Speech Recog Report (2)

PART -1

PRELIMINARY INVESTIGATION

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1.1 INTRODUCTION

This report is a System analysis and design project, which is a study of global

positioning system software receiver Technology. In this project we studied how

gps receiver will works and processed the signal get desired location ,time and

position . We start with gps and its various components ,process and receiver

tracking system . Hence, this system makes it possible tracking the location of

things which consists gps receiver. This processes changes the signal to digits..

The process involves many models and theories that makes the gps successful.

Gps is used in large number of areas. For example mobile phone tracking vehicle

tracking system information providing using automated call defence uses, robotics,

etc. It facilitates the human computer interaction and also provides a way to

communicate with satellite communication.

The ultimate goal of the technology is to be able to produce a system that can

recognize with 100% accuracy the time and location . Even after years of research

in this area, the best gps software applications still cannot recognize location with

100% accuracy. Some applications are able to recognize over 95% position when

environment factors are constant.

Computer software that tracks the location of real world objects enable user to

have conversations with the satellite.

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1.2 OBJECTIVE

To study global positioning system receiver and its various hardware

components and software used for this. . In this project our aim is to:

Working of gps receiver

Hardware components of gps

Software used for gps receiver

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1.3 PROBLEM DEFINITION

Software GPS receivers can provide full access to base Band signal processing

inside the receiver channels. Thus It has become the key component when

investigating and Developing advanced GPS signal processing techniques.

In this presentation, a pure software gps receiver, developed in the plan group of

the university of Calgary, It consists of receivers that decode the signals from the

satellites.

The receiver performs following tasks:

Selecting one or more satellites

Acquiring GPS signals

Measuring and tracking

Recovering navigation data

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1.4 WORKING OF GPS

For those who are unfamiliar with the term, GPS stands for Global Positioning

System, and is a way of locating a receiver in three dimensional space anywhere on

the Earth, and even in orbit about it.

GPS is arguably one of the most important inventions of our time, and has so many

different applications that many technologies and ways of working are continually

being improved in order to make the most of it.

To understand exactly why it is so useful and important, we should first look at

how GPS works. More importantly, looking at what technological achievements

have driven the development of this fascinating positioning system.

1.4.1 SIGNALS

In order for GPS to work, a network of satellites was placed into orbit around

planet Earth, each broadcasting a specific signal, much like a normal radio signal.

This signal can be received by a low cost, low technology aerial, even though the

signal is very weak.

Rather than carrying an actual radio or television program, the signals that are

broadcast by the satellites carry data that is passed from the aerial, decoded and

used by to the GPS software.

The information is specific enough that the GPS software can identify the satellite,

it’s location in space, and calculates the time that the signal took to travel from the

satellite to the GPS receiver.

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Using different signals from different satellites, the GPS software is able to

calculate the position of the receiver. The principle is very similar to that which is

used in orienteering – if you can identify three places on your map, take a bearing

to where they are, and draw three lines on the map, then you will find out where

you are on the map.

The lines will intersect, and, depending on the accuracy of the bearings, the

triangle that they form where they intersect will approximate your position, within

a margin of error.

GPS software performs a similar kind of exercise, using the known positions of the

satellites in space, and measuring the time that the signal has taken to travel from

the satellite to Earth.

The result of the “trilateration” (the term used when distances are used instead of

bearings) of at least three satellites, assuming that the clocks are all synchronized

enables the software to calculate, within a margin of error, where the device is

located in terms of its latitude (East-West) and longitude (North-South) and

distance from the center of the Earth.

1.4.2 TIMING & CORRECTION

In a perfect world, the accuracy should be absolute, but there are many different

factors which prevent this. Principally, it is impossible to ensure that the clocks are

all synchronized.

Since the satellites each contain atomic clocks which are extremely accurate, and

certainly accurate with respect to each other, we can assume that most of the

problem lies with the clock inside the GPS unit itself.

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Keeping the cost of the technology down to a minimum is a key part of the success

of any consumer device, and it is simply not possible to fit each GPS unit with an

atomic clock costing tens of thousands of dollars. Luckily, in creating the system,

the designers designed GPS to work whether the receiver’s clock is accurate or not.

There are a few solutions. However the solution that was chosen uses a fourth

satellite to provide a cross check in the trilateration process. Since trilateration

from three signals should pinpoint the location exactly, adding a fourth will move

that location; that is, it will not intersect with the calculated location.

This indicates to the GPS software that there is a discrepancy, and so it performs

an additional calculation to find a value that it can use to adjust all the signals so

that the four lines intersect.

Usually, this is as simple as subtracting a second (for example) from each of the

calculated travel times of the signals. Thus, the GPS software can also update its’

own internal clock; and means that not only do we have an accurate positioning

device, but also an atomic clock in the palm of our hands.

1.4.3 MAPPING

Knowing where the device is in space is one thing, but it is fairly useless

information without something to compare it with. Thus, the mapping part of any

GPS software is very important; it is how GPS works our possible routes, and

allows the user to plan trips in advance.

