Michel Nahas

Base stations evolution: Toward 4G technology

Recently, a distributed architecture for base stations was proposed. In this new configuration, the base station is separated into two parts: the radio frequency part near the antenna and the baseband processing unit. The interface connection between them is ensured by an optical fiber. In this paper, we present the ongoing works on standardization of the optical interface and the proposed solutions by telecommunications equipment manufacturers for this new architecture. Moreover, key technologies of 4G are recalled and the effect of the evolution of base station models on future cellular systems is evaluated.

Bounded Delay-Tolerant Space Time Block Codes for Asynchronous Cooperative Networks

When distributed cooperative nodes are communicating with a destination, the received signal can be asynchronous due to the propagation or processing delays. This can destroy the space time block code properties designed initially for synchronous case. In this paper, a new construction method of bounded delay tolerant codes is presented. These new codes preserve the full diversity with optimal rates if the relative delays are in a designed delay tolerance interval. The general design method is based on the concatenation and permutation of optimal synchronous space time block codes and works for an arbitrary number of transmitting and receiving antennas. Examples of bounded delay tolerant codes based on the Alamouti code, the Golden code and Threaded Algebraic Space-Time (TAST) codes are given. Theoretical proofs are used to show that the new codes respect the design criteria. Simulation results manifest better error rate performance of the new codes compared to other known delay tolerant codes.

Performance of asynchronous two-relay two-hop wireless cooperative networks

In wireless cooperative networks, the asynchronism between the relays can be a source of diversity which is similar in its essence to the multipath diversity of frequency selective channels. In this context, an asynchronous two-relay cooperative wireless network is studied for Decode-and-Forward (DF) and Amplify-and-Forward (AF) protocols. The outage probability in the high Signal to Noise Ratio (SNR) regime is derived and the impact of the relative delay between the two relays on this outage probability is evaluated. It is shown that for a sufficiently high relative delay, the outage probability performance becomes independent from the relative delay and approaches from the synchronous protocol performance. Besides, an optimization of the power distribution between the transmitting nodes of the network is carried out in the high SNR regime based on the outage probability minimization. Moreover, the Diversity Multiplexing Tradeoff (DMT) of the network is characterized for the two cooperative protocols DF and AF. The DMT curve does not depend on the relative delay as long as the latter is non-zero.

Reducing energy consumption in cellular networks by adjusting transmitted power of base stations

With the growth of cellular networks and emergence of new technologies, the power consumption of mobile communication networks has become an important and worrying topic that should be taken into consideration in any future cellular evolution. Recently, many solutions were proposed in the literature to reduce the power in cellular communications while maintaining the quality of service, in the purpose of achieving, what is known now as “Green Communications”. In this paper, we are interested in power-efficient methods altering the transmitted power of base stations, especially Sleep Mode and Cell Zooming techniques. After presenting the advantages, drawbacks and implementations of these two green solutions, we will introduce a new algorithm that should be implemented and applied on the base stations to reduce their total power consumption. This algorithm considers several cases including Cell Zooming and combination of Sleep Mode and Cell Zooming depending on the cell loads and mobile distribution. It also computes the power needed in each case and then chooses the most power-efficient scenario. Moreover, we will study the performance and efficacy of implementing our algorithm in some practical cellular network settings.

Dynamic Clustering Protocol for coordinated tethering over cellular networks

Abstract Tethering has been recently proposed as an efficient solution for the increase in number of mobile users and the requested bandwidth in cellular networks. The idea is to group the mobile nodes into clusters, each containing slaves served by a hotspot. To save licensed spectrum, the hotspot–slave link can use other frequency channels like the newly vacated TV white space (TVWS) bands. A recent work has proposed an iterative clustering algorithm for cellular networks. Despite its computational complexity and signaling overhead, this algorithm did not handle the nodes׳ mobility inside the cell neither the change in their required data rate. In this work, we propose a new dynamic protocol for clustering the nodes taking into account the possible changes occurring in a cellular network. Specifically, the Dynamic Clustering Protocol (DCP) adapts the network configuration with the variable mobiles׳ requirements and the different network events. This will reduce the needed time and signaling and offers better service quality for the clustered users. After presenting the various network events, the handover scenarios and signaling for the Dynamic Clustering Protocol, the performance of the proposed protocol is studied. This was accomplished by modeling different network scenarios and computing the required number of handovers as a function of user mobility, available network resources and data rate requirements for a given clustered nodes configuration.

Enhancing LTE - WiFi interoperability using context aware criteria for handover decision

To improve the interworking between LTE and WiFi wireless technologies, an efficient handover mechanism is proposed. Dynamic and critical measures like mobile-assisted parameters are inserted to the Access Network Discovery and Selection Function (ANDSF) entity defined by 3GPP standard. Moreover, Context Aware (CA) decision algorithm is integrated within the ANDSF server so that the inserted measurements are expeditiously invested to improve the handover decision policy. The performance enhancement of the proposed model compared to the traditional one is shown by numerical simulations.

Bounded delay-tolerant Space Time Codes with optimal rates for two cooperative antennas

For distributed antennas based communications, the received signal from different sources can be asynchronous due to the propagation or processing delays. This can destroy the space time block code properties designed initially for synchronous case. In this paper, we introduce the delay-diversity tradeoff showing that it is possible to preserve the maximum diversity of a code without reducing its rate as long as the relative delays are in a designed delay tolerance interval. New delay tolerant block codes are proposed and it is shown that they achieve full diversity and optimal rates for both synchronous and asynchronous cases. Their performances are compared to other delay tolerant codes.

On the Outage Probability of Asynchronous Wireless Cooperative Networks

In wireless cooperative networks, the asynchronism between the relays can be a source of diversity which is similar in its essence to the multipath diversity of frequency selective channels. In this context, an asynchronous two-relay two-hop cooperative wireless network using the Decode-and-Forward protocol is studied. The outage probability in the high Signal to Noise Ratio (SNR) regime is derived and the impact of the relative delay between the two relays on this outage probability is evaluated. We show that for a sufficiently high relative delay, the outage performance becomes independent from the relative delay. Moreover, an outage probability minimization with respect to the power distribution between the transmitting nodes of the network is carried out in the high SNR regime.

RSSI range estimation for indoor anchor based localization for wireless sensor networks

Range estimation using RSSI (received signal strength indicator) for localization application for wireless sensor networks is a challenging task. Interference from the shared 2.4GHz channel and fading due to multipath propagation and shadowing deteriorate the process of range estimation. In this work an estimation of these noise levels that are present in the environment is being carried out by anchor nodes which are placed throughout the sensing field. These anchor nodes will compare the actual distance between them with distance computed from the measured RSSI. Four different techniques have been devised that applies a smoothing coefficient on the measured RSSI taking into consideration information about the environment from the anchor nodes. Simulation shows that even when the error introduced is equivalent to 100% of the transmission range, the error in range estimation was around 25%.

iSee: An Android Application for the Assistance of the Visually Impaired

Smart phone technology and mobile applications have become an indispensable part of our daily life. The primary use however, is targeted towards social media and photography. While some camera-based approaches provided partial solutions for the visually impaired, they still constitute a cumbersome process for the user. iSee is an Android based application that benefits from the commercially available technology to help the visually impaired people improve their day-to-day activities. A single screen tap in iSee is able to serve as a virtual eye by providing a sense of seeing to the blind person by audibly communicating the object(s) names and description. iSee employs efficient object recognition algorithms based on FAST and BRIEF. Implementation results are promising and allow iSee to constitute a basis for more advanced applications.