Method and apparatus for hybrid multiplexing/de-multiplexing in passive optical network

Abstract

The present disclosure discloses a method and an apparatus for hybrid multiplexing/de-multiplexing in a passive optical network, the method comprising steps of: dividing N first intermediate frequency sub-bands averagely into M clusters, wherein each of the clusters contains K first intermediate frequency sub bands and N=M*K, and wherein each of the K first intermediate frequency sub-bands carries a baseband digital electrical signal; selecting, by a software defined first intermediate frequency multiplexer, the baseband digital electrical signals of K first intermediate frequency sub-bands from the N first intermediate frequency sub-bands for software defined frequency division multiplexing and forming a cluster; and frequency division multiplexing, by an analog hardware cluster multiplexer, analog electrical signals of the M clusters on a second intermediate frequency sub-band.

Claims

1. A method for hybrid multiplexing in a passive optical network, the method comprising: dividing N first intermediate frequency sub-bands evenly into M clusters, wherein each of the clusters contains K first intermediate frequency sub-bands and N=M*K, and wherein each of the K first intermediate frequency sub-bands carries a baseband digital electrical signal; selecting, by a software defined first intermediate frequency multiplexer, baseband digital electrical signals of K first intermediate frequency sub-bands for each M cluster of the N first intermediate frequency sub-bands for software defined frequency division multiplexing to form multiplexed digital electrical signals for each M cluster suitable for conversion into analog electrical signals for each M cluster; and frequency division multiplexing, by an analog hardware cluster multiplexer, the analog electrical signals of the M clusters on a second intermediate frequency sub-band to form a multiplexed analog electrical signal.

2. The method according to claim 1, wherein, after the selecting, further comprising: converting each multiplexed digital electrical signal obtained by multiplexing of the corresponding software defined first intermediate frequency multiplexer into the analog electrical signal for the corresponding cluster, and employing a hardware cluster local oscillator to convert each analog electrical signal to a second intermediate frequency in an analog hardware second frequency mixer in an analog hardware manner so as to provide a local oscillation signal source for each cluster.

3. The method according to claim 2, wherein, before the selecting, further comprising: converting, by a nth software defined local oscillator, a nth baseband digital electrical signal to a nth first intermediate frequency sub-band through a nth first frequency mixer in a digital software manner, a frequency of the first intermediate frequency being not higher than that of the second intermediate frequency to implement multi-stage frequency division multiplexing, wherein n denotes an index of the first intermediate frequency sub-band and n is a positive integer not greater than N.

4. The method according to claim 3, wherein a variable frequency of the software defined local oscillators can be adjusted according to a load demand, wherein adjusting parameters for adjusting said variable frequency of the software defined local oscillators include frequency, amplitude and phase.

5. The method according to claim 1, wherein K is the number of antennas equipped in a cell.

6. The method according to claim 1, wherein, after the frequency division multiplexing by the analog hardware cluster multiplexer, further comprising: modulating the multiplexed analog electrical signal obtained by the frequency division multiplexing of the analog hardware cluster multiplexer into an optical signal.

7. An apparatus for hybrid multiplexing in a passive optical network, the apparatus comprising: M software defined first intermediate frequency multiplexers, each of which is configured to select baseband digital electrical signals of K first intermediate frequency sub-bands to form a cluster from N first intermediate frequency sub-bands for software defined frequency division multiplexing to form a multiplexed digital electrical signal for the corresponding cluster that is suitable for conversion into an analog electrical signal for the corresponding cluster, wherein the N first intermediate frequency sub-bands are divided evenly into M clusters each containing the K first intermediate frequency sub-bands and N=M*K, and wherein each of the K first intermediate frequency sub-bands carries a baseband digital electrical signal; and an analog hardware cluster multiplexer configured to frequency division multiplex the analog electrical signals of the M clusters on a second intermediate frequency sub-band to form a multiplexed analog electrical signal.

8. The apparatus according to claim 7, wherein the apparatus further comprises: M digital to analog converters, each of which is configured to convert the multiplexed digital electrical signal obtained by multiplexing of the corresponding software defined first intermediate frequency multiplexer into the analog electrical signal for the corresponding cluster; and M hardware cluster local oscillators, each of which is configured to convert the analog electrical signal for the corresponding cluster to a second intermediate frequency in an analog hardware second frequency mixer in an analog hardware manner so as to provide a local oscillation signal source for the corresponding cluster.

