Jee-Hoon Kim

Performance Improvement of Cooperative MB-OFDM System Based Coming Home Network

Since ultra wideband (UWB) system aims at low complexity, low cost, and low power consumption, employing multiple antennas seems not to be a good approach to improving error performance for UWB devices. On the contrary, recently developed cooperative diversity technique, which profits the transmit diversity only with the existing hardware by constituting a virtual antenna array, can be a solution. However, most of the introduced cooperative techniques have a common fault of decreased transmission rate because the destination should receive the decodable compositions of symbols from the source and the relay. In this paper, we propose an alternative use of hierarchical modulation and a suitable cooperative space-time block code (C-STBC). This technique is free from the rate-loss and allows seamless cooperative communication while similar diversity gain is benefited. The proposed technique is evaluated in terms of bit error rate (BER) for multi-band orthogonal frequency division multiplexing (MB-OFDM) system. Simulation results show that cooperative system based on our technique outperforms noncooperative one when relatively reliable source-to-relay link (S-R link) is guaranteed.

Efficient detection scheme in MIMO-OFDM for high speed wireless home network system

This paper proposes a MIMO-OFDM scheme reducing the computational complexity and providing comparable performance to QRD-M detection scheme in IEEE 802.11n. The proposed scheme checks the channel condition per subcarrier and then selects either ordered DFE scheme or adaptive QRD-M detection scheme according to that information. The post-detection SNR which judges channel condition depends on Moore-Penrose pseudo-inverse matrix G. The proposed scheme selects the ordered DFE detection scheme in case of good channel condition and the adaptive QRD-M detection scheme in case of bad channel condition per subcarrier. The adaptive QRDM detection scheme selects the number of variable survival symbols M in accordance with the channel condition at each layer. Compared with the conventional QRD-M (M=16) detection scheme, the proposed detection scheme reduces the computational complexity about 67 percents and achieves similar performance.

Cooperative Transmission Technique Using Space Time Delay Code in OFDMA Uplink System

Multiple antennas are used to an essential part in order to support high link quality in wireless communication systems. The diversity techniques with multiple antennas provide better reliability than existing systems. But these techniques generally require more than one antenna at the transmitter or receiver. So, the system with multiple antennas has several limitations including size, cost, hardware complexity, and antenna space. In this letter, we propose a cooperative transmission technique that uses space time delay code in OFDMA uplink system; DVB-RCT. The proposed technique overcomes these limitations and gives the diversity gain of cooperative transmission in a concept of virtual MIMO with single transmit antenna.

Cooperative OFDM system for high throughput in wireless personal area networks

Wireless Personal Area Networks (WPANs) is a promising application in future wireless communication. Multiple-input multiple-output - orthogonal frequency division multiplexing (MIMO-OFDM) systems have allowed the improvement of the system performance. However MIMOOFDM systems exist limitations of supporting high data rate and reliable transmission, as the size and cost of device become smaller and lower. Recently, cooperative OFDM systems are developed to be a solution. It makes that service providers supply both increased throughput and reliability. Although the performance of applications is developed, consumers still demand better performance. Therefore, we propose the novel cooperative OFDM system for high throughput with signal space diversity (SSD). Our proposed scheme adds the operation for rotation, superposition, and demodulation for the SSD signal on each user device before relaying. Simulation results show the throughput of our proposed cooperation scheme is increased by twice as compared with the conventional cooperative OFDM scheme.

Performance analysis of mutual decode-and-forward cooperative communication for OFDMA based mobile WiMAX system

A cooperative communication has been frequently studied because it provides reliability to the previous communication system without the addition of antenna. However, in a cooperative communication, the throughput of the communication system is decreased by half because each station cannot transmit own signal for relaying process. To overcome above limitation and provide more reliability, we propose and analyze the mutual decode-and-forward (DF) cooperative communication for orthogonal frequency-division multiple access (OFDMA) based mobile WiMAX system with single antenna in the Rayleigh fading channel environment. By adopting the proposed scheme, the performance of the mobile WiMAX system is improved in proportion as the quality of inter-user channel is increased.

MSE Performance Evaluation of Zero-Padded CAZAC Sequence for Reasonable Utilization

The classical 4-phase constant-amplitude zero-autocorrelation (CAZAC) sequence with the length of 16 has been used for multifarious purposes such as channel estimation and frequency/timing synchronizations since it presents good performance even in low signal to noise ratio (SNR) conditions. However, as multiple transmit antennas are employed, its properties are easily destroyed by the effect of multipath. In this letter, we propose a technique which ensures that the conventional CAZAC sequence is reliable in a multi-antenna system by inserting nulls. The performance of the modified sequence is verified through the mean s quare error (MSE) performance with the least squares (LS) method.

Cooperative Communication for High Diversity Gain with Single Antenna

Cooperative communication enables single antenna to realize a virtual multiple antenna by sharing their antennas. Therefore, it offers transmit diversity. In this letter, we apply pre-coding scheme to the transmit symbols. Although pre-coding has shortcomings, it is possible to employ Space-Time Block Codes (STBC) with single antenna and achieve high gain.

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.

Bandwidth- efficient space–time coded cooperation for resource-constrained networks

In cooperative transmission, cooperating nodes must hear the source messages first and forward it to the destination node with decodable composition of symbols. This restriction is one of big questions in cooperative networks since it decreases overall bandwidth-efficiency. In this paper, we propose a scheme which alleviates it through novel use of dual carrier modulation (DCM) and an adequately designed distributed space–time block code (DSTBC). The proposed scheme achieves comparable error performance to the conventional one while providing 20% higher transmission rate. The performance is always guaranteed by the signal-to-noise ratio (SNR) based adaptive cooperation algorithm. Copyright