DE102015004152B4 - Radio communication synchronization system - Google Patents

Abstract

Procedure that includes the following steps:
Receiving (402), at a receiver (120) of a global navigation satellite system, GNSS, (100), a plurality of GNSS signals (150) transmitted by a GNSS satellite (110), wherein a GNSS signal (150) comprises a primary code sequence (160), a secondary code sequence (170) and
has a data portion (180);
Extracting (408) the secondary code sequence (170) in each of the received GNSS signals (150);
analyzing (410) the extracted secondary code sequence (170) based on a plurality of reference secondary code sequences, the reference secondary code sequences comprising delayed versions of a predetermined secondary code sequence (170);
Identifying, based on the analysis, the delay associated with a reference secondary code sequence from the plurality of reference secondary code sequences as a phase offset to be used for synchronizing the GNSS receiver (120) with the GNSS satellite (110); and
Outputting (460) the phase offset to be used for synchronizing the GNSS receiver (120) with the GNSS satellite (110).

Description

Cross-reference to related patent applications

This patent application claims priority from the provisional US patent application with the official file number 61/975,309 , submitted on April 4, 2014

Technical area

The present disclosure relates to radio code synchronization including radio code synchronization for global navigation satellite systems (GNSS).

The US 8401546 B2 discloses a method and a detection and tracking device for tracking digitized spread spectrum navigation signals modulated with a spreading code, the device comprising a plurality of universal tracking channels, each coupled to an interrupt module, the universal tracking channel comprising modules for efficient use of the correlator resources.

The EP 1724602 A1 discloses a system for processing a received signal to which at least one code is applied and the signal has a frequency, wherein a first correlation circuit correlates the signal with a first code and a second correlation circuit correlates the signal with a second code different from the second code, and processing means jointly processes the outputs of the first and second correlation circuits to compensate for the frequency.

The US 6873664 B1 discloses a method and a digital receiver for detecting a coded signal, wherein the receiver receives a long pseudo-noise code signal consisting of two shorter interleaved codes, a correlator unit correlates the received signal with one or more reference codes, each corresponding to the two interleaved codes, and generates correlation signals. Even and odd code detectors detect codes from the correlation signals, and a delay unit is coupled to the even and odd code detectors and delays the even or odd correlation signals to align the correlation signals.

The US 5600670A discloses a GPS receiver system in which the channels are dynamically assigned in acquisition mode to hierarchically chain a slave channel module to a master channel.

background

Typical digital communication systems involve using a transmitter to send a bitstream to a receiver. The bitstream contains digital information that the receiver decodes and uses. In some communication systems, the digital information is extracted by first converting the analog representation of the bitstream into digital samples. Each sample represents the signal at the time of sampling. Due to noise and other effects, signal transitions may not be represented cleanly.

Such digital communication can be used in various systems, such as a global navigation satellite system (GNSS). GNSS is a satellite system comprising a network of satellites in space. Each satellite wirelessly transmits coded signals at precise intervals. A receiver analyzes the signal information to determine a position, speed, and time estimates. The GNSS signal is used for various applications, such as determining the geographical location of a user's receiver anywhere in the world. Using the information in the transmitted signal, the receiver on or near the Earth's surface can calculate the exact position of the transmitting satellite and the distance (from the transmission time delay) between the satellite and the receiver. For accurate operation of a system based on the reception of GNSS signals, the transmitting satellite and the receiver are time-synchronized.

GNSS systems are particularly sensitive because GNSS signals are communicated between satellites above Earth's atmosphere and receivers on the Earth's surface. Furthermore, the signals transmitted to the receiver are generated by the transmitter and are therefore synchronized to the transmitter's time base. As a result, the signals are not synchronized to the receiver's time base, and therefore the position of bit transitions in the receiver's time base cannot be captured or estimated.

Brief summary of the invention

• Empfangen, unter Verwendung einer Schaltungsanordnung an einem Empfänger eines globalen Navigationssatellitensystems (GNSS), einer Vielzahl von GNSS-Signalen, die von einem GNSS-Satelliten gesendet werden, wobei ein GNSS-Signal eine Primärcodefolge, eine Sekundärcodefolge und einen Datenanteil aufweist;
• Extrahieren, unter Verwendung der Schaltungsanordnung, der Sekundärcodefolge in jedem der empfangenen GNSS-Signale;
• Analysieren, unter Verwendung der Schaltungsanordnung, der extrahierten Sekundärcodefolge auf der Basis einer Vielzahl von Referenz-Sekundärcodefolgen, wobei die Referenz-Sekundärcodefolgen verzögerte Versionen einer vorbestimmten Sekundärcodefolge aufweisen;
• Identifizieren, unter Verwendung der Schaltungsanordnung, auf der Basis der Analyse, der Verzögerung, die mit einer Referenz-Sekundärcodefolge aus der Vielzahl von Referenz-Sekundärcodefolgen assoziiert ist, als einen Phasenversatz, der für das Synchronisieren des GNSS-Empfängers mit dem GNSS-Satelliten verwendet werden soll; und
• Ausgeben, unter Verwendung der Schaltungsanordnung, des Phasenversatzes, der für das Synchronisieren des GNSS-Empfängers mit dem GNSS-Satelliten verwendet werden soll.

In accordance with one aspect, a method comprises the following steps:

• Receiving, using circuitry at a global navigation satellite system (GNSS) receiver, a plurality of GNSS signals transmitted from a GNSS satellite, wherein a GNSS signal comprises a primary code sequence, a secondary code sequence, and a data portion;
• Extracting, using the circuitry, the secondary code sequence in each of the received GNSS signals;
• analyzing, using the circuit arrangement, the extracted secondary code sequence based on a plurality of reference secondary code sequences, the reference secondary code sequences comprising delayed versions of a predetermined secondary code sequence;
• Identifying, using the circuitry, based on the analysis, the delay associated with a reference secondary code sequence from the plurality of reference secondary code sequences as a phase offset to be used for synchronizing the GNSS receiver with the GNSS satellite; and
• Output, using the circuitry, the phase offset to be used for synchronizing the GNSS receiver with the GNSS satellite.

• Extrahieren, unter Verwendung der Schaltungsanordnung, einer ersten Sekundärcodefolge aus dem ersten GNSS-Signal und einer zweiten Sekundärcodefolge aus dem zweiten GNSS-Signal;
• Erzeugen, unter Verwendung der Schaltungsanordnung, einer komplex Konjugierten (konjugiert komplexen Zahl) der zweiten Sekundärcodefolge; und
• Berechnen, unter Verwendung der Schaltungsanordnung, eines Produkts aus der ersten Sekundärcodefolge und wenigstens einem Teil der erzeugten komplex Konjugierten der zweiten Sekundärcodefolge.

