Emerging TechnologyLTE-Advanced

Presented by: Himani Dutta(7475662)

CSI5169 Wireless Networks / Mobile Computing

Outline

• Motivation• LTE-A Architecture• LTE-A Features

– Carrier Aggregation– Enhanced MIMO– Coordinated Multi point– Heterogeneous Network– Relays

• Link Adaptation Algorithm• Data Offloading

Releases of 3GPP specifications

www.3GPP.Org

Motivation of LTE-A

• Capability Requirement– Peak data rate– Cell edge bit rate– Latency

• System Performance Requirements– Average user Throughput– Spectrum Efficiency– Mobility– Coverage

• Deployment Related Requirement– Deployment Scenario– Spectrum Feasibility

Key Features of LTE-Advanced

• Downlink 3 Gbps, Uplink 1.5 Gbps• Higher spectral efficiency, from a maximum of 16bps/Hz

in R8 to 30 bps/Hz in R10• Increased number of simultaneously active subscribers• Improved performance at cell edges, e.g. for DL 2x2

MIMO at least 2.40 bps/Hz/cell.

LTE-A Architecture

OFDM• OFDM stands for Orthogonal Frequency Division Multiplexing

and is a modulation technique for transmitting large amountsof digital data over a radio wave.

• Based on the Fast Fourier transform• Orthogonality indicates that there is no cross talk between the sub channels. Orthogonal subcarriers=No inter carrier interference (ICI)

OFDM systems have overlapped spectra with ICI = 0.

Advantages of OFDM

• Allows flexible utilization of frequency spectrum• Long symbol time and guard interval increases robustness to

multipath• Allows optimization of data rates for all users by transmitting

on the best sub carrier

LTE-Frame Structure

• LTE Communication is available in different frequency bands.• Paired band Unpaired bandUL & DL transmissions use UL & DL share theSeparate frequency bands same frequency band.• LTE use different bandwidths ranging from 1.4MHz to 20 MHz

MIMO• Data is organized into spatial streams that are transmitted

simultaneously, is known as spatial multiplexing.• SISO: Single-Input/Single-Output; MIMO: Multi-Input/Multi-

Output; SIMO: Single-Input/Multi-Output• N*M MIMO (2*2, 4*4, 2*3)

N transmit antennasM receive antennas

• MIMO transmission uses multipath to send two or more streams of data.

Transmitter

X

Receiver

Y

h11

h21

h31

hNM

MIMO• Y = H*X• H =

The rank defines the number of linearly independent rows or columns in H

• Transmission matrix H contains impulse response, m represents transmit antenna and n represents receive antenna. Rank indicates how many independent data streams can be transmitted simultaneously.

• Increasing the robustness of data transmission – transmit diversity

• Increasing the data rate – Spatial Multiplexing• Beam Forming- enhances signal reception through directional

array gain

nmhnh

nh

nh

mhhhhm

hhhhm

hhhh

.21

...........

2..2221

1..1211

nmh

LTE-Advanced

LTE-Advanced

• Leverage wider BandwidthCarrier aggregation across multiple carriers, multiple bands

• Leverage More AntennasDownlink MIMO up to 8*8, enhanced multiuser MIMO and uplink MIMO up to 4*4

• Leverage HetNetsAdvanced interferenceManagement (eICIC/IC)

Higher Data Rates

Higher Spectral Efficiency

Carrier AggregationMotivation• Support of high data rates

• Efficient utilization of fragmented spectrum

• Support of heterogeneous network deployments by means of cross-carrier scheduling.

A UE that is configured for carrier aggregation connects to one p-cell and up to 4 s-cell.

MIMO Enhancement

• Multiple antennas at both the base station and terminal can significantly increase data rates with sufficient multipath.

• Downlink peak spectrum efficiency of 30bps/Hz and uplink 15bps/Hz.• 8*8 for downlink transmission and 4*4 for uplink.

Coordinated Multipoint Transmission

Motivation:• Increases throughput at thecell edge• User experiences low QoS atthe cell edge if no coordination amongdifferent BSs.• 4G overcome this degradationby eICIC (enhanced intercell interference coordination)Advantages:• Increase network density• Network coverage extension 

Heterogeneous Network- Bring more out of small cells

Motivation:• To provide flexible capacity expansion or offloading.

LTE-A provides efficientsupport for a mixture ofmacro cells and lowpower eNBs.

