An Adaptive Network Coded Retransmission Scheme for Single-Hop Wireless Multicast Broadcast Services

네트워크 코딩(Network Coding)은 통신망의 성능 향상에 도움을 줄 수 있으나 이의 소프트웨어적 구현은 부호화/복호화 단계에서 매우 큰 지연시간을 유발할 수 있어 이를 줄일 수 있는 병렬화된 구현이 필수적이라 할 수 있다. 본 논문에서는 랜덤 리니어 네트워크 코딩(Random Linear Network Coding)과 랜덤 리니어 네트워크 코딩의 단점을 보완하고자 최근 제안된 파이프라인 네트워크 코딩(Pipeline Network Coding)의 병렬처리 성능을 비교한다. 또한, 네트워크 코딩의 CPU에서의 병렬처리 기법과 GPGPU(General Purpose Graphics Processing Units)에서의 병렬처리 기법을 비교하여 네트워크 코딩의 사용 시 그 파라미터에 따라 적절한 병렬처리 기법을 선택할 필요성이 있음을 보여준다. Network coding has been shown to improve various performance metrics in network systems. However, if network coding is implemented as software a huge time delay may be incurred at encoding/decoding stage so it is imperative for network coding to be parallelized to reduce time delay when encoding/decoding. In this paper, we compare the performance of parallelized decoders for random linear network coding (RLC) and pipeline network coding (PNC), a recent development in order to alleviate problems of RLC. We also compare multi-threaded algorithms on multi-core CPUs and massively parallelized algorithms on GPGPU for PNC/RLC.

As a substantial means for improving throughtput, network coding has recently attracted much attention to apply in wireless multicast services. To guarantee the reliable multicast, packet retransmission schemes are employed. With one source, network coding has been well studied for the reliable multicast. But for the multicast cell with two sources, the presented schemes are not good enough to approach an impressive effect with the multiple receivers, demands and link situations. In this paper, for the 2-1-(D1,D2) multicast cell, which has two sources, one relay and two groups users with the receivers numbers of D1 and D2, we propose three schemes to reduce the number of retransmission, which combine the lost packets and retransmit them with network coding, and obtains the least number of retransmissions. Some theoretical results are derived on the bandwidth efficiency of the traditional automatic repeat-request scheme (ARQ), network coding with ARQ scheme (XOR-ARQ) and the improved network coding with ARQ scheme (iXOR-ARQ). Compared with ARQ and XOR-ARQ, iXOR-ARQ is more advantageous on the bandwidth efficiency and the coding gain, which has been confirmed by both simulations and theoretical analysis.

Network coding has recently been applied to wireless networks and has achieved some initial success. Researches in wireless network coding have been mostly focusing on utilizing the broadcast nature of the wireless networks. In this paper, we propose a novel network coding framework for wireless relay networks that also takes into consideration the fading and error prone nature of the wireless networks. First, we extend the traditional network coding in lossless networks which operates on 0-1 bits, to a new framework which defines network coding on the posterior probability of each bit. This new framework allows an imperfect decode-recode process at a relay node and avoids possible error propagation when a hard decision is made at the relay node. It implicitly integrates decode-and-forward and estimate-and-forward strategies for wireless network coding to address the technical issues of channel fading and transmission errors. The proposed approach is validated through both theoretical analysis and extensive simulations. Both analysis and simulation confirm that this new framework is able to achieve significant gain over traditional network coding. This new framework also enables the introduction of adaptive scheme into network coding. We demonstrate a basic adaptation scheme and present some preliminary experimental results. The proposed adaptive scheme will lay down an essential foundation in this emerging field of wireless network coding in order to address issues related to link heterogeneity.

Recently, it has been proven that retransmission based on Network Coding (NC) can greatly improve the performance of wireless networks with broadcast erasure channels. However, network coding also introduces additional delay at the both sending and receiving sides, resulting in the decline of the Quality of user Experience (QoE). In this paper, we consider the users' waiting time and the decoding delay as the performance metrics and then propose MixCode, a NC-based loss recovery method, to improve the delay performance in heterogeneous wireless networks. MixCode incorporates Opportunistic Network Coding (ONC) with Random Linear Network Coding (RLNC), where a NC packet can be decoded by simply XORing operation at some destinations, but by Gaussian elimination at other destinations. Simulation results show that our proposed algorithm can efficiently reduce both the waiting time and the decoding delay in comparison with the existing NC-based schemes.