9. The apparatus according to claim 8, wherein the apparatus further comprises: N software defined local oscillators, each of which is configured to convert a nth baseband digital electrical signal to a nth first intermediate frequency through a nth first frequency mixer in a digital software manner, a frequency of the first intermediate frequency being not higher than that of the second intermediate frequency to implement multi-stage frequency division multiplexing, wherein n denotes an index of a first intermediate frequency sub-band and n is a positive integer not greater than N.

10. The apparatus according to claim 9, wherein a variable frequency of the N software defined local oscillators can be adjusted according to a load demand, wherein adjusting parameters for adjusting said variable frequency of the N software defined local oscillators include frequency, amplitude and phase.

11. The apparatus according to claim 7, wherein K is the number of antennas equipped in a cell.

12. The apparatus according to claim 7, wherein the apparatus further comprises: a photoelectric modulator configured to modulate the multiplexed analog electrical signal obtained by the frequency division multiplexing of the analog hardware cluster multiplexer into an optical signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features of the present disclosure will become more obvious by making references to the following detailed description of the embodiments in conjunction with the accompanying drawings, and in the accompanying drawings of the present disclosure, the same or similar reference signs represent the same or similar steps.

(2) FIG. 1A shows a schematic diagram of a D-RoF based optical network architecture;

(3) FIG. 1B shows a schematic diagram of the existing D-RoF solution employing CPRI;

(4) FIG. 2A shows a schematic diagram of an optical network architecture employing an intermediate frequency multiplexer;

(5) FIG. 2B shows a schematic diagram of an A-RoF solution having ADC/DAC and IF multiplexer/de-multiplexer;

(6) FIG. 3 shows a schematic diagram of an optical network architecture of a hybrid A-RoF containing a software defined IF multiplexer and an analog hardware cluster multiplexer according to embodiments of the present disclosure;

(7) FIG. 4 shows a schematic diagram of the conventional A-RoF optical line terminal;

(8) FIG. 5 shows a schematic diagram of an A-RoF optical line terminal according to embodiments of the present disclosure;

(9) FIG. 6 shows a schematic diagram of an A-RoF optical line terminal according to another embodiment of the present disclosure;

(10) FIG. 7 shows a schematic diagram of an optical network architecture of an optical line terminal as shown in FIG. 6;

(11) FIG. 8 shows a schematic diagram of the experimental validation configuration according to embodiments of the present disclosure; and

(12) FIG. 9 shows a schematic diagram of a constellation diagram of the experimental validation configuration as shown in FIG. 8.

DESCRIPTION OF PREFERRED EMBODIMENTS

(13) In the following specific description of the preferred embodiments, the appended accompanying drawings constituting part of the present disclosure will be referred to. The appended accompanying drawings illustrate by way of example the particular embodiments capable of achieving the present disclosure. The exemplary embodiments do not aim to exhaust all embodiments of the present disclosure. It needs to be explained that although steps about the method in the present disclosure are described here in a specific order, it does not require or suggest that these operations must be executed according to the specific order, or all of the illustrated operations must be executed to achieve an expected result; on the contrary, the steps described here can be changed in the execution order. Additionally or alternatively, some steps may be omitted, multiple steps can be combined into one for execution, and/or one step may be decomposed into multiple steps for execution.

(14) The method and apparatus for multiplexing/de-multiplexing in a passive optical network as disclosed by the present application will be introduced in detail in conjunction with FIGS. 3-7.

(15) FIG. 3 shows a schematic diagram of an optical network architecture of a hybrid A-RoF containing software defined IF multiplexers and analog hardware cluster multiplexers according to embodiments of the present disclosure. A BBU pool outputs in parallel for example baseband data of 96 branches. Each of the 96 baseband data is firstly QAM mapped and multiplexed in frequency domain, and an Electrical to Optical Converter (EOC) modulates the analog data onto light-waves, which is transmitted over an access network of Passive Optical Network (PON) architecture to a remote base station. At the receiver side, each cell selects its corresponding IF cluster containing 24 data channels and has the cluster sampled and quantized, and then performs DSP based IF de-multiplexing (DeMUX) and QAM demodulation, and finally transmits 24 baseband data to each antenna.

(16) FIG. 4 shows a schematic diagram of the conventional A-RoF Optical Line Terminal (OLT). The conventional A-RoF has a time domain multiplexer (MUX) implemented in DSP. In order to support 96 antennas, 12 pieces of DSP and optical TRx are required.

