Artyom Lomayev

Experimental investigations of 60 GHz WLAN systems in office environment

This paper presents the results of an experimental investigation of 60 GHz wireless local area network (WLAN) systems in an office environment. The measurement setup with highly directional mechanically steerable antennas and 800 MHz bandwidth was developed and experiments were performed for conference room and cubicle environments. Measurement results demonstrate that the 60 GHz propagation channel is quasioptical in nature and received signal power is obtained through line of sight (LOS) and reflected signal paths of the first and second orders. The 60 GHz WLAN system prototype using steerable directional antennas with 18 dB gain was able to achieve about 30 dB baseband SNR for LOS transmission, about 15-20 dB for communications through the first-order reflected path, and 2-6 dB SNR when using second-order reflection for the office environments. The intra cluster statistical parameters of the propagation channel were evaluated and a statistical model for reflected clusters is proposed. Experimental results demonstrating strong polarization impact on the characteristics of the propagation channel are presented. Cross-polarization discrimination (XPD) of the propagation channel was estimated as approximately 20 dB for LOS transmission and 10-20 dB for NLOS reflected paths.

Impact of Polarization Characteristics on 60-GHz Indoor Radio Communication Systems

This letter presents experimental results for the polarization impact on 60-GHz indoor radio communication systems. Different transmit and receive antenna polarizations (linear polarizations with different electrical field vector orientations and circular polarizations with different handedness) were used to analyze the degradation in the received signal power due to nonoptimally matched polarization characteristics between the transmit antenna, the propagation channel, and the received antenna. Different signal propagation paths including line-of-sight (LOS) propagation and first- and second-order reflections were investigated. It was found that the degradation due to polarization characteristics mismatch could be as large as 10-20 dB. Polarization characteristics of the transmit and receive antennas providing maximum received signal power were found to be dependent on the type of the signal propagation path. The most robust antenna polarization configuration was identified as a configuration using linear polarization at one end of the communication link and circular polarization at the other end, giving the degradation relative to the optimally matched case of 2-3 dB only.

Performance analysis of dynamic adjustment of TDD uplink-downlink configurations in outdoor picocell LTE networks

The dynamic adjustment of TDD UL-DL configurations to the instantaneous traffic conditions at small cells (e.g. Pico cells) in heterogeneous LTE networks can be used to further optimize the system performance. The dynamic adaptation of TDD configuration may result in opposite transmission directions in the neighboring cells and thus cause BS-BS and UE-UE inter-cell interference that may significantly affect the overall system performance. To avoid this problem all homogeneous Macro cell TDD deployments typically operate synchronously. However in heterogeneous networks low power small cells are rather isolated from each other in terms of mutual interference and thus can be considered as candidates for dynamic TDD adaptation. In this paper we investigate the possibility of using dynamic adjustments of TDD UL-DL configurations in application to outdoor Pico cell deployments. In particular, we show the feasibility of using opposite DL and UL transmission directions in neighboring Pico cells in terms of interference environment. Furthermore we evaluate the performance benefits from traffic adaptation in LTE TDD networks where cells can dynamically select TDD configuration and show that substantial gains in packet throughput performance may be achieved comparing to the traditional synchronous TDD networks.

Comparison of Power Amplifier Non-Linearity Impact on 60 GHz Single Carrier and OFDM Systems

This paper presents a detailed analysis of the impact of power amplifier (PA) non-linearity on the performance of single carrier (SC) and OFDM systems in 60 GHz spectrum. The efficiency of the considered systems was analyzed by estimating values of the power amplifier output backoff needed to meet the requirements on the transmit spectrum mask (TSM) compliance and error vector magnitude (EVM). Different models of the PA including an experimentally measured model for the 60 GHz PA were considered. It was estimated that for many types of modulations and PA models, SC system can have up to 1.5 dB higher output power than OFDM system. However, for the experimental PA model accounting for amplitude modulation-phase modulation distortion in addition to amplitude modulation - amplitude modulation distortion, the difference between the OFDM and SC output power levels was minimal, and OFDM even had approximately 1 dB better performance than SC for the BPSK modulation. A potential improvement in the transmit power due to application of digital predistortion techniques was estimated for both systems to be in the range from 1.5 to 3.4 dB.

MIMO and multihop cross-layer design for wireless backhaul: A testbed implementation

In this article, the design of a highly efficient and flexibly deployable wireless backhaul is addressed as a promising alternative to the typical wired solutions. To this end, two novel approaches are presented, one proposing relay transmissions with multiple antennas based on the notion of data splitting and a second one addressing resource allocation with distributed scheduling. A proof-of-concept hardware prototype was developed as a means to demonstrate the efficiency of the proposed concepts and algorithms and investigate the performance benefits and complexity requirements.

Feasibility Analysis of Dynamic Adjustment of TDD Configurations in Macro-Femto Heterogeneous LTE Networks

The dynamic adaptation of TDD configurations to traffic conditions at low power base stations (femtocells and picocells) in heterogeneous LTE networks can be used to optimize the system performance. For instance, a significant performance improvement can be achieved in DL and UL packet throughputs. However, in practical multi-cell deployments the TDD configuration adaptation may result in opposite transmission directions in the neighboring cells and thus cause new types of inter-cell interference such as BS-BS and UE-UE. These interference types are often called DL-UL cross interference and may significantly deteriorate the overall system performance. For this reason all homogeneous Macro cell TDD deployments typically operate synchronously (i.e. use same TDD configurations). However the recent advances in the field of heterogeneous networks have reopened the dynamic TDD problem since low power small cells are rather isolated from each other and thus can be considered as candidates for dynamic TDD adaptation. In this paper we provide a feasibility analysis of dynamic TDD configuration adjustment in application to Macro-Femto LTE TDD networks.

Testbed for wireless Mesh Backhaul Networks MEMBRANE demonstrator

Wireless Backhaul mesh networks have attracted attention during the past few years due to their ease of deployment, flexibility and adaptiveness, compared to non-mesh networks. Besides studying and evaluating novel techniques and algorithms for such systems, IST project MEMBRANE aims to develop demonstrators to act as proof of concept and provide an implementation oriented perspective. Two demonstrators are being implemented within the project, addressing different aspects of the proposed system. The first demonstrator focuses on link level cooperative communication for wireless mesh networks and the second focuses on optimized distributed scheduling and routing. This paper briefly describes the techniques and algorithms used in each case and provides the basic design principles of each of the demonstrators.