3GPP(LTE)coursePresented By: Eng.karim Banawan. Eng.Yasser Youssry.

Mobile Communication part (4) : 4G mobiles

Eng. Karim Banawan Faculty of Engineering Electronics and communication department

OFDM AND OFDMA TECHNOLOGIES

OUTLINE

NEED FOR MULTI-CARRIER OFDM ENTERS INTO THE PICTURE FFT / IFFT GUARD TIME INSERTION OFDM DRAWBACKS CHANNEL ESTIMATION OFDM

BLOCK DIAGRAM

SIMULATION

RESULTS

NEED FOR MULTICARRIERTime Domain Analysis

NEED FOR MULTICARRIER cont.

Pulse completely distorted. ISI is significant in this case.

Pulse extended but the extension are much smaller than T the output behaves like the transmitted rectangular pulse.

NEED FOR MULTICARRIER cont.Frequency Domain Analysis

NEED FOR MULTICARRIER cont.Conclusion

Wide pulses is needed for simple equalization, But Narrow pulses is needed for high data rate

Solution

Multiplexing

NEED FOR MULTICARRIER cont.

NEED FOR MULTICARRIER cont.Problem

Orthogonality

Solution

NEED FOR MULTI-CARRIERcont.

NEED FOR MULTI-CARRIERcont.

OFDM ENTERS INTO THE PICTUREInterference Orthogonality B.W efficiency Min Separation

OFDM ENTERS INTO THE PICTURE cont.Min

Separation ProblemSolution

Difficult Implementation with traditional oscillators DFT But DFT needs high processing Solution Easy implementation using FFT/IFFT

FFT / IFFT

FFT/IFFT

GUARD TIME INSERTIONChannel Filtering

GUARD TIME INSERTIONcont.Problem

.ISI occurs

GUARD TIME INSERTIONcont.Solution Cyclic Prefix

. No ISI Circular Convolution achieved .

Cyclic prefix The

CP allows the receiver to absorb much more efficiently the delay spread due to the multipath and to maintain frequency Orthogonality. CP that occupies a duration called the Guard Time (GT), often denoted TG, is a temporal redundancy that must be taken into account in data rate computations.

The

OFDM DRAWBACKScont.

Peak to Average Power Ratio (PAPR)

OFDM DRAWBACKScont.Sensitivity

to frequency offset

CHANNEL ESTIMATIONPilotR e ce i d ve S i n a l a fte r g FFT

Based Channel EstimationE sti a te d m C hannel R e sp o n se

K n o w n Pi o ts l

CHANNEL ESTIMATIONcont. Pilot Time (OFDM Symbols) High channel frequency selectivity

Arrangement Types Block Pilot Patterns Comb Pilot PatternsFrequency( sub carriers)Time (OFDM Symbols) rapid changing channels

Frequency( sub carriers)

Pilot symbols Data symbols

OFDMAOFDMA is

a multiple access method based on

OFDM signaling that allows simultaneous transmissions to and from several users along with the other advantages of OFDM.

OFDM versus OFDMA

IEEE802.16d Fixed WiMAX,256-OFDM

IEEE802.16e Mobile WiMAX

DIVERSITY AND MIMO PRINCIPLES

What is diversity?

Is a technique that combats the fading by ensuring that there will be many copies of the transmitted signal effected with different fading over time, frequency or space.

1-Time diversity:We averaging the fading of the channel over time by using : 1-The channel coding and interleaving. 2-Or sending the data at different times. to explain this we will see an example:

1-time diversity:|H ( t ) |

t

No interleaving x1 x2 x3 x4 y1 y2 y3 y4 z1 z2 z3 z4 h1

h2 h3 h4 interleaving z4 h4

x1 y1 z1 h1 x2 y2 z2h2 x3 y3 z3h3 x4 y4

So we can see that only the 3rd symbol from each codeword lost and we can recover them from the rest symbols in each

2- frequency diversity:This type of diversity used for the frequency selective channels as we will averaging the fading over the frequency by using: 1-Multi-carrier technique like OFDM. 2-FHSS (frequency hope spread spectrum). 3-DSSS (direct sequence spread spectrum).

2- frequency diversity:

We can see that each sub-band will effecting with different fading over the frequency.

3-spatial diversity:we will have many copies of the transmitted signal effects with different fading over the space . we use multi-antenna systems at the transmitter or the receiver or at both of them.

Receive diversity:

1-The receiver will has many antennas . 2-Each one has signal effecting with different fading. 3-number of different paths =Mr.

Diversity order=Mr

MIMO:

In this type we use multi antennas at both the transmitter and receiver as shown. Diversity order=Mt x Mr

Notes:

The higher diversity order we have the better we combat the fading

Notes:1-The diversity reduces the BER of the communication system. 2-Diversity order

BER

.

