Jungho Myung

Identification of Non-Ideal Receiver Condition for Orbital Angular Momentum Transmission

Although orbital angular momentum (OAM) was first introduced for optical communications, it is drawing attention as a new transmission technique for millimeter wave communication. Due to the additional orthogonal transmit dimension by photon OAM, the theoretical throughput can increase dramatically with various OAM modes. In practice, since OAM by uniform circular arrays (UCAs) has the implementation problem such as twisted axis between transmitter and receiver, the performance degradation happens frequently. Hence, this paper investigates the imperfect receiver condition and the effect of this problem. In particular, the off-axis and non-parallel location problems are focused. Here, the capacity with inter-mode interference (IMI) of OAM is first considered and the receiver compensation method is proposed. Numerical results show that the throughput after compensation is better than that without compensation.

Performance Analysis of a Dual-Hop Relay With STBC-CIOD over Rayleigh Fading Channels

In this paper, a symbol error rate (SER) study is presented for the dual-hop relay networks employing space-time block code (STBC) from coordinate interleaved orthogonal design (STBC-CIOD), where a relay with either a decode-and-forward (DF) or an amplify-and-forward (AF) protocol is equipped with multiple antennas. More specifically, we provide the union upper and lower bounds on the average SER by deriving an accurate closed-form formula for the corresponding symbol pairwise error rate (SPER). In addition, the asymptotic diversity order is analyzed. The theoretically derived bounds are in good agreement with the simulation results.

Non-Cooperative Feedback Control Game for Secondary Transmitter in Cognitive Radio Network

In this letter, we propose a non-cooperative feedback control game for secondary transmitter, where we assume that secondary users are rational and thus selfish, i.e., they will choose the feedback rate to maximize their own utility functions. The utility function of each user is defined as the downlink data-rate minus a linear price function of the channel state information (CSI) feedback rate. The existence of the Nash-equilibrium of the proposed game is analyzed. Also, in order to satisfy the primary users interference threshold, power control algorithms are proposed. Simulation results show that the sum-rate of the proposed game is better than that of the equally distributed feedback-size scheme.

Throughput enhancement of secondary transmitter under target physical layer security rate

In this paper, we investigate the cognitive radio (CR) network, in which the secondary link works as a helper node to improve the physical layer secrecy rate of primary user. Depending upon the operation of secondary link, we consider two operation modes: (i) Spectrum-spatial leasing (SSL), which is introduced in the previous work, and (ii) Spectrum-time leasing (STL), which we propose. In guaranteeing the given secrecy rate and ensuring the throughput of the secondary link, the SSL considers both simultaneously, whereas the STL considers them separately. Therefore, there exists a performance gap between SSL and STL in terms of secrecy rate. We analyze both modes under the constraint of target physical layer secrecy rate compared with no helper node case. Since the performance of both modes has changed over different channel conditions, we propose a mode selection algorithm to increase the expected secondary throughput. We demonstrate that our analysis is in good agreement with the simulation results.

Efficient S-SCH Detection Algorithm for LTE Downlink Channel

The cell-search procedure in the long-term evolution (LTE) downlink includes the time synchronization, the frequency synchronization of frames, and the acquisition of cell identity (ID). This paper presents a low-complexity detection algorithm for a secondary synchronization channel (S-SCH) in the acquisition of cell ID. The proposed algorithm classifies total S-SCH sequences into subgroups based on the correlation among sequences, and thus, the number of correlators for S-SCH detection is significantly reduced. Despite the complexity reduction, the numerical results show that the proposed algorithm provides a comparable detection probability (DP) compared with existing low-complexity approaches. To verify the performance of the proposed algorithm, the complexity analysis and analytical derivation of the DP are also presented.

