1. 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

2. 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

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

4. 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.

5. 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

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

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

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

9. Control Channel Design

10. Experiment Setup ’
Base-station Locations
User Locations

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

12. Beacon Performance

13. 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.