Signal Format Research Articles

FPGA Based Implementation and Comparison of Beamformers for CDMA2000

For the integration of smart antennas into third generation code division multiple access (CDMA) base stations, it still remains as a challenging task to implement smart antenna algorithms on programmable processors. In this paper, we study implementations of some CDMA compatible beamforming algorithms, namely least mean square (LMS), constant modulus (CM), and space code correlator (SCC) algorithms, using Xilinx's Virtex family FPGAs. This study exhibits feasibility of implementing even simple, practical, and computationally small algorithms based on today's most powerful FPGA technologies. 16 and 32 bits floating point implementations of the algorithms are investigated using both Virtex II and Virtex IV FPGAs. CDMA2000 reverse link baseband signal format is used in the signal modeling. Randomly changing fading and Direction-of-arrivals (DOAs) of multipaths are considered as a channel condition. The implementation results in terms of beamforming accuracy, FPGA resource utilization, weight vector computation time, and DOA estimation error are presented. Beamformer weight vectors using LMS and CM can be computed within less than 20 μs on Virtex II FPGA and 10 μs on Virtex IV FPGA, and using SCC it can be achieved within less than 22 μs on Virtex IV FPGA. These results show that FPGAs provide approximately 500 times faster speed in implementations than our previous work with DSPs.

Multiband Video Signal Coding with H.264/AVC, MPEG-4 Studio Profile and Motion JPEG 2000 and Associated Signal Format

Multiband Video Signal Coding with H.264/AVC, MPEG-4 Studio Profile and Motion JPEG 2000 and Associated Signal Format

Combining Alkaline Phosphatase Treatment and Hybrid Linear Ion Trap/Orbitrap High Mass Accuracy Liquid Chromatography−Mass Spectrometry Data for the Efficient and Confident Identification of Protein Phosphorylation

Protein phosphorylation is a vital post-translational modification that is involved in a variety of biological processes. Several mass spectrometry-based methods have been developed for phosphoprotein characterization. In our previous work, we demonstrated the capability of a computational algorithm in mining phosphopeptide signals in large LC-MS data sets by measuring the mass shifts due to phosphatase treatment (Wu, H. Y.; Tseng, V. S.; Liao, P. C. J. Proteome Res. 2007, 6, 1812-1821). Mass accuracy seems to play an important role in efficiently selecting out phosphopeptide signals. In recent years, the hybrid linear ion trap (LTQ)/Orbitrap mass spectrometer, which provides a high mass accuracy, has emerged as a powerful instrument in proteomic analysis. Here, we developed a process to incorporate LC-MS data that was generated from an LTQ/Orbitrap mass spectrometer into our strategy for taking advantage of the accurate mass measurement. LTQ/Orbitrap raw files were converted to the open file format mzXML via the ReAdW.exe program. To find peaks that were contained in each mzXML file, an open-source computer program, msInspect, was utilized to locate isotopes and assemble those isotopes into peptides. An in-house program, LcmsFormatConverter, was utilized for signal filtering and format transformation. A proposed in-house program, DeltaFinder, was modified and used for defining signals with an exact mass shift due to the dephosphorylation reaction, which generated a table that listed potential phosphopeptide signals. The retention times and m/z values of these selected LC-MS signals were used to program subsequent LC-MS/MS experiments to get high-confidence phosphorylation site determination. Compared to our previous work finished by using a quadrupole/time-of-flight mass spectrometer, a larger number of phosphopeptides in the casein mixture were identified by using LTQ/Orbitrap data, demonstrating the merit of high mass accuracy in our strategy. In addition, the characterization of the lung cancer cell tyrosine phosphoproteome revealed that the use of alkaline phosphatase treatment combined with accurate mass measurement in this strategy increased data repeatability and confidence.

A Magnetic Field Probe With MHz Bandwidth and 7-Decade Dynamic Range

The design process of a general-purpose high-performance instrument for magnetic field measurements is presented. Demanding requirements have been extracted from standards, regulations, and the literature in some fields of application [e.g., human exposure and industrial and military electromagnetic compatibility (EMC)], consisting of a frequency range of 1 Hz to 400 kHz, an approximately seven-decade dynamic range with impact on designed voltage levels and internal noise, an output signal format, and postprocessing algorithms. The experimental characterization of the prototype is also reported, showing that the frequency response of the instrument is extended up to the megahertz range. The comparison of the instrument's performances with those of commercial products and published equipment confirms the extremely good performances.

Optically controlled loop buffer using a SOA loop mirror and a circulator based reflector

In this paper, an optically controlled loop buffer is proposed and experimentally demonstrated. It utilizes a semiconductor optical amplifier (SOA) based loop mirror as a fast switch to realize the writing and reading of packets within this buffer and a circulator based optical reflector to achieve internal re-circulations. By adding fibers with different lengths between the loop mirror and the circulator, variable delay time per circulations can be obtained. We also demonstrate the performance of the 2.5 and 10 Gb/s data packets in this buffer structure, as well as the influence of the two different control signal formats on the packet signal degradation during buffering. This loop buffer has the merits of low cost and improved performance compared to other similar loop buffer structures. According to the obtained results, the achieved number of circulations is greatly increased.