(17) FIG. 5 shows a schematic diagram of an A-RoF OLT according to an embodiment of the present disclosure. The OLT in FIG. 5 has Software Defined IF MUXs (SD IF MUXs) and Software Defined Local Oscillators (SD LOs) implemented in DSP. Assuming that there are 96 baseband digital electrical signals, the nth software defined local oscillator converts the nth baseband digital electrical signal to the nth first intermediate frequency sub-band through the nth first frequency mixer in a digital software manner. Then, the software defined first IF multiplexer performs software defined frequency division multiplexing on the 96 first intermediate frequency sub-bands. The digital electrical signal obtained by the multiplexing of the software defined first IF multiplexer is converted into an analog electrical signal, and a photoelectric modulator modulates the multiplexed electrical signal into an optical signal. Since the baseband digital electrical signals are directly multiplexed in the SD IF MUX in DSP, a full bandwidth DAC is needed.

(18) FIG. 6 shows a schematic diagram of an A-RoF OLT according to another embodiment of the present disclosure.

(19) Firstly, N (e.g., N=96) first intermediate frequency sub-bands are averagely divided into M (e.g., M=4) clusters, wherein each of the clusters contains K (K=24) first intermediate frequency sub-bands and N=M*K, and wherein each of the 24 different first intermediate frequency sub-bands carries a baseband digital electrical signal. K can be the number of antennas equipped in the cell. N denotes the number of the first intermediate frequency sub-bands, M denotes the number of the clusters, and K denotes the number of the first intermediate frequency sub-bands in a cluster.

(20) Then, a software defined first intermediate frequency multiplexer selects baseband digital electrical signals of K first intermediate frequency sub-bands from the N first intermediate frequency sub-bands for software defined frequency division multiplexing and forming a cluster.

(21) Thirdly, an analog hardware cluster multiplexer applies frequency division multiplexing to analog electrical signals of the M clusters on a second intermediate frequency sub-band.

(22) In the DSP block as shown in FIG. 6, the nth software defined local oscillator converts the nth baseband digital electrical signal to the nth first intermediate frequency sub-band through the nth first frequency mixer in a digital software manner, and a frequency of the first intermediate frequency is not higher than that of the second intermediate frequency to implement multi-stage frequency division multiplexing, wherein n denotes an index of the first intermediate frequency sub-band and n is a positive integer not greater than N. It should be understood by those skilled in the art that although FIG. 6 shows two-stage frequency division multiplexing, it does not constitute a limit to the implementation and application manners of the present disclosure, and if necessary, the same or similar idea can also be used to implement three-stage or higher-stage frequency division multiplexing.

(23) For example, 96 baseband digital electrical signals are converted to 96 different first IF sub-bands through respective first frequency mixers, and then a software defined first IF multiplexer selects the baseband digital electrical signals of 24 first IF sub-bands from the 96 first IF sub-bands for software defined frequency division multiplexing and forming a cluster. The digital electrical signal obtained by multiplexing of the software defined first IF multiplier is converted into an analog electrical signal, and a hardware cluster LO is employed to convert the analog electrical signal to a second IF in the analog hardware second frequency mixer in an analog hardware manner so as to provide a local oscillation signal source. The analog hardware cluster multiplexer applies frequency division multiplexing to the analog electrical signals of 4 clusters on the second intermediate frequency sub-band to form an analog electrical signal. Finally, the electrical signal obtained by the multiplexing of the hardware cluster multiplexer is modulated into an optical signal.

(24) The software defined first IF multiplexer has flexibility in changing or adjusting the frequency of the first intermediate frequency sub-bands due to an expansion of bandwidth and/or an increase in the number of the intermediate frequency sub-bands. The hardware cluster multiplexer has the advantage of reducing the hardware request on ADC/DAC bandwidth and the corresponding cost. In this way, the solution of hybrid A-RoF having the software defined first IF multiplexer and the hardware cluster multiplexer achieves a balance between software capacity and hardware complexity, and the above solution of hybrid A-RoF has good compatibility with the existing CPRI based MFH link system architecture.

(25) As shown in FIGS. 5 and 6, a variable frequency of the software defined local oscillator can be adjusted according to load demand, wherein adjusting parameters include frequency, amplitude and phase.

(26) Taking 96 baseband digital electrical signals in FIG. 6 as an example, the OLT in FIG. 6 may include:

(27) 4 software defined first intermediate frequency multiplexers, each of which is configured to select the baseband digital electrical signals of 24 first intermediate frequency sub-bands from 96 first intermediate frequency sub-bands for multiplexing and forming a cluster; and

(28) 1 hardware cluster multiplexer configured to apply frequency division multiplexing to the electrical signals of 4 clusters on a second intermediate frequency sub-band.

