Cellular Networks and Mobile Computing COMS 6998 8

Cellular Networks and Mobile Computing COMS 6998 -8, Spring 2012 Instructor: Li Erran Li (lierranli@cs. columbia. edu) http: //www. cs. columbia. edu/~coms 6998 -8/ 1/30/2012: Cellular Networks: UMTS and LTE

Outline • Wireless Communications Basics – Signal propagation, fading, interference, cellular principle • Multi-access Techniques and Cellular network air-interfaces – FDMA, TDMA, CDMA, OFDM • 3 G: UMTS – Architecture: entities and protocols – Physical layer – RRC state machine • 4 G: LTE – Architecture: entities and protocols – Physical layer – RRC state machine 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 2

Basic Wireless Communication Information is embedded in electromagnetic radiation Lossy signal and interference Noise Recover information Transmitter 10/7/2020 Receiver 3

Noise & Interference • Thermal Noise – Generated due to random motion of electrons in the conductor and proportional to temperature – No= Ko. T d. Bm/Hz where Ko is Boltzmann’s constant – Receiver Noise Figure – extent to which thermal noise is enhanced by receiver front end circuitry ~ 10 d. B • Interference – signals transmitted by other users of the wireless network • Signal transmitted by other wireless devices from different wireless networks – Example: Microwave ovens near 802. 11 network 4 10/7/2020

Impact of White Gaussian Noise Shannon Capacity 10 Capacity (bits/sec/Hz) 9 SNR = 8 Signal Power Noise Power 7 6 5 C = log (1 + SNR) 4 3 2 1 0 -10 -5 0 5 10 15 20 SNR (d. B) 10/7/2020 5 25 30

Scattering of Signals - Multipath Fading Reflection Diffraction Absorption Multiple paths with random phases and gains combine constructively and destructively to cause significant amplitude variations 10/7/2020 6

Impact of Mobility Doppler Shift = Signal Amplitude Multipath Fading time 10/7/2020 7

Flat & Frequency Selective Fading • When the multipath delay is small compared to symbol duration of the signal, fading is flat or frequency non-selective 1 Symbol -1 -1 1 • Happens when signal bandwidth is small • Urban macro-cell delay spread is 10 micro seconds • When signal bandwidth is large different bands have different gains – frequency selective fading 10/7/2020 8

Typical Pathloss 1. 0 100. 0 -50 -70 Free space : 20 d. B/decade A decade : transmitter and receiver distance increase 10 times -90 -110 Shadow fading Log-normal with std ~ 8 d. B Urban Macro cell -40 d. B/decade 10/7/2020 9

Spectrum Reuse A B Ib Ia SINRa = S Sa b Sa I a+ N a and b can receive simultaneously on the same frequency band if SINRa and SINRb are above required threshold This happens if the respective transmitters are sufficiently far apart 10/7/2020 10

The Cellular Principle • Base stations transmit to and receive from mobiles at the assigned spectrum – Multiple base stations use the same spectrum (spectral reuse) • The service area of each base station is called a cell • The wireless network consists of large number of cells – Example – The network in Northern NJ is about 150 base stations for a given operator • Cells can be further divided into multiple sectors using sectorized antennas • Each terminal is typically served by the “closest” base station(s) 10/7/2020 11

Fixed Frequency Planning Each base is assigned a fixed frequency band g 1 g 4 g 6 g 5 g 7 g 2 g 3 g 6 g 1 g 5 g 7 g 1 g 2 g 6 g 5 g 4 g 2 g 7 g 1 g 2 g 3 g 3 g 1 g 2 Reuse of 3 g 6 g 1 g 4 Reuse of 1/3 Reuse of 7 – nearest co-channel interferer is in the second ring 10/7/2020 g 3 g 1 12

Operational Cellular Networks • Structure 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 13

Operational Cellular Networks Cell level statistics

Impact of Mobility • The network needs to know where the mobile is at any given time to originate an incoming call – Data base management problem • As the mobile moves across cells the base station transmitting to the mobile has to change – When to switch over – Make before break or break before make? • Information bits must be sent to the appropriate base station to be transmitted to the mobile – Network has to keep track of mobile location throughout the call 10/7/2020 15

Cellular Network Evolution CDMA 2000 IS-95 CDMA ANALOG FDMA 1 X-DO IS- 136 TDMA/CDMA TDMA GSM EDGE TDMA 10/7/2020 16 UMTS CDMA LTE OFDM

The Multiple Access problem • The base station has to transmit to all the mobiles in its cell (downlink or forward link) – Signal for user a is interference for user b – Interference is typically as strong as signal since a and b are relatively close – How to avoid interference? • All mobiles in the cell transmit to the base station (uplink or reverse link) – Signal from a mobile near by will swamp out the signal from a mobile farther away – How to avoid interference? 10/7/2020 17

Meeting Room Analogy Simultaneous meetings in different rooms (FDMA) Simultaneous meetings in the same room at different times (TDMA) Multiple meetings in the same room at the same time (CDMA) 10/7/2020 18

Frequency Division Multiple Access Guard Band Each mobile is assigned a separate frequency channel for the duration of the call Sufficient guard band is required to prevent adjacent channel interference Mobiles can transmit asynchronously on the uplink 10/7/2020 19

Time Division Multiple Access Time is divided into slots and only one mobile transmits during each slot FRAME j SLOT 1 FRAME j+2 FRAME j + 1 SLOT 2 SLOT 3 SLOT 4 SLOT 5 SLOT 6 Guard time – Signal transmitted by mobiles at different locations do not arrive at the base at the same time 10/7/2020 20

