4g technology in unlicensed bands: an opportunity to deliver new … · 4g technology in unlicensed...

4G technology in unlicensed bands: an opportunity to deliver new services

TELECOMS AND MOBILE

white paper4G technology in unlicensed bands

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Cambridge Consultants believes that 4G technology will emerge in unlicensed bands in the near future and that this emergence will not only extend mobile operator service offerings but also enable a new class of applications for private networks. This white paper examines the case for developing 4G technologies in unlicensed bands, explores the challenges involved and looks at the characteristics of the technology that make this more likely.

4G mobile broadband technology has already staked its place

as the future of mobile communications technology. Initially

WiMAX and today LTE, 4G technologies provide low-latency,

high data-rate data services, replacing the voice-call oriented

technologies of 2G and 3G. And being ‘carrier-grade’ wireless

technology, 4G offers characteristics that are very attractive

to a wide array of applications. But, because 4G technology

is designed for deployment by mobile operators, it is

inherently designed for deployment in licensed (and hence

unshared) spectrum. This has two effects:

� 4G technology can only be deployed in the licensed

spectrum bands made available in any one market

� Only a small number of spectrum licence holders can

deploy it

Building any new wireless network requires spectrum;

broadband networks require large allocations of spectrum.

Large allocations of unlicensed spectrum exist, especially at

higher frequencies such as above 5GHz. If 4G technology

was available in unlicensed spectrum, then two key benefits

would emerge:

� Users with applications where 4G capabilities have strong

advantages could readily make use of the technology in

their own private networks

� Mobile operators could provide a seamless capacity

extension of their broadband services by making use

of unlicensed bands to increase their overall spectrum

resources

white paper 4G technology in unlicensed bands

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Many applications have broadband requirements

Most of us are familiar with broadband wireless technologies

like WiMAX, LTE and Wi-Fi from the use we make of

them when our tablets and smartphones connect to the

internet. Most of us also use Wi-Fi when connecting to

private networks at home and at work. Thinking about these

technologies providing mobile data connectivity to transfer

IP traffic, such as files, downloads, browsing and streaming,

is commonplace. As the amount of data we transfer grows,

the capacity required increases to maintain the perceived

performance at a level where we are happy.

But not all applications target smartphones, tablets and

PCs. There are many broadband applications that have

different requirements, ranging from industrial monitoring

and control to professional audio distribution to machine-

type communications (MTC) – or machine-to-machine (M2M)

communications, as it is also known.

Applications seem to fall into a number of categories:

� Public broadband cellular data networks

� Private or public Wi-Fi data networks

� M2M or MTC networks

� Industrial data networks

Building one technology that meets all these sets of

requirements has long been a utopian dream, but just

possibly 4G has a unifying effect where its IP-network roots

and its scale of interest could satisfy all three.

There are many characteristics that define the segmentation

of these applications, but we have chosen one that illustrates

a separation by the tolerance of the applications to the

real-time nature of the communications, and the number of

simultaneous users per cell.

As M2M, cellular and Wi-Fi networks are well documented,

we shall focus on the fourth segment in this document as it

appears to be an underserved segment today, and one that

4G technologies could address in unlicensed bands.

For the ‘Industrial’ segment, we have seen a number of

common requirements emerge:

1. These applications need to support large numbers of

simultaneous users1, with high user density

2. These systems are often deployed indoors (although not

universally)

3. Often the users are highly mobile while communicating

(more so than is typical of smartphone or tablet users when

indoors, who tend to be nomadic and often stationary for

long periods of time)

4. These users have moderate data-rate requirements for

the majority of their traffic; although this in combination

with the high simultaneous user numbers means very

high aggregate traffic levels, and hence the match to a

broadband system

5. High-speed data transfer is often useful on an occasional

basis for supplementary services but rarely needed to all

users at once

6. These users require low latency (often with a near-real-time

characteristic)

1 Here we use the term users to mean user equipment (UE) in 4G parlance, but not necessarily people – these may be elements of a wider industrial system

Figure 1: Application segmentation

SmallSimultaneous

User Countper cell

LargeSimultaneousUser Count per cell

Low Toleranceto non-Real-Time

traffic

High Toleranceto non-Real-Time

traffic

BroadbandCellularPublic or

private WiFi

M2M

“Industrial”


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7. A high quality of service (in the form of low dropped or

blocked packet rates) is important

8. Data has only a shortterm value (much like many stream

services, data is only relevant when immediately delivered,

later delivery has limited or no value), so high levels of

datagram-style communications are common

9. These systems typically are local systems (ie while

users are mobile, they only roam in constrained buildings

or campuses) but can require a scale of installation where

options to support multiple cells with seamless handover is

a key benefit

While not a complete list of requirements, it is clear that

the combination of these requirements makes this segment

different from that of other users.

