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Performance Analysis and Comparison of Radio Frequency Propagation Models
for Outdoor Environments in 4G LTE Network
Asad Saeed Habib Ur Rehman
Muhammad Hassan Masood
This thesis is presented as part of the Degree of Master of Sciences in Electrical Engineering
Blekinge Institute of Technology 2013
School of Engineering
Blekinge Institute of Technology, Sweden Supervisor: Muhammad Shahid
Examiner: Benny Lövström
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Abstract
The dissertation concerns about the path loss calculation of Radio Frequency (RF) propagation models for 4G Long Term Evolution (LTE) Network to prefer the best Radio Frequency propagation model. The radio propagation models are very significant while planning of any wireless communication system. A comparative analysis between radio propagation models e.g. SUI model, Okumura model, Cost 231 Hata Model, Cost 231-Walfisch Ikegami and Ericsson 9999 model that would be used for outdoor propagation in LTE. The comparison and performance analysis has been made by using different geological environments e.g. urban, sub-urban and rural areas. The simulation scenario is made to calculate the lowest path loss in above defined environments by using selected frequency and height of base station antennas while keeping a constant distant between the transmitter and receiver antennas.
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Dedication
To our Parents and Teachers who motivated and encouraged us to attain this Hallmark in the best way
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Acknowledgment
Our thesis was an endeavour, much greater in magnitude than any of projects we have ever done. To see this endeavor turn into accomplishment was a dream that would have never come true without the support of many individuals.
First of all, we would like to thank Allah, the Almighty who did not let our faith die, who answered all of our prayers and granted us only the best ones.
Secondly, we are highly grateful to Mr. Muhammad Shahid, our project supervisor who guided, encouraged, stood by us and accepted nothing less than our best efforts.
Thirdly, we are indebted to our families and friends who were not with us on this venture of technology but were connected with each and every sentiment affiliated to it.
They may not understand a word of our thesis but they know that it is important and so are they to us.
Finally we are grateful to Blekinge Tekniska Hogskolan, Karlskrona Sweden and to all our teachers we had, in the course of 2 year degree that nurtured and prepared us.
Asad Saeed, Habib Ur Rehman and Hassan Masood August 2013
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Contents
1 INTRODUCTION ... 11.1 WIRELESS TECHNOLOGY: ... 1
1.1.1 The First Generation (1G): ... 2
1.1.2 The Second Generation (2G): ... 2
1.1.3 The Third Generation (3G): ... 2
1.1.4 The Fourth Generation (4G): ... 3
1.2 THE OUTLINE OF THE THESIS: ... 3
2 LONG TERM EVOLUTION ... 4
2.1 INTRODUCTION: ... 4
2.2 LTESTANDARD: ... 5
2.3 SERVICES PROVIDED BY LTE: ... 5
2.4 FREQUENCY BANDS ALLOCATION: ... 5
2.4.1 Frequency Division Duplex (FDD) Bands Allocation: ... 8
2.4.2 Time Division Duplex (TDD) Bands:... 9
2.5 LTETECHNICAL INFORMATION: ... 9
2.6 MODULATION SCHEMES:... 9
2.6.1 Analog Modulations: ... 10
2.6.2 Digital Modulations: ... 10
2.7 MULTIPLE ACCESS TECHNIQUES: ... 10
2.7.1 Frequency Division Multiple Access (FDMA): ... 10
2.7.2 Time Division Multiple Access (TDMA): ... 11
2.7.3 Code Division Multiple Access (CDMA): ... 11
2.8 CHANNEL EQUALIZATION: ... 12
2.9 SINGLE CARRIER MODULATION: ... 13
2.10 ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING: ... 14
2.10.1 Channel Bandwidths and Characteristics of LTE: ... 14
2.10.2 LTE OFDM Cyclic Prefix (CP):... 15
2.10.3 LTE OFDMA in the Downlink: ... 17
2.10.4 Downlink Carriers and Resource Blocks: ... 17
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2.10.5 LTE SC-FDMA in the Uplink: ... 18
2.11 MULTIPLE INPUT MULTIPLE OUTPUT (MIMO): ... 19
2.12 LTEARCHITECTURE: ... 19
2.12.1 LTE Network Elements: ... 20
2.12.2 Frame Structure ... 20
2.12.3 LTE Channels and MAC Layer: ... 22
2.12.4 LTE MAC Layer Functionality:... 22
2.12.5 LTE Channel Architecture: ... 23
2.13 LTEDOWNLINK CHANNELS:... 24
2.13.1 Downlink Logical Channels: ... 24
2.13.2 Downlink Transport Channels: ... 24
2.13.3 Downlink Physical Channels: ... 24
2.14 LTEUPLINK CHANNELS: ... 25
2.14.1 Uplink Logical Channels: ... 25
2.14.2 Uplink Transport Channels: ... 25
2.14.3 Uplink Physical Channels:... 25
2.15 LTEMOBILITY,CELL RANGE &ECONOMIC TARGETS: ... 26
3 WIRELESS PROPAGATION MODELS ... 27
3.1 INTRODUCTION: ... 27
3.2 RADIO WAVE COMPONENTS: ... 28
3.3 FREE SPACE MODEL: ... 28
3.4 INDOOR RFPROPAGATION MODELS: ... 29
3.5 OUTDOOR RFPROPAGATION MODELS:... 30
3.5.1 Foliage models: ... 31
3.5.2 Terrain models: ... 31
3.5.3 City models: ... 31
3.5.4 Band-specific models: ... 31
4 RF PROPAGATION MODELS IN LTE ... 33
4.1 INTRODUCTION: ... 33
4.2 OUTDOOR RFPROPAGATION MODELS FOR LTE: ... 34
4.2.1 SUI Path Loss Model: ... 34
4.2.2 Ericsson 9999 Model: ... 35
4.2.3 Okumura Model: ... 36
4.2.4 COST 231 Hata Model: ... 38
5 EXPERIMENTAL RESULTS ... 39
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5.1 SIMULATION OF PATH LOSS FOR DIFFERENT RFMODELS: ... 41
5.1.1 Simulation Results of Okumura Path Loss Model: ... 42
5.1.2 Simulation of SUI Path Loss Model:... 43
5.1.3 COST 321 Hata Model... 44
5.1.4 Simulation of COST-231 Walfisch-Ikegami Model ... 45
5.1.5 Simulation of Ericsson Model ... 46
6 CONCLUSION AND FUTURE WORK ... ERROR! BOOKMARK NOT DEFINED. 6.1 CONCLUSION ... 48
6.2 FUTURE WORK ... 51 7 REFERENCES ... ERROR! BOOKMARK NOT DEFINED.
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1 Introduction
1.1 Wireless Technology
he wireless technology has changed the world with technological development in wireless communication and brought revolution in the wireless networks. In the beginning of new millenary, we saw an amazing world of telecommunication.
