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Complex Beaco n Simulations in AWGN

Complex Beaco n Simulations in AWGN. Authors:. IEEE P802.22 Wireless RANs Date: 2007-01-15.

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Complex Beaco n Simulations in AWGN

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  1. Complex Beacon Simulations in AWGN Authors: IEEE P802.22 Wireless RANs Date: 2007-01-15 Notice:This document has been prepared to assist IEEE 802.22. 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 grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22. Patent Policy and Procedures:The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee.org. > David Mazzarese, Samsung

  2. Abstract Proposition of complex spreading sequences with QPSK and dual channel beacon. Simulation results of proposed enhancements to IEEE 802.22.1 Draft 06-238. David Mazzarese, Samsung

  3. Changes from 06-234-r2 (Nov 2006) • DBPSK and DQPSK beacon simulations fixed • There was a problem with the noise variance • Improved synchronization procedure • Calibration of DBPSK beacon with TG1 Draft 06-238 • Addition of an alternative for the use of a QPSK beacon • Demonstration with appropriate receiver • Simulations • Slides not related to the beacon proposal have been removed David Mazzarese, Samsung

  4. Outline • Reminder of current draft • Motivations for dual channel beacon • Transmitter structure • Frame structure • Proposed complex PN spreading sequence • Receiver structure • Simulation conditions • Simulations in AWGN and Rayleigh fading channels • Beacon-to-beacon interference • Conclusions David Mazzarese, Samsung

  5. 44+3k octets Reminder of Current TG1 Draft 06-238Sync burst sequence followed by PPDU • 1 bit ~ 0.1041 ms • 1 octet ~ 0.8326 ms • 3 octets ~ 2.4978 ms Synchronization burst sequence and PPDU are sent sequentially David Mazzarese, Samsung

  6. Problems in TG1 Draft 06-238 • Sync burst cannot be received all the time (e.g. when PPDU is being transmitted) • The WRAN cannot detect the presence of the beacon if it only receives part of the PPDU during a short periodic quiet interval. • Sequential transmission of the sync bursts and the PPDU may have a bad timing with the WRAN superframe • If the PPDU falls during the transition of 2 superframes, the WRAN will have problems scheduling the long quiet period and maintaining its regular operation, since it would lose the superframe header • We may design the lengths of the synchronization burst sequence and the period of the PPDU to match the WRAN superframe timing, but it may not be appropriate for another license-exempt device to detect the 802.22.1 beacon. • The PPDU cannot be sent many times every 2 second (currently only twice) • It may not be possible to decode the PPDU within 2 seconds, considering other constraints such as scanning time, sensing time, and the presence of other WRAN cells on adjacent channels. • The PPDU period can be set by choosing the length of the counter, but a specific choice can only be made with respect to a specific receiver (e.g. a WRAN receiver) David Mazzarese, Samsung

  7. Motivations for dual-channel beacon • Transmit the sync burst and the payload in parallel • I and Q channels using QPSK modulation • Complex spreading • Separate I and Q real spreading has lower performance • Continuous transmission of the payload (data rate increase) • Transmit payload every 40 ms, rather than once (40 ms) every second • WRAN can start decoding the payload at any time, and finish decoding once the counter has cycled through. Namely, no need to wait for the count down to reach zero and then decode the payload • Fairness • Any system has a chance to decode the beacon with the same fairness • TG1 Draft 06-238 is not fair since the periodicity of beacon sync and payload may not suit different systems equally David Mazzarese, Samsung

  8. Reminder of Original ProposalTransmitter with complex spreading on dual channel Z-1 PSDU Data Q + Beacon Signal Pilot: sync & count-down I Complex spreading • PSDU data is DBPSK modulated • Sync burst is BPSK modulated • Ok in AWGN channel, but problematic in fading channels David Mazzarese, Samsung

  9. Z-1 Transmitter with complex spreading and dual channel, using DQPSK modulation Pilot: sync & count-down I + Beacon Signal Q PSDU Data Complex spreading • Trade-offs of using differential modulation (vs. Es/No) • DQPSK is 2.3 dB worse than QPSK, whereas DBPSK is 0.5 dB worse than BPSK • QPSK already suffers a 3 dB loss vs. BPSK in Es/No (with double the bit rate) • DQPSK is 4.8 dB worse than DBPSK vs. Es/No on the Gaussian channel • Therefore we explore the use of a coherent receiver that allows to use QPSK. • We demonstrate that a simple receiver by today’s standards can do the trick. David Mazzarese, Samsung

