Jean-Marie Gorce

Scalable versus Accurate Physical Layer Modeling in Wireless Network Simulations

In wireless networking, due to the high complexity of analytical and theoretical models, simulations are generally considered as the most convenient methodology for performance evaluation. Nonetheless, the physical complexity of the wireless medium induces a clear tradeoff between accuracy and scalability in a wireless network simulator design. In this paper, we focus on this tradeoff and study the impact of physical layer (PHY) modeling accuracy in the computational cost of simulations. We first discuss the main aspects of the wireless medium and briefly show how they have been handled in existing simulators. Then, we introduce a flexible and modular PHY simulation framework to analyze in more details their influence on the scalability of simulations.

QoS constrained wireless LAN optimization within a multiobjective framework

Wireless LANs have experienced great success in the past five years. This technology has been quickly adopted in private and public areas to provide convenient network access. The fast pace of development has often induced an uncoordinated deployment strategy where WLAN planning tools have barely been used. This article highlights the difficulty of planning such wireless networks in indoor environments. The first issue that must be faced in WLAN planning is accurate description of the quality of a network based on realistic propagation predictions. The second issue is to implement a search strategy that provides several alternative solutions. Thus, the radio engineer can choose the most promising one among them based on his/her experience and maybe some additional constraints. A description of already proposed planning strategies is given and opens out onto a new multiobjective planning formulation. This formulation evaluates coverage, interference level, and quality of service (in terms of data throughput per user) to measure the quality of a planning solution. A Tabu multiobjective algorithm is then implemented to search for the optimal set of non-dominated planning solutions, and a final selection process extracts the most significant solutions for the end user. This multiobjective QoS-oriented method is illustrated with a practical example that shows the performance of looking for several solutions, each expressing different trade-offs between the planning objectives

Green transmission technologies for balancing the energy efficiency and spectrum efficiency trade-off

As 4G wireless networks are vastly and rapidly deployed worldwide, 5G with its advanced vision of all connected world and zero distance communications is already at the corner. Along with the super quality of user experience brought by these new networks, the shockingly increasing energy consumption of wireless networks has become a worrying economic issue for operators and a big challenge for sustainable development. Green Transmission Technologies (GTT) is a project focusing on the energy-efficient design of physical-layer transmission technologies and MAC-layer radio resource management in wireless networks. In particular, fundamental tradeoffs between spectrum efficiency and energy efficiency have been identified and explored for energy-efficiency-oriented design and optimization. In this article, four selected GTT solutions are introduced, focusing on how they utilize the degrees of freedom in different resource domains, as well as how they balance the tradeoff between energy and spectrum efficiency. On top of the elaboration of separated solutions, the GTT toolbox is introduced as a systematic tool and unified simulation platform to integrate the proposed GTT solutions together.

Cooperative Scheduling for Coexisting Body Area Networks

Body area networks (BANs), referring to embedded wireless systems in, on, and around bodies, are expected to take an important role for health, leisure, sports, and all the facets of our daily life. In many cases, several BANs coexist in a small area, resulting in very strong inter-BAN interference, which seriously disturbs intra-BAN communications. The goal of this paper is to decrease inter-BAN interference by cooperative scheduling, hence increasing packet reception rate (PRR) of intra-BAN communications. Cooperative scheduling here is divided into two sub-problems: single-BAN scheduling as an assignment problem and multi-BAN concurrent scheduling as a game. For the first sub-problem, a low complexity algorithm, horse racing scheduling, is proposed, which achieves near-optimal PRR for the BAN performing scheduling. For the second sub-problem, we prove the existence of a set of mixed strategy Nash equilibria (MSNE). Then, we propose a distributed cooperative scheduling scheme, which efficiently achieves higher PRR than the MSNE without degrading fairness.

Performance evaluation of direct and cooperative transmissions in body area networks

Body area networks (BAN) offer amazing perspectives to instrument and support humans in many aspects of their life. Among all possible applications, this paper focuses on body monitoring applications having a body equipped with a set of sensors transmitting in real time their measures to a common sink. In this context, at the application level, the network fits with a star topology, which is quite usual in the broad scope of wireless networks. Unfortunately, the structure of the network at the physical layer is totally different. Indeed, due to the specificity of BAN radio channel features, all radio links are not stationary and all sensors suffer from link losses during independent time frames. In wireless networks, link losses are often coped with multi-hop transmission schemes to ensure a good connectivity. However, since the radio links are not stationary, the multi-hop routes should adapt quickly to BAN changes. We instead propose in this work a different approach based on opportunistic relaying. The concept relies on electing some sensors to support the transmission of other ones having a worst connection. Instead of changing the relay time to time, we rather select a relay node from a statistical perspective. We evaluate this approach from a theoretical point of view and on realistic simulations using the packet error rate outage probability as a performance criterion.

