Spl Ges Research Articles

Modeling and measurement of the acoustic lead sensitivity in sagnac fiber sensor arrays

In this study, a theoretical model of the lead (delay coil and array buses) sensitivity in Sagnac sensor arrays (SSA) for underwater acoustic detection, which induces a spurious pickup and thus a sensor error, is described. In the worst-case scenario, the pickup in a 20-km coil is predicted to be reasonable in deep waters (quietest) (about 17 dB higher than the hydrophone signal) but fairly high (/spl sim/ 52 dB) in shallow waters (noisiest). We show that this pickup can be eliminated for the first few hydrophones in the array by optically folding or double winding the coil, although these approaches are not as effective for the most distant hydrophones in long arrays (/spl ges/ 1 km). These figures are confirmed experimentally in an SSA: Folding a 5-km coil decreased the relative pickup from /spl sim/-42 dB for the first hydrophone and by /spl sim/-8 dB for a hydrophone 1 km down the array. These results concur that for most practical arrays, it is imperative to isolate the coil in an acoustically shielded enclosure, which will reduce the coil pickup to an arbitrarily low level for all hydrophones. Theory and experiment also agree that the pickup in the array buses increases in proportion to the distance along the array. In the worst-case scenario (spherical acoustic wave incident normal to the array), the pickup in a 1-km bus is predicted to be /spl sim/-7 dB in quiet waters and /spl sim/-40 dB in noisy waters. However, in the field, the probability of this event is expected to be extremely low, and these values will be typically at least 15 dB weaker. Nevertheless, in long arrays, the bus pickup must be reduced, which can be achieved by desensitizing the bus fiber and/or pickup subtraction. Combined, these two techniques are expected to make the bus pickup under normal conditions negligible in deep-water applications (/spl sim/-48 dB) and acceptable in noisier shallow-water applications (/spl sim/-15 dB).

On constructions of algebraic space-time codes with AM-PSK constellations satisfying rate-diversity tradeoff

Constructions of space-time codes having amplitude-modulated phase-shift keying (AM-PSK) constellations are presented in this paper. The first construction, termed p-radii construction, is obtained by extending Hammons' dyadic dual-radii construction to the cases when the size of the constellation is a power of a prime p, p /spl ges/ 2. The resultant code is optimal with respect to the rate-diversity tradeoff and has an AM-PSK constellation with signal points distributed over p- concentric circles in the complex plane, i.e., there are p radii. Also contained in this paper is the identification of rich classes of nontrivial subset-subcodes of the newly constructed space-time codes and it is shown that these subset-subcodes are again, all optimal. Finally, a new generalization of the super-unified construction by Hammons is presented. It is shown that codes obtained from several previously known constructions are subset-subcodes of the one derived from this generalized construction.

On the scaling limit of ultrathin SOI MOSFETs

In this paper, a detailed study on the scaling limit of ultrathin silicon-on-insulator (SOI) MOSFETs is presented. Due to the penetration of lateral source/drain fields into standard thick buried oxide, the scale-length theory does not apply to thin SOI MOSFETs. An extensive two-dimensional device simulation shows that for a thin gate insulator, the minimum channel length can be expressed as L/sub min//spl ap/4.5(t/sub Si/+(/spl epsiv//sub Si///spl epsiv//sub I/)t/sub I/), where t/sub Si/ is the silicon thickness, and /spl epsiv//sub I/ and t/sub I/ are the permittivity and thickness of the gate insulator. With t/sub Si/ limited to /spl ges/ 2 nm from quantum mechanical and threshold considerations, a scaling limit of L/sub min/=20 nm is projected for oxides, and L/sub min/=10 nm for high-/spl kappa/ dielectrics. The effect of body doping has also been investigated. It has no significant effect on the scaling limit.