Advantageously, the plurality of received GNSS signals comprises a first GNSS signal and a second GNSS signal, and the method further comprises the following steps:

• Extracting, using the circuit arrangement, a first secondary code sequence from the first GNSS signal and a second secondary code sequence from the second GNSS signal;
• Generating, using the circuit arrangement, a complex conjugate (complex conjugate) of the second secondary code sequence; and
• Calculating, using the circuit arrangement, a product of the first secondary code sequence and at least a portion of the generated complex conjugate of the second secondary code sequence.

• Berechnen, unter Verwendung der Schaltungsanordnung, einer Vielzahl von Kreuzkorrelationen des berechneten Produkts und jeder Sekundärcodefolge von der Vielzahl von Referenz-Sekundärcodefolgen.

Advantageously, the method further comprises the following step:

• Calculating, using the circuitry, a plurality of cross-correlations of the calculated product and each secondary code sequence from the plurality of reference secondary code sequences.

• Identifizieren, unter Verwendung der Schaltungsanordnung, einer Kreuzkorrelation mit einem maximalen Größenwert aus den berechneten Kreuzkorrelationen; und
• Identifizieren, unter Verwendung der Schaltungsanordnung, der Referenz-Sekundärcodefolge, die mit der identifizierten Kreuzkorrelation mit der maximalen Größe assoziiert ist.

Advantageously, the method further comprises the following steps:

• Identifying, using the circuitry, a cross-correlation having a maximum magnitude value from the calculated cross-correlations; and
• Identifying, using the circuitry, the reference secondary code sequence associated with the identified cross-correlation having the maximum magnitude.

Advantageously, the delay associated with the identified reference secondary code sequence is used as the phase offset to be used for synchronization.

• Ermitteln, unter Verwendung der Schaltungsanordnung, eines Winkels, der mit der resultierenden Folge der berechneten Korrelation mit dem maximalen Ergebnis assoziiert ist; und
• Ausgeben, unter Verwendung der Schaltungsanordnung, des ermittelten Winkels als den Frequenzversatz, der für die Synchronisation des GNSS-Empfängers mit dem GNSS-Satelliten verwendet werden soll.

Advantageously, the method further comprises the following steps:

• Determining, using the circuit arrangement, an angle associated with the resulting sequence of the calculated correlation with the maximum result; and
• Outputting, using the circuitry, the determined angle as the frequency offset to be used for synchronizing the GNSS receiver with the GNSS satellite.

Advantageously, the angle is determined by calculating an arctangent of the resulting sequence of the calculated correlation with the maximum magnitude value.

Advantageously, the angle is determined by calculating a weighted combination of a subset of the calculated cross-correlations, wherein the subset of the calculated cross-correlations includes the calculated cross-correlations with corresponding magnitudes above a predetermined threshold. Advantageously, the second GNSS signal is received after a predetermined delay since the reception of the first GNSS signal.

• eine Schaltungsanordnung zum Empfangen von Funksignalen bzw. drahtlosen Signalen, wobei jedes Funksignal ein Spreizspektrumsignal aufweist, das eine periodische Erweiterung eines Primärcodes, eine periodische Erweiterung eines Sekundärcodes und einen Datenanteil aufweist;
• eine Schaltungsanordnung zum Ermitteln, aus einem ersten empfangenen Funksignal, einer ersten Chipfolge, die repräsentativ für den Sekundärcode ist, durch das Extrahieren des Primärcodes und des Datenanteils aus dem ersten empfangenen Funksignal;
• eine Schaltungsanordnung zum Ermitteln, aus einem zweiten empfangenen Funksignal, einer zweiten Chipfolge, die repräsentativ für den Sekundärcode ist, durch das Extrahieren des Primärcodes und des Datenanteils aus dem zweiten empfangenen Funksignal;
• eine Schaltungsanordnung zum Identifizieren eines Phasenversatzes, der mit den empfangenen Funksignalen assoziiert ist, durch das Analysieren der ersten Chipfolge und der zweiten Chipfolge; und
• eine Schaltungsanordnung zum Synchronisieren des Funksignalempfängers mit einem Sender der empfangenen Funksignale unter Verwendung des identifizierten Phasenversatzes.

In accordance with one aspect, a radio signal receiver comprises:

• a circuit arrangement for receiving radio signals or wireless signals, each radio signal comprising a spread spectrum signal having a periodic extension of a primary code, a periodic extension of a secondary code and a data portion;
• circuitry for determining, from a first received radio signal, a first chip sequence representative of the secondary code by extracting the primary code and the data portion from the first received radio signal;
• circuitry for determining, from a second received radio signal, a second chip sequence representative of the secondary code by extracting the primary code and the data portion from the second received radio signal;
• circuitry for identifying a phase offset associated with the received radio signals by analyzing the first chip sequence and the second chip sequence; and
• a circuit arrangement for synchronizing the radio signal receiver with a transmitter of the received radio signals using the identified phase offset.

• eine Schaltungsanordnung zum Berechnen eines konjugiert komplexen Produkts von der ersten Chipfolge und der zweiten Chipfolge;
• eine Schaltungsanordnung zum Berechnen einer Vielzahl von Kreuzkorrelationen einer Referenz-Chipfolge und einer verzögerten Version des konjugiert komplexen Produkts, wobei das konjugiert komplexe Produkt um eine von einer Vielzahl von vorbestimmten Verzögerungen verzögert ist; und
• eine Schaltungsanordnung zum Identifizieren einer Verzögerung aus der Vielzahl von vorbestimmten Verzögerungen derart, dass eine Größe der Kreuzkorrelation, die bei der identifizierten Verzögerung berechnet wird, das Maximum unter den Größen der berechneten Kreuzkorrelationen ist.

Advantageously, the radio signal receiver further comprises:

• a circuit arrangement for calculating a complex conjugate product of the first chip sequence and the second chip sequence;
• circuitry for calculating a plurality of cross-correlations of a reference chip sequence and a delayed version of the complex conjugate product, wherein the complex conjugate product is delayed by one of a plurality of predetermined delays; and
• circuitry for identifying a delay from the plurality of predetermined delays such that a magnitude of the cross-correlation calculated at the identified delay is the maximum among the magnitudes of the calculated cross-correlations.

Advantageously, the radio signal receiver further comprises circuitry for identifying the delay as the phase offset for synchronization.

Advantageously, the radio signal receiver further comprises a circuit arrangement for determining a frequency offset used in the synchronization of the radio signal receiver with the transmitter on the basis of the calculated cross-correlations.

Advantageously, the phase offset and the frequency offset for synchronizing the radio signal receiver with the transmitter are determined without searching through a set of frequency offsets.