TDMA Characteristics • Discontinuous transmission with information to be transmitted buffered until transmission time – Possible only with digital technology – Transmission delay • Synchronous transmission required – Mobiles derive timing from the base station signal • Guard time can be reduced if mobiles pre-correct for transmission delay – More efficient than FDMA which requires significant guard band 10/7/2020 21

Orthogonality in TDMA/FDMA Every information signal lasts a certain duration of time and occupies a certain bandwidth and thus corresponds to a certain region in the time-frequency plane frequency Granularity is determined by practical limitations time Time division and frequency division are invariant under transformation of the channel and retain the orthogonality Any orthogonal signaling scheme for which orthogonality is preserved will be a useful multiple access technique 10/7/2020 22

Code Division Multiple Access • Use of orthogonal codes to separate different transmissions • Each symbol or bit is transmitted as a larger number of bits using the user specific code – Spreading • Spread spectrum technology – The bandwidth occupied by the signal is much larger than the information transmission rate – Example: 9. 6 Kbps voice is transmitted over 1. 25 MHz of bandwidth, a bandwidth expansion of ~100 10/7/2020 23

Spread Spectrum systems frequency time code Code orthogonality is preserved under linear transformations and hence near orthogonality is preserved under signal propagation 10/7/2020 24

Orthogonal Walsh Codes Spread factor 4 Walsh Array Information 1 1 1 -1 -1 1 De-spreading Spreading bit chip Walsh Code Transmitter 10/7/2020 Receiver 25

Power Control is critical • The dynamic range of the pathloss for a typical cell is about 80 d. B • The signal received from the closest mobile is 80 d. B stronger than the farthest mobile without power control – Code orthogonality is not sufficient to separate the signals - Near-far problem in CDMA – Strict orthogonality in TDMA/FDMA makes power control not critical • Power Control – Mobiles adjust their transmit power according to the distance from the base, fade level, data rate 10/7/2020 26

Why CDMA? • Simplified frequency planning – Universal frequency reuse with spreading gain to mitigate interference – Interference averaging allows designing for average interference level instead of for worst case interference TDMA / FDMA 10/7/2020 27 CDMA

Why CDMA? • Variable rate Vocoder with Power Control – Advanced data compression technology is used to compress data according to content – Typical voice activity is 55% - CDMA reduces interference by turning down transmission between talk spurts – Reduced average transmission power increases capacity through statistical multiplexing – Compensate for fading through power control - transmit more power only under deep fades avoiding big fade margins 10/7/2020 28

Why CDMA? • Simple multipath combining to combat fading Each signal arriving at a different time can be recovered separately and combined coherently The resulting diversity gain reduces fading Spreading sequence in is offset by one chip compared to spreading sequence in 10/7/2020 29

Why CDMA? Mobile can transmit and receive from multiple base stations because all base stations use the same frequency • Soft Handoff - Make-before-break handoff Signals from different bases can be received separately and then combined because each base uses a unique spreading code 10/7/2020 30

What is OFDM ? Orthogonal Frequency Division Multiplexing is block transmission of N symbols in parallel on N orthogonal sub-carriers Traditional Multi-carrier Guard Band 1 T OFDM Implemented digitally through FFTs Frequency OFDM invented in Bell Labs by R. W. Chang in ~1964 and patent awarded in 1970 Widely used: Digital audio and Video broadcasting, ADSL, HDSL, Wireless LANs 31 | NGN Cellular Algorithms | November 2007

High Spectral Efficiency in Wideband Signaling 1 T T large compared to channel delay spread § Closely spaced sub-carriers without guard band § Each sub-carrier undergoes (narrow band) flat fading - Simplified receiver processing Frequency Narrow Band (~10 Khz) Wide Band (~ Mhz) Sub-carriers remain orthogonal under multipath propagation 32 | NGN Cellular Algorithms | November 2007 § Frequency or multi-user diversity through coding or scheduling across sub-carriers § Dynamic power allocation across sub-carriers allows for interference mitigation across cells § Orthogonal multiple access

Reverse link Orthogonal Frequency Division Multiple Access User 1 § Users are carrier synchronized to the base § Differential delay between users’ signals at the base need to be small compared to T W User 2 § Efficient use of spectrum by multiple users § Sub-carriers transmitted by User 3 different users are orthogonal at the receiver - No intra-cell interference § CDMA uplink is non-orthogonal 33 | NGN Cellular Algorithms | November 2007 since synchronization requirement is ~ 1/W and so difficult to achieve

Typical Multiplexing in OFDMA Frequency Each color represents a user Each user is assigned a frequency-time tile which consists of pilot sub-carriers and data sub-carriers § Yellow color indicates pilot subcarriers § Channel is constant in each tile Block hopping of each user’s tile for frequency diversity Time 34 | NGN Cellular Algorithms | November 2007 Typical pilot ratio: 4. 8 % (1/21) for LTE for 1 Tx antenna and 9. 5% for 2 Tx antennas

Outline • Wireless Communications Basics – Signal propagation, fading, interference, cellular principle • Multi-access Techniques and Cellular network air-interfaces – FDMA, TDMA, CDMA, OFDM • 3 G: UMTS – Architecture: entities and protocols – Physical layer – RRC state machine • 4 G: LTE – Architecture: entities and protocols – Physical layer – RRC state machine 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 35

UMTS System Architecture Iu Node B RNC MSC/ VLR GMSC External Networks Uu Node B USIM Cu ME Iub Iur HLR Node B RNC Node B UE UTRAN SGSN GGSN CN 36

UMTS Protocol Stacks • Control plane 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 37

