Sphere Detection Research Articles

Reduced Complexity Soft-Output MIMO Sphere Detectors—Part I: Algorithmic Optimizations

Optimum soft-output (SO) multiple-input multiple- output (MIMO) tree-search detection algorithms pose significant implementation challenges due to their nondeterministic processing throughput and high computational complexity. In this two-part work, we present extensive algorithmic and architectural optimizations of the sphere-decoding algorithm targeted at achieving practical tradeoffs between desired link performance and affordable computational complexity. The algorithmic optimizations in this part span the tree-search traversal scheme, leaf processing step, internal node-pruning and skipping step, child enumeration based on a state-machine, adaptive radius scaling for LLR clipping, QR-decomposition based on minimum cumulative residuals, and multitree configurations. The optimizations demonstrate that a 64-QAM SO MIMO detector for LTE is capable of attaining almost ML performance with an SNR loss of only 0.85 dB at 1% BLER by visiting at most 200 tree nodes.

Sphere Detection Technique: An Optimum Detection Scheme for MIMO System

In this paper, various multiple input and multiple output (MIMO) detection techniques have been compared on the basis of BER performance and complexity. Maximum likelyhood (ML) detection method has shown optimal solution in MIMO systems compared to conventional detection techniques. However, higher receiver complexity leads to use of lower complexity techniques such as zero forcing (ZF) and minimum mean square error (MMSE) having relatively poor performance. Successive interference cancellation combined with ZF or MMSE has much improved performance but vulnerable to error propagation. Ordered succesive interference cancellation with MMSE (MMSE-OSIC) has reduced error propagation probability and gave the better performance. A new detection technique sphere detection (SD) based on Schnorr-Euchner enumeration has provided ML solution with much less computational complexity. For simulation, Rayleigh channel model has been considered.

SU‐F‐BRE‐11: Neutron Measurements Around the Varian TrueBeam Linac

Purpose:With the emergence of flattening filter free (FFF) photon beams, several authors have noted many advantages to their use. One such advantage is the decrease in neutron production by photonuclear reactions in the linac head. In the present work we investigate the reduction in neutrons from a Varian TrueBeam linac using the Nested Neutron Spectrometer (NNS, Detec). The neutron spectrum, total fluence and source strength were measured and compared for 10 MV with and without flattening filter and the effect of moderation by the room and maze was studied for the 15 MV beam.Methods:The NNS, similar to traditional Bonner sphere detectors but operated in current mode, was used to measure the neutron fluence and spectrum. The NNS was validated for use in high dose rate environments using Monte Carlo simulations and calibrated at NIST and NRC Canada. Measurements were performed at several positions within the treatment room and maze with the linac jaws closed to maximize neutron production.Results:The measurements showed a total fluence reduction between 35‐40% in the room and maze when the flattening filter was removed. The neutron source strength Qn was calculated from in‐room fluence measurements and was found to be 0.042 × 102 n/Gy, 0.026 × 102 n/Gy and 0.59 × 1012 n/Gy for the 10 MV, the 10 MV FFF and 15 MV beams, respectively. We measured ambient equivalent doses of 11 mSv/hr, 7 mSv/hr and 218 mSv/hr for the 10 MV, 10 MV FFF and 15 MV by the head.Conclusion:Our measurements revealed a decrease in total fluence, neutron source strength and equivalent dose of approximately 35‐40% across the treatment room for the FFF compared to FF modes. This demonstrates, as expected, that the flattening filter is a major component of the neutron production for the TrueBeam.The authors greatly acknowledge support form the Canadian Nuclear Commission and the Natural Sciences and Engineering Research Council of Canada through the CREATE program. Co‐authors Dubeau and Witharana are employees of Detec (Gatineau, Quebec), manufacturer of the Nested Neutron Spectrometer.

