Mattias Gustafsson

Characterization of Implemented Algorithm for MIMO Spatial Multiplexing in Reverberation Chamber

Previously, the throughput for a single-input multiple-output (SIMO) system was successfully tested in a reverberation chamber (RC), and the results were in good agreement with a model based on the ideal threshold receiver. In the present communication, we measure the throughput of a 2 × 2 open loop multiple-input multiple-output (MIMO) system with full spatial multiplexing (i.e., two data streams), and we compare the results with an extended throughput model taking the spatial multiplexing into account. The measured throughput is found to be in agreement with the simulated one of a simple zero-forcing (ZF) receiver. The throughput degradations due to correlation and power imbalance (caused by different embedded radiation efficiencies of antennas) are studied and referred to as a throughput multiplexing efficiency. These can, to a large extent, be explained by the ZF algorithm. The results show clearly that the rich isotropic multipath (RIMP) environment generated by an RC can be used to study how effective different MIMO algorithms are when there is correlation and efficiency imbalance between the antenna elements.

MIMO Characterization on System Level of 5G Microbase Stations Subject to Randomness in LOS

Wireless systems have become more and more advanced in terms of handling the statistical properties of wireless channels. For example, the 4G long term evolution (LTE) system takes advantage of multiport antennas [multiple-input multiple-output (MIMO) technology] and orthogonal frequency division multiplexing (OFDM) to improve the detection probability of single bitstream by diversity in the spatial and frequency domains, respectively. The 4G system also supports transmission of two bitstreams by appropriate signal processing of the MIMO subchannels. The reverberation chamber emulates according to previous works rich isotropic multipath (RIMP) and has proven to be very useful for characterizing smart phones for LTE systems. The measured throughput can be accurately modeled by the simple digital threshold receiver, accounting accurately for both the MIMO and OFDM functions. The throughput is equivalent to the probability of detection (PoD) of the transmitted bitstream. The purpose of this paper is to introduce a systematic approach to include the statistical properties of the user and his or her terminal, when characterizing the performance. The user statistics will have a larger effect in environments with stronger line-of-sight (LOS), because the angle of arrival and the polarization of the LOS contribution vary due to the users orientation and practices. These variations are stochastic, and therefore, we introduce the term random-LOS to describe this. This paper elaborates on the characterization of an example antenna in both RIMP and random-LOS. The chosen antenna is a wideband microbase transceiver station (BTS) antenna. We show how to characterize the micro-BTS by the PoD of one and two bitstreams in both RIMP and random-LOS, by considering the user randomly located and oriented within the angular coverage sector. We limit the treatment to a wall-mounted BTS antenna, and assume a desired hemispherical coverage. The angular coverages of both one and two bitstreams for the random-LOS case are plotted as MIMO-coverage radiation patterns of the whole four-port digital antenna system. Such characterizations in terms of PoD have never been done before on any practical antenna system. The final results are easy to interpret, and they open up a new world of opportunities for designing and optimizing 5G antennas on system level.

A Step Toward 5G in 2020: Low-cost OTA performance evaluation of massive MIMO base stations.

Massive multiple-input, multiple-output (MIMO) is seen as an enabling technology to fulfill dramatic improvements in spectral efficiency for fifth-generation (5G) deployment in 2020. For massive MIMO systems, the learning loop from early-stage prototype design to final-stage performance validation is expected to be slow and ineffective. There is a strong need to evaluate massive MIMO base station (BS) performance with over-the-air (OTA) methods. Until now, such OTA solutions have not been discussed for massive MIMO BS systems.

A self-grounded dual-polarized wideband bowtie with improved MIMO performance in Random-LOS

We present a new improved design of the self-grounded dual-polarized wideband bowtie antenna for MIMO application. The antenna is evaluated for the case when the original four ports are combined to two orthogonally polarized ports. The new antenna covers the previous bandwidth but has lower gain and wider beamwidth over the frequency band of interest. The 2×2 MIMO performance of the antenna in Random-Line of Sight (Random-LOS) is evaluated for two bitstreams using the threshold receiver model and Zero-Forcing receiver. The simulated results show an improvement in terms of MIMO multiplexing coverage over a hemisphere for two bitstreams, compared to the previous solution.

OTA methods for 5G BTS testing — Survey of potential approaches

Through the recent decades, the technical area of antenna testing has undergone disruptive changes, since modern telecommunication systems demand ever increasing test cases. OTA (Over the Air) testing initially mostly concerned making sure that cellular phones complied with radiation pattern and efficiency requirements [1]. For future BTS (Base Transceiver Station) systems, OTA testing will cover a much larger proportion of the testing needed for a transceiver product. Testing of multi-antenna devices will further require more advanced test methods, in many times involving spatial channel models [2]. This paper presents different existing OTA test methods of wireless transceivers, and what adaptations of these which may be needed for testing future 5G BTS systems. Aspects of both conformance testing and performance testing are discussed.