RESOLUTIONReconfigurable Systems for Mobile Local Communication and Positioning

RESOLUTION ProjectRESOLUTION ProjectIST - 026851IST - 026851

Assembling of ASIC and FPGAs on BB boardAssembling of ASIC and FPGAs on BB board [D8][D8]

Document Information

Title D8 – Assembling of ASIC and FPGAs on BB board

Workpackage

WP5 – Baseband

Responsible

Due Date Project Month 15 (April 2007)

Type Report

Status Version 1.4

Security Public

Authors D. Doumenis

Project URL http://www.ife.ee.ethz.ch/RESOLUTION/

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Table of contents

TABLE OF CONTENTS .............................................................................................................. 2

1 INTRODUCTION ............................................................................................. 3

1.1 SCOPE.........................................................................................................31.2 METHODOLOGY..............................................................................................32 SYSTEM DEVELOPMENT ................................................................................. 6

2.1 FPGA SELECTION...........................................................................................72.2 DATA CONVERTERS.........................................................................................92.2.1 ANALOG TO DIGITAL CONVERTERS (A/D).............................................................................92.2.2 DIGITAL TO ANALOG CONVERTERS (D/A)...........................................................................152.3 BOOT ROM................................................................................................162.4 EXTERNAL RAM...........................................................................................182.5 INTERFACING WITH WIRELESS LAN...................................................................202.6 INTERFACING WITH THE ANALOG FRONT-END.......................................................223 TEST SETUP ................................................................................................ 25

3.1 THE PROTOTYPING BOARD..............................................................................253.2 THE ANALOG FRONT-END...............................................................................284 BILL OF MATERIALS .......................................... ERROR! BOOKMARK NOT DEFINED.

5 IMPLEMENTATION ....................................................................................... 30

6 CONCLUSIONS ............................................................................................. 32

7 REFERENCES ............................................................................................... 32

8 APPENDIX I: FPGA Schematics ......................................................................................... 33

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1 Introduction

This report elaborates on the baseband hardware details of the RESOLUTION positioning system. Every effort has been made to produce a hardware design which is both, flexible and upgradeable, as well as capable of being integrated into larger systems as the range of applications is very broad. The baseband board will be able to integrate a wide range of FPGAs having the same footprint, from medium sized to very large ones, as well as a number of analog channels for communicating with the antennae. Any type of system will be able to be implemented in this reconfigurable architecture, ranging from simple single antenna cheap PDA implementations to MIMO-type complex systems running on a laptop PC.

1.1 ScopeA number of system architectures were considered before reaching the proposed one where a reconfigurable system will be developed having the resources to interface to single or multi-antennae systems by downloading different VHDL codes on smaller or larger FPGAs which can be assembled on exactly the same Printed Circuit Board (PCB). The system will also have the ability to interface with WLAN subsystems where such infrastructure is not already built-in, as well as a number of A/D and D/A channels for interfacing with the outside world.

1.2 MethodologyThe methodology for producing a reconfigurable baseband board, required the assembly of a prototype system using off-the-shelf modules (e.g. A/D evaluations board, FPGA development board, prototyping area etc) which gave an insight on the requirements of a compact (in size), yet powerful architecture combining analog and digital subsystems, having low power consumption. The range of system applications, call for designs of varying complexity, size, cost and power consumption. As seen in Table 1, the main applications categories (as shown in more detail in Deliverable D2), require a varying degree of system complexity, from low cost, simple PDA-based systems for interactive guiding to more complex customer-specific hardware as in the case of Automated Guided Vehicles (AGVs)

In Deliverable D4 (“Definition of architecture, link budget and specifications for the components”), it was further shown what the possible hardware platforms for the two main applications should be, as shown in Table 2. Based on this information, one could provide two basic system architectures. A simple, low cost solution, interfacing to printed antennae (see Deliverable D3) implemented in a PDA platform for interactive guiding and a more involving and expensive one with interfaces to multiple antennae and a larger FPGA for AGV applications. The AGV solution would have to be implemented in a PC-Card format which can interface directly to a laptop PC, whereas the PDA solutions would have to be substantially smaller, such as a compact flash (CF) or secure digital (SD) card. However, a CF or SD implementation can use a PC-Card adapter to interface to a laptop, whereas the opposite is not possible due to size constraints. Please refer to Fig. 1.1 for an approximate scale model of most necessary components conducted during the preparation of Deliverable D4 and placed in the three possible PCB sizes (PC-Card, CF, SD).

