| 1. |
- Hammarberg, Peter, et al.
(författare)
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On the performance of iterative receivers for interfering MIMO-OFDM systems in measured channels
- 2008
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Ingår i: 42nd Asilomar Conference on Signals, Systems and Computers. - 1058-6393. - 9781424429400 ; , s. 141-145
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the gains harvested through base station cooperation in the up-link for a multi-user (MU) Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system, operating in a real indoor environment. The base stations perform joint detection using an iterative receiver that carries out multi-user detection and channel estimation via soft information from the single-user decoders. Performance evaluation is carried out using real channels from an indoor dynamic dual MIMO link measurement campaign. The measured scenario represent a real life situation where two users communicate with two base stations, each with two antennas, in an environment resembling a shopping mall or an airport terminal. System performance is evaluated in terms of both Bit-Error Rate (BER) vs. Signal-to-Interference Ratio (SIR) and Cumulative Distribution Functions (CDF) for the instantaneous BER. Also, the impact of using soft information in the channel estimation is analyzed.
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| 2. |
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| 3. |
- Salvo Rossi, Pierluigi, et al.
(författare)
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Performance of an Iterative Multi-User Receiver for MIMO-OFDM Systems in a Real Indoor Scenario
- 2008
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Ingår i: [Host publication title missing]. - 1930-529X. - 9781424423248
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Konferensbidrag (refereegranskat)abstract
- This paper aims at validation of an iterative receiver for multiple-input multiple-output with orthogonal frequency division multiplexing (MIMO-OFDM) systems using real-measurement channel data from an indoor scenario. The receiver performs iterative multi-user detection (MUD) and Channel Estimation (CE) via soft information from the single- user decoders. The channel measurements were performed for a dynamic dual MIMO link scenario. The case with two users with multiple antennas interfering each other is considered. CE at the receiver exploits the frequency correlation of the MIMO link. Simulation results for the performance are shown in terms of bit- error rate (BER) vs. signal-to-noise ratio (SNR). Performance for the whole system are provided and compared with respect to the case of perfect channel-state information (PCSI) at the receiver, as well as for the single user. We also provide an analysis of BER with respect to signal-to-interference ratio (SIR). CE performance are evaluated in terms of normalized mean square error (NMSE).
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| 4. |
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| 5. |
- Almers, Peter, et al.
(författare)
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Antenna subset selection in measured indoor channels
- 2007
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Ingår i: IET Microwaves, Antennas & Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725. ; 1, s. 1092-1100
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Tidskriftsartikel (refereegranskat)abstract
- Antenna subset selection can greatly reduce the implementation complexity of multiple input multiple output (MIMO) systems while retaining most of their benefits. This paper investigates the diversity gain and capacity of such systems in wireless personal area networks. Considered scenarios include both the communication between access point to a laptop, and between two handheld devices. We analyse the performance of different antenna selection algorithms and signal combining methods in measured dual-polarised narrowband and wideband propagation channels. We find that line-of-sight and non-line-of-sight situations have fairly similar behaviour. Different polarisations result in similar signal-to-noise ratio gains when the multiple antennas are used for diversity, but result in noticeably different capacities in spatial-multiplexing systems. We also find that radiofrequency (RF) preprocessing of the signals is less effective for handheld handsets with non-uniform antenna arrangements than for uniform linear arrays. For communications between handheld devices, simple selection (of one out of four antennas) shows extremely high performance gains compared to no-selection. Finally, we compare bulk selection (same antenna subset is used for all frequency sub-channels) to per-tone selection (different antenna subsets can be used for each frequency sub-channel) for wideband channels. Bulk selection together with RF preprocessing performs almost as well as per-tone selection for some scenarios.
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| 6. |
- Almers, Peter, et al.
(författare)
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Effect of random walk phase noise on MIMO measurements
- 2005
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Ingår i: [Host publication title missing]. - 1550-2252. ; 61:1, s. 141-145
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Konferensbidrag (refereegranskat)abstract
- In this paper we study the influence of phase noise from free-running local oscillators on SAGE signal parameter estimation. Phase noise is here modeled as a random-walk process. We present phase noise estimates from our LUND RUSK MIMO channel sounder, and draw conclusions on requirements on local oscillators' phase noise in terms of the Allan variance. We investigate an error propagation effect in SAGE, and finally, we present random-walk phase noise effect on channel capacity.
