Cost-Effective LTE Advanced Relay Station Deployment

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Chapter- 1
INTRODUCTION
1.1 Introduction to LTE Advanced and IEEE 802.16m
The 3GPP Technical Report (TR) 36.913 [9] details the requirements for LTE-Advanced to
satisfy. The document stressed backward compatibility with LTE in targeting IMT-Advanced. It
does, however, also indicate that support for non-backward compatible entities will be made if
substantial gains can be achieved. Minimizing complexity and cost and enhanced service
delivery are strongly emphasized. The objective of reduced complexity is an involved one, but it
includes minimizing system complexity in order to stabilize the system and inter-operability in
earlier stages and decreases the cost of terminal and core network elements. For these
requirements, the standard will seek to minimize the number of deployment options, abandon
redundant mandatory features and reduce the number of necessary test cases. The latter can be a
result of reducing the number of states of protocols, minimizing the number of procedures, and
offering appropriate parameter range and granularity. Similarly, a low operational complexity of
the UE can be achieved through supporting different RIT, minimizing mandatory and optional
features and ensuring no redundant operational states. Enhanced service delivery, with special
care to Multimedia Broadcast/ Multicast Service (MBMS), will be made. MBMS is aimed at
realizing TV broadcast over the cellular infrastructure. It is expected, however, that such services
will be undersubscribed in 3G networks. It is hence very critical to enhance MBMS services for
4G networks as it will be a key differentiating and attractive service. LTE-Advanced will feature
several operational features. These include relaying, where different levels of wireless multi hop
relay will be applied, and synchronization between various network elements without relying on
dedicated synchronization sources. Enabling co-deployment (joint LTE and LTE-Advanced) and
co-existence (with other IMT-Advanced technologies) is also to be supported. Facilitating self-
organization/healing/optimization will facilitate plug-n-play addition of infrastructure
components, especially in the case of relay and in-door BS. The use of femto cells, very short-
range coverage BSs, will enhance indoors service delivery. Finally, LTE-Advanced systems will

also feature facilitating advanced radio resource management functionalities, with special
emphasis on flexibility and opportunism, and advanced antenna
techniques, where multiple antennas and multi-cell MIMO techniques will be applied. LTE-
Advanced will support peak data rates of 1 Gbps for the downlink, and a minimum of 100 Mbps
for the uplink. The target uplink data rate, however, is 500 Mbps. For latencies, the requirements
are 50 ms for idle to connected and 10 ms for dormant to connected. The system will be
optimized for 0–190 km/h mobility, and will support up to 500 km/h, depending on operating
band. For spectral efficiency, LTE-Advanced requirements generally exceed those of IMT
Advanced, for example, the system targets a peak of 30 bps/Hz for the downlink and 15 bps/Hz
for the uplink, while average spectrum efficiency (bps/Hz/cell) are expected to reach 3.7 (4 × 4
configuration) for the downlink and 2.0 (2 × 4 configuration) for the uplink. Support for both
TDD and FDD, including half duplex FDD, will be made possible. The following spectrum
bands are targeted.
WiMAX2 or IEEE 802.16m is the advance version of WiMAX which is based on its previous
version IEEE 802.16e with added features such as it supports 300 Mbps data rates with mobility
whereas 802.16.2-2004 supports data rate of 100 Mbps. Therefore, IEEE 802.11 can increase
VoIP capacity with low latency to meet the requirement of 4G (International telecommunication
union). WiMAX forum has name IEEE 802.16m as WiMAX2. WiMAX2 uses the OFDM
(orthogonal frequency division multiplex) and other advance antenna technology like MIMO
(multiple inputs and multiple outputs) for better performance. The main purpose of IEEE
802.16m WiMAX standard is to improve spectral efficiency, improve VoIP capacity, handover,
and speed coverage range. The IEEE 802.16m works with the radio frequency range from 2 to 6
GHz as well as it also supports scalable bandwidth of range 5 to 20MHz.
The main features of WiMAX2 are [1]:
 The peak and channel spectral efficiency has been increased which helps and provides
better spectral efficiency for the users at the cell edge.
 The overall VoIP capacity has also increased with the help of user plane latency, also the
handover drawback also decreased. The available channel bandwidth in WiMAX2 is
scalable to 40MHz.

 Throughput supposes to be at least three times more than the existing IEEE 802.16e or
mobile WiMAX.
 Mobility support should extend to 350 km/h
 Single user and multi user MIMO for throughput enhancement
 New and enhance RS which provides better throughput capability with MIMO
 It support multi cast and broadcast services
 Enhanced energy efficiency enabled for power savings
 It supports femtocells which are low power base station (BS) to enhance the coverage.
1.3 Problem Statement
In a LTE Advanced network there are two main entities involved in communication which are
Subscriber Station (SS) and a BS. A BS is typically a service provider which has backhaul
connectivity and SS subscribes to the BS for the service. A BS exchange control messages and
negotiate the connection parameters with SS before setting up the communication link with it.
These parameters may vary during the communication depending on the requirements and
availability of resources between the two entities. When a BS try to create link with a SS and if
the SS is within the range then BS communicate directly with SS. Otherwise, if SS station is out
of the range of the BS or there is coverage limitations or no LOS (line of sight) between the BS
and SS then RS is a cost effective solution to overcome this problem. There are two approaches
applied in the research towards improving the LTE Advanced network performance. Firstly the
placement method should need to be determined in order to cut down the cost as well as maintain
the QoS standard. The second scenario is based on the performance evaluation of WiMAX2
network using relay station with in depth analysis of how to increase throughput and reduce
delay parameters to improve overall network performance. The QoS class’s comparison also will
be included for network flow and its resource usage. In the course of research, various issues
have been addressed by providing solutions based on selection of RS and using different modes
of RS. LTE Advanced nodes are incorporated to produce useful functionalities; communication
models, antennas and other devices are technically enhanced. And using these ideas and products
LTE Advanced communication is brought to an advanced level, where multi-hop scenarios were

successfully simulated and studied. OPNET Modeller, version 16.0 is used for simulations and
all the models used in this research are based on features available or added to OPNET Modeller.
The performance of a LTE Advanced communication system is also based on some assumptions
as IEEE 802.16m relay station which support advance antenna technology like MIMO (Multiple
input multiple output) and directional antennas and it also will have the capability to work as full
fledge BS (Base Station). These enhanced features are not supported by OPNET Modeller 16.0.
To make the LTE Advanced relay system more competitive and applicable to meet the QoS
demands, LTE Advanced RS has been considered as a promising solution for throughput and
coverage enhancement. There are many open issues regarding cost effective deployment and
enhanced QoS need to be considered including: The main responsibility of RSs to work as
middle node and regulate the data transmission between the BS and Subscriber Stations (SSs).
As discussed earlier, RS are used to extend coverage of BS by placing RS at cell edge or
boundary where BS signals start to fades and there is no direct link between BS and SS or link
quality for the user out of the boundary is not very strong to communicate. To cover the cell area,
normally four relay stations are used to provide services to the users out of the range of BS,
however four relay stations can provide better QoS but overall cost also increase. In order to get
better QoS as well minimize overall cost, RS should need to be placed at in cost effective manner
so better results could be achieved as well as save the overall cost.
Another important aspect should need to consider for network performance evaluation
measurement by improving the QoS standards in different RS usage scenarios such as multihop,
with three and with four RS in order to compare the performance with throughput and delay
parameters to maximize the overall system capacity.
1.4 Aim and Objectives
The aim and objectives of the thesis are described below.
1.4.1 Aim
The aim of the thesis is to cost effectively deploy the RS in a LTE Advanced network and also to
takes measures to enhance the QoS and conduct an analysis
1.4.2 Research Objectives
 To acquire detail knowledge of LTE Advanced and WiMAX2 technology

 To investigate different methods and techniques for RS deployment in order to cut down
the costs.
 To understand the different problems in maintaining cost effective deployment of RS.
 To investigate and analyse different QoS characteristics such as throughput, network load
and end to end delay.
 To investigate and evaluate different techniques to improve overall system performance
which provides guaranteed QoS.
 To assess published major approaches (through literature review) on LTE Advanced RS
planning and optimization.
 To investigate advance antenna technology and MIMO to further improve coverage and
throughput in WiMAX2.
 To investigate and implement an efficient way to reduce delay and enhance throughput to
meet the QoS standard in 802.16m.
1.2 Relay Stations (RS)
Relay stations enhance the capacity, throughput and coverage area of BS (Base station) in the
technologies like WiMAX-2 and LTE. At early stages, relay stations were used to work as
repeaters, and their primary task was to boost the signals received from BS. However, the
booster did not have the capability to remove errors, increase throughput for long distance
communication and also cause inter cell interference. But, after the introduction of IEEE 802.16j
which is the first standard for relay station, various new features are added in RS to enhance the
functionality of the relay stations making them much more intelligent devices to work well with
BS and provide better performance to end users. The RS is capable of boosting the signal and
also it has some extra features like compression and decompression, error correction, and DF
(decode and forward). In LTE Advanced relay stations are either deployed at the cell edge to
extended coverage area or they are deployed within the cell to relay the BS signal into coverage
holes. Relay stations provide a cost effective, low coverage and easy to install solution for
coverage area extension and to eliminate coverage holes. Multi-hop wireless networks use two or
more relays to provide services to the users which are out of the range of BS. Instead of
installing multiple BS, use of multiple relay stations is a very cost effective solution. Relay
stations are very useful to ensure QoS in LTE Advanced as they increase coverage area,
eliminate coverage holes, increase throughput and capacity of the network. The figure above

shows the operation of relay stations in a LTE Advanced network. Here RS of NTR-RS (non
transparent relay station) is used to extend the coverage are as it installed at the edge of the cell
and relay stations of TR-RS (transparent relay station) are used to eliminate the coverage hole as
they are deployed within the cells where signal are obstructed, possibly by tall building or
mountains or base signal signals are not strong enough to communicate.