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Application Short description Potential customers Location accuracy/ Range

Data volume Equipment Building type

Number of concurrent users

AGVs Control of automated vehicles Logistics Companies 5cm/<500m Medium (text,photos)

Customer-specific Factory halls <5

Interactive guiding application

Real-time active mapping and guiding for advanced sightseeing

Museums, art galleries, archaeological sites, botanical gardens, zoos, exhibitions, etc.

30cm/<50m Large (text, photographs, video, 3D, etc)

Specialized hand-held device (PDA-like)

Numerous rooms, different room sizes

30–50 (visitors)

Table 1: Main application categories from the marketing report (Deliverable D2)

ApplicationAccuracy

[m]Service

Area [m2]

position update

rate

SystemOperational

modes

Communication Data Transfer

Volume & SpeedEnviron-

ment2D vs

3D

Location-Based information resides with

Dynamic Range

Mobiles battery-

operated?AGV vehicle guidance 0.05 500 x 500 10ms FDD „high“ Indoor 2D mobile unit (m.u.) n/a No

Smart (museum) guiding 0.3 500 x 500~10

seconds TDD, FDD High, MB/s Indoor 2Dfixed infrastructure

(f.i.) 2-50mYes, ~3 hours

Application MarketInterface requirements

mobile unit Design ObjectivesNumber of mobile

units in service areaRatio of

BS/mobilesIndoor Propagation Channel short-

time quasi-static ?AGV vehicle guidance Industry Proprietary / tbd Accuracy, Performance 1-2 > 1 Potentially yes

Smart (museum) guiding Consumer SDIO, CF, PCMCIA Look, size, cost 50-200 << 1 Probably not (people)

Table 2: Some technical requirements of the two main target applications (Deliverable D4)

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Figure 1: Indicative dimensions of main components in PC-Card, Compact Flash and Secure Digital card (1 square mm grid)

A PC-Card implementation would have to be 54mm wide by a minimum of 85.6mm long which is more than enough space to place and route all the necessary components as one can see on the top part of Figure 1. A very powerful FPGA and multi-channel ADCs and DACs could be employed for even the most demanding AGV application employing multi-antenna systems.

Next in size is the Compact Flash type card which has to be 43mm wide by a minimum of 36mm long. The length can be more than 36mm and this is usually the case in PDA cards, where part of the card is protruding from the PDA surface, incorporating connectors, antennae etc. In the case of a TYPE I CF card, the thickness of the card can be up to 3.3mm and for a TYPE II CF card, it can be up to 5mm thick. Both thicknesses provide enough headroom for all the necessary components with a good compromise between small size and flexibility, as a CF card can be connected to a laptop PC-Card slot, through inexpensive adaptors (see Figure 2).

The smallest of the 3 possible implementations is the Secure Digital Input/Output (SDIO) card which must have a width of 24mm and a length of at least 32mm. The red boundary in the bottom right part of Fig.1 shows the actual SDIO card dimensions, whereas the blue boundary indicates the extended length (a minimum of 21mm) that the card must have in order to fit the

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basic components. Another limitation of the SDIO architecture is the maximum thickness of 2.1mm that such a card must have. Such a thickness constraint will force the use of very exotic low-profile FPGA, data converter and memory packages which will increase the cost, or force most of the components to be placed outside the slot (by increasing the “blue” area), making the design much prone to breakages, as the stresses and strains to the connector will increase due to the sheer weight of the components.

Figure 2: Compact Flash to PC-Card adaptor

To avoid having to develop 2 separate systems (AGV and cultural guiding), a single reconfigurable CF system with standard CF interface was envisaged having the necessary infrastructure to implement either of the two scenarios. This approach would allow standard PDA and PC applications to be developed in order to interface with the CF card which will behave to the “outside world” as a simple memory card updating some memory locations containing the distances from the mobile station to each of the basestations. These distances can then be displayed, or use the PDA or PC to perform triangulation and obtain the x,y,z coordinates of the mobile station.

For a comparative description of the sizes and speeds of the three card architectures (Secure Digital, Compact Flash and PC-Card), please refer to Table 3.

