Joint Data-Pilot Acquisition and Tracking of Galileo E 1 Open Service Signal

Bashir Ahmed Siddiqui, Jie Zhang, Mohammad Zahidul H. Bhuiyan and Elena Simona Lohan

Department of Communication Engineering Tampere University of Technology

Tampere, Finland Emails:{bashir.siddiqui.jie.zhang.mohammadbhuiyan.elena-simonalohan}@tut.fi

Abstract- Global Navigation Satellite Systems (GNSSs), such as

the modernized Global Positioning System (GPS) and the ongoing European satellite navigation system Galileo, incorporate the new composite GNSS signals (e.g., Galileo EI Open Service (OS) signal), which consist of two different

components, the data and pilot channels. The existence of dual channel allows one to adopt special techniques to acquire and track these new signals. In this paper, the authors analyze the performance of three different implementation strategies, namely, i. Data-only, ii. Pilot-only, and iii. Joint Data-Pilot, for two different receiver modes: one with Sine Binary Offset Carrier (1,1) (SinBOC(I,I)) reference receiver, and the other one with Composite BOC (CBOC) reference receiver. All the simulations have been carried out in TUT Galileo EI open source

signal simulator, based on the most recent Galileo Signal-In­Space Interface Control Document (SIS-ICD). The simulation results show that acquisition with individual channel is not the best approach to acquire the signal as intuitively expected. Joint Data-Pilot channel combines all the significant power from data and pilot channels non-coherently that ultimately improves the signal detection around 2.8 dB, which has been verified via simulations in the context of the paper. Joint Data-Pilot channel

also provides around 3 dB improvement over any individual channel in terms of tracking error variance. It will also be shown

in the paper that the performance deterioration caused by using Sine BOC(I,l) reference receiver instead of CBOC reference receiver is negligible. Most of the findings based on data-pilot combination are as intuitively expected. However, the main novelty of the paper stays in presenting a realistic and detailed Simulink-based simulator for Galileo El signal that takes into

account two receiver modes, and has already been made open access for research purpose.

Keywords- acquisition, Composite Binary Offset Carrier, Simulink, tracking

I. INTRODUCTION

On July 26, 2007, the United States (US) and the European Commission (EC) announced their decision to jointly implement a new modulation, namely Multiplexed Binary Offset Carrier (MBOC), on the Galileo Open Service (OS) signal and the GPS block III Ll C signal (1]. The power spectral density of this new modulation is a mixture of BOC(I,I) and BOC(6,1) spectra, which can be generated by

978-1-4244-7879-8/101$26.00 ©2010 IEEE

a number of different time waveforms that allows flexibility in implementation. The Time-Multiplexed BOC (TMBOC) implementation, chosen for GPS Ll C signal interlaces BOC(6,1) and BOC(I,I) spreading symbols in a regular pattern; whereas Composite BOC (CBOC) implementation, chosen for Galileo El signal uses multilevel spreading symbols formed from the weighted sum (or difference) of BOC(I,I) and BOC(6,1) spreading symbols. The CBOC( +) modulation is employed for the data channel (or ElB), while CBOC(-) is used for the pilot channel (or EIC) [ 2]. More details about CBOC modulations can be found in [ 3, 4].

The Galileo E 1 OS signal consists of two different components, the data and pilot channels. The existence of dual channel allows one to adopt special techniques to acquire and track El signal. One such technique would be to acquire the composite signal ignoring the data channel and processing only the pilot channel, or vice versa. This will eventually mean that only half of the useful power is employed and the GNSS receiver could not be able to acquire and track the signal that would be easily processed if the whole useful power were used. In other words, a joint data-pilot combining allows recovering all the available power, thus improving the acquisition performance as well as providing more reliable signal detection [5].

