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A Cognitive PHY/MAC Proposal for IEEE 802.22 WRAN Systems

A Cognitive PHY/MAC Proposal for IEEE 802.22 WRAN Systems. IEEE P802.22 Wireless RANs Date: 2005-11-07. Authors:.

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A Cognitive PHY/MAC Proposal for IEEE 802.22 WRAN Systems

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  1. A Cognitive PHY/MAC Proposal for IEEE 802.22 WRAN Systems IEEE P802.22 Wireless RANs Date: 2005-11-07 Authors: 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. Carlos Cordeiro, Philips

  2. PHY Abstract Digital modulation systems presently make use of two basic modulation technologies: single carrier and multi-carrier. Their features are well-known since they have been deployed for several years around the world for broadcasting applications. Wireless access applications differ from broadcasting since they require : • flexibility on the downstream link : variable number of user, variable throughput per user, variable level of protection, etc; • multiple access on the upstream link. Single carrier modulation can tackle these objectives through time multiplexing techniques. Multi-carrier modulation is however more flexible since it enables to control the signal in both time and frequency domains. This gives the opportunity to define two dimensional (time and frequency) slots and to map the services to be transmitted in both directions onto a subset of these slots. Two types of multi-carrier modulation has been retained in IEEE 802.16 (WiMAX) standard: OFDM in the fixed MAN version and OFDMA in the mobile version. In the continuity of IEEE 802.16, it is proposed here to consider OFDMA modulation for downstream and upstream links with two technological improvements: • Spreading; • OQAM waveforming. To meet the tight link budget requirements of WRAN, duo binary turbo code is proposed for service ranges up to 100 Km Carlos Cordeiro, Philips

  3. MAC Abstract We propose the Cognitive MAC (CMAC) layer to be used as the basis for the future IEEE 802.22 WRAN standard operating in the TV bands. The proposed CMAC is in some respects inspired by the IEEE 802.16 standard, but it provides major extensions, improvements and also simplifications in order to meet the 802.22 functional requirements. CMAC is based on a superframe architecture which is general enough to allow multiple wireless systems to coexist in addition to support the flexibility to group multiple vacant TV channels and hence achieve greater capacity. To coexist with incumbent services, CMAC is able to efficiently manage distributed incumbent measurement, control, and recovery procedures, while also providing the necessary spectrum management features. To coexist amongst 802.22 systems, CMAC is the first of its kind to implement a novel coexistence beacon protocol (CBP) that allows BSs with overlapping coverage areas to coordinate and efficiently share the radio spectrum, hence minimizing interference. The efficiency of CBP is further improved by a new scheme that dynamically synchronizes overlapping BSs. Additional characteristics of CMAC include the support of various traffic types with different QoS requirements, flexible bandwidth management, and a combination of access mechanisms. Carlos Cordeiro, Philips

  4. Presentation Outline • Introduction • A Glimpse of IEEE 802.22 • The Cognitive PHY Proposal • The Cognitive MAC Proposal • Conclusions Carlos Cordeiro, Philips

  5. Presentation Outline • Introduction • A Glimpse of IEEE 802.22 • The Cognitive PHY Proposal • The Cognitive MAC Proposal • Conclusions Carlos Cordeiro, Philips

  6. Carlos Cordeiro, Philips

  7. The IEEE 802.22 • From 18 Mbps to 24 Mbps • Propagation delays in excess of 300 µs • Operates in TV bands • 54 to 862 MHz • 6 MHz, 7 MHz and 8 MHz channel bandwidth Carlos Cordeiro, Philips

  8. Deployment Scenario • Master/Slave relationship • Entities • Base Station (BS) • Consumer Premise Equipment (CPE) • 4W CPE transmit power Carlos Cordeiro, Philips

  9. Presentation Outline • Introduction • A Glimpse of IEEE 802.22 • The Cognitive PHY Proposal • The Cognitive MAC Proposal • Conclusions Carlos Cordeiro, Philips

  10. PHY Presentation Outline • Background • Top-level description of modulation/coding • Channel bonding • Modulation Parameters • Spreading OFDMA • Sensing techniques • OQAM/OFDMA • Duo-binary CTC Carlos Cordeiro, Philips

  11. 802.22 requirements consideration • Regional Area Network (up to 30Km) • 4 watt transmission power • Large delay spread and roundtrip time • Data rate: from 1.5 Mbps DS and ~300 Kbps US • -70dB OOB emission • Should not cause harmful interference to other devices (incumbents) Carlos Cordeiro, Philips

