The Personal Digital Assistants

Published Date: 02 Nov 2017

CHAPTER 1

INTRODUCTION

1.1 Overview

People have come into contact with wireless networks. From small Children to the most senior citizens are using mobile devices such as Personal Digital Assistants (PDAs), cell phones, and smart phones. In Day to Day life, Wireless networks have penetrated into almost every aspect of human life. With the constant demand for bigger, better, and faster, with no doubt the devices continue to push the boundaries of human imagination and capabilities. The popularity of wireless networks and mobile devices has led to the desire for research in the area of Mobile Ad Hoc Networks (MANETs).

Significant work has been done in the area of MANETs, right from the mid 1990s. The Internet Engineering Task Force (IETF) and the Institute of Electrical and Electronics Engineers (IEEE) have worked vigorously to standardize routing and medium access protocols for MANETS. When societies are faced with emergencies like natural disasters, military conflicts, and emergency medical situations, MANETs present enormous promise so that these organizations, as well as many others, recognize the tremendous value they bring to the table.

1.2 State of the art

A set of wireless mobile nodes that are capable of communicating with each other is called Mobile Ad Hoc NETwork (MANET). MANETs have no fixed network infrastructure or administrative support. For one host to transfer data to another one across the network several intermediate hosts may be needed as the transmission range of wireless network interfaces is limited. Thus, each node may operate as a terminal host and as a router to forward packets of other mobile nodes. Frequent changes in the network topology occurs as nodes are free to move arbitrarily accordingly, MANETs should become accustomed with dynamism to sustain on-going communications in spite of these changes.

MANETs are helpful in a huge diversity of circumstances, such as universities, museums, emergency rescues or exploration missions, wherever video-streaming services are expected to be used. Quality of Service (QoS) provision in multimedia services remains an open issue in Ad Hoc networks. The strange distinctiveness of MANETs, such as mobility, dynamic network topology, energy constraints, lack on centralized infrastructure and variable link capacity, make the QoS terms over these networks is a really challenging target.

For real time application data flows, the reservation of bandwidth and the assurance of specified delay are the challenges that are to be sustained for QoS in adhoc networks, which are how to reserve bandwidth and how to assure the specified delay for real-time application data flows. The channel is mutual amid neighbors for wireless transmissions, hence the available bandwidth depends on the neighboring traffic status, as does the delay. Owing to this characteristic, sustaining QoS cannot be done by the host itself, on the other hand assistance from the hosts surrounded by a node’s interference range is required This requires an pioneering plan to synchronize the communication amid the neighbors in order to maintain QoS in MANETs.

Opportunely, multimedia applications can deal with a firm amount of packet losses depending on the sequence characteristics and error suppression strategies available at the receiver. accordingly contrasting file transfers, real-time multimedia applications do not entail absolute padding from packet losses, other than that the application layer collaborate with the subordinate layers to choose the finest wireless transmission tactic that maximizes multimedia performance.

1.3 Motivation

In latest years the investigation focus has been to get accustomed with existing algorithms and protocols for multimedia compression and transmission to the hastily unstable and frequently inadequate resources of wireless networks. Nonetheless these solutions regularly do not offer ample prop up for multimedia applications in teeming wireless networks, when interference is high or stations are mobile. This is for the reason that managing the resources, adaptation, and preserving strategies available in the lower layers of the stack — the physical (PHY), medium access control (MAC), and network/transport layers — are optimized without openly making an allowance for the unambiguous characteristics of multimedia applications, and in opposition, multimedia compression and streaming algorithms do not gaze at the mechanisms provided by the lower layers for error protection, scheduling, resource management, and so on. This "layered" optimization leads to a simple autonomous performance, but fallout in suboptimal multimedia (objective and/or perceptual quality) presentation.

Then again, under unpleasant situation, wireless stations have to optimally acclimatize their multimedia compression and transmission strategies mutually across the protocol stack in order to pledge a predetermined quality at the receiver. Latent solutions for strong wireless multimedia communication over error-prone networks include application-layer packetization, (rate-distortion optimized) scheduling, joint source-channel coding, error resilience, and error concealment mechanisms. At the PHY and MAC layers, remarkable gains have been reported by adopting cross-layer optimization, such as link adaptation, channel aware scheduling. plain deliberation of multimedia characteristics and necessities can hold increase the significant advances achieved in cross-layer design at the lower layers.

