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Beyond the bits – co operative packet recovery
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Transcript of Beyond the bits – co operative packet recovery
Beyond The Bits – Co Operative Packet Recovery
Grace Woo,Pouya Kheradpour,Dawei Shen,Dina Katabi @ MIT
Presented By : Venkata Nanda KishoreUBID: 3764-8659
OUTLINE
• Introduction• Related Work• Architecture• Combining Algorithm• DSSS• Estimating the Variance• Reducing Overhead • Implementation• Results• Conclusion
Abstract and Introduction
• Dead Spots• Loss Rate• Addressing these problems-Physical Layer info• SOFT
Related Work
• SPATIAL DIVERSITY: -Similar to Softer Handoff -Less Overhead -Different Modulation Schemes• SOFT DECODING:– Also used in RS codes and LDPC– Focuses on Compatibility,practical
Networks,Experimental Results
Bit-Math : Exploiting Spatial Diversity
• BER: 0.001• Packet Size:1500B=12000bits• Here,Probability that a node receives a
correctly transmitted packet. …..????• Combining physical layer information using
SOFT increases this to 0.99
SOFT SYSTEM ARCHITECTURE
• Sits between MAC, between Physical and Data Link Layer
• Combining Packets occur both on UPLINK and DOWNLINK
• Considers ONLY BINARY MODULATION
UPLINK
• Leverage the high bandwidth of Ethernet• AP to COMBINING AGENT• Invoking COMBINING procedure
-Identify packets-Hash table-Redundancy
• Decoding: Two options: Forward or Combining Agent
DOWNLINK
• EXPLOITS TIME DIVERSITY• Rest of the procedure is similar to UPLINK
ACKs Retransmission & Reordering
• Receiver sends synAck for a correctly received packet and communicates correctly to Combining agent
• If faulty packet arrives,it sends an asynchronous Ack to sender
• No Reordering on DOWNLINK• UPLINK orders the packets using packet_id• Also uses forwarding_time
COMBINING ALGORITHM
• How to combine the s-packets? >= 0Here, is the noise variance in i th AWGN channel
DSSS
• Direct Sequence Spread Spectrum• Eg. 1 - 11100010101 0 - 00011101010STEPS:1. Spreading2. De-spreading
Can this be efficient?
(-)/>=0
Here,y correspond to same codewords.X correspond to either codeword sent for logical 1 or logical 0.
Estimating Noise Variance
=hx+h is attenuationY is the sv-value of bitn is guassian noise
Reducing Overhead
• Currently:10Gb/s Ethernet (10GbE)• Working on 100GbE• Depends on how we express SVApproach: 3 bits – 1 for sign,2 for magnitudeAlso,provide cut-offs.
IMPLEMENTATION
• SDR: Software Defined Radios
• Uses GMSK- Gaussian Minimum Shift Keying
• Also tested with DBPSK-Differential Binary Phase Shift Keying.
Experimental Results:Compared Approaches
• SOFT• Max Confidence• Majority Vote• Current Approach• MRD
Experimental Results:Metrics
• Packet Delivery Rate• No of Retransmissions
Importance of Soft Values
Role Of Combining Rule
Experimental Results Cont.
• Impact of Noise Variance
• Impact of quantization
• BER
Conclusion
• Existing protocols are inadequate• We have seen SOFT (Its approach,
implementation and results)• Novel ideas due to temporal and spatial diversity• Soft increases mean packet deliver and reduces
retransmissions.
Thank You!
Questions/Comments/Suggestions??