Basic Repeater Presentation

www.axellwireless.com

Repeaters in wireless networks: from

coverage to capacity

Dr Mike Lewis

SDR repeater architect

1


Topics

• Repeaters in wireless systems

• Design challenges in repeaters

• Capacity-centric versus coverage-centric

design

2


Repeaters in wireless systems

3


“Gap-filling” coverage extension

4

Aerial FacilitiesLimited

Service Antenna

Donor Antenna

Donor BTSRepeater


Tunnel coverage

5

Donor BTS

Repeater located externally

or in equipment room

Donor Antenna

Aerial FacilitiesLimited

Radiating cable in tunnel


In-building coverage

6

Direct signal from the BTS cannot penetrate the building; signal is distributed within the building via panel antennas

and radiating cable

Donor BTS

Donor antenna and remote

repeater

80% of mobile phone calls originate in buildings!


Fibre-fed systems (active DAS)

7

ControllerHI

BPOWER

SUPPLY

+5V

+10

V

+15

V

POWER

SUPPLY

+5V

+10

V

+15

V

ControllerHI

BPOWER

SUPPLY

+5V

+10

V

+15

V

POWER

SUPPLY

+5V

+10

V

+15

V

EMP

c

c

Indoor 1

Repeater

7/16 type

Connect

or

Fibre

input

Indoor 2

Repeater

7/16 type

Connect

or

Fibre

input

Indoor 3

Repeater

7/16 type

Connect

or

Fibre

input

Indoor 4

Repeater

7/16 type

Connect

or

Fibre

input

Hydrid

Lightning

protection

2 x 30dB

CouplerMaster Unit


In building Coverage with active DAS


On-board repeaters

9


Why use repeaters?

• Why not just install another base station?

– Cheaper! Cost of a base station may not be

motivated if not enough users being served.

• Rural areas / coverage black spots

• Roll-out of new technology with few users

– No need for data connection to core network

• Remote sites (or moving ones!)

– Operator-neutral

• Example: coverage for a shopping mall or

stadium, installed by building owner

• Multi-hop relaying introduced in LTE

– Not clear if this will be cost-effective

10


REPEATER DESIGN

CHALLENGES

11


Basic repeater

12

LNA

MCPA

Control logic

RMS

power

ADC

MCPA

LNA

Control logic

RMS

power

ADC

Donor

(BT

S s

ide)

Serv

er (m

obile

sid

e)

Downlink path

Uplink path


Overlap-zone interference

13

Service Antenna

Donor Antenna

Donor BTS

Repeater

• In overlap area:

– Direct signal coming from base station

– Delayed signal from the repeater

• Signal from repeater appears as

strong ISI

– Often find some pathological region

where signals almost equal

Must minimize repeater delay

– “Repeater” multipath adds to “real”

multipath for receiver to handle • Goals: < 6µs for GSM, 14µs TETRA

– Delay also has an effect on max cell

size (round-trip time)


TX – RX isolation

• High gain typically desirable (80-90dB)

• Finite isolation between transmit and

receive antennae

𝐼𝑠𝑜𝑙𝑎𝑡𝑖𝑜𝑛 𝑚𝑎𝑟𝑔𝑖𝑛(𝑑𝐵) = 𝐼𝑠𝑜𝑙𝑎𝑡𝑖𝑜𝑛 − 𝐺𝑎𝑖𝑛

• Isolation margin ≤ 0dB: oscillation

• Low isolation margin: self-interference 14

GAIN

(dB)

Path loss

-ISOLATION (dB)


Frequency-shifting repeater

• Frequency shift gives very large isolation (due to filter rejection)

