PHY, MAC, and RLC Layer Based Estimation of Optimal Cyclic Prefix Length

Area of Science:

• Wireless Communications
• Signal Processing
• Telecommunications Engineering

Background:

• The standard Cyclic Prefix (CP) length in Long Term Evolution (LTE) is oversized for many environments.
• 5G New Radio (NR) scalable CP length reduction maintains relative overhead.
• Existing optimization methods focus solely on physical layer (PHY) performance.

Purpose of the Study:

• To develop a cross-layer analytical model for optimizing Cyclic Prefix (CP) length.
• To derive a closed-form expression for the optimal CP length.
• To minimize effective average codeblock length considering retransmissions.

Main Methods:

• Developed a novel cross-layer analytical model.
• Derived a closed-form expression for optimal CP length.
• Incorporated Medium Access Control (MAC) and Radio Link Control (RLC) retransmissions.

Main Results:

• Optimal CP length minimizes effective average codeblock length.
• Optimal CP length depends on channel's root mean square (rms) delay spread.
• Derived optimal CP lengths are significantly lower than industry standards.

Conclusions:

• Current CP lengths offer potential for throughput improvement.
• Adaptive CP length optimization is crucial for enhanced wireless performance.
• Cross-layer analysis provides a more accurate approach to CP length optimization.