Behavior Of Wireless Channels Research Articles

Law recognitions by information criteria for the statistical modeling of small scale fading of the radio mobile channel

Information criteria based methods are proposed to select the best probability law to model the distribution of samples resulting from the small-scale fading of the propagation channel. The first is based on the estimation of an optimal histogram approximating the probability density function. The second one employs the direct use of an information criterion. Indeed, the modelling of the radio mobile channel small-scale fading is crucial in digital communications. It is the reason why several propagation models have been implemented to take into account the electromagnetic phenomena inherent in radio wave channels. Amongst these models is the family of statistical distributions which is rapid in computation time. In the context of this study our concern is to find, among different probability laws, the one which best coincides with radio channel behaviour. The experimental results show that the proposed methods are better than those methods already employed, such as the classical Kolmogorov–Smirnov test using cumulative distribution functions, or methods using different estimators of probability density functions, like the kernel density estimator and the Gaussian mixture model. Results are provided in supervised and unsupervised contexts.

Sensing the human user as a part of multiple-antenna system design [Wireless Corner

Summary form only given. Telecommunications techniques, MIMO, and cognitive radio are reviewed, and sensing the human user is presented as a part of radio-channel behavior. The effect of the user can be measured and optimized as a single element of the radio channel, in order to maximize the links performance. User-induced effects (both head and hand) were found to be as high as 5-15 dB, of which 5 dB could be compensated for by using antenna selection in the 1800 MHz band tested. Existing statistical measurements have proven that 40% of consumers commonly use lossy usage positions. A dual-antenna confi guration was designed at 1800 MHz and equipped with capacitive proximity sensors, providing a method for measuring and controlling the effects of users. The user proximity-sensor system is likely to improve the performance of four-antenna MIMO systems.

Sensing the Human User as a Part of Multiple-Antenna System Design [Wireless Corner

Summary form only given. Telecommunications techniques, MIMO, and cognitive radio are reviewed, and sensing the human user is presented as a part of radio-channel behavior. The effect of the user can be measured and optimized as a single element of the radio channel, in order to maximize the links performance. User-induced effects (both head and hand) were found to be as high as 5-15 dB, of which 5 dB could be compensated for by using antenna selection in the 1800 MHz band tested. Existing statistical measurements have proven that 40% of consumers commonly use lossy usage positions. A dual-antenna confi guration was designed at 1800 MHz and equipped with capacitive proximity sensors, providing a method for measuring and controlling the effects of users. The user proximity-sensor system is likely to improve the performance of four-antenna MIMO systems.

Design of Transmitter for CDM Based 2×2 Multiple Input Multiple Output Channel Sounder for Multipath Delay Measurement

Problem statement: Multiple Input Multiple Output (MIMO) wireless communication system is an innovative solution to improve the ban dwidth efficiency by exploiting multipath-richness of the propagation environment. The degree of multi path-richness of the channel will determine the capacity gain attainable by MIMO deployment. Approach: Therefore, it is very important to have accurate knowledge of the propagation environment/radio channel before MIMO implement. The radio channel behavior can be anticipated by channel meas urement or channel sounding. Code Division Multiplexing (CDM) is one of the channel sounding techniques that allow accurate measurement at the cost of hardware complexity. CDM based channel sounder, requires code with excellent auto- correlation and cross-correlation properties which generally difficult to be achieved simultaneously. Results: In this study, an efficient transmitter for CDM-ba sed 2◊2 MIMO channel sounding technique with Loosely Synchronous (LS) codes is designed. Si mulation results shows that the channel sounding scheme using LS codes gives very good performance for measuring 2◊2 MIMO channel behavior. The BPSK transmitter is designed using MATLAB, Verilog and Xilinx system generator blocks. Conclusion: The whole design is simulated as a single ISE proj ect by using ModelSim simulation tool and compiled using ISE 9.2. However the proposed design of transmitter using LS code of length 8190 bits can measure multipath delay of minimum 0.13 µs and maximum 520 µs.

