ES2334759A1 - Digital wireless links with modulation of multilevel phase based on photonic. (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

A digital wireless information transmission system comprising at least one optical infrastructure (1, 4b) for the generation, coding, modulation and demodulation of a wireless signal, at least one wireless electrical transmission and reception system (3a, 3b) and less an interface (2, 4a) between each optical infrastructure and each electrical system, characterized in that the optical structure is adapted to perform a differential multilevel modulation by phase shift. Thanks to this system, high spectral efficiency is achieved without the need for synchronization of the carrier. (Machine-translation by Google Translate, not legally binding)

Description

Wireless digital links with modulation of multilevel phase based on photonics.

Field of the Invention

The present invention applies to the field of telecommunications, and in particular to communication systems Wireless

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Background of the invention

Wireless communication is defined usually as the transmission of information by means, such as  the air, between two or more sources and recipients without the use of lines of transmission. As an example, a communication link Typical wireless consists of a transmitter and a receiver. He transmitter uses a radio frequency electric carrier signal (RF), which can be modulated with a baseband signal with the In order to transmit the signal wirelessly. In the receiver performs a reverse modulation (i.e. a demodulation) of the RF signal and the original band data stream is retrieved base.

There are several modulation techniques for wireless transmission Modulation techniques are identified often by the number of bits per symbol (n), that is, the spectral efficiency, being able to have different configurations in frequency, phase and / or amplitude of the modulated signal. Efficiency spectral is a key parameter in the wireless systems of high speed communication since the emission bands are very limited

Wireless communication systems with Gigabit per second (Gbps) capabilities can be based on photonic technology, as described in US 2008/0063028 A1. By way of example, the two optical signals with a frequency separation equal to the desired carrier frequency \ nu can be isolated and  one of the optical signals can be modulated by the data in baseband to be transmitted over the air interface. The described system in US 2008 / 0063028A1 it has been carried out using the technique of Binary modulation OOK (on-off keying) of low spectral efficiency, which allows the transmission of information (in its digital format (bits)) by modulating the signal optics with a binary state of on and off and performing on the side of the receiver a direct detection of the signal envelope without carrier synchronization requirement.

In another example, baseband data can modulate on the optical carrier in a modulation format multilevel in phase and / or intensity for communications wireless allowing a very high spectral efficiency. However, these transmission systems require complex receivers with synchronization and with a multitude of components electronic

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Object of the invention

The object of the present invention is to achieve an information transmission system with high efficiency spectral and less complex without requiring synchronization of the carrier

To achieve this objective, the invention provides a wireless digital information transmission system according to claim 1 and a method according to claim 12, wherein the information is recovered transparently for the optical system, that is, by demodulating the signal in a receiver optical without carrier synchronization requirement. Thus, using a multilevel type modulation, with a higher spectral efficiency, allows a signal of an increased bit rate (bits per second) to be transmitted without increasing the bandwidth compared to only two levels, ie n = 1 bit per symbol. The system comprises at least one optical infrastructure for the generation, modulation and demodulation of a wireless signal, at least one wireless electrical transmission and reception system and at least one interface between each optical infrastructure and each electrical system. The optical structure is adapted to perform a differential multilevel modulation by phase shift. Preferably, this modulation is a DQPSK, D8PSK or D16PSK modulation. The system, optionally, is adapted to carry out a phase multilevel differential modulation to perform an intensity modulation. Optionally it also comprises a signal splitter and a plurality of optical transmitters and receivers coupled to the transmitters through interfaces for generating a plurality of signal transmission channels in different RF bands, optical splitters, delay elements and additional elements. to perform a redundant transmission. The optical demodulator can be identical for wireless connections and wired connections. The optical transmission and reception units can be multiband and the same optical transmitter is adapted to be used individually for each band.

Some additional advantages of the system are that demodulation can be done using only components passive photonics, making the system much easier while that the nature of the signal is not degraded, and that the same Transmitter can be used individually for each band. This It also reduces consumption and costs.

Description of the drawings

In order to help a better understanding of the characteristics of the invention according to an example preferred for practical realization of it, the following description of a set of drawings where with character Illustrative the following has been represented:

Fig. 1 is a block diagram of an example system based on DxPSK modulation including the link wireless

Fig. 2 is a block diagram of an example DQPSK optical transmitter.

