Modern Wireless Communication Systems Research Articles

Internet-based Robot-supported RF and Wireless Laboratory for Engineering Education

The rapid growth of modern Radio Frequency (RF) and wireless communication systems requires experienced professionals in the RF and wireless areas. In the curriculum of engineering education, university departments are introducing courses on high frequency telecommunication or radio communication related courses to equip students for the needs of industry. Effective learning in education can only be achieved by combining theoretical course with the corresponding laboratory. Distant access of robot-supported laboratories through the Internet is an important and new issue in distance education. This study is an application of new technologies for active learning methodologies, in order to increase both the self-learning and comprehension of the students. This study aims to find out requirements and needs to be fulfilled in developing a robot-supported remote-controlled RF and wireless laboratory. Development and implementation of a robot-operated internet-based RF and wireless laboratory is described in detail.

Bandwidth improvement of a zeroth-order resonant antenna for WiMax applications

A new multiband coplanar waveguide fed zeroth-order resonant (ZOR) antenna structure with improved bandwidth is proposed. This antenna achieves multiband functionality in five different frequency bands in the range of 2.5–5 GHz. The ZOR frequency is observed to be at 3.97 GHz. The bandwidth improvement, gain, and antenna efficiency at this frequency is found to be 3.28%, 1.9769 dB, and 73.42%, respectively. The proposed antenna is measured at antenna measurement facility, and results were compared with the simulated results. A good agreement between the measured and the simulated results validates the proposed design. The designed antenna proposed in this article holds potential applications in modern wireless communication systems which require multiband antennas with good radiation characteristics. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22:569–574, 2012.

A new ultra-wideband fractal monopole antenna

Modern wireless communication systems need antennas with further bandwidth and smaller size. Fractals have unique properties such as self-similarity and space-filling. The concepts of fractals can be applied to the design of low-profile and multi-band antennas. In this article, a super wideband antenna by applying a new fractal geometry to a wire monopole antenna is presented. The modelling and simulation are performed using SuperNEC electromagnetic simulator. The results show that the proposed antenna can be used for frequency range 10–40 GHz, i.e. it is a super wideband antenna with 30 GHz bandwidth. Radiation patterns and gain are also studied and show a good agreement over the bandwidth.

An Enhanced Modulated Waveform Measurement System

Microwave power transistors used in modern day wireless communication systems need to be characterised under complex modulated excitations into variable load impedances for the determination of optimum matching conditions. This paper presents a refined modulated waveform measurement system for the robust characterisation and optimisation of non-linear microwave devices when driven by broadband multi-tone stimuli. This enhanced system has the ability to present specific, constant broadband impedances, not only at baseband frequency, but also at radio frequencies, particularly, around the carrier and significant harmonics. Achieving such comprehensive impedance control across wide modulation bandwidths is critical in allowing the emulation of new power amplifier modes and architectures, and the subsequent waveform characterisation of devices operating in these complex and often dynamic impedance environments. The capability of the enhanced system is experimentally demonstrated through the measured adjacent channel intermodulation power behaviour of a 10 W GaN HEMT biased in class AB and tuned for maximum output peak envelope power.

An enhanced modulated waveform measurement system

Microwave power transistors used in modern day wireless communication systems need to be characterised under complex modulated excitations into variable load impedances for the determination of optimum matching conditions. This paper presents a refined modulated waveform measurement system for the robust characterisation and optimisation of non-linear microwave devices when driven by broadband multi-tone stimuli. This enhanced system has the ability to present specific, constant broadband impedances, not only at baseband frequency, but also at radio frequencies, particularly, around the carrier and significant harmonics. Achieving such comprehensive impedance control across wide modulation bandwidths is critical in allowing the emulation of new power amplifier modes and architectures, and the subsequent waveform characterisation of devices operating in these complex and often dynamic impedance environments. The capability of the enhanced system is experimentally demonstrated through the measured adjacent channel intermodulation power behaviour of a 10 W GaN HEMT biased in class AB and tuned for maximum output peak envelope power.

