Dynamic Spectrum Access (DSA) MAC protocols allow a Cognitive Radio (CR) device to opportunistically access unused or less crowded spectrum while ensuring protection for the incumbents. Though DSA shows great potential to enhance spectrum efficiency, the associated constraints on QoS may limit its usefulness. QoS support in a DSA-based network is not trivial due to the fact that in addition to unfavorable characteristics of the wireless medium, the secondary devices are subject to additional interference and interruption from incumbents. In this paper, we present a case-study of key QoS provisioning techniques in DSA protocol design that facilitate the required application QoS. Specifically, we consider a CR system that supports high quality multimedia (including HDTV) streaming over UHF frequency bands. We model and evaluate the QoS- oriented CR system together with the underlying QoS-Provisioned DSA Protocol (referred as QPDP) through extensive simulations. The results show the effectiveness of DSA coupled with QoS provisioning, in supporting QoS-demanding consumer- oriented network applications in TV bands. This outcome is significant as FCC has recently approved UHF bands for unlicensed operations in the second Report and Order in the USA, and various DSA-based personal/portable CR systems are being actively considered by the consumer wireless industry.

In recent years, we have seen tremendous growth in the applications of wireless sensor networks (WSNs) operating in unlicensed spectrum bands. However, there is evidence that existing unlicensed spectrum is becoming overcrowded. On the other hand, with recent advances in cognitive radio (CR) technology, it is possible to apply the dynamic spectrum access (DSA) model in WSNs to get access to less congested spectrum, possibly with better propagation characteristics. In this paper we present a conceptual design of CR-based WSNs, identify the main advantages and challenges of using CR technology, and suggest possible remedies to overcome the challenges. As an illustration, we study the performance of CR-based WSN used for the automation and control applications in residential and commercial premises. Our simulation results compare the performance of a CR-based WSN with a standard ZigBee/802.15.4 WSN.

Spectrum sensing is essential to the realization of spectrum agility in cognitive radio (CR) networks. Although fundamental tradeoffs and theoretical limits associated with spectrum sensing have been studied extensively, there have been very few experimental studies focused on building a spectrum "sensor" with commercial off-the-shelf devices. We have therefore built a prototype of CR-based sensor implementation with off-the-shelf IEEE 802.11 devices. 1 In particular, we have explored issues in implementing a spectrum sensor, mostly at the MAC layer, as well as the difficulty in implanting sensing functions into industrial network interfaces. Our experimental results demonstrate the feasibility of building a spectrum sensor and the construction of an incumbent-detection mechanism with off-the-shelf devices. We have also identified technical difficulties, such as device-dependency in determining the detection threshold, in-band signal jamming between secondary devices, and adjacent channel interference due to out-of-band signal emission. This experimental experience has led us to suggest a sensor design guideline for commercial wireless interfaces which can also facilitate other CR-related research.

Radio spectrum is very scarce today because a considerable amount of the spectrum is set aside for licensed wireless applications. With the rapid growth of wireless technologies, spectrum scarcity has become a serious problem as more and more wireless applications compete for very little spectrum. On the other hand the licensed spectrum allocated to applications like television, cellular telephony and public safety show very little usage over time at different geographical locations. The evolution of newer technologies has been seriously impaired because of current regulatory constraints on the operation of these networks in licensed spectrum, such as TV bands, and is being addressed by FCC through its recent rule making. With the goal of ubiquitous communication in mind, we look into spectrum agile radio, a new technology enabled by such FCC rule making, and study its advantages over conventional radios. In this paper, we first show the utilization achievable by agile radios through simple analysis. Then we will outline two types of agile radios and derive their maximum capacities. Then we will go ahead and derive the rules that increase the spectrum utilization using agile radios. We then highlight how spectrum agile radio impacts quality of service as defined in conventional sense.

Radio spectrum allocation is undergoing radical rethinking. Regulators, government agencies, industry, and the research community have recently established many initiatives for new spectrum policies and seek approaches to more efficiently manage the radio spectrum. In this paper, we examine new approaches, namely, spectrum agile radios, for opportunistic spectrum usage. Spectrum agile radios use parts of the radio spectrum that were originally licensed to other radio services. A spectrum agile radio device seeks opportunities, i.e. unused radio resources. Devices communicate using the identified opportunities, without interfering with the operation of licensed radio devices. The identification of spectrum opportunities is coordinated by policies, which are defined by, and under the control of, the radio regulator. Our approach is motivated by the publications of the next generation communications, XG, research project of the USA-based Defense Advanced Research Projects Agency, DARPA. We focus on IEEE 802.11k for radio resource measurements as an approach to facilitate the development of spectrum agile radios.

The MPEG-4 standard enables the representation of video as a collection of objects. This paper describes an automatic system that exploits such a representation. Our system consists of two parts: real-time content extraction algorithms and a real-time multi-object rate control method. We present two approaches to content extraction: foreground segmentation based on two cameras and face segmentation based on a single camera. The main contributions of this paper are: 1) under a stereo camera setup, we improve a disparity estimation algorithm to obtain crisp and smooth boundaries of foreground objects; 2) for a single camera scenario, we propose a novel algorithm for face detection and tracking, combining facial color and structure information; and 3) we develop a constant-quality variable bitrate (CQ-VBR) control algorithm that guarantees the quality specification for each object obtained from the two content extraction methods. Both segmentation algorithms run in real-time on a low-cost media processor, and have been tested extensively in various indoor environments. The CQ-VBR control algorithm is a useful tool for the evaluation of object-based coding. For low-bit-rate applications, we can achieve significant reduction in the overall bitrate, while maintaining the same visual quality of the foreground/face object as compared to conventional frame-based coding. Based on tests conducted on several sequences of different complexity levels, the bit-rate savings can be up to 48%. The satisfactory foreground segmentation (results presented) permits porting a live foreground object into arbitrary scenes to create composite video.

