Ideal Receiver Research Articles

Energy Detection under IQ Imbalance with Single- and Multi-Channel Direct-Conversion Receiver: Analysis and Mitigation

Direct-conversion radio receivers can offer highly integrated low-cost hardware solutions for cognitive radio (CR) devices. Such receivers are, however, also very sensitive to various radio frequency (RF) impairments such as IQ imbalance, which can considerably limit the spectrum sensing capabilities. Most of the existing spectrum sensing studies in literature assume an ideal RF receiver and hence neglect the impacts of such practical RF hardware limitations. In this article, we study energy detection (ED) based spectrum sensing in both single-channel and multi-channel direct-conversion receiver scenarios impaired by IQ imbalance. With complex Gaussian primary user (PU) signal models, we first derive the detection and false alarm probabilities in closed-form for both receiver scenarios. The analytical results, confirmed through extensive simulations, show that while the single-channel receiver scenario is fairly robust to IQ imbalance, the wideband multi-channel sensing receiver is very sensitive to the image channel crosstalk induced by IQ imbalance. More specifically, it is shown that the false alarm probability of multi-channel energy detection increases significantly, compared to ideal RF receiver case, and the exact performance depends on the image channel power level and IQ imbalance values. In order to prevent such degradation in the ability to identify free spectrum, a waveform level interference cancellation method is then proposed to mitigate the image channel crosstalk. The optimum cancellation coefficient yielding interference-free signal is first derived, being also complemented with a practical coefficient sample estimator. An explicit condition is also derived for which the proposed cancellation scheme deploying the practical coefficient sample estimator provides performance gain in the sensing decisions compared to uncompensated energy detection. Extensive computer simulations with various signal and imbalance conditions are provided which demonstrate that the proposed enhanced energy detection can suppress the image channel crosstalk efficiently, yielding detection and false alarm probabilities essentially identical to those of an ideal RF receiver.

Performance Analysis of a Six-Port Receiver in a WCDMA Communication System including a Multipath Fading Channel

Third generation communication systems require receivers with wide bandwidth of operation to support high transmission rates and are also reconfigurable to support various communication standards with different frequency bands. An ideal software defined radio (SDR) will be the absolute answer to this requirement but it is not achievable with the current level of technology. This paper proposes the use of a six-port receiver (SPR) front-end (FE) in a WCDMA communication system. A WCDMA end-to-end physical layer MATLAB demo which includes a multipath channel distortion block is used to determine the viability of the six-port based receiver. The WCDMA signal after passing through a multipath channel is received using a constructed SPR FE. The baseband signal is then calibrated and corrected in MATLAB. The six-port receiver performance is measured in terms of bit error rate (BER). The signal-to-noise ratio (SNR) of the transmittedIQdata is varied and the BER profile of the communication system is plotted. The effect of the multipath fading on the receiver performance and the accuracy of the calibration algorithm are obtained by comparing two different measured BER curves for different calibration techniques to the simulated BER curve of an ideal receiver.

High temperature solar thermal central-receiver billboard design

The design of central receivers in solar thermal power plants is critical for efficient plant operation and sufficient operational lifetimes. The high, non-uniform concentration ratios used in central receivers lead to high, non-uniform receiver temperatures. For the same operational conditions, small changes to the receiver design can make a big impact on the expected lifetime of the receiver. This is due to limitations of the receiver materials to high temperatures and thermal cycling. In this study, we investigate the effect of several engineering concepts on the resultant surface temperatures of tubular billboard receivers. Four tubular billboard designs are investigated along with the sensitivity these designs have to high temperatures resulting from changes in the aiming point of the heliostat array. We examined a receiver with single diameter tubes, an ideal flow receiver, a receiver using various diameter tubes and a receiver made of tube panels in series. The single-diameter and multi-diameter receivers were found to have high temperatures and high sensitivity under non-standard irradiation. The multi-pass receiver was found to out-perform the other designs by reducing both the maximum surface temperatures under standard irradiance and the risk of high temperatures from irradiance changes. The results provide insights into tubular billboard receiver design, material selection and design for extended life.

Characterization of Implemented Algorithm for MIMO Spatial Multiplexing in Reverberation Chamber

Previously, the throughput for a single-input multiple-output (SIMO) system was successfully tested in a reverberation chamber (RC), and the results were in good agreement with a model based on the ideal threshold receiver. In the present communication, we measure the throughput of a 2 × 2 open loop multiple-input multiple-output (MIMO) system with full spatial multiplexing (i.e., two data streams), and we compare the results with an extended throughput model taking the spatial multiplexing into account. The measured throughput is found to be in agreement with the simulated one of a simple zero-forcing (ZF) receiver. The throughput degradations due to correlation and power imbalance (caused by different embedded radiation efficiencies of antennas) are studied and referred to as a throughput multiplexing efficiency. These can, to a large extent, be explained by the ZF algorithm. The results show clearly that the rich isotropic multipath (RIMP) environment generated by an RC can be used to study how effective different MIMO algorithms are when there is correlation and efficiency imbalance between the antenna elements.

