1. 1 ANAND. P Roll No. SP1101 M.Tech - Signal Processing SCT College of Engineering A ROBUST LUBY TRANSFORM ENCODING WITH AWARE SYMBOL PACKETIZATION BASED CROSS CODING SCHEME FOR ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING SYSTEMS

2. 2 ABSTRACT Through this project, I try to propose a novel cross coding scheme for Orthogonal Frequency Division Multiplexing (OFDM) systems which combines the separate coding and the joint coding over all the sub-carriers. The key elements of this proposed scheme are Luby Transform (LT) encoding and Aware Symbol Packetization (ASP). By transmitting a LT encoded packet over a single sub- carrier, the packets can be discarded if they have encountered a low energy channel. The ASP algorithm is designed to minimize packet loss effects.

3. 3 CONTENTS  Aim  Motivation and Scope  Literature Review  Project Design  Implementation  Advantages  Applications  Future Scope  Work Schedule  Work Completed  Reference

4. 4 AIM  To propose a novel cross coding scheme for OFDM systems based on LT encoding and ASP algorithm  To check feasibility of the OFDM system using the proposed scheme under low SNR (<10dB) conditions.  To perform BER analysis of an OFDM system using the proposed scheme.  Compare results with existing encoding schemes.

5. 5 MOTIVATION AND SCOPE  Though OFDM systems are being modeled, absence of encoding scheme that can support the high bit rate systems at low SNR are still being researched.  The biggest motivation for my project is the urge to contribute to the field of communication engineering  The expansion of OFDM systems to the next level depends on errorless high bit rate transmission and encoding schemes to support it is the need of the hour

6. 6 LITERATURE REVIEW  OFDM  Need for Error Correction Coding  Need for Cross Coding  Opportunistic Error Correction (OEC) Layer

7. 7 OFDM  OFDM is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method with a large number of closely-spaced orthogonal sub-carriers are used to carry data.  The data is divided into several parallel data streams or channels, one for each sub-carrier.  Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.

8. 8 NEED FOR ERROR CORRECTION CODING  To overcome the effects of noise and interference encountered in transmission of signal  To utilize the wireless channels at maximum capacity.

9. 9 NEED FOR CROSS-CODING  In 4G and 5G networks, Bit Error Rate (BER) of OFDM is higher and existing Forward Error Correction (FEC) layers cannot be used.  To make system adapt to severe channel conditions  Cross-coding jointly over the sub-carriers yields a smaller error probability than that can be achieved by coding separately over the sub-carriers at the same rate.  Deeply faded channels can be discarded  Errors due to Packet Losses can be corrected

10. 10 OPPORTUNISTIC ERROR CORRECTION (OEC) LAYER  OEC is a cross FEC layer based on fountain codes.  LT codes are fountain codes which follow a systematic arrangement  Only a minimum amount of packets have to be received correctly to recover the original data.

11. 11 Project Design  Basic Block Diagram  Proposed Cross Coding Scheme  Detailed Explanation of Each Encoding Block  OFDM System Model with Proposed Cross Coding Scheme

12. 12 BASIC BLOCK DIAGRAM Cross-CodingOFDM Transmission Transmitter

13. 13 OFDM Reception Discard RX Packet Receiver Decoding ≥ threshold < threshold

14. 14 PROPOSED CROSS-CODING SCHEME  This scheme implements three types of encoding 1. LT Encoding with ASP 2. Cyclic Redundancy Check (CRC) Encoding 3. Low Density Parity Check (LDPC) Encoding LT Encoding with ASP CRC Encoding LDPC Encoding

15. 15 LT Codes  LT codes make packets that are systematically arranged random combinations of the message bits.  The transmitter sprays packets at the receiver without any knowledge of which packets are received.  Once the receiver has received any N packets, where N is just slightly greater than the original size K, the whole data can be recovered. N = K(1 + ε) where ε is the overhead

16. 16  LT codes are designed for communication over Erasure Channels, which means that the encoded packet is either received error free or not received at all.  The wireless channels are not erasure, but fading and noisy channels.  In communication systems, LT codes are used in combination with other error correction algorithms to convert the noisy channels into erasure channels

17. 17 ASP Algorithm  Step 0: Select the first source symbol as a root.  Step 1: Select a source symbol among all encoded bits of the root that has not been assigned to any packet until now (if all symbols of root are already packetized, go directly to Step 4).  Step 2: Put the source symbol into the target packet chosen by the following rules. If any packet is not chosen by the rules below, go to Step 4.

18. 18  Rule 1: If an empty packet exists, choose the packet as the target packet.  Rule 2: If the available space at a packet is not less than one more than control variable, then choose the packet as the target packet.  Rule 3: When any packet does not satisfy Rule 2, control variable is updated to be one less than minimum distance and choose the packet as the target packet  Step 3: Determine encoded bits in dependent level and put them into the target packet.  Step 4: If no more roots exist, go to Step 5. Otherwise, the next source symbol is sequentially selected as a root. Repeat Step 1–3 with the new root.  Step 5: Randomly distribute the remaining encoded symbols into the residual spaces of the packets.

