Academic Year 2011/2012 ELECTRICAL AND COMPUTER ENGINEERING THE INSTITUTE OF TELECOMMUNICATIONS FACULTY OF ELECTRONICS AND INFORMATION TECHNOLOGY WARSAW UNIVERSITY OF TECHNOLOGY Bachelor of Science Thesis Modeling and Simulation of Scheduling Algorithms in LTE Networks Dinesh Mannani Supervisor: Dr. Mirosław Słomiński, Associate Professor Consultant: Dr. Sławomir Pietrzyk, IS-Wireless ........................................................... Evaluation ........................................................... Signature of the Head of Examination Committee Warsaw, January 2012
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Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
This thesis is mainly to understand the scheduling algorithms for LTE by means of modeling and simulation of the process and in the end verify the results by conducting tests in a LTE test environment. Furthermore, work out a method to examine LTE scheduling performance evaluation for teaching purposes.
The analysis of these scheduling algorithms has been done through simulations executed on a MATLAB-based system level simulator from IS-Wireless, which is part of 4G University Suite with their verification in a LTE network test environment
For more information about 4G University Suite, please have a look http://is-wireless.com/products/4g-university-suite.
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Fig. 5 : LTE Downlink channels [18] ...................................................................................... 19 Fig. 6 : LTE Uplink Channels [18] .......................................................................................... 20 Fig. 7 : Single user MIMO transmission principle [8] ............................................................. 22 Fig. 8 : Multi-user MIMO transmission principle [8] .............................................................. 22 Fig. 9 : Layer 2 functionalities for dynamic packet scheduling, link adaptation, and HARQ
Management [8] ....................................................................................................................... 23 Fig. 10 : Flow Chart for Round Robin Algorithm ................................................................... 24
Fig. 11 : Flow chart for Max SNIR algorithm ......................................................................... 25
Fig. 12 : Flow chart for Proportional Fair Algorithm .............................................................. 26 Fig. 13 : A tree diagram for all the scenarios under consideration for simulations ................. 28 Fig. 14 : PRB allocation based on SNIR values for single user downlink Case 1................... 29 Fig. 15 : Resource Allocation for a single user in downlink Case 1 ........................................ 30
Fig. 16 : Throughput Results for single user in downlink Case 1 ............................................ 30 Fig. 17 : PRB allocation based on SNIR values for 3 users .................................................... 31
Fig. 18 : Resource allocation by RR algorithm for 3 users in downlink Case 2 ...................... 31 Fig. 19 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 2 .......... 32 Fig. 20 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 2 ......... 32
Fig. 21 : Comparison of PRB allocation in all three algorithms over time Case 2 .................. 33 Fig. 22 : Comparison of throughput obtained from all three algorithms Case 2 ..................... 33
Fig. 23 : Resource allocation by RR algorithm for 3 users in downlink Case 3 ...................... 34
Fig. 24 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 3 .......... 35
Fig. 25 : Resource allocation by PF algorithm for 3 users in downlink Case 3....................... 35 Fig. 26 : Comparison of PRB allocation in all three algorithms over time Case 3 .................. 36
Fig. 27 : Comparison of throughput obtained from all three algorithms Case 3 ..................... 36 Fig. 28 : Resource allocation by RR algorithm for 3 users in downlink Case 4 ...................... 37 Fig. 29 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 4 .......... 38
Fig. 30 : Resource allocation by PF algorithm for 3 users in downlink Case 4....................... 38 Fig. 31 : Comparison of PRB allocation in all three algorithms over time downlink Case 4.. 39 Fig. 32 : Comparison of throughput obtained from all three algorithms downlink Case 4 ..... 39
Fig. 33 : PRB allocation based on SNIR values for single user in uplink Case 1 ................... 40 Fig. 34 : Resource Allocation for a single user in uplink Case 1 ............................................. 41 Fig. 35 : Throughput results of single user in uplink Case 1 ................................................... 41 Fig. 36 : PRB allocation based on SNIR values for 3 users .................................................... 41 Fig. 37 : Resource allocation by RR algorithm for 3 users in uplink Case 2 ........................... 42
