802.15.4+system+design+proposa

Customer ELCOTEQ
Project 802.15.4 System Design Proposal
Product Short Range Radio Device Prototype
System Short Range Radio Device Prototype

802.15.4 System Design Proposal

Other documents in this Proposal:
1 Technology Evaluation
2 Device Operation Description
3 Chipcon DK

Table of Contents:
1. Purpose of the Document............................................................................................................ 3
2. Justification. .................................................................................................................................. 4
3. General System information ....................................................................................................... 7
3.1 Project Description .............................................................................................................. 7
3.2 Technology Evaluation ....................................................................................................... 7
3.2.1 Technology Evaluation Description. ........................................................................... 8
3.2.2 Protocol Stack Complexity ........................................................................................... 9
3.2.3 Physical Layer...............................................................................................................11
3.2.4 Other Important Technical Characterstics .................................................................12
3.2.5 Frame Sctructure ..........................................................................................................13
3.2.6 Network Topology ......................................................................................................14
3.3 Device Operation................................................................................................................15
3.3.1 Device Partitioning ......................................................................................................16
3.3.2 Implementation of 802.15.4 Standard, Overview ......................................................18
3.4 Strategy of Design...............................................................................................................27
3.5 Design issues that require further investigation..............................................................43
4. Resources and Project development..........................................................................................44
5. References ....................................................................................................................................47

1. Purpose of the Document
The purposes of this document are next:
1.- Description of how a Device based on Standard 802.15.4 can be
designed and prototyped as a path to introduce Design services of
wireless devices in Elcoteq Monterrey Plant.
2.-References to other technical documents and requirements.

Abbreviations

WPAN Wireless Personal Area Network
IEEE Institute of Electrical and Electronics Eng.
ISM Industrial Scientific Medical Band
OSI Open System Interconnection
HVAC Heat, Ventilating and Air Conditioning

2. Justification.

JUSTIFICATION
In recent years there’s has been an exponential growth in wireless
communications, particularly wireless data networks have led this
growth due to the increasing exchange of data through service like the
World Wide Web, e-mail and data transference, the main characteristic
has been a increasing need of bandwidth, for example, from the Original
(1997) Wireless Local Area Network , IEEE 802.11 Standard which had
a gross rate of 2 Mb/s to nowdays where both 802.15 and 802.11
organizations have begun the definitions of protocols with data
throughputs greater than 100Mb/s
However another potential wireless applications exist, those were very
relaxed troughput requirements are needed and are often measured in a
few bits in a day, because most of these low-rate data applications
involve sensing of one form or another, networks supporting them have
been called Network Sensor Networks or Low-Rate-WPANs. (Based on
the 802.15.4 standard)

MARKET ANALYSIS
Having a moderate approach, It is expected that 802.15.4 (Zigbee)
chipset sales by 2009 exceed $123 million USD,19 million Zigbee chips
delivered alone by the end of 2006; devices enabled by this technology
range from consumer electronics (home networking applications) to
industry (control) and medical applications; very well established
companies like Honeywell, Motorola, Samsung, Philips, ABB, Atmel,
Danfoss, LG, TI, ZMD are already promoting and implementing this
technology, while other start ups like Ember (founded by former
Microsoft executives), Airbee and Millenial Net are well positioned
already. (see www.zigbee.org for more information)
Figures about market share and consolidation of the standard can vary
from source to source, instead, it is more important to numerate
examples where the impact of this technology will be strong, leading this
to broad business opportunities where Elcoteq Monterrey could take
advantage like a specialized Design House of 802.15.4-Enabled devices
as a value added to its current services portfolio given its current
position like EMS and close contact with OEMs with Operations in the
Americas.

Some examples of such applications are:

1)Asset tracking
Asset tracking can take many forms, one example can be the tracking of a
shipping container in a large port, normally there are thousand of
containers, knowing the exact location of all of them can save a lot of time
and resources either to locate one or to know which containers are next
needed.
2)Home Automation and Consumer Electronic
A major application at home is expected to be for personal computer
peripherals, such applications take advantage of low cost and low power
consumption, also another application in the home is sensor-based
information appliances that transparently interact and work symbiotically
together as well as with the home occupants.
3)Industrial Control and Monitoring
Sensors describing the state of a Plant, their displays in a the control room,
the control input devices and the actuators are often relatively inexpensive
when compared with the cost of armored cable that must communicate
between them in a wired installation, significant cost saving can be achieved
if an inexpensive wireless means were available to provide that
communication; i.e a wireless HVAC system can solve the issue of
balancing heating and air conditioning.
4)Health Monitoring
Some examples are by attaching wireless sensors athletic performance
monitoring can be made tracking one’s pulse and respiration and sending
such information to a computer for storage; another application ; a
developing filed in health monitoring is that of implanted medical devices.
6) Environmental Sensing
Large farms and ranches may cover several square miles, as irrigation is
expensive , deploying wireless sensor could help determine the area that
needs irrigation, also if some other sensors can be used, the farmer’s owner
can get graphical view of moisture, temperature, the need of pesticides,
herbicides and fertilizers, received sunshine and some other quantities.
Note: A Business Case should complement this part.

3. General System information
3.1 Project Description
The proposed device to be developed is expected to provide real time
information about a certain process, It should comply with low
throughput, low power consumption and is also expected that such
wireless device be able to auto-setup in a star and mesh topology; these
features are required to be part of the device to allow their
implementation be more cost-effective than that of current wireless and
wired systems.
3.2 Technology Evaluation
To select the right technology on which the development will be based ,
next features are considered when comparing technologies:

1.-Robustness, the device(s) should be able to work where another RF
signals are produced without interference to and from other devices.
2.-Easy to Setup, the device(s) should be easy to setup an easy to
communicate with.
3.-Easy to develop, the proposed development should not be complex
and also it should allow scalability and flexibility at the OSI’s Application
Layer.
4.-It should work on the 2.4Ghz ISM Band; it is intended to avoid usage
of spectrum allocated for cellular bands and at the same time be able to
work within a certain spectrum worldwide.
5.-the development is also required to produce a small Bill of Materials.
6.-It has to be based on a IEEE Standard to allow product
interoperability.

