Mobile Communication Networks and Systems UMTS / WCDMA Introduction Baiguanysh S. B.
UMTS 3 rd generation mobile cellular system ● Developped by 3 GPP ● Uses W-CDMA ● Made by Baiguanysh S. B. 2
3 GPP UMTS Specification & Management 3 GPP – The Third Generation Partnership Programme (coop: ARIB, CCSA, ETSI, ATIS, TTA, TTC) ● The scope of 3 GPP was to produce globally applicable Technical Specifications and Tech. Reports for a 3 G Mobile Com. System. It is based on core network and the radio access tech. that they support. ● Made by Baiguanysh S. B. 3
3 GPP UMTS capabilities Employs a 5 MHz channel bandwidth. ● 100 simultaneous voice calls or data transmission up to 2 Mbps (14. 4 Mbps with HSDPA and HSUPA) ● SIM->USIM ● It allow FDD and TDD modes ● Made by Baiguanysh S. B. 4
3 GPP UMTS/WCDMA technologies Radio interface ● CDMA technology ● UMTS network architecture ● UMTS modulation schemes ● UMTS channels ● UMTS TDD ● Handover ● Made by Baiguanysh S. B. 5
UMTS WCDMA specification summary PARAMETER SPECIFICATION Maximum data rate RF channel bandwidth 2048 kbps low range 384 kbps urban and outdoor 5 MHz Multiple access scheme CDMA Duplex schemes FDD and also TDD Made by Baiguanysh S. B. 6
Mobile Communication Networks and Systems NETWORK ARCHITECTURE Baiguanysh S. B.
Network Architecture Core network RNS UE UE Made by Baiguanysh S. B. RNS UE 8
User Equipment UE RF circuitry. Handle all elements of the signal, both RX and TX. Modulation used for W-CDMA requires linear amplifier. ● Baseband processing. Consists of digital circuitry. ● Battery. Li-ion batteries. ● Universal Subscriber Identity Module. Stores IMSI, MSISDN, preferred language, preferred and prohibited PLMN ● Made by Baiguanysh S. B. 9
Radio Network Subsystem Interfaces to both the UE and Core Network ● UTRAN UMTS Radio Access Network ● Made by Baiguanysh S. B. 10
Core Network Circuit switched elements ● ● ● Mobile Switching Centre Gateway MSC Packet switched elements ● ● Serving GPRS Support Node (SGSN): Mobility management, session management, interaction with other areas of the network Gateway GPRS Support Node (GGSN) Shared elements ● ● ● HLR Equipment identity register Authentication centre Made by Baiguanysh S. B. 11
Mobile Communication Networks and Systems UTRAN Baiguanysh S. B.
UTRAN Radio network controller ● Node B ● Made by Baiguanysh S. B. 13
UTRAN Interfaces Iub – Iub connects the Node. B and the RNC ● Iur – The Iur interface allows communication between different RNCs within ● Iu – The Iu interface connects the UTRAN to the core network ● Made by Baiguanysh S. B. 14
UTRAN uplink & downlink Uplink – (reverse link) link from the User Equipment to the Node B or base station ● Downlink – (forward link) from the Node B or base station to the User Equipment ● Made by Baiguanysh S. B. 15
UTRAN FDD & TDD PARAMETER UTRA FDD UTRA TDD Multiple access method CDMA TDMA, CDMA Channel spacing 5 MHz (and 1. 6 MHz for TD-SCDMA) Carrier chip rate 3. 84 Mcps Spreading factors 4. . 512 1. . 16 Time slot structure 15 slots / frame 15 / 14 slots / frame Frame length (ms) 10 10 Multirate concept Multicode, and OVSF[1] Multicode, multislot and OVSF[1] Burst types N/A (1) traffic bursts (2) random access burst (3) synchronisation burst Detection Coherent based on pilot symbols Coherent based on mid-amble Dedicated channel power control Fast closed loop 1500 Hz rate Uplink: open loop 100 Hz or 200 Hz rate Downlink: closed loop max 800 Hz rate Made by Baiguanysh S. B. 16
Mobile Communication Networks and Systems Physical Layer & Radio Interface Baiguanysh S. B.
