LTE changes the game for indoor coverage

The arrival of Long Term Evolution sets a new challenge for those in the in-building wireless industry. Colin Abrey of Zinwave explains the implications

LTE changes the game for indoor coverage
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

Written by Wireless magazine
Wireless magazine

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