Diversity Techniques to Boost Wireless Performance

In wireless communication systems, ensuring strong and reliable signal quality remains a constant problem. Fading occurs due to factors like multipath propagation, interference and other environmental factors. We can reduce the impact of these issues by leveraging different techniques based upon the context. Diversity technique is one of those techniques to overcome the drawbacks of multipath propagation.

Diversity enhances signal quality by sending multiple versions of signal ensuring a reliable reception of transmitting signal. There are few types of diversity methods in RF communication. Major diversity methods are Spatial diversity, Time diversity, Frequency diversity and Polarization diversity.

Spatial Diversity

Spatial diversity or space diversity uses multiple transmitter and receiver antennas to deploy varying channel conditions. The idea is that, due to spatial separation, the probability that all antennas experiencing a deep fade at same time is significantly reduced. This arrangement of multiple antenna system minimizes the signal fading as they ensure at least one antenna will receive a strong signal. On the other hand, multiple antennas will receive different versions of the same signal through different propagation paths. Upon receival, these signals are combined at the receiver to improve signal quality.

Spacing antennas with a sufficient distance provides better performance by minimizing the correlation. But, there is a tradeoff as higher spacing will require larger infrastructures making it challenging to be used in small devices.

Polarization Diversity

In Polarization diversity, different signal polarizations (vertical and horizontal) are used to improve the signal reception. These systems capture independent signal components. As a signal’s polarization can be changed due to multipath effects like reflection and scattering, capturing multipath polarizations gives uncorrelated paths for this method. This technique leverages the ability of electromagnetic waves to be transmitted and received with different orientations. Usually the polarization angle would be ±45°. A real life example is using two antennas to receive orthogonally polarized versions of the same signal. Since multipath propagation can differ the signal's polarization, capturing multiple polarizations will improve the signal's robustness.

Unlike spatial diversity, polarization diversity offers it performance without requiring large and complex physical setups. Thus, it remains ideal for compact devices like smartphones and IoT sensors.

Time Diversity

Time diversity is used to mitigate the affects of time varying phenomena like multipath fading and doppler effect. It sends the same signal at different time instances, making the probability of reception higher. The main idea of time diversity is to exploit the time variability of the communication channel. As fading is often time-selective, a signal experiencing a deep fade at one moment will be received with high quality at another moment. In slow fading environments which the mobility of the user equipment changes frequently, time diversity techniques are said to be much useful.

Even though, time diversity improves signal reliability, it might introduce issues such as latency and reduced spectral efficiency. So, it is usually combined with other diversity techniques for optimal performance.

Frequency Diversity

In Frequency diversity, the same data is sent across multiple frequency channels. This techniques mitigates the impacts of frequency selective fading as fading is not affecting all frequencies in a similar way.