Notes:

The distance between the antennas must be larger than the coherent distance to ensure that data streams are not correlated .

Question?

How the receiver get the signal from the many copies reached ? Answer

Diversity combining technique1-Combines the independent fading paths signals to obtain a signal that passed through a standard demodulator. 2-The techniques can be applied to any type of diversity. 3-combining techniques are linear as the output of is a weighted sum of the different fading signals of branches. 4-It needs co-phasing.

Diversity combining technique

The signal output from the combiner is the transmitted signal s(t) multiplied by a random complex amplitude term

Fa d i g o f th e n p a th

Type of technique

Diversity order

R a n d o m S N R fro m th e co m b i e r n

Diversity combining technique

selection combining technique1-the combiner outputs the signal on the branch with the highest SNR . 2-no need here for the cophasing.

0

0

1

0

Threshold combining technique

As in SC since only one branch output is used at a time and outputting the first signal with SNR above a given threshold so that co-phasing is not required.

NR so that its performance less than the SC technique .

Special case at diversity order = 2 ( SSC )

Maximal ratio combining

In maximal ratio combining (MRC) the output is a h1* weighted sum of all branches due to its SNR

h2*

h3*

hi *

Equal gain combining technique A simpler technique is equal-gain

combining, which co-phases the signals on each branch and then combines them with equal weighting

MIMO Traditional

diversity is based on multiple receiver antennas Multiple-In Multiple-Out (MIMO) is based on both transmit and receive diversity Also known as Space Time Coding (STC) With Mt transmission antennas and Mr receiver antennas we have Mt Mr branches Tx

and Rx processing is performed over space (antennas) and time (successive symbols)

47

MIMO or STC In

Mobile communication systems it may be difficult to put many antennas in the mobile unit Diversity in the downlink (from base station to mobile station) can be achieved by Multiple-In Single-Out (MISO) (i.e., Mr=1) In

the uplink (from mobile station to base station) diversity is achieved my conventional diversity (SIMO) Hence, all diversity cost is moved to the base station All 3G and 4G mobile communication system employ MIMO in their standard48

Type of MIMOTwo

major types of space time coding Space time block coding (STBC) Space time trellis coding (STTC)

STBC

is simpler by STTC can provide better performance STBC is used in mobile communications. STTC is not used in any systems yet We will talk only about STBC49

Space Time Block CodesThere

are few major types

Transmit diversity: main goal is diversity gain Spatial multiplexing: main goal is increase data rate Eigen steering: main goal is both. Requires knowledge of the channel at the transmitter side Mix of the above: Lots of researchTransmit

diversity, spatial multiplexing and simplified version of Eigen steering are used in 3G50

Transmit DiversityTake Two

Mt=2 and Mr=1

symbols so and s1 are transmitted over two transmission periods No change in data rate (denoted as rate 1 STBC) Channel is known at receiver only

51

Transmit Diversity Transmission TransmissionA nt Ant1 matrix:6 4 o7 48 s o s1 Timeo S = * s1 s o* Time1

matrix columns are orthogonal to guarantee simple linear processing at the receiver Other transmission matrices are defined in literature ro s o s1 g o n o R = = + Received signalr is: s * s * g n o 1 1 1 1 Performance

is same as MRC with M=2 However, if Tx Power is the same, then

52

Transmit Diversity Take

Mt=2 and Mr=2

Performance

is the same as MRC with M=4 However, if Tx Power is the same, then transmit diversity (2x2) is 3 dB worse than (1x4)

53

PerformanceRatio Receiver Combining Note 3 dB difference in favor of Rx MRC diversity Reference: S. Alamouti, a simple transmit diversity technique for wireless communications, IEEE JSAC, October 98No diversity Order 2 Orde r 4

MRRC=Maximal

54

Spatial Multiplexingro = s o g o + s1 g 1 r1 = s o g 2 + s1 g 3 Purpose

is to increase data rate (2x2 gives twice data rate) The 4 gains must be known at receiver Simplest way zero forcing algorithm:

ro g o g 1 so r = g g s 3 1 2 2 43 1 14G

r 1 s o H H o s = G G G r 1 155

Spatial Multiplexingro = s o g o + s1 g 1 r1 = s o g 2 + s1 g 3

Optimum

method: Maximum Likelihood

eo2 + e1 = ro s o g o s 1 g 1 + r1 s o g 2 s 1 g 3

Try all combinations of s1 and s2 Find the combination that minimizes the squared error: 2 2 2 Complexity increases with high order modulation56

