The Luby transform (LT) code is the first practical implementation of the digital fountain code, and its utilisation over a noisy channel invokes iterative decoding with soft information. For a good decoding performance, the role of the encoder degree distribution is vital. Especially, when utilising the soft iterative decoder, the bit error rate (BER) performance of the LT code can be improved by increasing the number of the degree‐1 encoding nodes and reducing the number of lower‐degree variable nodes. This study proposes an efficient LT‐code encoding algorithm that satisfies the conditions for improving the BER performance. The proposed scheme applies different priorities for selecting the neighbouring source nodes for given degrees of the encoding nodes. The simulation results demonstrate that the proposed scheme outperforms the existing schemes.

In order to achieve more efficient communication performances in vehicular ad hoc network (VANET) for road safety related message propagation, we propose a special nonbinary network coding scheme to improve the system reliability by reducing the outage probability of the communication system. Suppose all users in the network are provided with multiple antennas, which are responsible for message transmitting, relaying and receiving. Moreover, a cooperative phase is applied into the network. We analyze the exact expression of outage probability and give an approximation expression for calculating the outage probability over the Rayleigh fading channel. The simulation results indicate that the approximation expression has good performances on describing the exact expression.

Minimum mean square error (MMSE)‐based techniques are often used for the joint iterative detection and decoding that is for coded multi‐input–multi‐output (MIMO) system due to a sound complexity and the performance trade‐off. This study proposes an enhanced MMSE‐based soft MIMO‐detection scheme by using three main ideas. The first idea is an efficient complexity‐reduced soft‐bit estimation technique, the second one is a performance improvement method utilised inside the MMSE detection process, and the third one is a complexity‐reduced soft‐symbol estimation method for quadrature amplitude modulation. The proposed ideas enable the interference‐cancellation processes to be activated in parallel on each symbol layer, thereby reducing the processing time. The simulation results show that the proposed method efficiently contributes to the improvement of the performance in addition to its reduction of the linear‐order complexity.

This paper proposes soft bit estimation methods for high-order amplitude and phase shift keying (APSK) schemes defined in the DVB-S2X system. The proposed method first maps the detected symbol to a limited range in a recursive manner, so that the search ranges to find a symbol with the minimum distances can be greatly reduced. Subsequently, amplitude of the detected symbol automatically determines a single symbol to estimate the distance. We present the proposed soft bit estimation methods for 256- and 16+16+16+16-APSK schemes, and the simulation results demonstrate that the proposed methods produce almost the same performance as the full search method, with only one distance estimation per bit.

In this study, the authors propose an efficient universal soft demodulation method for M ‐ary phase shift keying (PSK) and quadrature amplitude modulation (QAM) schemes. The proposed method achieves the same performance as the Max‐log method with much lower, linear‐order complexity. The proposed demodulator recursively maps the detected symbol to a specific region in the first quadrant, so that finally there is only one constellation symbol left in the region, and thus it requires approximately one distance estimation per bit. The authors first derive the equations to estimate soft decision bit information for a few well‐known M ‐ary PSK and QAM schemes, and subsequently present compact universal equations applicable to any M ‐ary PSK and QAM schemes, respectively. The simulation results reveal that the proposed method produces exactly the same performance as the Max‐log method with greatly reduced computational complexity.

Raptor codes are a class of rateless codes that were originally designed for binary erasure channels. To enhance their performance, multiple soft iterative loops can be employed in the decoder. In this study, the authors propose a method to construct modified Tanner graphs for systematic raptor codes in order to increase the efficiency of soft decoding. A modified Tanner graph is drawn in terms of bit and check nodes for each component code, instead of encoding and information nodes, as in conventional Tanner graphs, for its component Luby transform codes. This modified Tanner graph enables the use of a more simplified soft iterative decoding algorithm and provides improved decoding performance compared with the conventional method. In addition, they propose an efficient joint iterative soft decoding method with a parallel process to speed up the iterative decoding. The simulation results in this study reveal that the modified Tanner graph works better than the conventional Tanner graph for joint iterative decoding, and that the proposed parallel decoding method can contribute to further enhance the performance as well as the decoding speed by reducing the average number of iterations.

In this study, the authors propose a compact soft demodulation method for M ‐ary modulation schemes defined in the Digital Video Broadcasting via Satellite – Second Generation (DVB‐S2) system. They first derive a conventional soft demodulation method for quadrature phase shift keying and 8‐ary phase shift keying with a linear order of complexity, and apply this to the modulation schemes defined in DVB‐S2. In particular, they propose a new constellation for 32‐ary amplitude and phase shift keying (32‐APSK), which provides better performance, regardless of the soft demodulation scheme. In addition, the proposed constellation enables us to apply a very simple and efficient soft demodulation method. The proposed soft demodulation method estimates the soft information by simple distance calculation, and greatly reduces the computational complexity, compared with maximum‐log‐likelihood detection. They demonstrate the bit error rate (BER) performance of various soft demodulation methods, combined with the low density parity check codes specified in DVB‐S2. The BER simulation results reveal that the proposed constellation for 32‐APSK can achieve better performance than the conventional one, regardless of the soft demodulation method. In addition, the proposed soft demodulation method can highly reduce the computational complexity, with reasonable performance degradation.

In this paper, we present a very simple soft demapping algorithm for M-ary PSK and QAM schemes and their universal implementation for adaptive modulation systems. The proposed scheme estimates soft bit information contained in a symbol, with complexity that increases linearly, with modulation order, and achieves approximating performance to maximum likelihood detection. In addition, universal implementation of any M order modulation enables simple single hardware implementation of a demodulator in adaptive systems employing multiple modulation orders.

Excellent performance of turbo codes approximating to the Shannon limit should be conditioned on a large codeword length which inherently requires very long trellis. There have been a number of parallel decoding algorithms in order to accelerate the decoding speed. In these algorithms, the long trellis was partitioned into a number of shorter sub-trellises so that the the parallel search along the partitioned the sub-trellises can be performed. This trellis partition usually show performance degradation. In this paper, we propose an efficient parallel decoding algorithm for double binary turbo codes. The simulation results investigated in this paper reveal that the proposed scheme speed up the decoding time almost 4 times compared to the conventional full trellis searching method with negligible performance degradation, for various code rates and codeword lengths.

In this paper, we propose a new dynamic rain attenuation model using a Markov process. We derive statistical properties of the rain attenuation data measured in second time interval in Korea and define four states in the Markov process. We synthesize the rain attenuation data using 4-state Markov process, and compare statistical properties of the simulated data to those of the measured data. The investigated results in this paper show that the statistical properties of the synthesized data are well matched to the measured one.