Beam-forming and Power Control in flexible Spectrum USage for LTE Adavnced System
Author
Ricci, Massimiliano
Term
10. term
Publication year
2008
Pages
98
Abstract
Denne afhandling undersøger stråleformning og effektstyring i forbindelse med intern spektrumdeling (Flexible Spectrum Usage, FSU) i LTE Advanced. FSU udnytter ledige frekvenser opportunistisk for at øge den gennemsnitlige spektraleffektivitet og begrænse interferens mod andre systemer. For at reducere interferens analyseres og implementeres algoritmer for stråleformning (at styre signaler mod ønskede brugere) og effektstyring (at justere sendeeffekt) i MATLAB. Som udgangspunkt antages perfekt kanaltilstandsinformation (CSI) ved senderen, og single-user (SU) MIMO downlink-stråleformning implementeres for at vurdere linkpræstationen. Som casestudie anvendes en linkniveausimulator, der følger LTE-standarden. Derudover undersøges multi-user (MU) MIMO downlink med OFDM (Orthogonal Frequency Division Multiplexing) og SDMA (Spatial Division Multiple Access), med to stråleformningsalgoritmer: zero-forcing (ZF) og successive minimum mean square error (SMMSE). Ydeevnen evalueres på linkniveau ved at gennemsnitliggøre bitfejlrate (BER) og gennemstrømning (TH) for alle kandidatusere. En Dominant Eigen Transmission (DET) effektalgoritme anvendes for at maksimere signal-støj-forholdet (SNR) ved modtageren og minimere BER. Numeriske simuleringer viser klare gevinster: tilsvarende SNR-forbedringer på cirka 3–5 dB afhængigt af den anvendte modulation og omkring 3 dB ved lav SNR, hvilket resulterer i lavere BER og højere gennemstrømning sammenlignet med samme system uden stråleformning. Yderligere resultater viser, at SMMSE overgår ZF med omkring 3 dB forbedring i både BER og gennemstrømning.
This thesis investigates beamforming and power control in intra-system spectrum sharing (Flexible Spectrum Usage, FSU) for LTE Advanced. FSU opportunistically uses available frequencies to increase average spectral efficiency while limiting interference to other systems. To reduce interference, algorithms for beamforming (steering signals toward intended users) and power control (adjusting transmit power) are analyzed and implemented in MATLAB. As a starting point, the work assumes perfect channel state information (CSI) at the transmitter and implements single-user (SU) MIMO downlink beamforming to evaluate link performance. A link-level simulator compliant with the LTE standard is used as a case study. The study then considers multi-user (MU) MIMO downlink with OFDM (Orthogonal Frequency Division Multiplexing) and SDMA (Spatial Division Multiple Access), using two beamforming algorithms: zero-forcing (ZF) and successive minimum mean square error (SMMSE). Performance is evaluated at link level by averaging bit error rate (BER) and throughput (TH) across candidate users. A Dominant Eigen Transmission (DET) power algorithm is applied to maximize the signal-to-noise ratio (SNR) at the receiver and minimize BER. Numerical simulations show clear gains: equivalent SNR improvements of about 3–5 dB depending on modulation and around 3 dB at low SNR, leading to lower BER and higher throughput compared with the same system without beamforming. Additional results show that SMMSE outperforms ZF by about 3 dB in both BER and throughput.
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