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Modified Adjacent Frequency Coding For Increased Notch Depth under DAA/Spectral Sculpting Kevin A. Shelby, Johann Chiang, Dr. Jim Lansford Alereon Inc.

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Presentation on theme: "Modified Adjacent Frequency Coding For Increased Notch Depth under DAA/Spectral Sculpting Kevin A. Shelby, Johann Chiang, Dr. Jim Lansford Alereon Inc."— Presentation transcript:

1 Modified Adjacent Frequency Coding For Increased Notch Depth under DAA/Spectral Sculpting Kevin A. Shelby, Johann Chiang, Dr. Jim Lansford Alereon Inc. CrownCom Mykonos June 2006

2 WiMedia Confidential 2 Outline -Objectives -Regulatory Outlook -System Overview -System Design Considerations -Simulation Results -Closing Remarks

3 WiMedia Confidential 3 Objectives -Extend adjacent frequency coding to include some form of multi-carrier modulation: -Reuse antipodal signaling aimed at canceling sidelobe contributions in adjacent carriers; -Introduce multi-carrier modulation to minimize the impact on the existing WiMedia PHY Specification: -Preserve the existing time/frequency spreading characteristics in order to maintain system performance in the presence of a variety of channel impairments, SOP interference most notably; -Preserve the existing tone mapping to minimize the impact on the interleave and cyclic shift structures.

4 WiMedia Confidential 4 Current Regulatory Outlook Band Group 1 Band Group 2 Band Group 3 Band Group 4 Band Group 5 DAA Required DAA Required DAA Requirement Postponed in Europe until June 30, 2010 Increased Rolloff

5 WiMedia Confidential 5 Adjacent Sidelobe Contributions -AFC leverages the observation that sidelobe contributions in adjacent tones are similar in amplitude:

6 WiMedia Confidential 6 Sidelobe Cancellation -The achievable notch depth can be increased by canceling adjacent sidelobe contributions:

7 WiMedia Confidential 7 Existing DCM Mechanism -Dual Carrier Modulation as originally conceived can be described in terms of a linear transformation, M, as follows: -Where the indices {a,b,c,d} represent a mapping from the interleaved transmit bitstream, -and M={m ij }; i,j=[1:2] constitutes a linear mapping of tones in the transmit OFDM symbol.

8 WiMedia Confidential 8 Modified AFC -Building directly on the original AFC proposal, a linear mapping resembling that employed by DCM can be identified, aimed at canceling mutual interference in adjacent subcarriers: -Where c k = x k +j y k corresponds to the output of the symbol mapper, QPSK or DCM encoded, depending on the selected data rate.* *The extent to which M-AFC can be applied at rates above 200Mb/s is still under investigation.

9 WiMedia Confidential 9 Baseband Transmitter IFFT Symbol Mapper Coding/ Puncturing ScramblerInterleaver Pilots Zero DC DACs P/S (  )* 2X Preamble Add Zero Suffix Analog Filters Tone Nulling Guard

10 WiMedia Confidential 10 System Design Considerations Notch Depth Notch depth varies as a function of the scaling factor, , with the benefit of antipodal signaling maximized as  approaches unity.   1 Invertible Matrix The principal objective in introducing the scaling factor was to permit an invertible matrix at the receiver. Det(M) = 1-  2   ≠ 1 Tone Erasure The potential for symbol erasure occurs whenever the data content in adjacent tones is the same, i.e. c 2n = c 2n+1. y 2n = c 2n (1-  )   < 1 RX SNRSNR in the RX constellation is maximized when the TX mapping results in evenly distributed constellation points.  = 1/2

11 WiMedia Confidential 11 Achievable Notch Depth

12 WiMedia Confidential 12 TX Constellation(  =8/16 )

13 WiMedia Confidential 13 RX Constellation Equalizer Output DeMapper Output DeSpread Output

14 WiMedia Confidential 14 System Simulation Simulation results were compiled using the following system configuration: -WiMedia compliant 1.0 PHY -Mandatory rates ( Mb/s)[1][1] -M-AFC,  = 0.5 -~20MHz tone notching ( GHz) -Incumbent service passive during link tests [1][1] The applicability of M-AFC to higher data rates is still under investigation

15 WiMedia Confidential 15 DAA Spectral Scultping Simple Tone NotchingModified AFC

16 WiMedia Confidential 16 Link Performance

17 WiMedia Confidential 17 Closing Remarks -M-AFC applies a linear transformation at the symbol mapper output leaving tone assignment and existing interleaver structure unchanged; -Resembling DCM, M-AFC achieves antipodal signaling without sacrificing the time/frequency spreading present in the existing spec; -The resulting notch depth approaches that demonstrated with the original AFC, less ~5dB once considerations affecting link performance are taken into account; -The rate of OOB rolloff also increases similarly to the original AFC proposal over that without antipodal signaling.

18 WiMedia Confidential 18 Backup - Decoding A practical decoder can be derived similar to that employed for DCM. With received symbols z 1 and z 2 : The soft-demapper computes:


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