Get started !
online LTE test
online C test

Updated or New
5G NR Data Rate calculator New
5G NR TBS calculator New
5G NR UE Registration New
Python programming
C++ programming
MIMO for 3GPP Developer - 2
Uplink power control
MIMO for 3GPP Developer
NR ARFCN and GSCN
5GS Interfaces



About
Feedback
Information Theory
Modulation
Multiple Access
DSP (wip)
OSI Model
Data Link layer
SS7
Word about ATM
GSM
GPRS
UMTS
WiMAX
LTE
CV2X
5G
Standard Reference
Reference books
Resources on Web
Miscellaneous
Mind Map
Magic MSC tool
Bar graph tool
C programming
C++ programming
Perl resources
Python programming
Javascript/HTML
MATLAB
ASCII table
Project Management

another knowledge site

3GPP Modem
Simulator


Sparkle At Office comic strip

UMTS (Radio access layers briefly) - 11

Radio access layers briefly [Under UMTS]
» Radio interface layer - 25.301 «
» MAC - 25.321 «
» RLC - 25.322 «
» PDCP - 25.323 «
» BMC - 25.324 «
» RRC - 25.331 «
» Phy layer services - 25.302 «

Let us have a quick look at the way various Radio access functions have been organised in layers.

Below diagram shows the various entities of access layers in UE (RNS access layers will be similar).

Phy layer access is based on WCDMA. It uses Scrambling codes and Channelisation codes. Scrambling codes (PN sequences) separate out UEs and Node Bs. Channelisation codes separate out channels. Channelisation codes are orthogonal in nature and spreads the signal with 3.84 Mcps chip rate. Scrambling codes are applied after Channelisation codes. Scrambling codes are useful in Asynchronous operation. Location of UE changes and also location differs for each UE, so Asynchronous operation is more suitable. Modulation techniques used are QPSK and 16QAM for HS (high speed) operations. We will see more about it in later articles on Phy layer.

Phy layer provide an abstraction of "Transport channels" to MAC, which in turn provide an abstraction of "Logical channels" to RLC. If you recall, GSM too have Logical channels and Physical channels (e..g. FACCH and TCH are different logical channels, but actually same physical channel). MAC layer has entities to handle broadcast channels (MAC-b), high speed channels (MAC-hs, added in R5), control and shared channels (MAC c-sh), and dedicated channels (MAC-d).

RLC along with PDCP and BMC provide an abstraction of Signaling radio bearers (SRB) and Radio bearers (RB) to L3. In User plane, RLC provide generic modes of transmission (like Transparent, Ack, and Unack). Unlike GPRS, RLC and MAC are better separated..

PDCP (Packet Data Convergence Protocol) is equivalent to SNDCP for GPRS, taking care of functions compression/decompression etc.

BMC (Broadcast/Multicast Control protocol) takes care of broadcast and multicast services. BMC messages could be cell broadcast SMS or multimedia messages. Till R6, only cell broadcast SMS messages are supported. R6 makes a major addition with MBMS (Multimedia Broadcast Multicast Services).

RRC bridge the gap between Layer 2 and NAS entities. It gives an abstraction of RRC "connection", required for NAS entities to operate. Overall control of AS entities (cell selection, configuration of radio bearers, etc.) comes from RRC. RRC has functional entities for broadcast (BCFE), paging/notification (PNFE), dedicated control (DCFE), shared control (SCFE).

Above diagram also shows the control connections ending on RRC; these are used for configuring the layers etc.

References: UMTS by Sanchez and Thioune, and WCDMA for UMTS by Holma and Toskala.

Copyright © Samir Amberkar 2010§ § §

Iu interfaces « UMTS Index » Insight into Uu access stratum