Telecommunication [1] is a combination of cellular networks, computers, telephones, internet and television. Today wireless networks are used where the transmission is by means of infrared and radio waves. The great mobility is present in wireless networks and we can use the network everywhere, while in the wire networks, the availability of services in specific areas is a main problem. The demand of wireless broad band services has been increased. Wireless networks have been regularized by the Institute of Electrical and Electronics Engineers (IEEE). Different networks have different standards. The most common standards given by IEEE are IEEE 802.11 for WLAN and 802.15 for Bluetooth etc as illustrated in Figure 1.1 [1].
Figure 1.1: IEEE and ESTI Standards for Wireless Networks.
T
2 The cellular network is most popular type of wireless networks. The cellular network is a combination of small cells. The cellular network can provide better network coverage with increasing number of users. The quality of service and mobility management is also improved in cellular networks [2]. The advancement in cellular networks is divided into different generations, which are described below
In a wireless transmission the quality of signal, degrades due to the fading effects in channel caused by the multipath propagation. In order to reduce these effects, cooperative communications is one of the best methods. The cooperative communication may employ path diversity to transfer the signal from source to destination. Here path diversity means to introduce relay in the channel [6][3].
Several relaying protocols and their combination considered to view the performance of the system [3]. The transmission relaying protocols used in this thesis are: Amplify and Forward (AF), Decode and Forward (DF) and Decode, Amplify and Forward (DAF).
1.1.1 The First Generation (1G)
The cellular networks, deployed in early 1980’s, are called First generation (1G) cellular networks. The first cellular network was introduced in Japan. The first analog cellular network distributed in Europe was Nordic Mobile Telephone (NMT) and in America it was Advance Mobile Phone System (AMPS) in 1981.
1.1.2 The Second Generation (2G)
The Second generation (2G) cellular networks were proposed in early 1991’s. The GSM and the CDMA 1 were introduced in Europe and America respectively. The GSM consists of digital circuits and almost 2 billion users are still using it in many countries.
The GSM has two frequency bands 900 MHz and 1800 MHz. The GSM supports more services i.e. Caller Identification, roaming, Short Messaging Services (SMS) etc. The Enhanced Data rates for GSM Evolution (EDGE) and General Packet radio Service (GPRS) are enhancements in GSM.
1.1.3 The Third Generation (3G)
The Third Generation (3G) cellular networks including Universal Mobile Telecommunication System (UMTS) have higher data rates as compared to GSM. The 3G enables many services i.e. wireless television, wireless broadband and video
3 conferencing. In order to accomplish the goal of global coverage, UMTS was introduced. The CDMA 2000 was introduced in America.
1.1.4 The Fourth Generation (4G)
The Fourth Generation (4G) of cellular networks is currently under its development phase and will be available in coming years. It will be having a download rate of at least 10 Mbps, more effective spectral resources and other services as well. The LTE network [2] provides wireless internet facility. LTE advance is in its research phase.
1.2 The Outline of the thesis
The chapter 2 discusses the technical information and architecture of the LTE network.
The LTE architecture, different modulation schemes and LTE frequency bands are explained. The LTE frame format and media access control layer functions are also described in detail. The LTE network channel allocation has also been discussed. The chapter 3 covers the RF propagation models in detail. The different propagation models with their suitable applications according to the population and area are explained.
The chapter 4 starts with the RF propagation models for LTE and explain the mathematical formulations for RF outdoor propagation models used in LTE. This chapter describes the SUI path loss model, Ericson 9999 model, Okumura model and Cost 231 Hata model. The chapter 5 shows the simulation results for path loss of different propagation models. It also concludes with the thesis conclusion and the possible future works.
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2 Long Term Evolution
LTE stands for Long Term Evolution. It is a 3GPP Project and is known as 4G LTE. It is standard for wireless communication of high-speed data. It is based on the GSM/EDGE and UMTS/HSPA network technologies. It is targeted to get high speed and capacity by using a different radio interface with improvements in the core network [2]. TeliaSonera was the first company to launch LTE in Oslo and Stockholm in December 2009. The comprehension of broadband Internet access anywhere and anytime was seem to be difficult but this has become possible now-a-days . LTE network is most recent wireless technology. The wireless broadband access to urban and rural areas has become possible by these networks with low rates [2].
2.1 Introduction
When it comes to the enhancement of the mobile communication and to improve the future requirements, LTE [1] is a better choice in wireless communication networks.
The LTE project is initiated by 3GPP under the supervision of European Telecommunications Standards Institute (ETSI). LTE network has some features like, an uplink of 75 Mbps and a downlink of 300 Mbps with more than 200 active users per cell. The goals of LTE are; cost effectiveness, best use of new spectrum, better compatibility with other standards and improving of spectral efficiency. LTE Advanced [8] is purely a 4G technology and LTE itself is the advanced version of 3G. The evolution is illustrated in Figure 2.1.
5 Figure 2.1: Mobile Technologies -2G to beyond 3G [3]
2.2 LTE Standard
LTE [2] is adopted by 3GPP which operates under the ETSI. LTE is a wireless technology that can be useful to deliver IP services over large areas. Its certification indicates interoperability of the equipment built to the 3GPP, 3GPP2 or compatible standard. LTE network is a scalable wireless platform for making alternative and balancing broadband wireless networks.
2.3 Services Provided by LTE
Various services provided by LTE network, these are discussed in Table 2.1 below [2].
Table 2.1: LTE Network Services Services Details
Voice Primarily Packet
Data High Speed
Multimedia Mixed Media
Multicast Shared Video and Audio Channels Location Services GPS and Systems
2.4 Frequency Bands Allocation
Frequency band allocation is the most important task when planning a network. Since different regions of the world use even a single frequency for different cellular systems, so this means that we are lacking global standards for cellular communications. Almost every country has its own regulatory authority. For instance, Federal Communications
6 Commission (FCC) is the authority, which is responsible for the allocation of frequency bands in the US. The International Telecommunication Union (ITU) is a United Nation based organization, which is working to standardize the frequency bands all over the world [3].
In order for a user to use the same equipment and technology anywhere in the world, the same frequency bands should be used in order to set a standard.
Due to historical and political reasons, there are different frequency bands allocated for cellular communication systems in US, Europe and Asia. The world is divided into three regions and all the three regions (as shown in Figure 2.2 [4]) have different frequency bands.