 Fig.1.1 Operation of relay stations in a LTE Advanced network
 The link from BS to Rs called relay link and from SS (subscriber station) to RS called
access link.
2.9 Overview of LTE Advanced Relay station
The RS technology works as middle node as it transmits the BS data to SS which is can be out of
the range of BS or in the area where signal strength is very low. The RS are widely used in all
the main today’s wireless technologies such LTE advance and WiMAX2 A RS does not have
backhaul connectivity as it get the signal from BSs in line of sight connectivity and it can be
connected with a BS through a wired, leased cable or radio link [2]. There are two types of
connections in RS communication known as access link and relay link which can be further
define as, the communication path between RS and BS is called a relay link where
communication is possible from BS to RS or RS to BS. The second path can be described as the
communication path between RS and EN is called access link. The main advantage of RS is to
extend the coverage, throughput and minimize the coverage gaps. The BS usually covered a cell
territory, however in NLOS communication due to tall buildings, forest and mountains can cause

in coverage gap where RS can be used to fill the gap and improve overall system performance.
There are different types of scenarios in wireless communication where RS plays vital role to
overcome and provide better performance, some of the key factors are:
 Low coverage due to poor SNR at the cell boundary.
 Less coverage or very low signal reception in dense urban area
 Cost of BS deployment too high in rural area.
RS can be deployed at the edge of the cell to extend the coverage or top of the building
in NLOS communication of BS for EN.
Chapter 1 Relaying Techniques
Based upon relaying or forwarding schemes Relays can be broadly classified in three categories
where each category have its own functionality depends on QoS demands and link adaptation.
The main techniques widely used in RS are
2.10.1 Amplify and Forward
In this technique, relays receive the signal, amplify it and retransmit it. It is the simplest form of
relaying and it requires minimum processing power at the RS. This is a non transparent
technique which means BS has no knowledge of RS. One major demerit of this technique is that,
since the relay amplifies the received signal, it also amplifies the noise received with the signal
which can degrade its performance.
2.10.2 Decode and Forward
This technique overcome the noise amplification problem by decoding the received data and
error correction before forwarding it hence only error free data is forwarded. This kind of
relaying is good if there is a good channel between BS and RS. If the channel is not good then
this causes ARQ overhead and degrades the performance.
2.10.3 Compress and Forward

In this technique RS compress the data before forwarding to EN or users. It is assumed that MS
also have direct transmission from BS. This technique can perform better if there is direct
transmission from BS to EN without using RS.
2.10.4 Adaptive Forwarding
This is additional technique used in new wireless standards such as 3GPP LTE and
IEEE802.16m. In this technique the methods of transmission can be changed depends on the
channel state information of both access link and relay link.
2.10.5 Pairing Schemes for Selection of Relay
There are two types of pairing schemes which can be used in selection process of RS when more
than two RS exist in the same cell.
2.10.6 Centralized Pairing Scheme
The BS collects information from all the neighboring RS and subscriber stations for paring of RS
with mobile stations because BS have full access to all the RS and subscriber stations within the
cell and range of BS. This scheme works with transparent RS mode and BSs updates pairing
information frequently.
2.10.7 Distributed Pairing Scheme
In this scheme, RS used two mechanisms for pairing with subscriber stations which are
 Contention based mechanism
 Local channel information In this pairing scheme BS has no fully access on all the
subscriber stations because
in this scheme paring scheme handled by non transparent RS for selection and communication.
2.10.8 Architecture of Relay Station
To understand the architecture of RS there are two basic fundamental can be used which are:
 Firstly, whether BS has awareness about nearest RS or not, if BS knows nothing about
RS then RS integration with service area is simpler, no change to the BS and no special
signaling between BS and RS are required. Here RS only act as a helper to the BS and it
poses no burden over BS. Earlier cellular systems such as GSM (global system for
mobile communication) used this kind of RS also called repeaters.
 Secondly, Two kinds of characteristics are popular in relay types which are DF and
second one is amplify and forward (AF), each has their own merits and demerits and
hence the use. Generally, AF equipment is less expensive than decode and forward

1.5 Research Design
The author divided the whole research thesis into four stages.
1) Problem Identification and Selection.
2) Literature study.
3) Building simulation.
4) Result analysis.
Fig.1.1 Research Methodology
1) Problem Identification and Selection
The most important phase, where it is important to select the proper problem area. Different
areas are studied with in mind about the interest of authors. Most of the time is given to this
phase to select the hot issue. The authors selected ZIGBEE as the area of interest and within
ZIGBEE the focus was given to the security issues.
2) Literature Study
Once the problem was identified the second phase is to review the state of the art. It is important
to understand the basic and expertise regarding ZIGBEEs and the security issues involved in
ZIGBEEs. Literature study is conducted to develop a solid background for the research.
Different simulation tools and their functionality are studied.
3) Building Simulation

The knowledge background developed in the literature phase is put together to develop and build
simulation. Different scenarios are developed according to the requirements of the problems and
are simulated.
4) Result Analysis
The last stage and important and most of the time is given to this stage. Results obtained from
simulation are analyzed carefully and on the basis of analysis, conclusions are drawn.
5) Simulation Tool
QUALNET tool is selected to carry out the simulation. QUALNET provide technologies,
protocols, communication devices for academic research, assessment and improvement. It is
efficient, robust and highly reliable which grant the user the ease of graphical interface,
developing and running the simulation and validation of the results.
6) Simulation Statistics
In QUALNET there are two kinds of statistics, one is Object statistics and the other is Global
statistics. Object statistics can be defined as the statistics that can be collected from the
individual nodes. On the other hand Global statistics can be collected from the entire network.
When someone choose the desired statistics then run the simulation to record the statistics.

Chapter 2
Background and Literature Review
Khan Mubeen Ahmed et al., [1] here author performed analysis of RS in WiMax networks by
using bandwidth allocation algo(BWA). Light WiMax simulator (LWX) is used for simulation
purpose. This paper focuses on wireless access as it is flexible and cost effective .RS are used in
order to extend the range of base stations for long distances .Various simulation parameters such
as routing protocol (AODV),transmission protocol(TCP) ,simulation time (300sec) etc are taken
in order to analyze the performance of RS.
Ehab H.Abdelhay et al.,[2] in this paper LTE-A multihop networks are used to satisfy the
requirements of coverage and capacity in minimum cost . Resource blocks (RB),adaptive
modulation and coding (AMC) schemes are used for zero multi-hop links overflow and for
maximizing network throughput with low bit error rate respectively.this paper mainly focus on
position of RS in LTE-A cell and for improving network performance and minimizes
asymmetric multi hop links data overflow.
Arra Ashok et al., [3] in this paper author introduced LTE-A and its various standards and
technical aspects. It is a radio platform technology .carrier aggregation scheme is employed to
fully utilize the wider bandwidth of up to 100 MHz .Antenna system and relaying are also used
to enhance the performance of radio communication and LTE.LTE-A works on providing
various world wide functionality such as roaming effects ,interworking, service of compatibility
etc .
Seonghwa Yun et al., [4] here author uses DRX mechanism (or discontinuous receive) for
energy efficient relay selection scheme. Relay energy efficiency metric is used .Two relay
selection schemes SNR-based and random selection are employed in Discrete Time Markov
Chain (DMTC) model of DRX .This paper shows high energy efficiency is achieved with
tolerable delay .
Naveed Ahmed et al., [5] in this paper author introduced Efficient Deployment of Relay
Stations in IEEE802.16m in order to achieve Cost Effective Performance.for this purpose author
uses Adaptive Modulation and Coding; Relay Station; Directional Antenna.He used three cells ,
each being divided into three sectors.he had efficiently placed 3 relay stations instead of 4 to

cover the cell territory of a base station. He used Adaptive modulation and coding scheme based
on QPSK with the coding rate of ¾ and directional antennas are used to simulate the topology in
OPNET.

2.2 LTE System Architecture
3GPP LTE system are designed to ensure a seamless Internet Protocol (IP) based connectivity
between UE and core network. The main component of LTE system architecture includes UE,
Radio-Access Network (RAN), Evolved Packet Core (EPC), while the combination of LTE RAN
and EPC is known as Evolved Packet System (EPS) as shown in figure 2.1.
1. Core Network
EPC is the evolution of GSM and WCDMA core network. Its flat architecture enables high
throughput services with lower latency level. The EPC consists of different logical nodes which
are briefly described below [4].
- Mobility Management Entity (MME) acting as control plane node of EPC, which is responsible
for handling the security keys and control the signaling between the UE and EPC. Serving
Gateway (S-GW) is the user-plane node acting as a mobility anchor point between EPC and LTE
RAN. It provides connectivity to other 3GPP technologies such as GSM/GPRS and HSPA.
 Packet Data Network Gateway (P-GW) is responsible for connecting EPC to the internet.
It also allocates the IP address to UEs. The P-GW is acting an mobility anchor point
between EPC and non-3GPP radio-access technologies, such as CDMA2000.
 Policy and Charging Rules Function (PCRF) controls the quality-of-service (QoS) and
charging.
 Home Subscriber Service (HSS) is a database node contains the subscriber related
information.
 Multimedia Broadcast Multicast Services (MBMS) implants the multicast/ broadcast
services in cellular systems in parallel with unicast services.
2. Access Network
The LTE radio-access network posses flat architecture, consists of Evolved Node B (eNB). It
handles all the radio-related functionalities of cellular network. The eNB uses S1 interface to
connect with EPC. It also connects with its neighbouring eNB via X2 interface, to enable
seamless active-mode mobility [4]. The EPC uses SGi interface to connect with internet.
3. Radio Protocol Architecture
A 3GPP LTE radio-access protocols comprised of a layered architecture offering radio bearers
for carrying the IP packets as described below [4].

