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Space Time Block Coded Design for Low Complexity based LDPC Coded OFDM

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DThe space time block coded (STBC) based orthogonal frequency division multiplexing (OFDM) system exhibits high peak-to-average power ratio (PAPR) and high complexity if discrete Fourier transform (DFT)/ inverse discrete Fourier transform (IDFT) is applied at the transmitter/receiver .In this paper, a low density parity code (LDPC) based space time coded OFDM system is considered . Compared to the general LDPC based STC-OFDM system, the proposed system can significantly achieve better PAPR property and also exhibits lower transceiver complexity the by exploiting both spatial diversity and the selective fading diversity in wireless channels. An analysis on the capacity and performance of Alamouti like STBC OFDM systems over correlated fading channel, in the case of the channel being known at the receiver is considered in this paper and complexity analysis of LDPC based ST coded OFDM system is evaluated and studied.
Keywords:LDPC, OFDM, STBC.
The key challenge encountered in future broadband wireless communication systems is to provide high speed data-rate wireless access at high quality of service (QoS) through severe multipath propagation channels[1]-[3]. In recent years, the spatial dimension in a broadband wireless communication system has been explored by employing multiple transmit and/or receive antennas. This offers the following several advantages over the traditional single antenna system: Spatial multiplexing gain which leads to higher capacity. Diversity gain which leads to more reliability. The increasing demand for higher date rates requires transmission over a broadband channel which is frequencyselective [4]. As a result, inter-symbol interference (ISI) is The space time coding OFDM (STC-OFDM) system was proposed in [6]. The performance of OFDM systems using the Alamouti space time block code, which uses two transmit antennas and one receive antenna in its simplest form of (2 × 1 MISO channel) for the following reasons [7]: 1. The 2×1 Alamouti scheme offers full diversity gain of 2 without rate loss; 2. The Alamouti scheme is practically relevant. It has been included in various 3.5G/4G wireless communication standards such as 802.16-2005WiMAX and 3GPP LTE, where it is used in the downlink to allow for low complexity mobile terminals. 3. The Alamouti scheme does not require channel state information (CSI) at the transmitter. 4. The Alamouti scheme has a low complexity maximumlikelihood (ML) decoding algorithm and hence no dedicated feedback channel. Several research groups have been proposed low-density parity-check (LDPC) code design for high-order modulations on single-input single-output (SISO) channels to achieve spectral efficiency[8]-[12]. introduced, which severely degrades the system performance. On the other hand, the orthogonal frequency division multiplexing (OFDM) transforms a frequency-selective MISO channel into a set of parallel frequency-flat channel [5]. In this contribution, we design a low complexity transceiver structure for LDPC based STC –OFDM system. Compared with the general LDPC based STC-OFDM system, the proposed system can significantly achieve both spatial diversity and the selective fading diversity in wireless channels, better PAPR property and also exhibits lower transceiver complexity. More recently, in [13], the complexity reduction and performance of convolutional coded STBC- OFDM system in fading channels is investigated. Since the STBC based on LDPC codes turns out to be good candidate for higher order modulations to achieve spectral efficiency. Here, we study the realization of LDPC based MISO diversity for OFDM systems over correlated Rayleigh channel, assuming that the CSI is known only to the receiver. As a promising coding technique to approach the channel capacity, Alamouti like STC is employed as the channel code in this system. The goal of this paper is to provide a review of the basics of LDPC based STC-OFDM wireless system with a focus on transceiver design, implementation aspects. The remainder of this article is organized as follows. The next section contains a brief introduction into LDPC based STC-OFDM wireless systems. We have then discussed capacity, outage capacity and complexity analysis for the system. An analysis of LDPC based STC-OFDM wireless systems is followed by a summary of results on the computer simulation of LDPC based STC-OFDM wireless systems transceiver. Finally, a list of relevant open areas for further research is provided. 2.


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