Path Loss Parameters Research Articles

Tracking Mobile User through Adaptive Beamforming for Wireless Cellular Networks in a 2D Urban Environment

The interference reduction capability of array antennas and the power control (PC) algorithms have been considered separately as means to increase the capacity in wireless communication networks. The capability of the smart antenna systems to track the user with the main lobe and interference with the nulls creates a significant impact on the current and future wireless sensor networks. In this paper, we use constrained least mean square (CLMS) and conjugate gradient adaptive beam-forming (CGBF) algorithms for narrowband adaptive beam-forming for tracking mobile user in a 2D urban environment without using PC algorithm. The CLMS algorithm is capable of efficiently adapting according to the environment and able to permanently maintain the chosen frequency response in the look direction while minimizing the output power of the array. In addition, with the CGBF algorithm, the desired users' signal in an arbitrary path is passed and the inter-path interference (IPI) is canceled in other paths in each RAKE finger. The adaptability of the algorithms is closely observed for uniformly spaced linear array. Also in this paper, we present switched-beam (SB) technique. In the SB technique by using a number of fixed, independent, or directional antennas we increase the uplink capacity of the wireless systems. Simulation results indicate that the SB technique is able to considerably increase the signal to interference plus noise ratio (SINR) of mobile user in comparison with other algorithms. In addition, we observe that the SINR in the CLMS algorithm is lower than the CGBF algorithm. Finally, we discuss perfect power control and path loss parameter in urban environments and their effects on system capacity by simulations.

Tracking mobile user through adaptive beamforming for wireless cellular networks in a 2D urban environment

The interference reduction capability of array antennas and the power control (PC) algorithms have been considered separately as means to increase the capacity in wireless communication networks. The capability of the smart antenna systems to track the user with the main lobe and interference with the nulls creates a significant impact on the current and future wireless sensor networks. In this paper, we use constrained least mean square (CLMS) and conjugate gradient adaptive beam-forming (CGBF) algorithms for narrowband adaptive beam-forming for tracking mobile user in a 2D urban environment without using PC algorithm. The CLMS algorithm is capable of efficiently adapting according to the environment and able to permanently maintain the chosen frequency response in the look direction while minimizing the output power of the array. In addition, with the CGBF algorithm, the desired users’ signal in an arbitrary path is passed and the inter-path interference (IPI) is canceled in other paths in each RAKE finger. The adaptability of the algorithms is closely observed for uniformly spaced linear array. Also in this paper, we present switched-beam (SB) technique. In the SB technique by using a number of fixed, independent, or directional antennas we increase the uplink capacity of the wireless systems. Simulation results indicate that the SB technique is able to considerably increase the signal to interference plus noise ratio (SINR) of mobile user in comparison with other algorithms. In addition, we observe that the SINR in the CLMS algorithm is lower than the CGBF algorithm. Finally, we discuss perfect power control and path loss parameter in urban environments and their effects on system capacity by simulations. Keywords: Antenna, Switched-beam, Power control, Urban signal propagation simulator, Wireless cellular network.

Performance of Ultrawideband Wireless Tags for On-Body Radio Channel Characterisation

Experimental characterisation of on-body radio channel for ultrawideband (UWB) wireless active tags is reported in this paper. The aim of this study is to investigate the performance of the commercially available wireless tags on the UWB on-body radio channel characterisation. Measurement campaigns are performed in the chamber and in an indoor environment. Statistical path loss parameters of nine different on-body radio channels for static and dynamic cases are shown and analyzed. Results demonstrated that lognormal distribution provides the best fits for on-body propagation channels path loss model. The path loss was modeled as a function of distance for 34 different receiver locations for propagation along the front part of the body. A reduction of 11.46% path loss exponent is noticed in case of indoor environment as compared to anechoic chamber. In addition, path loss exponent is also extracted for different body parts (trunk, arms, and legs). Second-order channel parameters as fade probability (FP), level crossing rate (LCR), and average fade duration (AFD) are also investigated.