 Packet Data Convergence Protocol (PDCP) execute the IP header compression, to
transmit with less number of bits over the radio interface. It also perform the ciphering
and ensures the security of transmitted data. There is one PDCP entity per radio bearer
configured for a terminal.
 Radio Link Control (RLC) handles the segmentation/concatenation and retransmission
of data. It offers services to the higher layers (PDCP) in the form of radio bearers. There
is one RLC entity per radio bearer configured for a terminal.
 Medium Access Control (MAC) controls the multiplexing of logical channels. MAC
layer is also responsible for hybrid-ARQ retransmissions and scheduling. It provides
services to RLC layer.
 Physical Layer (PHY) is responsible for typical physical layer functions such as
coding/decoding, modulation/demodulation etc. It provides services to MAC layer.
Figure 2.1: General Structure of LTE Architecture
2.3 LTE System Requirements
The concept of LTE is a step towards 4G communication technologies, ensuring the competitive
advantage of 3G technologies for future. The LTE system needs to provide long term efficient
solutions comparatively to its predecessor’s technologies, in order to enable improved network
coverage and capacity. The LTE system requirements are enlisted as follow [3]: 1. System
capability
a. Peak data rates
The LTE system aims to provide instantaneous peak data rates of 5 Mbps (with spectral
efficiency of 2.5 bps/Hz) and 100 Mbps (with spectral efficiency of 5 bps/Hz) in uplink (UL) and
downlink (DL) respectively, within a 20 MHz spectrum allocation.
b. Latency
The reduction of the system latency (in terms of control-plane and user plane latencies), is also
included in LTE main targets. The former refers to the time required for transition from non-
active states to active state. The non-active states comprised of camped-state and dormant state

and transition should be less than 100 ms and 50 ms respectively. The user-plane latency is
defined as the required one-way transmit time for Internet Protocol (IP) packet from UE to Radio
Access Network (RAN) edge node or vice versa.
2. System performance
a. Throughput
The LTE systems seeks to enable a uniform user experience over the cell area, by improving the
cell edge performance. Comparatively, it provides 2 to 3 times of HSDPA Release 6 cell-edge
user throughput in DL while 2 to 3 times of HSUPA in UL. In terms of averaged user
throughput, it is 3 to 4 times of HSDPA Release 6 in DL while 2 to 3 times of HSUPA in UL.
b. Spectrum efficiency
In DL case, LTE aims to achieve 3 to 4 times the spectrum efficiency of HSDPA Release 6, with
2 Tx and Rx antennas at the Node B and UE, respectively. While for UL, it is 2 to 3 times of
Release HSUPA 6. It has the ability to coexist with the earlier 3GPP technologies.
c. Mobility
The LTE allow the user mobility across cellular network. It needs to provides best performance
with good quality of service at low speed (0-15 km/h) as well as at high speed (15 to 20 km/h)
mobility.
d. Coverage
The LTE system should attain the performance targets for 5 km of cell radius in terms of
throughput, spectral efficiency and mobility. However, there might be a minor degradation in
throughput and spectral efficiency for 30 km cell range.
- Enhanced MBMS
The LTE system should allow the simultaneous provisioning of voice calls and Multimedia
Broadcast/Multicast Services (MBMS). The MBMS enables the multicast/broadcast services in
the mobile cellular networks.
3. Spectrum allocation
The LTE system support the inter-system handover with the existing deployed GSM and UMTS
networks under the constraint of acceptable impact on terminal complexity. Moreover, it should
operates in both, paired and unpaired spectrum, i.e. Frequency Division Duplexing (FDD) and

Time Division Duplexing (TDD). It also provides bandwidth scalability to operate at different
frequency bandwidth i.e. 1.25, 1.6, 2.5, 5, 10, 15, 20 MHz.
4. Architecture
Though having all IP based architecture, LTE system also needs to support real time and
conversational class traffic. Comparatively, LTE reduces the number of network interfaces
exiting in other technologies, such as, Evolved Node B (eNB) is the only radio interface between
the UE and Core Network (CN), which acts as base station reducing the network signaling and
jitters.
5. Cost
The Self-organizing Network (SON) features will enable the LTE systems of doing the self-
configuration and self-optimization of its network which will reduce the network planning and
optimization cost.
2.4 LTE system models:
In homogeneous networks, only a network of macrocells (MeNodeBs) serves the mobile users in
each cell. In such networks, the MeNodeBs have similar characteristics, e.g. antenna pattern,
transmission power, modulation, access method, etc. The cell splitting seems to be an applicable
approach to solve thecapacity problems in LTE networks, by allocation of more base stations in
the cells. However this approach is not economically feasible in dense urban areas to deploy
more number of MeNodeBs within the network. Therefore deploying a two-tier HetNet seems to
be an appropriate solution in a cost-effective way for both the network operator and users. The
two-tier network contains the macro nodes as the first tier, overlaid with the low-power/low-
complexity nodes in the second tier [51].
In this part, the functions of the proposed SON resource management algorithm in macro-femto
LTE-A networks are discussed. The application of the proposed resource management technique
is to share the available spectrum band among both the macrocell and femtocell layers in a two-
tier LTE-A network. In this regard, the additional femtocell sub-network (layer) is added into the
existing LTE macro sub-network, followed by the proposed modification in node model of home
evolved node-B (HeNodeB) in the network.
3.4.1. Channel Division

In this model, the initial resource channel of the system is divided into two main resource
sections, called as “Macro Sub-Channel” and “Femto Sub-Channel” to support macrocell and
femtocell users respectively. Each of the network sub-channels includes a number of component
carriers (CCs) which are positioned into the spectrum band, as is shown in Figure 3-4.
Figure 3-4: Sub-channel allocation for LTE-A macrocells and femtocells
To remove the coverage holes in homogeneous networks, picocells are generally used with a
coverage area between 40-75 meters, and an omnidirectional antenna with about 5dBi antenna
gain provides indoor coverage to users in public places e.g. schools, airports, etc. [52]. However
on the other hand, femtocells with 10-25 meters coverage and 10-100 mW power are used as
access points (APs) in home applications, which operate in licensed spectrum that is managed by
mobile operators. Femtocells connect to the cellular network via broadband communication
links, e.g. digital subscriber line (DSL) to enable fixed mobile convergence (FMC) [53].
3.4.2. Macrocell and Femtocell Air Interfaces
The macro-femto coordination architecture could be defined either within a centralised
coordination, or a distributed coordination [54]. In centralised coordination architecture, the
channel quality information from different BSs is gathered by a centralised controller. The
controller could be part of the radio network controller (RNC) entity in previous technologies

like HSPA and UMTS. However, in conventional LTE systems, due to the lack of RNC, this idea
has not been applicable.
On the other hand, in distributed coordination architecture, there is direct coordination among the
adjacent base stations to allocate appropriate resources to the users, especially the cell edge
users, as well as to mitigate inter-cell interference. The coordination is established through the
LTE interfaces X2 and S1 in evolved universal terrestrial radio access network (E-UTRAN)
platform [55]. The LTE X2 interface is used to make a direct communication between different
eNodeBs to exchange signalling information when needed, while a full mesh is not mandated
within an E-UTRAN network. The X2 interface is mainly used to exchange two types of
information: load/interference-related information and handover-related information. In addition
to this, LTE S1 interface is widely used for eNodeBs in SON networks to communicate with the
mobility management entity (MME) and serving gateway (S-GW) in the evolved packet core
(EPC) unit. Each of the X2 and S1 interfaces are split into two interfaces of control plane, and
user plane, which are based on stream control transmission protocol/IP (SCTP/IP), and general
packet radio service (GPRS) tunnelling and user datagram protocols (GTP/UDP5/IP) stacks
respectively [56]. At the proposed internal interfaces, as shown in Figure 3-5, the X2 interface is
used to communicate with the macrocell stations (eNodeBs), but obviously this X2
implementation is not applicable to directly link the femtocell stations (HeNodeBs), because of
their diversity and personal indoor implementation
Figure 3-5: Interfaces map for macro and femto tiers in LTE-A network

As a solution to link the fomtocells to the systems, the HeNodeB gateway (HeNB GW) is
proposed to be added into the system, as well as the existing MME/S-GW units for the femto tier
within EPC. Therefore, the S1 interface is used to initiate communication between HeNBs and
HeNB GW, as well as the MME/S-GW units [57]. LTE-A femtocells nodes use orthogonal
frequency division multiple access (OFDMA) air interface technology in cooperation with the
existing eNodeBs within the HetNets [51].
Figure 3-6 shows the S1 interface set in macro-femto interfaces, including the proposed
gateways and units. The HeNB nodes communicate with EPC module via S1-U and S1-MME
interfaces, while the HeNodeB gateway and management system entities and serving gateway
are relaying the packets from and to the femtocell stations.
Figure 3-6: The S1 interface set in macro-femto interfaces
Figure 3-6: The S1 interface set in macro-femto interfaces
3.4.3. Fractional Frequency Reuse
A frequency reuse scheme is introduced as an applicable solution in channel optimisation, while
also being the most effective solution in mitigating the effects of interference. All the
interference types in this regard happen only when the aggressor node and victim node use the
same frequency sub-channel [51]. Therefore, the fractional frequency reuse (FFR) scheme is
required for a planned sub-channel allocation among macrocell and femtocell users.
In case of using the frequency reuse scheme for channel optimisation, the main types of
interference are categorised into two main categories. The first category is when a femtocell

station interferes with another femtocell user, because of using the same sub-band, which is
called “Co-Tier Interference”. The second interference category is when a macrocell (or
femtocell) station interferes with a femtocell (or macrocell) user because of using the same sub-
band, which is called “Cross-Tier Interference”. Figure 3-7 shows the example scenarios of these
interference possibilities in frequency reuse. In practical assumptions, because of considering
macrocells as long-range base stations, the macro-to-macro co-tier interference is avoided in
practice, due to the long distances between the macrocell base stations.
Figure 3-7: Co-tier vs. cross-tier interference in frequency reuse
3.4.3.1. Strict Fractional Frequency Reuse Scheme
To obtain better network optimisation, each cell is divided into two zones called as centre-zone
and edge-zone. In strict FFR, for a cluster of N cells, the frequency reuse factor (FRF) of N is
applied to edge-zone macro users (MUEs), while the centre zone MUEs are allocated with a
common frequency sub-band, i.e. the FRF of 1. Therefore, the total of N+1 sub-bands are
required to cover all the MUEs in the cells. Although, the inter-cell co-tier interference is
mitigated for eNodeBs in strict FFR schemes, the cross-tier interference would be significant,
especially near the transition areas of the centre-zone and edge-zone [51]. In addition to this, the
co-tier interference may become severe for HeNodeBs in edge zones, as is shown in Figure 3-8.

