How do you balance diversity and multiplexing gains in cellular networks?

1 Diversity gain

Diversity gain is the improvement in signal quality that results from using multiple antennas or channels to combat fading, interference, and noise. Fading is the variation of signal strength due to obstacles, reflections, or distance. Interference is the unwanted signal from other sources that affects the desired signal. Noise is the random fluctuation of signal due to thermal or electronic factors. By using diversity techniques, such as beamforming, spatial diversity, or frequency diversity, you can reduce the effects of fading, interference, and noise, and increase the reliability and coverage of wireless communication.

2 Multiplexing gain

Multiplexing gain is the improvement in data rate that results from using multiple antennas or channels to transmit or receive multiple data streams simultaneously. By using multiplexing techniques, such as spatial multiplexing, frequency division multiplexing, or code division multiplexing, you can increase the spectral efficiency and capacity of wireless communication. Spectral efficiency is the amount of data that can be transmitted per unit of bandwidth. Capacity is the maximum data rate that can be achieved by a wireless channel.

3 Trade-off between diversity and multiplexing

Diversity and multiplexing gains are both desirable for wireless communication, but they cannot be achieved simultaneously. There is a trade-off between them, which depends on the channel conditions and the system requirements. Generally, when the channel is poor, such as in low signal-to-noise ratio (SNR) or high fading scenarios, diversity gain is more important than multiplexing gain, because it can enhance the signal quality and reliability. When the channel is good, such as in high SNR or low fading scenarios, multiplexing gain is more important than diversity gain, because it can increase the data rate and capacity.

4 How to balance diversity and multiplexing

There is no single optimal way to balance diversity and multiplexing gains in cellular networks, as different applications and users may have different preferences and demands. Adaptive modulation and coding (AMC) adjusts the modulation scheme and the error correction code according to the channel conditions. For example, when the channel is good, higher-order modulation and a lower code rate can be used to achieve higher multiplexing gain, while when the channel is bad, a lower-order modulation and a higher code rate can be used to achieve higher diversity gain. Transmit antenna selection (TAS) is another possible strategy that selects the best antenna or subset of antennas to transmit or receive signals based on the channel quality. Lastly, hybrid schemes combine diversity and multiplexing in different ways, such as spatial modulation, space-time block coding, or precoding. These techniques are able to encode information in both the amplitude and phase of the signal, as well as in both the time and spatial domains using multiple antennas.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?