arXiv subjects

Riku Jäntti

Publications and source records attributed to Riku Jäntti.

48 records · Page 3Linked to original sources

arXiv2015

Energy Efficiency of Massive MIMO: Coping with Daily Load Variation

Massive MIMO is a promising technique to meet the exponential growth of mobile traffic demand. However, contrary to the current systems, energy consumption of next generation networks is required to be load adaptive as the network load varies significantly throughout the day. In this paper, we propose a load adaptive multi-cell massive MIMO system where each base station (BS) adapts the number of antennas to the daily load profile (DLP) in order to maximize the downlink energy efficiency (EE). In order to incorporate the DLP, the load at each BS is modeled as an M/G/m/m state dependent queue under the assumption that the network is dimensioned to serve a maximum number of users at the peak load. The EE maximization problem is formulated in a game theoretic framework where the number of antennas to be used by a BS is determined through best response iteration. This load adaptive system achieves around 24% higher EE and saves around 40% energy compared to a baseline system where the BSs always run with the fixed number of antennas that is most energy efficient at the peak load and that can be switched off when there is no traffic.

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arXiv2015

Energy-Efficient Load-Adaptive Massive MIMO

Massive MIMO is a promising technique to meet the exponential growth of global mobile data traffic demand. However, contrary to the current systems, energy consumption of next generation networks is required to be load adaptive as the network load varies significantly throughout the day. In this paper, we propose a load adaptive massive MIMO system that varies the number of antennas following the daily load profile (DLP) in order to maximize the downlink energy efficiency (EE). A multi-cell system is considered where each base station (BS) is equipped with a large number of antennas to serve many single antenna users. In order to incorporate DLP, each BS is modeled as an M/G/m/m state dependent queue under the assumption that the network is dimensioned to serve a maximum number of users at the peak load. For a given number of users in a cell, the optimum number of active antennas maximizing EE is derived. The EE maximization problem is formulated in a game theoretic framework where the number of antennas to be used by a BS is determined through best response iteration. This load adaptive system achieves overall 19% higher EE compared to a baseline system where the BSs always run with the fixed number of antennas that is most energy efficient at peak load and that can be switched-off when there is no traffic

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arXiv2015

Asymptotic Analysis of Multi-Antenna Cognitive Radio Systems Using Extreme Value Theory

We consider a spectrum-sharing cognitive radio system with antenna selection applied at the secondary transmitter (ST). Based on the extreme value theory, we deduce a simple and accurate expression for the asymptotic distribution of the signal to interference plus noise ratio at the secondary receiver. Using this result, the asymptotic mean capacity and the outage capacity for the secondary user (SU) are derived. The obtained asymptotic capacities approach the exact results as the number of transmit antennas $N$ increases. Results indicate that the rate of the SU scales as $\log(N)$ when the transmit power of the ST is limited by the maximum allowable interference level, while rate scales as $\log(\log(N))$ if ST is limited by the maximum transmit power.

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arXiv2015

Coordination protocol for inter-operator spectrum sharing in co-primary 5G small cell networks

We consider spectrum sharing between a limited set of operators having similar rights for accessing spectrum. A coordination protocol acting on the level of the Radio Access Network (RAN) is designed. The protocol is non-cooperative, but assumes an agreement to a set of negotiation rules. The signaling overhead is low, and knowledge of competitor's channel state information is not assumed. No monetary transactions are involved; instead, spectrum sharing is based on a RAN-internal virtual currency. The protocol is applicable in a scenario of mutual renting and when the operators form a spectrum pool. The protocol is reactive to variations in interference and load of the operators, and shows gains in a simulated small cell scenario compared to not using any coordination protocol.

