Kyoungwoo Lee, Minyoung Kim, Nikil Dutt, and Nalini Venkatasubramanian Error-Exploiting Video Encoder to Extend Energy/QoS Tradeoffs for Mobile Embedded Systems Kyoungwoo Lee, Minyoung Kim, Nikil Dutt, and Nalini Venkatasubramanian Department of Computer Science University of California at Irvine

DIPES ’08 Strategy 25 mins talk and 5 min QnA Very broad audience 10 to 15 mins for motivation and problem background High level presentation Technical depth is not that high, and deep technical highlights are in the backup slides

Outline Motivation and Problem Statement Our Solution Experiments Conclusion

Energy Reduction is Essential Battery-Operated Mobile Embedded Systems Energy reduction is essential in battery-operated mobile embedded systems Mobile video applications demand high energy consumption Complex video encoding algorithms incur high overheads in terms of performance and power Network Mobile Video Applications

Active Error Exploitation Network f1 f4 f3 f2 Active Error Exploitation – Intentional Frame Dropping Skip the expensive video encoding algorithm  Energy saving Degrade the video quality Inherent error-tolerance mitigates the impact of frame drops on video quality

Frame Drop Types Intentional Frame Drop (one way to actively exploit errors) can result in energy reduction for each operation FDT-1 affects the following components with respect to power, performance, and QoS in mobile video applications Error-prone Networks Mobile Video Application Enc Tx Rx Dec CPU WNI WNI CPU FDT-1 FDT-2 FDT-3 FDT: Frame Drop Type Enc: Encoding, Dec: Decoding WNI: Wireless Network Interface Packet Loss

Inherent Error-Tolerance of Video Data Spatial and temporal correlation among consecutive video frames Lossy video encoding (e.g.) High Quantization Scale Energy Reduction and Error-Tolerance Error-tolerance can be used for energy reduction (e.g.) partial ME vs. Full ME One frame loss may not be noticed by users (e.g.) One frame loss out of 30 frames per second Mobile Video Encoding ME DCT Q EE ME – Motion Estimation DCT – Discrete Cosine Transform Q – Quantization EE – Entropy Encoding

Frame Losses due to Packet Losses Mobile Video Applications f1 f4 f3 f2 f3 f2 f1 Error-Prone Network f4 is lost Error-Induced Video Data Inherent Error-Tolerance of Video Data Error-Resilient/Error-Concealment Techniques

Error-Induced Video Data Error-Resilience f1 f4 f3 f2 f3 f2 f1 Error-Prone Network f4 is lost Error-Induced Video Data Error-Resilient Techniques Insert Intra-frames (I-frames) periodically (e.g.) GOP-10 inserts I-frame every 10 P-frames Intra Refresh video encoding techniques (e.g.) PBPAIR (Probability Based Power Aware Intra Refresh) encodes video data resilient against 25% frame loss rate (1 frame out of 4 frames)

Error-Induced Video Data Energy Efficiency f1 f4 f3 f2 f3 f2 f1 Error-Prone Network f4 is lost Error-Induced Video Data Energy-efficient error-resilient video encodings (e.g.) PBPAIR or Probability-Based Power Aware Intra Refresh [Kim, MCCR06] It may improve not only the video quality but also energy consumption

Outline Motivation and Problem Statement Our Solution Experiments Error-Exploiting Video Encoding EE-PBPAIR Experiments Conclusion

Our Proposal Error-exploiting video encoder Intentional frame dropping + error-resilient video encoding Extends the tradeoff space for energy consumption / QoS

Error-Resilient Video Encoder Data Original Video Data Error-Resilient Encoder Parameters

Error-Exploiting Video Encoder Injected Video Data Error- Aware Video Data Original Video Data Error-Injecting Unit Error-Canceling Unit Error Controller Error-Resilient Encoder Constraints Parameters & Feedback

Intentional Frame Dropping and PBPAIR Error-Induced Video Data f1 f4 f3 f4 is lost Error-Prone Network Intentional Frame Dropping PBPAIR EE-PBPAIR Error-Injecting Unit Error-Canceling Unit f2 is dropped Energy Efficiency Frame Dropping (e.g.) f2 is dropped PBPAIR Quality Management Error-Resilience (e.g.) EE-PBPAIR encodes video data resilient against f2 and f4 Error-Tolerance

EIR – Error Injection Rate EE-PBPAIR Error- Aware Video Data Original Video Data Error-Injecting Unit Error-Canceling Unit Frame Dropping PBPAIR Quality Constraint and Quality Feedback Parameters EIR EIR adjusts the rate of intentional frame dropping EIR is translated for PBPAIR (considering it as PLR) Feedback-based quality adjustment High EIR increases energy saving but degrades video quality