  12. 802.22 requirements consideration (cont.) • Flexibility • Bandwidth • Access and services • Data protection • Power • Maximise Bit-rate/Hertz x Watt Carlos Cordeiro, Philips

  13. PHY Overview • OFDMA both in uplink and downlink • QPSK, 16-QAM, and 64-QAM, spreaded QPSK/OFDMA • More than 32 sub channels • Contiguous channel bonding upto 3 TV channels ( and beyond in a stack manner) • Data rate range from 5Mbps to 60Mbps • Option of OQAM/OFDMA and turbo code Carlos Cordeiro, Philips

  14. Why OFDMA ? • Single carrier and multi-carrier have been used for broadcasting, wireless access, etc • Their behavior is well understood (capacity, filtering requirements, PAPR, equalization, flexibility, efficiency) • 802.22 Wireless access differ from broadcasting and most other system • Flexibility in downstream link, variable # of users, variable throughput, variable level of protection, round-trip signal delay • Multiple access on the upstream • Multi-carrier system more suitable to meet these objectives • It enables to control the signal in time and frequency • Results in a two dimensional grid to assign resources to a user  OFDMA • Resources can be allocated on a per user basis • OFDM used in standards such as • WiMedia UWB, WiMAX (Fixed MAN), DAB, DMB, DVB-T, DVB-H, ISDB-T • OFDMA used in WiMax, DVB-RCT Carlos Cordeiro, Philips

  15. OFDMA • Based on OFDMA (sub-channels per user) • US/DS • Reduces overhead for short messages • Flexibility in choosing modulation/coding for CPE • Reduced PAPR for CPEs Carlos Cordeiro, Philips

  16. Coding Carlos Cordeiro, Philips

  17. Modulation Carlos Cordeiro, Philips

  18. Channel Bonding • Shannon Capacity • Capacity proportional to BW • but logarithmic with SNR or signal power) • Multi-path Diversity • Small BW signal can have deep fade or flat fade • Wider-bandwidth signal provides more frequency/multipath diversity • Interference • Wider-band reduced the amount of interference Carlos Cordeiro, Philips

  19. Channel bonding/capacity • Aggregate TV channels to get more capacity • Shannon: C = B.log2(1+S/N) • If S/N is fixed, then capacity increases linearly with bandwidth • If signal power is fixed, but bandwidth is increased. • C = B.log2(1+S/(BNo)) • Capacity still increases as bandwidth is increased • Assuming S/(BNo) is fixed where B is bandwidth of 1 TV channels, then overall network capacity can be increased by using subchannels (OFDMA) • C = KB.log2(1+S/(BNo)), K number of parallel channels Carlos Cordeiro, Philips

  20. Capacity of aggregated channels as a ratio of available capacity (fixed power) Carlos Cordeiro, Philips

  21. Channel bonding • 6, 12, 18 MHz channels • Depends on availability • Several receiver techniques to deal with flexible BW • Selectable analog filters • Up sampling digital filters Carlos Cordeiro, Philips

  22. 6K FFT over 3 TV channels 2K per TV channel Null out the outer carriers for 1 or 2 TV channels Fixed inter-carrier spacing Several implementation possibilities Channel bonding structure 6 MHz 12 MHz 18 MHz Carlos Cordeiro, Philips

  23. Spectrum of the signal (before further filtering) Produced using a 6K FFT for a single TV channel Carlos Cordeiro, Philips

  24. Table 2: Inter-carrier spacing and FFT/IFFT period values for different bandwidth options 6 MHz based channels (6, 12 and 18 MHz) 7 MHz based channels (7, 14 and 21 MHz) 8 MHz based channels (8, 16 and 24 MHz) Inter-carrier spacing, DF (Hz) 3348.214 3906.625 4464.286 FFT/IFFT period, TFFT (ms) 298.666 256.000 224.000 Inter-carrier spacing and FFT/IFFT period values for different bandwidth options Carlos Cordeiro, Philips

  25. OFDMA parameters Carlos Cordeiro, Philips

  26. Modulation/coding modes and corresponding rates Carlos Cordeiro, Philips

  27. Frame structure: Superframe Carlos Cordeiro, Philips

  28. Preamble • Superframe preamble • Over 1512 sub-carriers (every fourth or second non-zero), • 5 MHz BW • Simply duplicate for additional TV channels • 1 MHz gap between adjacent channels to relax filtering • 2 symbol duration (1 more for data) • Frame preamble: 1-3 TV channels • 1728*N sub-carriers • Short preamble is optional (short) (long) Carlos Cordeiro, Philips

  29. Spreaded QPSK/OFDMA • Spreaded QPSK • Spread data over 16 sub-carriers (Hadamard) • Increases capturing of multipath diversity • Increases resiliency to interferers • Simple receiver structure (MMSE) Carlos Cordeiro, Philips