Several wireless technologies were investigated and the final evaluation
between different technologies can be seen in the next table:

Further investigation suggests that range can vary depending on design,
70meters (@ the 802.15.4 Standard) might be optimistic, however due
to the characteristics of 802.15.4, range can be enhanced according to
the 802.15.4 mesh topology intrinsic feature capability.

From the information provided previously the Standard 802.15.4 seems
the right technology on which the proposed development should be
based on.

Note: Cellular technologies were not considered in this evaluation
mainly due to the cost of design; from a budgetary perspective, it is very
different to design a headset/modem than to design a wireless
monitoring device, normally the cost of a mobile design (irrespective of
how high it is) will be covered by the end customer through the services
offered by an operator through its infrastructure (cellular network) ; when
developing a wireless monitoring device, such infrastructure doesn’t
exist , this reduces the cost of development of such device but also the
design becomes more cost-sensitive as the overall cost of design will be
covered by the Design House; in other words, instead of designing for
the maximum possible capacity (cellular device), the design (short range
RF device) must be based on the lowest possible unit cost.

3.2.1 Technology Evaluation Description.

Even though at a first glance Bluetooth(802.15.1) and ZigBee
(802.15.4)seem to be redundant technologies also because both are
suitable for the Consumer Electronics market segment, there are a few
differences that set them a part from each other; each one suitable for
certain need.

Technical features of Zigbee compared to those of Bluetooth are shown
in the next table:

Bluetooth ZigBee
Transmission FHSS DSSS
Scheme
Modulation GFSK QPSK or
BPSK
Frequency 2.4Ghz 2.4Ghz,
Band 915Mhz,
868Mhz

Raw Data Bit 1 MBPS 250
Rate Kbps 40
or 20
Kbps,
dependi
ng on
freq.
band
Power Max. Minimum
Output 100mW, .5mW,
2.5mW maximu
or 1mW m as
dependin allow by
g on local
class regulator
Minimum sensitivity -70 dBm for 0.1% -85dBm (2.4Gh)
BER or -92dBm (915
or 868Mhz)
Network Topology Master- Slave, 8 Star or peer to
active nodes peer, 255 active
nodes.

Zigbee is designed for dynamic environments, where many nodes can
be active at a time, while Bluetooth is more focused on static simple
networks where a few nodes are active at a time.

All previous differences are very much related to the next two main
characteristics that set the real issue when choosing a technology on
which the proposed development should be based on:

3.2.2 Protocol Stack Complexity

The protocol Stack as can be noted below is more complex in a
Bluetooth application and very difficult to program, while in ZigBee the
protocol stack is shorter and simpler to understand and program
(Bluetooth needs 131 service primitives while Zigbee only 26)

Also, the overall protocol stack is 250kb for Bluetooth and only 28kb for
Zigbee.

Applicatio
n Layer
Network
Layer

Data Link
Layer

PHY Layer

ZigBee Bluetooth

Service primitives are capabilities that are offered from one layer to the
next layer or sub-layer in the protocol stack by building its functions in
the next layer’s lower layer; even though primitives’ behavior are already
SDL modeled on the IEEE Std 802.15.14, this document doesn’t cover
“coding” nor implementation techniques, which need to be defined
according to the developer’s needs.

Next figure shows an example how different service primitives interact
in different layers.

3.2.3 Physical Layer

The transmission scheme is directly related to the Physical layer (PHY)
and is here where the real difference lays (between Zigbee and
Bluetooth) as the physical layer is made of ICs and other components.

Spread Spectrum modulation is widely used under the 802.xx.xx
enabled devices as it offers next advantages:
-Reduces co-channel interference (very suitable for the already
congested ISM Band)
-Reduces Multipath interference
-High power transmission are allowed in the unlicensed bands.

The methods for spreading the signal of the Spread Spectrum
transmission are FHSS (Frequency Hopping Spread Spectrum) for
Bluetooth and DSSS (Direct Sequence Spread Spectrum) for Zigbee,
both techniques present advantages and disadvantages.

FHSS is divided into Low-FHSS and High-FHSS; slow hopping is used
when high rate transmission is needed (several bits are sent in one
frequency hopping), frequency synthesizers, which control transmitter’s
and receiver’s frequency oscillator are not able to switch fast enough
amongst different frequencies, Fast hopping occurs when there is
frequency hopping between bits transmitted; the receiver must be able
to detect a transmission and synchronize its synthesizer to that of the
transmitter, once synchronized the IF Frequency is constant and signal
can be demodulated, if a frequency change occurs both receiver and
transmitter must remain synchronized, when hopping and a frequency
is occupied by an interfering signal, bits can be lost, hence redundancy
and error correction techniques must be implemented in the design and
be part of the transmitted packet.

RF AMP MIXER IF
LNA
AMP
DATA DATA
MODULATOR DETECTOR

FREQ. FREQ. CONTROL
CONTROLLER
SYNTHESIZER SYNTHESIZER LER

DSSS uses Pseudo random spreading code to modulate the transmitter
carrier frequency which is then modulated by the data, the bandwidth

is twice the chip rate, enough to keep the signal to noise rate very low at
the receiver, the receiver at the same time uses a copy of the pseudo
random spreading code which is multiplied by the oscillator frequency
and then mixed with the received signal; acquisition and tracking are two
stages related to the technique used to synchronize transmitter and
receiver pseudo random codes and these two stages are design
dependant; once synchronization is achieved, the resulting narrow band
signal has SNR equal to received SNR plus the process gain and it can
be demodulated as any narrow band signal.