In this paper, the authors analyze the performance of three different implementation strategies, namely, i. Data-only, ii. Pilot-only, and iii. Joint Data-Pilot, for two different receiver modes: one with Sine Binary Offset Carrier (1,1) (SinBOC(I,I» reference receiver, and the other one with Composite BOC (CBOC) reference receiver. The motivation for having two receiver types can be stated by the fact that CBOC signal can be processed both by a CBOC receiver and by a SinBOC(I,I) receiver The processing with Sine BOC(I, 1) component is possible because CBOC consists of a superposition of two Sine BOC waveforms: a SinBOC(I,I) component and a SinBOC( 6,1) component. This paper analyzes how much deterioration occurs when we process a CBOC signal with a SinBOC(1,l) receiver (instead of processing it with a CBOC receiver) for different bandwidth requirements (i.e., varying from narrowband to wideband). The performance is analyzed both in the acquisition

Acquisition

Oull -------. IX " 101 (lull 101

n channel

Front-end

Transmitter �� .. " Operator

Data Store

Read : Trackin9-Ena I I Tracking_Ena I I EsCfreq I I Est_code_delay I

Data Store Data Store Data Store

Memory Memory 1 Memory 2

Fig. 1: TUT Galileo E 1 signal simulator (upper level block diagram)

and tracking stages in terms of detection probability and tracking error variance, respectively, for different Carrier-to­Noise-density-ratios (CINo) in different receiver bandwidth requ irem ents.

The rest of this paper is organized as follows. Section II provides a detail overview of the TUT Galileo E 1 signal simulator. Simulation results in acquisition and tracking stages are presented in Section III and Section IV, respectively. Finally, some general conclusions are drawn in Section V based on the research fmdings.

II. TUT GALILEO E 1 SIGNAL SIMULATOR

The TUT Galileo E 1 signal simulator has been developed in Simulink-based platform at Tampere University of Technology (TUT), Finland. The Simulink model used to generate the simulation results is shown in Fig. 1. The Simulink model, as presented here, consists of five parts:

A. A transmitter block, B. A multi path channel in Additive White Gaussian

Noise (A WGN), C. Front-end filter, D. An acquisition block, and E. A tracking unit (which incorporates a Frequency

Locked Loop (FLL), a Phase Locked Loop (PLL) and a Delay Locked Loop (DLL)).

A. Transmitter The Galileo El transmitter block is implemented according

to the most recent Galileo Signal-In-Space Interface Control Document (SIS-ICD) [ 2]. E 1 B and E 1 C channels are modeled according to the following equation [ 2]:

1 SEI(/) = r,;-(eEIB(/)(ascEIBa(t)+ PSCE1Bb(t)) -

�2 . .

eE1C (/)(a SCE1Co (I) - P SCE1Cb (I))) (1)

� tracking_en

Incsig

Trackmg UOII

where sex (I) = sgn(sin(2n Rs,xt)) , eElB(I) and eElC(t) are binary

signal components and a and f3 represent weighting factors.

Above, Rs,x is the sub-carrier rate corresponding to channel X

(i.e., either E 1 B or E 1 C). As explained in [ 2], a = � and

f3 = Jm; Fig. 2 shows the snapshot of the E 1 transmitter block. The

code length for the Galileo as signal is 4092 chips, which is four times higher than the GPS C/ A code length of 1023 chips. The code epoch length is 4 milliseconds (ms). The block utilizes the frame data with frame duration of 1 ms, in order to speed up the simulation. In each frame, Is * 10'3 samples are included, where Is is the sampling rate. The sampling frequency Is is a variable of the model (results reported in this paper were obtained with Is = 1 0 MHz in case of 4 MHz double-sided bandwidth at/IF = 2.5 MHz; andls = 34 MHz in case of 16 MHz double-sided bandwidth at/IF = 8.5 MHz).

E1CSe�ndaryCode Zer()-Ordlr Kold

Fig. 2: Galileo E 1 transmitter block

Elb+Elc OS signal

B. Channel In the channel block, the multipath signals and the

complex Additive White Gaussian Noise (A WGN) are generated. The basic function of the channel block can be modeled according to the following equation:

I

rEI (t) = L ai (t)s EJt - ,, ) + ry(t) (2) i=l

Here rEI (t) is the received E 1 signal at the output of the

channel block; ai and'i are the path gain and path delay for

the i-th path, respectively, and 1/(1) is the complex A WGN. Fig. 3 depicts the block diagram of the channel used in this model.

