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1Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE802.22-05-0005r1 Slide 1 Tutorial on Multi Access OFDM (OFDMA) Technology.

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Presentation on theme: "1Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE802.22-05-0005r1 Slide 1 Tutorial on Multi Access OFDM (OFDMA) Technology."— Presentation transcript:

1 1Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 1 Tutorial on Multi Access OFDM (OFDMA) Technology IEEE P Wireless RANs Date: Authors: Notice: This document has been prepared to assist IEEE 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 IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs 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 Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures 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 Chairhttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf Carl R. StevensonCarl 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 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at >

2 2Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 2 Abstract The contribution presents a tutorial on Multi Access OFDM (OFDMA) technology which has been endorsed in leading standards such as- ETSI DVB-RCT and IEEE802.16a,d and 16e. Essential parameters of UpLink and DownLink and simulation results are presented. System capabilities and advantages are also discussed. The tutorial could offer an insight and understanding of OFDMA technology to be considered as a candidate for WRAN system

3 3Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 3 Tutorial on Multi Access OFDM (OFDMA) Technology Eli Sofer Runcom Technologies Ltd

4 4Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 4 Contents OFDMA System Architecture Illustrated Example OFDMA System Properties Coverage and Capacity

5 5Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 5 OFDMA System Architecture

6 6Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 6 Duplexing Technique FDD/TDD Multiple Access Method TDMA/OFDMA OFDM Symbols allocated by TDMA Sub-Carriers within an OFDM Symbol allocated by OFDMA Diversity Frequency, Time, Code (CPE and BS), Space Time Coding, Antenna Array

7 7Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 7 FDD (Frequency Division Duplexing ) Uses One Frequency for the DownLink, and a Second Frequency for the UpLink. TDD (time Division Duplexing) Uses the same frequency for the Downlink and the Uplink. In any configuration the access method is OFDMA/TDMA. Duplexing - Principles

8 8Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 8 Using OFDMA/TDMA, Sub Channels are allocated in the Frequency Domain, and OFDM Symbols allocated in the Time Domain. OFDMA-TDMA Principles

9 9Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 9 Combining TDMA and FDMA TDMA/FDMA operation = OFDMA Frequency sub-channels are composed of multiple, non-adjacent carriers

10 10Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 10 Multipath – The challenge The RF signal travels through multiple paths The RF channel is characterized by a delay profile Problematic when delay spread is comparable to symbol duration

11 11Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 11 Multipath – The solution OFDM modulates in parallel multiple narrow band sub-carriers Multipath duration becomes short relative to symbol duration Pilot and guard sub-carriers are also inserted

12 12Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 12 Multipath – The solution The sub-carriers are converted by IFFT to a time domain signal A guard interval (cyclic prefix) is added to collect multipath A long guard interval (GI) reduces efficiency but enhances multipath handling capability OFDM/OFDMA enable handling peak delay spread as large as the GI

13 13Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 13 DownLink OFDMA Symbol

14 14Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 14 Burst Structure is defined from one Sub-channel in the Frequency domain and n OFDMA time symbols in the time domain, each burst consists of N data modulated carriers. Adaptive Modulation and Coding per Sub-Channel in the Down-Link Forward APC controlling (+6dB) – (-6dB) digital gain on the transmitted Sub-Channel Supporting optional Space Time Coding employing Alamouti STC. Supporting optional Adaptive Array. DownLink Specification

15 15Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 15 FFT size : 2048 Guard Intervals : ¼, 1/8, 1/16, 1/32 Coding Mandatory: concatenated RS GF(256) and Convolutional coding (k=7,G1=171,G2=133, keeping overall coding rate to = ½, ¾ Coding Optional: Convolutional Turbo Code (CTC), Turbo Product Code (TPC) with coding rates close to = ½, ¾ QPSK, 16QAM, 64QAM modulation Modulo 4, Pilot based Symbol Structure. 32 Sub-Channels of 48 data carriers each Example- DownLink Specification