90Y PET/CT quantitative accuracy and image quality

Purpose: To optimize 90Y-PET/CT image reconstruction for quantitative accuracy and optimal image quality. Methods : PET/CT scans of a NEMA IEC phantom (3GBq 90YCl2, sphere uptake ratio of ~7) were acquired on 4 GE (BGO:DSTE, DST & LYSO:DRX, D690) and 1 Siemens (LSO:mCT) scanners in 3D list mode with 30 min/bed; replayed to 20, 15, 10 min/bed. Iterative reconstruction parameters explored were SUB × IT (3 – 80) and post-reconstruction filters: transaxial: 5 – 25 mm cutoff & z-axis (GE only): std vs. heavy. The effects of PSF modeling and TOF correction were evaluated for D690 and mCT. VOIs were drawn inside spheres and in adjacent background regions. The accuracy of sphere activity concentration (AC in kBq/mL) and contrast to noise ratio (CNR) was calculated as function of SUB × IT. Reconstructed PET images were also evaluated qualitatively for sphere detectability and artifacts. Results: AC converged to 70 – 90% accuracy for 37 mm sphere and further degraded for smaller spheres. Spheres at max CNR might not reach AC convergence yet. Smaller spheres have slower convergence but reach CNR max together with other spheres. Scan duration did not strongly affect sphere convergence but shorter scans increased noise and reduced detectability; 13 mm spheres were not visible going from 30 to 15 min/bed. Heavy z-axis (GE) and transaxial filter with 10 – 15 mm cutoff helped suppress noise and increase sphere detectability at the expense of accuracy. Images with PSF+TOF corrections had higher sphere detectability and converged faster. Hot cluster artifacts 5 – 7 times the background were seen in some cases with SUB × IT near convergence and lower filtration. Conclusion : Accurate 90Y AC was not achieved even at convergence and noise is a major concern. 90YPET/CT reconstruction parameters are different than those for 18F and benefit substantially from PSF+TOF corrections. Optimum image quality and accurate AC may not be simultaneously achievable. ---------------------------------------- Cite this article as: Siman W, Mawlawi O, Kappadath SC. 90Y PET/CT quantitative accuracy and image quality. Int J Cancer Ther Oncol 2014; 2(2):020235. DOI: 10.14319/ijcto.0202.35

Absolute quantum cutting efficiency of Tb3+-Yb3+ co-doped glass

The absolute quantum cutting efficiency of Tb3+-Yb3+ co-doped glass was quantitatively measured by an integrating sphere detection system, which is independent of the excitation power. As the Yb3+ concentration increases, the near infrared quantum efficiency exhibited an exponential growth with an upper limit of 13.5%, but the visible light efficiency was reduced rapidly. As a result, the total quantum efficiency monotonically decreases rather than increases as theory predicted. In fact, the absolute quantum efficiency was far less than the theoretical value due to the low radiative efficiency of Tb3+ (<61%) and significant cross-relaxation nonradiative loss between Yb3+ ions.

A novel pre-processing and adaptive statistical threshold for sphere detection in MIMO systems

Abstract In this paper, an efficient sphere detection (SD) scheme for multiple-input multiple-output (MIMO) systems is presented. The proposed SD scheme can substantially reduce computational complexity by introducing a pre-processing scheme and an adaptive threshold. In particular, our proposed pre-processing scheme is based on an iterative successive interference cancelation (SIC). The proposed adaptive threshold is used to judge whether a traversed path is correct or not and obtained by analyzing the distributions of the correct and erroneous estimates which have the minimum error pattern among all the SD searching paths. Simulation results show that our proposed scheme offers a substantial complexity reduction in terms of the number of visited nodes while keeping a significantly small performance degradation compared to conventional approaches.

