Hongyi Yu

We focus on the Direct position determination (DPD) of a moving narrowband source based on Doppler frequency shifts of signals with known waveforms. Two common motion models are considered: the Constant velocity (CV) model and the Constant acceleration (CA) model. The DPD cost function is obtained after some algebraic manipulations using the Maximum likelihood (ML) criterion. To develop a computationally efficient optimization algorithm, we present a preliminary mathematical result that plays a fundamental role in development of the proposed algorithm. Subsequently, a Newton iterative algorithm is tailored to the two motion models to determine the moving transmitter's trajectory. When compared with multidimensional grid searching, the proposed algorithm is more computationally attractive without compromising its estimation accuracy. Simulation results confirm the superiority of the proposed algorithm.

Non-orthogonal multiple access (NOMA) simultaneously provides multi-user access over the same frequency band or time period, which can significantly improve system throughput in visible light communication (VLC) networks. However, the different interference components of NOMA and the diversified user requirements in VLC are difficult to coordinate. To guarantee both throughput enhancement and quality of service (QoS) satisfaction, this paper presents a power allocation scheme based on dynamic user priority in indoor NOMA-VLC networks. We introduce fuzzy logic (FL) to flexibly analyse user priority and assign signal power using multi-dimensional user features. The experimental results show that our method achieves the best performance in terms of user fairness and satisfaction. In indoor VLC, which has small cells with a high user density, our method outperforms contrastive schemes in terms of the average user data rate (AUDR). Therefore, in comparisons between static and dynamic user priority, our study indicates the fairness advantages of FL for the dynamic evaluation of user priority. In comparisons between NOMA and orthogonal multiple access, our study reflects the AUDR advantages of non-orthogonal methods. Furthermore, in comparisons of user satisfaction, our method outperforms existing methods, indicating the achievement of the QoS guarantee.

In this paper, we investigate the design of energy-efficient space-time modulation for peak-limited MISO broadcast visible light communication (VLC) systems by cooperatively managing the nonnegative multiuser interference. We first characterize a constellation-optimal structure that maximizes the worst-case minimum Euclidean distance of all users for a general space-time modulation design. It turns out that the optimal space-time constellation can be constructed via the spatial repetition of the optimal multidimensional constellation in time dimension over ideal additive white Gaussian noise (AWGN) channels. Then, based on this structure, we specifically design two classes of energy-efficient time-dimensional constellations: 1) For the integer overall bit rate, we design the optimal linear precoded block design, which admits fast maximum likelihood (ML) demodulation algorithms. 2) For the non-integer case, we propose a nonlinear precoding scheme called block coded modulation, which sums the codeword sets of the optimal linear design and a block channel code. In addition, we show that these two classes of designs are addition-unique, thus, generating an energy-efficient mapping from users’ data to the transmitted constellations. This property enables the efficient demodulation of the sum signal from a noisy received signal as well as the decoding of individual signal from the estimated sum signal. Extensive computer simulations indicate that our addition-unique designs have remarkable performance gains over the currently available zero-forcing (ZF), minimum mean square error (MMSE) and time-division multiple access (TDMA) methods for the multiuser MISO VLC broadcast systems.

The direct position determination approach was recently presented as a promising technique for the localization of a transmitting source with accuracy higher than that of the conventional two-step localization method. In this paper, the theoretical performance of a direct position determination estimator proposed by Weiss is examined for situations in which the array model errors are present. Our study starts from a matrix eigen-perturbation result, which expresses the perturbation of eigenvalues as a function of the disturbance added to the Hermitian matrix. The first-order asymptotic expression of the positioning errors is presented, from which an analytical expression for the mean square error of the direct localization is available. Additionally, explicit formulas for computing the probabilities of a successful localization are deduced. Finally, Cramér–Rao bound expressions for the position estimation are derived for two cases: (1) array model errors are absent and (2) array model errors are present. The obtained Cramér-Rao bounds provide insights into the effects of the array model errors on the localization accuracy. Simulation results support and corroborate the theoretical developments made in this paper.