On-line routing and wavelength assignment for dynamic traffic in WDM ring and torus networks

We develop on-line routing and wavelength assignment (RWA) algorithms for WDM bidirectional ring and torus networks with N nodes. The algorithms dynamically support all k-allowable traffic matrices, where k denotes an arbitrary integer vector [k/sub 1/, k/sub 2/,... k/sub N/], and node i, 1 /spl les/ i /spl les/ N, can transmit at most k/sub i/ wavelengths and receive at most k/sub i/ wavelengths. Both algorithms support the changing traffic in a rearrangeably nonblocking fashion. Our first algorithm, for a bidirectional ring, uses [(/spl Sigma//sub i=1//sup N/ k/sub i/)/3] wavelengths in each fiber and requires at most three lightpath rearrangements per new session request regardless of the number of nodes N and the amount of traffic k. When all the k/sub i/'s are equal to k, the algorithm uses [kN/3] wavelengths, which is known to be the minimum for any off-line rearrangeably nonblocking algorithm. Our second algorithm, for a torus topology, is an extension of a known off-line algorithm for the special case with all the k/sub i/'s equal to k. For an R /spl times/ C torus network with R /spl ges/ C nodes, our on-line algorithm uses [kR/2] wavelengths in each fiber, which is the same as in the off-line algorithm, and is at most two times a lower bound obtained by assuming full wavelength conversion at all nodes. In addition, the on-line algorithm requires at most C - 1 lightpath rearrangements per new session request regardless of the amount of traffic k. Finally, each RWA update requires solving a bipartite matching problem whose time complexity is only O (R), which is much smaller than the time complexity O(kCR/sup 2/) of the bipartite matching problem for an off-line algorithm.

Passive geolocation and tracking of an unknown number of emitters

An algorithm for the geolocation and tracking of an unknown number of ground emitters using the time difference of arrival (TDOA) measurements in practical scenarios is proposed. The focus is on solving the important issue of data association, i.e., deciding from which target, if any, a measurement originated. A previous solution for data association based on the assignment formulation for passive measurement tracking systems relied on solving two assignment problems: an S-dimensional (or SD, where S /spl ges/ 3) assignment for association across sensors and a 2D assignment for the measurement-to-track association. In this paper, (S + 1 )D assignment algorithm - an extension of the SD assignment formulation - that performs the data association in one step, is introduced. It will be shown later that the (S + 1 )D assignment formulation reduces the computational cost significantly without compromising tracking accuracy. The incorporation of correlated measurements, as with the case of TDOA measurements, into the SO framework that typically assumes uncorrelated measurements, is also discussed. The nonlinear TDOA equations are posed as an optimization problem and solved using SolvOpt, a nonlinear optimization solver. The interacting multiple model (IMM) estimator is used in conjunction with the unscented Kalman filter (UKF) to track the geolocated emitters.

Many-to-many disjoint path covers in hypercube-like interconnection networks with faulty elements

A many-to-many k-disjoint path cover (k-DPC) of a graph G is a set of k disjoint paths joining k distinct source-sink pairs in which each vertex of G is covered by a path. We deal with the graph G/sub 0/ /spl oplus/ G/sub 1/ obtained from connecting two graphs G/sub 0/ and G/sub 1/ with n vertices each by n pairwise nonadjacent edges joining vertices in G/sub 0/ and vertices in G/sub 1/. Many interconnection networks such as hypercube-like interconnection networks can be represented in the form of G/sub 0/ /spl oplus/ G/sub 1/ connecting two lower dimensional networks G/sub 0/ and G/sub 1/. In the presence of faulty vertices and/or edges, we investigate many-to-many disjoint path coverability of G/sub 0/ /spl oplus/ G/sub 1/ and (G/sub 0/ /spl oplus/ G/sub 1/) /spl oplus/ (G/sub 2/ /spl oplus/ G/sub 3/ ), provided some conditions on the Hamiltonicity and disjoint path coverability of each graph G/sub i/ are satisfied, 0 /spl les/ i /spl les/ 3. We apply our main results to recursive circulant G(2/sup m/, 4) and a subclass of hypercube-like interconnection networks, called restricted HL-graphs. The subclasses includes twisted cubes, crossed cubes, multiply twisted cubes, Mobius cubes, Mcubes, and generalized twisted cubes. We show that all these networks of degree m with f or less faulty elements have a many-to-many k-DPC joining any k distinct source-sink pairs for any k /spl ges/ 1 and f /spl ges/ 0 such that f+2k /spl les/ m - 1.

Sampled grating tunable twin-guide laser diodes with over 40-nm electronic tuning range

Device and tuning characteristics of sampled grating tunable twin-guide laser diodes are presented. The vertically integrated, monolithic widely tunable laser requires only two tuning currents to fully cover a wavelength range of more than 40 nm by electrooptic tuning. Its tuning behavior is quasi-continuous with up to 8.2-nm broad continuous tuning regions. High sidemode suppression (SMSR /spl ges/ 35 dB) as well as large output power (P /spl ges/ 10 mW) are obtained over the wavelength range from 1520.5 to 1561.5 nm.