Process gain is a property of any spread spectrum technique that
indicates the difference in DB between the output SNR after
unspreading and the input SNR to the receiver.
PG=(SNR)out-(SNR)in

MIXE
IF AMP LNA
DATA R
DATA
MODULATOR
DEMODULATOR
PA

SPREADING CODE MIXER
SPREADING CODE RF OSCILLATOR
ACQUISITION AND
TRACKING

MIXER
RF
RECEIVER
OSCILLAT
OR
TRANSMITTER

To sum up, when using FHSS it is difficult to extend a network due to
synchronization issues and at the same time this synchronization
requires high power consumption; also adding of components as
synthesizers and extra filters for the FHSS technique adds more cost to
design. Bluetooth was designed to be used when power is cycled
(headsets, cellphones, printers, etc). ZigBee nodes only become active
when they are required.

3.2.4 Other Important Technical Characterstics

-Message acknowledgement and an optional beacon structure
-Multi-level security
-Three bands, 27 channels specified
2.4 GHz: 16 channels, 250 kbps
868.3 MHz : 1 channel, 20 kbps
902-928 MHz: 10 channels, 40 kbps

Next characteristics are part of the MAC Layer:

-Channel Access is via Carrier Sense Multiple Access with collision
avoidance and optional time slotting.
-Employs 64-bit IEEE & 16-bit short addresses
-Using local addressing, simple networks of more than 65,000 (2^16)
nodes can be configured, with reduced address overhead

-Three devices are specified
Network Coordinator
Full Function Device (FFD)
Reduced Function Device (RFD)
-Simple frame structure
-Reliable delivery of data
-FFD and RFD Devices Association/disassociation
-AES-128 security
-Optional superframe structure with beacons
-Optional GTS (guaranteed Time Slot) mechanism

3.2.5 Frame Sctructure

Zigbee frame construction is very similar to that of Bluetooth but less
complex, for example, Zigbee’s PSDU (PHY Service Data Unit) is a
maximum of 1016 bits which is enough for monitoring and control
applications; Bluetooth’s packets need an Access Code (72 bits) to
allow synchronization and identification and its PSDU is up to 2745 bits.

PSDU is the frame data payload at the PHY layer received from the
MAC Layer (called MPDU ), next figure shows Zigbee’s Data frame
structure.
Note Zigbee Standard defines three kinds of frames: Beacon Frame,
Data Frame and Acknowledge Frame.

3.2.6 Network Topology .

While Bluetooth works in a Master-Slave topology where 1 Master can
control up to 8 slaves, if more nodes are needed the complexity of the
network synchronization increases, Zigbee can connect up to 255 nodes
and can define as many RFDs and FFDs as needed, Zigbee nodes
allow more flexibility as they can work in star, peer to peer or cluster-tree
topology.

3.3 Device Operation.
It is expected that the device works like an interface between a process
(that is measurable i.e. counting, power consumption measurement or
material tracking ) and a physical interface (radio frequency); this
interface (or device) should basically consist of a transceiver and a
microcontroller and some external circuitry as shown below:

Data and control communication between the transceiver is through a
SPI (Serial Peripheral Interface) Bus, which allows messages exchange
between the 802.15.4 MAC and PHY Layer (contained mainly in the
transceiver); the 8-bit microcontroller needs to be programmed to work
with certain application or profile (@ at the Application Layer) and it also
should contain the interface (i.e. RS232, one or several ADCs, etc) with
the process to be measured; the transceiver is an IC that contains
de/modulator, PA, LNA, Baseband, Freq generator, etc, Power
management circuitry can be in the same IC or separated, this will be
analysed in the DEVICE OPERATION DESCRIPTION.doc document.

3.3.1 Device Partitioning

A generic wireless device can be seen next:

ROM/Non Volatile memory

. RAM

Protocol Application
RF Transceiver Transducer
Handler Processor

. . .
Power Conditioning User Interface
Energy
Scavening *

Power Source

The way this design should be partitioned depends in several factors,
some of the most important are next:

-In terms of memory requirement, it is expected that the device do not
perform complex processing tasks, so only a reasonably small amount
of RAM or ROM should be enough.

-It is intended that the device will not used host (computational)
resources, as it will not be part of any mobile phone or PDA, etc.

-One very important factor is to design to allow market flexibility as much
as possible, but at the same time keep a reduced BOM, this factor is key
not only because it affects price but also because this standard
(802.15.4) is a new standard and at this current moment what will be the
market requirements or killing applications is still unknown.

-As this device will work as RFD (Reduced Function Device) or FFD
(Full Function Device) the processing requirements are different in both
cases, thus the processing function must be in a separate block to be
able to re-use other parts of the design.

-Power consumption will be the real limitation in the design of the
device, if a user interface will be required , normally it requires higher
voltage, also depending on the process to be measured high current

might be needed, additionally if some high speed signals will be involved
in the functioning of the device , normally they involve more power
consumption; thus it would be a good idea to have the power
management block separated just to allow flexibility in the design in
case several power management block designs have to be developed
and its selection depending basically on the application.

A basic possible block diagram of the purposed design would be as
follows:
Antenna

RF Transceiver Protocol Handle Application processor

Data

Power Management

Another factor not shown in the diagram above, but vital is the
transducer interface either like an Integrated Sensor or External
Interface.

