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MRC (maximal ratio combining)

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Maximal ratio combining (MRC) is a technique used to improve the performance of wireless communication systems by combining multiple received signals to achieve a better quality of the received signal. This technique is widely used in various wireless communication systems, including cellular communication, satellite communication, and wireless local area networks (WLANs).

In this article, we will explain the concept of MRC, its working principle, and the advantages and disadvantages of using MRC in wireless communication systems.

What is MRC?

MRC is a signal processing technique used to combine multiple received signals with the same information to enhance the signal quality. The basic principle behind MRC is to weight each received signal according to its signal-to-noise ratio (SNR) and then combine them in a way that maximizes the overall SNR of the combined signal.

In wireless communication systems, the received signal is usually affected by various impairments, including noise, fading, and interference. These impairments can significantly degrade the quality of the received signal, leading to errors and data loss. MRC helps to mitigate the effects of these impairments by combining multiple copies of the same signal, each of which is affected differently by the impairments, to improve the overall quality of the received signal.

How does MRC work?

MRC works by combining multiple copies of the same signal, each of which is affected differently by the impairments, to improve the overall quality of the received signal. The basic steps involved in MRC are:

  1. Reception of multiple copies of the same signal: The first step in MRC is to receive multiple copies of the same signal. These copies can be received through multiple antennas or multiple transmissions from the same antenna.
  2. Weighting of each received signal: The second step in MRC is to weight each received signal according to its SNR. The SNR of each received signal is estimated based on the received signal power and the noise power in the received signal.
  3. Combining of the weighted signals: The final step in MRC is to combine the weighted signals to obtain a single signal that has the maximum overall SNR. The combining process involves multiplying each weighted signal by a complex weight factor and then summing up the products.

The complex weight factors are calculated in such a way that the overall SNR of the combined signal is maximized. The weight factors depend on the channel coefficients, which are the complex gains of the channel for each received signal.

Advantages of MRC

MRC offers several advantages over other signal processing techniques in wireless communication systems. Some of the main advantages of MRC are:

  1. Improved signal quality: MRC improves the quality of the received signal by combining multiple copies of the same signal that are affected differently by impairments. This improves the overall SNR of the combined signal, reducing errors and data loss.
  2. Robustness to fading and interference: MRC is robust to fading and interference because it combines multiple copies of the same signal that are affected differently by these impairments. This reduces the impact of fading and interference on the quality of the received signal.
  3. Increased diversity: MRC increases the diversity of the received signal by combining multiple copies of the same signal. This increases the probability of having a good quality copy of the signal, even in the presence of impairments.
  4. Increased capacity: MRC increases the capacity of wireless communication systems by improving the quality of the received signal. This allows for higher data rates and better performance in high traffic scenarios.

Disadvantages of MRC

MRC also has some disadvantages that should be taken into consideration when designing wireless communication systems. Some of the main disadvantages of MRC are:

  1. Increased complexity: MRC requires multiple antennas or multiple transmissions from the same antenna to receive multiple copies of the signal. This increases the complexity of the receiver and requires additional hardware and processing power.
  2. Increased power consumption: MRC requires multiple copies of the same signal to be received and combined, which increases the power consumption of the receiver.
  3. Decreased reliability: MRC is less reliable than other signal processing techniques in scenarios where only one copy of the signal is available. This is because MRC relies on having multiple copies of the same signal to improve the quality of the received signal.
  4. Limited performance in highly mobile scenarios: MRC is not very effective in highly mobile scenarios where the channel conditions change rapidly. This is because the channel coefficients used to calculate the weight factors may not accurately represent the current channel conditions.

Applications of MRC

MRC is used in various wireless communication systems to improve the performance of the system. Some of the main applications of MRC are:

  1. Cellular communication: MRC is used in cellular communication systems to improve the quality of the received signal in areas with poor coverage or high interference.
  2. Satellite communication: MRC is used in satellite communication systems to improve the quality of the received signal in areas with weak satellite signals or high atmospheric interference.
  3. Wireless local area networks (WLANs): MRC is used in WLANs to improve the quality of the received signal in areas with high interference from other wireless devices.
  4. Multiple-input multiple-output (MIMO) systems: MRC is used in MIMO systems to improve the quality of the received signal by combining the signals received on multiple antennas.

Conclusion

MRC is a signal processing technique used to improve the performance of wireless communication systems by combining multiple received signals to achieve a better quality of the received signal. MRC is robust to fading and interference and increases the diversity and capacity of the received signal. However, MRC also has some disadvantages, including increased complexity, increased power consumption, and decreased reliability in scenarios where only one copy of the signal is available. MRC is widely used in various wireless communication systems, including cellular communication, satellite communication, and WLANs, to improve the performance of the system.