In fact, it is often the mapping data which elevates the price of the GPS solution; it

must be accurate and updated reasonably frequently. There are, however, several

kinds of map, and each is intended for different users, with different needs.

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Road users, for example, require that their mapping data contains accurate

information about the road network in the region that they will be traveling in, but

will not require detailed information about the lie of the land – they do not really

worry about the height of hills and so forth.

On the other hand, hiking GPS users might wish to have a detailed map of the

terrain, rivers, hills and so forth, and perhaps tracks and trails, but not roads. They

might also like to adorn their map with specific icons of things that they find along

the way and that they wish to keep a record of – not to mention waypoints;

locations to make for on their general route.

Finally, marine users need very specific information relating to the sea bed,

navigable channels, and other pieces of maritime data that enables them to navigate

safely. Of course, the sea itself is reasonably featureless, but underneath quite some

detail is needed to be sure that the boat will not become grounded.

Fishermen also use marine GPS to locate themselves and track the movement of

shoals of fish both in real time, and to predict where they will be the next day. The

advent of GPS fixing has also meant that co-operative fishing has become much

easier, where there are several boats all relaying their locations to each other while

they locate the best fishing waters.

Special kinds of marine GPS known as fish finders also combine several functions

in one to help fishermen. A fish finder comprises GPS and also sonar, along with

advanced tracking functions and storage for various kinds of fishing and maritime

information.

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SYSTEM ANALYSIS OF GPS RECEIVER

Part-11

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2. REQUIREMENTS OF GPS

2.1 HARDWARE COMPONENTS

Antenna

RF Board

RF Front End

RF/IF down-conversion board (with FPGA)

DSP Board

DSP

2.2 SOFTWARE COMPONENTS

Firmware

RF Board FPGA

DSP Board FPGA

S/W

Signal Processing S/W

Navigation S/W

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2.1 HARDWARE COMPONENTS

GPS SIGNAL RECEIVER

2.1.1 ANTENNA

The GPS antenna combines a planar antenna and a frequency converter, which

translates the high-frequency phase-modulated spread spectrum signal of the GPS

system to an intermediate frequency. This way a standard coaxial cable (e.g.

RG58) can be used for the connection with the GPS clock and a distance of up to

300 meters (with RG58) or even 700 meters (with a low-loss cable type like

RG213) between receiver and antenna is possible without additional amplifier.

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Ambient temperature: -40 ... 65°C Warranty: Three-Year Warranty RoHS-

Status of the product: This product is fully RoHS compliant WEEE status of the

product: This product is handled as a B2B category product. In order to secure a

WEEE compliant waste disposal it has to be returned to the manufacturer. Any

transportation expenses for returning this product.

2.1.2 RF BOARD

RF board stands for Radio Frequency Printed Circuit Boards. The frequency

for RF board is normally between 300MHz ~ 3GHz, or much bigger, so normally

FR4 board cannot meet the requirements, so we need to use special material to

achieve the high frequency and we named this kind of boards as RF boards. RF

board is excellent in high frequency performance due to its low dielectric tolerance

and loss of material.

RF board is ideal for applications with higher operating frequency requirements.

Right now, we normally use following material The fabricate process is similar

like FR4, but the copper plating is more complex than FR4, because material

characteristics, it’s much harder to metalize the

through hole (copper plating), and other process is complex than FR4, so need

unique handling method and experienced workers from the computer fans,

squeaking chairs, or heavy breathing. e.g., creative sound cards, intel sound cards,

acer sound card, philips sound cards.

2.1.3 RF FRONT:

In a radio receiver circuit, the RF front end is a generic term for all the circuitry

between the antenna and the first intermediate frequency (IF) stage. It consists of

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all the components in the receiver that process the signal at the original incoming

radio frequency (RF), before it is converted to a lower intermediate frequency (IF).

In microwave and satellite receivers it is often called the low-noise block (LNB) or

low-noise down converter (LND) and is often located at the antenna, so that the

signal from the antenna can be transferred to the rest of the receiver at the more

easily handled intermediate frequency.

For most super-heterodyne architectures, the RF front end consists of:

An impedance matching circuit to match the input impedance of the receiver

with the antenna, so the maximum power is transferred from the antenna;

A 'gentle' band-pass filter (BPF) to reduce input noise and image frequency

response;

An RF amplifier, often called the low-noise amplifier (LNA). Its primary

responsibility is to increase the sensitivity of the receiver by amplifying

weak signals without contaminating them with noise, so they are above the

noise level in succeeding stages. It must have a very low noise figure (NF).

The mixer, which mixes the incoming signal with the signal from a local

oscillator (LO) to convert the signal to the intermediate frequency (IF).

2.1.4 RF/IF DOWN CONVERSION:

The LBC-4000 L-Band IF to 70 MHz IF (140 MHz optional) indoor converter is a

1RU 19-inch chassis with two front panel accessible up converter or down

converter modules. It contains two diode “OR-ed” internal power supplies, for

increased reliability and microprocessor-based Monitor & Control (M&C)

functions. The LBC-4000 up converter module translates a 70 MHz IF input signal

(140 MHz optional) up to a user selected frequency at L-Band (950 to 2000 MHz).

