|
While wireless device networks are self-organizing and nodes are continuously monitoring transmission and re-arrange it when necessary, explicit planning and engineering of the radio environment allows to design safety-margins into the systems and thus predictable performance.
Site-surveys are the method of choice to eliminate the guesswork. Such a site-survey basically consists of three step:
The “energy-scan” is used to identify sources of interference. All channels are checked for signals present, e.g. from WLAN-routers or bluetooth devices. Although SenzaNET’s RF-devices are capable of filtering it’s own signals from a “background-noise” of such sources, channels with extreme levels of disturbing signals should be avoided, because low signal-to-noise ratios will cause re-sending of data to occur more often resulting in higher power-consumption and extended latency.In SenzaNET, the user can “blackmail” specific channels, so that they are not being used for transmission at all. When heavy WLAN-usage is required in parallel to SenzaNET, we recommend to assign specific channels to WLAN and use others for SenzaNET to be on the safe side.
|
|
While an energy-scan checks the RF environment at a given point within the site, the link-quality check is used to determine the signal-strength between two nodes. Also, the range of the network in a given environment can be tested by keeping one node fixed and moving the other one while monitoring link quality and how it deteriorates with distance.
For the final testing, the operator has to place the network nodes at site based on the results of steps 1 and 2 and send test-data. This can also be done over extended periods of time to get a very accurate picture also when conditions of operation change over time. As a result, one gets statistics of the packets sent and how often SenzaNET needed to repeat data packets due to radio-link failure. Usually, a repeat-rate of less than < 0.1 % of packets can be achieved without major engineering efforts.
|
|
|
In general, such RF engineering is recommended whenever heavy usage of SenzaNET is foreseen in a given environment and reliability and/or power-consumption are a major concern.
For most applications, putting the nodes in field and looking at the linkquality will be sufficient. The link-quality is permanently displayed on the SenzaWMS user interface.
SenzaNET yet achieves in most critical environments a 99,9 % data transmission reliability due to its innate store-and-forward mechanism. For it allows buffering of data and transmission timestamp for the period of interference and retransmits it immediately once the communication link is restored.
|
|
