Iterative multiuser detection with integrated channel estimation for coded DS-CDMA

A practically interesting approach for iterative channel estimation, multiuser detection, and single-user decoding based on maximum a posteriori symbol-by-symbol estimation for direct sequence/code-division multiple-access (DS-CDMA) is proposed. The receiver relies on the output of a bank of matched filters for each user and each path, and combines interference cancellation with iterated soft-decision feedback to improve channel estimation accuracy and data symbol reliability in course of a few iterations. We show that in this way, near single-user channel phase and amplitude estimation accuracy is achieved for frequency-selective fading channels, even in highly loaded systems, and illustrate that reliable data symbol estimation can be performed.     

The Periscope: supporting a computer enhanced field trip for children

This paper describes an interactive device, the Periscope, designed to be used as an educational tool featured during a children's digitally enhanced field trip in a woodland setting. The Periscope assembly, including a display and RFID equipped tangibles, is controlled using handles that enable it to be raised and rotated. The display is controlled by rotating the Periscope, or alternatively by twisting the handles. A set of tangibles, a collection of Petri dishes fitted with RFID tags, enable the children to carry out experiments with the results being shown on the display. Field trials are also outlined in which the effectiveness of this design is established. In conclusion, we discuss the aesthetic design issues raised by introducing digital technology into everyday environments.     

Coded continuous phase modulation with low-complexity noncoherentreception

Coded continuous phase modulation based on a feedback-free modulator with noncoherent detection is discussed. Low-complexity receiver processing is achieved by using only two or three linear filters for demodulation and applying noncoherent sequence estimation with reduced-state Viterbi decoding and simple branch metric calculation. Overall, the proposed noncoherent receiver provides significant advantages over previously presented approaches     

Artemin, a novel member of the GDNF ligand family, supports peripheral and central neurons and signals through the GFRalpha3-RET receptor complex

The glial cell line-derived neurotrophic factor (GDNF) ligands (GDNF, Neurturin [NTN], and Persephin [PSP]) signal through a multicomponent receptor system composed of a high-affinity binding component (GFRalpha1-GFRalpha4) and a common signaling component (RET). Here, we report the identification of Artemin, a novel member of the GDNF family, and demonstrate that it is the ligand for the former orphan receptor GFRalpha3-RET. Artemin is a survival factor for sensory and sympathetic neurons in culture, and its expression pattern suggests that it also influences these neurons in vivo. Artemin can also activate the GFRalpha1-RET complex and supports the survival of dopaminergic midbrain neurons in culture, indicating that like GDNF (GFRalpha1-RET) and NTN (GFRalpha2-RET), Artemin has a preferred receptor (GFRalpha3-RET) but that alternative receptor interactions also occur.     

Migration of reactable UVAs and HALS in automotive plastic coatings

Loss of light stabilizers from automotive finishes can significantly reduce the durability of coatings on plastic substrates. Minimizing movement by retaining the stabilizers in the targeted layer can greatly improve coating longevity. This article examines the migratory patterns of a series of traditional UVA and HALS additives in fully formulated 1K silane crosslinked coatings applied over both plastic and steel substrates, comparing their migratory patterns to that of reactable light stabilizers containing hydroxyl functionality. Analysis of the coating layers with the various UVAs and HALS revealed that functionalization of the light stabilizer with reactable hydroxy groups can prevent migration into the plastic; whereas nonreactable light stabilizers migrate into lower coating system layers and even into the plastic substrate. The greatest extent of migration does not occur during initial cure of the wet coating, but during exposure. Significant depletion of the nonreactable light stabilizers from the topcoat occurs as early as 1500 hours of Xenon boro/boro exposure. This paper was awarded first place in the Shelby F. Thames Best Paper Award, at the 30th International Waterborne, High-Solids and Powder Coatings Symposium, February 26–28, 2003, in New Orleans, LA.     

Bit-interleaved coded differential space-time modulation

Bit-interleaved coded differential space-time modulation for transmission over spatially correlated Ricean flat fading channels is discussed. For improved noncoherent detection without channel state information at the receiver, iterative decoding employing hard-decision feedback and prediction-based metric computation is applied. The performance is assessed based on the associated cutoff rate, analytical expressions for the bit error rate and the outage probability, respectively and simulations. It is shown that the proposed scheme offers high power efficiency exploiting both space and time diversity, while the computational complexity is kept at a relatively low level.     

Equalization concepts for Alamouti's space-time block code

In this paper, we develop receiver concepts for transmission with space-time block codes (STBCs) over frequency-selective fading channels. The focus lies on Alamouti's space-time block-coding scheme, but the results may be generalized to other STBCs as well. We show that a straightforward combination of conventional equalizers and a space-time block decoder is only possible if at least as many receive antennas as transmit antennas are employed, but not for the practically interesting case of pure transmit diversity, for which space-time coding had been originally developed. This restriction is circumvented by our approach. Here, the structural properties of the transmit signal of space-time block coding, which is shown to be improper (rotationally variant), are fully used. For this, equalizers with widely linear (WL) processing are designed, such as a WL equalizer, a decision-feedback equalizer with WL feedforward and feedback filtering, and a delayed decision-feedback sequence estimator with WL prefiltering. Simulation results demonstrate that the proposed concepts may be successfully employed in an enhanced data rates for GSM evolution (EDGE) receiver, especially for pure transmit diversity. Here, significant gains can be observed, compared with a conventional single-input single-output transmission.     

Distributed space-time coding for multihop transmission in power line communication networks

In this paper, we consider transmission in relatively wide-stretched power line communication (PLC) networks, where repeaters are required to bridge the source-to-destination distance. In particular, it is assumed that each network node is a potential repeater and that multihop transmission is accomplished in an ad hoc fashion without the need for complex routing protocols. In such a scenario, due to the broadcasting nature of the power line channel, multiple repeater nodes may receive and retransmit the source message simultaneously. It is shown that, if no further signal processing is applied at the transmitter, simultaneous retransmission often deteriorates performance compared with single-node retransmission. We therefore advocate the application of distributed space-time block codes (DSTBCs) to the problem at hand. More specifically, we propose that each network node is assigned a unique signature sequence, which allows efficient combining at the receiver. Most notably, DSTBC-based retransmission does not require explicit collaboration among network nodes for multihop transmission and detection complexity is not increased compared with single-node retransmission. Numerical results for multihop transmission over PLC networks show that DSTBC-based retransmission achieves a considerably improved performance in terms of required transmit power and multihop delay compared with alternative retransmission strategies.     

Imaging and surgery in hyperparathyroidism: a 10-year review

OBJECTIVE: This study was designed to analyze the common cause of asthenopia, mixed astigmatism. METHODS: The types and characters of mixed astigmatism in 356 eyes (207 patients) were analyzed and their naked and corrected visual acuities were investigated. Some problems of mixed astigmatism were discussed. RESULTS: Most of the patients had evident visual defects, the average naked visual acuity being 0.3 (20/60). However, all the patients had better corrected visual acuities with an average of 0.6 (20/30). CONCLUSIONS: Due to the presence of accommodation during the examination, an incorrect lens may be prescribed. Three mistakes might occur, (1) A mixed astigmatism is not detected, and a simple myopic lens is prescribed; (2) An eye with mixed astigmatism is diagnosed as simple or compound myopic astigmatism; (3) A hyperopic astigmatism is diagnosed as mixed astigmatism. The visual defects caused by mixed astigmatism can be satisfactorily corrected by spectacles.