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| 7. |
- Almers, Peter, et al.
(författare)
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Exercises
- 2005
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Ingår i: Wireless Communications. - 9780470848883 - 047084888X - 0470848871 ; , s. 561-593
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Almers, Peter, et al.
(författare)
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Keyhole effect in MIMO wireless Channels - Measurements and Theory
- 2006
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Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276. ; 5:12, s. 3596-3604
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Tidskriftsartikel (refereegranskat)abstract
- It has been predicted theoretically that for some environments, the capacity of wireless multiple-input multiple-output systems can become very low even for uncorrelated signals; this effect has been termed "keyhole" or "pinhole". In this paper the first unique measurements of this effect are presented. The measurements were performed in a controlled indoor environment that was designed to obtain a keyhole channel. We analyze limitations due to measurement imperfections for measurement-based capacity calculations and keyhole investigations. We further present a bound for the higher eigenmodes as a function of the finite measurement signal-to-noise ratio and multipath component leakage. The bound is compared to the measurement results and shows excellent agreement. Finally, we analyze the envelope distribution and, as expected from theory, it follows a double-Rayleigh distribution
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| 9. |
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| 10. |
- Almers, Peter
(författare)
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MIMO Channels - Measurements and Analysis
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Providing increased transmission speed, quality and an efficient spectrum utilization is crucial for high speed wireless services of today and the future. This thesis is a collection of papers that address an important step in that direction -- the utilization of the spatial domain of the wireless channel. Paper I provides a survey of the most important concepts in channel and radio propagation modeling for spatial wireless channels. A couple of key features of channels and radio propagation, which are not sufficiently included in current MIMO models, are also described. Paper II presents the first conclusive experimental evidence of the keyhole effect in wireless MIMO channels, and concludes that the keyhole effect in real wireless scenarios is not probable. Analysis of the limitations due to measurement imperfections for measurement-based capacity calculations and keyhole investigations are also presented. In addition, a bound for the higher eigenmodes as a function of the finite measurement signal-to-noise ratio and multipath component leakage is derived. Paper III presents a comparison of the waterfilling gain in the different domains, i.e., frequency, spatial and joint spatial-frequency waterfilling, and shows that the largest gain resides in the spatial domain. Paper IV investigates the performance of seven antenna subset selection schemes, with and without pre-processing both in a diversity and capacity sense and the influence of antenna selection on diversity in wideband channels. The evaluations are based on measured wireless personal area network (WPAN) channels, covering both line-of-sight (LOS) and non-line-of-sight (NLOS) channels, and synthetic MIMO channel models. Paper V presents results from one of the first measurement campaigns for the double-directional characterization of outdoor-to-indoor wireless propagation channels. Measurements were performed at 5.2 GHz between 53 different receiver locations in an office building, and three "base station" positions on a nearby rooftop. Results for angular-delay profiles, RMS angular spread, and other statistical parameters characterizing delay and angular dispersion are given. Paper VI studies the influence of measurement random-walk phase noise (in terms of Allan variance of the sum of the phase noise of two free-running local oscillators) on the SAGE estimation algorithm, and the random-walk phase noise effect on capacity estimates. Paper VII analyses the impact of receiver antenna horizontal orientation on the channel capacity of a 6×6 MIMO system. It shows that in a "wave guiding" environment such as a long corridor with the presence of a strong LOS, a significant difference in capacity is observed when the orientation of the uniform linear array at the receiver is changed from parallel to perpendicular (to the LOS).
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| 11. |
- Almers, Peter, et al.
