Wireless Channel Performance Research Articles

Miniaturized Antenna Array-Based Novel Metamaterial Technology for Reconfigurable MIMO Systems.

In this work, a highly miniaturized microstrip antenna array based on two elements is proposed for multiple inputs multiple outputs (MIMO) application systems at sub-6 GHz frequency bands. The antenna is structured from a meander line in conjugate with an interdigital capacitor when excited through the monopole basic antenna. The proposed antenna elements are separated with a Minkowski factor-shaped metamaterial (MTM) column to achieve a separation distance (D) of 0.08λ at 3 GHz when printed on an FR-4 substrate. Later on, the antenna performance in terms of bandwidth and gain is controlled using a photonic process based on optical active switches based on light-dependent resistances (LDR). Therefore, the reconfiguration complexity with such a technique can be eliminated significantly without the need for a biasing circuit. The antenna design was conducted through several parametric studies to arrive at the optimal design that realizes the frequency bandwidth between 3 and 5.5 GHz with a maximum gain of about 4.5 dBi when all LDR terminals are off. For a wireless channel performance study-based massive MIMO environment, the proposed antenna is suitable to be configured in arrays of 64 × 64 elements. From this study, it was found the maximum bit error rate (BER) does not exceed 0.15 with a channel capacity (CC) of 2 Gbps. For validation, the antenna was fabricated based on two elements and tested experimentally. Finally, it was revealed that the measured results agree very well with simulations after comparing the theoretical calculations with the measured data.

Effect of Breathing on UWB Propagation Characteristics for Ingestible and Implantable Devices

Wireless in-body devices are those in which a medical sensor is introduced&#x2013;implanted or ingested&#x2013; inside the human body and communicates with a remote node. Some in-body applications demand high data rates, so ultrawideband (UWB) spectrum has been proposed as a good candidate because of its large bandwidth available. Besides, breathing can lead to internal movement of the torso and consequently, of devices installed in this area. Thus, the radio channel performance can be affected by such movement leading to a malfunction of the radio interface of the medical device. This work aims at analyzing the effect of breathing on the propagation channel by means of <i>in vivo</i> measurements in living animal models. Continuous wave (CW) measurements have been carried out for five different frequencies in the lower part of the UWB band, and the effects of breathing on the relative received power (module and phase) are analyzed and discussed.

V2V Radio Channel Performance Based on Measurements in Ramp Scenarios at 5.9 GHz

This paper focuses on vehicle-to-vehicle (V2V) radio channel properties under ramp scenarios with different structures. Ramps are categorized according to different construction structures into: 1) viaduct ramp with soundproof walls in an urban area and 2) a general ramp without soundproof walls in a suburban region. Furthermore, considering whether the line of sight is available, the entire propagation process of the radio signal is divided into various propagation zones. Propagation characteristics, including the distribution of fading, fading depth (FD), level crossing rate, average fade duration, Root-Mean-Square (rms) delay spread, propagation path loss, and shadow fading, have been estimated and extracted. In particular, the radio channel properties in different types of ramp scenarios are compared and some interesting findings are obtained: 1) an abrupt fluctuation of the received signal level (RSL) in the urban viaduct ramp scenario indicates the nonignorable impact of soundproof walls on V2V radio channel and 2) continuous changes of RSL and different FD values in various propagation zones can be observed in suburban ramp scenarios. Furthermore, the statistical characteristics of RMS delay spread are fitted using a generalized extreme value model with a good fit. Furthermore, propagation path loss is modeled, demonstrating the difference of path loss values in the transition region owing to the impact of soundproof walls. Overall, the research results emphasize the significance of the V2V radio channel modeling under ramp scenarios.

Belief propagation‐based compressed video sensing for mobile Internet

SummaryThe very high data rate applications such as streaming high‐definition video have attracted much attention of researchers in 5G systems. However, the design of 5G communication terminals faces several challenges, including how to reduce the computational burden of signal acquisition at the terminals and how to improve both the reconstruction quality and robust performance in wireless channels. How simple and fast online video acquisition can be implemented and how the original images can be recovered effectively by an offline algorithm for mobile Internet are taken into consideration in this paper. Specially, we firstly propose a Markov chain model to characterize variations of the video sequences' temporal correlation, wherein we utilize the measurement residue that reflects the intensity changes to estimate the transition matrix. Then, a compressed video sensing framework for mobile Internet is presented with the belief propagation algorithm and the proposed video signal model. Numerical results show that our proposal could efficiently utilize the temporal correlation in video and then obtain both the improved reconstruction quality and robust performance in wireless communication systems. Copyright © 2015 John Wiley &amp; Sons, Ltd.

