Digital Wireless Communication Research Articles

Multipurpose Modular Wireless Sensor for Remote Monitoring and IoT Applications.

Today, maintaining an Internet connection is indispensable; as an example, we can refer to IoT applications that can be found in fields such as environmental monitoring, smart manufacturing, healthcare, smart buildings, smart homes, transportation, energy, and others. The critical elements in IoT applications are both the Wireless Sensor Nodes (WSn) and the Wireless Sensor Networks. It is essential to state that designing an application demands a particular design of a WSn, which represents an important time consumption during the process. In line with this observation, our work describes the development of a modular WSn (MWSn) built with digital processing, wireless communication, and power supply subsystems. Then, we reduce the WSn-implementing process into the design of its modular sensing subsystem. This would allow the development and launching processes of IoT applications across different fields to become faster and easier. Our proposal presents a versatile communication between the sensing modules and the MWSn using one- or two-wired communication protocols, such as I2C. To validate the efficiency and versatility of our proposal, we present two IoT-based remote monitoring applications.

Design and Investigation of Photonic Crystal Antenna Performance for Expeditious Data Rate in Wireless Communication

Design and Investigation of Photonic Crystal Antenna Performance for Expeditious Data Rate in Wireless Communication

Experimental Results of Magnetic Communication Using the Giant Magnetoimpedance Receiver in Underwater Environments

This letter presents the topology of a novel approach to magnetic communication using a giant magnetoimpedance (GMI)-based receiver with a GMI sensor in underwater media such as freshwater. In addition, practical channel test results for the magnetic communication link of a GMI receiver in freshwater are first presented. For this test, a magnetic communication system using a GMI-based receiver, including triangularly arranged transmission coil antennas, was proposed. Wireless digital communication using quadrature phase shift keying (QPSK), which is less sensitive to noise and has a high data rate, was used to evaluate the proposed GMI receiver. Several performance metrics, such as constellation, data rate, and error vector magnitude, were measured at 20 kHz. The test results were meaningful, indicating that the proposed magnetic communication system using a GMI-based receiver can be a promising solution for wireless communication in extreme environments, such as underwater media.

Retracted: Research on the Inheritance of Miao Costume Culture Based on Digital Wireless Communication Technology

Retracted: Research on the Inheritance of Miao Costume Culture Based on Digital Wireless Communication Technology

A component-based coding–decoding approach to set-membership filtering for time-varying systems under constrained bit rate

This paper is concerned with the set-membership filtering (SMF) problem for a class of discrete time-varying systems with unknown-but-bounded noises under bit rate constraints. The communication between sensor nodes and filters is implemented through a wireless digital communication network with limited bandwidth. A bit rate constraint is first established to quantify the extent to which the network is constrained. A component-based coding–decoding procedure is proposed that enables individual decoder to decode messages from different components scattering in different physical locations. Based on this procedure, a decoded-measurement-based recursive SMF scheme with a prediction–correction structure is put forward. The desired parameters of the set-membership filter can be calculated recursively by the proposed recursive SMF scheme. Furthermore, the co-design issue of the bit rate allocation protocol and the filter gain is converted into the mixed-integer nonlinear programming problem that is solved by means of the particle swarm optimization and the recursive filtering algorithms. Finally, numerical simulations on two scenarios are conducted to validate the effectiveness of the proposed SMF approach.

Distributed Filtering Under Constrained Bit Rate Over Wireless Sensor Networks: Dealing With Bit Rate Allocation Protocol

This article is concerned with the distributed filtering issue for linear discrete-time systems under bounded noises and constrained bit rate over wireless sensor networks. The communication between different sensor nodes is implemented via a wireless digital communication network with limited bandwidth. A bit rate constraint, which is subject to the so-called bandwidth allocation strategy, is placed to quantify the effect of the network bandwidth on the distributed filtering performance. An improved coding–decoding procedure is proposed to enable each node to decode messages from its neighbor nodes. Based on this procedure, a decoded-innovation-based distributed filtering scheme is put forward and a sufficient condition is established to ensure that the filtering error dynamics is ultimately bounded. Subsequently, a relationship between the bit rate and certain specific filtering performance is discovered. The desired parameters of the distributed filter are determined via solving two optimization problems whose objectives are actually the filtering performance indices including the smallest ultimate bound and the fastest decay rate. Furthermore, the codesign issue of the bit rate allocation protocol and the filter gain is converted into the mixed integer nonlinear programming problem, which is solved by means of the particle swarm optimization algorithm and the linear matrix inequality technique. Finally, numerical simulations on three scenarios are provided to verify the validity of the proposed distributed filtering approach.

