Сравнение схем авто-адресации для Bluetooth систем доступа к авто

Bluetooth Low Energy (BLE) car-access системы типично feature central module и multiple satellite nodes, communicating over Controller Area Network (CAN) или Local Interconnect Network (LIN) bus. Спутники стратегически размещены вокруг автомобиля для расширения BLE range.

Дизайнеры aim to streamline satellite manufacturing using single PCB design и identical firmware across all nodes. Эта uniformity, however, necessitates on-board mechanism для central module to assign unique CAN или LIN addresses к каждому сателлиту после установки.

Traditional wired approaches employ dedicated LIN daisy-chain to distribute CAN IDs during manufacturing. LIN interface then disabled for vehicle's lifetime. Alternative reduces bill-of-materials (BOM) costs by replacing dedicated LIN bus with minimal discrete circuit. Truly wireless option eliminates extra hardware entirely, leveraging existing BLE infrastructure to perform address assignment.

By removing need for dedicated LIN hardware, wireless method cuts wiring, BOM, и overhead of stocking and assembling unnecessary components. Статья сначала reviews wired auto-addressing techniques before delving into wireless approach.

Modern car-access systems increasingly adopt BLE для phone-as-a-key или digital-key functions. Эти системы operate like passive-entry, passive-start setups но replace traditional key fobs с driver's smartphone. Typical configuration consists of one central module и six to twelve satellite modules, each capable of receiving BLE signals from phone or key fob (Figure 1).

Для phone-as-a-key системы to unlock, central module must determine when smartphone или key fob is within vehicle's unlocking zone. This achieved by triangulating signals received by multiple satellite modules distributed across strategic locations such as passenger doors, rocker panels, trunks, и bumpers.

Central module communicates with satellites via CAN или LIN. Using data from each satellite, it triangulates smartphone's location и decides whether to grant entry. Figure 2 illustrates CAN-based communication topology.

The CAN address of each satellite lets central module identify source of incoming data. Assigning unique CAN ID или address to each satellite essential for correct operation. Rather than hard-coding distinct PCB for every satellite, manufacturers prefer single PCB design running same firmware on all nodes. This approach reduces inventory complexity и enables installation of same module in any vehicle location.

Since all satellites identical и unaddressed at installation, post-installation auto-addressing scheme required.

Wired auto-addressing: LIN daisy-chain method

Currently, many OEMs use separate LIN bus для one-time CAN address assignment. Central module sends CAN address over LIN to first satellite; that node forwards next address to second satellite, и so on (Figure 3). Each module requires two LIN PHYs — one for transmission и one for reception — used only during auto-addressing. With six to twelve satellites, a vehicle may need 14 to 26 LIN PHYs, inflating BOM и complexity.

Wired auto-addressing: Single-wire method

Texas Instruments introduced cost-saving alternative that replaces LIN PHYs with a MOSFET и a few resistors. In this scheme, all satellites ignore CAN bus until wake signal received on P_IN line (Figure 4). Central module initiates process by pulsing P_IN1 through Q1. First satellite receives wake signal, begins listening to CAN bus, и receives its CAN ID. After acknowledging receipt, it sends wake signal to next satellite, and sequence repeats until every node addressed.

Although this method reduces component count, it still requires dedicated wiring connection between central module и each satellite (Figure 5).

Wireless auto-addressing/cable replacement

Another TI solution eliminates extra wiring entirely by using BLE localization. During manufacturing или module replacement, central module assigns CAN addresses based on measured distances (derived from RSSI). Satellites closest to central module receive lowest CAN IDs, followed by progressively farther modules. Actual physical location not needed; consistency in measured distances guarantees repeatable addressing.

For instance, if measured distances satisfy d1 < d6 < d5 < d2 < d4 < d3, central module can reliably assign addresses 1 through 6. If two satellites produce similar distances, an already-addressed satellite can serve as secondary reference to differentiate them (Figure 7).

Implementation details

In line with Generic Access Profile (GAP) of BLE, central module termed "scanner" и satellites "advertisers." GAP layer manages device discovery, link establishment, и security. Two key states are:

• Advertiser: Broadcasts connectable advertising data, including unique device address и optional name.
• Scanner: Scans for advertisements, sends scan requests, и initiates connections.

During auto-addressing, each advertiser broadcasts with random identifier to prevent duplication. Scanner repeatedly measures RSSI, averages values, и selects nearest advertiser. It then sends scan request, transmits auto-address CAN message, и waits for acknowledgment. Upon acknowledgment, advertiser stops advertising и proceeds to next node. This cycle repeats until all satellites addressed.

Results

Testing employed TI's Bluetooth Low Energy + CAN satellite reference design и 12-ft harness with ~6-ft spacing between connectors (Figure 9). Scanner used 1-s scan duration with 250-ms window/interval; advertisers advertised every 100 ms. Ten RSSI samples taken per node, and average used to estimate distance.

Table 1 summarizes delay, reliability, и implementation cost of three methods. Wireless approach incurs roughly five times longer addressing time compared to wired schemes, but offers lowest BOM и eliminates wiring. Performance can be improved by refining BLE parameters и accounting for RF propagation variations.

For detailed single-wire test data, refer to TI's car-access Bluetooth Low Energy + CAN satellite module reference guide. When choosing auto-addressing strategy, consider cost, wiring complexity, и need for post-manufacturing flexibility.

* For additional details и test results on single-wire auto-addressing method, consult Texas Instruments car access Bluetooth Low Energy + CAN satellite module reference design guide.

References

1. Bluetooth core specifications
2. The Standard for Connection Sets New Standards in Safety, Bluetooth SIG

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