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Title: Performance of LDPC decoder with accurate llr metric in LDPC-coded pilot-assisted OFDM system
Keywords: LDPC,LLR metric,pilot-assisted,OFDM
Issue Date: 31-Jul-2011
Source: LI ZHIPING (2011-07-31). Performance of LDPC decoder with accurate llr metric in LDPC-coded pilot-assisted OFDM system. ScholarBank@NUS Repository.
Abstract: Modern communication systems are increasingly adopting advanced technologies such as OFDM modulation and LDPC codes. OFDM modulation is spectrally efficient and able to mitigate the multipath fading in the wireless channel, whereas the LDPC code is a very powerful error correcting code with a near Shannon-limit performance. A common practice in OFDM system is to transmit pilots on some subcarriers periodically along with the data subcarriers for the purpose of channel estimation. The combination of these technologies is becoming the trend of many modern wireless communication standards. Hence, in this thesis, we study a LDPC-coded pilot-assisted OFDM system with the focus on how to optimally insert pilot and which LLR metric to use in the LDPC decoder, in order to achieve the best performance. The thesis starts with a literature review on OFDM modulation, LDPC codes and pilotassisted communication. Based on the knowledge of these technologies, we first study the LDPC-coded pilot-assisted single-carrier communication system over Rayleigh flat fading channel. Based on the pilot-aided MMSE channel estimator, two LLR metrics, namely PSAM-LLR and A-PSAM-LLR, are defined and their impact on the BER performance is studied through simulation. Secondly, we study the LDPC-coded pilot-assisted OFDM system over multipath fading channel. Similarly, pilot-aided MMSE channel estimator is used and two LLR metrics are derived for the OFDM system. Simulation is conducted for the OFDM system with different configurations. The simulations serve several purposes. One objective is to investigate the optimal pilot spacing in various scenarios. Another objective is to compare the two LLR metrics in terms of decoder performance and implementation complexity.
Appears in Collections:Master's Theses (Open)

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