Lars Erling Bråten

Automatic antenna tilt control for capacity enhancement in UMTS FDD

Simulations were performed to evaluate the effect of adaptively adjusting the base station antenna vertical tilt angle to adapt to the current geographical traffic load distribution and thereby achieve an overall capacity increase in UMTS FDD. The capacity increase is very dependant on the traffic conditions. Using a generic 21-cell scenario and positioning three traffic hotspots within the area with varying position relative to the base stations, the capacity increase was in the order of 30% on average at a 99% grade-of-service. The capacity improvement by using tilt adjustment increases with increasingly unbalanced traffic, as expected. Automatic tilt control represents a viable alternative for interference reduction purposes and thereby provisioning of better overall network capacity during dynamically changing traffic situations.

An evaluation of adaptive antennas for UMTS FDD by system simulations

A system simulator for performance evaluation of adaptive antennas in UMTS FDD has been developed. The simulator is flexible, it uses realistic channel and system assumptions, and, for a given scenario, provides the maximum number of users that can be supported by the network. The antenna types included in the simulator are switched lobe, phased array and adaptive array, as well as conventional fixed sector antennas. Results point to a capacity increase of more than a factor of two by using adaptive antennas compared to conventional sector antennas. Most of the increase is obtained by using the relatively simple switched lobe antenna implementation. Using adaptive antennas can alternatively increase range or reduce transmit power. The reduction in transmit power points to MS battery lifetime being increased by at least 4 times compared to conventional sector antennas. Sector and switched lobe antennas are approximately equally sensitive to downlink orthogonality loss. The total network capacity was roughly 20 % higher when increasing the downlink code orthogonality from 0.4 to 0.8.

Space - time dynamic channel model for broadband fixed wireless access

Broadband fixed wireless access is a point-to-multipoint technology for providing broadband services. These systems need a space-time channel model which accounts for the spatial and temporal variation of rain attenuation for simulating fading mitigation techniques such as adaptive coding and modulation, and other capacity enhancing techniques. In this paper we study the space-time correlation of rain attenuation, and propose a simulation model for generating correlated rain attenuation time series base on the generalised Maseng-Bakken model. In addition, the parameter beta controlling rain attenuation dynamics in the Maseng-Bakken model have been extracted from measurements and shows variations with location within a single rain event.

Prediction of coverage for a LEO system in mid- and high-latitude urban areas using a photogrammetric technique

The performance of a Globalstar-like low-Earth-orbit system is predicted based on hemispherical photographs taken in Ottawa, Canada, and Lillestrom, Norway. The pictures are sorted into three states: vegetation, solid obstacles and clear sky. The simulated satellite look angles are combined with the digital pictures to determine the path state for each satellite, i.e., shadowed, blocked or clear line-of-sight. Cumulative distributions of narrowband fading at L-band are developed for the case when the receiver utilizes one (best or highest) satellite, and up to three-fold diversity with either switching or coherent combining of the received signals. By selecting the best satellite instead of the highest, a significant reduction in fading is obtained. For Lillestrom, the necessary fade margin to obtain 1% outage is reduced by 13 dB when using 3-fold coherent combining diversity instead of the single best satellite.

An evaluation of adaptive antennas for a UMTS FDD network deployed in a suburban area of Norway

A system simulator for performance evaluation of adaptive antennas in UMTS FDD networks has been developed. The simulator is flexible, it uses realistic channel and system assumptions, and for a given scenario provides the maximum network capacity. The antenna types included in the simulator are switched lobe, phased array and adaptive array as well as conventional fixed sector antenna. Analyses of a UMTS network deployment in a suburban area of Oslo, Norway, reveal that adaptive antenna techniques potentially can more than double the radio capacity compared to conventional sector antennas. The majority of the gained capacity is obtained by using a relatively simple switched lobe antenna implementation, providing approximately 75% of the capacity compared to the adaptive arrays. The phased array alternative offered a slight improvement over switched lobe, with average throughputs per base station of 2.4 Mbit/s and 2.3 Mbit/s respectively. These results demonstrate that beam forming techniques can provide significant radio capacity gains for UMTS FDD.

