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Calibrating RSSI values reported by CC2420 radios

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The IEEE 802.15.4 standard specifies that a radio's PHY layer must provide an 8-bit integer value as an estimate of the received signal power. This value is commonly known as the Received Signal Strength Indication (RSSI) in the wireless sensor networks (WSN) community. While many protocols directly use the measurements that the radios provide, the standard only requires that the reported RSSI values should be linear and within ±6 dB of the actual RSSI values. However, ±6 dB is a wide error margin. For example, Packet Reception Ratio (PRR) can decrease from 100% to 0% with a 2 or 3 dB difference in the received signal strength. We examined two 802.15.4 compliant radios, the widely used TI CC2420 and Atmel AT86RF230, and discovered that they indeed introduce systematic errors when providing the RSSI readings. Therefore, we also developed a calibration scheme to effectively minimize the adverse effects associated with inaccurate RSSI values.

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CC2420 Security Support

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To effectively provide security to packets using TI/Chipcon CC2420 radios, we provided support in TinyOS 2.x to enable the CC2420 radio's in-line security features. We use the CC2420 security features for the data transmitted in the MEDiSN project to protect packets that contain patient's physiological data. The code is included in the official distribution of TinyOS 2.1.1. Additional information on its usage can be found in the official TinyOS tutorial webpage.
   

Koala + Phoenix

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koala

Koala is a data-collection system for TinyOS. Sensor nodes periodically sample their sensors, delta-compress the data, and store it to external flash. Periodically, a basestation PC is used to wake up the nodes, establish multi-hop paths to them, and retrieve the buffered data.

This distribution also integrates the Phoenix time reconstruction algorithm. Sensor nodes periodially exchange time-state information. After data is collected, this information can be used to map measurements (timestamped in node-local time) to a global timeframe (provided by a GPS or PC clock).

(Koala photo by Erik Veland)

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TinyOS Code Contributions

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To serve our own needs and as a service to the WSN community, we have actively contributed code to the TinyOS community.

  1. We have ported Deluge to TinyOS 2 (called Deluge T2). The code has been included in the official TinyOS distribution starting version 2.02.
  2. Tos.py is a Python implementation of the TinyOS 2 serial stack. This was first introduced as part of the Deluge T2 tools.
  3. Through a collaboration with Stanford, Berkeley, and USC, we have been involved with the development of the TOSThreads library. TOSThreads has been included in the official TinyOS distribution starting version 2.1.
 

HiNRG Software Copyright Information

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This is the copyright written in all software code that we have developed. Please read this carefully.

Copyright (c) 2010 Johns Hopkins University. All rights reserved.

 Permission to use, copy, modify, and distribute this software and
its documentation for any purpose, without fee, and without written
agreement is hereby granted, provided that the above copyright
notice, the (updated) modification history and the author appear in
all copies of this source code.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
CONTRIBUTORS `AS IS' AND ANY EXPRESS OR IMPLIED WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES(INCLUDING,
BUT NOT LIMITED TO, LOSS OF USE, DATA, OR PROFITS) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.