UMTS Protocol Stacks (Cont’d) • Data Plane 3 GPP: PDCP L 3 CE RLC MAC WCDMA MS Uu Relay GTP UDP RAN GTP GTP UDP UDP IP IP L 2 L 2 L 1 L 1 Iu 3 G Serving Node RAN protocols (Access Stratum, AS) Gn 3 G Gateway Node 38 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8)

UTRAN UE UTRAN CN UMTS Terrestrial Radio Access Network, Overview ¡ Two Distinct Elements : Base Stations (Node B) Radio Network Controllers (RNC) ¡ ¡ 1 RNC and 1+ Node Bs are group together to form a Radio Network Sub-system (RNS) Handles all Radio-Related Functionality l l ¡ Soft Handover Radio Resources Management Algorithms Maximization of the commonalities of the PS and CS data handling Node B RNC Node B RNS Iur Iub Node B RNC Node B RNS UTRAN 39

UTRAN UE UTRAN CN Logical Roles of the RNC Controlling RNC (CRNC) Responsible for the load and congestion control of its own cells Node B Serving RNC (SRNC) Terminates : Iu link of user data, Radio Resource Control Signalling Performs : L 2 processing of data to/from the radio interface, RRM operations (Handover, Outer Loop Power Control) Node B Drift RNC (DRNC) Performs : Macrodiversity Combining and splitting CRNC Node B UE Node B Iu SRNC Iur Iu DRNC 40

UE UTRAN CN Radio Resources Management • Network Based Functions – Admission Control (AC) • Handles all new incoming traffic. Check whether new connection can be admitted to the system and generates parameters for it. – Load Control (LC) • Manages situation when system load exceeds the threshold and some counter measures have to be taken to get system back to a feasible load. – Packet Scheduler (PS): at RNC and Node. B (only for HSDPA and HSUPA) • Handles all non real time traffic, (packet data users). It decides when a packet transmission is initiated and the bit rate to be used. • Connection Based Functions – Handover Control (HC) • Handles and makes the handover decisions. • Controls the active set of Base Stations of MS. – Power Control (PC) • Maintains radio link quality. • Minimize and control the power used in radio interface, thus maximizing the call capacity. 41

Connection Based Function Power Control ¡ Prevent Excessive Interference and Near-far Effect ¡ Fast Close-Loop Power Control l l ¡ Feedback loop with 1. 5 k. Hz cycle to adjust uplink / downlink power to its minimum Even faster than the speed of Rayleigh fading for moderate mobile speeds Outer Loop Power Control l l Adjust the target SIR setpoint in base station according to the target BER Commanded by RNC UE UTRAN CN Outer Loop Power Control If quality < target, increases SIRTARGET Fast Power Control If SIR < SIRTARGET, send “power up” command to MS 42

Connection Based Function UE UTRAN CN Handover ¡ Softer Handover l l l ¡ Soft Handover l l ¡ A MS is in the overlapping coverage of 2 sectors of a base station Concurrent communication via 2 air interface channels 2 channels are maximally combined with rake receiver A MS is in the overlapping coverage of 2 different base stations Concurrent communication via 2 air interface channels Downlink: Maximal combining with rake receiver Uplink: Routed to RNC for selection combining, according to a frame reliability indicator by the base station Hard handover ¡ HSDPA ¡ Inter-system and inter-frequency 43

Handoff Impact on Performance UE UTRAN • TCP loss rate at the cell is highly correlated with EDCH to non EDCH handoff events (Event 1 J) – Non EDCH is less efficient than EDCH Each data point is a cell CN

HSDPA UE UTRAN CN High Speed Downlink Packet Access ¡ Improves System Capacity and User Data Rates in the Downlink Direction to 10 Mbps in a 5 MHz Channel ¡ Adaptive Modulation and Coding (AMC) l l ¡ HARQ provides Fast Retransmission with Soft Combining and Incremental Redundancy l l ¡ Replaces Fast Power Control : User farer from Base Station utilizes a coding and modulation that requires lower Bit Energy to Interference Ratio, leading to a lower throughput Replaces Variable Spreading Factor : Use of more robust coding and fast Hybrid Automatic Repeat Request (HARQ, retransmit occurs only between UE and BS) Soft Combining : Identical Retransmissions Incremental Redundancy : Retransmits Parity Bits only Fast Scheduling Function l which is Controlled in the Base Station rather than by the RNC 45

Core Network UE UTRAN CN Core Network CS Domain : l l l ¡ Mobile Switching Centre (MSC) ¡ Switching CS transactions Visitor Location Register (VLR) ¡ Holds a copy of the visiting user’s service profile, and the precise info of the UE’s location Gateway MSC (GMSC) ¡ The switch that connects to external networks PS Domain : l l Serving GPRS Support Node (SGSN) ¡ Similar function as MSC/VLR Gateway GPRS Support Node (GGSN) ¡ Similar function as GMSC HLR Iu-ps ¡ SGSN External Networks ¡ MSC/ VLR Iu-cs GGSN Register : l Home Location Register (HLR) ¡ Stores master copies of users service profiles ¡ Stores UE location on the level of MSC/VLR/SGSN 46

Standardization of WCDMA / UMTS WCDMA Air Interface, Main Parameters Multiple Access Method DS-CDMA Duplexing Method FDD/TDD Base Station Synchronization Asychronous Operation Channel bandwidth 5 MHz Chip Rate 3. 84 Mcps Frame Length 10 ms Service Multiplexing Multiple Services with different Qo. S Requirements Multiplexed on one Connection Multirate Concept Variable Spreading Factor and Multicode Detection Coherent, using Pilot Symbols or Common Pilot Multiuser Detection, Smart Antennas Supported by Standard, Optional in Implementation 47

