IEEE 802.15 <subject>

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
DS-UWB Responses to TG3aVoter NO Comments
Equalizer, SOP, ADC, RFI Date Submitted
September 2004 Source Matt Welborn, John
McCorkle, Michael McLaughlin Company
Freescale Semiconductor, Inc DecaWave,
Ltd. Address 8133 Leesburg Pike Voice703-269-
3000, E-Mailmatt.welborn _at_freescale.com Re
Abstract Response to NO voter comments and
feedback regarding the DS-UWB (Merger 2)
Proposal Purpose Provide technical information
to the TG3a voters regarding DS-UWB (Merger 2)
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.
2
Topic Equalization

• Typical comments
• A single carrier receiver requires a decision
  based equalizer (DFE) for meeting reasonable
  performance. Under severe multipath scenarios
  (non line of sight) such equalizers introduces an
  error propagation effect
• lack of sufficient high fidelity simulations of
  equalizer performance
• Current evidence shows that DFE works well at
  very high SNRs (9.6 and 12.6 dB). Must show
  evidence that DFE will not suffer from error
  propagation at realistic operating points such at
  1 dB
• I believe that a big application area for UWB
  will be in personal and portable devices. I have
  not been convinced that the DS-SS proposal will
  provide good performance in the face of changing
  propagation conditions, potential due to device
  movement or movement of people and objection in
  the propagation path. I have not seen an
  explanation and a simulation of how the equalizer
  will quickly adapt

3
Responses Equalization

• Comments Fully Resolved
• There is no need for an adaptive equalizer. The
  system is assumed to see a psuedo-stationary
  channel for the duration of the packet.The
  equalizer re-trained for each packet.
• At 110 Mbps, packets will be lt 0.1ms in duration
• Equalizer performance is demonstrated in
  system-level simulations
• Our simulations show that although error
  propagation is present, it does not significantly
  reduce the range achieved by DS-UWB

4
DS-UWB in Multipath

• Indoor multipath channels provide several
  challenges for UWB systems
• Multipath fading
• Inter-symbol interference (ISI)
• Energy capture
• Effects are well-understood and are analyzed as
  trade-off between performance versus complexity
• DS-UWB minimizes fading and provides scalable
  energy capture
• Other approaches can provide good energy capture
  at the expense of significant multipath fading

5
Compensating for ISI

• ISI occurs as a result of non-uniform channel
  frequency response
• Multipath delay spread exceeds the symbol
  interval
• ISI is compensated for using an equalizer
• Linear equalizer (digital filter)
• Decision-feedback equalizer (DFE)
• If left uncompensated, ISI can cause high BER
  error floor phenomenon
• Equalizer technology is widely used in many types
  of systems
• Telephone modems
• WLAN (e.g. 802.11b)
• HDTV
• OFDM systems use frequency domain equalization to
  compensate for phase and amplitude response of
  channel
• If delay spread exceeds CP length, residual ISI
  compensation would require additional time-domain
  equalization

6
Example of ISI Effects on BER

• Un-equalized system experiences high BER and
  error floor
• 9-tap DFE with 16-finger rake performance
  approaches AWGN

7
Eye diagram at Eb/No 5 dB Noise dominates ISI
8
Eye diagram at Eb/No 10 dBNoise/ISI at similar
levels
9
Eye diagram at Eb/No 15 dB ISI dominates AWGN
10
Eye diagram at Eb/No 20 dB ISI dominates AWGN
11
Responses Equalization

• Comments Fully Resolved
• There is no need for an adaptive equalizer. The
  system is assumed to see a psuedo-stationary
  channel for the duration of the packet.The
  equalizer re-trained for each packet.
• At 110 Mbps, packets will be lt 0.1ms in duration
• Equalizer performance is demonstrated in
  system-level simulations
• Our simulations show that although error
  propagation is present, it does not significantly
  reduce the range achieved by DS-UWB

12
Topic Simultaneous Piconets (SOP)

• Typical comments
• SOP numbers are inconsistent with any of the
  sanity checks. Please revise numbers via full
  level simulation. Do not assume that the
  interference is white Gaussian noise and shift
  curves. To verify numbers are based on
  simulations, please provide each curve used in
  the averaging process
• Isolation between interfering piconets occupying
  the lower band needs to be better than the stated
  d_int/d_ref 0.66 for 2-3 uncoordinated
  interfering piconets in some applications - I
  would like to see evidence of how this can be met