SD Compact Flash PCMCIAType I Type II Type I Type II Type III

Length*width 24x32mm2 36.4x42.8 mm2 54x85.6 mm2

Thickness 2.1mm 3.3mm 5.0mm 3.3mm 5.0mm 10,5mmConnector 9 pins 50 pins 68 pins

Transfer Speed <100Mb/s 16 MB/s .. 66 MB/s166 MB/s (Ultra DMA)

16b I/O Transfer: 3.9/7.8MB/s16b Mem Transfer: 10/20MB/s

CardBus (32b bursts): 33/66MB/s I/O Voltages 2,0..3,6 V 3V3 (100mA) or

5V0 (75mA)Table 3: Comparative dimensions and speeds of the 3 interfaces

2 System development

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2.1 FPGA SelectionInitially, a series of time-critical VHDL codes were developed and simulations were run to validate their operation and performance. The main purpose of this exercise was to get a rough estimate for the required gate-count that the FPGA must employ. The main FPGA manufacturers having the lion’s share of the global market are Altera (www.altera.com) and Xilinx (www.xilinx.com). Due to more recent exposure to Xilinx design flows and the availability of inexpensive evaluation boards as well as free (or cheap) software, it was decided that the development should be done using Xilinx tools and hardware. Another advantage of the Xilinx architecture is the fact that it allows dynamic reconfiguration in the field, so that the binary file implementing the FPGA architecture can be altered at runtime, or various different such codes can be stored in the same ROM and selected during operation. From these initial investigations (as detailed in the WP5 annual report), it was shown that an FPGA with at least 500K gates would be adequate for implementing most subsystems excluding the Adaptive Antenna Combining (AAC) algorithms. The more relevant Xilinx FPGA families for implementing such designs are the following:

Spartan-3: Low cost alternative to small ASIC designs with the ability to implement DSP functions. The Spartan-3 family suffers from limited routing capabilities compared to the Virtex families to keep manufacturing costs down.

Virtex-4: Long established high-end family with strong DSP support and some family members offer embedded Power-PC microprocessors or synthesizable soft-core MicroBlaze processors.

Virtex-5: More recent, 65nm technology FPGAs with superior routing and speed improvements.

A good compromise between the two ends would be the Virtex-4 family which offers more routing capabilities (required for a small-sized PCB) without the extreme packages offered by the Virtex-5 propositions. In Figure 3, one can observe the available packages existing for a Virtex-4 LX FPGA. There also exist, the SX and FX families giving a greater choice of application optimised devices.

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Figure 3: Choosing the most flexible Virtex-4 package

Choosing the FF668 Ball Grid Array (BGA) package, one can have the following options without changing footprint (see Table 4):

Table 4: Resources of footprint-compatible devices

Hence, there will be a very wide choice of gate-counts with or without a PowerPC hard core. Soft MicroBlaze processor cores can be implemented using standard logic and about 2000 Logic Cells for each core. The downside of such flexibility is that the FF668 package is physically larger than the SF363 that was originally considered in Figure 1. For a comparison between the two packages, consider the fact that the SF363 is 17mm by 17mm, whereas the FF668 is 27mm

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by 27mm. This is a 2.5 times increase in area, but gives a whole range of different implementable architectures, that the SF363 package cannot match. The SF363 supports devices up to LX25 (24192 Logic Cells) and the FF668 goes all the way up to LX60 (59904 Logic Cells). Hence a 2.5 times increase in area, gives almost 2.5 times more resources for high-end applications. It is like designing a multi-chip system, only with much easier overall routing and communication between the constituent FPGAs.For an overview of how the FPGA pins, divided into banks are connected to the rest of the peripherals, please consult Appendix I.

2.2 Data Converters

2.2.1 Analog to Digital Converters (A/D)

As presented in Deliverable D3 (“Characterisation and Modelling of Radio Channel”), a radio channel exhibiting multipath phenomena exists in the measurement sites. To combat such multipath effects, one can consider multiple antennae with a clever Adaptive Antenna Combining (AAC) algorithm to improve the performance of the system. Hence, the single reconfigurable baseband system must be able to combine inputs from a number of Intermediate Frequency (IF) channels which are being fed by separate antennae. The general idea behind the AAC and the need for multiple A/D channels is shown in Figure 4.