Figure 3-8: Strict fractional frequency reuse scheme
3.4.3.2. Soft Fractional Frequency Reuse Scheme
The cell partitioning in soft FFR is similar to the strict FFR scheme. However in soft FFR
scheme the MUEs in the centre-zone are allowed to use the MUE sub-bands of the cell-edge
zone of the neighbouring cells. Also for the femtocells, the FUEs in the centre zone are allowed
to use the FUE sub-bands of cell-edge zone of the neighbouring cells, if is not used by macros in
the same cell-centre. Therefore, the soft FFR scheme is more bandwidth efficient, i.e. has higher
spectrum efficiency, in compared to the strict FFR. As a result of having more options in
selecting the sub-bands by the nodes, the co-tier interference would be reduced for both macro
and femto nodes.
However on the other hand, the cross-tier interference still needs to be mitigated for users near
the boundary of the centre and edge zones, as is shown in Figure 3-9. As the different colours
show the different combinations of sub-bands for the cell centres and also the cell edges (for
macrocell), each of the cell-centre areas is also allocated with a sub-channel from a different sub-
band compared to the neighbouring cells, which aims to reduce the drops in QoS by reducing the
possibility of co-tier interference with the neighbouring cells.

Figure 3-9: Soft fractional frequency reuse scheme
Figure 3-10 shows the sub-channel allocation for the cells 1, 2 and 3, using the power (p) versus
frequency (f). It can be observed in this figure, for example in the hexagonal cell 1, both the
macrocell in the cell centre and femtocell in the cell edge use F1 and F3 sub-bands, which could
result in cross-tier interference, especially in the centre-border transition area. Therefore, it is
also required for the sub-channel allocations, even in soft frequency reuse, to consider the cross-
tier interference, as well as co-tier interference.

Figure 3-10: Sub-channel allocation function in soft frequency reuse
3.4.3.3. Hybrid Fractional Frequency Reuse (HFFR) Scheme
As is previously discussed in soft FFR scheme, the co-tier interference is reduced due to the
dynamic sub-channel allocation, but on the other hand, the cross-tier interference still remains
and requires mitigation. Therefore, the hybrid fractional frequency reuse (HFFR) scheme is
proposed, which consists of both co-channel and orthogonal deployments for a two-tier network
[58].
Figure 3-11shows the orthogonal resource allocation for macrocell and femtocell tiers in the
proposed technique. At the first stage, the soft FFR is applied and the cell-centre nodes are
allocated with sub-channels from different sub-bands, as well as the cell-edge nodes. In addition
to this, the macrocell and femtocell tiers (including the cell-centre and cell-edge users) are
allocated with sub-bands in an orthogonal way similar to OFDMA. Therefore, the cross-tier
interference is also mitigated when the macrocells and femtocells with the same sub-bands
follow the orthogonal allocations.

Figure 3-11: Resource allocation for macrocell and femtocell in HFFR
This approach comes from a similar idea in dealing with intra-frequency/intra-cell interference,
which is normally avoided inside the cells due to the orthogonality between subcarriers in
OFDMA. The quality of some reference signals received by UE also plays a great role in
resource allocation of LTE networks. These reference signals in LTE are reference signal
received power (RSRP) and reference signal received quality (RSRQ) and each user is assigned
part of the spectrum based on these two signals. However RSRQ provides a more effective
metric for the complex optimisation of the reference signal, since it is based on SINR [15,59].
2.3 LTE-Advanced
The LTE-Advanced (Release 10) is an evolution of LTE, which is to compliant with the IMT-
Advanced requirements and targets. It aims to provide peak data rates of up to 1 Gbps (for low
mobility) and 500 Mbps in DL and UL respectively. LTE-Advanced is required to reduce the
user- and control-plane latencies as compared to LTE (Release 8). It targets to achieve peak
spectrum efficiency of 30 bps/Hz and 15 bps/Hz in DL and UL respectively. LTE-Advanced
enhances the cell edge user throughput (5%-ile user throughput) in order to achieve a
homogeneous user experience in cell. It will support the mobility across the cell from 350 km/h
to 500 km/h depending on operating frequency band [5]. The LTE-A is backward compatible
with existing LTE system and support the existing LTE enabled UEs. LTE-Advanced is expected
to be bandwidth scalable and support wider bandwidth up to 100 MHz. It should also support the
FDD and TDD duplexing for the existing paired and unpaired band, respectively. It enables

network sharing and handover with existing legacy radio-access technologies. LTE-Advanced
also considers low cost infrastructure deployments. It will allow the backhauling using LTE
spectrum in order to reduce the cost per bit. Summary of 3GPP LTE-Advanced system
performance in comparison with 3GPP LTE is given by table 3.1.
Wimax In 2WIMAX
2.11 WiMAX
The WiMAX family (802.16) concentrate on two types of usage models: a fixed WiMAX and
mobile WiMAX. The basic element that differentiates these systems is the ground speed at
which the systems are designed to manage. Based on mobility, wireless access systems are
designed to operate on the move without any disruption of service; wireless access can be
divided into three classes; stationary, pedestrian and vehicular. A Mobile WiMAX network
access system is one that can address the vehicular class, whereas the fixed WiMAX serves the
stationary and pedestrian classes.
2.11.1 Types of WiMAX:
This raises a question about the nomadic wireless access system, which is referred to as a system
that works as a fixed WiMAX network access system but can change its location.
A. Fixed WiMAX: Broadband service and consumer usage of fixed WiMAX access is
expected to reflect that of fixed wire-line service, with many of the standards-based
requirements being confined to the air interface. Because communications takes place via
wireless links from WiMAX Customer Premise Equipment (WiMAX CPE) to a remote
Non Line-of-sight (NLOS) WiMAX base station, requirements for link security are
greater than those needed for a wireless service. The security mechanisms within the
IEEE 802.16 standards are sufficient for fixed WiMAX access service. Another
challenge for the Fixed WiMAX access air interface is the need to set up high
performance radio links capable of data rates comparable to wired broadband service,
using equipment that can be self installed indoors by users, as is the case for Digital
Subscriber Line (DSL) and cable modems. IEEE 802.16 standards provide advanced

physical (PHY) layer techniques to achieve link margins capable of supporting high
throughput in NLOS environments.
B. Mobile WiMAX 802.16a extension, refined in January 2003, uses a lower frequency of
2 to 11 GHz, enabling NLOS connections. The latest 802.16e task group is capitalizing
on the new capabilities this provides by working on developing a specification to enable
Mobile WiMAX clients. These clients will be able to hand off between WiMAX base
stations, enabling users to roam between service areas.
2.11.2 WiMAX Architecture
WiMAX is based on IEEE standard for high layer protocol such as TCP/IP, Voice over Internet
Protocol (VoIP), and SIP etc. WiMAX network is offering air link interoperability. The
Architecture of WiMAX is based on all IP platforms. The packet technology of WiMAX needs
no legacy circuit telephony. Therefore it reduces the overall cost during life cycle of WiMAX
deployment. The main guidelines of WiMAX Architecture are as under
 It support structure of packet switched. WiMAX technology including IEEE 802.16
standard and its modification, suitable for IETF and Ethernet.
 Offers flexibility to accommodate a wide range of deployment such as small to large
scale. WiMAX also support urban, rural radio propagation. The uses of mesh topologies
make it more reliable. It is the best coexistence of various models.
 Offers various services and applications such as multimedia, Voice, mandated dogmatic
services as emergency and lawful interception. Provides a variety of functions such as
ASP, mobile telephony, interface with multi internetworking, media gateway, delivery of
IP broadcasting such as MMS, SMS, WAP over IP.
 Supports roaming and Internet working. It support wireless network such as 3GPP and
3GPP2. It support wired network as ADSL.
 Supports global roaming, consistent use of AAA for billing purposes, digital certificate,
subscriber module, USIM, and RUIM.
 The range is fixed, portable, nomadic, simple mobility and fully mobility.
The WiMAX architecture consists of three logical entities: BS, ASN, and CSN. All three
correspond to a grouping for functional entities which may be single or distributed physical
device over several physical devices may be an implementation choice. The manufacturer
chooses any implementation according to its choice which is may be individual or combine.

 Base station (BS): The responsibility of Base station (BS) is to provide that the air
interface to the MS. The other functionality of BS is micro mobility supervision
functions. The handoff prompting, supervision of radio resource, classification of traffic,
DHCP, keys, session and multicast group management.
 Access service network (ASN): The ASN (Access Service Network) used to describe
an expedient way to explain combination of functional entities and equivalent
significance flows connected with the access services. The ASN offers a logical boundary
for functional of nearby clients. The connectivity and aggregation services of WiMAX
are personified by dissimilar vendors. Planning of functional to logical entities
represented in NRM which may execute in unusual ways. The WiMAX forum allows
different type of vendors implementation that is interceptive and well-matched for a
broad variety of deployment necessities.
 Connectivity Service Network (CSN): CSN is a set of functions related to network
offering IP services for connectivity to WiMAX clients. A CSN may include network
fundamentals such as AAA, server, routers, and user database and gateway devices that
support validation for the devices, services and user. The Connectivity Service Network
also handled different type of task such as management of IP addresses, support roaming
between different NSPs, management of location, roaming, and mobility between ASNs
The WiMAX architecture is offering a flexible arrangement of functional entities when
constructing the physical entities, Because AS may be molded into BTS, BSC, and an
ASNGW, which are equivalent to the GSM model of BSC, BTS and GPRS Support
(SGSN).
2.11.3 How WiMAX Works?
WiMAX make possible the broadband access to conservative cable or DSL lines. The working
method of WiMAX is little different from Wifi network, because Wifi computer can be
connected via LAN card, router, or hotspot, while the connectivity of WiMAX network
constitutes of two parts in which one is WiMAX Tower or booster also known as WiMAX base
station and second is WiMAX receiver (WiMAX CPE) or Customer Premise Equipment. The
WiMAX network is just like a cell phone. When a user send data from a subscriber device to a
base station then that base station broadcast the wireless signal into channel which is called