COMPARISON OF TWO MEASUREMENT TECHNIQUES FOR UWB OFF-BODY RADIO CHANNEL CHARACTERISATION

This paper presents comparison of two measurement techniques for ultra wideband (UWB) off-body radio channel characterization. A measurement campaign was performed in indoor environment using UWB wireless active tags and reader installed with the tag antenna and same set of measurement was repeated in the frequency domain using Vector Network Analyser (VNA) and cable connecting two standalone tag antennas for comparison/with a view to finding out the cable effects. Nine different off-body radio channels were experimentally investigated. Comparison of path loss parameters and path loss model for nine different off-body radio channels for the propagation in indoor environment both measurement cases are shown and analyzed. Results show that measurement taken by VNA connecting two standalone antennas through cables experiences lower path loss value for all nine different off-body channels. Least square fit technique is obtained to extract the path loss exponent. Increase of 12.96% path loss exponent is noticed when measurements are made using UWB tags and reader, i.e., without cable measurement scenario.

Reverse Link Performance of DS-CDMA Cellular Systems through Closed-Loop Power Control, Base Station Assignment, and Antenna Arrays in 2D Urban Environment

The interference reduction capability of antenna arrays, base station assignment, and the power control algorithms have been considered separately as means to increase the capacity in wireless communication networks. In this paper, we propose smart step closed-loop power control (SSPC) algorithm and base station assignment method based on minimizing the transmitter power (BSA-MTP) technique for direct sequence-code division multiple access (DS-CDMA) receiver in a 2D urban environment. This receiver consists of conjugate gradient adaptive beamforming and matched filter in two stages using antenna arrays. In addition, we study an analytical approach for the evaluation of the impact of power control error (PCE) on the DS-CDMA cellular systems. The simulation results indicate that the SSPC algorithm and the BSA-MTP technique can significantly improve the network bit error rate in comparison with conventional methods. Our proposed methods can also significantly save total transmit power and extend battery life in mobile units. In addition, we show that the convergence speed of the SSPC algorithm is faster than that of conventional algorithms. Finally, we discuss two parameters of PCE and channel propagation conditions (path-loss parameter and variance of shadowing) and their effects on the capacity of the system via some computer simulations.

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The signal-to-interference & noise ratio (SINR) model is one of the most commonly studied physical (or fading channel) models for wireless networks. We survey some recent studies aiming at achieving a better understanding of the SINR model and its structural properties and developing efficient design algorithms and communication protocols for it. Physical models and SINR Traditional (wired, point-to-point) communication networks can be described satisfactorily using a graph representation. A station s is able to transmit a message to another station s′ if and only if there is a wire connecting the two stations. This condition is independent of the locations, connections and activities of the two stations or of other nearby stations1. Accurately representing a wireless network is considerably harder, since it is nontrivial to decide whether a transmission by a station s is successfully received by another station s′; this may depend on the positioning and activities of s and s′, and on other nearby stations, whose activities might interfere with the transmission and prevent its reception This means that a transmission from s may reach s′ in some settings but fail to reach it under other settings. Moreover, the question of successful reception is more complex, since connections can be of varying quality and capacity. In fact, there are many other relevant factors, such as the presence of physical obstacles, the directions of the antennae at s and s′, the weather, and more. Obtaining an accurate solution taking all of those factors into account involves solving the corresponding Maxwell equations. Since this is usually far too complicated, the common practice is to resort to approaches based on approximation models. For instance, one way to predict the behavior of wireless systems in an urban environment is using a ray tracing model, based on the assumption that radio waves behave according to geometric optics where walls are modeled as reflective mirrors. The uncertainly involved in the dynamics of a radio channel can be modeled using a Markov process. For more information we refer the interested reader to Chapters 2 and 3 of [9]. For the purposes of the current discussion, we follow the approach of ignoring those complicating factors, and assuming a relatively clean abstract setting where the only players are the transmitting and listening ∗Partially supported by a gift from Cisco research center and by the Israel Science Foundation, grant 894/09. excepting certain types of wired local area networks. ACM SIGACT News 74 June 2010 Vol. 41, No. 2 stations, and the antennae are omni-directional. In this setting, the rules governing the reception quality of wireless transmissions can be described schematically by physical or fading channel models. Among those, one of the most commonly studied is the signal-to-interference & noise ratio (SINR) model. In this model, the energy of a signal fades with the distance to the power of the path-loss parameter α. When a station s transmits, the message is successfully received by a listening station s′ if and only if the strength of the signal received by s′, divided by the strength of the interferences from other simultaneous transmissions (plus the background noise N ), exceeds some threshold β. Hence for a collection S = {s1, . . . , sn} of simultaneously transmitting stations in the plane, it is possible to identify with each station si a reception region H(si) around it, consisting of the points where the transmission of si is received correctly. More precisely, denote by dist(p, q) the Euclidean distance between p and q, and assume that each station si transmits with power Ei. At an arbitrary point p, the transmission of station si is correctly received if Ei · dist(p, si) N + ∑ j 6=iEj · dist(p, sj)−α ≥ β . This formula represents a rather general model concerning the allowed transmission power, referred to as the power control model, in which each station can control the power with which it transmits. A simpler (and weaker) model is the uniform wireless network model, which assumes that all transmissions use the same amount of energy, i.e., Ei = 1 for every i.