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The L-Band output can drive the input of the Comtech EF Data MBT-4000 block

up converter or other RF equipment with an L-Band input.The LBC-4000 down

converter module translates an L-Band (950 to 2000 MHz) IF input signal down to

a user selected frequency in the 70 MHz (140 MHz optional) IF band. The LBC-

4000 can be locked to an internal reference or an external 5 or 10 MHz reference

signal. The LBC-4000 is an excellent choice forinterfacing legacy 70 or 140 MHz

equipment to quad-band or tri-band block converters.

2.1.5 DSP BOARD:

DSP boards or digital signal processor computer boards are central to the

implementation of high-performance industrial systems. They collect and process

digital data from many sources, and distribute the results to other elements of the

system. There are three main sources of data in a real system: signals (in and out

from the DSP processor), messages to communicate with system controllers, and

messages to communicate with other DSP boards. Important features of DSP

boards include a fast processor and good communication channels as DSP boards

need to collect and distribute data from/to many different sources.

Computer backplane or bus choices for DSP boards include PCI, ISA or EISA,

PCMCIA, PC/104, Mac PCI, SUN Sbus, PMC bus, PXI bus, Multi bus, STD bus,

VME bus, VXI or MXI bus, and DT-connect I and II interface.  PCI is a local bus

system designed for high-end computer systems.  ISA is a standard for I/O buses

that was set back in 1984 when IBM was the standard.  PCMCIA devices (PC

Cards) are credit-card-sized peripherals predominantly used in laptop computers. 

PC/104 gets its name from the desktop personal computers designed by IBM

(PCs), and from the number of pins used to connect the cards together (104).  Mac

PCI is a local bus standard developed by the Intel Corporation.  Designed by Sun

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in 1989, the SBus board was the standard I/O inter-connect for Sun computers,

which typically run under the Solaris or SunOS flavor of the UNIX operating

system.  The PMC Bus is actually a form factor, not a bus -- it is electrically the

same as the PCI Bus, but the shape of the card and the bus connectors are

different.  PXI is a superset of Compact PCI and adds timing and triggering

functions, imposes requirements for documenting environmental tests, and

establishes a standard Windows-based software framework.  STD bus is often

referred to as the "Blue Collar Bus" because of its rugged design and small size,

the STD Bus was originally designed for factory and industrial environments. It

uses 16-bit architecture.  VME bus is a 32-bit bus used in industrial, commercial

and military applications.  Motorola developed the VME standard, with others, in

the late 1970s. DT-connect I and II is Data Translation's DT-Connect Interface. 

Important processor or DSP performance specifications to consider for DSP boards

include number of processors, clock speed, floating point performance, integer

performance, operations, maximum addressable memory, and operating

temperature.  General features and options to consider when looking for DSP

boards include real-time clock, interrupt controller, memory management unit,

dual port memory, and direct memory access.  Communications options include

serial I/O ports, parallel I/O ports, on board A/D converter, and on board D/A

converter.  Some DSP boards can accept daughter boards and some DSP boards

are daughter boards.  An important environmental parameter to consider when

searching for DSP boards is the operating temperature.

2.1.6 DSP

Digital signal processing algorithms typically require a large number of

mathematical operations to be performed quickly and repetitively on a set of data.

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Signals (perhaps from audio or video sensors) are constantly converted from

analog to digital, manipulated digitally, and then converted again to analog form,

as diagrammed below. Many DSP applications have constraints on latency; that is,

for the system to work, the DSP operation must be completed within some fixed

time, and deferred (or batch) processing is not viable A simple digital processing

system

Most general-purpose microprocessors and operating systems can execute DSP

algorithms successfully, but are not suitable for use in portable devices such as

mobile phones and PDAs because of power supply and space constraints. A

specialized digital signal processor, however, will tend to provide a lower-cost

solution, with better performance, lower latency, and no requirements for

specialized cooling or large batteries.

The architecture of a digital signal processor is optimized specifically for digital

signal processing. Most also support some of the features as an applications

processor or microcontroller, since signal processing is rarely the only task of a

system. Some useful features for optimizing DSP algorithms are outlined below.

2.2 SOFTWARE COMPONENTS

2.2.1 FIRMWARE:

Firmware is software that is embedded in hardware. You can update your firmware

in most GPS receivers. Firmware is the software that controls how hardware works

and responds to inputs. It’s called firmware instead of software because users

generally aren’t supposed to play around with it. But you’re not just any old user,

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are you? Almost all electronic hardware contains some form of firmware. A

television remote control contains firmware that controls what signals are sent via

IR depending on what button is pressed. A cell phone contains a lot of firmware

controlling cell access, phone books, security etc

A GPS contains a lot of firmware controlling many of the key functions of the

device

Reception of satellite data

Decoding of positional information

Processing of data

Conversion of data into different formats

Interpretation and display of information

External communication with devices

Storing and managing route/waypoint data

2.2.2 RFPGA:

The FPGA (Field-Programmable Gate Array)implementation of an adaptive filter

for narrow band interference excision in Global Positioning Systems is described.

