Eugène David Ngangue Ndih

On Enhancing Technology Coexistence in the IoT Era: ZigBee and 802.11 Case

ZigBee is often chosen as a technology to connect things because of characteristics, such as network resilience, interoperability, and low power consumption. In addition, Zigbee Pro, with its Green Power feature, allows low-power networking capable of supporting more than 64 000 devices on a single network, making it an excellent choice to connect things. However, in recent years, we have witnessed the proliferation of smart devices using either 802.11 or ZigBee technologies, which operate in the same frequency band. Proposing and developing techniques that may improve the fair operation and performance of these technologies in coexistence scenarios have been a major concern in industry and academia. In this paper, we propose the use of traffic prioritization for ZigBee nodes in order to improve their performance when coexisting with IEEE 802.11 nodes. We develop an analytical model based on Markov chains, which captures the behavior of channel access mechanisms for both 802.11 nodes and different ZigBee priority class nodes. Based on extensive simulations, we validate the accuracy of the proposed model, and demonstrate how traffic prioritization of ZigBee nodes effectively improves their performance when coexisting with 802.11 nodes. We also demonstrate that this improvement comes at the cost of negligible degradation in the performance of the 802.11 nodes.

Improved multi-channel operation for safety messages dissemination in vehicular networks

In this paper we discuss the performance of IEEE 1609.4 multi-channel operation over the 5.9 GHz DSRC spectrum, and we propose an improved multi-channel switching in which the whole Sync interval can be used for the control channel when vehicles are not interested to use service channels. Based on intensive simulations conducted in ns-2, we demonstrate that significant improvements in terms of safety packet received within a Sync interval can be obtained with a negligible degradation of the service provisioning.

Analytic Modeling of the Coexistence of IEEE 802.15.4 and IEEE 802.11 in Saturation Conditions

With the increasing deployment of smart wireless devices using different technologies such as IEEE 802.15.4 and IEEE 802.11 which operate in the same frequency band, it becomes urgent to deeply understand the impact of this coexistence on the performance of the involved networks. We present in this letter an analytic framework based on Markov chains that captures accurately the behavior of channel access mechanisms in IEEE 802.11 DCF and the unslotted IEEE 802.15.4 when both technologies are coexisting together. The model allows the derivation of metrics such as the probability of successful transmissions, the probability of collision, and the fraction of time that the channel is idle, or experiences successful transmissions for both 802.11 and 802.15.4 nodes. Through extensive simulations of diverse coexistence scenarios, we validate the accuracy of the proposed model, and we analyze the performance of both 802.11 networks and 802.15.4 networks in saturation conditions.

Mac for Physical-Layer Network Coding in VANETs

In this paper, the authors present VPNC-MAC, a PNC-based MAC protocol for efficient and reliable periodic beacon broadcasts in VANETs. In addition to PNC-based scheduled transmissions, VPNC-MAC makes use of CSMA/CA to ensure fairness and flexibility with transmissions from CSMA-based nodes. VPNC-MAC consists of two phases: In the setup phase, a quasi-optimal mechanism of selecting a relay node is proposed to take into account both the position, and the remaining time the relay needs for delivering its current beacon. In the packet exchange phase, they define two priority modes to deal with the cohabitation of both the CSMA-based and the VPNC-based nodes, and also with unpredictable events such as emergency broadcasts. Contrary to the high-priority mode, the VPNC-based nodes AIFS in the low-priority mode is set such that the medium access is granted prior to CSMA-based nodes. Simulations results show that the global PRR in high-priority mode outperforms existing MAC.

Modulation network coding

In this study, we propose a four-dimensional modulation, referred to as modulation network coding (MNC), to address the problem of decoding a signal from multiple source node transmissions in mobile fast fading channels. The MNC scheme judiciously mixes a two-dimensional (2D) pilot symbol with a 2D information symbol, and makes use of a π/4 rotated M-pulse-amplitude modulation (PAM) constellation to guaranty an effective decoding of all the interfering symbols even in the case of a smaller channel Doppler spread compared with the period of the MNC symbol. In addition, because the MNC scheme makes use of an additional dimension introduced through orthogonal pulse waveform, the use of the pilot symbols does not reduce the effective information rate. The analytical and simulation results show that it is possible to achieve a low symbol error probability with a good signal-to-noise ratio when controlling a few parameters impacting the performance of the system such as the synchronisation in time and in frequency of the source nodes.

