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The aim of this paper proposes an orthogonal frequency-division multiplexing (OFDM) with network coding to improve the error performance of the system when the messages are transmitted from user to receiver. Two-way relay (TWR) networks are applied to reduce the transmission time slots. The exclusive-OR (XOR) coding is used for network coding in which source nodes exchange their information via TWR nodes. The XOR coded bits provides redundancy to achieve the transmit diversity gain which improves the error performance of the TWR network. OFDM is exploited for TWR to obtain the frequency selective fading nature of wireless channels. The different modulation schemes such as Quadrature Phase Shift Keying (QPSK), 16-Quadrature Amplitude Modulation (QAM) and 64-QAM with OFDM system are simulated and QPSK is selected as it gives the lowest bit error rate (BER). The multiple relaying schemes with different numbers of the information packets are also considered in this paper. Simulation results show that multiple relay schemes provide faster transmission time and better error rate performance. Moreover, different kinds of channel coding schemes such as Convolutional, Reed-Solomon (RS) and turbo codes are applied in OFDM system with network coding to compare and evaluate the BER performance of the proposed system. From the simulation results, network coded OFDM scheme with turbo codes give better BER performance for given Signal-to-Noise Ratio (SNR) in relaying scheme with different numbers of information packets compared to those of convolutional and RS codes. It shows that, the error rate performance and transmission time is reduced 10 percent than the conventional scheme at even at low SNR value.

The combination of Non-orthogonal Multiple Access (NOMA) and Multi-antenna Multi-input Multi-output (MIMO) approach has been considered as an assuring multiple access for fifth generation (5G) technology to improve the system network capacity and the efficiency of the spectrum. In this paper, we investigated a MIMO-NOMA based network code, exclusive-OR (XOR) scheme which applies physical layer network coding (PNC) in two-way relay networks to reduce the transmission time slots. The Quadrature Phase Shift Keying (QPSK) modulation technique is selected to apply to enable the data source transmitting with the carrier wave. In this paper, convolutional codes and the Soft Decision Viterbi algorithm is used to encode and decode the information bits. The coded MIMO-NOMA gives the less bit error rate compared to coded NOMA alone. Moreover, we have analyzed the spectral efficiency and energy efficiency in NOMA and MIMO-NOMA. The sum capacity and transmission rate are also compared in NOMA and MIMO-NOMA scheme. The simulation results show that MIMO-NOMA has higher spectral efficiency and faster transmission rate than NOMA scheme. Finally, the user fairness of MIMO-NOMA has been evaluated.

Orthogonal Frequency Division Multiplexing (OFDM) is one of the popular methods that used to transmit the data in high speed rate in cellular communication. However, OFDM has a high Peak to Average Power Ratio (PAPR) which caused by the non-linearity of the High Power Amplifier (HPA) that provides transmission power to the OFDM signal. The high PAPR caused the OFDM signal to be low in efficiency and giving a high bit error rate. Thus, in this paper, a method for PAPR reduction that caused by the HPA is proposed. Precoding technique is one of the popular way to compensate the bad impact of the HPA by reducing the PAPR of the signal. In this paper, the bad impact caused by the HPA model on the OFDM signal will be analyzed. Moreover, the PAPR of the OFDM signal by using precoding techniques will be compared with the PAPR of the OFDM signal without precoding technique. From the simulation results, it was found that the ZCT-OFDM has a better PAPR reduction compared to the DCT and WALSH technique. It was also found that the lower the order of modulation scheme is, the better the PAPR reduction performance for OFDM signal compared to higher order modulation scheme.

In this paper, MIMO system is used to improve the performance of transmitted signal by reducing the signal fading rate. MIMO VBLAST technique is implemented to enhance the spectral efficiency and bandwidth with spatial diversity. Multiple antennas allowed the system to transmit multiple same data signal at the same time in which the data will not fade simultaneously, hence, improving the Signal to Noise Ratio (SNR) of the system. Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) detection scheme are used to minimize the effect of channel estimation errors. The simulation was carried out in MATLAB software. Based on the simulation result, the proposed scheme for MIMO VBLAST has better network throughput in term of successful message delivery performance compared to the traditional scheme.

In this paper wireless communications network is considered to transmit source information to destination. N number sources transmitting data to a destination receiver, through M relays nodes by employing random linear network coding (RLNC). Two methods of failure decoding probability on performance of wireless communication are explained and discussed in this paper. The major parameter that will impact on the decoding probability of RLNC are quantity of relays, a finite field size, and erasure probability. The comparison of two old bounds method (Seong's approach) and new bounds method (from Khan's approach) is explored in this research. Simulation results, shows that new bounds method on probability of decoding failure having better simulation results compared to old bound method. It is also concluded that calculating the bounds of the decoding probability is an easy method to analyze failure decoding probability compared to Chiasserini's approach method which is based on network coded matrix.