lecture 13 umts long term evolution - unipa.itilenia/course/13-lte-2013.pdf · release 99 (mar...
TRANSCRIPT
I. Tinnirello
Beyond 3G
� International Mobile Telecommunications (IMT)-2000
introduced global standard for 3G
� Systems beyond IMT-2000 (IMT-Advanced) are set to
introduce evolutionary path beyond 3G
� Mobile class targets 100 Mbps with high mobility and
nomadic/local area class targets 1 Gbps with low mobility
� 3GPP and 3GPP2 are currently developing
evolutionary/revolutionary systems beyond 3G
� 3GPP Long Term Evolution (LTE)
� 3GPP2 Ultra Mobile Broadband (UMB)
� IEEE 802.16-based WiMax is also evolving towards 4G
through 802.16m
I. Tinnirello
3GPP Evolution
�Release 99 (Mar 2000): UMTS/WCDMA
�Release-5 (Mar 2002): HSDPA
�Release-6 (Mar 2005): HSUPA
�Release-7 (2007): DL MIMO, IMS (IP Multimedia Subsystem), optimized realt time services (VoIP, gaming, push-to-talk)
�Long Term Evolution (LTE)
�3GPP work started in Nov 2004
�Standardized in the form of Release 8
�Spec finalized and approved in Jan 2008
�Target deployment starting from 2010
�LTE-Advanced study in progress
I. Tinnirello
IEEE 802.16 Evolution
�802.16 (2002): Line-of-isght fixed operation in 10 to 66 GHz
�802.16a (2003): Air interface support fro 2 to 11 GHz
�802.16d (2004): Minor improvements
�802.16e (2006): Support for vehicular mobility and asymmetrical links
�802.16m (2011): Higher data rate, reduced latency, efficient security mechanisms
I. Tinnirello
Requirements of LTE
� Peak data rate
� 100 Mbps DL/50 Mbps UP within 20 MHz bandwidth
� Up to 200 active users in a cell (5 MHz)
� Less than 5 ms user-plane latency
� Mobility
� Optimized for 0-15 Km/h
� 15-120 Km/h supported with high performance
� Supported up to 350 Km/h or even up to 500 Km/h
� Enhanced multimedia broadcast multicast service (E-MBMS)
� Spectrum flexibility: 1.25-20 MHz
� Enhanced support for end-to-end QoS
I. Tinnirello
LTE Enabling Technologies
�OFDM (Orthogonal Frequency Division Multiplexing)
�SC-FDMA (Single Carrier FDMA)
�MIMO (Multi-input Multi-output)
�Multicarrier channel-dependent resource scheduling
�Fractional frequency reuse
I. Tinnirello
LTE Enabling Technologies
�Single Carrier FDMA (SC-FDMA)
�A new multiple access technique which has similar
structure and performance to OFDMA
�Linearly pre-coded OFDMA
�Utilizes single carrier modulation and orthogonal frequency multiplexing using DFT-spreading in the transmitter and frequency domain equalization in the receiver
�Low PAPR respect to OFDMA
�H.G: Myung et al, “Single Carrier FDMA for Uplink wireless transmission”; IEEE Vehic. Tech.
I. Tinnirello
Key Features of LTE
� Multiple access scheme
� DL: OFDMA; UP: SC-FDMA
� Adaptive modulation and coding
� DL/UP modulations: QPSK, 16QAM and 64QAM
� Convolutional codes and Rel-6 turbo codes
� Advanced MIMO spational multiplexing techniques
� (2 or 4)x(2 or 4) downlink and uplink supported
� Multi-user MIMO
� TDD/FDD
� H-ARQ, mobility support, rate control, security, etc.
I. Tinnirello
LTE Network Architecture
� E-UTRAN: Evolved Universal Terrestrial Radio Access Network
I. Tinnirello
LTE Network Architecture
�eNB: enhanced Node B
�All radio interface-related functions
�MME: Management Mobility Entity
�Manages Mobility, UE identity and security parameters
�S-GW: Serving Gateway
�Node that terminates the interface towards E-UTRAN
�P-GW: Packet Data Network Gateway
�Node that terminates the interface towards PDN
I. Tinnirello
Novel Components
�The overall system architecture was revisited:�New Radio-Access Network (RAN)
�New Core Network (referred as EPC)
�The RAN is responsible of:�Scheduling and radio-resource handling
�Retransmission protocols
�Coding and antenna schemes
�The EPC is responsible of:�Authentication
�Charging functionality
�Connections setup
Evolved Packet System (EPS)
I. Tinnirello
Core Network
�The EPC is a radical evolution from the other core network (GSM/GPRS, WCDMA/HSPA)
�Supports access to the packet-switched domain only (no access to the circuit-switched domain)
�Contains several nodes:�Mobility Management Entity (MME)
�The Serving Gateway (S-GW)
�The Packet Data Network Gateway (PDN/P-GW)
�Other nodes:�Policy and Charging Rules Function
�Home Subscriber Service
�Multimedia Broadcast Multicast Services
�All this nodes are logical nodes!
