International Conference on Computer and Communication Engineering (ICCCE 2012), 3-5 July 2012, Kuala Lumpur, Malaysia

978-1-4673-0479-5/12/$31.00 ©2012 IEEE

Studying Different Propagation Models for LTE-A System

1,2Yassir A. Ahmad, 1Department of Communications Engineering

Engineering College , University of Diyala Ba'aqubah 32001, Diyala, Iraq

2Wireless Communication Center (WCC) Faculty of Electrical Engineering, University of Technology

Malaysia (UTM) 81310 Skudai, Johor Bahru yassirameen22@gmail.com

Walid A. Hassan, Tharek Abdul Rahman Wireless Communication Center (WCC)

Faculty of Electrical Engineering, University of Technology Malaysia (UTM) 81310 Skudai, Johor Bahru

walid.a.hassan@gmail.com tharek@fke.utm.my

Abstract— This paper investigates the different empirical propagation models for the next mobile generation known as the Long Term Evolution – Advanced (LTE-A) in the 2GHz band.. The effects of the propagation models are analyzed in urban, suburban and rural environments by using Monte-Carlo statistical methodology. The Joint Task Group 5-6 (JTG5-6) propagation model is discussed in the paper along with the free Space, Extended Hata and the ITU-R P.1546-4. The results show that the Extended Hata model is feasible for LTE-A system to compute the path loss when deployed in different environments. Keywords-component; Propagation model, JTG5-6; LTE-A; Monte Carlo; 2GHz Band.

I. Introduction Mobile radio communications in cellular radio take

place between a fixed base station (BS) and a number of roaming mobile receivers (MR). From the literatures, the mobile communication involves characterization and modeling of the radio propagation channels and considered as the most important and fundamental aspect. The propagation channel results in limits to the performance mobile radio system. For instance, the multipath propagation, which is the major characteristic of mobile radio channels. It is caused by diffraction and scattering from terrain features and buildings, that leads to distortion in analogue communication systems and severely affects the performance of digital systems by reducing the carrier-to-noise (C/I) and carrier-to interference ratios (I/N). In addition, understanding of mathematical modeling of the channel is a necessity to accurately predict the system performance and provide the mechanism to analyze the effects caused by radio channel [1].

A. Survey of related work The LTE-A system has the ability of satisfying the

requirements of next-generation mobile networks for existing 3GPP standards. It is one of the expect candidates for the next mobile communication system know as the International Mobile Telecommunication – Advanced (IMT-A) standard. The LTE-A provides the advantages of

high performance, and mass market mobile broadband services. This is achieved by combining low latency high bit-rates and system throughput, in both the uplink and downlink communications. [1].

In [2], a comparative study is conducted for evaluating the suitable propagation models for LTE system. The SUI model, Okumura model, Hata COLTE, COST Walfisch-Ikegami and Ericsson 9999 model were investigated. The analysis considers different terrains, urban, suburban and rural area. The study results revealed that the terrains, model gave the lowest path loss for all the terrains. The COST 231 Hata model prediction results in high path losses in the urban environment, while the COST Walfisch-Ikegami model has the highest path loss for suburban and rural environments.

Finally, the study [3] provides a comparison of achieved measurements obtained from the received power in urban and suburban areas of Osijek city in Croatia. The study investigates four prediction models: SUI model; COST 231 Hata, Macro model and model 9999. Analyses were done separately for each location with Line of Sight (LOS) and non-Line of Sight (NLOS) propagation conditions. Results showed that the standard deviation of the prediction error for NLOS condition is low for the SUI model. The Macro model achieved the lowest error in terms of standard deviation for LOS propagation conditions.

B. Significance of the study . Our study investigates the preferred radio propagation

model for LTE-A system. The selected model should satisfy the least path loss in a particular terrain. Since the LTE-A system operates in the 2GHz band, different radio propagation models are available that can be used in different terrains for LTE-A system. The results recommend the suitable empirical propagation model for LTE-A system in rural, urban and suburban deployment, based on the calculation of the signal carrier as a function of separation distance and terrain affect. The study also highlights on the new ITU Joint Task Group 5-6 (JTG5-6) model for LTE-A.