  10. I Pilot: sync & count-down + Beacon Signal PSDU Data Q Complex spreading Transmitter with complex spreading and dual channel, using QPSK modulation David Mazzarese, Samsung

  11. Frame structure: dual channel with sync-N burst and complex DSSS Variable N  variable length PSDU (e.g. beacon-to-WRAN payload vs. beacon-to-beacon payload) I sync sync sync N N-1 0 Rx period ANP Q PSDU One Packet, constant length 49 bytes with proposed revision (doc06-0254 Nov 2006) • WRAN uses sync burst to determine when the PSDU has been fully received • WRAN uses sync burst to schedule a long quiet period to decode the PSDU • Fixed-length beacon-to-WRAN PSDU assumed (doc06-0254) David Mazzarese, Samsung

  12. Properties of the Complex PN Sequences • Further divide by the square root of 2 • Any one of these 3 sequences could be used • (sequence C was used in simulations) David Mazzarese, Samsung

  13. * Auto-Correlation Properties * Real sequence of 22-06-0196-0000_Motorola_TG1_PHY_MAC_spec_draft David Mazzarese, Samsung

  14. Receiver structure with DQPSK David Mazzarese, Samsung

  15. Receiver structure with QPSK Option 2 (burst diversity) David Mazzarese, Samsung

  16. Coherent receiver for QPSK Random correlation with the quadrature data creates an error floor below 1% packet error rate, which can easily be removed by synchronizing with more than 2 bursts (cf simulation results) David Mazzarese, Samsung

  17. Correlation of BPSK m-sequence with a random BPSK sequence (quadrature data) David Mazzarese, Samsung

  18. Correlation of BPSK m-sequence with a complex QPSK beacon sync-burst David Mazzarese, Samsung

  19. Simulation Conditions • AWGN channel, and quasi-static Rayleigh fading channel • For each sync burst (e.g. packet or header): a different simulation run • Perfect chip pulse synchronization assumed at the receiver (no oversampling) • Synchronization with 8-chip complex spreading PN sequence • Sliding window length = 12 chips (PN sequence length + 4 chips) • Synchronize with the maximum correlation value 5 times • Estimate synchronization time with respect to median value • Synchronization with 15-bit sync-burst • Option 1 (simplest receiver) • Same type of procedure as for synchronizing with the complex spreading PN sequence • Option 2 (time diversity): synchronization with more than 2 consecutive sync bursts • For quiet periods longer than 3 sync-bursts (one WRAN frame) and for PPDU-long quiet period • Definition of Packet Error Rate (one packet = one header = sync burst = 3 bytes) • If PN sequence synchronization fails: declare a packet error (no decoding) • If PN sequence synchronization is successful: synchronize with sync-burst, estimate the channel, decode the data (24 bits) and declare a packet error if at least one bit is in error • Fairness: exactly same transmitted power for real and complex sequences of length 8 • Comparison vs. Es/No • Symbol energy Es normalized to one (8 chips) • BPSK transmission with a real PN sequence (+1,-1) • QPSK transmission with a complex PN sequence (+1,-1,+i,-i after spreading) David Mazzarese, Samsung

  20. Rayleigh Fading AWGN Packet Error Rate of 24-bit Sync Burst • DQPSK • ~4.5 dB loss at 1% PER vs. DBPSK (Draft 06-238) • ~1 dB loss at 1% PER vs. QPSK w/ burst diversity • QPSK • With burst (time) diversity • ~3.5 dB loss at 1% PER vs. DBPSK (Draft 06-238) • Without burst (time) diversity • ~4.5 dB loss at 1% PER • 0.1% PER not reachable David Mazzarese, Samsung

  21. David Mazzarese, Samsung

  22. Beacon-to-Beacon Interference • To be updated before conference call on January 9 David Mazzarese, Samsung

  23. Conclusions • Dual channel beacon design offers • Continuous transmission of fast sync-burst • Continuous transmission of beacon payload • Trade-off between receiver complexity and packet error rate • DQPSK or QPSK modulations possible, with a tradeoff between beacon detection rate and receiver complexity • QPSK better for lower SNR and longer quiet period • DQPSK better for higher SNR and shorter quiet period • FEC protection of the beacon payload should still be included to match the PER of the payload to the PER of the sync-burst. David Mazzarese, Samsung

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