Control Channel Design for Many-

Antenna MU-MIMOJihoon 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

• 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

Traditional Sync MU-MIMO

M Base Station AntennasK Users

M2/K

M

Open-Loop Beamforming

• Sweep extra-long synchronization sequences across the coverage area

Coverage Gap

Traditional Sync

Open-loop Beam

MU-MIMO

Coding Gain

• Achieved by sending a signal over a longer period of time

Traditional Sync

Open-loop Beam

MU-MIMO

Faros

Full Coverage

Control Channel Design

Experiment Setup

’’’’’’

Base-station LocationsUser Locations

Beacon Performance

Method

Beac

on S

wee

ps D

etec

ted

(%)

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.