Fig. 3a-c are traces in the frequency domain of examples of optical signals of (a) input and (b) optical transmitter output and (c) photo output  detector.

Fig. 4a-b is a diagram of blocks of an example of (a) electrical to optical converter for convert an electrical signal to optics and (b) an optical demodulator DxPSK

Fig. 5a-c are traces in the frequency domain of optical signal examples of (a-b) the inlet and (c) the outlet of the filter in the electrical to optical converter.

Fig. 6 is a block diagram of an example optical transmitter for a redundant data link including a wired link and a wireless.

Fig. 7 is a block diagram of an example of transmitter for multiband transmission.

Fig. 8 is a block diagram of an example of system based on DxPSK-ASK modulation.

Fig. 9 is a block diagram of an example system based on DxPSK-ASK demodulation.

Detailed description of the invention

In the present invention, formats of multilevel modulation to achieve spectral efficiency higher (in terms of bits / Hz). The object of the invention is achieved using differential multilevel coding by phase shift (DxPSK) with a high bit rate, always  maintaining receiver configuration without needing carrier synchronization reducing the cost and / or consumption of power.

The wireless signal is received in the electrical to optical converter and converted to an optical signal and demodulated by a DxPSK optical demodulator. Optical demodulator DxPSK is identical for the present invention and for connections fiber optics. This specific feature allows the invention, the wireless DxPSK system, can be used without modification at any point of an optical system, allowing a redundancy link in which the data stream can transmitted through the fiber optic connection or through The wireless electrical connection. The transmitter uses a signal photonics with several components to generate one or more carriers RF electrical for wireless transmission. The photonic signal it can consist of a minimum of two components, with a separation of frequency corresponding to the carrier frequency RF electrical

In the transmitter the optical signal components they are isolated and routed through the modulator, where the sequence of data modulates at least one of the components using a DxPSK modulation, and at least one component is not modulated. TO then the different optical components are combined, before of photodetection. The photodetector output signal is the RF signal with the modulated data on the electric carrier. At other end of the wireless link, the receiver receives the RF signal and converts it into an optical signal using a converter electrical to optical The optical signal of DxPSK format is recovered at the output of the optical receiver. The DxPSK optical demodulator retrieves the data stream through a modulation operation inverse In some examples demodulation can be executed using only passive photonic components, such as couplers and binary delay elements, before the photodetection

Some embodiments of DxPSK modulation can provide very high bit rates using a larger number of bits per symbol. DxPSK embodiments so far demonstrated are DQPSK (RA Griffin and AC Carter, "Optical differential quadrature phase shift key (oDQPSK) for high-capacity optical transmission", in Proc. Optical Fiber Communication Conf. (OFC), 2002, Paper WX6) n = 2 bits per symbol, D8PSK ("Direct-detection optical differential 8-level phase-shift keying (OD8PSK) for spectrally efficient transmission", Cheolhwan Kim and Guifang Li, Optics Express, Vol. 12, Issue 15, pp. 3415 -3421) n = 3 bits per symbol, D16PSK ("16-level differential phase shift keying (D16PSK) in direct detection optical communication systems", Rakesh Sambaraju, Torger Tokle, Jesper Bevensee Jensen, and Palle Jeppesen, Optics Express, Vol. 14, Issue 22, pp. 10239-10244) n = 4 bits per symbol. Any depth of DXPSK modulation can be used in the present invention.

The invention can be applied to connections of Wireless access at high binary rate, and solve problems such as network island connectivity and local area networks, deployment Rapid communications in emergency situations or catastrophes Natural or wireless backup connections.

As an illustrative example, the transmitter optical routes an optical signal consisting of two lengths of wave in the near infrared region separated with the carrier frequency RF \ nu, 60 GHz (eg \ lambda_ {1} = 1550.00 nm and λ2 = 1550.48 nm). In this example, the data sequence modulates one of the optical components according to a DQPSK modulation format as an example of DxPSK. This signal DQPSK optics is photodetected and radiated by a wireless link in RF. The wireless link contains a radiation system composed of antennas and electrical amplifiers. In the converter electrical to optical the RF signal becomes an optical signal by an electro-optical modulator. This conversion normally results in a double sideband optical signal, although it Other modulations can be used as single, double sideband side band with suppressed carrier, or single side band with carrier suppressed. Before demodulation, at least one Sideband containing RF information is filtered. The Filtered sideband contains the data in DQPSK modulation. This signal passes through an optical DQPSK demodulator and recovers the data streams An example of DQPSK demodulation is a DMZI demodulator (Delayed Mach-Zehnder Interferometer). Another example of an optical demodulator is a system of integrated resonant rings.