13
SOP Mechanism

• SOP performance values reported for DS-UWB were
  based on full simulations of all interfering
  signals (not based on statistical signal
  distributions)
• SOP mechanism is based on spread-spectrum
  techniques
• Other piconet signals look like uncorrelated
  noise
• Analysis results show PHY layer interference
  ratios
• Equivalent to fully loaded piconets
• Actual MAI will depend on MAC actual traffic
  loading
• 15.3 MAC co-existence mechanisms (child
  neighbor piconets) can allow co-existence at much
  shorter ranges

14
SOP Performance

• DS-UWB also has the potential for enhanced SOP
  performance using advanced receiver architectures
• MAI is not truly random noise, but has structure
• Different piconet codes chip rates are known
• Multi-user detection (MUD) techniques could allow
  for significant SOP performance improvements

15
AWGN SOP Distance Ratios
Test Distance 1 Interferer Distance Ratio 2 Interferer Distance Ratio 3 Interferer Distance Ratio
110 Mbps 15.7 m 0.65 0.92 1.16
220 Mbps 11.4 m 0.90 1.28 1.60
500 Mbps 5.3 m 2.2 3.3 -

• AWGN distances for low band
• High band ratios expected to be lower
• Operates with 2x bandwidth, so 3 dB more
  processing gain

16
Multipath SOP Distance Ratios
Test Transmitter Channels 1-5 Single Interferer
Channels 6-10 Second Interferer Channel 99 Third
Interferer Channel 100
110Mbps 1 Interferer Distance Ratio 2 Interferer Distance Ratio 3 Interferer Distance Ratio
CM1 0.66 0.86 1.09
CM2 0.64 0.91 1.14
CM3 0.72 0.97 1.24

• High band ratios expected to be lower (3 dB more
  processing gain)

17
Topic ADC Issues

• Typical comments
• DS-UWB must demonstrate a receiver structure
  would be suggested that can achieve range
  comparable with the MBOA proposal, with a digital
  sampling rate of no more than 528Mbit/s
• The Silicon implementation feasibility is
  substantiated satisfactorily. ----The Silicon
  implementation size/power/complexity claims of
  the ADC/DAC/FEC/ Rake/equalizer at high speed do
  not agree with general knowledge

18
ADC Power Requirements Scaling

• ADC complexity is a function of both sample rate
  and bit width
• Concerns of comments seem to be that ADC
  requirements are much higher for DS-UWB than for
  alternative approaches (e.g. MB-OFDM) because
  clock rate is higher
• ADC performance is described by efficiency
  quotient
• EQ power / 2 (ENOB BW)
• ENOB effective number of bits BW input
  bandwdith
• This agrees with ADC scaling estimates based on
  MB-OFDM-proposed methodology
• Available in IEEE Document 03/343r1 describing
  MB-OFDM complexity and power consumption
• DS-UWB digital receiver architecture can use a
  fixed bit width for all data rates up to 1.326
  Gbps
• MB-OFDM proposes to use 4-5 bits at 528 MHz

19
ADC Relative Complexity Bounds

• Relative complexity (power)
• 528 MHz _at_ 4 bits ? 0.8x 1326 MHz _at_ 3 bits
• 528 MHz _at_ 5 bits ? 1.6x 1326 MHz _at_ 3 bits
• Both approaches can likely scale to lower
  resolution ADCs with some sacrifice in
  performance
• Research on the lower bounds for ADC resolution
  indicates that OFDM-UWB will have error floors
  for low ADC resolution (not true for
  single-carrier UWB)
• Digital Architecture for an Ultra-Wideband Radio
  Receiver, Raul Blazquez, Fred S. Lee, David D.
  Wentzloff, Puneet P. Newaskar, Johnna D. Powell,
  Anantha P. Chandrakasan, Microsystems Technology
  Laboratory, Massachusetts Institute of
  Technology, VTC 2003

20
Topic Interference Rejection

• Comments
• Authors of Merged 2 showed heuristic arguments
  for performance in the presence of narrowband
  interferers. The selection criteria ask for
  simulation results. Authors need to do
  simulations.
• I find the DS approach hard to achieve good
  performance under narrow band interferers. I will
  change my vote if I get explanation how this
  approach can function under narrow band
  interferers