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II. Methodology The methodology is based on the comparison of

different radio propagation models in order to find the preferred model for particular deployed environment of the LTE-A system. This is achieved on the basis of path loss evaluation, which is a function of separation distance between the BS and MR. The flow chart of the study is illustrated in Figure 3.

A. Monte Carlo Simulation (MCS)

Numerous statistical methods have been employed in solving scientific problems. One such successful method was developed in 1940 by physicists working on the nuclear weapon projects at Los Alamos National Laboratory [4]. The method is called ‘MSC random processes. The basic idea behind the MCS method, is to randomly distribute the samples and calculate the results based on a probability of distribution [5].

A mobile radio communication system can be likened to a random series of variables. Thus, if the inputted values (such as system parameters, appropriate propagation model..etc) are accurately defined, a real-time system can be simulated when enough samples are available. In our study we used the user MR to obtain accurate path loss from MCS method with respect to a desired received carrier level. This facilitates the calculation of probability of the path loss and hence reception quality [6].

Figure 1 shows the process of selecting the suitable propagation model for LTE-A system. In the figure, the radio system parameters for the simulation are defined as a constant such as a BS or MR position. Using MSC, with a large number of samples/events (.i.e. > 10,000), the MSC is applied to give reliable results [6]. After randomizing the users in the coverage area, The wanted signal is calculated for each sample. The path loss is obtained for each sample after a sufficient number of MRs have been distributed.

III. RADIO PROPAGATION MODELS In wireless communication systems, information is

transmitted between the transmitter and the receiver antenna by electromagnetic waves. An interaction occurs in the environment during electromagnetic wave propagation which causes a degradation of transmitting signals, called the path loss. The path loss (PL) in dB can be expressed as [7]:

T T R R T RPL P G G P L L� (1)

Path loss (PL) is defined as the difference between transmitted and received power (in dBm). PT and PR are the powers in dBm for transmitter and receiver respectively. GT and GR (dBi) are the gains of transmitting and receiving antenna respectively, and LT and LR are

feeder losses (dB) for the transmitter and receiver respectively.

Figure 1. The simulation flow chart

LTE-A systems operating in the frequency range of 2 – 11 GHz [8] are suitable for communication in LOS and NLOS conditions. In the NLOS conditions, the signal experiences, reflecting, diffraction and scattering before it reach its destination. For this purpose, the wireless network planning requires a suitable propagation model based on the electric field strength calculation and the path loss evaluation. The path loss is characterized by two main types of models: deterministic (site-specific theoretical) and empirical (statistical) models. The former models make use of some physical laws governing electromagnetic wave propagation and calculates received signal power at a particular location. These models require detailed geometric information on terrain profile, location, and dimensions of buildings, and so on. The latter models are based on measurements and predict the mean path loss as a function of various parameters, e.g. antenna heights, distance, frequency, etc. deterministic models are easier to implement, with less computational cost, but they are less accurate [7].

Propagation prediction for LTE-A systems are usually conducted by one of empirical models. In this paper we investigate the following four models:

1. Free Space [9].

2. Extended Hata [2].

3. ITU-R P.1546-4 [10].

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4. JTG5-6[11].

A. JTG5-6 propagation model

Mobile services propagation models developed by Okumura/Hata are optimized. The optimization covers path lengths varying between 1 to 20 km, the low antenna heights of mobiles, BS antennas installed above rooftop level, and urban environments. On the other hand, broadcasting propagation models are optimized for antenna heights that exclude clutter at station vicinity, atmospheric effects by using time probability and very long distances (up to 1000 km).

The formula for the interpolation between d=0.1 and 1 km:

� �� �

� �log( ) log(0.1)( ) (0.1) (1) (0.1) (2)

log(1) log(0.1)d

L d L L L�

where:

L(1): path loss computed with P.1546-3 at 1 km

L(0.1): path loss computed with Hata at 0.1 km

From the sketch in Figure. 2, there are two possible ways to perform the interpolation [5] in the distance between 100-1000 m.

