20-03-2012, 03:18 PM
Unlicensed Mobile Access (UMA) Handover and Packet Data Performance Analysis
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Introduction
There is an ongoing emergence of various radio
access technologies that provide interesting technical
solutions to offer new services through other than
cellular access. New radio access technologies might
provide higher throughput, and they also ease the load
of cellular access networks. The possibility of using
e.g. home WiFi routers or public WiFi hotspots with
the same handset, provides a challenger alternative to
cellular access, and thus an access to general Internet
services without the operator restricting or managing
the ownership of the customer. This is the core of the
disruptive potential of actors such as Skype, who are
planning a mobile entry.
UMA Overview
The core idea of UMA is to provide an access to the
operator’s network through not only cellular, but also
through unlicensed radio access technologies such as
WiFi. Originally, UMA was developed to provide an
access to GSM/EDGE networks through unlicensed
radio access points. The technology, however, is
nowadays developed in the 3GPP consortium under the
name GAN (generic access network), which also
considers the link to WCDMA[3].
UMA Access and Handovers
The UMA cell is analogous to a GSM base station
controller (BSC). For that reason, it is perceived as
such by the cellular network and roaming between
UMA and GSM is considered an inter-BSC handover.
From the BSC perspective the UNC is just another
BSC. In theory, if the UNC is in the BSC neighbors
list, it is possible to perform a handover. However, the
individual WiFi cells are independent from the UMA
system. Regardless of the similarities between the
UNC and the BSC, the cell size does not directly
correlate.
GSM-UMA Mobility
Handovers between the GSM and UMA systems are
in most of the cases originated by the MS. Depending
on the operating mode, the MS will decide how often it
will attempt to establish a connection and/or start a
handover. The handover triggers are likely to be based
on received signal strength measurements. However,
the standard also provides the means to originate the
handover based on a request from the UNC.