Synchronization techniques for navigation and ... fine terzo... · C. Palestini –Synchronization...

C. Palestini – Synchronization techniques for navigation and communication systems - 13-1-2010

• Aligning the time scales between two or more processes

• Necessary convention for the aggregation of human behaviors

• Key element for the evolution of human beings

What is Synchronization?

• Necessity of a finer synchronization grown together with the increased possibilities enabled by modern technologies

• Synchronization has strained from a powerful concept to a critical and harmful design issue

But in the last years…

• Iterative approaches and a very strict combining between equalization and synchronization

• Novel aiding paradigms

• Synchronization in every bandwidth and with any possible standard

What about the future of

synchronization?

• From the social perspective, synchronization will come back to be the main aspect for national or international identity

• Future technological innovations will push the limits of globalization, and synchronization will become the effective common point for human collaboration and cooperation

… and the future of the world?



Navigation

GPS and Glonass have been

introduced in 80’s

Growing interest in the last ten

years

Galileo

New modulations adopted

Better performance required

Integration with communication

needed to guarantee new services

and applications

Communication

Two great revolutions in the past

two decades

Spread spectrum CDMA

– UMTS – 3G DS-SS

– DVB-RCS UWB

OFDM

Explosion as a very hot topic in scientific community in 2002

Ubiquitous service is the target

Synchronization is the basic principle for both the systems




Galileo is the European global navigation satellite system

Highly accurate, guaranteed global positioning service under civilian control

Interoperable with GPS and GLONASS (frequency bands, waveforms)

Constellation: 30 satellites (27 operational + 3 active spares), positioned in

three circular Medium Earth Orbit (MEO) planes at 23 222 km altitude above

the Earth

High system reliability is of primary importance

Especially for operation in critical environments, like for

air navigation and SoL services


Binary Offset Carrier (BOC) Modulation

Acquisition

is in charge of exploring the entire code epoch domain (uncertainty region) in order to get a first rough estimate

Tracking

is asked to eventually detect erroneous synchronization events and to refine the estimate to a higher precision

Low complexity receivers Limiting complexity with no performance loss

Professional receivers Extracting information from different signals in different bands

Multipath

Signal distortion

Interference

Aiding Concepts

Assisted GNSS

GNSS/INS Hybridization

P2P Positioning


We have to estimate the code epoch (transmission delay)

The uncertainty region (epoch domain) is discretized into cells or hypotheses

Estimation problem detection problem

Search for the autocorrelation peak

H1: synchronous hypothesis (about the peak)

H0: misaligned hypothesis

0 1-1

Peak =1

Normalized Offset

p

Hypotheses

H1

Hypotheses

H0

Hypotheses

H0

0.5-0.5


BOC (1,1) waveform

Spreading of the input signal with a square wave subcarrier that has a frequency multiple of the code rate

Adopted in order to guarantee interoperabilty with the GPS system

-6 106

-4 106

-2 106

2 106

4 106

6 106

-110

-100

-80

-70

-60

-0.75 -0.5 -0.25 0.25 0.5 0.75

-1

-0.5

0.5

1


BOC autocorrelation function opens two challenges

Code Acquisition

Code Tracking

It decreases rapidly and becomes equal to zero for d=1/3Tc. After this value, a secondary peak is present for d=0.5Tc. This very peculiar shape of RBOC(d) directly reflects on detection performance

-1 -0.5 0.5 1

-0.4

-0.2

0.2

0.4

0.6

0.8

1

H1

Secondary Peak:

the tracking block can

lock onto this outlier peak

Zero Value:

Code Acquisition block

collects only noise


BOCc(15,2.5)

The highest ratio of sub-carrier frequency to code chip rate of any GPS or Galileo signals

Low energy around the carrier frequency

to avoid interference with the other GNSS signals

Two main spectral lobes further away from the carrier

Centered in 15.345MHz

Autocorrelation function (ACF) with a large number of false peaks

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Fractional delay (Normalized to the Chip duration)

Co

rre

lati

on

fu

nc

tio

n

Infinite Bandwidth


Considering

c(t) as the BPSK reference consisting only of the code

s(t) as the BOC waveform with an entire spreading length of ones

It is possible to obtain the 2D correlation for all the possible combination of (ts, tc)

Note that the classical 1D correlation is the one on the diagonal (ts = tc)

Without signal distortion the maximum lies on the diagonal


In the following a Butterworth 6-taps filter with 40MHz bandwidth is considered as an example