We propose a video streaming scheme over wireless LAN using novel rate-distortion optimized data partitioning scheme and prioritized adaptive packet transmission. The new algorithm enables DCT data partitioning up to the DCT block level without rate overhead using backward adaptation. For channel adaptation, we selectively drop enhancement layer packets when the channel throughput is not sufficient. Real video streaming experiments with 802.11b testbed have demonstrated excellent performance of the algorithm under severe interference such as microwave oven.

Robust video transmission over wireless LAN remains a key technical obstacle against the mass deployment of wireless multimedia home networking, due to the lack of guaranteed Quality of Service over the wireless medium and the sensitivity of single-layer coded video (MPEG-2, MPEG-4, etc) to packet losses. This paper describes a robust video transmission system over wireless LAN utilizing layered and prioritized transmission mechanisms. Specifically, a single layer coded video is first organized into multiple layers of different importance. The different layers are then packetized and transmitted with different priorities to ensure that vital video information is sent with higher priority while the rest (enhancement layer(s)) are sent with only best effort. Realtime streaming tests show that our streaming system can effectively minimize the video quality degradation under channel throughput variation.

With the development of ISO-MPEG-4 and ITU-T H.26L video coding standards, and a growing interest in low computational complexity video solutions for mobile devices, there is a need for simple yet accurate statistical representations to model the rate-distortion characteristics of video data. In this paper we propose a new rate-distortion model, specifically, a new distortion-quantization model. Although more generally applicable, the model proposed in this paper is especially useful for low bitrate coding. We discuss the plausibility of the model using analytical means. We then examine coded video data from several sequences to evaluate the accuracy of the proposed model. The chi-squared test and the coefficient of determination are used for this purpose. Finally, we show the use of the model in real-time rate control for a very-low-bitrate video communication application.

The emergence of the MPEG-4 standard has facilitated the development of new approaches to very-low bitrate coding, including model-based coding for human faces. As a tool in the synthetic/natural hybrid coding part of the standard, a face object is defined in terms of its shape-consisting of a set of facial feature points and texture. In addition, this face object can be animated by controlling these facial feature points to obtain a visual manifestation of speech and facial expression. However, the extraction of these facial feature points based on a particular human face is not a trivial task, and lies outside the scope of the MPEG-4 standard. In this paper, we introduce a system that automatically extracts 3-D facial feature points and calibrates a generic face model to a particular speaker's face. Our approach differs from previous work in that we extract facial feature points in 3-D using a stereoscopic camera leading to an automatic robust calibration of the face model to the particular face. Preliminary experimental results show promising performance.

We investigate the problem of MPEG-2 video quality degradation due to re-encoding using different coding parameters. We examined the statistical properties of pre-coded video and discovered that the coding parameters can be recovered from pre-coded video because the compressed video is represented by a limited set of parameters. We present an algorithm to detect if a picture is intra-coded or original and extract coding parameters if the picture is intra-coded. We show with numerical results that the coding parameters can be effectively extracted from pre-coded video and used to reduce additional coding loss, thus greatly improving the performance of multiple-generation coding.

The US HDTV process has fostered substantial research and development activity over the last several years. The Advisory Committee on Advanced Television Service (ACATS) was formed to advise the FCC on the technology and systems suitable for delivery of high definition service over terrestrial broadcast channels. Four digital HDTV systems where tested at the Advanced Television Testing Center. All the systems gave excellent performance, but the results were inconclusive and a plan for a second round of tests was prepared. As each of the four systems where being readied for retest. The proponents of the four individual digital HDTV proposals worked together to define a single HDTV system which incorporated the best technology from the individual systems. The consortium of companies, called the Grand Alliance (GA), announced a combined system and submitted it to ACATS for consideration. After ACATS certification, the GA began construction of a prototype system to submit for laboratory testing at the end of 1994. This paper describes the video compression subsystem and the hardware prototype. The preprocessing, motion estimation, quantization, and rate control subsystems are described. The system uses bidirectional motion compensation, discrete cosine transform, quantization and Huffman coding. The resulting bitstream is input into a transport system which uses fixed length packets. The multiplex transport stream is input into the 8-VSB transmission system. Finally, the specifics of the hardware implementation are described and some simulation results are presented.>

Transmission aspects of the advanced digital high definition television (AD-HDTV) system, for terrestrial simulcast delivery of HDTV are described. In AD-HDTV, two quadrature-amplitude-modulated (QAM) carriers, with different power spectral densities, are employed in a frequency division multiplex (FDM) mode within the standard 6-MHz channel. The resulting spectral shaping allows a larger power to be transmitted, compared to that for a single QAM carrier, for the same level of perceptual interference into cochannel NTSC. The coded video data are split into high-priority (HP) data and standard-priority (SP) data, and the vital information is sent on the appropriate QAM carrier, resulting in a robust audio and video transmission system. The availability is higher in scenarios where the carrier-to-noise ratio (CNR) is above the threshold for HP reception but below the threshold for SP reception; this is important in fringe areas. The NTSC planning factors, suitably modified for HDTV delivery, are used to estimate the coverage area for AD-HDTV. The calculated AD-HDTV coverage area of 54.5 miles is comparable to that for NTSC transmission.>