Fuzzy MIMO detector for MC-CDMA systems with carrier frequency offset over multipath fading channels

A multistage fuzzy minimum output energy (MOE) detector is proposed for multiple input multiple output (MIMO) multi-carrier code-division-multiple access (MC-CDMA) uplink systems with carrier frequency offset (CFO) over multipath fading channels. The first stage of the receiver uses a novel MIMO receiver model with offset symbols to achieve a fuzzy CFO-constrained MOE detector that suppresses multiple access interference (MAI) and minimizes cancellation of the desired signal. To suppress noise and to enhance signal reception after the fuzzy MOE detector, a signal subspace projection and minimum mean square error weight combiner is proposed to enhance signal-to-interference-plus-noise ratio and bit error rate performances. Simulation results show that the proposed MIMO detector outperforms conventional MOE detectors and achieves the ideal receiver performance against MAI and CFO effects.

Noise immunity of ideal receiver under exposure to interferences with nonuniform spectrum

The noise immunity of ideal receiver has been estimated in the presence of the interference different from the white noise at its input. The amplitude-frequency characteristics (AFC) of optimal whitening and compensating filters and the signal-to-noise ratio at the receiver input were also determined.

CRLB-Achieving I/Q Mismatch Estimator for Low-IF Receiver Using Repetitive Training Sequence in the Presence of CFO

This paper presents a method for estimating the in-phase/quadrature-phase (I/Q) mismatch in low-intermediate frequency receivers for orthogonal frequency division multiplexing (OFDM) signals in the presence of carrier-frequency offset. The proposed estimator operates on the repetitive training sequence of the OFDM packet preamble. To derive a practical maximum-likelihood estimator, an invertible mapping operation is applied on the observation vectors, so that a closed-form expression of the likelihood function can be obtained. The proposed estimator is shown to achieve the Cramer Rao lower bound at high image signal power levels. The error variance of the estimator is analyzed, which closely matches simulation results. The uncoded bit-error-rate is shown via simulation to be approximately that of an ideal receiver without I/Q mismatch.

Lidar, space communication, and the search for signals from extraterrestrial civilizations at the radiation wavelength of an iodine-photodissociation laser—1315 µm

This paper discusses the possibilities of lidar, laser space communication, and the search for signals from extraterrestrial civilizations, using iodine-photodissociation lasers, on the basis of which a virtually ideal receiver–transmitter pair with a quantum sensitivity limit has been created. This pair is capable of detecting signals consisting of only a few photons on the background of any natural source of thermal radiation and of emitting optical pulses of diffraction divergence with energy up to 10 J when operating in the pulsed-periodic regime and up to several kilojoules in single radiation pulses.

Threshold Receiver Model for Throughput of Wireless Devices With MIMO and Frequency Diversity Measured in Reverberation Chamber

We present a simple theoretical model for the throughput data rate of a wireless LTE device including the improvements of data rate due to diversity in frequency (OFDM) and spatial domains (MIMO) under frequency selective fading. The model is based on defining an ideal threshold receiver for the line-of-sight (LOS) case, corresponding to reception with advanced error-correcting codes. The theoretical throughput model is in agreement with measurements in a reverberation chamber of a commercial LTE device for the 1 × 2 SIMO case, both regarding diversity and MIMO array gains, and it can therefore be used to complement measured results in evaluation of performance of LTE devices.

Measurements of RFID Tag Sensitivity in Reverberation Chamber

The reverberation chamber is now commonly accepted and used for fast and accurate performance evaluation of mobile phones and other wireless devices for in particular new systems such as LTE 4G and IEEE 802.11n Wi-Fi. In this letter, we describe a new methodology of measuring sensitivity of RFID tags in a reverberation chamber, and we show how the measurements time can be shortened by using the fact that the RFID tag behaves like an ideal threshold receiver. We then extend to tag population measurements that can be used to select the best tag among the many during the same measurement sequence.