The capacity of wireless ad hoc networks with multi-packet reception

We compute the throughput capacity of random dense wireless ad hoc networks for multi-pair unicast traffic in which nodes are endowed with multi-packet reception (MPR) capabilities. We show that ? ((R(n))(1-2)/?/n1/?) and ? (R(n)) bits per second constitute tight bounds for the throughput capacity under the physical and protocol model assumptions, respectively, where n is the total number of nodes in the network, ? > 2 is the path-loss parameter in the physical model, and R(n) is the MPR communication range. In so doing, we close the gap between the lower and upper bounds of throughput capacity in the physical model. Compared to the capacity of point-to-point communication reported by Gupta and Kumar, MPR increases the order capacity of random wireless ad hoc networks under both protocol and physical models by at least ?(log n) and ? ((log n) ?-2/2?), respectively. We address the cost incurred in increasing the throughput capacity of wireless ad hoc networks over what can be attained when sources and destinations communicate over multi-hop paths under the physical model assumption. We define the power efficiency ?(n) as the bits of information transferred per unit time (second) in the network for each unit power, and compute such power efficiency for different techniques. We show that a lower power efficiency is attained in order to achieve higher throughput capacity.

Calibration of a UWB Sub-Band Channel Model Using Simulated Annealing

This communication presents a calibration method of an indoor UWB sub-band deterministic channel model by means of simulated annealing. Based on the characterization of the channel at sub-bands with a subset of measurement locations, the calibration optimizes the dielectric material parameters of the environment, which improves the accuracy of the model in terms of path loss (L) and time dispersion parameters (root mean square delay spread sigma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tau</sub> and maximum excess delay tau <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) at all test locations within the test area. The performance of the calibration has been assessed by two indoor measurement campaigns, including line of sight (LOS) office and corridor and non line of sight (NLOS) corridor-office at the Antenna, Propagation and Networking Section building at Aalborg University and at the building of the Institut fur Nachrichtentechnik at Braunschweig Technical University. A reasonable performance of the calibration is noticed in improving the model accuracy within the building, requiring a few pilot measurements.

Statistical Characterization of 60-GHz Indoor Radio Channels

An extensive review of the statistical characterization of 60-GHz indoor radio channels is provided from a large number of published measurement and modeling results. First, the most prominent driver applications for 60 GHz are considered in order to identify those environment types that need to be characterized most urgently. Large-scale fading is addressed yielding path-loss parameter values for a generic 60-GHz indoor channel model as well as for the office environment in particular. In addition, the small-scale channel behavior is reviewed including the modeling of time-of-arrival and angle-of-arrival details and statistical parameters related to delay spread, angular spread and Doppler spread. Finally, some research directions for future channel characterization are given.