Fig. 38 : Resource allocation by Max SNIR algorithm for 3 users in uplink Case 2 .............. 42 Fig. 39 : Resource allocation by PF algorithm for 3 users in uplink Case 2 ........................... 43
Fig. 40 : Comparison of PRB allocation in all three algorithms over time uplink Case 2 ...... 43 Fig. 41 : Comparison of throughput obtained from all three algorithms uplink Case 4 .......... 44
Fig. 42 : Resource allocation by RR algorithm for 3 users in uplink Case 3 ........................... 45 Fig. 43 : Resource allocation by Max SNIR algorithm for 3 users in uplink Case 3 .............. 45 Fig. 44 : Resource allocation by PF algorithm for 3 users in uplink Case 3 ........................... 46 Fig. 45 : Comparison of PRB allocation in all three algorithms over time uplink Case 3 ...... 46 Fig. 46 : Comparison of throughput obtained from all three algorithms uplink Case 3 .......... 47
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Fig. 47 : Resource allocation by RR algorithm for 3 users in uplink Case 4 ........................... 48
Fig. 48 : Resource allocation by Max SNIR algorithm for 3 users in uplink Case 4 .............. 48 Fig. 49 : Resource allocation by PF algorithm for 3 users in uplink Case 4 ........................... 48 Fig. 50 : Comparison of PRB allocation in all three algorithms over time uplink Case 4 ...... 49 Fig. 51 : Comparison of throughput obtained from all three algorithms uplink Case 4 .......... 49
Fig. 52 : Throughput results from Download within 5m of eNodeB: 100 MB file ................ 51 Fig. 53 : Throughput results from Download within 5m of eNodeB: 200 MB file ................ 51 Fig. 54 : Throughput results from Download within 5m of eNodeB: 500 MB file ................ 52 Fig. 55 : Throughput results from Download within 5m of eNodeB: 1 GB file ..................... 52 Fig. 56 : Throughput results from HTTP Download with user 3 at cell edge ......................... 53
Fig. 57 : Throughput results from HTTP Download with user 1 & 3 at cell edge .................. 53 Fig. 58 : Throughput results from HTTP Download with all 3 users at cell edge ................... 54 Fig. 59 : Throughput results from FTP Download within 5m of eNodeB : 500 MB file ........ 54 Fig. 60 : Throughput results from FTP Download with user 3 at cell edge ............................ 55
Fig. 61 : Throughput results from FTP Download with user 1 & 3 at cell edge ..................... 55 Fig. 62 : Throughput results from FTP Download with all 3 users at cell edge ...................... 56
Table 4.1 summary of simulation parameters used for all the testing scenarios ..................... 28 Table 4.2 : LTE Test Environment Test 1 ............................................................................... 51
Table 4.3 : LTE Test Environment Test 2 ............................................................................... 51 Table 4.4 : LTE Test Environment Test 3 ............................................................................... 52 Table 4.5 : LTE Test Environment Test 4 ............................................................................... 52
Table 4.6 : LTE Test Environment Test 5 ............................................................................... 53
Table 4.7 : LTE Test Environment Test 6 ............................................................................... 53 Table 4.8 : LTE Test Environment Test 7 ............................................................................... 54 Table 4.9 : LTE Test Environment Test 8 ............................................................................... 54
Table 4.10 : LTE Test Environment Test 9 ............................................................................. 55 Table 4.11 : LTE Test Environment Test 10 ........................................................................... 55
Table 4.12 : LTE Test Environment Test 11 ........................................................................... 56
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Abbreviations
3GPP – 3rd
Generation Partnership Project
LTE – Long Term Evolution
MMOG – Multimedia Online Gaming
HSPA – High Speed Packet Access
3G – Third Generation of Cellular Wireless Standards
GSM – Global System for Mobile Communication
UMTS – Universal Mobile Telecommunications System
UTRA –UMTS terrestrial radio access
E-UTRA – Evolved UMTS terrestrial radio access
UTRAN – UMTS Terrestrial Radio Access Network
E-UTRAN – Evolved UMTS Terrestrial Radio Access Network
MIMO – Multiple Input Multiple Output
FDD – Frequency Division Duplex
TDD – Time Division Duplex
OFDM – Orthogonal Frequency Division Multiplexing
OFDMA – Orthogonal Frequency Division Multiple Access
SC-FDMA – Single Carrier Frequency Division Multiple Access
FDMA – Frequency Division Multiple Access
PAPR – Peak to Average Power Ratio
BS – Base Station
eNodeB – Base Station
MS – Mobile Station
UE – User Equipment
RB – Resource Block
RE – Resource Element
SNIR – Signal to Noise-Interference Ratio
RR – Round Robin
PF – Proportional Fair
CQI – Channel Quality Indicator
TPSA – Telekomunikacja Polska S.A.
