pôle SIS / Cross-layer approaches in networks

Pôle SIS (Signal, Images et Systèmes)

Pôle SIS (Signal, Images et Systèmes)

Cross-layer approaches in networks
The networking activites of SIS are mainly carried out in SigNet. The SigNet group is aimed at proposing a new architecture, fully compliant with current IP networks, for fixed/mobile wireless networks. This new architecture will allow the deployment of cross-layer protocols, from the Transport layer to the Physical layer. The most recent technologies are being applied to this new architecture, like MIMO system with directional antennas, network coding paradigms and routers-assisted transport protocols with context-aware capabilities.

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Cross-layer approaches in networks NEWS

Signal processing for communications has been instrumental in the development of wireless networks, for example the introduction of MIMO (Multiple Input Multiple Output, i.e. multiple antennas at the transmitter and multiple antennas at the receiver) has significantly increased the capacity of wireless links and hence networks. Unfortunately, the huge capacity gains on the link level does not scale at the network level, either for fundamental reasons that can be formalized by network information theory, or for technical reasons, in particular when high layer protocols are not specifically designed with the wireless channel in mind. Taking this two aspects in mind, as well as the opportunity given by the recruitement of to associate professors in networking at IUT and EPU as well as a professor in networking at EPU, I3S has decided to promote an activity which is at the frontier between “signal processing for communications” (more broadly Physical Layer related research) and networking, mainly in the frame of wireless networks. Main people involved in this activity are Jérôme Lebrun and Luc Deneire, who are active in signal processing for communications, Dino Lopez, who is active in networking, Lucile Sassatelli, who is active in both communication theory and networking and Guillaume Urvoy-Keller (recruited in september 2010) who is active in networking.
The current activities are:

Transport and routing protocols for wireless mobile ad hoc networks
This starting activity has been awarded an “ANR jeunes” project, led by Lucile Sassatelli.
The main target of this activity is the so-called MANET (Mobile Ad-hoc Networks), which is made of mobile users, mostly without the help of an infrastructure (no base stations). Owing to node mobility and device heterogeneity, connectivity between nodes is intermittent, leading to volatile networks. To cope with volatility, new internet architectures and protocols have to be developed. Networks that cope with this volatility are named Delay Tolerant (DT) networks.
The main challenges of these DT-MANETs are the design of an architecture and protocols that work well in an environment characterized by uncertain networking conditions, high mobility and frequent network partition. Specifically, one has to design transport and routing protocols for DT-MANETs, but also determine the capacity of the DT-MANETs.
The major novelty of the approach proposed, besides the inherent cross-layer nature of the problemis the use of network coding. Network coding is a (by now popular in the research community) technique that takes advantage of linear combination of data to lower the global resources needed to transfer data in a network. This technique has proved to be beneficial in specific transport layer design for wireless networks and we want to investigate further its benefits for DT-MANETs.

Transport protocols for large and dynamic bandwith/delay produc networks
This activity has been supported by a master thesis and is led by Dino Lopez.
The complete independence of the End-to-End (E2E) protocols to the network infrastructure, allow their incremental deployment in heterogeneous IP networks, such as the Internet. The commonly used E2E protocols is TCP NewReno (referred to as, simply, TCP) as it provides the best performance in terms of link usage, fairness and congestion control in wired networks with low bandwidth (less than 100Mbps) and low latency (less than 150ms of base RTT). However, the interconnection of networks and the introduction of new technologies, have lead to the creation of networks with long delay and/or high bandwidth (known as large bandwidth-delay product -BDP- networks). In such a large BDP network, TCP is unable to grab all the available resources. Moreover, the use of wireless networks change the nature of the links, which become much more dynamic than the wired links. To fully utilize the resources in large BDP networks, several approaches have been proposed. For instance, high speed versions of TCP, TCP versions with delay-based techniques to detect the under-utilization of the resources (e.g. TCP Vegas), and Explicit Rate Notification (ERN) protocols, where the routers inform the sender about the maximum achievable rate (e.g. XCP). However, high speed and delay-based TCP versions introduce inter and intra protocol unfairness. On the other hand, Explicit Rate Notification (ERN) protocols have demonstrated a very high performances and fairness. Moreover, the ERN protocols are not compliant with current network protocols, limiting their use to experimental networks.
The main goal of this activity is hence to propose transport protocols that can cope with large BDP networks, that are interoperable with the other TCP versions and that can cope with the (by now classical) problems encountered in the wireless segments.