Investigation of the antenna characteristics with the impact of hexagonal metamaterial

SummaryAntenna miniaturization is a typical trend in contemporary wireless systems, notably for current wireless technology, to meet multiband needs while preserving high transmission qualities. The terahertz (THz) regime is helpful in advanced applications and significantly impacts wireless technology. This paper proposes a double‐layered hexagonal split ring resonator (HSRR) based on a microstrip patch antenna (MPA) and analyzes the simulated characteristics. The HSRR width is varied for different thickness “w” values and compares the analysis of with and without HSRR in the antenna. Due to the impact of metamaterials, the optimized antenna produces −44.02‐dB return loss, 1.012 voltage standing wave ratio (VSWR), 6.47‐dBi gain, and 4.78‐dB directivity at 1.8‐THz frequency. This proposed antenna is suitable for THz applications, which include high‐speed data rate in wireless communication, bio‐medical field, and THz spectrometer.

Assessment and Categorization of Biological Effects and Atypical Symptoms Owing to Exposure to RF Fields from Wireless Energy Devices

Nowadays, environmental electromagnetic fields exist everywhere and the whole population is exposed. The most widespread technologies engendering exposure to electromagnetic fields for the public and workers are radiofrequency wireless communication systems. Such exposure can have direct effects on living tissue involving biological problems or personal symptoms, as well as indirect effects restricting healthcare appliances. This assessment aims to analyze, examine and categorize the consequences of non-ionizing electromagnetic fields emitted by radiofrequency devices. This concerns biological effects in living tissues and atypical personal symptoms for short and long-term exposures. The evaluation methodology in this field of investigation is also discussed. In the article, these consequences as well as their evaluation techniques, in the case of wireless digital communication tools, are analyzed and reviewed. The categorization of exposure sources, the corresponding effects and their assessment methodologies are analyzed. The concept of systematic reviews and meta-analyses and their applications in various assessments of these effects and symptoms are reviewed and discussed.

Analysis of Different Types of Antenna for Television Network and Extracting C Band Channels

Television network is a system of transmitting and receiving television signals over a large area. Antenna is a device that converts electromagnetic waves into electric currents or vice versa. Antenna plays a crucial role in the performance and quality of television network. In this paper, we will analyze different types of antenna for television network, such as dipole antenna, yagi antenna, parabolic antenna and fractal antenna. We will compare their advantages and disadvantages, and suggest some criteria for choosing the best antenna for different scenarios. Dipole antenna is the simplest and most common type of antenna for television network. It consists of two metal rods or wires of equal length that are connected to a transmitter or receiver. Dipole antenna can receive signals from any direction in a horizontal plane, but has a low gain and a narrow bandwidth. Dipole antenna is suitable for local television stations or indoor applications. Yagi antenna is a directional antenna that consists of a dipole antenna and several parasitic elements, such as reflectors and directors. Yagi antenna can focus the signals in one direction and reject the signals from other directions, thus increasing the gain and reducing the interference. Yagi antenna has a moderate bandwidth and can be easily adjusted to different frequencies. Yagi antenna is suitable for long-distance television network or outdoor applications. Parabolic antenna is another directional antenna that consists of a parabolic reflector and a feed horn. Parabolic antenna can concentrate the signals into a narrow beam and achieve a high gain and a wide bandwidth. Parabolic antenna can also receive signals from satellites or other high-altitude sources. Parabolic antenna is suitable for satellite television network or high-definition television network. Fractal antenna is a novel type of antenna that uses fractal geometry to design its shape and structure. Fractal antenna can have multiple resonant frequencies and a large effective area, thus increasing the bandwidth and the efficiency. Fractal antenna can also have self-similarity and scalability, which means it can be miniaturized or enlarged without affecting its performance. Fractal antenna is suitable for digital television network or wireless communication network. In conclusion, different types of antenna have different characteristics and applications for television network. Depending on the factors such as distance, frequency, direction, interference, quality and cost, one can choose the best antenna for their specific needs