WCDMA Air Interface f Wideband f Spreading User N Wideband Multipath Delay Profile Code Gain Despreading Received f Narrowband CN Direct Sequence Spread Spectrum Spreading User 1 UTRAN UE f f Narrowband f Þ Frequency Reuse Factor = 1 Variable Spreading Factor (VSF) Spreading : 256 t User 1 f Wideband f Spreading : 16 Wideband t Þ 5 MHz Wideband Signal allows Multipath Diversity with Rake Receiver User 2 f Þ VSF Allows Bandwidth on Demand. Lower Spreading Factor requires Higher SNR, causing Higher Interference in exchange. 48

UE UTRAN CN WCDMA Air Interface • Channel concepts 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 49

WCDMA Air Interface (Cont’d) UE UTRAN CN Mapping of Transport Channels and Physical Channels Broadcast Channel (BCH) Forward Access Channel (FACH) Paging Channel (PCH) Random Access Channel (RACH) Dedicated Channel (DCH) Downlink Shared Channel (DSCH) Common Packet Channel (CPCH) Primary Common Control Physical Channel (PCCPCH) Secondary Common Control Physical Channel (SCCPCH) Physical Random Access Channel (PRACH) Dedicated Physical Data Channel (DPDCH) Dedicated Physical Control Channel (DPCCH) Physical Downlink Shared Channel (PDSCH) Physical Common Packet Channel (PCPCH) Synchronization Channel (SCH) Common Pilot Channel (CPICH) Acquisition Indication Channel (AICH) Highly Differentiated Types of Channels enable best combination of Interference Reduction, Qo. S and Energy Efficiency, Paging Indication Channel (PICH) CPCH Status Indication Channel (CSICH) Collision Detection/Channel Assignment 50 Indicator Channel (CD/CA-ICH)

WCDMA Air Interface (Cont’d) UE UTRAN CN • Code to channel allocation 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 51

Codes in WCDMA • Channelization Codes (=short code) – Used for • channel separation from the single source in downlink • separation of data and control channels from each other in the uplink – Same channelization codes in every cell / mobiles and therefore the additional scrambling code is needed • Scrambling codes (=long code) – – – Very long (38400 chips = 10 ms =1 radio frame), many codes available Does not spread the signal Uplink: to separate different mobiles Downlink: to separate different cells The correlation between two codes (two mobiles/Node Bs) is low • Not fully orthogonal TLT-5606 Spread Spectrum Techniques / 25. 4. 2008

RRC State Machine • IDLE: procedures based on reception rather than transmission – Reception of System Information messages – PLMN selection Cell selection Registration (requires RRC connection establishment) – Reception of paging Type 1 messages with a DRX cycle (may trigger RRC connection establishment) Cell reselection – Location and routing area updates (requires RRC connection establishment) 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 53

RRC State Machine (Cont’d) • CELL_FACH: need to continuously receive (search for UE identity in messages on FACH), data can be sent by RNC any time – Can transfer small PS data – UE and network resource required low – Cell re-selections when UE mobile – Inter-system and inter-frequency handoff possible – Can receive paging Type 2 messages without a DRX cycle 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 54

RRC State Machine (Cont’d) • CELL_DCH: need to continuously receive, and sent whenever there is data – Possible to transfer large quantities of uplink and downlink data – Dedicated channels can be used for both CS and PS connections – HSDPA and HSUPA can be used for PS connections – UE and network resource requirement is relatively high – Soft handover possible for dedicated channels and HSUPA Inter-system and inter-frequency handover possible – Paging Type 2 messages without a DRX cycle are used for paging purposes 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 55

RRC State Machine (Cont’d) • State promotions have promotion delay • State demotions incur tail times Tail Time Delay: 1. 5 s Delay: 2 s IDLE Tail Time Page 56 Courtesy: Feng Qian Channel Radio Power Not allocated Almost zero CELL_FACH Shared, Low Speed Low CELL_DCH High Dedicated, High Speed

Outline • Wireless Communications Basics – Signal propagation, fading, interference, cellular principle • Multi-access Techniques and Cellular network air-interfaces – FDMA, TDMA, CDMA, OFDM • 3 G: UMTS – Architecture: entities and protocols – Physical layer – RRC state machine • 4 G: LTE – Architecture: entities and protocols – Physical layer – RRC state machine 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 57

LTE Overview 3 GPP R 8 solution for the next 10 years Peaks rates: DL 100 Mbps with OFDMA, UL 50 Mbps with SC-FDMA Latency for Control-plane < 100 ms, for User-plane < 5 ms Optimised for packet switched domain, supporting Vo. IP Scaleable RF bandwidth between 1. 25 MHz to 20 MHz 200 users per cell in active state Supports MBMS multimedia services Uses MIMO multiple antenna technology Optimised for 0 -15 km/h mobile speed and support for up-to 120350 km/h • No soft handover, Intra-RAT handovers with UTRAN • Simpler E-UTRAN architecture: no RNC, no CS domain, no DCH • • • www. nethawk. fi 3 May 2007

LTE technical objectives and architecture • User throughput [/MHz]: – Downlink: 3 to 4 times Release 6 HSDPA – Uplink: 2 to 3 times Release 6 Enhanced Uplink • Downlink Capacity: Peak data rate of 100 Mbps in 20 MHz maximum bandwidth • Uplink capacity: Peak data rate of 50 Mbps in 20 MHz maximum bandwidth • Latency: Transition time less than 5 ms in ideal conditions (user plane), 100 ms control plane (fast connection setup) www. nethawk. fi 3 May 2007