uplink and base station transmit the same or another user is called downlink. The base station of
WiMAX has higher broadcasting power, antennas and enhanced additional algorithms. WiMAX
technology providers build a network with the help of towers that enable communication access
over many kilometres. The broadband service of WiMAX technology is available in coverage
areas. The coverage areas of WiMAX technology separated in series of over lied areas called
channel. When a user sends data from one location to another the wireless connection is
transferred from one cell to another cell. When signal transmit from user to WiMAX base station
or base to user (WiMAX receiver) the wireless channel faces many attenuation such as fraction,
reflection, refraction, wall obstruction etc. These all attenuation may cause of distorted, and split
toward multi path. The target of WiMAX receiver is to rebuild the transmitted data perfectly to
make possible reliable data transmission. The orthogonal frequency division multiplexed access
(OFDMA) in WiMAX technology, is a great technique used to professionally take advantage
from the frequency bands. The transmission frequencies of WiMAX technology from 2.3MHz to
3.5 GHz make it low price wireless network. Each spectral profile of WiMAX technology may
need different hardware infrastructure. Each spectrum contains its bandwidth profile which
resolved channel bandwidth. The bandwidth signal is separately in OFDMA (Orthogonal
Frequency Division Multiplexed Access) which is used to carry data called sub carrier.
Transmitted data divided into numerous data stream where everyone is owned to another sub
carrier and then transmitted at the same broadcast interval. At the downlink path the base station
broadcast the data for different user professionally over uninterrupted sub-carriers. The
independency of data is a great feature of OFDMA (Orthogonal Frequency Division Multiplexed
Access) that prohibit interfering and be multiplexed. It also makes possible power prioritization
for various sub carriers according to the link quality. The sub carrier having good quality carry
more data since the bandwidth is narrow. WiMAX is providing quality of service (WiMAX
QoS) which enables high quality of data like Voice over Internet Protocol (VoIP) or TV
broadcasts. The data communication protocol from base station is alternative of quality of
service (WiMAX QoS) application and offering video streaming. These types of data translated
into parameters or sub carriers per user. All type of technique is carrying out together to speed up
coverage, bandwidth, efficiency and number of users. The base station of WiMAX has ability to
cover up 30 miles. WiMAX technology supports various protocols such as VLAN, ATM, IPv4
Ethernet, etc.

.13 Advantages of WiMAX Technology:
 Coverage: The single station of WiMAX can operate and provide coverage for hundreds
of users at a time and manage sending and receiving of data at very high speed with full
of network security.
 High Speed: The High speed of connectivity over long distance and high speed voice
makes it more demanded in hardly populated areas plus compacted areas.
 Multi-functionality: WiMAX perform a variety of task at a time such as offering high
speed internet, providing telephone service, transformation of data, video streaming,
voice application etc. WiMAX is a great invention for new era because WiMAX has
enough potential for developing and opportunity to offer various types of services for
new generation. Now you can connect Internet anywhere and browse any site and make
possible online conference with mobile Internet, multimedia application never let you
bored, IPTV stay you up to date etc.
 Stay in touch with End user: WiMAX network always keep stay in touch with your
friends and all others using same WiMAX network because it provide absolute
communication service to the end users to make possible rich communications.
 Infrastructure: WiMAX infrastructure is very easy and flexible therefore it provides
maximum reliability of network and consent to actual access to end users.
 Cheap Network: WiMAX is a well-known wireless network now days because it
provides a low cost network substitute to Internet services offered via ADSL, modem or
local area network.
 Rich Features: WiMAX is offering rich features which make it useful. WiMAX offers
separate voice and data channel for fun, the semantic connection make your network
more secure then before, fast connectively, license spectrum, liberty of movement etc.
 WiMAX vs Wifi: The WiMAX network providing much higher speed and very long
range as compared to Wife Technology.
 Smart antenna and Mesh Topology: The use of smart antenna in WiMAX network
offering high quality widest array which enable you to make possible communication on
long route without any encryption. It offers 2.3, 2.7, 3.3 and 3.8 GHz frequency ranges.
The use of Mesh topology in WiMAX network for the expansion is an extensive
spectrum of antennas for commercial as well as for residential users.

 Ultra wide Band: The unique and excellent infrastructure of WiMAX is offering Ultra-
Wideband. Its exclusive design is providing range from 2 to 10 GHz and outstanding
time response.
 Homeland Security: Security options of WiMAX Technology also offer very high
security because of encryption system used by WiMAX. Now you can exchange your
data on whole network without any fear of losing data.
2.14 WiMAX Limitations:
 Low bit rate over Long distance: WiMAX technology offering long distance data range
which is 70 kilometres and high bit rate of 70Mbit/s but both features doesn‟t work
together when we will increase distance range the bit rate will decreased and if we want
to increase bit rate then we should reduce the distance range.
 Speed of connectivity: The WiMAX other drawback is that any user closer to the tower
can get high speed up to 30Mbit/s but if a user exist at the cell edge from the tower can
obtain only 14Mbit/s speed.
 Sharing of bandwidth: In all wireless technology the bandwidth is shared between users
in a specified radio sector. Therefore functionality could go down if more than one user
exists in a single sector. Mostly user have a range of 2- to 8 or 12 Mbit/s services so for
better result additional radio cards added to the base station to boost the capability as
necessary.
 WiMAX vs Wi-Fi: Any one can build up a Wi-Fi network but to set up a WiMAX
network is really expensive so it is very hard for everyone that they pay large mount for
the setup and frequency license of WiMAX in a region.
2.15 Standards Used:
The IEEE 802.16 standards is the back bone to which Wi-Max is based, there have been a
number of different standards over the years from 2001. It is important to note for WiMax to be
successful and accepted world wide a universally compatible set of specifications and settings
should be agreed on to consider it to break in the world wide market. One example of this would

be the allocation of spectrums (Shon and Choi, 2007). The list below shows the main Current
standards as well as the future standards in WiMAX
2.15.1 Current Standards used:
WiMAX architecture entails looking at the “nuts and bolts “on how the operation of WiMax is
carried out from the different levels of OSI layer and to get a deeper understanding of the set up
of WiMax. A separate section on the Security side will follow. A first look at the first start of the
features of WiMax.
Table 6 Current Standards used
Standard Description
802.16.2-2004 This standard provides recommendations for
the design and coordinated deployment of
broadband wireless systems enabling a
control over interference and allow for
coexistence with other devices using radio
waves such as Radio and other transmissions.
(802.16.2-2004 ) (IEEE standard, 2003).
802.16k-2007 This standard is a revised version of the
802.1D standard to accommodate the support
of WImax. It links many 802 Projects such as
Ethernet and Wifi to allow communication,
to and from the MAC (Medium Access
Control Layer).

802.16j-2009 Specifies the standard for multihop relaying .
Multihop relaying occurs when there is more
than one Base Station used in the
communication process in which
communication between Base stations
themselves is needed. (802.16j-2009)
(Dai and Xie, 2010)
802.16m-2011 This is one of the most recently released
amendments to a version of the 802.16
standard that will offer significantly higher
coverage and capacity improvements. I t
With the standard being commercially
available in June 2012. (802.16m).
802.16-2009 This standard allows for interoperability
between the fixed and mobile broadband
wireless access which caters for a multiple of
wireless technologies from 3G to HSPDA
(High Speed Download Packet Access).
2.16 Layers in WiMAX Architecture
WiMAX architecture entails looking at the “nuts and bolts “on how the operation of WiMax is
carried out from the different levels of OSI layer and to get a deeper understanding of the set up
of WiMax. A separate section on the Security side will follow. A first look at the first start of the
features of WiMAX.
Physical Layer
The physical layer represents the transmission of raw bits rather than the logical data packets
over physical link connecting network nodes or in WiMAX case stations. This layer represents
the foundations of data communication between devices and is where the WiMAX structure can
be further understood in more detail (Andrews, et al. 2007).
The WiMAX Physical layer is based on a transmission scheme known as orthogonal frequency
division multiplexing (OFDM) (Ergen, 2009). This scheme is widely used by Wi-Fi as well as

DSL networks and is considered an efficient scheme for a large data rate transmission in NLOS
(None line of Site) Data communications. (Andrews, et al. 2007). OFDM is a type of
multicarrier modulation which divides a high-bit-rate data stream in to several parallel lower bit-
rate streams and modulates each stream on a separate carrier theses carriers are also known as
subcarriers (Cho et al, 2011). It is essential the through the separation of data into smaller
parallel streams it allows the data to be transmitted with limited delay spread (Ergen, 2009).
Delay spread is the term used to compare the difference between the fastest data transmission
time possible with the current transmission time (Cho et al, 2011).
The WiMAX Physical layer is also responsible for slot allocation and framing over the radio
frequency. The minimum time-frequency resource that can be allocated by a WiMAX base
station to a given link is called a slot. Each slot consists of one sub channel over one, two, or
three OFDM symbols, depending on the particular sub channelization scheme being used (Cho
et al, 2011). A continuous series of slots assigned to a given user is called that user’s data
region; scheduling algorithms could allocate data regions to different users, based on demand,
and the type of QoS required (Andrews, et al. 2007). As there is some foundation in this layer
from being used with success in other network configurations such as Wi-Fi. What are the
advantages of using this form of transmission for WiMAX?
There are also a number of disadvantages associated with OFDM that have room for
improvements one problem that stands out is OFDMs susceptibility to phase noise and frequency
dispersion and OFDM will eventually need to mitigate these imperfections in the long run for
further improvements to be made in download and data access rates (Andrews, et al. 2)
Table 8 Feature of OFDMA used in WiMAX
Feature of OFDMA used in WiMax Description
Reducing Complexity of Communications Reducing complexity of Communications
can save on Processing power and thus
save on battery bower when using battery
powered mobile stations. (PHY2).

