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We compare three different differential quadrature phase-shift keying (DQPSK) transmitters: One with parallel Mach-Zehnder modulators (MZM), one with a MZM and a phase modulator (PM) in series and a new one with a single PM. Although they all generate optical DQPSK signals, it turns out that their performance differs with respect to bit error probabilities, chromatic dispersion and nonlinearity tolerance for nonrectangular impulse shaping. Ohm, M.; Freckmann, T.: "Comparison of different DQPSK transmitters with NRZ and RZ impulse shaping", IEEE/LEOS Workshop on Advanced Modulation Formats, San Francisco, USA, CA, July 2004.

This paper presents a differential 8-level phaseshift keying (8-DPSK) modulation format with a simple new receiver for transmission of 3 bit/symbol. The receiver with direct detection is based on a differential quadrature phaseshift keying (DQPSK) receiver with binary decision devices and a combinational network for estimating the transmitted bit sequences from the detected multilevel electrical signals. The 8-DPSK transmitter is based on a differential quadrature phaseshift keying (DQPSK) transmitter with an additional phase modulator. Spectral properties of 8-DPSK and chromatic dispersion tolerance are investigated.

Health problems associated with the indoor climate have aroused an increasing scientific interest, and the term "sick-building syndrome" (SBS), which describes the most frequent symptoms in this context, has been coined. However, it has been difficult to demonstrate objectively any pathophysiological changes in the subjects affected. Thirty-three healthy and nonatopic persons were randomly selected on the basis of answers in a postal questionnaire dealing with discomfort or health symptoms experienced in their home environment. Twenty-three lived in a residential area with indoor climate problems (SBS area) and 10 lived in an area without climate problems (non-SBS area). Twelve persons from the SBS area reported nasal symptoms, which they ascribed to their home environment. The remaining 11 persons from the same area, as well as the 10 subjects from the non-SBS area, had no nasal distress. They were examined with rhinostereometry during histamine provocation. Hyperreactivity, defined as mucosal swelling exceeding 0.4 mm at 5 and 10 minutes after provocation with 0.14 ml of 2 mg/ml histamine chloride, was frequent in the symptomatic SBS group as well as in the asymptomatic SBS group. The analysis of the increment of mucosal swelling for the whole range of histamine chloride concentrations (0.1 mg/ml to 16 mg/ml) showed significantly different growth curves for the three groups in the residential areas and an external reference group, (p< 0.0001). Subjects living in the SBS area were prone to nasal hyperreactivity, whether they reported symptoms from the upper airways or not. The results support the hypothesis that living in an SBS area increases the risk of developing nonspecific nasal hyperreactivity.