Ruiyuan Tian

Alimetrics Ltd, Espoo, Finland, Helsinki, Uusimaa, Finland

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Publications (16)11.61 Total impact

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    ABSTRACT: In recent years, adaptive impedance matching (AIM) has been used to compensate for severe performance degradation in terminal antennas due to user proximity. In particular, user effect compensation is critical for multiple-input multiple-output (MIMO) terminals, to achieve high data rates. In this study, the AIM performance of a MIMO terminal is measured for three user scenarios at two locations in an indoor office environment, using real impedance tuners. It was established that AIM leads to MIMO capacity gains of up to 25%, corresponding to 2.2 dB of power gain. On the other hand, the insertion loss of the tuners was found to be about 0.3 dB for free-space conditions. These results suggest that AIM can offer significant net performance gains in practice. Moreover, we provide physical insight into the similar AIM results for the two measured locations, representing geometrical line-of-sight (LOS) and non-LOS links, respectively.
    No preview · Conference Paper · Jul 2014
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    Azremi Abdullah Al-Hadi · Ruiyuan Tian
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    ABSTRACT: In this letter, the impact of antenna real estate is investigated and generalized to multiantenna diversity and multiple- input–multiple-output (MIMO) performance. In particular, an extensive study of two-antenna capacitive coupling elements with different antenna volumes and locations in a small mobile terminal is presented. The discussion reveals the optimally compact two-antenna system that can attain promising 80% and 100% MIMO performance separately at the lower (698–960 MHz) and higher (1710–2690 MHz) frequencies for next-generation mobile communications .
    Full-text · Article · Dec 2013 · IEEE Antennas and Wireless Propagation Letters
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    ABSTRACT: Absorption and impedance mismatch due to the proximity of a user as well as certain propagation channel characteristics can severely degrade the multiple-input-multiple-output (MIMO) performance of multiantenna terminals in real usage scenarios. In this context, we investigated the potential of adaptive impedance matching (AIM) to mitigate performance degradation from these effects based on channel measurements involving a terminal prototype in three user scenarios and two propagation environments. First, optimal AIM state for the terminal in a given user-channel setup was found by post-processing the measured channels. The optimal state was then experimentally verified with two Maury Microwave mechanical tuners. The results show that by employing AIM instead of 50- Ω termination, the average capacity is increased by up to 25%. Moreover, the observed capacity gains can be partly explained by physical mechanisms underlying the propagation conditions. Furthermore, the achieved gains with real tuners are only marginally affected by the tuners' actual insertion losses, estimated to be 0.1-0.7 dB. Therefore, we conclude that AIM can be a viable solution to enhance MIMO terminal performance.
    No preview · Article · Jan 2013 · IEEE Antennas and Wireless Propagation Letters
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    Ruiyuan Tian · Bo Wu · Buon Kiong Lau · Jonas Medbo
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    ABSTRACT: Capacity improvement of intrasite cooperative multiple-input–multiple-output (MIMO) using all three 120$^{\circ}$ sectors of a base station (BS) site is studied for the first time in a measured urban environment at 2.65 GHz. The results show that the mean uplink capacity gain exceeds 40% in as much as 1/4 of the coverage area, relative to the best single-sector link with no cooperation. In addition, a simple simulation model is developed for predicting the capacity gain from intrasite multisector cooperation. The model is used to unravel the respective roles of the BS antenna patterns and propagation mechanisms in determining cooperative performance .
    Full-text · Article · Dec 2012 · IEEE Antennas and Wireless Propagation Letters
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    Ruiyuan Tian · Buon Kiong Lau
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    ABSTRACT: It has been postulated that six colocated orthogonally polarized electrical and magnetic dipoles can offer up to six degrees of freedom (DOFs) in a multipath scattering environment. In other words, a sixfold increase in channel capacity can be achieved in the context of multiple-input-multiple-output (MIMO) systems. 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 77 MHz. The experiment involves the design and fabrication of two six-port arrays. In particular, one array is made compact with colocated antenna elements enclosed in a small cubic volume of (0.24λ)3. Using the two arrays, MIMO channel measurements are performed in an RF shielded laboratory in order to measure a multipath scattering environment. Analysis on eigenvalues of the measured channel shows that six DOFs are attained due to the orthogonality in radiation patterns of the two arrays.
    Preview · Article · Jul 2012 · IEEE Transactions on Antennas and Propagation
  • Ruiyuan Tian · Buon Kiong Lau
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    ABSTRACT: In this paper, we confirm that angle and polarization diversities are indeed the dominant diversity mechanisms of a recently proposed compact six-port MIMO antenna array, as it exhibits similar effective degree-of-freedom (EDOF) performance as that of the ideal array with co-located antenna elements evaluated in propagation scenarios with different angular spreads. Furthermore, the same approach can also be applied to determine the relative contributions of different diversity mechanisms to the EDOF performance of a given array.
    No preview · Conference Paper · Jul 2012
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    Ruiyuan Tian · Buon Kiong Lau · Jonas Medbo
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    ABSTRACT: The paper examines the impact of Rician fading on the orthogonality of dual-polarized MIMO channels in a measured urban macrocellular scenario. The measurements confirm the previous finding that the Rician k-factors of the cross-polarized channels are strongly correlated to those of the co-polarized channels. However, the Rician k-factors do not in general give direct indications on the orthogonality of dual-polarized channels. Our results show that, in the presence of strong Rician fading, the co- and cross-polarization ratios largely determine the channel orthogonality. In particular, good channel orthogonality is achieved when the co- and cross-polarization ratios are close to 1 and very small, respectively. Nevertheless, more than 70% of the measured route achieves better channel orthogonality than the average performance of the reference IID Rayleigh channel, indicating that efficient multi-stream MIMO communication can be achieved in the measured scenario.
