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In this study, results of wideband dual polarised measurements conducted in indoor environments including office, factory, corridor and computer foyer, using state-of-the-art 2×2 multiple-input-multiple-output frequency modulated continuous wave-based channel sounder, are presented. The measurements were performed in two frequency bands with 6 GHz bandwidth, centred at 54 and 70 GHz, with directional steerable ~20 dBi (18° beamwidth) horn antennas. Using twists at the transmitter and at the receiver simultaneous co-polar and cross-polar measurements were performed to quantify the polarisation effects on channel parameters such as angular spread, delay spread and path loss. The results show that the co-polarised radio links experienced lower angular spread and delay spread compared with the cross-polarised links. For co-polarised links, the estimated synthesised omnidirectional path loss exponent was found to be in the range of 1.5-2 (close-in model) and 0.9-1.9 (log-distance model) in the respective environments. In individual scenarios, the median cross-polarisation ratio was found to be within 11.7-14.4 and 7.5-17.6 dB at 54 and 70 GHz, respectively. [ABSTRACT FROM AUTHOR]

This article presents a simple and efficient method for the design of a self-diplexed antenna based on loading asymmetric grounding-vias. The structure consists of two antenna elements loaded with two asymmetric grounding-vias, specifying the uplink and downlink operation frequencies. By choosing the appropriate positions of the two grounding-vias, high isolation between the two antennas can be achieved. To validate the feasibility of the proposed structure, two self-diplexed antennas with different operational frequencies have been fabricated and tested. Experimental results verify the multi-functionalities of the proposed compact structure in terms of high isolation and low cross-polarization discrimination. [ABSTRACT FROM AUTHOR]

Differential amplitude phase shift keying (DAPSK) is a promising modulation technique for use in high-mobility environments, as it does not require channel estimation. In this paper, a novel reduced complexity soft demodulator for high-order DAPSK constellations is proposed. The main idea relies on a two-step approximation of the sum-log demapper. In the first step, a parallel factor analysis (PARAFAC) decomposition is used to approximate log-likelihood ratios. Next, the basis functions obtained through the first step are approximated by piecewise-linear curves. Numerical optimization techniques are employed for the PARAFAC decomposition and its piecewise-linear approximation whose parameters are then stored in a lookup table. It has been verified through computer simulations that the proposed scheme clearly outperforms the scheme proposed in the paper “Reduced-complexity noncoherent soft-decision-aided DAPSK dispensing with channel estimation,” (IEEE Trans. Veh. Technol., vol. 62, pp. 2633–2643, 2013.), while also having lower computational cost. Moreover, it is shown that the performance of the exact sum-log demapper and the proposed demapper is very close for \text2\times \text4 and \text4\times \text16 DAPSK constellations. [ABSTRACT FROM AUTHOR]

The majority of techniques that deal with the mitigation of in-phase and quadrature-phase (I/Q) imbalance at the transmitter (pre-compensation) require long training sequences, reducing the throughput of the system. These techniques also require a feedback path, which adds more complexity and cost to the transmitter architecture. Blind estimation techniques are attractive for avoiding the use of long training sequences. In this paper, we propose a blind frequency-independent I/Q imbalance compensation method based on the maximum likelihood (ML) estimation of the imbalance parameters of a transceiver. A closed-form joint probability density function (PDF) for the imbalanced I and Q signals is derived and validated. ML estimation is then used to estimate the imbalance parameters using the derived joint PDF of the output I and Q signals. Various figures of merit have been used to evaluate the efficacy of the proposed approach using extensive computer simulations and measurements. Additionally, the bit error rate curves show the effectiveness of the proposed method in the presence of the wireless channel and Additive White Gaussian Noise. Real-world experimental results show an image rejection of greater than 30 dB as compared to the uncompensated system. This method has also been found to be robust in the presence of practical system impairments, such as time and phase delay mismatches. [ABSTRACT FROM AUTHOR]