Satellite visibility in Northern Europe based on digital maps

A rapid growth of new satellite systems utilizing the Ka-band (27 – 40 Ghz) and even higher frequencies is expected in the coming years. The services offered will include broadband communication, interactive broadcasting, multimedia applications, interconnection of local area networks and Internet connectivity. Many of the new systems will use technologies as multiple spot-beams, onboard processing, and switching of packets between beams and inter satellite links. Because of congestion in the lower bands such ad C (4 – 8 Ghz) and Ku-band (12 – 18 Ghz), numerous of these services will use Ka-band. One additional advantage to the spectrum availability at Ka-band is the potential of smaller terminals compared to those used in lower frequency bands.Several mobile satellite systems have recently started operation and more are planned or scheduled for implementation within a few years to provide personal and data communication at L-band (1 – 2 Ghz) and S-band (2 – 4 Ghz) frequencies. The systems will utilize different orbit types, for example low, medium or geostationary earth orbits, to provide voice and data services to mobile users.Understanding of the propagation aspects is important for successful design of a satellite system obtaining the targeted service quality and availability. For systems operating above about 10 Ghz, attenuation caused by hydrometeor effects is the dominant propagation impairment on line-of-sight (LOS) links. For mobile communications systems operating at lower frequencies, the impairments resulting from multipath propagation, shadowing and blockage from obstacles on the ground severely affect the radio signals. Estimation of dynamic propagation is essential for the design of reliable and spectrum efficient communication systems. The system can adapt the transmission methodology that maximizes the throughput of information and optimizes the delivery time. The design of such mitigation techniques will depend on the dynamics and how often the events occur.The research conducted in this study on mobile propagation effects of terrain at L-band has led to an improved three-state channel model for land mobile satellite systems. The time spent in each of the states is quite realistic, facilitating better simulation of the performance of communication systems. A new methodology was developed to perform large area coverage estimation by calculating satellite visibility for low earth orbit and geostationary constellations based on digital terrain maps. The procedure takes into account large terrain obstacles and procedures a gross overview of the potential area covered with one or several satellites. A photogrammetric technique to assess performance of non-geostationary orbit (NGSO) systems in mid- and high latitude urban areas was used to estimate channel fading and diversity improvement. Some measurements of the maximum obtainable call duration for the Iridium system are included as well.The studies on atmospheric propagation effects between 20 and 60 Ghz included analyses of fade and inter-fade duration statistics, which are important when evaluating fade mitigation techniques and estimating system outages. Fade duration measurements were analyzed and an effort made to find a common statistical fade duration model. Based on this work, a new prediction method for fade durations on satellite-earth paths was developed. This ability to forecast rain attenuation was investigated with the aid of statistical prediction methods and terrestrial measurements on a 60 Ghz link. Finally, beacon measurements at 50 Ghz from Italsat F1 were used to test and compare available scintillation prediction models.The work has improved the ability to estimate and simulate propagation effects on mobile and fixed satellite system performance.

Development and role of broadband wireless access networks for fixed and nomadic users

Hybrid wireless network technologies are well suited to providing broadband access everywhere with enhanced performance in term of coverage, capacity and throughput compared to access networks based on a single technology. Wireless broadband technologies have implicit advantages such as an ability to serve the customer everywhere and mitigate the digital divide, offer right capacity at right cost and remain connected on the move. Wireless is scalable in both capacity and coverage areas, an imperative as requested services evolve towards increasingly bandwidth hungry applications. There is a rapid development that takes place today, with a considerable interest in establishing WiMAX solutions copying the success of WiFi. This may well happen, but many challenges are still to be overcome. Interoperability of hybrid networks is a key design objective to drive solution costs down. Efficient utilisation of the frequency spectrum requires progress in various fields such as interference suppression and smart radios, efficient resource management and access control. The designing and planning of hybrid networks require suitable software tools taking into account user and service characteristics as well as evolving technical and economical factors. This paper is based on work in the project BROADWAN (BROADWAN, 2004; Tjelta et al., 2004), partly funded under the Information Society Technologies (IST) priority of the European Commission Sixth Framework Programme.