EGC (equal gain combining)

Equal gain combining (EGC) is a signal processing technique used in wireless communication systems to improve signal reception. EGC is a simple technique that combines multiple received signals, often from multiple antennas, with equal weighting factors. This technique is based on the assumption that the received signals are uncorrelated, which is often true in practice.

EGC is particularly useful in environments with fading channels, where the strength of the received signals may vary due to multipath propagation. In such environments, the use of multiple antennas can help to mitigate the effects of fading and improve the overall quality of the received signal. By combining multiple received signals, EGC can improve the signal-to-noise ratio (SNR), reduce the effects of fading, and improve the overall reliability of the wireless communication system.

In this article, we will explain the basics of EGC, including the theory behind the technique, the practical implementation of EGC in wireless communication systems, and some of the advantages and disadvantages of using EGC.

EGC Theory

EGC is a technique that involves combining multiple received signals with equal weighting factors. The received signals are assumed to be uncorrelated, which means that they are not affected by the same sources of interference and noise. This assumption is often true in practice, especially when the received signals are from multiple antennas or from different spatial locations.

The mathematical model of EGC can be expressed as follows:

y(t) = w1x1(t) + w2x2(t) + ... + wn*xn(t)

where y(t) is the combined output signal, w1, w2, ..., wn are the weighting factors, and x1(t), x2(t), ..., xn(t) are the received signals from the n antennas.

In EGC, the weighting factors are set to be equal, which means that:

w1 = w2 = ... = wn = 1/n

This ensures that all received signals are given equal importance when they are combined to form the output signal. Since the received signals are uncorrelated, this approach can help to improve the overall SNR of the combined signal.

The output signal y(t) can be expressed as:

y(t) = (1/n)*(x1(t) + x2(t) + ... + xn(t))

where (1/n) is a scaling factor that ensures that the output signal is properly normalized.

EGC Implementation

EGC is a relatively simple technique that can be implemented using a variety of hardware and software components. In wireless communication systems, EGC is typically implemented using multiple antennas, each connected to a separate receiver. The received signals from each antenna are then combined using a simple combiner circuit or software algorithm.

One of the most common implementations of EGC is based on the use of multiple antennas in a MIMO (Multiple-Input, Multiple-Output) system. In a MIMO system, the transmitter uses multiple antennas to send multiple streams of data simultaneously. The receiver then uses multiple antennas to receive the transmitted signals and combine them using EGC.

The implementation of EGC in a MIMO system typically involves the use of a digital signal processing (DSP) algorithm to combine the received signals. The DSP algorithm takes the received signals from each antenna and applies a scaling factor to each signal to ensure that the signals are properly normalized. The signals are then combined using a simple averaging function, which ensures that each signal is given equal importance.

One of the advantages of EGC in a MIMO system is that it can help to improve the overall reliability and quality of the wireless communication system. By using multiple antennas and combining the received signals, EGC can help to mitigate the effects of fading and improve the SNR of the received signals. This can result in fewer errors and a more robust wireless communication system.

Advantages and Disadvantages of EGC

While EGC has several advantages, it also has some disadvantages that must be considered when designing and implementing wireless communication systems.

One of the main disadvantages of EGC is that it assumes that the received signals are uncorrelated. In practice, however, the received signals may be affected by correlated interference, such as co-channel interference or adjacent channel interference. When this occurs, EGC may not be effective in improving the overall SNR of the received signals.

Another disadvantage of EGC is that it requires multiple antennas and receivers, which can increase the cost and complexity of the wireless communication system. In addition, the use of multiple antennas and receivers may require additional power, which can reduce the battery life of mobile devices.

Finally, EGC may not be effective in environments with strong directional interference, such as in urban areas or near large buildings. In these environments, the use of more advanced techniques, such as beamforming, may be necessary to improve the overall reliability and quality of the wireless communication system.

Conclusion

EGC is a simple and effective technique for improving the SNR and reliability of wireless communication systems in environments with fading channels. By combining multiple received signals with equal weighting factors, EGC can help to mitigate the effects of fading and improve the overall quality of the received signal.

EGC is particularly useful in MIMO systems, where multiple antennas are used to transmit and receive signals simultaneously. However, EGC does have some limitations, including its assumption of uncorrelated received signals and its potential for increased cost and complexity in wireless communication systems.

Overall, EGC is a valuable technique that can help to improve the performance of wireless communication systems in a variety of environments. By carefully considering the advantages and disadvantages of EGC, wireless communication system designers can determine when and how to use this technique to optimize the performance of their systems.