption - meets or
    exceeds requirements

50
Summary
  • Chirp Spread Spectrum (CSS) Proposal Meets the
    PAR and 5C
  • Precision ranging capability accurate to one
    meter or better
  • Extended range over 802.15.4-2003
  • Enhanced robustness over 802.15.4-2003
  • Enhanced mobility over 802.15.4-2003
  • International standard
  • Ultra low complexity (comparable to the goals for
    802.15.4-2003)
  • Ultra low cost (comparable to the goals for
    802.15.4-2003)
  • Ultra low power consumption (comparable to the
    goals for 802.15.4-2003)
  • Support coexisting networks of sensors,
    controllers, logistic and peripheral devices in
    multiple compliant co-located systems.
Write a Comment
User Comments (0)
About PowerShow.com