1. Date Submitted: November 11, 2005]
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Numerical results on the ranging packet with superimposed preamble]
Date Submitted: November 11, 2005]
Source: [Yihong Qi, Huan-Bang Li, Shinsuke Hara, Bin Zhen and Ryuji Kohno, Company: National Institute of Information and Communications Technology ]
Contact: Yihong Qi
Voice: ,
Abstract: [Numerical results using the ranging packet with superimposed preamble are presented. These results include extra energy consumption, ranging accuracy improvement and carrier sense probability.]
Purpose: [To propose a new ranging packet structure]
Notice: This document has been prepared to assist the IEEE P 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 P
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2. Numerical results on the ranging packet with superimposed preamble
Yihong Qi, Huan-Bang Li, Shinsuke Hara, Bin Zhen and Ryuji Kohno National Institute of Information and Communications Technology (NICT)
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3. Outlines Review of the current ranging packet
Problems with the current packet
Low throughput with CSMA or ALOHA
No flexibility for a variety of ranging applications
Review of the proposed packet with superimposed preamble
Numerical results with the proposed packet
Carrier sense (CS) probability
Ranging accuracy improvement
Extra energy consumption
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4. Current ranging packet
Preamble
Header
Payload
Data on timing, crystal offset, etc
Acquisition; channel sounding
Control information
contents
modulation
length
average PRF
preamble
Acquisition; channel sounding
Ternary code (determined)
three lengths: 500us, 1ms, 4ms (proposed)
same (determined)
header
Control information
TBD
payload
Data on timing, crystal offset, etc
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5. Problem with ranging cf: current solution (?)
A variety of ranging applications require tradeoff among
Ranging accuracy VS.
Mobility
Update rate
On-air time
cf: current solution (?)
three preamble lengths: 500us, 1ms and 4ms.
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6. Problem with ALOHA Low throughput From Bin Zhen’s Doc 619r010 -1 1
0.05
0.1
0.15
0.2
offered load
normalized payload throughput
preamble-only CS
whole packet CS
pure aloha
Low throughput
From Bin Zhen’s Doc 619r0
1ms preamble, 0.25ms data(1Mbps, 32 bytes data)
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7. The proposed ranging packet
Preamble
+ (code multiplexing)
Preamble
Header
Payload
Preamble is superimposed in the header and payload section.
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8. An Illustration of the proposed packet
power level
Preamble section
Header and payload sections s2 s2 s2 s1 s1 s1 s1 s1
superimposed preamble s1 t
s1: spreading code for preamble symbol; s2: spreading code for data symbols
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9. Key point 1
The power level of the superimposed preamble is much lower than that of the regular preamble and data sequences.
For minimizing the resulting interference to data demodulation and SOP.
Power reduction of 7~15dB examined in the numerical results
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10. Key point 2.
The superimposed preamble is constructed by repetition of one preamble symbol s1.
Hence, potential ``spreading gain” is high.
E.g., with symbol duration 1us and the payload section of 256us, ``spreading gain”=14dB.
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11. Advantages Extra preambles for channel sounding/ranging is available.
Improve ranging accuracy
Provide flexibility to an application to determine its tradeoff among ranging accuracy, mobility, update rate, etc.
Superimposed preamble embeds ``regularity” in the header and payload section.
CS (carrier sense) of an entire packet is possible, hence can improve the throughput performance.
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12. Numerical Results
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13. Parameters and assumptions
Pulse:
Bandwidth 500MHz with duration 2ns,
Peak PRF= 494MHz; average PRF=16MHz
Preamble:
Ternary code with length 31, symbol duration=1us
Total length: 0.5ms, 1ms, 4ms
Data
Modulation: 2 PPM + BPSK,
Walsh code with length 8, symbol duration=0.5us
Data length: 256us
Assumptions:
The power of the regular preamble and data sequences of the header and payload sections is same.
The power of the superimposed preamble is 7~13dB lower than the regular level.
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14. Ratio of extra energy consumed by the superimposed preamble
Observation:
Extra energy consumption is low, less than 5% for power reduction of less than 8dB.
Power reduction = pulse energy of data / pulse energy of the superimposed preamble.
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15. An illustration of the extra energy consumption
Regular preamble
Header and
payload
Less than 5%
Superimposed preamble
0.5, 1, 4ms
0.25ms
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16. Improvement in ranging accuracy
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17. How to approximate the ranging accuracy improvement
Assumption:
Coherent ranging estimate
the variance of a ranging estimate proportional to 1/SNR.
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18. Improvement in ranging accuracy
L= number of symbols used for channel sounding/ranging in the preamble section.
Observation:
Accuracy improvement around 40~70% is available due to small number of symbols actually used for channel sounding in the regular preamble section.
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19. Rationale of the accuracy improvement
0.5, 1, 4ms
0.25ms
Regular preamble
data
Superimposed preamble
Small number of symbols in the regular preamble section is used for ranging.
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20. Carrier sense (CS) probability
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21. A CS scheme Receiving a signal within certain time window
Matched filter to the
ternary code S
BPF
``de-spreading”
``Energy detection”
CS is to use the energy detector to determine whether the received signal contains a preamble structure.
The energy detector is to test whether the computed energy is over certain threshold or not.
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22. Key points of the CS scheme
The preamble is a periodic signal with period Ts1, where Ts1 is the duration of the preamble symbol s1.
After passing a multipath channel, the received preamble is still a periodic signal with period Ts1.
regardless symbol synchronization,
regardless multipath distortion
The CS scheme exploits the ``spreading gain” of the periodic received signal.
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23. Successful CS probability with Eb/N0=10dB and false alarm around 5%
CS window=16us
Observation:
Successful CS probability is over 70% for power reduction of less than 10dB.
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24. Successful CS probability with Eb/N0=10dB and false alarm around 5%
CS window=25us
Observation:
Successful CS probability is over 90% for power reduction of less than 10dB.
Power reduction = pulse energy of data / pulse energy of the superimposed preamble.
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25. Including crystal offset
Analytically
For CS window of 16us, crystal offset 40ppm corresponds to timing error 0.64ns, i.e., 30% of pulse duration 2ns
For CS window of 25us, crystal offset 40ppm corresponds to timing error 1ns, i.e., 50% of pulse duration 2ns
Limited effect on CS performance
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26. Successful CS probability with Eb/N0=10dB, false alarm around 5% and +40ppm crystal offset
CS window=16us
Observation:
Successful CS probability is over 70% for power reduction of less than 10dB.
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27. Successful CS probability with Eb/N0=10dB, false alarm around 5% and +40ppm crystal offset
CS window=25us
Observation:
Successful CS probability is almost over 80% for power reduction of more than 10dB.
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28. On non-coherent issue
The proposed packet has little interference on the current non-coherent ranging and data detection because of
Quasi-orthogonal between the payload and the superimposed preamble codes
Power of the superimposed preamble is sufficiently reduced.
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29. Conclusions
The proposed packet with superimposed preambles of power reduction 10dB
Low interference to data detection and SOP
Low extra energy consumption of less than 5%
Good ranging accuracy improvement of 40%~70%
Effective CS performance, success probability 85~95% with CS window of 25us and crystal offset 40ppm
No confliction with the non-coherent reception
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