(29) Comparing to FIG. 5, the DAC module in the solution of FIG. 6 has a relatively narrow bandwidth and achieves high cost-effectiveness of devices and flexibility of configuration through two-stage frequency conversion of software and hardware. Correspondingly, at the receiving end, after the frequency conversion of hardware, the sampling bandwidth of ADC in each RRH only needs to reach of the total data bandwidth to obtain the required data, and then through the frequency conversion of software, the 24 frequency division multiplexed baseband data can be parsed.

(30) The optical line terminal as shown in FIG. 6 further includes:

(31) 4 digital to analog converters, each of which is configured to convert the digital electrical signal obtained by multiplexing of respective software defined first intermediate frequency multiplexer into an analog electrical signal;

(32) 4 hardware cluster local oscillators, each of which is configured to convert the analog electrical signal to a second intermediate frequency in an analog hardware second frequency mixer in an analog hardware manner so as to provide a local oscillation signal source;

(33) 96 software defined local oscillators, each of which is configured to convert the nth baseband digital electrical signal to the nth first intermediate frequency through the nth first frequency mixer in a digital software manner, a frequency of the first intermediate frequency being not higher than that of the second intermediate frequency to implement multi-stage frequency division multiplexing, wherein n denotes an index of a first intermediate frequency sub-band and n is a positive integer not greater than N; and

(34) a photoelectric modulator configured to modulate the electrical signal obtained by multiplexing of the hardware cluster multiplexer into an optical signal.

(35) It should be understood by those skilled in the art that according to the embodiment as shown in FIG. 6, the number of the first frequency mixer and the second frequency mixer may be 96 and 4, respectively.

(36) FIG. 5 and FIG. 6 show solutions of intermediate frequency multiplexing of the hybrid A-RoF in OLT in the downlink direction. It should be appreciated by those skilled in the art that in the corresponding Optical Network Unit (ONU), there is also a de-multiplexing solution corresponding to the intermediate frequency multiplexing solution of the hybrid A-RoF in the OLT, which is not detailed here. Similarly, in the uplink direction, the ONU may also employ the hybrid A-RoF multiplexing solution as same as or similar to that in the OLT as shown in FIG. 5 and FIG. 6, and thus a corresponding de-multiplexing solution can be employed in the OLT for uplink.

(37) FIG. 7 shows a schematic diagram of an optical network architecture of an optical line terminal as shown in FIG. 6. It is possible to achieve the compatibility in smooth evolution from current PON to next generation PON by only changing the conventional Transceiver (TRx) into Time and Wavelength Division Multiplexed TRx (TWDM-TRx).

(38) In the next generation PON architecture based on A-RoF MFH having hardware cluster multiplexers and software defined multiplexers, each remote cell must have an extra step to select the target wavelength first before the cluster selection and then to perform IF de-multiplexing and QAM demodulation.

(39) FIG. 8 shows a schematic diagram of the experimental validation configuration according to embodiments of the present disclosure. In order to verify the solution of a hybrid A-RoF having software defined first intermediate frequency multiplexers and hardware cluster multiplexers, as shown in FIG. 8, 3 clusters each containing 8 first intermediate frequency sub-bands are generated at the transmitting end. Each of the 24 baseband digital electrical signals is formatted in 64 QAM and with 25 Mbps baud rate. 20 km of single mode fiber represents the MFH distance from the BBU pool to the RRHs. After passing through the photoelectric modulator, each cluster containing 8 first intermediate frequencies is converted to 3.5 GHz radio frequency (3 dB bandwidth of the antenna is about 200 MHz around 3.5 GHz), and is launched over a wireless interface to a wireless receiver. DSP in a PC demodulates the data over the 8 first intermediate frequency sub-bands contained by each cluster, and meanwhile tests its Block Error Rate (BER). FIG. 9 shows a schematic diagram of a constellation diagram of the experimental validation configuration as shown in FIG. 8. As the experimental results indicate, the BER of each sub-band is below 10.sup.3.

(40) For those skilled in the art, it is obvious that the present disclosure is not limited to the details of the above exemplary embodiments, and the present disclosure can be implemented in other specific forms under the premise of not departing from spirits or basic characteristics of the present disclosure. Thus, at any rate, the embodiments should be regarded as exemplary and nonrestrictive. In addition, obviously, the term comprising or including does not exclude other elements and steps, and the term a or an does not exclude a plurality. Multiple elements recited in the apparatus claims can also be implemented by one element. The terms such as first, second, etc. are used to represent names, rather than representing any specific order.