Benoît Escrig

Improving satellite services with cooperative communications

SUMMARY This paper proposes new transmission schemes for the delivery of satellite services. In the proposed scenarios, mobile terminals are allowed to forward the signal received from the satellite. This scheme provides spatial diversity just like MIMO transmission schemes. Moreover, the coverage area is extended because masked terminals have an additional opportunity to get the service from neighboring terminals. We use the paradigm of cooperative communications to compare the advantages and limitations of several scenarios in hybrid terrestrial/satellite systems. In particular, we study the following basic transmission scheme: in a first time slot, the satellite sends its signal and, in a second time slot, mobile terrestrial terminals are relaying the satellite signal. An analysis framework is proposed and applied to this cooperation scenario at the destination terminal. The framework is modeling the cooperation process and clearly separates the control part from the data user part. The paper outlines the importance of the control part by evaluating the relay selection policy on a basic hybrid satellite/ad hoc system. Copyright

Exact outage probability of a hybrid satellite terrestrial cooperative system with best relay selection

In this paper, we derive the exact outage probability of a hybrid satellite-terrestrial cooperative system (HSTCS). A selective decode-and-forward scheme is implemented between a source node (the satellite) and a destination node (a terrestrial station), and a selection of the best relay terminal is performed. In this proposed system, a two time-slot scenario is considered. During the first time slot, the satellite is broadcasting the information to the terrestrial relays and the destination. In the second time slot, only the best relay is transmitting toward the destination node. Then, both signals are combined using the maximum ratio combining (MRC) technique. The analytical expression of the outage probability is evaluated and is then verified with the simulation. The results show that our analytical expression matched well to the simulation results.

Turbo receivers for interleave-division multiple-access systems

In this paper several turbo receivers for Interleave-Division Multiple-Access (IDMA) systems will be discussed. The multiple access system model is presented first. The optimal, Maximum A Posteriori (MAP) algorithm, is then presented. It will be shown that the use of a precoding technique at the emitter side is applicable to IDMA systems. Several low complexity Multi-User Detector (MUD), based on the Gaussian approximation, will be next discussed. It will be shown that the MUD with Probabilistic Data Association (PDA) algorithm provides faster convergence of the turbo receiver. The discussed turbo receivers will be evaluated by means of Bit Error Rate (BER) simulations and EXtrinsic Information Transfer (EXIT) charts.

Exact Symbol Error Probability of Hybrid/Integrated Satellite-Terrestrial Cooperative Network

In this paper, we study the Symbol Error Probability (SEP) performance of a hybrid/integrated satellite-terrestrial cooperative network. In particular, we focus on the case of mobile relays that forward the satellite signal to a masked mobile destination node. The Selective Decode-and-Forward (SDF) transmission scheme is implemented and only the relay nodes which can successfully decode the satellite message are selected to retransmit the signal. The destination node exploits the spatial diversity advantages by implementing a typical Maximum Ratio Combining (MRC) technique. The closed-form expressions for the exact average SEP of the arbitrary M-ary phase shift keying and M-ary quadrature amplitude modulation signaling with MRC diversity reception over independent but not necessarily identically distributed fading channels are derived using a Moment Generating Function (MGF) approach. These closed-form expressions are represented in terms of a finite sum of Lauricella hypergeometric functions. The analytical expressions show excellent agreement with the simulation results. Numerical results show that for a system using QPSK under the frequent heavy shadowed fading condition, the diversity gain of approximately 7 dB can be obtained at the SEP of 10-1 with respect to the direct transmission, when only one relay is used. It increases to around 12 dB in the case of 3 relays.

On-Demand Cooperation MAC Protocols with Optimal Diversity-Multiplexing Tradeoff

This paper presents access protocols with optimal Diversity-Multiplexing Tradeoff (DMT) performance in the context of IEEE 802.11-based mesh networks. The protocols are characterized by two main features: on-demand cooperation and selection of the best relay terminal. The on-demand characteristic refers to the ability of a destination terminal to ask for cooperation when it fails in decoding the message transmitted by a source terminal. This approach allows maximization of the spatial multiplexing gain. The selection of the best relay terminal allows maximization of the diversity order. Hence, the optimal DMT curve is achieved with these protocols.