(författare)
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Survey of channel and radio propagation models for wireless MIMO systems
- 2007
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Ingår i: Eurasip Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499. ; 2007
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides an overview of the state-of- the-art radio propagation and channel models for wireless multiple-input multiple-output (MIMO) systems. We distinguish between physical models and analytical models and discuss popular examples from both model types. Physical models focus on the double-directional propagation mechanisms between the location of transmitter and receiver without taking the antenna configuration into account. Analytical models capture physical wave propagation and antenna configuration simultaneously by describing the impulse response (equivalently, the transfer function) between the antenna arrays at both link ends. We also review some MIMO models that are included in current standardization activities for the purpose of reproducible and comparable MIMO system evaluations. Finally, we describe a couple of key features of channels and radio propagation which are not sufficiently included in current MIMO models. Copyright c 2007 P. Almers et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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| 12. |
- Koivunen, Jukka, et al.
(författare)
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Dynamic multi-link indoor MIMO measurements at 5.3 GHz.
- 2007
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Ingår i: Proc 2nd European Conference on Antennas and Propagation (EuCAP 2007).
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Konferensbidrag (refereegranskat)abstract
- A dynamic multi-link MIMO channel indoor measurement campaign at 5.3 GHz is presented in this paper. The system setup is described and capacity with interference (with and without power control) results based on the dynamic multilink MIMO measurements are shown, and we experience a strong correlation between the relative capacity and SIR. Furthermore, an interference suppression metric is introduced and pathloss exponents and delay spreads are also presented, when moving from a typical office corridor to a large entrance hall at the premises of Lund University, Sweden.
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| 13. |
- Kåredal, Johan, et al.
(författare)
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A measurement-based statistical model for industrial ultra-wideband channels
- 2007
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Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276. ; 6:8, s. 3028-3037
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Tidskriftsartikel (refereegranskat)abstract
- The results of three ultra-wideband (UWB) measurement campaigns conducted in two different industrial environments are presented. A frequency range of 3.1 - 10.6 or 3.1 - 5.5 GHz was measured using a vector network analyzer and a virtual array technique enabling the investigation of smallscale statistics. The results show that the energy arrives in clusters, and that the abundance of metallic scatterers present in the factory hall causes dense multipath scattering. The latter produces a small-scale fading that is mostly Rayleigh distributed; the only exception being the delay bin containing the line-of-sight component. The power delay profile can be modeled by a generalized Saleh-Valenzuela model, where different clusters have different ray power decay constants. It is also noted that the number of multipath components required to capture a majority of the energy is quite large. More than a hundred components can be needed to capture 50% of the total available energy.
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| 14. |
- Molisch, Andreas, et al.
(författare)
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Implementation Aspects of Antenna Selection for MIMO Systems
- 2006
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Ingår i: First International Conference on Communications and Networking in China, 2006. ChinaCom '06.. - 1424404630 ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- Antenna selection is a promising technique for reducing complexity of multiple-antenna (MIMO) systems. In antenna selection, more antenna elements than RF transceiver chains are available for up-conversion and down-conversion. A subset of the available antenna elements is selected and connected to the RF chains. The reduction in the number of RF chains helps to reduce the implementation cost of multi-antenna systems. This paper considers a number of "practical" issues in the implementation of such systems. We discuss schemes for the channel estimation for all all antenna elements, and show that antenna selection is robust to channel estimation errors. RF preprocessing can be used to enhance the array gain of antenna selection schemes; the performance is robust to errors in the RF elements used for the preprocessing Finally, we analyze both bulk selection and per-tone selection in MIMO-OFDM systems, and show that the former is usually preferable. Results from simulations with 802.11n-compliant systems, and capacity results in measured channels show that SNR and capacity gains can be achieved with antenna selection in practical situations.
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| 15. |
- Santos, Telmo, et al.
(författare)
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Scatterer detection by successive cancellation for UWB - method and experimental verification
- 2008
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Ingår i: [Host publication title missing]. - 1550-2252. - 9781424416448 ; , s. 445-449
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Konferensbidrag (refereegranskat)abstract
- We present a new high delay resolution method to detect ultra-wideband (UWB) scatterers when using frequency domain measurements. Our approach makes use of the impulse response envelope amplitudes and delays measured over a distance that is larger than the region of stationarity, and detects the 2D coordinates of the channel scatterers, assuming that only single-scattering (single-interaction) processes occur. The identification methodology is based on multiple application of interference cancellation: at every step, we detect the strongest scatterer from an array of measurements, save its information, cancel it from the channel and search for the next strongest scatterer. To precisely define the strength of each scatterer, we present a method to define its birth and death locations along the measurement array. Finally, we verify the method by applying it to measurement results in an outdoor environment; the scatterer locations identified from the measurements show excellent agreement with the physically present objects like walls and columns.