On the Convexity of ROC Curves Estimated from Radiological Test Results

Although an ideal observer's receiver operating characteristic (ROC) curve must be convex-ie, its slope must decrease monotonically-published fits to empirical data often display "hooks." Such fits sometimes are accepted on the basis of an argument that experiments are done with real, rather than ideal, observers. However, the fact that ideal observers must produce convex curves does not imply that convex curves describe only ideal observers. This article aims to identify the practical implications of nonconvex ROC curves and the conditions that can lead to empirical or fitted ROC curves that are not convex. This article views nonconvex ROC curves from historical, theoretical, and statistical perspectives, which we describe briefly. We then consider population ROC curves with various shapes and analyze the types of medical decisions that they imply. Finally, we describe how sampling variability and curve-fitting algorithms can produce ROC curve estimates that include hooks. We show that hooks in population ROC curves imply the use of an irrational decision strategy, even when the curve does not cross the chance line, and therefore usually are untenable in medical settings. Moreover, we sketch a simple approach to improve any nonconvex ROC curve by adding statistical variation to the decision process. Finally, we sketch how to test whether hooks present in ROC data are likely to have been caused by chance alone and how some hooked ROCs found in the literature can be easily explained as fitting artifacts or modeling issues. In general, ROC curve fits that show hooks should be looked on with suspicion unless other arguments justify their presence.

Fast Multi-Symbol Based Iterative Detectors for UWB Communications

Ultra-wideband (UWB) impulse radios have shown great potential in wireless local area networks for localization, coexistence with other services, and low probability of interception and detection. However, low transmission power and high multipath effect make the detection of UWB signals challenging. Recently, multi-symbol based detection has caught attention for UWB communications because it provides good performance and does not require explicit channel estimation. Most of the existing multi-symbol based methods incur a higher computational cost than can be afforded in the envisioned UWB systems. In this paper, we propose an iterative multi-symbol based method that has low complexity and provides near optimal performance. Our method uses only one initial symbol to start and applies a decision directed approach to iteratively update a filter template and information symbols. Simulations show that our method converges in only a few iterations (less than 5), and that when the number of symbols increases, the performance of our method approaches that of the ideal Rake receiver.

System feasibility of using stimulated Brillouin scattering in self coherent detection schemes

We demonstrate the first self-coherent detection of 10 Gbit/s BPSK signals based on narrow-band amplification of the optical carrier by means of Stimulated Brillouin effect in a common fiber. We found that this technique is very effective only if it is combined with proper line coding and high-pass electrical filtering at the receiver. In this case we obtain OSNR-performance close to the ideal coherent receiver.

Quasi-perfect state transfer in a bosonic dissipative network

In this paper we propose a scheme for quasi-perfect state transfer in a network of dissipative harmonic oscillators. We consider ideal sender and receiver oscillators connected by a chain of nonideal transmitter oscillators coupled by nearest-neighbour resonances. From the algebraic properties of the dynamical quantities describing the evolution of the network state, we derive a criterion, fixing the coupling strengths between all the oscillators, apart from their natural frequencies, enabling perfect state transfer in the particular case of ideal transmitter oscillators. Our criterion provides an easily manipulated formula enabling perfect state transfer in the special case where the network nonidealities are disregarded. We also extend such a criterion to dissipative networks where the fidelity of the transferred state decreases due to the loss mechanisms. To circumvent almost completely the adverse effect of decoherence, we propose a protocol to achieve quasi-perfect state transfer in nonideal networks. By adjusting the common frequency of the sender and the receiver oscillators to be out of resonance with that of the transmitters, we demonstrate that the sender's state tunnels to the receiver oscillator by virtually exciting the nonideal transmitter chain. This virtual process makes negligible the decay rate associated with the transmitter line at the expense of delaying the time interval for the state transfer process. Apart from our analytical results, numerical computations are presented to illustrate our protocol.

Analysis and mitigation of phase noise and sampling jitter in OFDM radio receivers

This article addresses the analysis and digital signal processing (DSP)-based mitigation of phase noise and sampling clock jitter in orthogonal frequency division multiplexing (OFDM) radios. In the phase noise studies, the basic direct-conversion receiver architecture case is assumed with noisy downconverting oscillator. In the sampling jitter case, on the other hand, the so-called direct-radio-frequency-sampling receiver architecture is deployed utilizing bandpass sub-sampling principle. The basis for the DSP-based impairment mitigation techniques is first formed using analytical receiver modeling with incoming OFDM waveform, where the effects of both oscillator phase noise and sampling clock jitter are mapped to certain type subcarrier cross-talk and distortion compared to ideal receiver case. Then iterative detection principles and interpolation techniques are developed to essentially estimate and cancel the subcarrier distortion. Also some related practical aspects, like channel estimation, are addressed. The performance of the proposed mitigation techniques is analyzed and verified with extensive computer simulations. In the simulations, realistic phase-locked-loop-based oscillator models are used for phase noise and sampling clock jitter. In addition, different received signal conditions like plain additive white Gaussian noise channel and extended ITU-R Vehicular A multipath channel are considered for practical purposes. Altogether the obtained results indicate that the effects of oscillator and sampling clock instabilities can be efficiently reduced using the developed signal processing techniques.

