Yahya M. Khawaja

Performance evaluation of shortest multipath source routing scheme

Multipath routing in mobile ad-hoc networks allows the establishment of multiple paths for routing between a source-destination pair. It exploits the resource redundancy and diversity in the underlying network to provide benefits such as fault tolerance, load balancing, bandwidth aggregation and the improvement in quality-of-service metrics such as delay. Previous work shows that on-demand multipath routing schemes achieve better performance under certain scenarios with respect to a number of key performance metrics when compared with traditional single-path routing mechanisms. A multipath routing scheme, referred to as shortest multipath source (SMS) routing based on dynamic source routing (DSR) is proposed here. The mechanism has two novel aspects compared with other on-demand multipath routing schemes: it achieves shorter multiple partial-disjoint paths and allows more rapid recovery from route breaks. The performance differentials are investigated using NS-2 under conditions of varying mobility, offered load and network size. Results reveal that SMS provides a better solution than existing source-based approaches in a truly mobile ad-hoc environment.

Location tracker for a mobile robot

This paper presents landmark based self-localization of a two-wheeled differential drive autonomous mobile robot in a known but highly dynamic environment. The robot is equipped with a pivoted stereo vision system, two digital encoders, a gyro sensor, two lOg accelerometers and a magnetic compass. Global position of the robot is estimated using range measurements of distinct features such as color transitions, corners, junctions and line intersections in the robot environment. However, due to scarcity of distinct features, it is not possible to extract the minimum required features for global position estimation from everywhere in the state space. Therefore, the robot position is tracked between intermittent global localization to have an all time position estimate available to the robot. The robot observation vector is composed of range and bearing measurements of distinct features in the robot environment which is merged with the current position estimate to suppress the accumulating errors. Simulation results illustrate the performance of the location tracker.

Comparison of reconstruction and example-based Super-Resolution

By comparing two classes of Super-Resolution (SR) namely Example-Based Super-Resolution (EBSR) and Reconstruction-Based Super-Resolution (RBSR), we investigate two points: Firstly, which SR technique EBSR or RBSR will produce SR image that preserves Structure Similarity (SSIM) to the original image? Secondly, which SR technique will produce SR image that is more appealing to human eyes? For resultant SR image, EBSR predicts the relation between high and low frequencies in an image, whereas RBSR algorithms rely on a sequence of frames. From the experimental results on test images, we find that compared to RBSR, EBSR preserves the structure of the original image. Knowing this capability is important for detection and recognition systems. In terms of visual appearance, RBSR is preferred except when there are large motions in consecutive frames. Moreover, the aliasing artifacts cannot be removed by EBSR algorithms.

An area reduced, speed optimized implementation of viterbi decoder

A fast implementation of the Viterbi decoder is discussed in this paper. It is shown that the proposed design is area efficient, reduces memory requirements and has a larger throughput then parallel Viterbi implementations. Techniques used to achieve these goals are retiming, pipelining and parallel to serial conversion which are implemented at the gate level. VLSI designs of constituent blocks of the decoder are shown and thorough analysis of the critical path delay of each decoder segment is deliberated which illustrates that the resulting design imposes minimum penalties in terms of clock speed and circuit area.

Real Time Object Tracking in a Video Sequence Using a Fixed Point DSP

In this paper we propose implementation of a viable algorithm for real time tracking of objects in a video sequence on a Digital Signal Processor (DSP). Three different tracking algorithms are simulated and on the basis of simulation results, the best algorithm is proposed for hardware implementation. The selected algorithm tracks objects by minimizing the error iteratively. A modification of the selected algorithm is suggested that suits the hardware implementation. The algorithm is tested on different video sequences, both synthetic and real, which demonstrates its performance.

Stereo vision based self-localization of autonomous mobile robots

This paper presents vision based self-localization of tiny autonomous mobile robots in a known but highly dynamic environment. The problem covers tracking the robot position with an initial estimate to global self-localization. The algorithm enables the robot to find its initial position and to verify its location during every movement. The global position of the robot is estimated using trilateration based techniques whenever distinct landmark features are extracted. Distance measurements are used as they require fewer landmarks compared to methods using angle measurements. However, the minimum required features for global position estimation are not available throughout the entire state space. Therefore, the robot position is tracked once a global position estimate is available. Extended Kalman filter is used to fuse information from multiple heterogeneous sensors. Simulation results show that the new method that combines the global position estimation with tracking results in significant performance gain.

A hybrid approach towards vision based self-localization of autonomous mobile robots

This paper presents a hybrid approach towards self- localization of tiny autonomous mobile robots in a known but highly dynamic environment. The proposed algorithm is intended for two-wheeled differential drive robots which are equipped with a pivoted stereo vision system, two digital encoders, a gyro sensor, two 10g accelerometers and a magnetic compass. The global position of the robot can be estimated by extracting two distinct landmarks from the robot environment and measuring their range and orientation using the stereo vision system. However, distinct landmarks are not available through the entire state space and it is required to track the robot position once a global estimate is available. Tracking of the globally estimated position is performed within the framework of extended Kalman filter. Constant monitoring of the robot observation enables it to detect any unexpected situation. Simulation results show that robot can successfully localize itself at startup and is capable of detecting and recovering from localization failures.

Updating Farmland Satellite Imagery Using High Resolution Aerial Images

This paper presents a new approach for updating farmland satellite imagery by registering it with high resolution aerial images. It is based on Field Boundary Junction (FBJ) as feature for registration. Fields connected to FBJ are grouped together to form FBJ descriptor. Fields are described by sampling Field Boundaries (FB) relative to FBJ locations. Every field gets different description for each FBJ connected to it. It makes FBJ descriptor unique and helps in finding the correct FBJ matches reliably. It is invariant to scaling, in-plane rotation and translation. Experimental results also show its invariance to non rigid transformations, splitting/merging of fields and localization errors in FBs and FBJs.

An invisible dual watermarking scheme for authentication and copyrights protection

This paper focuses on two problems, authentication and copyrights protection, faced by digital media in general and digital images in particular. We discuss how two algorithms defined separately can be combined to produce a secure digital camera which provides a solution to these problems. First, a robust quantization based wavelet domain scheme is applied to embed a robust watermark in the image for the purpose of owner identification. After that, a semi-fragile scheme is used to watermark the robust watermarked image for authentication. Experimental results show that recovered robust watermark had high correlation with the embedded robust watermark after different attacks. Under perfect conditions, recovered fragile watermark also showed perfect correlation with embedded fragile watermark, but after attacks, the similarity index dropped indicating that image is not authentic.

A new software approach for real time OFDM

This paper discusses real time implementation of a new software defined radio (SDR) for orthogonal frequency division multiplexing (OFDM). The proposed SDR is implemented on a single PC, which does not include any external hardware and solely rely on the capabilities of the PC. A step by step comparison of the proposed SDR with the real world system for OFDM is presented and the errors encountered by the proposed SDR due to sampling offsets are also discussed. Since the proposed SDR does not include any external hardware, its portability is tremendous and upgradation is economical, and the approach can be extended to other communication techniques. The SDR is a multi-standard device and a flexible and economical approach for communication because it incorporates the newer technologies without considerable change of hardware.