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GL1800 Refarming, a cost-effective way to win in MBB
GL1800 Refarming,
A Cost-effective Way to Win in MBB
Mobile broadband is ushering in a brand-new era of communications, in which
wireless network traffic will grow explosively by up to 500 times in ten years.
Traditional GSM voice subscribers are no longer satisfied with low-speed data access.
This has led to some tough questions: What is the right way to leverage the spectral
resources of the existing networks? How should the increasing demand for mobile
data services be addressed? What should be done to protect the existing network
equipment investment and ensure smooth evolution to LTE? Mobile operators
worldwide are desperately looking for the answers, and the GL1800 Refarming
solution has been proved to be one of the best.
1800MHz: Premier Frequency Band for LTE Deployment
The 1800MHz frequency band is now used mainly on GSM networks the world over,
according to 3GPP in its definition of frequency bands for radio communications. It is
also one of the bands defined for LTE FDD, others including DD800MHz and
2600MHz. In addition, Band 3 of 1800MHz has the richest spectral resources, as its
paired FDD spectrum bandwidth reaches 75MHz. More than 50 operators in over 20
European countries each have more than 10MHz bandwidth in this band, according to
statistics from existing networks. Mainstream Asia-Pacific operators in countries such
as China, Australia, and Singapore also each have more than 10MHz bandwidth. This
basically guarantees access to spectral resources for 1800MHz frequency refarming.
More importantly, voice traffic carried over GSM900 and GSM1800 is decreasing due
to the increasing penetration of UMTS services, subscriber migration, and UMTS
traffic being mostly carried over the 2,100MHz band. Frequencies in the 1800MHz
band can therefore be gradually refarmed to be used for more advanced LTE
networks.
The 1800MHz band features lower propagation and penetration losses than the
mainstream 2600MHz band for LTE. It achieves wider coverage as it can multiply the
coverage radius of a single LTE station, slashing the number of sites and reducing
carbon emissions while ensuring high-quality coverage. That will greatly reduce TCO
for operators and bring end users better mobile broadband QoE. The GL1800
Refarming solution results not only in significant savings on expenditure for new
spectral resources but also faster LTE network deployment. In actual deployment,
operators may also opt to reuse sites or even equipment based on the status of their
existing network equipment, realizing smooth evolution to LTE from GSM. When it
comes to purchasing new bands and planning new networks, a refarmed 1800MHz
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GL1800 Refarming, a cost-effective way to win in MBB
band can play a greater role among the existing spectral resources. It is a premier
frequency band.
Three Technologies Critical to Refarming
To come up with an effective 1800MHz frequency refarming solution, three critical
technologies need to be taken into account. The first is about how to reallocate
frequencies and control interferences between neighboring GSM and LTE
frequencies. The second is about the method of migrating GSM voice service
subscribers to release part of the 1800MHz spectrum. And the third is how different
networks should be coordinated.
For frequency reallocation, there are two mainstream methods commonly used in the
industry, namely full refarming and partial refarming. Full refarming is suitable for
mobile operators with well developed GSM and UMTS networks and rich spectral
resources. The number of GSM/GPRS subscribers is decreasing as UMTS services
are growing and these subscribers are being migrated to UMTS networks, leading to
fewer loads on the GSM network at 1800MHz. Therefore, the 1800MHz spectrum can
be fully refarmed to be used for LTE networks, while all the voice services are borne
by GSM900.
Partial refarming is suitable for the operators with limited spectral resources who have
no UMTS networks and have difficulty in subscriber migration or who have a large
number of GSM subscribers that will remain stable in the short term. These operators
need to consider how to retain the existing subscribers and provide competitive
high-speed mobile data access. They may therefore phase in the band refarming to
LTE by 5MHz or 10MHz spectrum bandwidth. Partial refarming is done by two
methods – the sandwich method and the edge allocation method. The sandwich
method releases the middle portion of the 1800MHz band of an operator to LTE by
5MHz or 10MHz spectrum bandwidth. Portions on both ends are still used by GSM.
As for the edge allocation method, it allocates either end of the band possessed by
the operator to LTE and keeps the other end for GSM. The sandwich method is
recommended, given the GSM frequency reuse plan, interferences between
frequencies and, in particular, interferences with other operators. Control over
interferences between GSM and LTE can be done within the frequency band owned
by an operator without needing to coordinate neighboring bands of other operators.
Also based on the preceding two frequency refarming methods, space division may
be used to effectively reduce mutual frequency interferences between GSM and LTE.