Chapter 1 - An Introduction to Network Coding

In this paper we propose two adaptive schemes for improving the achievable bandwidth efficiency (BE) of cooperative diversity aided wireless networks. These schemes are capable of accommodating the channel signal-to-noise ratio (SNR) variation of wireless systems by near-instantaneously adapting the uplink transmission configuration. Explicitly, the first adaptive transmission scheme is constituted by a novel reconfigurable four-antenna-aided cooperative uplink space-time block coded (STBC) structure designed for communicating with a base station (BS) equipped with a single receive antenna. By contrast, the second adaptive scheme is constituted by a reconfigurable cooperative uplink vertical Bell Labs layered space time (V-BLAST)-like architecture constituted by single-antenna-aided mobiles communicating with a BS equipped with multiple receive antennas. Our results demonstrate that significant effective BE improvements can be achieved by both systems, while maintaining a target bit-error-ratio of 10-3. Explicitly, when neglecting the Nyquist excess bandwidth, the first system is capable of attaining an effective BE varying between 0.316 bits/sec/Hz and 2.18 bits/sec/Hz, while the second has a BE varying between 2 bits/sec/Hz and 8 bits/sec/Hz.

This paper considers the interplay between rate adaptation and inter-session network coding gains in wireless mesh or ad hoc networks. Inter-session network coding opportunities at relay nodes depend on packets being overheard by surrounding nodes ? The more packets nodes overhear, the more opportunities relays have to combine packets, resulting in a potential increase in network throughput. Thus, by adapting its transmission rate, a node can increase the range over which its packets are overheard, enabling additional opportunities for coding and increased overall throughput. This paper considers inter-session coding, restricted to a single relay (bottleneck) node, or star network topology. Even for such simple topologies the optimal joint rate adaptation and network coding policy is known to be NP-hard. Optimal rate vector selection is a combinatorial optimization problem, which is NP-hard, and finding optimal coding scheme turns out to be a clique partitioning problem which is also NP-hard. So, we provide heuristics to find a suboptimal rate vector and coding scheme. Additionally, we provide a linear programming formulation for network coding when only pairwise intersession coding is allowed. We evaluate the averaged throughput in two different scenarios, in which relays have different access opportunities, giving some intuition on the impact of rate adaptation in lightly and heavily loaded systems. The gains of joint rate adaptation and network coding are marginal when the relay has a higher access opportunity than other nodes, or when the MAC operates ideally it ranges from 9% to 19% as compared to a network without network coding and 4% over a network using regular network coding. While, when the relay has equal access opportunity as other source nodes, which is more typical of todays MAC protocols under heavy loads, the gain ranges from 40% to 62% as compared to the standard relaying case and is upto around 20% as compared to a network with regular pairwise network coding. This can further be increased to a gain of 40% to 120% by replacing pairwise coding with sub-optimal general network coding scheme.

Network coding has been proven with the capability to improve the network bandwidth efficiency for multicast communications. Streaming based IPTV services provided by network operators match the paradigm of using network coding. However, the major research works in the literature focus on the selection of network codes under given routing paths. Few research work jointly considers routing and network coding together to obtain survivable multicast routing and minimum bandwidth provision. In this paper, we investigate this new research topic and propose mathematical models that can be used to obtain an optimal routing for survivable multicast communications against any single link/node failure. To clarify the gain from applying network coding, we also made performance comparisons between the network-coding-based protection schemes and those without using network coding. We observe that the network coding scheme holds the best performance for all cases we had simulated. The trade-offs between the network protection schemes with and without using network coding are also identified in this paper.

Short signature scheme for multi-source network coding

Analysis and scheduling of practical network coding in OFDMA relay networks

In this paper, we present the functional design and experimental validation of network coding technology over hybrid networks including satellite links. We first describe our design framework based on a holistic modelling of (overlay) heterogeneous networking satellite scenarios. We then define different types of logical nodes depending on their encoding, re-encoding and decoding functionalities and whether or not the satellite (overlay) application designer has control over them. Nodes are assumed strategically chosen to recode, which may result in a small number of re-encoding nodes that suffice to optimize selected performance metrics. Our main contribution is a system-oriented functional design of network coding that enables flexible instantiation of different types of network codes via configurable network coding (C-NC) functions. Random or structured NC coefficients can be remotely or locally generated and a packet scheduler can forward packets according to different policies. The choice of coefficients and overall NC scheme depend on the SATCOM-specific performance target, namely delay or bandwidth constraints. Here, we present a preliminary design and experimental testebed validation for the case of delay constrained transmission. Our results show the practical benefits of re-encoding and performance tradeoffs of different network coding schemes. In particular, our results show the good structural properties and delay-reliability tradeoffs of our novel proposal of structured network codes using Pascal matrices due to the regenerative properties of the coding coefficients.

