Sungho Jeon

Soft-output ML detector for spatial modulation OFDM systems

The spatial modulation (SM) divides input data into antenna indexes and data symbols, and transmits data symbols via the specific antenna chosen by the antenna index. Soft decision technology for the SM system has not been developed, and there is room for improving the receive performance. In this paper, soft-output maximum likelihood (ML) detector for antenna index and data bit is derived to recover the desired signals by soft decision. Simulation results show that the conventional SM system with hard decision has a limitation in its performance as compared to SIMO (single-input multiple-output) system. On the other hand, the proposed SM with soft decision outperforms the SM with ML detector based on hard decision.

Cooperative Networks with Amplify-and-Forward Multiple-Full-Duplex Relays

In this paper, we present a cooperative system with amplify-and-forward (AF) multiple-full-duplex relays (FDRs) that receives and transmits signals simultaneously. In the first, we propose a new concept of delayed M-FDR relaying (M-D-FDR) scheme being able to achieve the full spatial diversity. At this time, we consider each delayed FDR receives a signal from source, adjacent relays and its delayed loop interference signal from its transmit antenna. In the second, we propose an efficient iterative successive interference cancellation (SIC) technique at destination that gradually cancels a delayed signal in order to fully obtain link diversity generated from M-D-FDR. Then, we investigate the various properties of the proposed M-D-FDR network by analyzing the pairwise-error-probability (PEP) analysis, especially in terms of signal-to-noise ratios (SNRs) between source to relays and source to destination links, respectively. Finally, we accomplish the performance evaluations to verify the analysis results and to compare with a non-delayed M-FDR (M-N-FDR) network.

Component-Interleaved Receive MRC with Rotated Constellation for Signal Space Diversity

A signal space diversity (SSD) scheme combined with receive maximal ratio combining (MRC) was investigated in order to achieve more diversity gain in fading channels. By approximating noise as a Gaussian distribution after performing receive MRC, an exact expression for the symbol error rate for SSD schemes combined with receive MRC in Rayleigh fading channels can be derived for 4-QAM and 16-QAM. By performing simulations, the accuracy of our analysis, which exactly coincides with the empirical simulations for Rayleigh fading channels, was verified. Furthermore, using the formula derived by using the upper bound approach, it can be confirmed that the diversity order is 2MR where 2 stems from SSD and MR from receive MRC with multiple receive antennas. Numerical evaluation performed using the formula under various conditions indicated that the angle rotation affects the performance; this numerical evaluation had low computational complexity.

Performance evaluation of MIMO-OFDM with signal space diversity over frequency selective channels

Vertical Bell labs layered space-time (V-BLAST) is known to provide a good tradeoff between performance and complexity for multiple antenna systems. In this paper, an improved scheme which utilizes signal space diversity is proposed for multiple-input multiple-output (MIMO) bit interleaved coded modulation (BICM). The signal space diversity (SSD) has the advantage to increase the diversity order without the expansion of extra bandwidth and power by means of rotating the modulated symbols and interleaving the in-phase and quadrature components separately. BICM combined with the SSD would further enhance the diversity gains. Simulation results show that the proposed scheme is superior to V-BLAST, regardless of the number of antennas and modulation order.

Interleaved Spatial Diversity Transmission with Coordinate Interleaver for MIMO-OFDM Systems

Multiple input multiple output (MIMO) system provides a promising means to increase the spectral efficiency. Orthogonal frequency division multiplexing (OFDM) allows broadband transmission over frequency selective fading channels. Recently, a coordinate interleaver (CI) is considered in order to maximize the diversity gain for MIMO system. In this paper, a new concept of coordinate interleaver for MIMO-OFDM system and an optimum receiver structure are suggested. Using the CI, the real and imaginary components of signals experience different fading channels and it provides additional diversity gains. Simulation results show that the system employing the proposed CI outperforms the conventional V-BLAST architecture.

