Comparative Measurement of RF Link Budget between SUI and Theoritical Models in a Densely Populated Area
M.H Ibrahim, K.N Puniran, M.H Mohd Hashim
Faculty of Electrical Engineering
University Technology Malaysia
Kuala Lumpur
Abstract - This paper presents the analysis of the RF link budget measurement performed for LTE network in a densely populated area (i.e. Kuala Lumpur) by comparing the result of propagation between theoretical model and Standard University Interim (SUI). The aim of this paper is to establish assumptions of system design at the eNodeB (transmitter) and the user equipment (UE) for both uplink and downlink transmissions. Consequently, the maximum allowable path loss (MAPL) in the LTE system and the maximum coverage area based on the above propagation model is determined and estimated accordingly.
Keywords - LTE, Link Budget, SUI Model, MAPL, Link Budget, eNodeB, UE, Free Space Loss, EIRP
I. INTRODUCTION
A. Background
The MCMC is recently granted a license to service provider to operate LTE network in 3GPP Band 7, with consideration of uplink frequency in between 2500 MHz to 2570 MHz, and downlink frequency at the range of 2620 MHz to 2690 MHz. The LTE will be in operation in year 2013. This paper is to establish the RF link budget and to determine the maximum allowable path loss (MAPL) in LTE and estimate the maximum coverage area due to propagation model for the site.
B. Problem Statement
All gains and losses at transmitter (eNodeB) and receiver (UE) for both uplink and downlink transmissions shall be considered in the RF link budget calculation. From the link budget’s tabulated result for both uplink and downlink as shown in this paper, the value of calculated MAPL will determine the maximum coverage area based on the chosen propagation model. The MAPL is determined based on the difference of maximum RF power output of the transmitter and the maximum sensitivity of the receiver [5]. The consequences of limiting the coverage area will cause an additional base station which is required to cover the target area. Thus, MAPL is one of the factors which involves in determining the performance of the model.
The SUI model is selected mainly due to the fact that the model has been developed and benched marking for the frequency bands below 11 GHz [3]. In the US, this model is defined for Multipoint Microwave Distribution System (MMDS) frequency band from 2.5 GHz to 2.7 GHz which is suitable for the LTE network frequency in Malaysia, for both uplink and downlink transmissions. The SUI model has better performance in analytical process and has been widely used in propagation model. Furthermore, the model also considers a different type of terrains with different type of parameters and correction factors, which makes the result more accurate to determine and design the RF link budget modelling for LTE network [3].
C. Assumption
In designing a cellular network which is involving the high speed data link such as LTE network, there are two common questions which are the governing points on how to determine the performance of the network. The questions are how far can it go and what will the throughput be? There are several factors that may impact the performance of the network specifically in a wireless communication. Available and permitted output power, available bandwidth, receiver sensitivity, antenna gains, radio technology, and environmental conditions are some of the major factors that may impact system performance.
A link budget involves a relatively simple addition and subtraction of gains and losses within a RF link. When these component gains and losses are determined and summed, the result is an estimation of end-to-end system performance [4].
To arrive at an accurate answer, factors must be taken into account such as:
- The frequency bands
- The uplink power
- Amplifier gain and noise factors
- Transmit antenna gain
- Path loss without assuming any relative error
- Receive antenna and amplifier gains and noise factors
- Other attenuation
In this paper, the values and figures in relative to the above factors have been tabulated in the methodology and result sections. The figures are taken from various LTE products specification particularly the antenna for both transmitter and receiver.
