Perspectives and challenges with millimetre wave communications (author Isabelle Tardy)

Technology for a better society

Perspectives and challenges with millimetre-wave

(mmW) communications

TEK.NO konferansen 28-29/05/2015 – Kragerø

Isabelle Tardy & Jan E. Håkegård


Answering 5G soaring capacity need

• Three paths to increase the system

capacity

1. Allocate additional spectrum through

re-farming or introducing new bands,

2. Improve the spectral efficiency of the

technologies (e.g., MIMO),

3. Cell densification.

• But, decreasing cell size may induce

more interference, affecting in turn the

spectrum efficiency.

Non-interfering frequencies within dense

deployments, e.g., mmW.

2

(from I.Wang et al. Qualcomm tech., "A holistic view on hyper-dense

heterogeneous and small cell networks", IEEE Comm. Mag, June 2013)


Which mm-bands? How much gain is expected?

Frequency

band (GHz)

Available

bandwidth

(GHz)

Duplexing Max EIRP (dBm) Comments

28 1.3 Paired bands

with center gap

85

Freed FS spectrum (ITU2).

P-P, P-MP, M-P-P for feeding small cells and large

cells.

32 1.6 Paired bands

with center gap

80

Worldwide freed FS spectrum.


cells.

40 3 Duplex-

neutral blocks

80 Freed FS spectrum (ITU1).


cells. Block assignment recommended.

60

"V-band"

7 Duplex-

neutral blocks

Up to 85 P − MPUp to 55 P− P

Depending on

antenna gain (EU).

Worldwide. HDFS in 57-59 and 64-66 GHz. Unlicensed

for SRD with EIRP=20 dBm.

Gmin=30 dBi (EU only, [1]).

High attenuation possible, small range or indoor

usage preferred.

70&80

"E-band"

10 Duplex-

neutral blocks

Up to 85

Depending on

antenna gain (EU).

Worldwide FS/HDFS in 71-76 and 81-86 GHz bands,

but national allocations vary.

Gmin=38 dBi, Pmax=10dBm (EU only, [1]).

Small range (but higher than at 60 GHz, see next §).


cells.

3

mmW = [30 -300] GHz, per def.

Internationally agreed, license-exempt and lack sharing constraints


mmW usages

• Historically, mmW communications for

point-to-point (P-P) terrestrial and

satellite radio links.

• More recently, solutions for indoors short-

distance, high-capacity networks

• Outdoor backhauling to cellular base

stations or between them (x2-interface).

– mmW are not expected to be backward-

compatible with cmW radio access technologies

– mmW are not expected to be standalone

– Control information through the macrocells

(fallback and directionality tradeoffs)

4

(from I. Tardy and J.E. Håkegård, "Millimeter-wave communication in 5G"

chap.5 of the white paper of the IEEE Special Interest Group on Cognitive

Radio in 5G, Novel Spectrum Usage Paradigms for 5G. Editors M. Mueck,

W. Jiang, G. Sun, H. Cao. E. Dutkiewicz, S. Choi, Nov. 2014.)


Propagation characteristics in mmW range

• Indoor– A number of different semi-empirical models exist, with

clustering of signal energy both in the temporal and spatial domains

– Offices/cubicles, hospitals, etc…

• Outdoor– Direct measurements and a few modelling examples, e.g., in

New York city or on university campus

– Lack of good and exhaustive channel models

• Free space path attenuation increases with the square of frequencies, but OK for short distances

• Atmospheric losses and rain attenuation, but OK for short distances

• Blocking causes outage

5


mmW communication standards – 60 GHz

• Mosty indoor in the 57-66 GHz range, e.g., as replacement for High-Definition Multimedia Interface (HDMI) cables or similar.

• IEEE 802.11 ad (WiGig): • Adaptive beamforming, Single Carrier and optional

OFDM, backward compatibility with 2.4 and 5 GHz IEEE 802.11 n/ac

• Rates up to 7 Gbit/s (x10 highest 802.11n rate) and channel BW=2.16 GHz

6

(from Wilocity )(from Tensorcom)

(tri-band routers

from Netgear)

http://www.digikey.com/en/articles/techzone/2013/jul/high-speed-60-ghz-wireless-connectivity-finally-takes-off

http://www.digikey.com/en/articles/techzone/2013/jul/high-speed-60-ghz-wireless-connectivity-finally-takes-off

http://forwardthinking.pcmag.com/none/307264-7-more-big-trends-from-ces-2013

http://forwardthinking.pcmag.com/none/307264-7-more-big-trends-from-ces-2013


mmW MIMO (1/2)

