Energy-Efficient, Large-scale Distributed Antenna System

(L-DAS)

under revision for JSTSP

Parts of this work have been presented at the IEEE GLOBECOM, Atlanta, GA, USA, Dec. 2013

Jingon Joung, Yeow Khiang Chia, Sumei Sun

Modulation and Coding Department

Institute for Infocomm Research, A*STAR

Internal Meeting with Prof. Moe Z. Win

14 January 2014

Motivation

• To achieve high spectral efficiency (SE) and energy efficiency (EE)

• For high SE– MU-MIMO: LTE-A beyond Re-7– Distributed systems: e.g., coordinated multi-point

operation (CoMP), LTE-A Re-11– Massive (large) MIMO: recent trend

• For high EE– Power control (PC): efficient-power transmission

L-DAS System

BBU: baseband unit (signal processing center)

IAD: intra-ant distance

U usersM antennas

H: U-by-M MU-MIMO ch. matrixS: M-by-U binary AS matrixW: M-by-U precoding matrixP: U-dim diagonal PC matrixx: U-by-1 symbol vectorn: U-by-1 AWGN vector

Objectives & Contribution

• Study an L-DAS

• Provide a practical power consumption model

• Formulate an EE maximization problem

• Resolve issue on huge signaling, complexity requirement:– Antenna selection (AS) method– Threshold-based user-clustering method – MU-MIMO precoding method– Optimal and heuristic power control methods

• Verify the EE merit of L-DAS

Power Consumption Model

Power consumption TPI (transmit power independent) termTPD (transmit power dependent) term

eRF (electric RF)oRF (optical RF)

Cont.

• TPD term

• TPI term

Pcc1: eRFPcc2: per unit-bit-and-second of oRFRu: target rate of user uβ>=0: implies overhead power consumption of MU processing compared to SU-MIMO

EE Maximization Problem

Splitting Problem

• Channel-gain-based greedy AS: RSSI

• Min-dist-based greedy AS: localization Info.

Cont.

• SINR-threshold-(γ)-based clustering– SINR btw users in the same cluster < γ– SINR btw users in diff clusters > γ

γ = 25dB γ = 32dB

Per-Cluster Optimization

• Now, AS matrix is given

• For fixed PC matrix,

– ZF-MU-MIMO precoding matrix

Cont.

• Now, AS and precoding matrices are given

• Assumption: ICI is negligible

– Optimal for MU: using bisection algo, convex feasibility test

– Heuristic for MU and optimal for SU:

Numerical Results

Single cell

Single antenna for each user

No adaptation for - # of antennas for each user- clustering threshold

Remaining Issues for L-DAS

• Deployment, implementation, and operation– Cell planning,– Regular/irregular deployment of antennas– Synchronization for large cluster– Robustness against CSI error– Infrastructure cost for wired optical fronthaul– Comparative, quantitative study of L-DAS and L-

CAS considering Capex and Opex

Cont.

• Iteration for – # of antennas– clustering threshold

Cont.

• Example at cell boundary of two cells

• Outage increase # of active DAs

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0=-Inf

1=-Inf

Colored Square:Active distributed antenna (DA)

Circle: Non-outage userCircle color stands for the cluster/DA

Black Dot: outage userCircle color stands for the cluster/DA

Colored Thick Circle: Active DAallocated to the outage user

X: Deactivated DA

Cont.

• Outage

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0=-Inf

1=-Inf

Threshold Update

Cont.

• Increase clustering threshold γ outage

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0=1e-005

1=1e-005

Cont.

• Increase # of active DAs outage

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0=1e-005

1=1e-005

Threshold Update

Cont.

• Increase clustering threshold γ outage

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0=4

1=4

Cont.

• Increase # of active DAs outage

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0=4

1=4

Threshold Update

Cont.

• No outage: threshold update (2,3) times

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0=4

1=8

Cont.

• Demo

• cell_no_outage

Cont.

• Demo

• cell_outage