Since it is a non-linear

filter: group delay and

phase delay are different


The filtered case shows that a shift of (tΦ,tg) in the space (ts,tc) is obtained

The maximum is outside the diagonal

In this case for a 40MHz Butterworth the maximum of the correlation

function is in the point (4; 5), which is the rounded value of the (tΦ,tg)


-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Fractional delay (Normalized to the Chip duration)

Co

rre

lati

on

fu

nc

tio

n

Infinite Bandwidth

Bw = 120MHz

Bw = 80MHz

Bw = 40MHz

1D correlation function: only the diagonal of the 2D

Increase of the ratio between the first false peak and the correct peak (about 0.9 in the ideal case, about 0.96 using a 40MHz Butterworth 6-taps filter) Rounded effect on the peaks


State-of-the-art algorithms They have been designed for ideal scenarios and they are not robust in the presence of distortion

2D correlation to account for different delays (ts, tc) It shows that in the presence of receiver distortion or multipath the two delay are different

Two delays combining can increase the robustness of the tracking schemes and maintaining the low tracking errors The code delay is noisy but not biased while the subcode delay is less noisy but can be biased in the

presence of distortion

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

0 50 100 150 200 250 300 350 400 450

Iterations

Tim

ing

De

lay

[s

am

ple

s]

Code Delay

SubCode Delay

Rounding

Smoothing

Averaging


Pre-FFT synch The estimation algorithms operate in the time domain

Coarse Timing Estimation (CTE)

Fractional Frequency Estimation (FFE)

The Pre-FFT algorithms are usually Guard Interval (GI) based

they exploit the correlation between the useful symbol part and the cyclic

prefix of the received signal

Post-FFT synch The estimation algorithms operate in the frequency domain

Integer Frequency Estimation (IFE)

Fine Timing Estimation (FTE).

The Post-FFT algorithms are usually based on a data aided estimation on the

pilot tones

Frame acquisition which consists in the detection of the Start of Frame (SoF)


A DVB-T2 based preamble, called P1, has been consideredIntroduction of a preamble needs an entirely different optimization in order to minimize the overhead and to be able to transmit all the necessary parameters with a sufficient protectionThe work presented herein is focused only on the possibility of estimate jointly timing and frequency, leaving to further works these considerations

P1 is composed by an OFDM symbol, called ‘A’, of length 1024 samples, with two frequency shifted guard interval portions added at both sidesThe length in samples is fixed, regardless of the FFT mode and guard-interval configuration


A novel detection scheme has been proposed Two correlations running in parallel, each one searching for maximum similarity with its

respective part of the repetition Multiplication of the two outputs


Fractional carrier frequency offset has to be estimated

In order to preserve the mutual orthogonality amongst subcarriers

Using P1

the angle of the correlation between the received part B and the corresponding portion of received part A, and the angle of the correlation between the received part C and the corresponding portion of received part A can be combined to obtain a fractional frequency estimate

Note that this method is robust against timing misalignment


A comparison with classical Cyclic Prefix approach (Guard Interval Based) has been carried out

taking into account that the CP is 1/8 of the frame length (256 samples)

The proposed approach can overcome the classical Guard Interval Based techniques even for very low SNRs in the Hybrid Channel

P1 Frequency

Estimation

Guard Interval

Based


New acquisition strategies for BOC modulation

Quadribranch detector

Staggered Time and Frequency Search

2D Correlation for High-Order BOC Acquisition and Tracking in the presence of signal distortion

A novel concept of Aided GNSS

Ultra Tight

A synthetic correlation function in order to aid the tracking loops

A joint code acquisition interference mitigation approach for assisted GNSS

Analytical model

Results of acquisition for DVB-RCS+M inserted in Guidelines

Analysis of synchronization aspects in the most important OFDM standards

LTE

WiMAX

DVB-SH

A novel broadcasting paradigm: Single Frequency Satellite Networks


Foreign Fellowship European Space Research and Technology Center (ESTEC) - European Space Agency (ESA)

Division: RF Payloads Systems – Section: Radio Navigation

01/02/2009 – 31/07/2009

Topic: Acquisition and Tracking of Galileo E1-A in the Presence of Signal Distortion

European Reviewers Prof. Carlos Mosquera (University of Vigo)

Dr. Jose Angel Avila Rodriguez (University FAF Munich)

Journal articles:

*1+ C. Palestini, R. Pedone, M. Villanti, G.E. Corazza, “Integrated NAV-COM Systems: Assisted Code Acquisition and Interference Mitigation”, Systems Journal IEEE, Special Issue on “Recent Advances in Global Navigation and Communication Satellite Systems (GNCSS)”, vol.2, no.1, pp.48-61, March 2008.