When radar and communication systems are colocated and operating simultaneously in the same frequency band, interference can be addressed by designing the systems to share resources. This paper develops a framework for cooperative operation of single-input single-output bistatic radar and wireless communication systems. We adopt a low-complexity linear minimum mean square error (LMMSE) optimal pilot symbol aided modulation scheme, and show the achievability region of the joint radar-communication system designed for simultaneous operation in a wireless channel that is both frequency and time-selective. Since the LMMSE estimate requires accurate knowledge of channel statistics, we give a lower bound on performance using least-squares estimation that operates purely on the received signal. Finally, to better match power levels between systems, we compare the performance using optimal training sequences with a suboptimal scheme using Barker sequences. [ABSTRACT FROM PUBLISHER]

In telecommunications, the capture effect is a phenomenon associated with frequency modulation reception in which two strong signals at, or near, the same frequency or channel will be demodulated. In wireless networks, a frame collision does not necessarily result in all the simultaneously transmitted frames being lost. Depending on the relative signal power and the arrival time of the involved frames, one frame can survive the collision and be successfully received by the receiver. Efficient object identification with passive RFID tags. In former works, many researches focus on the RFID anticollision protocol only, however, less did pay special attention to the capture effect mainly to keep the design simple and cost low. Nonetheless, the capture effect occurs frequently in real deployments. In this paper, we have taken the capture effect into consideration and combined this thought to an efficient RFID anti-collision protocol, then proposed an efficient method to estimate the optimal frame length to adjust the quantity of RFID tags. After setting an optimal frame length by using the proposed method, furthermore, we obtained higher identification efficiency. RFID technology can be used for real-time recording and tracking of the learning process, which comprises real-time records of learners and their partners learning process such as experience, debate, cooperation, competition, problem solving, and other learning experiences. [ABSTRACT FROM AUTHOR]

In a multiple-receiver wireless power transfer (WPT) system, determining the condition for uniform power distribution at a high transfer efficiency is a challenging issue. In this paper, a selective WPT technique using magnetic resonance coupling (MRC) is introduced for smart power delivery in a multiple-receiver system. The proposed method selectively and exclusively delivers power to only one designated receiver among multiple receivers, eliminating the cross-coupling effect and unbalanced power division problem across the receivers. This is achieved by separating the resonant frequencies of the receivers to isolate the coupling effects between coils. The power division ratio of the receivers is controlled by changing the duration time ratio for power transfer. In this paper, a one-transmitter three-receiver selective MRC system is designed and fabricated. The power distribution is demonstrated under impedance matched condition, showing a power transfer efficiency of 24%–29% at a very small coupling coefficient of 0.01 with a 12-mm-diameter receiver coil. Distance compensation and a one-way communication of time division multiple access are demonstrated for a multiple-receiver system, using the proposed method. [ABSTRACT FROM PUBLISHER]

The Sine Non-linear Chirp Keying (SNCK) is one kind of the SFM schemes, which play an important role as the commonly useful signals in sonar, radar and wireless communication systems. By adjusting its time-bandwidth product, the SNCK can satisfy different requirements of the quality of service and has better ability in Doppler shift inhibition than the ordinary MSK. However, no mathematical analysis for the time-bandwidth product (modulation factor) estimation of the SNCK scheme has been available. In this paper, a SCD-based estimation algorithm for the modulation factor of the SNCK scheme has been proposed. The mathematical model and diagrams of the three-dimensional SCD and the corresponding bi-frequency plane make it easy to understand how the SCD-based algorithm localizes the center frequency and the keying rate, as well as estimates the modulation factor. The simulation results show that the proposed estimation algorithm is useful under different SNR conditions. The corresponding Cramer-Rao lower bound are derived and used as the reference of the estimation algorithm. Moreover, we improve the estimation algorithm when the modulation factor varies, by using a set of the local ratio data, which compensates the differences between the simulation ratio values and the theoretical ratio results. This algorithm can be effective for the communication system with the SNCK scheme to synchronize the carrier and the symbol, as well as to demodulate the transmitted signals with unknown parameters. It is concluded that the obvious features of the SCD can be extracted for other similar signals with high reliability. [ABSTRACT FROM AUTHOR]

