Murata Electronics North America 5811M Manual Do Utilizador
© 2003 Cirronet
Incorporated
9
M-5811-0008 Rev -
This corresponds to the base sending just over 750Kbps and the aggregate of the remote
throughput equaling about 250Kbps. This is clearly setup for predominantly base to remote
transmission. The balance between base and remote transmission is varied using the Set Base
Slot Size and Set Hop Duration commands. Details of these commands are provided in the
Modem Commands section of this manual.
It is often difficult to predict what throughput a remote will obtain in a point-to-multipoint
network. The worst-case scenario would be when there are 26 remotes transmitting
continuously. In this case, each remote would get 1/26
throughput equaling about 250Kbps. This is clearly setup for predominantly base to remote
transmission. The balance between base and remote transmission is varied using the Set Base
Slot Size and Set Hop Duration commands. Details of these commands are provided in the
Modem Commands section of this manual.
It is often difficult to predict what throughput a remote will obtain in a point-to-multipoint
network. The worst-case scenario would be when there are 26 remotes transmitting
continuously. In this case, each remote would get 1/26
th
of the remote to base aggregate
throughput of about 250Kbps or about 9600bps. In practice, given the over-the-air data rate
of the radio (1.2288Mpbs) is faster than the serial input to the radio (921.6Kbps), it is rare
that this circumstance will exist more than briefly. Also, in applications where there is more
remotes to base communication than base to remotes, the base slot size will be reduced
accordingly. These calculations are provided as a means of only estimating the capacity of a
multipoint WIT5811 network.
of the radio (1.2288Mpbs) is faster than the serial input to the radio (921.6Kbps), it is rare
that this circumstance will exist more than briefly. Also, in applications where there is more
remotes to base communication than base to remotes, the base slot size will be reduced
accordingly. These calculations are provided as a means of only estimating the capacity of a
multipoint WIT5811 network.
2.2.5. Full Duplex Communication
From an application perspective, the WIT5811 communicates in full duplex. That is, both
the user application and the remote terminal can be transmitting data without waiting for the
other to finish. At the radio level, the base station and remotes do not actually transmit at the
same time but rather use a Time Division Duplex (TDD) scheme. As discussed earlier, the
base station transmits a synchronization signal at the beginning of each hop followed by a
packet of data. After the base station transmission, the remotes will transmit. Each base
station and remote transmission may be just part of a complete transmission from the user
application or the remote terminal. Thus, from an application perspective, the radios are
communicating in full duplex mode since the base station will receive data from a remote
before completing a transmission to the remote.
From an application perspective, the WIT5811 communicates in full duplex. That is, both
the user application and the remote terminal can be transmitting data without waiting for the
other to finish. At the radio level, the base station and remotes do not actually transmit at the
same time but rather use a Time Division Duplex (TDD) scheme. As discussed earlier, the
base station transmits a synchronization signal at the beginning of each hop followed by a
packet of data. After the base station transmission, the remotes will transmit. Each base
station and remote transmission may be just part of a complete transmission from the user
application or the remote terminal. Thus, from an application perspective, the radios are
communicating in full duplex mode since the base station will receive data from a remote
before completing a transmission to the remote.
2.2.6. Error-free Packet Transmission Using ARQ
The radio medium is a hostile environment for data transmission. In a typical office or
factory environment, 1% - 2% of the 5.8GHz frequency band may be unusable at any given
time at any given station due to noise, interference or multipath fading. For narrowband
radio systems (and also many spread spectrum radio systems which use direct sequence
spreading), this would imply a loss of contact on average of over 30 seconds per hour per
station. The WIT5811 overcomes this problem by hopping rapidly throughout the band in a
pseudo-random pattern. If a message fails to get through on a particular channel, the
WIT5811 simply tries again on the next channel. Even if two thirds of the band are
unusable, the WIT5811 can still communicate reliably.
Data input to the WIT5811 is broken up by the radio into packets. A 24-bit checksum is
attached to each packet to verify that it was correctly received. If the packet is received
correctly, the receiving station sends an acknowledgment, or
The radio medium is a hostile environment for data transmission. In a typical office or
factory environment, 1% - 2% of the 5.8GHz frequency band may be unusable at any given
time at any given station due to noise, interference or multipath fading. For narrowband
radio systems (and also many spread spectrum radio systems which use direct sequence
spreading), this would imply a loss of contact on average of over 30 seconds per hour per
station. The WIT5811 overcomes this problem by hopping rapidly throughout the band in a
pseudo-random pattern. If a message fails to get through on a particular channel, the
WIT5811 simply tries again on the next channel. Even if two thirds of the band are
unusable, the WIT5811 can still communicate reliably.
Data input to the WIT5811 is broken up by the radio into packets. A 24-bit checksum is
attached to each packet to verify that it was correctly received. If the packet is received
correctly, the receiving station sends an acknowledgment, or
ACK
, back to the transmitting
station. If the transmitter doesn't receive an
ACK
, at the next frequency hop it will attempt to