I. Tinnirello
Circuit-Switched Fall Back
(CSFB)
�LTE is a pure PS-switched network!
�natively supports VoIP using IMS services
�CSFB mechanism allows to handle voice calls by means of
3G/2G networks
I. Tinnirello
OFDM Basic Concept
� OFDM is a special case of Frequency Division Multiplexing (FDM)
� For FDM� No special relationship between the carrier
frequencies
� Guard bands have to be inserted to avoid Adjacent Channel Interference (ACI)
� For OFDM� Strict relation between carriers: fk = k·∆f where
∆f = 1/TU
(TU - symbol period)
� Carriers are orthogonal to each other and can be packed tight
I. Tinnirello
OFDM Transmission model
Channel, h(t)
Modulatorand transmitter
Wireless channel
Receiver and demodulator
I. Tinnirello
Orthogonality – the essential property
� Example: Receiver branch k
� Ideal channel: No noise and no multipath
Tu = 1/∆f gives subcarrier orthogonality over one Tu
=> possible to separate subcarriers in receiver
( )
≠=
==⋅
⋅ ∑ ∫∫ ∑
−
=
⋅−π∆π−
−
=
∆π
qk,0
qk,adte
T
adteea
T
1 k1N
0q
T
0
tT
1kq2j
U
qT
0
ftk2j1N
0q
ftq2jq
U
c U
U
U c
Received signal, r(t)
I. Tinnirello
Example of OFDM
�Lets we have following information bits
�1, 1, -1, -1, 1, 1, 1, -1, 1, -1, -1, -1, -1, 1, -1, -1, …
�Just converts the serials bits to parallel bits
C1 C2 C3 C4
1 1 -1 -1
1 1 1 -1
1 -1 -1 -1
-1 1 -1 -1
-1 1 1 -1
-1 -1 1 1
I. Tinnirello
Example of OFDM cont..
Modulated signal for C1 Modulated signal for C2
Modulated signal for C3 Modulated signal for C4
Modulate each column with corresponding sub-carrier using BPSK
I. Tinnirello
Example of OFDM cont..
�Final OFDM Signal = Sum of all signal
)2sin()()(1
0nttItV
N
nn
π∑−
==
Generated OFDM signal, V(t)
V(t)
I. Tinnirello
Multipath channel
],[ 00 τα
],[ 11 τα
Diffracted and Scattered Paths
Reflected Path
LOS Path
],[ kk τα
I. Tinnirello
Multipath channel (cyclic prefix)
Time[τ]
Amplitude [α]
Example multipath profile
τ0 τ1 τ2 The prefix is made cyclic to avoid inter-carrier-interference (ICI) (maintain orthogonality)
Multipath introduces inter-symbol-interference (ISI)
TU
Prefix is added to avoid ISITUTCP
I. Tinnirello
Multipath channel (cyclic prefix)
� Tcp should cover the maximum length of the time dispersion
� Increasing Tcp implies increased overhead in power and bandwidth (Tcp/ TS)
� For large transmission distances there is a trade-off between power loss and time dispersion
CP Useful symbol CP Useful symbolCP Useful symbol
TUTcp
TS
I. Tinnirello
Multipath channel (frequency diversity)
=
• The OFDM symbol can be exposed to a frequency selective channel
• The attenuation for each subcarrier can be viewed as “flat”– Due to the cyclic prefix there is no need for a complex equalizer
• Possible transmission techniques– Forward error correction (FEC) over the frequency band– Adaptive coding and modulation per carrier
I. Tinnirello
Frequency/subcarrier
Pilot carriers /reference signalsData carriers
Multipath channel (pilot symbols)
� The channel parameters can be estimated based on known symbols (pilot symbols)
� The pilot symbols should have sufficient density to provide estimates with good quality (tradeoff with efficiency)
� Different estimation methods exist� Averaging combined with interpolation
� Minimum-mean square error (MMSE)
Pilot symbol
Time
Frequency
I. Tinnirello
The Peak to Average Power
Problem� A OFDM signal consists of a number of independently
modulated symbols
� The sum of independently modulated subcarriers can have large amplitude variations
� Results in a large peak-to-average-power ratio (PAPR)
∑−
=
∆π⋅=1N
0k
tfk2jk
c
ea)t(x
PA
I. Tinnirello
The Peak to Average Power
Problem
� Example with 8 carriers and BPSK modulation � x(t) plotted
� It can be shown that the PAPR becomes equal to Nc
I. Tinnirello 38
The Peak to Average Power Problem
� High efficiency power amplifiers are desirable� For the handset, long battery life
� For the base station, reduced operating costs
� A large PAPR is negative for the power amplifier efficiency
� Non-linearity results in inter-modulation� Degrades BER performance
� Out-of-band radiation
PA
PIN
POUT
IBO
AM/AM characteristic
OBO
Average Peak
I. Tinnirello
The Peak to Average Power Problem
� Different tools to deal with large PAPR
� Signal distortion techniquesClipping and windowing introduces distortion and out-of-band radiation, tradeoff with respect to reduced backoff
� Coding techniquesFEC codes excludes OFDM symbols with a large PAPR (decreasing the PAPR decreases code space). Tone reservation, and pre-coding are other examples of coding techniques.