PerformanceEqual rate comparison Reference: David Gesbert, Mansoor Shafi, Da-shan Shiu, Peter J. Smith, and Ayman Naguib, From theory to practice: an overview of MIMO space time coded wireless systems, IEEE JSAC, April 2003 57

Z e ro fo rci g n ML

A l m out a i

Eigenvalue SteeringAssume

a MIMO system

58

Eigenvalue Steering Example Any

with Mt = 2 and Mr=4

y 1 h11 y h 2 = 21 y 3 h31 y 4 h4 2 1 41

matrix H can be represented using Singular Value H =U V H Decomposition as

H

h12 h 22 h32 h 42 43

n1 x 1 n 2 x + n 2 3 n 4

[ y ] = H [ x ] +[ n]

U

is Mr by Mr and V is Mt by Mt unitary matrices is Mr by Mt diagonal matrix,

59

Eigenvalue Steering Using

transmit pre-coding and receiver shaping

% y =U H ( H x + n ) = U H ( U VH

% = U H ( U V H V x + n ) % = U H U V H V x +U H n % % = x +n60

x +n)

Eigenvalue Steering This

way we created r paths between the Tx and specific Rx without any cross interference The channel (i.e., Channel State Information) must be known to both transmitter and receiver The value of r= rank of matrix H, r min(Mt, M r) Not

all r paths have good SNR Data rate can increase by factor r See Appendix C for Singular Value Decomposition See Matlab function [U,S,V] = svd(X)

61

Example

Reference: Sanjiv Nanda, Rod Walton, John Ketchum, Mark Wallace, and Steven Howard, A high-performance MIMO OFDM wireless LAN, IEEE Communication Magazine, February 2005

62

INTRODUCTION TO LTE AND ITS UNIQUE TECHNOLOGIES.

What is LTE??The

3GPP LTE is acronym for long term evolution of UMTS . In order to ensure the competitiveness of UMTS for the next 10 years and beyond, concepts for UMTS Long Term Evolution ( LTE ) have been introduced in 3GPP release 8. 8 LTE is also referred to as EUTRA (Evolved UMTS Terrestrial Radio Access) or E - UTRAN (Evolved UMTS Terrestrial Radio Access Network)

What is LTE(cont.)?The

architecture that will result from this work is called EPS (Evolved Packet System) and comprehends E - UTRAN (Evolved UTRAN) on the access side and EPC (Evolved Packet Core) on the core side. Can be considered the real 3 . 9G & invited to join the 4G family. Also considered a competitive system to mobile WiMAX as we will show

What is LTE (cont.)?

LTE DESIGN TARGETS

( a ) capabilities:Scalable BW: 1.25, 2.5, 5.0, 10.0 and 20.0 MHz. Peak data rate:Downlink (2 Ch MIMO) peak rate of 100 Mbps in 20 MHz channel Uplink (single Ch Tx) peak rate of 50 Mbps in 20 MHz channel

Supported antenna configurations:Downlink: 4x4,4x2, 2x2, 1x2, 1x1 Uplink: 1x2, 1x1

Duplexing modes: FDD and TDD Number of active mobile terminals: LTE

should support at least 200 mobile terminals in the active state when operating in 5 MHz. In wider allocations than 5 MHz, at least 400 terminals should be supported

Spectrum efficiencyD o w n l n k : 3 to 4 x H S D PA R e l 6 5 b i / s/ H z i . ts U p l n k : 2 to 3 x H S U PA R e l 6 2 . 5 b i / s/ h z i . ts

LatencyC - p l n e : < 5 0 1 0 0 m se c to e sta b l sh U a i pl ne a U -p l n e : < 1 0 m se c fro m U E to se rve r a

MobilityO p ti i d fo r l w sp e e d s (< 1 5 km / h r) m ze o H i h p e rfo rm a n ce a t sp e e d s u p to 1 2 0 g km / h r M a i ta i l n k a t sp e e d s u p to 3 5 0 km / h r n n i

CoverageFu l p e rfo rm a n ce u p to 5 km l

INTRODUCTION TO LTE KEY TECHNOLOGIES

(1)OFDM and OFDMA:One of the key technologies used in LTE and WiMAX systems. The problem ???Due to the multipath the signal is received from many paths with different phases that will result in DELAY SPREAD :symbol received along a delayed : path to bleed into a subsequent symbol (ISI)

FREQUENCY SELECTIVE FADING: : some frequencies within the signal passband undergo constructive interference while others encounter destructive interference.The composite received signal is distorted

Old solutions of multipath fading include directchannel equalization or spread spectrum techniques(complex receiver is needed).

OFDM:OFDM systems break the available bandwidth into many narrower sub-carriers and transmit the data in parallel streams each OFDM symbol is preceded by a cyclic prefix (CP), which is used to effectively (CP eliminate ISI.