Figure 2. : Illustration of the path loss between 100 m and 1000 m,

source [11]

� Option A

A restricted application of the Extended Hata model [6] to free space generates point B and values for path losses, which compared to free space attenuation, are greater than or equal to the distance considered (green dashed curve).

(0.1) MAX{ Hata(0.1) , FREE SPACE(0.1)} (3)L �

It should be noted that L(d) is not restricted by the free space[11].

� Option B

Removal of the free space restriction of the original Hata formula generates point A. The interpolated values are lower than free space attenuation if the path loss computed with Hata is less than the free space (red dotted curve). The reverse holds true. The curve B to C gives the variable location for a break point if there is a restriction to free space depending on the height of the BS.

(0.1) Hata(0.1) (4)L �

( ) MAX{ L(d) , FREE SPACE(d)} (5)L d �

The calculate path loss values based Hata or Extended Hata model are greater than free space implies that the green and red curves are identical. In some cases, low path loss values could be predicted by Hata, for certain antenna constellation, which is smaller than free space. In such cases, it is recommended to restrict the path loss at 100 m to free space or values greater than the free space attenuation (green curve), i.e. use of option A[11].

� Rural and open area

The Hata model contains a basic environmental variable “open area”. A height correction for the “rural” environment is available in P.1546. Annex 5 section 9 in [11] states that “the field-strength values given by the land curves are for a reference receiving/mobile antenna at a height, R (m), representative of the height of the ground cover surrounding the receiving/mobile antenna, subject to a minimum height value of 10 m. Examples of reference heights are 20 m for an urban area, 30 m for a dense urban area and 10 m for a suburban area.” For a receiving/mobile antenna that is on rural or open land, it is stated that a correction be computed for a fixed clutter value of 10 m for all receiver antenna heights. As a result of the clutter height, the predicted path loss like the Hata model path loss is considerably larger than for real “open area” without clutter.

The Hata model “open area” is not synonymous with “rural” in P.1546 and JTG5-6. However, an amended JTG5-6 model using the height correction for “rural” in [11]may be particularly applied in rural areas in the radio band 790-862 MHz .

� Correction for short urban/suburban paths

In Annex 5 section 10 of [11],it is noted,

“If a path of length less than 15 km covers the buildings of uniform height over flat terrain, a correction representing the reduction of field strength due to building clutter should be added to the field strength”. The correction is given by:

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3.3(log( ))(1 0.85log( )) ... ... (1 0.46log(1 )) (6)a

Correction f dh R

� ��

where ha is the antenna (mast) height above ground (m) and R is representative of the height of the ground cover surrounding the receiving/mobile antenna as defined in [11], which also represents the height of ground cover surrounding the transmitting/base antenna.

It is pointed out that this correction only applies when d is less than 15km and (ha-R) is less than 150m. For example, assuming the operating frequency is 800 MHz, and d=1 km, h1–R equal to 10m results in a correction of about -5dB for the field strength or +5 dB for the path loss, and for 10 km in about +0.5 dB for the path loss.

It is recommended to add this correction in the JTG5-6 model, because particularly the cell radius of mobile radio in rural area is expected to below 5 km and the BS antenna height exceed the environmental clutter typically in the range 10 to 20 m.

IV. SYSTEM PARAMETERS AND SHARING SCENARIO

In order to conduct the sharing scenario, the system parameters are required. The LTE-A parameters that are used in our simulations are described in Table 1.

The JTG5-6 propagation model is implemented for three cases that are urban, rural and suburban respectively, to analyze the terrain effect. For all the propagation models the distance between BS and MR is between 1 to 10km, as shown in figure 3.

TABLE 1. SHOWS THE INPUT PARAMETERS [12]

Parameter Value Units Frequency 2000 MHz

Transmitting antenna height 30 m Receiving antenna height 1.5 m

Antenna polarization Horizontal Percentage of time 50 %

Percentage of localization 50 % Noise floor -95 dBm

Antenna gain for transmitter 15 dB Antenna gain for receiver 0 dB

Carrier to interference ratio(C/I)

11 dBm

Distance between Tx & Rx 1-10 km

Figure 3. Scenario with fixed links

V. RESULTS AND DISCUSSION

A. JTG5-6 propagation model The results of the carrier signal attenuation based on the

JTG 5-6 model under different deployment scenarios is shown in Figure 4.