Advantageously, the first received radio signal and the second received radio signal are received sequentially.

• Befehle zum Empfangen eines ersten Signals und eines zweiten Signals, wobei jedes Signal wenigstens eine periodische Erweiterung eines Primärcodes, einen Datenanteil und eine periodische Erweiterung eines Sekundärcodes aufweist;
• Befehle zum Identifizieren der Sekundärcodefolge in dem empfangenen ersten Signal;
• Befehle zum Identifizieren der Sekundärcodefolge in dem empfangenen zweiten Signal;
• Befehle zum Ermitteln eines Versatzes, der mit den empfangenen Signalen assoziiert ist, auf der Basis der identifizierten Sekundärcodefolgen; und
• Befehle zum Synchronisieren einer lokalen Taktquelle auf der Basis des Versatzes.

In accordance with one aspect, there is provided a non-transitory computer storage medium comprising instructions executable by one or more processors, the instructions comprising:

• Instructions for receiving a first signal and a second signal, each signal comprising at least one periodic extension of a primary code, a data portion, and one periodic extension of a secondary code;
• Instructions for identifying the secondary code sequence in the received first signal;
• Instructions for identifying the secondary code sequence in the received second signal;
• Instructions for determining an offset associated with the received signals based on the identified secondary code sequences; and
• Commands to synchronize a local clock source based on the offset.

• Befehle zum Berechnen eines konjugiert komplexen Produkts der Sekundärcodefolge in dem empfangenen ersten Signal und der Sekundärcodefolge in dem empfangenen zweiten Signal.

Advantageously, the non-volatile computer storage medium further comprises:

• Instructions for calculating a complex conjugate product of the secondary code sequence in the received first signal and the secondary code sequence in the received second signal.

Advantageously, the complex conjugate product is coherently integrated into the epoch of the primary code.

• Befehle zum Berechnen von Korrelationen des konjugiert komplexen Produkts mit jedem Referenzsignal einer Menge von vorbestimmten Referenzsignalen;
• Befehle zum Berechnen einer Größe jeder der Korrelationen und zum Ermitteln, als einen Phasenversatz, einer Verzögerung, die mit einem vorbestimmten Referenzsignal aus der Menge von vorbestimmten Referenzsignalen assoziiert ist, wobei die Größe des vorbestimmten Referenzsignals das Maximum unter den berechneten Größen ist; und
• Befehle zum Berechnen des Frequenzversatzes auf der Basis einer gewichteten Kombination einer Teilmenge der Korrelationen des konjugiert komplexen Produkts mit jedem Referenzsignal der Menge von vorbestimmten Referenzsignalen, wobei die Teilmenge eine vorbestimmte Anzahl von Korrelationen aufweist.

Advantageously, the non-volatile computer storage medium further comprises:

• Instructions for calculating correlations of the complex conjugate product with each reference signal of a set of predetermined reference signals;
• Instructions for calculating a magnitude of each of the correlations and for determining, as a phase offset, a delay associated with a predetermined reference signal from the set of predetermined reference signals, the magnitude of the predetermined reference limit signal is the maximum among the calculated quantities; and
• Instructions for calculating the frequency offset based on a weighted combination of a subset of the correlations of the complex conjugate product with each reference signal of the set of predetermined reference signals, the subset having a predetermined number of correlations.

Advantageously, the real parts of the complex conjugate product are integrated into the epoch of the primary code.

BRIEF DESCRIPTION OF THE DRAWINGS

• 1 shows an exemplary communication system that benefits from radio code synchronization.
• 2 illustrates a composition of an exemplary signal used during radio code synchronization.
• 3 illustrates an example signal receiver.
• 4 illustrates an exemplary flowchart including at least some of the steps involved in detecting a code phase offset.

DETAILED DESCRIPTION

The discussion below makes reference to the accompanying drawings, which show, by way of illustration, specific embodiments described in the present document. Other embodiments may be utilized, and structural changes may be made without departing from the scope of the present document. Furthermore, embodiments are described in the context of a global navigation satellite system (GNSS), but the features described in the embodiments may also be applied to other areas of digital communications that use spread spectrum signals, such as wireless communications that use code division multiple access (CDMA). The embodiments may be advantageous for accurate and computationally efficient code phase synchronization of spread spectrum signals, such as GNSS signals, in the presence of frequency uncertainty. The presented techniques may be used, for example, during the synchronization of secondary codes, such as those present in modern GNSS constellations such as Beidou and Galileo. Because the described code phase synchronization is computationally efficient, less processing power is required in the system associated with receiving communications, and this power can therefore be allocated to other functions. In the GNSS example, if the GNSS is implemented with application-specific integrated circuits on one or more microchips, the communications portion of the GNSS may not only have less computational demand, but it also consumes fewer of the microchip's resources.

1 shows an exemplary communication system 100 in which a transmitter 110 transmits a signal 150 that is received by a receiver 120. Although 1 While only a single transmitter 110 and a single receiver 120 are illustrated, more than one transmitter 110 may communicate with more than one receiver 150 in other examples. For illustrative purposes, the following description focuses on communication from a single transmitter to a single receiver. 1 further illustrates components of signal 150, including a primary code 160, a secondary code 170, and a data portion 180. In other examples, signal 150 may not include a data portion 180. Receiver 120 may receive a combination of signals such that some received signals include data, while some signals do not include a data portion. Each signal component may have a different periodicity, but they may have a phase relationship with each other.

Transmitter 110 may transmit signal 150 at a fixed rate. Transmitter 110 may also transmit signal 150 randomly based on a triggering event, such as receiving a command to transmit data. Transmitter 150 may be a satellite, or it may be located on a satellite, such as a global position satellite (GPS), in which case transmitter 110 may continuously transmit signal 150 at a predetermined rate. Alternatively, signal 150 may be transmitted from a pseudolite or pseudosatellite, such as a ground-based signal transmission system. Transmitter 110 may be stationary, or it may move when transmitting signal 150.

The transmitter 110, such as a satellite, may be designed to transmit the radio signal 150 as a spread spectrum radio signal. The examples described further use a satellite in the role of the transmitter 110, but the transmitter may be any other transmitting A device such as a radio signal tower or repeater station that can repeat a received signal. The satellite may include a modulator that uses phase-shift keying (PSK) as a digital modulation method for transmitting the data 180 by changing or modulating the phase of a carrier wave. PSK uses a finite number of phases, each associated with a unique pattern of binary digits. Typically, each phase encodes an equal number of bits. Each pattern of bits forms a symbol represented by the particular phase. A demodulator, such as receiver 120, determines the phase of the received signal and maps it back to the symbol that represents it, thereby recovering the output data. Receiver 120 may be specifically designed for the symbol set used by the modulator. As a result, radio signal 150 may have at least three parts or components, which will be described later. In addition to the three components, examples of the radio signal 150 may also include other components that benefit from the described embodiments.

