Highly directional transmissions are essential for cellular communication in mmWave frequencies to compensate for higher isotropic path loss. This reliance on directional beamforming, however, complicates initial cell search since mobiles and base stations must jointly search over a potentially large angular directional space to locate a suitable path to initiate communication.
In this work we propose an initial access procedure where base stations periodically transmit synchronization signals, potentially in time-varying directions, to scan the angular space randomly or sequentially. Five different design options are compared considering different scanning, beam forming methods and signaling procedures to evaluate access delay, detectability range and system overhead. Detectors for these signals are derived based on a Generalized Likelihood Ratio Test (GLRT). The detectors are then simulated under realistic design parameters and channels based on actual experimental measurements at 28 GHz in New York City.
The study reveals two key findings: 1) digital beamforming can significantly outperform analog beam- forming even when digital beamforming uses very low quantization to compensate for the additional power requirements and 2) omnidirectional transmissions of the synchronization signals from the base station generally outperform random directional scanning.
|C. N. Barati, S. A. Hosseini, M. Mezzavilla, S. Rangan, T. Korakis, S. S. Panwar, M. Zorzi, "Initial Access in Millimeter Wave Cellular Systems," in IEEE Transactions on Wireless Communications, vol. 15, no. 12, pp. 7926-7940, Dec. 2016.||initial access, MmWave cellular system design, mmWave Channel Modeling||2016/12/23|
|C.N. Barati, S.A. Hosseini, M. Mezzavilla, P. Amiri-Eliasi, S. Rangan, T. Korakis, M. Zorzi, "Directional initial access for millimeter wave cellular systems." in IEEE Transactions on Wireless Communications, vol. 15, no. 12, pp. 7926-7940, Dec. 2016.||initial access||2016/12/01|
|M. Giordani, M. Mezzavilla, M. Zorzi, "Initial Access in 5G mm-Wave Cellular Networks", to appear in IEEE COMMAG.||initial access||2016/08/22|
|M. Giordani, M. Mezzavilla, C. N. Barati, S. Rangan and M. Zorzi, "Comparative analysis of initial access techniques in 5G mmWave cellular networks," 2016 Annual Conference on Information Science and Systems (CISS), Princeton, NJ, 2016, pp. 268-273.||initial access, mmWave MAC||2016/03/18|
|C. N. Barati, S. A. Hosseini, S. Rangan, P. Liu, T. Korakis, S. S. Panwar, and T. S. Rappaport, “Directional Cell Search for Millimeter Wave Cellular Systems,” Proc. IEEE Signal Processing Advances in Wireless Communications (SPAWC), Toronto, Canada, pp. 120-124, June 2014.||initial access, Low-Power Fully Digital Transceivers, mmWave MAC, Network Design||2014/06/22|