Received Signal Quality Research Articles

Security Optimization of Exposure Region-Based Beamforming With a Uniform Circular Array

This paper investigates the impact of a uniform circular array (UCA) in the context of wireless security via exposure region-based beamforming. An improvement is demonstrated for the security metric proposed in our previous paper, namely, the spatial secrecy outage probability (SSOP), by optimizing the configuration of the UCA. Our previous paper focused on formalizing the SSOP concept and exploring its applicability using a uniform linear array example. This paper proposes the UCA as a superior candidate because it is more robust against the effects of mutual coupling. The UCA’s SSOP configuration is explored and a special expression is derived from the general expression for the first time, and a closed-form upper bound is then generated to facilitate analysis. By carefully designing the UCA structure particularly the radius, an SSOP optimization algorithm is derived and explored for mutual coupling. It is shown that the information leakage to eavesdroppers is reduced while the legitimate user’s received signal quality is enhanced due to the use of beamforming.

Digital Pre-Distortion of Carrier Frequency Offset for Reliable Wi-Fi Enabled IoTs

The Internet of Things (IoTs) will change the requirements for wireless connectivity significantly, mainly with regard to service coverage, data rate, and energy efficiency. Therefore, to improve robustness and reliability, WiFi-enabled IoT devices have been developed to use narrowband communication. However, narrowband transmission in WiFi such as IEEE 802.11ah causes relatively higher frequency error due to the reduced subcarrier space, which is larger than legacy wireless local area networks (WLANs) in 2.4/5 GHz frequencies. In a direct conversion receiver, this error degrades the signal quality due to the presence of direct current (DC) offset cancellation circuits. In this paper, a digital carrier frequency offset (CFO) predistortion scheme is proposed for a reliable communication link in dense networks. Evaluation results demonstrate that the proposed scheme can improve received signal quality in terms of packet error rate and error vector magnitude.

Mitigation of Scintillation Effects in WDM FSO System using Multibeam Technique

Free Space Optical communication (FSO) has engrossed a large section of researchers in recent times due to its wide bandwidth, effortless deployment and immune links making it appropriate for communication purposes. This wireless optical technique requires clear and non-turbulent atmospheric conditions for efficient transmission. In this paper, authors aim at reducing the effect of turbulent atmospheric conditions like scintillation effect on FSO. Multibeam technique, which uses spatially diverse transmitters for transmission, has been used for increasing the achievable link distance of the FSO system. Parameters like quality factor and bit error rate have been used to check the received signal quality.

Power-Efficient Distributed Beamforming for Full-Duplex MIMO Relaying Networks

Multiple-input–multiple-output (MIMO) full-duplex relaying (FDR) has been considered an efficient technique to provide coverage to users where their direct links from the base station (BS) are too weak for reliable signal reception. However, when multiple MIMO full-duplex relays are deployed in a network, the signal reception quality relies on the effective suppression of multiple types of interference. In this paper, the distributed beamforming is studied for the MIMO FDR network by formulating a power minimization problem with a nonstrict convex objective function (total transmit power of both the BS and all the relays in the network) under individual user rate constraints. We come up with two iterative distributed beamforming algorithms, Algorithm 1 for relays equipped with single receive antenna and Algorithm 2 with multiple receive antennas. The former can yield a global optimal solution of the power minimization problem, whereas the latter can yield only a local optimal solution due to conservative successive convex approximations (SCAs) performed at each iteration, and a rigorous analysis on the upper bounds of step sizes is proposed to guarantee their convergence. The proposed two algorithms only require local information exchange between relays and hence are scalable for different network sizes and topologies. An “early termination” strategy in the operation of the proposed two algorithms is also presented to acquire an acceptable transmit power solution with less computation time consumption and thus suitable for realistic applications. Finally, some simulation results are provided to demonstrate that the proposed two algorithms perform well and significantly better than the existing state-of-the-art scheme reported in the work of Lee and Shin.

