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UMTS system architecture, protocols & processes

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UMTS system architecture, protocols & processes

UMTS system architecture, protocols & processes

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  • 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
  • Transcript

    • 1. UMTS System Architecture, Protocols (Module 2) by, Usman Qureshi SINA- Feb 2014
    • 2. UTRAN Logical Architecture
    • 3. WCDMA Network Architecture
    • 4. Interfaces Open Interfaces: The function of the Network Elements have been clearly specified by the 3GPP. 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 manufacturers. 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.
    • 5. 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
    • 6. Node-B 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 the Iub.  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.
    • 7. Multiple Access Technology
    • 8. Multiple Access Techniques Advantages FDMA 1. Simple Implementation 1. Frequency Reuse 2. privacy AMPS, TACS TDMA Defect Disadvantages 1.Privacy 1. Need synchronized of frame 1. Reduction the interference 1. Sophisticated power control for mobile GSM, PDC CDMA IS95, W-CDMA 2. Diversity Hand-over 3. Privacy
    • 9. Multiple Access Techniques FDMA/TDMA f f 5 f 5 7 f 7 1 f 1 f f 6 f 6 7 f 7 f 2 2 f f 6 6 7 7 f f 3 3 f f 4 4 f f 5 5 f f 1 f 6 1 f 6 f 4 f 4 2 2 f f f 5 f 5 1 f 1 f f 6 f 6 7 7 f f f 2 f 2 3 3 f f 7 7 f f 3 3 f f 4 4 CDMA f f 2 2 f f 1 1 f f f 1 f 1 f f f 1 f 7 f 71 f 1 1 f 1 1 f f 1 f f 1 f 1 1 1 1 f 4 f 4 1 f 1 f 1 1 f f 1 1 f f f 1 1 2 2 f f 1 1 f f f f 1 7 71 f f 1 1 f f 1 1 f f f f 5 1 51 f f f 6 6 1 1 f f 1 1 f f 1 1 f f 1 1 f f 1 1 f f 1 1 f f 1 1 Frequency is different in each sector. Frequency is same. Need for No need for frequency plan frequency plan (Frequency Reuse) Reuse
    • 10. CDMA Concept
    • 11. UMTS Bandwidth
    • 12. UMTS Bandwidth Channel Spacing The nominal channel spacing is 5 MHz, but this can be adjusted to optimize performance in a particular deployment scenario. Channel Raster The channel raster is 200 KHz, which means that the center frequency must be an integer multiple of 200 KHz. Channel Number The carrier frequency is designated by the UTRA Absolute Radio Frequency Channel Number (UARFCN), where Fcenter = UARFCN * 200 KHz
    • 13. WCDMA – Wideband & codes
    • 14. 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 kHz raster We can have carrier spacings between 4.2MHz and 5.8MHz This may be set within the license conditions, or to the operators discretion
    • 15. Characteristics of CDMA System  High Spectral Efficiency – Frequency multiplex coefficient is 1.  Soft capacity – Quality – Coverage – Interference  Self-interference system – A UE transmission power is interference for another UE.
    • 16. 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.
    • 17. 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
    • 18. UMTS Signaling Protocol Stack
    • 19. Radio Channels, Protocols & Network Elements
    • 20. 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 (RAB) service, 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.
    • 21. 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
    • 22. Radio Resource Control (RRC) The RRC functions are: Call management  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 Paging procedure Measurements control (UTRAN side) and reporting (UE side) Outer Loop Power Control  Control of radio channel ciphering and deciphering
    • 23. 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)
    • 24. 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) selection Reporting of monitoring to RRC Ciphering for RLC transparent data (if not performed in RLC)
    • 25. 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 RF processing 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
    • 26. 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 figure)
    • 27. Radio Access Bearers The RAB provides confidential transport of signaling and user data between UE and CN with the appropriate QoS.
    • 28. UMTS Modulation - QPSK
    • 29. UMTS Modulation – 16 QAM
    • 30. Quadrature Amplitude Modulation