    Full-text · Conference Paper · Mar 2012
  • Ruiyuan Tian · Buon Kiong Lau · Zhinong Ying
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    ABSTRACT: Recently, the multiplexing efficiency metric is proposed for characterizing the MIMO performance of terminal antennas. Here, we show that it can also provide useful insights into the impact of user on MIMO terminal performance. In particular, the impact of user hand and head on the efficiency and correlation of a MIMO antenna can be conveniently quantified using the multiplexing efficiency metric. For example, we find that the hand introduces a 4 dB loss in total efficiency relative to the free space case, for a penta-band two-element MIMO terminal antenna operating at 750MHz. However, the multiplexing efficiency drops by only 2.4 dB, due to the de-correlation effect of the hand partly compensating the loss in total efficiency.
    No preview · Conference Paper · Jan 2012
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    Ruiyuan Tian · Buon Kiong Lau · Zhinong Ying
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    ABSTRACT: Multiplexing efficiency has recently been proposed as a performance metric for characterizing the absolute efficiency of MIMO antennas in a reference channel. In this work, we generalize this metric to account for arbitrary propagation channels, so the impact of the channel can also be studied. Using the extended definition of multiplexing efficiency, the respective roles of effective antenna gain and signal correlation due to non-isotropic incident fields can be clearly identified. A numerical evaluation based on two MIMO terminal prototypes and four different propagation scenarios is performed to demonstrate the effectiveness of the generalized metric. We find that the MIMO antenna with high total antenna efficiency and good pattern diversity offers a robust multiplexing efficiency performance in all the considered propagation scenarios.
    Full-text · Conference Paper · Jan 2012
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    V. Plicanic · I. Vasilev · R. Tian · B.K. Lau
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    ABSTRACT: Reported is the capacity performance of a handheld dual-band dual-antenna compact MIMO terminal, which utilises uncoupled adaptive impedance matching for capacity maximisation. The capacity is evaluated at 0.825 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.
    Preview · Article · Sep 2011 · Electronics Letters
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    Ruiyuan Tian · Buon Kiong Lau
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    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.
    Preview · Conference Paper · Aug 2011
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    Ruiyuan Tian · Buon Kiong Lau · Zhinong Ying
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    ABSTRACT: A simple and intuitive metric of multiplexing efficiency is proposed for evaluating the performance of multiple-input-multiple-output (MIMO) antennas in the spatial multiplexing mode of operation. Apart from gaining valuable insights into the impact of antenna efficiency, efficiency imbalance, and correlation on multiplexing performance, 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.
    Full-text · Article · Feb 2011 · IEEE Antennas and Wireless Propagation Letters
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    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 efficient antenna 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 2.65 GHz in indoor office scenarios 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 with the 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 as the 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.
    Full-text · Article · May 2010 · IEEE Transactions on Antennas and Propagation
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    Ruiyuan Tian · Buon Kiong Lau
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    ABSTRACT: This paper proposes a simple and improved approach of estimating MIMO capacity from antenna magnitude patterns, i.e., the antenna patterns are phaseless. The simple approach synthesizes the phases according to the antenna spacing, and it compares favorably with an existing approach based on random phase synthesis. Moreover, the simple approach can be improved by taking into account the correlation between the magnitude patterns. The performance of the existing and proposed approaches in estimating MIMO capacity is investigated for dipole antenna systems with different gain and correlation characteristics, under different conditions of antenna spacings, impedance matching networks and propagation scenarios. It is found that an average capacity estimation error of under 0.5% is achieved for the proposed approach, as compared to up to 20.6% error for the random phase approach.
    Preview · Conference Paper · Apr 2009
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    Ruiyuan Tian · Buon Kiong Lau
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    ABSTRACT: Some MIMO applications require antennas to be closely spaced, which result in mutual coupling among antennas and high spatial correlation for signals. In order to compensate for the performance degradation due to correlation and coupling, impedance matching networks may be used. Recently, it was shown that uncoupled matching networks could be optimized against a given performance metric with the constraint of similar matching impedance for all antennas, i.e., balanced matching. In this paper, we investigate the use of uncoupled matching networks with both balanced and unbalanced load impedances, where either the received power or the channel capacity is optimized. For two- and three-element dipole arrays, we show numerically that a significant performance improvement can be achieved by introducing unbalanced matching. Observations suggest that the achieved improvement varies with array geometry and propagation environment. For example, a large capacity gain of up to 23% is realized when matching a uniform linear array to propagation environments that are asymmetrical about the array broadside, whereas the symmetrical environments do not benefit as much from unbalanced matching.
    Preview · Conference Paper · Jun 2008
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    Ruiyuan Tian · Buon Kiong Lau · Zhinong Ying

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