One of the Goals of this proposal it to keep the devices as flexible as
possible, having this in mind, integrating a sensor into the transceiver or
in a separate dice but in the same package of the transceiver might not
viable as this would cause a shrinking of the applications where this
device could be useful, even tough such integration could be cost-
effective in terms of a very high mass production if a large market were
already detected; the device we are intended to develop is just a
prototype with high flexibility, so in our case instead of integrating a
sensor, an external interface might be more suitable.

When referring to Flexibility in terms of the proposed Device, two issues
must be considered: the proposed wireless monitoring device should be
able to be interfaced with current and old processes (as analog sensors
and actuators), thus an ADC-DAC Converter should be part of the
Design’s interface, and on the other hand current trends on process
automation and the need of a (digital) universal serial communication

lead us to consider an USB 2.0 interface as well as part of the Design,
such interface is intended to provide the device with a good
transmission speed (ideal for must of the monitoring applications) , also
full universal compatibility with must of the new device (sensors,
actuators, electronic devices, etc..) likely to be monitored and controlled
and also such universal serial interface can be easily converted into
parallel, firewire, etc, if an external adapter is used.

Note: Further investigation on the impact of implementing both
interfaces on the Power Consumption’s Design is advised on a second
stage of this Proposal.

Also further investigation is required on the part of the ongoing
developmet Standard for Smart Transducers :

IEEE P1451.5 * defines a transducer-to-NCAP interface and TEDS for wireless
transducers. Wireless standards such as 802.11 (WiFi), 802.15.1 (Bluetooth),
802.15.4 (ZigBee) are being considered as some of the physical interfaces. *
The proposed standard is being developed. NCAP=Network Capable
Application Processor.

“The IEEE 1451, a family of Smart Transducer Interface Standards, describes
a set of open, common, network-independent communication interfaces for
connecting transducers (sensors or actuators) to microprocessors,
instrumentation systems, and control/field networks. The key feature of these
standards is the definition of a TEDS. The TEDS is a memory device attached
to the transducer, which stores transducer identification, calibration, correction
data, and manufacture-related information. The goal of 1451 is to allow the
access of transducer data through a common set of interfaces whether the
transducers are connected to systems or networks via a wired or wireless
means. The family of IEEE 1451 standards are sponsored by the IEEE
Instrumentation and Measurement Society’s Sensor Technology Technical
Committee chaired by Kang Lee (kang.lee@nist.gov).”

3.3.2 Implementation of 802.15.4 Standard, Overview

The physical layer (RF transceiver functions) can be implemented either
for Band 2.4Ghz or 868/915 Mhz but not both at the same time,
frequencies, modulation and data rates are quite different in both cases,
transmission scheme remains the same (DSSS) as well as all the
embedded software above PHY layer.

Above the PHY Layer is the Data Link Layer that consists of MAC Layer
and LLC Layer; in the proposal we will only covering PHY and MAC
layers as the whole Zigbee Standard implementation basically deals
with the implementation of these two layers, upper layers are related to
specific application and not covered in the present document.

PHY Layer has three main functionalities :

-Provide frame exchange between the PHY and MAC layers.
-To transmit frames through the physical medium by using spread
spectrum modulation.
-Senses activity in the physical medium and gets back to the MAC layer.

PHY contains an entity called PLME (Physical Layer Medium Entity)
which contains the interfaces through which PHY management functions
are invoked.

PHY provides two services : PHY Data services (through PD-SAP) and
PHY Management services (through PLME-SAP).

SAP stands for Service Access Point.
PHY PIB is a database containing all the objects managed by the PHY
layer.

Each service contains primitives, in this case:

PD-SAP primitives:

PLME-SAP primitives:

For example, how the Standard 802.14.5 has intended these primitives
to be implemented is shown next:

In the Standard, there are charts that show messages exchanges for a
given operation, for example, below can be seen the PD-DATA.request
primitive being exchanged between the PHY and MAC layers during
normal a normal data transmission.

The way these primitives are actually implemented (in design) is by
using a Specification a Description Language (SDL).

SDL is an OO language used for system specification, it consists of
blocks, processes, and services , blocks are connected by channels,
blocks can consist of substructures (more blocks inside itself) ,
processes can be executed concurrently triggered either by signals or
procedure calls, state transitions model the behaviour of each process,
services as part of process execute only one at a time.

For example, the way the whole PHY and MAC layer are specified in the
Standard is shown next, this specification shows only the top level, more
specific blocks are also described in the Standard:

This block covers five SAPs, each of them is a channel and each
channel carries primitives.

MAC Layer has the next funcionalities:

-Management of the PHY Layer.
-Provides access to the Physical medium ((here CSMA-CA is
implemented).
-Protects data that will be delivered to the medium (AES-128 security)

MAC Layer provides an interface with LLC, it has an entity called MLME
which includes a database called MAC PIB , and it provides two
services : MAC Common Part Sublayer (MCPS) data SAP and MAC
Management Service (MLME). These two services provide the interface
between LLC and PHY via the PD-SAP and PLME-SAP.

MCPS SAP has the next primitives

MLME SAP primitives are next:

Also the standard defines charts with messages exchange, for example
next figure shows messages when a device wishes to associate with a
coordinator and how this one grants permission to be associated:

As can be noticed, the implementation of such standard requires
knowledge in different areas such, programming at low level, use of
state machines, electronics design, etc, as one of the goals of this
proposal is to come out with a simple design, the next step of this
document is to choose a development methodology than can help
leverage and speed up this proposed development. (please see clause
3.4 of the Zigbee Proposal System).

The whole development should comply with the IEEE 802.15.4
Standard; blocks inside the microcontroller and transceiver depend on
the approach taken for development. SEE Paragraph 3.4

A typical deployment would be made of several devices measuring
processes connected each other (in redundancy) and with some
coordinators (devices with routing capabilities), one of more of them
connected to a PC where data is stored.