Defining Spatial Secrecy Outage Probability for Exposure Region-Based Beamforming

With the increasing number of antennae in base stations, there is considerable interest in using beamforming to improve physical layer security, by creating an “exposure region” that enhances the received signal quality for a legitimate user and reduces the possibility of leaking information to a randomly located passive eavesdropper. This paper formalizes this concept by proposing a novel definition for the security level of such a legitimate transmission, called the spatial secrecy outage probability (SSOP). By performing a theoretical and numerical analysis, it is shown how the antenna array parameters can affect the SSOP and its analytic upper bound. While this approach may be applied to any array type and any fading channel model, it is shown here how the security performance of a uniform linear array varies in a Rician fading channel by examining the analytic SSOP upper bound.

TCP and MP-TCP in 5G mmWave Networks

Future 5G networks will likely include mmWave radio access communication links, because of their potential multi-gigabit-per-second capacity. However, these frequencies are characterized by highly dynamic channel conditions, which lead to wide fluctuations in the received signal quality. This article explains how the end-to-end user experience in mobile mmWave networks could be affected by a suboptimal interaction between the most widely used transport protocol, TCP, and mmWave links. It also provides insights on the throughput-latency tradeoff when Multipath TCP (MP-TCP) is used judiciously across various links, such as Long-Term Evolution (LTE) and mmWave.

Self-Learning RF Receiver Systems: Process Aware Real-Time Adaptation to Channel Conditions for Low Power Operation

Prior research has established that dynamically trading-off the performance of the radio-frequency (RF) front-end for reduced power consumption across changing channel conditions, using a feedback control system that modulates circuit and algorithmic level “tuning knobs” in real-time based on received signal quality, leads to significant power savings. It is also known that the optimal power control strategy depends on the process conditions corresponding to the RF devices concerned. This leads to an explosion in the search space needed to find the best feedback control strategy, across all combinations of channel conditions and receiver process corners, making simulation driven optimal control law design impractical and computationally infeasible. Since this problem is largely intractable due to the above complexity of simulation, we propose a self-learning strategy for adaptive RF systems. In this approach, RF devices learn their own performance vs. power consumption vs. tuning knob relationships “on-the-fly” and formulate the most power-optimal control strategy for real-time adaptation of the RF system using neural-network based learning techniques during real-time operation. The methodology is demonstrated using SISO and MIMO RF receiver front-ends as test vehicles and is supported by hardware validation leading to 2.5X-3X power savings with minimal overhead.

A Survey on Multiple-Antenna Techniques for Physical Layer Security

As a complement to high-layer encryption techniques, physical layer security has been widely recognized as a promising way to enhance wireless security by exploiting the characteristics of wireless channels, including fading, noise, and interference. In order to enhance the received signal power at legitimate receivers and impair the received signal quality at eavesdroppers simultaneously, multiple-antenna techniques have been proposed for physical layer security to improve secrecy performance via exploiting spatial degrees of freedom. This paper provides a comprehensive survey on various multiple-antenna techniques in physical layer security, with an emphasis on transmit beamforming designs for multiple-antenna nodes. Specifically, we provide a detailed investigation on multiple-antenna techniques for guaranteeing secure communications in point-to-point systems, dual-hop relaying systems, multiuser systems, and heterogeneous networks. Finally, future research directions and challenges are identified.

Macro cellular network transition from traditional frequency range to 28 GHz millimeter wave frequency band

The target of this article is to analyze the impact of transition from cellular frequency band i.e. 2.1 GHz to Millimeter Wave (mmWave) frequency band i.e. 28 GHz. A three dimensional ray tracing tool “sAGA” was used to evaluate the performance of the macro cellular network in urban/dense-urban area of the Helsinki city. A detailed analysis of user experience in terms of signal strength and signal quality for outdoor and indoor users is presented. Indoor users at different floors are separately studied in this paper. It is found that in spite of considering high system gain at 28 GHz the mean received signal power is reduced by almost 16.5 dB compared with transmission at 2.1 GHz. However, the SINR is marginally changed at higher frequency. Even with 200 MHz system bandwidth at 28 GHz, no substantial change is witnessed in signal quality for the outdoor and upper floor indoor users. However, the users at lower floors show some sign of degradation in received signal quality with 200 MHz bandwidth. Moreover, it is also emphasized that mobile operators should take benefit of un-utilized spectrum in the mmWave bands. In short, this paper highlights the potential and the gain of mmWave communications.

