Optimal Packet Scheduling and Radio

Resource Allocation

By

Subhendu Batabyal

Basabdatta Palit

Prabhu chandar

Dr. Suvra Sekhar Das

Cellular Layout User Distribution

& Mobility

Traffic

GenerationSINR per UE

1.Path Loss

2.Shadowing

3.Small Scale Fading

(ITU-R M.2135)

CQI Feedback

(Sub Band)

Link AdaptationPower ControlHARQ

Packet Scheduling and Radio Resource

Allocation

Link Level

Simulator

EESM(Link to System

Mapping)

Throughput Capacity

SINR

ResultsFrequency

Selective

Channel Model (ITU-R M.2135)

SINR vs. BLER

TxModulator

Turbo

Encoder

Rx

Demodulator

Turbo

Decoder

Background - System Flow for Packet Scheduling

QoS

Physical Resource Block in OFDMA

4

OFDM(A)

B.S

Physical (Radio) Resource Block Allocation

UE1 UE2UE3

UE4

UE5

Path gain

Shadowing

Small Scale Fading

• Multi path

• Velocity

Sub Frame DurationSub Band

BE - 256 kbps, No Delay Constraint

VoIP - 16 kbps, Delay Constraint

Video - 64 kbps, Delay Constraint

eNode-B Target cells

Sector/cellDirection of antenna main-lobe

Generalized System Model

HARQLink

Adaptation

Admission

Control QoS

RRM

Equivalent BW

Estimator

CQI

Estimation

CQI

CQI

Data

Data

HARQ

Call

Request

Reference Signal

Reference Signal

ACK/NACK

ACK/NACK

Beam forming

Data Stream 1

Data Stream 2MIMO

MIMO

• Diversity

• SU-MIMO

• MU-MIMO

Packet Scheduler

Time

Domain

Frequency

Domain

Transport Block Size

CB CB CB

CB CB CB

TBS Form

CB

Segmentation

&

CRC

Background – Packet Scheduling

• Packet Scheduling

– Time Domain Packet Scheduling (TDPS)

• to arrange the packets according to their Time to Live

• to give priority to packets which have smaller time to expire

– Frequency Domain Packet Scheduling (FDPS)

• to allocate the packets to the Physical Resource Blocks

• minimize the usage of the number of available resources and exploit multiuser frequency diversity

Background – Packet Scheduling in Time and Frequency

Buffer

Management

Pending ReTx

Buffer

Time Domain

Packet

Scheduling

Radio

Resource

Allocation

and

Frequency

Domain

Packet

Scheduling

(FDPS)

New Packets

ReTx Packets

V10 V9 H5 V6 V12 H3 H11 V20

Packets with Lifetime>Current

Time

Packets with Lifetime Validity

User PRB

1

3

H5 V10 H3 H11 V9 V6 V12 V20

9 0 8 4 4 8 4 1

Drop packets with

Lifetime<Current Time

CQIs Reported for each packet

Packets arranged as per TDPS Algorithm

H5

H3

Rmax

2

Motivation

• Efficiency of Resource Allocation plays a crucial role in determining

network efficiency.

• If the no. of users exceeds a certain limit, there is a exponential fall in

system performance.

• It is crucial to quantify the above limit accurately, while also maximizing it

in order to dimension the network properly with maximum network

efficiency for the operator.

• Computational resources are limited, therefore exhaustive search is

impossible.

State of the Art

• Existing Time Domain Scheduling Algorithms

– Based on Time to live (delay criterion) – considers only packet expiry criterion

– Round Robin (Allocation Fairness criterion) – considers users in their arrival sequence only.

– Based on best channel condition – considers only present throughput

– Blind equal throughput – considers only past throughput

• Existing Frequency Domain Scheduling Algorithms

– Round Robin (RR)

– Max C/I – greedy approach that ignores fairness

• Existing Joint Time/Frequency Domain Scheduling

Algorithms

– Proportional Fair (PF) – considers past and present throughput but ignores factors such as time to live of the packets, no. of packets per user etc.

Gaps in Literature

• We need an algorithm that combines fairness with optimal capacity in

terms of no. of supported real time (VoIP) users.

• We need an algorithm that reduces the exponential complexity of

exhaustive search without compromising too much on performance.

• We need an algorithm that considers packet life-time, no. of packets per

user as well as user’s past throughput and error rates.

