Millimeter-Wave Based Device-toDevice Communications - Research Activities at Aalto Dr. Linsheng Li Department of Radio Science and Engineering, Aalto University 13.04.2015 OUTLINE • Background • Overview of technical challenges • On-going research activities OUTLINE • Background • Overview of technical challenges • On-going research activities Overview of the project • Title of research project: – Device-to-device communications at millimetre-wave frequencies • Principal Investigators & contributors: – Prof. Katsuyuki Haneda, Aalto University School of Electrical Engineering(PI) • Sinh Nguyen, Linsheng Li and Jan Järveläinen – Prof. Andreas F. Molisch, University of Southern California (USC), Communications Sciences Institute(PI) • Rui Wang, Umit Bas and Daoud Burghal • Duration of the project: – 24 months (two years) starting from 15 November 2014. Background: Millimeter-Wave (Mm-Wave) Radios • > 1 GHz bandwidth available for high-data-rate radio communications • Higher free space loss with a fixed physical size of receive antenna aperture Free space loss 4m Transmit omnidirectional antenna Transmit omnidirectional antenna Background: Millimeter-Wave (Mm-Wave) Radios • Directional radio transmission required to ensure link budget – Small-cell operation preferable; effective spatial coexistence of multiple links Antenna array 2 mm @ 60GHz 2 mm Ideal beam pattern Device-to-Device (D2D) Communications at Millimeter-Wave Radio Frequency • D2D comm. improves the spectral efficiency per area in cellular comm. Legacy (< 5GHz) frequency has wider coverage Indoor Use of legacy bands as a fall back option of mm-wave bands Mm-wave (>30GHz) frequency has smaller coverage Directional isolation allows effective D2D comm at mm-wave OUTLINE • Background • Overview of technical challenges • On-going research activities D2D Comm. at Mm-Wave Frequency: Technical Challenges (1) • How far mm-wave radios can reach in comparison to legacy radios? Outdoor-to-indoor penetration/isolation? We address this challenge by extensive mm-wave radio channel sounding. ? ? ? ? D2D Comm. at Mm-Wave Frequency: Technical Challenges (2) • How should the mm-wave radios coordinate with legacy cellular? We address this challenge by considering the legacy cellular as a fall-back option to mm-wave radios. D2D Comm. at Mm-Wave Frequency: Technical Challenges (3) • Directional antennas allow highly isolated links. At the beginning, how efficient it is to find a device to communicate? ? ? We address this challenge by developing an efficient neighbor discovery method. ? ? ? ? D2D Comm. at Mm-Wave Frequency: Technical Challenges (4) • What is the feasible beamforming architecture at mm-wave? Tradeoff between complexity (energy losses) and flexibility? Hybrid analog-digital beamforming RFchain RFchain RFchain RFchain RFchain RFchain Baseband control Fully digital beamforming Baseband control We address this challenge by developing a hybrid analog-digital beamforming architecture. OUTLINE • Background • Overview of technical challenges • On-going research activities On-going research activities • Channel measurements and modeling – Accurate channel measurement is the essential step to get a quantitative model of the environment effects and channel characteristics. – Vector network analyzer based channel sounder for 60GHz have been used to carry out outdoor/indoor channel measurement. The sounder for 28GHz has been designed and tested in the laboratory. Channel measurement will be carried out in the airport in May 2015. – A switched array channel sounder is under development for 60GHz channel sounding. Measurement equipment Tx Rx 60 GHz Indoor and O2I measurement Indoor cafeteria O2I cafeteria Deterministic field prediction • Spatio-temporal channel propagation prediction requires accurate description of environment • Laser scanning Point cloud environment data No surface description ray tracing cannot be used Point Cloud-Based Propagation Prediction – Synthesis of Power Delay Profile (PDP) Path power [dB] = |Es|2 + GTx + GRx - FSPL Power delay profile: bandwidth limited form Discrete channel impulse response -70 -70 -90 -100 -110 -120 -130 0 S=0.5, R=50 S=0.2, R=50 -80 Amplitude [dB] Amplitude [dB] -80 -90 -100 -110 -120 5 10 15 Delay [ns] 20 25 30 Channel transfer function over 5 GHz BW L H i l exp( j2f i l ) l 1 -130 0 5 10 15 Delay [ns] 20 25 30 PDP derivation from channel transfer functions 2 L PDP( ) E H l exp( j2f l ) l 1 18 Point-cloud based Channel Simulation PDP for Tx4 11, S 0.6 -60 Measured Predicted Amplitude [dB] -70 -80 -90 -100 -110 -120 0 10 20 30 Delay [ns] 40 Measured Predicted Mean delay 5.3 ns 5.2 ns RMS delay spread 3.1 ns 2.5 ns 50 8 On-going research activities • Neighbor discovery – For D2D communication, the first step is to discover its neighbors, i.e., which other devices it can communicate with. – Solution methods for mm-waves are significantly different from those at lower frequencies, due to the high directionality of the channels. – Measurements complemented with point-cloud simulations will be of use for this analysis. On-going research activities • Beamforming and beamtracking – Due to the highly dynamic nature of the D2D channel and the sensitivity to the interaction with the body of the person holding the device, adaptive beamforming is necessary. – Hybrid analog-digital beamforming based on an antenna array at 60 GHz working in multipath environments is under development. – Analysis with spatial degrees-of-freedom of multipath channel is under development. Hybrid analog-digital beamforming scheme . . . DAC . . . Baseband (digital beamforming) DAC Analog beamforming . . . Antenna array Hybrid analog-digital beamforming scheme Research plan
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