Characterization of On-Body Communication Channel and Energy Efficient Topology Design for Wireless Body Area Networks

Wireless body area networks (WBANs) offer many promising new applications in the area of remote health monitoring. An important element in the development of a WBAN is the characterization of the physical layer of the network, including an estimation of the delay spread and the path loss between two nodes on the body. This paper discusses the propagation channel between two half-wavelength dipoles at 2.45 GHz, placed near a human body and presents an application for cross-layer design in order to optimize the energy consumption of different topologies. Propagation measurements are performed on real humans in a multipath environment, considering different parts of the body separately. In addition, path loss has been numerically investigated with an anatomically correct model of the human body in free space using a 3-D electromagnetic solver. Path loss parameters and time-domain channel characteristics are extracted from the measurement and simulation data. A semi-empirical path loss model is presented for an antenna height above the body of 5 mm and antenna separations from 5 cm up to 40 cm. A time-domain analysis is performed and models are presented for the mean excess delay and the delay spread. As a cross-layer application, the proposed path loss models are used to evaluate the energy efficiency of single-hop and multihop network topologies.

Many-to-many communication for mobile ad hoc networks

We introduce a collaboration-driven approach to the sharing of the available bandwidth in wireless ad hoc networks, which we call many-to-many communication, that allows concurrent multi-packet transmissions (MPTs) and multi-packet receptions (MPRs). Many-to-many communication also permits one-time multi-copy relaying of the same packet, which reduces the packet delivery delay compared to single-copy relaying without any penalty in capacity. Our scheme is based on the integration of multi-user detection and position-location information with frequency and code division in mobile ad hoc networks (MANETs). Transmissions are divided in frequency and codes according to node locations, and successive interference cancellation (SIC) is used at receivers to allow them to decode and use all transmissions from strong interfering sources. Consequently, the interference is divided into constructive interference (COI) and destructive interference (DEI). We show that, if each node is allowed to expand its bandwidth, both the link's Shannon capacity and the per source-destination throughput scale like O(nalpha/2) (upper-bound) and Omega[f(n)] (lower-bound), for n nodes in the network, a path loss parameter alpha > 2, and 1les f(n) < nalpha/2.

Reference Tag-based Indoor Localization Techniques

In WSN-based localization, there are many challenging points. The difficulty lies in the fact that communication signals in a space-limited indoor office environment are interfered and attenuated by multi-path, reflection, channel fading, deflection, diffraction, etc. In fact, it is quite difficult to develop a reliable signal propagation model in an office environment because it is challenging to accurately estimate the signal path loss parameter. This paper proposes using reference tags for online estimation of signal propagation model and for the reliable calculation of the time of flight of radio signals. Thus main contribution of this paper is to suggest localization schemes based on reference tag, which is so-called reference tag-based indoor localization (RTIL).

Analysis and modeling of upstream throughput in multihop packet CDMA cellular networks

We consider the problem of throughput modeling of wireless multihop packet CDMA networks with cellular overlay using simple forwarding strategies in the upstream. Considering the effect of shadowing and distance-dependent path loss, we approximate the probability density of interference at each base station (BS) and compare numerical and simulation results for different path-loss parameters. We derive the probability density of the received power at each BS due to transmission of one packet from a random node, as well as the probability distribution of the number of packets received at each node per time slot. Subsequently, we use the above results to approximate the probability density of the total received power at each BS based on calculations of moments. We observe that the probability density of intercell interference due to transmissions from terminals and routers may be approximated by normal and log-normal densities, respectively. We quantify the network performance based on throughput, total consumed power, and outage probability for different system parameters. For homogeneous link efficiencies, introducing routers into the network while reducing the transmission power increases the mean and variance of interference to the desired signal, hence higher outage probability. However, there are ample opportunities inherent to multihop structure, applicable to any of the physical, data link, and network layers, which help increase the overall achievable network throughput.