New Efficient MDS Array Codes for RAID Part II: Rabin-Like Codes for Tolerating Multiple (greater than or equal to 4) Disk Failures

For pt.1 see ibid., vol.54, no.9, p.1071-1080 (2005). A new class of binary maximum distance separable (MDS) array codes which are based on circular permutation matrices are introduced in this paper. These array codes are used for tolerating multiple (/spl ges/ 4) disk failures in redundant arrays of inexpensive disks (RAID) architecture. The size of the information part is m /spl times/ n, where n is the number of information disks and (m + 1) is a prime integer; the size of the parity-check part is m /spl times/ r, the minimum distance is r + 1, and the number of parity-check disks is r. In practical applications, m can be very large and n ranges from 20 to 50. The code rate is R = n/(n+r). These codes can be used for tolerating up to r disk failures, with very fast encoding and decoding. The complexities of encoding and decoding algorithms are O(rmn) and O(m/sup 3/r/sup 4/), respectively. When r = 4, there need to be 9mn XOR operations for encoding and (9n + 95)(m + 1) XOR operations for decoding.

Measurement of Low-Frequency Noise of Modern Low-Noise Junction Field Effect Transistors

A description of the low-noise measurement system designed for experimental investigation of low-frequency noise of modern low-noise junction field effect transistors (JFETs) at a frequency range from 0.5 Hz to 50 kHz is presented. The noise floor of the system in terms of noise voltage spectral density is about 1.3 nV//spl radic/Hz at frequency 0.5 Hz, 0.6 nV//spl radic/Hz at frequency 1 Hz, 0.08 nV//spl radic/Hz at frequency 10 Hz, and /spl les/0.04 nV//spl radic/Hz at frequencies 100 Hz-50 kHz. Such a system makes it possible to measure 1/f noise and channel thermal noise of modern very low noise n-channel JFETs. Specifically, discrete samples of JFETs, IF9030, IF1801, IF3601, and 2N4338, were investigated at the frequency range mentioned above. The system provided negligible contribution of all noise sources except intrinsic noise of measured JFETs which was a 1/f noise at frequencies f < 10 Hz and a channel thermal noise at frequencies f /spl ges/ 10 Hz. The measured values of the equivalent input noise voltage spectral density e/sub n/ of the best samples from investigated JFETs IF9030, IF1801, IF3601, and 2N4338 were 2.7, 3.2, 3.4, and 22 nV//spl radic/Hz at frequency 0.5 Hz; 1.5, 2.1, 1.8, and 14 nV//spl radic/Hz at frequency 1 Hz; and 0.5, 0.4, 0.6, and 3.2 nV//spl radic/Hz at frequencies more than 1 kHz, correspondingly.

A Model to Predict Climate-Change Impact on Fish Catch in the World Oceans

Water temperature plays a very important role in fish production. The assessment of the impact of water-temperature changes on fish catches in world fishery is essential for the sustainable management of world fishery resources. Fish catch includes different species, but using information analysis, it is shown that total fish catch can be used without significant loss of information about the dynamic properties of the system. A new method for the forecasting of the fish catch of the major fishing areas in the world's oceans under global climate change (temperature) has been developed. This method predicts the tendency (increase or decrease) for fish catch, with quantitative predictor's power, if the temperature is known. This method has been applied to the Indian Ocean to assess the climate-change impact on fish catch. Based on the temperatures predicted using the CLIMate-BiospheRE model for the years 2000-2100, a decrease of fish catch in the Indian Ocean, with the confidence of the predictor's power at /spl ges/ 90%, has been predicted.

Reduction of grain size and ordering temperature in L1/sub 0/ FePt thin films

In this research, a more effective procedure for reducing the ordering temperature of the L1/sub 0/ FePt thin films is proposed. These thin films, with thickness varying from 10 nm to 200 nm, are prepared by conventional magnetron sputtering system with a dc power supply and then postannealed in vacuum. The phases and microstructures of the films are characterized by X-ray diffraction (XRD) with Cu-K/spl alpha/ radiation and transmission electron microscopy (TEM) bright field image, respectively. TEM bright field images show that the films have average grain sizes of about 6 nm. XRD patterns show that there is no evidence that ordered structure exists in the film when annealing temperature (T/sub an/) /spl les/ 300/spl deg/C. For T/sub an/ /spl ges/ 350/spl deg/C, the disordered fcc FePt phase transforms into the ordered L1/sub 0/ FePt phase. Vacancies into the film are formed easily due to the high deposition rate process in this investigation. Some extra energy is introduced into the as-deposited film during deposition and reduced the order-disorder energy barrier.

