Time-domain Multiplexing Research Articles

Multiple output semiconductor ring lasers with high external quantum efficiency

The external quantum efficiency of semiconductor ring lasers has been significantly improved by introducing output couplers that couple more light out of the ring cavity. Improvements from 10% and 16% to 14% and 27% of a comparable single 2×2 MMI coupler device were achieved by using 3×3 multimode interference (MMI) couplers and dual 2×2 MMI couplers, respectively. A further increase to the value of 33% (or 2 times that of the previous devices) was obtained by AR coating the output facets of the dual 2×2 MMI coupler devices. These devices also provided four output beams as required in an integrated optical time domain multiplexing (OTDM) system.

Are crossbars really dead?

Crossbar switches are rarely considered for large, scalable multiprocessor interconnect systems because they require O(n 2 ) switching elements, are difficult to control efficiently and are hard to implement once their size becomes too large to fit on one integrated circuit. However these problems are technology dependent and a recent innovation in fiber optic devices has led to a new implementation of crossbar switches that does not share these problems while retaining the full advantages of a crossbar switch: low latency, high throughput, complete connectivity and multi-cast capability. Moreover, this new technology has several characteristics that allow a distributed control system which scales linearly in the number of attached nodes.The innovation that led to this research is an optical and-gate that can be used to demultiplex multiple high speed data streams that are carried on one common optical medium. Optical time domain multiplexing can combine the data from many nodes and broadcast the result back to all nodes. This paper discusses OTDM technology only to the extent necessary to understand its characteristics and capabilities. The main contribution lies in the description and analysis of interconnect architectures that utilize OTDM to achieve a level performance that is beyond electronic means. It is expected that cost-reduced OTDM systems will become competitive with the next generation of interconnect systems.

A four‐channel time domain multiplexer: A cost‐effective alternative to multiple receivers

The concept of simultaneous image acquisition as originally conceived by Hyde has been implemented by Roemer et al. using a multiple receiver system. This article describes an alternative technique that uses time domain multiplexing (TDM) to acquire simultaneous images using a single receiver channel. This method requires few modifications to the existing receiver and has been shown to be equivalent to a true four channel receiver in most applications. The multiplexing technique was implemented and tested on a standard commercial scanner that has also been equipped with a four channel receiver. Signal-to-noise results demonstrate that four independent images can be multiplexed through a single receiver channel with no degradation in image quality. Additionally, spine images that were obtained from a normal volunteer with both a multiplexed single channel receiver and a true four channel receiver system are presented.

Selective synchronization of time-domain multiplexed sensors by correlation of pseudo-orthogonal codes

A new approach to time-domain multiplexing of fiber-optic sensors is presented: a synchronization pulse is sent back only by the questioned sensor. This selective synchronization is obtained by correlating a pulse sequence and the codes which are assigned to each sensor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Responsive, deterministic IEEE 802.5 token ring scheduling

This paper presents a novel approach for scheduling the IEEE 802.5 token ring. This approach not only guarantees deadlines for synchronous class messages, but also dramatically reduces asynchronous class response times. Further, highly responsive guaranteed service is introduced for alert class asynchronous messages. Conventional use of the IEEE 802.5 token ring standard guarantees synchronous communication services using Time Domain Multiplexing (TDM) techniques while relegating asynchronous class message services to background status. The result is poor responsiveness. Further, the TDM schedules tend to be fragile and difficult to modify and extend. This paper presents an algorithmic-based scheduling approach that supportsa priori schedulability determination for arbitrary synchronous message sets without the costly development, testing, and tuning of TDM schedules. This capability allows the IEEE 802.5 standard to support dynamic, adaptive, and reconfigurable run-time environments where the inflexibility of TDM would be prohibitive. Advanced real-time scheduling theory is applied to the IEEE 802.5 token ring standard and dramatically enhances asynchronous class messages' responsiveness while still maintaining guaranteed service for the synchronous class. The result is a highly responsive real-time ring that can form the backbone of predictable, stable, and extendible real-time systems.

Optimal multiplexing of sampled signals on noisy channels

This paper deals with the joint optimization of transmitting and receiving filters in multiplex transmission of pulse-amplitude-modulated (PAM) signals. A mean-square-error criterion is used. The signal processes are assumed to be mutually uncorrelated and with equal power spectral densities. Transfer matrix functions for the transmitting and for the receiving filters are used as an expedient tool. It is shown that optimal multiplexing systems can be achieved with a bandwidth of M/T . The transfer matrix functions of optimal transmitters (and corresponding optimal receivers) are defined up to premultiplication by an arbitrary unitary matrix function. This provides for freedom of choice between various multiplexing techniques like frequency-domain multiplexing, time-domain multiplexing, or combinations thereof.