LXRS & LXRS+ Wireless Protocols

This article will attempt to explain the difference between the LORD Sensing MicroStrain term LXRS and their new LXRS+ wireless communication protocol.

Lossless eXtended Range Synchronized is the proprietary LORD Sensing data communications protocol used in their wireless sensor network. It was initially developed in 2013 to support applications including flight test and heavy machine monitoring, when applications such as these require large amounts of raw sensor data, synchronization between sensor nodes, and no lost data. The Lossless protocol allows the user to achieve near lossless data collection in most environments by using data buffering, radio acknowledgments, and retransmissions. Each node buffers collected data and timestamps to an internal 2 Mbit FIFO buffer, then for each transmission, data is pulled from this buffer, and upon receiving the data packet, an acknowledgment is sent from the WSDA gateway that is providing the beacon. The node will retransmit data until this acknowledgment is received. Inherent overhead in the transmission scheduling protocol assures the node time to recover from periods of poor radio communication. This feature allows lossless performance in environments where the node achieves as high as 50% packet error rate. It also allows for operation in situations where the gateway and node move in and out of range of each other. The Lossless feature is only available when Synchronized is enabled. If the application requires consistent latency or can tolerate lost data, then the user can disable the lossless feature.

By selecting Synchronized, all the nodes in the network will periodically synchronize their time clocks to a beacon that is broadcasted by the WSDA gateway. Each beacon contains a UTC timestamp, allowing nodes to timestamp their collected data within an accuracy of +/- 50 µs. Each node will also buffer data and transmit this data in time-slots allocated prior to sampling. Using time-slots assures the transmissions will not “collide”, or corrupt each other. It also provides a means for efficiently scaling the size of the network to allow as much data throughput as possible. If Synchronized is deselected, the node will not require a beacon time source and will transmit a data transmission for each measurement sweep. The user should deselect Synchronized if, either low latency, or the lowest possible power at slow sample rates, is required.

LXRS allows for dependable synchronized wireless sensing for both long term monitoring and high bandwidth test and measurement. LXRS+ is the second generation of LXRS, and has been developed to accommodate customers who want more data over their wireless networks, at shorter range. Customers using the V-Link-200 or G-Link-200 with the new WSDA-200-USB gateway may toggle their network into either LXRS or LXRS+ mode, depending on whether their application prioritises range or network throughput.

LXRS uses the 802.15.4 protocol, has a -93.5 dBm Rx Sensitivity, and 4000 samples/s maximum for a single channel full scale. The new LXRS+ uses a proprietary protocol, has a -86.5 dBm Rx sensitivity, with 16000 samples/second maximum for a single channel full scale. The table shows the number of nodes that can be used simultaneously for continuous data transmission using each protocol at various sample rates.