Figure 2.2: Different regions of frequency allocation in the world [4]
The First Region, Region 1 consists of Europe, Africa, Russia and some parts of the Middle East. The Second Region, Regions 2 covers USA, Canada and all the Latin America while in the Third Region, Region 3 China, Australia, India, Pakistan, Japan and other countries of Asia and Oceania are located. Most cellular technologies have different frequency bands in these three regions. But sometimes even in the same region there are different frequency bands for same technology.
7 UMTS/HSDPA/HSUPA bands
Band I (W-CDMA 2100) is used in Europe, Africa (ITU Region 1), Asia, Oceania and Brazil (part of ITU Region 2)
Band II (W-CDMA 1900) is used in North America and South America (ITU Region 2)
Band IV (W-CDMA 1700 or Advanced Wireless Services) is used in the United States of America
Band VIII (W-CDMA 900) is used in Europe, Asia and Oceania (ITU Region 1 and ITU Region 3)
Band V (W-CDMA 850) in used in Australia, Brazil, Canada, United States, some parts of South America and Asia (ITU Region 2 and ITU Region 3)
Band XII - XIV was introduced to be used in 700MHz spectrum, in USA and Canada in 2008 [3]
Frequency license is an issue with high priority while implementing a cellular network.
For this purpose a higher cost have to be paid by the companies to the local regulatory authorities. The overall bandwidth of the system depends on that frequency band. Since theses authorities have predefined frequency bands for different cellular technologies the cellular companies do not have a choice for the acquisition of frequency bands.
The LTE defined 3GPP standard, spectrum bands, duplexing techniques and channel bandwidth. In DL, we use OFDM while in UL, we use SC-FDMA. The licensed spectrum band used for LTE network is different for different countries. Frequency Division Duplex (FDD) [8] and Time Division Duplex (TDD) [8] are used as duplexing techniques in LTE network.
The LTE Frequency bands are planned as follow.
700 MHz and 1700 MHz in North America
900 MHz, 1800 MHz and 2600 MHz in Europe
1800 MHz, 2100 MHz and 2600 MHz in Asia
1800 MHz in Australia
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2.4.1 Frequency Division Duplex (FDD) Bands Allocation
LTE network uses large number of frequency bands [2]. FDD system uses these bands.
The LTE-FDD frequency bands as shown in Table 2.2 are used for simultaneous two way communications. These bands have enough separation that is required to improve the receiver efficiency but the receiver may be blocked if the signals are so close. For enabling the roll-off of the antenna filtering, the separation between signals must be competent within the received band.
Table 2.2: LTE-FDD Frequency Bands [2]
LTE Bands Regions of Use Uplink (MHz) Downlink (MHz)
1 Asia, Europe 1920 – 1980 2110 – 2170
2 Americas, Asia 1850 – 1910 1930 – 1990
3 Americas, Asia,
Europe 1710 – 1785 1805 -1880
4 Americas 1710 – 1755 2110 – 2155
5 Americas 824 – 849 869 – 894
6 Japan 830 – 840 875 – 885
7 Asia, Europe 2500 – 2570 2620 – 2690
8 Asia, Europe 880 – 915 925 – 960
9 Japan 1749.9 - 1784.9 1844.9 - 1879.9
10 Americas 1710 – 1770 2110 – 2170
11 Japan 1427.9 - 1452.9 1475.9 - 1500.9
12 USA 698 – 716 728 – 746
13 USA 777 – 787 746 – 756
14 USA 788 – 798 758 – 768
17 USA 704 – 716 734 – 746
18 Japan 815 – 830 860 – 875
19 Japan 830 – 845 875 – 890
20 Europe 832 – 862 791 – 821
21 Japan 1447.9 - 1462.9 1495.5 - 1510.9
22 3410 – 3500 3510 – 3600
Note: LTE bands 15 and 16 are reserved, but still undefined.
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2.4.2 Time Division Duplex (TDD) Bands
There are several unpaired frequencies allocations associated with LTE-TDD. These band allocations as shown in Table 2.3 are unpaired. In fact, these are Time Multiplexed, so frequency is not involved in these allocations.
Table 2.3: LTE-TDD Frequency Bands [2]
LTE Band Regions of Use Allocations (MHz)
33 Asia (not Japan), Europe 1900 – 1920
34 Asia, Europe 2010 – 2025
35 Americas 1850 – 1910
36 Americas 1930 – 1990
37 1910 – 1930
38 Europe 2570 – 2620
39 China 1880 – 1920
40 Asia, Europe 2300 – 2400
41 USA 2496 – 2690
2.5 LTE Technical Information
Long Term Evolution (LTE) is a wireless technology, which describes interoperable implementations and standards of UMTS/3GPP. Here, we will discuss some technical aspects of LTE.
2.6 Modulation Schemes
Different modulation schemes are used for different types of communication in wireless technology. It is very important to select the most efficient modulation scheme that fulfills all the requirements. In modulation, a baseband signal (low frequency signal) is multiplied with a carrier signal or modulator signal (normally a high frequency signal).
Signals can be transmitted for long ranges by the use of modulation. The de-modulator demodulates the signal at the other (receiver) end. There are two types of modulations, analog modulations and digital modulations.
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2.6.1 Analog Modulations
The high frequency carrier is multiplied with the baseband signal in analog modulations.
Generally, the baseband signal is a continuous signal. The following are some important types of analog modulations [6]:
Amplitude Modulation (AM)
Quadrature Amplitude Modulation (QAM)
Phase Modulation (PM)
Frequency Modulation (FM)
2.6.2 Digital Modulations
In digital modulations, a digital signal is multiplied with a carrier signal. The following are some important types of digital modulation [6]:
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)
Quadrature Differential Phase Shift Keying (QDPSK)
Multi-frequency Shift keying (MFSK)
Binary Phase Shift keying (BPSK)
Orthogonal Frequency Division Multiplexing (OFDM)
Quadrature Phase Shift keying (QPSK)
Differential Phase Shift Keying (DPSK)
Gaussian Minimum-shift keying (GMSK)
2.7 Multiple Access Techniques
In cellular communication, numbers of channel are limited within a cell. Hence, the capacity of the whole network is limited. Therefore, multiple access techniques are very important. Multiple accesses is the utilization of service by several users at the same time. These multiple access techniques are used on the physical layer. Some important multiple access techniques are described below:
2.7.1 Frequency Division Multiple Access (FDMA)
In FDMA [7], the combination of smaller frequency bands results into whole frequency band and this smaller frequency band is assigned to each user. These frequency bands
11 are allocated to the users by ensuring minimum interference between different frequency bands.