Exploration of Lattice Reduction Aided Soft-Output MIMO Detection on a DLP/ILP Baseband Processor

Lattice Reduction aided soft output MIMO detectors (LR-SOMD) have been demonstrated to offer a promising gain. This work explores the potential of implementing a LR-SOMD on a parallel programmable baseband processor. In this paper, first a LR algorithm called the Data Regularized Parallel Lattice Reduction algorithm (DRP-LR) is proposed. Afterwards, a low-complexity LR-SOMD, Radius Constrained Multi-Tree Selective Spanning (RC-MTSS) is presented. RC-MTSS uses a novel multiple-tree search approach for LR-SOMD, while combining the benefits of Sphere Detection (SD) and Selective Spanning with Fast Enumeration (SSFE). A fixed complexity LR-SOMD, Multi-Tree Selective Spanning (MTSS) is also proposed for implementation. Both the algorithms, DRP-LR and MTSS, are enabled to exploit data level parallelism (DLP) and instruction level parallelism (ILP). In order to evaluate performance, the proposed DRP-LR and MTSS are implemented on the ADRES baseband processor for a 4 × 4 LTE system using QAM-64. DRP-LR achieves an average throughput of 33.33 M LR per second, which is comparable to recently reported ASIC implementations, while MTSS shows an average throughput of 730 Mbps on the same processor. To the best of authors' knowledge, this is the first reported implementation of a LR-SOMD algorithm on a parallel programmable baseband processor.

MC-OFDMA FOR MULTI-USER DETECTION SCHEMES IN POWERLINE COMMUNICATION

Support of multiple users in wideband powerline communication (PLC) is essential to enhance the dependence on such emerging systems. This paper presents novel adaptations of the space division multiple access (SDMA) techniques to PLC. Multicarrier data transmission and orthogonal frequency division multiple access (OFDMA) techniques are invoked to mitigate the technical challenges of PLC channel impairments and enhance the spectral efficiency. Performance is enhanced using orthogonal Walsh–Hadamard codes. Linear and nonlinear multi-user detection (MUD) schemes are investigated, including the optimal maximum likelihood (ML) methods and the near-optimal sphere detectors(SDs). Presented results indicate the potential of the proposed scheme to enhance wideband PLC systems.

Scale effect analysis of early-termination fixed-complexity sphere detector

In this paper, we show that the early-termination fixed-complexity sphere detector (ET-FSD) has a scale effect when being employed in multi-antenna systems that have to detect signals of multiple users under the constraint of sum complexity. The so-called scale effect stands for a kind of effect in which the complexity per user can be reduced as the number of users increases without loss of diversity order. The main contributions of this study are as follows: (1) we establish a mathematical model based on the large deviation principle to apply the concept of scale effect to ET-FSD; (2) we prove the existence of the scale effect of ET-FSD in a multi-user scenario; and (3) we demonstrate that within multi-user systems, the scale effect can be exploited to realize ET-FSD that has the optimal performance in the point view of diversity order under polynomial complexity constraint per user.

New Computational Complexity Reducing IDD Scheme Designed with Optimum Parameters

An Iterative Detection and Decoding (IDD) scheme in a high-order Multiple-Input Multiple-Output (MIMO) wireless communication system requires a heavy computational complexity for an outstanding Bit Error Rate (BER) performance in a given Signal-to-Noise Ratio (SNR) environment. A new computational complexity reducing IDD scheme designed with optimum parameters is proposed in this paper to guarantee Quality of Service (QoS) without the loss of BER performance. There are three parameters to control the trade-off between computational complexity and BER performance of an IDD scheme: a candidate list size of Dynamic List Sphere Detector (D-LSD), a number of intra-iteration of Turbo decoder, and a number of IDD iteration. A complexity reduction of about 70 % is demonstrated in this study, when the target BER is around 1.0×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(-4)</sup> at E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =7dB in the case of a 4 x 4 MIMO system with 16-ary Quadrature Amplitude Modulation (QAM).