Channel

Multipath Channel

Fig. 3: The channel block

C. Front-end Filter

Out 1 100001(1 Itipathsignal

AWGNgeneratlon

Simulations have been carried out for two different cases: i. Narrow front-end filter with 4 MHz double-sided bandwidth (suitable for mass-market receivers), and ii. Wide front-end filter with 16 MHz double-sided bandwidth (suitable for high­end receivers). In the first occasion, we have a Chebyshev type I filter with a 3-dB double-sided bandwidth 4 MHz and filter order 6; while in the later occasion, we have a Chebyshev type I filter with a 3-dB double-sided bandwidth 16 MHz and filter order 4. Simulink's 'Digital Filter Design' toolbox is used to design the filter with specified parameters.

D. Acquisition

The acquisition block utilizes an FFT-based acquisition technique. The Fourier transform of the down-converted input signal is multiplied with the Fourier transform of the conjugate of the reference code. The result of the multiplication is then transformed into time domain by taking inverse Fourier transform. The absolute value of the output of the inverse Fourier transform represents the correlation between the input signal and the reference code. Fig. 4 shows the block diagram of a 'Joint Data-Pilot' acquisition block implemented in Matlab-based S-function. In the simulations, the acquisition block is continuously running and generates output after each 4 ms, which are stored in memory for later use to compute the final statistics.

The acquisition detection is implemented according to the Constant False Alarm Rate (CF AR) algorithm as described in [ 7]. With CF AR algorithm, the decision is made based on the correlation output. For example, the average of the absolute of E 1 B and E 1 C correlation outputs is used in case of 'Joint Data-Pilot' implementation, whereas only EIB or EIC

correlation output is used for 'Data-only' or 'Pilot-only' implementation. The decision variable for signal detection is computed according to the ratio of peaks [ 7]. While determining the second maximum peak, we set zero to a neighborhood of -3 to +3 chips in time axis and -664 to +664 Hz in frequency axis around the first maximum peak, as explained in [ 7]. The detection threshold is currently set to 1.3, which offers a good tradeoff between detection and false alarm probability.

�Xll ",

Level-2 '-I-file

S-Function

Fig. 4: Acquisition block for non-coherent 'Joint Data-Pilot' acquisition

The coherent integration used to run the simulations is 4 ms (or one code epoch). The frequency uncertainty range is from -5 kHz to +5 kHz with a step of 166 Hz, which follows the rule of thumb: fre�bin_step_size ::; 2/(3Tcoh) Hz, as mentioned in [ 8], where Tcoh is coherent integration time. The time uncertainty range is equal to the code epoch length (i.e., 4092 chips) with time-bin step equals to 1 sample (i.e., 0.1023 chips) in case of 4 MHz double-sided bandwidth, and 4 samples (i.e., 0.1204 chips) in case of 16 MHz double-sided bandwidth. We remark that two reference receivers, namely SinBOC( 1,1) and CBOC, are used in the acquisition block at the receiver side.

E. Tracking

The tracking Unit consists of three major blocks: 'Carrier Wipe-Off' block, 'Code NCO' block, and 'Dual Channel Correlation and Discriminators' block, as shown in Fig. 5. The incoming signal is down converted to the baseband in the 'Carrier Wipe-Off' block. The carrier wipe-off is performed according to the following equation:

_ () -)(2")+4» rEI BB(t) - rEI t e (3)

where j is the frequency with some initial frequency error

( j = IfF + M , where !!f <= 125 Hz, and ffF is the fmal

Intermediate Frequency (IF)); (jJ is the estimated phase from

the PLL or FLL. After the carrier wipe-off, the real part and the imaginary part of the complex signal are separated as the in­phase (i.e., I charmel in Fig. 5) channel and the quad-phase (i.e., Q channel in Fig. 5) channel in baseband. The 'Code NCO' block considers the estimated code phase error from the DLL loop filter in order to shift the code phase accordingly. This block generates four signals as output: the adjusted E 1 B

and EIC replicas, the trigger enabling signal and the shifted NCO phase. The trigger enabling signal is used in conjunction with 'Tracking_ Ena' which eventually enables both FLL/PLL and DLL blocks of EIB and EIC channels (when both the variables are set to 1). Both the code and carrier NCOs are implemented using C-language based S-function, the details of which are not addressed here for the sake of compactness.

� �1 I�_------'�_ Ints.g

., z

Fig. 5: Tracking unit

f---�"""" 1------1 ... """.