2.7.2 Time Division Multiple Access (TDMA)
In order to use shared resources in wireless networks, TDMA [7] is also used. In TDMA same frequency band is used by all users in different time intervals. In TDMA each user has a time slot and during respective time period, only one of the users can utilize the whole frequency band. TDMA is used in 2G cellular networks while a combination of TDMA and FDMA is used in GSM.
2.7.3 Code Division Multiple Access (CDMA)
CDMA [7] scheme adopts the method for transmission of data of multiple users simultaneously with a code. In FDMA scheme, the bandwidth is divided among the users, while in TDMA the time is divided among the users whereas in CDMA, both time and frequency are divided among the users. In Figure 2.3, the difference between FDMA, TDMA and CDMA is shown [7].
Figure 2.3: Comparison of FDMA, TDMA and CDMA [7]
In LTE, OFDM is used for DL and SC-FDMA is used for UL transmissions.
A signal faces distortion when it is transmitted over a wireless channel in a network.
The distortion can be of different types (i.e. multipath, reflection, delay etc).
12 When the signal reach at the receiver by traveling along these paths they are said to be time shifted (i.e. delayed). When signals are required to be transmitted without any delay, a direct line-of-sight path is chosen between the receiver and transmitter.
Figure 2.4: Multipath caused by reflections of objects
2.8 Channel Equalization
In general cases, distortions such as channel distortion are removed by SC-FDMA in time domain. So channel equalization [14] becomes practically possible (i.e. simplify) and done by any method described below:
Channel Inversion: The channel equalizer can easily detect the channel response upon receiving data sequence since a data sequence is already known to receivers. In order to remove the delay, an incoming data signal is multiplied with the inverse of the channel response at the equalizer.
A CDMA system uses another technique at the equalizers to resolve the delay issue by combining the digital copies of the time shifted received signal but the SNR (Signal-to-Noise Ratio) will be increased in this case.
In either case, the circuit becomes more complex and symbol times become shorter with increasing data rates.
The Inter Symbol Interference (ISI) is another important issue to be discussed as it is spilled into several symbol periods. As a common equalizer, the transversal filter having finite impulse response as shown in Figure 2.5 is used. More number of samples are
13 required to compensate the delay amount since the receiver sample clock (τ) running slow. As the number of delay taps increases the adaptive algorithm becomes more complex. This approach becomes impractical for LTE data rates.
Figure 2.5: Transversal Filter Channel Equalizer [6]
2.9 Single Carrier Modulation
All cellular systems are using single carrier modulation schemes whereas in LTE, OFDM scheme is used. Here our main discussion is the dealing of single carrier systems with channel distortion. In cellular applications the amount of delay can reach up to several microseconds. Here the term “delay” means the amount of time delay of transmitted signal along different paths.
In telecommunication, inter symbol interference (ISI) is a kind of distortion in a signal in which one symbol interferes with other symbols, and makes the communication undependable. This also introduces unwanted delay at receiver side. ISI is shown in Figure 2.6 when talking about a single carrier system, the symbol time decrease by increasing data rates.
Figure 2.6: Multipath-Induced Time Delays Result in ISI [6]
A particular phase shift is caused by reflection and every different path length. All of the signals are together at the receiver. Sometimes this can cause constructive
14 interference and sometime destructive interference. Finally the composite (i.e. mixed) received signal is deformed by fading as shown in Figure 2.7
Figure 2.7: Received Signal Distorted By Fading [7]
2.10 Orthogonal Frequency Division Multiplexing
In Orthogonal Frequency Division Multiplexing (OFDM) [2], a large number of closely spaced carriers are used. The modulation of these carriers occurs at lower data rates.
The interference between these carriers can take place, but Orthogonality between these causes no mutual interference. Orthogonality means to make these carriers perpendicular to each other, which means that the space between these carriers must be equal to the reciprocal of period of symbol. All the carriers occupy the transmitted data.
If there is any loss of the carriers, the data can be reconstructed by using error correction techniques. This loss is due to multi-path effects. The effects of reflections and ISI can be reduced. The single frequency networks can be implemented on a same channel, in which all transmitters can transmit their information.
In LTE network, OFDM is the best efficient multiplexing scheme. It meets the exact requirements for LTE. Both TDD and FDD formats are used by OFDM which provide more advantage.
2.10.1 Channel Bandwidths and Characteristics of LTE
One of the major parameters to be decided in a wireless network is the choice of bandwidth. The number of carriers and the symbol length are the major aspects associated within the available bandwidth.
15 A number of channel bandwidths are reserved for LTE network. It is obvious that an increment in bandwidth also increases channel capacity.
The bandwidths for LTE network as per channel are below:
Channel Number Channel Bandwidth
1 1.4 MHz
2 3 MHz
3 5 MHz
4 10 MHz
5 15 MHz
6 20 MHz
15 KHz is spacing between each sub-carrier. For Orthogonality, the symbol rate formula is given as:
1 / 15 KHz = of 66.7 µs.
Where Channel Spacing= 15 KHz
Each individual subcarrier can carry data at a max rate i.e.; 15 kilo symbols per second.
It provides 20 MHz bandwidth and 18 Mbps symbol rate.
2.10.2 LTE OFDM Cyclic Prefix (CP)
The methods of adding flexibility to the system is still necessary to reduce the ISI. In order to reduce ISI a period can be added into the time slot at the beginning of a data sequence, such phenomena is called guard period. By this the copy of section of symbol from the beginning of signal to its ending and sampling of waveform at the worst time will become possible. This is called cyclic prefix (CP). All this is done so that ISI will be avoided.
The length of CP should be enough long in order to reduce multipath delay, but it has a trade-off, i.e. if length of CP becomes too long the data output capacity will be reduced.
Therefore selection of its length is a critical issue. The standard length of cyclic prefix (CP) is approx. 4.69 µs for LTE network. Figure 2.8, 2.9 and 2.10 describes the process of OFDM in LTE network.
16 Figure 2.8: OFDM Eliminates ISI [6]
Figure 2.9: Baseband FFT Resolves Subcarriers [6]
17 Figure 2.10: Orthogonal Frequency Division Multiplexing (OFDM) [7]
2.10.3 LTE OFDMA in the Downlink
There are 2048 different sub-carriers that are used by OFDM signal. Every mobile station must have the capability to receive all 2048 sub-carriers. But in fact, the base station supports only 72 sub-carriers. So in this way, all mobile stations can talk to any base station.
In OFDM signal, three types of modulation schemes are used:
1. QPSK (= 4QAM)
2. 16QAM
3. 64QAM
The exact format depends upon the prevailing conditions. There is no need of large SNR for QPSK. But it can’t send the data at fast rate.
