View detail for AVR2014: AT86RF230 Receiver sensitivity measurements

View detail for AVR2014: AT86RF230 Receiver sensitivity measurements
AVR2014: AT86RF230 Receiver sensitivity
measurements
Features
•
•
•
•
Hardware setup description
Cable loss measurements
Measurement method
Sensitivity Measurement Results
Application Note
1 Introduction
The Atmel AT86RF230 radio transceiver has a specified receiver sensitivity of -101
dBm. The following document shall provide the information that is required for
measuring this value with available Hard- and Software.
2 HW Setup description
For the measurement setup the standard Atmel ATAVR®RZ502 kit is used. This kit
consists of two radio boards, each with one AT86RF230 transceiver chip and a
standard SMA antenna connector.
Figure 2-1. ATAVRRZ502 - single radio extender board
Rev. 8115A-AVR-04/08
Each radio extender board is connected to a setup which consists of an AVR
STK®500 with an AVR STK501 board on top. The AVR STK501 board is equipped
with an AVR ATmega1281 microcontroller chip.
Figure 2-2. STK500+STK501+RZ502
Both setups are identical and are connected via cables with an adjustable attenuator
in between. The Attenuator setup that is used for this measurement consists of one
Agilent 8494H and one Agilent 8496H attenuator blocks and an Agilent 11713A
attenuator driver.
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Figure 2-3. Agilent 8494H + 8496H attenuator blocks
Figure 2-4. Agilent 11713A attenuator driver
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The two STK-board setups are placed approximately 1.5 m away from each other
with the radio extender boards facing outwards.
Figure 2-5. Transmitter setup
Figure 2-6. Receiver setup
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3 SW setup preparation
For the measurements both AVR ATmega 1281 microcontrollers are programmed
from AVR Studio® over a standard AVR JTAGICE mkII with a software package that
is called Radio Evaluation Software (RES). This software is offering low level
functions to use the Atmel AT86RF230 transceiver to generate data frames and do
radio measurements.
The software has a terminal command interface which is accessible over the UART
interface of the STK500 boards. The RES software on the Transmitter setup (called
“A”) will be configured to transmit a fixed number of data frames with a payload of 20
octets. To get a significant measurement result the number of packets is set to 10000
packets.
The RES software on the Receiver setup (called “B”) is configured to receive these
10000 frames. The software will count the received packets and will then directly
calculate the resulting Packet Error Rate (PER). To have a statistical method all
measurements are repeated three times. The UART interfaces of both STK 500
boards are connected to the serial ports of a control Laptop or PC.
4 Cable loss measurement
In order to have dedicated signal strength on the receiver side there is the need to
measure also the loss of the cables and connectors as well as of the attenuator block
itself.
Setup “A” is configured to send 10000 frames. The attenuator setting is 0 dB which
means the attenuator is off. The SMA connector on Setup “B” is now disconnected
and will be connected to an Agilent E4440A Spectrum Analyzer.
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Figure 4-1. cable connected to Spectrum Analyzer
The RES allows the user to adjust the output power of the AT86RF230 transceiver in
the steps described in [2]. For this measurement the output power is set to 0 dBm
(actual register setting is -0.2 dBm).
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Figure 4-2. Agilent E4440A Spectrum Analyzer
The measurement result shows that the used cables and connectors have an
attenuation of approximately 3dB. This value will be added to the attenuation settings
applied by the attenuator block and will be used in the PER calculation. A schematic
block diagram of the measurement setup including the related signal loss diagram is
shown in the next figure.
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Figure 4-3. Signal loss diagram
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5 Measurement execution
The measurement is performed in different steps where each step is using a different
attenuator setting. The PER is measured as described in [1].
To avoid any reception of packets through the air over some line of sight path the
receiver or transmitter setup could be separated from each other by an absorbing
material as shown in the following figure.
In order to get more accurate results its is recommended to do the measurements in
a shielded box environment, but since this might not be possible for all users this
method is not shown here.
To further reduce the level of unwanted transmissions from the transmitting board the
measurement is done with a output level of -17dBm (actual register value in
AT86RF230 is -17.2dBm).
Figure 5-1. absorbing material
The user interface of the RES gives the user the possibility to adjust the parameters
of the radios with easy commands. The complete command reference is part of the
RES software package [3].
