Browsing by Subject "Union bound"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Open Access On polarization adjusted convolutional codes over fading and additive white Gaussian noise channels(Bilkent University, 2022-05) Seyedmasoumian Charandabi, Seyed SadraUltra-reliable and low-latency communications (URLLC), which focuses on delay sensitive applications and services, is one of the three main pillars of 5G New Radio (NR) network architecture. URLLC's physical layer design is challenging since it must meet two contradictory requirements: ultra-low latency and ultra-high reliability. Short packets are used to minimize latency but at the cost of a significant loss of coding gain. Alternatively, system bandwidth can be increased, which is not always practical, particularly for some URLLC applications in industrial control that use unlicensed spectrum. In order to improve reliability, we must utilize robust channel codes in conjunction with retransmission techniques. Therefore, the construction of block codes with short blocklengths (e.g., a thousand or less information bits) is receiving significant attention with emerging wireless communications applications. In this thesis, we review existing channel coding bounds with short blocklengths for both additive white Gaussian noise (AWGN) and block fading channels. Furthermore, we investigate the performances of tail-biting convolutional, polar, and polarization adjusted convolutional (PAC) codes. With the motivation of reducing the decoding complexity of PAC decoders, we implement an alternative sequential decoding algorithm, namely, creeper algorithm, and describe a simplified list decoding approach. We also conduct an investigation on the performance of PAC codes and channel coding limits for block fading channels. Furthermore, we derive a method for computing approximate weight distribution of PAC codes, which can be used for an accurate performance bound; and, employing this approximation, we design PAC codes utilizing simulated annealing for optimization of the rate profiles. The results show that the newly designed PAC code rate profiles offer superior performance.Item Open Access Performance analysis of concatenated coding schemes(Bilkent University, 1999) Akkor, GünIn this thesis we concentrate on finding tight upperbounds on the output error rate of concatenated coding systems with binary convolutional inner codes and Reed-Solomon outer codes. Performance of such a system can be estimated by first calculating the error rate of the inner code and then by evaluating the outer code performance. Two new methods are proposed to improve the classical union bound on convolutional codes. The methods provide better error estimates in the low signal-to-noise ratio (SNR) region where the union bound increases abruptly. An ideally-interleaved system performance is evaluated based on the convolutional code bit error rate estimates. Results show that having better estimates for the inner code performance improves the estimates on the overall system performance. For the analysis of a non-interleaved system, a new model based on a Markov Chain representation of the system is proposed. For this purpose, distribution of errors between the inner and outer decoding stages is obtained through simulation. Markov Chain parameters are determined from the error distribution and output error rate is obtained by analyzing the behavior of the model. The model estimates the actual behavior over a considerable SNR range. Extensive computer simulations are run to evaluate the accuracy of these methods.Item Open Access Short block length code design for interference channels(IEEE, 2016) Sharifi, S.; Dabirnia, Mehdi; Tanç, A. K.; Duman, Tolga M.We focus on short block length code design for Gaussian interference channels (GICs) using trellis-based codes. We employ two different decoding techniques at the receiver side, namely, joint maximum likelihood (JML) decoding and single user (SU) minimum distance decoding. For different interference levels (strong and weak) and decoding strategies, we derive error-rate bounds to evaluate the code performance. We utilize the derived bounds in code design and provide several numerical examples for both strong and weak interference cases. We show that under the JML decoding, the newly designed codes offer significant improvements over the alternatives of optimal point-to-point (P2P) trellis-based codes and off-the-shelf low density parity check (LDPC) codes with the same block lengths.