Control Channel Design for Many-Antenna MU-MIMO Jihoon Yun C. Shepard, A. Javed, and L. Zhong, “Control Channel Dsign for Many-Antenna MU-MIMO”, Mobicom 2015

Introduction The lack of an efficient and reliable control channel in current MU- MIMO architectures. In existing systems all control channel operations are performed in the no-CSI mode -> the operational range is limited Use a combination of open-loop beamforming and coding gains -> reduce the range gap between the CSI and no-CSI modes Provide their control channel design for many-antenna MU-MIMO C. Shepard, A. Javed, and L. Zhong, “Control Channel Dsign for Many-Antenna MU-MIMO”, Mobicom 2015

Background: Multiple-Input Multiple-Output Multiple-Input Multiple-Output(MIMO) Single-User MIMO (SU-MIMO) Multi-User MIMO (MU-MIMO)

Background: Beamforming Utilizes multiple antennas transmitting at the same frequency to realize directional transmission Open-loop Beamforming : uses precomputed beamforming weights without knowledge of the user’s location Closed-loop Beamforming(adaptive beamforming) : employs channel state information (CSI) to calculate the beamweights.

Background: Control Channel Performs operations required to setup data communication Synchronization Since nodes in wireless networks do not share oscillators , their time-frequency reference is subject to drift Association Before a user can transmit or receive data, it must first identify the nearby base stations, select one, then connect to it. Beacon: base stations typically transmit a unique identifier Channel state information(CSI) Collection Pilot : to obtain CSI, the transmitter sends a pre-known sequence Paging and Random Access Paging : the control channel handles notifying users when they have incoming data The control channel handles coordinating users to randomly access the network when they have outgoing data

Gap grows between no-CSI and CSI mode M Base Station Antennas K Users M M2/K Traditional Sync MU-MIMO

Open-Loop Beamforming Sweep extra-long synchronization sequences across the coverage area Coverage Gap Traditional Sync MU-MIMO Open-loop Beam

Coding Gain Achieved by sending a signal over a longer period of time Full Coverage Traditional Sync MU-MIMO Open-loop Beam Faros

Control Channel Design

Experiment Setup ’ Base-station Locations User Locations

Beacon Sweeps Detected (%) Beacon Performance Beacon Sweeps Detected (%) Method

Beacon Performance

Summary A fundamental re-design of the wireless control channel in many- antenna MU-MIMO systems Improve the range, or transmission efficiency by over 40dB Most of experiments held in stationary status.(Briefly explain mobility but there is no detailed explanation. For mobile network(LTE), the mobility have to be considered.