Frequency pulling of an oscillator integrated in a quadrature phase-shift keying wireless transmitter degrades the performance of the wireless system. This paper analyses the behavior of an oscillator in the presence of coupling between the oscillator and a power amplifier or antenna. Symbol switching in the modulator will cause frequency shifts in the oscillator at the modulation frequency. A new architecture for a 120 GHz quadrature frequency generator with large tuning range and immunity against PA-VCO coupling is presented. Combining the output signals of two independent oscillators, the pulling effect is removed and the frequency generator can be integrated with a PA and an antenna on the same chip. This architecture also makes quadrature generation with large tuning range feasible at 120 GHz. The chip is fabricated in a 45 nm CMOS technology and shows a tuning range of 16.2 GHz (13.5 $$\%$$ ), a phase noise of $$-$$ 112 dBc/Hz @ 10 MHz offset and a phase error of 5 $$^\circ$$ (Volkaerts et al. in: IEEE Radio Frequency Integrated Circuits Symposium (RFIC), ). [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a wide band linearly polarized beam squinted radial line slot array (RLSA) antenna at 5.8-GHz band. The open ended air gap technique was used to broader the bandwidth, reduce the antenna size but maintain the high-performance characteristic. The antenna implemented radiating slot design with diameter of 200 and 1.6 mm hybrid FR4 and 8-mm open ended air gap for dielectric height. The antenna also successfully fabricated and performed a good result. The measured results show a wide 38% of bandwidth with 16 dBi gain at 5.8-GHz frequency. The beamwidth obtained below 15° for E and H plane. The research found a wide band RLSA antenna can be achieved using air gap technique and will be a potential candidate for future point to point application for fixed broadband wireless access. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:938-944, 2014 [ABSTRACT FROM AUTHOR]

In this paper, we present a brief overview of historical developments of wireless power and an analysis on the use of Tesla's resonators in domino forms for wireless power transfer. Relay resonators are spaced between the transmitter and receiver coils with the objectives of maximizing energy efficiency and increasing the overall transmission distance between the power source and the load. Analytical expressions for the optimal load and maximum efficiency at resonance frequency are derived. These equations are verified with practical measurements obtained from both coaxial and noncoaxial domino resonator systems. To avoid the use of high operating frequency for wireless power transfer in previous related research, the technique presented here can be used at submegahertz operation so as to minimize the power loss in both the power supply and the output stage. We demonstrated both theoretically and practically that unequal spacing for the coaxial straight domino systems has better efficiency performance than the equal-spacing method. Also, the flexibility of using resonators in various domino forms is demonstrated. [ABSTRACT FROM PUBLISHER]

This work explores the generation of a local oscillator for WCDMA band VII based on frequency multiplication of a GSM reference. The frequency multiplier is based on a PLL, which includes a compact VCO based on a ring oscillator. A proper PLL design allows to sufficiently reject the relative high VCO phase noise, complying with the WCDMA requirements. The effectiveness of the proposed approach is proved with the design of the whole multiplier in a 90 nm CMOS technology. The generated oscillation ranges from 3 to 6 GHz, while the simulated phase noise is −120 and −144 dBc/Hz at a frequency offset of 0.6 and 20 MHz, respectively, dissipating 6.3 mW. [ABSTRACT FROM AUTHOR]

Dense deployments of hybrid WLANs result in high levels of interference and low end-user throughput. Many frequency allocation mechanisms for WLANs have been proposed by a large body of previous studies. However, none of these mechanisms considers the load that is carried by APs in terms of channel conditions, number of affiliated users as well as communication-load, in conjunction. In this paper, we propose LAC, a load-aware channel allocation scheme for WLANs, which considers all the above performance determinant factors. LAC incorporates an airtime cost metric into its channel scanning process, in order to capture the effects of these factors and select the channel that will provide approximately maximum long-term throughput. We evaluate LAC through extensive OPNET simulations, for many different traffic scenarios. Our simulations demonstrate that LAC outperforms other frequency allocation policies for WLANs in terms of total network throughput by up to 135%. [ABSTRACT FROM AUTHOR]

