18-07-2012, 01:22 PM
A ROBUST LUBY TRANSFORM ENCODING WITH AWARE SYMBOL
Design Phase.ppt (Size: 799 KB / Downloads: 49)
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.
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
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.
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
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