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Advanced Antennas in Wireless Communications: co-located & distributed
KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Communication Systems, CoS.
2006 (English)Doctoral thesis, monograph (Other scientific)
Abstract [en]

In a wireless radio network system, with an evolving standard, there is a need to increase system capacity due to the increase in the traffic demands, the higher data rate usage, and the need to further extend the coverage of the system. One possible solution is to use multiple antennas (co-located or distributed) for the radio links. The aim of this thesis is to estimate the capacity gain for these advanced antenna scenarios in comparison to the ones in current use (e.g. single antenna in a 3-sector site) with special emphasis on transmit diversity and beamforming techniques. The quantification of such gain is mainly performed, evaluated and analyzed in dynamic system simulators with an accurate interference modeling. A generalized Signal to Interference Noise Ratio (SINR) estimation for a MIMO DS-CDMA system is derived, and as a by-product a closed-form solution of the orthogonality factor is obtained. Moreover the effectiveness of an antenna system is evaluated in a MIMO-test bed.

Transmit diversity (TXDiv) is evaluated in WCDMA systems for flat fading (i.e. Pedestrian A (PedA)) and frequency selective channels (i.e. Typical Urban (TU)). While in flat fading channels, TXDiv schemes such as Space Time Transmit Diversity (STTD) and Closed Loop Mode 1 (CL1) offer a substantial system capacity gain, the gain is negligible in frequency selective channels. In HSDPA systems, TXDiv offers negligible gain in flat fading channels and causes a significant loss in frequency selective channels. The loss is mainly due to random spatial interference patterns (the so called Flashlight Effect), that are present in the HSDPA system. A simple scheme that mitigates this phenomena is presented. The scheme yields a 70% gain for CL1 in a PedA channel, while 10% gain is observed in the TU channel.

The introduction of beamforming in WCDMA systems leads to a substantial system capacity and coverage gain. Three different implementations are evaluated and analyzed: Higher Order Sectorization (HOS), Fixed Beams (FB) with S-CPICH as a phase reference and finally FB as P-CPICH as a phase reference. Further, the impact of angular spread, the interaction and impact of radio resource management as power tuning of the common channel, scrambling code allocation technique, admission control, handovers and various antenna configurations are analyzed. The 12-sector sites yield the best system capacity gain in comparison to 3-sector sites equipped with a single antenna, slightly more than a 3-sector sites equipped with 4 FB each. In HSDPA systems, FB offers an impressive capacity gain, up to 200% for a 4 FB system.

Capacity estimations with a dynamic system simulator give a clear indication about the gain of the simulated system, but the robustness of any method have to be verified through test-beds. STTD with receive diversity is implemented and tested in a real-time DSP MIMO test-bed for a single carrier frequency domain equalization system. A new pilot structure for joint Carrier Frequency Offset (CFO) and channel estimation is proposed and evaluated to address the inter-symbol interference and the severe CFO due to hardware impairments. The new pilot scheme results in significant reduction of the required overhead signalling compared to previous schemes.

Instead of having antennas co-located and connected to the same radio unit (i.e. BS or UE), antennas can be distributed but having the potential to cooperate together. Furthermore, the system provides a macro-diversity gain and also relaxes the hardware complexity at the BS and/or UE. Two novel methods that provide frequency and spatial diversity are proposed. The first one called Relay Cyclic Delay Diversity (RCDD), provides frequency and spatial diversity for a multihop system while requiring a lower overhead than the methods proposed in the literature. RCDD yields a high SINR gain which translates into a substantial cell throughput gain in comparison to a single hop system. The second method called two dimensional cyclic prefix (2D-CP), introduces artificial time diversity and requires only a single transmission phase for each direction in a cooperative relaying wireless communication system. Besides not requiring an antenna specific pilots, the 2D-CP provides a substantial data rate increase.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , xxii, 201 p.
Trita-ICT-COS, ISSN 1653-6347 ; 0602
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-3966OAI: diva2:10206
Public defence
2006-05-29, Sal C1, KTH-Electrum, Isafjordsgatan 22, Kista, 13:00
QC 20100915Available from: 2006-05-16 Created: 2006-05-16 Last updated: 2010-09-15Bibliographically approved

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