2002

School of E

lectrical Engineering &

Telecom

munications

Phillip King – 2247807 – Supervisor: Aruna Seneviratne

Bluetooth Serial Modem Prototype

ENGINEERING @ UNSW

U N S W

1. Objectives and Product Specification

S c o p eSponsored by Itron Australasia, th is thes is took an unorthodox approach by implement ing the product deve lopment cyc le in the creation of a Bluetooth product , re levant to Automat ic Meter Reading. The pro ject object ives were as fo l lows:

• To des ign, implement and test Bluetooth enab led , modem-l ike devices capable of performing a point -t o -point serial cable emulation.• To do a high level design of the embedded appl icat ion which wi l l implement the emulat ion and permit control v ia AT commands.

R e q u i r e m e n t s D e f i n i t i o n & P r o d u c t S p e c i f i c a t i o n sThe above ob ject i ves were encompassed by the funct iona l and non-functional specif icat ion, which were formulated at the outset to guide the project. Goals def ined during this early stage included:

1 . Target Range : 100m 4. Power supply versati l i ty2. Target throughput: 100kbps 5. Diminut ive s ize (W<33mm)3. Cont ro l v ia AT commands 6. Interoperabil i ty as per the

SPP

2. High level Design

Hardware and so f tware sub -systems were then ident i f ied, and interface signals defined, with design spl it into hardware & software.

H a r d w a r e

Five subsystems were def ined, according to the fo l lowing d iagram.

S o f t w a r eThe software archi tecture consisted of the legacy dialler application, Bluetooth protocol stack & the cable emulation appl icat ion. With the former two implemented as HyperTermina l and

BlueStack respect ively, only the cable emulat ion appl icat ion needed creat ion. The subsystem part i t ions in the system protocol s tack are shown be low:

3. Low Level Design

Al l subsys tems were r igorous ly des igned in PROTEL, w i th some o f t he more comp lex sub -sys t ems based on CSR r e f e r ence des i gns . C lass one and two rad io operat ion was ent i re ly dependent on the radio sub-system, o f which two des igns were created for incrementa l implementation. The Bluetooth sub -s y s t em was based on t he B lueCore02- Ext Bluetooth t ransce iver IC wh ich boasts a 16-Bi t R ISC

processor plus dedicated hardware for a l l Baseband functionality.

So f tware l ow l e ve l des ign was based on numerous CSR examp le des igns which were merged and modi f ied to rea l ise the cable emulat ion . Implementat ion o f AT commands however , was le f t to another team member as i t was outs ide the scope o f th is thes is .

To Bluetooth Modem

Tim

e D

elay

(m

s)M

ean

Thr

ough

put (

Kbp

s)

4. Implementation

A three phase approach was taken to hardware implementat ion , culminating in a long-range, c lass one prototype. The prototypes, shown be low, incorporated var ious Bluetooth modules to implement the radio and Bluetooth subsystems, avo id ing complex i t ies associated with RF design. Addit ional ly, a “Serial Peripheral Interface Blaster”

was constructed, enabl ing the prototypes to be reprogrammed and f i rmware to be al tered through a standard LPT port .

SPI Blaster & prototype 1 Prototype 2 Prototype 3

5. Testing & Performance EvaluationNumerous tests were carr ied out to determine conformance wi th the

specif ication. Metrics quanti f ied included page & inquiry delays, throughput , range, BER and power consumpt ion. Throughput and connect ion delay as a funct ion of d istance ( in meters) are shownbelow:

6. Conclusion & RecommendationsAlthough the cable emulat ion was successfu l and a l l non funct ional

speci f icat ions were met , the exper imenta l range was only 20-25m, with an average throughput o f 55kbps (a l though up to 80kbps was observed) .

The former was due to poor antenna pos i t ion ing of the module on t h e PCB and the fact that the module was only qual i f ied at 15 instead of 20dBm. The former could be improved by repos i t ion ing the module a s

in (a) or implement ing a λ/4 dipole antenna as in (b), using a module wi thout an on board antenna.

L imited throughput was due to the per formance h i t imposed by running the cable emulat ion on the B lueCore ’s R ISC p rocessor , wh ich reduced throughout by up to 40%. This could be improved by exper iment ing with di f ferent l ibraries used by the cable emulat ion or just waiting for

the re lease o f the BlueCore03, which would sure ly feature improved process ing power. F ina l ly , cost & space

sav ings could be achieved wi thout us ing a module , as shown in (c ) .

(a) ( b ) (c)