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| 16. |
- Wyne, Shurjeel, et al.
(författare)
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A cluster-based analysis of outdoor-to-indoor office MIMO measurements at 5.2 GHz
- 2006
-
Ingår i: [Host publication title missing]. - 1550-2252. ; , s. 22-26
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present a cluster based analysis of an outdoor-to-indoor Multiple-Input Multiple-Output (MIMO) measurement campaign, and extract model parameters for the COST273 channel model. The measurements were performed at 5.2 GHz for 159 measurement locations in an office building. Multipath component (MPC) parameters have been extracted for these positions using a high-resolution algorithm. We analyze the clustering of MPCs, i.e., grouping together of MPCs with similar DOAs, DODs, and delays. We compare cluster identification by visual inspection to automatic identification by the recently proposed algorithm of Czink et al. In the paper we include results on the intercluster properties such as the distribution of the number of clusters and the cluster powers, as well as intracluster properties such as the angle and delay spreads within the clusters. In particular, we extract parameters for the COST 273 channel model, a standardized generic model for MIMO propagation channels. © 2006 IEEE.
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| 17. |
- Wyne, Shurjeel, et al.
(författare)
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Outdoor-to-indoor office MIMO measurements, and analysis at 5.2 GHz
- 2008
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 57:3, s. 1374-1386
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Tidskriftsartikel (refereegranskat)abstract
- The outdoor-to-indoor wireless propagation channel is of interest for cellular and wireless local area network applications. This paper presents the measurement results and analysis based on our multiple-input-multiple-output (MIMO) measurement campaign, which is one of the first to characterize the outdoor-to-indoor channel. The measurements were performed at 5.2 GHz, the receiver was placed indoors at 53 different locations in an office building, and the transmitter was placed at three "base station" positions on a nearby rooftop. We report on the root-mean-square (RMS) angular spread, building penetration, and other statistical parameters that characterize the channel. Our analysis is focused on three MIMO channel assumptions often used in stochastic models. 1) It is commonly assumed that the channel matrix can be represented as a sum of a line-of-sight (LOS) contribution and a zero-mean complex Gaussian distribution. Our investigation shows that this model does not adequately represent our measurement data. 2) It is often assumed that the Rician K-factor is equal to the power ratio of the LOS component and the other multipath components (MPCs). We show that this is not the case, and we highlight the difference between the Rician K-factor often associated with LOS channels and a similar power ratio for the estimated LOS MPC. 3) A widespread assumption is that the full correlation matrix of the channel can be decomposed into a Kronecker product of the correlation matrices at the transmit and receive array. Our investigations show that the direction-of-arrival (DOA) spectrum noticeably depends on the direction-of-departure (DOD), therefore, the Kronecker model is not applicable, and models with less-restrictive assumptions on the channel, e.g., the Weichselberger model or the full correlation model, should be used.
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| 18. |
- Wyne, Shurjeel, et al.
(författare)
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Statistical evaluation of outdoor-to-indoor office MIMO measurements at 5.2 GHz
- 2005
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Ingår i: 2005 IEEE 61st Vehicular Technology Conference. - 0780388879 ; 1, s. 146-150
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present a statistical evaluation of an outdoor-to-indoor multiple-input multiple-output (MIMO) measurement campaign performed at 5.2 GHz. 159 measurement locations in an office building are analyzed. Our analysis pays special attention to two key assumptions that are widely used in stochastic channel models. An assumption that is used in practically every channel model is that the channel can be represented as a sum of a line-of-sight (LOS) component plus a (possibly correlated) zero-mean complex Gaussian distribution. Our investigation shows that this model does NOT adequately represent our measurement data. Our analysis also highlights the difference between the LOS power factor and the Rician K-factor. We show that the direction-of-arrival (DOA) spectrum depends noticeably on the direction-of-departure (DOD). Therefore, the popular Kronecker model is not applicable, and the more general Weichselberger model should be used
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