We present new frequency allocation schemes for wireless networks and show that they outperform all other published work. Two categories of schemes are presented: 1) those purely based on measurements and 2) those that use site-specific knowledge, which refers to knowledge of building layouts, the locations and electrical properties of access points (APs), users, and physical objects. In our site-specific knowledge-based algorithms, a central network controller communicates with all APs and has site-specific knowledge so that it can a priori predict the received power from any transmitter to any receiver. Optimal frequency assignments are based on predicted powers to minimize interference and maximize throughput. In our measurement-based algorithms, clients periodically report in situ interference measurements to their associated APs; then, the APs' frequency allocations are adjusted based on the reported measurements. Unlike other work, we minimize interference seen by both users and APs, use a physical model rather than a binary model for interference, and mitigate the impact of rogue interference. Our algorithms consistently yield high throughput gains, irrespective of the network topology, AP activity level, number of APs, rogue interferers, and available channels. Our algorithms outperform the best published work by 18.5%, 97.6%, and 1180% for median, 25th percentile, and 15th percentile user throughputs, respectively. [ABSTRACT FROM AUTHOR]

Abstract  Software-defined radio (SDR) is a revolution in radio design due to the ability to create radios that can self-adapt on the fly. In SDR devices, all of the signal processing is implemented in the digital domain, mainly on DSP blocks or by DSP software. By simply downloading a new program, a SDR device is able to interoperate with different wireless protocols, incorporate new services, and upgrade to new standards. Therefore, massively parallel signal processing at higher frequencies are needed to implement a realistic SDR. Thus, FPGAs have been used extensively for implementing essential functions in SDR architectures at lower frequencies. In this paper, we explore the design of a digital FM receiver using the approach of an All-Digital Phase Locked-Loop (ADPLL). The circuit is designed in VHDL, then synthesized and simulated using LeonardoSpectrum Level 3 and ModelSim SE 6, respectively. It operates at a frequency up to 150 MHz and occupies the area of roughly 15 K logic gates. [ABSTRACT FROM AUTHOR]

An integrated quadrature demodulator with an on-chip frequency divider is reported. The mixer consists of a transconductance stage, a passive current switching stage, and an operational amplifier output stage. A complementary input architecture has been used to increase the transconductance for a given bias current. The circuit is inductorless and is capable of operating over a broad frequency range. The chip was implemented in a 0.13-µm CMOS technology. From 700 MHz to 2.5 GHz, the demodulator achieves 35 dB of conversion voltage gain with 250-kHz IF bandwidth, a double-sideband NF of 10 dB with 9-33 kHz 1/f-noise corner. The measured IIP3 is +4 dBm for a 0.1-MHz IF frequency and +10 dBm for a 1-MHz IF frequency. The total chip draws 20 to 24 mA from a single 1.5-V supply. [ABSTRACT FROM AUTHOR]

The FFT (fast Fourier transform) processor is the most speed and power consumption critical part in the orthogonal frequency division multiplexing (OFDM) communication system. In this paper, a low power consumption and small area FFT processor architecture suitable for OFDM demodulators is proposed. In order to meet the requirements of high-speed data throughput and low power and small area consumption, distributed memory architecture is developed to meet the requirement of non-stopping and high-speed data throughput. One clock-cycle mixed radix-2/4 butterfly architecture is proposed for OFDM Meanwhile, due to the two radix-2 and radix-4 butterflies share in the two complex multipliers, the FFT processor with the proposed radix-2/4 butterfly can make the 64% power consumption reduction and the 35% gate count reduction, respectively. Performance analysis shows that the proposed FFT architecture can meet the requirement of OFDM demodulators in DVB-T and other high speed wireless applications. [ABSTRACT FROM AUTHOR]

Bluetooth is a short-range communication system facilitating ad hoc networking between various devices and terminals, using Gaussian-frequency-shift-keying modulation. In this paper, the authors present and analyze a novel receiver structure for Bluetooth, which is based on zero-crossing detection in combination with zero-forcing block linear equalization. Simulation results are presented, showing a favorable performance compared to other detectors. [ABSTRACT FROM AUTHOR]

We consider blind signal detection in an asynchronous code-division multiple-access (CDMA) system employing short spreading sequences in the presence of unknown multipath fading. This approach is capable of countering the presence of multiple-access interference (MAI) in CDMA fading channels. The proposed blind multiuser detector is based on an independent component analysis (ICA) to mitigate both MAI and noise. This algorithm has been utilised in blind source separation (BSS) of unknown sources from their mixtures. It can also be used for estimating the basis vectors of BSS. The aim is to include an ICA algorithm within a wireless receiver in order to reduce the level of interference in wideband systems. This blind multiuser detector requires no training sequence compared with the conventional multiuser detection receiver. The proposed ICA blind multiuser detector is made robust with respect to knowledge of signature waveforms and the timing of the user of interest. Several experiments are performed in order to verify the validity of the proposed ICA algorithm. [ABSTRACT FROM AUTHOR]