Meandered multiband PIFA with coplanar parasitic patches

A meandered multiband planar inverted-F antenna with two coplanar parasitic patches is presented. The antenna has a very wide impedance bandwidth of 743 MHz covering the frequencies from 1.765 to 2.508 GHz with the return loss L/sub rtn/ /spl ges/ 6 dB. The antenna also operates in the GSM band with a high radiation efficiency.

Broad-band photoresponse from InAs quantum dots embedded into InGaAs graded well

A broad-band photoresponse is obtained from undoped InAs multiple quantum dots grown by the molecular beam epitaxy (MBE) technique on a (100) GaAs substrate. The quantum dots were embedded in an In/sub x/Ga/sub 1-x/As graded well where the In mole fraction is chosen in the range of 0.3 /spl ges/ x /spl ges/ 0.0. The photoresponse of the reversed biased device, obtained at 80.5 K and using the normal incident configuration, was found to span the spectral range of 3.5 - 9.5 /spl mu/m. While the photoresponse is significantly high under the influence of the reverse bias voltage, the forward bias photoresponse is found to be negligible.

Complement block coding for reduction in peak-to-average power ratio of OFDM signals

In this article a new coding scheme, complement block coding (CBC), is proposed to reduce the PAPR of OFDM signals. This method utilizes the complement bits that are added to the original information bits, which can effectively reduce the PAPR of OFDM signals with random frame size N and the coding rate R /spl les/ (N - k)/N, where k is a positive integer and k /spl les/ N/2. The performance results obtained with CBC are given and compared with that of some well known schemes, such as simple block coding, modified simple block coding, simple odd parity code, and cyclic coding, for the same purpose. The results show that at the same coding rate 3/4, CBC can achieve almost the same performance as SBC and MSBC, but with lower complexity, and the same performance can be obtained with a higher coding rate using CBC. The PAPR reductions of CBC with coding rate (N - 1)/N are almost the same as with a coding rate less than (N - 1)/N, but almost the twice as these of SOPC when N /spl ges/ 16. Moreover, we can find that PAPR is the lowest for all block codes using CBC with coding rate 3/4. So modified CBC (MCBC) is also proposed and analyzed, combined with the subblock processing technique to make CBC effective for OFDM systems with large frame sizes. The flexibility in coding rate choice and low complexity make the proposed CBC more suitable for random frame size with high coding rate and can also provide error detection.

Locally Testable Cyclic Codes

Cyclic linear codes of block length n over a finite field F/sub q/ are linear subspaces of F/sub q//sup n/ that are invariant under a cyclic shift of their coordinates. A family of codes is good if all the codes in the family have constant rate and constant normalized distance (distance divided by block length). It is a long-standing open problem whether there exists a good family of cyclic linear codes. A code C is r-testable if there exists a randomized algorithm which, given a word x/spl isin//sub q//sup n/, adaptively selects r positions, checks the entries of x in the selected positions, and makes a decision (accept or reject x) based on the positions selected and the numbers found, such that 1) if x/spl isin/C then x is surely accepted; ii) if dist(x,C) /spl ges/ /spl epsi/n then x is probably rejected. (dist refers to Hamming distance.) A family of codes is locally testable if all members of the family are r-testable for some constant r. This concept arose from holographic proofs/PCP's. Recently it was asked whether there exist good, locally testable families of codes. In this paper the intersection of the two questions stated is addressed. Theorem. There are no good, locally testable families of cyclic codes over any (fixed) finite field. In fact the result is stronger in that it replaces condition ii) of local testability by the condition ii') if dist (x,C) /spl ges/ /spl epsi/n then x has a positive chance of being rejected. The proof involves methods from Galois theory, cyclotomy, and diophantine approximation.

