[Paper Review] MmWaves Cellular V2X for Cooperative Diversity Relay Fast Fading Channels

Elyes Balti, Brian K. Johnson|arXiv (Cornell University)|Oct 23, 2020

Millimeter-Wave Propagation and Modeling45 references16 citations

TL;DR

This paper proposes a millimeter wave (mmWave) cellular vehicle-to-everything (V2X) system using a decode-and-forward (DF) cooperative relay to combat fast fading in high-mobility vehicular environments. By employing maximal ratio combining (MRC) and maximal ratio transmission (MRT), the system achieves diversity gain, with closed-form expressions derived for outage probability, symbol error rate, and ergodic capacity under Jakes’ fast fading model, revealing key insights into diversity and coding gains.

ABSTRACT

In this work, we present a framework analysis of millimeter waves (mmWaves) vehicular communications systems. Communications between vehicles take place through a cooperative relay which acts as an intermediary base station (BS). The relay is equipped with multiple transmit and receive antennas and it employs decode-and-forward (DF) to process the signal. Also, the relay applies maximal ratio combining (MRC), and maximal ratio transmission (MRT), respectively, to receive and forward the signal. As the vehicles' speeds are relatively high, the channel experiences a fast fading and this time variation is modeled following the Jakes' autocorrelation model. We also assume narrowband fading channel. Closed-form expressions of the reliability metrics such as the outage probability, the probability of error and the channel capacity are derived. Capitalizing on these performances, we derive the low and high power regimes for the capacity, and the high signal-to-interference-plus-noise-ratio (SINR) asymptotes for the outage and error probability to get full insights into the system gains such as the diversity and coding gains.

Motivation & Objective

• To address spectral scarcity and high data rate demands in vehicular networks by leveraging mmWave spectrum for 5G and beyond.
• To mitigate the challenges of mmWave propagation—such as high path loss, blockage, and fast fading—through cooperative relaying in high-mobility vehicular scenarios.
• To analyze the performance of a relay-assisted mmWave V2X system under fast fading using Jakes’ autocorrelation model.
• To derive closed-form expressions for key reliability metrics: outage probability, symbol error rate, and ergodic capacity.
• To extract diversity and coding gains from high-SINR asymptotes and power regime analysis.

Proposed method

• Models the mmWave V2X channel as a two-hop decode-and-forward (DF) relay system with a relay acting as an intermediary base station.
• Applies maximal ratio combining (MRC) at the relay for diversity gain in signal reception and maximal ratio transmission (MRT) for beamforming in signal forwarding.
• Models fast fading using the Jakes’ autocorrelation model to reflect high Doppler spread due to high vehicle speeds.
• Derives closed-form expressions for outage probability, symbol error rate, and ergodic capacity using generalized Meijer-G and Fox H-functions.
• Performs asymptotic analysis in high-SINR and high/low power regimes to extract diversity and coding gains.
• Utilizes special functions (Meijer-G and Fox H) to express cumulative distribution functions and integrals for performance evaluation.

Experimental results

Research questions

• RQ1 How does cooperative relaying with MRC/MRT improve reliability in mmWave V2X systems under fast fading?
• RQ2 What are the closed-form expressions for outage probability, symbol error rate, and ergodic capacity in a DF-relay mmWave V2X system?
• RQ3 What are the diversity and coding gains achieved in the high-SINR regime, and how do they scale with system parameters?
• RQ4 How do low and high transmit power regimes affect the ergodic capacity of the relayed mmWave V2X system?
• RQ5 What is the impact of channel correlation and fading statistics (Jakes’ model) on the performance of mmWave V2X with cooperative relays?

Key findings

• The system achieves full diversity gain due to the use of MRC and MRT, with diversity order determined by the number of antennas and fading parameters.
• Outage probability and symbol error rate exhibit diversity gain in the high-SINR regime, with diversity order equal to the sum of the effective diversity gains from both hops.
• Ergodic capacity is derived in closed form using Meijer-G and Fox H-functions, enabling precise performance evaluation under fast fading.
• The high-power regime analysis reveals that capacity scales logarithmically with SNR, indicating spectral efficiency limitations despite high bandwidth.
• The low-power regime shows that capacity is proportional to the product of the average SNR and the number of antennas, highlighting the role of array gain.
• Asymptotic analysis confirms that coding gain is influenced by the relay’s antenna configuration and channel correlation, with higher gains achieved for larger $ N_i m_i $ and $ M_{r,i} m_{r,i} $.