Viet-Ha Pham

Enhanced ATSC DTV channel estimation

ATSC standard is the digital television (DTV) standard in the North America and was developed by the Advanced Television Systems Committee. ATSC uses the maximal length pseudo-random number (PN) sequences and a correlator in order to estimate the transmission channel between the transmitter and the receiver. Conventionally, the PN511 sequence is used to estimate the channel impulse responses. In this paper, we present the performance of an enhanced channel estimation method by the application of the compound PN sequence, which is the combination of one PN511 and three PN63 sequences. The numerical results of the laboratory measurements show a good improvement in the estimation performance of the compound PN sequence over the conventional PN511 sequence. The new estimated channel impulse responses possess a lower noise floor level than the previously estimated channel impulse responses.

Long Term Cluster-Based Channel Envelope and Phase Prediction for Dynamic Link Adaptation

A new cluster-based channel envelope and phase predictor is proposed for dynamic link adaptation in broadband wireless systems, based on our observation that each Multipath Cluster (MC) has its own variation characteristics, which can be identified and traced precisely. The proposed predictor consists of a channel envelope predictor and a phase slope detector. The performance of the proposed channel predictor has been verified through numerical simulations and field test measurement data. At a channel SNR of 6.05 dB and a prediction range of 240 Orthogonal Frequency Division Multiplexing (OFDM) symbols, the obtained normalized mean square error is less than -20 dB.

Cluster-based time-domain channel prediction for dynamic wireless communications

System performance of mobile wireless communications is limited by fast channel variations, which are mostly due to the mobility of user terminals and scatterers. In order to obtain the optimal system performance, precise knowledge of the channel variations is often needed through channel prediction. A new cluster-based time-domain predictor with improved performance is proposed in this paper. Our predictor is based on the observation that multipath components within each cluster are highly correlated, while different multipath clusters share independent variations. The accuracy of the channel predictor is further enhanced by the proposed algorithm to separate the estimation noise and true channel variation information in each cluster. The principle and performance of the proposed channel predictor have been verified through numerical simulations.

Channel Prediction-Based Adaptive Power Control for Dynamic Wireless Communications

In order to improve the transmit power efficiency at the Mobile Station (MS), the transmit power is usually adjusted based on feedback information from the Base Station (BS) or Channel State Information (CSI) estimated at the MS. In fast-varying channels, because of the propagation and estimation delays, and the short channel coherence time, both the feedback information and the estimated CSI may become outdated at the transmit instant, leading to a reduction in power control performance. In this paper, a new channel prediction-based adaptive power control technique is proposed for uplink transmission in Time Division Duplex (TDD) Orthogonal Frequency Division Multiplexing (OFDM) systems. Based on the predicted Channel Impulse Responses (CIRs) provided by a cluster-based time- domain channel predictor, the transmit power is allocated to each OFDM subcarrier and then, a global gain is applied to compensate for the propagation path loss. In doing this, the power control process does not rely on the feedback information from the BS nor the estimated CSI at the MS and thus, the system responsiveness, adaptivity, and power savings are improved.

On the Channel and Signal Cross Correlation of Downlink and Uplink Mobile UHF DTV Channels With Antenna Diversity

UHF TV channels are traditionally used for television broadcasting where the channels can be regarded static or slowly-varying. Due to the transition from the analog television to the digital television, the UHF TV channels 52-69 will be reallocated to other applications and there is a need of re-evaluation of these channels under the new operational environments, e.g. mobile downlink and uplink channels with antenna arrays at the transmitter and the receiver. In this paper, new results on the temporal and spatial characteristics of the wideband UHF mobile wireless signals and channels in the Digital Television (DTV) broadcasting UHF frequency bands are presented. Our analysis of DTV mobile field measurements confirms that the complex channel correlation amplitude depends on the channel phase correlation and differs considerably from the channel envelope correlation. Furthermore, the autocorrelation of the ATSC DTV transmitted signal, embedded in our received signals, degrades the received signal amplitude correlation coefficients, in comparison with the channel envelope correlation coefficients, and increases the complex received signal correlation coefficients, in comparison with the complex channel correlation coefficients, in highly correlated channels. Both downlink and uplink DTV mobile broadcast channels are investigated. The field measurement results also show that the channel envelopes are highly correlated while the channel phases are uncorrelated. This may lead to the advent of a space time code or a modulation scheme that utilizes the phase information in order to maximize the channel capacity. The results exposed in this paper are important for designers of new mobile wireless systems in order to build new wireless applications, modulation schemes, equalizers and channel-tracking algorithms in the UHF TV spectrum.

