Jan Erik Håkegård

On multiuser MIMO capacity benefits in air-to-ground communication for air traffic management

In this paper, we focus on communication from airplanes to Air traffic Control (ATC) towers at airports, employing multiple antennas at the ATC. The whole air-to-ground communication system can then be modeled as a MIMO MAC channel with mobile users. The main aim is to demonstrate that multiuser MIMO systems can be useful for achieving spectrally efficient aeronautical communications, to quantify the achievable capacity gains when using such systems, and to show that they can be implemented by deploying multiple antennas at reasonable inter-antenna distances at the ATC. In particular, we analyze the issue of antenna separation of a uniform linear array (ULA) at the ATC, for the case of line of sight (LoS) air-to-ground channels. It turns out that at high frequency (1 GHz), the use of large ULAs is indeed possible since the maximum (ergodic) capacity gain is achieved already for antenna separation on the order of a few centimeters. We also observe the system performance in Ricean fading channels. The performance is evaluated with respect to ergodic multiuser capacity throughout.

Measurement and modeling of the 5 GHz airport surface channel at Barajas Airport

AeroMACS is a system currently under development to be used for airport surface communications. It is based on the IEEE802.16–2009 standard, and is developed in cooperation with the WiMAX forum. The frequency band allocated to AeroMACS is 5091–5150 MHz. When specifying the AeroMACS system, knowledge of typical propagation conditions at airports is of importance. Typical path loss models are necessary to estimate the range of a transmitter within different zones of the airport, and typical fading characteristics are used to estimate the performance of e.g. the selected coding and modulation schemes.

User requirements for HEO SATCOM for ATM in high latitudes

It is currently a significant ongoing effort worldwide to develop the future Air Traffic Management (ATM) system. As part of this work, a satellite communication system may ease the congestion problem for ATM services in high density airspace, and in addition provide coverage in oceanic, remote and polar (ORP) areas. For coverage over polar areas, satellites in highly elliptical orbits (HEO) are particularly suitable. In this paper, an overview of user categories is given and the channel characteristics of an aeronautical satellite channel are considered. Both Molniya and Tundra orbits are included. Curves show how parameters like elevation angle, free space path loss and Doppler shift vary as function of satellite movements. In addition, atmospheric effects due to signal propagation through the ionosphere and the troposphere is considered, and finally the effect of multipath propagation due to signal reflections by the aircraft surface and ground.

Empirical Path Loss Models for C-Band Airport Surface Communications

AeroMACS is a system currently under development for airport surface communications. It is based on the IEEE802.16-2009 standard, and is developed in cooperation with the WiMAX forum. The frequency band allocated to AeroMACS is 5091-5150 MHz. When specifying the AeroMACS system, knowledge of typical propagation conditions at airports is of importance. Typically, path loss models are used to estimate the range of a transmitter within different zones of the airport, and typically fading characteristics are used to estimate the performance of, e.g., the selected coding and modulation schemes. Propagation measurements have been performed at the Barajas airport in Madrid, Spain. The measurements includes Non-Line-Of-Sight (NLOS) as well as Line-Of-Sight (LOS) conditions. Based on these measurements, path loss parameters and path loss models are developed for different zones of large airports.

Dynamic Spectrum Access in realistic environments using reinforcement learning

We study the use of reinforcement learning to model Dynamic Spectrum Access in a realistic multi-channel environment. Three different approaches from the literature on the multi-armed bandit problem are compared on a set of realistic channel access models - two are based on stochastic models of the channel occupancy, while a third assumes an adversarial model. The algorithms are experimentally tested on channels occupied by primary users that behave according to a simple fair scheduler and a semi-Markov model based on WLAN traffic measurements; models that generate more realistic channel occupancy patterns than allowed by fixed i.i.d. probability models. The experiments show that the UCB1 algorithm of Auer et. al. [1] outperforms the other algorithms, and we support these findings using some simple theoretical results.