Physical layer signal format The UMTS physical layer utilises direct sequence spread spectrum format to enable a multiple access scheme called Code Division Multiple Access, CDMA to be used. ● Using CDMA, multiple users share the same channel, but different users are allocated different codes, and in this way the system is able to distinguish between the different users. ● The CDMA signal is 5 MHz and in view of this, the UMTS physical layer is often referred to as Wideband CDMA, W-CDMA. This compares to the US based cdma. One and cdma 2000 systems that use a 1. 25 MHz bandwidth. ● Made by Baiguanysh S. B. 18
Transmitted Signal Characteristics The pulse shaping applied to the transmitted signal is root raised cosine filtering with the roll-off-factor of 0, 22 ● The nominal carrier spacing is 5 MHz, and the carrier centre frequencies are normally divisible by 5, but the carrier frequency can be adjusted in increments of 200 k. Hz ● ACLR 1 ACLR 2 UE / handset* 33 d. B 43 d. B Base station 45 d. B 50 d. B Made by Baiguanysh S. B. 19
Synchronisation P-SCH ● ● Uses primary code. Allows the UE to sync with the base station S-SCH ● ● 16 different secondary codes One code is sent at the beginning of the time slot. Consists of 15 sync codes with 64 different scrambling code groups Scrembling codes enable the UE to identify the base station ● Made by Baiguanysh S. B. 20
Power Control Near-far effect ● Node Bs power is kept to the minimum required by the UEs being served ● Open Loop ● ● ● Before communication between the UE and Node B has been established. Received signal is measured and thereby the required transmitter power is estimated Closed Loop ● ● After the communication has been established Signal strength is measured in each time slot Power is changing continiously Made by Baiguanysh S. B. 21
Mobile Communication Networks and Systems Frequency Bands & UARFCN Baiguanysh S. B.
UMTS bandwidth UMTS channels are spaced by 5 MHz ● 0, 58 MHz guard bands on both sides ● Effective bandwidth = 5 – 0, 58 = 3, 84 MHz ● Roll-off factor 0, 22 ● Total signal bandwidth = 4, 68 MHz ● Made by Baiguanysh S. B. 23
UARFCN channel numbers UTRA Absolute Frequency Channel Number ● ● UARFCN = 5 x Frequency Made by Baiguanysh S. B. 24
Frequency Bands - FDD BAND NUMBER BAND COMMON NAME UL FREQUENCIES DL FREQUENCUES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 19 20 21 22 25 26 2100 1900 1800 1700 850 800 2600 900 1700 1500 700 700 800 1500 3500 1900 850 IMT PCS A-F DCS AWS A-F CLR 1920 - 1980 1850 - 1910 1710 - 1785 1710 - 1755 824 - 849 830 - 840 2500 - 2570 880 - 915 1749. 9 - 1784. 9 1710 - 1770 1427. 9 - 1447. 9 699 - 716 777 - 787 788 - 798 832. 4 - 842. 6 832 - 862 1447. 9 - 1462. 9 3410 - 3490 1850 - 1915 814 - 849 2120 - 2170 1930 - 1990 1805 - 1880 2110 - 2155 869 - 894 875 - 885 2620 - 2690 925 - 960 1844. 9 - 1879. 9 2110 - 2170 1475. 9 - 1495. 9 729 - 746 - 756 758 - 768 877. 4 - 887. 6 791 - 821 1495 - 1510. 9 3510 - 3590 1930 - 1995 859 - 894 IMT-E E-GSM EAWS A-G LPDC LSMH USMH C USMH D EUDD UPDC EPCS A-G ECLR Made by Baiguanysh S. B. 25
Frequency Bands - TDD BAND REFERENCE A Lower A Upper B Lower B Upper C D E F BAND NAME IMT PCS PCS duplex gap IMT-E Made by Baiguanysh S. B. FREQUENCIES 1900 - 1920 2010 - 2025 1850 - 1910 1930 - 1990 1910 - 1930 2570 - 2620 2300 - 2400 1880 - 1920 26
Mobile Communication Networks and Systems CDMA Baiguanysh S. B.