Jamming Resistance Capabilities of Spectrally Phase Encoded OCDMA Communication Systems With Optimum and Suboptimum (Nonlinear Two-Photon-Absorption) Receiver Structures

In this paper, we study three types of jammers, namely, pulse-jammer, partial-band jammer, and follower-jammer, in a typical fiber-optic-based spectrally phase-encoded optical code division multiple-access (SPE-OCDMA) system. We analyze, mathematically, the effects of the aforementioned jammers on the performance of an SPE-OCDMA system for two scenarios, namely, ideal noiseless channel with an ideal optimum receiver and an ultrahigh-speed nonlinear receiver based on two-photon-absorption (TPA) in a noisy channel. Also, for each of the above cases, two types of modulation, namely, on-off keying (OOK) and two-code keying (2CK) are investigated and their system performances are compared. It is shown that under certain conditions, the system performance can be dramatically degraded due to the jamming signals; also, systems using 2CK modulation show a better resistance and performance when compared to systems using OOK modulation.

Substantiation of the possibility of direct measurements of radiative heat influx in the atmosphere

Numerical experiments simulating measurements with ideal (linear) and real receivers are performed to estimate the possibility of using an optical-acoustic detector for measuring a radiative heat influx (RHI) based on line-by-line calculations. The error of the real receiver is estimated with respect to an ideal one. To this end, a long-wave RHI is calculated in detectors of different sizes where the concentrations of water vapor and carbonic acid gas and the spectral composition of incident radiation is characteristic for the atmospheric surface layer. The consideration of some hypothetical situations allows us to simulate a wide range of conditions in the atmospheric surface layer and to evaluate how they affect measurement errors. Line-by-line calculations of absorption are performed using the HITRAN database. A connection between the relative error attributed to the nonlinearity of absorption, the size of the receiver, and the measurement conditions is analyzed. This is vitally important in the case when large vertical temperature gradients are observed at the point of measurements. For a receiver not larger than 2 cm and in case of normal conditions in the atmospheric surface layer, the error does not exceed 10–20%. The calculation confirms the admissibility of using optical-acoustic detectors for direct measurements of the radiative heat influx in the atmosphere.

Simplifying the error probability analysis in optical direct detection DPSK systems

This letter describes a rigorous formulation based on an eigenfunction expansion technique to estimate the performance of optical direct detection DSPK systems and discusses appropriate procedures to simplify the process without solving any eigenvalue problem. A great emphasis is put on an approach derived from the wide-band optical filtering assumption. The results show that this simplification is acceptable for ideal receivers with time-bandwidth products far larger than 1, but it is clearly inadequate for more realistic receivers.

Cross-Well Radar. II: Comparison and Experimental Validation of Modeling Channel Transfer Function

Close agreement between theory and experiment is critical for adequate understanding and implementation of the cross-well radar (otherwise known as cross-borehole ground penetrating radar) technique, mentioned in a previous paper by the authors. Comparison of experimental results to simulation using a half-space dyadic Green's function in the frequency domain requires development of transfer functions to transform the experimental data into a compatible form. A channel transfer function (CTF) was developed to avoid having to model the transmitting and receiving characteristics of the antennas. The CTF considers electromagnetic wave propagation through the intervening media only (soil in this case) and hence corresponds to the simulation results that assume ideal sources and receivers. The CTF is based on assuming the transmitting antenna, soil, and receiving antenna as a cascade of three two-port microwave junctions between the input and output ports of the vector network analyzer used in the experimental measurements. Experimentally determined CTF results are then compared with computational model simulations for cases of relatively dry and saturated sandy soil backgrounds. The results demonstrate a reasonable agreement, supporting both the model and CTF formulation.

SAGE based iterative receiver for joint synchronization and channel estimation in uplink MIMO-OFDMA systems

A new Turbo iterative receiver structure is proposed for the uplink multiple-input multiple-output orthogonal frequency division multiple access (MIMO-OFDMA) systems. The space-alternating generalized expectation-maximization (SAGE) algorithm is naturally embedded in the framework of iterative receiver to perform synchronization and detection using the Turbo detector outputs. In each iteration, the expectation step intends to remove the multiple access interference (MAI) caused by other asynchronous users, and the maximization step is utilized to estimate the required parameters (i.e., timing offset, carrier frequency offset, channel state information, etc.) sequentially for each user. Simulation results show that the proposed algorithm can approach the performance of ideal receiver closely, while the processing complexity is rather lower than the conventional detectors.