Variable weight Khazani-Syed code using hybrid fixed-dynamic technique for optical code division multiple access system

Future Internet consists of a wide spectrum of applications with different bit rates and quality of service (QoS) requirements. Prioritizing the services is essential to ensure that the delivery of information is at its best. Existing technologies have demonstrated how service differentiation techniques can be implemented in optical networks using data link and network layer operations. However, a physical layer approach can further improve system performance at a prescribed received signal quality by applying control at the bit level. This paper proposes a coding algorithm to support optical domain service differentiation using spectral amplitude coding techniques within an optical code division multiple access (OCDMA) scenario. A particular user or service has a varying weight applied to obtain the desired signal quality. The properties of the new code are compared with other OCDMA codes proposed for service differentiation. In addition, a mathematical model is developed for performance evaluation of the proposed code using two different detection techniques, namely direct decoding and complementary subtraction.

Field Trial of Licensed Shared Access with Enhanced Spectrum Controller Power Control Algorithms and LTE Enablers

This paper presents the results from a field trial of the Licensed Shared Access (LSA) concept using TD-LTE network in the 3rd Generation Partnership Project spectrum band 40 (2.3–2.4 GHz) in Finland. In the field trial, the LTE network shared the spectrum with a program making and special events Incumbent. New LSA concept elements, LSA Repository for Incumbent protection information and LSA Controller for controlling the mobile broadband network in the same spectrum band were implemented in the trial environment. The trial utilized commercially available network elements like multimode multiband terminals, LTE base stations, core network and network management system. Incumbent spectrum usage data was collected to the LSA repository, which further converts it to spectrum availability information for the LSA controller. The trial goes beyond previous LSA demonstrations by presenting LSA controller power control concept algorithm that formulate the optimization objective as a function of base station cell transmit powers. An advantage of this procedure is that considering aggregated interference from the LTE network to Incumbent and adjusting the transmit power levels do not result in abrupt changes in the received signal quality and results better overall throughput. The developed LSA controller was implemented as self-organizing network solution integrated into network management system. Numerical results are presented to quantify the duration of the LSA procedure flow. The performance results on the LSA system workflow indicated that in the program, making special event use case the LSA band can be managed timely manner and the Incumbents’ rights can be protected.

Increasing Accuracy of Combined GPS and GLONASS Positioning using Fuzzy Kalman Filter

In this paper, combined GPS and GLONASS positioning systems are discussed and some solutions have been proposed to improve the accuracy of navigation. Global Satellite Navigation System (GNSS) is able to provide position, velocity and time with respect to coordinated universal time. GNSS positioning is based on received satellite signals, so its performance is highly dependent on the quality of these received signals. The effect of noise and multi-path can often be large enough to produce significant errors in positioning. Satellite navigation is difficult in this situation. In such circumstances, GPS or GLONASS alone are often not able to ensure consistency and accuracy in positioning due to the absence (or low quality) of signals. The combination of these two systems is an appropriate solution to improve the situation. In positioning a receiver, one of the ways that is often used to reduce the error due to observation noise and calculation errors is Kalman Filter (KF) estimation. In this paper, some changes in the structure of the KF is applied to improve the accuracy of positioning. Process of updating KF's gain, is done in fuzzy form based on the parameters available in RINEX files, including the P code pseudo-range used as an input of the proposed fuzzy system. Simulation results show that applying a fuzzy KF based on P code pseudo-range on the available data sets, in terms of noise and blocking condition, reduces the positioning error respectively from 24 to 14 meters and 90 to 25 meters.