RTD Round trip delay time of UMTS compared to ADSL and early GPRS implementation. ● It is very noticeable in a webbrowsing session ● Made by Baiguanysh S. B. 28
What did UMTS propose? UMTS increased the bandwidth per carrier frequency from 200 k. Hz to 5 Mhz (cheaper mobile devices can be manufactured) ● Instead of a FTDMA, UMTS introduces CDMA. ● ● ● All users communicate on the same carrier frequency and at the same time Before transmission, a user’s data is multiplied by a code that can be distinguished from codes used by other users The signals add up on the Tx path to the base station The base station uses the inverse of the math approach that was used by the mobile device Made by Baiguanysh S. B. 29
Panic at the disco • • • Communication during a lecture: The bandwidth of the “Tx channel” is high as it is only used by a single person. The low power can be used to communicate. The whispering of the students creates a slight background noise. Communication during a party: If many users communicate with base station at the same time, all users will experience a high background noise. All users have to send at a higher power to overcome the background noise. Each user can still increase the power level the system remains stable Communication in a disco: the background noise is very loud and no other communication is possible. If user is close to a base station and increases its power above the level commanded by the network, it could interfere with the signals of mobile devices that are further away and thus weaker. Made by Baiguanysh S. B. 30
MATH • The user data bits of the individual users are first multiplied with a vector with a length of 128 (Example) => elements of the resulting vector are called chips. • A vector with a length of 128 has the same number of chips • Instead of transmitting a single bit, 128 chips are transmitted – ‘spreading’ • • On the receiver side the multiplication can be reversed and the 128 chips are used to find out if the sent bit represents a 0 or 1 Advantages: • • Tx errors that change the values of some of the 128 chips can easily be detected and corrected As there are many 128 -chip vectors, each user can be assigned a unique vector that allows calculation of the original bit out of the chips at the receiver side. Made by Baiguanysh S. B. 31
Spreading Factor • Spreading factor defines the number of chips used to encode a single bit • • Chip rate • • • The speed with which the chips are transferred over the UTRAN is called the chip rate = 3. 84 Mchips/s Increasing the spreading factor means decreasing of the datarate. The longer the code, the more codes exist that are orthogonal to each other The higher spreading factor the higher error rate can be accepted If number of users in a cell is low, the transmission power can be reduced (SNR is lower) Process Gain • • • If the spreading factor 8, it corresponds to a user datarate of 384 kbit/s in the downlink direction. Only 8 users can communicate at this speed. If the spreading factor 256, only 256 users can communicate at the same time with the base station. The speed is a lot slower. The shorter spreading code, the lower processing gain. Power level of each user has to increase to minimize transmission errors Made by Baiguanysh S. B. 32
Spreading Factor Made by Baiguanysh S. B. 33
The OVSF Code Tree • If the spreading factor was constant, all users of a cell would have to communicate with the network at the same speed. • • • Single cell has to support many users with many different applications simultaneously Voice calls, video streaming or web surfing require different bandwidth. The solution is called Orthogonal Variable Spreading Factors • It is up to the network to decide how many codes are used from each level of the tree. Thus, the network has the ability to react dynamicly to different usage scenario Made by Baiguanysh S. B. 34
Scrambling in Uplink and Downlink Direction • Some of the OVSF codes are quite uniform (monotonous). • • Modulation of long sequences that never change their value would result in a very uneven spectral distribution. To counter this effect the chip stream that results from the spreading process is scrambled. The chip stream is multiplied with pseudo random code called the scrambling code. The chip rate of 3. 84 Mchips/s is not changed. Made by Baiguanysh S. B. 35
Scrambling in Uplink and Downlink Direction • In the downlink direction • • Scrambling code is used to enable the mobile device to differentiate between base stations Allows base station to use the complete code tree instead of sharing it with the neighboring cells The system is limited by the number of available codes from the code tree as well as the interference of other base stations In the uplink direction • • Each UE is assigned its own scrambling code. Each UE could theoretically use all codes of the code tree. Removes the need for a timing advance by preserving the orthogonal nature of the codes Necessary for soft handover The system is not limited by the number of codes but by the max Tx Power of the UE and by the interference that is created by other UE Made by Baiguanysh S. B. 36