In practice, the OFDM signal can be generated using IFFT with a CP of sufficient duration, preceding symbols do duration not spill over into the FFT period and also this satisfy that the output convolution with channel is complex gain multiplication. multiplication Also, Once the channel impulse response is determined (by periodic transmission of known reference signals), distortion can be corrected by applying an amplitude and phase shift on a subcarrier-by-subcarrier basis. Problems of OFDM are: susceptibility to carrier frequency errors (due either to local oscillator offset or Doppler shifts) and a large signal peak-to-average power ratio (PAPR).

OFDMA OFDMA is

a multiple access method based on OFDM signaling that allows simultaneous transmissions to and from several users along with the other advantages of OFDM.

OFDM versus OFDMA

IEEE802.16d Fixed WiMAX,256-OFDM

IEEE802.16e Mobile WiMAX

( 2 ) Multi antenna transmission LTE

and WiMAX targets extreme performance in terms of Capacity Coverage Peak data rates

Advanced multi-antenna solutions is the key tool to achieve this Multi antenna systems are integral part of those systems Different antenna solutions needed for different scenarios/targets High peak data rates spatial multiplexing Good coverage Beam-forming

(3 ) Hybrid ARQ with soft combining

in LTE and WiMAX to allow the terminal to rapidly request retransmissions of erroneously received transport blocks. The underlying protocol multiple parallel stop-and-wait hybrid ARQ processes Incremental redundancy is used as the soft combining strategy and the receiver buffers the soft bits to be able to do soft combining between transmission attempts.

used

( 1 ) Spectrum

flexibility :

A high degree

of spectrum flexibility is one of the main characteristics of the LTE radio access. The aim of this spectrum flexibility is to allow for thedeployment of the LTE radio access in diverse spectrum.The

flexibility includes:

Different duplex arrangements. Different frequency-bands-of-

(a) 3G LTE Duplex arrangement

(b) 3G LTE Bandwidth flexibility

LTE physical layer supports any bandwidth from 1.25 MHz to well beyond 20 MHz in steps of 200 kHz (one Resource Block)

(2) Channel-dependent scheduling and rate adaptationLTE

use of shared-channel transmission, in which the timefrequency resource is dynamically shared between users.

(3)Interference coordination(soft reuse)Adaptive

reuse

Cell-center users: Reuse = 1 Cell-edge users: Reuse > 1Relies

on access to frequency domain Applicable for both downlink OFDM and uplink SC-FDMA

( 4 ) SC - FDMA :LTE uplink requirements differ from downlink

requirements.

power consumption is a key consideration for UE

terminals. The high PAPR and related loss of efficiency associated with OFDM signaling are major concerns.

As a result, an alternative to OFDM was sought

for use in the LTE uplink. Single Carrier Frequency Domain Multiple Access (SC-FDMA) is well suited to the LTE uplink requirements. The basic transmitter and receiver architecture is very similar (nearly identical) to OFDMA, and it offers the same degree of multipath protection. because the underlying waveform is essentially single-carrier, the PAPR is lower.

Basic block diagram: transmitter :a QAM modulator coupled withthe addition of the cyclic prefix. This will eliminate ISI as OFDMA

Reciever: by using FFT & CP simple equalizerare used (as OFDM). Multipath distortion is handled in the same manner as in OFDM(removal of CP, conversion to the frequency domain, then apply the channel correction on a subcarrier-by subcarrier

LTE practical SC - FDMA :-

The practical transmitter is likely to take advantage of FFT/IFFT blocks as well to place the transmission in the correct position of the transmit spectrum in case of variable transmission bandwidth.

SC-FDMA receiver

Frequency domain equalization (FDE) using DFT/IDFT is more practical for such channels.

The fact of transmitting only a single symbol at a time ensures a low transmitter waveform, compared with the OFDMA case. The resulting PAR/CM impact on the amplifier is thus directly dependent on the modulation, whereas with the OFDMA case it is the amount of subcarriers. SC-FDMA subcarriers can be mapped in one of two ways: localized or distributed However, the current working assumption is that LTE will use localized subcarrier mapping. mapping This decision was motivated by the fact that with localized mapping, it is possible to exploit frequency selective gain via channel dependent scheduling (assigning uplink frequencies to UE based on favorable propagation conditions).