Fountain-Coding Aided Strategy for Secure Cooperative Transmission in Industrial Wireless Sensor Networks

Cooperative relaying communications is an efficient paradigm for end-to-end data delivery in industrial wireless sensor networks. However, due to the broadcast nature of radio propagation, it is challenging to guarantee the secrecy of cooperative transmissions under eavesdropping attacks. To deal with this issue, a fountain-coding aided relaying scheme is proposed in this paper, for which all the source packets are first encoded with fountain codes (FCs) and then transmitted over the channels. Based on the basic characteristic of FC transmissions, a sufficient number of coded packets have to be successfully received to recover the original data. Therefore, transmission secrecy is guaranteed if the legitimate receiver can accumulate the required number of FC packets before the eavesdropper does. To satisfy this condition, a cooperative jamming method is utilized to worsen the received signal quality at the eavesdropper. By applying the constellation rotation approach, the information-bearing signal and the jamming signal are designed carefully to reduce the negative effect of the jamming procedure on the legitimate receiver. To evaluate how the scheme behaves in wireless fading channels, the authors propose a novel performance metric, i.e., the quality-of-service violating probability (QVP), and derive its closed-form expression. Compared to the commonly used metrics in physical-layer security such as secrecy outage probability, QVP can give a more comprehensive performance evaluation for the system, including the delay, the reliability, and the security level as well. Finally, the theoretical analysis is validated by simulation results.

Interference Avoidance through Pilot-Based Spectrum Sensing Algorithm in Overlaid Femtocell Networks

Co-channel interference between macro–femtocell networks is an unresolved problem, due to the frequency reuse phenomenon. To mitigate such interference, a secondary femtocell must acquire channel-state knowledge about a co-channel macrocell user and accordingly condition the maximum transmit power of femtocell user. This paper proposes a pilot-based spectrum sensing (PSS) algorithm for overlaid femtocell networks to sense the presence of a macrocell user over a channel of interest. The PSS algorithm senses the pilot tones in the received signal through the power level and the correlation metric comparisons between the received signal and the local reference pilots. On ensuring the existence of a co-channel macrocell user, the maximum transmit power of the corresponding femtocell user is optimized so as to avoid interference. Time and frequency offsets are carefully handled in our proposal. Simulation results show that the PSS algorithm outperforms existing sensing techniques, even at poor received signal quality. It requires less sensing time and provides better detection probability over existing techniques.

Identifying the Effective Parameters for Vertical Handover in Cellular Networks Using Data Mining Techniques

The need for seamless mobility within the heterogeneous environment of cellular networks imposed the need for finding different vertical handover (VHO) mechanisms to select the best network. The selection process is based on different factors, such as: cost, battery status of Mobile Terminal (MT), the capacity of each network link, available bandwidth (ABW), received signal strength (RSS), etc. However, the major problem here is to find the most effective parameters for VHO and their priorities for these decision mechanisms. Besides, it would be useful to know the values of these parameters for data mining (DM). For this purpose, we collected real log data server of two mobile telecom companies in Lebanon, Touch and Alfa for Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS) networks. After preprocessing and discretizing the data, frequent patterns (FP) were extracted to summarize the log data files. The summarized data was then analyzed by using descriptive and visualization techniques in order to find the most effective parameters for handover (HO) process. Three effective parameters were obtained: the Received Signal Strength (RxLev/RSCP), the Available Bandwidth (ABW) and the Received Signal Quality (RxQual/EcNo). Results showed that they cooperatively work together to accomplish the same task. This paper provide an effective solution to identify the most valuable factors for vertical handover mechanism in telecommunication area by using frequent pattern mining.

Overhearing Protocol Design Exploiting Intercell Interference in Cooperative Green Networks

The conventional two-way relaying (TWR) protocol requires that the transmitter (receiver) in one direction must be the receiver (transmitter) in the other direction, a limitation precluding the application of the TWR for sophisticated real-world wireless networks. In this paper, the authors study a more general multicell system consisting of a downlink (DL) traffic in one cell and an uplink (UL) traffic in an adjacent cell, with a multiantenna relay located in the cell edge and shared by both cells. For the coexistence of DL and UL transmissions, the authors propose exploiting the overheard signals from the adjacent cell (commonly known as the intercell interference) to improve the quality of signal reception in both cells. To reduce the power consumption to suit for green networks, the authors design the optimum relay precoder to minimize the total power at the relay yet satisfying the rate constraints for both the DL and UL traffic flows. The original precoder design is a nonconvex problem that is difficult to solve. To make the problem tractable, the authors transform the nonconvex problem to an equivalent quadratically constrained quadratic program (QCQP), which is then solved by the semidefinite relaxation (SDR) technique. Finally, simulations validate the effectiveness of the authors proposed protocol together with the optimized relay precoder.

