Werbung
Verfügbare Sprachen
Verfügbare Sprachen
BIS U Basic Manual
10
Operating Several Processor Units
Due to the large range available for UHF fields, it is possible that processor units will have a
negative influence on one another if they are operated simultaneously and randomly select the
same operating frequency.
10.1 Frequency
One way of avoiding interference is to configure the processor units to switch to a different
Hopping Method
transmitting channel in a random sequence (frequency hopping).
The probability of multiple readers transmitting at the same channel at the same time decreases
in relation to the number of available channels within the permitted frequency band.
The number of channels can vary depending on the national provisions of different countries.
10.2 Listen Before
Another way to avoid interference is a contention-based protocol called the listen before talk
Talk
operating procedure. Only ten channels are available in some countries, such as European
Community countries. Since the probability that several readers will be transmitting on the same
channel is rather high in such cases, the availability of the channel is checked before
transmission.
The processor unit only starts transmitting if the selected channel is available (listen before talk)
to prevent overlapping or collisions. In order to guarantee dynamic use of the transmitting
channels, the transmission time may not exceed 4 seconds. The processor unit must then wait
100 ms or switch directly to a new unused channel.
Following the amendment of ETSI standard EN 302 208 (V1.2.1), this procedure for reducing
mutual interference is no longer mandatory. The procedure mentioned in section 10.3 is
preferred.
10.3 Creating a
Increasing the channel spacing (ETSI 302 208 V1.2.1) to 600 kHz already rules out the mutual
Transmission
overlapping of transmitted and received signals traveling between adjacent transmitting channels
Plan
for all available radio profiles; the position of the side band in relation to the transmission
frequency is determined here.
Mutual interference is prevented by allocating different transmitting channels to the processor
units involved, i.e. creating a transmission plan.
The distance to the side band can be as much as 320 kHz in Dense Reader Mode (according
to ETSI TS 102 562) and allows more than one reader to be operated on each channel.
www.balluff.com
25
Werbung
