Martin Hundebøll

Novel concepts for device-to-device communication using network coding

Device-to-device communication is currently a hot research topic within 3GPP. Even though D2D communication has been part of previous ad hoc, meshed and sensor networks proposals, the main contribution by 3GPP is that the direct communication among two devices is carried out over a dynamically assigned, licensed spectrum; thus, it is under full control of the cellular network. D2D communication creates a market potential for new services, new approaches to efficient spectrum use, and security concepts. This is especially true if D2D communication is extended to larger communication groups organized in meshed clusters. In this article, we discuss the potential and shortcomings of D2D communication as proposed today, advocating for the use of network coding as an enabling technology for enhanced security and communication efficiency using the PlayNCool and CORE protocols as key examples to deliver smarter D2D systems.

CORE: COPE with MORE in Wireless Meshed Networks

State-of-the-art in network coding for wireless, meshed networks typically considers two problems separately. First, the problem of providing reliability for a single session. Second, the problem of opportunistic combination of flows by using minimalistic coding, i.e., by XORing packets from different flows. Instead of maintaining these approaches separate, we propose a protocol (CORE) that brings together these coding mechanisms. Our protocol uses random linear network coding (RLNC) for intra- session coding but allows nodes in the network to setup inter- session coding regions where flows intersect. Routes for unicast sessions are agnostic to other sessions and setup beforehand, CORE will then discover and exploit intersecting routes. Our approach allows the inter-session regions to leverage RLNC to compensate for losses or failures in the overhearing or transmitting process. Thus, we increase the benefits of XORing by exploiting the underlying RLNC structure of individual flows. This goes beyond providing additional reliability to each individual session and beyond exploiting coding opportunistically. Our numerical results show that CORE outperforms both forwarding and COPE-like schemes in general. More importantly, we show gains of up to 4 fold over COPE-like schemes in terms of transmissions per packet in one of the investigated topologies.

CATWOMAN: Implementation and Performance Evaluation of IEEE 802.11 Based Multi-Hop Networks Using Network Coding

This paper investigates the performance of network coding for an IEEE802.11 enabled meshed network. By means of basic setups the impact of the medium access control in combination with network coding is investigated. In contrast to prior work the network coding approach is tailored to commercial WiFi hardware without any special tweaks. The implementation of network coding is done on top of an existing routing scheme known as B.A.T.M.A.N. which has some inherent advantages to support network coding. We present schemes to utilize the B.A.T.M.A.N. routing to detect coding opportunities. One finding is that the performance gain for the well known Alice and Bob scenario using network coding is 60% compared to a pure relaying scheme. The software used in the presented measurement campaign is made publicly available.

Comparison of analytical and measured performance results on network coding in IEEE 802.11 ad-hoc networks

Network coding is a promising technology that has been shown to improve throughput in wireless mesh networks. In this paper, we compare the analytical and experimental performance of COPE-style network coding in IEEE 802.11 ad-hoc networks. In the experiments, we use a lightweight scheme called CATWOMAN that can run on standard WiFi hardware. We present an analytical model to evaluate the performance of COPE in simple networks, and our results show the excellent predictive quality of this model. By closely examining the performance in two simple topologies, we observe that the coding gain results from the interaction between network coding and the MAC protocol, and the gap between the theoretical and practical gains is due to the different channel qualities of sending nodes. This understanding is helpful for design of larger mesh networks that use network coding.

Sharing the Pi: Testbed Description and Performance Evaluation of Network Coding on the Raspberry Pi

This paper presents the design and performance evaluation of an inexpensive testbed for network coding protocols composed of Raspberry Pis. First, we show the performance of random linear network coding primitives on the Raspberry Pi in terms of processing speed and energy consumption under a variety of configuration setups. Our measurements show that processing rates of up to 230 Mbps are possible with the Raspberry Pi. Also, the energy consumption per bit can be as small as 3 nJ/bit, which is several orders of magnitude smaller than the transmission/reception energy use. Surprisingly, overclocking the Raspberry Pi from 700 MHz to 1000 MHz not only produces an increase in processing speed of up to 68 % for large generation sizes, but also provides a reduction of 64 % in the processing energy per bit for most tested scenarios. Then, we show Raspberry Pi as an inexpensive, viable, and flexible platform to deploy large research networking testbeds for the evaluation of network coding protocols. We propose key parameters and representations to evaluate protocol performance in network nodes as well as validating the testbeds statistics using the case of a one-hop broadcast with random linear network coding, which is well understood in theory.

