Error
Performance of BIM Transceiver with RPC
Application Note: 100
|
Sabananthan Paramananthan |
| Date: 12 August 1997 |
Applications Engineer |
Introduction
The Radiometrix Radio Packet Controller (RPC-000) is designed to give maximum bit rate
communications through a BiM-UHF Transceiver at 40 kbits/s. It is designed to have High
Receiver Sensitivity with Wide Frequency Tolerance. This experiment was carried out to
prove its performance quantitatively.
Test Set-up
RPC Packet Generator produces a stream of data packets with fixed interval between
them. These packets are taken out from TXD output and fed to Filter circuit to get the
right signal level & frequency needed by the Signal Generator to generate a Frequency
Modulated RF output which is fed to the BIM Transceiver. If the check sum succeeds, the
RXR is set LOW, which discharges the Capacitor. It is reset to HIGH when a corrupted data
packet is received, which charges up the capacitor. RF Output Level was varied, which
effectively varied the Signal to Noise ratio. The Voltage across the capacitor gives the
Average Percentage of Packet Error.
Figure 1
(S+N)/N was measured by taking the ratio of the Audio output level with & without
FM deviation.
 Figure 2.
The graph on the right shows the result obtained. RPC can receive data packets without any
Packet Error above an RF level of -101dBm (2µV). This corresponds to Signal+Noise to
Noise ratio of 18 dB.
Percentage Error graph was given here instead of Bit Error Rate (BER) graph because it
is more practical and convenient to interpret the performance of RPC.
 Figure 3.
Note:
1 Test Packet is 13.8ms long, consisting of 5ms of preamble and 8.8ms of data &
check sum code. Each data/checksum code bit is 25µs (40 kbits/s) wide.
Number of data & checksum bit per packet is 352 bits/packet
  for 
For example 10% Packet Error (PER=0.1) is equivalent to  or 1 Bit Error in 3520 bits!
Effect of Frequency Error on Sensitivity of Receiver
Test Set-up
The same set-up was used but this time the Signal Generator Frequency was varied and
the RF level was adjusted to get same voltage on the voltmeter.
 Figure 4.
The graph on the right shows the RF level required for a constant 4.5% Packet Error
when the Transmitter Carrier Frequency drifts. RPC receiver has a frequency tolerance
greater than 200 kHz.
Note:
The Carrier Detect has a smaller bandwidth compared to the actual RPC receiver
bandwidth.
Conclusion.
For reliable data communication using RPC Signal+Noise to Noise ratio should be above
18dB or the RF power level at the RF input should be greater than -101 dBm (2µV).
The frequency error tests demonstrate negligible loss of sensitivity under worst case
TX & RX frequency tolerance.
References
[1] Radiometrix BIM-UHF Data Sheet
[2] Radiometrix RPC Data Sheet
[3] Bernard Sklar, Digital Communications-Fundamentals and Applications,
Prentice-Hall, 1988.
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