• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.13 no.10
• /
• pp.2197-2204
• /
• 2009

In this paper, we analyze the performance of the sphere decoding algorithm at MIMO system. The BER performance of this algorithm is the same as that of ML receiver, but computational complexity of SD algorithm is much less than that of ML receiver. The independent signals from each transmit antennas are modulated by using the QPSK and 16QAM modulation in the richly scattered Rayleigh flat-fading channel. The received signals from each receivers is independently detected by the receiver using Fincke & Pohst SD algorithm, and the BER output of the algorithm is compared with those of ZF, MMSE, SIC, and ML receivers. We also investigate the Viterbo & Boutros SD algorithm which is the modified SD algorithm, and the BER performance and the floting point operations of the algorithms are comparatively studied.

• Journal of Internet Computing and Services
• /
• v.4 no.5
• /
• pp.1-9
• /
• 2003

In this paper, we combine AMC (Adaptive Modulation and Coding) with MIMO (Multiple Input Multiple Output) multiplexing to improve the throughput performance of AMC in Next Generation Communication Mobile Systems. In addition, we propose a system that adopts STD (Selection Transmit Diversity) in the combined system. The received SNR (Signal to Noise Ratio) is improved by adopting STD techniques and an improved SNR increases a probability of selecting MCS (Modulation and Coding Scheme) level that supports higher data rate. The computer simulation is performed in flat Rayleigh fading channel. The results show that higher throughput is achieved by AMC-TD schemes. AMC-STTD scheme shows about 250kbps increase in throughput. And AMC-STD with 2 transmit antennas achieves about 420 kbps throughput improvement over the conventional AMC at 9dB SNR.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.26 no.9
• /
• pp.1340-1346
• /
• 2022

In this paper, we consider a downlink non-orthogonal multiple access (NOMA) using multiple transmit antennas, where the transmit antenna selection scheme is used to reduce the system complexity. Thus, in this paper, we propose radio resource allocation and receiver selection schemes in order to improve the outage probability performance of the downlink NOMA system using the transmit antenna selection scheme. In particular, the receiver selection scheme is a method of grouping the receivers to improve the outage probability performance, and the radio resource allocation scheme is a method of allocating radio resources to each group in order to enhance the outage probability performance. In addition, through the computer simulation under the assumption of independent Rayleigh fading channels, we show that the proposed radio resource allocation and receiver selection schemes can improve the outage probability performance at the expense of the sum rate performance.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.7 no.4
• /
• pp.632-650
• /
• 2013

The paper considers a spectrum sharing cognitive radio (CR) network coexisting with a primary network under the average interference power constraint. In particular, the secondary user (SU) is assumed to carry delay-sensitive services and thus shall satisfy a given delay quality-of-service (QoS) constraint. The secondary receiver is also assumed to be equipped with multiple antennas to perform maximal ratio combining (MRC) to enhance SU performance. We investigate the effective capacity of the SU with MRC diversity under aforementioned constraints in Nakagami fading environments. Particularly, we derive the optimal power allocation to achieve the maximum effective capacity of the SU, and further derive the effective capacity in closed-form. In addition, we further obtain the closed-form expressions for the effective capacities under three widely used power and rate adaptive transmission schemes, namely, optimal simultaneous power and rate adaptation (opra), truncated channel inversion with fixed rate (tifr) and channel inversion with fixed rate without truncation (cifr). Numerical results supported by simulations are presented to consolidate our studies. The impacts on the effective capacity of various system parameters such as the number of antennas, the average interference power constraint and the delay QoS constraint are investigated in detail. It is shown that MRC diversity can significantly improve the effective capacity of the SU especially for cifr transmission scheme.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.8C
• /
• pp.767-774
• /
• 2007

A new transmit antenna selection and shuffling($AS^2$) method for spatially correlated double space time transmit diversity(DSTTD) systems is proposed. The proposed method allows dumb antennas and the superposition of multiple signals at the same transmit antenna, whereas the conventional methods consider the antenna shuffling(AS) only. According to the simulation result, the proposed method provides a 1.8 dB signal-to-noise ratio(SNR) gain over the conventional methods for spatially correlated transmit antennas. Although the number of candidates for $AS^2$ is much higher than that of AS, it is found that the number of candidates for $AS^2$ can be reduced to 36 by using the characteristics and properties of preprocessing matrices, and among them, only 6 candidates are almost always chosen. Next, we empirically compare the bit-error-rate (BER) performance of the proposed method with the conventional spatial multiplexing(SM) technique with antenna selection. Simulation results show that the proposed method outperforms the SM technique.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.2C
• /
• pp.247-254
• /
• 2004

