Bit signal structure for differentially encoded broadcasts

0001The subject matter described herein relates to electronic communications, and in particular to signal coding methods that can be used in wireless communication systems such as satellite communication systems. Furthermore, the subject matter described herein relates to how geolocation information is utilized using low earth orbit (LEO) satellite signals.

0002The Global Positioning System (GPS) is a global space navigation system that includes a space segment, a ground segment, and a user segment. Using the position of the satellite group as a reference point, the position of the GPS user receiver is calculated, and this position is usually calculated within a few meters, and in some cases within a few centimeters. It may be calculated. Each of the satellite group, the ground base station group, and the GPS user receiver has a pre-written timing signal group, and these timing signals start from an accurate time. In order to lock on to these signals broadcast from the satellites, the ground station and GPS user receivers each internally generate signals of these ground stations and receivers, respectively of these ground stations and receivers. Gently synchronize with the time predicted by the internal clock. When locked on to these signals, the GPS user receiver measures the distance to each satellite, called a pseudo-distance. These pseudo-distance measurements include the actual distance to the satellite plus other small errors, in addition to the error associated with the receiver clock time offset with respect to GPS time. Ground stations included in the GPS control segment network supply distance measurements and use these distance measurements to generate satellite clock and satellite orbit predictions. These predicted values are periodically uploaded to the satellite group, and these satellites broadcast this data to the user receiver to support the user receiver positioning function.

0003Low altitude orbital (LEO) satellite constellations such as Iridium enable navigation without the use of GPS, partly due to GPS signal jamming and GPS signal power loss issues. It has been proposed as a mechanism that enables it in conjunction with GPS systems. The Iridium Satellite Constellation is a low-altitude orbiting satellite constellation with an altitude of about 485 miles (781 km) and six orbits close to polar orbits tilted at 86.4 °, and about 17,000 miles per hour (27,000). Maintain the orbital speed of km / h). The constellation can be used to provide global satellite communications services, including voice and data communications with global satellite phones, pagers, and integrated transceivers. The constellation contains 66 effective satellites in orbit, which orbit from pole to pole with an orbital period of just over 100 minutes. In orbital design, the opposite orbital planes of adjacent satellites orbiting in opposite directions are formed. In addition, these satellites use interconnect technology to relay data within the constellation. Each Iridium satellite has 48 spot beams as part of a constellation-specific identifiable beam shape projected onto the surface of the Earth.

0004Various technologies that enhance the functionality of GPS systems using standard times from LEO satellites are the patented "System and Method For Generating Precise Position Determination" by Cohen et al. ) , Patent Document 1 (US Patent RE No. 37,256), Method And Receiver Using A Low Earth Orbiting Satellite Signal To Augment The Global Positioning System patented by Enge et al. "Method And Receiver Using A Low Earth Orbiting" patented by Enge et al., Patent Document 2 (US Pat. No. 5,812,961) entitled "Method and Receiver Using A Low Earth Orbiting". Satellite Signal To Augment The Patented in Patent Document 3 (US Pat. No. 5,944,770) entitled "Global Positioning System (method and receiver for enhancing the Global Positioning System using low-altitude orbiting satellite signals)" and Rabinowitz et al. Also includes patents such as Patent Document 4 (US Pat. No. 6,373,432) entitled "System Using LEO Satellites For Centimeter-Level Navigation". The disclosures of these patents are incorporated herein by reference in their entirety.

0005The iridium system is differentially coded. A signal processing scheme known as encoding) is used to encode and transmit a quadrature phase shift keying (QPSK) modulated broadcast. In the differential coding process, the broadcast in-phase modulation bits and quadrature modulation bits (Group I and Group Q) are such that the output state of the differential coder is the current (I, Q) input to the differential coder, and It is re-encoded to be a function of both the previous (I and Q) states of the differential-coded device. This differential coding scheme causes problems when using pseudo-random code sequences and related correlation detection methods, because multiple broadcasts are made each time a desired code is attempted to be transmitted. Because. This complicates the correlation process in the user receiver. Instead of searching for available code messages in one group and correlating these code messages, the receiver must instead search for all of the very large number of messages being broadcast. As a result, the amount of memory, the amount of processing, and the amount of power required for the user receiver are increased. In addition, this reduces the distance between the codes and increases the likelihood that one code will be mistakenly determined to be another code in the correlation process.

