Search results for "Communications system"
showing 10 items of 78 documents
A Non-Stationary Mobile-to-Mobile Channel Model Allowing for Velocity and Trajectory Variations of the Mobile Stations
2017
In mobile-to-mobile (M2M) communication systems, both the transmitter and the receiver are moving with a certain velocity, which is usually assumed to be constant over time. However, in realistic propagation scenarios, the velocity of the mobile stations (MSs) is subject to changes resulting in a non-stationary fading process. In this paper, we develop a non-stationary narrow-band M2M multipath fading channel model, where the transmitter and the receiver experience changes in their velocities and trajectories. For this model, we derive expressions for the local autocorrelation function (ACF), the Wigner-Ville spectrum, the local average Doppler shift, and the local Doppler spread under isot…
Performance Analysis of Cooperative Communication Systems with Imperfect Channel Estimation
2009
This paper investigates the effects of channel estimation errors on the symbol-error-rate (SER) performance of a cooperative communication system operating in an amplify-and- forward (AF) mode. A pilot symbol assisted modulation scheme with linear minimum mean square estimation (LMMSE) is used for the channel estimation. An accurate and easy-to-evaluate SER expression is presented for uncoded cooperative communication systems with quadrature amplitude modulation (QAM) and phase-shift keying (PSK) constellations. Numerical simulations are conducted to verify the correctness of the proposed analytical formulation. It is shown that the performance loss caused by channel estimation errors incre…
System Times and Channel Availability for Secondary Transmissions in CRNs: A Dependability Theory based Analysis
2017
[EN] Reliability is of fundamental importance for the performance of secondary networks in cognitive radio networks (CRNs). To date, most studies have focused on predicting reliability parameters based on prior statistics of traffic patterns from user behavior. In this paper, we define a few reliability metrics for channel access in multichannel CRNs that are analogous to the concepts of reliability and availability in classical dependability theory. Continuous-time Markov chains are employed to model channel available and unavailable time intervals based on channel occupancy status. The impact on user access opportunities based on channel availability is investigated by analyzing the stead…
A reconfigurable platform for evaluating the performance of QoS networks
2010
Nowadays, high performance System and Local Area Networks (SAN/LAN) have to serve heterogeneous traffic consisting of information flows with different bandwidth and latency requirements. This makes it necessary to provide Quality of Service (QoS) and optimize the design of network components. In this paper we present a hardware tool designed to analyze the performance of QoS networks, under given traffic conditions and server models. In particular, a reprogrammable multimedia traffic Generator/Monitor platform has been built. This permits prototyping the communication system of a high speed LAN/SAN on a single FPGA device. Hence, it can be used at design to produce more efficient devices. T…
An On-Demand Energy Requesting Scheme for Wireless Energy Harvesting Powered IoT Networks
2018
Energy harvesting (EH) delivers a unique technique for replenishing batteries in Internet of Things (IoT) devices. Equipped with an energy harvesting accessory, EH-enabled sensor nodes/IoT devices ...
Trust enhancement of P2PSIP communication systems
2011
Today, peer-to-peer (P2P) session initiation protocol (SIP)-based communication systems have attracted much attention from both academia and industry. The decentralised nature of P2P might provide the distributed P2P communication system without help of the traditional SIP server. However, it comes to the cost of reduced trustworthiness and may cause security problems, e.g., privacy leaks, unpredictable availability, etc. In this paper, we investigate P2PSIP security issues and propose a subjective logic-based trust model that offers trust-based security services during P2PSIP session establishment. The main issues considered in this model include opinion calculation, opinion maintenance, d…
Blind multi-user detection by fast fixed point algorithm without prior knowledge of symbol-level timing
2003
We consider the estimation of the source process of the desired user an the downlink of a code-division multiple access (CDMA) communication system. In downlink signal processing, only the code of the mobile telephone user is known, while the codes of the interfering users are unknown. Blind source separation or independent component analysis is an approach offering the solution to this problem. In this work we apply the fast fixed point algorithm to the separation problem. The algorithm is based on fourth-order statistics optimization. Knowledge about the symbol level timing has to be known only coarsely.
Brain Controlled Architecture for Human-Human Interaction Mediated by a Humanoid Robot
2017
This paper presents an Assistive social robots architecture designed for social interaction with humans, mediated by a humanoid robot. The architecture has been designed for being used by people with severe paralysis and the architecture has been tested by a user affected by amyotrophic lateral sclerosis (ALS) in a locked-in state. The system allows the patient to communicate with the stakeholders using a Brain Controlled Interface, based on Evoked Response Potentials (ERP), to express needing, feelings or writing phases. Stakeholders visualize messages sent by the patient on a GUI and use a tele operated humanoid robot as an avatar of them to extend their physical presence to interact with…
On the statistical properties of the capacity of amplify-and-forward channels under LOS conditions
2008
Amplify-and-forward channels in cooperative networks provide a promising improvement in the network coverage and system throughput. Under line-of-sight (LOS) propagation conditions in such cooperative networks, the overall fading channel can be modeled by a double Rice process. In this article, we have studied the statistical properties of the capacity of double Rice fading channels. We have derived the analytical expressions for the probability density function (PDF), cumulative distribution function (CDF), level-crossing rate (LCR), and average duration of fades (ADF) of the channel capacity. The obtained results are studied for different values of the amplitudes of the LOS components in …
Signal detection for spread spectrum communication systems with gradient algorithm
2012
Retrieval process of original symbols of a spread spectrum based communication system is tried to be improved by Gradient Algorithm (GA) and Blind Source Separation (BSS) principles. Two simple schemes, based on two energy functions are presented. Time correlation properties of the channel are used as advantages in developing the filter coefficients for the receiver. Direct Sequence - Code Division Multiple Access (DS-CDMA) technique based system setup is used for algorithm testing purposes. This is identified as one of the most stable spread spectrum communication technique where most of the technologies developed for that are highly compatible with High Speed Packet Access (HSPA) transmis…