II. METHODOLOGY
A. Pathloss Model
The propagation model using theoretical model to determine the path loss between eNodeB and UE is described in below equation. The path loss is derived by the transmission path from an eNodeB to UE with the consideration of all the losses [1], [2]
PL (dB) = PTX + GTX – LTX – PRX – LRX–M (1)
Where:
PTX = Transmitted output power (dBm)
GTX= Transmitter antenna gain (dBi)
LTX = Transmitter losses (dB)
PRX = Receiver power (dBm)
LM = Miscellaneous losses (dB)
The Free Space Path Loss (FSL) is a distinguished and prevailing loss in cases where there are no obstacles along the path. The path loss according to theoretical model (FSL) can be calculated by [1], [2]
LFSL (dB) = 32.44 + 20log10d (km) + 20log102600 (MHz) (2)
Where:
f = Operating frequency
d = Separation distance between eNodeB and UE
B. Stanford University Interim (SUI) Model
The propagation model selected in comparing the theoretical model as mentioned in Section II.A is Standard University Interim (SUI) model. In this paper, a Terrain A which is associated with a maximum path loss and moderate to a highly dense populated area is considered. The expression of path loss propagation with correction factors according to SUI model is shown as per below equation [1], [2]
PL SUI (dB) = A+ 10γlog10 ( + Xf + Xh +
s for
d >
do (3)
Where:
d = the distance between the eNodeB and UE antennas
d0 = 100m
s = a log normally distributed factor that is used to account for the shadow fading owing to trees and other clutter and has a value between 8.2dB and 10.6dB. The other parameters are defined as [1], [2]
A = 20log10 (4)
γ= a – bhb + (5)
Where:
hb = base station height above ground
a,
b and
c = constant values given in Table 1.1
γ= equal to the path loss exponent, for a given terrain type the path loss exponent is determined by hb
| Table 1.1: Terrain Types and Parameters for SUI Model [3] Model Parameter |
Terrain
A |
Terrain
B |
Terrain
C |
| a |
4.6 |
4.0 |
3.6 |
| b(m-1) |
0.0075 |
0.0065 |
0.005 |
| c(m) |
12.6 |
17.1 |
20 |
The correction factor for the operating frequency above 2GHz and for the receiver antenna height are defined in below equation [1], [2]
Xf = 6.0log10 (6)
The expression of type A and B terrain is determined per below equation [3], [4]
Xh = -10.8log10 (7)
While for type C terrain [3], [4]
Xh = -20 log10 (8)
Where:
f = Frequency (in MHz)
hr = Receiver antenna height
The shadowing correction,
S is calculated using the equation [1], [2]
S = 0.65 (log f) 2 – 1.3(log f) + α (9)
Where:
α = 5.2dB for urban and suburban area
α = 6.6dB for rural area
the EIRP has to be calculated [1], [2]
E.I.R.P = PTX + GTX - Loss
To determine the
maximum allowable path loss (MAPL),
Where:
PTX = Transmitter output power (dBm)
GTX = Transmitter antenna gain (dBi)
Thus, the MAPL equation as described below [1], [2]
MAPL = EIRP + GRX – PTRmin – I – Co (11)
Where:
GRX = Receiver antenna gain (dBi)
PTRmin = Receiver sensitivity (dBmW)
I = Interference margin (dB)
Co = Loss of cable (dB)
III. RESULT AND FINDING
The RF link budget for uplink and downlink with 2600 MHz of carrier operating frequency are tabulated in below section. The results are obtained based on the theoretical propagation model and SUI propagation model.
A) Theoretical Propagation Model
Table 2.1 shows the result obtained for the transmitter and receiver data with all parameters required in downlink and uplink link budget. Assumptions have been made in calculating the link budget by taking into consideration of antenna gain, height and all the losses. The losses may due to the cable loss, medium loss or loss due to the building penetration.
| Table 2.1: Link Budget Design Specification for LTE Network Description |
LTE (2600 MHz) |
| Transmitter (eNodeB) |
Downlink |
Uplink |
| Tx (dBm) |
46 |
23 |
| Tx Antenna Gain (dBi) |
18 |
0 |
| Cable Loss (dB) |
2 |
0 |
| EIRP (dBm) |
62 |
23 |
| Receiver (UE) |
Downlink |
Uplink |
| UE Noise Figure (dB) |
7 |
2 |
| Thermal Noise (dB) |
-104.5 |
-118.4 |
| Receiver Noise Floor (dBm) |
-97.5 |
-116.4 |
| SNR (dB) |
-9 |
-7 |
| Receiver Sensitivity (dBm) |
-106.5 |
-123.4 |
| Interference Margin (dB) |
4 |
1 |
| Control Channel Overhead (%) |
20 |
0 |
| Rx Antenna Gain (dBi) |
0 |
18 |
| Body Loss (dB) |
0 |
0 |
| Max Allowable Path Loss (dB) |
163.5 |
B) SUI Propagation Model Table 2.2 shows the result obtained from SUI model. Several parameters have been assumed such as type A terrain, the base station height, receiver height and distance between transmitter and receiver, d.
