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| 2. |
- Czink, Nicolai, et al.
(författare)
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Tracking time-variant cluster parameters in MIMO channel measurements: algorithm and results
- 2007
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a joint clustering-and-tracking framework to identify time-variant cluster parametersfor geometry-based stochastic MIMO channel models.The method uses a Kalman filter for tracking and predicting cluster positions, a novel consistentinitial guess procedure that accounts for predicted cluster centroids, and the well-known KPower-Means algorithm for cluster identification.We tested the framework by applying it to three entirely different sets of MIMO channel measurementdata obtained by different channel sounders: indoor measurements conducted at 2.55GHz, outdoor rural measurements at 300 MHz, and outdoor sub-urban measurements at 2.0 GHz.The time-variant cluster parameters of interest are: (i) cluster movement, (ii) change of clusterspreads, (iii) cluster lifetimes, and birth and death rates of cluster.We find that clusters show significant movement in parameter space depending on the environment.The spreads of individual clusters change rather randomly over their lifetime, with astandard deviation up to 150% of their mean spread. The cluster lifetime is approximately exponentiallydistributed, however additionally one has to account for long-living clusters coming fromthe line-of-sight path or from major reflectors.
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| 3. |
- Lau, Buon Kiong, et al.
(författare)
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Antenna matching for performance optimization in compact MIMO systems
- 2007
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Ingår i: Microwave Exhibition and Workshop, 2007.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The implementation of MIMO technology on compact mobile terminal devices poses a unique challenge for system designers. This is because it requires that multiple antennas be closely separated in a confined volume, which results in strong mutual coupling among the antennas and high spatial correlation for the signals. In this paper, we present a review on the latest developments of using uncoupled impedance matching networks to counteract performance degradation due to the aforesaid effects. Then, we extend our previous study of utilizing identical uncoupled matching networks to optimize performance by allowing them to be different across the antennas. The numerical examples reveal that the enlarged optimization search space is effective in improving the received power and correlation, whereas only a modest gain in channel capacity is observed.
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| 4. |
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| 5. |
- Plicanic, Vanja, et al.
(författare)
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Capacity maximisation of a handheld MIMO terminal with adaptive matching in an indoor environment
- 2011
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 47:16, s. 900-901
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Tidskriftsartikel (refereegranskat)abstract
- This letter reports the capacity performance of a handheld dual-band dual-antenna compact MIMO terminal, which utilizes uncoupled adaptive impedance matching for capacity maximisation. The capacity is evaluated at 0.825 GHz and 2.35 GHz in an indoor office environment. The results show that adaptive matching enhances capacity by up to 44% and 22% at the low and high frequency bands, respectively, relative to no matching. At the low band, the capacity gain is attributed to both increased received power and decreased channel eigenvalue dispersion, whereas at the high band, the capacity gain is only due to increased power.
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| 6. |
- Tian, Ruiyuan, et al.
(författare)
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A compact six-port dielectric resonator antenna array: MIMO channel measurements and performance analysis
- 2010
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 58:4, s. 1369-1379
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Tidskriftsartikel (refereegranskat)abstract
- MIMO systems ideally achieve linear capacity gain proportional to the number of antennas. However, the compactness of terminal devices limits the number of spatial degrees of freedom (DOFs) in such systems, which motivates efficientantenna design techniques to exploit all available DOFs. In this contribution, we present a compact six-port dielectric resonator antenna (DRA) array which utilizes spatial, polarization and angle diversities. To evaluate the proposed DRA array, a measurement campaign was conducted at 2.65GHz in indoor officescenarios for four 6 × 6 multiple antenna systems. Compared to the reference system of monopole arrays which only exploit spatial diversity, the use of dual-polarized patch antennas at the transmitter enriches the channel’s DOF in the non-line-of-sight scenario. Replacing the monopole array at the receiver withthe DRA array that has a 95% smaller ground plane, the 10% outage capacity evaluated at 10 dB reference signal-to-noise ratio becomes equivalent to that of the reference system, due to the DRA’s rich diversity characteristics. In the line-of-sight scenario, the DRA array gives a higher DOF than the monopole array asthe receive counterpart to the transmit patch array. However, the outage capacity is 1.5 bits/s/Hz lower, due to the DRA array’s lower channel gain.
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| 7. |
- Tian, Ruiyuan, et al.
(författare)
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Characterization of MIMO antennas with multiplexing efficiency
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A simple and intuitive metric of multiplexing efficiency is proposed for evaluating the performance of MIMO antennas in the spatial multiplexing mode of operation. The metric is particularly useful for antenna engineers whose goal is to achieve the optimum antenna system design. Experimental results involving prototype mobile terminals highlight the effectiveness of our proposal.
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| 8. |
- Tian, Ruiyuan, et al.
