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Non-Orthogonal HARQ-CC over SDR: A GNU Radio-Based Implementation

Hongling Huang, Jintao Wang, Zheng Shi, Xu Wang, Guanghua Yang, Shaodan Ma, Haichuan Ding

TL;DR

This paper proposes an efficient Non-Orthogonal HARQ with Chase Combining (N-HARQ-CC) transmission strategy, which allocates a larger portion of retransmission resources to new data packets, reserving only a small fraction for retransmitting previously erroneous packets.

Abstract

Hybrid Automatic Repeat Request (HARQ) schemes typically allocate all available resources to retransmit failed packets to ensure reliability. However, under stringent delay constraints, these schemes often exhibit low spectral efficiency and increased transmission latency. To address these challenges, this paper proposes an efficient Non-Orthogonal HARQ with Chase Combining (N-HARQ-CC) transmission strategy. Specifically, the proposed approach allocates a larger portion of retransmission resources to new data packets, reserving only a small fraction for retransmitting previously erroneous packets. This is based on the observation that only a small number of information bits are typically incorrect, enabling surplus communication resources to be utilized for transmitting new messages. The N-HARQ-CC scheme retransmits the same redundant version of a failed packet and employs Maximum Ratio Combining (MRC) for decoding. To minimize complex packet scheduling and decoding complexity, the proposed scheme limits superposition to at most two messages per transmission round. At the receiver, Successive Interference Cancellation (SIC) is used to decouple the superimposed messages. The proposed N-HARQ-CC system was implemented using GNU Radio and USRP platforms for validation. Compared to conventional Type-I HARQ and HARQ-CC schemes, the proposed scheme achieves a significant improvement in spectral efficiency of approximately 0.5 bps/Hz, aligning with the low-latency requirements of 6G networks.

Non-Orthogonal HARQ-CC over SDR: A GNU Radio-Based Implementation

TL;DR

This paper proposes an efficient Non-Orthogonal HARQ with Chase Combining (N-HARQ-CC) transmission strategy, which allocates a larger portion of retransmission resources to new data packets, reserving only a small fraction for retransmitting previously erroneous packets.

Abstract

Hybrid Automatic Repeat Request (HARQ) schemes typically allocate all available resources to retransmit failed packets to ensure reliability. However, under stringent delay constraints, these schemes often exhibit low spectral efficiency and increased transmission latency. To address these challenges, this paper proposes an efficient Non-Orthogonal HARQ with Chase Combining (N-HARQ-CC) transmission strategy. Specifically, the proposed approach allocates a larger portion of retransmission resources to new data packets, reserving only a small fraction for retransmitting previously erroneous packets. This is based on the observation that only a small number of information bits are typically incorrect, enabling surplus communication resources to be utilized for transmitting new messages. The N-HARQ-CC scheme retransmits the same redundant version of a failed packet and employs Maximum Ratio Combining (MRC) for decoding. To minimize complex packet scheduling and decoding complexity, the proposed scheme limits superposition to at most two messages per transmission round. At the receiver, Successive Interference Cancellation (SIC) is used to decouple the superimposed messages. The proposed N-HARQ-CC system was implemented using GNU Radio and USRP platforms for validation. Compared to conventional Type-I HARQ and HARQ-CC schemes, the proposed scheme achieves a significant improvement in spectral efficiency of approximately 0.5 bps/Hz, aligning with the low-latency requirements of 6G networks.
Paper Structure (15 sections, 11 equations, 8 figures)

This paper contains 15 sections, 11 equations, 8 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. N-HARQ-CC Scheme
  4. Initial Transmission Mode
  5. Retransmission Mode
  6. Signal Reconstruction and SINR Analysis
  7. Decoding of the New Message
  8. Decoding of the Old Message
  9. No SIC Failure
  10. One SIC Failure
  11. SDR-Based Implementation of N-HARQ-CC
  12. Transmitter
  13. Receiver
  14. Experimental Results
  15. CONCLUSION

Figures (8)

  • Figure 1: The example of one SIC failure in decoding the old message with $M=3$.
  • Figure 2: Experimental setup of N-HARQ-CC transmission over SDR using two USRP B210 devices.
  • Figure 3: System architecture of the proposed N-HARQ-CC scheme based on GNU Radio.
  • Figure 4: GNU Radio flowgraph of the proposed N-HARQ-CC through 2 USRPs.
  • Figure 5: QPSK constellation in ITM mode.
  • ...and 3 more figures