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WiFLEX - FLEXible physical layer for WiDOM implementations

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WiFLEX - FLEXible physical layer for WiDOM implementations

Its the "kernel" of Ricardo Gomes's work towards the achievement of his MSc in Electronics and Computers Engineering, at the Engineering School of the Polythecnic Institute of Porto (ISEP-IPP).

 

Efficient Implementation of a Dominance Protocol for Wireless Medium Access:

The main goal of this work is the development of radio communication modules for Wireless Sensor Networks (WSN) to enable efficient implementations of bit dominance-based Medium Access Control (MAC) Protocols. These modules should be compatible with existing WSN platforms (MicaZ and CMU-FireFly).

The supervision and scientific orientation is being played with the common effort of Björn Andersson and Nuno Pereira at CISTER/IPP-Hurray! R&D Group.

This project intents to solve some of the problems that are limiting the acceptance of WiDOM and WiDOM-MBD bit dominance-based wireless MAC protocols, acting as a proof of feasibility and/or hardware state of the art requirement for the implementation of such protocols. 
 

Context

The research work done by N. Pereira, B. Andersson and E. Tovar demonstrated that it is feasible to implement a collision-free dominance protocol for wireless medium access, which implements static-priority scheduling, supports a large number of priority levels and is fully distributed. Hence this protocol, known as “WiDOM: A Dominance Protocol for Wireless Medium Access”, has the capability of efficiently scheduling sporadic messages and is able to fulfill real-time requirements [1]. Further on, along with A. Rowe, they also extended their developments to deal with multiple broadcast domains (MBD) wireless networks (WiDOM - MBD) [2].
In addition, [1] presented a comprehensive study on the response-time calculations for the protocol.

The hardware platforms used for the WiDOM implementation, i.e. existing Wireless Sensor Networks (WSN) platforms, namely MICAz and CMU-Firefly, do not have the necessary characteristics for a real world, highly efficient implementation. The pursuit for efficiency, through the reduction of the protocol’s overhead introduced by the inappropriate physical layer, lead to the identification of two crucial characteristics that the radio modules should have: (i) the ability to reliably switch between transmit and receives modes in the shortest time possible and (ii) the ability to reliably transmit and detect (receive) a carrier pulse with the shortest duration possible. Searching for such characteristics, A. Rowe developed a hardware extension for the CMU-Firefly [3]. However, due to several characteristics, its use was surrounded by considerable limitations and, among many problems, the efficiency improvement was not very significant and it was incompatible with other WSN platforms, such as MICAz.

 

Past and ongoing work

The analysis of the problems found so far, as well as a comprehensive study of the state-of-the-art in OOK transmitters, receivers and transceivers, faced with the requirements for the implementation of such protocols led to the development of new hardware modules.
Characteristics such as (i) and (ii) were the main objectives of the developed prototypes. A simple interface with WSN platforms and physical compatibility with MICAz and CMU-FireFly WSN platforms was also assured.

Common concerns in area of WSN platform design like low power consumption, low voltage operation, transmission range and overall size, where also given considerable attention. Despite being fully dedicated to Research & Development purposes, the hardware development also tried to take in account a straightforward out-of-lab implementation, meaning that, although not primary, the achievement of a low cost equipment was also pursued.


The hardware developed consists in three independent modules that compose the “FLEXible physical layer for WiDOM implementations - WiFLEX”. Additionally was developed a TTL to RS232 transceiver in order to allow auxiliary debugging capabilities through the microcontroller USART. This hardware opens the possibility to implement WiDOM and WiDOM – MBD with or without external out-of-band synchronization.


The hardware is currently in its second version. Nevertheless, the architecture that was implemented in the first version of the developed hardware unveiled that it is possible to switch from transmit to receive mode in 48 µs, and from receive to transmit mode in less than 1 µs. It was also possible to determine that carrier pulses as short as 35 µs can be transmitted and detected. Despite many other positive characteristics that were achieved, namely the ones referred in the design guidelines, this first prototype approach proved that it is possible to increase the efficiency of the hardware layer in a significant way. However, several manufacturing problems were compromising the overall performance of the equipment, and new prototypes had to be produced. Taking advantage of this situation, several design improvements and corrections were made.

 

Presently are being done tests in order to accurately determine the characteristics of the new hardware. Although very promising results have been achieved, at this stage, it is not possible to advance any further developments.

 

More details about the developed hardware, among other information and related work, can be found at the PRIOMAC official webpage at the CISTER/IPP-Hurray! R&D Group website. (click the hyperlink to go directly to the webpage "A Platform for Scalable Aggregate Computations in Cyber-Physical Systems" ) 

 

 

 

 

References
[1] N. Pereira, B. Andersson, and E. Tovar, "WiDom: A Dominance Protocol for Wireless Medium Access", IEEE Transactions on Industrial Informatics, vol. 3, issue 2, May 2007.
[2] N. Pereira, B. Andersson, E. Tovar, and A. Rowe, "Static-Priority Scheduling over Wireless Networks with Multiple Broadcast Domains", In proc. of the 28th IEEE Real-Time Systems Symposium (RTSS'07), Tucson, Arizona, USA, 2007.
[3] A. Rowe, “Nano-RK – RFLINX OOK add-on board a.k.a. Wings”, online at:
http://www.nanork.org/nano-RK/wiki/wings.

 

 

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