In the 'Dual Channel Correlation and Discriminators' block, E 1 B and E 1 C are implemented as two separate channels, as shown in Fig. 6. However, these two channels are approximately the same, except the replicas used for integration and dump, which are either CBOC(+)/CBOC(-) modulated, or Sin BOC(1 ,I)-modulated, according to the type of receiver. In the reported simulation, SinBOC(1,I) modulated reference codes are considered.

The tracking loop discriminator is based on normalized Narrow Early-Minus-Late (NEML) power, which has the following discriminator function [ 6]:

/2+Q2_(I2+Q2) D= E E L L

/2 + Q 2 p I' (4)

The discriminator is implemented using an m-Ianguage based S-function. The code tracking loop filter bandwidth is currently set to 2 Hz. The early-late spacing for NEML is set according to [9]:

tl = fc EL BW

(5)

where fc is the chip rate and BW is the available double-sided

front-end bandwidth. In case of 4 MHz bandwidth, the early­late spacing becomes 0.2557 chips, whereas for 16 MHz bandwidth, the early-late spacing is set to 0.0639 chips.

'.-

E1Bitplic.l

P,oducl

Fig. 6: Dual Channel Correlation and Discriminators block

The variables shown in Fig. 1, namely 'Tracking_Ena', 'Est_freq' and 'Est_code_delay', are stored in memory. The stored variables are read outside the acquisition block, for use in the tracking unit. The variable 'TrackinL Ena' is intentionally set to 1 in order to run the Tracking Unit continuously. In addition, the estimated frequency 'Est_freq' and the estimated code delay 'Est_code _delay', which are to be used by the Tracking Unit, are also set such that the initial frequency error is less than ±88 Hz, and the initial code delay error is less than ±0.1 chips. The reason for such a scheme is to run the Tracking Unit along with the Acquisition block in parallel, so that we can calculate the acquisition and tracking performance for the same channel profile in one simulation run.

III. SIMULATION RESULTS IN ACQUISITION STAGE

The developed Simulink model can choose between two acquisition blocks depending on which reference modulation we choose at the receiver: one is based on SinBOC(I,1) modulated reference code, termed hereafter as SinBOC(I,1) reference receiver, and the other one is based on CBOC modulated reference code (CBOC(+) for data channel, and CBOC(-) for pilot channel), termed here as CBOC reference receiver. The idea for such a design is to investigate the deterioration in performance caused by implementing a SinBOC(I,I) reference receiver over a CBOC reference receiver in different bandwidth requirements.

Galileo E 1 signal simulator has been simulated in single path channel for 3 seconds with a frequency step size equals to 166 Hz and time-bin step size equals to 1 sample (i.e., 0.1023 chips with /s=10 MHz) in case of 4 MHz double-sided bandwidth, and equals to 4 samples (i.e., 0.1204 chips with /s=34 MHz) in case of 16 MHz bandwidth. The acquisition threshold is set to 1.3 for both the reference receivers. The statistics are computed for 3 seconds in each ClNo, giving a total of 750 statistical points. The probability of detection (Pd) vs. ClNo plots for SinBOC(I,I) and CBOC reference receivers

in single path channel with 4 MHz double-sided bandwidth are shown in Figs. 6 and 7, respectively. As shown in the figures, the Joint Data-Pilot channel offers up to 2.8 dB improvement over Data-only or Pilot-only channel for both the receiver types.

Single path channel, SinBOC(1,1) reference receiver, BW: 4 MHz 1 .-------------.---�----����----� -&-Data �Pilot -e- Joint Data-Pilot 0 . 8 1---------,------'

0.4 -----------------f-----·--------

0.2 -----------------�-----------

35 40 C/No [dB-Hz]

45 50

Fig. 6: P d vs. ClNo in single path channel for SinBOC(I, I) reference receiver with 4 MHz double-sided bandwidth

Single path channel, CBOC reference receiver, BW: 4 MHz 1 -&-Data

�Pilot -e- Joint Data-Pilot 0.8 1--..:...:.c.:...:...:,-:--,-.:...:...:�

�LO--�--�3� 5�--�--4LO--------4L 5------�50 C/No [dB-Hz]

Fig. 7: Pd vs. ClNo in single path channel for CBOC reference receiver with 4 MHz double-sided bandwidth