Once the RES firmware is programmed into the STK-501 boards AVR 1281
microcontroller the STK’s spare RS232 connector is connected to a PC or Laptop
running a standard terminal program. On the STK-500 the RS232 SPARE Pin Header
needs to be connected to the PORTD Pin Header with the following configuration:
RXD – PD2, TXD – PD3
The serial interface needs to be configured with the following settings:
38400 bps, 8 data bits, 1 stop bit, no parity, no flow control
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Once the computer and the STK-boards RS232 are connected a reset is made on the
STK-board. On the terminal software the user needs to press CTRL+t to switch the
RES into the terminal command mode. The complete command set is displayed on
some kind of a help menu when the “?” is pressed. The required commands to start
the test on the receiver as well as on the transmitter side are highlighted in the next
figure.
Figure 5-2. RES commands
The software parameters used for this test are as follows:
Transmitter settings
Channel: 24
No. of packets: 10000
Power: -17.2 dBm
Receiver settings
Channel: 24
No. of packets:10000
Power: -0.2 dBm (default)
After the transmitter setup as well as the receiver setup have been configured with
these parameters the receiver side needs to be switched into receiving mode by
using the “r” command from the main RES command menu. Then the receiver is
waiting until the first packet gets received.
The transmission test will be initiated by using the “t” command from the main RES
command interface. The transmitter will start to transmit the configured number of
frames and the terminal window should show a visual indication of this.
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Figure 5-3. RES transmission mode
The transmission and reception of the 10000 packets is now repeated for different
settings of the attenuator block. The used attenuation values are shown in the first
column of the result table in section 6. To have some control it is possible to verify the
actual signal strength at the receiver side with the method described in chapter 4.
Depending of the availability of measurement equipment it is also possible to use a
power meter instead of the spectrum analyzer on the receiver end to measure the
signal strength.
In section 4 the attenuation of the cables and connectors were measured with 3 dB –
so this value will be used to get the resulting signal strength at the receivers SMA
connector. Since the ATAVRRZ502 has a balun in the signal path that also adds a
small amount of signal attenuation, the actual resulting signal strength at the
transceiver chip is approximately even 0.5 dB lower. But this is not taken into the
calculation as [1] requires a sensitivity value in dBm that is measured at the antenna
terminals.
The receiver side is automatically calculating the PER once the reception has been
finished. The receiver is also showing the numeric RSSI value of the last
measurement run and it is reporting the lowest, the highest and the average value of
the RSSI during that run. See figure 5-4 for an example with an attenuation block
setting of 81 dB. The values that have been reported by the receiver after each
measurement run are also shown in the result table in section 6.
Figure 5-4. RES result output
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6 Measurement results
The results of the tests showed that with a basic measurement setup it is easily
possible to verify the specified receiver sensitivity of the Atmel AT86RF230. The
accuracy of the measurements described here varies by +/- 0.5 dBm due to the basic
setup without a shielded box, but it should be very easy to reproduce these results by
using the described procedures.
The results are listed in the following table:
Table 6-1. Measurement results
12
Attenuation
Block
setting
Signal
strength
@ receiver
No. of
tx
packets
[ in dB ]
[ in -dBm ]
63
83
10000
10000
0
10000
0
10000
0
3
69
89
10000
10000
0
10000
0
10000
0
1
70
90
10000
10000
0
10000
0
10000
0
1
72
92
10000
10000
0
10000
0
10000
0
0
74
94
10000
10000
0
10000
0
10000
0
0
76
96
10000
10000
0
10000
0
10000
0
0
78
98
10000
10000
0
10000
0
10000
0
0
79
99
10000
9999
0,01
9999
0,01
10000
0
0
80
100
10000
9999
0,01
9999
0,01
10000
0
0
81
101
10000
9997
0,03
9989
0,11
9992
0,08
0
82
102
10000
8597
14,03
8486
15,14
8732
12,68
0
83
103
10000
7114
28,86
6744
32,56
6837
31,63
0
1st run
rec.
packets PER
2nd run
rec.
packets
PER
%
3rd run
rec.
packets
PER
%
average
RSSI
value
%
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7 References
[1] IEEE 802.15.4 – 2003, section 6.1.6Receiver sensitivity definitions
[2] Atmel AT86RF230 Datasheet Rev.D, section 10 register reference
[3] Atmel ZLink Radio Evaluation Software User Guide, Rev.1.
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