4G technology delivers great capabilities

Even the most ardent technophobe cannot have failed

to notice the emergence of 4G. Promoted widely as the

future of mobile networks and delivering an excellent user

experience on a smartphone or tablet, 4G technology is the

fastest growing wireless technology and the quickest rollout

of a major new technology in telecoms history. It is the

great new capabilities that have driven this success. It goes

without saying that 4G delivers high-speed data connectivity

to large numbers of users – that’s it’s primary purpose.

But so did Wi-Fi, so what is it about 4G that makes it so

important?

A user’s experience of internet or ‘cloud-based’ services on

a computer, smartphone or tablet is not only influenced by

the data connection speed but also by the latency - the time

taken to send a packet and, importantly, get a response

packet back from the other end. The headline transmission

speed of 100Mbit/s is very exciting but, if you have to

wait even a tenth of a second to start sending your packet,

you could have sent one megabyte of information while

waiting. If your packet was only a kilobyte in length (to

ask for a status update or to request the next element of a

web page be sent), then waiting time would dominate the

transmission time by an order of magnitude or more. To make

transactional2 services seem fast, you not only need fast

transmission speeds. It is essential that you can achieve low

latency as well – which means very low waiting times. A key

characteristic of 4G is that it has been designed to deliver

very low latency as well as high data speeds.

4G technologies differ from 3G and 2G before them in

that they are based upon a modulation technique called

orthogonal frequency-division multiple access (OFDMA) –

and SCFDMA in LTE’s uplink case. OFDMA is a spectrally

efficient technique to transmit large amounts of data in a

broadband channel (channels that are typically 1MHz wide

or more) and be able to recover the signal at the other end

of the link efficiently. The OFDM base of OFDMA is used in

a wide variety of systems from digital TV and digital radio,

to Wi-Fi and even the digital transmission on phone lines –

digital subscriber line (DSL) – that delivers fixed broadband

connectivity to many homes.

OFDM is an interesting technique as it breaks the channel of

interest into many ‘orthogonal3’ sub-channels packed closely

together, each of which is easier to send data in because

they each run at a relatively slow data speed. By combining

hundreds or even thousands of these sub-channels together

into one OFDM channel, high data rates can be achieved

efficiently. The specific design of the OFDM systems in 4G

means they can be used in highly mobile systems. We have

worked on 4G technology specifically designed to work from

a base station to a high-speed train (handling mobility of

users travelling at >120mph).

In Wi-Fi, TV, radio and DSL, the whole of the broadband

OFDM channel is used by a single transmitter (at any

one time, in the case of Wi-Fi). The subtle change in 4G

compared with Wi-Fi, for example, is to allow multiple users

to transmit simultaneously on different sub-channels and

at different times, so that a two-dimensional map of use

(in frequency and time) can be used to share the resource

between many users. The peak data rates can be delivered

by allocating all the sub-channels and all the time to a single

user (which is the way Wi-Fi works), but it can also deliver

connectivity to many users in a burst ‘simultaneously’. To

2 Transactional services are those services where there are requests and responses, which happens when web browsing for example.

3 Orthogonal in this case means these many channels are designed to not interfere with one another, even though they are very tightly packed together, so that data sent in parallel can

be decoded at the receiver


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avoid clashing, a scheduler in the base station controls which

users can access the system at what time and frequency.

Some random access time is allocated to allow a UE to

request resources and, once communicating with the base

station, they can negotiate more or less traffic as they go.

4G has a very flat architecture as well. Architecturally it looks

much more like a clever IP router network with knowledge of

mobility mechanisms and base stations providing connectivity

to UE. It is much less complex than the 2G and 3G networks,

where many different hardware ‘devices’ were to build a

system. This makes it easier to scale up or down in size.

