3,209 research outputs found
Robust Pilot Decontamination Based on Joint Angle and Power Domain Discrimination
We address the problem of noise and interference corrupted channel estimation
in massive MIMO systems. Interference, which originates from pilot reuse (or
contamination), can in principle be discriminated on the basis of the
distributions of path angles and amplitudes. In this paper we propose novel
robust channel estimation algorithms exploiting path diversity in both angle
and power domains, relying on a suitable combination of the spatial filtering
and amplitude based projection. The proposed approaches are able to cope with a
wide range of system and topology scenarios, including those where, unlike in
previous works, interference channel may overlap with desired channels in terms
of multipath angles of arrival or exceed them in terms of received power. In
particular we establish analytically the conditions under which the proposed
channel estimator is fully decontaminated. Simulation results confirm the
overall system gains when using the new methods.Comment: 14 pages, 5 figures, accepted for publication in IEEE Transactions on
Signal Processin
Spatio-Temporal processing for Optimum Uplink-Downlink WCDMA Systems
The capacity of a cellular system is limited by two different phenomena, namely
multipath fading and multiple access interference (MAl). A Two Dimensional (2-D)
receiver combats both of these by processing the signal both in the spatial and temporal
domain. An ideal 2-D receiver would perform joint space-time processing, but at the
price of high computational complexity. In this research we investigate computationally
simpler technique termed as a Beamfom1er-Rake. In a Beamformer-Rake, the output of a
beamfom1er is fed into a succeeding temporal processor to take advantage of both the
beamformer and Rake receiver. Wireless service providers throughout the world are
working to introduce the third generation (3G) and beyond (3G) cellular service that will
provide higher data rates and better spectral efficiency. Wideband COMA (WCDMA)
has been widely accepted as one of the air interfaces for 3G. A Beamformer-Rake
receiver can be an effective solution to provide the receivers enhanced capabilities
needed to achieve the required performance of a WCDMA system.
We consider three different Pilot Symbol Assisted (PSA) beamforming techniques,
Direct Matrix Inversion (DMI), Least-Mean Square (LMS) and Recursive Least Square
(RLS) adaptive algorithms. Geometrically Based Single Bounce (GBSB) statistical
Circular channel model is considered, which is more suitable for array processing, and
conductive to RAKE combining. The performances of the Beam former-Rake receiver are
evaluated in this channel model as a function of the number of antenna elements and
RAKE fingers, in which are evaluated for the uplink WCDMA system. It is shown that,
the Beamformer-Rake receiver outperforms the conventional RAKE receiver and the
conventional beamformer by a significant margin. Also, we optimize and develop a
mathematical formulation for the output Signal to Interference plus Noise Ratio (SINR)
of a Beam former-Rake receiver.
In this research, also, we develop, simulate and evaluate the SINR and Signal to Noise
Ratio (Et!Nol performances of an adaptive beamforming technique in the WCDMA
system for downlink. The performance is then compared with an omnidirectional antenna
system. Simulation shows that the best perfom1ance can be achieved when all the mobiles
with same Angle-of-Arrival (AOA) and different distance from base station are formed in
one beam
ใปใซใฉใผใทในใใ ใซใใใๅจๆณขๆฐๅฉ็จใจใจใใซใฎใผๅฉ็จๅน็ๆนๅใซ้ขใใ็ ็ฉถ
ๆฉๅคงๅญฆไฝ่จ็ชๅท:ๆฐ7583ๆฉ็จฒ็ฐๅคง
๋๊ท๋ชจ ๋ค์ค ์ํ ๋ ํ๊ฒฝ์์ ๋ฎ์ ๋ณต์ก๋์ ๋ค์ค ์ฌ์ฉ์ ์ ํธ์ ์ก์ ๊ดํ ์ฐ๊ตฌ
ํ์๋
ผ๋ฌธ (๋ฐ์ฌ) -- ์์ธ๋ํ๊ต ๋ํ์ : ๊ณต๊ณผ๋ํ ์ ๊ธฐยท์ปดํจํฐ๊ณตํ๋ถ, 2020. 8. ์ด์ฉํ.Advanced wireless communication systems may employ massive multi-input multi-output (m-MIMO) techniques for performance improvement. A base station equipped with an m-MIMO configuration can serve a large number of users by means of beamforming. The m-MIMO channel becomes asymptotically orthogonal to each other as the number of antennas increases to infinity. In this case, we may optimally transmit signal by means of maximum ratio transmission (MRT) with affordable implementation complexity. However, the MRT may suffer from inter-user interference in practical m-MIMO environments mainly due to the presence of insufficient channel orthogonality. The use of zero-forcing beamforming can be a practical choice in m-MIMO environments since it can easily null out inter-user interference. However, it may require huge computational complexity for the generation of beam weight. Moreover, it may suffer from performance loss associated with the interference nulling, referred to transmission performance loss (TPL). The TPL may become serious when the number of users increases or the channel correlation increases in spatial domain.
