Blind Subband Adaptive Equalization

Document type: Researchreports
Full text:
Author(s): Jörgen Nordberg
Title: Blind Subband Adaptive Equalization
Translated title: Blind Adaptiv Subband baserad Kanalutjäming
Series: Research Report
Year: 2002
Issue: 11
ISSN: 1103-1581
Organization: Blekinge Institute of Technology
Department: Department of Telecommunications and Signal Processing (Institutionen för telekommunikation och signalbehandling)
Department of Telecommunications and Signal Processing S-372 25 Ronneby
+46 455 38 50 00
Authors e-mail: jno@bth.se
Language: English
Abstract: It is predicted that a large portion of future wireless communication capacity will be used to provide wireless data services. This new emphasis results in a significant change in substantial parts of the wireless infrastructure, it is important to have low bit error transmission links to get Quality of Service similar to the internet. Future services will also demand higher data rates. These factors mean that there will be a significant need for good quality equalization schemes in the receiver to reduce the different effects of the radio channels, such as intersymbol interference and multipath propagation. The use of linear equalizers leads to high numerical complexity filters even for short delay spread channels. High complexity equalizers implies slow convergence and high numerical load per processed symbol. To save the amount of training or pilot signals and thus increasing the useful data bits, a blind adaptation of the equalizer weights is commonly used. A blind adaptation algorithm in combination with a long equalizer result in even slower convergence. It is therefore desirable to improve the convergence properties of such equalizer schemes. A blind delayless subband equalizer structure is shown to improve the convergence properties of the equalizer. This equalizer consists of a combination of a fullband filtering and and a subband adaptation.

In this paper a novel filter bank design and also improved subband-to fullband filter transformation methods is presented. By optimizing the filter bank design, and improving the subband-to-fullband transformation, considerable improvements have been achieved both when it comes to convergence speed and the level of equalization obtained.

Simulation results show that the new subband equalization structure has a 12 times faster convergence than its fullband counterpart. The bit error rate is almost the same in both schemes. Thus, there are only advantages by using the suggested equalizer implementation compared to a conventional fullband implementation. The convergence improvement combined with computational savings make it a very attractive technique to use.
Summary in Swedish: I moderna telekommunikationssystem behövs ofta väldigt komplexa (beräkningskrävande) kanalutjämnare för att man ska kunna ha hög kapacitet i sitt system. Ett sätt att reducera komplexiteten är att implementera en subband baserad kanalutjämnare. I denna rapport presenteras just en sådan blind adaptiv subband baserad kanalutjämnare. Denna struktur har flera positiva egenskaper än låg komplexitet, som snabb konvergens dvs. kanalutjämnare kan snabbt följa förändringar i insignalen. Blind Kanalutjämning, CMA, Filter Design,
Subject: Signal Processing\General
Telecommunications\General
Signal Processing\Filter Design
Keywords: Subband Equalization, Filter Design, Blind Equalization, CMA
URN: urn:nbn:se:bth-00200
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