DL – Downlink
UL – Uplink
HSDPA – High Speed Downlink Packet Access
C.D.F – Cumulative Distribution Function
EUL – Enhanced Uplink
SC – Single Carrier
SISO – Single Input Single Output
MME – Mobility Management Entity
SGW – Serving Gateway
PGW – PDN Gateway
CP – Cyclic Prefix
DwPTS – Downlink Pilot Time Slot
GP – Guard Period
UpPTS – Uplink Pilot Time Slot
PBCH – Physical Broadcast Channel
PCFICH – Physical Control Format Indicator Channel
PDCCH – Physical Downlink Control Channel
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PHICH – Physical Hybrid ARQ Indicator Channel
HARQ – Hybrid Automatic Retransmission Request
RS – Reference Signal
CIR – channel impulse response
PRN – pseudorandom number
P-SS and S-SS – Primary and Secondary Synchronization Signal
DC – Dedicated Control
ACK – Acknowledge
NACK – Not Acknowledge
PDSCH – Physical Downlink Shared Channel
PMCH – Physical Multicast Channel
PUCCH – Physical Uplink Control Channel
PUSCH – Physical Uplink Shared Channel
PRACH – Physical Random Access Channel
WCDMA – Wideband Code Division Multiple Access
PHY – Physical layer
MAC – Medium Access Control
RLC – Radio Link Control
RRC – Radio Resource Control
IEEE – Institute of Electrical and Electronics Engineers
4G – Fourth Generation of Cellular Wireless Standards
SNR – Signal to Noise Ratio
PS – Packet Scheduler
TTI – Transmission Time Interval
MCS – Modulation and Coding Scheme
QoS – Quality of Service
AMC – Adaptive modulation and coding
PRBs – Physical Resource Blocks
RRM – Radio Resource Management
CCI – co-channel interference
VoIP – Voice over Internet Protocol
QPSK – Quadrature Phase-Shift Keying
QAM – Quadrature Amplitude Modulation
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1. Introduction This chapter is dedicated to the introduction to the concept of 3
rd Generation Partnership
Project (3GPP) Long Term Evolution (LTE) and technological features associated with it.
The first section, 1.1, of this chapter will discuss the background information on the subject
of LTE and scheduling. The motivation and goals for the thesis have been discussed in the
sections 1.2 and 1.3 respectively with the last section 1.3 presenting the outline of the thesis.
1.1 Background
Over the recent years we have seen mobile broadband become a reality as more and more
internet users are getting accustomed to having broadband access wherever they go, and not
just at home or in the office. Multimedia applications such as Multimedia Online Gaming
(MMOG), mobile TV, Web 2.0, streaming contents through the Internet have gathered more
attention by the internet generation and have motivated the 3GPP to work on the LTE which
is a successor to High Speed Packet Access (HSPA) currently being used in the 3rd
Generation of Cellular Wireless Standards (3G) networks. LTE is an answer to deliver better
applications and services to mobile users which consume a lot of bandwidth.
