Core Network 2 separated domains: Circuit Switched (CS) and Packet Switched (PS) which reuse the infrastructure of GSM and GPRS respectively. UTRAN – UMTS Radio Network new radio interface: CDMA new transmission technology: ATM Core Network independent of Access Network The specificity of the access network due to mobile system should be transparent to the core network, which may potentially use any access technique. Radio specificity of the access network is hidden to the core network. UE radio mobility is fully controlled by UTRAN.
A manufacturer can produce only the Node-B (and not the RNC). This is not possible in GSM (A-bis is a proprietary interface) The Iur physical connection can go through the CN using common physical links with Iu-CS and Iu-PS. However there is a direct logical connection between the 2 RNCs: the Iur information is not handled by the CN.
An RNS (Radio Network Subsystem) contains one RNC (Radio Network Controller) and at least one Node-B. The RNC takes a more important place in UTRAN than the BSC in the GSM BSS. Indeed RNC can perform soft HO, while in GSM there is no connection between BSCs and only hard HO can be applied.
An RNS (Radio Network Subsystem) contains one RNC (Radio Network Controller) and at least one Node-B. A Node-B is also more complex than the GSM BTS, because it handles softer HO. Controlling RNC (CRNC): a role an RNC can take with respect to a specific set of Node-Bs (ie those Node- Bs belonging to the same RNS). There is only one CRNC for any Node-B. The CRNC has the overall control of the logical resources of its Node-Bs
In a CDMA system, the network radio equipment has a “conversation” with multiple subscribers at the same time and in the same frequency allocation. But each subscriber is assigned a unique code, so the subscriber equipment only “hears” the conversation that is encoded with that code. The network equipment “hears” all conversations simultaneously and decodes each one using the appropriate code. The network radio equipment controls the volume level of each conversation, by requesting more power from those subscribers that are faint and requesting less power from those that are too strong. Similarly, the subscriber equipment can request more or less power from the network. This process is called power control. It ensures that each conversation is just loud enough to be heard, but not so loud that it drowns out the other conversations.
The UMTS signaling protocol stack is divided into Access Stratum (AS) and Non-Access Stratum (NAS). The Non-Access Stratum architecture evolved from the GSM upper layers and includes: • Connection Management – Handles circuit-switched calls and includes sublayers responsible for call control (e.g., establish, release), supplementary services (e.g., callforwarding, 3-way calling), and short message service (SMS). • Session Management – Handles packet-switched calls (e.g., establish, release). • Mobility Management – Handles location updating and authentication for CS calls. • GPRS Mobility Management – Handles location updating and authentication for PS calls.
QPSK is a phase modulation algorithm. •Phase modulation is a version of frequency modulation where the phase of the carrier wave is modulated to encode bits of digital information in each phase change. •The "PSK" in QPSK refers to the use of Phased Shift Keying. Phased Shift Keying is a form of phase modulation which is accomplished by the use of a discrete number of states. QPSK refers to PSK with 4 states. With half that number of states, you will have BPSK (Binary Phased Shift Keying). With twice the number of states as QPSK, you will have 8PSK. •The "Quad" in QPSK refers to four phases in which a carrier is sent in QPSK: 45, 135, 225, and 315 degrees. Because QPSK has 4 possible states, QPSK is able to encode two bits per symbol.
HSDPA uses both the modulation used in WCDMA—namely QPSK—and, under good radio conditions, an advanced modulation scheme—16 QAM. The benefit of 16 QAM is that 4 bits of data are transmitted in each radio symbol as opposed to 2 bits with QPSK. Data throughput is increased with 16 QAM, while QPSK is available under adverse conditions. HSPA Evolution will add 64 QAM modulation to further increase throughput rates.
QAM bits per symbol •The advantage of using QAM is that it is a higher order form of modulation and as a result it is able to carry more bits of information per symbol. By selecting a higher order format of QAM, the data rate of a link can be increased. QAM noise margin •While higher order modulation rates are able to offer much faster data rates and higher levels of spectral efficiency for the radio communications system, this comes at a price. The higher order modulation schemes are considerably less resilient to noise and interference. •As a result of this, many radio communications systems now use dynamic adaptive modulation techniques. They sense the channel conditions and adapt the modulation scheme to obtain the highest data rate for the given conditions. As signal to noise ratios decrease, errors will increase along with re-sends of the data, thereby slowing throughput. By reverting to a lower order modulation scheme, the link can be made more reliable with fewer data errors and re-sends
UMTS system architecture, protocols & processes
UMTS System Architecture,
SINA- Feb 2014
The function of the Network Elements have been clearly specified by
Their internal implementation issues are open for the manufacturer
All the interfaces have been defined in such a detailed level that the
equipment at the endpoints can be from different manufacturers.
“Open Interfaces” aim at motivating competition between
Physical implementation of Iu interfaces:
Each Iu Interface may be implemented on any physical connection
using any transport technology, mainly on E1 (cable), STM1 (Optic
fiber) and micro-waves.
ATM will be provided in the 3GPP R4 release and IP is foreseen for
the 3GPP R6.
RNC: Radio Network Controller
Main Functions of this Intelligent part of UTRAN System includes;
Radio resource management (code allocation, Power Control,
congestion control, admission control)
Call management for the users
Connection to CS and PS Core Network
Radio mobility management
A Node-B can be considered, as first approximation, like a transcoder
between the data received by antennas and the data in the ATM cell on
Radio transmission and reception handling
Involved in the mobility management
Involved in the power control
Modulation / Demodulation
Closed loop power control
An RNS (Radio Network Subsystem) contains one RNC (Radio
Network Controller) and at least one Node-B.
