Riku Jäntti

Machine-type communications: current status and future perspectives toward 5G systems

Machine-type communications (MTC) enables a broad range of applications from mission- critical services to massive deployment of autonomous devices. To spread these applications widely, cellular systems are considered as a potential candidate to provide connectivity for MTC devices. The ubiquitous deployment of these systems reduces network installation cost and provides mobility support. However, based on the service functions, there are key challenges that currently hinder the broad use of cellular systems for MTC. This article provides a clear mapping between the main MTC service requirements and their associated challenges. The goal is to develop a comprehensive understanding of these challenges and the potential solutions. This study presents, in part, a roadmap from the current cellular technologies toward fully MTC-capable 5G mobile systems.

Energy-Efficient Relay Selection and Power Allocation for Two-Way Relay Channel with Analog Network Coding

In this letter, we consider a two-way relay channel (TWRC) with two end nodes and k relay nodes, where end nodes have the full channel-state information (CSI) and relay nodes only have the channel-amplitude information (CAI). With the objective of minimizing transmit power consumption at required end-to-end rates, energy-efficient relay selection (RS) and power allocation (PA) scheme is studied for TWRC based on analog network coding (ANC). Firstly, we propose an energy-efficient single RS and PA (E-SRS-PA) scheme, where the best relay node is selected to minimize total transmit power. Then, we prove that E-SRS-PA scheme is the optimal energy-efficient RS and PA (OE-RS-PA) scheme in ANC-based TWRC, and thus the optimal number of relay nodes to be selected in energy efficiency sense is equal to one. In addition, the closed-form expressions of optimal power allocation of E-SRS-PA scheme are derived. Numerical simulations confirm the optimality of proposed E-SRS-PA and demonstrate the energy efficiency of ANC-based TWRC compared with the other relaying schemes.

Asymptotically fair transmission scheduling over fading channels

The problem of scheduling delay insensitive data over a direct sequence code-division multiple-access downlink fading channel is considered. This work considers the case where only one user at a time is allowed to transmit. As the channels can be considered to vary asynchronously among the users, multiuser diversity gains can be obtained by exploiting channel adaptive scheduling. For this, schedulers of different adaptation rate are suggested and compared. In particular, the authors analyze a simple fast scheduler that schedules a user to transmit when its channel is good relative to its mean. This scheduler is resource fair in the sense it can provide the users with the same asymptotic channel access. They show that the achievable scheduling gain compared to round robin is equal to the gain of a selection diversity scheme. The scheduling gain is determined, both on closed-form and by numerical integration, for several scenarios, including multicellular systems and the effect of time delayed channel estimates. The results show that the scheduling gain is larger for channels with low average quality.

Joint power control and intracell scheduling of DS-CDMA nonreal time data

The performance of DS-CDMA systems depends on the success in managing interference arising from both intercell and intracell transmissions. Interference management in terms of power control for real time data services like voice has been widely studied and shown to be a crucial component for the functionality of such systems. In this work we consider the problem of supporting downlink nonreal time data services, where in addition to power control, there is also the possibility of controlling the interference by means of transmission scheduling. One such decentralized schedule is to use time division so that users transmit in a one-by-one fashion within each cell. We show that this has merits in terms of saving energy and increasing system capacity. We combine this form of intracell scheduling with a suggested distributed power control algorithm for the intercell interference management. We address its rate of convergence and show that the algorithm converges to a power allocation that supports the nonreal time data users, using the minimum required power while meeting requirements on average data rate. Numerical results indicate a big potential of increased capacity and that a significant amount of energy can be saved with the proposed transmission scheme.