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Figure 4: AAC and the need for multiple A/D channels

Trying to implement a large number of A/Ds in the limited space offered by a compact flash design is a conflicting requirement. It was decided (in the Athens meeting, Dec 8 th

2006 in the premises of RESIT/AIT) to have the infrastructure for interfacing with 6 A/D channels. Such channels should have a resolution of 14-bits (as required by Siemens) and therefore, if such an A/D existed with parallel outputs, it would sport at least

6 X 14 = 84 pins for the digital data alone

Adding ground pins etc, it would be a very large data converter with a lot of interference due to many data lines switching together. Alternatively, more twin or quad A/D converters could be used, taking precious PCB real estate. A more suitable choice would be an octal A/D converter with serial differential outputs for improved noise immunity. Such a converter is the AD9252 from Analog Devices, having 8 channels with 14-bit resolutions and a maximum sampling rate of 50 MSPS. The AD9252, instead of providing separate data buses for each converter, uses serial LVDS outputs where each bit is serially transmitted (signal D) and a sampling clock (DCO) is generated from the converter to sample the data on its rising and falling edges. Another signal (FCO) indicates the start of each new 14-bit word. For a more detailed description of the

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relevant signals, please consult Figure 5 where the A/D sampling clock (CLK) is also shown.

Figure 5: AD9252 serial differential output signals

The mode of operation is as follows. A 14-bit shift register is fed with bits from “D” sampled at the rising and falling edge of “DCO”. At the rising edge of “FCO”, the bits stored within the shift register are unloaded in parallel to a bus Din[13..0] which feeds a 4096 position buffer collecting data for the FFT operation. When 4096 such word are collected (i.e. after 14*4096=57344 edges of the “DCO” signal) the FFT has enough data to perform its operation and then extract the peak location etc. In the meantime, the shift register is collecting the next batch of data and so on. Please note that the “DCO” clock is 14 times higher than the A/D sampling clock. Hence as the A/D input will be a sinewave whose frequency will vary from 500 Hz to almost 5 MHZ, the sampling clock will be of the order of 10 MHz and the DCO clock will be 14x10=140 Mbit. This clock can eventually be the only clock going to the FPGA, as it will be used to format all incoming data into parallel words and batches. From then on, the data can be calculated in batch mode, producing input peak locations (and corresponding distance measures) for every 4096-word batch, producing a theoretical update rate of:

10x10^6/4096=2441 distance measures per second

There will of course be more than one distance measure necessary for triangulation (producing the mobile station’s x,y,z coordinates), so the above update rate will be reduced. It was shown in previous WP5 progress reports, that a minimum of 4 basestation distance measures are necessary for accurate positioning, so the update rate will be reduced by at least a factor of 4, namely 2441/4=610 updates per second peak. This

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reasoning requires the calculation of the distance measure to be completed in less time than it is required for the buffer to fill with the next 4096 14-bit words. Presently, the peak location calculation takes less than 3000 A/D sampling intervals (with a maximum target of 4096), so the measurements can be sustained at the full rate described above. If the required clock cycles to process a 4096 point batch become greater than 4096, then one will have to process only odd-numbered batches, ignoring the even numbered ones, reducing the update rate to half.

In order to simplify the demonstration setup and defer the testing of the serial to parallel data conversion until the card has been manufactured, a similar A/D converter with parallel outputs has been considered. This converter is the AD9248, also from Analog Devices which is a dual 14-bit converter with parallel outputs and maximum sampling rate of 65 MSPS. In Figure 6 one can observe the evaluation boards for the 8-channel AD9252 and the dual channel AD9248. Notice the digital output connector on the right hand side of each board, where the AD9252 has much fewer lines (appropriate for a compact flash sized card) whereas the AD9248 has much more lines (appropriate for system development and debugging).

Figure 6: Boards for 8-ch AD9252 (left) and 2-ch AD9248 (right)

In Figure 7 one can compare the enormous area savings made possible with the utilisation of the AD9252. Both chips have almost the same area, but in order to implement 6 A/D channels using AD9248s, a total of 3 chips would be required, whereas a single AD9252 includes 8 channels. The design of the AD9252 Evaluation Board, gave a lot of insight on the approach that had to be taken when the analog and digital subsystems had to co-exist (signal tracks, ground planes, routing “tricks” etc). However, the code was being continuously developed, so the debugging flexibility of the AD9248 was very beneficial.

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Figure 7: Space savings using the octal AD9252

In Figure 8, the schematic for connecting the AD9252 to the board is shown. Notice the use of “only” six analog channels, out of eight for interfacing with the analog front-end and being able to implement a series of Adaptive Antenna Combining algorithms, using up to six antennae depending on the application.