LTE technical objectives and architecture (Cont’d) • Mobility: Optimised for low speed but supporting 120 km/h – Most data users are less mobile! • Simplified architecture: Simpler E-UTRAN architecture: no RNC, no CS domain, no DCH • Scalable bandwidth: 1. 25 MHz to 20 MHz: Deployment possible in GSM bands. www. nethawk. fi 3 May 2007

LTE Architecture • Entities and functionalities 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 61

LTE Protocol Stack • Control plane 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 62

LTE Protocol Stack (Cont’d) • Data plane 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 63

Functions of e. Node. B • Terminates RRC, RLC and MAC protocols and takes care of Radio Resource Management functions – – – Controls radio bearers Controls radio admissions Controls mobility connections Allocates radio resources dynamically (scheduling) Receives measurement reports from UE • Selects MME at UE attachment • Schedules and transmits paging messages coming from MME • Schedules and transmits broadcast information coming from MME & O&M • Decides measurement report configuration for mobility and scheduling • Does IP header compression and encryption of user data streams www. nethawk. fi 3 May 2007

Functions of MME • Mobility Management Entity (MME) functions – Manages and stores UE context – Generates temporary identities and allocates them to UEs – Checks authorization – Distributes paging messages to e. NBs – Takes care of security protocol – Controls idle state mobility – Ciphers & integrity protects NAS signaling www. nethawk. fi 3 May 2007

Session Establishment Message Flow 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 66

Session States 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 67

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LTE PHY Basics • Six bandwidths – 1. 4, 3, 5, 10, 15, and 20 MHz • Two modes – FDD and TDD • 100 Mbps DL (SISO) and 50 Mbps UL • Transmission technology – OFDM for multipath resistance – DL OFDMA for multiple access in frequency/time – UL SC-FDMA to deal with PAPR ratio problem

Frame Structure Type 1 (FDD) Frame Structure Type 2 (TDD)

Resource grid One downlink slot, Tslot 6 or 7 OFDM symbols Resource block : Transmission BW Resource element 12 subcarriers : l=0 l=6 • 6 or 7 OFDM symbols in 1 slot • Subcarrier spacing = 15 k. Hz • Block of 12 SCs in 1 slot = 1 RB – 0. 5 ms x 180 k. Hz – Smallest unit of allocation

2 -D time and frequency grid 0 20 7 0 #19 #18 #17 #16 s) T x 3 a 1 r o di #4 e m f- ra #0 #1 #2 e #5 #3 Nsc. RB subcarriers (=12) 1 0. 5 slot m = se c Power b Su m Tim e m a fr 0 =1 c( e s Frequency NBWDL subcarriers

DL PHY Channels and Signals • Signals: generated in PHY layers – P-SS: used for initial sync – S-SS: frame boundary determination – RS: pilots for channel estimation and tracking • Channels: carry data from higher layers – PBCH: broadcast cell-specific info – PDCCH: channel allocation and control info – PCFICH: info on size of PDCCH – PHICH: Ack/Nack for UL blocks – PDSCH: Dynamically allocated user data

DL Channel Mapping P-SCH - Primary Synchronization Signal - Secondary Synchronization Signal • S-SCH PBCH - Physical Broadcast Channel PDCCH -Physical Downlink Control Channel PDSCH - Physical Downlink Shared Channel Reference Signal – (Pilot) 16 QAM 64 QAM QPSK Time Frequency

UL PHY Signals and Channels • Signals: generated in the PHY layer – Demodulation RS : sync and channel estimation – SRS: Channel quality estimation • Channels: carry data from higher layers – PUSCH: Uplink data – PUCCH: UL control info – PRACH: Random access for connection establishment

UL Channel Mapping 64 QAM 16 QAM QPSK PUSCH Demodulation Reference Signal (for PUSCH) QPSK BPSK PUCCH Demodulation Reference Signal (for PUCCH format 0 or 1, Normal CP) Time Frequency

RRC State Machine • Much simpler than UMTS 1/23/12 Cellular Networks and Mobile Computing (COMS 6998 -8) 77

Thank you!

Backup slides

MIMO in LTE • Rel 8 defines MIMO only for DL • 1, 2 and 4 transmit antennas defined for – Transmit Diversity (Tx. Div) – Spatial Multiplexing (Sp. Mux) • Control channels undergo Tx. Div based on SFBC • Data channels may undergo Tx. Div or Sp. Mux

Orthogonal RS locations • channel matrix needs to be known in advance for equalization

SC-FDMA

Outline • Introduction • 3 GPP Evolution • Motivation • LTE performance requirements • Key Features of LTE • LTE Network Architecture • System Architecture Evolution(SAE) • Evolved Packet Core(EPC) • E-UTRAN Architecture • Physical layer • LTE Frame Structure • Layer 2 • OFDM • SC-FDMA • Multiple Antenna Techniques • Services • Conclusions • LTE vs Wi. MAX • References

Introduction • LTE is the latest standard in the mobile network technology tree that previously realized the GSM/EDGE and UMTS/HSx. PA network technologies that now account for over 85% of all mobile subscribers. LTE will ensure 3 GPP’s competitive edge over other cellular technologies. • Goals include ØSignificantly increase peak data rates, scaled linearly according to spectrum allocation Øimproving spectral efficiency Ølowering costs Øimproving services Ømaking use of new spectrum opportunities ØImproved quality of service Øbetter integration with other open standards

3 GPP Evolution ØRelease 99 (2000): UMTS/WCDMA ØRelease 5 (2002) : HSDPA ØRelease 6 (2005) : HSUPA, MBMS(Multimedia Broadcast/Multicast Services) ØRelease 7 (2007) : DL MIMO, IMS (IP Multimedia Subsystem), optimized real-time services (Vo. IP, gaming, push-to-talk). ØRelease 8(2009? ) : LTE (Long Term Evolution) • • • Long Term Evolution (LTE) 3 GPP work on the Evolution of the 3 G Mobile System started in November 2004. Currently, standardization in progress in the form of Rel-8. Specifications scheduled to be finalized by the end of mid 2008. Target deployment in 2010.