Outline Motivation and Problem Statement Our Solution Experiments Conclusion

End-to-End Experimental Framework Mobile video applications such as video conferencing consist of mobile encoding, wireless(and wired) networks, and mobile decoding They affect each other in terms of energy consumption and QoS System Prototype and NS2 Simulator System Prototype Runs video encoding and decoding on system prototype emulating mobile devices, and returns video quality in PSNR Estimates the energy consumption of a processor (CPU power) NS2 Network Simulator Estimates the energy consumption of WNI (transmission power)

Experimental Setup System System NS2 Prototype Prototype Mobile Video Encoding Mobile Video Decoding Encoder Transmit Transmit Encoder Network System Prototype System Prototype NS2 CPU energy for encoding video quality (frame drop) CPU energy for encoding video quality (packet loss) WNI energy for transmit WNI energy for receive

Evaluation Video Encoding Energy Consumption Video Quality GOP-K PBPAIR EE-PBPAIR Energy Consumption Enc EC (Energy Consumption for Encoding) + Tx EC (Energy Consumption for Transmission) Rx EC (Energy Consumption for Receiving) + Dec EC (Energy Consumption for Decoding) Video Quality Video Quality at encoder after intentional frame dropping Video Quality at decoder after packet losses in networks

Experimental Results Energy Reduction from Active Error Exploitation Extended Energy/QoS Tradeoff

Extended Tradeoff Space PLR = 5% and EIR = 0% to 50% EE-PBPAIR extends interesting tradeoff spaces

PSNR: Peak Signal to Noise Ratio Energy Saving EC = Energy Consumption Enc EC = EC for Encoding Tx EC = EC for Transmission Dec EC = EC for Decoding Rx EC = EC for Receiving PLR = 10% and EIR = 10% Energy saving occurs at every component in a path from encoding to decoding in mobile video applications PSNR: Peak Signal to Noise Ratio

Energy Reduction at QoS Cost At 10% cost of video quality, EE-PBPAIR can save the energy consumption of Enc and Tx by up to 49%

Outline Motivation and Problem Statement Our Solution Experiments Conclusion

Conclusion Future Work Intentional Frame Drop is one way to exploit errors actively Propose an error-aware video encoding (EE-PBPAIR) Intentional frame dropping and the nature of energy-efficiency of PBPAIR reduces the energy consumption for video encoding Present a knob (EIR) to adjust the amount of errors considering the QoS feedback Maintain the video quality using error-resilience of PBPAIR Future Work Intelligent Frame Dropping Techniques Extend Active Error Exploitation to the system level with error-aware architecture and network protocols in distributed embedded systems

Any Questions? kyoungwl@ics.uci.edu Thanks! Any Questions? kyoungwl@ics.uci.edu Thank you! Any questions?

Backup Slides

Intentional Frame Drop and Packet Loss Error-prone Networks Packet Loss Intentional frame drop

Error-Exploiting Video Encoder EE-PBPAIR Error-prone Networks Intentional frame drop Packet Loss Error-Exploiting Video Encoder Error- Resilient Video Error- Aware Video Original Video Error-Controller (e.g., frame dropping) Error-Resilient Encoder (e.g., PBPAIR) EIR

Error Controller

Error-Induced Video Data Error-Concealment f1 f4 f3 f2 f3 f2 f1 Error-Prone Network f4 is lost Error-Induced Video Data Error-Concealment Techniques Interpolate the lost frame using near frames Substitute the near frame for the lost one (e.g.) f2 is copied for f3 (the lost one) in displaying frames

GOP (Group of Picture) Standard H.263 Video Encoder with varying IP-ratio Higher IP-ratio generates more compressed video output, which consumes more energy Encoder GOP Intra Frame Static Constraint of Compression Rate IP-ratio (KNOB) Standard video encoding, which is unaware of energy consumption and error-resiliency

PBPAIR Proactively estimate the probability of the correctness, and adapt the intra_th (KNOB) based on the current network PLR (Packet Loss Rate) Encoder PBPAIR Intra MB PLR from Network Channel Intra_Th (KNOB) Error-Resilient Encoding, which can satisfy a given PSNR, and reduce the energy consumption for encoding

EE-PBPAIR EE-PBPAIR introduces another KNOB (intentional EIR) other than Intra_Th, and can further save the energy consumption Encoder EE-PBPAIR Intra MB PLR from Network Channel I-FS Intentional EIR (KNOB) Intra_Th (KNOB) Error-Introduced Video Encoding, which can still satisfy a given PSNR, and further maximize the energy saving compared to PBPAIR

System Prototype + NS2

Adaptive EE-PBPAIR