| Table 2.2: Link Budget Design Specification for SUI Model Parameter |
Downlink |
Uplink |
| π |
3.1429 |
3.1429 |
| do (m) |
100 |
100 |
| d (m) |
1000 |
1000 |
| a |
4.6 |
4.6 |
| b (m-1) |
0.0075 |
0.0075 |
| c (m) |
12.6 |
12.6 |
| C (m/s) |
3.0E+08 |
3.0E+08 |
| f (hz) |
2.60E+09 |
2.60E+09 |
| hr (m) |
1.65 |
40 |
| hb (m) |
40 |
1.65 |
| λ |
1.15E-01 |
1.15E-01 |
| s (dB) |
8.5 |
8.5 |
| A |
80.74 |
80.74 |
| γ |
4.615 |
12.22 |
| Xf |
0.68 |
0.68 |
| Xh |
33.30 |
18.35 |
| PLSUI (dB) |
169.38 |
230.52 |
IV. ANALYSIS AND DISCUSSION
A) Downlink Analysis
Figure 1.1 shows the comparison of path loss obtained by using SUI model and theoretical model namely as Free Space Loss (FSL) for downlink transmission.
Figure 1.1: Comparison of Path Loss using SUI Model and Theoretical Model
From the downlink graph, the estimated maximum distance coverage area is approximately d = 0.7Km. However, for the ideal model, the MAPL is doubled the difference by computing below equation:
MAPL =32.44 + 20log10d (km) + 20log102600 (MHz)
Then, d = 1374.1km
B) Uplink Analysis
Figure 1.2: Comparison of Path Loss using SUI Model and Theoretical Model
Figure 1.2 shows the comparison of path loss obtained by using SUI model and theoretical model namely as Free Space Loss (FSL) for uplink transmission.
From the uplink graph, the estimated maximum distance coverage area is approximately d = 0.29Km. However, for the ideal model, the MAPL is shown per below equation:
MAPL =32.44 + 20log10d (km) + 20log102600 (MHz)
Then, d = 1364.6km
V. DISCUSSION
The estimated link budget analysis is engineered and designed by network engineer to investigate the maximum allowable path loss (MAPL) between eNodeB and UE in any wireless technology specifically LTE. MAPL is used to determine maximum allowable attenuation between eNodeB and UE. The assumption for the case study is to take sample starting from 100m up to 1000m. The assumptions made in determining the link budget are as per below:
- The estimated isotropic radiated power (EIRP) to be 62dBm for downlink and 23dBm for uplink
- The gains for transmitter antenna and receiver antenna are as per Table 2.1
- Standard eNodeB height is 40m from the sea level and UE height is 1.65m
- The MAPL obtained from standard LTE design is 163.5dB for downlink while 163.4dB for uplink
The result of path loss for ideal model is compared with SUI model to determine which equation gives more accurate result in relative to the maximum coverage area. By using SUI model, maximum PL for downlink is 169.38dB while 230.52dB for uplink.
From the downlink graph shown in Figure 1.1, the maximum cell size for LTE network coverage by using SUI model is 0.7Km (from eNodeB to UE). In this case study that is implemented in Kuala Lumpur, about 268 cells are required for LTE network. Besides, from the graph shown in Figure 1.2, the maximum coverage for uplink is 0.29Km (from UE to eNodeB). As for the comparison, the coverage area for downlink is higher than uplink. It is due to the fact that the UE power transmitter is lower than the eNodeB power transmitter. The UE is required a small amount of power to transmit the signal.
VI. SUMMARY AND CONCLUSION
Most of service providers in cellular technology are implementing cell splitting and frequency reuse techniques in order to have a better coverage and to double the capacity. However, careful consideration and technique shall be employed in order to establish a good design by minimizing and eradicating issues especially the interference issue. As an initial part of the design, the MAPL and maximum coverage area in the network shall be determined.
In this paper, the aim is to develop the assumptions of system design for uplink and downlink transmission at transmitter and receiver sides. A key part of the work is to find the MAPL and the maximum coverage area for signal transmission in LTE network. Standard University Interim (SUI) model at densely populated area with maximum path loss is considered in this work. From the design obtained, it is found that SUI model has greater path loss as compared with theoretical model.
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