The effect of Long Term Evolution (LTE) on the need for
ubiquitous wireless coverage systems in buildings is a hot topic
within the in-building wireless industry. And with up to 19
networks expected to be launched this year, it's an issue that is
not going to disappear.
Discussion has now moved on from the challenges presented by
3G/Universal Mobile Telecommunications System (UMTS) to the even
more demanding requirements of LTE. The Third Generation
Partnership Project (3GPP) developed the specification for LTE as
an evolution of UMTS. It is set to provide a number of advantages
including increased capacity and reduced latency, improved
spectrum efficiency and cell edge performance as well as offering
both GSM/HSPA and CDMA/EVDO service providers a migration path to
a 4G platform that addresses interoperability issues.
However, the benefits of the LTE evolution will only be felt if
service providers are able to effectively reach their customers.
In ABI Research's 2009 report, it forecast that by 2013 more than
67% of all handsets shipped will be 3G+ capable. The volume of
mobile traffic originating from inside buildings is already in
excess of 60% for voice calls and is set to grow above 90% for
data sessions. Taking the technical issues and user patterns
together, it can be seen that the majority of the mobile data
revenue opportunity is to be found in buildings. It is therefore
essential to have ubiquitous in-building wireless coverage and is
an issue that has to be addressed for both the service provider
and subscriber alike.
Poor indoor wireless coverage is now recognised globally as one
of the biggest obstacles facing mobile subscribers today. This is
particularly acute with data services and with LTE licences being
issued in frequencies as high as 2.6GHz with a promise of 100Mbps
download and 50Mbps upload speeds per cell. There are many issues
to be considered for effective in-building wireless coverage with
some of the key questions to be asked by those looking to deploy
a solution for LTE.
Different solutions
Traditionally, cellular networks have been designed using an
'outside in' approach, where the service provider uses the macro
and micro networks to penetrate buildings. With most sessions
originating in-building coupled with modern, eco-friendly and
energy efficient building techniques and materials, penetration
of buildings from the macro network is no longer viable.
Therefore service providers, building owners and enterprises must
deploy systems to provide effective wireless coverage from within
the building. This is the only way to maintain good signal
strength and meet the level of service and data rates demanded by
today's mobile broadband subscribers, while ensuring efficient
use of network infrastructure for the service provider.
LTE comes with the option of antenna diversity provided by
Multiple-In-Multiple-Out (MIMO) technology. MIMO was developed
for outdoor deployments and there is a lot of debate as to the
need for MIMO deployments in a building. There is also
uncertainty as to whether it is cost effective. However, there
may be specific projects where MIMO could be a benefit, so it is
important that any coverage solution deployed should have this
flexibility available. Careful planning of antenna locations and
link budgets of the coverage solution will ensure the cell edge
performance needed by the handset user delivers the appropriate
bandwidth.
Frequency and duplexing
The LTE standard allows for both Frequency Division Duplex (FDD)
and Time Division Duplex (TDD) variants with licences being
considered across a wide range of frequencies including 700MHz,
800MHz, 900MHz, 1800MHz, 2100MHz and 2600MHz. The ABI 2009 report
on in-building wireless has found that LTE deployments in China
will almost certainly be TDD. This provides a challenge when
selecting an appropriate in-building wireless coverage technology
that has the flexibility to support all of these options and
variants. In multi-operator deployments, it is possible that
multiple frequencies and both duplexing schemes are required on
the same system. In addition, such a multi-operator deployment
may also need to support existing 2G and 3G services at the same
time.
There are three main options available to improve in-building
wireless coverage including distributed repeaters, distributed
radio solutions and Distributed Antenna Systems (DAS). DAS is
typically favoured in moderate to large infrastructures for being
able to offer improved and unified indoor wireless coverage for
multiple services at lower capital expenditure and running costs.
Distributed antenna system
A DAS comprises a network of antennas, which are placed
throughout a building to provide dedicated in-building coverage.
Traditionally, there are two types of DAS available, passive and
active. Hybrid solutions are also in use where active units are
distributed in a building with each feeding a small passive
antenna network.
Passive DAS consists of a network of coaxial cables, couplers and
power splitters to distribute wireless signals throughout
buildings. ABI Research identifies in its 2009 report that
passive DAS systems are known for suffering higher losses at
higher frequencies
and are therefore not easily suitable for LTE. It also recognises
that buildings above 20,000m2 will need an active DAS deployment.
Active DAS takes service feeds from a base station or repeater
and distributes amplified wireless signals inside buildings over
fibre optic and RF cable, which connect to multiple remote
antenna units placed in various areas of the building. In the
past there has been a question with active DAS solutions relating
to their ability to support TDD and multiple frequencies
simultaneously on a single hardware infrastructure. With the need
for additional hardware overlays in order to add in services at a
later date, there are hidden cost implications for upgrading many
active DAS solutions.
More recently, another cost effective DAS option has been
introduced which has taken a truly wideband, active approach.
This alternative DAS simultaneously supports any number or
combination of wireless services, protocols, duplex schemes or
frequencies on one system without the need for service specific
overlays. The system has the ability to support any service type,
which also provides peace of mind by future-proofing new
investments in in-building wireless infrastructure, allowing new
services to be added without extra components or costly upgrades.
Zinwave is the first DAS vendor to offer this unique, truly
wideband approach to in-building wireless coverage. With a
platform that supports any service type across a frequency range
from 136MHz to 2.7GHz.
There is a clear and immediate need to introduce improved
in-building wireless coverage to support the rapidly evolving
mobile broadband/4G/LTE requirement. Service providers, building
owners and facility managers need to act now and educate
themselves on the wireless technologies available if they are to
fully benefit from the potential LTE can offer. This Active
wideband Distributed Antenna System approach is unique in its
ability to deliver on a financial level, while also bringing
widespread coverage of must-have wireless services to all
subscribers.
About the author
Colin Abrey is VP of sales and marketing at Zinwave