1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Resolution of TG6 comments: S10-13, S10-24, S10-467, S10-468, S ]
Date Submitted: [12 September, 2010]
Source: [Laurent Ouvry] Company [CEA-Leti]
Address [17 rue des Martyrs, Grenoble, 38054, France]
Voice:[ ], FAX: [ ],
Re: [Proposed Resolution of D0 Comment S10-13, -24, -467, -468, -469 ]
Abstract: [Comment resolution for letter ballot 55 for S10-13, -24, -467, -468, -469]
Purpose: [Propose Resolution of D0 Comment S10-13, -24, -467, -468, -469 (and the other S10-xxx comments which are identical to them)]
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.
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Laurent OUVRY, CEA-Leti

2. Proposed Resolution of D0 Comment S10-13, S10-24, S10-467, S10-468, S (and the other S10-xxx comments which are identical to them)
Laurent OUVRY, CEA-Leti

3. Note
The comments addressed here relates to the SHR structure and length (Preamble and SFD) to enable sufficient PER, frame efficiency and reduced complexity
Both simulations and analysis are under work to better assess the performance impact of the different choices for the different modulations
At CEA-Leti
At the University of Oulu (thanks to Heikki Karvonen, Leonardo Goratti, Jussi Haapola)
All simulations being not completed at present time, they will not be used in the current proposals for comments resolution
Laurent OUVRY, CEA-Leti

4. D0 Comment S10-13
Comment: Figure 116: "S_0" is not defined anywhere in the text.
Proposed Change: Defined SFD signal structure.
Analysis:
In the D0 draft, the SFD is not fully defined. The draft suggests that the SFD is made of another spreading sequence “S_0” than the preamble but does not tell what it is. The examples of the a standard or of the f draft standards can be used.
The SFD can be using the same sequence than the preamble, and the SFD codeword could be [ ] like for the 15.4f draft, with the same bit to symbol mapping than for the modulation under use for the PHR (i.e. OOK or DBPSK respectively). Such a solution leads to a very long, not acceptable SFD.
SFD_length*Sequence_length shall be limited to keep frame efficiency
In 15.4a, the nominal SFD length is 8us. In the D0, it is 16us with a single sequence
Proposed Resolution:
Since according to the proposed resolution of S10-24, S and S we propose to use a sequence length of 31, the SFD would use the same sequence length of 31.
To have an SFD codeword is not feasible, not to increase SFD length too much: a two bits (0, 1) SFD is proposed with a different sequence than the preamble sequence. The two bits SFD makes possible a differential approach compatible with the modulation formats.
Slide 4
Laurent OUVRY, CEA-Leti

5. D0 Comment S10-24
Comment: N_sync = 4 is not large enough to accomplish all the necessary assessment, acquisition, and estimation at the receiver.
Proposed Change: Find the optimized repetition number (N_sync) considering all the receiver functionalities and procedures, and detailed simulation study.
Analysis:
A typical receiver has to perform successive tasks before demodulating the useful data in the PHR and the PSDU. The preamble shall be long enough to perform signal detection, AGC, AFC, chip synchronisation, symbol synchronisation, clock offset estimation, carrier offset estiamation, etc.
After that, the SFD is used for frame synchronisation. A typical receiver would use correlators with the spreading sequence S_X of the preamble to perform such tasks.
Having only N_Sync=4 suggests only 4 steps are possible, e.g. a massive use of parallelism which is not wishable in low complexity and low power receivers.
See the analysis for S for further comments
Proposed Resolution:
See the proposed resolution for S10-468
Slide 5
Laurent OUVRY, CEA-Leti

6. D0 Comment S10-467 Comment: Sequence length of 63.
Proposed Change: Shorter sequences (eg 31) would simplify the receiver implementation, especially in presence of large time drifts.
Analysis:
A typical receiver would use correlators with the spreading sequence S_X of the preamble to perform detection and synchronisation operations.
The complexity of such correlators grows ~linearly with the sequence length.
Using partial correlations complicates the receiver unnecessarily
The SNR at the output of the correlator has to be better by a few dBs compared to the SNR for symbol demodulation.
In the proposed timing parameters, one preamble symbol (i.e. one sequence) has 9dB more SNR than one symbol (i.e. 62kbps compared to 482kbps in the mandatory mode) which is way too much
In relationship with comments S10-24 and S10-468, the most important is to have sufficient time during the preamble, therefore N_sync * Sequence Length is the key parameter
We can easily trade one parameter for the other
For the purpose of piconets and adjacent channel separations we need a set of sequences with good cross correlation properties
The small Kasami set is an option, but close performances can be obtained with (larger) Gold code sets
The clock accuracy is +/-20ppm, thus maximum time drift is 10.3ps per PRP
The clock drift impact over the single sequence correlation is negligeable if the signal is downconverted in baseband or in energy detection receivers, whatever the sequence length up to 63
The clock drift impact over the single sequence correlation is too high if the signal is processed at its central frequency (not a desirable option)
Proposed Resolution:
Use of sequence length of 31 for the preamble and the SFD to reduce receiver implementation complexity and have more steps to perform classical detection/synchronisation with full sequence correlation.
Slide 6
Laurent OUVRY, CEA-Leti

7. D0 Comment S10-468 Comment: Number of sequences Ns = 4.
Proposed Change: More sequences of smaller length would benefit the performance and the receiver implementation
Analysis:
As stated about S10-24 comment, it is more desirable to have a higher value for N_sync to decompose detection and synchronisation in full sequence correlations.
Nsync*Sequence_length shall be limited to keep frame efficiency: in 15.4a, the nominal preamble length at the ~same PRF is 64us made of Ns=64 sequences of 1us each and length 31. In the D0 draft, Ns=4 and each sequence is 16us with length 63.
Proposed Resolution:
Use a sequence length of 31 and Ns=N_sync=8 for the preamble
Slide 7
Laurent OUVRY, CEA-Leti

8. D0 Comment S10-469 Comment: 8 sequences in the proposed Kasami set.
Proposed Change: A larger set (eg Gold codes, which has nearly as excellent crosscorrelation properties than Kasami sequences) could be used to improve coexistence according to the TG TRD, and would offer a large choice for the SFD specification.
Analysis:
As stated for S comment analysis, it is desirable to have a minimum of 8 different sequences, 4 for the even channels and 4 for the odd channels. For a given channel, 4 sequences are let to further mitigate interference from simultaneously operating independent networks.
In D0 the small Kasami set of 8 sequences of length 63 is proposed.
In D0 however, another sequence is used for the SFD (S_0) which in principle shall also be taken from the set, breaking the original reasoning
When implementing the resolution of comment S10-467, i.e. sequence length of 31, we can no longer use a small Kasami set (not existing), but it can be replaced by the Gold codes of length 31
The Gold codes are easily built from the m-sequences
Proposed Resolution
Use the Gold code set of 32 sequences of length 31 and divide the set in four subsets
1:8 for even channels preamble
9:16 for even channels SFD
17:24 for odd channels preamble
25:32 for odd channels SFD
Slide 8
Laurent OUVRY, CEA-Leti