Iterative joint data detection and channel estimation for uplink MC-CDMA systems in the presence of frequency selective channels

This paper is concerned with joint multiuser detection and multichannel estimation (JDE) for uplink multicarrier code-division multiple-access (MC-CDMA) systems in the presence of frequency selective channels. The detection and estimation, implemented at the receiver, are based on a version of the expectation maximization (EM) algorithm and the space-alternating generalized expectation-maximization (SAGE) which are very suitable for multicarrier signal formats. The EM-JDE receiver updates the data bit sequences in parallel, while the SAGE-JDE receiver reestimates them successively. The channel parameters are updated in parallel in both schemes. Application of the EM-based algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithms have excellent BER end estimation performance.

Signal processing agorithms for unmanned undersea vehicles navigation and collision avoidance.

In this paper, signal processing algorithms for dynamic UUV homing and docking, navigation, and collision avoidance are presented. Many conventional techniques are image-based, which involved computation-intensive image reconstruction procedures, which is ineffective in dynamic real-time environment. Therefore, it is of great importance to develop computationally effective signal processing algorithms for high-precision UUV geolocation. To optimize the applicability, the algorithms presented in this paper cover all key modalities, including both active and passive, with temporal pulse and FMCW signal formats. In terms of operating configurations, the first case is classified as the passive-receiver systems. The transmitting signal format for this case is in the form of a twin-pulse set, with opposite polarity. The bearing angle is estimated from the temporal offset of the pulses. The dual version of this configuration is in the form of an active system and the double-integration algorithm can be effectively applied to both versions. The active configuration can then be extended to incorporate the FMCW signaling format. For the FMCW case, estimation of the bearing angle and range distance can be accomplished with the Fourier transform methods. In this paper, the presentation includes theoretical analysis, signal processing algorithms, and experiments.

Micro flexible ultrasound imaging array systems.

Medical ultrasonography has continued to be an important biomedical imaging modality for its various advantages. Conventional medical ultrasound systems typically utilize a rigid transceiver phase array, with a relatively small transceiver contact area. A micro conformal system increases observation aperture by using a large, flexible transducer array that conforms to curved body surfaces, providing increased angular coverage and 3‐D imagery. In addition, the frequency‐modulated continuous wave (FMCW) signaling format requires lower peak power than pulse‐echo systems and exhibit more favorable receiver noise characteristics. This paper provides an overview of the hardware development of the micro flexible ultrasound array system. The image formation procedure is first presented in the form of pulse‐echo imaging modality. Subsequently, image reconstruction algorithms are formulated for the FMCW imaging format. In addition, the equivalence between the pulse‐echo and FMCW imaging modes is developed. This enables us to conduct image reconstruction process in both space as well as spatial‐frequency domain. The presentation includes theoretical analysis, image formation algorithms, and laboratory experiments. [This research project was supported by the Telemedicine and Advanced Technology Research Center (TATRC), Department of Defense under award numbers W81XWH‐07‐1‐0672 and W81XWH‐07‐1‐0668.]

Ultra-low-loss optical fiber enabling purely passive 10 Gb/s PON systems with 100 km length

We demonstrate time division multiplexing (TDM) and wavelength division multiplexing/TDM (WDM/TDM) long reach 10 Gb/s passive optical network (PON) architectures of 100 km reach with no infield amplification or dispersion compensation. The purely passive nature of the 100 km systems is enabled by the use of ultra-low-loss optical fiber with average attenuation of 0.17 dB/km and downstream transmission with a 10 Gb/s signal modulated with the duobinary format. The high tolerance of duobinary to dispersion, stimulated Brillouin scattering (SBS), and self-phase modulation (SPM) are all key factors to achieving good system performance at this distance, as is the significantly reduced loss from the ultra-low-loss fiber. We show that this combination of fiber and downstream signal format allow split ratios up to 1:128 for both system architectures. The achievable split ratio is reduced for standard single-mode fiber and/or use of an NRZ modulated downstream signal. Standard strength forward error correction (FEC) is used for the WDM/TDM system but is not required for the TDM system.

