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Impact of MB-OFDM and DS-UWB Interference on C-Band Receivers

This project investigates the impact of MB-OFDM and DS-UWB interference on a C-band DTV receiver through simulation. The objective is to provide an unbiased comparison based on universally accepted assumptions.

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Impact of MB-OFDM and DS-UWB Interference on C-Band Receivers

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Impact of MB-OFDM and DS-UWB Interference on C Band Receivers] Date Submitted: [] Source: [Torbjorn Larsson] Company [Paradiddle Communications] Address [13141 Via Canyon Drive, San Diego, CA 92129, USA] Voice:[+1 858 538-3434], FAX: [+1 858 538-2284], E-Mail:[tlarsson@san.rr.com] Re: [Analysis of the impact of MB-OFDM and DS-UWB interference on a DTV receiver made in earlier contributions, in particular 802.15-04/547r0 and 802.15-04/0412r0] Abstract: [The impact of MB-OFDM and DS-UWB interference on a C-band DTV receiver is investigated by simulation] Purpose: [To present an unbiased comparison of the impact of MB-OFDM and DS-UWB interference based on a minimal set of universally accepted assumptions] 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. Torbjorn Larsson

  2. Impact of MB-OFDM and DS-UWB Inteference on C-Band Receivers Torbjorn Larsson Paradiddle Communications, Inc. Torbjorn Larsson

  3. Motivation and Objective • Motivated by two contributions: • 04/0412r0, In-band Interference Properties of MB-OFDM, by C. Razell, Philips • 04/547r0, Responses to “In-Band Interference Properties of MB-OFDM”, by C. Corral, G. Rasor, S. Emami, Freescale Semiconductor • The emphasis in the above contributions is on qualitative analysis • In contrast, the approach here is “brute force” simulation • Our hope is that the assumptions made are universal enough to be accaptable to the entire 802.15.3a task group • The author is an independent consultant, not affiliated with any UWB company. This work was not carried out under any consulting contract Torbjorn Larsson

  4. C-Band DTV Systems • The C-band downlink spans 3.7 – 4.2 GHz • C-band antennas are typically 6 – 12 feet in diameter • Based on the DVB-S (Digital Video Broadcasting – Satellite) standard (EN 300 421) • DVB-S was designed for MPEG-2 broadcasting in the Ku-band, but is also used in the C-band • DVB-S does not specify a unique set of data rates or symbol rates; However… • Typical transponder bandwidth is 36 MHz (33 MHz also used) • Typical symbol rate 27 – 29 Msps • DVB-S2 is the next generation with improved bandwidth efficiency and FEC Torbjorn Larsson

  5. DVB-S Torbjorn Larsson

  6. Typical C-Band Downlink Channelization (Telesat satellite Anik F2. Footprint: North America) • Total of 24 channels • Each polarization has 12 channels • Transponder bandwidth is 36 MHz with a 4 MHz guard band • The center frequencies are separated by 40 MHz • The center frequencies for the two polarizations are offset by 20 MHz • The result is 24 center frequencies separated by 20 MHz Torbjorn Larsson

  7. DTV Simulation Model • Excludes Reed-Solomon coding and interleaving • Impossible to simulate error rates with RS coding • Will probably favor DS-UWB • Symbol rate: 27 Msps • No quantization (including input to Viterbi decoder) • Ideal pulse shaping/matched filters (0.35 roll-off) • No nonlinarity • No frequency offset • No phase noise • Pre-computed phase error and time offset • Receiver noise figure: 4 dB • Intend to run simulations for all code rates – Results presented only include rate 1/2 and 2/3 Torbjorn Larsson

  8. MB-OFDM Transmitter Model • Based on the Sep. 2004 release of the MB-OFDM PHY Specifications (P802.15-04/0493r1) • Complete Matlab implementation of the specifications • System operating in band-hopping mode • Includes (5-bit) DAC and realistic filter characteristics • Spectral pre-shaping to compensate for non-ideal filter characteristics (=> worst-case in this context!) • Channel number 9 (Band group 1, TFC 1) • Data rate “110” Mbps (106.7 Mbps) Torbjorn Larsson

  9. DS-UWB Transmitter Model • Based on the July 2004 release of the DS-UWB PHY specifications (P802.15-04/0137r3) • Complete Matlab implementation of the specifications • No DAC • Ideal RRC pulse shaping filter truncated to 12 chip periods (=> worst-case!) • Channel number 1 (chip rate: 1313 Mcps) • Data rate: “110” Mbps (109.417 Mbps) • BPSK modulation • Spreading code for preamble and header (PAC): -1 0 +1 -1 -1 -1 +1 +1 0 +1 +1 +1 +1 -1 +1 -1 +1 +1 +1 +1 -1 -1 +1 • Spreading code for frame body: +1 0 0 0 0 0 Torbjorn Larsson

  10. Interference Spectra Resolution: 10 kHz PSD averaged over 10 packets (roughly 0.9 ms) • Transmit power is set so as to push each spectrum as close as possible to the FCC limit (worst-case condition) • MB-OFDM transmit power is -10.3 dBm • DS-UWB transmit power is -10.8 dBm (data rate dependent) Torbjorn Larsson

  11. Interference Spectra – Close Up • Both spectra exhibit substantial variations • Solution: run simulation for multiple DTV center frequencies DTV center frequencies Torbjorn Larsson

  12. Simulated DTV Center Frequencies • Rate 1/2 simulations: 3.8 – 4.3 GHz in steps of 10 MHz • Arbitrary choice across 500 MHz bandwidth • Rate 2/3 simulations: 3.72 – 4.18 GHz in steps of 20 MHz • According to channelization plan on slide 6 Torbjorn Larsson

  13. Simulation Block Diagram • Attenuation 1 is set so that the received DTV power is 3 dB above sensitivity • Each simulation is performed with multiple DTC center frequencies • Simulation results are plotted as a function of center frequency and attenuation 2 • No multipath! Torbjorn Larsson

  14. BER Performance without Interference Noise Figure = 4 dB • Sensitivity for rate 1/2 is -92.5 dBm (Eb/No = 3.2 dB) • Sensitivity for rate 2/3 is -90.7 dBm (Eb/No = 3.7 dB) Defines sensitivity Torbjorn Larsson

  15. BER versus Center Frequency (Code Rate 1/2) Interference attenuation = 67 dB Center frequencies separated by 10MHz Torbjorn Larsson

  16. Average BER (Code Rate 1/2) Torbjorn Larsson

  17. Worst-Case BER (Code Rate 1/2) Torbjorn Larsson

  18. BER versus Center Frequency (Code Rate 2/3) Interference attenuation = 67 dB Center frequencies separated by 20MHz Torbjorn Larsson

  19. Average BER (Code Rate 2/3) Torbjorn Larsson

  20. Worst-Case BER (Code Rate 2/3) Torbjorn Larsson

  21. Conclusions • For the two simulated cases (rate 1/2 and 2/3), the difference in average BER across the C-band is 1 dB or less • The difference in worst-case BER is less than 0.5 dB • More general conclusions should be postponed until all code rates have been simulated Torbjorn Larsson

  22. Onward… • Run simulations for code rates 3/4, 5/6, 7/8 • Run simulations for TFC 3 or 4 • Include multipath • Suggestions? tlarsson@san.rr.com Torbjorn Larsson

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