Contributions and Conclusions
This chapter summarizes the main research contributions of the included pa-pers. Some general conclusions regarding the research area are also provided as a separate section.
Regarding the operation modes of a user, the data mode or browsing mode where the user holds the mobile phone (or a laptop) in a position as to watch the screen, is perhaps the most interesting scenario nowadays for investigation of user effects on MIMO performance, since it is in this position we expect the highest data transfer rates.
As a feature, the paper also investigated the possibility to explore the sin-gular vectors of the MIMO channel matrix as a tool to find the antenna signal weights and, thus, the individual importance or performance of the antennas.
This technique was not known to the authors to have been published prior to the writing of this paper.
The work was done in cooperation with Sony Ericsson Mobile Communi-cations AB, who provided the test terminals. I did the analysis and wrote the manuscript. The measurements were done together with Henrik Asplund and Mathias Riback. The work was supervised by Prof. Anders Derneryd.
6.1.2 Paper II: “Efficient Experimental Evaluation of a MIMO Handset with User Influence”
This paper extends and improves the evaluation of the composite channel method that was first published in a conference paper [40]. Here, the method is verified for both an outdoor-to-indoor and an indoor-to-indoor scenario, and very good agreement is found between the statistics of the synthetically found channel matrix and direct measurements. The results support the validity of this useful concept for channel modeling with the specific focus to target the important user effects in evaluating realistic MIMO performance of hand-held mobile devices and provide a tool to improve multiple-antenna design on ter-minals.
Novel contributions of this paper are the final validation of the composite channel method with a full phantom user model including hand, arm, upper torso and head. We also reevaluated the impact of different hand positions and usage positions of the handset, i.e., holding it in the browsing position vs.
the standard talk position. Furthermore, we reanalyzed the MIMO capacity as well as the eigenvalue distributions and diversity performance for a realistic four antenna handset mock-up in the presence of a user phantom.
I wrote the manuscript together with Prof. Andreas F. Molisch, and I did the analysis and modeling, except for the double-directional channel estima-tion, to which Dr. Jonas Medbo has contributed. I and Dr. Medbo did the measurements and Dr. Anders J. Johansson contributed to the preparations of the user phantom. Prof. Molisch and Dr. Fredrik Tufvesson supervised the work. The antenna range measurements were done in cooperation with Sony Ericsson Mobile Communications AB.
6.1.3 Paper III: Evaluation of User Hand and Body Im-pact on Multiple Antenna Handset Performance
This conference paper evaluates the performance of a multiple antenna hand-set in realistic radio channels. Specifically, we utilize the previously established approach where the radiation pattern of the user-plus-antenna, is considered as one radiating unit (a super-antenna), and evaluates the performance impact of the user body and hand on properties like the antenna efficiency, performance of different diversity combining approaches, and potentialMIMO channel per-formance. It is found that apart from efficiency loss due to the user hand, the mutual efficiency impact on the antenna elements and the directional impact of the user body shadowing, have small influence on the diversity and capacity performance. We also find that the top and bottom placements of antennas are the most efficient to be used with up to two antenna elements, and that signifi-cant diversity and capacity gain can be explored by using up to four distributed antennas, also with only two radio chains by the use of hybrid selection and combining schemes.
I wrote the manuscript and I did the analysis and modeling with valu-able support by Prof. Anders Derneryd. Dr. Jonas Medbo has contributed to both measurements and channel estimations, and Dr. Anders J. Johansson has contributed to the preparations of the user phantom. Dr. Fredrik Tufvesson su-pervised the work. The antenna range measurements were done in cooperation with Sony Ericsson Mobile Communications AB.
6.1.4 Paper IV: Evaluation of an Outdoor-to-In-Car Ra-dio Channel with a Four-Antenna Handset and a User Phantom
This conference paper evaluates the influence of a car on the MIMO radio channel, from a base station antenna array, to a multiple antenna handset in the hand of a user placed inside. A measurement campaigns is performed that mimic a 2.6 GHz micro-cell urban or rural scenario with two different locations and orientations of the car. The analysis includes important observables like the car penetration loss, impact on fading statistics, terminal antenna branch correlation, eigenvalue distributions, as well as the performance of various hy-brid diversity combining and spatial multiplexing schemes, with and without the vehicle present in the channel. It is found that the car, in general, makes the channel statistics become closer to Rayleigh-distributed by increased inner scattering, increases multipath channel richness, improving the potential of di-versity gain and, to some extent, spatial multiplexing. The overall impact of these effects is found to depend substantially on the orientation of the car and
the outer channel scenario.
I wrote the manuscript and I did the analysis and modeling. The mea-surements were done together with Dr. Tommy Hult. Dr. Jonas Medbo has contributed to both measurements and channel estimations, and Dr. Anders J.
Johansson has contributed to the preparations of the user phantom. Dr. Fredrik Tufvesson supervised the work.
6.1.5 Paper V: Experimental Investigation of the Direc-tional Outdoor-to-In-Car Propagation Channel
This submitted journal paper evaluates the possibility to accurately enough perform channel estimation inside a car in an outdoor-to-in-car environment, despite the violation of the required “rule-of-thumb” Rayleigh distance to the surrounding channel scatterers. The investigation is based on 32 × 128 and MIMO channel measurements with probe array antennas for channel charac-terization, and 32 × 4 MIMO reference channel measurements with an upper body phantom and a four-antenna handset mock-up located outside and in-side of a standard family car. It investigates whether the combination of a plane-wave spectrum propagation representation combined with arbitrary but realistic multiple antenna representations, in the presence of a difficult confined scattering environment, can appropriately account for and model important statistics of the channel. In both cases the results of this investigation show that this is possible with high accuracy. The main specular components of the channel seem to account for the important statistical properties.
The novel contributions of the paper are the test of the composite channel model with a body phantom that includes hand and upper body placed inside and outside a car, the impact of a car environment (outdoor-to-in-car), and the investigation of the possibility to perform directional channel estimation inside the car. Furthermore, we test the accuracy of the synthetic channel based on the estimated channel in the presence of a user inside and outside the car, regarding MIMO channel statistics, diversity and capacity gain.
I wrote the manuscript and I did the analysis and most of the modeling.
The measurements were done together with Dr. Tommy Hult. Dr. Jonas Medbo has assisted with the channel estimations, and Dr. Anders J. Johansson has contributed to the preparations of the user phantom. Dr. Fredrik Tufvesson supervised the work.