� Scrambling techniquesDifferent scrambling sequences are applied, and the one resulting in the smallest PAPR is chosen
I. Tinnirello
Summary
� Advantages
� Splitting the channel into narrowband channels enables significant simplification
of equalizer design
� Effective implementation possible by applying FFT
� Flexible bandwidths enabled through scalable number of sub-channels
� Possible to exploit both time and frequency domain variations (time domain
adaptation/coding + freq. domain adaptation/coding)
� Challenges
� Large peak to average power ratio
I. Tinnirello
Frame Structure
�Two radio frame structures
�Type 1: FS1 FDD
�Type 2: FS2 TDD
�A radio frame has a duration of 10 ms
�A resource block (RB) spans 12 subcarriers over a slot duration of 0.5ms
�One subcarrier has a 15 KHz bandwidth, thus 180
KHz per RB
I. Tinnirello
LTE Physical Channels
� A set of subcarriers lasting some symbols
� DL:
� Physical Broadcast Channel (PBCH)
� Physical Control Format Indicator Channel (PCFICH)
� Physical Downlink Control Channel (PDCCH)
� Physical Hybrid ARQ Indicator Channel (PHICH)
� Physical Downlink Shared Channel (PDSCH)
� Physical Multicast Channel (PMCH)
� UP:
� Physical Uplink Control Channel (PUCCH)
� Physical Uplink Shared Channel (PUSCH)
� Physical Random Access Channel (PRACH)
I. Tinnirello
LTE Transport Channels
�DL:
�Broadcast Channel (BCH)
�Downlink Shared Channel (DL-SCH)
�Paging Channel (PCH)
�Multicast Channel (MCH)
�UP:
�Uplink Shared Channel (UL-SCH)
�Random Access Channel (RACH)
I. Tinnirello
LTE Logical Channels
�Control channels for control-plane info
�Broadcast Control Channel (BCCH)
�Paging Control Channel (PCCH)
�Common Control Channel (CCCH)
�Multicast Control Channel (MCCH)
�Dedicated Control Channel (DCCH)
�Traffic channels for user-plane info
�Dedicated Traffic Channel (DTCH)
�Multicast Traffic Channel (MTCH)
I. Tinnirello
RRC Layer
�Terminated in eNB on the network side
�Broadcast, Paging
�RRC connection management
�Radio Bearer management
�Mobility Functions
�UE measurement reporting and control
�RRC states:
�RRC_IDLE, RRC_CONNECTED
I. Tinnirello
Resource Scheduling of Shared
Channels
�Dynamic resource scheduler resides in eNB on MAC layer
�Radio resource assignment based on radio condition, traffic volume and QoS requirements
�Radio resource assignment consists of:
�Physical Resource Block (PRB)
�Modulation and Coding Scheme (MCS)
I. Tinnirello
Radio Resource Management
�Radio Bearer Control (RBC)
�Radio Admission Control (RAC)
�Connection mobility Control (CMC)
�Dynamic resource allocation (DRA) or packet scheduling
�Inter-cell interference coordination (ICIC)
�Load Balancing (LB)
�Other: ARQ, H-ARQ, Rate Control, DRX, QoS, Scurity
I. Tinnirello
Uplink Channels
� Transport Channels (TrCH)
� UL-SCH Uplink Shared Channel
� RACH Random Access Channel
� Control Information
� UCI Uplink Control Information
� Mapping to Physical Channels
I. Tinnirello
Uplink Control Signalling
�Conveys L1 and L2 control information
�HARQ acknowledhements for DL-SCH blocks
�Channel quality reports: CQI, RI and PMI
�Scheduling requests
�Transmitted on
�PUCCH if no resources are allocated to UL-SCH
�Multiplexed with UL-SCH on the PUSCH (before
SC_FDMA) if there is a valid schedule grant
I. Tinnirello
Channels and Signals
� A physical channel is defined as a set of resource elements carrying information originating at a higher layer or in support to the physical layer itself
� For the uplink, the following PHY channels are defined..
