Department of Electrical Engineering, Study Program of Digital Telecommunication Networks, State Polytechnic of Malang
ABSTRACT
Microwave are a type of the radio wave with a high-speed signal transmission that uses Line Of Sight(LOS) transmission to avoid obstacles from buildings or earth medium(terrain). Microwave transmission system are typically installed in open areas and aligned according to the desired target. Since microwaves propagate through the atmosphere, they are affected by atmospheric conditions and the Earth’s relief, leading to the signal attenuation and fading.
Fading refers to the weakening and distortion of wave signals, or a reduction in signal strength, caused by obstacles during satellite or terrestrial communication as the signal travels through the atmosphere. This leads to a decline in communication system performance and quality. To reduce the effect of fading, need to applied diversity techniques.
Keywords: Radio Waves, Telecommunication, Line Of Sight, Fading, Diversity.
Fading is the variation in signal strength over time, resulting from changes in the environment or the path the signal takes to reach the receiver. Fading depends on atmosphere condition. Selective fading occurs when the transmission medium varies with the time, affecting different frequency differently. In contrast, non selective fading happens when all frequency components fade at the same level. To reduce the effect of fading, need to applied diversity techniques.
Fading Types
Fading can occur anywhere where both ground waves and skywaves (ionospheric) are received, and the two waves arrive with different phases. This usually happens in long-distance communication over water, where wave propagation can reach far distances.
Additionally, fading can occur beyond the range of ground waves or skywaves. This is often caused by two skywaves traveling differently-part of the wave is refracted back to Earth by the E-layer, while another part is refracted and returned bye the F-layer.
These two effect can cause cancellation(destructive interference) if the waves arrive at the receiver 180 degrees out of phase but with the same amplitude. As a result, one signal becomes weaker than the other one signals.
multiple waves simultaneously and then combining them at the receiver or selecting the best one.
There are several types of diversity including time diversity, space diversity, angle diversity, frequency diversity and polarization diversity.
Polarizations Diversity have principle work by using radio waves that propagate with different polarizations- typically horizontal and vertical polarizations. Two antennas receive the same signals but with different polarizations(one horizontal, one vertical). Since fading affects polarizations differently, usually at least one of the signals remain usable.
Time Diversity have principle work by transmitting the same signals repeatedly at different time intervals to overcome short-term fading. This is often implemented with error correction coding. If one transmission is affected by fading, the next transmission might still be clear(potentially unaffected by fading).
Angle diversity have principle work by transmitting signals at two or more different angles which creates two or more propagations paths with different scattering volumes.
Space diversity have principle working concepts of frequency diversity involves transmitting two information signals at different frequency. The best signal is selected and then processed by the receiver.
Frequency Diversity have principle working concepts of frequency diversity involves transmitting two information signals at the different frequencies. These different frequencies will experience fading and are transmitted or received by the same antenna. Finally at the end, the receiver selects the best signal.
On its implementation, diversity has been used in various experiments such as:
· Implementation of Millimeter Wave Communication System Using Adaptive Coded Modulation and Diversity To meet High Speed Data Access Needs in Indonesia.
· Performance evaluation of a novel relay assisted hybrid FSO / RF communication system with receive diversity
· Performance Analysis of Receive Diversity in Wireless Sensor Networks over GBSBE Models
In Implementation of Millimeter Wave Communication System Using Adaptive Coded Modulation and Diversity To meet High Speed Data Acess Needs in Indonesia. An analysis was conducted for a coded communication system to ensure the signal remains strong and stable during heavy rainfall by employing a hybrid technique, which combines adaptive coded modulation with diversity Technique.
Hybrid Selection /Maximal Ratio Combining Diversity(HS/MRC), more commonly known as Generalized Selection Combining(GSC), is a method implemented by selecting a subset(a portions of the diversity branch set) using Selection Combing(SC, based on the Snr values of the diversity branches)and finally combining them using Maximal Ratio Combining(MRC) rules.
Block Diagram (HS/MRC)
The working principle of the diversity technique lies in application of mitigation techniques, which impact the systems SNR improvement. It operates by increasing the diversity gain, achieved when the Hybrid Selection/Maximal Ratio Combining Diversity undergoes Selection Combining on the east and northeast links, as well as on the north and west link simultaneously. Subsequently, the two results are fed into the Maximal Ratio Combining Process.