Next figure shows an example of a typical application (Material
Handling) at the Floor level:

PLANT 1

Wireless
Counter Wireless
Device
with Device
Display Coordinator
and
numeric RS232
keyboard
Shelf containig rolls of
Shelf containig rolls of inductors @ PL2
10k resistances @ PL1

Counter
with
Display
and
numeric
Shelf containig pipes of keyboard
Shelf containig stack of
BGAs @ PL1
VCOs@ PL2

Counter
with
Display
and
numeric
Shelf containig stack of keyboard
PCBs @ PL1 Shelf containig stack of
PCBs @ PL2

Each wireless device is capable of transmitting/receiving data from one
another device, they make a network in mesh topology, and they can be
moved from one place to another, one of them is fixed as it is connected
to a PC that stores information in real time about the stock available on
the floor.

The counter with display and keyboard ideally (for end cost reduction )
should be plug in enabled, the counter is used by manually input of
number of rolls or stacks of a certain component or material, the
wireless device has capability to update information and transmit it, the
input information on each of these wireless devices is automatically
stored on a PC, also each wireless device should be capable to
determine its position in the network, this feature can be helpful to find
where the material is at a given moment.

Each Wireless device is considered a node, the network, and the
wireless connection between nodes should look like this:

Note: In detail technical description of the Device’s Operation, see

Device Operation
Description.doc
document: DEVICE OPERATION DESCRIPTION.doc

3.4 Strategy of Design

There are several ways to carry out the proposed development:

-Using Wireless Modules.-These are devices already developed, all is
needed is to set them up and connected them, each set of transceivers
(normally 10) with its software, costs around $4000 dlls. Very expensive
if hundreds of these devices need to be deployed, not viable for the
purposes of this Proposal.

-Using System on a chip.- There are some manufacturers that sell the
transceiver and a Development Kit that can consist of an evaluation kit,

software and development guidance; some external circuitry
implementation might be needed, the price depends on the manufacturer
and varies between 6000-16000 US dlls. This is Cost-effective because
once a prototype is tested and built the end cost of the device after mass
production should go down, also if more developments are required the
built prototype could be easily modified.

-Design based on own ASIC devices.- Not viable to be considered
provided that it requires RF development skills already in place, this
option is normally chosen only by big design houses who have the
resources to develop a design from scratch.

As can be noted, the most viable option is to use a system on a chip with
its development kit; it is expected that by choosing a given development
kit, the next requirements are met:

1.-It should be cheap to develop and mass produce.
2.-Develop Current RF design skills at Elcoteq-Monterrey.
3.-Reduce Time to market
4.-Reduce possibilities of expensive mistakes.

Two Software Development Kits (SDK) are known to meet above
requirements, one is based on Freescale’s MC13192 Zigbee Platform
ready solution (see www.freescale.com) and the another one on
Chipcon’s CC2420 Zigbee Development kit (see www.chipcon.com).
Both companies are members of the ZigBee Alliance (www.zigbee.org)
which main objective is to develop and promote this Standard.

At this time no comparison is made between this two SDK because
Freescale documents are not available in its website, however some
differences are that Freescale has a vast amount of microcontrollers
(MCU) to choose and its development platform has been used
worldwide, on the other hand Chipcon’s SDK is based on the
Atmega128L from Atmel but provides full access to CC2420 Zigbee
Development kit documents, including reference designs and code, it is
a very complete solution; hence this option is fully evaluated in this
Proposal.

Chipcon’s solution provides tools to work from the PHY layer to Profile
building which is application-specific.

Hardware included with this solution is next:

Next software components are part of Chipcon’s SDK ,all these
components are used for prototyping:

-ZigBee Stack (z-Stack), it contains source and object code of the full
ZigBee Alliance Stack (see previous protocol stack figure) for the Atmel
AVR microcontroller;
-AVR Studio, this software is used with a software called AVRISP or
JTAG ICE to configure switches, download code and debugging for the
Atmel.
-AVR GCC is used to generate the image running on the Atmel of the
Development Board.
-Wireless Sample applications.
- AVRISP or JTAG ICE is used to debug or download source code using
the Z-Stack (.cof) or (.hex) files this is via the ISP interface.
-Z configurator is a windows program that allows to customize the
applications, mapping of the device as RFD or FFD, routing tables,
selection of profiles.

-Z Profile Builder is a windows application allows to create profiles to be
ported to the Z-Stack
-Z-trace is a windows application used for tracing and debugging, this
software is runs on the development board connected via a rs232.
-Programmer’s notepad used to write code.

3.4.1 C2420 Development Board Description

The CC2420 transceiver is the core of the CC2420 Development Board:

An overview of the transceiver description is shown next:

Pinout Simplified Block Diagram

Transceiver

Microcontroller

The Development Board also contains a Microcontroller, the AVR
Atmega128L from Atmel, This controller has 128 kB of Flash program
memory, 4 kB of SRAM data memory and 4 kB of non-volatile EEPROM
data memory. The controller is interfaced to the CC2420 via its built-in
SPI interface as well as few general-purpose I/O pins.

Another important part of the Development Board is the 32k External
Memory which might be not necessary for a development:

RAM requirements for a ZigBee application are :
• End Device(RFD)s: minimum 1.5 kB
• Coordinator or Router(FFD): minimum 2.5 kB
These numbers are highly dependent on how the end user configures
their solution.

The overall Z-Stack memory requirement will depend upon compiler,
code optimization level, application specific code including application
profiles, microcontroller platform, and additional features, e.g. security.

The complete ZigBee Protocol Stack will have a memory requirement in
the range of 60kB for a ZigBee Coordinator. Additional flash size must
be available for the application. These numbers are preliminary and are
microcontroller dependant; also it should also be considered the ZigBee
stack profiles memory requeriments.