� PUSCH: Phy Uplink Shared Channel
� PUCCH: Phy Uplink Control Channel;
� PRACH: Phy Random Access Channel
� ..plus the following signals
� Souding Reference Signal (SRS)
�Not associated with any other transmission
� Demodulation Reference Signal (DRS)
�associated with PUSCH or PUCCH, for channel estimation
�Desired features: small power variations in time and frequency
I. Tinnirello
Sounding Reference Signal
� eNodeB needs channel quality information in order to assign resources
� From DRS eNobeB can only get channel estimates on UE allocated spectrum
� No information available out of assigned spectrum
� SRS overcomes this problem!
I. Tinnirello
Sounding Reference Signal (2)
� May cover large frequency span (not assigned to UE)
� Multiple of 4 resource blocks span
� Can be transmitted from every 2ms to every 160ms
� Transmitted on last symbol of subframe (at most every 2 subframes)
� Multiple UEs can transmit simultaneously thanks to cyclic shifts (orth codes)� Wideband: one transmission covers band of interest
� Frequency hopping: narrowband, location changes with time
I. Tinnirello
Physical Uplink Control Channel
�PUCCH:
�Conveys uplink control information
�Used when UE has no valid schedule grant
�Never transmitted simulanteously with PUSCH
�Transmitted with frequency hopping on band edges to leave contiguos bandwidth to PUSCH
�Multiple PUCCH over a RB by means of orthogonal codes
I. Tinnirello
Physical Uplink Shared Channel
� PUSCH:
� Carries data and control information, by means of the following
processing chain
� Allocated spectrum to a UE can changge every subframe
I. Tinnirello
Downlink Channels
� Transport Channels (TrCH)
� DL-SCH Downlink Shared Channel
� BCH Broadcast Channel
� PCH Paging Channel
� MCH Multicast Channel
� Control Information
� CFI Control Format Indicator
� HI HARQ Indicator
� DCI Downlink Control Information
� Mapping to Phy Channels
I. Tinnirello
Downlink Channels and Signals
� Phy Channel: set of resource elements carrying information from higher layers
� Phy DL Shared Ch PDSCH; Phy DL Control CH PDCCH; Phy Multicast
Ch PMCH; Phy Broadcast Channel PBCG; Phy Control Format Indicator
Channel PCFIC; Phy HARQ Indicator Channel PHICH
� Phy Signal: set of resource elements used for physical layer information
� Reference Signals
� Synchronization Signals
I. Tinnirello
Phy Donwlink Channels
�PCFICH: Specifies how many OFDM symbols are used for PDCCH transmission
�PDCCH: carries control information including scheduling assignments;
�PHICH: hybrid ARW and NACK indicators for Ues
�PDSCH: main downlink channel to transport data blocks to the mobiles
�PBCH: broadcast information with a coded block of 1920 samples every 40 ms
I. Tinnirello
Donwlink Reference Signals
�Used for channel estimations and to obtain quality measurements at the UE side
�Cell-specific:
�Structure depends on the cell ID
�UE- specific
�Used for beamforming
�Arranged across time and frequency
I. Tinnirello
Synchronization Signals
�Always transmitted in the same place regardless of the total bandwidth
�First 72 carriers around DC carrier
�OFDM symbols 5 and 6 of first slot in subframe 0 and 5
I. Tinnirello
Downlink Processing Chain
�The general structure of downlink physical channels processing is the following one (for PDSCHs)
I. Tinnirello
Cell Search
� UE acquires time and frequency synchronization with a cell and detects the cell ID of that cell
� Based on BCH and hierarchical Synchronization signals
� Primary-SCH and Secondary-SCH are transmitted twice per radio frame for FDD
� Cell search:
� 5 ms timing identified using P-SCH
� Radio timing and group ID from S-SCH
� Full cell ID from DL RS
� Decode BCH
I. Tinnirello
Random Access
�Open loop power controlled with power ramping
�RACH signal bandwidth: 1.08 MHz (6RBs)
I. Tinnirello
LTE Release 10 and beyond
�Carrier aggregation to give up to 100MHz bandwidth
�Downlink transmission with 8 antennas and layers
�Uplink multi-antenna up to 4 antennas
�Coordinated Multi Point transmission
�Relaying from Relay Nodes to eNB
�Latency Improvements
�Self Optimising Networks enhancements
�Home eNobeB (femtocells)