On the Error Rate Performance and Asymptotic Diversity Order of Multi-Hop Two-Antenna Decode-and-Forward Relay Systems with STBC-CIOD over Rayleigh Fading Channels

In this letter, we analyze a symbol error rate (SER) of the multi-hop relay network employing space-time block code from coordinate interleaved orthogonal design (STBC-CIOD), where a source, a destination, and multiple relays with decode-and-forward (DF) protocol are equipped with two antennas. Especially, the union upper and lower bounds on the average SER and the asymptotic diversity order are provided by deriving an accurate closed-form formula for the corresponding symbol pairwise error rate (SPER). We demonstrate that the theoretically derived bounds are in good agreement with the simulation results.

Adaptive Cooperative Spectrum-Sensing Scheme for Cognitive Radio System

In this paper, we propose an adaptive cooperative spectrum-sensing scheme for cognitive radio system. Since our propose scheme chooses an adaptive criterion value which decides the usage of spectrum based on sensing environments such as the number of cooperative secondary users and the target miss-detection probability of cognitive radio system, we can achieve high frequency utilization. We firstly obtain an adaptive criterion value which gratified low false-alarm probability and kept target miss-detection probability using empirical searching. Then, we find a simple linear equation determined an appropriate criterion value quickly based on empirical searching results. Since our propose scheme always keeps the target miss-detection rate within primary users coverage and provides lower false-alarm rate than any other schemess false-alarm rate out of the coverage, it expects to contribute to high frequency utilization for cognitive radio systems.

Multiuser MIMO Downlink with Linear Precoding for Full Multiplexing Gain

Block diagonalization (BD) and coordinated beamforming (CBF) are two major signal processing schemes to achieve the sum rate close to the sum capacity of a multiuser multiple-input multiple-output (MU-MIMO) downlink. However, they do not achieve the full spatial multiplexing gain except under a special antenna configuration. In this paper, therefore, we propose a new linear precoding algorithm for achieving the full spatial multiplexing gain in a general antenna configuration. To obtain the full spatial multiplexing gain, the proposed algorithm divides the users into the two groups in terms of the number of data streams transmitted. In addition, to maximize the sum rate, we choose the member of each groups by comparing the eigenvalues of each effective channel. Simulation results confirm that the proposed scheme performs close to the sum capacity and achieves the full multiplexing gain.

Non-Cooperative Feedback Control Game for Improving Throughput Fairness in MIMO Broadcast Channels

Channel state information (CSI) is known to play crucial role for downlink transmissions of multi-user multiple-input multiple-output (MU-MIMO) systems. The existing works have been widely researched on the CSI feedback problem for system throughput aspects. With limited available radio resources, system throughput and fairness are usually in conflict with each other, balancing system throughput and fairness with high resource efficiency is necessary. Also, the analysis of feedback-rate allocation considering these two performance measures is needed. Therefore, in this paper, we propose the non-cooperative feedback-rate control game for improving throughput fairness in MU-MIMO system. Based on the game theory, the utility function of each user is considered both throughput fairness and total throughput. Moreover, we investigate the existence of the Nash-equilibrium of the proposed game and outage probability in terms of CSI feedback-rate. Simulation results show that the proposed game improves throughput fairness, and thus achieves better outage performance, as compared to the conventional equal-sized feedback scheme.

Non-cooperative feedback control game under a sum feedback-rate constraint in MIMO broadcast channels

Channel state information (CSI) is known to play crucial role in multiple-input multiple-output (MIMO) broadcast channels. To acquire CSI at the base station, feedback from users is necessary. Since the optimal feedback-rate to maximize the total system throughput is possibly changed by the channel condition, the conventional equal-sized feedback can be inefficient in multi-user MIMO system. Therefore, in this paper, we investigate the effect of different-sized feedback-rate and propose the non-cooperative feedback-rate control game in multi-user MIMO system with multiple frequency bands. Based on the game theory, the utility function of each user is defined as the downlink throughput minus a linear price function of the CSI feedback-rate. Moreover, we suggest a simple algorithm to find the proper pricing factors for the proposed game considering multiple users and multiple frequency bands. Simulation results show that the sum-rate of the proposed game yields better performance than that of the conventional equal-sized feedback-rate scheme.