A Synchronized Wireless Sensor Network for Experimental Modal Analysis in Structural Health Monitoring

Structural health monitoring aims to provide an accurate diagnosis of the condition of civil infrastruc- tures during their life span using data acquired by sen- sors. Wireless sensor networks represent a suitable mon- itoring technology to collect reliable information about the structures condition, replacing visual inspections, and reducing installation and maintenance time and costs. This article introduces a time synchronized and configurable wireless sensor network for structural health monitoring enabling a highly accurate identification of the modal properties of the monitored structure. The wireless sensor nodes forming the network are equipped with a 3-axis digital accelerometer and a temperature and humidity sensor. The implemented Medium Access Con- trol layer time synchronization protocol (μ-Sync) en- sures a highly accurate synchronicity among the samples collected by the nodes, the absolute error being constantly below 10 μs, also when high sampling frequency (up to 1 kHz) and extended sampling periods (up to 10 min- utes) are applied. The experimental results obtained on a wooden model bridge, compared with those derived from acceleration signals acquired by high-quality wired sensors, show that the so synchronized wireless sensor nodes allow a precise identification of the natural fre- quencies of vibration of the monitored structure (1% maximum relative difference).

5GrEEn: Towards Green 5G mobile networks

In 2020, mobile access networks will experience significant challenges as compared to the situation of today. Traffic volumes are expected to increase 1000 times, and the number of connected devices will be 10-100 times higher than today in a networked society with unconstrained access to information and sharing of data available anywhere and anytime to anyone and anything. One of the big challenges is to provide this 1000-fold capacity increase to billions of devices in an affordable and sustainable way. Low energy consumption is the key to achieve this. This paper takes as starting point the situation of today, and tries to pinpoint important focus areas and potential solutions when designing an energy efficient 5G mobile network architecture. These include system architecture, where a logical separation of data and control planes is seen as a promising solution; network deployment, where (heterogeneous) ultra dense layouts will have a positive effect; radio transmission, where the introduction of massive antenna configurations is identified as an important enabler; and, finally, backhauling solutions that need to be more energy efficient than today.

Transmission rate scheduling for the non-real-time data in a cellular CDMA system

The main focus of this letter is on the non-real-time service where the so-called best effort type of resource management is applicable. Given an amount of data packets to each user, the problem of minimizing the time span to send all the packets is investigated. In particular, the problem is elaborated in the CDMA contest. With Bellmans (1957) principle of optimality, we derive an optimal scheduling, in which users transmit data through a hybrid of CDMA and TDMA. Numerical results show that by having optimal scheduling, we can significantly reduce the transmission time span, and thereby increase the radio network capacity.

Non-invasive respiration rate monitoring using a single COTS TX-RX pair

Respiratory rate is an important vital sign that can indicate progression of illness but to also predict rapid decline in health. For the purpose, non-contact monitoring systems are becoming more popular due to the self-evident increase in patient comfort. As a cost effective solution for non-invasive breathing monitoring, utilizing the received signal strength measurements of inexpensive transceivers has been proposed. However, the applicability of the available solutions is limited since they rely on numerous sensors. In this work, considerable improvement is made, and a respiratory rate monitoring system based on a single commercial off-the-shelf transmitter-receiver pair is presented. Methods that enable estimation and enhance the accuracy are presented and their effects are evaluated. Moreover, it is empirically demonstrated that the performance of the system is comparable to the accuracy of a high-end device for 3-4 orders of magnitude less price; achieving mean absolute error of 0.12 breaths per minute in the most realistic scenario of the experiments.

Detection of Unknown Signals in a Fading Environment

In this letter we consider the effect of combined slow and fast fading on the energy detection. We model the received signal power distribution and propose a simplified approximation to this distribution. The approximation allows us to derive the distribution of the decision variable at the detectors output in closed-form. By using the suggested distribution, we find that in the block fading channel the impact of slow fading is not significant. In the case of multiple independent fast fading realizations with commo.n slow fading value we can show how the slow fading starts to dominate the detection performance.

Opportunistic Uplilnk Scheduling for 3G LTE Systems

In this paper we propose a heuristic opportunistic scheduler that is consistent with the resource allocation constraints of the uplink channel for 3G long term evolution (LTE) systems. Retransmission processes as well as channel conditions are taken into account in the formation of the scheduling decision. The heuristic scheduler could be seen a reasonable choice for solving the constrained resource allocation maximization problem since it is computationally feasible and can find a practical solution. We also formulate an integer programming problem that provides a theoretical optimal solution. The heuristic scheduler was found to perform relatively well when compared to the optimal solution.