The Small UWB Monopole Antenna with Stable Omnidirectional Radiation Pattern

Ultra Wideband (UWB) technology is an unmodulated wireless digital communication system that uses an extremely short duration pulse to transmit information bit. Because of this pulse, the UWB system needs a very wide bandwidth. Federal Communication Commission (FCC) has regulated the 3.1 – 10.6 GHz frequency spectrum for UWB. Since FCC released this frequency, many research in telecommunication have been done on UWB systems. One of them is a development of an Antenna that is suitable for UWB devices. UWB antenna characteristics require FCC band, omnidirectional radiation pattern, and compact size. In order to meet these needs, an antenna with a simple structure in the form of a monopole patch antenna with a similar patch size and ground width has been designed. The antenna is built on an FR4 – epoxy substrate material, with 4.4 dielectric constant and 1.6 mm thickness. The antenna feeding structure consists of two 100 Ω and 50 Ω lines with a wideband impedance matching scheme using tapered side and tapered transformers. The antenna design and optimization processes are conducted using electromagnetic simulation software, and measurements are carried out in an anechoic chamber. Simulation and measurement results show good agreement, and the antenna can work at frequencies 3.5 - 11.3 GHz with a gain of 1.5 – 3.25 dBi and stable omnidirectional radiation patterns. The antenna has dimensions of 27 × 8 × 1.6 mm, which are smaller than the antenna reported in the last research and suitable to be applied on various UWB devices.

The Collaboration and Harmonization of Digital Biomarkers for Alzheimer's Research.

Among prominent unmet needs of the Alzheimer's disease and related dementia (ADRD) research community is the ability to leverage opportunities to improve the assessments of persons with and at risk for ADRD. This vision can be realized by providing the tools and infrastructure to transform dementia assessment using remote sensing and digital technologies, pervasive computing, and wireless communications, all in concert with high dimensional data analytics. The Collaborative Aging Research using Technology (CART) initiative (carthome.org), a non-proprietary, sharable end-to-end system for capturing and handling diverse kinds of digital data has been developed. The CART technology platform offers the opportunity to bring new assessment methodology and data types to NIA Alzheimer's Disease Research Centers (ADRC) and related centers and transform the clinical research enterprise. Herein we report on progress in capturing digital data across multiple ADRC's. Participants were recruited from affiliated studies at five NIA ADRC's (Digital Technology Core at Oregon Health & Science University, Minority Aging Research Study at Rush University, Cognitive Empowerment Program at Emory University and Georgia Institute of Technology, ALLFTD study at University of California San Francisco, and a pilot study of Mexican Americans at University of Texas Health Science Center at San Antonio). Field technicians at each center installed the CART technology platform in the home of each participant. A total of 195 research participants have been enrolled across the 5 centers and followed for a median of 19 months (range 1-46). A summary of the center cohorts is provided in the table. The flexibility of the platform and its components has allowed it to successfully be adapted for research in each of these studies with diverse cohorts, use cases, and research aims. Attrition due to technology concerns has been very low (0.5%). Digital biomarker and related data can be readily captured across diverse cohorts, research teams, and settings using a common platform. The largely passive, continuous, and objective data generated with this approach promises to improve the opportunity to create more quantitative and ecologically valid measurements for ADRD phenotypes within the ADRD research community and related research settings.

The Collaboration and Harmonization of Digital Biomarkers for Alzheimer’s Research