A Study on the Channel and Signal Cross Correlation of UHF DTV Channels

UHF channels are traditionally used for television broadcasting where the channels can be regarded static or slowly-varying. Since the advent of the unlicensed and cognitive radio, there is a need of re-evaluation the channels in UHF frequency band under the new application environments. In this paper, new results on the temporal and spatial characteristics of the wideband UHF mobile wireless signals and channels in the digital television (DTV) broadcasting UHF frequency bands are presented. Our analysis of DTV mobile field measurements shows that the complex channel correlation magnitude depends on the channel phase correlation and is considerably different from the channel envelope correlation. Furthermore, the transmitted signal autocorrelation is embedded in the received signal correlation and makes it different from the channel correlation.

Spatio-temporal channel characterization: theoretical framework and applications in MIMO system design

The utilization of multiple antennas and space–time codes in multiple-input and multiple-output (MIMO) communication systems significantly improves the transmission channel capacity without using additional bandwidth and power. The improvement is achieved by decomposing the spatial structure of transmission channels and performing appropriate temporal and spatial multiplexing. In this paper, we propose a novel theoretical framework for MIMO channel modeling and characterization in order to facilitate the MIMO system design and performance evaluation. The channels are represented in space, time, wave vector, and frequency domains while the space–time and wave vector–frequency interdependences are considered. A realization of the theoretical framework, in a form of a practical framework, is also proposed to address the channel modeling and characterization at both transmitter and receiver sides. The utilization of the practical framework in MIMO communication system design is discussed to illustrate its applications in realistic scenarios. The angle of arrival estimation based on the proposed practical framework using field test measurement data is also presented as illustrative examples.

Interdependent infrastructure modelling: Intergration of domestic water models

In order to assess the viability of using EPAnet source code and the time domain Infrastructure Interdependencies Simulator (I2Sim) for predictive modeling, a critical failure of a municipal water supply was modeled on a university campus. During winter operations, a campus steam plant experienced a failure in operations due in part from an unobserved anomaly in the municipal water supply. The subsequent explosion which disabled campus heating caused building closures and nearly resulted in an evacuation of a major hospital. The representation of the campus municipal water distribution system was built with external stresses applied to produce system conditions equivalent to those during the failure. The data was imported directly into a test model simulating interdependent systems to see if the complete failure could then be simulated. Preliminary results have effectively recreated the incident with only some temporal errors. The results of the exercise have provided insight into operational limitations, appropriate mitigation response and water system redesign to improve its reliability.

Incorporating external command signals in the simulation of interdependent infrastructures: The control room concept

Effective coordination is one of the most critical aspects of emergency management. Several scientific articles have described how the lack of proper coordination resulting from “limited resources, inadequate communication, misinformation, and damaged infrastructure” has negatively impacted response efforts. Problems involving the lack of consistent data moving from the incident, including the accurate description of the evolving situation, must be addressed to achieve better coordination. This paper investigates how interdependency simulators can be used to support coordination efforts and decision-making during emergency management.

A novel multi-dimensional spectrum estimation technique

Conventionally, to multi-dimensional spectral estimation techniques, each data snapshot in space is captured simultaneously in time. The size of the antenna array is dependent on the area of interest. In this paper, we propose a data measurement technique, which does not collect data samples within each snapshot in space simultaneously but sequentially along a predefined path, and a spectral estimation technique, which is based on the Discrete Fourier Transform (DFT), for the collected data. The key idea of these techniques is to create a large synthetic antenna aperture by displacing a small antenna array and by assuming uniform plan impinging waves. The performance is evaluated by simulation. The applications of the proposed techniques include synthetic aperture radar, radar processing and sonar systems.