TU-A-116-05: Evaluation of Relative X-Ray Imaging Detector Performance Using the Metric of Relative Object Detectability (ROD)

Purpose: To determine the relative detectability performance of two x‐ray imaging detectors for specific clinical objects and devices. Methods: The relative object detectability (ROD) can be defined as the ratio of the integral of the detective quantum efficiency (DQE) of a detector weighted by the square of the Fourier Transform (or frequency spectrum) of the object to the same integral for a second detector. Three different detectors, namely the micro‐angiographic fluoroscope (MAF), the solid state x‐ray image intensifier (SSXII) and a flat panel detector (FPD), were assessed for their relative performance with respect to the detectability of wires and spheres. The RODs were calculated for three sets of detectors: MAF‐FPD, MAF‐SSXII and SSXII‐FPD, for wires of a fixed length of 20 mm and solid spheres made of different materials (aluminum, titanium and nickel) ranging in diameters from 100 micron to 1.0 mm to simulate endovascular devices. Results: For the 100‐micron diameter, the ROD is 1.4 [2.0] for the MAF‐SSXII and SSXII‐FPD sets and 1.9 [3.9] for the MAF‐FPD for the wire [sphere] indicating superior performance of the MAF over the FPD and SSXII and of the SSXII over the FPD for small sized objects. However, the ROD decreased monotonically as the object diameter increased and showed equivalent performance for wires with diameter over 300 microns and spheres with diameters above 400 microns. Conclusion: The ROD depends upon the physical geometry of the object and is useful in quantifying the relative performance of detectors regarding detectability of specific objects. Because of their higher spatial resolution both the MAF and the SSXII perform better than the FPD for viewing wires with diameters under 300 microns and spheres with diameters under 400 microns; however, the MAF performance is shown to be superior to the SSXII as well. NIH Grant 2R01EB002873

Robust Spherical Shell Clustering Using Fuzzy-Possibilistic Product Partition

One of the main challenges in the field of clustering is creating algorithms that are both accurate and robust. This paper introduces a novel fuzzy-possibilistic shell clustering model aiming at accurate detection of circles, spheres, and multidimensional spheroids in the presence of outlier data. The proposed fuzzy-possibilistic product partition c-spherical shell algorithm (FP3CSS) combines the probabilistic and possibilistic partitions in a qualitatively different way from previous, similar algorithms. The novel mixture partition is able to suppress the influence of extreme outlier data, which gives it net superiority in terms of robustness and accuracy, compared to previous algorithms.

SNR‐dependent radius control sphere detection for MIMO systems and relay networks

AbstractA new sphere decoder algorithm for uncoded spatial multiplexing multiple‐input multiple‐output (MIMO) systems is proposed. It overcomes the drawbacks of traditional sphere decoders: variable complexity and high complexity in low signal‐to‐noise ratios (SNRs). Its main novelty lies in scaling the search radius by a heuristic SNR‐dependent factor. This new SNR‐dependent radius control sphere decoder offers near maximum likelihood performance over the entire range of SNRs, while keeping its complexity roughly constant. This algorithm also incorporates channel ordering to save complexity. To quantify the variability of complexity, the normalised variance of the complexity is evaluated. This algorithm is also extended for joint iterative detection and decoding in coded MIMO systems and for MIMO‐relay networks. Simulation results and theoretical analysis demonstrate the benefits of the proposed algorithm.Copyright © 2013 John Wiley &amp; Sons, Ltd.

Quantitative Comparison of PET and Bremsstrahlung SPECT for Imaging the In Vivo Yttrium-90 Microsphere Distribution after Liver Radioembolization