UMTS Frequency and Cell Planning • • • As all cells in a UMTS radio network can use the same frequency, the frequency plan is greatly simplified compared to a GSM radio access network No frequency adaptations are necessary for new UMTS cells If a new cell is installed to increase the bandwidth in an area that is already covered by other cells, the most important task in a UMTS network is to decrease the Tx Power of the neighboring cells Made by Baiguanysh S. B. 37
The Near-Far Effect and Cell Breathing • • As all users transmit on the same frequency, interference is the most limiting factor for the UMTS. Near-far effect • • • Cell Breathing • • • Users that are farther away from the base station have to send with more power than those closer to the base station. Network can instruct each UE 1500 times per second to adapt its Tx Power. There is a high number of users in the coverage area and the users are dispersed at various distances from the center of the cell. The most distant user needs to transmit at the highest possible power. If the network accepts the new connection request the interference level for all users will rise. All users have to increase their Tx Power. The user at the border of the cell is already transmitting at his maximum power. As a result his signal cannot be correctly decoded and the connection is broken. This means that the geographical area the cell can cover is reduced. Avoiding Cell Breathing effect • • The network has the possibility to reject a new user to protect the ongoing sessions Reduce the interference to a level that allow all users to communicate (longer spreading factor) Made by Baiguanysh S. B. 38
Mobile Communication Networks and Systems UMTS Channel Structure on the Air Interface Baiguanysh S. B.
User Plane and Control Plane User plane ● ● Data which is directly and transparently exchanged between the users of a connection like voice data or IP packets Control Plane ● ● All signaling data that is exchanged between the users and the network. Made by Baiguanysh S. B. 40
Common and Dedicated Channels User plane data and control plane data is transferred over the UTRAN in so-called ‘channels’ ● Dedicated ch ● ● ● Tx data for a single user E. g. Voice connection, IP packets between user and the network, location update message Common ch ● ● ● Data transferred in common channels is destined for all users of a cell E. g. Broadcast ch, which Tx general info about network to all users of a cell (the network the cell belongs to, the current state of the net) Shared ch ● ● These channels are not monitored by all devices but only by those that have been instructed by the net to do so Made by Baiguanysh S. B. 41
Logical, transport and Physical Channels In downlink ● In upnlink ● Made by Baiguanysh S. B. 42
Logical, transport and Physical Channels Logical Ch ● ● ● Are used to separate different kinds of data flows that have to be transferred over the air interface These channels contains no info on how the data is later transmitted over the air. Transport Ch ● ● Prepare downlink data frames for transmission over the air interface by splitting them up into smaller parts, which are encapsulated into RLC/MAC-frames that are more suitable for transmission over the air interface. Physical Ch ● ● ● Responsible for offering a physical transmission medium for one or more transport channels. Also, responsible for channel coding, that is, the addition of redundancy and error detection bits to the data stream The intermediate products between transport ch and physical ch are called Composite Coded Transport Ch (CCTr. Ch) and are a combination of several transport ch, which are subsequently transmitted over one or more physical ch. Made by Baiguanysh S. B. 43
Logical, transport and Physical Channels Logical Ch ● ● ● Are used to separate different kinds of data flows that have to be transferred over the air interface These channels contains no info on how the data is later transmitted over the air. Transport Ch ● ● Prepare downlink data frames for transmission over the air interface by splitting them up into smaller parts, which are encapsulated into RLC/MAC-frames that are more suitable for transmission over the air interface. Physical Ch ● ● ● Responsible for offering a physical transmission medium for one or more transport channels. Also, responsible for channel coding, that is, the addition of redundancy and error detection bits to the data stream The intermediate products between transport ch and physical ch are called Composite Coded Transport Ch (CCTr. Ch) and are a combination of several transport ch, which are subsequently transmitted over one or more physical ch. Made by Baiguanysh S. B. 44
Mobile Communication Networks and Systems Core Network Mobility Management Baiguanysh S. B.
