New 2-D interleaving grouping LBC applied on image transmission

The modern technologies of the image transmission look for ultra-reducing of the error transmission in addition to enhancing the security over a wireless communication channel. This paper is applied and discussed two different techniques to achieve these requirements, which are linear block code (LBC) and two-dimensions (2-D) interleaving approach. We investigate a new approach of 2-D interleaving that increases the security of the image transmission and helps to diminution the bit error probability (BER). Using an investigated 2-D interleaving grouping LBC approach on image transmission, the system achieves a higher-security information and a better BER comparing with the other systems. It was done by means of peak signal to noise ratio (PSNR) and histogram analysis tests. Simulation results state these enhancements

Low complexity hardware interleaver for MIMO-OFDM based wireless LAN

Abstract-A low complexity hardware interleaver architecture is presented for MIMO-OFDM based Wireless LAN e.g. 802.11n. Novelty of the presented architecture is twofold; 1) Flexibility to choose interleaver implementation with different modulation scheme and different size for different spatial streams in a multi antenna system, 2) Complexity to compute on the fly interleaver address is reduce by using recursion and is supported by mathematical formulation. The proposed interleaver architecture is implemented on 65nm CMOS process and it consumes 0.035 mm 2 area. The proposed architecture supports high speed communication with maximum throughput of 900 Mbps at a clock rate of 225 MHz

Evaluation of Channel Coding in OFDM Systems

Channel coding plays a very important role in OFDM systems performance. The structure of OFDM systems makes channel coding more effective in confronting fading channels. Sometimes Coded OFDM is known as COFDM. The role of channel coding in conjunction with frequency and time interleaving is to provide a link between bits transmitted on separated carriers of the signal spectrum, in such a way that the information conveyed by faded carriers can be reconstructed in the receiver. Frequency selectivity, currently known to be a disadvantage, is then turned into an advantage that can be called frequency diversity. Using Channel State Information (CSI), channel coding can yield some additional gain. Channel state information is frequency response of the channel or signal to noise ratio in each carrier. This thesis analyzes OFDM system and the effect of channel coding in reducing BER. Along with this soft decoding and decoding with CSI is also studied. Besides, performance of convolutional codes Turbo codes in OFDM systems is compared and compared. Besides, we compare the performance of convolution and turbo codes in OFDM systems. The results have been validated through simulations. This thesis also presents Space-Frequency Coded OFDM system consisting of two transmitters and a single receiver. Simple Alamouti space time code is used. An Mary PSK modulation is used to modulate the symbols across an OFDM channel. We also proposed a variation of the scheme which tries to spread additional symbols across timefrequency attempting to increase the rate of transmission without changing the type of modulation employed or increasing the bandwidth. A Rayleigh frequency selective slow fading channel is assumed through out the analysis. SER performance of the above systems is carried out with emphasis on the modulation scheme and number of carriers

Analysis of coded OFDM system over frequency-selective fading channels

This thesis considers the analysis of system performance and resource allocation for a coded OFDM system over frequency selective fading channels. Due to the inseparable role taken by channel coding in a coded OFDM system, an information theoretical analysis is carried out and taken as the basis for the system performance and throughput. Based on the results of the information theoretical analysis, the optimal system BER performance of a coded OFDM system is first shown to converge to the outage probability for large OFDM block lengths. Instead of evaluating the outage probability numerically, we provide in this thesis a simple analytical closed form approximation of the outage probability for a coded OFDM system over frequency selective quasi-static fading channels. Simulation results of the turbo-coded OFDM systems further confirm the approximation of the outage probability. By taking the instantaneous channel capacity as the analytical building block, system throughput of a coded OFDM system is then provided. With the aim to compare the performance difference between adaptive and uniform resource allocation strategies, the system throughput of different allocation schemes under various channel conditions is analyzed. First, it is demonstrated that adaptive power allocation over OFDM sub-carriers at the transmitter achieves very little gain in terms of throughput over a uniform power distribution scheme. Theoretical analysis is then provided of the throughput increase of adaptive-rate schemes compared with fixed-rate schemes under various situations. Two practical OFDM systems implementing rate-compatible-punctured-turbo-code-based (RCPT-based) hybrid automatic-repeat-request (Hybrid-ARQ) and redundancy incremental Hybrid-ARQ protocols are also provided to verify the analytical results

Block Turbo Code and its Application to OFDM for Wireless Local Area Network

To overcome multipath fading and Inter symbol Interference (ISI), in convolutional single carrier systems equalizers are used. But it increases the system complexity. Another approach is to use a multicarrier modulation technique such as OFDM, where the data stream to be transmitted is divided into several lower rate data streams each being modulated on a subcarrier. To avoid ISI, a small interval, known as the guard time interval, is inserted into OFDM symbols. The length of the guard time interval is chosen to exceed the channel delay spread. Therefore, OFDM can combat the multipath fading and eliminate ISI almost completely. The another problem is the reduction of the error rate in transmitting digital data. For that we use error correcting Codes in the design of digital transmission systems. Turbo Codes have been widely considered to be the most powerful error control code of practical importance. Turbo codes can be achieved by serial or parallel concatenation of two (or more) codes called the constituent codes. The constituent codes can be either block codes or convolutional codes. Currently, most of the work on turbo codes have essentially focused on Convolutional Turbo Code (CTC)s and Block Turbo Code (BTC)s have been partially neglected. Yet, the BTC solution is more attractive for a wide range of applications. In this paper, Block Turbo Codes or Turbo Product Codes are used which is similar to the IEEE 802.11a WLAN standard. In this thesis work simple explanation of BTCOFDM theory is given. The BER performance is evaluated for the Block Turbo coded BPSK and QPSK OFDM system, under both AWGN channel and Rayleigh fading channel. It also compares the BER performance of Block Turbo coded OFDM with the uncoded OFDM. It is verified in the present work that the BTCOFDM system with 4 iterations is sufficient to provide a good BER performance. Additional number of iterations does not show noticeable difference. The simulation results shows that the BTCOFDM system achieves large coding gain with lower BER performance and reduced decoding iterations, therefore offering higher data rate in wireless mobile communications