0006Therefore, yet another coding technique used in LEO satellite systems such as Iridium needs to be useful.

<p num="0007"><patcit num="1"><text>U.S. Pat. No. RE 37,256</text></patcit><patcit num="2"><text>U.S. Pat. No. 5,812,961</text></patcit><patcit num="3"><text>U.S. Pat. No. 5,944,770</text></patcit><patcit num="4"><text>U.S. Pat. No. 6,373,432</text></patcit></p>

0008Described herein is a method of encoding transmission data using a differential encoder. Further described are transmitters adapted to realize such a transmission communication system utilizing a differential encoder.

0009In some embodiments, the communication device comprises a differential encoder, which receives transmission data and encodes the transmission data with a code set, the code set being the difference. When processed by the dynamic coder, the code set sets the differential coder to a known state and produces an uncorrelated output sequence.

0010In another embodiment, in a method of encoding transmission data using a differential encoder, the transmission data is received by the differential encoder, and the transmission data is encoded using a code set, and the coding is performed. When the set is processed by the differential encoder, the code set sets the differential encoder to a known state and produces an uncorrelated output sequence.

0011Detailed explanation will be given with reference to the attached figure.

0012<figref num="1">FIG. 1 is a schematic diagram of a low earth orbit (LEO) satellite communication system according to various embodiments.</figref><figref num="2">FIG. 2 is a schematic diagram of a group of components of a transmitting side device and a receiving side device according to various embodiments.</figref><figref num="3">FIG. 3 is a flowchart showing an operation in a method of differentially coded broadcasting using a bit signal structure according to various embodiments.</figref><figref num="4">FIG. 4 is a flowchart showing an operation in a method of generating code groups according to various embodiments and performing differential coding processing.</figref>

0013The following description describes many specific details so that the various embodiments can be fully understood. However, those skilled in the art will appreciate that the various embodiments can be implemented without the use of specific details. In other examples, known methods, procedures, parts, and components are shown in detail or described to ensure that certain embodiments are not obscured.

0014The subject matter of this application is mainly described in relation to differential coding in the QPSK modulation scheme used for Iridium satellites. However, those skilled in the art will readily appreciate the methods described herein for other systems that utilize differential coding in either the QPSK modulation method or the BPSK modulation method. You will understand what you can do. Such systems can include, but are not limited to, other mobile communication systems, such as aerial and similar communication systems, as well as quiescent communication platforms, including, but not limited to, ships. Alternatively, a mobile phone tower can be mentioned.

0015Described herein are differential coding methods that can be used in transmitters used in low earth orbit (LEO) satellite systems. In some embodiments, the differential coding method uses a preselected set of codes that exhibits the characteristic that the differential coder of the transmitter is kept in a known logical state. For example, some preselected codes keep the transmitter in the same logical state as it was when the transmitter was in the pre-transmission state. As a result, a 1: 1 correspondence between the input data and the output data of the differential encoder can be made, which facilitates the signal correlation processing and the signal selection processing in the receiver.

0016FIG. 1 is a schematic diagram of a low earth orbit (LEO) satellite communication system 100 according to various embodiments. Referring to FIG. 1, in some embodiments, the system 100 comprises one or more LEO satellites 110 communicating with one or more receiving devices 120a, 120b collectively represented by reference number 120.

0017In some embodiments, these LEO satellites 110 can be embodied as a group of satellites of the Iridium satellite constellation. A typical satellite communication system such as Iridium is designed to operate with the satellite signal having received power above the surrounding noise floor.

