Joonas Kokkoniemi

Frequency and Time Domain Channel Models for Nanonetworks in Terahertz Band

Time and frequency domain channel models are proposed for nanonetworks utilizing the terahertz band (0.1-10 THz) for wireless communication. Nanonetworks are formed by tiny nanodevices which consist of nanoscale (molecular scale) components. Channel models capturing the unique peculiarities of the THz band are needed for designing proper physical layer techniques and for accurate performance analysis. Existing channel models have included the free space path loss and the molecular absorption loss, which is significant in the THz band. This paper theoretically analyzes scattering including multiple scattering referring to a sequence of scattering events from small particles, such as aerosols. Both the frequency and the impulse responses are derived. It is shown that the small particle scattering can result into significant additional loss that needs to be taken into account with the loss depending on the density and size distribution of the particles. It is shown that multiple scattering leads to a long tail in the impulse response. As most of the physical layer proposals for nanonetworks are based on the on-off keying, the channel response to pulse waveforms is specifically considered.

Measurements and analysis of spectrum occupancy with several bandwidths

Opportunistic use of the 2.4 GHz industrial, scientific, and medical (ISM) band has recently received a growing interest. Numerous measurement campaigns have been conducted to analyze the spectrum use in the ISM band in several locations. However, the parameter setting in measurements regarding the bandwidth and time resolution has not been analyzed in detail to support opportunistic use in the band. In this paper, measurement analysis with several bandwidths in two different locations is conducted. The study shows that the bandwidth strongly affects the results. However, there is clearly room for opportunistic operation in all the cases. The results also show that the idle times in the ISM band are geometrically distributed when the time resolution of the analysis is 1 second.

Performance evaluation of vehicular LTE mobile relay nodes

European Telecommunication Standards Institute (ETSI) is standardizing the 3GPP Long Term Evolution Advanced (LTE-A) relay nodes (RNs) which are intended to be used for providing enhanced cell edge coverage and capacity. We present simulation results on the prospected LTE-A mobile relay node (MRN) applications. The future vehicles can communicate with their environment by exchanging information with surrounding sensor networks and objects. This is related to the concept of Internet of Things (IoT), in which even the smallest objects are equipped with sensors and connectivity capabilities, in order to report information on, e.g., temperature and air pressure. We consider a scenario where in-car connectivity is provided by a short range wireless link such as Wi-Fi or Bluetooth, which can be utilized by the passengers, various sensors, or the vehicle itself. We study the achievable system performance improvement when MRNs are utilized in comparison with the case, in which the users are independently connected to the LTE network. Through simulations, we show that the wireless links via MRNs can give significant advantage when compared to the direct connections from personal handsets to LTE base stations (eNBs).

Reflecting QoS of low-cost multi-provider municipal WiFi on commercial 3.G mobile data and ISM spectrum occupancy

We present two measurement campaigns reflecting the end-user QoS of a large municipal WiFi (IEEE 802.11 WLAN) network on the end-user QoS of three commercial 3.5G (HSPA) mobile data networks and on the spectrum occupancy of the 2.4 GHz ISM band. Our study shows that municipal provisioning of public wireless Internet access with IEEE 802.11 WLAN technology to achieve end-user QoS comparable to that of 3.5G mobile data networks is feasible and cost-efficient, despite the poor overall spectrum utilization of the ISM band by the IEEE 802.11 WLAN technology.

Frequency domain penetration loss in the terahertz band

Results on penetration loss measurements in the THz frequencies between 0.1-2 THz are reported. The measurements were conducted with time domain spectroscopy using the TeraView TeraPulse 4000 measurement equipment. We concentrate on the frequency-dependent penetration characteristics of various materials typical for indoor environments, providing both qualitative and quantitative assessment. The results show that the lower end of the THz band (<; 0.5 THz) suffers only modest loss in comparison to the higher frequencies. For the materials considered in this paper, plastic, glass and hard-board, the exact penetration properties are both frequency- and material-dependent. The incident angle to the material increases the penetration loss through increased path length inside the material. The exact values of these losses are provided.

