Presented by:Elaheh RahmaniMay 2005

ZigBee/IEEE 802.15.4

Class Presentation of Custom DSP Implementation Course on:ECE Department – University of Tehran

Outline: Introduction to ZigBee Application PHY Layer MAC Layer Comparison between Bluetooth & ZigBee Designing a ZigBee-ready IEEE 802.15.4- compliant radio

transceiver Physical Layer for the Specknet – Design and Implementation Conclusion Refrences

What is ZigBee/IEEE 802.15.4? ZigBee: - Technology that addresses the market needs for cost-

effective ,standards-based wireless network that supports low data rates, low power consumption, security, and reliability, based on IEEE 802.15.4 standard.

IEEE 802.15.4: - The IEEE 802.15.4 standard defines the PHY and MAC

layers, for low-rate wireless personal area networks (LR-WPANs), which are used by Zigbee.

- The IEEE 802.15.4 standard and the ZigBee technology address easy, low-cost deployment of power-friendly and flexible implementations of a virtually unlimited number of wireless low data rate monitoring and control applications.

What is ZigBee/802.15.4 ?

ZigBee Alliance: The Zigbee alliance is responsible for the Zigbee wireless

technology, which defines the network, security, and application layers upon the IEEE 802.15.4 PHY and MAC layers, and also provides interoperability and conformance testing specifications.

Ref. [7]

Why ZigBee?

Reliable and self healing Supports large number of nodes Easy to deploy Very long battery life Secure Low cost Can be used globally

Application:

- industrial monitoring and control

- home automation- sensor networks - personal health care- PC & peripherals- gaming, and automotive

solutions.

The application sphere of this wireless personal area network (WPAN) technology ranges from :

Ref. [2]

ZigBee/IEEE 802.15.4 General Characteristics: 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

ZigBee/IEEE 802.15.4 General Characteristics: Low power (battery life multi-month to years) Multiple topologies: star, peer-to-peer, mesh Addressing space of up to:

- 18,450,000,000,000,000,000 devices (64-bit IEEE and 16-bit short addresses )- 65,535 networks

Range: 50m typical (5-500m based on environment)

IEEE 802.15.4 and ZigBee working model. The IEEE 802.15.4 standard specifies the PHYsical (PHY) and Media Access Control (MAC) layers at the 868 MHz, 915 MHz and 2.4 GHz ISM bands.

Ref. [1]

Physical (PHY) Layer[11]: The 802.15.4 physical layer specifies: - Transmit power of at least .5 milliwatt - Receiver sensitivity of less than or equal to

85 dbm in the 2.4 GHz band - Receiver energy detection (ED) - Link quality indication (LQI) - The air interface is direct sequence spread

spectrum (DSSS) using BPSK for 868 MHz and 915 MHz and O-QPSK for 2.4 GHz.

IEEE 802.15.4 PHY Parameters:

Ref. [10]

Media Access Control (MAC) layer[6]: The 802.15.4 MAC layer envisions two classes of

devices: one is the Full Function Device (FFD), which works with any topology (star, mesh and cluster tree), can function as a network coordinator, and can talk to any other device in the network. The other is the Reduced Function Device (RFD), which is limited to start network topology, can't be a network coordinator.

The access method in IEEE 802.15.4-enabled networks is carrier sense multiple access with collision avoidance (CSMA-CA).

The MAC layer also specifies three security levels including access control lists, data freshness timer and 128-bit encryption.

Topology Models:

Ref. [2]

Bluetooth (IEEE 802.15.1) & ZigBeeIEEE (IEEE 802.15.4) Their similarities and differences[8]: Bluetooth and ZigBee have much in common. ZigBee aims more for grand-scale automation and

remote control. Bluetooth eliminates cabling between electronic

products and accessories, such as between computers and printers.

Both are types of IEEE 802.15 "wireless personal-area networks," or WPANs.

Both run in the 2.4-GHz unlicensed frequency band . Both use small form factors and low power.

Technical differences between Bluetooth and ZigBee [8]:

Modulation techniqueBluetooth: Frequency Hopping Spread Spectrum (FHSS)ZigBee: Direct Sequence Spread Spectrum (DSSS)

Protocol stack sizeBluetooth: 250K bytesZigBee: 28K bytes

BatteryBluetooth: Intended for frequent rechargingZigBee: Not rechargeable (one reason batteries will last for up to 10 years)

Technical differences between Bluetooth and ZigBee [8]:

Maximum network speed:Bluetooth: 1M bit/secZigBee:  250K bit/sec

Network range:Bluetooth: 1 or 100 meters, depending on radio classZigBee: Up to 70 meters

Typical network join timeBluetooth: 3 secondsZigBee: 30 milliseconds

Comparison of Key Features of Complementary Protocol:

Ref. [2]

Designing a ZigBee-ready IEEE 802.15.4- compliant radio transceiver[1]:

An efficient implementation of IEEE 802.15.4-compliant radio-on-a-chip by identifying potential low-power features in the standard, suitable transceiver architectures and considering standard CMOS design issues.

The foremost benefits of CMOS are low cost and single-chip integration capability. CMOS enables the integration of digital baseband processing, RF/analog circuits and system memory in the same physical silicon.

[1] Khanh Tuan Le ,”Designing a ZigBee-ready IEEE 802.15.4- compliant radio transceiver”, Next Generation Wireless,November 2004.

Receiver Architecture : Traditional heterodyne receiver architectures are not optimal solutions for achieving the low-cost, low-power targets of the IEEE 802.15.4 PHY specification.