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arXiv2015

Energy saving market for mobile operators

Ensuring seamless coverage accounts for the lion's share of the energy consumed in a mobile network. Overlapping coverage of three to five mobile network operators (MNOs) results in enormous amount of energy waste which is avoidable. The traffic demands of the mobile networks vary significantly throughout the day. As the offered load for all networks are not same at a given time and the differences in energy consumption at different loads are significant, multi-MNO capacity/coverage sharing can dramatically reduce energy consumption of mobile networks and provide the MNOs a cost effective means to cope with the exponential growth of traffic. In this paper, we propose an energy saving market for a multi-MNO network scenario. As the competing MNOs are not comfortable with information sharing, we propose a double auction clearinghouse market mechanism where MNOs sell and buy capacity in order to minimize energy consumption. In our setting, each MNO proposes its bids and asks simultaneously for buying and selling multi-unit capacities respectively to an independent auctioneer, i.e., clearinghouse and ends up either as a buyer or as a seller in each round. We show that the mechanism allows the MNOs to save significant percentage of energy cost throughout a wide range of network load. Different than other energy saving features such as cell sleep or antenna muting which can not be enabled at heavy traffic load, dynamic capacity sharing allows MNOs to handle traffic bursts with energy saving opportunity.

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arXiv2015

Spectrum Allocation for Multi-Operator Device-to-Device Communication

In order to harvest the business potential of device-to-device (D2D) communication, direct communication between devices subscribed to different mobile operators should be supported. This would also support meeting requirements resulting from D2D relevant scenarios, like vehicle-to-vehicle communication. In this paper, we propose to allocate the multi-operator D2D communication over dedicated cellular spectral resources contributed from both operators. Ideally, the operators should negotiate about the amount of spectrum to contribute, without revealing proprietary information to each other and/or to other parties. One possible way to do that is to use the sequence of operators' best responses, i.e., the operators make offers about the amount of spectrum to contribute using a sequential updating procedure until reaching consensus. Besides spectrum allocation, we need a mode selection scheme for the multi-operator D2D users. We use a stochastic geometry framework to capture the impact of mode selection on the distribution of D2D users and assess the performance of the best response iteration algorithm. With the performance metrics considered in the paper, we show that the best response iteration has a unique Nash equilibrium that can be reached from any initial strategy. In general, asymmetric operators would contribute unequal amounts of spectrum for multi-operator D2D communication. Provided that the multi-operator D2D density is not negligible, we show that both operators may experience significant performance gains as compared to the scheme without spectrum sharing.

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arXiv2014

Performance Analysis of Mean Value-Based Power Allocation with Primary User Interference in Spectrum Sharing Systems

In this paper, we provide an exact expression for the ergodic capacity of the secondary user, and a unified closed-form expression for its bounds with taking the consideration of the primary interference at the secondary receiver. In addition, a simple but accurate approximation of the the ergodic capacity of the primary user is presented. Moreover, a primary user capacity loss based power allocation scheme for the secondary user is also proposed. Finally, we compare the performance of the two power allocation schemes in terms of the sum capacity. The results are validated through using numerical results and simulations.

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arXiv2014

Dimensioning of PA for massive MIMO system with load adaptive number of antennas

This paper takes into consideration the non-ideal efficiency characteristics of realistic power amplifiers (PAs) along with the daily traffic profile in order to investigate the impact of PA dimensioning on the energy efficiency (EE) of load adaptive massive MIMO system. A multicellular system has been considered where each base station (BS) is equipped with a large number of antennas to serve many single antenna users. For a given number of users in a cell, the optimum number of active antennas maximizing EE has been derived where total BS downlink power is assumed to be fixed. Under the same assumption, the PAs have been dimensioned in a way that maximizes network EE not only for a single time snapshot but over twenty four hours of operation while considering dynamic efficiency characteristics of the PAs. In order to incorporate this daily load profile, each BS has been modeled as an M/G/m/m state dependent queue under the assumption that the network is dimensioned to serve a maximum number of users at a time corresponding to 100% cell traffic load. This load adaptive system along with the optimized PA dimensioning achieves 30% higher energy efficiency compared to a base line system where the BSs always run with a fixed number of active antennas which are most energy efficient while serving 100% traffic load.

