Page 307 - From GMS to LTE

Long Term Evolution (LTE) and LTE-Advanced Pro 293

4.14 Voice in Combined LTE and CDMA2000
Networks (SV‐LTE)

Although GSM/UMTS network operators have deployed CS‐fallback for voice services
as described in the previous sections, some CDMA network operators decided to take
a different route. Instead of falling back to a legacy network, most CDMA/LTE‐capable
devices are designed to support two cellular radios transmitting and receiving simulta-
neously. They can thus be active in LTE for data transfers and active in the CDMA
network for voice calls simultaneously. This however means that the mobile device
needs to keep track of two cellular networks even while no voice call is ongoing, which
results in higher battery consumption to some extent. For further details, see Klug [27]
and [28]. Also, the dual‐radio approach requires close coordination between the LTE
and the CDMA parts of the device while a voice call is ongoing to keep the power
output of the device within acceptable limits.
It should be noted at this point that the main reason why GSM/UMTS network opera-
tors have not chosen this approach is likely because of the fact that UMTS networks also
offer, besides circuit‐switched voice services, excellent high‐speed data services so that
there is no need for a dual‐radio approach.

4.15 Network Sharing – MOCN and MORAN

Due to the significant investment required to roll out a radio network, regulatory bodies
in most countries allow network operators some form of network sharing. The most
common type of sharing is to share locations and antenna towers while all radio equipment,
from the antennas to the base station itself and the backhaul link, is installed separately by
each network operator. On the other end of the scale are deployments where several
network operators deploy a single shared radio network while keeping their core networks
separate. Such deployments exist in practice but are less common than site sharing. This
is because sharing everything from antenna to backhaul can have significant implications
on competition between network operators and is thus not always permitted by national
telecommunication regulation. Also, sharing a single radio network makes it difficult for
network operators to distinguish themselves from others in terms of performance,
network optimization, providing better coverage than the competition, or trading lower
coverage and other factors for lower subscriber prices. Several methods exist and are used
in practice to share some or all active elements of a radio network.

4.15.1 National Roaming
One way to share a single radio network is national roaming. National roaming is typi-
cally used when a new network operator enters the market and signs an agreement with
an existing network operator to share their infrastructure for a limited time until they
have rolled out their own radio network. Another application for national roaming is to
support the consolidation of two radio networks after a merger of two network opera-
tors in a country.
In practice, national roaming requires that two mobile network operators agree that
the customers of one operator are allowed to use a combination of the 2G, 3G or LTE