H. S. Jamadagni

Comparison of voice activity detection algorithms for VoIP

We discuss techniques for voice activity detection (VAD) for voice over Internet Protocol (VoIP). VAD aids in saving the bandwidth requirement of a voice session, thereby increasing the bandwidth efficiently. We compare the quality of speech, level of compression and computational complexity for three time-domain and three frequency-domain VAD algorithms. Implementation of time-domain algorithms is computationally simple. However, better speech quality is obtained with the frequency-domain algorithms. A comparison of the merits and demerits along with the subjective quality of speech after removal of silence periods is presented for all the algorithms. A quantitative measurement of speech quality for different algorithms is also presented.

A scalable distributed VoIP conferencing using SIP

Session initiation protocol seems to be proffered standard for voice-over-IP. In this paper, we consider the limitations of existing SIP conferencing methods and propose a distributed architecture using controllers (SIP proxy servers) and conference servers which facilitate the control and media handling of a VoIP conference. The conference servers are designed on the basis of H.323s multipoint processors and handle the audio part of the conference. We provide conferencing messages on SIP that bring these controllers and conference servers together along with the clients for scalable conference on the Internet. The schematic of the proxy server and conference server is presented to aid in implementation. We also explain the mechanism we use to improve the quality of mixed output speech by selecting the streams at the clients.

Sensor Network Deployment For Agronomical Data Gathering in Semi-Arid Regions

We share our experience in planning, designing and deploying a wireless sensor network of one square kilometre area. Environmental data such as soil moisture, temperature, barometric pressure, and relative humidity are collected in this area situated in the semi-arid region of Karnataka, India. It is a hope that information derived from this data will benefit the marginal farmer towards improving his farming practices. Soon after establishing the need for such a project, we begin by showing the big picture of such a data gathering network, the software architecture we have used, the range measurements needed for determining the sensor density, and the packaging issues that seem to play a crucial role in field deployments. Our field deployment experiences include designing with intermittent grid power, enhancing software tools to aid quicker and effective deployment, and flash memory corruption. The first results on data gathering look encouraging.

Near Field Communication – Applications and Performance Studies

Near Field Communication (NFC), is an integration of Radio Frequency Identification (RFID) technology with mobile devices. NFC offers a quick and convenient method of interaction between humans and NFC enabled devices. Current research concerning NFC appears to mainly focus on development of NFC enabled applications and services. In this paper, we study the performance of NFC devices by considering metrics such as achieved data rates and received power for several distances. Knowledge of these metrics may be useful for application developers to build applications efficiently. We have developed various applications on NFC enabled devices for public transport systems. We also describe the design of 13.56 MHz antenna which was used for measurements of the received power.

A Proposal for Distributed Conferencing on SIP Using Conference Servers

Session Initiation Protocol (SIP) is the de facto standard for Voice over IP implementations. Although this standard does not define conferencing directly, many drafts and papers suggest extensions and solutions to this essential service. In this paper, we first define the issues that are to be considered when building a conference service, and then we motivate our work on some of the limitations of the existing suggested solutions. This framework facilitates the conference control and media handling of a VoIP conference and aims to create a scalable and distributed conferencing system both in terms of load and control. The conference control as well as media is distributed over the network using SIP Servers and Conference Servers, which are described. The floor control is made dynamic by using a metric called Loudness Number [10] that provides a feel of a physical face-to-face conference.

VAD for VoIP Using Cepstrum

As telephony services are being supported on Internet the focus is now on multiplexing many speech streams by exploiting the speech characteristics. The multiplexing gain is an important factor when applications such as teleconference service are ported on to the Internet. Here we discuss Voice Activity Detection (VAD) for Voice over Internet Protocol (VoIP) based on Cepstrum. VAD aids in saving bandwidth of a voice session. Such a scheme would be implemented in the application layer thus VAD is independent of the lower layers. The standard codecs would inherently have the VAD algorithms to reduce the bandwidth. However they are costly and computationally complex. In this paper, we compare the quality of speech, level of compression and computational complexity of our method of Cepstrum based VAD with the standard GSM and ITU-T G.729 codecs. Bandwidth reduction is achieved by not transmitting the non-speech packets. Our algorithm adapts to the varying background noise.

Self-jamming: Who wins? An implementation study

Physical layer security is one possible alternative for the exploding Internet of Things in the coming years. We advance the state of art in physical layer security by implementing self-jamming on ultra low power transceivers without the assistance of “friendly” nodes. The implementation supports flexible payload sizes; where the simplest implementation carries a full data payload. We consider a passive eavesdropper with varying attack potentials; constantly attempting to recover the original data from the transmitter. We show that a 3dB shift and transmit power control between transmitter and receiver is good enough to ensure data security. The key insights from this work is that large payloads have a 50% lower throughput compared to smaller payloads. Also smaller payloads have the advantage of a 25% delay performance improvement over large payloads.

Architecture of Run-Time Reconfigurable Channel Decoder

Modern wireline and wireless communication devices are multimode and multifunctional communication devices. In order to support multiple standards on a single platform, it is necessary to develop a reconfigurable architecture that can provide the required flexibility and performance. The Channel decoder is one of the most compute intensive and essential elements of any communication system. Most of the standards require a reconfigurable Channel decoder that is capable of performing Viterbi decoding and Turbo decoding. Furthermore, the Channel decoder needs to support different configurations of Viterbi and Turbo decoders. In this paper, we propose a reconfigurable Channel decoder that can be reconfigured for standards such as WCDMA, CDMA2000, IEEE802.11, DAB, DVB and GSM. Different parameters like code rate, constraint length, polynomials and truncation length can be configured to map any of the above mentioned standards. A multiprocessor approach has been followed to provide higher throughput and scalable power consumption in various configurations of the reconfigurable Viterbi decoder and Turbo decoder. We have proposed A Hybrid register exchange approach for multiprocessor architecture to minimize power consumption.

Heuristic algorithms for server allocation in distributed VoIP conferencing

To allocate audio conference servers (CS) [R. V. Prasad et al., June 2003] for virtual conferencing over IP, we leverage session initiation protocol (SIP) for signaling. We address here the problem of facilitating seamless conference amongst participants using CSs. This demands a proper allocation of CSs to clients to maximize the number of participants served and at a reduced cost. Seeking a more realistic approach, we avoid over-simplifying assumptions; hence the problem becomes relatively harder. We present three heuristic algorithms for these NP-hard problems and bring about the effectiveness of their performance.

Second and third order adaptable threshold for VAD in VoIP

Reducing the Internet traffic is a requirement to share the bandwidth with many sessions. When circuit switched applications are ported on to the Internet, bandwidth saving becomes all the more prominent. An efficient adaptable threshold VAD (voice activity detection) for voice over IP systems is presented in this paper. The discussion includes two energy-based algorithms with higher order threshold refreshing schemes. The performance of all the schemes is presented, and the results bring out clearly the usefulness of the schemes for VoIP applications with saving in bandwidth.