SIMO channel performance evaluation on indoor environment at 2.4 GHz

This work presents an experimental study of single-input multiple-output (SIMO) channel performance in the indoor radio propagation environment. Indoor channel measurements at the 2.4-GHz ISM frequency band have been conducted using a versatile channel sounder test-bed platform. A single transmitting antenna, four receiving antennas with two proposed geometries and a four-branch receiver circuitry were used in order to achieve channel sounder measurements exploiting baseband signal-processing techniques. In-depth investigation of SIMO wireless channel performance was realised through three types of metrics: signal strength, gain coefficient and capacity. Performance results indicate SIMO channel capacity enhancement and illustrate differences between the two proposed geometries.

Comprehensive Design and Propagation Study of a Compact Dual Band Antenna for Healthcare Applications

In this paper, a dual band planar inverted F antenna (PIFA) has been investigated for cooperative on- and off-body communications. Free space and on-body performance parameters like return loss, bandwidth, radiation pattern and efficiency of this antenna are shown and investigated. The on- and off-body radio propagation channel performance at 2.45 GHz and 1.9 GHz have been investigated, respectively. Experimental investigations are performed both in the anechoic chamber and in an indoor environment. The path loss exponent has been extracted for both on- and off-body radio propagation scenarios. For on-body propagation, the path loss exponent is 2.48 and 2.22 in the anechoic chamber and indoor environment, respectively. The path loss exponent is 1.27 for off-body radio propagation situation. For on-body case, the path loss has been characterized for ten different locations on the body at 2.45 GHz, whereas for off-body case radio channel studies are performed for five different locations at 1.9 GHz. The proposed antenna shows a good on- and off-body radio channel performance.

Characterization of UHF Radio Channels for Wireless Sensor Systems Embedded in Surfboards

The radio propagation for wireless systems embedded in surfboards has been characterized with the aim of testing the quality of a person to surfboard communication and person to infrastructure in aquatic environments, by means of wireless body area networks combined with an adequate transport technology. Wireless channel performance was analyzed using an in house developed 3-D Ray Launching Method and validated by empirical measurements, showing good agreement with differences below 3 dB, showing the influence of multipath components generated in this context as well as the strong influence of the average height of sea waves, which was introduced within the deterministic algorithm employed. The adoption of precise radioplanning techniques can aid in the deployment of efficient and cost effective new wireless solutions and optimal antenna location, applied to surfing and extendable to other aquatic sports and applications.

Experimental Study of On-Body Radio Channel Performance of a Compact Ultra Wideband Antenna

In this paper, on-body radio channel performance of a compact ultra wideband (UWB) antenna is investigated for body-centric wireless communications. Measurement campaigns were first done in the chamber and then repeated in an indoor environment for comparison. The path loss parameter for eight different on-body radio channels has been characterized and analyzed. In addition, the path loss was modeled as a function of distance for 34 different receiver locations for propagation along the front part of the body. Results and analysis show that, compared with anechoic chamber, a reduction of 16.34% path loss exponent is noticed in indoor environment. The antenna shows very good on-body radio channel performance and will be a suitable candidate for future efficient and reliable body-centric wireless communications.

A Ray Launching-Neural Network Approach for Radio Wave Propagation Analysis in Complex Indoor Environments

A novel deterministic approach to model the radio wave propagation channels in complex indoor environments reducing computational complexity is proposed. This technique combines a neural network and a 3-D ray launching algorithm in order to compute wireless channel performance in indoor scenarios. An example of applying the method for studying indoor radio wave propagation is presented and the results are compared with a very high resolution fully 3-D ray launching simulation as the reference solution. The new method allows the use of a lower number of launched rays in the simulation scenario whereas intermediate points can be predicted using neural network. Therefore a high gain in terms of computational efficiency (approximately 80% saving in simulation time) is achieved.

Quantization Error's Influence on the Channel Estimation

To improve the transmission performance of wireless channel, the improvement of the Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) channel estimation algorithm based on the superimposed training sequence is proposed. We take advantage of training and information sequences unrelated, without loss of bandwidth preliminary estimate the channel parameters; Then using the weighted factor of channel parameters between adjacent signal weighted average, get the final channel parameters. Compared with previous superimposed training sequence estimation method, using the algorithm has a lower estimation mean square error (MSE), and is suitable for the time-varying channel. The computer simulation results show that the estimation method improves the accuracy and performance of channel transmission.

