Performance Transmission Analysis of AF and DF Protocols in Wireless Relay Cooperation Systems

In wireless communication systems, relay cooperation technology enhances signal coverage and transmission reliability by introducing relay nodes. Among these, Amplify-and-Forward (AF) and Decode-and-Forward (DF) are two classic relay cooperation protocols, whose performance analysis is particularly critical in Rayleigh fading channel environments.

### Characteristics of AF Protocol In the AF protocol, the relay node directly amplifies the received signal and forwards it without performing decoding operations. Its advantages include simple implementation and low latency, but it also amplifies noise along with the signal, leading to signal quality degradation as the number of relay stages increases. In Rayleigh channels, due to multipath effects, the performance of the AF protocol is directly influenced by channel fading coefficients, requiring analysis of bit error rate (BER) or outage probability through signal-to-noise ratio (SNR). Code Implementation Insight: AF relaying can be simulated by modeling the channel gain and noise variance, then applying a simple amplification gain factor. For example, in MATLAB, the received signal at the relay can be represented as y_r = h*s + n, and the transmitted signal as x_r = G*y_r, where G is the amplification gain typically set to meet power constraints.

### Characteristics of DF Protocol In the DF protocol, the relay node first decodes the received signal, re-encodes it, and then forwards it. Its benefit is the elimination of noise accumulation, but it has higher complexity, and decoding errors can lead to error propagation. The random fading characteristics of Rayleigh channels mean that the decoding success rate of the DF protocol is closely related to instantaneous channel conditions, often requiring evaluation of its diversity gain in combination with modulation schemes (e.g., QPSK). Algorithm Explanation: DF protocol implementation involves error detection and correction at the relay. Simulation code may include a threshold-based decoding step; if the SNR at the relay exceeds a certain threshold, the signal is decoded and re-encoded, otherwise, the relay remains silent. This can be modeled using conditional statements in simulation scripts.

### Key Points for Performance Comparison Noise Resistance: DF performs better under high SNR conditions, while AF is more practical in low SNR or simple systems. Spectral Efficiency: DF requires additional coding resources, which may reduce effective throughput. Applicable Scenarios: AF is suitable for fast time-varying channels, while DF is more appropriate for static or high SNR environments.

Through theoretical derivation or simulation (e.g., Monte Carlo methods), metrics such as BER curves and outage probability for both protocols in Rayleigh channels can be quantified, providing references for practical deployment. Simulation Approach: Monte Carlo simulations for BER analysis typically involve generating random channel realizations, applying the AF or DF relay model, and counting errors over many iterations. Key functions in MATLAB might include raylchan for Rayleigh channel modeling and berfading for theoretical BER reference.