AbstractBackgroundAmong prominent unmet needs of the Alzheimer’s disease and related dementia (ADRD) research community is the ability to leverage opportunities to improve the assessments of persons with and at risk for ADRD. This vision can be realized by providing the tools and infrastructure to transform dementia assessment using remote sensing and digital technologies, pervasive computing, and wireless communications, all in concert with high dimensional data analytics. The Collaborative Aging Research using Technology (CART) initiative (carthome.org), a non‐proprietary, sharable end‐to‐end system for capturing and handling diverse kinds of digital data has been developed. The CART technology platform offers the opportunity to bring new assessment methodology and data types to NIA Alzheimer’s Disease Research Centers (ADRC) and related centers and transform the clinical research enterprise. Herein we report on progress in capturing digital data across multiple ADRC’s.MethodParticipants were recruited from affiliated studies at five NIA ADRC’s (Digital Technology Core at Oregon Health & Science University, Minority Aging Research Study at Rush University, Cognitive Empowerment Program at Emory University and Georgia Institute of Technology, ALLFTD study at University of California San Francisco, and a pilot study of Mexican Americans at University of Texas Health Science Center at San Antonio). Field technicians at each center installed the CART technology platform in the home of each participant.ResultA total of 195 research participants have been enrolled across the 5 centers and followed for a median of 19 months (range 1‐46). A summary of the center cohorts is provided in the table. The flexibility of the platform and its components has allowed it to successfully be adapted for research in each of these studies with diverse cohorts, use cases, and research aims. Attrition due to technology concerns has been very low (0.5%).ConclusionDigital biomarker and related data can be readily captured across diverse cohorts, research teams, and settings using a common platform. The largely passive, continuous, and objective data generated with this approach promises to improve the opportunity to create more quantitative and ecologically valid measurements for ADRD phenotypes within the ADRD research community and related research settings.

A Low-Cost Laboratory Practice for Fundamental Learning of Wireless Digital Communication

Several studies have shown that the main challenge in teaching complex systems involving many theoretical backgrounds to senior students is their lack of confidence. In this paper, we present an approach to the teaching methodology of an undergraduate course in a telecommunication study program. The first goal of this methodology is to help students understand the theoretical concepts behind wireless digital communication systems through direct practice to give them more exposure to a real system through affordable practice activities in an experiential context, utilizing an HF radio and a single-board computer (SBC). The second goal is to challenge senior students to understand the data link layer by using white box testing of the syntax of the programming language embedded in the SBC. This approach is ideally carried out based on offline and hands-on class activities, however, the pandemic condition made it unavoidable to do it online using a demonstration model. Feedback from students was collected through written comments, post-testing, including a facility index analysis, and a questionnaire that was distributed using the available e-learning system. The post-test results showed that the average score was 72 out of a maximum of 100.

Perspectives On The Philosophy Of Education Progressivism In Learning Models Ubiquitous Learning

The development of technology in the world of education gave birth to various new learning models and methods, one of which is Ubiquitous Learning. Ubiquitous Learning is u-u-learning, referred to as u-learning, leveraging digital content, physical environments, mobile devices, pervasive components, and wireless communication to provide users with a teaching-learning experience anytime, anywhere, and anywhere. The birth of Ubiquitous Learning is in line with and in line with the philosophical view of progressivism which considers education to always innovate or change in accordance with the changing times and science and technology in another sense the philosophy of progressivism is a school of modern educational philosophy that wants a change in the implementation of education to be more advanced. This study aims to analyze uLearning learning in the perspective of the philosophy of progressivism to see the relationship and assess the compatibility of the two concepts in indonesian education today, the research method uses qualitative methods with a literature review approach on Ubiquitous Learning and analyzed using the philosophical theory of progressivism. The results of the study can be explained as follows, first: Ubiquitous Learning is a learning model in which there is a separation between students and teachers in the teaching and learning process so that students are emphasized to learn more independently from where and at any time by using technological facilities and networks both the philosophy of progressivism education is a belief in the natural power of man, the power that is passed on to humans from birth who have been bring basic talents and abilities or potentials, especially their resourcefulness, so that humans will be able to overcome all the problems of their lives Third: the philosophy of progressivism education views the elements contained in distance education model Ubiquitous Learning as an effort to provide alternative education that is constrained to follow education in general.

