Performance of Low-Density Lattice Codes in COFDM Systems
Orthogonal Frequency Division Multiplexing (OFDM) is suitable for high-bit-rate data transmission in multipath environments. Many error-correcting codes have been applied in COFDM to reduce the high bit error rate (BER). Recently, low-density lattice code
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Performance of Low-Density Lattice Codes in COFDM Systems Shuanlei Hu and Lianxiang Zhu
Abstract Orthogonal Frequency Division Multiplexing (OFDM) is suitable for high-bit-rate data transmission in multipath environments. Many error-correcting codes have been applied in COFDM to reduce the high bit error rate (BER). Recently, low-density lattice codes (LDLC) attracted much attention. LDLC was proposed by Sommer in 2007, and the performance is very close to Shannon limit with iterative decoding. We applied LDLC in COFDM system and the simulation results showed that the LDLC is effective to improve the BER of the system in multipath environments. Keywords Low-density lattice codes
COFDM Iterative decoding
36.1 Introduction In the future, high quality communications are attractive to people, high-bit-rate transmission is required. Orthogonal Frequency Division Multiplexing technology divides the bandwidth into numbers of narrowband sub channels, in which the parallel signals are transmitted in a lower rate. In that way, it turns the high-bit-rate signals into low ones [1]. OFDM is a very suitable technique for high-bit-rate data transmission in multipath environments. In other words, the OFDM technique can reduce the number of the inter symbol interference (ISI) which emerges in the multipath environments, but the subcarriers may lose completely when the amplitudes become too small [2]. Hence, the overall BER turn out to be very high S. Hu (&) L. Zhu Chongqing University of Posts and Telecommunications, Chongqing, China e-mail: [email protected]
W. Lu et al. (eds.), Proceedings of the 2012 International Conference on Information Technology and Software Engineering, Lecture Notes in Electrical Engineering 210, DOI: 10.1007/978-3-642-34528-9_36, Ó Springer-Verlag Berlin Heidelberg 2013
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even most of the subcarriers are transmitted without ISI. So error correcting is essential to avoid the high BER which was caused by the weak subcarriers. And many codes have been applied in the OFDM system, such as convolution codes, Turbo codes, R-S codes, LDPC [3], and so on. Recently, LDLC has attracted much attention especially in the field of coding theory. LDLC was proposed by Sommer in 2007 and the performance is very close to Shannon limit with iterative decoding. LDLC is a kind of lattice which was defined by a sparse inverse generator matrix in which the nonzero elements only take a small part of the total number. Sommer proposed this lattice construction, described its iterative decoder which is similar with decoder in LDPC, and also gave extensive convergence analysis. The results showed that LDLC decoder has a linear complexity [4]. The paper is organized as follow, the basic definitions of LDLC are described in Sect. 36.2, the LDLC iterative decoding algorithm is described in Sect. 36.3, the structure of the LDLC-COFDM is given in Sect. 36.4 and Sect. 36.5 describes the simulation results.
36.2 Low Density Lattice Codes 36.2.1 Basic Definitions of LDLC 36.2.1.1 Lattice Codes and Par
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