Motivation §Need for higher data rates and greater spectral efficiency Ø Can be achieved with HSDPA/HSUPA Ø and/or new air interface defined by 3 GPP LTE §Need for Packet Switched optimized system Ø Evolve UMTS towards packet only system §Need for high quality of services Ø Use of licensed frequencies to guarantee quality of services Ø Always-on experience (reduce control plane latency significantly) Ø Reduce round trip delay §Need for cheaper infrastructure Ø Simplify architecture, reduce number of network elements

LTE performance requirements • Data Rate: • Instantaneous downlink peak data rate of 100 Mbit/s in a 20 MHz downlink spectrum (i. e. 5 bit/s/Hz) • Instantaneous uplink peak data rate of 50 Mbit/s in a 20 MHz uplink spectrum (i. e. 2. 5 bit/s/Hz) • • Cell range • 5 km - optimal size • 30 km sizes with reasonable performance • up to 100 km cell sizes supported with acceptable performance • Cell capacity • up to 200 active users per cell(5 MHz) (i. e. , 200 active data clients)

LTE performance requirements • Mobility • Optimized for low mobility(0 -15 km/h) but supports high speed • Latency • user plane < 5 ms • control plane < 50 ms ØImproved spectrum efficiency ØCost-effective migration from Release 6 Universal Terrestrial Radio Access (UTRA) radio interface and architecture ØImproved broadcasting ØIP-optimized ØScalable bandwidth of 20 MHz, 15 MHz, 10 MHz, 5 MHz and <5 MHz ØCo-existence with legacy standards (users can transparently start a call or transfer of data in an area using an LTE standard, and, when there is no coverage, continue the operation without any action on their part using GSM/GPRS or W-CDMA-based UMTS)

Key Features of LTE • Multiple access scheme Ø Downlink: OFDMA Ø Uplink: Single Carrier FDMA (SC-FDMA) • Ø Ø Ø Adaptive modulation and coding DL modulations: QPSK, 16 QAM, and 64 QAM UL modulations: QPSK and 16 QAM Rel-6 Turbo code: Coding rate of 1/3, two 8 -state constituent encoders, and a contention- free internal interleaver. • Bandwidth scalability for efficient operation in differently sized allocated spectrum bands • Possible support for operating as single frequency network (SFN) to support MBMS

Key Features of LTE(contd. ) § Multiple Antenna (MIMO) technology for enhanced data rate and performance. § ARQ within RLC sublayer and Hybrid ARQ within MAC sublayer. § Power control and link adaptation § Implicit support for interference coordination § Support for both FDD and TDD § Channel dependent scheduling & link adaptation for enhanced performance. § Reduced radio-access-network nodes to reduce cost, protocol-related processing time & call set-up time

[Source: Technical Overview of 3 GPP Long Term Evolution (LTE) Hyung G. Myung] LTE Network Architecture [Source: Technical Overview of 3 GPP Long Term Evolution (LTE) Hyung G. Myung http: //hgmyung. googlepages. com/3 gpp. LTE. pdf

System Architecture Evolution(SAE) • System Architecture Evolution (aka SAE) is the core network architecture of 3 GPP's future LTE wireless communication standard. • SAE is the evolution of the GPRS Core Network, with some differences. The main principles and objectives of the LTE-SAE architecture include : A common anchor point and gateway (GW) node for all access technologies IP-based protocols on all interfaces; Simplified network architecture All IP network All services are via Packet Switched domain Support mobility between heterogeneous RATs, including legacy systems as GPRS, but also non 3 GPP systems (say Wi. MAX) Ø Support for multiple, heterogeneous RATs, including legacy systems as GPRS, but also non-3 GPP systems (say Wi. MAX) • Ø Ø Ø

SAE [Source: http: //www. 3 gpp. org/Highlights/LTE. htm]

Evolved Packet Core(EPC) • MME (Mobility Management Entity): • -Manages and stores the UE control plane context, generates temporary Id, provides UE authentication, authorization, mobility management • UPE (User Plane Entity): • -Manages and stores UE context, ciphering, mobility anchor, packet routing and forwarding, initiation of paging • 3 GPP anchor: • -Mobility anchor between 2 G/3 G and LTE • SAE anchor: • -Mobility anchor between 3 GPP and non 3 GPP (I-WLAN, etc)

E-UTRAN Architecture [Source: E-UTRAN Architecture(3 GPP TR 25. 813 ]7. 1. 0 (2006 -09))]

User-plane Protocol Stack [Source: E-UTRAN Architecture(3 GPP TR 25. 813 ]7. 1. 0 (2006 -09))]

Control-plane protocol Stack [Source: E-UTRAN Architecture(3 GPP TR 25. 813 ]7. 1. 0 (2006 -09))]

Physical layer • The physical layer is defined taking bandwidth into consideration, allowing the physical layer to adapt to various spectrum allocations. • The modulation schemes supported in the downlink are QPSK, 16 QAM and 64 QAM, and in the uplink QPSK, 16 QAM. The Broadcast channel uses only QPSK. • The channel coding scheme for transport blocks in LTE is Turbo Coding with a coding rate of R=1/3, two 8 -state constituent encoders and a contention-free quadratic permutation polynomial (QPP) turbo code internal interleaver. • Trellis termination is used for the turbo coding. Before the turbo coding, transport blocks are segmented into byte aligned segments with a maximum information block size of 6144 bits. Error detection is supported by the use of 24 bit CRC.

