Design and Implementation Of Highly Reliable, Low Power PHY Baseband Processor Based On IEEE 802.15.4

Abstract

lives, at least technically. Unlike other standard targeting high or moderate data rates applications, IEEE 802.15.4 standard is a global standard design for low data rates, low power consumption and low cost applications. This so called enabling standard will bring many simple, originally standalone devices into network and thus not only open the door to a numerous number of new application but also add values to many other existing application such as lighting control, automatic meter reading, wireless smoke detector, HVAC control, home security, medical sensing and monitoring. There are a multitude of standards that address mid to high data rates for voice, PC LANs, video, etc. However, up till now there hasn’t been a wireless network standard that meets the unique needs of sensors and control devices. Sensors and controls don’t need high bandwidth but they do need low latency and very low energy consumption for long battery lives and for large device arrays. There are a multitude of proprietary wireless systems manufactured today to solve a multitude of problems that also don’t require high data rates but do require low cost and very low current drain. These proprietary systems were designed because there were no standards that met their requirements. These legacy systems are creating significant interoperability problems with each other and with newer technologies. The Zigbee Alliance is not pushing a technology; rather it is providing a standardized base set of solutions for sensor and control systems. Zigbee is poised to become the global control/sensor network standard. The physical layer was designed to accommodate the need for a low cost yet allowing for high levels of integration. The use of direct sequence allows the analog circuitry to be very simple and very tolerant towards inexpensive implementations. The media access control (MAC) layer was designed to allow multiple topologies without complexity. The power management operation doesn’t require multiple modes of operation. The MAC allows a reduced functionality device (RFD) that needn’t have flash nor large amounts of ROM or RAM. The MAC was designed to handle large numbers of devices without requiring them to be “parked”. ii T he network layer has been designed to allow the network to spatially grow without requiring high power transmitters. The network layer also can handle large amounts of nodes with relatively low latencies. Zigbee has been designed to provide the following features: Dual PHY (2.4GHz and 868/915 MHz), Data rates of 250 kbps (@2.4 GHz), 40 kbps (@ 915 MHz), and 20 kbps (@868 MHz), Optimized for low duty-cycle applications (<0.1%), CSMA-CA channel access yields high throughput and low latency for low duty cycle devices like sensors and controls, Low power (battery life multi-month to years), Multiple topologies: star, peer-to-peer, mesh, Addressing space of up to: 65,535 devices (16 bit extended address), optional guaranteed time slot for applications requiring low latency, Fully hand-shaked protocol for transfer reliability, Range: 50m typical (5-500m based on environment). This project work involves the design and implementation of PHY base band processor for the Zigbee devices. The project work has been carried out in several stages. It started with the design of the architecture. Then a golden reference design has been done in the MATLAB and SIMULINK. This golden design was simulated in the MATLAB. The results of this simulation such as BER, PER etc. were compared with that given in the standard. Then the RTL design was done in VHDL. This design was then simulated in the Modelsim, synthesized using the Xilinx synthesis Tool (XST), and finally implemented using placing and routing Tool. Implemented design was then downloaded on the FPGA board. Some quantitative results from MATLAB simulation and logical synthesis have been discussed.