Upper bounds for small trellis codes

An upper bound on the minimum squared distance of trellis codes by packing Voronoi cells is derived and compared with previously known bounds. The authors focus on codes with small memory for modulation formats such as pulse amplitude modulation (PAM), m-ary quadrature amplitude modulation (QAM), and m-ary phase shift keying (PSK). The bound is tight to search results for coset codes with a small number of states     

Equal-power coordinated transmission for HDSL

In a two-channel transmission system, the signal-to-noise ratio (SNR) at the receiver can in general be different for the channels. Normally, performance will be dominated by the channel with the worst SNR, but it is possible to do much better. The general scheme proposed provides optimum performance when the SNR varies between the channels and/or when the interference is correlated, without varying the transmitted power for each channel. Simplified schemes attain nearly optimum performance under certain channel conditions     

The P2Y2 Receptor C-Terminal Tail Modulates but Is Dispensable for β-Arrestin Recruitment

The P2Y₂ receptor (P2Y₂R) is a G protein-coupled receptor that is activated by extracellular ATP and UTP, to a similar extent. This allows it to play roles in the cell’s response to the (increased) release of these nucleotides, e.g., in response to stress situations, including mechanical stress and oxygen deprivation. However, despite its involvement in important (patho)physiological processes, the intracellular signaling induced by the P2Y₂R remains incompletely described. Therefore, this study implemented a NanoBiT^® functional complementation assay to shed more light on the recruitment of β-arrestins (βarr1 and βarr2) upon receptor activation. More specifically, upon determination of the optimal configuration in this assay system, the effect of different (receptor) residues/regions on βarr recruitment to the receptor in response to ATP or UTP was estimated. To this end, the linker was shortened, the C-terminal tail was truncated, and phosphorylatable residues in the third intracellular loop of the receptor were mutated, in either singly or multiply adapted constructs. The results showed that none of the introduced adaptations entirely abolished the recruitment of either βarr, although EC₅₀ values differed and time-luminescence profiles appeared to be qualitatively altered. The results hint at the C-terminal tail modulating the interaction with βarr, while not being indispensable.     

A comparison of reduced complexity decoding algorithms for trelliscodes

Comparisons are made of a genie-aided sequential algorithm due to D. Haccoun and M.J. Ferguson (1975), the Viterbi algorithm, the M -algorithm, and the Fano algorithm for rate-1/2 and rate-2/3 trellis modulation codes on rectangular signal sets. The effects of signal-to-noise ratio and decoding-delay constraints on the choice of decoding algorithms for framed data are examined by computer simulation. Additionally, the genie-aided algorithm is used as a tool in estimating the asymptotic behavior of the M-algorithm. In general, the results conform closely to experience with convolutional codes due to the similar distance structure of the codes. The Fano algorithm produces good error performance with a low average number of computations when long decoding delay is permissible. The M-algorithm provides a savings in computation compared to the Viterbi algorithm if a small decoding delay is required     

A distributed access algorithm for cellular radio systems withchannel partitioning

Previous results in distributed power control and distributed channel access have demonstrated the possibility of high-capacity cellular radio networks without central control. However, these distributed algorithms may not converge completely in practical systems where the rate of channel variation (due to mobility, handoff, or interfering users entering or leaving the channel) approaches the rate at which power levels can be accurately measured and adjusted. We propose a new channel partitioning technique in which both dynamically allocated and fixed assignment channels are employed. This technique enables rapid distributed access that is inherently fair. Simulation results indicate that it is robust in responding to user mobility and handoff while yielding significant capacity gains over traditional fixed assignment systems     

Trellis codes for the optical direct-detection channel

It is observed that the reduced complexity minimum distance search method of Zehavi and Wolf (1987) can be extended from codes designed using the squared Euclidean distance measure to any measure which is additive over the code branches. C.N. Georghiades (1989) has derived such a metric for codes for the direct-detection optical channel. The search method is applied to find codes for four- and eight-point overlapping pulse position modulation (OPPM), with large minimum distance and a small number of codewords at that distance     

Quantifying short-range surface-to-surface communications links

As wirelessly connected embedded systems become ubiquitous, previously undocumented propagation environments must be explored to support their design. This paper describes the results of a study of such an environment: short-range wireless propagation outdoors, near the ground. In the study, frequencies were considered within three industrial, scientific, and medical (ISM) bands: 902-928 MHz, 2400-2426 MHz, and 5725-5752 MHz. Experimental propagation loss was summarized based on measurements in eighteen environments, at varying heights, distances, and polarizations. Based on the data collected, the appropriateness of a simple design guideline, based on a two-ray propagation model, is discussed. Summaries of the path loss, fading, and the influences of antenna height, antenna separation, and surrounding clutter in highly variable environments are given. Additionally, limited numerical modeling of the impact of surface roughness is provided. Particular focus was given in the study to heights and distances appropriate for randomly deployed wireless sensor networks, such as autonomous unattended ground-sensor systems.     

Channel coding strategies for cellular radio

To improve re-use of time/frequency slots in a cellular radio system, it is desirable for the average interference levels seen by all users to be made approximately equal. The authors provide constructions based on orthogonal latin squares that guarantee different sets of users will interfere in successive slots. When signal to interference ratios are independent from successive symbols, channel codes can provide a large diversity gain which is far in excess of the gain against additive noise. Consequently, coding with interleaving fits together very naturally with this construction. The authors illustrate how to achieve large performance improvement using convolutional codes with low decoding delay in a slow hopped system     

A memory-efficient formulation of the finite-difference time-domainmethod for the solution of Maxwell equations

With the increase in speed and memory storage in modern computer systems, the finite-difference time-domain (FDTD) method for the solution of electromagnetic problems is rapidly becoming an attractive choice due to its programming simplicity and flexibility in the analysis of a wide range of structures. However, this technique has the drawback of high computer memory requirements and computational power, when analyzing large geometries. In this paper, a modified version of the FDTD method with increased memory efficiency is presented and applied to the calculation of the resonant frequencies of a dielectric resonator coupled to a microstrip line. In this novel approach, the divergence relationship, which spatially links the three electric-field and three magnetic-field components, is used to eliminate one component each of E and H. This leads to a more memory-efficient formulation, where only four field components are stored in the whole domain, with a direct memory reduction of 33% in the storage of the fields     

Power-conscious design of wireless circuits and systems

The great importance of power consciousness is well understood in mobile wireless communications. However, with growing experience the fundamental principles underlying power conscious design of RF circuits, systems, and networks are only now becoming known. Using as example ultralow-power wireless devices for messaging such as paging receivers and wireless sensor networks, the first part of this paper presents the relationship between current consumption and dynamic range of low-noise amplifiers, mixers, oscillators, and active filters. The second part of the paper covers issues of modulation, protocols, and networking that would be required in dense networks of wireless sensors, which communicate using very little energy. These ideas are expected to find use in most forms of digital wireless communications