An algorithm for controlling packet size in IEEE 802.16e networks

This paper proposes an algorithm to be used in IEEE 802.16e networks for adapting MAC PDU size to wireless channel behavior when ARQ is adopted at MAC layer. The algorithm is based on an analytical approach for dynamically evaluating the optimal packet size. The latter is derived from an expression of the ARQ protocol efficiency, obtained by exploiting a finite-state Markov error model which also takes into account Adaptive Modulation/Coding. The effectiveness of the designed algorithm in improving TCP performance has been evaluated.

Maximizing area throughput in clustered wireless sensor networks

In this paper we present a mathematical model to study a multi-sink Wireless Sensor Network (WSN). Both sensors and sinks are assumed to be Poisson distributed in a given finite domain. Sinks send periodic queries, and each sensor transmits its sample to a sink, selected among those that are audible, thus creating a clustered network. Our aim is to describe how the Area Throughput, defined as the amount of samples per unit of time successfully transmitted to the sinks from the given area, depends on the density of sensors and the query interval. We jointly account for radio channel, Physical (PHY), Medium Access Control (MAC) and Network (NET) aspects (i.e., different network topologies, packet collisions, power losses and radio channel behaviour), and we compare the performance of two different simple data aggregation strategies. Performance is evaluated by varying the traffic offered to the network (i.e., the density of sensors deployed), the packet size, and, by considering IEEE 802.15.4 as a reference case, the number of Guaranteed Time Slots allocated, and the Superframe Order. The mathematical model shows how the Area Throughput can be optimized.

Experimental investigation of mobile radio propagation at 1.8 GHz over macrocellular dense urban regions of Delhi

The design of future-generation mobile communication systems depends critically on the suitability of path loss prediction methods and their suitability to various regions. To investigate the radio channel behavior, experimental measurements in the 1.8 GHz band were conducted in the dense urban regions of New Delhi for six GSM base stations. Path loss exponents and break point distances have been deduced, and observed results have been compared with various prediction methods, and their standard deviations have been presented. Measured regression line exhibited lowest standard deviations followed by rooftop propagation method compared with Cost 231 Hata and Cost 231 Walfisch–Ikegami (WI) prediction methods. Variation of observed results has been explained in terms of vertical and horizontal propagation mechanisms which is the novelty of this paper.

Application of information criteria for the selection of the statistical small scale fading model of the radio mobile channel

Modeling of radio channel behavior is very important for digital communication. It is the reason why several propagation models have been implemented to take into account the electromagnetic phenomena inherent to the radio wave channel. So, among these models is the family of statistical distributions, fast in computation time, to describe channel fast fading. In this study context, our problematic is to find among the different statistical laws the one which best coincides with radio channel behavior. Different research has been realized on this subject over about 20 years. Thus, the Kolmogorov–Smirnov (KS) test using cumulative distribution functions (CDF) is usually employed by the radio mobile community partly for its simplicity. Nevertheless, there exist other approaches like Kulback–Leibler (KL) divergence, which consider distances between probability density functions that may be respresented as histograms. The bins of those histograms are obtained empirically, i.e. the bins are same size and their number is arbitrary. The authors propose approaches allowing optimal histograms in terms of the number and size of bins. These approaches are based on information criteria and we show that the KL discriminative method is more stable with the optimal histograms than with the empirical one. Moreover, our approaches are more reliable than the KS test whatever the number of considered samples. This last point is directly connected to the campaign of measures or of deterministic simulations, the duration of which can be very significant.

