Ashok Jhunjhunwala

In planar bulk acoustic wave devices, an interdigital transducer (IDT) is generally used as the source of excitation. Grooves, which convert an incident SAW (surface acoustic wave) to bulk waves and vice versa, also have the potential to be used as an alternative (if secondary) source of excitation. A typical shallow rectangular groove etched into a crystalline substrate perpendicular to the propagation direction is considered. The groove is modeled as an interior perturbation to the substrate. Coupled-mode equations are developed and solved for the reflected SAW and the scattered bulk waves. The results are compared to those of the half-space geometry. The interior-perturbation approach produces a good match with earlier published results that used the boundary-perturbation method.

A recirculating, synchronous TDM (time division multiplexed) backbone loop operating at 1 Mbps that supports multiple 9600 baud point-to-point connections, and multiple low bit rate packet channels is described. Slots are deterministically allotted to groups of devices and any medium access protocol suitable for the ring topology can be used to regulate access to the transmission channel. Nodes on the backbone are interconnected through fiber optic or atmospheric optical links. The objective of the network is to satisfy the demands of a typical computing environment, viz., to offer a terminal distribution system and to simultaneously support multiple low bit rate packet channels. Devices communicate with the network through RS-232C serial lines.

Copper based wired local loop has served us well for over 100 years. However much we may decry the copper for its bottlenecks today, it has served us so long due to the following (i) it is a passive network, which does not fail unless cable is cut, (ii) it carries power for subscriber terminals, (iii) it carries voice signals both ways, (iv) 56 kbps data can be carried in 4 kHz copper loop, (v) n-isdn, HDSL, ADSL, VDSL is enabling tens of Mbps data to be carried on the copper loop. It is such a loop that one wishes to replace with Fibre. How does fibre handle these issues? While fibre finds it difficult to provide one to one replacement of copper loop, and is still struggling to make a mark in the Access Network of developed world, a certain kind of Fibre Access Networks is suddenly becoming the way of deploying new telecom networks in developing countries. Fibre in the Loop today provides the most cost-effective solution for new deployment in urban areas; most Basic Services Operators in India plan to use this in major way. It is likely that in the next three to four years, more Fibre in Access Network will be deployed in India than in any other country in the world. This paper examines the issues involved in use of Fibre in the Access Network and suggest solution which are likely to make it the technology of choice for new operators.

This paper illustrates the Battery Life Cycle Tester with intelligent charging and discharging unit comprising of measurement, data logging, remote monitoring and communication sections for data acquisition and control. The life cycle tester switches between different charging and discharging modes making it compatible with all battery chemistries. The discharger comprises of an electronic load using MOSFETs operated in their linear region to dissipate power. The required charging/discharging profiles for various applications like electric vehicle motor load and urban drive cycle tests can be programmed via an RS485 link and the data collection is done through Ethernet with an onboard SD card for backup. The user can also set their own test profiles within given limits. The Battery Life Cycle tester is used to perform required charging and discharging profiles at the specified Depth of Discharge (DOD), temperature, State of charge (SOC), charge and discharge rates for the desired number of cycles and store the data for analysis.

This paper describes and discusses the setting up of a DSP Cloud Lab, a setup to execute programs remotely. The programs can be executed on a variety of DSP boards; they could be microprocessor assembly language programs or programs written in assembly language requiring powerful DSP boards or even DSP boards with an FPGA accelerator. The boards used are based on Blackfin Architecture. For a student / developer who writes codes and tests on it, it appears as if they have exclusive use of the boards. However, the boards are highly shared, enabling a large number of students / developers to use them simultaneously. This paper also discusses the design choices made at different stages and the extent to which it facilitates or restricts the use of the DSP boards for a developer. © 2013 IEEE.

In this paper, we discuss efficient implementation of machine learning algorithms on DSPs. Specifically, we implement OCR and speech recognition on DSP and show how they can be optimized using fixed point routines. We illustrate the optimal usage of DSP resources like MAC units, shifters and software pipelining through assembly code structuring which massively reduces the MIPS consumed by the processor. We also describe how floating point overheads can be reduced by equivalent fixed point routines for real time implementations. Though the Blackfin-533 DSP is chosen for this illustration, the ideas presented here apply to other fixed point DSPs as well.

In this paper, we consider the problem of maximizing the time of first lightpath request rejection, T in the circuit-switched time division multiplexed (TDM) wavelength-routed (WR) optical WDM networks. TDM is incorporated into WDM, to increase the channel utilization when the carried traffic does not require the entire channel bandwidth. In TDM-WDM network, multiple sessions are multiplexed on each wavelength by assigning a sub-set of the TDM slots to each session. Thus, given a session request with a specified bandwidth, a lightpath has to be established by using the routing, wavelength and time-slot assignment (RWTA) algorithms. If the lightpath cannot be established, lightpath request rejection or call blocking occurs. As each lightpath is substantial revenue and long-lived, lightpath request rejection is highly unfavourable in the opitcal backbone networks. In this paper, we are proposing an intelligent routing, wavelength and time-slot reassignment algorithm for multi rate traffic demands, where, when a call gets blocked, the already established calls in the network are rerouted, wavelength and timeslot reassigned so as to accomodate the blocked call. Since we are talking of slow arrivals and long holding times for the lightpaths, it is possible to do this reassignment while provisioning a new call. Simulation based analyses are used to study the performance of the proposed reassignment algorithm. The results show that the proposed reassignment algorithm can be used to maximize the time of first call blocking, thereby accommodating more calls in the network before upgrading the network capacity. © 2006 IEEE.

As the current world moves towards e-learning, this paper discusses about a recently developed remote Digital Signal Processing lab at IIT Madras. This lab enables the students to use Blackfin 537 based DSP kits to perform their real-time experiments / projects over the Internet. The DSP boards are custom made, with uClinux ported onto them, to facilitate a multi-user environment. This paper delineates the motivation, hardware setup, software setup and remote user access for using the laboratry. Finally the performance, scope and scalability are discussed with emperical data. © 2012 IEEE.

Railway traffic Control requires dedicated point to point and point to multipoint circuits for communication over larger number of signal points spread along the track. A typical despatcher control section spreads over 200 kms with 30 to 40 signal points. Till mid 80s, such communication were economically provided by copper quad cable in electrified territory. Development in optical fibre technology has changed the scenario and fibre finds increasing use in Railway Telecommunication Network due to its distinctive advantages. However some of the railways' requirements are too specialized. These include omnibus circuits with large number of tappings, closely spaced repeaters, lineside emergency communication requirement, transmission of safety information and ability to provide on demand service. The technology of optical fibre therefore requires adoptions to meet these specialized requirements. In this paper we describe an optical fibre based Railway Communication system used by Indian Railways and conclude that even though large number of repeaters are used in the link, the performance quality is satisfactory and optical fibre based communications are economical in the railway environment. Reliability of the link can be improved through additional fibres or through alternate media. A hybrid solution based on optical fibre and copper cable is proposed to achieve economy without sacrificing quality and reliability.