Graceful degradation of performance
under excess delay spread.
OFDM is suited for adaptive modulation and
coding which allows the system to make best
of the available channel conditions e.g. if a
base station encounters noise2 from
external sources. (PHY2)
Exploitation of frequency diversity. OFDM accommodates coding and
interleaving across subcarriers in the
frequency domain i.e. can make full use of
the options and sources available to it and
get around issues such as fading. WiMAX
defines subcarrier permutations making it
easier to build systems that exploit
this.(PHY3)
Robust against Narrow band interference This type of interference can only affect a
small portion of the subcarriers. (PHY2)
Mac Layer
The primary function of the WiMAX MAC layer is to provide a effective interface between the
higher transport layers and the physical layer. One could look at it as connecting the next stage
of communication between devices. When transmitting a packet the MAC layer takes a packet
from the upper layer this packet is also known as MAC service data units (MSDUs) and then
organises them in to MAC protocol data units (MPDUs) (Andrews, et al. 2007).
The WiMAX MAC design includes another layer known as convergence sub layer that enables
it to communicate with a variety of higher –layer protocols such as ATM, IP and any unknown
future protocol. WiMAX MAC layer is designed to support high peak bit rates while
maintaining a high QoS it also allows for a lot of flexibility during transmission (Sekercioglu, et
al. 2009).
In WiMAX the MAC layer at the base station is in charge of allocating the bandwidth to all
users from uplink to downlink. However there are times when the mobile station (MS) is able to

request its own bandwidth depending on a particular service required to run e.g. browsing or
video (Ruuska, et al. 2011). This can increase the efficiency of service. However the ability to
request your own bandwidth is periodically handed out to MS also known as pollin (dependant
on the demand of the service and where there is high demand there would be less opportunity to
request own bandwidth.
The QoS is the fundamental part of the WiMAX MAC layer design it does this by maintaining
connection oriented MAC architecture. The BS and MS will first establish a connection but
prior to any data transmission the BS and the MS establish a unidirectional logical link, called a
connection, between the two MAC-layer peers (Sekercioglu, et al. 2009). Each connection is
identified by a connection identifier (CID), which serves as a temporary address for data
transmissions over the particular link. In addition to connections for transferring user data.
WiMAX also defines a concept of a service flow. A service flow is a unidirectional flow of
packets with a particular set of QoS parameters and is identified by a service flow identifier
(SFID). The QoS parameters could include traffic priority, maximum sustained traffic rate,
maximum burst and jitter. These will be just some of the parameters being measured in the
project as well (Sekercioglu, et al. 2009). There are a large list of WiMAX MAC scheduling
services but what are the main and vital MAC services used by WiMAX to ensure its reliability.
Table 9 Description of Mac Scheduling
MAC scheduling Description
Unsolicited grant services (UGS) Allows for fixed size data packets at a
constant bit rate. These would be especially
useful for VoIP (Voice over IP). Running
applications such
as Skype. Best measure by latency, tolerated
jitter request transmission policy (Ruuska, et
al. 2011).

Real-time polling Services Supports Applications such as MPEG video
that generate variable size data packets on a
periodic basis. Measured by maximum
latency.( Ruuska, et al. 2011)
Non-real-time polling service Design to support delay tolerant data
streams such as FTP or web Browsing.
Which include variable size data and a
minimum guarantee. (Villapol, and
Chatterjess, 2010).
Best-Effort Service Supports Web browsing and any other
applications that don’t require a minimum
service level guarantee.
Extended real-time variable rate Supports real time applications such as
video conferencing
2.4 Cost effective Deployment of Multi-hop Relay Networks
There are different types of challenges in planning and optimization of RS in order to get better
QoS with cost effective deployment. The cost is the main factor for any type of technology.
Therefore a cost effective deployment solution could provide better performance results as well
as save the overall deployment cost.
2.4.1 Cost Analysis of Relay station
Generally four RS cover the territory of the BS in order to get guaranteed QoS for the users out
of the range of BS. However, BS planning and placement is another major factor in wireless
industry. Generally a site can be divided into three parts consist of backhauling, BS equipment
and overall site infrastructure. The backhauling is the connection of BS to the core network with
point to point or leased line. The BS equipment can be antennas, material for tower height and
infrastructure can consist of number of equipments like back up power units. The RS does not
have any connection with backhaul as it connected with nearest BS to provide services to EN

(end nodes). The position of the RS is also an important issue for RS placement in the area where
SNR (signal to noise ratio) is high and link budget is good. The table below shows the elements
needs to be considered as CAPEX (Capital Expenditure) and OPEX (Operational Expenditure)
for BS and RS deployment. In the table the one of cost for spectrum licence, research and
marketing has not been considered. The CAPEX and OPEX may be different dependent on the
scenario type such as urban, dense urban or in rural areas.
2.4.2 Relay station Placement
The design and implementation of WIMAX2 relay station model based on non transparent
modes. The approaches and techniques used can improve the operation of non transparent mode.
Whether LTE Advanced operators could provide better services to end users depends on
available resources. The more capacity which is made available within cell or region, the large
amount of data can be delivered. The critical aspect of this drawback is the type of services the
end users can access e.g. video, voice or data. This could be more complex in multihop scenarios
where more than one RS connected and providing services to the users out of the range of BS
and primary RS. Therefore, to satisfy end users requirements and meet QoS standard, it is very
important to determine some key issues like the end users requirements, overall load and what
type of requirements end users are demanding e.g. video streaming, audio or data as the
applications like online gaming or video streaming consume too much bandwidth when
compared with voice and data applications. In order to achieve better QoS standards, the
placement of RS should be carefully examined with site location, placement methods and area
zone where RS can perform better. In [59], writer deployed RS with AMC (adaptive modulation
and coding) by dividing into zone based on QPSK (Quadrature phase shift keying), 16QAM
(Quadrature amplitude modulation) and 64 QAM. The writer explained the advantages of AMC
scheme with deployment of RS and differentiated the deployment in three zones. The available
SNR and useful bits per symbol can be calculated by modulation scheme and its coding rate [64].
The BS nearside zone can be assumed on higher modulation and coding rate where SNR is high
and high data rate can be sent and receive. However, the area nearside cell edge can be defined
as QPSK and depending on the coding rate data rate is not as much as in higher modulation
schemes. As an extension for PMP (point to multipoint) mode the MMR (mobile multi hop
relay) mode in IEEE 802.16j was introduced to fill the communication gaps. As far as the better

performance, coverage, capacity and considering some other major advantages of RS but we also
need to bear in mind some critical aspects of RS. For example it also cause interference and if
deploy more relays then it also exceeds the cost compare to BS as in [49, 51], the RS deployment
in cost effective manner and also by simulated work showed the reduction of cost. The authors in
[49] mentioned in detail and analyze the cost of BS and RS in order to achieve the guaranteed
QoS. The QoS standard is based on better throughput less delay and packet loss The location or
placement of relays station is also another problem as the network operators will always like to
have cost effective solution to provide satisfactory service. RS at the cell edges are better for
coverage extension and relays between the BS and the cell edge are better for capacity
enhancement.
2.4.3 Placement and Capacity Requirements for Relay station Deployment
Before the deployment of BS and RS, it is very important to measure the overall system capacity
then specify the capacity requirement as it’s good to investigate the target city or region based on
population density, population growth rate and customer distribution etc [48]. Different user
demand different applications and some applications require large bandwidth and spectrum in
order to fulfil the user requirement such as voice applications, video streaming, video
conferencing and all other multimedia applications require more bandwidth as compare to users
who just require only simple applications like emailing and surfing internet. Also it depends on
the zone where of RS based on AMC [59]. As compare with other multi-hop networks routings
issues of relay based networks are less challenging because of that if has purpose full effects on
achievable throughput of such type of systems. System capacity is been reduced during
transmission through RS in two different transmission phases comparing with a data duplication
over RS which may affect the capacity of system. In relay based system may be higher delay will
be occurred because of use of multi-hop networks as comparing with single-hop network. The
DF (decode and forward) has studied widely and has much research done on this technique as the
writer in [53]. In this paper the author developed an Omni-directional relay scheme with multiple
sources using DF relay scheme, in this scheme every node can transmit multiple messages in
different directions by combining them into a single signal. However by applying this Omni
directional relay technique it can cause interference and also can cause week signal strength by
spreading the signal around. In [18], the authors present a method for effective post processing

processes for throughput at the receiver, but some other factors should be taken in consideration
in addition to the previously mentioned issues. To sum up, the planning process in LTE
ADVANCED can be modeled as a multi objective optimization problem. The cost functions also
to be considered:
 Cost
 Coverage
 Performance (Throughput)
 Interference
Using the multi-objective optimization framework, the time used for simulation may be a little
long. A combination of both analytical study and simulation could be used to improve the speed
of optimization, for example, theoretical analysis on network relay. Also new simulation
techniques using OPNET can be considered to increase the simulator efficiency.
2.5 Adapted Approaches to Improve LTE Advanced Relay Station
Performance
There are so many key techniques used to improve the performance of LTE ADVANCED based
RS included radio resource allocation, Advance antenna techniques, relay protocols, link
adaptation, MIMO and frequency reuse etc.
2.5.1 QoS with Delay Minimization and Throughput Enhancement
AMC schemes used network for better performance [10, 11, 13]. The error correction techniques
can be applied to UL (uplink) and DL (downlink) transmission which is adjustable as the higher
modulation constellations can provide better throughput. However, the BS assigned higher
modulation constellations to the users allocated nearside of the BS. There are other physical
medium like advanced antenna systems can be uses to improve throughput and link reliability
[12]. LTE Advanced especially WiMAX2 allows multiple antennas to be used at the transmitter
and the receiver. In order to get enhanced results IEEE 802.16m use new antennas technologies
including MIMO, frequency reuse and Comp (Coordinated multipoint) etc. The frequency
planning and frequency reuse are another techniques used in WiMAX2. These techniques reduce
the interference and therefore increasing the capacity. [11]
 Optimum frequency assignments can be applied by considering
 Site locations

