Xetawave Xeta9-E, Руководство пользователя

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and type of errors that the radio receives. And this in turn is a function of the noise and
interference between the transmit antenna and the receiver antenna.
As a general rule, as the packet size increases, the required signal strength (or received
signal versus sensitivity) must also increase for comparable performance. Since
sensitivity measurements are done at 10
-4
error rates, approximately 10% of the packets
will be lost at 128 byte packets (1024 bits) when operating at the sensitivity point. If the
lost due to at least one error in the packet. Thus, the signal strength must be increased
to maintain the same 10% packet loss rate. Likewise, for very noise environments, small
packets will be more successful than large packets.
To achieve high user data rates, larger packets and higher modulation levels are desired.
In one slot time, there are fixed delays that are not a function of packet size or data
rate, thus as more data is sent in a packet per slot time, the utilization increases. For
example, at BPSK (883kbps), the user rate will vary from 719kbps to 788kbps as the
packet size changes from 64 Byte to 1024 Byte (89% efficiency). In contrast, at 16QAM
(3.5Mbps) the user rate will vary from 2.0Mbps to 2.5Mbps (71% efficiency). Since
16QAM is four times faster than BPSK, one could expect the user rate to be 4 x 788kbps,
or 3.15Mbps but due to the overhead time the actual user rate is only 2.5Mbps.
If a targeted data rate is desired, there are multiple options of packet size and
modulation that will result with the data rate. The choice of shorter packets with more
complex modulation or longer packets with simpler modulation will be determined by
the type of noise in the environment. More noise (interference) generally requires
shorter packets with resulting more complex modulation.
3.4.5 RF Settings for Xeta9x-E, Eman
The Xeat9x-E, Eman, supports modulations only supports modulations up to and
including 2651 kbps 8PSK.