On supporting mobile peer to mobile peer communications

In this paper, we propose a new method for assessing the sociability scalar of a mobile peer by the network, most importantly with no involvement of the mobile peer. The sociability metric can help in the Application Layer Traffic Optimization (ALTO) guidance in Mobile Peer-to-Mobile Peer (MP2MP) scenario to scale up the database search of an ALTO server. The proposed method models encounters of mobile peers with predetermined areas, such as cells, tracking areas, gateway service areas, etc, depending on the targeted granularity. The obtained metrics, pertaining to inter-mobile peer relationship (i.e., sociability) and mobile peers mobility, are adopted to ALTO in a MP2MP scenario. In addition, metrics reflecting the energy budget of a mobile peer, the type of a mobile terminal, history of a mobile terminal in sharing contents with other mobile peers, etc, can be also taken into account by ALTO in the peer recommendation.

Toward neighborhood prediction using Physical-Layer Network Coding

In this paper we investigate the improvements in the capability of neighborhood prediction when the Physical-Layer Network Coding (PLNC) is used for relaying messages in Vehiculars Ad Hoc Networks (VANETs). We compute the probability that a link between two nodes is available at a given time in a three-node cooperative network, and we demonstrate that the use of PLNC, compared to the use of Network Coding (NC)-based or traditional routing (TR)-based relaying techniques, leads to a better accuracy of the neighborhood prediction. We also demonstrate that the accuracy of the prediction is tightly related to the mobility model used and that this tight relationship can be relaxed by using PLNC-based relaying neighborhood prediction (PRNP). The results demonstrate that PRNP can improve the accuracy of neighborhood prediction due to the high network capacity of PLNC-based networks.

Toward a Network Coding Constellation for Two-Way Relay Node Channels

In Physical-Layer Network Coding (PNC), the symbol detected at the relay node in two-way relay channels (TWRC) is the superposition of the symbols transmitted by the sinks. We refer to these symbols as pnc-symbols. In traditional modulation constellations such as Quadrature Amplitude Modulation (QAM) and Phase Shift Keying (PSK), the demodulator may fail to optimally identify pnc- symbols formed from pairs of central symmetrical symbols (CSS) because their superposition may yield to the same output point (i.e., to the same decision region) due to the presence of a central symmetry point. In order to avoid such ambiguity, we propose a non central symmetry constellation (CSC), called 4-TRAQAM, which is used by the sinks such that the decision regions of the output points are pair-wise disjoint.We show that the sinks in the PNC-based TWRC can be considered as a single transmitter using the same modulation as the real sinks with a higher order.We further derive the average energy of pnc- symbols and the error probability of the derived PNC-based TWRC modulation, and we show that the 4- TRAQAM provides the best trade-off between the average energy and the disjointness of the decision regions, compared to other used QAM.

Adaptive 802.15.4 backoff procedure to survive coexistence with 802.11 in extreme conditions

With the increasing deployment of smart devices for the Internet of Things (IoT) using 802.15.4 in spaces where 802.11 devices are already deployed, wireless channels are getting densely populated in the 2.4 GHz ISM band, especially when nodes operate in saturation conditions. In addition to the fact that 802.15.4 and 802.11 use different CSMA/CA protocols with considerable different backoff durations, 802.15.4 is designed for ultra-low power, low rate WPAN while 802.11 is designed for higher power and high data rate WLAN. In this paper, we aim to tackle the resulting issues due to this asymmetric coexistence. Especially we propose a simple but efficient backoff mechanism for 802.15.4 in which the backoff duration is adaptively chosen, when WiFi transmissions are detected during the clear channel assessment. Through extensive simulations, we demonstrate the efficiency of the proposed adaptive backoff mechanism and the considerable improvements of the 802.15.4 performance even in case of erroneous decision regarding the type of packet detected during the clear channel assessment.

Improved Inter-Network Handover for Highly Mobile Users and Vehicular Networks

Mobility management is a critical issue in vehicular networks. In this paper, we consider the case of highly mobile users in heterogeneous wireless environments. We propose a mobility management, based on a recently proposed mobile IP-based mobility management architecture, optimizing the calculation of its dynamic registration message frequency. The new calculation takes into account both the size of the radio access networks and the velocity of the mobile users. Simulation results show that this approach yields an effective control of the policy function and alleviates the high signaling cost introduced by high registration message frequencies. The derived mobility management thus allows an efficient control of the use of registration messages at congested access networks and guarantees appropriate handoff decisions.