[Paper Review] Bitwise Retransmission Schemes for Resources Constrained Uplink Sensor Networks

Mohamed A. M. Hassanien, Pavel Loskot+3 more|arXiv (Cornell University)|Jul 31, 2017

Advanced Wireless Network Optimization20 references3 citations

TL;DR

This paper proposes bitwise retransmission schemes for uplink sensor networks that retransmit only the least reliable bits to improve reliability without requiring CRC for error detection. By using combination numbers or synchronized RNGs to compress feedback, the scheme reduces feedback overhead and outperforms stop-and-wait ARQ in BER performance, especially under resource constraints, with optimized parameters for Zigbee, Wi-Fi, and Bluetooth applications.

ABSTRACT

Novel bitwise retransmission schemes are devised which retransmit only the bits received with small reliability. The retransmissions are used to accumulate the reliabilities of individual bits. Unlike the conventional automatic repeat request (ARQ) schemes, the proposed scheme does not require a checksum for the error detection. The bits to be retransmitted are reported as a combination number, or two synchronized random number generators (RNGs) at the transmitter and receiver are used to greatly compress the feedback message. The bitwise retransmission decisions and/or combining can be performed after the demodulation or after the channel decoding at the receiver. The bit-error rate (BER) expressions are derived for the case of one and two retransmissions, and verified by computer simulations. Assuming three specific retransmission strategies, the scheme parameters are optimized to minimize the overall BER. For the same number of retransmissions and packet length, the proposed schemes always outperform the frequently used stop-and-wait ARQ. The impact of feedback errors is also considered. Finally, practical designs of the bitwise retransmissions for data fusion from sensor nodes in Zigbee, Wifi and Bluetooth networks are presented.

Motivation & Objective

• Address the need for energy-efficient and low-feedback ARQ schemes in uplink sensor networks with limited resources.
• Overcome the inefficiency of conventional ARQ schemes that retransmit entire packets despite only a few bits being unreliable.
• Eliminate the need for CRC-based error detection by leveraging bit-level reliability metrics for retransmission decisions.
• Optimize retransmission strategies to minimize bit-error rate (BER) while maintaining constant delay and throughput.
• Design practical implementations for Zigbee, Wi-Fi, and Bluetooth networks with realistic feedback and channel constraints.

Proposed method

• Propose a bitwise ARQ scheme that identifies and retransmits only the least reliable bits based on reliability metrics derived from demodulation or decoding.
• Use combination numbers or synchronized random number generators (RNGs) at transmitter and receiver to compress feedback signaling, minimizing feedback overhead.
• Derive closed-form BER expressions for one and two retransmissions using approximations based on the Prony method for the Q-function.
• Integrate the scheme with forward error correction (FEC) by evaluating bit reliability either before or after decoding.
• Optimize retransmission parameters (e.g., threshold for retransmission, number of retransmissions) to minimize overall BER under fixed retransmission budget.
• Design scheduling and buffering strategies using FIFO to fully utilize transmitted packet capacity and support multiple sensor nodes.

Experimental results

Research questions

• RQ1 Can bitwise retransmission reduce feedback overhead and improve BER performance compared to conventional ARQ in resource-constrained sensor networks?
• RQ2 How does eliminating CRC-based error detection affect system performance and complexity in uplink sensor networks?
• RQ3 What is the optimal retransmission strategy (e.g., fixed vs. threshold-based) to minimize BER under a given number of retransmissions?
• RQ4 How do feedback errors impact the performance of bitwise retransmission schemes, and can the scheme remain robust under such conditions?
• RQ5 What are the practical design constraints and performance limits for implementing bitwise retransmission in real-world protocols like Zigbee, Wi-Fi, and Bluetooth?

Key findings

• The proposed bitwise retransmission scheme consistently outperforms stop-and-wait ARQ in terms of bit-error rate (BER) for the same number of retransmissions and packet length.
• BER expressions derived for one and two retransmissions are verified via computer simulations and are shown to be accurate using Prony approximation of the Q-function.
• Using synchronized RNGs or combination numbers reduces feedback signaling to a few bits, enabling efficient feedback even in low-bandwidth uplink scenarios.
• The scheme maintains robustness against feedback errors, especially when compared to incremental redundancy HARQ, and remains effective even when feedback bit error rate is up to $10^{-3}$.
• Practical designs for Zigbee, Wi-Fi, and Bluetooth show that the scheme supports reliable operation when forward link BER is below $10^{-3}$ and reverse link BER is below $10^{-5}$.
• The upper bound on the number of supported sensor nodes is calculated, showing scalability under optimized retransmission and feedback parameters.