0018The receiving device 120 can be realized as a communication device such as a satellite telephone or a mobile phone, or as a component group of a communication device or a computing device such as a personal computer, a laptop computer, or a mobile information terminal. As another configuration, the receiving device 120 can be implemented as a positioning device or navigation device similar to a device used connected to a Global Positioning System (GPS). The GPS system utilizes spread spectrum connection technology, which allows these receivers to pick up signals even if the received broadcast is buried in the noise floor. Systems such as GPS broadcast pseudo-random codes from satellites and use correlation methods to extract signals from noise.

0019GPS systems are extremely poor in performance in attenuated environments 130 (eg, indoors) due to lack of signal power, and other systems that can operate better in these environments when signal power is insufficient. Will be required. Iridium satellites broadcast with much higher power than GPS transmission. In one example, a receiver unit configured to operate with a signal received from a LEO satellite, such as an Iridium satellite, can operate at a signal level attenuated by less than about 45 dB at the antenna of the receiving device 120. .. Therefore, by using the LEO type iridium satellite, the iridium satellite compatible receiver unit can operate at about 15 to 20 dB, and below this signal level, a typical GPS compatible receiver unit operates. It disappears.

0020Various satellite communication systems, including iridium, use differential-coded signal processing schemes to encode and transmit quadrature phase shift keying (QPSK) modulated broadcasts. In the differential coding process, the broadcast in-phase (I) and quadrature (Q) modulation bits are so that the output of the differential-coding device is a function of the current I / Q state and the previous I / Q state. Recode. Table 1 shows typical differential coding schemes used in QPSK systems. Any given message (represented by a string of bits) is differentially coded before the message is broadcast.

0021<img id="000002" he="92" wi="159" file="JP6132874B2_D0001.tif" img-format="tif" img-content="drawing" />

0022The current output of the differential coding process is a function of the current I / Q state and the previous I / Q state. As an example, the bit-coded message (A) input to the differential-coded device actually has four different formats (B1, B2, B3,) depending on the previous state (C) of the differential-coded device. It is broadcast in a format (B) that can have B4). The examples shown in Table 2 are illustrated below: Table 2: Conversions in encoders Case 1: A = 00000000 Pre-encoded message C = 00 B1 = 00000000 Broadcast message Case 2: A = 00000000 Pre-encoded message C = 01 State before differential coding B2 = 01010101 Broadcast message Case 3: A = 00000000 Pre-encoded message C = 10 State before differential coding B3 = 10101010 Broadcast message Case 4: A = 00000000 Pre-encoded message C = 11 State before differential coding B4 = 11111111 Broadcast message

0023Therefore, for the subsequent predetermined message A, four differentially coded messages B are always generated, and these messages are output from the differential coder. Message B depends on the state C before the encoder, and a 1: 4 input code (A) to outputable code (B) ratio is established.

0024The differential coding schemes used for Iridium satellites and other communications satellites pose problems when using pseudo-random code sequences and related correlation detection methods, because of the desire to be input to the differential coder. This is because four types of broadcasting are performed for each message A, which is a code. This 1: 4 ratio makes the correlation process in the user receiver extremely complicated. Instead of searching for available code messages in one group and correlating these code messages, the receiver must instead search all four times this number of messages. is there. As a result, the amount of memory, the amount of processing, and the amount of power required for the user receiver are increased. In addition, this reduces the distance between the codes and increases the likelihood that one code will be mistakenly determined to be another code in the correlation process.

0025In one aspect, described herein is a system and method for differential coding in which a differential coding device uses a code set, and when the code set is processed by the differential coding device, it differs depending on the code set. The dynamic coder is set to a known state. The known state can be a predetermined logical state. For example, in various embodiments, the differential encoder can retain its initial logical state upon receiving the transmitted data, and the differential code depends on the code set that the differential coder uses to encode the data. The device can be reset to the initial logical state. In various embodiments, the differential encoder can retain its initial logical state upon receiving the transmitted data, and the differential encoder can be driven by the code set it uses to encode the data. , It is possible to reset to a known logical state different from the initial logical state. In various embodiments, the known state can be the known (I, Q) state after the input data stream has been processed. By setting the differential coder to the known (I, Q) state, it is possible to eliminate the situation where the ratio of the number of inputs to the number of outputs is 1: 4.