We introduce a new space-time signal processing scheme that uses both transmitter diversity technique and transmitter beamforming technique for code-division multiple access (CDMA) systems. Over complex Gaussian Rayleigh channel, the introduced scheme achieves the diveristy gain through the transmitter diversity technique. and the SNR gain by th transmitter beamforming technique. Bit error rate (BER) analyses are given to each of the three cases in which the transmitter diversity scheme, the transmitter beamforming scheme and the introduced scheme are used, in the slowly varying Rayleigh frequency nonselective fading channel. The Monte-Carlo simulation results are shown to match to the analytic results. When the channels between distant antennas are independent, analytic results show that the introduced scheme achieves the lowest $E_{b/}$ $N_{0}$ at target BER 10$^{-6}$ . When the channels between distant antennas are correlated, analytic and simulation results show that the introduced scheme is more robust to the change of channel correlation.n.

• Journal of Satellite, Information and Communications
• /
• v.6 no.2
• /
• pp.20-25
• /
• 2011

The authors have proposed novel TDD-CDMA systems with Pre-Rake transmit diversity schemes (system 1 and system 2) using multiple transmit antennas in [2] and have also evaluated the system performance through the theoretical analysis and computer simulation. However, the performance of system 2 which transmit a signal using all antennas has not been evaluated for multi-user environment. Therefore in this paper, we analyze the performance of system 2 for multi-user environment and compare the performance with that of the already proposed system 1 which chooses only one antenna. From the numerical results, it is found that system 2 outperforms system 1 as the number of users increases while system 1 outperforms system 2 at a small number of users. Therefore in order to achieve the best system performance, the Pre-Rake transmit diversity type should be selected at the base station according to the number of users.

• Journal of Navigation and Port Research
• /
• v.27 no.4
• /
• pp.465-469
• /
• 2003

It has well known that MUSIC and ESPRIT algorithms estimate angle of arrival(AOA) with high resolution by eigenvalue decomposition of the covariance matrix which were obtained from the array antennas, However, the disadvantage of MUSIC and ESPRIT is that they are computationally ineffective, and then they are difficult to implement in real time. the other problem of MUSIC and ESPRIT is to require calibrated antennas with uniform features, and are sensitive ti the manufacturing fault and other physical uncertainties. To overcome these disadvantages, several method using neural model have been study. For multiple signals, those methods require huge training data prior to AOA estimation. This paper proposes the algorithm for AOA estimation by interconnected Hopfield neural model. Computer simulations show the validity of the proposed algorithm. It follows that the proposed method yields better AOA estimates than MUSIC. Moreover, out method does not require huge training procedure and only assigns interconnected coefficients to the neural network prior to AOA estimation.

• Journal of Advanced Navigation Technology
• /
• v.28 no.3
• /
• pp.362-368
• /
• 2024

In this paper, we investigated the performance of directional and omnidirectional precoding schemes when transmitting to improve downlink performance in massive MIMO. Omnidirectional precoding was used to broadcast a common signal, such as a synchronization or control signal, to all users. The main purpose of omnidirectional precoding is to design the precoding matrix so that the signal transmitted in the downlink is the same in all directions and emitted with maximum energy. We propose a flexible omnidirectional precoding method for full-dimensional massive MIMO that can set the spatial coverage range to less than 120 degrees. The constraints of omnidirectionality of all antennas, equal transmit power, and maximum transmit rate are used to design the encoding matrix of the proposed method. The performance was evaluated in terms of spatial coverage by considering changing the spatial coverage of the antenna array by changing the distance between neighboring antennas in the antenna array.

• Journal of Communications and Networks
• /
• v.6 no.4
• /
• pp.317-330
• /
• 2004

In this paper, we explore the utility of recently discovered multiple-antenna techniques (namely MIMO techniques) for medium access control (MAC) design and routing in mobile ad hoc networks. Specifically, we focus on ad hoc networks where the spatial diversity technique is used to combat fading and achieve robustness in the presence of user mobility. We first examine the impact of spatial diversity on the MAC design, and devise a MIMO MAC protocol accordingly. We then develop analytical methods to characterize the corresponding saturation throughput for MIMO multi-hop networks. Building on the throughout analysis, we study the impact of MIMO MAC on routing. We characterize the optimal hop distance that minimizes the end-to-end delay in a large network. For completeness, we also study MAC design using directional antennas for the case where the channel has a strong line of sight (LOS) component. Our results show that the spatial diversity technique and the directional antenna technique can enhance the performance of mobile ad hoc networks significantly.