The dramatic increase in traffic - both aggregate, and peak traffic per user - will soon outpace the capabilities of current cellular systems like LTE. To cope with the increased requirements, new systems need to be developed that both exploit the use of new spectrum, and new radio access methods. An especially promising method with those features is device-to-device (D2D) communications operating at millimeter-wave frequencies. D2D communications exploits the fact that in many situations, such as in social networks, two devices that want to communicate are in close proximity to each other. While such devices could talk to each other via infrastructure nodes, it is much more spectrally efficient to enable direct communications between the devices, especially for inter-device distances much smaller than the cell radius; this also enables higher data rates. Further data rate increases can be obtained by exploiting the large swatch of new spectrum in the millimeter-wave frequency bands. The use of millimeter-wave frequencies for WiFi-like systems is has already been standardized and first products are reaching the market. Furthermore, millimeter-wave links are now also considered for wireless access, i.e., connection from a mobile cellphone to a base station or access point. Recently, cellphone manufacturers have demonstrated prototypes of handsets with millimeter-wave transceivers and adaptive antennas, showing the practical viability for mobile applications. This opens up the possibilities for millimeter-wave based D2D systems as well.
This project will investigate fundamental questions of realizing D2D communications at millimeter-wave frequencies. Critically, such systems are not simply "regular D2D systems operating at higher frequencies"; rather, new and important challenges arise in the context of channel modeling, link setup, link adaptation, and robustness. To solve these, we tackle the following 4 main challenges: (i) measurement of D2D propagation channels at mm-wave frequencies, using innovative measurement techniques and evaluations such as laser-scanning based ray tracing; (ii) neighbor discovery, i.e., finding which devices can talk to each other, taking into account the directional nature of the device antennas; (iii) dynamic beamforming and beamtracking, which integrates a key property of millimeter-wave channels that the directions of the strongest multipath components can change rapidly; and (iv) capacity and reliability investigations. Results from this project will form the basis for systems that support wireless high-speed connections, as are relevant for video conferences, real-time gaming, situational awareness, and many others. Equally importantly, by offloading resource-consuming connections, cellular resources are freed up for other applications.