Non-perfect channel estimation in OFDM-MIMO-based underwater communication

The main focus in this publication is on the mean square error of underwater acoustic channel estimators as function of the delay and Doppler spreads of the channel, and the effect this estimation error has on the bit error rate performance of the system both using conventional single antennas (SISO) and when using multiple antennas (MIMO). It is investigated at which delay and Doppler spreads the decoding of the signal in the receiver becomes erroneous. It is assumed that there is no non-uniform Doppler shift. The radio communication standard IEEE 802.16e is modified to match underwater communication conditions. The system parameters are taken from measurements conducted in the Trondheim harbour in Norway in 2007. The channel estimator used is not optimal in the Wiener interpolator sense. Hence, the estimator is sub-optimal, but shows good performance and has relatively low complexity. For the described communication system to perform well the results indicate that movements in the water should be less than 0.01–0.1 m/s, and delay spreads should be less than 0.05–0.5 ms. In systems where the main problem is large Doppler spread, the number of sub-carriers should be small. In systems where the main problem is large delay spread, the number of sub-carriers should be large. The use of MIMO makes the system more robust against estimation errors. The density of pilot symbols may be increased to reduce the channel estimation error somewhat, at the expense of reduced efficiency. Considering the Trondheim harbour channel measurement results and their variability throughout the year, we find that the tested system copes well with the summer conditions while the winter conditions seems to be more challenging.

Effects of Channel Estimation Errors in OFDM-MIMO-Based Underwater Communications

State-of-the-art radio communication systems are in a large extent based on multi-carrier communication (OFDM) and multiple antennas (MIMO). In this paper the performance of such systems adapted to an underwater acoustic communication channel is assessed. The effect of the channel characteristics on an OFDM-MIMO scheme similar to that used in WiMAX (IEEE802.16e) is analyzed, in particular related to channel estimation error. Simulation results illustrate the relation between estimation error and BER performance for single antenna systems (SISO) and when a MIMO technique is applied.

Power control in HetNets and cognitive networks

In order to meet the demand for increased capacity in wireless networks, incorporating femtocells within the coverage of macrocells constitutes one of the strategies that currently receives most attention from both industry and academia. Femtocells may either be part of a HetNet as standardised within 3GPP, or constitute the secondary system in cognitive networks. Power control is a useful mechanism to allow efficient communications within both femto- and macrocells, but should be designed differently in the two cases. The performance of two different power control algorithms suitable for 3GPP femtocells and cognitive femtocells, respectively, is considered in this publication.

Compatibility study in the AeroMACS frequency band

This paper contains results from compatibility studies between AeroMACS and other systems operating in the same or adjacent frequency bands. These systems are RLAN, AMT, MLS and FSS feeder links. For compatibility with the terrestrial systems, the minimum distance to interferer is calculated, i.e. the minimum distance an interfering transmitter can be from a victim receiver without degrading the system performance beyond a permitted limit. For compatibility with FSS feeder links, the number of AeroMACS systems that may be installed in Europe without causing harmful interference to non-GEO satellite feeder link receivers is calculated. The results presented in this paper indicate that both MLS and AMT may cause harmful interference to AeroMACS if no precautions are made, while this is unlikely to happen when it comes to RLANs. Concerning compatibility with FSS feeder links, more than about 400 airports in Europe must be equipped with large AeroMACS installations to potentially cause harmful interference to FSS systems.

The Trondheim harbour: Acoustic propagation measurements and communication capacity

This paper presents results from a propagation measurement campaign carried out in the Trondheim harbour during the period from June to November 2007. Two vertically mounted transducers operating at a carrier frequency of 38 kHz permitted both single-input/single-output (SISO) and multiple-input/multiple-output (MIMO) channel measurements. The upper transducers at both sides were mounted around 2 meters from the sea surface. The sound velocity profile measurements showed large variations in the upper layers of the water column during the campaign period. Due to the fixed mechanical transducer constructions, the observed Doppler spread was low. The Delay spread however varied from 0.5 ms in the summer up to 9 ms in November. The calculated spatial multiplexing capacity within a 3 kHz bandwidth of the MIMO topology gave a factor in the order of 1.8 capacity improvement compared to derived SISO capabilities. The reference SISO propagation channels used in the calculations were one of the estimated elements of the corresponding MIMO channel matrices. Channel state information (CSI) at the transmitter maximises the capacity, particularly at low signal to noise (SNR) rations. Simulations comparing capacities achieved with and without transmitter CSI are shown. The results show that for the observed channels, spatial multiplexing MIMO capacity outperforms SISO and verified that CSI is beneficial at decreasing SNR values.