Mobility management and packet mobility management The MSC knows the following MM states: ● ● MM Detached. The mobile device is switched off and the current location of the subscriber Is unknown. Incoming calls for the subscriber cannot be forwarded to the subscriber and are either rejected or forwarded to another destination if the Call Forward Unreachable MM Idle. The UE is powered on and has successfully attached to the MSC. MM Connected. The UE and MSC have an active signaling and communication connection. The SGSN implements the following PMM ● ● PMM Detached. The mobile device is switched off and the location of the subscriber is unknown to the SGSN. No IP address is currently assigned to the subscriber PMM Connected. The UE and the SGSN have an active signaling and communication connection. GGSN has assigned an IP address for the connection. PMM Idle. In this state, the UE is attached to the network but no logical signaling connection is established with SGSN. E. g. if no PDP context is active for the subscriber. Made by Baiguanysh S. B. 46
Mobile Communication Networks and Systems Radio Network Mobility Management Baiguanysh S. B.
Mobility management in the Cell-DCH State For services like voice or video communication it is very important that no interruption of the data stream occurs during a cell change. Only-DCH state can be used. ● The network constantly controls the quality of the connection and is able to redirect the connection to other cells if the subscriber is moving – handover ● A handover is controlled by the RNC and triggered based on measurement values of the quality of the uplink signal and measurement reports on downlink quality sent by the UE ● Made by Baiguanysh S. B. 48
Handover criteria in UMTS RSSI ● ● ● Received Signal Strength Indication. Low signal -100 d. Bm, Strong Signal -60 d. Bm RSCP ● ● Received Signal Code Power Can be used to detect UMTS cell edge scenarios where no neighboring UMTS cell is available to maintain the connection. If the network is aware of neighboring GSM cells, it can activate the compressed mode so that the UE can search and report neighboring GSM cells that the connection could be handed over to. Ec. No ● ● The received energy per chip (Ec) of the pilot channel divided by the total noise power density (No). It is RSCP divided by RSSI. The better the Ec. No the better signal can be distinguished from noise. Can be used to compare the relative signal quality of different cells Made by Baiguanysh S. B. 49
Hard Handover By receiving measurement results from the UE of the active connection and measurement results of the signal strength of the broadcast channel of the neighboring cells, the RNC is able to recognize if a neighboring cell is more suitable for the connection. ● Before redirecting the call there must be performed operations such as the reservation of resources on the Iub interface and Iur interface if necessary. ● Once the new connection is in place, the mobile device receives a command over the current connection to change into the new cell ● ● ● The handover command contains: the frequency of the new cell, new channelization and scrambling cede The interruption of the data stream during the handover takes about 100 ms. Made by Baiguanysh S. B. 50
Soft Handover Voice call is not interrupted at any time during the procedure ● On the basis of signal quality meas, the RNC can decide to set the UE into soft handover state. ● All data will be sent and received over two or even more cells simultaneously. ● All cells that are part of the communication are put into so-called Active Set of the connection. ● Active Set can contain up to six cells. ● Made by Baiguanysh S. B. 51
Soft Handover Made by Baiguanysh S. B. 52
Soft Handover • • The Tx Power and energy consumption of the UE can be reduced in some cases The RNC receives the data frames from both cell 1 and cell 2 and can decide, on the basis of the signal quality, which frame is to be forwarded into the core network. Made by Baiguanysh S. B. 53
Soft Handover • • In the downlink, the UE receives identical frames from cell 1 and cell 2. Cells use different channelization and scrambling codes the mobile device is able to separate the two data streams. UE uses less Tx Power compared to a single cell scenario, and so interference is reduced in the uplink direction. This increases the capacity. The RNC receives a copy of each frame from all cells of the Active Set. Thus, the capacity that is taken by one user is much bigger then in single cell scenario. Made by Baiguanysh S. B. 54
Softer Handover • • • Is used when two or more cells of the same Node-B are part of the Active Set No additional resource are necessary on the Iub interface as the Node-B decides which of the frames, received from the mobile device via the different cells, are to be forwarded to the RNC. In the downlink direction the Node-B duplicates the frames that it receives from the RNC for all cells in the Active Set Made by Baiguanysh S. B. 55
