基于BOC调制信号的无歧义同步技术研究

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BOC调制信号同步技术 BOC（Binary Offset Carrier，二进制偏移载波）调制信号是一种常用的全球导航卫星系统（GNSS）信号调制方法。然而，BOC调制信号存在歧义问题，即在接收端无法确定信号的正确时延和相位信息。为了解决这个问题，本文提出了一种新的、无歧义的BOC调制信号同步技术。该技术的核心思想是使用合成相关函数来消除歧义问题。具体来说，就是将接收到的BOC信号与本地辅助信号进行交叉相关，然后从中减去BOC信号与另一个本地辅助BOC信号之间的交叉相关。通过这种方式，可以生成一个无歧义的相关函数，从而实现BOC调制信号的同步。理论上，该技术可以完全消除歧义问题，并且对低调制阶次的BOC信号只有轻微的获取和跟踪性能下降。该技术的优点是可以提高GNSS系统的导航精度和可靠性。 BOC调制信号同步技术的关键技术点包括： 1. 合成相关函数的生成：通过将接收到的BOC信号与本地辅助信号进行交叉相关，然后从中减去BOC信号与另一个本地辅助BOC信号之间的交叉相关，生成一个无歧义的相关函数。 2. 歧义问题的消除：通过使用合成相关函数，可以消除BOC调制信号的歧义问题，从而实现同步。 3. 低调制阶次BOC信号的同步：该技术可以对低调制阶次的BOC信号进行同步，而不需要进行复杂的信号处理。 4. GNSS系统的应用：该技术可以应用于GNSS系统，以提高导航精度和可靠性。本文提出的BOC调制信号同步技术可以解决BOC调制信号的歧义问题，提高GNSS系统的导航精度和可靠性。该技术可以广泛应用于GNSS系统、通信系统、雷达系统等领域。

986 IEEE COMMUNICATIONS LETTERS, VOL. 16, NO. 7, JULY 2012

Unambiguous BOC Modulated Signals Synchronization Technique

Jiamin Qi, Jiapin Chen, Zhenbo Li, and Dawei Zhang

Abstract—In this letter, a new unambiguous tracking technique

is proposed for binary offset carrier (BOC) modulated signals,

which will be utilized in global navigation satellite systems

(GNSS). The proposed technique is a synthesized correlation

function obtained by subtracting the cross-correlation between

the received B OC signal and the local auxiliary signal from the

cross-correlation of BOC signal between another local auxiliary

BOC signals. The theoretical standard tracking error formulas

are given. The results show that this technique can be a solution

to remove the ambiguity completely with slightly degradation in

acquisition and tracking for low modulation order BOC signals.

Index Terms—BOC modulation, ambiguity, synchronization,

standard deviation error.

I. INTRODUCTION

N order to enhance the code tracking performance and

provides the advantages of multipath effect reduction and

narrow band interference r ejection between the current GNSS

systems, a new type of modulated signals named BOC mod-

ulation have been adopted in modernized GPS [1], European

Galileo project [2] and Chinese Compass/BeiDou II [3]. The

BOC signal uses a square wave sub-carrier to modulate the

pseudo random noise (PRN) sequence.The subcarrier has

two types, sine phased or cosine phased. The sine phased

BOC signals are expressed as sBOC(m,n), where m and

n represents the ratio to 1.023MHz. However, there is an

ambiguity threat in acquisition and tracking processes, because

the auto-correlation fun c tion has more than one peak. With

the awkward ratio between subcarrier and local PN (Pseudo-

Noise) sequence, the difference b etween the maximum energy

of side peak and the m a in peak decreases. I n multipath a nd

interference e nvironments, it has the potential to lock on the

false zero point. If false acquisition occurs, the code tracking

loop will initially lock on the side peaks. In order to tackle

this problem, some unambiguous acquisition and tracking

approaches were proposed. These technique which can be

summarized into the following categories: the Bump Jumping

technique [4], the BPSK-like technique [5], The Sub Carrier

Phase Cancelation (SCPC) technique [6], and the Side-Peak

Cancelation Technique (SPCT) [7-10]. The essence of SPCT is

to minimize th e side-peaks of a uto-corre lation function since

they are the origin of the false lock tracking. The method

presented in [7, 8] have some drawbacks in the tracking stage,

because the effect of the side-peak is not removed completely.

So it can po tentially lock o n the false original peak. The

Manuscript received December 13, 2011. The associate editor coordinating

the revie w of this letter and approving it for publication was Y.-C. Wu.

The authors are with the Department of Information Process and System

Control, MNRI, JiaoTong University, ShangHai, China (e-mail: {chenjp, jmqi,

zbli, dawei}@sjtu.edu.cn).

Digital Object Identiﬁer 10.1109/LCOMM.2012.050112.112521

proposed method in [8], is only dedicated to sinBOC(n,n)

signals is another ﬂaw. For cosine BOC signals, it is useless.

In addition, bump-jumping (BJ) technique is also based upon

magnitude comparison, so it still has a high probability of

failure when signal-to-noise ratio is low. In this letter, a

Symmetrical Pulse Ambiguity Removing technique which is

suitable for all type BOC signals is proposed and its implement

structure is also simple and convenient to implement.

II. P

ROPOSED SYNCHRONIZATION TECHNIQUE

Inspired by autocorrelation correlated with its local replica

and cross-correlation function correlated with PRN sequence,

we can see that we can acquire a correlation function with only

one peak by construct several local auxiliary signals, the cross-

correlation of which with the received BOC signal can be

used to combine together to remove the undesired side peaks.

Taking the complexity into consideration, we choose the least

two correlations to combined the proposed correlation. So

the main idea of the proposed technique is to construct two

local auxiliary signals, the cross-correlation of w hich with

the received BOC signal can be used to combine together

to remove the undesired side peaks. We choose the combined

criterion as follows

comb

= |R

B/S1

|−|R

B/S2

| (1)

where R

B/S1

and R

B/S2

are the cross correlation between

the received BOC signal and two the local BOC-like signals,

respectively. The receiver locally generated reference BOC-

like waveform are two modiﬁed PRN deﬁned as (x =1, 2):

= P

⎧

⎨

⎩

1/2w, (k −1)T

<t<(k − 1+w)T

0, (k −1+w)T

<t<(k − w)T

(−1)

/2w, (k − w)T

<t<kT

(2)

where, S

is the subcarrier. P

is the PRN spreading sequence

and k is the chip number within the sequence respectively.

And w is the pulse width of the local BOC-like code. It is

well known that the cross-corr elation is a linear superposition

of several triangular functions (in Fig.1). So by choosing the

local auxiliary BOC-like waveform, one can change the shape

of the combined DLL discriminator. In order to completely

remove the effect of side-peak, the pulse width of the local

generated signal must be smaller than 3n/8m chips. Julien’s

method [8] can be taken as an example with the pulse width

0.5 chips for the proposed tracking method (in Fig.2). And it

is out of the local pulse width range. So it can not eliminate

the effect of the side-peaks completely. We can understand this

phenomenon clearly in Fig.2, which shows the envelope of the

proposed composed correlation function with different pulse

width. In Fig.2, we can clearly see that the side peaks could

be removed completely b y choosing correct pulse width of

1089-7798/12$31.00

 2012 IEEE

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