An Improved Adaptive Retransmission of RLP

In this article we focus on SIP session setup delay .It bases on adaptive RLP retransmission mechanism in the previous paper.It proposes a way used RLP retransmission strategy combined with the performance of wireless channels, that i s to say in different chain Road conditions use different RLP retransmission strategy approach. This method not only can complete the RLP adaptive retransmission of SIP messages at the link layer, and can select the appropriate link status of the different RLP retransmission strategy, thus effectively shortening the SIP session establishment delay, end to end QoS for IMS performance improvement. After a simulation experiment, the effectiveness of the proposed algorithm is tested.

Generalized Pollaczek-Khinchin Formula for Markov Channels

The wireless fading channels with finite input buffer, Poisson arrivals and two-state Markov modulated service processes (MMSP) are modeled as M/MMSP/1/K queues in this paper. The existing performance analyses of Markov channels are almost all based on the matrix-geometric method, which provides little physical insights for system design. By contrast, we focus on deriving closed-form analytic expressions with physical interpretations in terms of system parameters of interest. Our main contribution is to derive the generalized Pollaczek-Khinchin (P-K) formula of M/MMSP/1/K queue from start-service probability to explore the impact of state transitions on the queueing behavior of Markov channels. This generalized P-K formula reveals that the performance of wireless channels with varying rates can be fully characterized by a newly defined system parameter, called state transition factor β, which clearly explains the reason that the channel with slow state transition rate owns a larger delay for the same channel capacity. In the extreme case when the state transition factor β approaches 0, we show that the channel under consideration can be approximately modeled as an M/G/1 queue. We use the Type I Hybrid ARQ system with a fixed data-rate as an example in this paper to illustrate our results.

A New Nonbinary Quasi-cyclic LDPC Codes Construction Algorithm

An algorithm for constructing nonbinary Quasi-cyclic LDPC (QC-LDPC) codes on the basis of masking and puncturing techniques in consideration of the shortage of algebraic construction algorithm and time-varying performance of wireless channels is proposed . This scheme can reduce the complexity of the hardware implementation, enhance the error correction performance of the LDPC codes constructed by structure algorithm based on masking technology, and improve the average effectiveness of the communication system by realizing a rate-compatible encoding based on puncturing technology. The simulation results show that the nonbinary LDPC codes constructed with masking and puncturing techniques can provide significantly stronger error correction capabilities as compared with those constructed with algebraic method which are used directly.

Diversity in cascaded N*Nakagami channels

Short term fading conditions that are worse than those existing in typical Nakagami channels can be modeled using the cascaded approach where the received signal-to-noise ratio is treated as the product of N identical or nonidentical random variables that are either dependent or independent. Cascaded channels also permit the modeling of fading seen in amplify and forward relaying channels as well as keyhole channels. The simplest of these models, referred to as the N*Nakagami model, assumes that the received signal to noise ratio is the product of N independent and identically distributed gamma variables. The fading mitigation achieved in such cascaded channels through diversity is studied in this work. Through analytical approach and simulation, the performance of wireless channels is examined for the selection combining, equal gain combining, generalized selection combining, and maximal ratio combining algorithms. Results demonstrate the existence of severe degradations in cascaded fading channels and the comparative usefulness of the various algorithms in improving the data transmission capabilities. Even though the analysis was undertaken for the case of a coherent binary shift keying modem, results can easily be extended to other modems.

A Time-Domain Approach to the Analysis and Modeling of On-Body Propagation Characteristics Using Synchronized Measurements at 2.45 GHz

Modeling of on-body propagation channels is of paramount importance to those wishing to evaluate radio channel performance for wearable devices in body area networks (BANs). Difficulties in modeling arise due to the highly variable channel conditions related to changes in the user's state and local environment. This study characterizes these influences by using time-series analysis to examine and model signal characteristics for on-body radio channels in user stationary and mobile scenarios in four different locations: anechoic chamber, open office area, hallway, and outdoor environment. Autocorrelation and cross-correlation functions are reported and shown to be dependent on body state and surroundings. Autoregressive (AR) transfer functions are used to perform time-series analysis and develop models for fading in various on-body links. Due to the non-Gaussian nature of the logarithmically transformed observed signal envelope in the majority of mobile user states, a simple method for reproducing the fading based on lognormal and Nakagami statistics is proposed. The validity of the AR models is evaluated using hypothesis testing, which is based on the Ljung-Box statistic, and the estimated distributional parameters of the simulator output compared with those from experimental results.