The radio signal 150 may include a portion of data 180. The data 180 may contain information necessary for navigation, such as satellite time and ephemeris data. The data 180 may be a binary-coded message containing values referred to herein as "+A" and "-A." The message may be transmitted at a low frequency rate and may provide the navigation information. The value of +A may be 1, and the value of -A may be -1 or 0. The carrier wave may be modulated by the data portion 180 during transmission of the signal 150.

The signal 150 may further have a primary code 160. The primary code 160 may be a ranging code containing a relatively long, known sequence of values, referred to herein as "+B" and "-B." The value of +B may be a value of 1, and -B may be a value of -1. The transmitter 110 may modulate the carrier wave using the primary code. The primary code 160 may be satellite-specific and may be transmitted at a higher rate than the data 180. The primary code 160, also called a PRN (Pseudo-Random Noise) code, allows for accurate ranging so that multiple satellites or transmitters can broadcast signals at the same frequencies, which can be decoded using CDMA technology. Typically, the values of PRN codes are called “chips” rather than “bits” to emphasize that, unlike the bits of data 180, they do not carry any information.

The radio signal 150 may further include a secondary code 170, which may also be a PRN code. The secondary code 170, as its name suggests, is a second code that multiplies the primary code 160 to form a longer code (called a stepped code). The chipping rate of the secondary code 170 is typically lower than that of the primary code 160. The secondary code values may also be referred to as "chips" because they do not carry any data. 1 The length of one chip of secondary code 170 is shown to be equal to one period of primary code 160. However, any other relationship between the rates of primary code 160 and secondary code 170 is possible. For example, in another embodiment, one period of primary code 160 may correspond to two chips of secondary code 170. Secondary code 170 is typically used to detect very weak signals, such as in indoor or urban environments. Secondary code 170 may be a shorter code than primary code 160. The carrier wave is further modulated using secondary code 170 during transmission of signal 150.

2 illustrates an example composition of signal 150, such as a GNSS signal, received by a receiver 120, such as a GNSS receiver. A carrier wave 220, such as a 1575.42 MHz L1 carrier or a 1227.6 MHz L2 carrier, may be modulated using various components to obtain signal 150. For example, in an example GNSS, carrier wave 220 may be modulated using PSK based on data 180, primary code 160, and secondary code 170. For example, in one embodiment, the primary code 160, also referred to as a C/A (Coarse Acquisition) code sequence, may have a transmit signal rate (or chip rate) of 1.023 MHz and a code length of 1023 (i.e., 1 period = 1 millisecond). The data bits may be 20 milliseconds long and synchronized to the primary code 160. One of the 1 ms periods in each 20 ms period is selected by the transmitting satellite as the beginning of a data period. Furthermore, each 20 ms data bit may be additionally modulated by the secondary code 170. As shown, for example, in 2 As shown, the secondary code 170 may be a Neimann-Hoffman code with 20 characters or symbols (or 20 chips) (0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 1, 1, 0). The components may be used to generate the carrier wave 220 using modulate the use of different combinations. For example, in 2 As shown, the primary code 160 may be multiplied by the secondary code 170, and the resulting product (distance measurement code) and the data bits may be summed. The multiplication and addition may be performed using modulo-2 values. Alternatively, either multiplication or modulo-2 addition may be performed for the primary code 160. The result of the sum may then be modulated onto the carrier wave using binary phase shift keying (BPSK) to generate the signal 150, which may be transmitted. The signal 150 may include periodic extensions of the primary code sequence and the secondary code sequence along with the data. The code sequence may be a sequence of chips. The number of chips in the secondary code may be fewer than the number of chips in the primary code, and in some examples, considerably fewer. For example, the number of chips in a primary code sequence may be 1023, while the number of chips in a secondary code sequence may be 20.

Receiver 120 may search for the presence of signals, such as signal 150, traveling through space and attempt to synchronize with the signals identified by a corresponding transmitter. For example, a GNSS receiver may be a radio navigation user equipment that identifies and synchronizes with a satellite transmitting GNSS signals to demodulate and extract the measurements and navigation information in the received GNSS signals. Because signal 150 is out of phase, receiver 120 may reconstruct carrier wave 220 and extract the codes and navigation data 180 from received signal 150. Receiver 120 is designed to detect a shift in the phase of received signal 150 relative to the transmitted signal. Furthermore, receiver 120 may detect and determine the phase shift in the presence of frequency uncertainty. In another example, receiver 120 may additionally or alternatively determine a frequency offset in received signal 150 relative to the transmitted signal. The phase offset and frequency offset may be used to synchronize the radio signal receiver with transmitter 110.

3 illustrates an example receiver 120. The receiver 120 may include electronic circuitry for performing various operations. The circuitry may include one or more processors 392, such as signal processors, a microprocessor, and other such processors. The one or more processors may be capable of executing one or more computer-executable instructions. The instructions may be stored in a memory 396 of the receiver 120 or may be accessible to the one or more processors 392 via a communications interface, such as a communications port (not shown).

The receiver 120 may further include an antenna 310, a front-end (frontend section) 320, an oscillator 350, a baseband processing unit 370, and an application processing unit 380. The antenna 310 may receive the signal 150 as an analog radio frequency signal. The received signal 150 may be input to the front-end 320. The analog signal may be downconverted, filtered, and digitized in the front-end section 320. The front-end 320 may include a downconverter 322, an amplifier unit 324, and an analog-to-digital converter (ADC) 328 for operations. The components of the front-end 320 may be provided with a clock signal from the oscillator 350, which acts as a local clock source of the receiver 120. The front end 320 generates a baseband representation of the signal 150 in a desired spectrum, such as an intermediate frequency (IF) spectrum, in the baseband, which includes real and imaginary parts, or complex parts, namely I (in-phase) and Q (quadrature) components. The baseband representation can be forwarded to the baseband processing unit 370.

The baseband processing unit 370 is responsible for the signal processing tasks to be performed on the digital signal. The baseband processing unit may also be responsible for determining the code delay and carrier phase and frequency measurements to obtain the data 180 in the received signal 150. Accordingly, the baseband processing unit 370 may need to identify a starting point and/or an ending point of the components of the received radio signal 150. Although the primary code 160 and the secondary code 170 may have values known to the receiver 120, the codes may be continuously repeated during transmission. The received radio signal 150 may also be shifted in phase and/or frequency relative to the originally transmitted radio signal due to several factors. For example, the Doppler effect (relative movement of the receiver with respect to the transmitter), environmental influences, interference with other signals, and Other such factors may introduce a delay or offset, which in turn causes the radio signal 150 to be shifted relative to the transmitted signal. Furthermore, the oscillator 350 or clock source may not be precisely synchronized with a clock source used by the transmitter 110, which may cause a phase offset between the received signal and the generated local signals.