We introduce three soft-decision demodulation channel-optimized vector quantizers (COVQs) to transmit analog sources over space-time orthogonal block (STOB)-coded flat Rayleigh fading channels with binary phase-shift keying (BPSK) modulation. One main objective is to judiciously utilize the soft information of the STOB-coded channel in the design of the vector quantizers while keeping a low system complexity. To meet this objective, we introduce a simple space-time decoding structure that consists of a space-time soft detector, followed by a linear combiner and a scalar uniform quantizer with resolution q. The concatenation of the space-time encoder/modulator, fading channel, and space-time receiver can be described by a binary-input, 2q-output discrete memoryless channel (DMC). The scalar uniform quantizer is chosen so that the capacity of the equivalent DMC is maximized to fully exploit and capture the system's soft information by the DMC. We next determine the statistics of the DMC in closed form and use them to design three COVQ schemes with various degrees of knowledge of the channel noise power and fading coefficients at the transmitter and/or receiver. The performance of each quantization scheme is evaluated for memoryless Gaussian and Gauss-Markov sources and various STOB codes, and the benefits of each scheme is illustrated as a function of the antenna-diversity and soft-decision resolution q. Comparisons to traditional coding schemes, which perform separate source and channel coding operations, are also provided. [ABSTRACT FROM AUTHOR]

The Bluetooth discovery process requires use of the inquiry substate which not only consumes significant power, but prevents normal data traffic flow and simultaneously acts as a potential noise source for neighboring networks. Therefore, the inquiry substate dwell time should be limited to discovering an acceptable number of neighboring devices. Although an estimate of the probability density function of the time to discover scanning devices is straightforward, the complex temporal and spectral interactions between two devices make precise inquiry time characterization difficult. We characterize these interactions and derive detailed analytical expressions for the probability distribution of the inquiry time for a Bluetooth-enabled device that follows v1.1 of the Bluetooth specification and uses the default 11.25 ms inquiry scan window that opens every 1.28 s. Subsequently, we show a single inquirer will locate 99 percent of all scanning devices within transmission range in 5.12 seconds rather than the 10.24 s recommended in the specification. Using specification v1.2, we show that the inquiry time can be reduced to 3.84 seconds and 1.28 seconds using the standard and interlaced inquiry scan modes, respectively. Substantial inquiry time reduction results in reduced power requirements and increased throughput by increasing data traffic and reducing interference with neighboring piconets. Our results are validated via comparison with existing simulation models and measurement studies. The models used to derive the distribution also lend themselves to characterizing the discovery time with variations in the discovery process. [ABSTRACT FROM AUTHOR]

The article discusses various jamming attacks against wireless sensor networks and offers information on how to diagnose and defend against such interference. It identifies several attackers such as the constant jammer, deceptive jammer, random jammer, and the reactive ones. In order to cope up with jamming attacks, a contemporary approach to intercede jamming attacks was developed. The initial approach is to retreat from the interferer by channel surfing and spatial retreats. The second approach is designed to achieve communication even with the presence of the jammer by adjusting levels of power and by communication coding.

The significant loss in performance of multicarrier direct-sequence spread-spectrum multiple-access systems over fast-fading channels is investigated. First, the channel model for individual subchannels is obtained, using a canonical decomposition to a wide-sense stationary (WSS), uncorrelated scattering channel. Next, a receiver structure, which features both Doppler diversity and frequency diversity, is presented and analyzed. It is found that large Doppler spreads cause the average magnitude of the desired signals to diminish dramatically. Expressions for the bit-error rate are derived for both uncoded and coded systems by applying the standard Gaussian approximation. Numerical results, which show that Doppler diversity is preferable over frequency diversity in fast-fading channels, are provided for different combinations of the diversity orders. Numerical results, which show that the intersymbol and intersubchannel interference can be effectively suppressed, and the multiple-access interference tends to degenerate into a WSS process with the statistical periodicity destroyed by the fast-fading channels, are also provided. [ABSTRACT FROM AUTHOR]