Modified OFDM Model Based on Sub-Sliding Window Technique

In modern wireless communication systems, Doppler frequency reduction is employed for efficient transmission of data in noisy environments. Achieving a very less bit error rate (BER) has been the major task in the orthogonal frequency division multiplexing (OFDM), which is a popular multicarrier modulation technique in IEEE 802.11a wireless systems and is currently being used in the IEEE 802.16e (WiMax) standard. This paper presents a modified sub-sliding window (SSW) technique that is used to improve the performance of OFDM modem for the physical layer of IEEE 802.11a standard. To carry out the simulations, the bit error rate performance of the modified and standard models is compared under the additive white Gaussian noise (AWGN) and flat fading channel. The simulation results show that the combination of SSW and OFDM technology is superior to the OFDM standard technology.

Electromagnetic Characteristics of a Novel Radio-Frequency Complementary Metal–Oxide–Semiconductor Active Inductor

This paper presents a novel radio-frequency (RF) complementary metal-oxide-semiconductor (CMOS) active inductor for the design of RF integrated circuits (RFICs). The electromagnetic characteristics of the RF CMOS gyrator-based active inductor were investigated. The RF CMOS gyrator-based active inductor utilized a loss compensation circuit to produce equivalent negative resistance and compensate for the loss of transistors and bias circuitry. The proposed active inductor realized both high-inductance and high-quality factor. The quality factor was greater than 10 from 2.5 to 3.5 GHz. The maximum quality factor was 76.2. The active inductor was applied to the design of a microwave notch filter. The active notch filter with the RF CMOS gyrator-based active inductor was able to reject microwave image signals for modern wireless communication systems.

Designing Multisine Excitations for Measurement of Modern Wireless Communication System

Multisine signal is often employed as an appropriate excitation to represent the complex modulated RF signals for accurate measurement of modern wireless communication system. This paper presents a novel way of designing a multisine signal by using Discrete Fourier Transformation coefficients to represent the digital modulation signals. Investigations of the approach on the IS-95 reverse-link signal as original signal is demonstrated the designed multisine signal can approximate represent original signal.

ASIC Implementation of Soft-Input Soft-Output MIMO Detection Using MMSE Parallel Interference Cancellation

Multiple-input multiple-output (MIMO) technology is the key to meet the demands for data rate and link reliability of modern wireless communication systems, such as IEEE 802.11n or 3GPP-LTE. The full potential of MIMO systems can, however, only be achieved by means iterative MIMO decoding relying on soft-input soft-output (SISO) data detection. In this paper, we describe the first ASIC implementation of a SISO detector for iterative MIMO decoding. To this end, we propose a low-complexity minimum mean-squared error (MMSE) based parallel interference cancellation algorithm, develop a suitable VLSI architecture, and present a corresponding four-stream 1.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> detector chip in 90 nm CMOS technology. The fabricated ASIC includes all necessary preprocessing circuitry and exceeds the 600 Mb/s peak data-rate of IEEE 802.11n. A comparison with state-of-the-art MIMO-detector implementations demonstrates the performance benefits of our ASIC prototype in practical system-scenarios.

SNR Estimation Based on Metric Normalization Frequency in Viterbi Decoder

Signal-to-noise (SNR) estimation plays an important role in modern wireless communication systems because an accurate SNR value can aid the improvement of transmission performance in various aspects. In this letter, we propose a estimation method of noise variance based on the normalization frequency of path metric in Viterbi decoder, and the channel gains are evaluated by the least squares estimation and the energy estimator. Then, we derive the SNR from the ratio of the estimated channel gain to the estimated noise variance. The simulation results show that the proposed algorithm can estimate SNR more accurately than previously published SNR estimators.

Microstrip Rat-Race Couplers

With the rapid development of modern wireless communication systems, the desirable miniaturization, multifunctionality strong harmonic suppression, and enhanced bandwidth of the rat-race coupler has generated much interest and continues to be a focus of research. Whether the current rat-race coupler is sufficient to adapt to the future development of microwave systems has become a heated topic.

