LTE and Scheduling

8/12/2019 LTE and Scheduling

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LTE technology

and scheduling

19.03.2012.


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Zavod za telekomunikacije

Zagreb, March 2012. 2

Outline

Limitations of mobile communications

LTE

Scheduling in the LTE

LTE-Sim simulator


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Mobile Communications:

Limitations

Spectrum

SNR and SINR ratios

Distance from cell center has significant impact

on data rate


Grayson, Shatzkamer, Wainner; IP

Design for Mobile Networks, Cisco

Press, 2009.


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Mobile Communications:

Limitations (2)

Power

Limited

Supported technologies and parameters of UEs

Modulation and Conding Scheme (MCS)

LTE designed for one-cell frequency reuse

Inter-cell interference coordination (ICIC) needed

Overlapping cell layers

Femtocells



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System Architecture


Dahlman, Parkvall, Skld,4G

LTE/LTE-Advanced for Mobile

Broadband, Academic Press, 2011.


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Radio

Protocol

Architecture





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Time-domain structure



Broadband, Academic Press, 2


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Spectrum





O th l F Di i i


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Orthogonal Frequency Division

Multiplexing (OFDM)

Frequency spectrum divided in many subcarriers

Example: 600 subcarriers in a 10 MHz spectrum

Subcarriers frequency spectra overlap, but without

interference






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Flexible Channel Bandwidth






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Multi-Antenna Transmission

Multiple receive antennas

For receive diversity

Already used in many cellular systems for uplink

Multiple transmit antennas at the base station

Transmit diversity

Spatial multiplexing = Multiple Input Multiple

Output (MIMO)

Several parallel channels

Good at high SINR



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Carrier Aggregation

Intra-band

Inter-band






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Relaying

Reducing the distance between the terminal and

the network node

Amplify-and-forward (repeaters)

Decode-and-forward






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UE Diversity






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Zavod za telekomunikacijeScheduling

Selection of users

that the differentparts of the

shared resources

should be

assigned to ineach time instant

Controls user data

rate

In LTE: time and

frequency domain






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Time & Frequency Domains

Time and frequnecy structure of LTE downlink

and uplink - FIXME

Downlink: OFDMA

Uplink: Single Carrier FDMA (SC-FDMA)

Basic scheduling unit: 2 Resource Blocks (RB)

1 RB: 180 kHz, 0.5 ms


Kela et al., Dynamic Packet Scheduling Performace in

UTRA Long Term Evolution Downlink, ISWPC 2008, pp.

308-313.


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Basic Scheduling Strategies

Maximum rate (max C/I)

Round robin

Proportional fair (PF)






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Literature on Scheduling


Piro et al.,Two-Level Downlink Scheduling for Real-Time Multimedia Services in LTE Networks, IEEE Transactions on Multimedia, vol.13,

no. 5, October 2011.

QoS Oriented Time and Frequency Domain


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QoS Oriented Time and Frequency Domain

Schedulers (Monghal et al., 2008)

Time domain: limits the number of scheduled

users, thus controlling signalling overhead

Frequency domain: complexity depends on

number of users

Simple admission control included

Blocks new users when number of users in the cell is

equal to a predefined limit


Frame Level Scheduler


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Frame Level Scheduler

(G. Piro et al., 2011)

Two level scheduler

Upper level: determines how much data should be

transmitted by each data source to meet QoS

constraints

Lower level: determines how it will be transmitted, i.e.,

allocates RBs in each TTI by using the PF algorithm Best effort services packets put in a separted

queue, scheduled if there are free RBs


M i B t L


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Mapping Between Layers


Ramli et al., Performance of Well Known Packet Scheduling Algorithms in the Downlink 3GPP LTE System, Proc. of the IEEE 9th Malaysia

Intl. Conf. On Communications, pp. 815-820, December 2009.

LTE Si


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LTE-Sim

Developed by G. Piro et al. from Politecnico di

Bari, Bari, Italy, released under GPLv3 license

Simulates LTE downlink and uplink

Considers both the E-UTRAN and the EPS, multicell

simulation, user mobility, handover, radio resource

optimization, frequency reuse, adaptive modulation andcoding

Several traffic generators at the application layer

VoIP, infinite buffer, trace based, constant bit rate

No full PHY simulation, analytical model used

Only UDP and unacknowledged mode supported


LTE Si


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LTE-Sim

Example output trace


Scheduling With MDP how to?


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Scheduling With MDPhow to?

Hot to put it all together?

Low level factors: SINR, AMC

Medium level factors: buffer status, different traffic

source types

High level: QoE, MDP

When to react on changes (i.e., to switch MDP

configuration) ?

How to distinguish short term quality variations from the

long term ones?


Documents

LTE and Scheduling