S-RNC, D-RNC • Serving RNC • • • SGSN only aware of S-RNC All packets from SGSN are forwarded to the Serving RNC Drift RNC • • If a foreign cell needs to be included in the Active Set, the S-RNC has to establish a link to the D-RNC via the Iur interface. All data arriving at the S-RNC from the SGSN will be forwarded to the D-RNC The D-RNC forward all incoming data packets in uplink to the S-RNC. The S-RNC decide which o fthe packets to use on the basis of the signal quality indication Made by Baiguanysh S. B. 56
S-RNC relocation procedure • • if there will be a point at which not single Node-B of the S-RNC is part of the transmission chain anymore the S-RNC can call Serving Radio Network Subsystem (SRNS) Relocation Request. The D-RNC becomes the new S-RNC and the resources on the Iur Interface can be released Made by Baiguanysh S. B. 57
3 G to 2 G handover • • • While a user roams in an area covered by UMTS, voice calls and packet data are handled by the UMTS network. If the user roams into an area that is only covered by a 2 G network, the UE automatically switches over to GSM, and packet-switched connection use the GPRS network. Intersystem Handover – handover an active connection to a 2 G network Made by Baiguanysh S. B. 58
Blind intersystem handover • • • The RNC is aware of GSM neighboring cells for certain UMTS cells. In the event of sever signal quality degradation, The RNC reports to the MSC or SGSN that a handover into 2 G cell is necessary No measurement reports of the GSM cell are available for the handover decision Made by Baiguanysh S. B. 59
Compressed mode handover • • GSM cells works on different cells UE can’t process the UMTS quality measurements and the GSM quality measurements The only way for the UE is to stop transmitting and receiving frames in a predefined pattern to perform meas on other frequencies Made by Baiguanysh S. B. 60
Mobility Management in Idle State • • In Idle state the UE is passive, no data is sent or received To be able to respond to incoming calls, SMS, MMS messages, the PCH is monitored • • • If the subscriber has an active PDP context in Idle state • • • The UE establishes a connection with the network if a paging message with IMSI or TMSI is received. The UE have to listen for incoming paging messages only at a certain interval. Network also need to send a paging message in case of an incoming IP frame After receiving such paging message, UE has to reestablish a logical connection before the IP frame can be forwarded Cell reselection • Mobile device is responsible for mobility management as the network is not involved in the decision-making process. Made by Baiguanysh S. B. 61
Mobility Management in Idle State • No physical or logical connection exists between net and the UE • • • Physical connection must be reestablished over the air interface For the SGSN a PDP context can still be established, even thoug no data can be sent or received To Tx data the UE needs to reestablish the connection • • • DCH or FACH is used for data exchange. It takes about 2. 5 or 3 seconds. The UE should only be put into Idle state after a prolonged period of inactivity Made by Baiguanysh S. B. 62
UMTS Circuit Switched Call Establishment • First step is to perform and RRC Connection Setup procedure to establish a signaling connection • • • The UE sends a CM Service Request DTAP message. • • The goal is to establish a temporary radio ch that can be used for signaling between the mobile device, the RNC and a core network. The RNC decides to assign dedicated ch (Cell-DCH state) or to use the FACH (Cell. FACH state) The RNC has to establish SCCP protocol in order to forward this message to the MSC The MSC verifies the ID of the subscriber • • It is done via the attached TMSI or IMSI After authentication the MSC activates the ciphering of the radio ch Made by Baiguanysh S. B. 63
UMTS Circuit Switched Call Establishment • The UE proceeds to inform the MSC of the exact reason of the connection request • • It sends CC setup message that contains MSISDN of the destination The MSC requests the establishment of a speech path from the RNC. • • As a dedicated radio connection was already established it is only modified by the Radio Resource Allocation procedure. Allocation of a new spreading code. If the RNC has performed signaling via the FACH, it is necessary to establish a DCH. Made by Baiguanysh S. B. 64
UMTS Packet Switched Call Establishment • This process is called Packet Data Protocol (PDP) context activation. • From the user’s point of view it means getting an IP address to be able to communicate with the Internet. • It starts with an RRC connection setup procedure • Then the UE sends an ‘Activate PDP Context Request’ message • • It is forwarded by the RNC to the SGSN The authentication of the subscriber and activation of the air interface encryption are triggered SGSN establishes a tunnel to the GGSN (It assigns an IP address to the user) SGSN requests the establishment of a suitable bearer from the RNC on the basis of Qo. S Made by Baiguanysh S. B. 65
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