On the one hand, the wireless link can transmit data streams in different RF carriers using several optical components and modifying the multiplexer wavelength WDM-DEMUX (Wavelength Division Multiplexing - to select the optical carrier adequate, while at least one optical component is not modulated. In a similar aspect, the WDM-DEMUX can be designed to include a complete set of bands so that the same Optical transmitter can be used individually for each band without any modification and only changing the optical signal.

On the other hand, the optical signal may include multiple components, making it possible to generate a signal wireless in any of the frequency bands. Is incorporated a Nx1 switch to control the wavelength component unmodulated and thus select the link frequency band wireless

Also, the transmitter output signal Optical can be divided into two or more components, where one or more components are routed through the wireless link and one or more components are routed through a wired link, such as redundancy solution or for simultaneous distribution to Different types of users.

DxPSK multilevel modulation can be modified with intensity modulation resulting in a new modulation DxPSK-ASK (DxPSK - Amplitude Shift Keying) that achieves a higher binary rate.

Fig. 1 shows a photonic based wireless communication link according to the invention. The optical transmitter (1) is fed with an optical signal (100) which contains two or more optical components, where the frequency separations between the components correspond to the frequencies of the desired RF electrical carriers. The optical transmitter (1) modulates one or more of N optical components with the baseband data D1, D2 and D n . An example of how the optical transmitter (1) can modulate the electrical data to generate the wireless signals is described in Fig. 2 for DQPSK modulation. The optical signal (110) output of the optical transmitter (1) is converted into an electrical signal (120) using an optical to electrical converter (2), which contains one or multiple photodetectors that convert the optical signal into an electrical one. The electrical signal (120) of the photodetector output is the desired RF wireless signal. The electrical signal emitted by the photodetector has a carrier frequency set by the frequency separation of the components of the optical signal at (100). The system can provide a wireless communication link with a capacity greater than 10 Gb / s using the optimal carrier frequency. The system also has the ability to provide wireless links at various carrier frequencies, which can be chosen dynamically. The signal (120) is transmitted in a medium through the radiation system (3a), and after traveling a certain distance, the signal (130) is received in the receiving system (3b). The output signal (140) of the reception system (3b) passes through an electrical to optical converter (4a) to convert the electrical signal into an optical signal. Demodulation, the inverse operation to that of optical modulation, is performed in (4b). Fig. 2 shows an exemplary embodiment of the optical transmitter designed for DQPSK modulation of the baseband data. In the optical transmitter the components of the optical signal (100) with a frequency separation equal to the desired RF carrier nu are isolated using a WDM-DEMUX (5), in (210) (S1) and (211) (S2 ). The optical component (210) is modulated with the two data D1 and D2. The component (210) is divided into two paths using the divisor (6) in (220) and (221). The signals (220) and (221) in the two paths are phase modulated with the data sequences D1 and D2 using modulators (7a) and (7b) respectively. Before combining the signals (230) and (231) in the two paths, a phase shift is introduced in one of the two paths. As an example, the phase-modulated signal (231) is moved 90 ° in phase using a phase shifter (8). The signals (230) and (241) are combined using the combiner (9). The combined signal (250) is a component of the four-level differential phase modulated optical signal (DQPSK). The component (250) is combined with (211) using another combiner (10), forming the optical signal (110). After the optical-electronic conversion, said signal is converted into a wireless RF signal with modulation
DQPSK

Some examples of WDM-DEMUX that separates the optical signal (100) into two optical components (210) and (211), can be passive, or of the tunable electro-optical or thermo-optical type, based on gratings , guide sets of Waves, resonators or thin films. Some examples of electro-optical modulators, used in optical transmitters, can be of the Mach-Zehnder type or ring-resonator type, which may be based on various materials, such as lithium niobate, polymers or silicon.