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Figure 8: AD9252 Schematic

Another important consideration for the optimum operation of the A/D converter is the following. For best signal to noise ratio and interference rejection, the analog input at the ADC has to be 1 or 2 Volts peak to peak (depending on the mode of operation). For best performance, a 2 V ptp input is required giving a resolution of:

2/(2^14)=122 microVolts per LSB

Any input which is less than 2V ptp, would reduce the Effective Number Of Bits (ENOB) accordingly and hence the accuracy of the operations that follow.

Unfortunately, the signal provided by the analog front-end (LNA+MIXER) is only 120mV ptp. Feeding this signal to the converter directly would give less than 10-bits accuracy out of a 14-bit converter. Hence, this signal had to be amplified by a factor of 17 (2/0.120) using a Variable Gain Amplifier (VGA). Performing this amplification for the 6 ADC channels without claiming a lot of board real-estate, was also a difficult task.

The Analog Devices AD8334 (Quad VGA) and its little sibling, the AD8332 (Dual VGA) were originally considered as reliable choices with excellent noise performance and relatively small footprint. After an original design (see Figure 9) using the Analog Devices VGAs, we came across a limitation due to the power supplies needed.

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Figure 9: Voltage Gain Using Variable Gain Amplifier

Please note that the AD8334 and the AD8332, require a single 5V power supply. The Compact Flash specification, states that the CF host can provide either a 3.3V, or a 5V supply, but the CF card must be able to operate in either environment. Recent CF hosts, such as Personal Digital Assistants (PDAs), tend to become 3.3V only devices, in which case, the VGAs would not work. There is always the solution of a DC-DC converter, from 3.3V to 5V, but this would introduce current wastage and noise, in a system with already limited available current to operate. Therefore, a more straightforward, operational amplifier solution was adopted, as shown in Figure 10.

Figure 10: Voltage Gain using Operational Amplifiers

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2.2.2 Digital to Analog Converters (D/A)

The need for implementing a dual channel D/A converter on the baseband card was trigered by the work of RESIT/AIT on Electronically Steerable Passive Antenna Radiator (ESPAR) antennae. The idea behind ESPAR antennae is that one can control the lobe of our antennae electronically and therefore “steer” the antenna towards the required basestation as the mobile station moves. The steering is not physical (i.e. adjusting the azimuth and elevation), but electronic (increasing the sensitivity of the antenna towards some direction). The requirements imposed on the D/A converters were similar to the ones for the A/D converters regarding sampling rate and resolution, but only 2 channels were required. This prompted the selection of the AD9767 from Analog Devices which is a dual 14-bit converter with a maximum sampling rate of 125MSPS. Figure 11 shows the AD9767 footprint.

Figure 11: AD9767 D/A Converter footprint

In Figure 12, one can observe the connection of the two digital channels of the D/A converter, to the “outside world”. Notice that the AD9767, is a current output converter, with a full scale current drive capability of 20 mA. A 50 Ohm resistor and a 10pF capacitor were employed according to the manufacturer’s recommendations for providing a 2 V ptp analog output. An RF transformer such as the Mini-Circuits® T1-1T provides excellent common-mode distortion rejection (i.e. even-order harmonics), as well as noise reduction over a wide frequency range. For proper source termination, in cases where the output of the transformer is connected to the load via a passive reconstruction filter, or cable, an optional resistor is connected across the two current outputs (see also Figure13).

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Figure 12: Connecting the D/A Converter

Figure 13: Optional resistor when the load is directly connecter to the transformer

2.3 Boot ROM

Due to the wide range of FPGAs that the compact flash card will be able to accommodate, the boot ROM size, should be enough to contain code for the largest one, namely the LX60. In Table 5, one can see all the FPGAs that will be compatible with the compact flash PCB (circled in red) as well as the corresponding ROM required to program each one of them. The smallest memory capable of programming the full range

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of devices that the card will support is the XCF32P. This device can support up to 32Mbit files, whereas the LX60 requires an almost 17Mbit configuration file.

Table 5: Boot ROM compatibilities and sizes

The circuit for programming the FPGA using either a standard JTAG port, or the XCF32P ROM is shown in Figure 14 with LED for device programming and operation.

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Figure 14: Programming using JTAG port

A JTAG download cable, such as the Parallel cable IV, can be used to program the boot memory a maximum of 20,000 times without having to remove it from the PCB which gives great flexibility for subsequent standalone operation.