Multithreaded Simulation for Synchronous Dataflow Graphs

For system simulation, Synchronous DataFlow (SDF) has been widely used as a core model of computation in design tools for digital communication and signal processing systems. The traditional approach for simulating SDF graphs is to compute and execute static schedules in single-processor desktop environments. Nowadays, however, multicore processors are increasingly popular desktop platforms for their potential performance improvements through thread-level parallelism. Without novel scheduling and simulation techniques that explicitly explore thread-level parallelism for executing SDF graphs, current design tools gain only minimal performance improvements on multicore platforms. In this article, we present a new multithreaded simulation scheduler, called MSS, to provide simulation runtime speedup for executing SDF graphs on multicore processors. MSS strategically integrates graph clustering, intracluster scheduling, actor vectorization, and intercluster buffering techniques to construct InterThread Communication (ITC) graphs at compile-time. MSS then applies efficient synchronization and dynamic scheduling techniques at runtime for executing ITC graphs in multithreaded environments. We have implemented MSS in the Advanced Design System (ADS) from Agilent Technologies. On an Intel dual-core, hyper-threading (4 processing units) processor, our results from this implementation demonstrate up to 3.5 times speedup in simulating modern wireless communication systems (e.g., WCDMA3G, CDMA 2000, WiMax, EDGE, and Digital TV).

Does Fast Adaptive Modulation Always Outperform Slow Adaptive Modulation?

Link adaptation techniques are important modern and future wireless communication systems to cope with quality of service fluctuations in fading channels. These techniques require the knowledge of the channel state obtained with a portion of resources devoted to channel estimation instead of data and updated every coherence time of the process to be tracked. In this paper, we analyze fast and slow adaptive modulation systems with diversity and non-ideal channel estimation under energy constraints. The framework enables to address the following questions: (i) What is the impact of non-ideal channel estimation on fast and slow adaptive modulation systems? (ii) How to define a proper figure of merit which considers both resources dedicated to data and those to channel estimation? (iii) Does fast adaptive always outperform slow adaptive techniques? Our analysis shows that, despite the lower complexity and feedback rate, slow adaptive modulation (SAM) can achieve higher spectral efficiency than fast adaptive modulation (FAM) in the presence of energy constraint, diversity, and non-ideal channel estimation. In addition, SAM satisfies bit error outage requirements also in FAM-denied region.

A MASH-Controlled Multilevel Power Converter for High-Efficiency RF Transmitters

Envelope tracking (ET) is one of the most promising transmitter architectures proposed to increase the efficiency of modern wireless communication system. An ET transmitter consists of a linear RF power amplifier and a high-efficiency envelope amplifier, which is always a switched-mode power converter. The envelope amplifier provides a varying drain (collector) bias voltage, which tracks the envelope of the RF input signal, for the RF power amplifier. Thus, the RF power amplifier keeps working in high-efficiency region of most of the time. Therefore, the overall efficiency of the transmitter is increased. This paper proposes a multistage noise-shaping-technique-controlled multilevel power converter to perform as the envelope amplifier in an ET transmitter. Experimental results show that the proposed power converter can reproduce any envelope signals with the maximum spectrum component of 300 kHz and give maximum instantaneous power of 20 W. Compared with pulsewidth modulation, the noise-shaping technique can shape the ripple into noise and the noise will be attenuated by the low-pass filter, which results a better performance, while maintaining high efficiency as well.

ICI Reduction using Extended Kalman Filter in OFDM System

Orthogonal frequency division multiplexing (OFDM) is emerging as preferred modulation scheme in modern high data rate wireless communication systems. A well known problem of OFDM system is sensitivity to frequency offset between the transmitted and received signals, which may be caused by Doppler shift in the channel or by the difference between the transmitter and receiver local oscillator frequencies. This carrier frequency offset causes loss of orthogonality between sub carriers and the signal transmitted on each carrier are not independent of each other, leading to inter carrier interference (ICI)[1]-[4]. In this paper, the effects of ICI have been analyzed and two solutions to combat ICI have been presented. The first method is a self cancellation scheme, in which redundant data is transmitted onto adjacent subcarriers such that the ICI between adjacent sub carriers cancels out at the receiver. The other technique the Extended Kalman Filter (EKF) method statistically estimate the frequency offset and correct the offset using the estimated value at the receiver.