W-band Scalable 2×2 Phased-Array Transmitter and Receiver Chipsets in SiGe BiCMOS for High Data-Rate Communication

This article presents a pair of W-band phased-array transmitter (TX) and receiver (RX) chipsets in a 0.13- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> SiGe BiCMOS process for high data-rate wireless communication. Both the chips integrate four compact front-end channels in 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 distribution, and the distance between the adjacent RF pads is less than 1.8 mm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.56\lambda $ </tex-math></inline-formula> at 90 GHz) to fit for the tight antenna array and enable array scaling by tiling multiple unit cells. A 6-bit active phase shifter based on the improved phase-inverting variable gain amplifiers is leveraged to achieve high phase-shift precision and bandwidth concurrently. A noise reduction technique using a parallel inductor to resonate with the parasitic capacitors of the cascode transistors is adopted in the low-noise amplifier design. A novel miniature power combiner, which occupies a much more compact area than the Wilkinson power combiner while delivering great RF performance, is proposed and elaborately analyzed. System-level calibration for local oscillator (LO) leakage and dc-offset suppression is enabled by introducing digitally controlled current sources into the up-conversion and down-conversion mixers. On-wafer measurements for the TX chip exhibit a single-channel IF-to-RF conversion gain (CG) of 26 dB, a competitively high output 1-dB compression point (OP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {1\,dB}}$ </tex-math></inline-formula> ) of 11 dBm. The RX chip achieves an RF-to-IF CG of 19.5 dB with 9-/14-GHz IF/RF 3-dB bandwidth, a noise figure of 7.7 dB, and an input 1-dB compression point of −28 dBm. The phase-shift characteristics are verified by the TX/RX front-end measurements, achieving a 6-bit phase resolution with minimum rms phase/gain error smaller than 0.83°/0.45 dB and a large phase-shift bandwidth higher than 20 GHz. Preliminary wireless transmission test using a low-cost die-on-printed circuit board (PCB) prototype demonstrates wireless data rates of 1.6 and 0.8 gigabits per second (Gb/s) at distances of 0.4 and 1 m with 256-quadratic-amplitude modulation (QAM) and 16-QAM modulated signals, respectively.

Wireless Communication Signals: A Laboratory-Based Approach

The book provides a comprehensive set of tools for communication engineers and interested researchers for the analysis and design of wireless systems by discussing not only the basic theory, but also modeling, computer simulation, and hardware testing of the various building blocks of modern communication systems. The code snippets throughout the book enable readers to attain hands-on experience by implementing them on software and observing the effect of various parameters on the performance of the system. While the book is not explicitly divided into different parts, there is a general harmony and progression in the way the chapters are arranged. Considering the broad scope of this book and its in-depth coverage of many practical issues regarding modern wireless communication systems, we believe that it can be used as a textbook or a valuable reference for a senior undergraduate or graduate-level laboratory-orientied course focusing on wireless digital communications. The book is organized in such a way that it can be used to support various wireless and/or digital communication courses from beginner to advanced levels, and can serve as a reference for research projects of both undergraduate and graduate students. More importantly, the models and codes introduced in this book are universal and can be used in conjunction with any software-defined radio platform. Considering all these, this book is a valuable resource for our community.

Lamb Wave Wireless Communication Through Healthy and Damaged Channels With Symmetrical and Asymmetrical Steps and Notches.

Data transmission through solid metallic channels is recommended in certain industries where no other options are proposed, such as nuclear, aerospace, and smart vehicles. In addition to the Faraday shielding effect of electromagnetic waves, another issue related to damage presence due to mechanical loads exists. Severe damage in the transmission channel leads to signal loss at the receiver. For this sake, ultrasonic guided waves, such as Lamb waves, maybe a good substitute since they can propagate through long distances in solid metallic structures. The scope of this work is to build a reliable, reproducible, and high data-rate wireless communication experimental platform, using ultrasonic guided waves, through healthy and damaged plates for industrial usage. The target is to compensate at first for the effect of dispersion, reverberation, scattering, and boundary reflections for the healthy plate. The novelty of this work falls within the performance analysis of the demodulation algorithm based on cross-correlation combined with binary phase-shift keying (BPSK), using a finite-element simulation through healthy and damaged plates with different depths of symmetrical and asymmetrical notches (SN and AN) and steps based on the bit error percentage (BEP). Furthermore, another contribution related to the impact of multiple reflections and mode conversions caused by symmetrical and asymmetrical steps and notches is taken into account. After this, numerical results are validated using an ultrasonic guided wave experimental platform. Results based on BEP analysis prove that the algorithm has successfully compensated for the effect of dispersion and boundary reflections for the healthy plate and multiple reflections and mode conversions for the damaged ones. A highly effective data rate of up to 350 kb/s can be reached even in the presence of severe damage in the transmission channel.

