| 1. |
- 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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| 2. |
- 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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| 3. |
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| 4. |
- Bernadó, Laura, et al.
(författare)
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Non-WSSUS Vehicular Channel Characterization at 5.2 GHz - Spectral Divergence and Time-Variant Coherence Parameters
- 2008
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Konferensbidrag (refereegranskat)abstract
- The scattering environment in vehicle-to-vehicle communication channels at 5.2 GHz changes rapidly. Hence the wide-sense stationary (WSS) uncorrelated scattering (US) assumption for the fading process is valid for short time intervals only. We characterize the spectral divergence of the local scattering function (LSF) sequence in order to assess the non-WSSUS characteristics in different scenarios. We find that the vehicle-to-vehicle channels violate the wide-sense stationarity much stronger than the US assumption. Additionally, we use the LSF to quantify the time dependence of the channel coherence time and bandwidth. Both parameters vary strongly over time depending on the chosen scenario. Furthermore the effect of the antenna radiation pattern on the fading process is quantified, which can cause the strength of a multipath component to change by more than 40 dB in drive-by experiments.
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| 5. |
- Bernadó, Laura, et al.
(författare)
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Parametrization of the local scattering function estimator for vehicular-to-vehicular channels
- 2009
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Ingår i: [Host publication title missing]. ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- Non wide-sense stationary (WSS) uncorrelated scatterering (US) fading processes are observed in vehicular communications. To estimate such a process under additive white Gaussian noise we use the local scattering function (LSF). In this paper we present an optimal parametrization of the multitaper-based LSF estimator. We do this by quantizing the mean square error (MSE). For that purpose we use the structure of a twodimensional Wiener filter and optimize the parameters of the estimator to obtain the minimum MSE (MMSE). We split the observed fading process in WSS regions and analyze the influence of the estimator parameters and the length of the stationarity regions on the MMSE. The analysis is performed considering three different scenarios representing different scattering properties. We show that there is an optimal combination of estimator parameters and length of stationarity region which provides a minimum MMSE.
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| 6. |
- Johansson, Anders J, et al.
(författare)
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MIMO channel measurements for personal area networks
- 2005
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Ingår i: [Host publication title missing]. - 1550-2252. - 0780388879 ; 61:1, s. 171-176
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Konferensbidrag (refereegranskat)abstract
- This paper analyzes MIMO propagation channels for personal area networks. Such channels show important differences to propagation channels in wide-area networks, due to the different environments in which the systems are operated, as well as due to different mobility models, ranges, and presence of humans in the environment, and the impact of the antenna arrangement. We present results from a recent measurement campaign for this type of channel. We first analyze the requirements for measurement setups, especially in terms of different positions and orientations of the antenna arrays, to obtain meaningful results. We then analyze the measured data and present results for path loss, power delay profiles, spatial correlation and temporal correlation.
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| 7. |
- Khan, Muhammad Gufran, et al.
(författare)
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Measurements and Analysis of UWB Channels in Industrial Environments
- 2005
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Konferensbidrag (refereegranskat)abstract
- Communication in industrial environments is an important scenario for ultra wideband (UWB) systems. The characteristics of this environment differ considerably from office environments, where most of the channel measurements reported in the literature are performed. In this paper, we present the results and analysis of UWB channel measurements in an industrial environment. We investigate both peer-to-peer non-line-of-sight (P-P NLOS) and base station NLOS (BS NLOS) scenarios. The measurements are performed in the frequency range 3.1 to 8 GHz, at distances 2-16 m, using a vector network analyzer in conjunction with virtual antenna arrays. From these measurements, we extract channel model parameters such as power delay profiles, pathloss exponents, rms delay spread and the percentage of energy captured by RAKE receivers with a finite number of fingers. In addition, Saleh- Valenzuela parameters such as ray and cluster power decay constants and distribution of cluster interarrival times are extracted.
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| 8. |
- Kåredal, Johan, et al.
(författare)
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A geometry-based stochastic MIMO model for vehicle-to-vehicle communications
- 2009
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Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276. ; 8:7, s. 3646-3657
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Tidskriftsartikel (refereegranskat)abstract
- Vehicle-to-vehicle (VTV) wireless communications have many envisioned applications in traffic safety and congestion avoidance, but the development of suitable communications systems and standards requires accurate models for the VTV propagation channel. In this paper, we present a new wideband multiple-input-multiple-output (MIMO) model for VTV channels based on extensive MIMO channel measurements performed at 5.2 GHz in highway and rural environments in Lund, Sweden. The measured channel characteristics, in particular the non-stationarity of the channel statistics, motivate the use of a geometry-based stochastic channel model (GSCM) instead of the classical tapped-delay line model. We introduce generalizations of the generic GSCM approach and techniques for parameterizing it from measurements and find it suitable to distinguish between diffuse and discrete scattering contributions. The time-variant contribution from discrete scatterers is tracked over time and delay using a high resolution algorithm, and our observations motivate their power being modeled as a combination of a (deterministic) distance decay and a slowly varying stochastic process. The paper gives a full parameterization of the channel model and supplies an implementation recipe for simulations. The model is verified by comparison of MIMO antenna correlations derived from the channel model to those obtained directly from the measurements.
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| 9. |
- Kåredal, Johan, et al.
(författare)
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A measurement-based fading model for wireless personal area networks
- 2008
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Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276. ; 7:11, s. 4575-4585
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Tidskriftsartikel (refereegranskat)abstract
- Personal area networks (PANs) are wireless communications systems with high data rates but small coverage area. PAN propagation channels differ from the well-explored propagation channels of wide-area networks due to several reasons: (i) the distances are typically very small, (ii) the antenna arrangements can be quite different, and (iii) the influence from human presence in the environment is different. The current paper presents results of a channel measurement campaign, where measurements are conducted over distances of 1-10 m using several multi-antenna devices, combined to create different PAN scenarios. For each measured Tx-Rx separation, channel realizations are obtained by small spatial movements of the antenna devices, and by rotating the persons holding the devices. From the results, we draw two main conclusions: (i) The small-scale amplitude statistics, analyzed as the variations over a small sampling area and frequency subchannels, cannot be described in a satisfactory way using only the Rayleigh or Ricean distributions, rather a mixed distribution, the generalized gamma distribution, is more suitable; (ii) it is advantageous to distinguish between two types of large-scale fading: body shadowing (due to the orientation of the person holding the device) and shadowing due to surrounding objects (lateral movement). We also define and parameterize a complete statistical model for all fading.
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| 10. |
- 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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