E-UTRAN Study Items

 
E-UTRAN Study Items
The E-UTRAN WGs have dedicated normal meeting times to the Evolution activity, as well as
separate Ad Hoc meetings. RAN WG1 held one of these Ad Hoc meetings on June 20–21, 2005
(3GPP TSG RAN WG1 Ad Hoc on UTRA/UTRAN LT evolution, held in Sophia Antipolis, France),
where it started looking at, and evaluating new air-interface schemes. A set of six basic layer 1 or
physical layer proposals were then agreed for further study, which included the following:
• FDD UL based on SC-FDMA, FDD DL based on OFDMA
• FDD UL based on OFDMA, FDD DL based on OFDMA
• FDD UL/DL based on MC-WCDMA
• TDD UL/DL based on MC-TD-SCDMA
• TDD UL/DL based on OFDMA
• TDD UL based on SC-FDMA, TDD DL based on OFDMA.
The evaluations of these technologies against the requirements for the physical layer are collected
in TR25.814 [818].
The TSG RAN WG2 has also organized the first meeting to propose and discuss the air-interface
protocols of the Evolved UTRAN [819]. Although the details of these are very dependent on the
solutions chosen for the physical layer, some assumptions, and agreements have been taken, which
are summarized as follows:
• Simplification of the protocol architecture and the actual protocols is necessary. • There should be no dedicated channels, and so they form a simplified Medium Access Control
(MAC) layer (without MAC-d entity).
• A debate over Radio Resource Control (RRC) was held. It is generally supported that it should
be simplified and have less states. The location of its functions is open.
• Currently, there are very similar functions in the Radio Network and the Core. This should be
simplified.
• Other open issues include: (1) Macro diversity.1 (2) Security and ciphering; (3) Handover support;
and (4) Measurements.
The TSG RAN WG3 (as shown in Figure 10.2, the fifth layer from the top in the second column
from the left) is working closely with SA WG2 (as shown in Figure 10.2, the fourth layer from
the top in the third column from the left) in the definition of the new E-UTRAN architecture. SA
WG2 has started its own study for the System Architecture Evolution whose objective is to develop
a framework for an evolution or migration of the 3GPP system to a higher-data-rate, lower-latency,
and packet-optimized system that supports multiple RATs. The focus of this work will be on the PS
domain with the assumption that voice services are supported in this domain.
This study builds on the RAN Long-Term Evolution and on the All-IP Network work carried out
in SA WG1, and a long list of open points that needed clarification were identified, which include
the items stated below.
First, how will we achieve mobility within the Evolved Access System? This issue is closely
associated with the ways to overcome serious Doppler spread problems in a fast fading channel environment.
As the allowed mobility supported in E-UTRAN will be higher than the 3GPP 3G system,
this problem is very critical to the overall success of the E-UTRAN project.
Then, is the Evolved Access System envisioned to work on new and/or existing frequency bands?
As 3GPP UTRAN is working in 2 GHz carrier frequency bands with its bandwidth being 5 MHz, the
E-UTRAN may not be suitable for its operation in the same 2 GHz band as WCDMA is. The main
reason is that E-UTRAN can work on a much wider bandwidth (up to 20 MHz), and the existing
bandwidth allocation at 2 GHz is already very crowded. The real situation could be different from
country to country. As an example, the US radio spectrum allocation situation can be seen from
Figure 9.1 [792].
The more frequently discussed issues in SA WG1 include the following:
• Is connecting the Evolved RAN to the legacy PS core necessary?
• How do we add support for non-3GPP Access Systems (ASs)?
• WLAN 3GPP IP AS might need some new functionalities for Intersystem Mobility with the
Evolved AS.
• Clarify which interfaces are the roaming interfaces, and how roaming works in general.
• The issues on inter-AS mobility should be discussed.
• Possible difference between PCC functionalities, mainly stemming from the difference in how
Inter-AS mobility is provided.
• How do UEs discover ASs and corresponding radio cells? The options include autonomous
per AS versus the UEs scans/monitors of any supported AS to discover systems and cells.
Or, do ASs advertise other ASs to support UEs in discovering alternative ASs? How is such
advertising performed (e.g. system broadcast, requested by UE, etc.)? How do these procedures
impact battery lifetime? • In the case of ASs advertising other ASs: will any AS provide seamless coverage (avoiding the
loss of network/network search), or is a hierarchy of ASs needed to provide seamless coverage
for continuous advertisement?
The two model architectures [820], which summarize the broad range of proposals that have been
presented in several WG meetings, are shown in Figures 10.4 and 10.5. Note that the key difference
in the two model E-UTRAN architectures lies in the way that intersystem mobility is achieved and
managed, and thus the interactions among the E-UTRAN network and other 3GPP networks, such as
UTRAN (based on WCDMA technology) and GERAN (based on GSM standard).