Research on the Inheritance of Miao Costume Culture Based on Digital Wireless Communication Technology

The protection of the popular culture of local ethnic minorities is an inevitable requirement for building a multicultural system. Through the latest digital technology, through the Internet, digital images, and other technologies, traditional cultural resources are classified and integrated, so that they can be inherited. The purpose of this study is to study the cultural heritage of digitized Miao costumes. This paper introduces the background and importance of the digital protection of Miao costume culture, analyzes in detail the current situation of Miao costume culture, the application of digital protection technology at home and abroad, and analyzes and organizes the research content that introduces the importance of digital protection of Miao costumes. Provide real data support for clothing culture protection. Collect relevant data through questionnaire survey, conduct quantitative statistical analysis, and study the impact of modern cultural communication tools such as television, mobile phones, and the Internet on the inheritance of Miao costume culture under the digital background. The results showed that only 5 of the 216 people were reluctant to use digital dissemination of Miao costumes.

Experimental Assessment of a Magnetic Induction-Based Receiver for Magnetic Communication

This paper presents the topology of a novel approach to magnetic communication using a differential magnetic induction (MI)-based receiver and a differential MI receiving sensor. In this paper, a differential MI sensor based on two ferromagnetic cores is proposed as a receiving sensor, unlike the air coil-type MI sensor in the conventional search coil sensor concept. This differential MI sensor has the advantages of ultra-high sensitivity characteristics of the pT/√Hz level, which can detect weak magnetic fields in magnetic communication; moreover, the sensor is smaller than a conventional air coil MI sensor. The proposed differential MI sensor contributes to improving sensor performance by increasing its signal-to-noise ratio. The design and fabrication of the proposed MI sensor were based on a printed circuit board (PCB). The pickup coil of the PCB-based MI sensor directly wound the pickup coil onto a ferromagnetic core composed of Ni-Zn ferrite material. To analyze the key factors that affected the performance of the receiver, the magnetic field-to-voltage conversion ratio (MVCR) and equivalent magnetic spectral density measurements of the proposed PCB-based MI sensor were performed. Wireless digital communication using quadrature phase shift keying (QPSK), which is less sensitive to noise and has a high data rate, was used to evaluate the proposed MI-based receiver. The transmitted and received waveforms were compared to confirm that the transmitted digital data were accurately received as a result of the final demodulation of the receiver. Additionally, several performance metrics, such as constellation and error vector magnitude, were measured. The results of the comprehensive analysis confirmed the applicability of the proposed differential MI-based receiver to a magnetic field.

Coherent Radar Target Detection With In-Band Cyclostationary Wireless Interference

Spectral congestion necessitates the in-band operation or the spectrum-sharing of legacy radar and communication systems. Since these systems operate in the same band in spectrum-sharing mode, they interfere with one another. To address this problem from the radar&#x2019;s perspective, this paper considers the coherent detection of target-reflected radar signals in the presence of interference from an in-band cyclostationary digital modulated wireless communication signal. Three different cases of target-reflected radar signals, namely, deterministic signals, signals with random phase, and completely random signals, are considered in this paper. The optimum detection rules are derived for these three cases and the corresponding receiver structures for the equalization of the interfering signal are presented. Sub-optimum detection structures are also derived with the assumption that the in-band interference is a white stationary time-invariant Gaussian process. Further, considering the equalization, modified CFAR receiver structures are also presented. By considering the mathematical models for cyclostationary or periodic in-band interference, the performances of the optimum, sub-optimum detectors, and modified CFAR detectors are quantified analytically in terms of detection probability and false alarm probability, and the resulting receiver operating characteristic (ROC) curves are analyzed as a function of the signal-to-interference ratio. It is demonstrated that improper equalization of the interfering signal significantly affects the performance of the optimum detector and this impact is analyzed in detail. As spectrum-sharing becomes more prevalent due to spectrum congestion, the proposed optimal, sub-optimal, and modified CFAR detection rules and receiver structures can be incorporated into existing systems with substantial savings.