Cross Carrier SchedulingProvides support for (ICIC)Inter-cell interference coordination

Relays

Motivation:• Fiber coverage as a backhaul solution will improve but will not

reach everywhere.• Challenge is to improve Capacity/Coverage

Heterogeneous N/w provides Solution to the above problems

Scheduling Methods• Scheduler controls the allocation of shared time-frequency

resources among users at each time instant.

• Best CQI Scheduling

It assigns resource blocks to the user with the best radio link condition.

A higher CQI means better Channel condition.

Increases the cell Capacity.

Measure CQIs

Highest CQI ?

Schedule User

Highest CQI?

Start

No

Yes

Yes

Round Robin Scheduling

• The Principle of this scheduling is the guarantee of fairness for all users.

• Easy to implement

• Results of low user throughput.

Schedule the first user

Schedule the next user

Have all users been schedules?

Start

Yes

No

Proposed Algorithm

• To achieve better throughput and fairness among all users.

• It assigns RB to user that maximizes the CQI in the first slot period of each sub-frame

whereas, in the second slot

period the scheduler assigns

the RB in turn to each user.• Results an acceptable throughput

and fairness between users.

Measure CQIs

Highest CQI ?

Schedule User

Highest CQI?

Start

YesNo

Highest CQI ?

Highest CQI ?

Highest CQI?

YesNo

No

Highest CQI?

Zero Forcing Precoding- Beamforming

• Zero-forcing (or Null-Steering) precoding is a spatial signal processing by which the multiple antenna transmitter can null multiuser interference signals in LTE-A.

• Need to compensate the delays of receiving signals• Sum and average the weighted signals• Transmitter knows the downlink channel state

information (CSI) perfectly• ZF-precoding requires the significant feedback overhead

with respect to signal-to-noise-ratio (SNR) so as to achieve the full multiplexing gain

Dynamic Scheduling Algorithm

Key points of Dynamic Scheduling Algorithm

• Optimized Scheduling Method• Rather then scheduling on wide band , it doing the

optimized scheduling on sub bands.• Rather it follows dynamic approach for switching

between MU-MIMO and SU-MIMO for optimal performance

Link Adaptation- To improve QoS

When a resource block with a particular CQI value is available to a UE, we check if the CQI valueof this resource block can collectively enhance the overall transport block (TB) size with the resource blocks already allocated to this UE. If this CQI value is very low, then it will degrade the MCS mode of the transport block built with other resource blocks. In such a case, this resourceblock may be scheduled to other UE which may have better channel condition (better CQI) on it.

1: UE(i) allocated resource blocks PRB(j) (j = 1...K);2: The next resource block PRB(K + 1) allocated to UE(i);3: oldAvgCQI = Σj=1(CQIP RBj)2/Σj=1 CQIP RBj;4: oldMCS = GetMCSFromCQI(oldAvgCQI);5: oldTBSize = GetTBSizeFromMCS(oldMCS);6: newAvgCQI = Σj=1 (CQIP RBj)2/ Σj=1 CQIP RBj;7: newMCS = GetMCSFromCQI(newAvgCQI);8: newTBSize = GetTBSizeFromMCS(newMCS);9: if newTBSize > oldTBSize then10: Accept PRB(K + 1) and allocate to UE(i);11: else12: Reject PRB(K + 1) and leave it to other UEs.13: end if

Dynamic Component Carrier Assignment

Efficient assignment of component carriers to UEs to achieve higher network utilization and performance is an important issue that needs to be carefully addressed. In the existing carrier aggregation schemes, CCs are allocated statically when UEs attach to the network and the allocation does not change with time. In the proposed approach, we take channel conditions, network load and other impacting factors into account and dynamically allocate component carriers for UEs.

Case study : Data Offloading• What is internet offload- • LIPA is for residential/enterprise network, and is valid for

indoor femtocells and picocells.• While the SIPTO is for internet access in both femtocell and

macrocell.• Both aims to offloading traffic away from operator’s core

network.

LIPA breakout in the residential/enterprise network with collocated L-GW

Key benefits of LIPA• Reduced network congestion for Local IP access.• Better quality of experience for services delivered through LIPA

Benefits of SIPTO• Simultaneously support Services via SIPTO and operator’sCore network.

• Mobility for offloaded sessionsand services are possible.