Operators may push refarming from cities to suburbs, or vice versa, from the
perspectives of network loads and subscriber needs. They may first refarm some
frequencies for LTE to satisfy the demand for mobile data in urban areas, for example.
As for non-urban areas, they do not need to refarm frequencies and may instead keep
using their own full-bandwidth GSM bands since there is no strong demand for
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GL1800 Refarming, a cost-effective way to win in MBB
high-speed mobile data services in these areas.
Mutual interferences of the same band between LTE and GSM should be avoided, as
they often take place when this same band is used for LTE in urban areas and still for
GSM in non-unban areas. Geographically, a transitional zone may be set between a
city and its suburbs, where this band is left unused, to spatially prevent interferences
caused by the use of the same band for both technologies.
Migrating their GSM voice service subscribers is a tough choice for operators, who
have to increase the data access capacity of the existing networks – they have to
reduce the bandwidth of GSM and accommodate existing subscribers at the same
time. There are now two critical technologies to deal with this issue: half-rate voice
(HRV) and aggressive frequency reuse (AFR). HRV bears the same number of voice
service subscribers with a half bandwidth. AFR saves on bandwidth by 25 to 50%
depending on configurations ranging from S2/2/2 to S7/7/7. Operators may employ
those technologies flexibly.
Coordination between GSM/UMTS and LTE networks is another critical issue in
frequency refarming. It guarantees load balance between different types of networks
and the inheritance of voice services, while providing network selection priorities
based on services, loads, and subscriber characteristics. Meanwhile, mobility should
be guaranteed between the two networks, including handover and interoperability
between the CS and PS domains. 3GPP has already defined the coordination
between heterogeneous networks and set down specifications, laying a foundation for
coordination between networks using different technologies.
Three Schemes for Refarming Solution Deployment
If the preceding technologies are preconditions for deploying the GL1800 Refarming
solution, then equipment performance and evolution capabilities are tied to the TCO,
and the progress and feasibility of network deployment.
As the first of its kind, Huawei’s SingleRAN solution supports GSM, UMTS, and LTE
as well as the five bands of DD800MHz, 900MHz, 1800MHz, 2100MHz, and
2600MHz, in the same cabinet. Its advantages become more outstanding in GL1800
deployment. This solution supports sharing of stations, transmission, maintenance,
and RF. It helps operators evolve smoothly to LTE1800 from GSM1800, or realize
coexistence of GSM and LTE in the 1800MHz band.
As can be seen from RF modules to antenna feeder deployment schemes, the core
issue with deploying a new LTE1800 network on top of the existing GSM1800 network
is the RF module based antenna feeder solution. There are three deployment
schemes by scenarios:
The first scheme is completely separating RF modules and antenna feeders. As
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GL1800 Refarming, a cost-effective way to win in MBB
GSM1800 RF modules do not support multi-mode capabilities and have limited
transmission power, RF modules and antenna feeders are separated to ensure the
quality of coverage. This scheme is characterized by high investment, the
requirement for a site, and difficulties in deployment.
The second is separating RF modules but sharing antenna feeders. This scheme is
suitable for scenarios where RF module’s multi-mode support capabilities or operating
bandwidths are limited. Though requiring new RF modules, the scheme allows for the
sharing of the antenna feeder system through combiners to save on the space where
antenna feeders are mounted. The negative side of this scheme includes the addition
of combiners and, typically, additional 3dB insertion loss, which affects the
transmission power to some extent.
The third is sharing both RF modules and antenna feeders. This scheme fully reuses
the existing antenna feeder system and RF modules with no need to add any
hardware after they come out of the base band’s CRPI. Nonetheless, this scheme
requires RF modules to have multi-mode capabilities and higher operating
bandwidths, guarantee use in discrete frequencies at 1800MHz, and support future
bandwidth increases. Meanwhile, they should accordingly have higher transmission
power. In Huawei’s SingleRAN solution, the RF modules feature multi-mode
capabilities, dual channels, full bandwidth, and high power, helping operators save on
CAPEX and facilitating network deployment. The solution is the best choice for
GL1800 refarming.
The 1800MHz band is one of the main frequency bands commonly used by mobile
operators, and also an effective supplement to the GSM900 network. In the
foreseeable future, with mobile data services leapfrogging, traditional GSM voice
service subscribers will be gradually migrated to UMTS or LTE networks. Given
current spectral resources, the GL1800 Refarming is one of the best solutions for
keeping network competitiveness, reducing investment and rapidly deploying LTE
networks.
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