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Fig. 3a represents an example of an optical signal (100) of two wavelengths that feeds the optical transmitter (one). The signal consists of two components, S1 (300) and S2 (301) separated by the desired electric RF carrier frequency \ nu (302).

Fig. 3b represents an illustrative example of the output signal (110) generated by the optical transmitter (1) and with the input signal (100). Any of the components S1 or S2 of the signal (100) could be modulated. In this example, the component (303) is the signal modulated (S1) by the data to transmit (D1 and D2), and component (304) (S2) is separated by the carrier frequency RF \ nu, (302). In another example, the Component (304) is the modulated signal.

Fig. 3c represents an illustrative example of the RF wireless signal (120) produced by the photodetector (2) with the carrier frequency.

Fig. 4a-b represents a illustrative example of the electrical to optical converter (4a) and optical demodulator (4b) shown in Fig. 1. The converter electrical to optical converts the electrical signal (140) to a signal optics (420). This signal (140) can be received by the system of reception (3b). In the electrical to optical converter a signal Optical (410) continuous wave is modulated by the electrical signal received (140), using an electro-optical modulator. By way of example, the output of a double band modulation technique side, the signal (420) of the modulator (11) consists of the signal optics and two side bands modulated by the data, as shown in Fig. 5a. In another example, the output of a technique of single sideband modulation, the signal (420) consists of the optical signal and a sideband modulated by the data, as shown in Fig. 5b. Using an optical filter (12) a filter is filtered. of the modulated side bands. An illustrative example of the filtered signal (430) is shown in Fig. 5c. The signal (430) is an optical signal with DxPSK modulation, which is demodulated using a DxPSK optical demodulator. The demodulator can be a combination of optical dividers and delay elements. How For example, a DQPSK optical signal can be demodulated using a Mach-Zehnder interferometer (13) with 1 delay bit (DMZI). The demodulator provides two signals at its output electric in baseband, (440) (D1) and (441) (D2), demodulating the phase information of the optical signal (430).

The demodulation technique used does not require a local oscillator in the receiver, which is the typical case in the conventional demodulation of wireless DQPSK signals. She is continuous wave, which produces the signal (410), incorporated into the electrical to optical converter (4) can be a typical laser of communications based on DFB technology. In some examples, the optical modulator (11) can be a niobato based modulator of lithium, polymers or electro-absorption effect. He optical filter (12) may be based on diffraction networks of Bragg, waveguide sets or thin film.

Fig. 5a shows an example optical signal (420) modulated in double lateral band, as it can be in various embodiments, modulated by the received electrical signal (140). The optical signal (410) and the two lateral bands (503) and (505) are shown in the figure. In this example, the separation of frequencies between the central carrier (410) and the sidebands (503) or (505) corresponds to the carrier frequency \ nu of the wireless signal (140).

Fig. 5b shows an example of a signal Optic (420) modulated in single sideband, as it may be in  some embodiments, modulated by the electrical signal (140). The optical signal (410) and single sideband (505) are shown in the figure. In this example, the frequency separation between the signal central optics (410) and the side band (505) corresponds to the carrier frequency \ nu of the RF wireless signal (140). In another modulation format, you can get the sideband lower instead of the upper band.

Fig. 5c shows an example of the output of the optical filter (430) where one of the side bands (503) or (505)  It is isolated. The signal (430) can be demodulated later.

Fig. 6 describes an example of implementation of the proposed system in a communications link with redundancy. The system is capable of simultaneously generating signals wireless (130) or (131) and wired (620) or (621), which Provides redundancy. The signal from the optical transmitter (110) is Divide into N components, illustrated by (600), (601), (610) and (611) in the figure. This can be done using a 1xN splitter (14). The signal (600) or (601) feeds the optical to electrical converter (2) for wireless transmission, and signals (610) or (611) can be transmitted through wired links. In some embodiments the signal (610) or (611) can be isolated using a optical filter (15). The optical filter isolates the optical signal (620) or (621) with the baseband data and is transmitted over a link cabling. The signal (620) or (621) is demodulated using a demodulator to recover data in baseband D1, D2 and Dn. As an example, A signal modulated in DQPSK can be demodulated using a 1-bit delay Mach-Zehnder interferometer (16). In some embodiments of the system, the wired signal may be removed directly from the optical transmitter (1) without the need of the splitter (14) or of the optical filter (15).

