doc.: ieee 802.15-04/504r0 submission september 2004 welborn, freescale & mclaughlin,...

September 2004

Welborn, Freescale & McLaughlin, DecaWaveSlide 1

doc.: IEEE 802.15-04/504r0

Submission

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: [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]Voice:[703-269-3000], E-Mail:[matt.welborn @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.

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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 < 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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

Example of ISI Effects on BER

5 10 15 20-6

-5

-4

-3

-2

-1

Eb/No

Lo

g10

BE

RUncoded Equalization Performance on CM3-15, 16 Finger Rake

No Equalization9-Tap Least-Squares DFEAWGN Channel

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

Eye diagram at Eb/No = 5 dB Noise dominates ISI

5 10 15 20-6

-5.5

-5

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

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Eb/No

Log1

0 B

ER

Uncoded Equalization Performance on CM3-15, 16 Finger Rake


100 200 300 400 500 600 700 800 900 1000 1100

-1

-0.5

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16 Rake, No DFE, Eb/No = 5

100 200 300 400 500 600 700 800 900 1000 1100

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-0.5

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16 Rake, Post DFE, Eb/No = 5

Received BPSK Symbols

September 2004


doc.: IEEE 802.15-04/504r0

Submission

Eye diagram at Eb/No = 10 dBNoise/ISI at similar levels

100 200 300 400 500 600 700 800 900 1000 1100

-1

-0.5

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0.5

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100 200 300 400 500 600 700 800 900 1000 1100

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5 10 15 20-6

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Eb/No

Log1

0 B

ER



September 2004


doc.: IEEE 802.15-04/504r0

Submission

Eye diagram at Eb/No = 15 dB ISI dominates AWGN

5 10 15 20-6

-5.5

-5

-4.5

-4

-3.5

-3

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-1.5

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Eb/No

Log1

0 B

ER



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September 2004


doc.: IEEE 802.15-04/504r0

Submission

Eye diagram at Eb/No = 20 dB ISI dominates AWGN

100 200 300 400 500 600 700 800 900 1000 1100

-1

-0.5

0

0.5

1


100 200 300 400 500 600 700 800 900 1000 1100

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5 10 15 20-6

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Eb/No

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September 2004


doc.: IEEE 802.15-04/504r0

Submission

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 < 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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

AWGN SOP Distance Ratios

Test Distance

1 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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

110Mbps




CM1 0.66 0.86 1.09

CM2 0.64 0.91 1.14

CM3 0.72 0.97 1.24

Multipath SOP Distance Ratios

Test Transmitter: Channels 1-5Single Interferer: Channels 6-10Second Interferer: Channel 99Third Interferer: Channel 100

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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…

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

ADC Relative Complexity & Bounds

• Relative complexity (power)– 528 MHz @ 4 bits 0.8x 1326 MHz @ 3 bits– 528 MHz @ 5 bits 1.6x 1326 MHz @ 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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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 - Pd> 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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

NarrowBand Interference (NBI)Radio Frequency Interference (RFI)

3-Cases

MildProcessing Gain Adequate

ModerateLNA does Not saturate

Processing Gain inadequate

SevereLNA saturates

Must Filter

Out-of-BandBPF

No added complexity needed

DS-UWB1% (40 MHz) Notch Filter

=2% of DS-UWB band

2% = small impact

RFI

September 2004


doc.: IEEE 802.15-04/504r0

Submission

Moderate RFI

ModerateLNA does Not saturate

Processing Gain inadequate

DS-UWBSIR < -3.06 dB

Digital RFIExtraction

10+ dB gain

Erasure Detection& Erasure decoding

(same as turning tone off)

NotchFilter

MB-OFDMSIR < ? dB

SIR < -13 dBLOW COMPLEXITY

Only 4 MAC’sper symbolper tone!

SIR < -7 dB

See calculation next page

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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 = -87+5+1.5= 80.5• Sensitivity + 6dB (per spec) = signal power (S) = -74.5 dBm• Allowable (I+N) = -74.5 - 5.0 - 1.5 = -81 dBm (assume I is noise-like at

slicer)• Allowable I is therefore 10*log(10^(-81/10)-10^(-87/10)) = -82.24 dBm• At 110 Mbps, processing gain is 12:1 over (I+N) 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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

Before (SIR = 5 dB) After (SNR = 15 dB)

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

September 2004


doc.: IEEE 802.15-04/504r0

Submission

Quantized RFI Suppression Performance Vs. Frequency Error

0 50 100 150 200 25010

10.5

11

11.5

12

12.5

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13.5

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15

Frequency Error (kHz)

Out

put

SN

R (

dB)

3 Bits4 Bits5 Bits6 Bits7 Bits8 BitsInput SNR:15.0dBSIR:6.0dB

September 2004


doc.: IEEE 802.15-04/504r0

Submission

Spectrum Before Extraction

0 1 2 3 4 5

x 107

-20

-10

0

10

20

30

40

Frequency

Pow

er S

pect

rum

Mag

nitu

de (

dB)

Fd = 114e6

Resolution:Fd/1024 =111 kHz

September 2004


doc.: IEEE 802.15-04/504r0

Submission

Spectrum After Extraction

0 1 2 3 4 5

x 107

-20

-10

0

10

20

30

40

Frequency

Pow

er S

pect

rum

Mag

nitu

de (

dB)

Fd = 114e6

Resolution:Fd/1024 =111 kHz

September 2004


doc.: IEEE 802.15-04/504r0

Submission

BACKUP

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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.

September 2004


doc.: IEEE 802.15-04/504r0

Submission

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

doc.: ieee 802.15-04/504r0 submission september 2004 welborn, freescale & mclaughlin,...

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