Bottleneck Discovery and Overlay Management in Network Coded Peer-to-Peer Systems

The performance of peer-to-peer (P2P) networks depends critically on the good connectivity of the overlay topology. In this paper we study P2P networks for content distribution (such as Avalanche) that use randomized network coding techniques. The basic idea of such systems is that peers randomly combine and exchange linear combinations of the source packets. A header appended to each packet specifes the linear combination that the packet carries. In this paper we show that the linear combinations a node receives from its neighbors reveal structural information about the network. We propose algorithms to utilize this observation for topology management to avoid bottlenecks and clustering in network-coded P2P systems. Our approach is decentralized, inherently adapts to the network topology, and reduces substantially the number of topology rewirings that are necessary to maintain a well connected overlay. Moreover, this is done passively during the normal content distribution. This work demonstrates another value of using network coding and complements previous work that showed network coding achieves high utilization of the network resources

Processing along the way: forwarding vs. coding

We consider a source that transmits to a receiver by routing the information packets over a communication network and examine rate benefits that finite complexity processing at the intermediate nodes may offer. We show that the processing capabilities of the intermediate nodes affect not only the end-to-end achievable rate, but also the optimal routing strategy. For example, there exist network configurations where the maximal throughput is achieved only by coding across independent information streams

Bit vs. Symbol Interleaving for Parallel Concatenated Trellis Coded Modulation

This paper compares bit versus symbol interleaving for parallel-concatenated trellis-coded turbo codes, employing the turbo encoder structure proposed in Benedetto et al., (1996). To compare systems optimized with the same techniques, the paper extends the turbo-encoder design procedure proposed in Fragouli et al. (2001), to bit-interleaved systems. We discuss a method to jointly design the multiple required interleavers for the bit-interleaved system, and a procedure to select constituent encoders that can take advantage of the interleaver structure to achieve a low error floor. Simulation results for the designed bit-interleaved system show better performance than bit-interleaved performance reported in the literature. The symbol-interleaved system though achieves an earlier convergence, especially with an increased number of decoder iterations, but at the cost of a slightly higher error floor

Symbol interleaved parallel concatenated trellis coded modulation

This paper presents a method for efficient coding at high spectral efficiency using parallel concatenated trellis coded modulation (PCTCM) with symbol interleaving. The constituent encoders are optimized for symbol-wise free distance, and each has an infinite symbol-wise impulse response. In many cases of practical interest, the optimal structure for these constituent encoders connects the memory elements in a single row. Simulation results show that the performance is as close as 0.5 dB to the constrained capacity

Turbo Encoder Design for Symbol Interleaved Parallel Concatenated Trellis Coded Modulation

This paper addresses turbo-encoder design for coding with high spectral efficiency using parallel concatenated trellis-coded modulation and symbol interleaving. The turbo-encoder design involves the constituent encoder design and the interleaver design. The constituent encoders are optimized for symbol-wise effective free distance, and each has an infinite symbol-wise impulse response. We identify the canonical structures for the constituent encoder search space. In many cases of practical interest, the optimal structure for these constituent encoders connects the memory elements in a single row. This single row generally applies to turbo code constituent encoders for parallel concatenation and is not restricted to symbol interleaving. To lower the error floor, a new semi-random interleaver design criteria and a construction method extends the spread-interleaver concept introduced by Divsalar and Pollara (1995). Simulation results show that the proposed system employing symbol interleaving can converge at a lower signal-to-noise ratio than previously reported systems. We report simulation results between 0.5 and 0.6 db from constrained capacity for rates of 2 and 4 bits/s/Hz

Serially concatenated coding for broadcasting S-UMTS applications

Satellite-UMTS supports broadcast applications that involve transmission of the same encoded data over channels that may vary significantly. The same code must allow a user with a good channel to recover the information with low complexity, while a user with a bad channel should still be able to achieve an acceptable BER at the cost of increased complexity and/or decoding delay. To this end, we propose serially concatenated multilevel code structures that employ PSK modulation. The receiver has the flexibility to achieve turbo-code, trellis-code or uncoded performance, depending on the decoding effort. Design considerations include the constituent encoder design and the use of a non-uniform constellation. Simulation results investigate the system's performance and highlight different parameters trade-offs

Semi-random interleaver design criteria

A spread interleaver of length N is a semi-random interleaver based on the random selection without replacement of N integers from 1 to N under a design constraint. This paper extends the spread-interleaver design method to multiple error events, based on the interleaver's role in overall turbo code error event distances. The extension helps to explain why the spread interleaver is specifically designed to be semi-random. Simulation results show the performance achieved for a symbol-interleaved parallel concatenated trellis coded modulation (PCTCM) scheme