Andre Gustavo Degraf Uchoa

Generalised Quasi-Cyclic LDPC codes based on Progressive Edge Growth Techniques for block fading channels

Generalised Quasi-Cyclic Root-Check LDPC codes based on Progressive Edge Growth (PEG) techniques for block-fading channels are proposed. The proposed Root-Check LDPC codes are suitable for channels under F= 3, 4 independent fadings per codeword which is a scenario that has not been previously considered. A generalised Quasi-Cyclic Root-Check structure is devised for F= 3, 4 independent fadings. The proposed PEG-based algorithm for generalised Quasi-Cyclic Root-Check LDPC codes takes into account the specific structure, and designs a parity-check matrix with a reduced number of cycles. The performance of the new codes is investigated in terms of the Frame Error Rate (FER). Numerical results show that the codes constructed by the proposed algorithm perform about 0.5dB from the theoretical limit.

LDPC codes based on Progressive Edge Growth techniques for block fading channels

We propose an algorithm to design Root-Check LDPC codes based on Progressive Edge Growth (PEG) techniques for block-fading channels. The proposed algorithm imposes some restrictions on the traditional PEG algorithm to ensure that the LDPC code generated is Root-Check with the largest possible girth. The performance is investigated by means of the outage probability. By doing so, the codes generated by our proposed algorithm are shown to outperform the existing methods for generating Root-Check LDPC codes.

Cooperative Coded Partial Retransmission scheme using Type-I HARQ and LDPC codes

In this paper we present a novel Hybrid Automatic Repeat reQuest (HARQ) scheme for cooperative communication systems, called Coded Partial Retransmission (CPR). The method is based on the retransmission of only a fraction of the original codeword by the cooperating nodes, applying an appropriate power allocation. Numerical results using LDPC codes and Type-I HARQ with Chase Combining show that CPR outperforms regular cooperative HARQ techniques considering both amplify-and-forward (AAF) and selective decode-and-forward (SDF) protocols. Additionally, we show that the CPR throughput, using a single relay, may be considerably larger than the throughput of some regular cooperative HARQ schemes using multiple relays.

A Three-Pass Protocol for Cryptography Based on Padding for Wireless Networks

This paper proposes an alternative cryptography protocol based on padding for wireless networks. It uses an orthogonal set of rotation matrices and a three-pass exchanging protocol to reach the encryption. The communicating parties do not need to know cryptographically nothing from each other in order to guarantee the communication privacy. The security of the algorithm is based on the continuous changing of the orthogonal matrix set used on the encryption process. The proposed protocol does not require any kind of keys pre- distribution. This feature is desirable for wireless ad hoc networks, where there is no predefined infrastructure, as required on classical secure channel encryption. The prototype shows that the proposal is feasible and can be advantageous when compared to One-Time Padding.

Iterative detection and decoding algorithms for block-fading channels using LDPC codes

We propose an Iterative Detection and Decoding (IDD) scheme with Low Density Parity Check (LDPC) codes for Multiple Input Multiple Output (MIMO) systems in block-fading receivers and fast fading Rayleigh channels. An IDD receiver with soft information processing that exploits the code structure and the behaviour of the log likelihood ratios (LLR)s is developed. Minimum Mean Square Error (MMSE) receivers with Successive Interference Cancellation (SIC) and with Parallel Interference Cancellation (PIC) schemes are considered. The soft a posteriori output of the decoder in a block-fading channel with Root-Check LDPC codes has allowed us to create a new strategy to improve the Bit Error Rate (BER) of a MIMO IDD scheme. The proposed strategy has resulted in up to 3dB of gain in terms of BER for block-fading channels and up to 1dB in fast fading channels.

Type-I HARQ scheme using LDPC codes and partial retransmissions for AWGN and quasi static fading channels

In this paper we present a Type-I HARQ scheme for low density parity check codes (LDPC) using partial retransmissions and diversity combining. The proposed method divides the retransmissions in equal length sub-packets, and applies a power compensation. We demonstrate that the new scheme outperforms, in terms of throughput, the typical diversity combining methods for AWGN and quasi static fading channels, considering BPSK and 16-QAM modulation. Both theoretical and simulation results are presented, with a very good agreement between them. The numerical results show that the gains in terms of throughput, with respect to the typical methods, can be as large as 5 dB.

Novel hybrid ARQ scheme using LDPC codes and partial retransmissions

The design of a novel HARQ scheme using LDPC codes, partial retransmissions, and diversity combining is presented. The theoretical throughput of the proposed scheme is estimated by means of EXIT charts. It is shown that the proposed method outperforms the classical equal gain combining (EGC) method while requiring few more overall decoding iterations. The transmission control protocol (TCP) performance when the proposed method is used in the physical layer is also investigated. Simulation results show that the gains with respect to the classical EGC scheme can be as large as 3.5 dB.

Performance of a Partial Retransmissions Hybrid ARQ Scheme in Rayleigh Block Fading Channels

We propose a partial retransmission (PR) scheme to be used in block fading channels. The proposed method sends only a fraction of the original transmitted codeword at each retransmission, and makes use of an appropriate power allocation and of symbol by symbol combining at the receiver. The performance is investigated by means of the outage probability and the throughput. The proposed PR scheme is shown to outperform both the incremental redundancy (IR) and Chase combining (CC) HARQ methods, for some signal to noise ratio values and for the scenarios considered in this paper.