Alexey Khoryaev

Dynamic uplink-downlink configuration and interference management in TD-LTE

Transmissions in different cells of a time-division duplex system are typically synchronous in order to eliminate the base station-to-base station and terminal-to-terminal interference. The synchronous operation limits dynamic resource configuration for downlink and uplink transmissions. Today, as a large percentage of mobile traffic is generated in hotspots and indoor environments, heterogeneous networks comprising high-power/wide-area and low-power/local-area network nodes are becoming a reality. Such heterogeneous networks provide opportunities to exploit dynamic uplink-downlink configuration in TDD systems, adapting to the individual traffic needs of a specific cell area. This article presents a tutorial overview of dynamic uplink-downlink configuration and interference management in time-division Long Term Evolution, including motivations, target deployment scenarios, opportunities and challenges, system requirements, design aspects, and performance evaluations.

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.

Triangular systolic array with reduced latency for QR-decomposition of complex matrices

The novel CORDIC-based architecture of the triangular systolic array for QRD of large size complex matrices is presented. The proposed architecture relies on QRD using a three angle complex rotation approach that provides significant reduction of latency (systolic operation time) and makes the QRD in such a way that the upper triangular matrix R has only real diagonal elements

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.

Comparative Analysis of Spatial Covariance Matrix Estimation Methods in OFDM Communication Systems

The performance of the orthogonal frequency division multiplexing (OFDM) communication systems may be significantly improved by use of the multiple antenna techniques. One of the multiple antenna techniques applications is the co-channel interference mitigation by exploiting the minimum mean square error (MMSE) signal detection algorithm. The realization of the algorithm requires knowledge of interference plus additive noise spatial covariance matrix (SCM) estimate for every subcarrier of the OFDM symbol. In this paper the independent SCM estimation for every subcarrier of OFDM symbol is considered first and then the algorithm is proposed for the enhancement of such estimate by taking into account the frequency correlation of the propagation channel and additional knowledge of OFDM symbol structure. As a result, it is shown that exploiting of the a priori information about the channel impulse response delay spread and symbol structure may lead to the significant improvement of the estimation accuracy

Analysis of IEEE 802.16m and 3GPP LTE Release 10 technologies by Russian Evaluation Group for IMT-Advanced

The IMT-Advanced standardization process is executed by International Telecommunications Union Radiocommunication Sector (ITU-R) to define requirements to the next 4-th generation mobile communication systems and certify technologies meeting these requirements. This work presents results of the IEEE 802.16m and 3GPP LTE Release 10 technologies evaluation obtained by the Russian Evaluation Group (REG) as part of the ITU-R IMT-Advanced standardization process. The evaluation was done mainly by system level simulations and considered four mandatory test environments of IMT-Advanced: indoor, microcellular, base coverage urban and high speed. Cell spectral efficiency and cell-edge user spectral efficiency were evaluated for downlink and uplink transmissions. It was found out that performance of both IEEE and 3GPP technologies meets the IMT-Advanced requirements for all the considered evaluation scenarios. This conclusion was conveyed by the REG to ITU in the evaluation report submitted in June 2010.

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.

Performance analysis of spatial reuse mode in millimeter-wave WPAN systems with multiple links

This paper presents the results of the spatial reuse mode performance analysis for millimeter-wave (mmWave) WPAN systems with steerable high-directional antennas. The practical approach to the spatial reuse problem solution is proposed and two spatial scheduling algorithms for spatial reuse mode implementation are presented. The system level simulations are used to estimate the performance of the proposed algorithms. It is demonstrated that the introduction of the spatial reuse mode for the indoor mmWave WPAN system with 8 parallel communication links will increase the overall mmWave WPAN system throughput in 3-5 times in comparison with conventional time division mode.

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.