SIPTO Breakout above RAN - macro network

Questions

Question 1) How to enhance the performance of MU-MIMO in LTE-A, whether SU-MIMO served only one user within a cell over multiple streams ?

Answer:MU-MIMO definition: MU-MIMO is the enhanced form of MIMO technology that enables multiple independent radio terminals to access a system, which can provide significant performance gains over the SU-MIMO technology.

Advantage: • Enables multiple users to simultaneously access the same channel

by providing spatial degrees of freedom.• Very useful for downstream traffic due to sophisticated antenna

design and signal processing. Multi-user MIMO communication can provide significant gains by

exploiting spatial multiplexing. However, it requires better feedback

to provide accurate channel state information at the

transmitter (CSIT) for minimizing the multiuser

interference.

MU-MIMO provides PMI (Precoding Matrix

indicator) feedback for every sub band rather

than once for wideband. After getting the sub

band PMI feedback, Dynamic scheduling algorithm

of MAC layer deals with resource management on

every sub band rather than wideband and allows

dynamically switch between MU-MIMO and

SU MIMO to reduce the interference between

systems.

Question 2) How the LTE-A addresses the below challenges in the wireless backhaul network?

Challenges: Limited bandwidth, fragmented spectrum, big cell size, maintaining QoS at the cell edges, growing number of users

Answer) The below mentioned technologies caters to the need of wireless backhaul challenges:

Technology Cattered Challenges

Carrier Aggregation Fragmented spectrumLimited Bandwidth

MU-MIMO Growing number of usersCost reduction for bits per second per Hz

Relay node Increase in coverage areaMaintenance of QoS at cell edges

CoMP Maintenance of QoS at cell edges

Heterogeneous network / Small cell

OffloadingIncrease in coverage area

Question 3) How to overcome the traffic overload problem in LTE-A?

Answer: There are ways been suggested to offload the mobile data users traffic. Now depending on the part of the LTE network they are been classified as RAN (Radio Access Network) offloading and core network offloading.

LIPA is primarily for end users to access their local network or intranet through a local 3GPP access point (e.g., indoor femtocell /picocell).LIPA is subscription-based. With the mobile operator, a mobile device can use Local IP Access in its own network as well as in a visited network, subject to roaming agreements between mobile operators.

SIPTO allows cost-optimized handling of Internet traffic and is valid for both femtocell and macrocell. It enables routing of selected IP traffic through either the most optimal path in an operator’s core network or bypassing it completely.

RAN offloading Core Network offloading

Heterogeneous network LIPA

Femtocell SIPTO

Small cell

Wi-Fi offloading

Below table shows the distributed traffic offloading techniques:

REFERENCES

[1] Stefania Sesia “LTE The UMTS Long Term Evolution” [2] 4G Mobile Broadband Evolution 3GPP release 11 or 12 beyond [3] “Smart Scheduler” White Paper; nsn.com/system/files/document/lte_smart_scheduler_wp_31072013.pdf[4] Ian F. Akyildiz, “The evolution to 4G cellular systems: LTE-Advanced”[5] LTE Advanced—Evolving and expanding in to new frontiers[6] Takehiro Nakamura “Proposal for Candidate Radio Interface Technologies for IMT‐Advanced Based on LTE Release 10 and Beyond (LTE‐Advanced)”[7] Matthew Baker “LTE-Advanced Physiical Layer”[8] Tetsushi Abe, “3GPP Self-evaluation Methodology and Results “Self-evaluation Results”[9] Dr. Anthony Lo, “Downlink Scheduling in 3GPP Long Term Evolution (LTE)”[10] Zanjie Huang , An Efficient Resource Allocation Algorithm with Carrier Aggregation in LTE Advanced Systems, National Institute of Informatics, Tokyo, JapanUCB/EECS-2008-116. September, 2008.[11] Xiaolin Cheng,” Joint Carrier Aggregation and Packet Scheduling in LTE-Advanced Networks” 10th Annual IEEE Communications Society Conference on  2013

[12] Klaus Doppler, “Device-to-Device Communication as an Underlay to LTE-Advanced Networks”[13] Yuanye Wang, “Resource allocation for multi carrier LTE Advanced systems operating in backward compatible mode” [14] Gerhard Wunder,“5GNOW: Challenging the LTE Design Paradigms of Orthogonality and Synchronicity

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