This means 4G has several advantages, which have driven its

success:

� Users get a managed quality of service because the base

station is in control

� Latency can be very low and deterministic

� The spectrum can be very efficiently ‘filled’, with good

schedulers enabling better occupancy, so allowing more of

the theoretical bandwidth to be allocated to users, and not

kept in reserve to allow users to share

� The number of users can be very large while maintaining

great service

� The users can communicate while travelling at high speed

� The same infrastructure technology can be scaled up to

national networks, and scaled down to enterprise or even

domestic networks

Figure 2: Use of time and frequency in a typical 4G system


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4G technology in unlicensed bands increases access but introduces challenges

Moving 4G technology to unlicensed bands enables both operators to make use

of additional spectrum access, and provides organisations that wish to build

networks but don’t have their own spectrum licences with the ability to do so. But

it’s not that straightforward. There are a number of technical challenges (created

by the spectrum access rules) that need to be addressed to make this a success.

Shared spectrum 4G technology is designed to operate in its own spectrum. The technology enables many cells to be co-

ordinated – but it is not designed for different technologies to share the same spectrum, with equal access

to it. The unlicensed bands are common assets. They are regulated on the basis that no one user can ‘hog’

access to the spectrum.

Any 4G implementation in unlicensed spectrum would need to be designed to operate to the very different

spectrum access rules. The systems would not get unfettered access, so would need mitigation to enable CIO’s

planning to use the technology to manage their operation in the presence of interference, either by selecting

channels with minimal interference or by ensuring that they can plan their channel usage where possible.

Limited transmitter power and transmit

durations

The unlicensed spectrum places restrictions upon transmission power (often EIRP limits). To ensure fair

access to the spectrum, systems are required to ‘listen before transmitting’ (to allow other systems access to

the spectrum), and to limit transmission durations, to limit the time other systems have to wait before they can

attempt to access the spectrum. 4G systems have been designed without any concept of spectrum sharing

and, as such, the frame structures need to be adapted to enable this behaviour.

More complex system acquisition

4G UE looks for a base station (eNodeB), knowing the bands they will be in, and knowing that the base

stations will be present, and that they have only to look for 4G base stations. With shared spectrum, the

UE may look and have to deal with finding many different types of system, including Wi-Fi as well as other

proprietary systems in the band, and not just their expected 4G equipment.

TDD and FDD solutions

4G systems have been designed to operate in both FDD and TDD spectrum. Much of the unlicensed spectrum

would be more suited to TDD operation, but some applications could benefit from the FDD operation. Finding

solutions to allow FDD systems to operate in unlicensed spectrum is a challenge. Finding mechanisms to

enable effective TDD operation under the spectrum access rules also creates challenges.

High frequency more likely for unlicensed

bands

Because of the busyness of the 2.4GHz band, it is likely that any 4G implementation in unlicensed bands will

be implemented at 5GHz. This has a direct impact on the radio design and the baseband.

When users are mobile, the impact on the channel is related to the speed at which the users are moving and

the wavelength. In fact, the speed of movement should be considered in wavelengths per second, rather

than metres per second. A UE moving at jogging speed at 5GHz has the same rate of channel change as a

100kmph user at 900MHz. This has a direct impact on the equalisation approach required.

OFDMA, the basic multiplexing and modulation scheme used in 4G, is frequency sensitive. Where users are

simultaneously transmitting, they need to be co-ordinated in frequency to a high degree of accuracy to enable

them to be decoded effectively in the base station - to stop one user’s transmission from interfering with their

neighbour’s (in frequency). Doppler makes this situation worse, as does the use of higher frequencies.


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Flexible 4G technology platforms simplify move to unlicensed bands

4G technology is evolving very rapidly. The IEEE and 3GPP

standards bodies that define most of the 4G technology

have published a long roadmap of innovations and, with 4G

already in operation, many versions of the technology are at

different stages of conception, definition, implementation

and release. Most operators, the buyers of 4G technology

today, wish to adopt new capabilities as they emerge. The

technology supply chain faces continual competition to offer

the widest range of capabilities at any one time. Pressured

by the global increase in demand for data traffic, 4G has had

to support a proliferation of bands of operation – with more

than 40 licensed bands defined globally, with only a few

dominating in each geographical market.

