KyungHi Chang

A Novel Transmit Power Allocation Algorithm Combined with Dynamic Channel Allocation in Reuse Partitioning-based OFDMA/FDD System

This paper introduces a reuse partitioning-based dynamic channel allocation algorithm that guarantees quality of service (QoS) by considering fairness among mobile stations in an OFDMA/FDD system. To improve the SINR values for users around the cell edge and increase the overall system throughput compared with the conventional OFDMA/FDD system of frequency reuse factor (FRF) 1, an effective transmit power allocation algorithm is also combined with the proposed dynamic channel allocation to adjust the transmit power per user according to the average received SINR value. Simulation results show that the proposed DCA algorithm increases the sector throughput by about 25% when compared with the conventional case that do not apply the proposed DCA algorithm. When the proposed transmit power allocation algorithm is combined with the proposed DCA algorithm, a further increase in the sector throughput of about 6% is achieved than when using just the proposed DCA algorithm.

Design of radio transmission technologies for VHF band ship ad-hoc network

For the purpose of providing high data rate real-time services, radio transmission technologies for ship ad-hoc network are designed in this paper. Based on the Recommendation ITU-R 1842–1, physical layer parameters of SANET are contrived to meet the requirements of that specification. Furthermore, the multi-hop frame structure for SANET is proposed and the link-level system performances are evaluated based on the designed parameters. Under the measured maritime channel environment, simulation results show not only the BER comparisons, but also the optimal MCS level for single carrier SANET with the bandwidth of 25 kHz.

On transmit antenna selection for multiuser MIMO systems with dirty paper coding

In this paper, we address the transmit antenna selection in multi-user MIMO systems with precoding. The optimum and reduced complexity sub-optimum antenna selection algorithms are introduced. QR-decomposition (QRD) based antenna selection is investigated and the reason behind its sub-optimality is analytically derived. We introduce the conventional QRD-based algorithm and propose an efficient QRD-based transmit antenna scheme (maxR) that is both implementation and performance efficient. Moreover, we derive explicit formulae for the computational complexities of the aforementioned algorithms. Simulation results and analysis demonstrate that the proposed maxR algorithm requires only 1% of the computational efforts required by the optimal algorithm for a degradation of 1dB and 0.1dB in the case of linear zero-forcing and Tomlinson-Harashima precoding schemes, respectively.

On the achievable improvement by the linear minimum mean square error detector

Linear minimum mean square error (MMSE) detector has been shown to alleviate the noise amplification problem, resulting in the conventional zero-forcing (ZF) detector. In this paper, we analyze the performance improvement by the MMSE detector in terms of the condition number of its filtering matrix, and in terms of the post-precessing signal to noise ratio (SNR) improvement. To this end, we derive explicit formulas for the condition numbers of the filtering matrices and the post-processing SNRs. Analytical and simulation results demonstrate that the improvement achieved by the MMSE detector over the ZF detector is not only dependent on the noise variance and the condition number of the channel matrix, but also on how close the smallest singular values are to the noise variance.

Complexity optimized CP length pre-decision metric for cell searcher in the downlink of 3GPP LTE system

In the downlink of 3GPP LTE system, primary synchronization signal (PSS) and secondary synchronization signal (SSS) sequences are used for initial cell search and synchronization. The user equipment (UE) detects slot timing, frequency offset, and cell ID by PSS in the time domain. After Fast Fourier Transform (FFT), it detects frame timing, cell group ID, and cyclic prefix (CP) length by using SSS in the frequency domain. But in 3GPP LTE system, there are two kinds of CP length, so we operate FFT twice with different CP length. In this paper, we propose a CP length pre-decision metric which is able to reduce the arithmetic complexity by half at most, with negligible performance degradation.

Effective adaptive transmit power allocation algorithm considering dynamic channel allocation in reuse partitioning-based OFDMA system

This paper introduces an transmit power allocation (TPA) algorithm considering dynamic channel allocation (DCA) for a reuse-partitioning- based Orthogonal frequency division multiple access (OFDMA)/FDD cellular system. The proposed reuse partitioning-based DCA algorithm guarantees quality of service (QoS) by considering fairness among mobile stations in an OFDMA/FDD system. However, to improve the SINR values for users around the cell edge and increase the overall system throughput compared with the conventional OFDMA/FDD system of frequency reuse factor (FRF) 1, an effective TPA algorithm is also combined with the proposed DCA to adjust the transmit power per user according to the average received SINR value. Simulation results show that the proposed DCA algorithm increases the sector throughput by about 25% when compared with the conventional case that do not apply the proposed DCA algorithm. When the proposed TPA is combined with the proposed DCA algorithm, a further increase in the sector throughput of about 6% is achieved than when using just the proposed DCA algorithm.

Closed-Form Solution of Outage Capacity for Cooperative DF and AF Relay Network

Cooperative relaying permits one or more relays to transmit a signal from the source to the destination, thereby increasing network coverage and spectral efficiency. The performance of cooperative relaying is often measured as outage probability. However, appropriate measure for the channel quality is outage capacity. Although the outage probability for cooperative relaying protocol has been analyzed before, very little research has been addressed for the outage capacity. This paper is the first of its kind to derive a closed-form analytical solution of outage capacity using fixed decode and forward relaying and amplify and forward relaying in independent but non identically distributed (i.n.i.d.) Rayleigh fading channels, considering channel coefficients known to the receiver side. The analytical results show a tradeoff between the SNR and the number of relays for a specific outage capacity. A comparison between decode and forward relaying and amplify and forward relaying shows that decode and forward relaying outperforms amplify and forward relaying for a large number of relays.

ISO/IEC 18000-7 based on RFID multi-hop relay system

In this paper, we analyze the ISO/IEC 18000-7 active RFID system. In order to improve the coverage in sensor networks, which includes a large number of active RFID tags, we propose RFID multi-hop relay system using active RFID relay tags. To compare the performance of the existing ISO/IEC 18000-7 with that of the proposed RFID multi-hop relay system, we introduce new system efficiency and sensitivity-based measures of the achieved coverage. Also, we analyze the performance of the proposed system and compare it with that of the existing system through the analyses of minimum coupling loss (MCL) and system level simulation (SLS).

Wavelet-based multi-carrier CDMA for personal communications systems

Based on the properties of wavelet orthogonal basis, three novel wavelet-based multi-carrier CDMA (MC-CDMA) systems are proposed, and their advantages and performances are investigated by the comparison with the conventional MC-CDMA systems. For the additive white Gaussian noise (AWGN) channel, all three wavelet-based MC-CDMA systems possess the same bit error rates as the corresponding MC/BPSK-CDMA and MC/QPSK-CDMA systems, but have significant higher bandwidth efficiency than the conventional MC-CDMA systems by the suitable choice of wavelet functions. Their potential applications in the broadband wireless communications to improve bandwidth efficiency and combat the fading and narrowband interference are also discussed.

Performance and complexity evaluation of pilot-based channel estimation algorithms for 3GPP LTE downlink

Several pilot-based channel estimation algorithms for 3GPP LTE downlink are tested under multipath Rayleigh fading channel in this paper. The conventional channel estimation techniques, such as two dimensional (2-D) wiener filter, two 1-dimensional wiener filters (2×1)-D and maximum likelihood estimator (MLE) are applied first. Considering the practical implementation, we propose to estimate channel by combining time-dimension wiener filter and MLE, which shows a good tradeoff between system performance and complexity. The complexities of these algorithms are calculated in terms of the number of complex multiplications (CMs) and the performances are evaluated by showing the uncoded bit error rates (BER).