16 16Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 16 Downlink Pilot and Data Carriers Allocation Scheme

17 17Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 17 Space Time Coding Tx diversity encoder IFFTDACFilterRF IFFTDACFilterRF Subcarrier modulation IFFT input packing Tx Rx RFDACFilterFFT Diversity Combiner Sub- channel demod. Log- Likelihood ratios Decoder

18 18Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 18 UpLink OFDMA Symbol

19 19Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 19 Burst Structure is defined from one Sub-channel in the Frequency domain and 3 OFDMA time symbols in the time domain, each burst consists of 144 data modulated carriers. Adaptive Modulation and Coding per User in the UpLink User Can be allocated 1 up to 32 Sub-Channels 2 Sub-Channels are used as the Ranging Sub-Channels for User Ranging and fast Band-Width Request. Example of UpLink Specification

20 20Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 20 FFT size : 2048 Guard Intervals : ¼, 1/8, 1/16, 1/32 Coding Mandatory: concatenated RS GF(256) and Convolutional coding (k=7,G1=171,G2=133, keeping overall coding rate to = ½, ¾ Coding Optional: Convolutional Turbo Code (CTC), Turbo Product Code (TPC) with coding rates close to = ½, ¾ QPSK, 16QAM, 64QAM modulation Modulo 13, Pilot based Sub-Channel Structure. 32 Sub-Channels of 53 carriers each, 5 carriers used as pilots, 48 carriers used for data Example of UpLink Specification

21 21Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 21 Example for UpLink Sub-Channel Pilot and Data Carriers Allocation Scheme

22 22Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 22 All usable carriers are divided into 32 carrier groups named basic group, each basic group contains 53 sub- carriers Using Special Permutations for carrier allocation

23 23Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 23 Carriers are allocated by a basic series and its cyclic permutations for example: Basic Series: 0,5,2,10,4,20,8,17,16,11,9,22,18,21,13,19,3,15,6,7,12,14,1 After two cyclic permutations we get: 2,10,4,20,8,17,16,11,9,22,18,21,13,19,3,15,6,7,12,14,1,0,5 Using Special Permutations for carrier allocation

24 24Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 24 The Carriers of each Sub-Channel are spread all over the usable frequency for best frequency diversity The allocation by permutation gives an excellent Reuse factor - almost 1. The allocation by permutation give an excellent interference spreading and averaging. Using Special Permutations for carrier allocation

25 25Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 25 The CDMA like synchronization is achieved by allocating several of the usable Sub-Channels for the Ranging process, the logic unit they consist is called a Ranging Sub-Channel. Onto the Ranging Sub-Channel users modulate a Pseudo Noise (PN) sequence using BPSK modulation The Base Station detects the different sequences and uses the CIR that he derives from the sequences for: –Time and power synchronization –Decide on the user modulation and coding Using CDMA like modulation for Ranging

26 26Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 26 Aloha vs. CDMA BW request (32 codes) –CDMA efficiency is better by a factor of six –CDMA latency is better by a factor of four DVB-RCT MAC Performance

27 27Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 27 Illustrated Example

28 28Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 28 Subscriber Units at the Current OFDMA Symbol = 3 Sub-Channels Allocated to Subscriber-Unit #1 = 12 Sub-Channels Allocated to Subscriber-Unit #2 = 9 Sub-Channels Allocated to Subscriber-Unit #3 = 6 Number Of New Subscriber-Units Requesting Services = 3 All Subscriber-Units Suffer Different Multi-Paths and different Attenuation's Example

29 29Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 29 Constellation at the Base Station Example

30 30Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 30 Users Separation Example

31 31Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 31 User Estimation Example - Results

32 32Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 32 User Estimation Results

33 33Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 33 User Estimation Results

34 34Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 34 Finding New Subscriber-Units Requesting Services, Using the Ranging Pilots (CDMA/OFDM Techniques) Results

35 35Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 35 OFDMA System - Properties

