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Differential Beam-Forming Using Two-Dimensional Antenna Arrays in an LTE FDD System
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
2015 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Differentiell lobformning för tvådimensionella antennuppställningar i ett LTE-FDD-system (Swedish)
Abstract [sv]

Basstationer med flera antenner kan aktivt styra signalenergi mot en mottagare med hjälp av lobformning, vilket ger högre datatakt och lägre strömförbrukning än med en enda antenn. Lobformning kräver dock att kanalen skattas till varje antenn och i ett FDD-system måste denna skattning återkopplas till basstationen från mottagaren, vilket innebär en opraktiskt stor overhead, speciellt när loberna blir smalare. Differentiell lobformning är en robust teknik som med begränsad overhead möjliggör smala och välriktade lober genom differentiella justeringar av lobformen. Med hjälp av två förkodade referenssignaler från basstationen skattar mottagaren kanalen och rapporterar iterativt hur lobformningen ska förbättras så att SINR hos den mottagna signalen ökar. Den här uppsatsen utvecklar en algoritm som utökar differentiell lobformning till användandet av tvådimensionella antennuppställningar, vilket möjliggör justering av lobformen i två dimensioner och därmed potentiellt sett ökar mottagen signalstyrka. Algoritmen alternerar mellan att differentiellt justera lobformen horisontellt och vertikalt, utan ökad overhead. Algoritmen har testats för olika antennuppställningar i ett stadsscenario och ett landsbygdsscenario med horisontell användarfördelning, vilken dock har visat sig vara en begränsande faktor för att påvisa de potentiella vinster som differentiell lobformning i två dimensioner för med sig. Resultatet visar att det är viktigare att kunna erhålla en smal lob i den dimension där det finns många användare, i detta fall den horisontella dimensionen, än i den ortogonala dimensionen.

Abstract [en]

Base stations with multiple antenna elements can actively direct signal energy towards a user by means of beam-forming, which results in higher data rates and lower energy consumption compared to a single antenna element. However, beam-forming requires channel state estimates to each antenna element and in an FDD system, these estimates must be fed back to the base station from the user. This feedback infer an inconvenient amount of overhead, especially as the beam gets narrow. Differential beam-forming is a robust technique that, through differential adjustments to the beam shape, allows for narrow and well-directed beams at a low overhead cost. By means of two precoded reference signals from the base station, the user estimates the channel and iteratively reports how the beam-forming should be improved in order to increase the SINR of the sent signal. This thesis develops an algorithm that extends differential beam-forming to the usage of two-dimensional antenna arrays, which allows for adjustments of the beam in two dimensions. Thereby, the received signal strength is potentially increased. The algorithm alternates between differential adjustments to the beam horizontally and vertically, without increased overhead. The algorithm is simulated with different array sizes using an urban and a rural scenario with a horizontal user distribution. However, the biased user distribution has proven to constitute a limiting factor in order to demonstrate the potential benefits of differential beam-forming in two dimensions. The result shows that it is more important to obtain a narrow beam in the dimension where many users are located, in this case the horizontal dimension, than in the orthogonal dimension.

Place, publisher, year, edition, pages
2015. , 94 p.
Keyword [en]
Antenna Array, Beam Focusing, Beam-Forming, Feedback Process, Long Term Evolution, Precoding
National Category
Communication Systems
Identifiers
URN: urn:nbn:se:liu:diva-120844ISRN: LiTH-ISY-EX--15/4851--SEOAI: oai:DiVA.org:liu-120844DiVA: diva2:853478
External cooperation
Ericsson AB
Subject / course
Communication Systems
Supervisors
Examiners
Available from: 2015-09-14 Created: 2015-08-27 Last updated: 2015-09-16Bibliographically approved

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