Non-ideal Links Research Articles

D-SVM over networked systems with non-ideal linking conditions

This paper considers distributed optimization algorithms, with application in binary classification via distributed support vector machines (D-SVM) over multi-agent networks subject to some link nonlinearities. The agents solve a consensus-constraint distributed optimization cooperatively via continuous-time dynamics, while the links are subject to strongly sign-preserving odd nonlinear conditions. Logarithmic quantization and clipping (saturation) are two examples of such nonlinearities. In contrast to existing literature that mostly considers ideal links and perfect information exchange over linear channels, we show how general sector-bounded models affect the convergence to the optimizer (i.e. the SVM classifier) over dynamic balanced directed networks. In general, any odd sector-bounded nonlinear mapping can be applied to our dynamics. The main challenge is to show that the proposed system dynamics always have one zero eigenvalue (associated with the consensus) and the other eigenvalues all have negative real parts. This is done by recalling arguments from matrix perturbation theory. Then, the solution is shown to converge to the agreement state under certain conditions. For example, the gradient tracking (GT) step size is tighter than the linear case by factors related to the upper/lower sector bounds. To the best of our knowledge, no existing work in distributed optimization and learning literature considers non-ideal link conditions.

Fair Resource Allocation in Self-Organizing Heterogeneous Networks With Imperfect Connections

Interference management by controlling the transmission powers is crucial for unveiling the potential of heterogeneous networks. Power allocation has mostly been investigated using ideal communication links, where it is generally assumed that information can be relayed perfectly between base stations. The impact of delays and time-outs during communication is not well understood. We propose a model with nonideal links and a power adjustment algorithm for heterogeneous networks. Contrary to the power allocation approaches in the literature, channel state information is not required for power adjustment. The convergence properties of the proposed algorithm are investigated using tools from switched system theory and it is shown to converge to the max–min solution even with nonideal communication links. The simulation results are in agreement with the theoretical analysis.

A Waterfilling Algorithm for Multiple Access Point Connectivity With Constrained Backhaul Network

The 4G/5G paradigm offers user equipment (UE) simultaneous connectivity to a plurality of wireless access points (APs). We consider a UE communicating with its destination through multiple uplinks operating on orthogonal wireless channels with unequal bandwidth. The APs are connected via a tree-like backhaul network with destination at the root and non-ideal link capacities. We develop a power allocation scheme that achieves a near-optimal rate without explicit knowledge of the backhaul network topology at transmitter side. The proposed algorithm waterfills a dynamically selected subset of uplinks using a low-overhead backhaul load feedback.

SCTP performance improvement based on virtual receiver window

This article puts forward one algorithm for stream control transfer protocol (SCTP) improvement with limited receiver buffer (RBUF). As is well known, SCTP is one of the most important transfer control protocol, but most researches focus on the situations without the RBUF limit. In this study, we analyze the impact of the RBUF size on the performance. Computer simulations show that the network utility is low in reliable transfer, when the RBUF size is smaller than bandwidth delay product. By studying the transmission sequence number (TSN) transfer progress, we find that the peer receiver window (PEER_RWND), which lags behind the true receiver window (RWND), leads to the poor network utility. To improve SCTP performance with limited RBUF, the virtual receiver window (VIRTUAL_RWND) is introduced. Based on the VIRTUAL_RWND, one algorithm is proposed to increase the sending rate. Computer simulations have evaluated an excellent performance of the proposed algorithm at both ideal link without lost packet and nonideal link with lost packet.

Gray physical interference model based link scheduling algorithms

To improve the concurrent data transmission capability of wireless multi-hop networks, this paper proposes adopting a gray physical interference model instead of using the threshold physical interference model. The model allows non-ideal links to be involved in scheduling, under the premise of not affecting the quality of existing transmission links. In addition, we design two greedy algorithms to schedule more links with SINR values located in the transition region. The results show that a gray physical interference model is more accurate than a threshold physical interference one, the concurrent transmission capability of a network based on the gray physical interference model is significantly increased, and network throughput is increased by 20%.

