Vijay Anandrao Suryavanshi

Resilient packet header compression through coding

Header compression saves bandwidth, but it also introduces error propagation whenever packets are lost. We propose to use error correcting codes on the compressed packet headers. The result is an overall system that maintains most of the bandwidth savings of header compression and yet is robust with respect to errors. The key to achieving this tradeoff is appropriate distribution of parity symbols across the packets. The proposed system performs better than ordinary header compression and as well as the TWICE algorithm. In most cases, the effects of the error propagation can be almost removed, such that the end-to-end packet loss rate is similar to a system with no header compression, while the bitrate savings are largely maintained.

A Hybrid ARQ Scheme for Resilient Packet Header Compression

In this work we address resilient packet header compression in a setup similar to RFC 3095 (robust header compression - ROHC), where a noisy feedback channel is available. We propose a new predictive hybrid ARQ (HARQ), using a systematic convolutional code with delay-limited interleaving. The compressed packet headers are bit interleaved, encoded, and the parity bits are loaded onto the packets in a manner that is consistent with existing standards. Our HARQ design is distinct from previous ones in that it cannot wait until the end of a codeword for retransmission, rather, ARQs corresponding to individual packet headers arrive continually during a convolutional codeword and must be processed at that time. In our system, each time a NACK is encountered, the encoder estimates the state of the Viterbi decoder, deciding when a retransmission is necessary. The use of coding in conjunction with a specially designed interleaver, provides a flexible and powerful design methodology that makes it possible to improve the throughput via FEC and interleaving, while strictly limiting the delay to avoid timeout in higher layers. Simulations show that the throughput of the resulting system is superior to ROHC, and the delay is less sensitive to the channel conditions. Furthermore, over a large part of the operating range the delay is comparable to, or smaller than, the delay of RQHC

Convolutional coding for resilient packet header compression

This paper proposes a system using convolutional codes to mitigate error propagation in packet header compression. Convolutional codes are a class of forward error correction (FEC) codes, and their use is motivated because on uni-directional links loss of even one packet can render subsequent packets useless. A combination of two interleavers is used to address channel memory and increase the power of the code, and the optimum yet computationally efficient Viterbi algorithm is used for decoding at the receiver. Simulation results demonstrate the advantages of the proposed scheme.

Error-resilient packet header compression

Full packet headers consume valuable bitrate, which is especially costly in satellite links and some terrestrial wireless links. This has motivated the compression of packet headers by exploiting their correlation via using finite-state machines. The drawback is that compression in the presence of channel errors (packet loss) may result in error propagation. We offer several designs by adapting error control codes for the requirements of packet header compression in uni-directional and bi-directional links, and explore the tradeoffs in complexity, delay, and system performance. For the bi-directional link, we propose a new design called predictive hybrid ARQ and evaluate its performance. Experiments show significant gains in link-layer throughput as well as improved application layer performance demonstrated via video transfer experiments.