The algorithm implemented is a delayed LMS(Least Mean Squares) adaptive

algorithm improved by incorporating a leakage factor, rounding and constant

resetting of the filter weights. This was necessary as the original adaptive

algorithm had stability problems : the filter weights did not remain fixed, and

tended to drift until they overflowed, causing the filter response todegrade. Each

model was first tested in Simulink,implemented in VHDL (Verilog Hardware

Description Language) and then downloaded to an FPGA board for final testing.

Experimental measurements of anti-jammargins were obtained Single channel

adaptive filtering techniques have been shown to be an effective technique for

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mitigating multiple narrowband interferences to GPS systems. Since they can

beseamlessly inserted between the existing GPS antenna and receiver. they offer a

cost effective solution that involves minimum system disruption. However to

become a fully practical solution the size and power demands of their hardware

implementation should be minimised. FPGAs (Field-Programmable Gate Arrays)

offer the potential forachieving the goals of small size, weight and power

consumption and in this paper the implementation of an adaptive filter using an

FPGA device is described.In Section 2 an experimental system, termed mini-

GISMO, is described and an overview of the system architecture is presented. The

use of interpolation and decimation filters within the FPGA is also described.The

main adaptive algorithm implemented is the delayed LMS (Least Mean Squares)

adaptive algorithm (Haykin, 2002). As discussed in Section 3 this algorithm is well

suited to FPGA implementations. However, particularlyin the presence of strong

interferences, the originaladaptive algorithm had stability problems, as on

convergence, the filter weights did notremain fixed, and tended to drift until they

overflowed,causing the filter response to degrade. In Section 4 it is shown that

incorporating a leakage term and rounding instead of truncating resulted inthe

weights remaining near the optimal values. However, this solution introduced

memory effects, which produceda second null when the interference frequency was

changed. Resetting the weights every second removed this problem and appeared

to have the least stability effects, as a short pulse in the output every second didn’t

cause any undesirable results in this algorithm. Also, the bit allocations were

optimised to reduce the quantization error. By reducing the quantisation noise

power a smaller leakage factor is required to stabilise the adaptive algorithm

resulting in a slower drift of the weight.

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2.2.3 DIGITAL SIGNAL

Digital signal processing has traditionally been done using enhanced

microprocessors. While the high volume of generic product provides a low cost

solution, the performance falls seriously short for many applications. Until

recently, the only alternatives were to develop custom hardware (typically board

level or ASIC designs), buy expensive fixed function processors (eg. an FFT chip),

or use an array of microprocessor.

Signal processing:

The antenna preamplifier of a GPS receiver generally converts the incoming signal

to a signal of a lower frequency. This INTERMEDIATE FREQUENCY is

obtained by mixing the incoming signal with a pure sinusoidal signal generated by

the local oscillator (the quartz "clock"). The frequency of this BEAT

FREQUENCY is the difference between the original (doppler-shifted) received

carrier frequency and the local oscillator. The intermediate or beat frequency is

then processed by the signal tracking.

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2.2.4 NEVIGATIONAL SIGNAL PROCEESING

Digital signal processing is the processing of digitised discrete time sampled

signals. Processing is done by general-purpose computers or by digital circuits

such as ASICs, field-programmable gate arrays or specialized digital signal

processors (DSP chips). Typical arithmetical operations include fixed-point and

floating-point, real-valued and complex-valued, multiplication and addition. Other

typical operations supported by the hardware are circular buffers and look-up

tables. Examples of algorithms are the Fast Fourier transform (FFT), finite impulse

response (FIR) filter, Infinite impulse response (IIR) filter, and adaptive filters

such as the Wiener and Kalman filters.

Statistical signal processing — analyzing and extracting information from signals

and noise based on their stochastic properties

Audio signal processing — for electrical signals representing sound, such as

speech or music

Speech signal processing — for processing and interpreting spoken words

Image processing — in digital cameras, computers, and various imaging

systems

Video processing — for interpreting moving pictures

Array processing — for processing signals from arrays of sensors

Time-frequency signal processing — for processing non-stationary signals

Filtering — used in many fields to process signals

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2.3 SOFTWARE BASED RECEIVER

Global Navigation Satellite System has become a necessity tool for navigation and

positioning in both civilian and military field and applications. Global Positioning

System (GPS) is a satellite-based navigation system. It is based on the computation

of range from the receiver to multiple satellites by multiplying the time delay that a

GPS signal needs to travel from the satellites to the receiver by velocity of light.

GPS has already been used widely both in civilian and military community for

positioning, navigation, timing and other position related applications. The system

has already proved its reliability, availability and good accuracy for many

applications. Due to this nature, in future, other countries like Europe are going to

launch new satellite-based navigation system called Galileo. There is also a

proposal to launch Quasi Zenith Satellite System for navigation in Japan. It is

necessary to simulate and analyze new signal structures for the development of

new satellite-based navigation systems. In the research community, many

researchers come out with new ideas and algorithms for better accuracy of GPS by

mitigating or minimizing various types of errors and effects like multipath.