To afford QoS for multimedia applications, the IEEE 802.11 Working Group at present defined a new supplement to the existing legacy 802.11 MAC sublayer, called IEEE 802.11e. Note that despite the fact that budding MAC standards endow with QoS support, there are no QoS guarantees for multimedia applications, and system wide resource management is not always just or competent. This is owing to the time-varying scenery of the wireless channel and multimedia characteristics, and also the lack of cross-layer awareness of the application and MAC layers about each other.

To expand more insights into the doctrines that guide cross-layer design and to evaluate the various solutions the subsequent categorizations of the probable solutions are made which are based on the array in which cross-layer optimization is performed:

Top-down approach — The higher-layer protocols increase the efficiency of their parameters and the approaches at the next lower layer. This cross-layer solution has been mounted in the majority of the presented systems, wherein the APP shape the MAC parameters and policies, while the MAC chooses the most favorable PHY layer modulation scheme.

Bottom-up approach — The lower layers try to shield the higher layers from losses and bandwidth discrepancies. This cross-layer solution is not more advantageous for multimedia transmission, due to the acquired delays and pointless throughput diminution.

Application-centric approach — The APP layer extend the effectiveness of the lower layer factors one at a time in a bottom-up (starting from the PHY) or top-down manner, based on its necessities. Conversely this advance is not always efficient, as the APP maneuvers at slower timescales and cruder data granularities (multimedia flows or group of packets) than the lower layers (bits or packets), and thus is not able to right away adapt their feat to attain an best performance.

MAC-centric approach — In this approach the APP layer surpasses its traffic information and necessities to the MAC, which chooses which APP layer packets/flows ought to be conveyed and at what QoS level. The MAC also fixes on the PHY layer factor based on the offered channel information. The drawback of this approach resides in the failure of the MAC layer to execute adaptive source channel coding trade-offs given the time-varying channel conditions and multimedia requirements.

Integrated approach — In this approach, plans are resoluted jointly. Regrettably, profoundly trying all the probable approaches and their parameters in order to decide the combined approach leading to the most excellent quality concert is impossible due to the coupled intricacy. The above cross-layer approaches reveals diverse rewards and problems for wireless multimedia transmission, and the preeminent result depends on the application necessities, used protocols, and algorithms at the various layers, intricacy and power limitations, and so on.

1.4 OBJECTIVE

To improvise the Quality of Service of multimedia applications in MANETs, three cross layer approaches have been proposed.

In the first cross layer approach Multiple description coding is used in application layer(MDC), UDPLite is used transport layer, Split Multipath Multimedia Dynamic source routing protocol(SMMDSR) is used in network layer are integrated in such a way that the efficiency of the output video delivered to the end user has an improvement in quality along with increase in PSNR.

The second cross layer approach includes the video significance information gathered from the application layer, UDPLITE in transport layer, and dynamic Mapping in medium access layer that improves the quality of video under varying network conditions.

In the third cross layer approach An Active Queue Management for diffserv in MANETs has been designed that uses the video significance information gathered from application layer and UDPLite in transport layer, SIVIRED AQM ALGORITHM in network layer to avoid congestion, to reduce delay and jitter and to improve the performance of streaming.

1.5 Organization of the thesis

In chapter 2, IEEE 802.11 networks are overviewed. Also the concepts of multipath routing and Active queue management(AQM) techniques are discussed. Multiple Description coding techniques are also discussed.

In chapter 3, System architecture and design has been discussed.

In chapter 4, the Split Multipath Multimedia Dynamic Source Routing(SMMDSR) which is used to take better routing discussions along with UDPLite at transport layer and Multiple Description Coding(MDC) and has been discussed. This combination provides good quality of video at the receiver end. A performance evaluation is done to show the benefits of SMMDSR and MDC in terms of PSNR.

Section 4.1 discuss about Introduction. Section 4.2 and 4.3 we discuss the multiple description coding and UDPLite. Section 4.4 discusses the proposed designs. Section 4.5 establishes system simulation model and section 4.5 gives results to illustrate the significance of the work while conclusions drawn are given in section 4.7.

In chapter 5, congestion avoidance for video streaming in MANETs has been discussed. The SiVIRED AQM algorithm performance is compared with drop tail algorithm in terms of delay, jitter and PSNR. section 5.2 describes the proposed AQM approach in detail; section 5.3 presents the simulation analysis results and section 5.4 conclusion

In chapter 6, cross layer design for video streaming over MANETs have been discussed. The cross layer mapping scheme which is used under various traffic conditions is also discussed and concept has been simulated using NS2 and simulation results are shown.

Chapter 7 summarizes the result and provides conclusion. The future work is also recommended in this chapter.