The nominal channel spacing is 5 MHz, but this can be adjusted to optimize
performance in a particular deployment scenario.
The channel raster is 200 KHz, which means that the center frequency must be
an integer multiple of 200 KHz.
The carrier frequency is designated by the UTRA Absolute Radio Frequency
Channel Number (UARFCN), where
Fcenter = UARFCN * 200 KHz
Carrier Spacing & Carrier Spacing Raster
The nominal carrier spacing for UMTS is 5 MHz
It is possible to move the centre frequency of the carrier on a 200
We can have carrier spacings between 4.2MHz and 5.8MHz
This may be set within the license conditions, or to the operators
Characteristics of CDMA System
High Spectral Efficiency
– Frequency multiplex coefficient is 1.
– A UE transmission power is interference for another UE.
Characteristics of CDMA System
In CDMA system, mutual interference between users or cells is
permitted, so adjacent cells can be distributed with same frequency.
That is why the spectrum efficiency is very high and the capacity is
also very large in CDMA system. But it also causes self-interference,
if the interference is out of control, the capacity and quality of CDMA
system will be worse, so many technologies were invented to control
the interference, and it is not easy.
The second feature of CDMA is security. After spreading, the
narrowband signal of the user will be changed to broadband signal,
is close to noise, only people who use the same spreading code
can revert it. Of course, it causes the other shortcoming: more
frequency band needed.
The third feature of CDMA is soft capacity. Because all of the
carrier resource (the main resource is power) is “shared” by all of
the users, if some user occupy more power, it will cause the
capacity lower. Soft capacity will cause network planning more
complex, emulation is necessary.
Protocols in UTRAN
The Iu protocols
Used to exchange data (traffic and signaling) between RNCs, Node Bs and
the Core Network.
The Radio protocols
Used to process the data sent on the air and for the signaling between
UTRAN and the UEs
Important Radio Protocols
RRC: Radio Resource Control
RLC: Radio Link Control
MAC: Medium Access Control
Radio Channels, Protocols & Network Elements
The radio protocols are responsible for exchanges of signaling and user data
between the UE and the UTRAN over the Uu interface.
User plane protocols
These are the protocols implementing the actual Radio Access Bearer
i.e. carrying user data through the access stratum (EXAMPLES 1,2 and 4).
Control plane protocols
These are the protocols for controlling the radio access bearers and the
connection between the UE and the network from different aspects including
requesting the service, controlling different transmission resources,
handover & streamlining etc...
Also a mechanism for transparent transfer of Non Access Stratum (NAS)
messages is included.
Radio protocol stack
The radio protocols are responsible for exchanges of signaling and user
data between the UE and the UTRAN over the Uu interface
The radio protocols are layered into:
the RRC protocol located in RNC* and UE
the RLC protocol located in RNC* and UE
the MAC protocol located in RNC* and UE
the physical layer (on the air interface) located in Node-B and UE
Radio Resource Control (RRC)
The RRC functions are:
RRC connection establishment/release (initial access)
Radio Bearer establishment/release/reconfiguration (in the control plane and in
the user plane)
Transport and Physical Channels reconfiguration
Radio mobility management
Handover (soft and hard)
Cell and URA update
Measurements control (UTRAN side) and reporting (UE side)
Outer Loop Power Control
Control of radio channel ciphering and deciphering
Radio Link Control (RLC)
RLC main functions includes:
RLC Connection Establishment/Release in 3 configuration modes:
transparent data transfer (TM): without adding any protocol information
unacknowledged data transfer (UM): without guaranteeing delivery to the
peer entity (but can detect transmission errors)
acknowledged data transfer (AM): with guaranteeing delivery to the peer
entity. The AM mode provides reliable link (error detection and recovery, insequence delivery, duplicate detection, flow Control, ARQ mechanisms)
Medium Access Control (MAC)
Data transfer: MAC provides unacknowledged data transfer without segmentation
Multiplexing of logical channels (possible only if they require the same QoS)
Mapping between Logical Channels and Transport Channels
Selection of appropriate Transport Format for each Transport Channel depending
on instantaneous source rate.
Priority handling/Scheduling according to priorities given by upper layers:
- between data flows of one UE
- between different UEs
Priority handling/Scheduling is done through Transport Format Combination (TFC)
Reporting of monitoring to RRC
Ciphering for RLC transparent data (if not performed in RLC)
The Physical Layer
Physical layer main functions:
Multiplexing/de-multiplexing of transport channels on CCTrCH (Coded Composite
Transport Channel) even if the transport channels require different QoS.
Mapping of CCTrCH on physical channels
Spreading/de-spreading and modulation/demodulation of physical channels
Frequency and time (chip, bit, slot, frame) synchronization
Measurements and indication to higher layers (e.g. FER, SIR, interference power,
transmit power, etc.)
Open loop and Inner loop power control
Macro-diversity distribution/combining and soft handover execution
UMTS Global Services
A Radio Bearer is the service provided by a protocol entity (i.e. RLC
protocol) for transfer of data between UE and UTRAN.
Radio bearers are the highest level of bearer services exchanged between
UTRAN and UE
Radio bearers are mapped successively on logical channels, transport
channels and physical channels (Radio Physical Bearer Service on the
Radio Access Bearers
The RAB provides confidential transport of signaling and user data
between UE and CN with the appropriate QoS.