Figs. 8 and 9 show P d vs. ClNo plots for SinBOC( 1,1) and CBOC reference receivers with 16 MHz double-sided bandwidth, respectively. Here also, Joint Data-Pilot channel offers up to 2.8 dB improvement over any individual channel. Fig. 10 shows the P d vs. ClNo in two different bandwidth considerations for both the reference receivers in single path channel. As seen from the figure, the deterioration caused by implementing a SinBOC(l,I) receiver instead of a CBOC receiver is much less in case of 4 MHz bandwidth as compared to 16 MHz bandwidth. Therefore, SinBOC(I,I) reference receiver can be considered as a good choice for Galileo EI OS signal, since SinBOC(I,I) implementation is much easier than a CBOC implementation. In Fig. 10, the signal detection improvement due to increase in bandwidth is also clearly visible for both the reference receivers.

Single path channel, SinBOC(1,1) reference receiver, BW: 16 MHz 1 r-&--�D�at-a- --,--,��=-�r-�-�

�Pilot 0.8 -e- Joint Data-Pilot

0.6 ---------------+--------------

0..'"

0.4 -----------------f------------ ············ t················

0.2 -----------------�------

�LO--e---�'���--4� 0--------4� 5------�50 C/No [dB-Hz]

Fig. 8: Pd vs. ClNo in single path channel for SinBOC(J,1) reference receiver with 16 MHz double-sided bandwidth

'" 0..

Single path channel, CBOC reference receiver, BW: 16 MHz 1 ,---------,­

-&-Data �Pilot

0.8 -e- Joint Data-Pilot

0.4 -----------------f---------

, , , ._,- _ .. _------------ ,----------------- , , , , , , , , , , , , ,

�LO--�--�����--�40�------ 4�5�----� 50 C/No [dB-Hz]

Fig. 9: Pd vs. ClNo in single path channel for CBOC reference receiver with 16 MHz double-sided bandwidth

Single path channel, two different reference receivers

0.8 -----------------:------------------e- SinBOC(1 ,1),BW:4 MHz -&- CBOC(1,1),BW:4 MHz

: -+- SinBOC(1 ,1),BW:16 MHz 0.6 -----------------�------------- - - ----: : ---+- CBOC,BW:16 MHz

0.4 -----------------f-·------- - - - + --------------- + ------------.--- j

35

, , , ---- ,-----------------,----------------- ,

40 C/No [dB-Hz]

. . . , , , , ,

45 50

Fig. 10: Pd vs. ClNo in single path channel with two different reference receivers

IV. SIMULATION RESULTS IN TRACKING STAGE

The tracking unit consists of carrier tracking block, code NCO and discriminator block, as presented in Section II. The EIB and EIC channels are implemented separately in 'Dual Channel Correlation and Discriminators' block. Thus, the reference code can be different for EIB and EIC channels. Currently, the code NCO can generate SinBOC(I,I) for both EIB and EIC channels, or generate CBOC(+) reference code for E 1 B channel and CBOC( -) reference code for E 1 C channel, according to the receiver type we want to use. In case of 'Joint Data-Pilot' tracking, the estimated code delay is the mean of the estimated code delay from E 1 B and E 1 C channels. As mentioned in Section lIE, the tracking unit is always running along with the acquisition block with some pre-defmed initial frequency error (i.e., 9:88 Hz) and initial code delay error (i.e., 9:0.1 chips).

.. ... c .!!! :0 >

Single path channel . SinBOC(1,1) reference receiver, BW: 4 MHz 10' ............... ................................ . . :::::::::::::::;:::::::::::::::::::::::::::::::::�: � Data

:::::::::::::::�:::::::::::::::::::::::::::::::+.

-+- Pilot .:··::···:::::::::::::::::::::::::::::::::::::::: f:: -a- JOi�t Data·Pilot ......... "', ............. -:-............... � ............ ... � .............. . . . , , , , , . . ,

101 ......... . .. �.:::: ::::. __ ---::::::::::::: :::: �::::::::::::::: �::: :::::::::::: � � � � � � � � � � � � � �: �:: �;; � � � �:: � � � � :l: �;;; � � � � �:::: � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � , ,

10· ::� � � � � � � � � � � � � j � � � � �:���:�� � � � �:� � � � � � � � � � � � �::�H � � � � � � � � � � � � i � � � � ��>::: � �

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �l� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

:::::::::::::::;::::::::::::::::::::::::::::::::: ;:::::::::::::::;::::::::::::::: , ,

