Keizo Cho

High data-rate transmission with eigenbeam-space division multiplexing (E-SDM) in a MIMO channel

When channel state information is known at a transmitter in multiple-input multiple-output systems, the optimum capacity is given by eigenmode channel division with water-pouring power control. In this eigenbeam-space division multiplexing (E-SDM), bit assignment to substreams based on the capacity is not optimum due to the fact that the number of assigned bits is expressed by a discrete quantity. In the paper, a method to assign both bit and transmit power to each substream based on the criterion minimizing total bit error rate (BER) is developed, and the BER performance is numerically analyzed in comparison to spatial division multiplexing (SDM). The simulation results assuming 5-transmit and 2-receive antennas show that the E-SDM provides about 10 dB gain compared to the conventional SDM at average BER of 10/sup -3/.

A new calibration method of adaptive array for TDD systems

This paper proposes a new calibration method for adaptive base station antennas that is suitable for TDD communication systems; it offers real-time calibration. The effectiveness of the proposed calibration method is also demonstrated using an experimental adaptive array testbed. This paper first shows the distortion in the radiation pattern due to the amplitude and phase variations over time. The proposed calibration method is then described. Finally, a comparison of the measured radiation pattern between transmission and reception modes is shown that confirms the effectiveness of the proposed calibration method.

Multi-layer parasitic microstrip array antenna on LTCC substrate for millimeter-wave system-on-package

This paper proposes a novel multi-layer parasitic microstrip array antenna (MPMAA) structure for compact and low-cost quasi-millimeter-wave and millimeter-wave system-on-package modules. The design and performance of the proposed array antenna are described. The developed prototype MPMAA employs a multi-layer low-temperature co-fired ceramic (LTCC) substrate that is well suited to the assembly of MMIC chips. The fabricated MPMAA exhibits a -16 dB return loss and a 50-degree 3-dB beam width at 25 GHz. The spacing of the top layer of the parasitic array constructed by 2 × 2 elements has a free space wavelength of 0.37. The fabricated MPMAA realizes both compact and high directional gain.

Compact six-sector antenna employing patch Yagi-Uda array with common director

A novel compact planar six-sector antenna employing the patch Yagi-Uda array with common directors for mobile terminals is proposed. This antenna has square parasitic director elements that are shared by two sector arrays that face in opposite directions, and has a hexagonal central director element that is shared by all six sectors. These elements form three line arrays, which intersect at 60 degrees to each other. These shared elements enable the sector antenna to be compact. The antenna configuration is described, a numerical analysis of the properties of the front-to-back (F/B) ratio under termination conditions and the number of parasitic elements is given, the validity of the electrical characteristics and the downsizing effect based on the experimental results from a fabricated antenna are shown.

Automatic calibration method of adaptive array for FDD systems

This paper proposes an automatic calibration method that can be applied to frequency division duplex (FDD) systems. The effectiveness of the proposed calibration method is evaluated by measurements using an adaptive array testbed in an anechoic chamber. This paper first elucidates the required calibration for FDD systems. Then the proposed calibration method is described. Finally, the measurement results are shown.

Adaptive antennas employing vertical pattern control for street microcell

The paper first presents the measured results of the dependency of the angle of arrival (AOA) and delay profile on terminal locations when a base station is placed on the roof top of a building in a street cell. Then, it is shown that an adaptive antenna employing pattern control in the vertical plane can enlarge the cell size with the same delay reduction as an ordinary tilt antenna. In addition, the influence of a bidirectional pattern in the horizontal plane, which can further enlarge the cell size, is investigated, and a suitable antenna configuration for placing the base stations at a high location is proposed.

Novel SDMA system adopting spatial and polarization control with terminal polarization assignment

This paper proposes a novel space division multiple access system that comprises base station smart antennas and mobile terminals employing a dual-polarized antenna. The smart antennas adaptively control radiation patterns and polarization using a dual-polarized antenna array. Each mobile terminal communicates with the base station by assigning polarization to minimize the interference caused by the other mobile terminals. The simulation results indicate that the proposed system is advantageous in a large capacity cellular environment. Furthermore, we measured vertically- and horizontally-polarized propagation in an urban environment to confirm the actual performance of the proposed system.

Smart antenna testbed for SDMA systems using STBC

This paper presents the experimental results of a testbed for a new SDMA system whose base stations employ multibeam antennas and space time block codes (STBC). New channel response estimation circuits are developed to estimate channel response with high accuracy at terminals and are implemented into the testbed. To evaluate the effectiveness of the system and the testbed, measurements are performed using the testbed in an anechoic chamber. The measurement results confirm that the proposed SDMA system can reduce the influence of the multipath fading effects and the new channel estimation circuit works well.

Transmit nullforming for a MIMO/SDMA downlink with receive antenna selection

In this paper, we propose a novel downlink null-forming technique for space division multiple access (SDMA) in a multiple-input multiple-output (MIMO) channel where a base station and all terminal stations have multiple antennas. In the SDMA system, simple beamforming is not efficient to achieve good performance due to cochannel interference. The proposed method is based on nullforming and characterized by antenna element selection at each terminal where the selected antenna pair satisfies the lowest spatial correlation condition in all combinations. The results obtained by computer simulations show selective diversity gain of the proposed method and performance improvement due to joint detection at each terminal.

Beam forming network design using microstrip lens for cluster feeding

We propose a beam forming network (BFN) design that uses microwave lenses and that is suited to a multibeam reflector antenna. Its performance is assessed as a simple BFN that uses a symmetrically configured 16X16 lens. The proposed BFN is easily manufactured at low-cost by taking advantage of printed-circuit boards. Furthermore, the BFN does not require hybrids; thus, it has no complex interconnections to restrict its operating frequency range. Therefore, the BFN can offer a wide frequency band, and can be applied to large-scale circuits. The antenna radiation patterns that are calculated by applying the BFN to a parabolic antenna exhibit good performance since the proposed BFN configuration counterbalances odd-order aberrations of the microwave lenses.