In this dissertation, we consider complexity-reduced multi-user signal transmission in m-MIMO environments. We determine the beam weight to maximize the signal-to-leakage plus noise ratio (SLNR) instead of signal-to-interference plus noise ratio (SINR). We determine the beam direction assuming combined use of MRT and partial ZF that partially nulls out interference. For further reduction of computational complexity, we determine the beam weight based on the approximated SLNR.
We consider complexity-reduced ZF beamforming that generates the beam weight in a group-wise manner. We partition users into a number of groups so that users in each group experience low TPL. We approximately estimate the TPL for further reduction of computational complexity. Finally, we determine the beam weight for each user group based on the approximated TPL.์ฐจ์ธ๋ ๋ฌด์ ํต์ ์์คํ
์์ ์ฑ๋ฅ ํฅ์์ ์ํด ๋๊ท๋ชจ ๋ค์ค ์ํ
๋ (massive MIMO) ๊ธฐ์ ๋ค์ ์ฌ์ฉํ ์ ์๋ค. ๋๊ท๋ชจ ์ํ
๋๋ฅผ ๊ฐ์ง ๊ธฐ์ง๊ตญ์ ๋ง์ ์์ ์ฌ์ฉ์๋ค์ ๋นํฌ๋ฐ (beamforming)์ผ๋ก ์๋น์คํด์ค ์ ์๋ค. ์ํ
๋ ์๊ฐ ๋ฌดํํ ์ฆ๊ฐํจ์ ๋ฐ๋ผ์ ์ฑ๋์ ์ ๊ทผ์ ์ผ๋ก ์๋ก ์ง๊ต (orthogonal)ํ๊ฒ ๋๋ค. ์ด๋ฌํ ๊ฒฝ์ฐ, ๋ฎ์ ์ค์ฅ ๋ณต์ก๋๋ฅผ ๊ฐ์ง๋ ์ต๋ ๋น ์ ์ก (maximum ratio transmission)์ ์ฌ์ฉํจ์ผ๋ก์จ ์ ํธ์ ์ก์ ์ต์ ํํ ์ ์๋ค. ํ์ง๋ง, ํ์ค์ ์ธ ๋๊ท๋ชจ ๋ค์ค ์ํ
๋ ํ๊ฒฝ์์๋ ์ฑ๋ ์ง๊ต์ฑ์ด ์ถฉ๋ถํ์ง ๋ชปํ๊ธฐ ๋๋ฌธ์ ์ต๋ ๋น ์ ์ก์ ๊ฐ์ญ์ ์ํ ์ฑ๋ฅ ์ ํ๋ฅผ ๊ฒช์ ์ ์๋ค. ์ ๋ก-ํฌ์ฑ (zero-forcing) ๋นํฌ๋ฐ์ ๊ฐ์ญ์ ์ฝ๊ฒ ์ ๊ฑฐํ ์ ์๊ธฐ ๋๋ฌธ์ ๋๊ท๋ชจ ๋ค์ค ์ํ
๋ ํ๊ฒฝ์์ ํ์ค์ ์ธ ์ ํ์ด ๋ ์ ์๋ค. ํ์ง๋ง, ์ ๋ก-ํฌ์ฑ์ ๋น ๊ฐ์ค์น (beam weight) ์์ฑ์ผ๋ก ์ธํด ๋์ ๊ณ์ฐ ๋ณต์ก๋๋ฅผ ์๊ตฌํ ์ ์๋ค. ๋ฟ๋ง ์๋๋ผ, ์ ๋ก-ํฌ์ฑ์ ๊ฐ์ญ ์ ๊ฑฐ์ ๋ํ ๋๊ฐ๋ก ์ฌ๊ฐํ ์ฑ๋ฅ ์ ํ (์ฆ, transmission performance loss; TPL)๋ฅผ ๊ฒช์ ์ ์๋ค. TPL์ ์ฌ์ฉ์ ์๊ฐ ๋ง๊ฑฐ๋ ์ฑ๋์ ๊ณต๊ฐ ์๊ด๋๊ฐ ํด ๋ ๋ ์ฌ๊ฐํด์ง ์ ์๋ค.
