Content for TR 45.902 Word version: 16.0.1

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0 Introduction Word‑p. 5

A new type of physical layer is proposed for the GSM/EDGE Radio Access Network (GERAN): the flexible layer one (FLO). The main advantage of FLO is that the configuration of the physical layer (e.g. channel coding and interleaving) is specified at call setup. This means that the support of new services such as IP Multimedia Subsystem (IMS) services can be handled smoothly without having to specify new coding schemes in each release.

Through several enhancements such as reduced granularity and flexible interleaving, the radio bearers offered by FLO would not only fulfil the IMS requirements in terms of flexibility and performance, but also greatly improve the link level performance of real-time IMS services compared to GERAN Release 5.

The objective of this TR is to provide an overview of FLO, its architecture and study the impacts it has on the GERAN radio protocol stack.

1 Scope Word‑p. 6

The present document provides an overview of the flexible layer one, its architecture and studies the impacts it has on the GERAN radio protocol stack.

The present document specifies functions, procedures and information which apply to GERAN Iu mode. However, functionality related to GERAN Iu mode is neither maintained nor enhanced.

2 References

The following documents contain provisions, which, through reference in this text, constitute provisions of the present document.

References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
For a specific reference, subsequent revisions do not apply.
For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.

[1]

TR 21.905: "Vocabulary for 3GPP Specifications".

[2]

TS 22.101: "Service Principles".

[3]

TS 22.228: "Service requirements for the IP Multimedia Core Network Subsystem".

[4]

TS 23.107: "QoS Concept and Architecture".

[5]

TS 23.228: "IP Multimedia Subsystem".

[6]

TS 25.201: "Physical layer - General description".

[7]

TS 25.212: "Multiplexing and channel coding (FDD)".

[8]

TS 25.331: "RRC Protocol Specification".

[9]

TS 35.201: "Specification of the 3GPP Confidentiality and Integrity Algorithms".

[10]

TS 44.018: "Radio Resource Control protocol".

[11]

TS 44.118: Release 11 "Radio Resource Control protocol, Iu mode".

[12]

TS 44.060: "Radio Link Control/Medium Access Control protocol".

[13]

TS 44.160: Release 11 "Radio Link Control/Medium Access Control protocol, Iu mode".

[14]

TS 45.002: "Multiplexing and multiple access on the radio path".

[15]

TS 45.003: "Channel Coding".

[16]

TS 45.005: "Radio transmission and reception".

3 Definitions, symbols and abbreviations

3.1 Definitions

For the purposes of the present document, the following terms and definitions apply.

Active Transport Channel:

a transport channel is active during a TTI if it carries a transport block.

Dynamic attributes:

for one transport channel, the values of the dynamic attributes are different among transport formats. They are configured by Layer 3 and can change on a TTI basis under the control of the MAC sublayer.

Empty Transport Format:

a transport format such that no transport block is carried over the transport channel (i.e. the transport channel is inactive).

Empty Transport Format Combination:

a transport format combination that is made up only of empty transport formats.

Inactive Transport Channel:

a transport channel is inactive during a TTI if it does not carry a transport block (i.e. the transport block size is zero).

Radio Frame:

The result of applying rate matching to a transport block along with its associated CRC that have first been channel encoded.

Radio Packet:

The set of one or more radio frames together with the applicable coded TFCI that form the volume of payload that can be transmitted on a basic physical subchannel for any given TTI.

Semi-static attributes:

for one transport channel, the values of the semi-static attributes are common to all transport formats. They are configured by Layer 3 and can only be changed by Layer 3 signalling.

Transport Block:

block exchanged on a transport channel between the physical layer and the MAC sublayer.

Transport Channel:

SAP between the physical layer and the MAC sublayer.

Transport Format:

configuration of a transport channel, including for instance channel coding, CRC size, etc.

Transport Format Combination:

allowed combination of transport format(s) of the different transport channels that are multiplexed together on a basic physical subchannel.

Transport Format Combination Indicator:

layer one header that indicates the transport format combination that has been selected for each radio packet.

Transport Format Combination Set:

set of allowed transport format combinations on a basic physical subchannel.

Transport Format Indicator:

index identifying a particular transport format within the transport format set.

Transport Format Set:

set of all transport formats defined for a particular transport channel.

Transmission Time Interval:

rate at which transport blocks are exchanged between the physical layer and the MAC sublayer on a transport channel.

3.2 Abbreviations Word‑p. 7

For the purposes of the present document, the following abbreviations apply:

ADCH

Associated Dedicated CHannel

CCTrCH

Coded Composite Transport CHannel

CDCH

Control-plane Dedicated CHannel

CTFC

Calculated Transport Format Combinations

DCH

Dedicated CHannel

FLO

Flexible Layer One

GERAN

GSM/EDGE Radio Access Network

IMS

IP Multimedia Subsystem

MAC

Medium Access Control

QoS

Quality of Service

PDU

Protocol Data Unit

RAN

Radio Access Network

RLC

Radio Link Control

RRC

Radio Resource Control

Real Time

SDU

Service Data Unit

SAP

Service Access Point

Transport Block

TBF

Temporary Block Flow

Transport Format

TFI

Temporary block Flow Identity

TFS

Transport Format Set

TFIN

Transport Format INdicator

TFC

Transport Format Combination

TFCI

Transport Format Combination Indicator

TFCS

Transport Format Combination Set

TrCH

Transport Channel

TTI

Transmission Time Interval

UDCH

User-plane Dedicated CHannel

UTRAN

Universal Terrestrial Radio Access Network

Other abbreviations used in the present document are listed in TR 21.905.

4 Motivation Word‑p. 8

The need for a flexible layer one for the Release 6 of GERAN is driven by the introduction of IMS services. For an efficient support of IMS services, requirements are set on the radio bearer service of the RAN (see TS 22.101, TS 22.228, TS 23.228 and TS 23.107):

the radio bearers should be flexible enough to efficiently deploy any IP multimedia applications;
the radio bearers should allow the transport of several flows in parallel (e.g. text and video);
the radio bearers should satisfy the user in a spectral efficient manner;
the radio bearer should support the UMTS QoS concept and architecture.

So as to fulfil these requirements in an efficient manner, a flexible layer one is needed. Thanks to the flexible layer one optimised support of real time IMS services is made possible in GERAN.

5 Requirements

The flexible layer one should:

fulfil most of the IMS requirements in terms of radio bearer service attributes;
support the multiplexing of parallel flows on to a basic physical subchannel;
provide an optimisation of spectral efficiency through the support of different interleaving depths, unequal error protection/detection, reduced channel coding rate granularity and support of 8PSK and GMSK modulations;
provide an efficient support of real time IMS services;
be applicable to both modes of operation: A/Gb mode and Iu mode;
minimize the impacts on the radio protocols;
minimize the overhead introduced by the radio protocol stack;
not introduce an unfeasible number of test configurations;
be future proof;
within reason, be compatible with legacy transceiver implementations.