(5) LTE Multicast/Broadcast MBMS

Multimedia Broadcast/Multicast Service OFDM allows for high-efficient MBSFN operation Multicast/Broadcast Single-Frequency Networking Identical transmissions from set of tightly synchronized cells Increased received power and reduced interference

Substantial boost of MBMS system throughput LTE allows for multicast/broadcast and unicast on the same carrier as well as dedicated multicast/broadcast carrier

LTE RADIO INTERFACE ARCHITECTURE

IntroductionSimilar

to WCDMA/HSPA, as well as to most other modern communication systems, the processing specified for LTE is structured into different protocol layers. layers note that the LTE radio-access architecture consists of a single node the eNodeB . The eNodeB communicates with one or several mobile terminals, also known as UEs

Packet Data Convergence Protocol (PDCP)performs

IP header compression to reduce the number of bits to transmit over the radio interface. The header compression mechanism is based on Robust Header Compression (ROHC)a standardized headerROHC compression algorithm also used in WCDMA PDCP is also responsible for ciphering and integrity protection of the transmitted data. At the receiver side, the PDCP protocol performs the corresponding deciphering and decompression operations.

Radio Link Control (RLC) is

responsible for segmentation/concatenation, segmentation concatenation retransmission handling, and in sequence delivery to higher layers. Unlike WCDMA, the RLC protocol is located in the eNodeB since there is only a single type of node in the LTE radio-access-network architecture. The RLC offers services to the PDCP in the form of radio bearers . There is one RLC entity per radio bearer configured for a terminal.

Medium Access Control (MAC)handles

hybrid - ARQ retransmissions and uplink and downlink scheduling. scheduling The scheduling functionality is located in the eNodeB, which has one MAC entity per cell, for both uplink and downlink. The hybrid - ARQ protocol part is present in both the transmitting and receiving end of the MAC protocol. The MAC offers services to the

MAC scheduling

The basic operation of the scheduler is so-called dynamic scheduling , where the eNodeB in each 1 ms TTI makes a scheduling decision and sends scheduling information to the selected set of

Downlink scheduling

UL scheduling dynamically

dynamically

controlling the terminal(s) to transmit to the set of resource blocks upon which the terminals DLSCH should be transmitted. Transport-format selection(selection of transport-block size, modulation scheme, and antenna mapping) And logical-channel

control which mobile terminals are to transmit on their ULSCH

and

on which uplink time/frequency resources uplink scheduling decision is taken per mobile terminal and not per radio bearer.

Physical Layer (PHY)handles

coding/decoding, modulation/demodulation, multiantenna mapping, and other typical physical layer functions. The physical layer offers services to the MAC layer in the form of transport channels

DOWNLINK PHY LAYER OF (LTE)

LTE Generic Frame StructureThe generic frame structure is used with FDD.(TDD is also supported but not the trend). LTE frames are 10 msec in duration. They are divided into 10 subframes, subframes each subframe being 1.0 msec long. Each subframe is further divided into two slots, each of 0.5 msec duration. slots Slots consist of either 6 or 7 ODFM symbols, depending on whether the normal or extended cyclic prefix is employed.

Different

time intervals within the LTE radio-access specification are defined as multiples of a basic time unit Ts = 1/30 720 000. The time intervals can thus also be expressed as Tframe= 307 200 Ts and Tsubframe= 30 720 Ts

OFDMA For LTE Downlink :OFDMA is an excellent choice of multiplexing scheme for the 3GPP LTE downlink allows the access of multiple users on the available bandwidth. Each user is assigned a specific time frequency resource. resource Allocation of PRBs is handled by a scheduling function at the 3GPP base station (eNodeB). The total number of available subcarriers depends on the overall transmission bandwidth of the system. The LTE specifications define parameters for system bandwidths from 1.25 MHz to 20 MHz as shown in Table.

A PRB is defined as consisting of 12 consecutive subcarriers for one slot (0.5 msec) in duration. A PRB is the smallest element of resource allocation assigned by the base station scheduler.LTE does not employ a PHY preamble to facilitate carrier offset estimate, channel estimation,

Downlink resource block the

OFDM subcarrier spacing has been chosen to f = 15 kHz. Sampling rate fs =15 000NFFT , where NFFT is the FFT size the sampling rate f NFFT will be a multiple or submultiple of the WCDMA/HSPA chip rate (3.84 Mcps) in the frequency domain the downlink subcarriers are grouped into resource blocks where each resource block consists of 12 consecutive subcarriers. In subcarriers addition, there is an unused DC subcarrier in the center of the downlink band. it may be subject to un-

Downlink reference signalTo

carry out coherent demodulation of different downlink physical channels, a mobile terminal needs estimates of the downlink channel Cell-specific downlink reference signals. UE-specific reference signal. MBSFN reference signals

