Challenges in the design of the MAC protocols for wireless sensor networks using VHDL

Abstract

Abstract—In the design of MAC protocols for wireless sensornetworks (WSN) it is necessary to fulfill some requirementssuch as low energy consumption, scalability, simplicity, etc.These requirements are not easy to fulfill from the viewpoint ofimplementation on FPGA or ASIC technologies. Therefore, in thispaper we identify some challenges encountered during the designof MAC protocol for WSN. For some of these challenges, potentialsolutions are discussed. To illustrate the proposed solutions S-MAC protocol is chosen. VHDL design of the S-MAC protocols isexperimentally verified on the Altera EP2C5 FPGA developmentsystem. Keywords — MAC, WSN, FPGA, VHDL, S-MAC, proto-col.I. I NTRODUCTION Wireless sensor (and actuator) networks are a special classof wireless networks that are recognizable by their simplicityand orientation to perform domain-specific tasks. The greatestimpact on the quality of service of such networks generallyhave (wireless) medium access control protocols (MAC).There are several requirements which are necessary tofulfill during the design of MAC protocols in wireless sensornetworks. The most important factor is energy consumptionsince it increases the lifetime of the network. The processesthat significantly affect energy consumption are: collisions,permanent listening to the media, listening to the media inIDLE state, transmission of control packets, transmission tounavailable nodes, etc. [1] In addition, important factors arescalability and low complexity.Implementation platform can pose some restrictions on thedesign of MAC protocols for WSN. Today, there are twopopular approaches: 1) using of microcontrollers and RF com-munication modules, and 2) implementation of entire systemon a single chip. In the first approach, the microcontrollerruns a real-time operating system or a dedicated softwareand communication protocols that control the RF peripherals.In the second approach, all features and functionalities WSN(processor, memory, DSP, protocols, etc.) are implemented ona single chip (ASIC - application specific integrated circuit).The advantage of ASIC in relation to the microcontroller unit(MCU) solution lies in the possibility to optimize the energyconsumption by implementing only those functions that arerequired for the application. Today, the most popular methodof ASIC prototyping, is the use of FPGA technology.The implementation of wireless sensor node on the FPGAdevice is often resorted to the use of microprocessor archi-tecture (eg. Altera Nios, Xilinx PicoBlaze, OpenRISC etc).In this case, communication protocols are usually executedon the microprocessor instantiated within the FPGA device.However, focus of this paper is the pure implementation ofone of MAC protocols logical structure on the FPGA device.The logical structure is described in VHDL.When describing the MAC protocol in VHDL, it is neces-sary to make the mapping from protocol design to its logicalstructure, respecting the previously mentioned requirements:energy efficiency, scalability and lower complexity.The analysis will be applied to one representative of theMAC protocols in wireless sensor networks - the S-MACprotocol described in [2].Considering the the S-MAC protocol, its basic functionali-ties can be observed: