Comparative Study of Path Loss Models in
Different Environments
Manju Kumari1 Tilotma Yadav2 Pooja Yadav3
Final Year (ECE), DAVCET, Kanina (INDIA),
Purnima K sharma4 Dinesh Sharma5
Assistant Professor, DAVCET, Kanina (INDIA),
Abstract:
By using propagation path models to estimate the received signal level as a function of distance, it becomes possible to predict the SNR for a mobile communication system. Both theoretical and measurement-based propagation models indicate that average received signal power decreases logarithmically with distance. For comparative analysis we use Okumura’s model, Hata model, COST231 Extension to Hata model,ECEC-33 model,SUI model along with the practical data. Most of these models are based on a systematic interpretation of theoretical data service area like urban(Built-up city or large town crowded with large buildings), suburban (having some obstacles near the mobile radio car, but still not very congested) and rural (No obstacles like tall trees or buildings like farm-land, rice field, open fields) in INDIA at 900MHz & 1800MHz frequency .
Keywords: Cost 231 Model, Stanford University Interim (SUI) Model, Hata Model, ECC-33 Model, Okumura’s Model.
1. Introduction
In wireless communication the losses occurred in between transmitter and receiver is known as propagation path loss. Path loss is the unwanted reduction in power single which is transmitted. We measure this path loss in different area like rural, urban, and suburban with the help of propagation path loss models. Wireless communications provide high-speed high-quality information exchange between portable devices located anywhere in the world. These models can be broadly categorized into three types; empirical, deterministic and stochastic. Empirical models are those based on observations and measurements alone. These models are mainly used to predict the path loss, but models that predict rain-fade and multipath have also been proposed [4]. The deterministic models make use of the laws governing electromagnetic wave propagation to determine the received signal power at a particular location. Deterministic models often require a complete 3-D map of the propagation environment. An example of a deterministic model is a ray tracing model [5]. Stochastic models, on the other hand, model the environment as a series of random variables. These models are the least accurate but require the least information about the environment and use much less processing power to generate predictions. Empirical models can be split into two subcategories namely, time dispersive and non-time dispersive [2,10].
2. Different Types of Propagation Path Loss models
2.1 COST -231 Model
A model which is widely used for calculating path loss in mobile wireless system is the COST-231 Hata model. The COST-231 Hata model is designed to be used in the frequency band from 500 MHz to 2000 MHz. It also contains corrections for urban, suburban and rural (flat) environments. Although its frequency range is outside that of the measurements, its simplicity and the availability of correction factors has seen it widely used for path loss prediction at this frequency band. The basic equation for path loss in dB is [3,10],
PL = 46.3 + 33.9 log10 (f) − 13.82 log10 (hb) − ahm + (44.9 − 6.55 log10(hb)) log10 d + cm (1)
Where, f is the frequency in MHz, d is the distance between AP and CPE antennas in km, and hb is the AP antenna height above ground level in meters. The parameter cm is defined as 0dB for
ahm = 3.20(log10(11.75hr))2−4.97, for f > 400 MHz
(2) and for suburban or rural (flat) environments,
ahm = (1.1 log10 f − 0.7)hr − (1.56 log10 f − 0.8) (3)
Where, hr is the CPE antenna height above ground level. Observation of (7) to (9) reveals that the path loss exponent of the predictions made by COST-231 Hata model is given by,
nCOST = (44.9 − 6.55 log10(hb))/10 (4)
To evaluate the applicability of the COST-231 model for the 3.5 GHz band, the model predictions are compared against measurements for three different environments namely, rural (flat), suburban and urban.
2.2 . Okumura Model
The Okumura model is best suited for large cell coverage (distances up to 100 km) and it can extrapolate predictions up to the 2GHz band. This model has been proven to be accurate and is used by computer simulation tools.[1] Okumura’s model is one of the most widely used models for signal predication in urban areas. It can be used for base station antenna heights (ht) ranging from 30m to 1000m, and mobile antenna height (hr) of 3m. The model can be expressed as
PL(db) = Lf + Amu (f, d) - G (ht)-G (hr) - Garea
(5)
Where PL is the 50th percentile valve of propagation path loss, Lf is the free space propagation path loss; Amu is the median attenuation relative to free space. G (ht) is the base station antenna gain factor (hr) is the mobile station antenna height gain factor and Garea is the gain due to the area type (i.e. urban, suburban, and rural). The values of Amu and Garea are obtained from Okumura’s empirical plots. And
G (ht) = 20log (ht/200); where ht is in between 30m to 1000m (6)
G (hr) = 10log (hr/3); hr < 3m (7)
= 20log (hr/3); 3m<hr<10m (8)
Okumura’s model has a 10-14db empirical standard deviation between the path loss predicted by the model and path loss associated with one of the measurements used to develop the model. This model is fully based on measured data and doesn’t provide any analytical explanation. This model is not good in rural area and it is fairly good in urban and suburban area because of its slow response to the rapid changes in the terrain. [7,1]
2.3 . Hata Model
Hata model is based on Okumura’s field test results and it predicts various equations for path loss with different types of clutters. Limitations of the Hata Model test results include its carrier frequency (150 MHz to 1.8 GHz), the distance from BTS (50m to 20Km), and the height of base station antenna (30m to 200m) and the height of mobile antenna (1m to 10m). Mathematically, the Hata model path loss is expressed for different environments such as the urban, suburban and open area. Hata model may not produce good results for the hilly rural terrains because the geographic details for this environment are not specified. The path loss for urban clutter is expressed as:
Lp(urban)=69.55+26.16log(f)–13.82log(hb)–a(hm)+(44.9–6.55log(hb))log(d) ( 9) Where,
a(hm) = (1.11log(f)-0.7)hm–(1.56 log(f)-0.8) (10)
Path loss for suburban clutter is expressed as:
Lp(suburban) = Lp(urban)-2{log(f/28)} -5.4 (11)
Path loss for the open country is expressed as:
Lp(rural)=Lp(urban)-4.78{log(f)}+18.33log(f)-40.94
Although Hata’s model does not have any of the path specific corrections. The predications of the hata model compare very closely with the original Okumura’s model, as long as d exceeds 1km. this model well suited for large Cell mobile system, but not personal communications system (PCS) which have cells on the order of 1km radius.
2.4 . ECC-33 Model
The ECC 33 path loss model, which is developed by Electronic Communication Committee (ECC), is extrapolated from original measurements by Okumura and modified its assumptions so that it more closely represents a fixed wireless access (FWA) system. The path loss model is defined as,
PL(dB) = Afs + Abm - Gt - Gr (13) where,
Afs is free space attenuation, Abm is basic median path loss, Gt is BS height gain factor and Gr is received antenna height gain factor. [7,10]
These are separately defined as,
Afs = 92.4+20log(d)+20log(f) (14) Abm = 20.41+9.83log(d)+7.894log(f)+9.56[log(f)]² (15) Gt = log(hb/200)[13.98+5.8(log(d))²] (16) For medium city areas,
Gr = [42.57+13.7log(f)][log(hm)-0.585] (17) Where,f is the frequency in GHz,
The performance analysis is based on the calculation of received signal strength, path loss between the base station and mobile from the propagation model. The GSM based cellular d is distance between base station and mobile(km),hb is base station antenna height in meters and mobile antenna height in meters.
2.5. Stanford University Interim (SUI) Model
The frequency band below 11GHz use the channel model which is proposed by Stanford University called SUI model. These models are derived for the Multipoint Microwave Distribution System (MMDS) frequency band from 2.5GHz to 2.7GHz. The model covers three most common terrain categories However, other sub-categories and different terrain types can be found around the world The maximum path loss category is hilly terrain with moderate-to-heavy tree densities (Category A). The minimum path loss category is mostly flat terrain with light tree densities (Category C). Intermediate path loss condition is captured in Category B. [8,10] The basic path loss formula with correction factors is given as: [8,9]
PL=A+10γlog10 (d/d0) +Xf + Xh + s; for d>d0 (18)
Where, d is the distance between Access Point(AP) antenna and Customer Premises Equipment antenna in meter, d0 = 100m and s is a log distributed factor that is used to account the effect for the shadow fading owing to trees and other obstacles having value between 8.2db to 10.6db.and
A =20log (4πd0/λ) (19)
γ = a - b.ht+c/ht (20)
Where ht is the base station height from the ground in meters in between 10m to 80m.
The values of a, b, c is given in the table:
Table1: The parameters of SUI model in different types of areas
Model parameter Terrain A Terrain B Terrain C a b(m־¹) c(m) 4.6 0.0075 12.6 4.0 0.0065 17.5 3.6 0.005 20
Xf = 6.0log (f/2000) (21) And
Xh = -10.8log (hr/2000); for terrain types A&B
(22)
= -20Llog (hr/2000); for terrain types C
(23)
Where, frequency (f) is in MHz and hr is the mobile antenna height from the ground in meters. It is applicable to all three areas like urban, subuaban, rural areas.
3. Result with Practical data
The practical data was taken in the urban (high density region means market area of Kosli (State: Haryana, INDIA)) and Rural area (low density means in a village near to kosli named Jonawas (State: Haryana, INDIA)) using spectrum analyzer. The power from the transmitter taken is 43db.We analyses these models with the help of practical data given in the respective models in different environments, namely urban and rural at 900 MHz frequency.
4. Conclusion
References
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