1 2 3 4 5 6 7 8 9 10-120

-110

-100

-90

-80

-70

-60

Distance in Km

Ca

rrie

r V

alu

e i

n d

Bm

JTG5-6 Propagation Model

Rural Urban Suburban

Figure 4. The JTG 5-6 model in rural, urban and suburban

environments

From the results, it can be seen that carrier values for the rural site lies at the highest level as compared to the other two sites and is ranging in between -66.03dBm and -105 65dBm. Maximum carrier values for urban and suburban are -115.66 and -109.27dBm, while minimum results for these two sites were calculated as -80.57dBm and -72.86 dBm respectively. The carrier is declining with the extension in distance between BS and MR because of losses that appear due to medium interference and environmental effects. The curves (formulas) used as

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basic in the JTG5-6 are the land curves for 1 and 50 % time and 50 % location variability. The land curves refer to suburban or urban area with the receiving antenna height of 10 m above the environmental clutter height of 10 m. The approach is different to the previous model. Here the path loss is improved by the correction due to the increase the distance of MR to the BS from 10 (fixed) to 1 km. This height correction depends mainly on the clutter height: For suburban and urban areas the clutter heights of 10 and 20m is used, respectively. The correction of rural differs only very slightly from suburban.

B. The Propagation Models Effects

For each propagation model described in Section III, three environments are considered; rural, urban and suburban. So it is necessary to examine the effect of the received signal level for these three environments. In the following a comparative results based on the received signal level for each model with respect to specific environment are presented.

In a rural environment, the free space propagation model has the best performance (ideal case), compared with other propagation model, because it does not consider any obstacle in the path (clear LOS). While the Extended Hata propagation model, uses the low rate of local clutter, comparing with ITUR P. 1546 and JTG 5-6 models, since they use a high rate of local clutter are shown in Figure.5.

1 2 3 4 5 6 7 8 9 10-110

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-90

-80

-70

-60

-50

-40

-30

Distance in Km

Ca

rrie

r V

alu

e in

dB

m

Rural

JTG5-6 Extended Hata ITU-R P.1546-4 Free Space

Figure 5. Compares the value of Carrier (dBm) in Rural

The simulation, results achieved for urban area are shown in Figure.6. The results show that the attenuation of the signal based on the Extended Hata model is less compared to the ITU-R P.1546-4 and JTG5-6 models in urban deployment.

1 2 3 4 5 6 7 8 9 10-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

Distance in Km

Ca

rrie

r V

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n d

Bm

Urban

JTG5-6 Extended Hata ITU-R P.1546-4 Free Space

Figure 6. Compares the value of Carrier (dBm) in Urban

Results for of suburban area are shown in Figure.7. The results of this scenario lay in between the other two cases (that is, rural and urban) that were presented and discussed previously. The figure shows that the Extended Hata achieved better results compared to the urban deployments

1 2 3 4 5 6 7 8 9 10-110

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-90

-80

-70

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Distance in Km

Ca

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Bm

Suburban

JTG5-6 Extended Hata ITU-R P.1546-4 Free Space

Figure 7. Compares the value of Carrier (dBm) in Suburban

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VI. Conclusion The propagation models are one of the most principal contributors to many problems that appear today in the world of telecommunication. Investigating different propagation models for LTE-A system was conducted in this study. Results have shown that the JTG5-6 model path loss values are similar to the ITU-R P.1546.4 model as compared to its transmission features. The comparison shows a much higher loss when the JTG5-6 and ITU-R P.1546.4 models are used. However, this is because these models have more realistic path loss calculations. Meanwhile, the Extended Hata model achieved lower signal attenuation. Therefore, the Extended Hata model is recommended be used to find the path loss for studies that investigates the compatibilities between LTE-A, and other wireless communication systems.

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