Opportunistic relaying protocols for human monitoring in BAN

Body Area Networks (BAN) offer amazing perspectives to instrument and support humans in many aspects of their life. Among all possible applications, this paper focuses on body monitoring applications having a body equipped with a set of sensors transmitting in real-time their measures to a common sink. The underlying network topology is a star topology which is quite usual in the broad scope of wireless sensor networks. Therefore, a classical superframe structure as proposed in 802.15.3 or 802.15.4 seems to comply with the needs of such an application. Basically however, the specificities of the BAN channel can reduce the performance of such protocol. Indeed, channel time variations make the star structure unstable and temporary subject to a high packet error rate. A multi-hop mesh topology cannot counteract this problem efficiently, since the pathloss attenuation in a BAN environment is almost independent with the emitter-receiver distance. In this paper, we address this issue by considering the topology of a BAN network as a time-varying fully connected network instead of a star structure. We then show how an opportunistic cooperative mechanism based on a decode-and-forward protocol can address this issue. We derive a performance criterion based on a packet error rate outage and we discuss the implementation of this scheme in the classical superframe structure.

Stochastic analysis of energy savings with sleep mode in OFDMA wireless networks

The issue of energy efficiency (EE) in Orthogonal Frequency-Division Multiple Access (OFDMA) wireless networks is discussed in this paper. Our interest is focused on the promising concept of base station (BS) sleep mode, introduced recently as a key feature in order to dramatically reduce network energy consumption. The proposed technical approach fully exploits the properties of stochastic geometry, where the number of active cells is reduced in a way that the outage probability, or equivalently the signal to interference plus noise (SINR) distribution, remains the same. The optimal EE gains are then specified with the help of a simplified but yet realistic BS power consumption model. Furthermore, the authors extend their initial work by studying a non-singular path loss model in order to verify the validity of the analysis and finally, the impact on the achieved user capacity is investigated. In this context, the significant contribution of this paper is the evaluation of the theoretically optimal energy savings of sleep mode, with respect to the decisive role that the BS power profile plays.

On the complexity of an accurate and precise performance evaluation of wireless networks using simulations

In wireless multi-hop networks, there is a growing need for the performance evaluation of protocols and distributed applications. Due to the high complexity of analytical models and the difficulty of setting up large scale testbeds, simulations are generally considered as the most convenient methodology for evaluating the performance of wireless systems. However, evaluating a protocol can be a tedious task as it depends on several factors including the physical layer modeling and the dimensioning of protocol or environment parameters. As a consequence inferring an overall performance for a protocol is a real issue. In this paper, we highlight some main factors that may affect the accuracy of the performance evaluation of protocols using simulations. First, we focus on the physical layer (PHY) modeling which represent a key point for the sake of realism and confidence. Second, we discuss the impact of some protocol parameters on the behavior of the evaluated protocols.

Toward Increasing Packet Diversity for Relaying LT Fountain Codes in Wireless Sensor Networks

Diversity is a powerful means to increase the transmission performance of wireless communications. For the case of fountain codes relaying, it has been shown previously that introducing diversity is also beneficial since it counteracts transmission losses on the channel. Instead of simply hop-by-hop forwarding information, each sensor node diversifies the information flow using XOR combinations of stored packets. This approach has been shown to be efficient for random linear fountain codes. However, random linear codes exhibit high decoding complexity. In this paper, we propose diversity increased relaying strategies for the more realistic and lower complexity Luby Transform code in a linear network. Results are provided herein for a linear network assuming uniform imperfect channel states.

M-ary symbol error outage over Nakagami-m fading channels in shadowing environments

This letter addresses the problem of finding a tractable expression for the symbol error outage (SEO) in flat Nakagami-m fading and shadowing channels. We deal with M-ary phase shift keying (M-PSK) and quadrature amplitude modulation (M-QAM) which extends our previous results on BPSK signaling. We propose a new tight approximation of the symbol error probability (SEP) holding for M-PSK and M-QAM signals which is accurate over all signal to noise ratios (SNRs) of interest. We derive a new generic expression for the inverse SEP which facilitates the derivation of a tight approximation of the SEO in a lognormal shadowing environment.