Near-ML detection for MDL-impaired few-mode fiber transmission

Few-mode fiber transmission systems are typically impaired by mode-dependent loss (MDL). In an MDL-impaired link, maximum-likelihood (ML) detection yields a significant advantage in system performance compared to linear equalizers, such as zero-forcing and minimum-mean square error equalizers. However, the computational effort of the ML detection increases exponentially with the number of modes and the cardinality of the constellation. We present two methods that allow for near-ML performance without being afflicted with the enormous computational complexity of ML detection: improved reduced-search ML detection and sphere decoding. Both algorithms are tested regarding their performance and computational complexity in simulations of three and six spatial modes with QPSK and 16QAM constellations.

An investigation into the pharmacology of tics and tic-like movements

The study of tic-like movements in mice has demonstrated close parallels both in characteristics and in pharmacology with the tics which occur in TS. Head-shakes and/or other tic-like behaviours occurring spontaneously or induced by the selective 5-HT2/1C agonist DOI, alpha-melanocyte stimulating hormone, adrenocorticotrophic hormone (1-39), thyrotropin releasing hormone, or RX336-M were blocked when tested with neuroleptics such as haloperidol and/or the alpha-2 adrenoceptor agonist clonidine. The selective dopamine D1 antagonists SCH23390 and SCH39166 dose-dependently blocked spontaneous and DOI head-shakes but the selective dopamine D2 antagonists sulpiride and raclopride were ineffective. The 5-HT1A receptor agonists 8-OH-DPAT, ipsapirone, gepirone, MDL 73005EF and buspirone (i.p) dose-dependently blocked DOI head-shakes, pindolol blocked the inhibitory effect of 8-OH-DPAT on DOI head-shakes. Parachlorophenylalanine blocked the inhibitory effect of 8-OH-DPAT and buspirone, suggesting that the 5-HT1A receptor involved is located presynaptically. The alpha-2 adrenoceptor antagonists yohimbine, idazoxan, 1-PP and RX811059 prevented the inhibitory effect of 8-OH-DPAT on DOI head-shakes suggesting that this 5-HT1A - 5-HT2 receptor interaction is under the modulatory control of adrenoceptors. Because kynurenine has previously been found to potentiate head-shaking, plasma kynurenine concentrations were measured in seven TS patients and were significantly higher than controls, but neopterin and biopterin were unchanged. The relationship between tic-like movements in rodents and their implications for understanding the aetiology and treatment of TS is discussed.