Noncoherent Transmission Research Articles

Switched correlator receiver architecture for optical CDMA networks with bipolar capacity

A new optically switched correlator receiver architecture, based on the principle of unipolar-bipolar correlation, is proposed for optical fibre CDMA networks. The receiver BER performance is assessed as a function of the incident optical power for noncoherent transmission and direct detection, with the number of simultaneous users as a parameter.

Performance analysis of an optical correlator receiver for SIK DS-CDMA communication systems

An all-optical parallel delay line unipolar-bipolar correlator receiver is proposed for SIK DS-CDMA optical fibre communication systems such as LANs and the local loop. The receiver BER performance is assessed as a function of the incident optical power for noncoherent transmission with the number of simultaneous users as a parameter.

Performance of single-electrode 1.5- mu m DFB lasers in noncoherent FSK transmission

The author reports the results of an investigation of the performance of single-electrode 1.5- mu m DFB (distributed feedback) lasers in 1.7-Gb/s noncoherent frequency-shift-keyed (NC-FSK) transmission. Sixteen commercial laser transmitters were characterized in terms of FSK transmission sensitivity, eye-margin, chromatic dispersion penalty and pattern dependence. Using amplitude-shift-keying (ASK) performance as a baseline, FSK is shown to outperform ASK when dispersion is present, while ASK is slightly better with no dispersion. FSK transmitters with commercial single-electrode DFB lasers are shown to provide an attractive alternative to ASK in dispersion limited systems. The FSK degradations mainly result from an inadequate FM modulation index and a thermal-FM index manifested as a pattern length dependence. >

Combined Frequency and Time-Shift Keyed Transmission Systems

Consideration is given to a transmission technique which is based on the combination of frequency-shift keying (FSK) and time-shift keying (TSK). In the resulting frequency and timeshift keyed (FTSK) transmission, the two possible states of a binary waveform are represented by the order of two pulses which occur on different frequencies, for instance, f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> and f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . For example, if the ordered pair <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(f_{1}, f_{2})</tex> represents a Mark, then <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(f_{2}, f_{1})</tex> represents a Space. The power spectrum, as well as the performance of both coherent and noncoherent systems in an interference environment, is investigated. The following cases are considered: 1) white noise interference, with and without fading and 2) CW interference. It is shown that with white noise interference and no fading, the performance of a coherent FTSK system is identical to that of coherent FSK and TSK systems operating at the same data rate. Under similar conditions, the performance of a noncoherent FTSK system would be slightly degraded (less than 1 db for digit error probabilities less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) compared to that of noncoherent FSK and TSK systems. FTSK's dual frequency diversity is shown to provide a substantial antifading capability to both coherent and noncoherent transmissions. Furthermore, it is observed that FTSK offers the potential for: 1) complete rejection of CW and other forms of narrow-band interference, 2) simplified postdetection signal coupling circuits, 3) enhanced performance of digit synchronization circuits and 4) error detection and correction.

On Coded Phase-Coherent Communications

The merits of phase-coherent communications are widely recognized for both discrete and continuous modulation systems [1]-[3]. The relative performances of phase-coherent and noncoherent transmission of binary data in the presence of additive white Gaussian noise have been analyzed and compared [1] and [2]. This paper considers the result of encoding independent equiprobable binary words or sequences of independent binary digits into sets of binary code words. These are transmitted over a channel perturbed by additive white Gaussian noise and detected by correlating them with their stored or locally generated replicas at the receiver. The word error probabilities and bit error probabilities for low cross-correlation codes are determined as a function of the ratio (received signal energy)/bit/(noise power)/(unit bandwidth) The received information rate and the potential channel capacity are also computed. It is shown that in the limit as the code word length and the bandwidth approach infinity, the received information rate approaches the channel capacity for only one value of the above ratio.