2.10.4 Downlink Carriers and Resource Blocks
In case of DL, the sub-carriers are split-up into different resource blocks. So the system becomes able to divide into standard numbers of sub-carriers. The resource blocks comprise 12 subcarriers. The blocks also cover one time slot in a frame. This is shown in figure 2.11.
18 Figure 2.11: Downlink Resource Blocks [1]
2.10.5 LTE SC-FDMA in the Uplink
In UL, the SC-FDMA [14] scheme is used. This is a type of OFDMA technology.
Another important issue to be addressed here is battery life of mobile equipment. All the companies are nowadays working on improving mobile equipment battery performance, but still the main objective is that the mobiles must use battery power as low as possible.
RF power amplifier transmits the signals to the base station through the antennas. The signal format and radio frequency modulation scheme play an important role in this matter. The signals have a high-peak to-average ratio which requires linear amplification. So a constant operating power level is necessary to be implemented. But unfortunately, OFDM technique has a high peak-to-average ratio.
Since the base station has a lot of equipment and high power is also available, so it is not an issue for base station. But due to small size and less equipment than the base station the mobile station has some issues. In order to overcome this problem, LTE deploys a modulation scheme known as SC-FDM.
19 The combination of low peak-to-average ratio with flexible subcarrier frequency allocation and the multipath interference resilience results SC-FDM. This low peak-to- average is provided by single-carrier systems and flexible subcarrier frequency allocation is provided by OFDM.
2.11 Multiple Input Multiple Output (MIMO)
The efficiency of the system will be increased by using Multiple Input Multiple Output (MIMO) [8]. In MIMO, additional signal paths are used. These different paths are distinguished by multiple (2 X 2, 4 X 4 or 4 X 2 matrices) antennas. It is comparatively easy to install more antennas at a base station. As the number of antennas is limited due to dimensions of the user equipment so installation of more antennas is a big problem for mobile equipment.
2.12 LTE Architecture
In the LTE architecture, the access side consists of Evolved UTRAN (E-UTRAN) [10]
and core side consists of Evolved Packet Core (EPC).
Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) [10] consists of Evolved Node B (eNBs) which provide the E-UTRA control plane (RRC) protocol and user plane (PDCP/RLC/MAC/PHY) terminations towards the User Equipment (UE).
The LTE interfaces are following as shown in Figure 2.12
S1-MME, S1-U
S3, S4, S5, Rx
S6a, Gx, S8, S9
S10, S11, S12, S13, SGi
20 Figure 2.12: LTE Architecture [10]
2.12.1 LTE Network Elements
The Mobility Management Entity (MME)
The Serving Gateway (SGW)
The Packet Data Network Gateway (PDN-GW)
The Home Subscriber Server (HSS)
The Policy and Charging Rules Function (PCRF)
2.12.2 Frame Structure
There are two types:
Full and half-duplex FDD shared, the type-1 frame structure
TDD shared type-2 frame structure
The sub frame has a length of 1 ms and consists of two adjacent slots
Radio frame consists of 20 slots having length equal to 10 ms
It uses QPSK, 16QAM and 64QAM as modulation schemes
The QPSK is only used by broadcast channel
6144 bits is the maximum information block size
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For error detection, the CRC-24 is used
Figure 2.13: LTE Frame Structure [10]
Figure 2.14: Type-1 Frame Structure [10]
Figure 2.15: Type-2 Frame Structure [10]
22 Table 2.3: Sub-Frame Number Configuration
Configuration Sub-frame Number Switch-Point Periodicity 0 1 2 3 4 5 6 7 8 9
0 D S U U U D S U U U 5ms
1 D S U U D D S U U D 5ms
2 D S U D D D S U D D 5ms
3 D S U U U D D D D D 10ms
4 D S U U D D D D D D 10ms
5 D S U D D D D D D D 10ms
6 D S U U U D S U U D 10ms
2.12.3 LTE Channels and MAC Layer
Figure 2.16: LTE Channels and MAC Layer [11]
2.12.4 LTE MAC Layer Functionality
MAC layer performs the functions as shown in Figure 2.17
The mapping between Logical and Transport channels
The error correction via Hybrid Automatic Repeat Request (ARQ)
The prioritization of Logical Channels
The handling of priority by dynamic scheduling
23 Figure 2.17: LTE MAC Layer Functions [10]
2.12.5 LTE Channel Architecture
Figure 2.18: LTE Channel Architecture [12]
It consists of:
RLC layer
MAC layer
Physical layer
24 2.13 LTE Downlink Channels
Figure 2.19: Downlink Channels [10]
2.13.1 Downlink Logical Channels
Multicast Traffic Channel (MTCH)
Multicast Control Channel (MCCH)
Dedicated Control Channel (DCCH)
Dedicated Traffic Channel (DTCH)
Common Control Channel (CCCH)
Broadcast Control Channel (BCCH)
Paging Control Channel (PCCH)
2.13.2 Downlink Transport Channels
Downlink Shared Channel (DL-SCH)
Multicast Channel (MCH)
Broadcast Channel (BCH)
Paging Channel (PCH)
2.13.3 Downlink Physical Channels
Physical Multicast Channel (PMCH)
Physical Broadcast Channel (PBCH)
25
Multicast Control Channel (MCCH)
Physical Hybrid ARQ Indicator Channel (PHICH)
Dedicated Traffic Channel (DTCH)
Physical Downlink Control Channel (PDSCH)
Physical Downlink Shared Channel (PDSCH)
2.14 LTE Uplink Channels
Figure 2.20: Uplink Channels [10]
2.14.1 Uplink Logical Channels
Dedicated Traffic Channel (DTCH)
Dedicated Control Channel (DCCH)
Common Control Channel (CCCH)
2.14.2 Uplink Transport Channels
Uplink Shared Channel (UL-SCH)
Random Access Channel (RACH)
2.14.3 Uplink Physical Channels
Packet Uplink Control Channel (PUCCH)
Physical Uplink Shared Channel (PUSCH)
Physical Radio Access Channel (PRACH)
26
2.15 LTE Mobility, Cell Range & Economic Targets
The high mobility can be optimized for mobile [11]
The surety for quality of real-time services and voice over total speed range
The excellent performance surety for speeds up to 120 km/h
The best throughput, spectrum efficiency and mobility with cell range up to 30 km
Surety of well mobility maintenance for speeds up to 350 km/h
Some degradation in throughput and spectrum efficiency should be permitted
The reduction in capital & optional Expenditures (i.e. CAPEX and OPEX)
The avoidance of complicated architectures and unnecessary interfaces
The maximum reuse of existing sites
The optimized terminal complexity and power consumption
The optimization of backhaul protocols
The multi vendor environment
27
3 Wireless Propagation Models
Wireless Propagation Models [13] are very important in cellular networks. The available resources are very limited in cellular networks and we have to make use of them in the best possible manner. An optimized solution is required in order to make use of the spectrum efficiency. This is good in order to improve coverage, capacity and Quality of Service (QoS). The core principle of choosing preeminent and efficient wireless propagation model is to make light of the cost of network while maintaining the QoS in network. In wireless propagation model, we have parameters like path loss, antenna gain, attenuation (rain or fog), SNR etc.