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arXiv2014

Enhancing the Accuracy of Device-free Localization Using Spectral Properties of the RSS

Received signal strength based device-free localization has attracted considerable attention in the research society over the past years to locate and track people who are not carrying any electronic device. Typically, the person is localized using a spatial model that relates the time domain signal strength measurements to the person's position. Alternatively, one could exploit spectral properties of the received signal strength which reflects the rate at which the wireless propagation medium is being altered, an opportunity that has not been exploited in the related literature. In this paper, the power spectral density of the signal strength measurements are related to the person's position and velocity to augment the particle filter based tracking algorithm with an additional measurement. The system performance is evaluated using simulations and validated using experimental data. Compared to a system relying solely on time domain measurements, the results suggest that the robustness to parameter changes is increased while the tracking accuracy is enhanced by 50% or more when 512 particles are used.

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arXiv2014

Detecting Human-induced Reflections using RSS of Narrowband Wireless Transceivers

Radio frequency sensor networks are becoming increasingly popular as an indoor localization and monitoring technology for gaining unobtrusive situational awareness of the surrounding environment. The localization effort in these networks is built upon the well-established fact that the received signal strength measurements vary due to a person's presence on the line-of-sight of a transmitter-receiver pair. To date, modeling this decrease in received signal strength and utilizing it for localization purposes have received a considerable amount of attention in the research field. However, when the person is in the close vicinity of the line-of-sight but not obstructing it, the signal reflected from the human body is also affecting the received signal strength and can be used for occupancy assessment purposes. In this paper, we first model the effect of human-induced reflections as a function of communication frequency, and then use the model as a basis for energy based occupancy detection. The derived methods are evaluated numerically and the detection probability of the proposed detector is validated with experimental data. The results suggest that when more than eight frequency channels are utilized, presence of a person can be detected using RSS measurements of a single transmit-receive pair with detection probability higher than 0.95 and false alarm probability less than 0.01 in an area of 2 m x 2.5 m. Moreover, the important implications of the studied methods on the available narrowband radio frequency sensor network applications are discussed in detail.

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arXiv2014

A Three-State Received Signal Strength Model for Device-free Localization

The indoor radio propagation channel is typically modeled as a two-state time-variant process where one of the states represents the channel when the environment is static, whereas the other state characterizes the medium when it is altered by people. In this paper, the aforementioned process is augmented with an additional state. It is shown that the changes in received signal strength are dictated by: i) electronic noise, when a person is not present in the monitored area; ii) reflection, when a person is moving in the close vicinity of the line-of-sight; iii) shadowing, when a person is obstructing the line-of-sight component of the transmitter-receiver pair. Statistical and spatial models for the three states are derived and the models are empirically validated. Based on the models, a simplistic device-free localization application is designed which aims to: first, estimate the temporal state of the channel using a hidden Markov model; second, track a person using a particle filter. The results suggest that the tracking accuracy is enhanced by at least 65% while the link's sensitivity region is increased by 100% or more with respect to empirical models presented in earlier works.

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arXiv2013

Catch a Breath: Non-invasive Respiration Rate Monitoring via Wireless Communication

Radio signals are sensitive to changes in the environment, which for example is reflected on the received signal strength (RSS) measurements of low-cost wireless devices. This information has been used effectively in the past years e.g. in device-free localization and tracking. Recent literature has also shown that the fading information of the wireless channel can be exploited to estimate the breathing rate of a person in a non-invasive manner; a research topic we address in this paper. To the best of our knowledge, we demonstrate for the first time that the respiration rate of a person can be accurately estimated using only a single IEEE 802.15.4 compliant TX-RX pair. We exploit channel diversity, low-jitter periodic communication, and oversampling to enhance the breathing estimates, and make use of a decimation filter to decrease the computational requirements of breathing estimation. In addition, we develop a hidden Markov model (HMM) to identify the time instances when breathing estimation is not possible, i.e., during times when other motion than breathing occurs. We experimentally validate the accuracy of the system and the results suggest that the respiration rate can be estimated with a mean error of 0.03 breaths per minute, the lowest breathing rate error reported to date using IEEE 802.15.4 compliant transceivers. We also demonstrate that the breathing of two people can be monitored simultaneously, a result not reported in earlier literature.

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