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Performance Analysis and Blocklength Minimization of Uplink RSMA for Short Packet Transmissions in URLLC

Yixin Zhang, Wenchi Cheng, Jingqing Wang, Wei Zhang

TL;DR

This work tackles URLLC with short-packet uplink transmissions by analyzing a two-user uplink RSMA under finite blocklength (FBL). It derives FBL-based achievable rates and error-throughput expressions, formulates a blocklength minimization problem with power allocation, and solves it via alternating optimization that convexifies the non-convex constraints. The results show that, in the FBL regime, RSMA's instantaneous rate region need not dominate NOMA, yet with the proposed blocklength minimization RSMA can achieve the same rates with smaller blocklengths than NOMA, FDMA, or TDMA, enabling lower latency. The study also reveals that RSMA cannot reach the Gaussian MAC capacity in FBL, but PA-assisted RSMA still offers substantial delay reductions and flexible QoS support, highlighting its potential for URLLC in 6G networks.

Abstract

Rate splitting multiple access (RSMA) is one of the most promising techniques for ultra-reliable and low-latency communications (URLLC) with stringent requirements on delay and reliability of multiple access. To fully explore the delay performance enhancement brought by uplink RSMA to URLLC, in this paper, we evaluate the performance of two-user uplink RSMA and propose the corresponding blocklength minimization problem. We analyze the impact of finite blocklength (FBL) code on the achievable rate region and the effective throughput of uplink RSMA. On this basis, we propose the problem of minimizing the blocklength for uplink RSMA with power allocation under constrained reliability and effective throughput. Then, we present an alternating optimization method to solve this non-convex problem. Simulation results show that different from the infinite blocklength (IBL) regime, the achievable rate region of the uplink RSMA is not always larger than that of uplink non-orthogonal multiple access (NOMA) in the FBL regime. But with the help of our proposed blocklength minimization scheme, uplink RSMA can achieve the same achievable rate with a smaller blocklength compared to uplink NOMA, frequency division multiple access (FDMA), and time division multiple access (TDMA) without the need for time sharing in the FBL regime, showing the potential of uplink RSMA to achieve low delay for URLLC.

Performance Analysis and Blocklength Minimization of Uplink RSMA for Short Packet Transmissions in URLLC

TL;DR

This work tackles URLLC with short-packet uplink transmissions by analyzing a two-user uplink RSMA under finite blocklength (FBL). It derives FBL-based achievable rates and error-throughput expressions, formulates a blocklength minimization problem with power allocation, and solves it via alternating optimization that convexifies the non-convex constraints. The results show that, in the FBL regime, RSMA's instantaneous rate region need not dominate NOMA, yet with the proposed blocklength minimization RSMA can achieve the same rates with smaller blocklengths than NOMA, FDMA, or TDMA, enabling lower latency. The study also reveals that RSMA cannot reach the Gaussian MAC capacity in FBL, but PA-assisted RSMA still offers substantial delay reductions and flexible QoS support, highlighting its potential for URLLC in 6G networks.

Abstract

Rate splitting multiple access (RSMA) is one of the most promising techniques for ultra-reliable and low-latency communications (URLLC) with stringent requirements on delay and reliability of multiple access. To fully explore the delay performance enhancement brought by uplink RSMA to URLLC, in this paper, we evaluate the performance of two-user uplink RSMA and propose the corresponding blocklength minimization problem. We analyze the impact of finite blocklength (FBL) code on the achievable rate region and the effective throughput of uplink RSMA. On this basis, we propose the problem of minimizing the blocklength for uplink RSMA with power allocation under constrained reliability and effective throughput. Then, we present an alternating optimization method to solve this non-convex problem. Simulation results show that different from the infinite blocklength (IBL) regime, the achievable rate region of the uplink RSMA is not always larger than that of uplink non-orthogonal multiple access (NOMA) in the FBL regime. But with the help of our proposed blocklength minimization scheme, uplink RSMA can achieve the same achievable rate with a smaller blocklength compared to uplink NOMA, frequency division multiple access (FDMA), and time division multiple access (TDMA) without the need for time sharing in the FBL regime, showing the potential of uplink RSMA to achieve low delay for URLLC.
Paper Structure (12 sections, 19 equations, 6 figures, 1 algorithm)

This paper contains 12 sections, 19 equations, 6 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model
  3. Performance Analysis of Uplink RSMA in The FBL Regime
  4. Blocklength Structure And Achievable Rate Region
  5. Error Probability And Effective Throughput
  6. Uplink RSMA-Based Blocklength Minimization Problem
  7. Problem Formulation
  8. Problem Transformation
  9. Comparison to NOMA
  10. Comparison to OMA
  11. Numerical Results
  12. Conclusion

Figures (6)

  • Figure 1: Two-user uplink RSMA system model.
  • Figure 2: The power and blocklength of FDMA, TDMA, NOMA, and RSMA.
  • Figure 3: Achievable rate region comparison of different MA strategies with different blocklengths.
  • Figure 4: Blocklength comparison of different MA strategies versus the maximum transmit power.
  • Figure 5: The blocklength comparison of different MA strategies versus the error probability with $P_t = 2$ dB and $P_t = 5$ dB.
  • ...and 1 more figures