(författare)
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Correlation-based phase synthesis approach for MIMO capacity prediction using antenna magnitude patterns
- 2009
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper concerns the estimation of MIMO capacity in a given propagation environment from the magnitude patterns of multiple antennas. In our previous contribution, we presented a simple approach of synthesizing phase on the magnitude patterns by taken into account the antenna separation. Although this approach works well even when the antenna separation is small and the signal correlation is high, the use of sophisticated matching networks can drastically reduce the correlation, which in turn affects its performance. Therefore, in this paper, we propose a small refinement to the approach by making use of the correlation between the magnitude patterns. Simulation results show that an average capacity estimation error of up to 0.5% is achieved for the proposed approach, as compared to up to 20.6% error for existing approaches.
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| 9. |
- Tian, Ruiyuan, et al.
(författare)
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Degree-of-freedom evaluation of six-port antenna arrays in a rich scattering environment
- 2011
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Ingår i: IEEE International Symposium on Antennas and Propagation, 2011. - 9781424495627 - 9781424495634 ; 1, s. 51-54
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Konferensbidrag (refereegranskat)abstract
- It has been proposed that six co-located antennas, namely three electric and three magnetic dipoles, can offer up to a six-fold capacity increase in wireless channels, relative to that of single antennas. In other words, six degrees of freedom (DOFs) can be supported by co-located six-port transmit and receive antenna arrays. However, due to the complexity in designing and measuring such a six-port antenna, to our knowledge, no experimental verification has yet been successfully performed. In this paper, the six DOFs hypothesis is experimentally verified at the 300 MHz band. The experiment involved the design and fabrication of two six-port arrays, and MIMO channel measurements in a rich scattering environment with these arrays.
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| 10. |
- Tian, Ruiyuan
(författare)
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Design and Evaluation of Compact Multi-antennas for Efficient MIMO Communications
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of multi-antenna systems with multiple-input multiple-output (MIMO) technology will play a key role in providing high spectrum efficiency for next generation mobile communication systems. This thesis offers valuable insights on the design of compact multi-antennas for efficient MIMO communications. In the course of the thesis work, several novel six-port antenna designs have been proposed to simultaneously exploit all six possible degrees-of-freedom (DOFs) by means of various antenna diversity mechanisms (Paper I & II). Moreover, the thesis also examines the potential of using uncoupled matching networks to adaptively optimize compact multi-antenna systems to their dynamic usage environments (Paper III). Furthermore, a simple and intuitive metric is proposed for evaluating the performance of MIMO antennas when operating in the spatial multiplexing mode (Paper IV). Last but not least, cooperation among multi-antenna systems at all three sectors of a given cellular base station is shown to deliver significant benefit at sector edges (Paper V). The thesis with five included research papers extend the understanding of MIMO systems from an antenna and propagation perspective. It provides important guidelines in designing compact and efficient MIMO antennas in their usage environments. In Paper I, a fundamental question on the number of effective DOFs in a wireless channel is explored using two co-located six-port antenna arrays. The antenna elements of both arrays closely reproduce the desired characteristics of fundamental electric and magnetic dipoles, which can efficiently extract angle and polarization diversities from the wireless channel. In particular, one of the two array designs is by far the most electrically compact six-port antenna structure in the literature. Analysis of measured channel eigenvalues in a rich multi-path scattering environment shows that six eigenchannels are successfully attained for the purpose of spatial multiplexing. To study the potential of implementing different diversity mechanisms on a practical multi-port antenna, Paper II builds on an existing dielectric resonator antenna (DRA) to provide a compact six-port DRA array that jointly utilizes space, polarization and angle diversities. In order to fully substantiate the practicality of the DRA array for indoor MIMO applications, the compact DRA array together with two reference but much larger arrays were evaluated in an office scenario. The use of the compact DRA array at the receiver is shown to achieve comparable performance to that of the reference monopole array due to the DRA array's rich diversity characteristics. In Paper III, the study of uncoupled matching networks to counteract mutual coupling effects in multi-antenna systems is extended by allowing for unbalanced matching impedances. Numerical studies suggest that the unbalanced matching is especially effective for array topologies whose effective apertures can vary significantly with respect to the propagation channel. Moreover, it is also demonstrated that the unbalanced matching is capable of adapting the radiation patterns of the array elements to the dynamic propagation environment. Paper IV introduces multiplexing efficiency as a performance metric which defines the loss of efficiency in decibel when using a multi-antenna prototype under test to achieve the same multiplexing performance as that of an ideal array in the same propagation environment. Its unique features are both its simplicity and the valuable insights it offers with respect to the performance impacts of different antenna impairments in multi-antenna systems. In Paper V, intrasite cooperation among three 120°-sector, each with a cross-polarized antenna pair, is investigated in a measured urban macrocellular environment. The single-user capacity improvement is found to exceed 40% at the sector edges, where improvements are most needed. In addition, a simple simulation model is developed to analyze the respective impact of antennas and specific propagation mechanisms on the measured cooperative gain.
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