Bluetooth Low Energy PDU Sequence Number Expansion
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Solution Overview
Problem
Bluetooth Low Energy (BLE) systems face issues with packet reception failures due to short sequence numbers and implicit packet counters, leading to excessive retransmissions, aged data transmission, and connection disruptions, especially when encryption is enabled.
Innovation Solution
Expanding the sequence number to three bits using reserved bits in the PDU header and introducing a security sequence number to maintain packet counters consistently, allowing for more efficient packet management and secure retransmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a one-bit sequence number is used in BLE PDUs, then the protocol simplicity is maintained, but packet reception failures occur frequently leading to excessive retransmissions
Solution Approach 1:
The sequence number field is segmented into multiple bits (expanding from 1 bit to more bits) to provide sufficient unique identifiers for packets. This segmentation allows the system to track individual packets effectively without excessive retransmissions, while maintaining protocol structure through defined bit allocations for sequence numbers and packet counters.
Solution Approach 2:
The patent introduces an additional dimension by implementing both sequence numbers and packet counters as separate entities. The sequence number identifies individual packets within a connection, while the packet counter provides a global ordering mechanism. This dimensional expansion resolves the contradiction by providing reliable packet tracking without overly complicating the protocol, as each component has a specific, simplified role.
2Productivity
If implicit packet counters are used for encryption, then encryption efficiency is improved, but packet counter desynchronization occurs leading to connection disruptions
Solution Approach 1:
The patent implements feedback mechanisms where packet counters and sequence numbers are explicitly transmitted and acknowledged in PDU exchanges. This feedback loop ensures both devices maintain synchronized packet counter values, preventing desynchronization that would disrupt encryption. The explicit tracking provides continuous verification of counter alignment while maintaining encryption efficiency through the use of established cryptographic protocols.
3Reliability
If excessive retransmissions are performed to ensure data delivery, then data completeness is improved, but transmission latency increases and new data is delayed
Solution Approach 1:
The patent applies preliminary action by implementing robust packet identification mechanisms (sequence numbers and packet counters) before transmission issues occur. This allows devices to predict and prevent retransmission needs through accurate packet tracking and acknowledgment. By establishing reliable packet ordering and identification upfront, the system reduces the need for excessive retransmissions, thereby minimizing transmission latency while ensuring data completeness.
Data Source
AI summary
An expanded sequence number is added to PDUs in a Bluetooth® low energy system. The expanded sequence number provides more accurate identification of the PDUs and allows the system to avoid delaying transmission of PDUs while retransmitting other PDUs. A PDU security sequence number may also be added to the PDUs. The security sequence number is used to create a unique nonce for use in encrypting or decrypting and authenticating the PDU. Using the security sequence number, a failed connection can be reestablished between two devices without the need of generating an encryption key. The security sequence number allows the devices to perform encryption or decryption and authentication using an existing key and a nonce generated from the security sequence number.