3.4.2 Development Board Functional Description

The CC2420 can be programmed for a given application, through the
programmable configuration registers, the operations to be programmed
are:

-Tx/Rx Modes
-RF Channel Selection
-RF Output Power
-Power up/down mode
-Crystal oscillator Power up/down
-Clear Channel Assessment mode
-Packet handling hardware support
-Encryption / Authentication modes

The CC2420 acts like the slave and it includes an SPI compatible
interface, There are 33 16-bit configuration and status registers, 15
command strobe registers, and two 8-bit registers to access the
separate transmit and receive FIFOs. Each of the 50 registers is
addressed by a 6-bit address; The configuration registers can also be
read by the microcontroller via the same configuration interface.

Command strobes may be viewed as single byte instructions to
CC2420. By addressing a command strobe register internal sequences
will be started. These commands must be used to enable the crystal
oscillator, enable receive mode, start decryption etc.

The internal 368 byte RAM may be accessed through the SPI interface.
Single or multiple bytes may be read or written sending the address part
(2 bytes) only once. The address is then automatically incremented by
the CC2420 hardware for each new byte.

Register access, command strobes, FIFO access and RAM access may
be issued continuously without setting CSn high. E.g. the user may
issue a command strobe, a register write and writing 3 bytes to the
TXFIFO in one operation, as illustrated in the next. The only exception is
that FIFO and RAM access must be terminated by setting CSn high.

SYSTEM SPECIFICATION/PROPOSAL Document code:

Prepared by: Reviewed by: Approved by: Date: Version: Page/pages:
Luis Orozco 15 Sept 2005 1.0 35 of 47

3.4.3 Microcontroller Description

When used in a typical system, CC2420 will interface to a microcontroller. This
microcontroller must be able to:
-Program CC2420 into different modes, read and write buffered data, and read
back status information via the 4-wire SPI-bus configuration interface (SI, SO,
SCLK and CSn).

-Interface to the receive and transmit FIFOs

-Interface to the CCA pin for clear channel assessment.

-Interface to the SFD pin for timing information

A CC2420 to microcontroller interface example is shown :

The microcontroller uses 4 I/O pins for the SPI configuration interface (SI, SO,
SCLK and CSn). SO should be connected to an input at the microcontroller. SI,
SCLK and CSn must be microcontroller outputs. Preferably the microcontroller
should have a hardware SPI interface.

ET_033 Rev. 1



CC2420 Complies with 802.15.4 Data Frame

The Defined 802.15.4Data Frame has the next format:

At the PHY Layer the CC2420 allows full configuration of the Synchronization
Header (SHR) by using registers,

The SHR is made of Preamble Sequence and the SFD. The length of the
preamble can be changed by MDMCTRL0.PREAMBLE_LENGTH, while the
SFD is programmed in the SYNWORD register, next figure shows how this
mapping takes place:

The length field defines the size of MPDU (it includes the MHR, MAC Payload
and the MFR), the length field can be between 7 and 127 bits and always
need to be used for transmission and reception purposes.

ET_033 Rev. 1



RF DATA BUFFERING

CC2420 can be configured for different transmit and receive modes, as set in
the MDMCTRL1.TX_MODE and MDMCTRL1.RX_MODE control bits. Buffered
mode (mode 0) will be used for normal operation of CC2420, while other
modes are available for test purposes.

ACKNOWLEDGE FRAMES
CC2420 includes hardware support for transmitting acknowledge frames, If
MDMCTRL0.AUTOACK is enabled, an acknowledge frame is transmitted for all
incoming frames accepted by the address recognition with the acknowledge
request flag set and a valid CRC

RADIO CONTROL STATE MACHINE

CC2420 has a built-in state machine that is used to switch between different
operation states (modes). The change of state is done either by using
command strobes or by internal events such as SFD detected in receive mode.

Before using the radio in either RX or TX mode, the voltage regulator and
crystal oscillator must be turned on and become stable.

ET_033 Rev. 1



Enabling transmission is done by issuing a STXON or STXONCCA command
strobe; Turning off RF can be accomplished by using one of the SRFOFF or
SXOSCOFF command strobe registers.

After reset the CC2420 is in Power Down mode. All configuration registers can
then be programmed in order to make the chip ready to operate at the correct
frequency and mode. Due to the very fast start-up time, CC2420 can remain in
Power Down until a transmission session is requested.

ET_033 Rev. 1



LINEAR IF AND AGC SETTINGS
CC2420 is based on a linear IF chain where the signal amplification is done in
an analog VGA (variable gain amplifier). The gain of the VGA is digitally
controlled.
The AGC (Automatic Gain Control) loop ensures that the ADC operates inside
its dynamic range by using an analog/digital feedback loop. The AGC
characteristics are set through the AGCCTRL, AGCTST0, AGCTST1 and
AGCTST2 registers. The reset values should be used for all AGC control and
test registers.

RSSI/ ENERGY DETECTION

CC2420 has a built-in RSSI (Received Signal Strength Indicator) giving a digital
value that can be read form the 8 bit, signed 2’s complement RSSI.RSSI_VAL
register.
The RSSI register value RSSI.RSSI_VAL can be referred to the power P at the
RF pins by using the following equations:

P = RSSI_VAL + RSSI_OFFSET [dBm]

Where the RSSI_OFFSET is found empirically during system development
from the front end gain. RSSI_OFFSET is approximately –45. E.g. if reading a
value of –20 from the RSSI register, the RF input power is approximately –65
dBm.

LINK QUALITY INDICATOR
The link quality indication (LQI) measurement is a characterisation of the
strength and/or quality of a received packet, The RSSI value described in the
previous section may be used by the MAC software to produce the LQI value.
The LQI value is required to be limited to the range 0 through 255, with at least
8 unique values. Software is responsible for generating the appropriate scaling
of the LQI value for the given application.