Once the baseband processing unit 370 determines the offsets, contents of the signal 150 may be forwarded to the application processing unit 380. The application processing unit 380 may use the data 180 to provide navigation-related information to a user or another system or device in communication with the receiver 120. For example, the data 180 may be used to provide a geographic location of the receiver 120, which may be displayed to the user via a display unit. Alternatively or additionally, the geographic location may be transmitted to a separate system or device, such as a server computer, which may use the geographic location information to provide related information to the user. For example, the server computer may provide points of interest (POIs) near the geographic location of the receiver 120. Various other applications of the navigation information contained in the data 180 are possible.

Therefore, the receiver 120, such as a GNSS receiver using the baseband processing unit 370, may perform a synchronization operation, which may be part of a signal acquisition operation. 3 3 further illustrates exemplary components of baseband processing unit 370, specifically a local signal generator 372, a primary code correlator 375, and a secondary code correlator 377. The components may be used for the synchronization process. The components of baseband processing unit 370 may operate using oscillator 350 as a clock source.

The baseband processing unit 370, using the primary code correlator 375, may correlate the incoming signal 150 in the baseband form provided by the front-end 320 with a copy of the expected signal to extract the primary code 160. The local signal generator 372 may generate the copies of the expected signal. The locally generated expected signal may include similar components as those described with reference to 1 and 2 described, such as a primary code and a secondary code, values that are known a priori. The primary code correlator 375 may synchronize the primary code 160 in the received signal and in a locally generated expected signal and extract information related to the primary code 160 using a despreading process. To extract valid significance or data from the correlation, the local copy generated in the receiver must take into account the signal carrier frequency, the code delay, the Doppler frequency, the PRN, or the primary code 160 (which is unique for each satellite/signal), and the secondary code 170. The secondary code 170 may be unique to a satellite. Alternatively, satellites in a particular constellation, such as Galileo or Beidou, may share a secondary code 170.

As part of the synchronization process, secondary code correlator 377 may determine offsets associated with received secondary code 170. Secondary code 170 may be associated with one or both of a frequency offset and a code offset. A "frequency offset" refers to the frequency difference between received secondary code 170 and a locally generated expected secondary code. A "code offset" or "phase offset" refers to the degree of time synchronization between received secondary code 170 and the locally generated secondary code.

Therefore, synchronization may further involve searching for the signal energy over a plurality of hypothesized secondary code offsets and a plurality of hypothesized frequency offsets applicable to the secondary code 170. This is typically thought of as a two-dimensional search, where one dimension is the frequency offset and the other dimension is the code offset. Traditional approaches to secondary code synchronization in the presence of large frequency uncertainty involve calculating the energy associated with coherently or non-coherently integrated versions of the prompt correlator, or the primary code correlator output. The energy may be calculated over a two-dimensional grid of secondary code phase offset and frequency offset hypotheses. The secondary code phase(s) and frequency offset pair that results in the highest energy forms the basis for the estimates of the secondary code phase offset and the frequency offset, respectively. A full two-dimensional search over both the secondary code phase offset and the frequency offset can potentially result in an excess of Computational complexity can be associated with this. Furthermore, unless some additional processing is performed, the quality of the frequency estimate is limited by the frequency hypothesis bin spacing. Also, the secondary code phase estimate is degraded at frequency offsets that are relatively far from the nearest frequency bin hypotheses (for example, halfway between adjacent frequency bin hypotheses).

However, receiver 120 can determine the code offset and frequency offset by searching across a single dimension, such as the secondary code offsets, thereby determining the offsets in a computationally more efficient manner. Receiver 120 can achieve efficiency by searching for the secondary code phase offset in the secondary code chip transition region. Compared to conventional techniques, the techniques disclosed and described throughout this document and employed by the exemplary receiver 120 can provide more accurate and resource-efficient secondary code phase synchronization and frequency estimation of signals, such as GNSS signals, in the presence of frequency uncertainty.

wobei Z₊ die Menge an nichtnegativen ganzen Zahlen ist, s_k das Signal ist und n_k die Rauschkomponente ist.The output of the primary code correlator 375 at a k ^-th received C/A (Coarse Acquisition) epoch contains the following signal and noise components: $${\text{y}}_{\text{k}}={\text{s}}_{\text{k}}+{\text{n}}_{\text{k}}\text{ k}\in {\text{Z}}_{+}$$

where Z ₊ is the set of non-negative integers, s _k is the signal and n _k is the noise component.

$$\begin{array}{cc}{b}_m\in \left\{-\mathrm{1,1}\right\}& T_b-beabstandeteBPSK-Symbole\end{array}$$

$$p_k=\{\begin{array}{cc}{c}_k& k\in \left\{\mathrm{0,1,}\dots N-1\right\}\\ 0& k\notin \left\{\mathrm{0,1,}\dots N-1\right\}\end{array}$$

$$\begin{array}{cc}{c}_k\in \left\{-\mathrm{1,1}\right\}& T_{C/A}Sekundrärcodechips\end{array}$$

$$\begin{array}{cc}N=\frac{T_b}{T_{C/A}}& AnzahlSekundärcodeschipsproBit\end{array}$$

$$\begin{array}{cc}\varphi \in \left\{\mathrm{0,1,}\dots ,N-1\right\}& Sekundärcodeversatz\end{array}$$

wobei A, ω, and θ jeweils die Signalamplitude, die Frequenz (in Radianten pro C/A-Epoche) und die Phase sind. Außerdem sind T_C/A und T_b jeweils das C/A-Epochen-Intervall und das Bit-Intervall, während N die Anzahl an C/A-Epochen ist, die sich über ein Bit-Intervall erstrecken. Schließlich ist b_m das m^-te übertragene BPS-Symbol, ist p_k der k^-te Abtastwert einer Sekundärcode-Chip-modulierten Folge mit der Dauer T_b und ist φ der Bitphasenversatz.The signal component can be further expressed as: $$S_k=A{e}^{j\left(\omega k+\theta \right)}{\displaystyle \sum _{m=-\infty }^{\infty }{b}_m{p}_{k+mN-\varphi }}$$

$$\begin{array}{cc}{b}_m\in \left\{-\mathrm{1,1}\right\}& T_b-beabstandeteBPSK-Symbole\end{array}$$

$$p_k=\{\begin{array}{cc}{c}_k& k\in \left\{\mathrm{0,1,}\dots N-1\right\}\\ 0& k\notin \left\{\mathrm{0,1,}\dots N-1\right\}\end{array}$$

$$\begin{array}{cc}{c}_k\in \left\{-\mathrm{1,1}\right\}& T_{C/A}Sekundrärcodechips\end{array}$$

$$\begin{array}{cc}N=\frac{T_b}{T_{C/A}}& AnzahlSekundärcodeschipsproBit\end{array}$$

$$\begin{array}{cc}\varphi \in \left\{\mathrm{0,1,}\dots ,N-1\right\}& Sekundärcodeversatz\end{array}$$

where A, ω, and θ are the signal amplitude, frequency (in radians per C/A epoch), and phase, respectively. T _C/A and T _b are the C/A epoch interval and the bit interval, respectively, while N is the number of C/A epochs spanning one bit interval. Finally, b _m is the m ^-th transmitted BPS symbol, p _k is the k ^-th sample of a secondary code chip-modulated sequence of duration T _b , and φ is the bit phase offset.

