Jin-Hyuk Song

New transmission scheme with hierarchical modulation in dual-hop wireless relaying systems

Dual-hop transmission is a technique by which the channel from the source to the destination is split into two possibly shorter links using other nodes. The source transmits signals to the destination via a group of nodes that act as relays. It is an effective technique when the direct link between the source and the destination is in deep fading, severe shadowing, or non-line-of-sight (NLOS) environment. In this network, the reliability of the communications is improved whereas the throughput might go down since the transmission is performed by two times. In this paper, we propose a scheme that uses hierarchical modulation at the source and selective modulation based on cyclic redundancy check (CRC) code at the relays. Simulation results show that our scheme outperforms conventional schemes in terms of the bit error rate (BER) and throughput performances.

Performance Improvement of Cooperative Relaying Scheme Based on OFCDM in UWB Channel

Orthogonal frequency and code division (OFCDM) provides a good performance on broadband or wide-band channel, because it can mitigate multi-path interference with keeping high data rate. So, this scheme is suitable to employ the future wireless communication system. And, Cooperative relaying scheme has been proposed to get the spatial diversity gains in multiuser wireless systems. Because, this scheme need no multiple antenna, it makes devices with low cost and small size. In this paper, we proposed the cooperative relaying scheme based on OFCDM. This system has profit of OFCDM and cooperative relaying schemes. It is also not much more complex than the single antenna OFCDM system. This scheme is appropriate to the next generation mobile wireless system, because of having both advantages. The performance of the proposed scheme is evaluated in terms of bit error rate (BER) performance for the OFCDM in the UWB channel.

A new cooperative communication for orthogonal frequency and code division multiple access

Orthogonal frequency and code division multiplexing (OFCDM) has been spotlighted as a next generation communication system. Cooperative OFCDM relaying system has advantages that provide the high reliability while maintaining high data rate because of getting the frequency diversity and the spatial diversity. However, this system decreases a throughput performance when it employs many relays. Therefore, in this letter, we present that the proposed system combines CDD due to complement throughput performance problem. In addition to that, the proposed system based on orthogonal frequency and code division multiple access (OFCDMA) which efficiently communicates each other through assigning the subcarrier and the channel code according to channel state or other environments.

Performance improvement of layered modulation based cooperative relaying scheme

Cooperative communication is a novel approach utilizing limited resources to get reliability. However, overall transmission-rate is reduced to have decomposable composition at the destination node in time-division multiple access (TDMA) system, which diminishes the advantage of cooperation. Recently, a novel use of layered modulation and an adequate cooperative space-time block code (C-STBC) were proposed to solve this drawback. Even though it provided certain level of diversity gain without transmission-rate loss, there is room for improvement. In this paper, we enhance it through the constellation modification and adaptive cooperation schemes. Their effectiveness is evaluated for the multi-band orthogonal frequency-division multiplexing (MB-OFDM) system.

A Simple Cooperative Cyclic Delay Diversity in Wireless Networks

Cyclic delay diversity (CDD) was introduced to obtain spatial diversity in multi-input multi-output (MIMO) system. In practice, terminals are difficult to have multiple antennas due to high cost or limited size. Accordingly, the cooperative scheme has recently emerged and given considerable attention. In this paper, CDD is incorporated into the wireless cooperative communication system, in which each terminal has single antenna. The proposed cooperative CDD scheme is compared with cooperative orthogonal space time block code (STBC). Cooperative CDD attains generally worse performance than cooperative STBC from orthogonal design, but cooperative CDD can be easily applied with an arbitrary number of relays and do not require additional complexity at both transmitter and receiver.

Cooperative transmission of modified quasi-orthogonal stbc with multiuser-ofdm

In this paper, we propose a modified quasi-orthogonal space-time block code that the decoder decouples the symbol detection problem into not pairs of transmitted symbols but each symbol. And then, it is applied to cooperative communication systems with 4 transmit antennas. Simulation results present the BER performances in cases of amplify-and-forward and decode-and-forward.