Performance assessment of virtual multiple-input multiple-output systems with compress-and-forward cooperation

A cooperative virtual multiple-input multiple-output (MIMO) system using two transmit antennas that implements bit-interleaved coded modulation (BICM) transmission and compress-and-forward (CF) relay cooperation among two receiving nodes is presented here. To perform CF cooperation, we propose to use standard source-coding techniques for virtual MIMO detection, based on the analysis of its expected rate bound and the tightness of the bound. Since the relay and the destination are closely spaced, the authors first assume an error-free conference link between them, to focus on investigating the achievable gain from the CF cooperation. Then the system throughput expression and upper bounds on the system error probabilities over block fading channels are derived. The results show that the relay enables the proposed cooperative virtual-MIMO system to achieve almost ideal MIMO performance with low source-coding rates. Furthermore, when we consider a non-ideal cooperation link for practical considerations, a channel-aware adaptive CF scheme is proposed, so that the relay could always adapt its source-coding rate to meet the data rate on the non-ideal link. Owing to the short-range communication and the proposed scheme, the impact of the non-ideal link is too slight to impair the system performance significantly.

The design of networked distributed sliding mode controllers with non-ideal links

In this paper, a methodology is proposed for the design of Networked Distributed Sliding Mode Controllers (NDSMC) for large-scale systems consisting of interconnected discrete-time subsystems. The state of each of these subsystems has time varying delays and there is also delay and packet loss in their interconnection links. The Networked Distributed Control System (NDCS), which is subject to the non-idealities of these interconnection links, is modeled and a Linear Matrix Inequality (LMI) based sufficient condition for designing asymptotically stable sliding surfaces, as well as the stabilizing NDSMC, is proposed. Finally, the proposed NDSMC structure is employed for the formation control of Unmanned Aerial Vehicles (UAVs); in which five vehicles are flying in a leader–follower architecture, in two platoons, whilst attempting to maintain the desired speed with a constant desired Euclidean distance between successive vehicles despite the presence of external perturbations such as wind disturbances.

Effects of Nodes Geometry and Power Allocation in Space-Time Coded Cooperative Wireless Systems

Cooperative communications are effective in improving the performance and extend the coverage of wireless networks. One issue is to find proper methods to allocate cooperative nodes. In this paper we investigate the effects of relay position and power allocation strategy in cooperative communications employing space-time codes (STCs). We consider non-ideal links between source, relay, and destination enabling the analysis of relay allocation problem based on the performance of each link in realistic scenarios. The frame error rate for various channel conditions, available diversity, relay positions, and transmitted power levels is obtained. Both the situation of balanced and unbalanced transmit power levels for source, relay, and destination are compared. Cooperative pragmatic STCs in block fading channel (BFC) are considered for our analysis. The results provide insight on how to allocate relay nodes based on geometry, link quality, and transmitted power considerations.

Distributed Estimation Using Reduced-Dimensionality Sensor Observations

We derive linear estimators of stationary random signals based on reduced-dimensionality observations collected at distributed sensors and communicated to a fusion center over wireless links. Dimensionality reduction compresses sensor data to meet low-power and bandwidth constraints, while linearity in compression and estimation are well motivated by the limited computing capabilities wireless sensor networks are envisioned to operate with, and by the desire to estimate random signals from observations with unknown probability density functions. In the absence of fading and fusion center noise (ideal links), we cast this intertwined compression-estimation problem in a canonical correlation analysis framework and derive closed-form mean-square error (MSE) optimal estimators along with coordinate descent suboptimal alternatives that guarantee convergence at least to a stationary point. Likewise, we develop estimators based on reduced-dimensionality sensor observations in the presence of fading and additive noise at the fusion center (nonideal links). Performance analysis and corroborating simulations demonstrate the merits of the novel distributed estimators relative to existing alternatives.

FM subcarrier fiber optical transmission system design and its application in next-generation wireless access

This paper presents a design method of optical frequency modulation (FM) subcarrier (with super carrier) transmission modem. The nonideal link characteristics, including laser chirping, fiber dispersion, voltage controlled oscillator (VCO) phase noise, relative intensity noise (RIN), and equivalent network model of laser diode of such a system that may bring about signal distortion are discussed first. We then propose a hierarchical methods to establish the system equivalent model. Finally this FM modem is applied to a GSM wireless system, in which multichannel signals are transmitted over fiber between radio port and basestation, and system performance is appraised by its dynamic range. It is found that optical FM subcarrier (with super carrier) transmission technique can improve the system dynamic range, compared with the intensity modulated direct detection (IMDD) method, and this is a economical and efficient method.