In this paper, we consider an intensity modulated direct detection MIMO optical wireless communication (OWC) system. For such a system, a novel super-rectangular cover theory is developed to characterize both the unique identifiability and full reliability. This theory states that a transmitted matrix signal can be uniquely identified if and only if the cover order is equal to the transmitter aperture number, i.e., full cover. In addition, we prove that full reliability is guaranteed for space-time block coded MIMO-OWC over commonly used log-normal fading channels with an ML detector if and only if the STBC enables full cover. In addition, the diversity gain can be geometrically interpreted as the cover order of the super-rectangle, which should be maximized, and the volume of this super-rectangle, as the diversity loss, should be minimized. Using this established error performance criterion, the optimal linear STBC for block fading channels is proved to be spatial repetition code with an optimal power allocation. The design of the optimal non-linear STBC is shown to be equivalent to constructing the optimal multi-dimensional constellation. Specifically, a multi-dimensional constellation from Diophantine equations is proposed and then, shown to be more energy-efficient than the commonly used nonnegative pulse amplitude modulation constellation.

In this paper, we consider a multiple-input-multiple-output optical wireless communication (MIMO-OWC) system in the presence of log-normal fading. In this scenario, a general criterion for the design of full-diversity space code (FDSC) with the maximum likelihood (ML) detector is developed. This criterion reveals that in a high signal-to-noise ratio (SNR) regime, MIMO-OWC offers both large-scale diversity gain, governing the exponential decaying of the error curve, and small-scale diversity gain, producing traditional power-law decaying. Particularly for a two by two MIMO-OWC system with unipolar pulse amplitude modulation (PAM), a closed-form solution to the design problem of a linear FDSC optimizing both diversity gains is attained by taking advantage of the available properties on the successive terms of Farey sequences in number theory as well as by developing new properties on the disjoint intervals formed by the Farey sequence terms to attack the continuous and discrete variables mixed max-min design problem. In fact, this specific design not only proves that a repetition code (RC) is the optimal linear FDSC optimizing both the diversity gains, but also uncovers a significant difference between MIMO radio frequency (RF) communications and MIMO-OWC that space dimension alone is sufficient for a full large-scale diversity achievement. Computer simulations demonstrate that FDSC substantially outperforms uncoded spatial multiplexing with the same total optical power and spectral efficiency, and the latter provides only the small-scale diversity gain.

In multi-hop wireless networks, network coding can take advantage of the bi-directional traffic flows to increase the achievable throughput. To combat fading in wireless channel, cooperative diversity is integrated into the network-coding schemes. In this paper, we propose an opportunistic cooperative network-coding scheme based on space-time coding (OCNC), which combats channel fading and improves resource efficiency and network throughput. Focusing on the bi-directional traffic flows in wireless cooperative relaying networks, we develop and analyze the outage probabilities and the network-coding gain of different bi-directional relaying schemes. The numerical results show that in contrast to traditional scheme both full diversity (i.e. K-order diversity in case of K relay nodes) and asymptotical 4/3 times of network-coding gain are achieved by OCNC. In addition, because of opportunistic relaying of multiple nodes, the network-coding gain is more considerable in the low and middle SNR regimes.

Broadcast is a method that allows the nodes in the multi-hop wireless networks share the data efficiently among other nodes. Because the transmissions of broadcast packets are related to send or receive of multi-nodes, it is difficult to ensure the reliable transmission of broadcast packets. In this paper, a new single channel synchronous MAC protocol, termed the three-handshake broadcast protocol (THBP), is introduced for multi-hop wireless networks. In THBP, we design a receiver-based conflict detecting mechanism and a simple three-handshake process of the control packets, which allow nodes to schedule a reliable broadcast channel ensuring the reliable deliver of the broadcast packets. THBP is characterized by its simple structure, reduced control overhead, ease of implementation and compatibility of saving energy measures. The performance of this protocol is studied through mathematic analysis and simulation. It is proved that the protocol can operates efficiently in the multi-hop wireless networks and ensures high transmission reliability of the broadcast packets.

One of the main design issues for wireless sensor networks (WSNs) is the sensor deployment problem. This paper mainly studies the redeployment problem for WSNs, that is, when there have been some sensor nodes (called source node) in the deployment region, how to maximize the source nodes and minimize new deployed nodes. We formulate the problem as a 0-1 programming model. Some heuristic algorithms based on the redeployment models are developed to solve the problem. At last we derive the sufficient and necessary condition that all the source nodes can be utilized. The experimental results show that the proposed methods are very effective, scalable and robust.