19. 19 CRC Codes  A cyclic redundancy check (CRC) is an error- detecting code designed to detect accidental changes to data.  CRC calculates a short binary sequence for each block of data and adds it to the data forming a codeword.

20. 20 LDPC Codes Low-density parity-check (LDPC) codes are a class of linear block codes. LDPC codes are capacity approaching codes. Their main advantage is that they provide a performance which is very close to the capacity for a lot of different channels and linear time complex algorithms for decoding.

21. 21 OFDM SYSTEM WITH PROPOSED CROSS CODING SCHEME LT Encoding with ASP CRC Encoding LDPC Encoding IFFTDAC Up Conversion Transmitter

22. 22 Down Conversion ADCFFT Discard RX Packet Receiver LDPC Decoding CRC Decoding LT (ASP) Decoder ≥ threshold < threshold

23. 23 Implementation  Platform and Hardware Requirement  MATLAB Models of different Sections

24. 24 PLATFORM AND HARDWARE REQUIREMENT  The proposed cross coding scheme and the OFDM system model is to be simulated and analyzed using MATLAB 7.13 (R2011b)  A general purpose Computer with Core i5 2.4Ghz Processor with 3.0 GHz Turbo Boost and 4GB DDR3 SDRAM working under Windows 7 - 32bit is to be used for simulating the results.

25. 25 OFDM TRANSMITTER MATLAB MODEL Serial to Parallel Conversion ModulationIFFT Parallel to Serial Conversion

26. 26 AWGN CHANNEL SIMULATION AWGN Channel  Channels with SNR varying from 0dB to 15dB to be simulated  Signal Power assumed to be 1 Watt ( 0 dBW) SNR

27. 27 OFDM RECEIVER MATLAB MODEL Serial to Parallel Conversion FFTDemodulation Parallel to Serial Conversion

28. 28 ENCODER MATLAB MODEL  A (4,8) LT encoder with 4*8 ASP algorithm is considered. So 4 bit input converted to 4 8-bit packets using LT encoding with ASP.  CRC Encoding using 16-bit generator polynomial is to be used  LDPC Encoding using LDPC encoder object with default generator matrix is to be used LT Encoding with ASP CRC Encoding LDPC Encoding

29. 29 Discard RX Packet LDPC Decoding CRC Decoding LT (ASP) Decoder ≥ threshold < threshold DECODER MATLAB MODEL  Log Likelihood Decoder Model to be simulated so that Log Likelihood Ratios (LLR) are computed and used for thresholding

30. 30 ADVANTAGES  The proposed Cross-Coding Scheme will be compatible with all existing OFDM systems.  Increases system adaptability to severe channel conditions without complex equalization.  It makes the system more robust against narrow-band co-channel interference, Intersymbol interference (ISI) and fading caused by multipath propagation.  It makes the system less sensitive to time synchronization errors.  The system is capable of detecting and correcting both bit losses in packet as well as packet losses

31. 31 APPLICATIONS  The proposed Cross-Coding Scheme can be used in all existing OFDM systems like  PEP (Packetized ensemble protocol) via telephone lines  ADSL and VDSL broadband access via telephone service copper wiring  Power line communication (PLC)  Multimedia over Coax Alliance (MoCA) home networking  DVB-C2(an enhanced version of the DVB-C digital cable TV standard)  Wi-Fi (IEEE 802.11) and WiMAX (IEEE 802.16) Standards  It can also be used for future OFDM systems like 4G and 5G GSM communication systems

32. 32 FUTURE SCOPE  Hardware Implementation of the OFDM System with the Proposed Cross Coding Scheme is to be carried out.  Analysis is to be done with different OFDM system models – Using different input schemes, different Digital Modulation Schemes, taking antenna considerations, etc.  Improvement in BER vs Cost of hardware implementation is to be analyzed

33. 33 WORK SCHEDULE  October 2011 – December 2011 : Literature review  January 2011 – February 15, 2012 : Design Phase  February 15, 2012 – April 2012 : Implementation

34. 34 WORK COMPLETED  The different details of OFDM system are rcoding models researched and formulated. A collective Literature Review is prepared.  An OFDM system is designed for simulation and specifications of the encoding schemes confirmed for simulation.

35. 35 REFERENCE  Dongju Lee and Hwangjun Song, “A Robust Luby Transform Encoding Pattern-Aware Symbol Packetization Algorithm for Video Streaming Over Wireless Network “, IEEE Transactions on multimedia, Vol. 13, No. 4, August 2011  Xiaoying Shao and Cornelis H. Slump, “A Robust Cross Coding Scheme for OFDM Systems”, ISITA2010, Taichung, Taiwan, October 17-20, 2010  Xiaoying Shao and Cornelis H. Slump, “A Novel Cross Coding Scheme for OFDM Systems”, 2009 IEEE Information Theory Workshop  Hailiang Mei, “Modeling and Performance Evaluation of a BPPM UWB System (MSc thesis)”  H. Liu and G. Li, “OFDM-Based Broadband Wireless Networks: Design and Optimization”, IEEE Communications, vol. 182,no.3, 2006.  D.J.C. MacKay, “Fountain Codes”, IEEE Communications, vol. 152,no. 6, pp. 1062–1068, 2005.

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