 Power levels
 User distribution
 Spectrum availability
 Geography and building characteristics.
In OFDMA (Orthogonal frequency division multiple access) based technologies, hexagonal cell
is used to denote the area covered by BSs and RS. The RS cluster in the following includes
single RS or several adjacent RS; the frequency reuse method follows four rules [8]: Each RS
cluster has an isolation band [9].
 All the users are served by the BS except those within the coverage of RS cluster.
 The RS in each RS cluster could reuse the resource out of its isolation band.
 RS in each RS cluster could reuse the resource in its isolation band selectively depending
on the interference measurement or throughput decreasing.
2.5.2 Coverage and Capacity Enhancement Using Relay station
In LTE ADVANCED, most efforts have been aimed to improve spectral efficiency. This can be
achieved using one or more of the following approaches: MIMO large increase in signals
bandwidth and cross-layer optimizations. In [15] they present results for different simulation
scenarios and show that RS can provide an improvement in SINR coverage and spectral
efficiency. In [16] results for the coverage extension and capacity enhancement of RS in a
realistic scenario are presented. In [17], the writers introduce the algorithm of coverage angle and
coverage range to establish the relation between the coverage extensions achieved with RS. In
[18], the writers present an analysis of coverage extension with mobile relays and in [19] they
propose dynamic load balancing schemes based on the integrated cellular and using point to
multipoint point relaying systems. The BS and RS transmit signals with a certain power so that
the average received power at the border of the cell is reaching to the end users without path loss
and shadowing. The main factors in path loss are the frequency band and the distance from
source to destination as the path loss and attenuation caused by higher frequencies used by
neighboring cell. Also shadowing is caused by obstacles between the source and the destination
which cause reflection and scattering. The increase in the required received power results in the
decrease of the coverage. As more users increase in the cell or in the case of load, the coverage
area decreases. The coverage and the capacity in a cell have both advantage and disadvantage as
higher frequencies are a disadvantage for coverage, but it’s an advantage when it comes to

capacity. Capacity is another important factor which affects the LTE ADVANCED performance.
In general term we can determine capacity by the amount of data that can be delivered to the user
and from the user [26]. In a LTE ADVANCED system, user normally access internet for surfing
net, video streaming and voice applications and these applications or user requirements applies
or request different demands on the system depending on the applications type. Different
applications require a higher data rate and need more bandwidth for downloading purpose but
not on upload. The authors of [47] evaluate the performance of LTE Advanced using RS for the
purpose of cost effective coverage extension with link capacity model for 802.16 MMR and also
address the scheduling schemes for EN. However, they mentioned that with good RS antenna
gain and power, RS can be deployed further away from the cell coverage to increase the cell
coverage but it is not mentioned about the BS and RS link quality as placing the RS out of the
cell where signal strength normally very week can result in poor link or delay.
2.5.3 Optimization of Radio Resource Management in Relay station
The RRM (Radio Resource Management) in LTE Advanced network covers the management
and optimization of the radio resource utilization. The new developing standards like 802.16m
require better spectral efficiency with high data rates to fulfill user and QoS requirements [23].
There are so many ways to achieve better performance in IEEE 802.16m such as Link adaptation
techniques where different types of modulation scheme applied to get better results. Link
adaptation can be useful if before transmission the BS as transmitter has the knowledge about
channel state. To utilize the radio resources in LTE Advanced link adaptation plays an important
role. There are different approaches which help in good link adaptation. In [70], uplink
scheduling algorithm has been proposed for RS. The purposed algorithm enhances system
capacity, bandwidth efficiency and improves delay performance for real time applications. AMC
(Adaptive Modulation and Coding) plays an important role in wireless communication
technology for both fixed and mobile environments. The authors of [66] clearly defined and
implemented AMC scheme and its effects on QoS performance of LTE Advanced network. all
the new upcoming technology like LTE and 802.16m using advance antenna technologies such
as MIMO and directional which help to utilization of resources efficiently. MIMO has more than
four streams which are used in IEEE 802.16m [60, 52, 55]. In IEEE 802.16m, the enhanced
MIMO plays an important role for increasing the throughput [55]. The previous link adaptation
techniques based on MIMO can be classified into two general categories which are analytical

and heuristic which explain limitations of packet error rate. In [52], authors explain error rates
for link adaptation which is bit error rate (BER) or packet-error rate (PER) against SNR.
2.6 The QoS with Relay stations
The QoS based on MAC layer of IEEE 802.16m on the concept of connections as unidirectional
data flow from each side (from source to destination and from destination to source). The flow is
assigned a four bit flow ID also called FID. To generate the network-unique 16 bit identifier, the
FID can be combined with a 12 bit station ID (STID). As compare to IEEE 802.16m the existing
legacy model allowed full 16 bit connection ID for each connection which means almost 216
users can be connected per BS. But the disadvantage is, each of these connection IDs had to be
reestablish on handover which cause more overhead. Not much work is done on QoS in LTE
Advanced2 or IEEE 802.16m as compare to existing LTE Advanced networks. There has been
related work such as in [15], where the IEEE 802.16 QoS was simulated but mostly on BE (Best
Effort) services with limited scope and scenarios. Our research includes simulation and detailed
analysis of all the five service classes in varied conditions and scenarios. In [13] the authors,
worked on both physical and MAC layer and used NS-2 to simulate the scenario. However, the
work is only simulated for packet loss whereas there are different types of QoS characteristics
such as delay, network load and throughput to be pin pointed in order to improve the
performance. In contrast, the writers in [40] calculate the throughput to improve the performance
of LTE Advanced non transparent mode. The parameters chosen by writers in this work were
very basic. However, the idea was just based on non transparent mode where average throughput
inside and outside the coverage area of the BS is calculated. The simulation was made for UGS
(unsolicited grant service, BE (best effort) and rtPS (real time polling service) scheduler in [21],
in order to compare the results of all the mentioned above QoS scheduler, writer investigated and
implemented a new module to get and compare the results of all three QoS classes. In [42], the
writers present the flow management framework for multi-hop mobile systems and apply it to
QoS scheduling with different priorities. The writers mentioned that application sessions on the
Data Link Layer, flows are assigned priorities to distinguish QoS requirements and simulated
results are based on single and multi-hop scenarios. Writers in [43] evaluated on-demand
bandwidth allocation in RS. They develop new algorithm for spectrum efficiency based adaptive
resource allocation. The writers have in detail look and simulated the results of available

throughput, packet loss and delay but here it is needed to consider network load which the
writers did not mentioned. Because when the network load increases the QoS automatically
decreases [16]. The authors further describe in the paper about QoS and their problems in which
they considered the centralized scheduling using UL scheduling. They proposed an architecture
named as SQSA named as scheduling QoS scheduling architecture to ensure QoS and to find a
specific request for the quality of request. LTE Advanced forum worked on IEEE 802.16m
bandwidth request protocol for better performance [1]. Because in existing legacy system a five
message request was needed for bandwidth request but in 80.16m three messages grant request is
available by knocking off two to decreasing the latency. LTE Advanced channel bandwidth is
20MHz and WiMAX2 bandwidth has doubled and varying bandwidth is used based on the
traffic. LTE Advanced uses OFDMA to allocate sub carriers or modulated carrier to the users.
The available sub carriers to allocate in the UL and DL (down link) are based on UL and DL
transmits power ratio, frame structure and size and available bandwidth as utilization of
resources in OFDMA relay network relay on BS. The efficient and simple resource algorithm
proposed in [65] for relay network to maintain the fairness among users while maximized data
rate.
2.6.1 Relay stations Applications
RS can be used for different applications in LTE Advanced networks but it most commonly used
for three aspects which are coverage extension, capacity enhancement and throughput
enhancement [42]. The WiMAX2 have very challenging requirements for transmission rates and
there is a growing demand in LTE Advanced networks for coverage and capacity enhancement.
RS have been designed to meet these requirements with guarantee QoS support. The QoS in
relay technology can be:
 Better throughput with less delay
 Coverage Extension for the user out of the coverage of BS
 Reduce signal overhead/Latency
 Higher bandwidth efficiency
 Less delay and packet loss during mobility
Together with all mentioned above better performance and QoS results in relay networks can be
achieved. In RS communication, the SS or EN can receive the signal from the BS or via RS
through different paths depends on the end user location. It can be through the multi hop relay

link (transparent) and the multi hop (non transparent) where direct link from BS is also possible.
IEEE802.16j and IEEE802.16m define two different types of modes in relay technology called
transparent mode and non transparent mode [9, 16, 25]. The transparent mode can provide better
QoS demands for end users as compared to non transparent mode because the transparent mode
basically works to extend the capacity of BS not coverage because the end users may access the
service directly from BS or through RS depending on the link quality. Also, it enhances the
throughput within the cell. However, covering end users QoS demands we need to enhance the
throughput and minimize the delay in order to LTE Advanced RS work well. The performance
can be improved in RS by taking all the necessary QoS characteristics such as delay, throughput,
pack loss and network load. Most of the work has been done on individual factor by focusing on
single term to show the improvement by enhancing the system performance in that specific
parameters like in [18], the writers focus on throughput and packet loss but delay has not been
simulated as it is clear from the title but there is no simulation found for delay analysis. The
writers done simple simulation with only one BS and one RS connected with mobile node out of
the range of BS. The critical aspect in this paper is the antenna height mentioned in simulation
parameters which is 10 meters. The normal antenna height of both BS and RS should be above
25 meters to get better performance and signal strength.
2.6.2 Performance of Relay stations
LTE Advanced like other wireless systems suffers from different propagation characteristics and
resource allocation in reasonable manner. The performance of RS can be affected by different
characteristics such as antenna height, distance from BS and distance from SS as the SNR (signal
to noise ratio) decreases when distance increase. Also NLOS (non line of sight) communication
where signal reflects with objects like tall buildings, forest and mountains can affect the signal
quality. Throughput enhancement, capacity and reliability can be achieved if the users have
better SNR especially in the area where BS signal fades at the edge of the cell. The RS enhance
the link quality, throughput and coverage extensions. There are two approaches defined by IEEE
802.16 standard which are centralized and distributed [10]. In centralized approach, the BS can
cover the cell radius where RS also deployed and the second approach called distributed scheme,
where RS coordinates the performance of the SSs. RS is also very useful in load balancing.
During congestion or high load within same cell RS transfers the traffic of one cell to

