4g technology in unlicensed bands: an opportunity to deliver new … · 4g technology in unlicensed...
TRANSCRIPT
4G technology in unlicensed bands: an opportunity to deliver new services
TELECOMS AND MOBILE
white paper4G technology in unlicensed bands
1
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
2
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”
white paper4G technology in unlicensed bands
3
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
white paper 4G technology in unlicensed bands
4
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
white paper4G technology in unlicensed bands
5
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.
white paper 4G technology in unlicensed bands
6
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.
white paper4G technology in unlicensed bands
7
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.
white paper 4G technology in unlicensed bands
8
For further information or to discuss your comments,
please contact:
Tim Fowler, Head of Wireless
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