22-12-2012, 06:49 PM
The Physical Layer
The Physical.ppt (Size: 2.7 MB / Downloads: 142)
Objectives
At the end of this module, you will be able to
Describe the WCDMA channel structure including their mutual mapping
Explain transport channel format
List different code types
Name the main differences in uplink and downlink data organisation
Describe the UE cell synchronisation
Outline the paging organisation and its impact on the UE
Characterise the random access, its power power control and code planning
Describe the DPCHs, their power control, time organisation, and L1 synchronisation
Describe the HS-DSCH and other physical channels related to HSDPA
Name the different HSDPA physical channel types
What kind of enhancements are implemented with HSUPA ?
Describe the E-DCH capabilities
Radio Interface Channel Organisation
In GSM, we distinguish between logical and physical channels. In UMTS there are three different types of channels:
Logical
Transport
Physical
Logical Channels
Logical Channels were created to transmit a specific content.
There are for instance logical channel to transmit the cell system information, paging information, or user data.
Logical channels are offered as data transfer service by the Medium Access Control (MAC) layer to the next higher layer.
Consequently, logical channels are in use between the mobile phone and the RNC.
Transport Channels (TrCH)
The MAC layer is using the transport service of the lower lower, the Physical layer.
The MAC layer is responsible to organise the logical channel data on transport channels. This process is called mapping.
In this context, the MAC layer is also responsible to determine the used transport format.
The transport of logical channel data takes place between the UE and the RNC.
Physical Channels (PhyCH)
The physical layer offers the transport of data to the higher layer.
The characteristics of the physical transport have to be described.
When we transmit information between the RNC and the UE, the physical medium is changing.
Between the RNC and the Node B, where we talk about the interface Iub, the transport of information is physically organised in so-called Frames.
Between the Node B and the UE, where we find the WCDMA radio interface Uu, the physical transmission is described by physical channels.
A physical channel is defined by the UARFCN and the a spreading code in the FDD mode.
Transport Channel Formats
The above description refers to a situation, where the MAC-layer hands the TBS to the PHY layer. This happens in the UE. But TBSs are normally exchanged between the UE and the RNC. As a consequence, the TBS must be transmitted over an AAL2 virtual channel between the RNC and the Node B. The TBS is packet into a frame protocol defined for the traffic channel.
Different TBSs can be transmitted in one Transport Channel.
How do MAC and PHY layer know, what kind of TBS they exchanged?
When a transport channel is setup – or modified – the allowed Transport Block Sets are specified.
Each allowed TBS gets a unique Transport Format Indicator (TFI).
All TFIs of a Transport Channel are summarised in the Transport Format Set (TFS).
The TF consists of two parts (FDD mode):
Semi-static part
The attributes belonging to the semi-static part are set by the RRC-layer.
They are valid for all TBSs in the Transport Channel.
Semi-static attributes are the Transmission Time Interval (TTI), the error correction scheme, the CRC size, and the static rate matching parameter (used by the PHY layer for dynamic puncturing if the TBS is too long for the radio frame).
Dynamic part
The dynamic part comprises attributes, which can be changed by the MAC layer dynamically.
The affected attributes are the Transport Block Size and the Transport Block Set Size.