The 3GPP is the organisation which stipulates and standardises the specifications for LTE
along with Global System for Mobile Communication (GSM) and 3G Universal Mobile
Telecommunications System (UMTS) terrestrial radio access (UTRA) systems. It started
work on the evolution of 3G mobile system in November 2004, and the project came to be
known as LTE. The main focus of this initiative to introduce LTE was on enhancing the
UTRA and optimizing 3GPP‟s radio access architecture. A lot of research has been carried
out since 2004 and proposals have been presented on the evolution of the UTRAN. The
specifications related to LTE are formally known as the evolved UMTS terrestrial radio
access (E-UTRA) and evolved UMTS terrestrial radio access network (E-UTRAN), but are in
general referred as project LTE.
The end of year 2008 saw the Release 8 of the 3GPP, which cites the stable specifications for
LTE, being frozen. The initial deployment of LTE began in 2010 with many operators
adopting it gradually. According to Release 8 specs, LTE supports peak rates of 300Mb/s
which could be achieved with the help of Multiple Input Multiple Output (MIMO) and a
radio-network delay of less than 5ms. In addition to that it operates on both Frequency
Division Duplexing (FDD) and Time Division Duplexing (TDD) and can be deployed in
different bandwidths depending on the availability of spectrum. In TDD configuration the
uplink and downlink operate in same frequency band whereas with FDD configuration the
uplink and downlink operate in different frequency bands.
Orthogonal Frequency Division Multiplexing (OFDM) has been adopted as the downlink
transmission scheme for the 3GPP LTE [11]. The transmission which occurs from the base
station to the User Equipment is referred to as downlink whereas vice-versa uplink. OFDM
divides the transmitted high bit-stream signal into different sub-streams and sends these over
many different/parallel sub-channels. For uplink transmission scheme the 3GPP selected SC-
FDMA (Single Carrier – Frequency Division Multiple Access). An uplink is a transmission
from the mobile station to the base station. SC-FDMA is a modified form of Orthogonal
Frequency Division Multiple Access (OFDMA) and has similar throughput performance and
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essentially the same overall complexity as OFDMA. Like OFDM, SC-FDMA also consists of
sub-streams but it transmits on sub-channels in sequence not in parallel which is the case in
OFDM, which prevents power fluctuations in SC-FDMA signals i.e. low Peak to Average
Power Ratio (PAPR). A base station (BS) is called an Evolved NodeB (eNodeB) in the Long
Term Evolution and a mobile station (MS) is called a User Equipment (UE) in the Long Term
Evolution.
The data transmission in LTE is organized as physical resources which are represented by a
time-frequency resource grid consisting of Resource Blocks (RB). Resource blocks consist of
a no. of Resource Elements (RE). One of the major functionalities that have been assigned to
the BS is scheduling which is carried out by scheduler. The scheduler is responsible for
assigning the time and frequency resources to the different UE under the BS coverage. It does
that by allotting the RBs which are the smallest elements that can be assigned by a scheduler.
In the thesis we will be discussing the major scheduling algorithms that are used by the
schedulers, they are, Max Signal to Noise-Interference Ratio (SNIR) Scheduling, Round
Robin (RR) Scheduling and Proportional Fair (PF) Scheduling. In brief, the Max SNIR
scheduling assigns the resource blocks to the user with the highest Channel Quality Indicator
(CQI-received as a feedback from the UE by the BS) on that RB. In Round Robin scheduling
the UEs are assigned the resource blocks in turn (one after another) without taking the CQI
into account, allocating resources to the users equally. In Proportional Fair Scheduling the
UEs are assigned the resource blocks on the basis of the best relative channel quality i.e. a
combination of CQI & level of fairness desired.
