In wireless communication, the path loss is proportional to the square of the operating carrier frequency. As a result, the higher the frequency, the greater the path loss. Although path loss is affected by several parameters, including fading, shadowing, angle of arrival (AOA), and angle of departure (AOD), and others. In comparison to lesser frequencies, when the frequency is extremely high, it is easily absorbed by atmospheric gases, vapor, and rain. In the case of higher frequencies, however, the penetration loss is also greater. Path loss is linearly proportional to the carrier frequency, according to Firs' free space path loss. Path loss parameters are often divided into two categories. 1. Large Scale Path loss; 2. Small Scale Path loss. Large-scale path losses are basically path losses due to the distance between transmitter and receiver, shadowing loss, etc. Examples of small-scale path losses due to fading, angle of arrival & angle of departure, etc.
1. Free Space Pathloss:
This phenomenon occurs when a signal travels across empty space. The formula for free space path loss, or FSPL, is
Pathloss = 20log10(λ/4πd) ... (1)
Free space path loss, however, is not completely relevant when discussing real-world wireless communication systems, particularly cellular wireless networks. because the FSPL includes atmospheric path loss. In addition, variable environmental conditions, regardless of TX and RX distance, result in varied path loss. For various environments, the path-loss exponent (PLE) 'n' changes dramatically. Below, we've talked about PLE.
2. Close-in Path Loss Model:
The close-in path loss model is appropriate for current wireless communication systems operating at sub-6 GHz band or higher and is also applicable for millimeter wave 5G communication.
.... (3)
FSPL (d0) denotes free space path loss at the first few meters (i.e., 1 meter). The letter 'n' stands for path loss exponent. The letter 'd' represents the total path length between the transmitter and the receiver. The shadowing factor is denoted by the symbol, χσ.
This allows us to calculate path loss for current wireless communication bands, such as UWB communication, with excellent precision. This path loss model implies that it is extremely high for the first few meters, then exponentially increases based on the path loss exponent value for that environment (LOS or NLOS, urban or rural, etc.). In 28 GHz transmission, for example, path loss from the first meter is roughly 32 dB Following then, path loss grows by the wireless environment's path loss exponent value.
Received signal power in an atmospheric environment can be defined as
Pr = Pt + Gt + Gr + 20log10(λ/4Ï€d) + atmospheric pathloss……… (2)
Pr = Received Power & Pt = Transmitted Power
λ = wavelength of carrier frequency
d = distance between Tx & Rx
Gt & Gr = transmitter & receiver antenna gain, respectively
20log10(λ/4πd) = free space path loss at first propagation reference distance d
The close-in path loss model is appropriate for current wireless communication systems operating at sub-6 GHz band or higher and is also applicable for millimeter wave 5G communication.
.... (3)FSPL (d0) denotes free space path loss at the first few meters (i.e., 1 meter). The letter 'n' stands for path loss exponent. The letter 'd' represents the total path length between the transmitter and the receiver. The shadowing factor is denoted by the symbol, χσ.
This allows us to calculate path loss for current wireless communication bands, such as UWB communication, with excellent precision. This path loss model implies that it is extremely high for the first few meters, then exponentially increases based on the path loss exponent value for that environment (LOS or NLOS, urban or rural, etc.). In 28 GHz transmission, for example, path loss from the first meter is roughly 32 dB Following then, path loss grows by the wireless environment's path loss exponent value.
The path loss increases as the distance between the transmitter and receiver grow because the signal is attenuated in the atmospheric air as it travels the distance. When a path of equal length is propagated at different frequencies, the path loss is higher at higher frequencies than at lower frequencies. Similarly, path loss for LOS and NLOS pathways differs when TX and RX are positioned at a given distance. Because NLOS pathways typically cover a greater distance than LOS paths. The LOS path connects the transmitter and receiver in a straight line. [Read More about LOS and NLOS Paths]
3.2. Small Scale Pathloss:
Fading, angle of arrival (AOA) at the receiver, angle of departure (AOD) at the receiver, and other factors contribute to small-scale route losses. We send a signal from the transmitter antenna, which then spreads away from the antenna. There must be structures and vegetation there. As a result, the signal is reflected or refracted by the walls of the building or the foliage. The reflected or refracted signal then travels to the receiver via many NLOS paths other than the line of sight (LOS). Finding a LOS path between transmitter and receiver in densely built locations is tough. As a result, the same signal comes as MPCs at the receiver, and we find temporal dispersion for the arrival of the first and last MPCs for broadcasting the same signal from the transmitter side. Fading is caused by these MPCs. There are various types of fading, such as slow or fast fading, frequency selective fading, and so on. Fast fading occurs when the channel impulse response varies rapidly. Frequency selective fading refers to fading that varies according to frequency. We can see distinct fading patterns depending on the frequency. Assume we're looking at a different fading type/property for frequency F1 and a different fading type/property for frequency F2. Also read about
[1] Difference between AWGN and Rayleigh Fading
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