Several embodiments of the system can be used for wireless communications in various frequency bands. An exemplary embodiment is described in Fig. 7. The optical signal (100) includes the N components S 1, S 2, S 3 and S N. The WDM-DEMUX (5) isolates the optical signal (100) at S_ {1} (210) and S_ {{{}}}, S_ {3}, S_ {N} (710, 711 or 712). The optical component (210) is modulated with the optical modulator (17) using the sequence of n electrical data D1, D2 and D n . The output signal (250 of the optical modulator (17) is combined using the combiner (10 with the S N signal, which can be any of (710, 711 or 712). The combined signal (720) is used as 1xN optical switch input (18) The switch (18) can route the optical signal to one of the multiple output ports depending on the carrier frequency set by the signal S_ {2}, S_ {3} or S_ { N} The output signal (730, 731 or 732) is photodetected by one of the corresponding optical to electrical converters (2a, 2b or 2c) .The wireless signal (740, 741 or 742) is transmitted using one of the antennas corresponding (19a, 19b, or 19c).

In another embodiment, DxPSK modulation can be extended in spectral efficiency by adding intensity modulation by converting multilevel modulation into phase and intensity. Fig. 8. displays a DQPSK-ASK system with a symbol of n = 3 bits (D1, D2 and D3). In this example the phase-modulated signal (250) with n = 2 bits per symbol (DQPSK) is intensity modulated using an intensity modulator (20) converting the signal to a modulation of n = 3 bits per symbol (810). The receiver of said modulation is represented in a block diagram in Fig. 9. The signal (900) received by the electrical to optical converter (4a) with the DQPSK-ASK modulation is filtered and the signal (910) is divided into power using a splitter (21) to the two signals (920) and (921). One of the two signals is demodulated using the demodulator in (4b) recovering the data sequences D1 and D2 while the intensity modulation is demodulated with a direct detection recovering the data sequence D3.

Claims (18)

1. Wireless digital information transmission system comprising at least one optical infrastructure (1, 4b) for the generation, modulation and demodulation of a wireless signal, at least one wireless electrical transmission and reception system (3a, 3b) and at less an interface (2, 4a) between each optical infrastructure and each electrical system, characterized in that the optical structure is adapted to perform a differential multilevel modulation by phase shift. 2. System according to claim 1 characterized in that the modulation is DQPSK. 3. System according to claim 1 characterized in that the modulation is D8PSK. 4. System according to claim 1 characterized in that the modulation is D16PSK. 5. System according to any of the preceding claims characterized in that in addition to being adapted to perform a multilevel phase differential modulation, it can perform a intensity modulation at the same time. 6. System of any of the preceding claims characterized in that it further comprises a signal splitter (14) and a plurality of optical transmitters and receivers coupled to the transmitters via interfaces for generating a plurality of signal transmission channels. 7. System according to any of the preceding claims characterized in that it comprises optical signal dividers and delay elements. 8. System of any of the preceding claims characterized in that it comprises additional elements for performing a wired / wireless redundant transmission. 9. System according to claim 8 characterized in that it comprises an identical optical demodulator for wireless connections and wired connections. 10. System according to any of the preceding claims characterized in that the optical transmission and reception units are multiband. 11. System according to claim 10 characterized in that the same optical transmitter is adapted to be used individually for each band.

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12. Wireless digital transmission method of  information that includes the phases of: to. generation of a carrier optical signal b. differential multilevel modulation by phase shift of the signal and emission of the signal C. transformation into an electrical signal in RF d. wireless transmission of said signal. and. transformation of the received electrical signal  in an optical signal and demodulation of it in a receiver optical.

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13. Method according to claim 12 characterized in that the modulation is DQPSK. 14. Method according to claim 12 characterized in that the modulation is D8PSK. 15. Method according to claim 12 characterized in that the modulation is D16PSK. 16. Method according to any one of the preceding claims characterized in that in addition to performing a multilevel phase differential modulation an intensity modulation is performed. 17. Method according to any of the preceding claims characterized in that it comprises an additional phase for performing a wired / wireless redundant transmission. 18. Method according to any of the preceding claims characterized in that the transmission and reception signals are multiband.