Path-loss and time dispersion parameters for indoor UWB propagation

The propagation of ultra wideband (UWB) signals in indoor environments is an important issue with significant impacts on the future direction and scope of the UWB technology and its applications. The objective of this work is to obtain a better assessment of the potentials of UWB indoor communications by characterizing the UWB indoor communication channels. Channel characterization refers to extracting the channel parameters from measured data. An indoor UWB measurement campaign is undertaken. Time-domain indoor propagation measurements using pulses with less than 100 ps width are carried out. Typical indoor scenarios, including line-of-sight (LOS), non-line-of-sight (NLOS), room-to-room, within-the-room, and hallways, are considered. Results for indoor propagation measurements are presented for local power delay profiles (local PDP) and small-scale averaged power delay profiles (SSA-PDP). Site-specific trends and general observations are discussed. The results for path-loss exponent and time dispersion parameters are presented.

Comparison between two different antennas for UWB on-body propagation measurements

The effect of two different antenna types on radio propagation in ultrawideband (UWB) on-body channel measurement are analyzed. Statistical path loss parameters and time domain channel characteristics [mean delay and root mean square (rms) delay spread] are extracted from measurement data. Reduction in rms delay spread is experienced when using printed horn shaped self-complementary antennas (HSCA) for specific body area links in comparison to monopole-like omnidirectional antennas, e.g., planar inverted cone antennas (PICA). Results show that the hybrid use of different type UWB antennas can effectively improve channel behavior in body-centric wireless networks.

Sensitivity of Handover Performance to Path Loss Exponent: A Variable Hysteresis Margin based Handover Initiation Algorithm

In this paper, we analyze the sensitivity of handover initiation algorithm to path loss exponent. The effect of the propagating model parameters on both the mean number of handovers, and handover initiation delay are investigated. The algorithm is based on signal strength measurements using relative signal strength with hysteresis margin approach. The mean number of handovers is estimated for a single trip of mobile station from one base station to another, henceforth referred to as handover rate. Different path loss exponents varying from 2 to 8 are used for the simulation and the corresponding impact on handover rate and delay was studied. It is observed that handover rate depends on the path loss exponent. In a nonuniform environment, path loss parameters may be different and a given handover scheme cannot give optimum results consistently in the entire cellular network. A variable hysteresis margin based scheme for optimum handover performance under different propagation environments is proposed. The simulation results yield optimized tradeoff between handover rate and handover initiation delay.

Investigations on radio propagation channel measurements at 2.2 GHz and 3.5 GHz for the fixed wireless access in an urban area

Within a competitive context the wireless local loop is emerging as an alternative to the traditional wireline network. This solution is attractive because of its low capital cost and its flexible deployment. Nevertheless a propagation channel study has to be performed so as to develop specific engineering tools and propagation models. This paper presents wideband propagation measurement results carried out in Mulhouse in a small cell environment at 2.2 GHz and 3.5 GHz. Under different propagation scenarios, the propagation channel is characterised in terms of path loss and wideband selectivity parameters. Because of the experimental setting, the influence of the receiving height, the frequency and the receiving antenna pattern on the deviations of the path loss and the selectivity parameters have been investigated.

A least squares path-loss estimation approach to handover algorithms

In this paper, a new class of linear handover algorithms is introduced and analyzed for two conflicting performance measures, namely, the average number of outages and the average number of handovers, for a given trip of the mobile station (MS). The new algorithm is based on the least squares (LS) estimate of path-loss parameters of the various radio links, assuming the distances between the MS and surrounding base stations (BSs) are known. First, a simplified system scenario consisting of only two BSs in a lognormal fading environment is assumed. Performance measures are derived through a theoretical approach, along the trip of a mobile terminal from one BS to the other. It is seen that for an average number of 1.2 handovers (the minimum value is one, given by the ideal reference case), the LS algorithm reduces the average number of outages by more than 30% with respect to the classical averaging algorithm. Furthermore, the above performance measures improve for longer estimation windows: both the estimation of the mobile speed and the window length tradeoff of averaging algorithms do not apply to the LS method. By using an extended version of the basic algorithm, these results were also observed in simulations of a more general system scenario, consisting of several BS's and a mobile terminal moving along a generic path.