3.1 Introduction
The propagation means transmit the required signal intensity in the given time period and geographic/climatic region over desired distance/area/volume. The wireless propagation model is the relation between the signal radiated and signal received as a function of distance and other variables as shown in figure 3.1.
Figure 3.1: Radio Transmission [14]
28
3.2 Radio Wave Components
Direct wave
The wave in free space is called direct wave.
Attenuated wave
The wave attenuated by walls, buildings, atmosphere, is called attenuated in wireless communication.
Its frequency is equal or greater than 10 MHz.
Reflected wave
The wave after reflection from ionosphere, ground, passive antenna, wall etc is called as reflected wave. Its frequency is equal or less than 100 MHz.
Refracted wave
The wave which goes through standard refraction, sub refraction, super refraction, ducting, ionized layer refraction, is known as refracted wave. Its frequency is equal or less than 100 MHz.
Diffracted wave
The wave which results after ground diffraction, mountain diffraction, spherical earth diffraction etc, is called diffracted wave. Its frequency is equal or less than 5 GHz.
Surface wave
Its frequency is equal or less than 30 MHz.
Scatter wave
Tropo scatter wave, ionized-layer scatter wave, precipitation-scatter wave are the types of scatter wave.
3.3 Types of RF/Wireless Propagation Models
The following are the types of RF propagation models.
3.3.1 Free Space Model
The Path loss between receiver and transmitter plays a critical role while discussing Quality of Service (QoS). This formula is valid up to a distance of 55m [13]. It doesn’t take in to account any clutter loss or reflections.
Free Space Loss formula is given as:
29 Free Space Loss (dB)=20 log10 4πd
λ (3.1) Where
𝜆 = 𝑊𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡 (𝑚)
𝑑 = 𝑇𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑟 𝑡𝑜 𝑅𝑒𝑐𝑒𝑖𝑣𝑒𝑟 𝑠𝑒𝑝𝑎𝑟𝑎𝑡𝑖𝑜𝑛 (𝑘𝑚)
Figure 3.2: Simple Radio Link Model [14]
The Free Space model [13] means no reflection, no absorption or no other propagation effects. This is an ideal model.
Generally, there are two types of Wireless/RF Propagation Models.
Indoor RF Propagation Models
Outdoor RF Propagation Models
3.4 Indoor RF Propagation Models
Figure 3.3: Indoor Propagation [13]
30 The following indoor Propagation Models are used in Wireless Communication:
Log-distance path loss model
ITU Model for Indoor Attenuation
Keenan-Motley Model
Path Loss Slope Model
The Indoor Propagation can be affected due to following reasons:
Effects of obstructions
Energy Spreading
Effects of Ground
Wavelength
Frequency
Polarization
Environment
Climate
weather
Time
3.5 Outdoor RF Propagation Models
Figure 3.4: Outdoor Propagation [14]
31 In Wireless Communication the following Outdoor Propagation Models are used:
3.5.1 Foliage models
Updated ITU model
Single Vegetative Obstruction Model One Woodland Terminal Model
Early ITU Model
Weissberger's modified exponential decay model 3.5.2 Terrain models
ITU Terrain Model
Longley–Rice Model
Egli Model 3.5.3 City models
Lee Model (Point to Point)
Lee Model (Area to Area)
COST 231 Hata model
Hata Model (for Open Areas)
Hata Model (for Suburban Areas)
Hata Model (for Urban Areas)
Okumura Model
Young Model
3.5.4 Band-specific models
The ISM Band (i.e. 2.4 GHz, well used in LTE) Outdoor Propagation can be affected as follows:
Energy Spreading
Troposphere effects For Clear air For Non-clear air
32
Ionosphere effects
Wavelength
Effects of obstructions
Frequency
Polarization
Environment
Effects of Ground
Climate
weather
Time
33
4 RF Propagation Models in LTE
Long Term Evolution (LTE) is a 3GPP standard for wireless communication networks.
It is adopted by 3rd Generation Partnership Project (3GPP) which operates under the ETSI. LTE is a possible replacement of Digital Subscriber Line (DSL). The goals for LTE are reformed spectrum opportunities, lowering costs, best use of new spectrum, improving services, improving spectral efficiency and better integration with other open standards [8]. LTE is such type of wireless technology in which all IP centric services can be delivered over a large coverage area. Its certification indicates interoperability of the equipment built to the 3GPP, 3GPP2 or compatible standard. It is a scalable wireless platform for making alternative and complementary broadband networks. It is not purely 4G technology. It is actually an enhanced version of 3G (one can say it 3.9G).
But LTE Advanced is purely a 4G technology, which is still under its deployment phase.
4.1 Introduction
In the previous chapter, RF Propagation Models [13] were discussed in perspective of general cellular networks. Here, the focus will be on best choice of RF Models in LTE network. There is a similarity between architectures of LTE and general cellular networks. Hence, RF model is of great importance in LTE as well. The main function of choosing best RF Model is to ensure the QoS. The optimal solution in designing and planning a network is critical due to the limitation of resources.
We will discuss outdoor RF Propagation Models in LTE Network. We are taking two frequency bands for LTE (i.e. 1900MHz and 2100 MHz)
34
4.2 Outdoor RF Propagation Models for LTE
The following RF propagation models are used as outdoor propagation:
4.2.1 SUI Path Loss Model
The Stanford University Interim (SUI) Path Loss model [1] has been developed by IEEE for IEEE 802.16. This model is used for frequencies above 1900 MHz. As LTE will be using frequency band of 2100 MHz and 2600 MHz, so it is a suitable solution for LTE network.
In this propagation model, we have three different types of areas. These are called as terrain A, B and C. Terrain A represents an area with highest path loss which describes an urban area. Terrain B represents an area with moderate path loss which describes a sub-urban area. Terrain C represents the least path loss. Table 4.1 presents the terrains and the factors used in SUI model.