2.4 External RAM

In order to access more memory than the amount already embedded on the FPGA, some external RAM chip was required. This is a static RAM from Samsung and it can be arranged as 512K by 36-bits, or 1M by 18-bits or 2M by 9-bits. In Figure 15, we show the circuit for interfacing with the Samsung K7R160982B QDR-II RAM chip which is 2,097,152 words by 9-bits.

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Figure 15: Interfacing with external RAM

The Samsung RAM chip comes in a space saving 165-ball FBGA package, having dimensions of 13mm by 15mm and a 1mm pitch as shown in more detail in Figure 16. It is evident, that to meet the very stringent requirements with respect to PCB area utilisation, some more non-standard packages had to be found even for RAM chips, which in a larger card could be much bigger in size.

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Figure 16: SRAM package dimensions

2.5 Interfacing with Wireless LAN

A number of different system topologies were proposed as shown in Figure 17. This was due to marketing conclusions and results from the antennas and propagation studies which led to a few changes in the hardware partitioning of the RESOLUTION system. These changes were summarized in the half-year report on page 20 and are reproduced here. The four basic hardware components are the mobile unit for both applications (“A”, an FDD system), the HPLS receiver, or basestation (“B”), the low-cost TDD alternative to “A” for smart guiding applications (“C”), which will be considered later, and the commercially available WLAN access points “D”, to be procured for this project. The proposed compact flash implementation can encompass all these different applications through software updates. The radar will be able to either utilise an external WLAN module for communications, or take advantage of the built-in wireless LAN radio that most modern PDAs and laptops already possess. More details on how this is done are shown in the next paragraphs.

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Figure 17: Interfacing with the Wireless LAN

Depending on whether the mobile station has a built-in WLAN radio or not, a different architecture can be envisaged. Such an open reconfigurable design should call for the integration of a WLAN module with the radar, or the use of the client’s embedded WLAN module if available. Hence, an SDIO slot (see Figure 18) will be incorporated in the compact flash card, where an 802.11 type WLAN system can be connected. As wireless LAN standards evolve at a very rapid pace, it was thought that integrating a WLAN ASIC at the PCB level would not prove future-proof. However, integrating a complete SDIO WLAN module to the system, would allow us to use the most current technology, without committing the end-user to a certain standard (e.g. 802.11g) as newer (e.g. 802.11n etc) are continuously being developed.

Figure 18: Socket for connecting SDIO cards

For a selection of SDIO 802.11 wireless LAN cards available in the market, please see Figure 19. As newer WLAN standards evolve, newer such cards will become available, making the RESOLUTION PCB future-proof. Alternatively, the system will be able to utilise the PDA’s (or laptop’s) built-in WLAN module (if available), through software to

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A C

B D

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exchange content with the WLAN basestation. The general idea is that the FPGA will calculate the distances to each of the basestations and then, depending on the application and cost (cheaper or more expensive FPGA and peripherals), will perform the triangulation to extract the x,y,z coordinates of the mobile station. Alternatively, the triangulation will be done in software (e.g. PDA application) to off-load the FPGA of having to solve systems of linear equations. After having extracted the coordinates, we can request through the WLAN a webpage of the form:

http://x_y_z

where the basestation will recognise the x,y,z coordinates and fetch the required webpage pertaining to these coordinates (e.g. the picture of a museum exhibit at coordinates x,y,z).

Figure 19: A selection of SDIO 802.11 WLAN cards

Integrating the SDIO socket into the PCB design is shown in Figure 20.

Figure 20: Connecting the SDIO socket to the FPGA

2.6 Interfacing with the Analog Front-End

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The FPGA will need to interface with the analog front-end (LNA, mixer etc) through an analog connection feeding the input(s) to the A/Ds, as well as a series of control signals as shown in Figure 21. For this purpose a total of 40 general purpose I/O pins were reserved in the FPGA and are going to be routed to an expansion header.

Figure 21: Control signals to the analog front-end

To make sure that the track lines from the FPGA to the header were as short as possible to facilitate the routing and to have enough pins in both 1.8V and 3.3V levels, it was decided to have the following arrangement:20 I/O pins at 1.8V in BANK720 I/O pins at 3.3V in BANK8Different banks were configured for different voltage levels, making sure that BANK9 and BANK10 are not used to ensure pin compatibility with smaller devices of the same package, such as FX12. The bank layout of the FF668 package is shown in Figure 22.