The zero-IF (also often referred to as direct-conversion) and low-IF receiver architecturesare excellent candidatesfor completely integrated receivers with good performance at low power and small silicon area.

Ref. [1]

Transmitter Architecture : Similar to their heterodyne receiver counterparts, transmitters based on multiple upconversion and filtering stages do not comply with the low-cost and low-power philosophy of the IEEE 802.15.4 standard.

Efficient generation of the transmit signal according to the IEEE 802.15.4 PHY can be achieved by using single-step I/Q upconversion or VCO modulation transmitter topologies.

Ref. [1]

IEEE 802.15.4-compliant and ZigBee-ready CC2420 radio transceiver:

Ref. [1]

Physical Layer for the Specknet – Design and Implementation:(Zigbee chosen as demonstration platform)

Physical Layer Transmitter Design Flow Simulation, Implementation and Testing Conclusions

[4]Luise Crockett, University of Strathclyde, Speckled Computing.

Physical Layer:

Zigbee chosen as demonstration platform Development of prototype

- Gained design experience- Resolved some practical problems

Ultimate Physical Layer design may be simpler than Zigbee

NetworkLayers

Physical LayerDSP

RFSection

[4]Luise Crockett, University of Strathclyde, Speckled Computing.

Context of Physical Layer:

Digital signal processing of data for transmission, and data received

Simple protocol chosen for initial implementation - 802.15.4 (Zigbee)

Zigbee specifies:- Maximum data rate 250kb/s

Physical Layer

Higher Layers

RF transmit / receive

[4]Luise Crockett, University of Strathclyde, Speckled Computing.

Development system aims To design and implement a prototype physical layer on FPGA To interface with RF section To test performance and hardware requirements, and improve and

optimise where possible To aid in creating a channel model for further development To create IP blocks which can be integrated with MAC and network

layers onto a single FPGA

DAC RF DACRF

FPGA FPGA

Air interface

Transmit side Receive side

[4]Luise Crockett, University of Strathclyde, Speckled Computing.

Transmitter detail:

Data rates shown are for Zigbee – may be reduced in proportion

Bit to symbol mapping

Binary data

b3 b2 b1 b0

Symbol to chip mapping

Offset QPSK mapping

Transmit Filter I Phase

Transmit Filter Q Phase

250 kb/s

62.5 kbaud

2 Mchip/s

1 Mchip/s

1 Mchip/s

I phase

Q phase

[4]Luise Crockett, University of Strathclyde, Speckled Computing.

Design Flow:High level simulation

VHDL design entry

Synthesis

Place and Route

Download to FPGA

Test vectors Simulation

RTL Netlist

User Constraints File Reports, Floorplan etc.

Oscilloscope probe

[4]Luise Crockett, University of Strathclyde, Speckled Computing.

Simulation results: Active HDL simulator used to verify output

[4]Luise Crockett, University of Strathclyde, Speckled Computing.

Synthesis: Synplify Pro was used as the synthesis tool A netlist is created from the VHDL source This is the main input to the Place and Route stage It can also be used to visualise the design

[4]Luise Crockett, University of Strathclyde, Speckled Computing.

Implementation: Xilinx ISE was used to

target the Spartan II FPGA on board the Nallatech “Strathnuey” development board- 150,000 gates on User FPGA

A User Constraints File was created - Maps output signals to pins- Applies timing constraints

[4]Luise Crockett, University of Strathclyde, Speckled Computing.

On-board Testing: For testing, a “wrapper” had to be created around the transmitter entity. Included: - Test vectors,

- Formatting of I and Q outputs for DAC- SNDACINF entity to interface with on-board DAC- Mapping of selected outputs to on-board LEDs

[4] Luise Crockett, University of Strathclyde, Speckled Computing.

Conclusion:

ZigBee and the underlying IEEE 802.15.4 standard promise a low-cost, low-power

and reliable wireless network technology for a wide range of control and monitoring applications within the private sphere and industrial environment.

References:

[1] Khanh Tuan Le ,”Designing a ZigBee-ready IEEE 802.15.4- compliant radio transceiver”, Next Generation Wireless,November 2004.

[2] Bob HeileChairman, ZigBee Alliance,”Emerging Standards:Where does ZigBee fit”,Presentation,bheile@ieee.org

[3] ZigBee Alliance Website ,http://www.ZigBee.org [4] Luise Crockett,” Physical Layer for the Specknet –

Design and Implementation”, University of Strathclyde, Speckled Computing

[5] HTML Page.”I've heard a little about ZigBee and IEEE 802.15.4. What's the difference?”, Retired Expert - Robert _Poor.

[6] Larry Leob,(larryleob@prodigy.net. “Roaming charges ZigBee goes to work.htm”,18 Nov 2004,IBM.

References: [7] Ed Callaway,” Low Power Consumption Features of the

IEEE 802.15.4/ZigBee LR-WPAN Standard”, Florida Communication Research Lab, Motorola Labs, ed.callaway@motorola.com

[8] Joanie Wexler,” Bluetooth and ZigBee: Their similarities and differences, ZigBee challenges Bluetooth for mindshare,Network World, 02/28/05.

[9] ZigBee vendor group to wireless-enable facilities monitoring, Network World on Wireless in the Enterprise, 08/25/03.

[10] Bryon Gloden, Murat Senel, and Waseem Sheikh ,”Wireless sensor networks looking to Zigbee Alliance”.

[11] Steve Montgomery,” Wi.232DTS vs. Zigbee Comparing proprietary and standards based solutions”, October, 2004