LTE Frame Structure • One element that is shared by the LTE Downlink and Uplink is the generic frame structure. The LTE specifications define both FDD and TDD modes of operation. This generic frame structure is used with FDD. Alternative frame structures are defined for use with TDD. • LTE frames are 10 msec in duration. They are divided into 10 subframes, each subframe • being 1. 0 msec long. Each subframe is further divided into two slots, each of 0. 5 msec duration. Slots consist of either 6 or 7 ODFM symbols, depending on whether the normal or extended cyclic prefix is employed [source: 3 GPP TR 25. 814]

Generic Frame structure Available Downlink Bandwidth is Divided into Physical Resource Blocks LTE Reference Signals are Interspersed Among Resource Elements [source: 3 GPP TR 25. 814]

OFDM • LTE uses OFDM for the downlink – that is, from the base station to the terminal. OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates. OFDM uses a large number of narrow sub-carriers for multi-carrier transmission. • The basic LTE downlink physical resource can be seen as a time-frequency grid. In the frequency domain, the spacing between the subcarriers, Δf, is 15 k. Hz. In addition, the OFDM symbol duration time is 1/Δf + cyclic prefix. The cyclic prefix is used to maintain orthogonality between the sub-carriers even for a time-dispersive radio channel. • One resource element carries QPSK, 16 QAM or 64 QAM. With 64 QAM, each resource element carries six bits. • The OFDM symbols are grouped into resource blocks. The resource blocks have a total size of 180 k. Hz in the frequency domain and 0. 5 ms in the time domain. Each 1 ms Transmission Time Interval (TTI) consists of two slots (Tslot). • In E-UTRA, downlink modulation schemes QPSK, 16 QAM, and 64 QAM are available.

Downlink Physical Layer Procedures • For E-UTRA, the following downlink physical layer procedures are especially important: ØCell search and synchronization: ØScheduling: ØLink Adaptation: ØHybrid ARQ (Automatic Repeat Request)

SC-FDMA • The LTE uplink transmission scheme for FDD and TDD mode is based on SC-FDMA (Single Carrier Frequency Division Multiple Access). • This is to compensate for a drawback with normal OFDM, which has a very high Peak to Average Power Ratio (PAPR). High PAPR requires expensive and inefficient power amplifiers with high requirements on linearity, which increases the cost of the terminal and also drains the battery faster. • SC-FDMA solves this problem by grouping together the resource blocks in such a way that reduces the need for linearity, and so power consumption, in the power amplifier. A low PAPR also improves coverage and the cell-edge performance. • Still, SC-FDMA signal processing has some similarities with OFDMA signal processing, so parameterization of downlink and uplink can be harmonized.

Uplink Physical Layer Procedures • For E-UTRA, the following uplink physical layer procedures are especially important: ØRandom access ØUplink scheduling ØUplink adaptation ØUplink timing control ØHybrid ARQ

Layer 2 The three sublayers are Medium access Control(MAC) Radio Link Control(RLC) Packet Data Convergence Protocol(PDCP) [Source: E-UTRAN Architecture(3 GPP TR 25. 012 ]

Layer 2 • MAC (media access control) protocol Ø handles uplink and downlink scheduling and HARQ signaling. Ø Performs mapping between logical and transport channels. • Ø Ø Ø RLC (radio link control) protocol focuses on lossless transmission of data. In-sequence delivery of data. Provides 3 different reliability modes for data transport. They are § Acknowledged Mode (AM)-appropriate for non-RT (NRT) services such as file downloads. § Unacknowledged Mode (UM)-suitable for transport of Real Time (RT) services because such services are delay sensitive and cannot wait for retransmissions § Transparent Mode (TM)-used when the PDU sizes are known a priori such as for broadcasting system information.

Layer 2 • PDCP (packet data convergence protocol) Ø handles the header compression and security functions of the radio interface • RRC (radio resource control) protocol Ø handles radio bearer setup Ø active mode mobility management ØBroadcasts of system information, while the NAS protocols deal with idle mode mobility management and service setup

Channels • Transport channels • In order to reduce complexity of the LTE protocol architecture, the number of transport channels has been reduced. This is mainly due to the focus on shared channel operation, i. e. no dedicated channels are used any more. • Downlink transport channels are • Broadcast Channel (BCH) • Downlink Shared Channel (DL-SCH) • Paging Channel (PCH) • Multicast Channel (MCH) • • • Uplink transport channels are: Uplink Shared Channel (UL-SCH) Random Access Channel (RACH)

Channels • Logical channels can be classified in control and traffic channels. • • • Control channels are: Broadcast Control Channel (BCCH) Paging Control Channel (PCCH) Common Control Channel (CCCH) Multicast Control Channel (MCCH) Dedicated Control Channel (DCCH) • • • Traffic channels are: Dedicated Traffic Channel (DTCH) Multicast Traffic Channel (MTCH) Mapping between downlink logical and transport channels Mapping between uplink logical and transport channels

LTE MBMS Concept • MBMS (Multimedia Broadcast Multicast Services) is an essential requirement for LTE. The so-called E-MBMS will therefore be an integral part of LTE. • In LTE, MBMS transmissions may be performed as single-cell transmission or as multi-cell transmission. In case of multi-cell transmission the cells and content are synchronized to enable for the terminal to soft-combine the energy from multiple transmissions. • The superimposed signal looks like multipath to the terminal. This concept is also known as Single Frequency Network (SFN). • The E-UTRAN can configure which cells are part of an SFN for transmission of an MBMS service. The MBMS traffic can share the same carrier with the unicast traffic or be sent on a separate carrier. • For MBMS traffic, an extended cyclic prefix is provided. In case of subframes carrying MBMS SFN data, specific reference signals are used. MBMS data is carried on the MBMS traffic channel (MTCH) as logical channel.