High-resolution ocean color remote sensing of benthic habitats: a case study at the Roatan island, Honduras

Natural resource managers clamor for detailed reef habitat maps for monitoring smaller scale disturbances in reef communities. Coastal ocean color remote sensing techniques permit benthic habitats to be explored with higher resolution than ever before. The objective of this research was to develop an accurate benthic habitat map for an area off the northwest coast of Roatan Island, Honduras, using high-resolution multispectral IKONOS data. Atmospheric (Rayleigh and aerosol path radiance) and water column corrections (water depth and water column attenuation) were applied to the imagery, making it a robust method for mapping benthic habitats. Water depth for each pixel was calculated based on a site-specific polynomial model. A mechanistic radiative transfer approach was developed that removed the confound effect of the water column (absorption and scattering) from the imagery to retrieve an estimate of the bottom reflectance (albedo). Albedos were /spl les/ 12% for seagrass benthos, 12% to 24% for coral areas, and /spl ges/ 24% for sand-dominated areas. The retrieved bottom albedos were then used to classify the benthos, generating a detailed map of benthic habitats, followed by accuracy assessment.

BER performance of BPSK receivers over two-wave with diffuse power fading channels

This letter presents the bit error rate (BER) performance analysis for an uncoded binary phase-shift keying (BPSK) system in two-wave with diffused power (TWDP) fading channels. Simulation results of receiver performance, with or without maximal-ratio combining (MRC), are also presented. These performance studies quantitatively reveal that TWDP fading can produce a link worse than Rayleigh fading when the two direct waves are equal in strength and have a combined power of /spl ges/ 6 dB higher than the diffused power. These results point to using TWDP fading rather than Rayleigh fading as a worst case scenario in designing communication systems, especially in situations where TWDP fading is likely, such as when directional antennas or arrays and when wideband signals are used.

Optimal placement of known symbols for slowly varying frequency-selective channels

The problem of placing known symbols in a data stream for a slowly varying frequency-selective channel is considered from an information-theoretic perspective. Given the amount of redundancy associated with known symbols, placement schemes that minimize the outage probability are derived by assuming that the transmitted codewords consist of packets that are constrained to have the same known symbol placement. Under the assumption that each known symbol cluster is at least as large as /spl alpha/ /spl ges/ 2L + 1 (where L is the channel order), we show that the optimal placement is obtained by arranging the known symbols into as many clusters as possible and placing them such that the unknown symbol blocks are as equal as possible. It is shown that the optimal placement of known symbol clusters does not depend on the probability density of the channel. Numerical examples are used to illustrate the ideas and potential gains of using optimal known symbol placement.

Detection of Mobile Targets from a Moving Platform Using an Actively Shielded, Adaptively Balanced SQUID Gradiometer

Tests have been performed with a moving HTS dc SQUID gradiometer mounted on a nonmetal motion table. The system operated with sensitivity of 80 pT/m//spl radic/Hz (1 Hz) and 1 pT/m//spl radic/Hz (white) whilst undergoing pitch, roll and yaw motions of /spl plusmn/5/spl deg/ in an outside environment. Gradient anomalies of /spl ges/ 1 nT/m were detected with 12 dB signal-to-noise ratio and a measurement bandwidth of 1 kHz. In this paper, we describe the performance of the gradiometer at measuring remote moving ferromagnetic targets whilst it is in motion. These measurements have an important bearing on understanding the viability of SQUID-based systems as magnetic anomaly detectors, when mounted on airborne or seaborne platforms. In one early test, a target of approximately 300 Am/sup 2/ travelling at 2-5 m/s was detected at 25 m range with a signal to noise ratio of 4:1, whilst the gradiometer was undergoing motions of /spl plusmn/5/spl deg/ in pitch roll and heading.

Pragmatic trellis coding applied to rectangular QAM

Although Ungerboeck's TCM (trellis coded modulation) is attractive in terms of high efficiency with low descending data rate by coding and high coding gain, it is difficult to implement. To remove this complexity, a pragmatic approach to the TCM, which is realized by employing the de facto convolutional code (constraint length K=7 and rate 1/2), was proposed. In this paper, a simpler realization of the TCM of rectangle type 2/sup N/ QAM (N is even number; /spl ges/ 4) by using the pragmatic approach is presented. We have independently shown the convolutional coding and the Viterbi decoding by the decomposition from two-dimensions into each one-dimension. By this decomposition, it is possible to apply the pragmatic approach to minimize the hardware and cost. Therefore, it is very useful for 64 QAM or 256 QAM applications such as digital video broadcasting over digital cable TV (ITU-T J.83) and fixed wireless access (IEEE 802.16) systems. It can be applied not only to single carrier QAM but also to multi-carrier QAM like OFDM.