10. 1 ':-__ --,', ___ -" ___ -'-' ----'----' 35 38 41 44

GINo [dB-Hz) 47 50

Fig. II: Variance vs. ClNo for tracking themes with SinBOC(I,I) reference code with 4 MHz double-sided front-end bandwidth

2 Single path channel, CBOC reference receiver, BW: 4 MHz 10 ........................... ............ .

:::::::::::::�::::::::::::::;::::::::::::: _ Data :::::::::::::�:::: :::: :: :::: ;::::::::::::: -il>- Pilot

"'::::::::::;:::::::::::::: ;:::::::::::::_:_�_�_�int:�

at��Pi���_ , , ,

101 ::-----::::::�:::: .. -

-- :::::i::::::::::::::!:::::::::::::: j:: :::: ::::::: '1

------- ... ,.::::::::--- . --ecce:::::::::::::::::::::::::::::::::::::

::::::::::::::::::::::::::::!::::::::::::: ::::::::::::::: - � - - --------

� � ��� � �::::: T::::: � � � � � � r � � � � � � � � � � � f � � � � � �: � �:: T::::::: � �:: -------------1-------------- 1--------------r-------------1-------------

10-1 ':-__ --'-___ -'-__ --''--__ -'-__ ----' 35 38 41 44 47 50

C/No [dB-Hz) Fig. 12: Variance vs. ClNo for tracking themes with CBOC reference code with 4 MHz double-sided front-end bandwidth

Tracking performance is evaluated in terms of code tracking error variance in single path channel for both SinBOC(I,I) and CBOC reference receivers. The tracking

error variance vs. ClNo plots for SinBOC(I, 1) reference receiver is shown for two different bandwidths: i. 4 MHz (double-sided), and ii. 16 MHz (double-sided). From the Figs. 11 and 12, it can be seen that the Joint Data-Pilot tracking is up to 3 dB better in terms of tracking error variance than data-only or pilot-only tracking with 4 MHz bandwidth. Similar conclusion can be drawn for 16 MHz bandwidth, as shown in Figs. 13 and 14.

, Single path channel, SinBOC(1,1) reference receiver, BW: 16 MHz 10 ............... _ .............. ........ __ ..... .. :::::::::::::::;:::::::::::::::;:::::::::::::::;:: � Data :::::::::::::::i::::::::::::::T::::::::::::T -+- Pilot

:::::::::::::::;:::::::::::::::r:::::::::::::r -a- Joint Data-Pilot , . . , � "' �lli l � g ------�--------- -- '----------------:----- - ---------.� ---------------�--------------- ,-- -----------�---- ----------:---------------(IJ , , , I

> : : : : 10· , ,

---------------. - - - - - - - - - - - - - - - �- ------------ - - .. --------------- ---- - - ------. , . , , ---------------,--- - - - --------- ,------------- - - ... ----------------,---- - - - ------, . . , ---------------. - - - - - - - - - - - - - - - �- --------------.. ----------------,------- - -----, , , , --------------- t--------------- 1----------------j----------------j-------------

--------------- r--------------- 1--------------- -1----------------r--------------

10" �--�---_f:_-----:�--�:__--� � � M M U W

GINo [dB-Hz)

Fig. 13: Variance vs. ClNo for tracking themes with SinBOC(I,I) reference code with 16 MHz double-sided front-end bandwidth

N' oS '" u c '" .� >

2 Single path channel, CBOC reference receiver, BW: 16 MHz 10 ............................ ............ .

101

100

--------------,----- ---------,-------------------------- - ,-------------- - --------------- - - - - - - ------'---- - - - - - - - --- �-------------

, . --------------,--------------,-------------, , --------------,-------------- ,-------------, . --------------,-------------- --------------, ,

_Data -il>- Pilot -a- Joint Data-Pilot

--- - - - - - -----T---- - - - - -----l------ - - - - - ---r-------- - - - ---r---------- ---

- - - - - - - - - - - - - - ,- - - - - - - - - - - - --. - - - - - - - - - - - - - - � - - - - -- - - - - - - -