The Max SNIR Scheduling, RR Scheduling and PF Scheduling have been simulated in a
MATLAB-based System Level Simulator (LTE MAC Lab) from IS-Wireless. The
performance of these scheduling algorithms in terms of throughput is analysed. We have
considered various scenarios for proper analysis in the thesis. Furthermore, the algorithms
have been analysed with their implementation in an LTE network test environment (deployed
in the Institute of Telecommunications within the Smart City of TPSA in the Warsaw
University of Technology).
1.2 Motivation and goals of the thesis
1.2.1 Motivation
The rise of the wireless industry in the past years along with the innovation of technologies
bringing large amount of multimedia services to the mobile devices led me to work in a field
where I could be a part of this wireless revolution. With LTE the future of mobile broadband
becomes brighter and clearer. According to various statistics, LTE would be the leading
technology to serve mobile broadband to the majority of cellular users in the coming years [6,
7].
Time and Frequency being scarce resources, the impact and importance of scheduling is very
high in a LTE network. To work on such a topic will not only help me to understand the
present technology and solutions but also help develop a better solution for the future.
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1.2.2 Thesis goals
The main purpose of this thesis is to verify and compare selected downlink and uplink
schedulers in LTE MAC Lab (aka Matlab version of 4G System Lab provided by IS-
Wireless) with their implementation in an LTE network test environment (deployed in the
Institute of Telecommunications within the Smart City of TPSA in the Warsaw University of
Technology). The simulation part of the thesis enables us to understand the scheduling
algorithms for the LTE networks in much more detail and gain experience in modelling and
simulation of such networks in detail. During this thesis a detailed study of the network
architecture and layers being proposed for LTE networks is carried out.
One of the main contributions of this dissertation is to work out a method to examine LTE
scheduling performance evaluation for teaching purposes.
1.3 Thesis Scope
This thesis is organized in 7 chapters. The rest of the chapters are organized as follows:
Chapter 2 gives an overview of LTE. Chapter 3 describes the concept of scheduling along
with the description of the scheduling algorithms under consideration. Chapter 4 discusses
the simulation and testing scenarios and results. Chapter 5 presents teaching proposals in the
form of a laboratory experiment. Finally chapter 6 draws the conclusion and gives
recommendations for future works. Chapter 7 details the various sources and references of
study.
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2. An Overview of LTE
This chapter will provide an insight into the technical details of Long Term Evolution as
underlined by the 3GPP. The chapter starts with describing the LTE requirements, the
transmission schemes used for uplink and downlink, followed by other important features
like MIMO.
2.1 LTE requirements
The 3GPP has laid out specific requirements that need to be fulfilled by LTE which are listed
in [10], with some of them listed below:
Peak Data Rates:
E-UTRA should support significantly increased instantaneous peak data rates. The supported
peak data rate should scale according to size of the spectrum allocation.
Note that the peak data rates may depend on the numbers of transmit and receive antennas at
the UE. The targets for downlink (DL) and uplink (UL) peak data rates are specified in terms
of a reference UE configuration comprising:
a) DL capability – 2 receive antennas at UE
b) UL capability – 1 transmit antenna at UE
For this baseline configuration, the system should support an instantaneous downlink peak
data rate of 100Mb/s within a 20 MHz downlink spectrum allocation (5 bps/Hz) and an
instantaneous uplink peak data rate of 50Mb/s (2.5 bps/Hz) within a 20MHz uplink spectrum
allocation.
Latency:
A user plane latency of less than 5 ms one-way and a control plane transition time of less than
50 ms from dormant to active mode and less than 100 ms from idle to active mode.
User throughput:
Downlink:
2-3 times higher downlink throughput than High Speed Downlink Packet Access (HSDPA)
Release 6 at the 5% point of the Cumulative Distribution Function (C.D.F).
3-4 times higher average downlink throughput than HSDPA Release 6.
The user throughput should scale with the spectrum bandwidth.
Uplink:
2-3 times higher uplink than Release 6 Enhanced UL at the 5% point of the CDF.
2-3 times higher average uplink throughput than Release 6 Enhanced UL (EUL).
The user throughput should scale with the spectrum bandwidth provided that the Maximum
transmit power is also scaled.
