Jung-In Baik

Adaptive cooperative communications with multiple antennas

Although multiple-input multiple-output antenna transmission is advantageous on orthogonal frequency division multiple access system, it may not be possible that practical systems have more than two antennas because of its size and cost. Therefore, cooperative communication has been recently studied as a way to solve this problem in a wireless environment. However, if cooperative communication system selects relay in a bad channel environment between source and relay, the relay has a bad effect on the bit error ratio performance. Thus, selective relay technique is proposed in this paper. The proposed system can select the best relay which has the best SNR between source and relay among the candidates. The proposed system also easily finds the best relay with low complexity.

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.

Design of MIMO-OFDM multi-hop relaying with cooperative base station

Basically, in cellular network systems, the relay station (RS) is used to increase the cell coverage of mobile stations (MS) at a cell edge. But, the system performance due to the use of RS is interfered by the neighboring cells and decreased by the low power of received signals, generally. In order to overcome these disadvantages and get a diversity gain or a high data rate, we design and propose the multiple-input multiple-output (MIMO) multi-hop relaying system structure using the BS cooperation scheme, and evaluate the performance of the proposed system in this letter. Therefore, the MSs can effectively receive the signals through the proposed design which uses the RS in the overlapping regions.

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.

A Channel Estimation and Data Transmission Scheme Utilizing Superposition Modulation for Cooperative Communication

In cooperative communication, the channel estimation is important because the channel influences the transmission signal. General channel estimation schemes are conducted before the information signal. But, the channel is time-varying, dynamic and unpredictable. To cope with a constantly changing channel, a new scheme is proposed. In the proposed scheme, the new transmission signal utilizing superposition modulation is used. The proposed transmission signal is superimposed to the pilot signal for the channel estimation and the information signal for the transmission of information signal. As a result, the proposed scheme has similar to the bit error rate performance and throughput compared to when the channel estimation perfectly is performed. By using the proposed transmission signal in cooperative communication, the proposed scheme can estimate the channel through information signal and transmit the information signal at the same time. Therefore, the proposed scheme can estimate the channel that passes information signal and transmit information signal at the same time.

Cooperative Transmission Scheme Using the Single Antenna in the Broadcasting and Cellular System

In this paper, the cellular system and broadcasting system use a cooperative transmission scheme. The conventional scheme is not consider the condition of a channel between a cellular base station (CBS) and a destination user. In this conventional scheme, two CBSs communicate with the user by the cooperative transmission scheme when the user is located in the cell edge. If CBS is distant from a user and the channel condition is poor, the performance of communication is degraded. The proposed scheme using the relay between CBS and the user located in the edge of CBSs improves the performance of the communication when the channel state between CBS and the user is bad. Also, space time block code and cyclic delay diversity scheme are used for the reliable transmission in the proposed scheme. The proposed scheme using the relay achieves good BER and throughput performance. Through the simulation, it is confirmed that the proposed scheme is better than the conventional scheme.

Cooperative Relaying Scheme for Orthogonal Frequency and Code Division Multiple Access Uplink System

Orthogonal frequency and code division multiplexing (OFCDM) which can be extended orthogonal frequency and code division multiple access (OFCDMA) has a good performance, because it can mitigate multi path interference while maintaining high data rate. Furthermore, cooperative OFCDM relaying system provides these advantages, and this system can effectively use the limited resource with respect to data rate and each terminal’s energy efficiency. Therefore we proposed cooperative OFCDMA relaying uplink system because of the user’s requirement of the high data rate at uplink. However, a throughput performance decreases when this system employs many relays in case of each relay allocated code channel to separate each relay’s signal. Therefore, in this paper, we present that the proposed system combines cyclic delay diversity due to complement throughput performance problem. DF (Decode-and-Forward) is assumed in this paper. It is considered that the users which want to send data to BS only decode the data from other users. In addition to that, we propose the adaptive cooperative communication for the OFCDMA uplink system. The proposed adaptive system can easily select the cooperative relay.

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.