Cell-specific downlink reference signals consists

of known reference symbols inserted within the first and third last OFDM symbol of each slot and with a frequency-domain spacing of six subcarriers the mobile terminal should carry out interpolation/averaging over multiple interpolation reference symbols There are 504 different reference signal sequences defined for LTE, where eachsequence corresponds to one out of 504 different physical-layer cell identities

In

case of downlink multi - antenna transmission the mobile terminal should be able to estimate the downlink channel corresponding to each transmit antenna reference-signal structure for each antenna port in case of multiple antenna ports within a cell: In case of two antenna the

reference symbols of the second antenna port are frequency multiplexed with the reference symbols of the first antenna port, with a frequency-domain offset of three subcarriers. In case of four antenna ports ,the reference symbols for the third and

UE-specific reference signalsLTE

also allows for more general beam-forming. In order to allow for channel estimation also for such transmissions, additional reference signals are needed. As such a reference signal can only be used by the specific terminal to which the beam-formed transmission is intended, it is referred to as a UE-specific reference signal .

LTE block diagram (DL transport channel processing)

(1)CRC insertion:In

the first step of the transport-channel processing, a 24 - bit CRC is calculated for and appended to each transport block. The CRC allows for receiver side detection of errors in the decoded transport block. The corresponding error indication is then, for example, used by the downlink hybrid-ARQ protocol as a trigger for requesting retransmissions .

The

LTE Turbo-coder internal Turbo interleaver is only defined for a limited number of code-block sizes with a maximum block size of 6144 bits. bits In case the transport block, including the transport-block CRC, exceeds this maximum code-block size, codeblock segmentation is applied before Turbo coding. Code - block segmentation implies that the transport block is segmented into smaller code blocks

(2)Code-block segmentation and per-code-block CRC insertion:

In

order to ensure that the size of each code block is matched to the set of available codeblock sizes, filler bits may have to be inserted at the head of the first code An additional (24 bits) CRC is calculated for and appended to each code block. Having a CRC per code block allows for early detection of

(3) FEC(forward error The

correction):-

UL-SCH uses the same rate 1 / 3 turbo encoding scheme (two 8-state constituent encoders and one internal interleaver) as the DL-SCH.

The older interleaver used in HSPA been replaced by QPP based interleaving . the QPP interleaver provides a mapping from the input (non-interleaved) bits to the output (interleaved) bits according to the function:

(4) Rate-matching and physicallayer hybrid-ARQ functionality The

task of the rate-matching and physicallayer hybrid-ARQ functionality is to extract , from the blocks of code bits delivered by the channel encoder, the exact set of bits to be transmitted within a given TTI. The outputs of the Turbo encoder (systematic bits, first parity bits, and second parity bits) are first separately interleaved. interleaved The interleaved bits are then inserted into what can be described as a circular buffer with the systematic bits inserted first, followed by alternating insertion of the first and second parity bits. The bit selection then extracts consecutive bits from the circular buffer

(5) Bit-level scramblingLTE

downlink scrambling implies that the block of code bits delivered by the hybrid-ARQ functionality is multiplied (exclusive - or operation) by a bit-level scrambling sequence (usually a gold code). In general, scrambling of the coded data helps to ensure that the receiver-side decoding can fully utilize the processing gain provided by the channel code

(6) ModulationThe set of modulation schemes supported for

the LTE downlink includes QPSK, 16QAM, and 64QAM. All these modulation schemes are applicable to the DL-SCH, PCH, and MCH transport channels. only QPSK modulation can be applied to the BCH transport channel.

(7) Multi antenna transmissionLTE

supports the following multiantenna transmission schemes or transmission modes , in addition to single-antenna transmission: Transmit diversity Closed-loop spatial multiplexing including codebook-based beamforming Open-loop spatial multiplexing

Transmit diversityLTE

transmit diversity is based on Space Frequency Block Coding (SFBC) SFBC implies that consecutive modulation symbols Si and Si+1 are mapped directly on adjacent subcarriers on the first antenna port. On the second antenna port, the swapped and transformed symbols - S*i+1 and Si*are transmitted on the corresponding subcarriers

SFBC/FSTD(combined SFBC and (Frequency Shift Transmit Diversity

spatial

multiplexing implies that multiple streams or layers are transmitted in parallel, thereby allowing for higher data rates The LTE spatial multiplexing may operate in two different modes: closed-loop spatial multiplexing and open-loop spatial multiplexing where closed-loop spatial multiplexing relies on more extensive feedback from the mobile terminal.

Closed loop Spatial multiplexing

General beam-formingclosed-loop

spatial multiplexing includes beam-forming as a special case when the number of layers equals one. This kind of beamforming can be referred to as codebook-based beamforming , indicating that the network selects one pre-coding vector (the beam-forming vector) from a set of pre-defined pre-coding vectors (the codebook ) with the selection, for example, based on the terminal reporting a recommended precoding vector.