neighboring cell. The RS extends the coverage where there is no direct link between the BS and
the destination node.
2.6.3 Relay stations Selection in LTE Advanced System
In wireless networks such as IEEE 802.16m or 3GPP (Third Generation Partnership Project)
LTE, there are typically several fixed RS in the region deployed depending on the user’s access.
If source A as MS (mobile station) wants to send a message to Z (MS) as destination node and
there are several nodes (RS) in between A and Z then relay selection determines the best suited
RS for this communication. The selection process will operate in distributed manner in terms of
message complexity and delay. In the first step relay estimates the channel quality between itself
and source and itself and destination. For example A is source and z is destination and R is relay.
So it can be R and A and R and Z respectively. Source A send ready to send message to
destination Z or destination received this message. Also, all other neighbors of source A received
this message. When destination Z receives the RTS (request to send) message it then send CTS
(clear to send message) back to source A. When relay receive RTS message from source a, it
check or determine the channel state information (CSI) from source A to R (relay and R(relay to
destination Z. The main point we need to keep in mind on this stage that the Relay (R) assumes
the channels are the same from forward source (A) to relay(R) and backward relay(R) to
destination (Z) then each nodes or RS determines the best channel state information (CSI) value
and worst channel state information (CSI) value should served as relay. Relay selection plays an
important role in LTE ADVANCED network [29 – 30]. As discussed above, in congested
wireless networks there are different RS deployed in the region to fill the transmission gap and
user requirements. Determining from different relays which one should be selected for
communication is a difficult problem, because some RS may have a strong channel link or link
quality to the destination, but it may also be heavily loaded with traffic from other SS. In [29] the
authors proposed a relay selection algorithm to meet the QoS standard. However the writer did
not mention about the available throughput for each end user and their algorithm improved the
performance in accordance with signal to noise ratio and latency. Also the writer chooses very
simple services like HTTP and voice to be checked and meet the demand of user. The writer
suggests through effective relay selection algorithm, RS can play an important role by
considering the QoS parameters in order to get better performance. There are different types of
relay selection methods mentioned in by the writer.

The main relay selection methods are:
 RS selection with physical distance
 RS selection with path loss
 RS selection based on SINR
 RS based on transmission power
However, there are some disadvantages of above mentioned selection’s methods e.g. Delay can
cause while selection suitable relay for communication, also path loss transmission’s delay can
occur. In [30] the author proposes a cross-layer design relay selection algorithm for two hop
relay networks. The authors introduce a novel function for relay and proposed algorithm by
considering both channel state information on physical layer and queue state information at data
link layer. As compare to this, the authors of [34] proposed a method based on geographical
information, aiming to minimize the symbol error probability (SEP). Also the suitable relay is
determined withthe aim of minimizing the symbol error probability so the proposed scheme can
achieve better performance in selection process. Relay mainly works as half duplex and DF
technique can be applied for error free communication through RS. However, the half duplex
DF, the transmission of RS can be divided into two time slots. In the first attempt, the source
transmits the data to the RS where it demodulates and decodes received information. In the
second phase, the RS encode again the received data and retransmit it to the EN. There is also an
important factor in the selection process which is that when relay send a message to the end users
with signaling message indicating his availability. Then the pilot sequence used by BS estimate
the instantaneous SNRs of that RS for selection process but this type of scenario can cause time
delay.
2.7 Modulation Scheme in LTE Advanced
In wireless communication system, the selection of modulation scheme that includes both
modulation and channel schemes depends on radio resource management. The LTE Advanced
use OFDM which is most efficient schemes used by advance wireless technologies [22]. One of
the major advantages of OFDM is frequency signals with data can be transmitted by using
different modulation schemes depending on available resources and SNR As it depends on SNR
like if the value of SNR is high then the powerful modulation can be used, however when the

SNR is low then the lower type of modulation scheme can be used. In LTE Advanced, there are
four different modulation schemes used which are as follows:
2.7.1 Quadrature Phase Shift Keying (QPSK)
It uses four different possible phases, making it possible to send two bits for every symbol. The
QPSK is popular scheme where two bits accommodate one symbol. These two bits send
information by changing the phase of the radio wave. In the constellation diagram of QPSK, we
have four different points showing in the figure 2.4. QPSK efficiently used spectrum as
compared to BPSK, however it cannot guarantee against noise.
Figure 2.4 QPSK constellation
2.7.2 Quadrature Amplitude Modulation (QAM)
LTE Advanced also uses QAM which is combination of phase shift keying and amplitude
modulation is the efficient and reliable scheme. In QAM, the amplitude and phase by adjusting
signal wave and by combining these two phases a symbol can be generated. In LTE Advanced,
the area where have high SNR, the QAM can be utilize for better performance and throughput...
The figure 2.5 shows the different region of AMC scheme as we can see the area near to BS can
have better capacity but less coverage and in area in 16QAM have less capacity and more
coverage as compare to 64QAM. And in QPSK represent where it has large coverage area but
less capacity.

2.7.3 Quality of Service in LTE Advanced and Relay Station:
LTE Advanced allows the network operators to provide better services which differentiate them
from operators using other technologies; this edge attracts a range of subscribers. It provides
flow types which allow the provider to provide optimized data, video and voice services. In LTE
Advanced traffic can be prioritized via four services classes, each class prioritizes specific traffic
such as voice, video or data. These classes are listed below.
 UGS (Unsolicited Grant Service)
 rtPS (real-time Polling Service)
 nrtPS (non-real-time Polling Service)
 BE (Best Effort) The second phase of LTE Advanced with the support of mobility has
added fifth class which is extended real time polling service (ertPS);
A. Unsolicited Grant Service (UGS): The UGS scheduling service is suitable when the
constant data stream is required hence it is suitable for VoIP. In UGS, fixed size packets
are sent with as low jitter and latency as possible. It is important to mention that in UGS,
packets are sent at persistent intervals. UGS packets have higher priority over BE and
nrtPS and system first transmit the UGS packets and then transmit the BE or nrtPS
packets.
B. Real-Time Polling Service (rtPS): This service supports real time service flows where
variable size data packets are generated. It is important to mention that these packets are
generated periodically. This service is suitable for video transmission, such as MPEG
(Moving Pictures Experts Group) videos.
C. Non-Real-Time Polling Service (nrtPS): The nrtPS supports data streams which
consist of variable size packets tolerate delay. This service guarantees minimum data rate.
This service is suitable for FTP.
D. Best Effort (BE): The basic service class of QoS does not guarantee minimum data rate,
meaning at one instance data rate can be very low or idle and as soon as network
becomes less congested data rates increases allowing the traffic to move faster. This type
of service is not suitable for voice and video as at low data rates it cause interruptions. It
is more suitable for data streams which can be dealt on best available basis. BE packets

have lowest priority over the network and these packets are only transmitted if no packets
of UGS, rtPS, nrtPS and ertPS are waiting for transmission.
REFERENCES
[1] WiMAX forum, White paper Migration from WiMAX, Release 1 - 2 and Part 1- 3, “Air
Interface Migration with Network Reuse”.
[2]Y Yang,H Hu G Mao ”Relay Technologies for WiMAX and LTE Advanced Mobile Systems”
IEEE Communication Magazine Oct 2009.
[3] Chintan Patel “Relay technology for WiMAX and LTE-Advanced mobile systems” 06
September 2010
[4] T Unger and A Klein Research Article “Duplex Schemes in Multiple Antenna Two-Hop
Relaying” received 31 July 2007; Accepted 20 January 2008
[5] Anna Ferrer Bosch “Dynamic base station energy saving with relays”, July 2010
[6] J M. Westall and J J. Martin “Performance Characteristics of an Operational LTE Advanced
Network” IEEE VOL. 10, NO. 7, JULY 2011
[7] I Papapanagiotou, D Toumpakaris, J Lee and M Devetsikiotis “A Survey on Next Generation
Mobile LTE Advanced Networks: Objectives, Features and Technical Challenges” IEEE VOL.
11, NO. 4, FOURTH QUARTER 2009
[8] M Alasti and B Neekzad, C Jie Hui and R Vannithamby, “Quality of Service in WiMAX and
LTE Networks” IEEE Communications Magazine • May 2010
[9] D Soldani – Huawei technologies European research centre Germany “Multihop Relay
Networks Research”

[10] K Park – H.S Ryu – C.G Kang – D Chang – S Song – J Ahn and jongtae Ihm “ The
performance of relay enhanced cellular OFDMA-TDD network for mobile broadband wireless
services. Hindawi publications – volume 2009
[11] Vinit Grewal and Ajay K Sharma “On Performance Evaluation of Different QoS
Mechanisms and AMC scheme for an IEEE 802.16 based WiMAX Network” Volume 6– No.7,
September 2010
[12] J Rakesh – W.Vishal A and Dr. U Dalal “A Survey of Mobile LTE Advanced IEEE
802.16m Standard”. Vol. 8, No. 1, April 2010.
[13] J Elgered, A.S Moghaddam, and B Vedder, “How Quality of Service (QoS) is achieved in
LTE Advanced (IEEE 802.16)”
[14] D Ghosh, a Gupta, P Mohapatra “Adaptive Scheduling of Prioritized Traffic in IEEE
802.16j wireless networks” IEEE International Conference 2009
[15] F.G Sanchez and L Zhao “Efficient Mobile LTE Advanced Capacity Estimations in a
Multihop Environment” November 2008, pp. 1640 -1646.
[16] R. Balakrishnan, X. Yang, M. Venkatachalam and Ian F. Akyildiz “Mobile Relay and
Group Mobility for 4G LTE Advanced Networks” IEEE 2011
[17] Y Wang and H Li – “Full Rate and Full Diversity STBC in Decode-and- Forward Relay
Systems”. 2010 International Conference
[18] H. Dahmouni, H. El Ghazi, D. Bonacci, B. Sansò and A. Girard “Improving QoS of all-IP
Generation of Pre LTE Advanced Networks Using Delay-Jitter Model” VOLUME 2, ISSUE 2,
MAY 2010
[19] B AK Can, H Yomo and E De Carvalho “Link Adaptation and Selection Method for OFDM
Based Wireless Relay Networks” VOL. 9, NO. 2, JUNE 2007
[20] W. K Jia Y. C Chen “A Cut-Through Forwarding Scheme for Delay Optimization in IEEE
802.16j Simultaneous Transmit and Receive Multihop Relay Networks”. First International
Conference 2010
[21] A Belghith and L Nuaymi “Design and Implementation of a QoS-included WiMAX Module
for NS-2 Simulator” March 2008

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