Digital Beamforming as a Means for Interference Cancellation

Document type: Researchreports
Full text:
Author(s): Jörgen Nordberg, Sven Nordholm, Sven Nordebo, Ingvar Claesson
Title: Digital Beamforming as a Means for Interference Cancellation
Translated title: Digital lobformning som ett hjälpmedel för interferens undertryckning
Series: Research Report
Year: 1998
Issue: 21
ISSN: 1103-1581
Organization: Blekinge Institute of Technology
Department: Dept. of Signal Processing (Institutionen för signalbehandling)
Dept. of Signal Processing S-372 25 Ronneby
+46 455 780 00
http://www.hk-r.se/isb/isb_en.html
Authors e-mail: Jorgen.Nordberg@its.hk-r.se
Language: English
Abstract: The increasing demand for user capacity is a major challenge to network operators today. In order to increase the capacity of a mobile radio network, it is desirable to exploit the spatial domain in an efficient way.
An array adds spatial domain selectivity in order to improve the Carrier-to-Interference ratio(C/I).
An adaptive antenna array can further improve the Carrier-to-Interference ratio(C/I) by suppressing interfering signals.

The proposed circular array consists of K elements and combines fixed beamformers with interference cancellers. The fixed beamformers use a weight matrix to form multiple beams. The interference canceller suppresses undesired
signals, called jammers, leaking into the desired beam.

The desired signal is filtered out by the fixed beamforming structure. Due to the side-lobes, interfering signals will also be present in this beam. Two alternative
strategies may be chosen to cancel these interferers; use the other fixed beam outputs as inputs to an adaptive interference canceller, or regenerate the outputs from the other fixed beams and generate clean signals which are used as inputs to adaptive interference cancellers.

Results are presented using beamformer weights obtained from a Least Square (LS) minimisation as well as minimax.
Summary in Swedish: Ett sätt att öka kapaciteten i dagens mobiltelefoni-system är att använda flera antenner i basstationerna d.v.s använda digital lobformning. Denna rapporten beskriver hur man med hjälp utav digital lobformning kan förbättra kvaliteten på den mottagna signalen.
Subject: Signal Processing\General
Keywords: Beamforming, Interference cancellation, Adaptive Interference Cancellation, NLMS, leaky-LMS, mini-max beamformer
URN: urn:nbn:se:bth-00502
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