To meet this breadth and rapid change of demand, 4G

technology suppliers have chosen to build flexibility into

their offerings – often more flexibility than is common in

other technologies such as Wi-Fi. This flexibility reduces

the technical barriers to altering 4G technology to operate

in the unlicensed bands. It also means the technology can

be altered by those with access to the key technology and

development expertise to be optimised for different specific

applications.

It is this combination of ability for the technology to be

operated in accessible bands, optimised for specific target

applications and to deliver the key advantages of 4G that

makes it highly likely to emerge as a new wireless network

platform. Reference designs exist for 4G technology in the

form of programmable baseband processing, protocol stacks

and flexible radios. While not trivial, for the right applications

it is eminently possible to develop new variants of 4G that

can deliver significant performance benefits to new classes of

application that weren’t possible before.

Cambridge Consultants has the expertise to supply 4G in unlicensed bands

Cambridge Consultants has been working on 4G technology

for many years. In that time we have:

� Invested in the expertise of our team in the area of 4G

� Built strong relationships with key technology suppliers

(silicon and stack suppliers)

� Built development frameworks and models for 4G

technologies

� Invested in 4G-specific test capabilities that help us

deliver high quality rapidly

� Developed the world’s first mobile WiMAX reference

design for Picochip

� Assisted Airspan to enhance its LTE base station

products, adding LTE-A features

� Developed LTE technology from the ground up

� Filed our own patent in the area of enhanced uplink

receivers for LTE (DUEL™)

� Developed systems derived from 4G technologies for

clients

Our processes, facilities and expertise mean that we help our

clients to reduce the time to market and risk of adopting 4G

technology for their specific applications.


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Conclusion

In late 2013 Qualcomm (the leading supplier of 4G wireless

modem technologies) announced that it was considering

implementing 4G in unlicensed bands. They proposed

targeting the technology as an extension of the cellular

segment (as this, arguably, is where the highest volume

market exists and hence their greatest commercial interest).

In doing this, they have demonstrated their belief in the

viability of this technical evolution.

Cambridge Consultants works with clients across a wide

array of market segments, and has worked on wireless

projects from the oil and gas, energy, industrial, healthcare,

consumer, and defence and security markets, where

broadband networks that are not traditional M2M or cellular

systems have been needed. We have seen examples where

Wi-Fi does not provide an adequate solution, but where 4G

technology certainly would.

We believe that providing 4G technology and derived

products in the unlicensed bands promises to enable a new

wave of applications that can deliver significant benefits. The

technology has evolved significantly to support this and now

the time is right to take advantage of this opportunity.

Whether you are trying to keep pace or overtake your

competitors, creating something completely new – or if you

simply want to better understand how 4G technologies could

benefit your business – then contact us for a no-obligation

discussion with our experts.


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For further information or to discuss your comments,

please contact:

Tim Fowler, Head of Wireless

[email protected]

Published March 2014

About Cambridge Consultants

Cambridge Consultants is a world-class supplier of innovative

product development engineering and technology consulting.

We work with companies globally to help them manage the

business impact of the changing technology landscape.

With a team of more than 400 staff in Cambridge (UK),

Boston (USA) and Singapore, we have all the in-house skills

needed to help you – from creating innovative concepts right

the way through to taking your product into manufacturing.

Most of our projects deliver prototype hardware or software

and trials production batches. Equally, our technology

consultants can help you to maximise your product portfolio

and technology roadmap.

We’re not content just to create me-too products that make

incremental change; we specialise in helping companies

achieve the seemingly impossible. We work with some of the

world’s largest blue-chip companies as well as with some of

the smallest, innovative start-ups who want to change the

status quo fast.

We have one of the largest independent radio design teams

in the world and our wireless communications division has

created a number of world firsts, ranging from the miniature

to the global – from radios that are implanted into the human

body through to ones that allow air traffic control to talk to

aircraft across the globe. We’re experts in a bewildering array

of wireless technologies but agnostic to all of them; what we

care about most is creating the right solutions for a client’s

problem in order to give them a truly world-class product.

Cambridge Consultants is part of the Altran Group, a global

leader in innovation. www.Altran.com

Bluetooth®, Bluetooth® Smart and Bluetooth® Smart Ready are registered trademarks of the Bluetooth SIG Inc.

iPhone is a registered trademark of Apple Inc.

Cambridge Consultants is part of the Altran group, a global leader in innovation. www.Altran.com

www.CambridgeConsultants.com

Cambridge UK • Cambridge USA • Singapore

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