Definition and Properties of the Erasure Effect in Single-Frequency Network With Two Synchronized Transmitters

In this letter, the erasure probability of a received signal in a single-frequency network (SFN) is investigated. In particular, the definition and properties of such for a two-transmitter (two-TX) SFN are derived, which is known as the worst case of an erasure event. By definition, the erasure probability of a two-TX SFN is determined by the threshold level and the relative amplitude, and the relative delay does not have any effect on the erasure probability. Furthermore, the condition and the value of the maximum erasure probability are derived along with the erasure-free condition. Using the definition and properties, the erasure probability can be easily calculated and predicted for a given SFN condition.

Adaptive HPA Linearization Technique for Practical ATSC DTV System

In the digital television (DTV) broadcasting system, high power amplifier (HPA) is the most essential device to expand the service availability and coverage. However, as the input power level of HPA increases, the HPA is driven into the saturation mode and HPA output signal suffers nonlinear distortion. HPA nonlinearity is potentially responsible for adjacent channel interference and inter-symbol interference (ISI). To prevent these negative effects, digital pre-distortion (DPD) is one of the most widely used techniques for the HPA linearization. In order to estimate the HPA nonlinearity, DPD technique requires a feedback signal, which needs to be appropriately down converted and digitized from HPA output. However, since the feedback signal might be generally influenced by offset error, it is important to reduce the offset error in order to improve HPA linearization. In this paper, an adaptive DPD technique based on iterative look-up table (LUT) update and adaptive acquisition is proposed. The proposed DPD technique is validated on the advanced television systems committee (ATSC) terrestrial DTV broadcasting system by computer simulation and laboratory test.

Formulating the Net Gain of SISO-SFN in the Presence of Erasure Effect

In this paper, an analytical formula for the net gain of single-input single-output single frequency network (SISO-SFN) is derived. In order to formulate the net SISO-SFN gain (SISO-SFNG), we derive the average signal to noise ratio, where the SFN gain is calculated by the aggregate power sum as a function of the power imbalance, whereas the SFN loss is calculated by a two-term exponential model from a curve fitting as a function of the erasure probability, modulation order, and code rate. The accuracy and effectiveness of the derived formula are verified by comparing the measurement results with the analytical results. The derived formula helps to rationalize why the net gain is positive or negative under a given condition, e.g., a negative net gain is obtained if the power imbalance exceeds the erasure-free limit. The formula would be very useful to predict more realistic and accurate service coverage of SISO-SFN for various system configurations.

On the condition of adaptive digital predistorter with real-time update

This paper investigates the reason why the predistorted signal is sampled and feeds back to an adaptation block as reference for digital predistorter (DPD) to be updated in real-time (RT) by comparing a non-real-time (NRT) method with off-time processing. In addition, by deriving a simple algorithm based on gradient descent algorithm with minimum square error criterion, the steady-state condition can be obtained. In simulation, it is confirmed that RT method converges to the exact high power amplifier (HPA) model. Also, RT method can rapidly cope with the change of HPA characteristics caused during the operation, which is a major advantage with emphasis on the operation of real-time update. In addition, RT method shows more accurate performance and stability consistently compared to NRT method.

Path Loss Model for Coupling Loop Interference with Multiple Reflections over Single Frequency Network

Abstract Path loss models are important for predicting coverage area and for performance analysis in simulation and design of radio systems including an on-channel repeater (OCR). In this paper, an analytical path loss model for the coupling loop path is proposed to evaluate the performance of an OCR in a single frequency network (SFN). Since the receive antenna and the transmit antenna in the OCR are electrically coupled, the coupling loop interference (CLI) between the transmitting and receiving antennas at the OCR must be suppressed in order to avoid signal distortion and oscillation. Although numerous publications exist for path loss models, the assumption is commonly that transmit and receive antennas are fully separated. Therefore, an important step toward designing and installing an OCR station in an SFN is to model the actual propagation characteristics of CLI. Based on the ellipses model, an analytical path loss model in which the receiver and the transmitter are co-located is developed according to reflection distance.