Figure 22: FPGA bank layout

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For more details on the expansion header pin locations, please consult the corresponding BANK7 and BANK8 schematics, found in APPENDIX I.For the most demanding AGV application, the interconnection between the RESOLUTION RF chip and the FPGA card, will look like that of Figure 23, where the FPGA, through the control lines mentioned earlier, will configure the RF chip.

Figure 23: Frontend Architecture for AGV mobile stations

The architecture for smart guiding applications may be the same as that for AGVs if a CF interface is available on a PDA that lacks WLAN connectivity and radiolocation capabilities.

If a CF interface is available and the PDA does already host WLAN connectivity, the radar hardware is that of Figure 23.

For systems with SDIO only, or when power constraints are severe, radiolocation will be done with the power-saving active reflector according to Figure 24.

+ Amp

Pulse

Δ

Figure 24: Frontend architecture for smart guiding mobile stations

The equivalent radiolocation hardware for mobile stations is shown in Figure 25.One can easily observe that the scalability, reconfigurability and abundance of FPGA to analog control lines in the PCB design, allow for the implementation of all the above layouts in the same hardware.

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Figure 25: Radiolocation hardware for fixed receiver units

3 Test Setup

In order to have a working real-time prototype, even with limited functionality, a testbench had to be created using some of the modules presented so far. These off-the-shelf modules, with some modifications and tuning, would be connected to a prototyping board for real-time algorithm testing and optimisation.

3.1 The Prototyping BoardThe prototyping board used to interface all the necessary components is the Flite ETS-7000 Analogue and Digital Lab shown in Figure 26. It contains a number of useful features in a space-saving implementation. These features include:

(1) +5V power supply at 1A

(2) -5V power supply at 300mA

(3) Variable 0V to 15V and 0V to -15V power supplies at 500mA each

(4) Eight toggle switches

(5) Two debounced push-buttons

(6) Eight LEDs

(7) Two seven-segment displays (with Binary Coded Decimal inputs)

(8) Speaker

(9) Large Breadboard prototyping area

(10) Function generator from 1Hz to 100kHz producing sine, triangular and square wave outputs

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Figure 26: Prototyping board with its main features

After having developed part of the time-critical algorithm subsystems in VHDL, it was time to test their functionality as a complete system with live data from the A/D converter. The interested reader can refer to the WorkPackage 5, 4th Quarterly Report (WP5Q4) for a description of the underlying algorithms. In a nutshell, one is performing an FFT type operation on an input sinewave (coming through the A/D) and by accurately detecting the frequency of the sinewave (using interpolations etc), can convert that frequency into distance between the transmitter (basestation) and the receiver (mobile station).The quadratic interpolation used for obtaining a better estimate of the FFT peak location, requires a multi-bit division operation as explained in WP5Q4. The accuracy of this division can be controlled by the user (using VHDL generics) and at the moment is 70-bits long with a 60-bit integer part and a 10-bit fractional part. The integer part will be identical to the location detected from the FFT peak detector (e.g. FFT frequency bin), whereas the fractional part will provide a correction on the actual frequency (and hence distance to the basestation) giving the actual position between two adjacent bins. So as the FFT alone can detect peaks between integer frequency bins (e.g. from 55 to 56), the interpolation with its 10 bit fractional part can produce accuracy of 0.5^10=0.000976. Hence, there is a much greater resolution in displaying peaks in between two integer bins.

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Using the two seven-segment displays (eight bits) for the integer part and the eight LEDs for the fractional part, one can display the peak location detected in real time as the frequency of the input sinewave to the A/D is varied from the function generator. Therefore, very small changes in the input frequency will at least alter some of the fractional bits giving rise to a very accurate frequency detection. The preliminary real-time setup for testing the VHDL code (detecting sinewaves using FFT and improving on the estimate using quadratic interpolation) is shown in Figure 27. In this setup, one can see the A/D converter, FPGA board, prototyping board, JTAG download cable etc.

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Figure 27: Real-time prototype

The prototyping board, provides all the power lines to the A/D converter card (mainly 3V) as well as the sampling clock (shown in the top-left part of the white prototyping area). A variable frequency sinewave from the proto-board is fed to the analog input of the A/D and its digital output bits are fed through a flat cable to the FPGA board. The FPGA board, runs the VHDL code accurately detecting the position (frequency) of the sinewave (through FFT, peak extraction and quadratic interpolation) and then through another flat cable goes to the top of the proto-board where it is subsequently routed to the seven-segment displays and LEDs. Hence as the sinewave frequency is being swept, the seven-segment (coarse) and LEDs (fine) readings are updated.