Mobility:
LTE shall support mobility across the cellular network and should be optimized for 0 to 15
km/h. Furthermore, should support also higher performance at 15 and 120 km/h. Connection
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shall be maintained at speeds from 120 km/h to 350 km/h (or even up to 500 km/h depending
on the frequency band).
Spectrum efficiency:
3-4 times higher spectrum efficiency (in bits/s/Hz/site) in downlink and 2-3 times higher in
uplink, compared to Release 6 HSDPA and EUL respectively.
Bandwidth/Spectrum flexibility:
LTE should support several different spectrum allocation sizes such as: 1.25 MHz, 1.6 MHz,
2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. in both uplink and downlink where the
latter is used to achieve the highest peak data rate, with both TDD and FDD modes. It should
also support the flexibility to modify the radio resource allocation for broadcast transmission
according to specific demand or operator‟s policy.
Furthermore the communication can take place both in paired (FDD) and unpaired (TDD)
bands. Paired frequency bands means that the uplink and downlink transmissions use separate
frequency bands, while in the unpaired frequency bands downlink and uplink share the same
frequency band.
Coverage:
Cell ranges up to 5 km support the above targets; up to 30 km will suffer some degradation in
throughput and spectrum efficiency and up to 100 km will have overall performance
degradation.
Given some of the advantages of an OFDM approach, 3GPP has specified OFDMA as the
basis of its LTE effort.
2.2 Multiple Access Techniques
3GPP LTE have selected different transmission schemes in uplink and downlink due to
certain characteristics. OFDMA has been selected for downlink i.e. from eNodeB to UE and
SC-FDMA has been selected for uplink i.e. for transmission from UE to eNodeB [12].
2.2.1 Downlink - Orthogonal Frequency Division Multiple Access
(OFDMA)
For downlink transmission LTE uses OFDMA which splits the data stream into many slower
data streams that are transported over many carriers simultaneously. The main advantage of
many slow but parallel data streams is that it leads to elongation of the transmission steps
which in turn help to avoid the issues of multipath transmission on fast data streams. This
scheme helps allocate radio resources to multiple users based on frequency (subcarriers) and
time (symbols) using OFDM. For LTE, OFDM subcarriers are typically spaced at 15 kHz and
modulated with QPSK, 16-QAM, or 64-QAM modulation.
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Fig. 1 : OFDM and OFDMA [28]
The full potential of OFDMA is utilised by proper scheduling as it allows the resources to be
used between multiple users flexibly by sharing the subcarriers, with differing bandwidth
available to each user versus time.
2.2.2 Uplink - Single Carrier - Frequency Division Multiple Access (SC-
FDMA)
For uplink transmission the use of OFDMA is not ideal because of its high PAPR when the
signals from multiple subcarriers are combined and hence as a result an alternative to OFDM
was sought for use in the LTE uplink. And as we know power consumption is a key
consideration for UE terminals and for this there was a need to adopt a transmission scheme
which wouldn‟t comprise with the requirements of LTE without putting too much pressure on
the power consumption of UEs. The solution came up in the form of SC-FDMA that suits
very well with the LTE uplink requirements. The transmitter and receiver architecture is
nearly the same as OFDMA. Furthermore it also offers the same degree of multipath
protection.
Fig. 2 : OFDM and SC-FDMA [28]
In SC-FDMA instead of dividing the data stream and putting the resulting substreams directly
on the individual subcarriers, the time-based signal is converted to a frequency-based signal
with an FFT function. This distributes the information of each bit onto all subcarriers that will
be used for the transmission and thus reduces the power differences between the subcarriers
[18].
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2.3 LTE Frame Structure
As per the description of LTE frame structure in [28] the downlink and uplink transmissions
are grouped in (radio) frame of length 10 milliseconds (ms). Each radio frame is divided into
10 subframes of 1ms duration each, with the subrame being further divided into 2 slots that
are 0.5 ms each. Each slot consists of 7 or 6 OFDM symbols for normal or extended cyclic
prefix used respectively [5]. The LTE frame structure is illustrated in the Fig. 3.