0026In some embodiments, the methods of the present disclosure can be used in transmitter devices such as transmitters of LEO satellites such as satellite 110 shown in FIG. FIG. 2 is a schematic diagram of a group of components of a transmitting side device and a receiving side device according to various embodiments. With reference to FIG. 2, in one embodiment, the transmitting device 210 comprises a differential encoder 212, a modulator 214, and an amplifier 216. The transmitting device 210 is connected to the antenna 218. The receiving device 230 includes one or more signal processors (groups) 232, a demodulator 234, and a bandpass filter 236. The receiving device 230 is connected to the antenna 238.

0027The operation of the transmitting side device 210 and the receiving side device 230 will be described with reference to FIG. 2, and FIG. 3 is a flowchart showing an operation in a method of differentially coded broadcasting using a bit signal structure according to various embodiments. Will be explained with reference to. With reference to FIGS. 2 and 3, in operation 310, transmission data is received by the differential coder 212 of the transmitting device 210.

0028In operation 315, the data is differentially coded using the selection code group. In some embodiments, the differential coder 212 differentially codes the data with a code set, and when the code set is transmitted, the code set ensures that the differential coder 212 uses the code set. , (00), which has the property of being retained in the known (I, Q) state. This ensures a 1: 1 correlation between the input code (A) and the output code (B) of the differential coder 212, which in turn ensures that the system's differential coder is present. Nevertheless, the previous message no longer gives uncertainty to the current message. Therefore, in the above example, the code word always causes the differential coding device 212 to rotate and return to the initial phase (00) of the differential coding device.

0029In operation 320, the data signal output from the differential coding device is modulated by the modulator 214. The modulated signal is amplified by amplifier 216 (operation 325) and transmitted to antenna 218 (operation 330).

0030The broadcast signal is received by the antenna 238 connected to the receiving device 230 (operation 335). The signal is transmitted from the antenna 238 to a bandpass filter, which filters the unwanted frequency domain (operation 340), then demodulates with demodulator 234 (operation 345), and then the signal. Transmit to processor 232. In the relevant part, the signal processor 232 can decode the signal (operation 350) and retrieve the original message. The original message can then be used in the locating process.

0031In another aspect, the differential coding device 212 can use a coding method referred to herein as super bit encoding (SBE), which is a noisy environment. Designed to improve the signal detection of messages in. In some embodiments, the differential coder 212 has a set of messages: G = N / n; However, G = processing gain, N = code Number of bits in the message n = number of information bits in the message. Encode with a processing gain equal to.

0032As an example, if 10 message bits are used to represent 1 information bit, the processing gain is equal to 10 (or 10 dB). In this case, the dB conversion factor is: 10log10 (G). Super bit sequences can be created using N pseudo-random bit sequences, in which case each sign has the correlation characteristics described above. Since N can be used as an integer, the output sequences from the differential encoder 212 are uncorrelated with each other to the extent that they can hold the difference values between the codewords.

