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This article explains how eLocker utilises Bluetooth Low Energy (BLE) to connect to locks, how we ensure a secure connection, fast updates and long battery life
Advertising and Battery Life Control
eLocker uses Bluetooth Advertising as a basis for our wireless communications. Advertising data is configurable in the lock settings and is controllable from the online system. By using advertising, we can control the amount of time the lock is available for connection and, therefore, can control the battery life of the product. As defined below
eLocker has carried out detailed battery profile testing to understand the battery life of locks in the field. Locks were configured to different advertising settings and the power usage was monitored using highly sensitive measurement equipment, allowing us to accurately predict battery life.
In this style of operation, the master device (smart box) is only able to connect to locks after discovering their advertising packets; by using this method, we stop situations where locks are searching for the smart box as there is no constant connection. The smart box only initiates a connection to the lock when necessary. This means that the powered device is searching for the battery-operated device, minimising battery drain,
BLE operation
Locks only advertise on the following events:
- Contactless card operation either a successful or not
- Battery dropping below a certain threshold (30%)
- A ping every 4 hours
- As per a setting in the lock for advertising frequency / duration (as standard is 3 mins on / 5 mins off)
When a trigger event has occurred, the locks advertise, allowing the smart box to collect information through the advertising data or to establish a connection if required. The lock will only be connectable during this limited advertising period
If advertising is triggered by a drop in the battery level, then the lock will show an advertising flag that the battery is critical which is collected faster than standard logs in the system
Bluetooth Security
eLocker uses connectionless operation by making use of advertising data to communicate log information from locks to the smart box. Connections are only made for certain operations such as testing locks, firmware upgrades or configuration. This connection is made by mutual authentication
Link Security
Link security is not implemented to limit the need for the smart box to retain sets of bonding information. This means that the devices are not bonded and do bot not use MITM protection i.e. pairing. The devices include application-level security (mutual authentication)
Mutual Authentication
Mutual Authentication uses AES128 encrypted Bluetooth packets, which are created using a shared key which is stored in the lock and smart box, and are dynamically created using an algorithm
If the mutual authentication or, the smart box (or an attacking device) attempts to access a protected characteristic before authenticating, then the lock will disconnect immediately, creating a high level of security
Managing high density
eLocker uses protocols to communicate data between the online system and smart box. Managing thousands of locks in an area requires a very complex set of systems, which ensure that messages sent from the server arrive correctly at the smart box, ready to be sent to locks over BLE when they are found advertising
To ensure message delivery and to track messages efficiently, eLocker employs a range of queuing and message confirmation systems, which provide confirmation of delivery for every message sent to a smart box. This is backed by the eLocker message pipeline, which carries out a range of operations, checking if smart boxes are online prior to sending messages and a smart box priority service, which will try to send messages to a smart box several times if messages fail. Then, revert to a backup device if messages cannot be delivered. While also notifying the customer admin and eLocker support team
This solution has been stress-tested extensively in super-high-density environments
Using eLocker alongside your internal Wi-Fi
Yes, in theory, Wi-Fi and Bluetooth could disturb each other.
But both are equipped to handle situations where this can occur. A standard that is not capable to handle disturbance and/or interference will be unusable under many circumstances.
Wi-Fi uses a listen before transmit system. If the channel is busy, it holds off transmitting. Eventually it gets through. Each channel is fixed. If it tries to use a channel that is busy due to Bluetooth, then it will wait briefly for the channel to be available. Wi-Fi transceivers are also able to detect when certain data has been lost and can ask for a re transmission. It is also possible to lower the data rate which makes the link more "robust" in the sense that it is less sensitive to disturbances.
To reduce the requirement for Wi-Fi to handle traffic as defined above, channel hopping is used in BLE to reduce interference and improve throughput. The Bluetooth standard defines rules for switching between channels and algorithms used when performing channel hopping.
Use of the unlicensed 2.4GHz ISM band by several wireless technologies causes increased interference and results in retransmissions to correct errors in received packets. Since BLE is a low energy-oriented protocol, it is more susceptible to interference. BLE uses channel hopping to combat the impact of interference. When one channel is completely blocked due to interference, devices can still continue to communicate with each other on other channels.
Locks transmits advertising packets on the three advertising channels in a cyclic manner (starting from channel index 37). The same procedure is used by the Smart box, listening on the three advertising channels in a cyclic manner.
The Smart box changes to a new data channel for every connection event. A connection event is a sequence of data packet exchanges between two connected devices (mutual authentication). The connection events occur periodically with an interval called connection interval. All the packets within a connection event are transmitted on the same data channel. A new connection event uses a new data channel.
So yes, while interference could happen in theory, both the protocols used in your enterprise level Wi-Fi and BLE protocols employed by eLocker are built to handle and stop interference.