However, it is quite difficult to implement the user developed algorithms in the

current hardware-based GPS receivers. The hardware-based GPS receivers contain

ASICs that provide the least user flexibility. Thus, it is necessary to have Software-

based GPS receivers, at least in the research community for easy and quick

implementation, simulation and analysis of algorithms, parameters and threshold

values. Since, the CPU processing power is increasing with reduced cost, it is now

possible to build real-time software-based GPS receivers at least for static or low

dynamic environments. As predicted by Moor’s Law, the CPU power is increasing

and we hope that this trend will continue in future as well and hence, it will be

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possible to develop real-time all environment software-based GPS receivers. In this

paper, we briefly introduce the architecture of a SGR, signal processing technique

and give some examples of simulation using SGR.

2.3.1 SOFTWARE-BASED GPS RECEIVER ARCHITECTURE

The architecture of a conventional GPS receiver is shown in Figure 1. It consists of

RF front-end and signal processor that are all built upon IC chips. The outputs of

the signal processor are either displayed directly on the receiver display unit or fed

to a PC for further processing or integration with other devices. Since, the signal

processing is all done inside the hardware chips, users have limited access to

change the parameters or install new algorithms. Figure 2 shows architecture of a

software-based GPS receiver (SGR). It consists of a RF front-end device, which is

still a hardware component. The rest of the signal processing is done using high

level programming language like C/C++, Matlab etc. If we compare Figure a and

Figure b, the only difference we see is the replacement of hardware components by

software tools for signal processing. We still need RF front-end since the present

capacity of CPU is still not able to process the signal directly from the antenna at

1.5GHz. Figure c shows the merits and demerits of using hardware-based and

software-based receiver. A hardware-based receiver is fastest in signal processing

however, it has the least level of flexibility, where as a software-based receiver has

the highest level of flexibility but is the slowest in processing speed. There are

products using FPGA-based receivers which is the compromise between the two.

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Figure a and b

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2.3.2 GPS SIGNAL PROCESSING

L1 band GPS signal is transmitted at 1.5 Ghz and since the receiver cannot process

the signal directly at this frequency, the RF front-end device down converts from

1.5Ghz to a much lower frequency of about 4Mhz. This frequency is called

Intermediate Frequency (IF). During this conversion process, the signal is also

digitized (A/D conversion) at 1bit, 2bit or higher rate and sampled at some

frequency, e.g. 16Mhz. We use the down-converted signal for further processing.

The first task of signal processing is to identify the visible satellites by finding the

satellite code phase and Doppler frequency. The code phase provides the beginning

of C/A code Since the satellites are moving all the time (and probably the receiver

may also move) wealways have some Doppler frequency. The rough estimation

process of code phase and Doppler frequency is called acquisition. Basically, for

acquisition, we generate C/A code for the satellite and modulate with the carrier

wave. This receiver generated signal is then correlated with incoming signal and

the correlation value is evaluated to make decision whether a satellite visible. If we

think that the satellite is visible, then the code phase value and Doppler frequencies

noted. Once, we complete acquisition successfully, we know the satellites that are

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visible at that time. In the next step, we track the visible satellites continuously for

fine tuning of the code phase and Doppler frequency. This process is called

tracking. The tracking process removes the C/A code and carrier wave from the

GPS signal and hence the remaining signal represents navigation data and some

noise. Thus, from navigation output, we can extract navigation data parameters

which are necessary to compute pseudo range from the receiver to satellite. Figure

(a) shows raw GPS data collected from antenna and down converted to IF. This

data just looks like noise and no information can be known unless we perform

acquisition and tracking on the data. This is due to the fact that the GPS signal

level is below the noise level or the signal is weaker than the noise. Figure (b)

shows the result of acquisition from raw data shown in Figure (a). The acquisition

output shows the code phase(beginning point of C/A code) and Doppler frequency.

Figure (c) shows tracking results. The tracking result extracts navigation data bits

as shown in which are simply the sequence.

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2.3.3 SGR AS RESEARCH AND SIMULATION TOOL

We mentioned earlier that SGR has much flexibility compared to conventional

receiver. We will discuss and give some examples how these flexibilities of SGR

are used to extract information that are otherwise not possible in conventional GPS

receiver.

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some of the fundamental parameters of signal processing in SGR. IF frequency and

sampling frequency are fixed for a particular front-end device. By changing these

two values, we can use the same software tool for different types of frontend

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device that acquire GPS signal from the antenna. Below we will discuss some of

the flexibilities point by point.

2.3.4 WEAK SIGNAL PROCESSING

The Doppler frequency search step, code period acquisition integration time, noise

bandwidth code period tracking integration time depends on the signal

quality. If the signal level is normal, we can use 1000Hz Doppler frequency step

and 1ms code period integration time for acquisition.

However, if the signal is weak, and then we need Figure a: Basic parameters that

can be changed by a user in SGR for various types of signal processing and

simulation to reduce the Doppler frequency search step and increase the code

period integration time in acquisition. For example, if we integrate raw data for

3ms for acquisition then we need to reduce the Doppler frequency search step to

300Hz. This will increase processing speed but help us in detecting weak signals.