36 36Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 36 Narrowband Interference Rejection –Easy to Avoid/Reject Narrowband Dominant Interference. –Less Interfered Part of the Carrier Can Still Be Used. Interference Rejection/Avoidance

37 37Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 37 Using shaping on the signal peaks Limiting the PAPR to a constant value by vector reduction PAPR Reduction

38 38Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 38 Rectangular Spectrum Shape (Brick Wall) Small Frequency Guard band Spectrum Properties

39 39Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 39 Spectrum Properties

40 40Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 40 In OFDM, channel impairment are solved in the same way Group Delays are solved, by Channel estimation Group Delay

41 41Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 41 Phase Noise Effect on OFDM Phase Noise Effect on S.C Phase Noise Effects

42 42Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 42 Timing Sensitivity Low timing sensitivity is needed, and simple phase and channel estimators solve timing problems. Frequency Sensitivity solved by locking onto the Base-Station transmission and deriving the Subscriber Units clocks from it. Equalization No Equalizers are needed, channel impairment and timing problems are both solved with simple phase and channel estimators

43 43Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 43 System Coverage and Capacity

44 44Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 44 By allocating different Sub-Channels to different sectors we can reach reuse factor of 1 with up to 12 sectors (changing the polarity enhances the performance) Using Reuse Factor of 1

45 45Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 45 Use modulations with various Bit/Hz capabilities as Adaptive N-QAM. Use Adaptive FEC (Convolutional & Reed-Solomon or Turbo code) Maximal frequency reuse between cells/sectors (close to 1). Maximum sectors allocation. The use of statistical Multiplexing and concentration. Adaptive Carrier Allocations. Adaptive Power Control Capacity

46 46Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 46 Coverage

47 47Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 47 Coverage - Simulations

48 48Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 48 Coverage - Simulations Multi Sector Coverage, 3 Sectors, 3 Frequencies, achieves 2.8Bits/s/Hz/Cell, 22.5Mbps/Sector

49 49Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 49 Coverage - Simulations Multi Sector Coverage, 6 Sectors, 6 Frequencies, achieves 2.8Bits/s/Hz/Cell, 22.5Mbps/Sector

50 50Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 50 Averaging interference's from neighboring cells, by using different basic carrier permutations between users in different cells. Interferences within the cell are averaged by using allocation with cyclic permutations. Enables orthogonality in the uplink by synchronizing users in time and frequency. Enables Multipath mitigation without using Equalizers and training sequences. Enables Single Frequency Network coverage, where coverage problem exists and gives excellent coverage. OFDMA Advantages- Summary (1)

51 51Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 51 OFDMA Advantages - Summary (2) Enables spatial diversity by using antenna diversity at the Base Station and possible at the Subscriber Unit. Enables adaptive modulation for every user QPSK, 16QAM, 64QAM and 256QAM. Enables adaptive carrier allocation in multiplication of 23 carriers = nX23 carriers up to 1587 carriers (all data carriers). Offers Frequency diversity by spreading the carriers all over the used spectrum. Offers Time diversity by optional interleaving of carrier groups in time.

52 52Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 52 OFDMA Advantages - Summary (3) Using the cell capacity to the utmost by adaptively using the highest modulation a user can use, this is allowed by the gain added when less carriers are allocated (up to 18dB gain for 23 carrier allocation instead of 1587 carriers), therefore gaining in overall cell capacity. The power gain can be translated to distance - 3 times the distance for R 4 and 8 time for R 2 for LOS conditions. Enabling the usage of Indoor Omni Directional antennas for the users. MAC complexity is the same as for TDMA systems.

53 53Runcom Technologies Ltd. Submission Eli Sofer, Runcom January 2005 Doc.: IEEE r1 Slide 53 OFDMA Advantages - Summary (4) Allocating carrier by OFDMA/TDMA strategy. Minimal delay per OFDMA symbol of 300 sec. Using Small burst per user of about 100 symbols for better statistical multiplexing and smaller jitter. User symbol is several times longer then for TDMA systems. Using the FEC to the outmost by error detection of disturbed frequencies.


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