Simultaneous dibit recovery of a DQPSK signal using a single Mach-Zehnder Interferometer

The dibit recovery of a DQPSK signal will be demonstrated using a single Mach Zehnder Interferometer, containing a 1-bit delay, and a single balanced receiver. The electrical output levels of the balanced receiver are dependent upon the relative phase delay between the arms of the Mach Zehnder Interferometer. This paper will investigate this characteristic when the input signal is DQPSK modulated. It will also be shown that with a certain amount of phase shift the DQPSK signal can be converted into four different equally spaced electrical signal levels. With each decoded level representing one of the four possible dibits.

Statistical mechanics analysis of LDPC coding in MIMO Gaussian channels

Using analytical methods of statistical mechanics, we analyse the typical behaviour of a multiple-input multiple-output (MIMO) Gaussian channel with binary inputs under low-density parity-check (LDPC) network coding and joint decoding. The saddle point equations for the replica symmetric solution are found in particular realizations of this channel, including a small and large number of transmitters and receivers. In particular, we examine the cases of a single transmitter, a single receiver and symmetric and asymmetric interference. Both dynamical and thermodynamical transitions from the ferromagnetic solution of perfect decoding to a non-ferromagnetic solution are identified for the cases considered, marking the practical and theoretical limits of the system under the current coding scheme. Numerical results are provided, showing the typical level of improvement/deterioration achieved with respect to the single transmitter/receiver result, for the various cases. © 2007 IOP Publishing Ltd.

Gender and general practice: the single-handed woman General Practitioner

This research examines women GPs' careers, how they run their practices and how they reconcile professional and domestic lives. It looks at the particular experiences of women GPs who practise alone, and at the pressures in past practice experience which have led them to do so. It is argued that many of the problems of group practice which can be identified are attributable to gender. For example, one reason given for entering general practice is a desire to be able to provide the full range of medical care and not to specialise. Women GPs, however, may find themselves seeing more women patients for "women's problems" and children than they would freely choose. Women have not entered general practice in order to specialise in these areas of medicine. Indeed, if they had wanted to specialise in obstetrics, gynaecology or paediatrics they would have had difficulty advancing very far in these male-dominated areas of hospital hierarchy. Other gender related problems exist for women in general practice and practising single-handedly is one strategy that women GPs have used to counter the problems of working in male-dominated practices and partnerships. However, the twenty-four hour commitment of single-handed practice may bring further pressures in reconciling this with responsibility for home life. Out-of-hours cover, which can be viewed as the link between professional and domestic life, where the one intrudes into the other, is also examined in terms of the gender issues it raises. The interaction of gender and ethnicity is also considered for the 11 Asian women GPs in the study. Interviews were conducted with 29 single-handed women GPs in the Midlands. In addition, some cases were studied in greater depth by being observed in their surgeries and on home visits for a day each. A qualitative/feminist approach to analysis has been employed.

Performance enhancement of asymmetric filtered 40 Gb/s carrier suppressed return to zero-differential phase shift keying receiver in a 50 GHz grid

The authors present the impact of asymmetric filtering of strong (e.g. 35 GHz) optical filters on the performance of 42.7 Gb/s 67% (carrier suppressed return to zero)-differential phase shift keying systems. The performance is examined (in an amplified spontaneous emission (ASE) noise-limited regime and in the presence of chromatic dispersion) when offsetting the filter at the receiver by substantial amounts via balanced, constructive and destructive single-ended detections. It is found that with a slight offset (vestigial side band) or an offset of almost half of the modulation frequency (single-side band), there is a significant improvement in the calculated 'Q'. © The Institution of Engineering and Technology 2013.

Verification of the indoor GPS system, by comparison with calibrated coordinates and by angular reference

This paper details work carried out to verify the dimensional measurement performance of the Indoor GPS (iGPS) system; a network of Rotary-Laser Automatic Theodolites (R-LATs). Initially tests were carried out to determine the angular uncertainties on an individual R-LAT transmitter-receiver pair. A method is presented of determining the uncertainty of dimensional measurement for a three dimensional coordinate measurement machine. An experimental procedure was developed to compare three dimensional coordinate measurements with calibrated reference points. The reference standard used to calibrate these reference points was a fringe counting interferometer with the multilateration technique employed to establish three dimensional coordinates. This is an extension of the established technique of comparing measured lengths with calibrated lengths. The method was found to be practical and able to establish that the expanded uncertainty of the basic iGPS system was approximately 1 mm at a 95% confidence level. Further tests carried out on a highly optimized version of the iGPS system have shown that the coordinate uncertainty can be reduced to 0.25 mm at a 95% confidence level.