๋ณธ ๋
ผ๋ฌธ์์ ๋๊ท๋ชจ ๋ค์ค ์ํ
๋ ํ๊ฒฝ์์ ๋ฎ์ ๋ณต์ก๋์ ๋ค์ค ์ฌ์ฉ์ ์ ํธ์ ์ก์ ๊ณ ๋ คํ๋ค. ์ ์ ๊ธฐ๋ฒ์ ์ ํธ-๋-๊ฐ์ญ ๋ฐ ์ก์ ๋น (signal-to-interference plus noise ratio) ๋์ ์ ํธ-๋-์ ์ถ ๋ฐ ์ก์ ๋น (signal-to-leakage plus noise ratio)๋ฅผ ์ต๋ํํ๋ ๋น ๊ฐ์ค์น๋ฅผ ๊ฒฐ์ ํ๋ค. ์ ์ ๊ธฐ๋ฒ์ ์ต๋ ๋น ์ ์ก๊ณผ ๊ฐ์ญ์ ์ ํ์ ์ผ๋ก ์ ๊ฑฐํ๋ ๋ถ๋ถ ์ ๋ก-ํฌ์ฑ (partial zero-forcing)์ ์ฌ์ฉ์ ๊ธฐ๋ฐ์ผ๋ก ๋น ๋ฐฉํฅ์ ๊ฒฐ์ ํ๋ค. ๊ณ์ฐ ๋ณต์ก๋๋ฅผ ๋ ๊ฐ์์ํค๊ธฐ ์ํด์, ์ ์ ๊ธฐ๋ฒ์ ๊ทผ์ฌํ๋ ์ ํธ-๋-์ ์ถ ๋ฐ ์ก์๋น๋ฅผ ์ฌ์ฉํ์ฌ ๋น ๊ฐ์ค์น๋ฅผ ๊ฒฐ์ ํ๋ค.
๋ณธ ๋
ผ๋ฌธ์์ ๊ทธ๋ฃน ๊ธฐ๋ฐ์ผ๋ก ๋น ๊ฐ์ค์น๋ฅผ ์์ฑํ๋ ๋ฎ์ ๋ณต์ก๋์ ์ ๋ก-ํฌ์ฑ ๋นํฌ๋ฐ ์ ์ก์ ๊ณ ๋ คํ๋ค. ์ ์ ๊ธฐ๋ฒ์ ์ฌ์ฉ์๋ค์ด ๋ฎ์ TPL์ ๊ฐ๋๋ก ์ฌ์ฉ์๋ค์ ๋ค์์ ๊ทธ๋ฃน์ผ๋ก ๋ถ๋ฆฌ์ํจ๋ค. ๊ณ์ฐ ๋ณต์ก๋๋ฅผ ๋ ๊ฐ์์ํค๊ธฐ ์ํด์, ์ ์ ๊ธฐ๋ฒ์ TPL์ ๊ทผ์ฌ์ ์ผ๋ก ์ถ์ ํ๋ค. ๋ง์ง๋ง์ผ๋ก, ์ ์ ๊ธฐ๋ฒ์ ๊ทผ์ฌํ๋ TPL์ ๊ธฐ๋ฐ์ผ๋ก ํ์ฑ๋ ๊ฐ ์ฌ์ฉ์ ๊ทธ๋ฃน์ ๋ํ์ฌ ๋น ๊ฐ์ค์น๋ฅผ ๊ฒฐ์ ํ๋ค.Chapter 1. Introduction 1
Chapter 2. System model 10
Chapter 3. Complexity-reduced multi-user signal transmission 15
3.1. Previous works 15
3.2. Proposed scheme 24
3.3. Performance evaluation 47
Chapter 4. User grouping-based ZF transmission 57
4.1. Spatially correlated channel 57
4.2. Previous works 59
4.3. Proposed scheme 66
4.4. Performance evaluation 87
Chapter 5. Conclusions and further research issues 94
Appendix 97
A. Proof of Lemma 3-4 97
B. Proof of Lemma 3-5 100
C. Proof of strict quasi-concavity of SLNR_(k) 101
References 103
Korean Abstract 115Docto
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