Frequency domain scattering loss in THz band

Frequency domain scattering loss on small particles in terahertz frequency band (0.1-10 THz) is addressed. The wavelengths in THz band are short enough to enable scattering on small particles in the atmosphere. Rayleigh theories are utilized in estimating the scattering loss and it is shown that in proper conditions small particle scattering causes significant losses in the THz band. The small particle scattering is mainly an issue on the higher end of the THz band. This is due to the strong frequency dependency of the scattering. The effect of the scattering loss to the received signal strength is shown in the results.

Enabling simultaneous cooling and data transmission in the terahertz band for board-to-board communications

A system enabling simultaneous cooling and board-to-board communications is proposed and analyzed. It is shown that hollow pipes used in computer cooling systems can be applied for communications with extreme data rates at distances up to tens of centimeters. This is done by using wireless communications in the terahertz frequency band, 0.1-10THz. The experiments were performed in order to observe how straight and curved pipes of different diameters and lengths affect THz signals propagating inside the pipes. The measured pulses were recorded and used in numerical evaluation of bit error rate and throughput taking into account the effect of all possible combinations of N previous symbols. The numerical results show the dependency of the intersymbol interference on the delay profile of the channel and on the symbol period. The results demonstrate that even with simple on-off keying modulation the throughput reaches few terabits per second with qualitatively low bit error rates. This enables communications between rate-hungry electronics inside computers such as central and graphical processing units while simultaneously providing the cooling functionality.

Stochastic Geometry Analysis for Mean Interference Power and Outage Probability in THz Networks

Mean interference power and probability of outage in the THz band (0.1–10 THz) networks are studied. The frequency band has potential for enabling future short range communication systems because of the large available spectrum resources. This can enable huge data rates, or on the other hand, large numbers of users sharing the resources. The latter case is closely related to the subject of this paper on interference modeling for dense THz networks with stochastic geometry. We use it to estimate the average behavior of random networks. The literature has shown convenient closed form solutions for the mean interference power in ultrahigh frequency band (UHF, 300 MHz – 3 GHz). Those are not always readily applicable for the THz band. This is especially the case when THz band is modeled with the molecular absorption and free space path loss. Still, the mean interference power does have closed form solutions in all cases, but in some, numerical approximations have to be used. We provide the derivation and analysis of the mean interference power and the outage probability. The results are verified with computer simulations.

Reflection coefficients for common indoor materials in the terahertz band

We present some preliminary measurement results for the reflection properties of common indoor materials for 300 and 1000 GHz frequencies. These material include various wooden surfaces, concrete, rubber floor surface, and glass. All the presented materials are very smooth and only have a very small amount of diffuse scattering. For smooth surfaces, the reflection coefficients can reliably be estimated based on the Fresnel equations. The presented results are a part of a larger measurement campaign aiming at searching for refractive indices for different materials. Because these indices are unknown, we find them by fitting the measured path gains to those given by the Fresnel equations. Knowing the refractive indices, researchers can model the reflection loss/coefficients simply by Fresnel equations and, e.g., adjusting the polarization based on the desired application. The reflection coefficients have applications in all scales of communications, as the reflections are usually the most probable source of multipath signal components. Modeling these non-line-of-sight (NLOS) components properly is important when modeling realistic propagation environments.

Stochastic analysis of multi-tier nanonetworks in THz band

Future nanonetworks are formed by large numbers of autonomous, nano-sized sensors. These are often envisioned to be paired with one or more layers of higher complexity devices, providing access to the external networks. The number of devices sharing the same frequency resources can theoretically be very high, up to several hundreds per square meter. This causes the overall interference of the network to increase with the complexity of the network. In this work, stochastic geometry is utilized to derive the moments of the summed interference in the case of multi-tier nanonetworks in the terahertz frequency band (0.1--10 THz). All the devices in all the tiers of the network are assumed to be Poisson distributed. Based on this assumption, models for the moments of interference are derived and they are shown by computer simulations to predict the mean interference and its higher moments exactly.