A Scalable, Secure, and Energy-Efficient Image Representation for Wireless Systems

The recent growth in wireless communications presents a new challenge to multimedia communications. Digital image transmission is a very common form of multimedia communication. Due to limited bandwidth and broadcast nature of the wireless medium, it is necessary to compress and encrypt images before they are sent. On the other hand, it is important to efficiently utilize the limited energy in wireless devices. In a wireless device, two major sources of energy consumption are energy used for computation and energy used for transmission. Computation energy can be reduced by minimizing the time spent on compression and encryption. Transmission energy can be reduced by sending a smaller image file that is obtained by compressing the original highest quality image. Image quality is often sacrificed in the compression process. Therefore, users should have the flexibility to control the image quality to determine whether such a tradeoff is acceptable. It is also desirable for users to have control over image quality in different areas of the image so that less important areas can be compressed more, while retaining the details in important areas. To reduce computations for encryption, a partial encryption scheme can be employed to encrypt only the critical parts of an image file, without sacrificing security. This thesis proposes a scalable and secure image representation scheme that allows users to select different image quality and security levels. The binary space partitioning (BSP) tree presentation is selected because this representation allows convenient compression and scalable encryption. The Advanced Encryption Standard (AES) is chosen as the encryption algorithm because it is fast and secure. Our experimental result shows that our new tree construction method and our pruning formula reduces execution time, hence computation energy, by about 90%. Our image quality prediction model accurately predicts image quality to within 2-3dB of the actual image PSNR

Automatic Source Code Specialization for Energy Reduction

This paper presents a framework to reduce the computational eort of software programs, using value pro ling and partial evaluation. Our tool reduces computational eort by specializing a program for highly expected situations and such a reduction translates into both energy and performance improvement. Procedure calls executed frequently with same parameter values are de ned as highly expected situations (common cases). The choice of the best transformation of common cases is achieved by solving three search problems. The rst identi es eective common cases to be specialized, the second searches for an optimal solution for eective common case, and the third examines the interplay among the specialized cases. Our technique improves both energy consumption and performance of the source code up to more than twice and in average about 25% over the original program. Also, our pruning techniques reduce the searching time by 80% compared to exhaustive approach