Modelliert als eine Realisation einer unabhängigen, identisch verteilten (u.i.v.) Folge von zirkulär komplexen normalen Zufallsvariablen mit Mittelwert Null und der Varianz δ², wobei E[·] die statistische Erwartung bezeichnet.The noise component of equation 1 can be further expressed as: $$\begin{array}{cc}{n}_k\stackrel{\text{IID}}{\sim }CN\left(\mathrm{0,}{\sigma }^2\right)& {\sigma }^2\end{array}=E\left[{\left|n_k-E\left[n_k\right]\right|}^2\right]=E\left[{\left|n_k\right|}^2\right]$$

Modeled as a realization of an independent, identically distributed (uiv) sequence of circularly complex normal random variables with zero mean and variance δ ² , where E[·] denotes the statistical expectation.

der Länge K.In view of the above mathematical expressions, determining the phase offset of the output of the primary code correlator 375 involves estimating the secondary code phase offset φ given a sequence ${\left\{y_k\right\}}_{k=0}^{K-1}$

of length K.

A traditional two-dimensional search grid over N hypothesized secondary code phase offsets and Q hypothesized frequency offsets can be expressed as: $$\begin{array}{cc}\overline{\varphi }\in \overline{\Phi }=\left\{{\overline{\varphi }}_0{\overline{\varphi }}_1\dots {\overline{\varphi }}_{N-1}\right\}& {\overline{\varphi }}_i=i\\ \overline{\omega }\in \overline{\Omega }=\left\{{\overline{\omega }}_0{\overline{\omega }}_1\dots {\overline{\omega }}_{Q-1}\right\}& {\overline{\omega }}_q\in [-\pi ,\pi )\end{array}$$

Assume that the received samples span an integer number of bits/secondary code repetitions: K = PN, where P is an integer greater than 1. Therefore, a merit function expressing the search that must be performed to determine the code phase offset of the traditional two-dimensional method is: $$M_{\overline{\varphi },\overline{\omega }}={\displaystyle \sum _{p=0}^{P-2}{\left|{\displaystyle \sum _{i=0}^{N-1}{c}_i{y}_{i+pN+\overline{\varphi }}{e}^{-j\overline{\omega }i}}\right|}^2}$$

The arguments ϕ , ω̂, which jointly maximize the merit function, are considered to be the detected secondary code phase offset and the estimated frequency offset, which is mathematically expressed as: $$\widehat{\varphi },\widehat{\omega }=\underset{\overline{\varphi }\in \overline{\Phi }\mathrm{,}\overline{\omega }\in \overline{\Omega }}{{\displaystyle \text{arg}\_\text{max}}}\left\{M_{\overline{\varphi },\overline{\omega }}\right\}$$

Receiver 120 may detect and determine the code phase offset and the estimated frequency offset in a more efficient manner by searching a single dimension, unlike the two-dimensional search expressed in the merit function of Equation 5. Receiver 120 may determine the code phase offset and the estimated frequency offset by operating in the secondary code chip transition region via complex conjugate products of the prompt correlator outputs that are coherently integrated into the C/A epoch. The complex conjugate product may be correlated against delayed versions of an appropriately defined reference sequence that correspond to the expected complex conjugate products in the absence of noise and frequency errors. Alternatively, delayed versions of the complex conjugate product may be correlated against an appropriately defined reference sequence that correspond to the expected complex conjugate products in the absence of noise and frequency errors. The complex conjugate products and/or the reference secondary code sequence can be delayed using delays corresponding to the different secondary code phase hypotheses. The correlation results are either a constructive summation or a deconstructive summation depending on the sign of the corresponding chip transitions. The correlations can also be referred to as cross-correlations.

A magnitude of the resulting correlations can be calculated. The magnitude can be the absolute value of the final chip junction region correlation operation. The delay corresponding to the largest correlation can be used to estimate the secondary code phase offset. The phase associated with the largest correlation can be used to estimate the frequency offset. Based on the identified cross-correlation, a one-dimensional search over secondary code phase offsets can provide the code phase offset and the frequency offset of the secondary code. Furthermore, frequency estimates can be generated with minimal additional computation and with accuracy.

wobei (.)* die komplexe Konjugation bezeichnet. 4 illustrates an exemplary flowchart with at least some of the steps involved in detecting the code phase offset. The steps shown operate on the outputs of the prompt correlators of receiver 120 (402). For example, receiver 120, using baseband processing unit 377, may calculate (404) a complex conjugate product sequence with lag 1 of the secondary code component of received signal 150. Alternatively, a complex conjugate product sequence with lag p, such as lag 2 or lag 3, may be calculated. As a result, complex conjugate products of prompt correlator outputs coherently integrated into the C/A epoch or primary code epoch are formed. This can be expressed as follows: $$\begin{array}{cc}{\mathcal{l}}_k=y_k+1y_k^{\ast }& k\in \left\{\mathrm{0,1,}\dots ,K-2\right\}\end{array}$$

where (.)* denotes the complex conjugation.

