Mathias Riback

Propagation Characteristics of Polarized Radio Waves in Cellular Communications

Narrowband and wideband measurements of the radio channel using different combinations of transmit and receive polarization have been performed. The measurements cover a range of scenarios including urban, suburban and open terrain, as well as both outdoor and indoor terminals. The vertical-to-vertical (V-V) and horizontal-to-horizontal (H-H) polarization combinations are found to provide equal received power on average, while the cross-polarized combinations (V-H) and (H-V) typically provide 5-15 dB weaker received power due to the limited amount of cross-polarization scattering in the radio channel. Fast fading variations are further found to be uncorrelated between different combinations of transmit and receive polarization.

Carrier Frequency Effects on Path Loss

To study the carrier frequency effects on path loss, measurements have been conducted at four discrete frequencies in the range 460-5100 MHz. The transmitter was placed on the roof of a 36 meters tall building and the receive antennas were placed on the roof of a van. Both urban and suburban areas were included in the measurement campaign. The results show that there is a frequency dependency, in addition to the well known free-space dependency 20 log10(f), in most of the areas included in the measurements. In non line of sight conditions, the excess path loss is clearly larger at the higher frequencies than at the lower. A model capturing these effects is presented

MIMO channel characteristics in a small macrocell measured at 5.25 GHz and 200 MHz bandwidth

The purpose of this work is to improve the radio channel characterization in macrocellular scenarios. The effort has been put on the wideband and MIMO aspects. Measurements have been performed at two outdoor and three indoor locations at 5.25 GHz with bandwidth of 200 MHz using a vector network analyzer. An optical fiber was used to achieve distances between transmitter and receiver up to 300m. The channel parameters were estimated by means of maximum likelihood estimation, modeling the channel with a set of discrete plane waves. Based on the estimates joint double directional, delay and polarimetric distributions were determined. Moreover, clustering and statistical distribution of path amplitudes were studied.

Antenna Configurations for 4x4 MIMO in LTE - Field Measurements

The 3GPP LTE standard for mobile broadband includes multi-antenna transmission modes that improve performance, both in terms of coverage, spectral efficiency and peak throughput. The antenna system design, both at the eNB and at the UE is critical to a well performing system; it should be designed with the intended performance profile in mind. Field trials were performed in order to investigate the relative performance of several four and two transmit antenna setups in an LTE system. In general, multi-antenna technology gave substantial performance gains over single antenna transmission. A closely spaced co-polarized configuration gave the best performance for users with poor channel quality while dual-polarized and well-spaced antenna configurations gave better performance for users with good channel quality. The trial also shows that UE antenna polarization is an important parameter that must be kept in mind when designing the eNB antenna system.

Statistical analysis of measured radio channels for future generation mobile communication systems

Measurements of radio channels with 100 MHz bandwidth at 5.25 GHz have been performed in both indoor and outdoor environments. The statistical properties of the tap amplitudes have been analyzed together with general channel characteristics, such as path loss, delay spread and coherence bandwidth. With 100 MHz bandwidth, it was found that the average power delay profile consists of several delay time clusters. The tap amplitudes follow Rice or Nakagami statistics for some taps in the beginning of the clusters while the other taps are close to Rayleigh fading. An approach to model the average power delay profile and the frequency correlation is also presented.

Validation of 3GPP Spatial Channel Model Including WINNER Wideband Extension Using Measurements

This paper is intended to validate the 3GPP spatial channel model (SCM) and the corresponding WINNER wideband extension (SCME) by comparisons with measurement data. Basically the models are validated. The main channel characteristics in terms of angular, delay and polarimetric distributions are confirmed. Moreover, the corresponding MIMO channel capacities are also validated as the agreement with the measurements is good. However, some model deficiencies are identified such as missing important scenarios, like the outdoor-to-indoor scenario for which measured MIMO capacities are substantially lower than those of the SCM/SCME models.

Dual Antenna Terminals in an Indoor Scenario

The performance of two different dual antenna hand-held test mobile terminals has been investigated in a realistic indoor office environment and scenario, with respect to antenna performance, diversity combining and Shannon MIMO channel capacity. Measurements of a 2times2 MIMO channel at 1877.5 MHz (narrowband) were performed using a dual-polarized base station antenna. Analyses show that diversity gains, using ideal selection combining and maximum ratio combining, between 0.7 and 4.6 dB was achieved at the 10% outage probability level. Ideal dual-side beamforming (single branch) gives up to 3.3 dB capacity gain compared to single antenna systems at SNR less than 10 dB, however, decreases with rising SNR. Dual branch MIMO capacity gain is only significant at higher SNR above 10 dB. In addition, horizontal polarization at the base station was found to outperform vertical polarization in this scenario

Field Trial Results of 4-Way Receive Diversity in a Live GSM Network

Receive diversity is an efficient means to improve base station receiver sensitivity and thereby coverage of wireless communication systems. While 2-way receive diversity (2WRD) has been commercially available for different standards for a long time, this paper reports the improvements seen in a field trial of 4-way receive diversity (4WRD) conducted in a live GSM network. The results are also compared to what can be expected theoretically and shown by computer simulations. Depending on the conditions for the trial (e.g. set-up and propagation environment), theory and computer simulations suggest that the expected gain of 4WRD over 2WRD should be in the order of 3-5 dB. The performance measurements carried out during the trial verifies this expected gain. For example, when all traffic in the cell is used as basis for the measured statistics, the cell averaged 4WRD gain over 2WRD is in the order of 3.5-4 dB