UPLINK PHY LAYER OF (LTE)

Uplink transmission schemeLTE

uplink transmission is based on so-called DFTS - OFDM transmission Which is a single-carrier transmission scheme that allows for flexible bandwidth assignment orthogonal multiple access not only in the time domain but also in the frequency domain. the use of a cyclic prefix allows low-complexity frequency-domain equalization at the receiver side.

Transmission methodM determines the BW

Mapping is applied to consecutive carriers localized

DFT implementation The

DFT size should preferably be constrained to a power of two. However, such a constraint is in direct conflict with a desire to have a high degree of flexibility of the bandwidth that can be dynamically assigned to a mobile terminal for uplink transmission all possible DFT sizes should rather be allowed. For LTE, a middle way has been adopted LTE where the DFT size is limited to products of the integers two , three , and five . For example, DFT sizes of 60, 72, and 96 are allowed but a DFT size of 84 is not allowed.

Uplink physical resource parametersChosen

to be aligned, as much as aligned possible, with the corresponding parameters of the OFDM-based LTE downlink spacing equals 15 kHz resource blocks, consisting of 12 subcarriers Any number of uplink resource blocks ranging from a minimum of 6-110 resource blocks. time-domain structure, the LTE uplink is very similar to the downlink

However,

in contrast to the downlink, no unused DC -

Uplink reference signalsDemodulation

( DRS )

reference signals

reference signals for channel estimation are also needed for the LTE uplink to enable coherent demodulation of different uplink physical channels are transmitted on the uplink to allow for the network to estimate the uplink channel quality at different frequencies .

Sounding

reference signals ( SRS )

Basic principles of uplink DRS transmissionDue

to the importance of low power variations for uplink transmissions The principles for uplink reference - signal transmission are different from those of the downlink certain DFTS-OFDM symbols are exclusively used for referencesignal transmission, a reference signal is transmitted within the fourth symbol of

Uplink sequencesLimited

power variations in the frequency domain to allow for similar channel-estimation quality for all frequencies. Limited power variations in the time domain to allow for high power - amplifier efficiency. Furthermore, sufficiently many reference - signal sequences of the same length, should be available to easily assigning reference-signal sequences to cells

ZadoffChu sequenceshave

the property of constant power in both the frequency and the time domain.

ZadoffChu

sequences are not suitable for direct usage as uplink: to maximize the number of ZadoffChu sequences and to maximize the number of available uplink reference signals, prime - length ZadoffChu Zadoff sequences would be preferred. At the same time, the length of the uplink reference-signal sequences should be

Phase-rotated referencesignal sequencesby

cyclically extending different prime-length Zadoff Chu sequences . Additional reference-signal sequences can be derived by applying different linear phase rotations to the same basic reference-signal sequences

sounding reference signals (SRS) the uplink channel quality estimate

at different frequencies A terminal can be configured to transmit SRS at regular intervals ranging from as often as once in every 2 ms (every second subframe) to as infrequently as once in every 160 ms (every 16th frame the frequency-domain scheduling: entire frequency band of interest with a single SRS OR narrowband SRS that is hopping in the frequency domain in such a way that a sequence of SRS transmissions jointly covers the frequency band of interest.

Uplink transport-channel processinguplink

transportchannel processing are similar to the corresponding steps of the downlink transport-channel processing no spatial multiplexing or transmit diversity currently defined for the LTE uplink As a consequence,

LTE ACCESS PROCEDURE

LTE cell searchAim

Acquire frequency and symbol synchronization to a cell. Acquire frame timing of the cell, that is, determine the start of the downlink frame. Determine the physical-layer cell identity of the cell.two

special signals are transmitted on the LTE downlink, the Primary Synchronization Signal (PSS) Secondary Synchronization Signal (SSS)

System informationIn

LTE, system information is delivered by two different mechanisms relying on two different transport channels A limited amount of system information, corresponding to the so-called Master Information Block (MIB), is transmitted using the BCH. The main part of the system information, corresponding to different so-called System Information Blocks (SIBs), is transmitted using the downlink shared channel (DL-SCH).

Random accessA

fundamental requirement for any cellular system is the possibility for the terminal to request a connection setup, commonly referred to as random access . In LTE, random access is used for several purposes, including: purposes for initial access when establishing a radio link (moving from RRC_IDLE to RRC_CONNECTED; to re-establish a radio link after radio link failure; for handover when uplink synchronization needs to be established to the new cell;

pagingPaging

is used for networkinitiated connection setup. An efficient paging procedure should allow the terminal to sleep with no receiver processing most of the time and to briefly wake up at predefined time intervals to monitor paging information from the network. In LTE, no separate pagingindicator channel is used

LTE ARCHITECTURE AND SAE

LTE System Architecture

LTE System Architecture Evolved

cont.