Generation of optical millimeter-wave signals and vector formats using an integrated optical I/Q modulator [Invited

This study discusses two key technologies used in radio-over-fiber (RoF) systems, namely, the generation and transmission of millimeter-wave signals and optical modulation schemes capable of carrying vector signal formats and utilizing the continuous performance improvements offered by digital signal processing. A cost-effective frequency-quadrupling technique capable of generating millimeter-wave signals up to 72 GHz is proposed. The generated optical millimeter-wave signals have very high quality, with an optical carrier and harmonic distortion suppression ratio exceeding 36 dB. An optical modulation scheme that can support a 64-QAM, 16 Gbits/s orthogonal frequency-division multiplexing RoF system is also demonstrated. Results of this study demonstrate that both methods offer realistic solutions to support future wireless systems.

On the performance of a maximum likelihood method with delayed correlation for the coarse carrier frequency offset estimation of OFDM signals with multiple preamble symbols

Estimation of carrier frequency offset (CFO) is an important issue in the design of a wireless receiver that employs orthogonal frequency division multiplexing (OFDM) techniques. In this paper, using the ten short training symbols specified in the signal format of the IEEE 802.11a WLAN, we investigate the performance of a coarse CFO estimation scheme for OFDM signals with multiple preamble symbols. This scheme, which we call DC-ML, employs the maximum likelihood (ML) method with delayed correlation (DC). For AWGN channels under moderate signal to noise ratio (SNR) conditions, we develop an analysis to evaluate the variance of estimation error (VEER). The analysis is corroborated in light of simulations, and compared with the formulated Cramer-Rao lower bound (CRLB). VEER of the DC-ML in a multipath environment is studied via simulations. Numerical results show that a certain parameter combination can result in minimum VEER. Simulation results justify that the probability of estimation error (PEER) approximates Gaussian distribution in both AWGN and multipath scenarios. We also present a Two-Branch DC-ML (TBDC-ML) scheme, which comprises two correlation branches of DC-ML, and an associative ambiguity resolution algorithm. Numerical examples reveal that TBDC-ML outperforms DC-ML in both VEER and PEER. Assuming that the estimation error resulting from the two branches is jointly Gaussian, we derive the joint probability density function (pdf) and validate it via simulations.

Design and implementation for deinterlacing using the edge-based correlation adaptive method

Deinterlacing is a method to construct a complete image from an interlaced signal. The interlaced signal format is adopted by the Natural Television System Committee (NTSC) based on eye remanence. In previous work, such as traditional edge line averaging (ELA), it used the intra-interpolation to find the minimum difference value without considering the edge and boundary existence. Consequently, it will cause the interpolation value to be blurred at the edge. A novel algorithm, an edge-based correlation adaptive (ECA) method, is proposed. ECA is based on various edge directions to detect the edge. This new intrafield method has better performance on smoothing the edge and stripe. ECA is improved by using a weighted summation of the ELA component to facilitate the interpolation result. We also interpolate the half-pixel value to increase the accuracy for edge detection. We also mention the architecture and very large scale integration (VLSI) implement results.

N-continuous OFDM

In this letter we report a new OFDM signalling format characterized by a precoder that renders the emitted signal's phase and amplitude continuous. It achieves superior out-of- band power characteristics at the price of a slightly reduced receiver sensitivity.

Flexible block‐wise loading algorithm for effective resource allocation and reduction of uplink feedback information in OFDMA systems

AbstractAdaptive modulation and coding (AMC) is a well‐known technique that selects a suitable modulation level and coding rate according to the user's channel quality. The utilization of AMC in downlink (DL) requires the channel information of each user on DL to properly select the modulation and coding scheme (MCS) level. However, under a practical OFDMA system environment, it is unsuitable to feedback all the channel information over the whole frequency resources due to the limited uplink bandwidth. In this paper, to optimize the performance of the AMC system and to reduce the uplink feedback requirement, we propose a flexible block‐wise loading (FBL) algorithm combined with a novel channel quality information (CQI) feedback scheme requiring less number of CQI feedback bits, which is suitable for the general OFDMA system with AMC. The proposed FBL algorithm dynamically allocates groups of sub‐carriers to each user in DL based on the channel quality information encapsulated in a newly defined feedback signal format. As a result, the sector throughput and outage performance is improved due to the flexibility on the sub‐channel allocation and increased accuracy on the CQI feedback information by the proposed FBL algorithm. Copyright © 2008 John Wiley & Sons, Ltd.

Spectral precoding for rectangularly pulsed OFDM

Spectrally precoded orthogonal frequency-division multiplexing (OFDM) is a promising rectangularly pulsed OFDM signaling format which can provide very small power spectral sidelobes, while allowing for efficient implementation by fast Fourier transform and guard interval insertion. In this paper, general constraints on spectral precoding are developed for OFDM signals with zero padding (ZP-OFDM) or cyclic prefix (CP-OFDM) to warrant the desirable spectral property that the power spectral sidelobes decay asymptotically as f <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2K-2</sup> , where K is a preassigned positive integer. In accordance with the constraints, block partitioning is adopted to construct a general signaling format to facilitate the precoder design of the spectrally precoded CP-OFDM that can provide fast decaying sidelobes. New correlative and orthogonal precoders are also devised so that the desirable spectral property of fast sidelobe decaying is achieved with spectrally precoded ZP-OFDM and CP-OFDM signals.