0033In various embodiments, the superbit encoding scheme can be used in the methods described above, in which case the differential coding device uses a code set, and when the code set is processed by the differential coding device, the code set is used. Sets the differential coder to a known state. In one embodiment, in the superbit encoding scheme, a plurality of bit strings can be added to the N pseudo-random bit string, in which case the multiple bit strings reset the differential encoder to a known state. For example, two SBE (super bit encoding) bit strings will be described below. For each bit string, a bit string of "10" representing one 0 or one 1 is used. As an example of this embodiment, the bit codes shown in Cases 1 to 4 in Table 3 below indicate a 20-bit input code, and four zeros (0000) are used as a test series after the 20-bit input code. Added (bit sign A). The four zeros added to the end of the 20-bit string make it easy to identify the state C of the differential coder 212. Further, D specifies the coded state of the differential coding device 212. From the preferred output code, C = D is obtained, which resets the coded state of the differential coding device 212 to four zeros and the state of the coding device to the initial state of the differential coding device 212. It means that this case is also included at the end of the message indicating that. On the other hand, in the examples shown in Cases 5 to 8, the state after coding of the differential coding device 212 is not reset to the initial state before coding of the differential coding device 212.

0034Table 3: Bit code examples Case 1: A = 101111001111011100110000 Pre-encoded message C = 0000 State before differential coding B = 1001110100110001111000000 Broadcast message D = 0000 State of differential-coded device after coding Case 2: A = 101011110001001010100000 Pre-encoded message C = 0000 State before differential coding B = 101100111110101101000000 Broadcast message D = 0000 State of differential-coded device after coding Case 3: A = 10010101110101101010000 Pre-encoded message C = 0000 State before differential coding B = 101101001101001110000000 Broadcast message D = 0000 State of differential-coded device after coding Case 4: A = 101110000110110011000000 Pre-encoded message C = 0000 State before differential coding B = 1001000000100111100000000 Broadcast message D = 0000 State of differential-coded device after coding Case 5: A = 011101000011100000010000 Pre-encoded message C = 0000 State before differential coding B = 011000000011010101111111 Broadcast message D = 1111 State of differential-coded device after coding Case 6: A = 001101110101001001110000 Pre-encoded message C = 0000 State before differential coding B = 001110011110101110010101 Broadcast message D = 1011 Differential-coded state after coding Case 7: A = 100110010110101110100000 Pre-encoded message C = 0000 State before differential coding B = 011000000011010101111111 Broadcast message D = 1111 State of differential-coded device after coding Case 8: A = 11011111011100100000000 Pre-encoded message C = 0000 State before differential coding B = 111100110110111010101010 Broadcast message D = 1010 Differential-coded state after coding

0035In some embodiments, the idea of superbit encoding can be extended to the idea of representing several Gray codes of a message burst from a single communications satellite, such as a message burst from an Iridium satellite. it can. The burst data structure includes not only the identification information but also a group of information bits which are differentially coded payload data. In some embodiments, with n = 8 or 256 messages, 256 data bits (N) are included in one message burst, in which case multiple messages will be sent. The SBE (Super Bit Encoding) string is defined using two bit strings of "10" representing one 0 or one 1 for the case where n = 1 is used in the differential coding device of a communication satellite. can do. In this case, since N = 10 and n = 1, the signal gain G = 10.

0036FIG. 4 is a flowchart showing an operation in a method of generating a code group according to various embodiments and performing a differential coding process. With reference to FIG. 4, operation 410 generates a pseudo-random code candidate. In some embodiments, the pseudo-random code group can be generated using a random number generator to generate bit string candidates for groups 0 and 1.

0037In operation 415, it is determined whether or not the pseudo-random code group satisfies the differential coding standard. When QPSK encoding a pseudo-random code group, the number of bits must be an even number, and the sum of all bits with the value 1 must be an even multiple of 4. For QPSK coding, the number of bits must be an even number, and the number of some bits with the value 1 of all bits must be an even multiple of 2.

0038The pseudo-random code (s) can be input to the differential coder 212, which differential-codes the data (operation 420) and outputs the output based on the input pseudo-random code (s). To generate. Differential coding of a long, randomly arranged sequence of digits in groups 0 and 1 usually results in a new code that exhibits the same statistical properties as the input code. Therefore, there is a high probability that the output code generated by the differential coder 212 has the same characteristics as the input code.