3.2 The Analog Front-end To interface with a number of analog channels and provide adaptive antenna combining with the FPGA evaluation board, a system whose general operating principle is shown in Figure28 was designed. This frontend board operates with an external 5.8GHz synthesizer and provides four digitized IF signals to the FPGA. Beam steering will be possible in RX direction only. Combining and phase shifting of the four signals will be done in the digital domain by the FPGA.

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14-bitADCIF-amp

LNA

PA

14-bitADCIF-amp

LNA

PA

14-bitADCIF-amp

LNA

PA

14-bitADCIF-amp

LNA

PA

14-bitADCIF-amp

LNA

PA

14-bitADCIF-amp

LNA

PA

14-bitADCIF-amp

LNA

PA

14-bitADCIF-amp

LNA

PA

FPGA

Virtex 4Eval board

Antennaport

Multichannel frontend board

VCO board

Figure 28: 4-channel frontend board principle

Special care was taken regarding the number of available I/O pins of the Virtex-4 ML401/2/3 evaluation board. A VCO board (comprising a Direct Digital Synthesizer and a PLL) is developed in parallel. This VCO board will also be controlled by the FPGA and feeds a 5.8 GHz CW, FMCW or FSK signal into the LO ports of the multichannel board. By control of the RF switch, the FPGA has the possibility to select between TX and RX mode. The board schematic is shown in Figure 29.

Figure 29: Multi-channel frontend board schematicRESOLUTION 5/6/2023

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In Figure 30 the PCB board layout is shown with the four antenna ports, the LO port and the sockets to the FPGA board. The auxiliary socket pins are connected to unused FPGA I/Os.

AntennaPort 1

AntennaPort 2

AntennaPort 3

AntennaPort 4

LO/VCO inPort

Sockets to Virtex4 board

Auxilary socket

Connector to VCO-board

AntennaPort 1

AntennaPort 2

AntennaPort 3

AntennaPort 4

LO/VCO inPort

Sockets to Virtex4 board

Auxilary socket

Connector to VCO-board

Figure 30: Multichannel board PCB

4 ImplementationInstead of developing two lines of hardware, one for PDAs (e.g. museums, hospitals etc) and one for laptops (e.g. AGVs), it was thought that a single reconfigurable hardware platform could fit both scenarios. The same compact flash card with a smaller FPGA could fit the PDA applications, while the same card with a bigger FPGA in the same package could be used in a laptop, using a PC-Card adaptor as discussed in Figure 2.

Putting all the board subsystems together, namely A/D converter, FPGA, compact flash, RAM, ROM, D/A converter and SD looks something like Figure 31. One can notice the 6 analog connectors feeding the A/D converter, the 2 analog outputs from the D/A converter, as well as most connections between the card’s subsystems.

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Figure 31: Top-level hierarchical schematic

For a more analytic description of the FPGA pinout, the interested reader can refer to APPENDIX I where all the FPGA banks and their peripheral connections are shown.

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5 Conclusions

This report outlined the design of a printed circuit board, able to accommodate 6 analog input channels and 2 analog output channels. It can be configured as anything from a cheap and simple standard compact flash PDA card, utilising the power of the mobile station’s user interface, up to a full blown (and more expensive) platform for operation in a laptop. The integration of a WLAN radio can be done either in software, using a built-in module or by interfacing to a WLAN SD card available in the market to make the whole approach more future-proof. Interfacing with a four-channel analog frontend was also carried out. The whole design was based in prototyping the VHDL code using off-the-shelf components to assess the system complexity and pinout requirements. The scalability of the design ensures that even if additional functionality is required in the future, it can be met by employing a larger compatible FPGA.

6 References[1] RESOLUTION Project, Deliverable D2[2] RESOLUTION Project, Deliverable D3[3] RESOLUTION Project, Deliverable D4[4] Xilinx Virtex-4 User Guide (http://direct.xilinx.com/bvdocs/userguides/ug070.pdf)

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7 APPENDIX I: FPGA Schematics

Figure 32: RAM, D/A and SD connections

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Figure 33: CF, A/D connections and 1.8V expansion header

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Figure 34: JTAG, grounds and power pins

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Figure 35: 3.3V expansion header

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