Low-Power Wireless Video System

1. Low-Power Wireless Video System Advisor: Professor Alex Doboli Students: Christian Austin Artur Kasperek Edward Safo

2. Objective • Establish a low-power wireless client/server streaming video system. • Use a multimedia standard amenable to wireless networks. • Apply hardware software co-design techniques to reduce the power used by the system’s clients.

3. Hardware/Software Co-Design • Design methodology that splits a computer system’s design between hardware and software in an effort to improve some feature of the system. • Partitioning targets low power consumption in this design. • Achieved by relocating the functionality of high power sections of code to specialized hardware.

4. Project Flow • Decide on a multimedia standard. • Software. • Hardware. • Functional testing and hardware power analysis. • Design software from scratch . • Find and analyze existing software. • Isolate high power sections of software for a hardware port. • Determine a hardware architecture. • Hardware tuning for lower power consumption.

5. Multimedia Standard • MPEG-4 was a good match for the system’s requirements. • What is MPEG-4? • Object based video compression and decoding standard. • New object based compression technique compresses objects, rather than frames. • Objects are distinct entities in a scene; information can be associate with each one. • Builds on previous MPEG and H.263 standards.

6. MPEG-4 Framework

7. Why Use MPEG-4? • Non-proprietary standard. • High compression makes streaming over low bandwidth network practical (e.g. wireless). • Adjustable resolution coding allows for video continuity/quality trade off. • High bit-rate yields better quality video at the expense of lost frames… • Robust error resilience over noisy channels. • Emerging standard. • Superset of previous MPEG standards.

8. Object Based Compression • Video Scenes defined as a composition of objects in space at an instant in time. • Object color defined by pixel chrominance and luminance values; shape is defined by an alpha mask. • Object and bounding rectangle called Video Object Plane (VOP). • Each object compressed separately. • Main reason for improved compression. • Block based encoding scheme extended to handle arbitrary shaped objects.

9. Compression Illustration • Transparent Macroblocks. • Carry no information. • Boundary Macroblocks. • Compressed using block based scheme after padding. • Opaque Macroblocks. • Compressed as is using block based scheme.

10. Software Decisions • Used Open source MPEG-4 client and server software. • Darwin Streaming Server by Apple. • MPEG4IP, an open source project at Sourceforge. • Why Open Source? • Implementation of a video server was not an objective. • Design of software from scratch was not practical given the time constraints.

11. Locating Power Intensive Code • Hardware power measurement. • Accurate measurement requires expensive hardware. • Power measurement using software. • Instruction level power estimation. • SimplePower developed at Penn State. • Software profiling. • No direct power measurements. • Begin looking for high power sections of code in computationally intensive areas of code. • GPROF or Visual Studio.

12. The Inverse Discrete Cosine Transform (IDCT) • Highly utilized code. • Used each time a macroblock is decoded. • Computationally Intensive. • Inherent nested loop structure. • High frequency of memory accesses. • Results in elevated power consumption.

13. IDCT in an MPEG-4 Decoder • An MPEG-4 decoder consists of more than the IDCT

14. Hardware Requirements • An economical FPGA with a large gate equivalence. • A fast interface to the FPGA. • The hardware will implement a time critical function of an MPEG-4 decoder. • Peripheral memory, which the FPGA can use as a buffer for IDCT blocks.

15. Spartan-II 200 PCI Board • 200, 000 gate equivalent Xilinx Spartan-II FPGA. • 32-bit PCI interface. • 8 MB on-board memory. • JTAG interface • ISP PROM

16. PCI Core • PCI was the best solution for a high transfer rate interface. • Need to interface IDCT design to PCI Bus. • Xilinx LogiCore provides a PCI front end for the IDCT design. • Abstracts the details of the PCI specification away from the IDCT design.

17. Hardware Implementation • IDCT hardware design considerations. • Low power is primary concern, but design size and speed are also important. • Procedure. • Design an IDCT architecture in terms of a functional unit block diagram. • Code the design in VHDL. • Write a driver with an API that maps to the hardware’s functions. • Synthesize and place and route the design.

18. IDCT Architecture • Decodes an 8X8 block of IDCT coefficients. • Uses onboard memory as buffer for fetching and storing inputs. • Less CPU intervention. • Performs two 1-D IDCTs. • First half of data path performs 1-D IDCT on each row vector of the 8X8 input macroblock matrix. • Row results stored in an 8X8, transposed, and used as inputs to the second half of the data path. • Second half of data path performs another 1-D IDCT on each of the column vectors of its 8X8 input matrix, completing the 2-D IDCT of the macroblock.

19. Architecture Block Diagram

20. Architecture Features • Pipelined design for increased throughput and power reduction. • Exploits Symmetry of IDCT coefficient matrix. • Breaks 8X8 matrix operation into two 4X4 matrix operations and butterfly operations. • Parallel multiply and addition operations perform two 4X4 matrix multiplications in parallel. • Speed up of IDCT’s repetitive matrix operations.

21. Power Reduction • Clock Isolation. • Add additional logic to isolate sections of logic from the clock when not in use. • Glitch reduction. • Balance the number of synthesized logic levels. • Duplicate resources instead of sharing them. • Increase amount of pipeline registers.

22. Goals and Applications • Demonstrate that a low-power wireless video system is practical. • Design for a power constrained, low bandwidth PDA. • Applications: • Interactive shopping. • Request video of product information while shopping. • Multimedia preview. • Preview movie before buying or renting; watch music video while previewing new album.

23. Any Questions?