Thierry Lestable

Compression of associated signaling for adaptive multi-carrier systems

Link adaptation technology has been introduced in new generation transmission systems, such as 3G and 4G, optimizing both their throughput and their power consumption. Adaptation of the radio configuration requires information about the radio link quality. The information must be exchanged between the access point and the mobile terminal, leading to an associated signaling load, whose amount may decrease the system transmission efficiency. A mechanism for reducing the amount of signaling information has to be designed to increase the overall system capacity (more users, more available bandwidth). The paper addresses multi-carrier systems whose link adaptation is carried out by means of bit loading algorithms. However, the associated signaling load increases quickly with the number of sub-carriers, modulation schemes and users. These bit loading vectors are considered a-priori known at the receiver, and almost no literature concerning transmission of such information is available. In realistic transmission systems, correlation exists in time due to Doppler effects, and in frequency due to multipath delay spread. We intend to exploit this twofold redundancy to decrease signaling information load. An adaptive lossless compression system for an optimized compression performance and complexity is proposed, giving much higher compression ratio than the existing LZW bit loading algorithm (Lestable, T. and Battelli, M., 2002).

Throughput of the Multi-hop Slotted Aloha with Multi-packet Reception

Markov localization has been successfully deployed in robotics using highly precise distance sensors to determine the location and pose of mobile robots. In this setting the scheme has shown to be robust and highly accurate. This paper shows how this approach has been adapted to the problem of locating wireless LAN clients in indoor environments using highly fluctuating radio signal strength measurements. A radio propagation model is used to determine the expected signal strength at a given position in order to avoid tedious offline measurements. Some of the issues that had to be addressed include expressing the calculated signal strengths in terms of probability density functions and detecting movement of the mobile terminal solely on the basis of radio measurements. The conducted experiments show that the proposed technique provides a median error of less than 2 m even when there is no line-of-sight to an access point.

A Class of Structured LDPC Codes Over GF(q) for Efficient Encoding

In this paper we present a class of structured LDPC codes over GF(q) which are suitable for efficient encoding. We derive the conditions under which the Phi matrix defined by Richardson & Urbanke in (2001) is an identity matrix over GF(q). If the parity-check matrix satisfies the derived conditions, the inversion of the Phi matrix can be removed in encoding process so that the computational complexity grows linearly with the code length. Simulation results show that efficiently encodable structured LDPC codes have no performance degradation due to the constraint on their design structure, compared with randomly constructed LDPC codes.

Improving the MAC Layer of Multi-Hop Networks

Ad hoc and multi-hop networks will probably be a part of the fourth generation of wireless networks, which will integrate networks of several sizes and capacities with heterogeneous coverage: cellular networks (3G), WLAN hot spots, wireless personal area networks (WPAN) and wireless body area networks (WBAN). In this context, MAC protocols play a deciding role for a high utilization of the wireless channel. In this paper, several issues of the MAC layer and concepts for the definition of a new MAC protocol are presented. These concepts include synchronization, multi-user diversity, and multi-packet reception. It is shown that all these techniques can drastically increase the capacity of the MAC layer for multi-hop networks.

Impact of adaptive modulation on MC-CDMA receiver in beyond 3G systems

The study presented in this paper underlines the capacity increase resulting from the joint use of multicarrier (MC) adaptive modulation techniques and MC-CDMA receiver in the context of beyond 3G systems. The performance enhancement due to such near optimal rate and power adaptation decreases with diversity order. Moreover, results obtained through two different kinds of wireless channels (ETSI BRAN A and C) highlight convergence phenomena, independent of initial channel diversity order. Finally, complete single user detection (SUD) techniques are compared in tit is context of adaptive modulation.

Centralised power setting for femtocell cluster

Femtocell is a key technology to improve coverage and capacity in indoor environments. However, its co-channel deployment across a macrocell network may lead to severe interference in presence of a closed subscriber group (CSG) access policy. Power setting is a simple way to partly address this problem by adapting the femtocell power to its macrocell surroundings. In this paper, we propose a linear programming-based power management solution adapted to clusters of femtocells which outperforms traditional approaches in terms of outage and energy consumed. This centralized method allows the switch-off of the most disrupting femtocells in order to improve the overall network performance, which is particularly useful in the context of femtocells cluster broadcasting the same CSG. Since our proposed method does not rely on dedicated hardware, it could also be run in an open IT cloud platform.

Kalman filter-based localization for Internet of Things LoRaWAN™ end points

This paper addresses the problem of estimating the location of Internet of Things (IoT) Long Range Wide Area Networks (LoRaWAN) devices from time of arrival differences measured at gateways. An Extended Kalman Filter (EKF) based approach is considered to aggregate the measurements obtained at different time instants. Particular attention is paid to the processing of outliers. Based on experimental data obtained from field measurements conducted on a real LoRaWAN™ network an insight into the realistic localization accuracy of the considered localization approach is provided.

Sensitivity of interfering power estimation to combining strategies in MC-CDMA systems

In this paper, the problem of accuracy in noise/interfering power estimate for an MC-CDMA receiver is considered. This quality parameter is a key feature in the link control for next generation wireless systems. It is used for bit loading, power control, dynamic frequency selection, or even handover. Adaptation of physical layer can also be based on this quality estimate. Therefore, its accuracy is of paramount importance when designing such adaptive systems. The sensitivity of the noise/interfering power estimate are compared and discussed for different diversity combining schemes viz: maximal ratio combining (MRC), equal gain combining (EGC), and selective combining (SC).

Accuracy of interfering power estimation in MC-CDMA systems

In this paper, we present an analytical approach to study the power estimate of the interference in a MC-CDMA transmission scheme. The receiver is implementing a simple RAKE architecture that is not near-far resistant. The regenerated signal (RS) technique is applied on a symbol basis for power estimation of the jamming signal. An exact equation of this estimate is obtained for L uncorrelated diversity branches, and the impact of diversity order is discussed.