BackgroundAfter yttrium-90 (90Y) microsphere radioembolization (RE), evaluation of extrahepatic activity and liver dosimetry is typically performed on 90Y Bremsstrahlung SPECT images. Since these images demonstrate a low quantitative accuracy, 90Y PET has been suggested as an alternative. The aim of this study is to quantitatively compare SPECT and state-of-the-art PET on the ability to detect small accumulations of 90Y and on the accuracy of liver dosimetry.Methodology/Principal FindingsSPECT/CT and PET/CT phantom data were acquired using several acquisition and reconstruction protocols, including resolution recovery and Time-Of-Flight (TOF) PET. Image contrast and noise were compared using a torso-shaped phantom containing six hot spheres of various sizes. The ability to detect extra- and intrahepatic accumulations of activity was tested by quantitative evaluation of the visibility and unique detectability of the phantom hot spheres. Image-based dose estimates of the phantom were compared to the true dose. For clinical illustration, the SPECT and PET-based estimated liver dose distributions of five RE patients were compared. At equal noise level, PET showed higher contrast recovery coefficients than SPECT. The highest contrast recovery coefficients were obtained with TOF PET reconstruction including resolution recovery. All six spheres were consistently visible on SPECT and PET images, but PET was able to uniquely detect smaller spheres than SPECT. TOF PET-based estimates of the dose in the phantom spheres were more accurate than SPECT-based dose estimates, with underestimations ranging from 45% (10-mm sphere) to 11% (37-mm sphere) for PET, and 75% to 58% for SPECT, respectively. The differences between TOF PET and SPECT dose-estimates were supported by the patient data.Conclusions/SignificanceIn this study we quantitatively demonstrated that the image quality of state-of-the-art PET is superior over Bremsstrahlung SPECT for the assessment of the 90Y microsphere distribution after radioembolization.

Successive AF/DF Relaying in the Cooperative DS-CDMA Uplink: Capacity Analysis and Its System Architecture

A successive-relaying-aided network (SRAN) is designed for a multiuser spread-spectrum scenario conceived for noncoherent (NC) detection to convert the typical 50% half-duplex relaying induced throughput loss to a potential user-load reduction of the code-division multiple-access (CDMA) system, where the NC allows us to avoid the extra power consumption imposed by channel estimation. We commence by evaluating the NC discrete-input-continuous-output memoryless channel (DCMC) capacity of both the amplify-and-forward-based (AF) and decode-and-forward-based (DF) SRANs in the direct-sequence CDMA (DS-CDMA) uplink (UL). While NC detection has the added benefit of eliminating both the pilot overhead and the power-hungry channel estimation, it tends to form an error floor at high Doppler frequencies. We mitigate this problem using multiple-symbol detection, which increases the detection complexity upon extending the detection window. Finally, a relay-aided soft-input-soft-output multiple-symbol differential sphere detection (SISO-MSDSD) CDMA regime is proposed, which significantly reduces the system's complexity without sacrificing its performance.

A Sphere Detection Based Adaptive MIMO Detection Algorithm for LTE-A System

An adaptive MIMO detection algorithm for LTE-A system which is based on sphere detection is proposed in this paper. The proposed algorithm uses M-algorithm for reference to remove unreliable constellation candidates before search, and the number of constellation reservation is adaptively adjusted according to SNR. Simulations of LTE-A downlink show that the BER performance of the proposed detection algorithm is nearly the same as maximum likelihood (ML) detection algorithm. However, the complexity is reduced by about 30% compared with full constellation sphere detection.

New Parallel Sphere Detector Algorithm Providing High-Throughput for Optimal MIMO Detection

Multiple–input multiple-output (MIMO) detection techniques can vary significantly in complexity and detection performance. Finding the optimal Maximum Likelihood (ML) solution with high throughput was limited by the computational performance. In order to achieve high throughput non-ML algorithms were introduced, having degraded detection performance and lower complexity. In this paper we present a new parallel algorithm, inspired by the Sphere Detector (SD) algorithm, which can effi- ciently solve the ML detection of the MIMO systems with high throughput on parallel architectures. We also give an overview on how it is possible to map the Parallel Sphere Detector (PSD) onto GP-GPUs, however different parallel architectures are also suitable for adapting the presented algorithm.

Measurement of Scattering and Absorption Cross Sections of Dyed Microspheres.