Flight Test Result for the Ground-Based Radio Navigation System Sensor with an Unmanned Air Vehicle.

The Ground-based Radio Navigation System (GRNS) is an alternative/backup navigation system based on time synchronized pseudolites. It has been studied for some years due to the potential vulnerability issue of satellite navigation systems (e.g., GPS or Galileo). In the framework of our study, a periodic pulsed sequence was used instead of the randomized pulse sequence recommended as the RTCM (radio technical commission for maritime services) SC (special committee)-104 pseudolite signal, as a randomized pulse sequence with a long dwell time is not suitable for applications requiring high dynamics. This paper introduces a mathematical model of the post-correlation output in a navigation sensor, showing that the aliasing caused by the additional frequency term of a periodic pulsed signal leads to a false lock (i.e., Doppler frequency bias) during the signal acquisition process or in the carrier tracking loop of the navigation sensor. We suggest algorithms to resolve the frequency false lock issue in this paper, relying on the use of a multi-correlator. A flight test with an unmanned helicopter was conducted to verify the implemented navigation sensor. The results of this analysis show that there were no false locks during the flight test and that outliers stem from bad dilution of precision (DOP) or fluctuations in the received signal quality.

Physical layer analysis of AWG based optical packet switch architecture

Optical packet switching is the next generation switching technique in conjunction with mature electronic switching. In optical packet switching, the core router plays an important role in the routing and buffering of packets. In recent past, AWG based optical router are proposed and heavily investigated due to its very low insertion loss and very simple wavelength dependent routing pattern. In this paper, a further modification in an AWG based optical packet switch is proposed. These modifications improve the signal reception quality at the output. Power budget analysis is presented to evaluate the buffer capacity. As a physical layer parameters, the minimum switch power is evaluated using the mathematical model and at the BER level of 10−9 the maximum buffering capacity is evaluated. Finally, simulation results are presented in terms of network layer parameters, packet loss probability and average delay. The packet loss probability is as low as 10−7 well under acceptable limits.

Measurements of Field Strength and HD Radio Reception Quality at VHF

This letter presents the results of field trials conducted in Brazil to evaluate the performance of digital broadcasting systems. Analog FM and digital HD radio signals broadcasting the same content were simultaneously transmitted in the urban and suburban areas of the city of Belo Horizonte in Brazil. A mobile unit recorded the received signal intensity and reception quality along radial routes of up to 24 km from the transmitter, thereby enabling the comparative assessment of the systems performance and the evaluation of the propagation loss.

Handover Scheme for 5G C/U Plane Split Heterogeneous Network in High-Speed Railway

Being a promising technology for fifth-generation (5G) communication systems, a novel railway communication system based on control/user (C/U) plane split heterogeneous networks can provide a high-quality broadband wireless service for passengers in high-speed railways with higher system capacity, better transmission reliability, and less cochannel interference. However, due to its special architecture where the C-plane and the U-plane must be split and supported by a macro Evolved Node B (eNB) and a phantom eNB, respectively, it would suffer more serious handover problem, particularly in intermacrocell handover, which directly degrades its applicability and availability in high-speed railways. Moreover, no technical specification has been released about this network architecture. Therefore, this paper focuses on redesigning and analyzing technical details and handover procedures based on Long-Term Evolution (LTE) specifications to guarantee the proposed system's practicability and generality and its analytical tractability. To resolve the handover problem, this paper proposes a handover trigger decision scheme based on GM(1, $n$) model of the grey system theory. By this scheme, the received signal quality from the $(N + hbox{1})$th measurement report can be predicted from the $N$th measurement period, and the predicted values can be then utilized to make the handover trigger decision. The simulation results show that the proposed scheme is capable of triggering handover in advance effectively and of enhancing handover success probability remarkably.