Moonchang Choi

A new filter-bank multicarrier system for QAM signal transmission and reception

A filter-bank multicarrier - quadrature amplitude modulation (FBMC-QAM) system with two prototype filters for transmitting QAM signal is proposed. The proposed transmitter performs separate filtering for the even-numbered sub-carrier symbols and the odd-numbered sub-carrier symbols. We derive the orthogonality conditions for a FBMC-QAM system without the intrinsic interference. In order to satisfy the suggested orthogonality conditions, we perform a kind of block interleaving for the odd-numbered sub-carrier filtering. The receiver structure is the counterpart to the transmitter. Numerical results showed that the proposed FBMC-QAM system has almost the same bit error rate (BER) performance compared to the FBMC-OQAM and the orthogonal frequency division multiplexing (OFDM) system. with the proposed FBMC-QAM, multiple-input multiple-output transmission schemes and channel estimation schemes can be utilized similarly as in OFDM.

Simplified Power Allocation Scheme for Cognitive Multi-Node Relay Networks

The simplified optimization problem is considered since the power allocation (PA) problem is the nonconvex optimization problem in cognitive multi-node relay networks, which has the interference on the primary user and the maximum transmission power constraint. The maximum transmission power constraint is guaranteed after we obtained the closed-form solution of the simplified optimization problem which has only the interference constraint on the primary user. The proposed PA method with much lower complexity performs close to the suboptimal PA method using interior point method.

Synchronization Error in QAM-Based FBMC System

We investigate the impact of the time offset (TO) and carrier frequency offset (CFO) on the performance of a filter bank multicarrier - quadrature amplitude modulation (FBMC-QAM) system. As opposed to conventional FBMC system where offset QAM (OQAM) is utilized due to the intrinsic interference, the FBMC-QAM system cancels the intrinsic interference based on the orthogonality conditions between the two kinds of filters. Because the FBMC-QAM system uses two kinds of filters, the effects on the TO and CFO are different compared to the conventional FBMC system. The performance of this system is degraded by TO because the two-filter orthogonality conditions are not satisfied, resulting in severe inter-symbol interference (ISI). With respect to the CFO, the orthogonality between the two filters protects from performance degradation caused by intercarrier interference (ICI). Numerical results show that FBMCQAM is more robust against CFO while it is more sensitive to TO compared to the FBMC-OQAM system.

Low Complexity Multiple Relay Selection Scheme for Cognitive Relay Networks

Power allocation (PA) and multiple relay selection (MRS) for cognitive relay networks (CRNs) are considered in this paper. In CRNs, the power of each relay node is limited by the interference constraint on primary users. In order to satisfy the interference constraint, we propose a simple PA scheme in which the power of each relay is inversely proportional to the interference channel from the secondary relay to the primary user. That is, the interference constraint is satisfied by allocating more power to the relays which have less interference to the primary users. After satisfying the interference constraint by the proposed PA scheme, we consider the MRS in order to maximize the secondary system capacity. Since the optimal MRS requires the exhaustive search for all possible relay combinations, we propose a low complexity suboptimal MRS scheme based on the relay ordering. By applying the proposed PA and selecting the relays in order of achieving the larger SNR, we can find a relay combination that performs close to the optimal MRS. Some simulation results show that the proposed MRS scheme achieves about 50% throughput gain over the previously proposed schemes when the maximum transmission power of each relay is 20dBW. Also, the proposed suboptimal MRS scheme with much lower complexity performs close to the optimal MRS using the exhaustive search.

A New Filter-Bank Multicarrier System With Two Prototype Filters for QAM Symbols Transmission and Reception

A filter-bank multicarrier-quadrature amplitude modulation (FBMC-QAM) system with two prototype filters for transmitting QAM symbol is proposed, and the orthogonality conditions for the FBMC-QAM system without the intrinsic interference is derived. The proposed transmitter performs the individual filtering for the even and odd-numbered sub-carrier symbols, respectively. In order to satisfy the derived orthogonality conditions, we perform a sub-block wise reverse ordering procedure for the outputs of the odd-numbered sub-carrier filter. Also, this paper shows that the proposed FBMC-QAM system satisfies the suggested orthogonality conditions and can use the multiple-input multiple-output transmission schemes as the conventional orthogonal frequency division multiplexing (OFDM) systems. The signal-to-interference power ratio and the bit error rate (BER) for the proposed FBMC-QAM system are evaluated. Numerical results show that the proposed FBMC-QAM system has almost the same BER performance compared with the FBMC-OQAM and OFDM systems.

Channel Estimation and Interference Cancellation of Feedback Interference for DOCR in DVB-T System

This paper considers a problem of unwanted feedback interferences caused by coupling from the transmit antenna to the receive antenna in the digital video broadcasting-terrestrial (DVB-T) digital on-channel repeater (DOCR) system. We model the DVB-T DOCR system and propose a feedback interference cancellation method based on the linear minimum mean square error (LMMSE) estimation of the feedback interference channel. Since the accurate estimation of the feedback interference channel is an important factor that determines the performances of the feedback interference cancellation, the channel estimation by averaging the estimated channel and iterative decision feedback cancellation method are proposed. Simulation results of signal-to-noise ratio (SNR) relation between the reference SNR and the processed SNR are presented and the theoretical analysis is performed to verify the simulation results. The proposed methods are compared to the conventional method on the typical urban 6 channels with maximum Doppler frequencies of 0 Hz and 3 Hz in terms of SNR, bit error rate and various transmission modes in the DVB-T system. Simulation results and the theoretical results show that the proposed method outperforms the conventional method.

Self-mixed interference cancellation method in direct conversion receivers

A novel method for cancelling the time-varying offset due to self-mixed interferences in direct conversion receivers is proposed. The proposed method is based on the adaptive interference cancellation using the least mean square adaptation algorithm. Some simulation results show that the proposed method cancel the self-mixed interference almost perfectly.

Performance analysis on the self-mixed interference cancellation in direct conversion receivers

In this paper, we propose a novel receiver structure for cancelling self-mixed interferences in direct conversion receivers. The proposed receiver structure is based on the adaptive interference cancellation (IC) using an adaptive algorithm such as a least-mean-square (LMS). The reference signal for the adaptive IC is obtained from the received signal itself. Thus, the proposed method can mitigate the self-mixed interference without any additional information on the self-mixed interference. Moreover, the signal-to-interference ratio (SIR) performance of the proposed cancellation method is theoretically analyzed. The simulation results indicate that the numerical SIR performance is well matched with the theoretical SIR performance. Also, the proposed cancellation method cancel the self-mixed interference almost perfectly even when the power of the received interference signal is 50dB larger than that of the received desired signal.