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Also, we need to increase the integration time in tracking loop. This type of signal

processing by changing the parameter values is not possible in conventional GPS

receiver. Figure b shows an example for increase in integration time from 1ms to

3ms. When the integration time is 1ms, the correlation peak is not clear enough to

make a decision for satellite visibility. But, when the integration time is increased

to 3ms, we can see a very clear correlation peak and we can make a decision that a

particular satellite is now detected. Figure b (a) Signal acquisition using 1ms

integration time. The result is not so clear with multiple peaks. (b) Signal

acquisition using 3ms integration time with the same data as in (a). Now, the

correlation peak is quite clear and a decision can be made regarding visibility of

satellite.

2.3.5 MULTIPATH MITIGATION TECHNIQUE

In spite of continuing improvements in GPS receivers and antenna technology,

multipath signal has remained a major source of error in GPS positioning. In order

to minimize the error due to multipath, we need to understand the multipath

behaviour and corresponding signal characteristics. In order to understand the

effect of multipath we can analyze the signal by using various types of correlators

(narrow, wide etc) by defining chip delay (listed in Figure a) between early and

late chips. We can compute the correlation peak for every code period. A

correlation peak will appear as a perfect triangle.

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There has been no effect from multipath. Due to multipath, the two sides of the

triangle will be neither symmetrical nor straight lines. The shape and amplitude of

the triangle is deformed by the amount of multipath and some other noise. Thus by

analysing the correlation peak (triangular shape) we can estimate the amount of

multipathand hence develop a technique to minimize or mitigate the multipath. In

this regard, we are conducting research using left hand and right hand circular

polarized GPS antenna to analyze how the reflected signal (which accounts

formultipath) affects a correlation peak.

Figure c shows a correlation peak obtained by processing a raw GPS signal.

Correlation peak computed from raw GPS signal for 0.5 chip delay. The peak

shape is not a perfect triangular due to effect from multipath

2.3.6 REMOTE SENSING USING GPS SIGNAL:

Recently, GPS signals have been used for remote sensing purpose. GPS signals are

transmitted at 1.2Ghz and 1.5Ghz in two different bands. This is similar to

microwave remote sensing. GPS signals are transmitted with right hand circular

polarization. When, this signal is reflected by some object the polarization may

change from right hand to left hand and vice versa. Thus by observing the reflected

signal together with two different types of antennas with right hand and left hand

polarization, we can predict the object type that reflects the GPS signal. Using this

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technique, soil moisture and wind velocity has been estimated. In order to conduct

this type of analysis, we need software-based receiver so that we can process the

received signal with different parameter values using our own algorithms. The

reflected signals are much weaker than direct signal and hence a conventional

receiver cannot be used. Also, we need to compute many intermediate values like

shape of the correlation peak and it s amplitude rather than the position of the GPS

antenna itself. This is possible only in software-based receivers. Besides these

analysis and simulation listed above, we need software-based receiver for

analyzing noise and interference (jamming), simulate new codes, limitation of

navigation data length and many other things. In current GPS signal, the navigation

data length is limited to20ms. This impose a restriction on data integration beyond

20ms during the tracking process. However, for tracking very weak signal, we do

need to integrate longer data period. Thus we need to see what will happen if we

change the navigation data length from 20ms to something else in our new design.

On the other hand we can also have a data less component of the signal in one of

the phases of the signal which is now implemented in new forthcoming GPS

signals. This assists the receiver in processing weak signals and hence make the

receiver capable of indoor positioning. All these can be simulated if we have

software-based receivers. In SGR, we can generate different types of signals for

interference analysis. This will help us how different types of signal with different

level of strength affect GPS signal processing. For example, we can simulate the

effect of a TV signal on GPS or we can analyze the effect of other GNSS signals

on GPS or vice versa.

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2.4 FLOW CHART OF GPS WORKING

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TEST PLATFORM FOR RECIEVER

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2.4 WORKING MODEL OF GPS

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2.6 DATA FLOW DIAGRAM FOR GPS

2.6.1 CONTEXT LEVEL DIAGRAM FOR GPS

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A handheld gps system gets location data from satellites and the final destination

from the user. The system then directs the user to their destination.

2.6.2 LEVEL 1 DFD

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SYSTEM DESIGN ANALYSIS OF GNSS

SOFTWARE

PART -3

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3.1 INTERFACE DESIGN OF GNSS

Spider makes use of Microsoft SQL Database Server Desktop Engine to manage

the Configuration, operational parameters settings of GPS receivers and other

external devices in the stations. Multiple software modules and components in the

system can then access the data from the database simultaneously and this open

architecture allows the user customization and flexibility for

The software interface for generating different types of data file in different

formats Moreover the Spider server and the Microsoft SQL Database run

automatically and continuously as a Windows service, so the software modules and

database can be automatically launched once the computer server is started and the

whole system can run in normal operating condition according to predefined

operational parameters even if Windows is not logged or the Spider software

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interface is closed. In case of a total power failure, the software will restart as the

computer reboots in order to provide full reliability. At the start of the system, the

network operator will define the basic GPS station parameters such as station

name, coordinates, GPS receiver & antenna model, antenna height offset, data rate

of GPS receiver as well as other external sensors, data communication ports,

automatic data polling intervals and the storage path in the computer server. The