Measurements of absorbance and fluorescence emission were carried out on aqueous suspensions of polystyrene (PS) microspheres with a diameter of 2.5 µm using a spectrophotometer with an integrating sphere detector. The apparatus and the principles of measurements were described in our earlier publications. Microspheres with and without green BODIPY@ dye were measured. Placing the suspension inside an integrating sphere (IS) detector of the spectrophotometer yielded (after a correction for fluorescence emission) the absorbance (called A in the text) due to absorption by BODIPY@ dye inside the microsphere. An estimate of the absorbance due to scattering alone was obtained by subtracting the corrected BODIPY@ dye absorbance (A) from the measured absorbance of a suspension placed outside the IS detector (called A1 in the text). The absorption of the BODIPY@ dye inside the microsphere was analyzed using an imaginary index of refraction parameterized with three Gaussian-Lorentz functions. The Kramer-Kronig relation was used to estimate the contribution of the BODIPY@ dye to the real part of the microsphere index of refraction. The complex index of refraction, obtained from the analysis of A, was used to analyze the absorbance due to scattering ((A1- A) in the text). In practice, the analysis of the scattering absorbance, A1-A, and the absorbance, A, was carried out in an iterative manner. It was assumed that A depended primarily on the imaginary part of the microsphere index of refraction with the other parameters playing a secondary role. Therefore A was first analyzed using values of the other parameters obtained from a fit to the absorbance due to scattering, A1-A, with the imaginary part neglected. The imaginary part obtained from the analysis of A was then used to reanalyze A1-A, and obtain better estimates of the other parameters. After a few iterations, consistent estimates were obtained of the scattering and absorption cross sections in the wavelength region 300 nm to 800 nm.

Optical collection of multiple spheres in single tightly focused beams

The algorithm of multiple scattering is presented in this paper. The model of dynamic simulation and collision detection of multiple spheres is developed. The optical collection of multiple spheres in single tightly focused beams is simulated dynamically, considering the effects of Brownian motion of the spheres and the optical forces. The number of spheres with different parameters collected in a Gaussian beam is obtained using a program based on the T-matrix method and multiple scattering. Some interesting effects of the refractive index and size of spheres are revealed. The optical collection is explained physically in terms of optical binding. The method for modeling the collection of microspheres can be applied to the optical trapping and manipulation of multiple particles in general.

Measurement of Scattering and Absorption Cross Sections of Microspheres for Wavelengths between 240 nm and 800 nm.

A commercial spectrometer with a 150 mm integrating sphere (IS) detector was used to estimate the scattering and absorption cross sections of monodisperse polystyrene microspheres suspended in water. Absorbance measurements were performed with the sample placed inside the IS detector. The styrene absorption was non zero for wavelengths less than 300 nm. Correction for fluorescence emission by styrene was carried out and the imaginary part of the index of refraction, ni, was obtained. Absorbance measurements with the sample placed outside the IS detector were sensitive to the loss of photons from the incident beam due to scattering. The absorbance data was fitted with Lorenz-Mie scattering cross section and a correction for the finite acceptance aperture of the spectrometer. The fit parameters were the diameter, the suspension concentration, and the real part of the index of refraction. The real part of the index was parameterized using an expansion in terms of powers of the inverse wavelength. The fits were excellent from 300 nm to 800 nm. By including the imaginary part obtained from the absorbance measurements below 300 nm, it was possible to obtain a good fit to the observed absorbance data over the region 240 nm to 800 nm. The value of ni at 266 nm was about 0.0060±0.0016 for microspheres with diameters of 1.5 μm, 2.0 μm, and 3.0 μm. The scattering cross section, absorption cross section, and the quantum yield at 266 nm of microsphere with a diameter of 2.0 μm was 5.65±0.01 μm2, 1.54±0.03 μm2, and 0.027±0.002 respectively. The styrene absorption reduces the scattering cross section by 20 % at 266 nm.