[2] Pansoo Kim, A. Vanelli-Coralli, M. Villanti, R. Pedone, S. Cioni, M. Neri, C. Palestini, M. Papaleo, Ho-Jin Lee, G.E. Corazza, “Direct Sequence Spectrum Spreading Techniques for Next Generation Mobile Broadband Satellite Services", Wiley International Journal on Satellite Communications, special issue on DVB-RCS+M

[3] F. Bastia, C. Bersani, E.A. Candreva, S. Cioni, G.E. Corazza, M. Neri, C. Palestini, M. Papaleo, S. Rosati and A. Vanelli-Coralli, “LTE Air Interface over Broadband Satellite Networks", Eurasip Journal on Wireless Communications and Networking


Conferences articles:

*4+ G.E. Corazza, C. Palestini, R. Pedone, M. Villanti, “Soft Combining for Improved Sensitivity GNSS Code Acquisition”, Proceedings of Navitec 2006, 11-13 December 2006, ESTEC, Noordwijk, The Netherlands

*5+ G.E. Corazza, C. Palestini, R. Pedone, and M. Villanti, “Robust detectors for code acquisition with BOC modulation for GNSSreceivers”, Proceedings of International Workshop on Satellite and Space Communications 2007 (IWSSC2007), September 12-14, 2007, Salzburg, Austria, pp.299-303

*6+ M. Villanti, C. Palestini, R. Pedone, and G.E. Corazza, “Robust Code Acquisition in the Presence of BOC Modulation for Future Galileo Receivers”, IEEE International Conference on Communications, 24-28 June 2007, Glasgow, Scotland

*7+ C. Palestini, R. Pedone, M. Villanti, and G.E. Corazza, “Code Acquisition with Interference Mitigation for Galileo Receivers”, ION GNSS 2007, 25-28 September 2007, Fort Worth, Texas

*8+ G.E. Corazza, C. Palestini, R. Pedone, and M. Villanti, “Galileo Primary Code Acquisition Based on Multi-hypothesis Secondary Code Ambiguity Elimination”, ION GNSS 2007, 25-28 September 2007, Fort Worth, Texas

[9] A. Vanelli-Coralli, G.E. Corazza, C. Palestini, R. Pedone, M. Villanti, H.J. Lee, P.S. Kim, “Code Acquisition for Next Generation Mobile Broadband Satellite Services”, Proceedings of International Conference on Communications ICC 2008, 19-23 May 2008, Beijing, pages: 1871-1875

*10+ F. Bastia, C. Palestini, R. Pedone, M. Villanti, G.E. Corazza, “Staggered Time and Frequency Search to Aid Frame Synchronization”, Proceedings of International Symposium on Spread Spectrum Techniques and Applications 2008 (ISSSTA 2008), August 2008, Bologna

*11+ C. Palestini, F. Bastia, G.E. Corazza, A. Vanelli Coralli, M. Villanti, R. Pedone, “Time and Frequency Staggered Search for BOC Modulated Ranging Signals”, NAVITEC 2008, December 2008, Noordwijk, The Netherlands

*12+ F. Bastia, C. Palestini, S. Rosati, M. Neri, G.E. Corazza, “Preamble Insertion in Future Satellite-Terrestrial OFDM MobileBroadcasting Standards”, International Communications Satellite Systems Conference (ICSSC) 2009, June 2009, Edimburgh, Scotland

*13+ G.E. Corazza, C. Bersani, C. Palestini, A. Vanelli Coralli, “Single Frequency Satellite Networks: a Novel Approach for Multi-Spot Broadcasting”, International Communications Satellite Systems Conference (ICSSC) 2009, June 2009, Edimburgh, Scotland

*14+ G.E. Corazza, C. Palestini, E.A. Candreva, A. Vanelli Coralli, “The Single Frequency Satellite Network Concept: Multiple Beams for Unified Coverage”, Globecom 2009, December 2009, Honolulu

*15+ F. Bastia, L. Deambrogio, C. Palestini, M. Villanti, R. Pedone, and G.E. Corazza, “Hierarchical Code Acquisition for Dual Band GNSS Receivers”, to be presented in IEEE PLANS 2010

*16+ C. Palestini, L. Deambrogio, F. Bastia, and G.E. Corazza, “An Insider View on The Tracking Loops: a Novel Ultra-Tight GNSS/INS Hybridization Approach”, to be presented in IEEE PLANS 2010

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