In wireless communication, it is hard to set the optimal route between a source and a destination through relays, since for optimal relaying, the system operator should know all channel conditions from a source to a destination through relays and determine the path with all channel conditions. In this letter, a multiple relay selection strategy is proposed for the reliability of transmission. The proposed strategy establishes a relaying route to a destination and provides an efficient relay selection process regardless of all channel conditions.

The multiple-input multiple-output (MIMO)-Orthogonal frequency division multiplexing (OFDM) system has a serious drawback in that it has high peak-to-average power ratio (PAPR). Therefore, in this letter, we propose an effective PAPR reduction scheme for MIMO-OFDM systems with nonlinear high power amplifier (HPA). The proposed scheme very effectively reduces the PAPR through the adaptive nonlinear estimator (ANE) which estimates the MSE between the OFDM signals before and after the nonlinear HPA and the low probability of false side information (SI) by receive diversity.

Orthogonal frequency and code division multiplexing (OFCDM) is available as orthogonal frequency and code division multiple access (OFCDMA) by allocating subcarrier to users. OFCDMA is an efficient transmission method assigning the subcarrier and the channel code according to channel state or many different environments. However, OFCDMA is hard to apply many frequency spreading codes when it is compared with OFCDM because of the restrictive subcarriers. This problem leads to decrease the frequency diversity. Therefore we propose system that combines cyclic delay diversity (CDD) with cooperative relaying system based on OFCDMA. This system complements this restrict by spatial diversity. In addition to that, the proposed system obtains diversity gain without loss of the throughput when direct-path condition is not good.

This letter presents a successive partial interference cancellation (SPIC) scheme for full-duplex (FD) and multiple-input multiple-output (MIMO) relaying system. The proposed scheme coordinates the cancellation for the self-interference and inter-stream interference. The objective for the coordination focuses on simultaneously minimizing the two interferences. Simulation results under the measured data show that the system with the proposed scheme can achieve a significant performance gain compared to the conventional FD and half-duplex (HD) systems.

To improve the BER performance of the conventional cooperative communication, this letter proposes an efficient method for the reliability, and it uses hierarchical modulation that has both the high priority (HP) layer and the low priority (LP) layer. To compensate more reliable transmission, the proposed method uses the error correction capability of Reed-Solomon (RS) codes additionally. The simulation results show that the proposed method can transmit data more reliably than the basic RS coded decode-and-forward (DF) method.