A combination of RSSI and correlation values may also be used to generate
the LQI value; As described previously, in tthe Frame check sequence section
, the average correlation value for the 8 first symbols is appended to each
received frame together with the RSSI and CRC OK/not OK when
MDMCTRL0.AUTOCRC is set. A correlation value of ~110 indicates a
maximum quality frame while a value of ~50 is typically the lowest quality
frames detectable by CC2420.

Software must convert the correlation value to the range 0-255 defined by [1],
e.g. by calculating:

LQI = (CORR – a) · b

ET_033 Rev. 1



Limited to the range 0-255, where a and b are found empirically based on PER
measurements as a function of the correlation value.

CLEAR CHANNEL ASSESSMENT

The clear channel assessment signal is based on the measured RSSI value
and a programmable threshold. The clear channel assessment function is used
to implement the CSMA-CA functionality;

Carrier sense threshold level is programmed by RSSI.CCA_THR. The
threshold value can be programmed in steps of 1 dB. A CCA hysteresis can
also be programmed in the MDMCTRL0.CCA_HYST control bits.

All 3 CCA modes specified by [1] are implemented in CC2420. They are set in
MDMCTRL0.CCA_MODE, as can be seen in the register description. The
different modes are:

0 Reserved
1 Clear channel when received energy is below threshold.
2 Clear channel when not receiving valid IEEE 802.15.4 data.
3 Clear channel when energy is below threshold and not receiving valid IEEE
802.15.4 data

Clear channel assessment is available on the CCA output pin. CCA is active
high, but the polarity may be changed by setting the IOCFG0.CCA_POLARITY
control bit.

Implementing CSMA-CA may easiest be done by using the STXONCCA
command strobe, as described in the Radio control state machine section.

FREQUENCY AND CHANNEL PROGRAMMING

The operating frequency is set by programming the 10 bit frequency word
located in FSCTRL.FREQ[9:0]. The operating frequency FC in MHz is given by:

FC = 2048 + FSCTRL.FREQ[9:0] MHz

In receive mode the actual LO frequency is FC – 2 MHz, since a 2 MHz IF is
used. Direct conversion is used for transmission, so here the LO frequency
equals FC. The 2 MHz IF is automatically set by CC2420, so the frequency
programming is equal for RX and TX.

ET_033 Rev. 1



IEEE 802.15.4 specifies 16 channels within the 2.4 GHz band, numbered 11
through 26. The RF frequency of channel k is given by [1] :

FC = 2405 + 5 (k-11) MHz, k=11, 12, ..., 26

For operation in channel k, the FSCTRL.FREQ register should therefore be set
to:

FSCTRL.FREQ = 357 + 5 (k-11)

THE VCO

The VCO is completely integrated and operates at 4800 – 4966 MHz. The VCO
frequency is divided by 2 to generate frequencies in the desired band (2400-
2483.5 MHz).
THE PLL SELF CALIBRATION

The VCO's characteristics will vary with temperature, changes in supply
voltages, and the desired operating frequency.

In order to ensure reliable operation the VCO’s bias current and tuning range
are automatically calibrated every time the RX mode or TX mode is enabled,
i.e. in the RX_CALIBRATE, TX_CALIBRATE and TX_ACK_CALIBRATE
control states.
OUTPUT POWER TRANSMITTING

The RF output power of the device is programmable and is controlled by the
TXCTRL.PA_LEVEL register. Table 9 shows the output power for different
settings, including the complete programming of the TXCTRL control register.
The typical current consumption is also shown.

ET_033 Rev. 1



VOLTAGE REGULATOR

CC2420 includes a low drop-out voltage regulator. This is used to provide a 1.8
V power supply to the CC2420 power supplies. The voltage regulator should
not be used to provide power to other circuits because of limited power
sourcing capability and noise considerations.
The voltage regulator input pin VREG_IN is connected to the unregulated 2.1 to
3.6 V power supply. The voltage regulator is enabled / disabled using the active
high voltage regulator enable pin VREG_EN.
The regulated 1.8 V voltage output is available on the VREG_OUT pin. The
voltage regulator requires external components.

BATTERY MONITOR

The on-chip battery monitor enables monitoring the unregulated voltage on the
VREG_IN pin. It gives status information on the voltage being above or below a
programmable threshold.

The battery monitor is controlled through the BATTMON control register. The
battery monitor is enabled and disabled using the BATTMON.BATTMON_EN
control bit. The voltage regulator must also be enabled when using the battery
monitor.

CRYSTAL OSCILLATOR

An external clock signal or the internal crystal oscillator can be used as main
frequency reference. The reference frequency must be 16 MHz. Because the
crystal frequency is used as reference for the data rate as well as other internal
signal processing functions, other frequencies cannot be used.

RF INPUT / OUTPUT MATCHING
The RF input / output is differential (RF_N and RF_P). In addition there is
supply switch output pin (TXRX_SWITCH) that must have an external DC path
to RF_N and RF_P.
In RX mode the TXRX_SWITCH pin is at ground and will bias the LNA. In TX
mode the TXRX_SWITCH pin is at supply rail voltage and will properly bias the
internal PA.

The RF output and DC bias can be done using different topologies. Using a
differential antenna, no balun is required. If a single ended output is required
(for a single ended

ET_033 Rev. 1



connector or a single ended antenna), a balun should be used for optimum
performance.

TRANSMITTER TEST MODES

CC2420 can be set into different transmit test modes for performance
evaluation. The test mode descriptions in the following sections requires that
the chip is first reset, the crystal oscillator is enabled using the SXOSCON
command strobe and that the crystal oscillator has stabilised.
An unmodulated carrier may be transmitted by setting MDMCTRL1.TX_MODE
to 2, writing 0x1800 to the DACTST register and issue a STXON command
strobe.