::::::::::::: :i:::::::::::::: �:::::::::::::: �::::::::::::: :j:::: --:: --:::: , , . . --------------,--------------, - - - - - - - - - - - - - - � - -------------,-------------, f , • , f , , --- - - - - -------,----- - - - - - ---- � -- - - - - - - - - - - - - � - - - - - - - - - - - - - _.- - ------- -----, , , , , , ,

, , ,

10-1 L-__ --L ___ ..J'L-__ .....L' ___ ..1' ___ _

35 38 41 44 C/No [dB-Hz)

47 50

Fig. 14: Variance vs. ClNo for tracking themes with CBOC reference code with 16 MHz double-sided front-end bandwidth

Fig. 15 shows the tracking error variance vs. ClNo plots in different bandwidth considerations for both the reference receivers. As seen from Fig. 15, CBOC reference receiver slightly outperforms SinBOC(I,I) reference receiver in case of 4 MHz bandwidth, but has almost similar performance in case of 16 MHz bandwidth. Therefore, a SinBOC(I, 1) reference receiver can be considered as a good choice for Galileo E 1 OS signal from tracking perspective as well. The improvement in tracking error variance due to increase in bandwidth is also visible in Fig. 15.

N�

E. '" u C '" or; >

Single path channel, two difference refernce receivers 102 E:�::�::�::�::�:::�::�::�::�::�::�:_�::�::�:========�========�

101

100

-- - - -- - - -- - - -- - - -- - - -- - r-- - - -- - - - - - - - - - - - - - - - - - - - - - - � - - - -- -e- SinBOC(1 ,1),BW:4 MHz - - - - - - - - - - - - - - - - - - - - - - - � - - - --__ _ ___ _ ____ ___ _ ____ ____ L __ _ _ _ - CBOC,BW:4 MHz - - - - - - - - - - - - - - - - - - - - - - - � - - - - - --+- SinBOC(1 ,1), BW:16 MHz

-+- CBOC,BW:16 MHz

-::: -:: : - -:: ---:: :�� � ��!� ��� � ��� � ���� ��� � ���� ��! � ���� ���� ������� � ���� �� - - - - - - - - - - - - - - - - - - - - - - - � -- - - -- - - -- - - -- - - -- - - -- -

, , __ _ ___ _ ____ ___ _ ____ ____ L __ _ ___ _ ____ ___ _ ____ ____ � ___ ___ _ ___ _ ___ _ ___ _ __ _ , , . , ___ ___ _ ____ ___ _ ___ _ ___ _ � ___ ____ ___ _ ____ ___ _ ___ .l. _ _ ___ _ ____ ___ _ ___ _ ___ _ . , , , , ,

10.1 L-______ ''--_____ -'''--_____ -' 35 40 45

C/No [dB-Hz] 50

Fig. 15: Variance vs. ClNo in single path channel with two different reference receivers

V. CONCLUSION

In this paper, the authors analyzed the acquisition and tracking performance of three different implementation strategies for Galileo El OS signa\. The implemented strategies were compared in different bandwidth considerations (both narrow and wide front-end bandwidth assumptions) for two different receiver types, i.e., SinBOC( 1,1) reference receiver and CBOC reference receiver. All the simulations were carried out in TUT Galileo E 1 signal simulator, a detail description of which was also presented in the context of the paper. The simulation results showed that acquisition and tracking with an individual channel is not the best approach in tenns of signal detection and tracking error variance. It was shown that a non-coherently combined 'Joint Data-Pilot' channel offers around 2.8 dB improvement over any individual channel in terms of signal detection and around 3 dB improvement in tenns of tracking error variance. It was also shown that the performance deterioration caused by implementing a SinBOC(l,l) reference receiver is negligible as compared to implementing a CBOC reference receiver. Therefore, SinBOC(l,l) reference receiver can be considered as a good choice for Galileo E 1 OS signal due to its less complex implementation. Most of the findings based on data­pilot combinations were as intuitively expected. However, the

main novelty of the paper stays in presenting a realistic and detailed Simulink-based simulator for Galileo E 1 OS signals that takes into account two receiver modes, and has already been made open access for research purpose.

ACKNOWLEDGMENT

The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n0227890 (GRAMMAR project) and from the Academy of Finland, which are gratefully acknowledged. The authors also want to thank Xuan Hu, a fonner member of the Department of Communications Engineering at Tampere University of Technology, who created the basic version of the Simulink model used within the context of this research.

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