A framework for cooperative communications at the system level

In order to improve the communication efficiency without using multi-antennae terminals, cooperative communications implement one or several single antenna relays to assist the transmission between a source and a destination. The design of such a cooperative network, involves several layers of the OSI model. Transmission and multiplexing techniques are addressed at the physical layer whereas the management of the cooperative network (activation of a cooperative mode, selection of relays) is done at the Medium Access Control (MAC) layer and the layers above. After an overview of protocols that have been designed in this domain, we propose an original framework of a cooperative network, at the system level. Inspired from models of the ITU normative organization, our cooperative network model is based on two planes: a data plane and a control plane. A validation of the framework is given by modeling an existing cooperative MAC protocol.

Splitting algorithm for DMT optimal cooperative MAC protocols in wireless mesh networks

Abstract A cooperative protocol for wireless mesh networks is proposed in this paper. The protocol implements both on-demand relaying and a selection of the best relay terminal so only one terminal is relaying the source message when cooperation is needed. Two additional features are also proposed. The best relay is selected with a splitting algorithm. This approach allows fast relay selection within less than three time-slots, on average. Moreover, a pre-selection of relay candidates is performed prior to the splitting algorithm. Only terminals that are able to improve the direct path are pre-selected. So efficient cooperation is now guaranteed. We prove that this approach is optimal in terms of diversity-multiplexing trade-off. The protocol has been designed in the context of Nakagami- m fading channels. Simulation results show that the performance of the splitting algorithm does not depend on channel statistics.

An Environment for Building Customizable Software Components

Customization often corresponds to a simple functional customization, restricting the functionalities of a component to some configuration values, without performing any code optimization. However, when resources are limited, as in embedded systems, customization needs to be pushed to code customization. This form of customization usually requires one to program low-level and intricate transformations.This paper proposes a declarative approach to expressing customization properties of components. The declarations enable the developer to focus on what to customize in a component, as opposed to how to customize it. Customization transformations are automatically determined by compiling both the declarations and the component code; this process produces a customizable component. Such a component is then ready to be custom-fitted to any application.Besides the declaration compiler, we have developed a graphical environment both to assist the component developer in the creation of a customizable component, and to enable a component user to tailor a component to a given application.

Energy and throughput efficient transmission strategy with Cooperative Transmission in ad-hoc networks

In this paper, a new Medium Access Control (MAC) protocol combining Transmit Power Control (TPC), Rate Adaptation (RA) and Cooperative Transmission (CT) is proposed, in the context of multi-rate ad hoc networks. The protocol aims to achieve energy efficiency of data transmission while increasing the overall network throughput. The key idea of the protocol is to allow each wireless node to create a table with the optimal power-rate combinations based only on the network interface card specifications. In the presence of low data-rate nodes the network throughput is greatly degraded. To mitigate this well-known “rate anomaly” problem we use CT to replace the direct low-rate links by relayed high-rate links. By exchanging control frames and looking up the power-rate table, the wireless node chooses the most suitable transmission strategy (which consists of selecting the most optimal power-rate combination) for each data-frame as well as the transmission scheme (direct or relayed). Results reveal an important improvement in the overall network throughput as well as in the energy consumption with the new protocol compared to the scheme without TPC and without cooperation. Furthermore, simulation results show that our scheme deliver more data per unit of energy consumption than the IEEE 802.11 scheme.

DMT Optimal On-Demand Relaying for Mesh Networks

This paper presents a new cooperative MAC (Medium Access Control) protocol called BRIAF (Best Relay based Incremental Amplify-and-Forward). The proposed protocol presents two features: on-demand relaying and selection of the best relay terminal. “On-demand relaying” means that a cooperative transmission is implemented between a source terminal and a destination terminal only when the destination terminal fails in decoding the data transmitted by the source terminal. This feature maximizes the spatial multiplexing gain r of the transmission. “Selection of the best relay terminal” means that a selection of the best relay among a set of (m-1) relay candidates is implemented when a cooperative transmission is needed. This feature maximizes the diversity order d(r) of the transmission. Hence, an optimal DMT (Diversity Multiplexing Tradeoff) curve is achieved with a diversity order d(r) = m(1-r) for 0 ≤ r ≤ 1.