Spider server will automatically be linked to each GPS reference station during a

predefined interval (e.g. every 10 minutes, 30 minutes, 1 hour, etc) via different

communication strategies as previously discussed and will download the data files

stored in the memory of GPS reference station receivers. Besides, the Spider server

will then convert the raw data source to produce various data files in different data

rates, data file lengths and data formats such as Leica MDB proprietary format,

RINEX format and GPS Hatanaka compressed format to finally store into different

user assigned locations in the computer server. In case of having GPS reference

station receivers and Spider server connected by PSTN or wireless dial-up

communication, the Spider server can be automatically disconnected the

communication line once the data files are completely downloaded and thus save

the communication costs. Furthermore, if the communication link is not stable and

fails to complete the data downloading, the software will automatically re-

download that missing data files in the next downloading interval.

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In addition, the network operator is able to define a FTP server or a Web server

address, so Spider server will transmit raw data, RINEX files, and other associated

files such as quality checking files and event log files immediately when available

or at specific time intervals to one or multiple FTP or Web servers for an easy

access by the GPS users community. Different files can be pushed to different FTP

servers. The users can share and distribute these data files by the Internet.

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3.2 SYSTEM MANAGEMENT CONSOLE

The console management control of the whole GPS reference station network is

illustrated by the network operator has a full operational status view of each GPS

reference station of the whole network through the system management console

interface. It displays the entire network operation status including connection

status, receiver operation status such as power level and memory status of the GPS

receiver, data logging and real-time data broadcasting status, satellite tracking

status such as the number of tracking satellites on L1 and L2, signal to- noise ratio,

azimuth and elevation angles of each satellite; and external meteorology and tilt

sensor data stat In case of abnormal behaviors happening in GPS

In case of abnormal behaviors happening in GPS reference station such as

communication failure, receiver’s power low, low memory space, data logging

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failure or RTK data output failure, then the color of the corresponding functions

icons will change and error message will be displayed in order to clearly notify the

network operator.

The network operator has a full operational status view of each GPS reference

station of the whole network through the system management console interface. It

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displays the entire network operation status including connection status, receiver

operation status such as power

3.3 INTEGRITY MONITORING AND ERROR REPORTING

MECHANISM

A Spider server produces quality check report file automatically every time it

completes the GPS raw data files downloading and the quality control procedure

checks the completeness and consistency of all data downloaded, monitors the

various communication links and the operation status of the entire system. These

quality check report files can also be automatically forwarded to another server or

a web platform for any operators’ inspection.

In order to be more efficient and faster response in tackling system and data quality

problems, the network operator can define a range of inspection criteria and

tolerance values. The diagram 5 shows the checking criteria and tolerance values

defined as:

− GPS receiver’s related issues:

− Receiver’s power voltage, free memory space and internal temperature

− Receiver start up failure

− Receiver data logging status

− Receiver data downloading status

− Communication link related issues:

− Communication between Spider server and GPS receivers

− Upload / Download status

− FTP data forwarding status

− Event and alarm sending status

− Data quality related issues:

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In some countries, there is also an e-mail’s service to pager forwarding, so this

alarm e-mail message can also be shown on the operators’ pager for immediate

problem solving. Moreover, the network operator can make use of “Command line

processing” advanced feature to launch automatically another application script

which will launch for instance a SMS messaging program. In addition, this

command line processing feature can also be used for performing an integrity

monitoring by running other applications such the Teqc +QC developed by

UNAVCO. The new release of the Leica processing software SKI-Pro can also be

invoked automatically for computing the GPS baselines in a network adjustment.

By this way a comparison can be made immediately against the known values of

the baselines coordinates for a continuously and automatically station stability

checking which is definitively mandatory for such services.

3.4 REMOTE CONTROL & SECURITY

The software is designed in a modern Server / Client architecture and provides a

remote GUI client interface that can be installed on any remote computer.

Therefore, using Internet TCP/IP networks or dial-up connections, the network

operator with this GUI client interface can connect from anywhere to a Spider

server which has a fixed IP address assigned. The network operator can remotely

monitor the entire GPS network performances and also configure and control a

Spider server anywhere in the world which control all connected

As an Administrator, the client logged has full control over the Spider server and

the GPS receivers. He can start and stop the various operations, create and change

the configurations set parameters and modes, etc. This access right is usually only

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granted to network supervisors and operators. However, if the client has only the

Viewer privileges, he can only inspect the system and receiver status but not

control the operation of the software and configuration parameters setting.