Energy consumption model and measurement results for network coding-enabled IEEE 802.11 meshed wireless networks

This paper presents an energy model and energy measurements for network coding enabled wireless meshed networks based on IEEE 802.11 technology. The energy model and the energy measurement testbed is limited to a simple Alice and Bob scenario. For this toy scenario we compare the energy usages for a system with and without network coding support. While network coding reduces the number of radio transmissions, the operational activity on the devices due to coding will be increased. We derive an analytical model for the energy consumption and compare it to real measurements for which we build a flexible, low cost tool to be able to measure at any given node in a meshed network. We verify the precision of our tool by comparing it to a sophisticated device. Our main results in this paper are the derivation of an analytical energy model, the implementation of a distributed energy measurement testbed conducting a series of measurements, and finally a comparison of the analytical energy model and the data achieved by our testbed.

On the Coded Packet Relay Network in the Presence of Neighbors: Benefits of Speaking in a Crowded Room

This paper studies the problem of optimal use of a relay for reducing the transmission time of data packets from a source to a destination using network coding. More importantly, we address an effect that is typically overlooked in previous studies: the presence of active transmitting nodes in the neighborhood of such devices, which is typical in wireless mesh networks. We show that in systems with a fair medium access control mechanism (MAC), the use of a relay in a crowded medium brings forth considerable and unforeseen improvements, including up to 3.5x gains in terms of throughput compared to using only the direct link in some of our examples, and a considerable extension of the operating region where using a relay is beneficial. The problem is formulated as a Markov Decision Process (MDP) and numerical results are provided comparing simple, close-to-optimal heuristics to the optimal scheme.

Energy and data throughput for asymmetric inter-session network coding

In this paper we investigate the impact of asymmetric traffic patterns on the energy consumption and throughput in a wireless multi hop network. Network coding is a novel technique for communication systems and a viable solution for wireless multi hop networks. State of the art research is mainly focusing on ideal scenarios with symmetric traffic patterns that are not realistic in a real life scenario. The main contribution of this paper is the investigation of the asymmetric traffic patterns in terms of throughput and energy consumption, and a validation of these results by real measurements on commercial platforms. The outcome of this paper confirms the analytical expression, and the results shows that even with a large asymmetric data rate there is a gain in terms of energy consumption and throughput when network coding is applied in compare to the case when network coding is not applied.

Impact of network coding on delay and throughput in practical wireless chain topologies

In this paper, we present results from a practical evaluation of network coding in a setup consisting of eight nodes deployed in a chain topology. With the tradition pure relaying, delay increases dramatically as the network gets congested, and here network coding helps to moderate this increase in delay, as well improving throughput. The practical evaluation shows that network coding provides up to a five-fold decrease in delay, while retaining the expected gain in throughput. To address an unecessary delay when using network coding in low-load scenarios, we propose and evaluate a scheme for adaptive buffering. With this, we show that the benefits from pure relaying can be combined with the improved performance from network coding. The software used to apply network coding and evaluate this in a practical network is made publicly available for further research and tests.

Reliable Communication in Wireless Meshed Networks Using Network Coding

The advantages of network coding have been extensively studied in the field of wireless networks. Integrating network coding with existing IEEE 802.11 MAC layer is a challenging problem. The IEEE 802.11 MAC does not provide any reliability mechanisms for overheard packets. This paper addresses this problem and suggests different mechanisms to support reliability as part of the MAC protocol. Analytical expressions to this problem are given to qualify the performance of the modified network coding. These expressions are confirmed by numerical result. While the suggested reliability mechanisms introduce some signaling overhead, the results show that the performance is yet improved.