The Path Loss is given by:
PL (SUI)=A+10γlog10 d
d0 +Xf+Xh+S (4.1) Where
𝑃𝐿 (𝑆𝑈𝐼) = 𝑃𝑎𝑡 𝐿𝑜𝑠𝑠, 𝑖𝑛 𝑆𝑈𝐼 𝑀𝑜𝑑𝑒𝑙, 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑖𝑛 𝑑𝐵 𝐴 = 𝐹𝑟𝑒𝑒 𝑆𝑝𝑎𝑐𝑒 𝐿𝑜𝑠𝑠, 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑖𝑛 𝑑𝐵
𝑑 = 𝑇𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑟 𝑡𝑜 𝑅𝑒𝑐𝑒𝑖𝑣𝑒𝑟 𝑠𝑒𝑝𝑎𝑟𝑎𝑡𝑖𝑜𝑛 (𝑘𝑚) 𝑑0 = 100𝑚 𝑈𝑠𝑒𝑑 𝑎𝑠 𝑎 𝑅𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒
𝑋𝑓 = 𝐶𝑜𝑟𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 𝑓𝑜𝑟 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝑋 = 𝐶𝑜𝑟𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 𝑓𝑜𝑟 𝐵𝑆 𝑒𝑖𝑔𝑡 𝑆 = 𝑆𝑎𝑑𝑜𝑤𝑖𝑛𝑔
𝛾 = 𝑃𝑎𝑡 𝑙𝑜𝑠𝑠 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝜸 factor is given as:
γ= a-bbh+ c
hb (4.2) Where
𝑏 = 𝐻𝑒𝑖𝑔𝑡 𝑜𝑓 𝐵𝑎𝑠𝑒 𝑆𝑡𝑎𝑡𝑖𝑜𝑛 𝐵𝑆
35 Where a, b and c describes the terrain, and there values are selected from Table 4.1 [1].
Table 4.1: Different Terrains and Parameters for SUI Model [1]
Parameters
Terrain A Terrain B Terrain C
A 4.6 4 3.6
B 0.0075 0.0065 0.005
C 12.6 17.1 20
Where
𝑇𝑒𝑟𝑟𝑖𝑎𝑛 𝐴 = 𝑈𝑟𝑏𝑎𝑛 𝐴𝑟𝑒𝑎 𝑇𝑒𝑟𝑟𝑖𝑎𝑛 𝐵 = 𝑆𝑢𝑏 − 𝑈𝑟𝑏𝑎𝑛 𝐴𝑟𝑒𝑎 𝑇𝑒𝑟𝑟𝑖𝑎𝑛 𝐶 = 𝑅𝑢𝑟𝑎𝑙 𝐴𝑟𝑒𝑎
The frequency correction factor is given as:
Xf= 6.0 log10 f
2000 (4.3) For terrain A and B, correction factor of BS height is explained in following expression
Xh= -10.8 log10 hr
2000 (4.4) For terrain C, the correction factor for BS height is given by the following expression:
Xh= -20 log10 hr
2000 (4.5) The shadowing factor is given by:
S= 0.65 log10 f 2 - 1.3 log10 f+α (4.6) Where
𝛼 = 5.2 𝑑𝐵 𝑓𝑜𝑟 𝑇𝑒𝑟𝑟𝑎𝑖𝑛 𝐴 𝑎𝑛𝑑 𝐵 𝑎𝑛𝑑 6.6 𝑑𝐵 𝑓𝑜𝑟 (𝑇𝑒𝑟𝑟𝑎𝑖𝑛 𝐶)
𝑟 = 𝐻𝑒𝑖𝑔𝑡 𝑜𝑓 𝑅𝑒𝑐𝑒𝑖𝑣𝑒𝑟 𝐴𝑛𝑡𝑒𝑛𝑛𝑎 4.2.2 Ericsson 9999 Model
The Ericsson 9999 Model [15] is in fact an extend version of Hata Model and implemented by Ericsson in which we can adjust parameters according to the given scenario.
The Path Loss is given by:
36 PL (Eric)=Z1+Z2+Z3+Z4-Z5+Z6 (4.7)
Where
𝑃𝐿 (𝐸𝑟𝑖𝑐 )= 𝑃𝑎𝑡 𝐿𝑜𝑠𝑠, 𝑖𝑛 𝐸𝑟𝑖𝑐𝑠𝑠𝑜𝑛 𝑀𝑜𝑑𝑒𝑙, 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑖𝑛 𝑑𝐵 𝑍1= 𝑎0
𝑍2 = 𝑎1𝑙𝑜𝑔10(𝑑) 𝑍3 = 𝑎2𝑙𝑜𝑔10(𝑏)
𝑍4 = 𝑎3𝑙𝑜𝑔10 𝑏 𝑙𝑜𝑔10(𝑑) 𝑍5 = 3.2{𝑙𝑜𝑔10 11.75𝑟 }2
𝑍6 = 44.49 𝑙𝑜𝑔10 𝑓 − 4.78{𝑙𝑜𝑔10 𝑓 }2
Where
𝑎0 , 𝑎1 , 𝑎2 and 𝑎3 are values, which are changed according to the environments (i.e.
areas). For different areas, the parameters are described in following Table 4.2 [21].
Table 4.2: Parameters and Terrains for Ericsson 9999 Model [21]
Parameters Rural Area Sub-Urban Area Urban Area
𝒂𝟎 45.95 43.20 36.2
𝒂𝟏 100.6 68.93 30.2
𝒂𝟐 12.0 12.0 12.0
𝒂𝟑 0.1 0.1 0.1
4.2.3 Okumura Model
Okumura model [16][18] is one of the most widely used models used for signal prediction in urban areas. This model is applicable for frequencies from 150 MHz to 1920 MHz and a distance of 1 km to 100 km. It can be used for base station antenna heights ranging from 30m to 1000m. For dense cities, it is the best model.
Okumura gives overview of correction factors for open, sub-urban and quasi areas.
Okumura model is used to calculate path loss for up to 3 GHz. But we will discuss it at 2100 MHz and 2600 MHz frequencies.
37 The Path Loss is given by:
PL (Okum)=+Amn f,d -G hb -G hr -GAREA (4.8)
Where
𝑃𝐿 (𝑂𝑘𝑢𝑚 ) = 𝑃𝑎𝑡 𝐿𝑜𝑠𝑠, 𝑖𝑛 𝑂𝑘𝑢𝑚𝑢𝑟𝑎 𝑀𝑜𝑑𝑒𝑙, 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑖𝑛 𝑑𝐵 𝐿𝑓 = 𝐹𝑟𝑒𝑒 𝑆𝑝𝑎𝑐𝑒 𝑙𝑜𝑠𝑠
"𝐺 𝑏 " is called Base Station (BS) antenna height gain factor, which is given by:
G hb =20log10 hb
200 (4.9) 𝐺 𝑟 is called Mobile Station (MS) antenna height gain factor, which is given by:
G hr =10log10(hr
3 ) (4.10) 𝐺𝐴𝑅𝐸𝐴 = 𝐺𝑎𝑖𝑛 𝑑𝑢𝑒 𝑡𝑜 𝑡𝑒 𝑡𝑦𝑝𝑒 𝑜𝑓 𝑒𝑛𝑣𝑖𝑟𝑜𝑛𝑚𝑒𝑛𝑡
𝐴𝑚𝑛 𝑓, 𝑑 = 𝑀𝑒𝑑𝑖𝑎𝑛 𝑎𝑡𝑡𝑒𝑛𝑢𝑎𝑡𝑖𝑜𝑛 𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑡𝑜 𝑓𝑟𝑒𝑒 𝑠𝑝𝑎𝑐𝑒
The values of 𝐺𝐴𝑅𝐸𝐴 gain and Amn (f, d) factor, for different areas, are determined from graph as shown in Figure 4.1 [20].