A New Transmitted Reference Pulse Cluster System for UWB Communications

To meet the implementation constraint posed by ultra- wideband (UWB) delay lines, a new transmitted reference pulse cluster (TRPC) structure is proposed where a group of reference and data pulses with short uniform spacing is used for transmission. This structure enables a simple, robust, and practical autocorrelation detector to be implemented in the receiver. It overcomes the major hurdle to the practical implementation of conventional transmitted reference (TR) systems, i.e., the long-wideband-delay-line requirement. TRPC is also compatible with the signal format proposed within the IEEE 802.15.4a Working Group for coherent and noncoherent systems. The performance of the proposed TRPC receiver and noncoherent pulse-position modulation (NC-PPM) with energy detection are analyzed and compared. Simulation results show that TRPC outperforms the conventional TR, NC-PPM, the recently proposed dual-pulse scheme, and the frequency-shifted reference system. In particular, it achieves power saving over NC-PPM by about 1.3-1.9 dB for IEEE 802.15.4a channel model 1 and 1.3-2.3 dB for channel model 8.

A Method to Calculate PMD-Induced Eye-Opening Penalty and Signal Outage for RZ-Modulated Signal Formats

In this paper, we present a fast and computational low-intense method to calculate signal outage due to polarization mode dispersion (PMD) for RZ-based modulation formats. The presented tool serves mainly as a fast algorithm to calculate qualitative measures of signal outage for these modulation formats.

A Practical Space-Code Correlator Receiver for DSP Based Software Radio Implementation in CDMA2000

Development of practical algorithms for beamforming in 3G CDMA systems and their software radio implementations are still a challenging task, which will facilitate upgrading of traditional base stations into smart antenna capable 3G base stations. In this paper, we propose a practical space-code correlator (SCC) receiver structure for its software radio implementation a DSP. SCC's advantage comes from the fact that it doesn't require any training sequence or learning parameter as in other algorithms (LMS or CM). DSP implementations of the SCC are performed using Texas Instruments C67xx family platforms. In the simulations, reverse link base band signal format of CDMA2000 is used and the effects of different array topologies (uniform linear array-ULA or uniform circular array-UCA) are considered. The implementation results regarding beamforming accuracy, weight vector computation time (execution time), search resolution effect on DOA estimation accuracy, DSP resource utilization, and received SINR are presented. The results show that DSP based SCC beamformer can estimate weight vectors within less than 10 ms with DOA search resolution of 2° especially when C6713 DSP is used. With faster DSPs and larger search resolutions, execution time could be significantly reduced as well. It provides comparable SINR performance with LMS and CM algorithms.

Use of return-to-zero formats in electrical dispersion compensated optical single sideband transmission systems

The use of return-to-zero (RZ) formats is proposed to enhance the dispersion tolerance of intensity-modulated carrier-unsuppressed (IM-CUs) optical single sideband (oSSB) systems. The performance of these systems, employing electrical dispersion compensation (EDC), is accessed using unipolar and polar RZ signalling formats, and compared with common non-return-to-zero (NRZ). Simulation results at 10.7 Gb/s reveal that oSSB systems with EDC using both NRZ and unipolar RZ signalling formats are limited to low extinction ratio (ER) values. However, the use of polar RZ allows increased ER and transmission distances, because of higher inter-symbol interference tolerance and the absence of discrete spectral tones. Considering a minimum ER of 9 dB and resort to forward error correction schemes, polar RZ allows single-channel error free transmission over 1400 km of standard single-mode fibre, substantially improving the 980 km obtained for NRZ with ER of 6 dB. Dense wavelength-division multiplexing transmission was also assessed, retrieving improved resilience of IM-CUs oSSB polar RZ.

Partial bit delay correlative modulation used to improve the dispersion tolerance of an optical duobinary system

Phase effect of the optical duobinary (ODB) modulation on the chromatic dispersion (CD) tolerance is more important than the ODB modulation-induced bandwidth effect. To show this, we evaluate, respectively, the filter bandwidth effect and the phase effect of the partial bit delay correlative modulation (PBDCM) on the CD tolerance. Due to the cancellation between the CD-induced and the PBDCM-induced phase effects, the PBDCM method can increase the CD-limited transmission to 2 ??? 3 times of that using standard 1-bit delay modulation, while the optimized filter bandwidth method can increase the transmission by 50% or less, depending on the input signal format. The PBDCM can be physically realized by adjusting the delay time of the delay-and-add circuit in the conventional duobinary transmitter (without lower-pass filter). These conclusions are also valid for systems having non-negligible polarization-mode dispersion (PMD) and polarization dependent loss (PDL).