• Small form factor

• Beamforming to compensate for

losses

• Should strike a balance between

performance, complexity and power

– Analogue beamforming – simple

– Digital beamforming – better

performance, but costly DAC

• Design: number of antennas

addressing narrow beams, energy

efficiency, spectrum efficiency…

• Spatial multiplexing for additional

gain, capturing energy in selected

directions

7

2-stage, hybrid

BS with several antennas


mmW MIMO (2/2)

• Adaptive beamforming requires

precise channel state information

(CSI)

• But considering a spare channel

matrix, the Angle of Arrival/Departure

(AoA/AoD) are expected sufficient

• Hybrid beamforming is interesting in

the angular vicinity of the analog

counterpart

8

2K=subcarriers, N=transceivers, D=precision of AoD

Hybrid Analog


Beam-searching and transmission scheduling in mmW

• MAC design in mmW will differ from mW

1. Control channel architecture

2. Initial access, handover

3. Resource allocation

9

1

2 3

time


1. Four design options of the control channel

1. Omni-directional mmW for broadcasting inside

small cells

2. Semi-directional mmW also for broadcasting

inside small cells. Additionally, the channel can be

used for feedback such as Hybrid Automatic

Repeat reQuest (HARQ)

3. Fully-directional mmW if a good alignment

between BS and UE can be realized. HARQ is

indeed possible in this option.

4. Omnidirectional mW as a fallback option

10

Insufficient information to extract spatial

synchronization due to different

propagation characteristics

Control channel (omni) with a more limited

range than the data channel (directional)


2. Initial access and handover strategies

• Beam-searching: balance between narrower beams with better directivity gain

and wider beams with faster beam-search.

– Wider beams in the search phase, narrower beams for scheduling traffic

• Given a discovery probability, the full directionality option (3) requires more

time than a semi-directionality one (2).

• A priori angular selection to reduce the spatial search overhead while

providing a minimum level of coverage will lead to a good compromise.

• Additionally, exploit the channel or beam reciprocity of TDD channels to

determine the best beam that the terminal must use.

– Channel reciprocity holds if the duplexing time is much shorter than the coherence time of

the channel. mmW channels have a coherence time an order of magnitude lower than mW, as

the Doppler shift scales linearly with frequency.

mmW channels are best suited to scenarios with low mobility.

• More blockage, more handovers. Several active beams from UE to several BS?

11


3. Resource allocation in mmW

• Once the search is over, scheduling

can be done on a space diversity

basis, allocating a frequency slot for

each angular-separated beam

– time-frequency-space (t, f, s) allocation

• An extra relay station can be useful to

counter blockage.

12

Semi-directional Fully directional

(from H. Shokri-Ghadikolaei et al., "Millimeter wave cellular networks: a MAC

layer perspective", arXiv:1503.00697, mars 2015)


• Develop a flexible SW&HW mmW platform

• Develop competence in model based DSP design using Xilinx System Generator

and MATLAB & Simulink

• Demonstrate the platform in one or several use cases

• Facilitate contribution in national and international R&D projects within mmW and

5G

13

60 GHz communication project

Technology for a better society 14

HW&SW platform

Xilinx ZC706 evaluation board

Zynq7000

PC

MATLAB/Simulink

Xilinx System Generator

A/C and D/C

60 GHz

RX/TX

RF front-end

60 GHz

RX/TX

RF front-end

Model-Based DSP Design

• Contains two 2x2 MIMO transceivers

• Frequency range 57-64 GHz

• EIRP=23.5 dBm

• Four-channel, 16-bit A/D up to 370 MSPS

• Four-channel, 16-bit D/A up to 2.5 GSPS

Technology for a better society 15

Simulations with hardware in the loop


• Channel measurements at 60 GHz

• Indoor and outdoor

• Path loss

• Fading characteristics (impulse response, Doppler spread)

• Channel modelling

• Testing and demonstration of

• Communication protocols (PHY and MAC layers)

• 2x2 MIMO techniques

• Beam-forming (incl. DoA estimation)

• Spatial multiplexing & diversity gain

16

Potential use cases


Short distances

No spectrum costs

Beamforming and scheduling strategies

Product start for indoor case

Low complexity and still capacity gain?

Possibly standalone?

17

mmW take-away

THANK YOU

Date post:	13-Apr-2017
Category:	Technology
Upload:	edouard-deberdt
View:	58 times
Download:	0 times