General switch‐and‐examine relaying for demodulate‐and‐forward cooperative diversity

Two new demodulate‐and‐forward schemes of multi‐relay cooperative diversity with switch‐and‐examine relaying (SER) are analyzed. To reduce relay usage and enhance bandwidth efficiency, the two new cooperative diversity schemes employ a switch‐based relay selection. The proposed schemes consume less communication resource than regular relaying schemes, such as the selection combining (SC) or maximal ratio combining (MRC) schemes that always use all relays, and also achieve better performance than distributed switch‐and‐stay schemes. In the first scheme, the decision statistic for relay usage and selection is based on the signal‐to‐noise ratio (SNR). In the second scheme, the log‐likelihood ratio (LLR) of received signals is used for the decision of relay usage and selection. With the two SER schemes, the bit error probability (BEP) of binary phase shift keying (BPSK) and the average number of used paths are derived and expressed in closed‐form for the independent and identically distributed (i.i.d.) Rayleigh fading channels. Numerical and simulation results are presented for performance illustrations. According to the numerical results, the LLR‐based SER not only achieves a lower BEP but also consumes less relay resource than the SNR‐based SER. Furthermore, the LLR‐based SER scheme even outperforms the corresponding SNR‐based SC scheme for a range of average SNR. Copyright © 2014 John Wiley & Sons, Ltd.     

10‐Bit 200‐MS/s Current‐Steering DAC Using Data‐Dependant Current‐Cell Clock‐Gating

This letter proposes a low‐power current‐steering digital‐to‐analog converter (DAC). The proposed DAC reduces the clock power by cutting the clock signal to the current‐source cells in which the data will not be changed. The 10‐bit DAC is implemented using a 0.13‐μm CMOS process with V_DD=1.2 V. Its area is 0.21 mm². It consumes 4.46 mW at a 1‐MHz signal frequency and 200‐MHz sampling rate. The clock power is reduced to 30.9% and 36.2% of a conventional DAC at 1.25‐MHz and 10‐MHz signal frequencies, respectively. The measured spurious free dynamic ranges are 72.8 dB and 56.1 dB at 1‐MHz and 50‐MHz signal frequencies, respectively.     

Low‐Power‐Photon Up‐Conversion in Dual‐Dye‐Loaded Polymer Nanoparticles

Sensitized triplet–triplet annihilation in multicomponent organic systems is already demonstrated to be suitable for obtaining efficient up‐conversion in solution with excitation power densities comparable to solar irradiance, but loses efficiency in the solid state. Here, it is demonstrated that it is possible to reduce this limitation by incorporating a standard bicomponent system in polymer nanoparticles. The confinement of all of the involved photophysical processes in a nanometer‐scale volume makes each nanoparticle a single and isolated high‐efficiency up‐converting unit. As a consequence, these dual‐dye‐loaded nanoparticles can be used to produce drop‐cast films, as well as dopants for polymeric matrices, preserving the performances of the starting moieties in solution.     

iPTT: peer‐to‐peer push‐to‐talk for VoIP

This paper proposes iPTT, a peer‐to‐peer (P2P) Push‐to‐Talk (PTT) service for Voice over IP (VoIP). In iPTT, a distributed and mobile‐operator independent network architecture is presented to accelerate the deployment of the PTT service. Based on the serverless architecture, we develop two mechanisms, that is, flooding‐based floor control mechanism (FFC) and tree‐based floor control mechanism (TFC), for real‐time talk‐burst determination. The determination algorithms and the corresponding message flows for these two mechanisms are designed to show the feasibility of FFC and TFC. The performance of FFC and TFC is investigated through our analytical and simulation models in terms of the determination latency and the number of floor‐control message exchanges. Copyright © 2008 John Wiley & Sons, Ltd.     

Low‐Complexity Multi‐size Cyclic‐Shifter for QC‐LDPC Codes

The decoding process of a quasi‐cyclic low‐density parity check code requires a unique type of rotator. These rotators, called multi‐size cyclic‐shifters (MSCSs), rotate input data with various sizes, where the size is the amount of data to be rotated. This paper proposes a low‐complexity MSCS structure for the case when the sizes have a nontrivial common divisor. By combining the strong points of two previous structures, the proposed structure achieves the smallest area. The experimental results show that the area reduction was more than 14.7% when the proposed structure was applied to IEEE 802.16e as an example.     

Polymeric Alkoxy PBD [2‐(4‐Biphenylyl)‐5‐Phenyl‐1,3,4‐Oxadiazole] for Light‐Emitting Diodes

The syntheses are reported of the title polymeric alkoxyPBD derivative 5 and the dipyridyl analogue 12 using Suzuki coupling reactions of 1,4‐dialkoxybenzene‐2,5‐diboronic acid with 2,5‐bis(4‐bromophenyl)‐1,3,5‐oxadiazole, and its dipyridyl analogue, respectively. Thermal gravimetric analysis shows that polymers 5 and 12 are stable up to 370 °C and 334 °C, respectively. Films of polymer 5 spun from chloroform solution show an absorption at λ_max = 367 nm, and a weaker band at 312 nm, and strong blue photoluminescence at λ_max = 444 nm. The photoluminescence quantum yield (PLQY) was found to be 27 ± 3 %. For polymer 12 , the absorption spectra reveal bands of equal intensity at λ_max = 374 and 312 nm, with PL at λ_max = 475 nm. Device studies using polymer 12 were hampered by its instability under illumination and/or electrical excitation. Polymer 5 is stable under these conditions and acts as an efficient electron‐transporting/hole‐blocking layer. For devices of configuration ITO/PEDOT/MEH‐PPV/polymer 5 /Al an external quantum efficiency of 0.26 % and brightness of 800 cd/m² was readily achieved: orange emission was observed, identical to the MEH‐PPV electroluminescence.