Multiple Antenna Techniques • MIMO employs multiple transmit and receive antennas to substantially enhance the air interface. • It uses spacetime coding of the same data stream mapped onto multiple transmit antennas, which is an improvement over traditional reception diversity schemes where only a single transmit antenna is deployed to extend the coverage of the cell. • MIMO processing also exploits spatial multiplexing, allowing different data streams to be transmitted simultaneously from the different transmit antennas, to increase the end-user data rate and cell capacity. • In addition, when knowledge of the radio channel is available at the transmitter (e. g. via feedback information from the receiver), MIMO can also implement beam-forming to further increase available data rates and spectrum efficiency

Advanced Antenna Techniques • Single data stream / user • Beam-forming Ø Coverage, longer battery life • Spatial Division Multiple Access (SDMA) Ø Multiple users in same radio resource • Ø • • Ø Multiple data stream / user Diversity Link robustness Spatial multiplexing Spectral efficiency, high data rate support

Beamforming & SDMA • Enhances signal reception through directional array gain, while individual antenna has omni-directional gain • • Extends cell coverage • • Suppresses interference in space domain Source: Key Features and Technologies in 3 G Evolution, • • Enhances system capacity http: //www. eusea 2006. org/workshopsession. 2 • • Prolongs battery life 006 -01 -1 1. 3206361376/sessionspeaker. 2006 -0410. 9519467221/file/atdownload • • Provides angular information for user tracking

Services Source: Analysys Research/UMTS Forum 2007]

Conclusions • LTE is a highly optimized, spectrally efficient, mobile OFDMA solution built from the ground up for mobility, and it allows operators to offer advanced services and higher performance for new and wider bandwidths. • LTE is based on a flattened IP-based network architecture that improves network latency, and is designed to interoperate on and ensure service continuity with existing 3 GPP networks. LTE leverages the benefits of existing 3 G technologies and enhances them further with additional antenna techniques such as higher-order MIMO.

GSM History • Several incompatible analog networks precluded roaming – Operators initiated the design of pan-European system in 1982 • First GSM deployment in 1992 – 900 MHz, 1800 MHz and 1900 MHz • Services: 13 Kbps voice, 9. 6 Kbps fax/data, SMS text messages, supplementary services (call waiting, caller id, voice mail) • Objectives: International roaming, maximize system capacity while maintaining speech quality, small handsets, efficient use of battery 10/7/2020 116

GSM Air-interface Features Channel spacing Modulation Interleaving Voice Coder Bit Rate Channel coding 200 k. Hz GMSK 40 ms 13. 4 Kbps Convolutional coding with Viterbi decoding 4. 615 ms 0 3 10/7/2020 1 58 Data Bits 2 3 4 26 Training Bits 5 6 58 Data Bits 117 7 3 8. 25

GSM Transmit chain Rotation e jk Data Convolutional Encoder Interleaving & Framing Differential Encoding x 4 X D/A PA X D/A Gaussian Pulse Shaping Filter 10/7/2020 Analog Low Pass Filter 118 Upconvertor IQ - Mixer

GSM Network Architecture BTS BSC MSC VLR BTS BSC MSC - Mobile Switching Center VLR - Visitor Location Register GMSC - Gateway Mobile Switching Center HLR - Home Location Register EIR - Equipment Information Register Au. C - Authentication Center 10/7/2020 GMSC HLR EIR PSTN/ISDN 119 Au. C

IS– 95 Features • Second generation cellular system proposed by Qualcomm and standardized in U. S. under the TIA forum • IS-95 B enhancement is for packet data through supplemental channel allocation for data rates up to 64 Kbps 10/7/2020 Modulation QPSK Chip Rate 1. 2288 Mcps Nominal Data Rate (RS 1) 9600 Bps Filtered Bandwidth 1. 23 MHz Coding convolutional with Viterbi decoding Interleaving 20 ms span 120

IS-95 Transmit Chain Walsh i Symbol Repetition Convolutional Encoder(1/2, 9) I-Channel PN (1. 2288 Mcps) X SRRC PC bits Block Interleaver 19. 2 ksps 64: 1 Long-Code Generator 10/7/2020 Decimator MUX X 19. 2 ksps 24: 1 Decimator 800 bps X (1. 2288 Mcps) Q-Channel PN 1. 2288 Mcps 121

Forward and Reverse Channels PILOT PAGING SYNC Base Station Traffic Channel -1 ACCESS CHANNEL Traffic Channel -n REVERSE TRAFFIC 10/7/2020 122

CDMA 2000 Enhancements • Backward compatible with IS-95 • Faster forward link power control for enhanced performance • Higher data rates for packet data using supplemental channel allocation – Use of turbo codes for larger frame sizes • Coherent demodulation on the reverse link • Transmit diversity using multiple transmit antennas at the base station 10/7/2020 123

Voice capacity comparison 10/7/2020 124

Cellular Comms Evolution • 3 GPP – collaboration for 3 G based on GSM GPRS EDGE WCDMA HSPA+ TDSCDMA TDHSPA+ • 3 GPP 2 – collaboration for 3 G based on IS-95 CDMA 2000 EV-DO LTE