Project
IEEE 802.21
<http://www.ieee802.org/21/>
Title
Single Radio Handovers
Date
Submitted
September, 2009
Source(s)
Vivek Gupta (Intel Corporation), Shubhranshu Singh (Samsung)
Re:
IEEE 802.21 Session #34 in September 2009
Abstract
Single Radio Handovers
Purpose
Single Radio Handover Discussion
Release
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Patent
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Notice
Single Radio Handovers
Summary:
Mobile users need to maintain service continuity during handovers for real-time applications. Dual
radio handovers require multiple radios to be transmitting and receiving at the same time which
leads to higher cost, complexity, platform noise and co-existence issues for radios operating in
close proximity IMT-2000 bands. Single Radio handovers require only one radio to be operating
at a time and can overcome these issues.
As mobile users transition across coverage areas of different wireless technologies there is a
need to preserve user experience. This requires ability to maintain service continuity during
handovers for real-time and conversational class applications. Depending on the radio operation
handovers can be classified as Single Radio Handovers or Dual Radio Handovers.
In dual radio handovers a dual radio device can receive and transmit simultaneously on both the
radio modules. Since both the radios can be active simultaneously in these types of devices, the
target radio directly connects to the target network to prepare resources while maintaining the
connection with source network during handover. Dual radio handovers lead to several problems.
Because of the large difference between the transmission and receive signal levels of the two
radios (100 dB or more), the transmitter may shoot down the receiver of the other radio especially
when operating in close proximity frequency bands. Dual-radio operation leads to higher power
consumption since both radios need to remain active. This may cause the device to draw more
power from the battery and thus lead to shorter uptime (talk time). Enabling simultaneous
transmitter and receiver operation even in non-adjacent frequency bands is very complex and
requires expensive RF isolation, filtering or even active cancellation.
In single radio handovers the device can receive and transmit on only one radio at a time. This is
usually the mode of operation when radio frequencies are close to each other (e.g. IMT 2000
bands). Since only one radio can be active at a time in these types of devices, they use the
source radio and the back-end connection between the source and target network to prepare the
target network for handover. Using the back-end connection between source and target networks
the device sends a set of messages to target network and transfers user context (user identity,
security, resource information) to target network. The target network allocates necessary
resources and prepares for incoming connection. Thereafter the device shuts off the source radio
and performs only network entry on the target radio to hook up with the already established user
context to complete the handover.
Single Radio handover solution can alleviate issues associated with dual radio handovers.
Several products which have a single RF shared across several basebands can support
transmission/reception on only a single radio at a time. Single Radio handovers are absolutely
essential for maintaining session continuity on these products when transitioning across different
radio technologies. Optimized single radio handovers are supported across different 3GPP
technologies today (such as between GSM and UMTS). Work is underway in different standard
bodies to enable single radio handovers between WiMAX and 3GPP and WiMAX and WiFi.