21
Topic Interference

• Comments Fully Resolved
• Selection Criteria clearly ask for analysis or
  simulation results
• Detailed analysis shows that DS-UWB provides
  robust performance against RFI through UWB
  processing gain
• Additional implementation mechanisms available to
  significantly improve RFI rejection

22
Interference Criteria

• Interference criteria (03/031r11)
• When this interferer is present, using simulation
  results, analysis, or technical explanations,
  determine the average received interference
  power, PI, that can be tolerated by the receiver,
  after it has executed any interference mitigation
  algorithms, while still maintaining a PER less
  than 8 for 1024 byte packets
• Minimum criteria PI - Pdgt 3 dB (Pd is the
  received power which is defined here as 6 dB
  above the receiver sensitivity level)
• Out-of-Band Interference from Intentional or
  Unintentional Radiators
• Proposers should report the minimum out-of-band
  rejection in dB provided by the proposed system.
  This will provide a minimum standard for
  out-of-band interferer immunity

23
NarrowBand Interference (NBI)Radio Frequency
Interference (RFI)3-Cases
Out-of-Band BPF
RFI
Mild Processing Gain Adequate
Moderate LNA does Not saturate Processing Gain
inadequate
Severe LNA saturates Must Filter
DS-UWB 1 (40 MHz) Notch Filter 2 of DS-UWB band
No added complexity needed
2 small impact
24
Moderate RFI
Moderate LNA does Not saturate Processing Gain
inadequate
See calculation next page
DS-UWB SIR lt -3.06 dB
MB-OFDM SIR lt ? dB
Digital RFIExtraction 10 dB gain
Erasure Detection Erasure decoding (same as
turning tone off)
Notch Filter
LOW COMPLEXITY Only 4 MACsper symbolper tone!
SIR lt -13 dB
SIR lt -7 dB
25
Narrow-Band Interference

• DS-UWB receivers with 3-bit ADC architectures
• Simulations with no active NBI compensation
  indicate about 3 dB I-to-S is to be expected
• Simple analysis with NO ACTIVE COMPENSATION
  (worst case)
• Required Eb/No is 5.0 dB for rate-½ FEC code
• Assume 1.5 dB implementation loss (based on
  simulation results)
• Total noise-per-bit is 87 dBm -174dBm/Hz
  10log(110MHz) (6.6 dB NF)
• Sensitivity -8751.5 80.5
• Sensitivity 6dB (per spec) signal power (S)
  -74.5 dBm
• Allowable (IN) -74.5 - 5.0 - 1.5 -81 dBm
  (assume I is noise-like at slicer)
• Allowable I is therefore 10log(10(-81/10)-10(-8
  7/10)) -82.24 dBm
• At 110 Mbps, processing gain is 121 over (IN)
  in signal bandwidth ? 10.8 dB gain (worst case)
• Processing gain is a function of tone frequency
  depends on pulse shape. At band edges, gain is
  much higher
• Allowable I-to-S is therefore -81.24 10.8
  -(-74.5) 3.06 dB I-to-S
• Result for high-band operation is 6.0 dB
  allowable I-to-S
• 3 dB better than low band operation because 2x
  signal bandwidth provides 3 dB more processing
  gain

26
Digital RFI Removal

• Real signal and noise from hardware
• A/D samples fed into Matlab
• 6 bits used to represent basis functions
• Data processed in 128 sample blocks

After (SNR 15 dB)
Before (SIR 5 dB)
27
Quantized RFI Suppression Performance Vs.
Frequency Error
28
Spectrum Before Extraction
Fd 114e6 Resolution Fd/1024 111 kHz
29
Spectrum After Extraction
Fd 114e6 Resolution Fd/1024 111 kHz
30

• BACKUP

31
Bounds on ADC Resolution

• From Digital Architecture for an Ultra-Wideband
  Radio Receiver, Raul Blazquez, Fred S. Lee,
  David D. Wentzloff, Puneet P. Newaskar, Johnna D.
  Powell, Anantha P. Chandrakasan, Microsystems
  Technology Laboratory, Massachusetts Institute of
  Technology, VTC 2003.

32
DS-UWB Avoids the UNII Band

• DS-UWB already excludes bands used by most likely
  high power interferers (UNII bands WLAN, radars,
  DSRC, cordless phones, etc