3.5 REAL-TIME DATA BROADCASTING:

The software supports both RTK and DGPS data broadcasting on each networked

GPS reference station to be used by RTK and GIS GPS rover users. The real-time

data stream can be broadcasted in various formats such as the compacted Leica

proprietary, RTCM v2.x CMR and CMR+ through different communication

solutions including radio, GSM, ISDN and PSTN network and also Internet. The

real-time data can be either transmitted directly from the GPS reference stations in

the field or it can be routed back and centralized in the Spider server to be re-

distributed to the GPS rover users. Other sophisticated data distribution facilities

such as Access Servers, web application services and charging mechanisms can

complete the solution. A list of common use communication devices including

various brands of radio modems, GSM terminals and fax modems are already

defined in the device interface and the network operator can select the suitable one

and configure two streams of real-time data of any networked reference station in

different formats and output rates via different communication devices

simultaneously. This is a flexible solution to meet different users’ needs and area

coverage. It can also work in time-slicing mode for different real-time data streams

broadcasting of different GPS reference stations in different divided time intervals

by using the same radio frequency channel without signal interference or jamming

problem

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To broadcast any real-time data over the Internet, the data stream from each GPS

reference station needs to be routed to the Spider server and converted and

forwarded to a unique static IP address and port number of a web server which has

a permanent Internet connection. The real-time data stream is continuously

available on Internet. Multiple rover users can connected to this Internet Web

server by using a Pocket PC with a CDMA or GPRS PCMCIA modem, and then

access the real-time data stream from the specific IP address simultaneously.

People can receive real time data corrections from any GPS reference station

located in the world for real-time positioning where the wireless CDMA or GPRS

signals are available without any geographical distance restriction on corrections

transmission. The success of achieving high precision real-time positioning over

long baseline length is however still dependent on the resolving integer ambiguity

algorithms implemented on the GPS rover receivers.

According to the result of a RTK field test done in Beijing PRC in August 2003 by

using the SR530 GPS receiver, which accessed real-time data stream from two

GPS reference stations in Beijing via Internet, the horizontal accuracy for a short

baseline of around 10 km was on the 2 cm level (1 sigma); and for the long

baseline test of around 55 km was on the 4 Comment [M1]

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APPENDIX

HISTORY

The GPS System was created and realized by the

American Department of Defense (DOD) and was

originally based on and run with 24 satellites (21

satellites being required and 3 satellites as replacement).

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Nowadays, about 30 active satellites orbit the earth in a

distance of 20200 km. GPS satellites transmit signals

which enable the exact location of a GPS receiver, if it is

positioned on the surface of the earth, in the earth

atmosphere or in a low orbit. GPS is being used in

aviation, nautical navigation and for the orientation

ashore. Further it is used in land surveying and other

applications where the determination of the exact position

is required. The GPS signal can be used without a fee by

any person in posession of a GPS receiver. The only

prerequisite is an unobstructed view of the satellites (or

rather of the sky).

The correct name of the system is NAVSTAR

(Navigation System for Timing and Ranging), but

commonly it is referred to as GPS (Global Positioning

System).

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APPLICATION OF GPS

Navigation: GPS allows soldiers to find

objectives, even in the dark or in unfamiliar

territory, and to coordinate troop and supply

movement. In the United States armed forces,

commanders use the Commanders Digital

Assistant and lower ranks use the Soldier Digital

Assistan

Target tracking: Various military weapons

systems use GPS to track potential ground and air

targets before flagging them as hostile These

weapon systems pass target coordinates to

precision-guided munitions to allow them to

engage targets accurately. Military aircraft,

particularly in air-to-ground roles, use GPS to find

targets (for example, gun camera video .

Missile and projectile guidance: GPS allows

accurate targeting of various military weapons

including ICBMs, cruise missileprecision-guided

munitions. Artillery project

Rescue: Downed pilots can be located faster if

their position is known.

Reconnaissance: Patrol movement can be

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managed more closely.

GPS satellites carry a set of nuclear detonation

detectors consisting of an optical sensor (Y-

sensor), an X-ray sensor, a dosimeter, and an

electromagnetic pulse (EMP) sensor (W-sensor),

that form a major portion of the United States

Nuclear Detonation.

CONCLUSION

In this project we analysis basic concept that are used in

global positioning system. We performed the analysis gps

receiver using Gnss software . There are following things

that can be concluded from the study:-

Gps receiver can be implement into two ways:

Hardware based software receiver

Software based receiver

Gps receiver used bpsk digital modulation

technique for satellite signal

It uses wass system with two parameters

(corrected gps parameters ionospheric

parameters).

It uses six sec. time to alarm

It uses Inegrity for Montioring performed

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with in avionics in the RAIM.

MMR(mulitimode receiver )receive basic

gps and wass.

Mathematic Model of Low Cost :This

project allows us to differentiate between the

accuracy that can be achieved by Appling

different models.

Gps receiver used different model for

different system.

BIBLIOGRAPHY

1. Principles of digital communication by Taub

and Shilling.

2. Sins integrated system for vehicle tracking by

Cao Fu Xiang, Law

3. GPS Made Easy by Lawrence Letham

4. GPS for Land Surveyors by Jan Van Sickle

5. GPS Navigation Guide by Jack W. Peters

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6. Modeling and simulating GNSS signal structures

and receiver by jon olafur winkel

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