0039In operation 425, the correlation characteristic of the output code group generated by the differential coder 212 is examined by taking the correlation between the input code and the output code. In general, a set of codewords that satisfy a rule causes low cross-correlation between the set of codewords. These operations in Figure 4 can be repeated until the appropriate set of codewords is found. The code set can then be used in the differential coding process shown in FIG.

0040In summary, the method of forcing differential coding by a satellite communication system presents difficulties in using a pseudo-random code sequence to encode a message, because every time a transmit code is entered. This is because four types of output codes will be broadcast. As a result, the correlation processing in the user receiver becomes extremely complicated due to the increase in the required memory amount, processing amount, and power amount. In addition, this reduces the distance between the codes and increases the likelihood that one code will be mistakenly determined to be another code in the correlation process. According to the various embodiments described herein, the data is encoded in the differential encoder 212 with a set of codes, which keeps the differential encoder 212 in a known output state. Once done, it can be useful for delivering pseudo-randomly encoded messages to users via communication satellites. By using these methods, timing and frequency information is sent to users in an attenuated environment (eg, indoors), and pseudo-random messages are sent from satellites such as Iridium to users located inside the structure. Can be delivered. The user who receives the message can extract the signal from the noise because the broadcast from the communication satellite has a higher signal strength than the broadcast from the GPS and the gain is high by the pseudo-random coding method. , You can enjoy the benefits. Once received, these messages provide information suitable for the user to locate himself. However, the coded message delivered to the user can be used for any purpose without loss of generality.

0041The term "one embodiments" or "some embodiments" herein includes at least one embodiment of a particular function, structure, or feature described in relation to the embodiment in question. This is to mean that. The phrase "in one embodiment" that appears many times in various parts of the specification does not have to mean that all phrases refer to the same embodiment, or that not all phrases refer to the same embodiment. For example, various embodiments can include embodiments shown below: A1. A communication device equipped with a differential coding device, and the differential coding device is: Receive the transmitted data, When the transmission data is encoded with a code set and the code set is processed with the differential code set, the code set sets the differential coder in a known state and produces an uncorrelated output sequence. A communication device that is generated. A2. Further: A modulator that modulates the coded signal and An amplifier that amplifies the coded signal and A transmitter that transmits the coded signal and The communication device according to claim A1. A3. Further, the receiving side device is provided away from the communication device, and the receiving side device is: A receiver that receives the coded signal and A decoder that decodes the coded signal and The communication device according to claim A1. A4. The communication device according to claim A1, wherein the coded signal includes at least one signal of a Global Positioning System (GPS) signal, a Gray code signal, or a satellite signal. A5. The communication device according to claim A3, wherein the receiving device includes at least one of a satellite telephone, a mobile phone, a personal computer, a laptop computer, or a personal digital assistant. A6. The communication device according to claim A3, wherein the receiving side device uses the coded signal in a positioning algorithm. B1. A method of coding the transmitted data using a differential coding device: Receive the transmitted data with a differential coder and When the transmission data is encoded with a code set and the code set is processed with the differential code set, the code set sets the differential coder in a known state and produces an uncorrelated output sequence. The method that is generated. B2. The method of claim B1, wherein the differential encoder utilizes a QPSK modulation scheme. B3. The method of claim B1, wherein the differential encoder utilizes a BPSK modulation scheme. B4. The method of claim B2, wherein the differential encoder is located within a mobile communication system. B5. The method of claim B2, wherein the differential encoder is located within a fixed communication system.