Error rates of orthogonal frequency-division multiplexing (OFDM) signals in multipath slow fading Nakagami-m fading channels are considered. The exact probability density function of a sum of Nakagami-m random phase vectors is used to derive a closed-form expression for the error rates of OFDM signals. The precise error-rate analysis is extended to a system using multichannel reception with maximal ratio combining. An asymptotic error-rate analysis is also provided. For a two-tap channel with finite values of Nakagami-m fading parameters, our analysis and numerical results show that the asymptotic error-rate performance of an OFDM signal is similar to that of a single carrier signal transmitted over a Rayleigh fading channel. On the other hand, our analysis further shows that a frequency-selective channel that can be represented by two constant taps has similar asymptotic error-rate performance to that of a one-sided Gaussian fading channel. It is observed that, depending on the number of channel taps, the error-rate performance does not necessarily improve with increasing Nakagami-m fading parameters. [ABSTRACT FROM AUTHOR]

This letter addresses the effect of timing synchronization errors that are introduced by an erroneous detection of the start of an orthogonal frequency-division multiplexing (OFDM) symbol. Such errors degrade the performance of an OFDM receiver by introducing intercarrier interference (ICI) and intersymbol interference (ISI). They can occur due to either an erroneous initial frame synchronization or a change in the power delay profile of the channel. In this letter, we provide a mathematical analysis of the effect of timing errors on the performance of an OFDM receiver in a frequency-selective fading environment. We find exact formulas for the power of interference terms and the resulting average signal-to-interference ratio. We further extend the analysis to the subsample level. Our results show the nonsymmetric effect of timing errors on the performance of an OFDM system. Finally, simulation results confirm the analysis. [ABSTRACT FROM AUTHOR]

Recently, the use of coherent space-frequency coding in orthogonal frequency-division multiplexing (OFDM)-based frequency-selective multiple-input multiple-output (MIMO) fading channels has been proposed. Acquiring knowledge of the fading coefficients in a MIMO channel is already very challenging in the frequency-flat (fast) fading case. In the frequency-selective case, this task becomes significantly more difficult due to the presence of multiple paths, which results in an increased number of parameters to be estimated. In this paper, we address code design for noncoherent frequency-selective MIMO-OFDM fading links, where neither the transmitter nor the receiver knows the channel. We derive the code design criteria, quantify the maximum achievable diversity gain, and provide explicit constructions of full-diversity (space and frequency) achieving codes along with an analytical and numerical performance assessment. We also demonstrate that unlike in the coherent case, noncoherent space-frequency codes designed to achieve full spatial diversity in the frequency-flat fading case can fail completely to exploit not only frequency diversity but also spatial diversity when used in frequency-selective fading environments. We term such codes "catastrophic." [ABSTRACT FROM AUTHOR]

Considers the application of max-log-ML symbol estimation postprocessing for intermediate frequency limiter-discriminator-integrator (LDI) detectors, which can be used in Bluetooth or DECT receivers. Demonstration that this postprocessing considerably improves the error performance obtained with regular limiter-discriminator-integrator based receivers.

A compact microstrip tri-band bandpass filter using novel combined E-type resonators (CETRs) is presented. The CETR consists of a quarter-wavelength (λ/4) stepped-impedance resonator (SIR) and a quarter-wavelength (λ/4) unit impedance resonator through a viahole. These two components are relatively independent. The first and the third passband centre frequencies can be flexibly controlled by tuning the impedance ratio RZ of the SIR, whereas the second passband frequency is fixed. The centre frequency of the second passband can be independently controlled by tuning the lengths of L2. The filter is designed to operate at 1.95, 5.2, and 3.5 GHz. The simulated and measured results show good agreement. [ABSTRACT FROM AUTHOR]

We present the experimental evidence of RF demodulation by a graphene monolayer embedded in a coplanar structure. The demodulator was tested in the frequency range from 100 MHz to 25 GHz using amplitude modulated input signals. An input power of 0 dBm (1 mW) was used, which is the typical power emitted for short range wireless communication systems, such as Bluetooth. The graphene demodulator exhibits good signal responsivity in the frequency range associated to industrial, scientific and medical radio band with a peak of 1100 V/W at 3.5 GHz. [ABSTRACT FROM AUTHOR]