• Allows the use of omni antennas for coverage

F1

Link

Antenna

RF Link Path

Donor

Repeater

Remote

Repeater

F5

F5F1

F9

c

Link

Antenna

BTS

900 MHz 900 MHz 1800 MHz


Repeaters versus base station design

• Both repeaters and base stations need to

meet similar regulatory requirements

• Base station is master of system timing

– Processing delay allowed for as part of mobile

standards

– Repeater has to minimize delay

• Power control algorithms seek to

normalize power into base station

– Repeater located “out in the cell” and can see a

wide range of signal levels

16


Repeaters versus base station design

• Base station works with baseband data

– Can perform various data-aided algorithms to

compensate for non-ideal RX path, or pre-

compensate for TX path

– Repeater has (almost) no knowledge of the

underlying signals

• Repeater output power levels typically

lower than for (macro) base stations

– But wide bands, many carriers, high dynamic

range and less scope for crest factor reduction

17


Digital repeaters

• Traditional repeaters have been purely

analogue (other than supervision)

– Filtering fixed, defined by e.g. SAW filters

– Each passband has a separate down / upmixer

and IF path

• Proliferation of standards and multi-

operator scenarios require more flexibility

– And need very sharp filtering

18

GSM Filter WCDMA Filter GSM filter G

B

G

B


Traditional repeater

19

LNA

MCPA

Control logic

RMS

power

ADC

MCPA

LNA

Control logic

RMS

power

ADC

Donor

(BT

S s

ide)

Serv

er (m

obile

sid

e)

Downlink path

Uplink path

IF stages replicated once

per passband


Digital repeater

20

Donor

(BT

S s

ide)

Serv

er (m

obile

sid

e)

Downlink path

Uplink path


Advantages of digital repeater

• Easy to adapt to new requirements

– FPGA-based processing is a “blank sheet”

– Filter bandwidths, frequencies all flexible

• Better support for multiple passbands

– Cheaper, smaller, lower power

• Filtering numerically defined

– Can implement stable, sharp filters

21


Advantages of digital repeater

• Access to signal in digital form

– Easy to perform measurements on signal,

implement gain control algorithms

– Can use digital techniques to correct for

analogue imperfections

• Digital pre-distortion for PA linearization

• Feedback cancellation

• …

22


Disadvantages of digital repeater

• High performance A/D and D/A needed

– Wide signal band, and high-IF sampling used

due to image rejection issues

• Zero-IF not practical: I/Q compensation not

enough due to high gain from input to output

– High dynamic range

• Aliasing needs to be managed

• Processing delay of FPGA needs to be

carefully managed

… but high performance mixed signal

components and FPGAs now affordable.

23


CAPACITY-CENTRIC VERSUS

COVERAGE-CENTRIC DESIGN

24


The capacity problem…

• Coverage used to be the main focus of

mobile operators

– Explosion of data usage is changing that

• Need enough carrier frequencies to meet

bandwidth requirements

– Or users get kicked off onto older technologies

• Only solution: have denser base station

sector coverage

– Higher frequency re-use, fewer users per

sector

25


Base station hotels –

the solution to site acquisition issues

• Shortage of suitable

sites

• Requirements on air

conditioning

• Transmission needs

• Many base stations

will be needed in the

mature network




Phase 1: few users




Phase 2: more users




Phase 3: many users

Bill Boards


London 2012

• Axell providing a coverage system

across the park for both Cellular and

public safety

• There is one BTS hotel for the 4

operators with 600 base stations in

it

• Solution involves over 300 fibre-fed

repeaters across the campus


Venues for Axell Wireless

Current orders for the

Olympic park

Possible new

requirements


Repeaters versus RRHs

• Remote radio heads: base station

transceiver at end of digital fibre link

– How can a repeater-based distributed antenna

system compete?

– Also: micro / nano / pico base stations?

• Multi-operator support!

– For in-building applications, stadia, tunnel

systems: typically the site owner installs the

equipment.

– Don’t want to install separate equipment per

operator: costly and space issues

32


Conclusions

• Traditional repeaters will always have

their place in wireless networks, but…

• Distributed antenna systems blur the

borders between the base station and

repeater network

• Requirement to support multiple operators

will drive DAS business

• Managing capacity the next big challenge

33


THANK YOU!

34

Date post:	03-Jan-2016
Category:	Documents
Upload:	mainkeizer
View:	133 times
Download:	0 times

Basic Repeater Presentation

Documents