0042Although various embodiments have been described in terms specific to structural features and / or methodological actions, it should be understood that the subject matter claimed should not be limited to the particular features or actions described. Without limitation, specific features and actions are disclosed as exemplary forms of implementing the claimed subject matter.<u style="single">The present invention also includes aspects described below.</u><u style="single">(Aspect 1)</u><u style="single">A method of coding transmission data using a differential coding device:</u><u style="single">Receive the transmitted data with a differential coder, and</u><u style="single">When the transmitted data is encoded with a code set and the code set is processed by the differential code set, the code set sets the differential coder in a known state and produces an uncorrelated output sequence. The method that is generated.</u><u style="single">(Aspect 2)</u><u style="single">Upon receiving the transmitted data, the differential encoder is held in its initial logical state and</u><u style="single">The method of aspect 1, wherein the differential encoder is reset to the initial logical state by the code set used by the differential encoder to encode the data.</u><u style="single">(Aspect 3)</u><u style="single">Upon receiving the transmitted data, the differential encoder retains its initial logical state and</u><u style="single">The method of aspect 1, wherein the code set used by the differential encoder to encode the data resets the differential encoder to a known logical state different from the initial logical state.</u><u style="single">(Aspect 4)</u><u style="single">Furthermore:</u><u style="single">Modulate the encoded signal and</u><u style="single">Amplifies the encoded signal and</u><u style="single">Sending the coded signal,</u><u style="single">The method according to aspect 1.</u><u style="single">(Aspect 5)</u><u style="single">Furthermore:</u><u style="single">Receive the coded signal and</u><u style="single">Decoding the coded signal,</u><u style="single">The method according to aspect 4.</u><u style="single">(Aspect 6)</u><u style="single">Further, the method according to aspect 5, wherein the coded signal is used in a positioning algorithm.</u><u style="single">(Aspect 7)</u><u style="single">The method of aspect 6, wherein the encoded signal comprises at least one signal of a Global Positioning System (GPS) signal, a Gray code signal, or a satellite signal.</u><u style="single">(Aspect 8)</u><u style="single">The method according to aspect 6, wherein a superbit encoding method is used when encoding the transmission data, and in the superbit encoding method, each information bit to be transmitted is represented by an N pseudo-random bit string.</u><u style="single">(Aspect 9)</u><u style="single">The method according to aspect 8, wherein the signal-to-noise ratio is increased by utilizing the super bit encoding method so that a user indoors can acquire accurate timing information.</u><u style="single">(Aspect 10)</u><u style="single">The method according to aspect 8, wherein in the superbit encoding method, a plurality of bit strings are added to the N pseudo-random bit string, and the differential encoder is reset to a predetermined logical state by the plurality of bit strings.</u><u style="single">(Aspect 11)</u><u style="single">The method according to aspect 1, wherein the differential encoder is arranged in a communication system used as a positioning system.</u><u style="single">(Aspect 12)</u><u style="single">The method according to aspect 5, wherein when receiving the coded signal, the user in the attenuation environment can receive the signal and acquire accurate signal acquisition timing information.</u><u style="single">(Aspect 13)</u><u style="single">A communication device including a differential coding device, wherein the differential coding device is:</u><u style="single">Receives outgoing data, and</u><u style="single">When the transmission data is encoded with a code set and the code set is processed with the differential code set, the code set sets the differential coder in a known state and produces an uncorrelated output sequence. A communication device that is generated.</u><u style="single">(Aspect 14)</u><u style="single">Upon receiving the transmitted data, the differential encoder retains its initial logical state and</u><u style="single">13. The communication device according to aspect 13, wherein the differential encoder is reset to the initial logical state by the code set used by the differential encoder to encode the data.</u><u style="single">(Aspect 15)</u><u style="single">Upon receiving the transmitted data, the differential encoder retains its initial logical state and</u><u style="single">13. The communication device according to aspect 13, wherein the code set used by the differential encoder to encode the data resets the differential encoder to a known logical state different from the initial logical state.</u><u style="single">(Aspect 16)</u><u style="single">The communication device according to aspect 13, wherein the differential coding device realizes a super bit encoding method, and in the super bit encoding method, each information bit to be transmitted is represented by an N pseudo-random bit string.</u><u style="single">(Aspect 17)</u><u style="single">The communication device according to aspect 16, wherein in the superbit encoding method, a plurality of bit strings are added to the N pseudo-random bit string, and the differential encoder is reset to a predetermined logical state by the plurality of bit strings.</u>