Continuous phase space-time coded modulation
This ongoing activity was supported by a PhD project and is led by Jérôme Lebrun.
Continuous phase space-time coded modulation. To combine the power efficiency of Continuous Phase Modulation (CPM) with enhanced performance in fading environments, the use of CPM in combination with Space-Time Codes (STC) has recently been suggested [38G. Wang and X.-G. Xia. An orthogonal space-time coded CPM system with fast decoding for two transmit antennas. IEEE Trans. Inf. Theory, 50(3):486 – 493, March 2004.]. In this activity, we will further investigate our recently developed CPM ST-coding schemes based on L2 -orthogonality. In [15M. Hesse, J. Lebrun, and L. Deneire. L2 Orthogonal Space Time Code for Continuous Phase Modulation. In IEEE Workshop on Signal Processing Advances for Wireless Communications, (SPAWC’08), pages 1–5,
Recife, Brazil, 2008. http://hal.archives-ouvertes.fr/inria-00288334/en/., 14M. Hesse, J. Lebrun, and L. Deneire. Full Rate L2-Orthogonal Space-Time CPM for Three Antennas. In IEEE Global Telecommunications Conference, (GLOBECOM’08), pages 1–5, New Orleans, LA, USA, 2008.
http://hal.archives-ouvertes.fr/inria-00362141/en/., 16M. Hesse, J. Lebrun, and L. Deneire. Optimized L2-Orthogonal STC CPM for 3 Antennas . In Proc. IEEE International Symposium on Wireless Communication Systems, (ISWCS’08), pages 463– 467, Reykjavik, Iceland, 2008. http://hal.archives-ouvertes.fr/inria-00362167/ en/.], we already constructed a family of L2-orthogonal codes coined Parallel Code (PC). Now, by switching to multi-h CPM modulations [ 29E. Perrins and M. Rice. Optimal and reduced complexity receivers for m-ary multi-h cpm. In 2004 IEEE Wireless Communications and Networking Conference, pages 1165–1170, Atlanta GA, USA, March 2004.], we plan to generalize further these designs to non-parallel codes (typ. crosswise mapping [13M. Hesse. L2-orthogonal Space-Time Code Design for Continuous Phase Modulation.
PhD thesis, Université de Nice Sophia-Antipolis, 2010.]). We will also study the use of convolutional codes (LDPC type) [25R. Maw and D. Taylor. Space-time coded systems using continuous phase modulation.
IEEE Trans. Comm., 55(11):2047–2051, November 2007.] in the design of CPM based MIMO systems so as to alleviate some difficulties in the design of non-parallel codes. We also detailed in [17M. Hesse, J. Lebrun, L. Lampe, and L. Deneire. Separable implementation of L2-orthogonal STC CPM with fast decoding . In International Conference on Communications, (ICC’09), pages 1–5,
Dresden, Germany, 2009. http://hal.archives-ouvertes.fr/inria-00364952/en/.] that by using L2 -orthogonality, the decoding complexity, usually exponentially proportional to the number of transmitting antennas, can be reduced to linear complexity. However, some practical considerations such as synchronization [6G. Colavolpe and R. Raheli. Reduced-complexity detection and phase synchronization of cpm signals.
IEEE Trans. Comm., 45(9):1070–1079, 1997.] remain to be thoroughly studied in order to provide robust implementations of our CPM based MIMO systems. A major achievement in our designs is that the systems based on this family of codes have full rate and achieve full diversity. Furthermore, unlike classical pointwise-orthogonality based STC, the proposed code designs display no restriction when extended to three and more transmit antennas [14M. Hesse, J. Lebrun, and L. Deneire. Full Rate L2-Orthogonal Space-Time CPM for Three Antennas. In IEEE Global Telecommunications Conference, (GLOBECOM’08), pages 1–5, New Orleans, LA, USA, 2008. http://hal.archives-ouvertes.fr/inria-00362141/en/.]. However it is unclear how these properties may be used or extended in multi-user systems [2A. Barbieri, D. Fertonani, and G. Colavolpe. Spectrally-efficient continuous phase modulations. IEEE Trans. Wireless. Comm., 8(3):1564–1572, 2009.]. A promising approach relying on frequency-division multiplexing (FDM) for multi-user systems has recently been developed [1P. R. A. Perotti and S. Benedetto. Adaptive coded continuous-phase modulations for frequencydivision multiuser systems. Advances in Electronics and Telecommunications, 1(1):50–58, 2010.] for classical CPM. We plan to generalize this approach in our framework.

Cognitive radio
This starting activity will be supported by a PhD project, jointly with Infineon, and is led by Luc Deneire.
Current wireless networks use the radio spectrum in a very inefficient manner. Indeed, a frequency bandwitdh is allocated in a fixedmanner to the user, even when this user is not using the radio resource. This type of user is denoted as a “primary” user. When the primary user is not active, a “secondary” user could take advantage of the free spectrum: this is the idea behind cognitive radio. In this activity, the objective is to allow a primary user and a secondary user to transmit simultaneously. Indeed, if the interference casued by the secondary user is somehow known by the primary user, the latter can null out this interference and continue to transmit with the same througput. To be able to perform this interference cancellation, the different users must share some information (in the extreme case, share all the transmitted messages). The goal of this activity is to explore the cooperation strategies (which information have to be shared) to enable the development of cognitive radio networks where both primary and secondary users transmit simultaneously.

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