Tien Hoa Nguyen

A scheme of Dual Carrier Modulation with Soft-decoding for MB-OFDM MIMO systems

The basic structure of the Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra-Wide Band (UWB) System is discussed in this paper. The fixed-point simulation platform using the WiMedia Alliance proposed by ECMA 368 standards has been implemented. An extension of the physical layer using the Alamouti method to a Multiple-Input Multiple-Output (MIMO) system is also presented. Based on the theoretical Dual Carrier Modulation (DCM) supported by Media Alliance, we propose a scheme of the DCM-Modulation and DCM-Demodulation with Soft-decoding for a MB-OFDM MIMO system. The system performance is analyzed using the Saleh-Valenzuela channel model in terms of the bits error rate and the transmission range for indoor environments.

Implementation of an OFDM system based on the TMS320C6416 DSP

In this paper, we present the implementation of an OFDM system based on the TMS320C6416 DSP. Methods for synchronization and channel estimation are shortly described. Structure of the used DSP board, and the interface between host and target are reviewed. Protocols for implementing a whole real time system are introduced. Synchronization results and received signal obtained by the DSP are visualized to verify the implemented system.

CMI and IFI mitigation for TH-PPM Ultra Wideband systems with a low complexity receiver

Pulse Position Modulation (PPM) is a popularly adopted modulation scheme in the Impulse Radio based Ultra Wideband (UWB) systems. In order to shape the spectrum of the signal, a time dither on generated pulses leading to so-called Time Hopping UWB (TH-UWB) is introduced. Although of many advantages, the TH-PPM scheme faces serious challenges which are the Cross Modulation Interference (CMI) and the Inter Frame Interference (IFI) due to the multipath propagation. In this paper, Time Reversal is proposed as a technique for mitigating the CMI and IFI in TH-PPM UWB systems at the transmitter side. The CMI and IFI amount can be assessed by Signal-to-Interference-Ratio (SIR). Simulation results show that the proposed approach can improves the BER performance of the system considerably. We focus here on the single-user case, however, we can extend the result to the multi-user case by using different TH codes

An OFDM System Design with Efficient ICI Cancellation over Embedded LTE-R Channels Based on the USRP Platform

In this paper, we design an OFDM communication system with ICI cancellation embedded over LTE-R channel. In our proposed system, a very fast time-varying multipath fading channel is integrated with the use of D2a scenario of WINNER II channel model. The ICI cancellation approaches, wherein a PSK modulated symbol is mapped onto multiple subcarriers, are investigated and deployed in the Universal Software Radio Peripheral platform as the RF front-end. Experimental results confirm that the ICI cancellation techniques offer a notably high performance on eliminating the problem caused by frequency offsets. For instance, the ICI cancellation solutions achieve the same performance at Doppler frequency of 200 Hz compared to the system without using our approaches at a lower Doppler of 50 Hz.

A robust ICI suppression based on an adaptive equalizer for very fast time-varying channels in LTE-R systems

High-speed railway communication implemented based on Long-Term Evolution-Railway (LTE-R) Platform has strict requirements for quality of services to support high data-rate transmission for numerous mobile users. In such environment, there often exists inter-carrier interference. In this paper, we exploit a robust channel estimation method in the time domain for very fast time-varying LTE-railway channels, and then, we propose an effective and adaptive frequency-domain equalizer that can offer a tradeoff between performance and computational complexity. The simulation results show the robustness of our proposed method compared with previous ones. The computational complexity of the proposed method retain at a decent number by exploiting specified properties of channel matrices.

Performances analysis of vehicle-to-X communication systems

This paper investigates the influence of the inter-carrier interference on a vehicle to infrastructure (V2X) communication system, which has been defined in the IEEE 802.11p standard. The frequency shift due to high speed of cars destroys the orthogonality between subcarriers in OFDM signals and rises the inter-carrier interference (ICI). The main contributions of this paper are proposed analytic formulas and simulation results of the signal to interference power ratio (SIR) by considering the statistical effects of ICI and evaluation of symbol error rate (SER) for several types of fading and Doppler spread in time domain approach. The results show that for the Rayleigh fading model, SIR decreases when the maximum Doppler spread increases. On the other hand, in the Rician channel, SIR depends not only on maximum Doppler spread but also on the angle of arrival (AoA) and Rician factor of the LOS component. Moreover, the simulation result in terms of SER is obtained for different channel models. It shows an excellent agreement between the theoretical calculation of SIR and the simulation results of SER.

A synchronization method for implementing an OFDM system based on the TMS320C6416 DSP

This paper proposes a synchronization method for implementation of an OFDM system based on the TMS320C6416 DSP. The method is to meet the constraints of signal processing in real time conditions, and ensure the Quality of Services regarding the received signal quality. It is proven that the complexity of the proposed method is significantly reduced in comparison with the conventional one, and thus, the time constraint for synchronization is fulfilled. Moreover, the starting point of each OFDM frame stored in the receiver DSP buffers can be precisely detected. The data rate obtained by applying the Ping-Pong Buffer technique is significantly enhanced. Measurement results are compared with the theoretical results to validate our proposed mechanisms. Files and audio transfer are tested to demonstrate the performance of the implemented system.

Application of compressive sensing in time hopping multi-user UWB system

Recently, ultra-wideband (UWB) is one of the most attractive technologies in communications. UWB communication systems are designed to intent to low power, low cost, and low complexity devices. However, costly high-speed analog-to-digital converters (ADCs) is required to convert RF/IF signals to digital form for subsequent baseband processing in UWB system. By exploiting sparse property of UWB signal, using compressive sensing (CS) to reduce the sampling rate is a perspective approach. In this paper, we propose a UWB communications system using compressive sensing combined with time-hopping (TH) pulse position modulation (PPM) and pulse amplitude modulation (PAM), called CS-TH-UWB. This system is designed aims to reduce the sampling rate of the origin UWB system. CS technique possesses capability to implement under Nyquist sampling rate at transmitter side. At the receiver side, the under Nyquist rate samples are reconstructed with an acceptable loss. The simulation of this system is carried out to evaluate the BER of CS-TH-UWB. The results show that at low compression ratio of sampling rate, the different in BER performance is negligible. The higher compression ratio is the more degradation of BER performance.