  30. Simulation results for QPSK, rate 3/4 • Channels: • ATSC Brazil D • 802.22 Profile A • All with Doppler S-OFDMA gives 2-4dB gain! Carlos Cordeiro, Philips

  31. Preliminary Link Budget(LOS) Carlos Cordeiro, Philips

  32. Other Features • Ranging • Transmitter Power control (TPC) • Consideration of multiple antenna Carlos Cordeiro, Philips

  33. Channel Measurement • Received signal strength • Quality • Channel ‘busy’ detection • RSSI on a pilot-tone basis • Signal feature detection • Detection of the type of the signal • ATSC, DVB-T, Part 74, etc • Coherent detection • Should be robust to receiver imperfections Carlos Cordeiro, Philips

  34. Received Signal Strength • Can be measured in a number of ways • FFT, IOTA/FFT, simple low-pass filter etc • Possibility to measure a part of the spectrum • Various degrees of performance • Integration time and threshold is very important • BS sets essential parameters (constant) • Either the BS makes the detection decision based on the collective measurement results or CPE’s can make the decision • Can also be used for • Quality measurement of its own signal, TPC • Or simply as fast Channel ‘busy’ detection Carlos Cordeiro, Philips

  35. Simulated performances of OFDM and OQAM: detecting ATSC pilot 5ms integration time Carlos Cordeiro, Philips

  36. DTV signal feature detection • Should not be sensitive to frequency selective fading, and receiver impairments (e.g., frequency error) • Use field sync correlation detection for ATSC, similar correlation for other standards • Characterized the theoretical performance • Experimental tests Carlos Cordeiro, Philips

  37. Experimental setup for DTV detection 8VSB_SOURCE MULTIPATH SIMULATOR RECEIVER ATTENUATOR Carlos Cordeiro, Philips

  38. Based on DTV Laboratory Test Plan (Group C.1) “Static Echoes at various delays”. Carlos Cordeiro, Philips

  39. Based on DTV Laboratory Test Plan (Group D.1) “Static multipath with AWGN”. Carlos Cordeiro, Philips

  40. Based on Doc.: IEEE802.22-05/0055r7. Profile A. Carlos Cordeiro, Philips

  41. Based on Doc.: IEEE802.22-05/0055r7. Profile B. Carlos Cordeiro, Philips

  42. FFT avg W.F. V>k*avg Part 74 detection • Part 74 devices occupy a small portion of the spectrum • Thus, use spectral estimation and statistics of the estimated signal • Spectral estimation using FFTs (windowing techniques can also be employed to better localize the spectrum) • Perform FFT • Average each freq bin • Average across freq bin • Compute mean and “variance” Carlos Cordeiro, Philips

  43. Part 74 detection (cont.) • Detection • Theoretical performance Carlos Cordeiro, Philips

  44. Narrow-band detection (Part 74): Theoretical and simulated performance Carlos Cordeiro, Philips

  45. Probability of miss detection and false alarm Carlos Cordeiro, Philips

  46. PHY Presentation Outline • Background • Top-level description of modulation/coding • Channel bonding • Modulation Parameters • Spreading OFDMA • Sensing techniques • OQAM/OFDMA • Duo-binary CTC Carlos Cordeiro, Philips

  47. OFDM/OQAM Outline • Principles of OFDM/OQAM • The IOTA Waveform • Advantages of OFDM/OQAM • Simulation results

  48. OFDM/OQAM principles (1) • Aim: to increase OFDM spectral efficiency by : • Removing the guard interval (cyclic prefix); • Delivering a sharper spectral signal than OFDM. • How: The waveform that modulates OFDM sub-carriers is as much as possible localized in time and frequency domains to minimize inter-symbol and inter-carrier interferences.

  49. OFDM/OQAM principles (2) • The waveform must guarantee orthogonality between sub-carriers and multi-carrier symbols. • Orthogonality in the frequency domain (between sub-carriers) is guaranteed by OFDM; • Orthogonality in the real domain  OffsetQAM on each sub-carrier. • Example: IOTA waveform (optimally localized in time and frequency).

  50. OFDM/OQAM principles (2) • OFDM/QAM Transmitted signal: • takes the complex value representing the transmitted encoded data sent on the mth sub-carrier at the nth symbol; • and the basic functions are obtained by translation in time and frequency of a prototype function such as: • With • Unity function x used in OFDM has weak frequency localization. • OFDM/OQAM • Introduces a time offset between real and imaginary parts of symbols • takes real values; • And with

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