WRR (pulse width to average multipath component rate of arrival ratio)

The WRR (pulse width to average multipath component rate of arrival ratio) is an important parameter used in wireless communication systems to characterize the behavior of multipath propagation in the wireless channel. Multipath propagation is a phenomenon that occurs when wireless signals take multiple paths to reach the receiver, resulting in the reception of multiple delayed and attenuated copies of the transmitted signal. Understanding the characteristics of multipath propagation is crucial for designing robust and reliable wireless communication systems.

In wireless communication, the transmitted signal from the transmitter propagates through the wireless channel and arrives at the receiver. Due to the presence of obstacles, reflections, diffractions, and scattering in the environment, the transmitted signal undergoes multiple reflections and reaches the receiver through different paths. Each of these paths is associated with a different time delay and may experience different levels of attenuation.

The WRR is a metric that quantifies the effect of multipath propagation on the received signal. It is defined as the ratio of the pulse width of the transmitted signal to the average rate of arrival of multipath components at the receiver. Let's break down the components of this definition:

1. Pulse Width: The pulse width refers to the duration of the transmitted signal's main lobe or central portion. In digital communication systems, the transmitted signal is typically modulated to represent data in the form of pulses. The pulse width determines the time taken for one complete pulse to be transmitted.
2. Average Rate of Arrival of Multipath Components: The average rate of arrival of multipath components represents the rate at which delayed copies of the transmitted signal arrive at the receiver. Each delayed copy is associated with a specific delay time due to the different path lengths taken by the signal.

The WRR provides valuable insights into the behavior of multipath propagation and its impact on the wireless communication system. A high WRR indicates that the transmitted signal experiences significant spreading in time due to multipath propagation. This spreading can result in inter-symbol interference (ISI), where the delayed copies of the signal overlap with neighboring symbols, leading to errors in the receiver's symbol detection.

On the other hand, a low WRR indicates that the multipath components are spaced relatively far apart in time, resulting in less severe ISI. In such cases, the wireless channel may be considered less dispersive, and the receiver can more easily distinguish between different symbols.

The WRR is particularly relevant in systems that use pulse modulation techniques, such as pulse amplitude modulation (PAM), pulse position modulation (PPM), or pulse duration modulation (PDM). In these systems, the characteristics of multipath propagation significantly affect the system's performance and capacity.

To mitigate the effects of multipath propagation and improve the system's performance, several techniques can be employed:

1. Equalization: Equalization is a digital signal processing technique used at the receiver to mitigate the impact of ISI caused by multipath propagation. Equalizers attempt to reverse the effect of the wireless channel by applying appropriate filter operations to the received signal.
2. Rake Receiver: A rake receiver is a type of receiver that attempts to capture and combine the various multipath components coherently. It uses multiple correlators, each aligned to a different path, to improve the receiver's ability to detect the transmitted signal accurately.
3. Antenna Diversity: Using multiple antennas at the receiver can exploit the spatial diversity of multipath signals. By combining the signals received on different antennas, the receiver can improve signal quality and reduce the impact of fading caused by destructive interference.
4. Error Correction Coding: Error correction coding techniques, such as forward error correction (FEC), can be used to detect and correct errors introduced by ISI and fading caused by multipath propagation.
5. Frequency and Time Diversity: Frequency hopping and time diversity techniques spread the transmitted signal over different frequency bands or time slots to combat fading and ISI caused by multipath propagation.

The WRR is a valuable tool for wireless system designers and engineers as it provides valuable insights into the characteristics of the wireless channel and helps in optimizing system performance. By understanding the behavior of multipath propagation, wireless communication systems can be designed to be more robust, reliable, and capable of providing high-quality services even in challenging environments with significant multipath propagation effects.