38 Figure 4.1: Correction Factor and Median Attenuation for Okumura Model [20]
From above figure, we construct the following table.
Table 4.3: Different Terrains and Parameters for Okumura Model
Parameters Frequencies Open
Area
Sub-Urban Area
Quasi Open Area
(Correction Factor) At 2100 MHz 32 13 28
At 2600 MHz 34 13.5 29.5
(Median Attenuation)
At 2100 MHz 36 34 30.5
At 2600 MHz 38 35 32
4.2.4 COST 231 Hata Model
Hata Model [17] is introduced as an empirical formulation of the graphical path loss data provided by Okumura and is valid from 150 MHz to 1500 MHz. Hata model is used to calculate the median path loss at following conditions.
Distance between Tx and Rx of 20 km.
The height of transmitter antenna ranges from 30 m to 200 m.
The height of receiver antenna ranges from 1 m to 10 m.
Frequency range is 150 MHz to 1500 MHz.
An extend version of Hata Model is known as COST 231 Hata Model [18]. In three different areas (i.e. sub-urban, urban and rural), it is used to calculate path loss. It provides simple and easy ways for calculations.
The path loss model equation is given as:
PL(dB) = 46.3 + 33.9 log (f) - 13.02 log (hb) – a(hr) +[44.9 - 6.55 log (hb)].
log(d) + c (4.11) The path loss is also given by:
PL=N1+N2-N3-N4+N5+N6 (4.12) Where
39 𝑃𝐿 = 𝑃𝑎𝑡𝑙𝑜𝑠𝑠, 𝑖𝑛 𝐶𝑂𝑆𝑇 231𝐻𝑎𝑡𝑎 𝑀𝑜𝑑𝑒𝑙, 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑖𝑛 𝑑𝐵
N1=46.3
N2=33.3 log f
N3=13.82 hb log (4.13) N4=ahm
N5= 44.9-6.55 log hb log d (4.14) 𝑁6 = 𝐶𝑚
ahm parameter is given by:
For Urban Area:
ahm=32 log 11.75hr *2 -4.799 (4.15) For Rural and Suburban Areas:
ahm= {1.11 log (f) - 0.7}hr - {1.5 log (f) -0.8} (4.16) The Cm parameter, for different areas, is described in Table 4.4 [22]
Table 4.4: Different Terrains and Parameters for COST 231 Hata model [22]
Parameters
Rural Area Sub-Urban Area Urban Area
3dB 0dB 3dB
4.2.5 COST 231-Walfisch Ikegami Model
Another important and popular outdoor Propagation Model for LTE is COST 231- Walfisch Ikegami Model. This empirical model is a combination of the models from J.
Walfisch and F.Ikegami. It is also called as an extension of COST 231 Hata Model [18].
It is considered for both line of sight conditions. It is designed for 800 MHz to 2 GHz and is especially suitable for predictions in dense urban conditions [19]. The case of line
40 of sight is approximated by a model using free-space approximation up to 20 m and the following equation:
PL= 42.64 + 26 log (d) + 20 log (f) (4.17)
The path loss model equation for non line of sight takes into accounts various scattering and diffraction properties of the surrounding buildings which is shown below
PL= Lo + 𝐿𝑅𝑇𝑆 + 𝐿𝑀𝐷𝑆 (4.18)
𝐿𝑜 = 32.45 +20 log (d) + 20 log (f) (4.19)
𝐿𝑅𝑇𝑆 = -16.9 - 10 log (w) + 10 log (w) +20 log (𝑏 - 𝑟) + 𝐿𝑜𝑟𝑖 (4.20)
𝐿𝑜𝑟𝑖 =
−10 + 0.354𝑎 𝑓𝑜𝑟 0 < 𝑎 < 35 25 + 0.075 𝑎 − 35 𝑓𝑜𝑟 35 < 𝑎 < 55
4 − 0.114 𝑎 − 55 𝑓𝑜𝑟 55 < 𝑎 < 90
(421)
(3.18)
41
5 Experimental Results
The radio propagation model describes the behaviour of the signal when it is being transmitted from the transmitter towards the receiver. It gives a relation to the distance between the transmitter & receiver and the path loss. From the above relation, one can get an idea about the acceptable path loss and the maximum cell range. The path loss depends on different terrains and environment (urban, rural, dense urban, suburban, open, forest, sea etc) frequencies, atmospheric situation, and distance between transmitter and receiver.
5.1 Simulation of Path Loss for different RF Models
The path loss is calculated by using path loss equations discussed earlier for RF Propagation Models. The resulted graphs are plotted by using MATLAB.
In our calculations, we use different parameters such as carrier frequencies, distance between transmitter and receiver, receiver height and base station height. The simulation parameters for the propagation models are given in the Table 5.1.
These parameters are used in the simulation scenario to achieve the given results. All the propagation models are almost available to be used both in LOS & NLOS environment. To make our scenario more practical in the simulations, NLOS is used in urban, suburban & rural conditions. But for rural area in COST 231 W-I model LOS condition is considered because it does not provide any specific parameters.
42 TABLE 5.1: Simulation Parameters
5.1.1 Simulation Results of Okumura Path Loss Model
Figure 5.1 & Figure 5.2 gives simulation results for the path loss in Okumura model for 2100 MHz & 1900 MHz respectively.
Figure 5.1: Path Loss simulation results for Okumura Model (1900 MHz)
Parameters Values
Base station transmitter power 43 dBm
Mobile transmitter power 30 dBm
Transmitter antenna height 20 m & 70 m in urban, suburban and rural area
Receiver antenna height 2 m
Correction for shadowing
In suburban and rural (8.2 dB) and In urban area (10.6 dB)
Operating frequency Distance between Tx-Rx Building to building distance
Average building height Street width
1900 MHz & 2100 MHz 8 km
50 m 15 m 25 m
Street orientation angle 300 in urban and 400 in suburban