This paper presents a mesh-pull peer-to-peer (P2P) live video streaming system. The proposed XOR-based Network Coding (XOR-NC) system is based on GIA protocol and introduces new search and answer data formats for chunks which are used by the network coding algorithm for exchanging data among peers. The search message contains the XORed GOP (Group of Picture) keys and some meta-data such as search key. The answer message, however, has the XORed GOP data and a summary of video blocks of the encoded GOP. In order to reduce the encoding complexity at each peer, a new content-based cache (CCache) is also introduced. Comparison of LiveCod with traditional GIA and GIA with random network coding demonstrates that this system can achieve a significant improvement in average request delay, video layer providers' fast availability, network throughput and bandwidth redundancy usage performance metrics.

Passive network tomography uses end-to-end observations of network communication to characterize the network, for instance to estimate the network topology and to localize random or adversarial glitches. Under the setting of linear network coding this work provides a comprehensive study of passive network tomography in the presence of network (random or adversarial) glitches. To be concrete, this work is developed along two directions: 1. Tomographic upper and lower bounds (i.e., the most adverse conditions in each problem setting under which network tomography is possible, and corresponding schemes (computationally efficient, if possible) that achieve this performance) are presented for random linear network coding (RLNC). We consider RLNC designed with common randomness, i.e., the receiver knows the random code-books all nodes. (To justify this, we show an upper bound for the problem of topology estimation in networks using RLNC without common randomness.) In this setting we present the first set of algorithms that characterize the network topology exactly. Our algorithm for topology estimation with random network errors has time complexity that is polynomial in network parameters. For the problem of network error localization given the topology information, we present the first computationally tractable algorithm to localize random errors, and prove it is computationally intractable to localize adversarial errors. 2. New network coding schemes are designed that improve the tomographic performance of RLNC while maintaining the desirable low-complexity, throughput-optimal, distributed linear network coding properties of RLNC. In particular, we design network codes based on Reed-Solomon codes so that a maximal number of adversarial errors can be localized in a computationally efficient manner even without the information of network topology.

Broadcasting (communicating information from one to all or many to all nodes in a network) is an important communication primitive. It is used as a building block in many MANET routing protocols, for example. In addition, broadcasting is a key primitive in tactical networks to support to deliver applications of all-informed voice, group push-to-talk, situational information sharing etc. Supporting one-to-all or all-to-all communication patterns in multihop wireless networks efficiently is therefore important. In this paper, we compare efficient broadcasting protocols based on packet forwarding and based on network-coding. Using a number of network scenarios, we derive lower bounds for the required number of packet retransmissions at the MAC layer to support broadcast with and without applying network coding techniques. We compare these lower bounds with each other, as well as with protocols proposed for each approach. More specifically, we use SMF and PDP as sample forwarding-based broadcast protocols, and a multisource random linear network coding protocol as a representative network coding approach. The results show that network coding has advantages over pure packet forwarding. However, none of the existing solutions comes close to approaching their respective lower bounds, leaving much room for new and improved protocols.

This paper presents an efficient data gathering framework of network coding (NC) coupled compressed sensing (CS) in wireless sensor networks (WSNs), called network compressed coding (NCC). We employ network coding to adapt to the dynamic nature of WSNs, such as moving obstacles and link failure. Measurements from sensor networks are often correlated because sensors nodes nearby observe the contiguous phenomenon, and the operation of the random linear network coding (RLNC) scheme is similar to that of the random projection in compressed sensing. Therefore, we introduce compressed sensing into the network coding (NC), to prevent all-or-nothing impact on NC. NCC simultaneously transmits and encodes specific packets of sensor measurements to form random projections for CS recovery. CS technology guarantees that the data gathered at all nodes are accurately recovered with a high probability from a small number of projections, which is less than the total number of source nodes in the network. Our simulation results show that, only less than half number of packets are required to reconstruct measurements with reasonable quality compared with the traditional network coding schemes. Also, NCC increases the data gathering efficiency by over 20% compared to the conventional NC scheme.