Alternatively, in cases where a residual frequency offset is small, the real parts of the prompt correlator outputs can be integrated into the C/A as shown in Equation 6A. $$\begin{array}{cc}{l}_k=Re\left\{y_{k+1}{y}_k^{\ast }\right\}& k\in \left\{\mathrm{0,1,}\dots ,K-2\right\}\end{array}$$

Furthermore, the receiver 120 may calculate one or more reference secondary signal sequences (408). A reference secondary code sequence may be a lag-1 secondary code chip product sequence with N elements. An exemplary reference secondary code d _k may be expressed as: $$\begin{array}{cc}{d}_k=c_{\left(k+1\right)\text{ mod }{N}^C{}_k^{\ast }}& k\in \left\{\mathrm{0,1,}\dots ,N-1\right\}\end{array}.$$

Alternativ dazu können die hypothetisierten Codephasenversätze verwendet werden, um verzögerte Versionen der Referenz-Codefolgen zu erzeugen, die durch d_k dargestellt sind (480), und die Meritfunktion kann Korrelationen der verzögerten Versionen der Referenz-Sekundärcodefolge und der konjugiert komplexen Produkte der Prompt-Korrelator-Ausgänge, die kohärent in die Primärcodeepoche integriert werden, beinhalten (484). Für Lag-1-Produkte kann der Wert von p in 404 1 sein. Aber der Empfänger kann die Meritfunktion auf der Basis einer gewissen Kombination von konjugiert komplexen Produkten mit Lag p bilden, wobei p ≥ 1.The generated reference signals can be correlated with delayed versions of the complex conjugate product (410, 414). For example, based on different hypotheses of the code phase offsets ϕ Correlations of the generated reference signals and the delayed versions of the complex conjugates (conjugates of complex numbers) are calculated. A one-dimensional merit function representative of the operation can be expressed as: $$V_{\overline{\varphi }}={\displaystyle \sum _{i=0}^{N-1}{d}_i}\left({\displaystyle \sum _{p=0}^{P-2}{\mathcal{l}}_{i+pN+\overline{\varphi }}}\right).$$

Alternatively, the hypothesized code phase offsets can be used to generate delayed versions of the reference code sequences represented by d _k (480), and the merit function can include correlations of the delayed versions of the reference secondary code sequence and the complex conjugate products of the prompt correlator outputs coherently integrated into the primary code epoch (484). For lag-1 products, the value of p in 404 can be 1. However, the receiver can form the merit function based on some combination of complex conjugate products with lag p, where p ≥ 1.

und der Frequenzversatz ω̂ kann mit so gut wie keiner zusätzlichen Berechnung auf der Basis der resultierenden Korrelationen geschätzt werden Der Frequenzversatz kann zum Beispiel als der Arkustangens der Korrelation mit der maximalen Amplitude berechnet werden: $$\widehat{\omega }=L\left(V_{\widehat{\varphi }}\right).$$

Alternativ oder zusätzlich dazu kann der Frequenzversatz auf der Basis einer gewichteten Kombination von mehreren hohen Spitzenwerten berechnet werden, um die Frequenz bei diesen Verzögerungen zu schätzen. Es kann zum Beispiel eine Teilmenge der resultierenden Korrelationen ausgewählt werden, um den Frequenzversatz zu berechnen. Die Teilmenge kann eine vorbestimmte Anzahl von Korrelationen umfassen. Die Korrelationen, die in der Teilmenge ausgewählt sind, können auf einem vorbestimmten Größenschwellenwert basieren. So können zum Beispiel Korrelationen oberhalb des vorbestimmten Größenschwellenwerts als die Teilmenge für die Ermittlung des Frequenzversatzes ausgewählt werden. Alternativ oder zusätzlich dazu können andere Kriterien für die Auswahl der Teilmenge von Korrelationen verwendet werden.A value of the resulting correlations can be calculated. The correlation with the maximum magnitude can be identified (440). The delay associated with the correlation with the maximum magnitude can be used to determine the phase offset. The associated delay can be output, for example, as the secondary code phase offset (460). The detected secondary code phase offset ϕ can then be expressed as $$\widehat{\varphi }=\underset{\overline{\varphi }\in \overline{\Phi }}{\text{arg max}}\left|V_{\overline{\varphi }}\right|$$

and the frequency offset ω̂ can be estimated with almost no additional calculation based on the resulting correlations. The frequency offset can be calculated, for example, as the arctangent of the correlation with the maximum amplitude: $$\widehat{\omega }=L\left(V_{\widehat{\varphi }}\right).$$

Alternatively or additionally, the frequency offset may be calculated based on a weighted combination of multiple high peak values to estimate the frequency at these delays. For example, a subset of the resulting correlations may be selected to calculate the frequency offset. The subset may comprise a predetermined number of correlations. The correlations selected in the subset may be based on a predetermined size threshold. For example, correlations above the predetermined size threshold may be selected as the subset for determining the frequency offset. Alternatively or additionally, other criteria may be used to select the subset of correlations.

Das Exzidieren kann die Auswirkung von Datenbitübergängen an dem wahren Sekundärcodephasenversatz vermeiden.In one example, the receiver 120 may excise the complex conjugate products that span bit boundaries by using a variation of the merit function, such as: $$V_{\overline{\varphi }}={\displaystyle \sum _{i=0}^{N-2}{d}_i}\left({\displaystyle \sum _{p=0}^{P-2}{\mathcal{l}}_{i+pN+\overline{\varphi }}}\right).$$

Excision can avoid the effect of data bit transitions on the true secondary code phase offset.

Thus, the receiver 120 may detect and determine the code phase offset and the frequency offset based on the complex conjugate product sequence and the one or more reference secondary code sequences using a one-dimensional search.

The methods, devices, and logic described above may be implemented in circuitry in many different ways and in many different combinations of hardware, or both hardware and software. For example, the entire system or portions of the system may comprise circuitry that includes a controller, a microprocessor, and/or an application-specific integrated circuit (ASIC), or circuitry may be implemented with discrete logic or discrete components, or with a combination of other types of analog or digital circuitry, combined on a single integrated circuit or distributed among multiple integrated circuits. All or part of the logic described above may be implemented as instructions for execution by circuitry, which may include a processor, controller, or other processing device, and may be stored in circuitry comprising a tangible or non-transitory machine-readable or computer-readable medium such as flash memory, random access memory (RAM) or read-only memory (ROM), erasable programmable read-only memory (EPROM) or other machine-readable medium such as compact disc read-only memory (CDROM) or a magnetic or optical disk. As a result, a product of manufacture, such as a computer program product, may be circuitry comprising a storage medium and computer-readable instructions stored on the medium that, when executed in an endpoint, computer system, or other apparatus or device, cause the apparatus or device to perform operations or acts in accordance with each of the above descriptions.

The circuitry may further comprise access instructions for execution by the circuitry. The instructions may be stored in a tangible storage medium that is not a volatile signal, such as a flash memory, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM); or on a magnetic or optical disk such as a compact disk read-only memory (CDROM). Disc Read Only Memory), a hard disk drive (HDD), or other magnetic or optical disk; or in or on another machine-readable medium. A product, such as a computer program product, may comprise a storage medium and instructions stored in or on the medium, and the instructions, when executed by circuitry in a device, may cause the device to implement any of the processing described above or illustrated in the drawings.