Efficient characterization of multilayered microwave wireless circuits on gyrotropic dielectric media including magnetized ferrites

The ever-growing use of anisotropic ferrite devices in modern wireless communication systems highlighted the need for robust design tools to reliably characterize the dispersion behavior of such devices in radio frequency (RF)/microwave bands, especially for multilayered configurations. Indeed, as ferrites present a biaxial anisotropy, spectral analysis of multilayered configurations with such substrates is not generalized, however, restricted to some particular cases of tensors. Therefore, this article deals with the characterization of anisotropy effects on the dispersion parameters of multilayered wireless circuits with ferrite substrates, particular case of gyrotropic medias. In the proposed approach, a rigorous analysis was carried out by taking into account, for the first time, the electrical aspect of anisotropy. The computed results are in good agreement with those available in the literature. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:978–982, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25951

Compact and High Performance Bandpass Filter Based on an Improved Hybrid Resonator Using Beeline Compact Microstrip Resonator Cell (BCMRC)

In this paper, a compact microstrip bandpass filter is presented by using a proposed improved hybrid resonator. Without requiring the cross-coupling and the source-load coupling, the new filter has a transmission zero on the upper stopband to provide a high selectivity. The fabricated filter is designed at f 0 = 1 GHz and has a compact size of 0.112λg×0.057λg. Good agreement is observed between the measurements and simulations. The measured results show that the new filter has a wide −60 dB rejection upper stopband from 1.24f 0 to 4.05f 0. In addition, a −20 dB rejection ultra-wide upper stopband is measured from 1.08f 0 to 15.38f 0. The new filter can be fabricated using the standard printed-circuit-board (PCB) process and has a planar topology, which is easily integrated with the modern wireless communication system.

DUAL-BROADBAND TWIN-PAIR INVERTED-L SHAPED STRIP ANTENNA FOR WLAN/WIMAX APPLICATIONS

A simple and novel printed monopole antenna with dual broad operating bands is presented. The antenna fed by a 50-› microstrip line is composed by dual twin-pair inverted-L shaped strips as well as a small back truncated ground. By properly selecting widths of these inverted-L shaped stripes, dual broad bandwidths formed from triple resonances to meet the band requirement of the 2.4/5.2/5.8 WLAN or the 2.5(3.5)/5.5GHz WiMAX standard can be achieved. Experimental results for case of the obtained antenna prototype suitable for use in a 2.4/5.2/5.8GHz WLAN system have been done and shown good agreement with simulation. Good radiation performances including dual wide bandwidths of 270MHz and 3.16GHz, high average antenna gains of ‚ 2:6 and 4.6dBi, and monopole-like radiation patterns over the two operating bands, respectively, make this antenna a good candidate for use in the modern dual-broadband wireless communication system.

A New Compact Filter-Antenna for Modern Wireless Communication Systems

Design, fabrication, and measurement of a new compact filter-antenna for modern wireless communication systems are presented in this letter. Two microstrip square open-loop resonators, a coupled line, and a Γ-shaped antenna are used and integrated to be a filter-antenna. The Γ-shaped antenna is excited by a coupled line that is treated as the admittance inverter in filter design. The Γ-shaped antenna performs not only a radiator, but also the last resonator of the bandpass filter. Therefore, near-zero transition loss is achieved between the filter and the antenna. The design procedure follows the circuit approach-synthesis of bandpass filters. Measured results show that the filter-antenna achieves an impedance bandwidth of 16.3% (over 2.26-2.66 GHz) at a reflection coefficient |S11 | <; - 10 dB and has a gain of 2.41 dBi.

A MINIATURE CPW BALUN CONSTRUCTED WITH LENGTH-REDUCED 3DB COUPLES AND A SHORT REDUNDANT TRANSMISSION LINE

This work presents a new type of CPW balun consisting of 3dB coupled-line sections, which are one eighth wavelength long, and a short redundant transmission line for the applications of the modern wireless communication systems. A set of design equations that can determine the values of the elements of balun is proposed. A new type of coupler constructed with a structure similar to the conventional step impedance resonator is developed to further reduce the size of the balun. An experimental prototype operated at 1.0GHz was designed and fabricated to verify the proposed design method. The measurement results show quite good correspondences with the theoretical predictions and the EM simulations.