Cross-layer performance control of wireless channels using active local profiles

To optimize performance of applications running over wireless channels state-of-the-art wireless access technologies incorporate a number of channel adaptation mechanisms. While these mechanisms are expected to operate jointly providing the best possible performance for current wireless channel and traffic conditions, their joint effect is often difficult to predict. To control functionality of various channel adaptation mechanisms a new cross-layer performance optimization system is sought. This system should be responsible for exchange of control informationbetween different layers and further optimization of wireless channel performance. In this paper design of the cross-layer performance control system for wireless access technologies with dynamic adaptation of protocol parameters at different layers of the protocol stack is proposed. Functionalities of components of the system are isolated and described in detail. To determine the range of protocol parameters providing the best possible performance for a wide range of channel and arrival statistics the proposed system is analytically analyzed. Particularly, probability distribution functions of the number of lost frames and delay of a frame as functions of first- and second-order wireless channel and arrival statistics, automatic repeat request, forward error correction functionality, protocol data unit size at different layers are derived. Numerical examples illustrating performance of the whole system and its elements are provided. Obtainedresults demonstrate that the proposed system provide significant performance gains compared to static configuration of protocols.

Equation based rate control scheme for video streaming over wireless channels with link level ARQ

Equation based TCP-friendly rate control (TFRC) protocol has been proposed to support video streaming applications. In order to improve TFRC performance in wireless channels, the link level automatic repeat request (ARQ) scheme is usually deployed. However, ARQ cannot ensure strict delay guarantees, especially over multihop links. This paper introduces a theoretical model to deduce an equation for packet size adjustment in transport layer to minimize retransmission delay by taking into consideration the causative reasons inducing retransmission in link layer. An enhanced TFRC (ETFRC) scheme is proposed integrating TFRC with variable packet size policy. Simulation results demonstrate that higher goodput, lower packet loss rate (PLR), lower frame transmission delay and jitter with good fairness can be achieved by our proposed mechanism.

Effect of array orientation on performance of MIMO wireless channels

The orientations of the receive and transmit antennas are often omitted in research into the performance of wireless channels. The letter investigates the effect on performance of multiple-input-multiple-output (MIMO) wireless channels with an analytical method. Three results are obtained: 1) the effect cannot be neglected if either the transmit or the receive angular spread is small; 2) to attain higher capacity, each array should be rotated to make its normal point in the mean direction of arrival or departure (DOA or DOD); 3) the effect on the MIMO wireless channel capacity is dominated by the orientation of the array with the smaller angular spread.

Error modeling schemes for fading channels in wireless communications: A survey

Network system designers need to understand the error performance of wireless mobile channels in order to improve the quality of communications by deploying better modulation and coding schemes, and better network architectures. It is also desirable to have an accurate and thoroughly reproducible error model, which would allow network designers to evaluate a protocol or algorithm and its variations in a controlled and repeatable way. However, the physical properties of radio propagation, and the diversities of error environments in a wireless medium, lead to complexity in modeling the error performance of wireless channels. This article surveys the error modeling methods of fading channels in wireless communications, and provides a novel user-requirement (researchers and designers) based approach to classify the existing wireless error models.

Equal-gain diversity receiver performance in wireless channels

Performance analysis of equal-gain combining (EGC) diversity systems is notoriously difficult only more so given that the closed-form probability density function (PDF) of the EGC output is only available for dual-diversity combining in Rayleigh fading. A powerful frequency-domain approach is therefore developed in which the average error-rate integral is transformed into the frequency domain, using Parseval's theorem. Such a transformation eliminates the need for computing (or approximating) the EGC output PDF (which is unknown), but instead requires the knowledge of the corresponding characteristic function (which is readily available). The frequency-domain method also circumvents the need to perform multiple-fold convolution integral operations, usually encountered in the calculation of the PDF of the sum of the received signal amplitudes. We then derive integral expressions for the average symbol-error rate of an arbitrary two-dimensional signaling scheme, with EGC reception in Rayleigh, Rician, Nakagami-m (1960), and Nakagami-q fading channels. For practically important cases of second- and third-order diversity systems in Nakagami fading, both coherent and noncoherent detection methods for binary signaling are analyzed using the Appell hypergeometric function. A number of closed-form solutions are derived in which the results put forward by Zhang (see ibid., vol.45, p.270-73, 1997) are shown to be special cases.