The implementations may be circuitry distributed among multiple system components, such as multiple processors and memories, and optionally including multiple distributed processing systems. Parameters, databases or data sets, and other data structures may be stored and managed separately, may be integrated into a single memory or database, may be logically and physically organized in many different ways, and may be implemented in many different ways, including, for example, linked lists, hash tables, arrays, records, objects, or implicit storage mechanisms as data structures. Programs may be parts (e.g., subroutines) of a single program, of separate programs distributed across multiple memories and processors, or they may be implemented in many different ways, such as in a library, such as a shared library (e.g., a dynamic link library (DLL). The DLL may, for example, store instructions that, when executed by the circuitry, perform any of the processing described above or illustrated in the drawings.

Claims (15)

A method comprising the following steps: Receiving (402), at a receiver (120) of a global navigation satellite system (GNSS) (100), a plurality of GNSS signals (150) transmitted by a GNSS satellite (110), wherein a GNSS signal (150) comprises a primary code sequence (160), a secondary code sequence (170), and a data portion (180); Extracting (408) the secondary code sequence (170) in each of the received GNSS signals (150); Analyzing (410) the extracted secondary code sequence (170) based on a plurality of reference secondary code sequences, wherein the reference secondary code sequences comprise delayed versions of a predetermined secondary code sequence (170); Identifying, based on the analysis, the delay associated with a reference secondary code sequence from the plurality of reference secondary code sequences as a phase offset to be used for synchronizing the GNSS receiver (120) with the GNSS satellite (110); and Outputting (460) the phase offset to be used for synchronizing the GNSS receiver (120) with the GNSS satellite (110). Procedure according to Claim 1 , wherein the plurality of received GNSS signals (150) comprises a first GNSS signal (150) and a second GNSS signal (150), and the method further comprises the steps of: extracting a first secondary code sequence (170) from the first GNSS signal (150) and a second secondary code sequence (170) from the second GNSS signal (150); generating (404) a complex conjugate (complex conjugate) of the second secondary code sequence (170); and calculating a product of the first secondary code sequence (170) and at least a portion of the generated complex conjugate of the second secondary code sequence (170). Procedure according to Claim 2 further comprising the step of: calculating (414, 484) a plurality of cross-correlations of the calculated product and each secondary code sequence (170) from the plurality of reference secondary code sequences. Procedure according to Claim 3 , further comprising the steps of: identifying (440) a cross-correlation having a maximum magnitude value from the calculated cross-correlations; and identifying the reference secondary code sequence associated with the identified cross-correlation having the maximum magnitude. Procedure according to Claim 4 , where the delay associated with the identified reference secondary code sequence is used as the phase offset to be used for synchronization. Procedure according to Claim 4 , further comprising the steps of: determining an angle associated with the resulting sequence of the calculated correlation with the maximum result; and outputting the determined angle as the frequency offset to be used for synchronizing the GNSS receiver (120) with the GNSS satellite (110). Procedure according to Claim 6 , where the angle is determined by calculating an arctangent of the resulting sequence of the calculated correlation with the maximum magnitude value. A radio signal receiver comprising: circuitry (310) for receiving radio signals or wireless signals (150), each radio signal (150) comprising a spread-spectrum signal comprising a periodic extension of a primary code (160), a periodic extension of a secondary code (170), and a data portion (180); circuitry for determining, from a first received radio signal (150), a first chip sequence representative of the secondary code (170) by extracting the secondary code (170) and the data portion (180) from the first received radio signal (150); circuitry (320) for determining, from a second received radio signal (150), a second chip sequence representative of the secondary code (170) by extracting the secondary code (170) and the data portion (180) from the second received radio signal (150); circuitry (370) for identifying a phase offset associated with the received radio signals (150) by analyzing the first chip sequence and the second chip sequence; wherein, based on the analysis, the delay associated with a reference secondary code from the plurality of reference secondary codes is identified as a phase offset, the reference secondary codes comprising delayed versions of a predetermined secondary code (170); andcircuitry for synchronizing the radio signal receiver (120) with a transmitter (110) of the received radio signals (150) using the identified phase offset. Radio signal receiver according to Claim 8 , further comprising: circuitry for calculating a complex conjugate product of the first chip sequence and the second chip sequence; circuitry (375, 377) for calculating a plurality of cross-correlations of a reference chip sequence and a delayed version of the complex conjugate product, the complex conjugate product being delayed by one of a plurality of predetermined delays; and circuitry for identifying a delay from the plurality of predetermined delays such that a magnitude of the cross-correlation calculated at the identified delay is the maximum among the magnitudes of the calculated cross-correlations. Radio signal receiver according to Claim 8 , further comprising circuitry (377) for determining a frequency offset used in synchronizing the radio signal receiver (120) with the transmitter (110) on the basis of the calculated cross-correlations. Radio signal receiver according to Claim 10 , wherein the phase offset and the frequency offset for synchronizing the radio signal receiver (120) with the transmitter (110) are determined without searching over a set of frequency offsets. A non-transitory computer storage medium comprising instructions executable by one or more processors, the instructions comprising: Instructions for receiving a first signal (150) from a transmitter (110) and a second signal (150) from the transmitter (110), the first and second signals (150) each comprising at least a periodic extension of a primary code (160), a data portion (180), and a periodic extension of a secondary code (170); Instructions for identifying the secondary code sequence (170) in the received first signal (150); Instructions for identifying the secondary code sequence (170) in the received second signal (150); Instructions for determining a phase offset associated with the received signals (150) by analyzing the identified secondary code sequences (170); wherein based on the analysis, the delay associated with a reference secondary code sequence from a plurality of reference secondary code sequences is identified as a phase offset, the reference secondary code sequences comprising delayed versions of a predetermined secondary code sequence (170); and instructions for synchronizing a local clock source based on the identified phase offset. Non-volatile computer storage medium according to Claim 12 , the instructions further comprising: instructions for calculating a complex conjugate product of the secondary code sequence (170) in the received first signal (150) and the secondary code sequence (170) in the received second signal (150). Non-volatile computer storage medium according to Claim 12 , the commands further comprising: Instructions for calculating correlations of the complex conjugate product with each reference signal of a set of predetermined reference signals; instructions for calculating a magnitude of each of the correlations and for determining, as a phase offset, a delay associated with a predetermined reference signal from the set of predetermined reference signals, wherein the magnitude of the predetermined reference signal is the maximum among the calculated magnitudes; and instructions for calculating the frequency offset based on a weighted combination of a subset of the correlations of the complex conjugate product with each reference signal of the set of predetermined reference signals, wherein the subset has a predetermined number of correlations. Non-volatile computer storage medium according to Claim 12 , where: the complex conjugate product is coherently integrated into the epoch of the primary code (160); and the real parts of the complex conjugate product are integrated into the epoch of the primary code (160).

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