So, in Implementation of Millimeter Wave Communication System Using Adaptive Coded Modulation and Diversity To meet High Speed Data Access Needs in Indonesia .Diversity techniques have been proven to provide performance improvements to the system, both adaptive transmission systems and non-adaptive transmission systems with the presence of diversity gain power. At a link length of 1 km with an outage of 0.01%, a diversity gain of 5.675 dB was produced.
In Performance evaluation of a novel relay assisted hybrid FSO/RF communication system with receive diversity. An analysis, Receive Diversity is an advanced technique in wireless communication that functions like having multiple ears to capture the same signal simultaneously. The signal transmitted from the source (such as a cluster head or base station) reflects off various objects like buildings or trees before reaching the receiver, creating multiple distinct paths, each with unique characteristics including direction of arrival (DOA), time delay, and varying signal strength. The main challenge arises when these signals either reinforce or cancel each other (fading), compounded by random noise interference at each receiving antenna. However, the strength of receive diversity lies in its ability to capture all signal versions through multiple antennas, where
The system then intelligently combines these signals—for instance, using the Maximal Ratio Combining (MRC) method, which operates like adjusting each signal's volume according to its strength before merging them—resulting in significantly improved final signal quality with a higher Signal-to-Noise Ratio (SNR). This ensures more stable communication despite physical obstructions while also conserving battery energy, as devices avoid repeatedly retransmitting failed data packets. The principle is analogous to understanding a message more clearly by listening to multiple people relaying it simultaneously in a noisy room rather than relying on a single source.
Research on hybrid FSO/RF (Free Space Optics/Radio Frequency) systems is divided into three main groups.
1. First, single-hop structures that focus on the use of diversity techniques to improve signal quality in a single transmission path.
2. Second, dual-hop structures that analyze signal delivery performance through two stages, where some studies use diversity and others examine signal delivery in parallel.
3. Third, multi-hop structures that use several amplifier points (relays); in this structure, the more relays used, the smaller the possibility of signal interference or loss (outage probability) due to the assistance of diversity techniques.
So in this implementation because of diversity, increasing the number of relays decreases the Outage Probability.
In Performance Analysis of Receive Diversity in Wireless Sensor. An analysis was
Left Section
In sensor networks, receive diversity techniques are implemented in both single-antenna and multi-antenna systems because these techniques enhance system performance. There are numerous advantages to applying receive diversity in wireless sensor networks (WSNs), including:
1. Achieving high data reception success rates, thereby improving system performance.
2. Significantly saving energy due to its working principle, which reduces battery consumption (enabled by Luby Transform Codes-based relay strategies, where diversity is applied at the transmitter side).
3. Extending the network lifetime, as receive diversity supports high data fidelity and accurate resolution in WSN operations.
The independently fading signal branches can be combined through various methods. This paper focuses on three primary space diversity combining techniques
a) Maximal Ratio Combining (MRC), which weights and combines signals proportionally to their signal-to-noise ratios
b) Equal Gain Combining (EGC), which combines signals with uniform weighting after phase alignment; and
c) Selection Combining (SC), which simply selects the strongest signal branch.
MRC delivers optimal performance but requires complex implementation, EGC offers moderate performance with simpler processing, while SC provides the most straightforward implementation albeit with suboptimal results compared to the other methods - all three approaches aim to reconstruct the original signal as accurately as possible from multiple degraded versions.
Right Section
For example, the received signals are combined at the receiver using MRC to maximize the SNR and give the following expression:
In terms of the weight vector w ,the output x at the receiver is given by:
Where
is the sum of the channel powers across all the receive antennas.
In the presence of channel hj, the instantaneous SNR< 
receive antenna is given by:
So in this Performance Analysis of Receive Diversity in Wireless Sensor Networks over GBSBE Models justifies the use of receive diversity at the receiver for reliable communication between the cluster head and the receiving arrays and proves that MRC provides the best performance when applying receive diversity.
In communication terrestrial system, frequency diversity and space diversity is the most common used.
CONCLUSION
The implementation of diversity techniques in microwave radio communication systems is essential to mitigate the adverse effects of signal fading, thereby ensuring efficient performance across various communication environments in daily life.
Several diversity techniques can be employed, including space diversity, frequency diversity, polarization diversity, time diversity, and hybrid diversity, all of which provide effective solutions to maintain