Energy-Efficient Decentralized Cooperative Routing in Wireless Networks

Wireless adhoc networks transmit information from a source to a destination via multiple hops in order to save energy and, thus, increase the lifetime of battery-operated nodes. The energy savings can be especially significant in cooperative transmission schemes, where several nodes cooperate during one hop to forward the information to the next node along a route to the destination. Finding the best multi-hop transmission policy in such a network which determines nodes that are involved in each hop, is a very important problem, but also a very difficult one especially when the physical wireless channel behavior is to be accounted for and exploited. We model the above optimization problem for randomly fading channels as a decentralized control problem - the channel observations available at each node define the information structure, while the control policy is defined by the power and phase of the signal transmitted by each node. In particular, we consider the problem of computing an energy-optimal cooperative transmission scheme in a wireless network for two different channel fading models: (i) slow fading channels, where the channel gains of the links remain the same for a large number of transmissions, and (ii) fast fading channels, where the channel gains of the links change quickly from one transmission to another. For slow fading, we consider a factored class of policies (corresponding to local cooperation between nodes), and show that the computation of an optimal policy in this class is equivalent to a shortest path computation on an induced graph, whose edge costs can be computed in a decentralized manner using only locally available channel state information (CSI). For fast fading, both CSI acquisition and data transmission consume energy. Hence, we need to jointly optimize over both these; we cast this optimization problem as a large stochastic optimization problem. We then jointly optimize over a set of CSI functions of the local channel states, and a corresponding factored class of control policies corresponding to local cooperation between nodes with a local outage constraint. The resulting optimal scheme in this class can again be computed efficiently in a decentralized manner. We demonstrate significant energy savings for both slow and fast fading channels through numerical simulations of randomly distributed networks.

A Multi-Scale Statistical Control Process for Mobility and Interference Identification in IEEE 802.11

The user centric nature of mobile devices is an important issue for enhancing the user experience in a mobile wireless communication. A strategy for improving such experience consists of applying a resource management focused in providing both the user and the application valuable information about the network context. The communication quality in wireless systems heavily depends on several factors, and adjusting the application and/or alerting the user about the network conditions is an important service when managing this type of devices. The quality perceived by the user depends on the network context, which can be defined as the events that have significant impact on the wireless communication. The identification of the wireless channel behavior is necessary for obtaining a context description. Due to intrinsic features at the wireless signal propagation it is difficult to measure and assess the fundamental wireless network context, e.g., predicting when low quality signal is being caused by interference or fading effects. This work presents a new method for user centric management on IEEE 802.11b/g: a strategy for communication survival, focused in improving the user experience. Our proposal uses a multi-scale control chart approach, MCEWMA --- Moving Centerline Exponential Weighted Moving Average, associated with multi-resolution analysis using a wavelet transform.

Redundancy Concepts to Increase Transmission Reliability in Wireless Industrial LANs

Wireless LANs are an attractive networking technology for industrial applications. A major obstacle toward the fulfillment of hard real-time requirements is the error-prone behavior of wireless channels. A common approach to increase the probability of a message being transmitted successfully before a prescribed deadline is to use feedback from the receiver and subsequent retransmissions (automatic repeat request-ARQ-protocols). In this paper, three modifications to an ARQ protocol are investigated. As one of these modifications a specific transmit diversity scheme, called antenna redundancy, is introduced. The other modifications are error-correcting codes and the transmission of multiple copies of the same packet. In antenna redundancy the base station/access point has several antennas. The base station transmits on one antenna at a time, but whenever a retransmission is needed, the base station switches to another antenna. The relative benefits of using FEC versus adding antennas versus sending multiple copies are investigated under different error conditions. One important result is that for independent Gilbert-Elliot channels between the base station antennas and the wireless station the antenna redundancy scheme effectively decreases the probability of missing a deadline, in a numerical example approximately an order of magnitude per additional antenna can be observed. As a second benefit, antenna redundancy decreases the number of transmission trials needed to transmit a message successfully, thus saving bandwidth.

A Time-Slot Assignment Strategy for ATM Broadband Indoor Wireless Networks

The rapid development of wireless in-building communication systems, has widened the scope of supported applications. Remote terminals may be capable of producing broadband real-time traffic such as variable bit-rate (VBR) video or bursty data transfers. Consequently one of the important issues in indoor broadband wireless networks (IBWN) is employment of an efficient bandwidth management protocol. In such a protocol, both the effects of radio channel behavior and the traffic heterogeneity have to be considered. In this paper we present a bandwidth allocation scheme based on the interplay of the radio channel characteristics and the traffic parameters and requirements. In the proposed scheme the base station visits the terminals in a non-uniform cyclic fashion. The inter-visit interval and the amount of service which is provided to each user during a visit, is determined using the channel and traffic parameters based on an analytical approach. This system is evaluated by simulations and is found to provide improved performance in fulfilling the requirements of multimedia services in IBWN.