The CC2420 has a built-in test pattern generator that can generate pseudo
random sequence using the CRC generator. This is enabled by setting
MDMCTRL1.TX_MODE to 3 and issue a STXON command strobe. The
modulated spectrum is then available on the RF pins.

NOTE: FOR AN IN-DEPTH DESCRIPTION FOR EACH OF THE SECTIONS,
SYSTEM CONSIDERATION AND FINAL GUIDELINES HERE DESCRIBED
PLEASE REFER TO CHIPCON’S DOCUMENT: CC2420_Data_Sheet_

3.5 Design issues that require further investigation

-This document doesn’t cover RF interference issues, as the proposed
development is intended to work on the 2.4GhZ Band, comprehensive
investigation is required to know the implication of coexistence with other
technologies using the same Band.

-Antenna Design, circuitry needed to implement the antenna must be defined.

-As the proposed device is intended to work on an unlicensed band, power
transmission is not regulated, this implies that power consumption management
can vary a lot depending on the application and the final design, this can cause
not achieving the goals of this proposal, a comprehensive investigation is
required to understand how an optimal power consumption management can be
achieved.

-Investigate what applications profiles are currently available in the market for
802.15.4-enabled devices and see if this could be a limitation for the
development.

-Budget needed for mass production.

ET_033 Rev. 1



4. Resources and Project development.

Pricing
In terms of Budget,
Chipcon offers an Application Development Program (ADP) for $13,995 US
dlls, it includes:
-Training for 1 person.
-6 Months support, plus 25% discount per extra seat for training.
-Chipcon’s CC2420 Evaluation Kit.
-Figure 8’s Z-Tool Development Kit.

Some other hardware and software proposed for validation and debugging are:
Helicomm’s Signal Generator, used for testing PHY and MAC layers of the
802.15.4 standard.
The cost is $10 000 Usdlls

which has the next features:

ET_033 Rev. 1



Furthermore:

There are some 8012.15.4 Test Systems already in the market such as:

R&S Signal Analyzer FSQ3 costs $68 350 US Dlls
FSQ-K70 Firmware for the R&S FSQ3 which costs: $8 520 US Dlls (aprox)

Also it is advisable to be member (under Adopter category) of the ZigBee
Alliance, annual cost is: $ 3500 US Dlls, with the next benefits:

-Access to ZigBee Specifications
-Attend Alliance interop events
-Attend Alliance workshops and developers conferences
-Use Zigbee Alliance Logo.
-Receive Zigbee Alliance marketing.

Total Cost (Aprox): $ 104 365 US. Dlls.

Human resources and Technical expertise.

In Elcoteq, Monterrey Plant we have developed skills in Test Systems
Development (hardware, software and System Integration) for Cellular
technologies, our experience range from programming skills and Diagnostics of
RF circuitry to development of Testing System Proposals i.e. Antennas,
including collaboration with other Elcoteq sites in projects and products
transference as well as other cost saving and potentially profitable projects such
as development of a Calibration House in our site.

Proposed Project Development

The work in this project should be separated in several groups (called working
groups (WG)) and stages,

Stage 0 (system analysis), WG1, Services Definitions group; will be on charge
of technically defining the Device and specifying under which circumstances it
should work, The goal of this Group is to describe how the proposed device is
aimed to work, under which circumstances it is intended to work, and describe
all the different scenarios (per Importance of the industry, i.e. Oil, Automotive,
etc) either like RFD or FFD; also in this group design and testing requirements
are evaluated.

Stage 1 (Design), WG2 (Electronic Design) and WG 3 (Software development)
start working in parallel, their scope at this stage are both hardware and
ET_033 Rev. 1



software implementation of PHY and MAC layers, the roles of both groups are
next:

WG2.-Electronic Design.
This group will work on the electronic design of the device, the hardware itself,
ICs, filters, RF de/modulation, Baseband, state machines, primitives modeling,
power management, clock cycles, this is a key group that needs to know how
to integrate different blocks in the actual Design.

WG3.-Software Development, Integration and Implementation.
This is related to the Firmware, state machines implementation, languages,
routing techniques, objects modeled in other Groups might be implemented
(mainly in C language) by this Group.

Stage 2 (Integration and Prototyping); during this stage WG2 and WG3 will
continue working on the upper next layers and it is expected to have an
integration of both WGs ending with a prototype; WG 4 will start involvement at
this stage.

WG4 will be focused on the commercial interfaces which are used by the
Device to get connected to the “external world” , some popular interfaces are
RS232, Ethernet, but might also needs to cover those interfaces used by Digital
and Analog sensors, amongst other. Also this WG should know very well the
standard 802.15.4 and compatibility with other standards i.e. 802.11x and how
this Standard could evolve and be coupled with other standards, i.e. cellular
standards.

Note:more details about this Start-Up project should be cover in the
Business Case.

Note: Following stages are related to product industrialization, product
life cycle, and commercial issues, these stages will be defined upon
completion of Stage 2.

ET_033 Rev. 1



5. References

-IEEE 802.15.4 Standard
-CC2420 Chipcon Data Sheet
- CC2420Chipcon User Manual
- CC2420Chipcon ZigBee Development Kit User Manual.
-FreesCale ZigBee Brochure
-Short Range Wireless Design, Alan Bensky, Newnes, 2004.
-Wireless Sensor Networks, Callway Jr. Auerbach, 2004,
-2004 ZigBee Alliance Presentation.
-Time, Integrated Method for Systems Design.
-www.wireless-world-research.org , white papers and presentations
-grouper.ieee.org/groups/1451/5 , IEEE Smart Transducers white Paper.,

ET_033 Rev. 1

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