The IUP Journal of Electrical and Electronics Engineering
Two Efficient Schemes for Providing Feedback Connection to Recursive Convolution Encoder

Article Details
Pub. Date : Jan, 2019
Product Name : The IUP Journal of Electrical and Electronics Engineering
Product Type : Article
Product Code : IJEEE21901
Author Name : Simmi Garg, Anuj Kumar Sharma and Anand Kumar Tyagi
Availability : YES
Subject/Domain : Management
Download Format : PDF Format
No. of Pages : 16

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Abstract

Convolution codes are widely used error correction codes in wireless communication systems. In recursive non-systematic codes, the output of the encoder is more dependent on the previous input bits. Hence, the weight factor of the coded data increases that lead to improvement in the performance of the transmission system. The paper proposes two schemes for making the feedback connections to the recursive convolution encoder. Using these schemes, different feedback connections can be provided to the encoder for improving the performance of the system. The first scheme implements a tri-state buffer with synchronous counters in the feedback connection, and in the second scheme, a negative feedback is provided to the encoder using a NOT gate. Simulations are done using MATLAB software. The two schemes are studied using 16, 32 QAM and 16 PSK modulation schemes over AWGN channel. The results show that the first scheme leads to decrease in the Bit Error Rate (BER) as compared to conventional scheme, and the second scheme has been able to achieve the performance of conventional system.


Description

The main aim of the current wireless communication system is to improve the reliability of transmitted data without much increasing the complexity of the system. During the transmission of the signal through communication channel, the data gets distorted due to many factors. Distortion of the signal is worst in case of wireless communication (Moreire and Farrell, 2006). Multipath fading, noise and Doppler shift are some of the major challenges that have to be faced. Because of these factors, the performance of the signal is degraded to a large extent (Hara and Prasad, 2003). The errors corrupted in the received signal must be corrected before the final reception of the data (Goldsmith, 2005). To develop the consistency of the transmitted data, error detection and correction is the only way out. Error detection and correction is a scheme, in which data is sent in the form of codes and decoded at the receiver side (Engels, 2002). There are mainly two types of Error Detection and Correction (EDAC): Automatic Repeat Request (ARQ) and Forward Error Correction (FEC). In ARQ, the receiver sends an acknowledgment for each received data bits (Hamming, 1950). If receiver sends negative acknowledgment, the sender resends the corrupted bits again (Lin et al., 1984). Although this method is not suitable for the noisy channels. FEC is a scheme in which extra bits are sent along with the original data bits (Singh and Kumar, 2012). These extra bits are used for detection and correction of the corrupted bits. Since FEC codes correct the error bits at the receiver side, there is no need of retransmission of the data bits (Chen, 2011). Consequently, these codes are more economical, especially for the case of noisy channels. There are various EDAC codes designed till date. Low density parity check codes (MacKay and Neal, 1996; and Lu et al., 2002), turbo codes (Blakert et al., 1995; and Berrou and Glavieux, 1996) and cyclic redundancy code (Koopman and Chakravarty, 2004) are the most popular ones. Convolution codes are also widely used for coding the input data and correcting the errors at the receiver side (Divya and Kumar, 2016). Convolution encoder consists of shift registers and modulo-2 adder. Initially, the encoder is in 00 state. When input bits are sent, then modulo-2 adder performs its function and output bits are generated. After this, bits are shifted sequentially to obtain output bits or code word for the input bits (Malvino and Leach, 1975). Convolution encoder can be recursive or non-recursive in nature (Katsiotis et al., 2010). Non-recursive encoder is the encoder with no feedback connection (Kim, 2000), while the recursive encoder is obtained from the non-recursive encoder by feeding back its output to its input. Since the weight factor is more for recursive encoded data bits, it leads to improvement in its performance (Jain, 2003).


Keywords

Error Detection and Correction (EDAC), Automatic Repeat Request (ARQ), Forward Error Correction (FEC), Non-recursive convolution codes, Recursive convolution codes

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