Search

In this work, we address the problem of jointly optimizing the transmit power and blocklength of a two-users scenario for orthogonal multiple access (OMA) and non-orthogonal (NOMA) access schemes. We formulate an optimization problem to obtain the energy-optimal blocklength and transmit power under ultra-reliable and low-latency communications (URLLC) reliability and latency constraints. The aim is to minimize the energy consumption at short-blocklength regime. Due to the problem's complexity, we decompose it into two sub-problems for the OMA case, where the base station (BS) employs a 2D search for strong user, and the bisection method for the weak user. On the contrary, we find the sufficient transmit power conditions for NOMA to obtain the feasible solution. Our results show that the minimum required energy increases with the reliability requirement for both the OMA and NOMA, while NOMA consumes more energy than OMA for the same reliability target. Moreover, the results indicate that NOMA reduces latency due to better blocklength utilization compared to OMA when the channel gain disparity between the users is small.

As the market for low-power wide-area network (LPWAN) technologies expands and the number of connected devices increases, it is becoming important to investigate the performance of LPWAN candidate technologies in dense deployment scenarios. In dense deployments, where the networks usually exhibit the traits of an interference-limited system, a detailed intra- and inter-cell interference analysis of LPWANs is required. In this paper, we model and analyze the performance of uplink communication of a LoRa link in a multi-cell LoRa system. To such end, we use mathematical tools from stochastic geometry and geometric probability to model the spatial distribution of LoRa devices. The model captures the effects of the density of LoRa cells and the allocation of quasi-orthogonal spreading factors (SF) on the success probability of the LoRa transmissions. To account for practical deployment of LoRa gateways, we model the spatial distribution of the gateways with a Poisson point process (PPP) and Matern hard-core point process (MHC). Using our analytical formulation, we find the uplink performance in terms of success probability and potential throughput for each of the available SF in LoRa’s physical layer. Our results show that in dense multi-cell LoRa deployment with uplink traffic, the inter-cell interference noticeably degrades the system performance.

The Licensed Assisted Access (LAA) is shown as a required technology to avoid overcrowding of the licensed bands by the increasing cellular traffic. Proposed by 3GPP, LAA uses a Listen Before Talk (LBT) and backoff mechanism similar to Wi-Fi. While many mathematical models have been proposed to study the problem of the coexistence of LAA and Wi-Fi systems, few have tackled the problem of QoS provisioning, and in particular analysed the behaviour of the various classes of priority available in Wi-Fi and LAA. This paper presents a new mathematical model to investigate the performance of different priority classes in coexisting Wi-Fi and LAA networks. Using Discrete Time Markov Chains, we model the saturation throughput of all eight priority classes used by Wi-Fi and LAA. The numerical results show that with the 3GPP proposed parameters, a fair coexistence between Wi-Fi and LAA cannot be achieved. Wi-Fi users in particular suffer a significant degradation of their performance caused by the collision with LAA transmissions which has a longer duration compared to Wi-Fi transmissions.

Machine to Machine (M2M) communication networks are expected to connect a large number of power-constrained devices in long range applications with different quality of service (QoS) requirements. Medium access control with QoS support such as the enhanced distributed channel access (EDCA) defined by IEEE 802.11e provides traffic differentiation and corresponding priority classes, which guarantees QoS according to the needs of applications. In this paper, we employ a station grouping mechanism for enhancing the scalability of EDCA to handle the massive number of access attempts expected in large M2M networks. Furthermore, we develop a discrete time Markov chain (DTMC) model to analyze the performance of EDCA with station grouping. Using the developed DTMC model, we calculate throughput for each access category as well as for different combinations of grouping and EDCA parameters. The numerical results show that the model can precisely reveal the behavior of EDCA mechanism. Moreover, it is demonstrated that employing the proposed grouping mechanism for EDCA increases the normalized throughput significantly for all classes of priority.

Many applications for machine-to-machine (M2M) communications are characterized by large numbers of devices with sporadic transmissions and subjected to low energy budgets. This work addresses the importance of energy consumption by proposing a new Medium Access Control (MAC) mechanism for improving the energy efficiency of IEEE 802.11ah, a standard targeting M2M communication. We propose to use the features of IEEE 802.11ah MAC to realize a hybrid contention-reservation mechanism for the transmission of uplink traffic. In the proposed mechanism, any device with a buffered packet will first notify the Access Point (AP) during a contention phase before being given a reserved timeslot for the data transmission. We develop a mathematical model to analyse the energy consumption of the proposed mechanism and of IEEE 802.11ah. The results show that for a monitoring scenario, the proposed contentionreservation mechanism reduces the energy consumption for a successful uplink data transmission by up to 55%.

A multiconductor-transmission-line (MTL) model of the high-voltage dc power bus of electric vehicles (composed of two shielded cables running above a metallic ground) is proposed for the prediction of the propagation of conducted electromagnetic noise up to 100 MHz. Model parameters are computed by knowing the geometry of the system and the permittivity of dielectric materials. The proposed model is validated versus measurements. Finally, an approximate lumped-parameter circuit representation is also derived from the general MTL formulation, which is specifically useful for the implementation of the model in a SPICE circuit solver.