• We need to find the allocation order at a given snapshot of time that

results in the best possible usage of transmission resources

Exponential Complexity of Exhaustive Search

RB1 RB2 RB3 RB4 RBK-1 RBK

User1

User2

User3

UserU-1

UserU

RB

User

U Users assigned to K Resource Blocks UK combinations! Allocation order -> U! possible sequencesNeed for Heuristic Search schemes

Problem Description: Metric based prioritization for TDPS

A

un m ( )C

uC,

B

u m

m

p

D

uS , , , 0A B C Dum

,

u

u m

u

u

n

m

p

C

S

Time interval

Arrival time of uth user

pth packet of uth user arrived at mth time instant

Expected future throughput of uth user

Average past throughput of uth user

Problem Description: Improved FDPS

Each rectangular box represents a Physical Resource Block (PRB) and the number inside

indicates the Channel Quality Indicator (CQI)

User1:

User2: 4

7

5

108

9

10 3

510

Problem Description: Improved FDPS

Each rectangular box represents a Physical Resource Block (PRB) and the number inside

indicates the Channel Quality Indicator (CQI)

User1:

User2:

7

10 4559

7 10 3 10

Problem Definition

• Optimal and Fair PRB Allocation for VOIP Packets in

OFDMA Downlink for LTE to Maximize Spectral Efficiency

Work Plan

A. Optimal PS and RRA for a single eNB

– Best Order of Allocation Approach

1. 2 users

2. 4 users

3. Any no. of users

B. Joint PS and RRA with eNB coordination

– Design of Joint PS and RRA with eNB coordination

1. 2 eNBs

2. 3 eNBs

– Extensions of Simulator for Joint PS and RRA with eNB coordination

3. 2 eNBs

4. 3 eNBs

Pert Chart for Time Plan

Activity 2012 2013

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4

A(1,2,3)

B1

B2

B3

B4

Finally..

THANK YOU

Approach to Problem - Design Objectives

• Design of Improved TDPS considering

– Time to live of the packet

– User’s previous throughput

– User’s predicted future throughput

– No. of Packets to be Scheduled

• Design of Improved FDPS considering

– All possible allocation orders for a set of users

– Maximizing number of users scheduled per TTI

– Maximizing number of PRBs utilized per TTI

• Integrating improved TDPS and FDPS

– Make use of TDPS priorities in FDPS

Approach to Problem – Overall Objectives

• Design of Optimal Packet Scheduling and Radio Resource Allocation for OFDMA

Cellular Networks carrying Multimedia and Data traffic

• System Goals

Maximize number of supported real time users and bandwidth utilization

Fairness among the users

Inter Cell Interference Mitigation

Cell Edge User Throughput Maximization

Approach to Problem - Design Constraints

• Computational Complexity

• Allocation of resources to users while satisfying

User’s bandwidth requirement

Delay/Latency constraints

Control Channel Limitations

Maintaining a minimum FER for a minimum percentage of users

State of the Art

Sl. No. Paper Details Contents

1 Kyuho ’ 2009 Authors have formulated utility maximization problem with network wideProportional Fair (PF) as an objective in a multi-cell network with PartialFrequency Reuse (PFR)Proposed online algorithms are based on the inter/intra-handover andcell-site selection in which a metric is changed from the signal strength tothe average throughput.Centralized approach which needs fast information exchange andcomputational complexity

2 Xu Kai ’ 2007 Proposed optimal and sub-optimal inter-cell scheduling strategies basedon the coordinated transmission from the interfering cellsThis paper extends the utility function based multi-user packet schedulingstrategies derived for single cell scenario to multi-cell scenarioCentralized approach

3 Yavuz’ 2009 Proposed a scheduler that allows for opportunistic behavior from a singlesessions point of view but keeps the overall caused interference variation ata low level in order to improve the performance of Link AdaptationIgnores fairness among the users

4 Falconetti’ 2010 A codebook based inter-cell interference coordination scheme has been proposed where, the supporting cells try to use a precoding matrix for which the interference received by selected cell-edge UEs remains acceptable.Methods to solve the conflicts of interest are also discussed

1/23/2012 22

State of the Art

Sl. No. Paper Details Contents

5 Xinying’ 2009 A signal leakage information based scheme has been proposed fordesigning the precoding vector to reduce the Inter Carrier Interference (ICI).In the proposed method coordinating eNB uses PMIs that would result inminimum interference

6 Jianchi ’ 2010 A large-scale Channel State Information (CSI) for precoding has beenproposed to reduce the over-head involved in the coordination processA coordination scheme has been proposed to determine best groups oftransmission points and coordinated UEs

7 Jing ’ 2010 A joint PF scheduling algorithm has been for CoMP-SU-MIMOThe proposed algorithm treats the cell-edge UEs and cell-center UEsequally in every TTI without partitioning the frequency band for CoMPoperation

1/23/2012 23