The smallest modulation structure in LTE is one symbol in time vs. one subcarrier in
frequency and is called a Resource Element (RE). Resource Elements are further aggregated
into Resource Blocks (RB), with the typical RB having dimensions of 7 symbols by 12
subcarriers. The RE and RB structure is also shown in Fig. 3. The number of symbols in a RB
depends on the Cyclic Prefix (CP) in use. During the use of normal CP the RB contains seven
symbols, whereas in case of extended CP which is used due for extreme delay spread or
multimedia broadcast modes, the RB contains six symbols.
Fig. 3 : LTE frame structure [18]
Due to the spectrum flexibility two frame types are defined for LTE, with Type 1 being used
in FDD while Type 2 is being used in TDD. Type 1 frames consist of 20 slots with slot
duration of 0.5 ms as discussed previously; whereas Type 2 frames contain two half frames,
where at least one of the half frames contains a special subframe carrying three fields of
switch information including Downlink Pilot Time Slot (DwPTS), Guard Period (GP) and
Uplink Pilot Time Slot (UpPTS). If the switch time is 10 ms, the switch information occurs
only in subframe one. If the switch time is 5 ms, the switch information occurs in both half
frames, first in subframe one, and again in subframe six. Subframes 0 and 5 and DwPTS are
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always reserved for downlink transmission. UpPTS and the subframe immediately following
UpPTS are reserved for uplink transmission. Other subframes can be used for either uplink or
downlink. Frame Type 2 is illustrated in Fig. 4.
Fig. 4 : Frame Type 2 [27]
The number of RBs that can fit within a given channel bandwidth varies proportionally to the
bandwidth. Logically, as the channel bandwidth increases, the number of RBs can increase.
The transmission bandwidth configuration is the maximum number of Resource Blocks that
can fit within the channel bandwidth with some guard band [28]. The table 2.1 shows the
LTE bandwidth and resource configuration.
Table 2.1 : Bandwidth and Resource blocks specifications [1]
We can notice here that subcarrier spacing remains same in all bandwidth configurations. The
best results in terms of throughput can be achieved by the bandwidth with maximum amout
of RBs.
2.4 LTE Downlink Physical Channels
As in other networks like UMTS, all higher layer signalling and user data traffic are
organized by the means of proper channels. In LTE the downlink channels have been defined
in [28] the following way:
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Fig. 5 : LTE Downlink channels [18]
We will be discussing the role and description of the physical downlink channels [28]
involved in LTE:
Physical Broadcast Channel (PBCH)
The PBCH is used to send cell-specific system identification and access control parameters
every 4th
frame (40 ms) using Quadrature Phase Shift Keying (QPSK) modulation. The
structure of PBCH is independent of the actual network bandwidth.
Physical Downlink Shared Channel (PDSCH)
The PDSCH is used to transport user data and is designed for high data rates. The Resource
Blocks associated with this channel are shared among users via OFDMA. The various options
for modulation include QPSK, 16- Quadrature Amplitude Modulation (QAM), and 64-QAM.
Spatial multiplexing is exclusive to the PDSCH.
Physical Control Format Indicator Channel (PCFICH)
The PCFICH is used to inform the UE how many OFDM symbols will be used for the control
information in PDCCH in a subframe. The number of symbols used ranges from 1 to 3. The
PCFICH uses QPSK modulation.
Physical Downlink Control Channel (PDCCH)
The PDCCH is used to inform UE about the uplink and downlink resource scheduling
allocations. It maps onto resource elements in up to the first three OFDM symbols in the first
slot of a subframe and uses QPSK modulation. The value of the PCFICH indicates the
number of symbols used for the PDCCH.
Physical Multicast Channel (PMCH)
The PMCH carries multimedia broadcast information with the use of modulation including
QPSK, 16-QAM, or 64-QAM. Multicast information can be sent to multiple UE