A detailed comparison and optimisation of three different techniques to generate optical single sideband (OSSB) signals is presented. Three techniques are investigated: phase-shift (PS), optical filtering and Weaver&#...
详细信息
A detailed comparison and optimisation of three different techniques to generate optical single sideband (OSSB) signals is presented. Three techniques are investigated: phase-shift (PS), optical filtering and Weaver's method (WM). The conventional binary and alternate mark inversion (AMI) coding formats are used to assess the transmitter performance for signals with different spectral properties. Different duty-cycles are considered for each format to analyse the generation of OSSB signals from signals with enhanced tolerance to inter-symbol interference. The optimisation of each transmitter parameter is carried out by maximising the amount of accumulated dispersion, using 40 Gb/s bit rate signals, for a specific eye opening penalty. With the binary format, an increase by more than 150 ps/mn of the accumulated dispersion is observed using the WM and NRZ pulses, compared to a reference double sideband signal with NRZ pulses. The optical filtering and PS techniques present lower accumulated dispersion improvements, although the PS allows significant sideband suppression near the carrier frequency. With the AMI format, an increase of 35 ps/nm is achieved by most OSSB transmitters and considerable high sideband suppression is observed using the optical filtering technique.
In transmission of bursty traffic such as video and data, a network with a fu;ed capacity may have some unused bandwidth. The available bit rate (ABR) scheme in ATM networks can make use of this spare channel capacity...
详细信息
In transmission of bursty traffic such as video and data, a network with a fu;ed capacity may have some unused bandwidth. The available bit rate (ABR) scheme in ATM networks can make use of this spare channel capacity as a lower priority service. ABR has been developed initially for delay-tolerant services such as data. The authors demonstrate how, with the help of a video transcoder, delay-sensitive services such as video may be transmitted over ABR. The transcoder further compresses the video bit stream according to the rates dictated by the network with minimum degradation to the picture quality. The video quality has been optimised by combining the classical minimum cell rate (MCR) with the subjectively acceptable minimum quality (SAMQ). The performance of two different coding formats for ABR sources, namely the constant bit rate (CBR) and variable bit rate (VBR) video input to the transcoder are compared. The authors also present techniques for further reduction of congestion at the multiplexing switches and report on the impact of the forward and backward link delays on the ABR performance with a video transcoder.
暂无评论