1 / 22

UEP Rateless Codes and LT Parameters

UEP Rateless Codes and LT Parameters. Kai-Chao Yang VCLAB, NTHU. Outline. Unequal Error Protection Rateless Codes for Scalable Information Delivery in Mobile Networks (INFOCOM 2007) Rateless codes UEP for rateless codes Simulation results

michon
Télécharger la présentation

UEP Rateless Codes and LT Parameters

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. UEP Rateless Codes and LT Parameters Kai-Chao Yang VCLAB, NTHU

  2. Outline • Unequal Error Protection Rateless Codes for Scalable Information Delivery in Mobile Networks (INFOCOM 2007) • Rateless codes • UEP for rateless codes • Simulation results • Characterization of Luby Transform codes with small message size for low-latency decoding • LT Code Parameters (ICC 2008)

  3. Unequal Error Protection Rateless Codes for Scalable Information Delivery in Mobile Networks Ulaş C. Kozat and Sean A. Ramprashad IEEE INFOCOM 2007

  4. Rateless Codes • Rateless code • Original content  Infinite unique encoding blocks • Overhead (K,): Under probability (1-), receive (1+(K,))K encoding blocks can recover K message blocks • The same source for all senders  • Disregard of heterogeneous receivers and channels  • No need to check missing blocks  • High coding overhead for small content size  • Solution: concatenating many small sized contents to a large content

  5. Rateless Codes • LT Codes • Encoding process • For the ith encoding node, select degree di by Soliton distribution • Choose di input nodes • Perform XOR on chosen nodes • Decoding process • Decode degree-one nodes • Remove degree-one edges iteratively x1 x2 x3 x4 x5 x6 … y1 y2 y3 y4 y5 x2 x1x3 x2x5 x3x5x6

  6. Rateless Codes • Raptor Codes • Pre-codes + rateless codes • Example • LDPC + LT code • Modified Soliton distribution • Decrease probability of low-degree nodes …

  7. The Impact of Input Size • Decoder performance • 1 (in raptor codes) • Rapid change • Bad for small k • 2 (in LT codes) • Progressive change 1000 500 100

  8. Scalable Media • Scalable media • Different importance in the same content • e.g. • Software updates • Advertisements • Multimedia (pictures, audio, and video) • Scalable or layered video Media 1 Media 2 Media 3 Media 4 Layer 1 Layer 2 Layer 3 Layer 4

  9. UEP for Rateless Codes • Parameters • K1: Number of high-priority input nodes • K-K1: Number of low-priority input nodes • 1(N): ratio of unrecovered nodes for high-priority layer after receiving N blocks • 2(N): ratio of unrecovered nodes for low-priority layerafter receiving N blocks • Ni*: minimum number of encoding nodes needed to reach i fidelity • Goal • Minimize N1* and N2* s.t. N1*<<N2*N*

  10. Brute-Force UEP • The receiver download bitstreams separately • Let K1=100, 1*=0.01 and K2=500, 2*=0.1 • Overhead  2 • Let K =600, =0.01 • Overhead  1.3 K1 K2 … … Sender … … … Receiving order 1 2 … … Receiver

  11. UEP at the Rateless Encoding Stage • Type-1 Codes • Weakness • Change of degree distribution (input nodes) • It is likely that d1 = 0 for low-degree encoding nodes K1 K2 … … d1 = min([(K1/K)dkM,K1] d2 = d-d1 … … N. Rahnavard and F. Fekri, “Finite-length unequal error protection rateless codes: Design and analysis,” in IEEE GLOBECOM 2005.

  12. UEP at the Rateless Encoding Stage • Type-2 Codes • No change of Raptor codes (Pre-code + LT code) • Let ri = Ki/Ni • r1 r2  … N1 N2 N3 K1 K2 K3 … … … … … … Standard LT code

  13. UEP at the Rateless Encoding Stage • Pre-code rate • Design goal • 1* << 2* << ½ for K1 << K • Choose pre-coding rate of high priority layer at ½ • The difference between (K, 1*) and (K, 2*) decides the performance

  14. UEP at the Rateless Codes • Drawback (extreme case) • Suppose (K,)= *  K > K*, where * and K* are constant. • Let K1<<K and K2K. Two layers are recovered simultaneously.  1 (1+*)K overhead

  15. Simulation Results • Core layer: ½  r 1 • Enhancement layer: r = 1

  16. Simulation Results • Type 1 vs. Type 2 • K=500 Type 1: d1 = min([(K1/K)dkM,K1] d2 = d-d1

  17. Characterization of Luby Transform codes with small message size for low-latency decoding Elizabeth A. Bodine and Michael K. Cheng ICC 2008

  18. LT Code Parameters • Robust Soliton Distribution • Ideal Soliton distribution • Robust Soliton distribution • Normalization The expected degree-one encoding nodes

  19. LT Code Parameters • Influence of c (Success rate and operations) k=100 k=10

  20. LT Code Parameters • Influence of c and (Average degree and degree-one nodes)

  21. LT Code Parameters • Influence of c (Number of unrecovered input symbols)

  22. Conclusions • Minimize the overhead of LT codes • Reduce c • Minimize the decoding delay of LT codes • Increase c

More Related