Radio Access Network (RAN) UE: User Equipment eNB: enhanced Node B

-Contains PHY, MAC, RLC (Radio Link Control) , PDCP (Packet Data Control Protocol). eNBs are connected together through the SGW.

LTE System Architecture cont.

Functions of eNodeB: Radio Resources management. Admission control. Enforcement of negotiated UL QoS. Cell information broadcast. Ciphering/deciphering of user and control plane data Compression/decompression of DL/UL user plane packet

LTE System Architecture cont.Serving Gateway (SGW)-Routes and forwards user Data Packets. -Mobility anchor for eNB handovers and LTE to other 3GPP systems. (relaying the traffic between 2G/3G systems and PDN GW).

Packet Data Network Gateway (PDN GW)

-Connects UE to external packet data networks (serve IP functions) -Anchor for mobility between 3GPP and non3GPP technologies such as WiMAX and 3GPP2 (CDMA 1X and EvDO).

LTE System Architecture cont.

Mobility Management Entity (MME)-Manage the UEs mobility. -Idle-mode UE tracking and reachability . -Paging procedure. -Authentication and authorization. - choosing the SGW for a UE at the initial attach -Security negotiations.

OVERVIEW OF LTE ADVANCED

Fundamental requirements for LTE-Advancedcomplete

fulfillment of all the requirements for IMT - Advanced defined by ITU LTE-Advanced has to fulfill a set of basic backward compatibility requirements Spectrum coexistence, implyingthat it should be possible to deploy LTE-Advanced in spectrum already occupied by LTE with no impact on existing LTE terminals infrastructure , in practice implying that it should be

Extended requirements beyond ITU requirementsSupport

for peak - data up to 1 Gbps in the downlink and 500 Mbps in the uplink. Substantial improvements in system performance such as cell and user throughput with target values significantly exceeding those of IMT-Advanced. Possibility for low - cost infrastructure deployment and terminals. High power efficiency, that is, low efficiency power consumption for both

Technical components of LTE-AdvancedWider

bandwidth and carrier aggregation Extended multi-antenna solutions Advanced repeaters and relaying functionality Coordinated multi-point transmission

Wider bandwidth and carrier aggregation LTE-Advanced

will be an increase of the maximum transmission bandwidth beyond 20 MHz, perhaps up to as high as 100 MHz or even beyond In case of carrier aggregation, the aggregation extension to wider bandwidth is accomplished by the aggregation of basic component carriers of a more narrow bandwidth

Extended multi-antenna solutionssupport

for spatial multiplexing on the uplink is anticipated to be part of LTEAdvanced extension of downlink spatial multiplexing to more four layers benefits of eight-layer spatial multiplexing are only present in special scenarios where high SINR can be achieved

Coordinated multi-point transmission Coordinating

the transmission from the multiple antennas can be used to increase the signal to - noise ratio for users far from the antenna for example by transmitting the same signal from multiple sites. sites Such strategies can also improve the power amplifier utilization in the network, especially in a lightly loaded network where otherwise some power amplifiers would be idle

Advanced repeaters and relaying functionality Repeaters

simply amplify and forward the received analog signals and are used already today for handling coverage holes. L1 relays schemes where the network can control the transmission power of the repeater and, for example, activate the repeater only when users are present in the area handled by the repeater intermediate node may also decode and re-encode any received data prior to forwarding it to the served users. This is often referred to as decode - and - forward relaying

The proposals could roughly be categorizedfor Relay :Nodes into Various conceptsUE Dual TX antenna solutions for SU-MIMO and diversity MIMO Scalable system bandwidth exceeding 20 MHz, Potentially up to 100MHz Local area optimization of air interface Nomadic / Local Area network and mobility solutions Flexible Spectrum Usage Cognitive Radio Automatic and autonomous network configuration and operation Enhanced precoding and forward error correction Interference management and suppression Asymmetric bandwidth assignment for FDD Hybrid OFDMA and SC-FDMA in uplink UL/DL inter eNodeB coordinated MIMO

TimeframeStandardization

is expected to be included in 3GPP Release 10 timeframe. The importance and timeframe of LTE Advanced will of course largely depend on the success of LTE itself . If possible LTE-Advanced will be a software upgrade for LTE networks.

Technology DemonstrationsIn

February 2007 NTT DoCoMo announced the completion of a 4G trial where they achieved a maximum packet transmission rate of approximately 5 Gbit / s in the downlink using 100MHz frequency bandwidth to a mobile station moving at 10km / h