CN101141778A - Method and system for realizing partition coverage by using mirrored radio frequency unit - Google Patents

Abstract

The invention discloses a method and a system for realizing partition coverage by using a mirrored RRU. The system includes a plurality of cascaded RRUs and a BBU connected to the cascaded RRUs, and the cascaded RRUs include a main RRU and a mirror RRU. In the cascaded RRU, each RRU independently converts the signal received by at least one antenna from the corresponding coverage area from analog signal to digital signal, and the mirror RRU superimposes the digital signal transmitted by the upper RRU and the digital signal obtained by local sampling And transmit it to the next level, and transmit it level by level until a mirror image RRU transmits the superimposed digital signal to the signal channel of the BBU for baseband processing. With the present invention, the coverage radius of each RRU is maintained, the coverage capability of the cell can be expanded under the condition of unlimited capacity, and the demand on the processing capability of the BBU is reduced at the same time.

Description

Method and system for realizing partition coverage by using mirrored radio frequency unit

technical field

The invention relates to a partition coverage technology based on a baseband unit (BBU) and a radio frequency unit (RRU) structure in a mobile communication system, in particular to a method and a system for realizing partition coverage by using a mirrored RRU.

Background technique

Partitioned coverage of a wireless communication system is an essential requirement for providing continuous service. However, due to the characteristics of wireless signal propagation in the coverage area and the limited power amplifier of the wireless system, multi-channel technology has become an important means to solve partition coverage.

In the international patent application named "Cellular Telecommunications Network with an OMNI Directional TransmitterType and a Sectored Receiver Type" (OTSR) filed on December 20, 2000 with the patent number WO/2001/047148, an omnidirectional transmission fan is disclosed. The method of regionalized reception to increase the coverage area of the uplink and downlink. When the OTSR system is transmitting, the downlink power output by the power amplifier can be evenly distributed to several directional antennas through the power divider to realize omnidirectional transmission. In the domestic patent application No. 200410001028.3 filed on January 16, 2004, "A Method for Efficiently Covering Expressways", it discloses the technology of using dual antennas in the same sector to cover different directions to improve the coverage performance of expressways . In the TD-SCDMA system, an existing technical solution is to combine the multi-channel technology with the smart antenna technology to increase the coverage area of the uplink and downlink, as shown in Figure 1, the smart antenna is also called Array antennas can adaptively perform beamforming on mobile user signals and track user movements; another existing technology is to place different antennas on different floors to provide indoor coverage, as shown in Figure 2.

In addition, with the enhanced digital signal processing capability of equipment, centralized baseband signal processing becomes possible. Therefore, one baseband unit (BBU) can be connected with multiple radio frequency units (RRU) to fully utilize the processing capability of the BBU.

In the OTSR system, each antenna needs to correspond to an independent uplink channel processing unit in the baseband and intermediate frequency parts, so the number of channels occupied is large; and the power in the downlink direction is evenly distributed to multiple antennas, which may cause signal distortion and cause antenna coverage. The shortening of the distance. In a conventional multi-channel system, each antenna corresponds to an independent uplink and downlink channel processing unit; however, if a coupler is used to combine the analog signals of multiple antennas into one channel processing unit, it is not conducive to the management of multiple antennas. At the same time, because the analog signal may be distorted during the transmission process, the signal coverage distance of the uplink and downlink RRUs will be shortened, and the smart antenna technology cannot be used.

It can be seen that the realization of partition coverage in a wireless communication system faces many challenges. On the one hand, it is hoped that the coverage area is as large as possible; on the other hand, it is hoped that the minimum processing resources of uplink and downlink channels shall be occupied under the condition of ensuring normal signal processing. If the channel processing capability and antenna processing capability of the system can be balanced, it will play an important role in improving the application and performance of the system. The transmission of digital signals between the baseband processing part and the radio frequency processing part will improve the reliability and flexibility of signal transmission and reduce the complexity of construction, especially for wireless communication systems using multi-antenna technology.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method and system for realizing partition coverage by using a mirrored radio frequency unit, which not only expands the coverage capability of a cell but also does not increase the demand for BBU processing capability.

On the one hand, the present invention proposes a method for realizing partition coverage by using a mirrored radio frequency unit. In the cascaded radio frequency units, each radio frequency unit independently converts the signal received by at least one antenna from the corresponding coverage area from an analog signal to a digital signal, and the mirror radio frequency unit combines the digital signal transmitted by the upper radio frequency unit with the local sampling The digital signals are superimposed and transmitted to the next level until a mirror radio frequency unit transmits the superimposed digital signals to the signal channel of the baseband unit for baseband processing.

In the above method, the baseband unit transmits downlink digital signals to the cascaded radio frequency units, and each radio frequency unit independently converts the downlink digital signals into analog signals and sends them to corresponding coverage areas.

In the above method, the superposition is saturation superposition.

In the above method, the digital signal includes split signals on each signal channel.

In the above method, the mirror radio frequency unit performs alignment superimposition on the digital signal transmitted from the upper radio frequency unit and the digital signal obtained by local sampling according to the identification of each signal channel, and then transmits it to the next level.

On the other hand, the present invention proposes a system for implementing partition coverage by using mirrored radio frequency units. The system includes a plurality of cascaded radio frequency units and a baseband unit connected to the cascaded radio frequency units, the cascaded radio frequency units include a main radio frequency unit and a mirror radio frequency unit, wherein:

The main radio frequency unit and the mirror radio frequency unit include an antenna unit for receiving signals in corresponding coverage areas;

The main radio frequency unit and the mirror radio frequency unit include an uplink signal conversion unit for converting a signal received by the antenna unit from an analog signal to a digital signal;

The mirror radio frequency unit includes a digital synthesis unit, which is used to superimpose the digital signal transmitted by the upper radio frequency unit and the digital signal obtained by local sampling.

In the above system, the main radio frequency unit and the mirror radio frequency unit further include a downlink signal conversion unit, configured to convert the downlink digital signal transmitted by the baseband unit into an analog signal.

In the above system, the superposition is a saturation superposition.

In the above system, the antenna unit includes M antennas, the uplink signal conversion unit includes M analog-to-digital converters, and the digital synthesis unit includes M adders.

In the above system, the digital synthesis unit is used to superimpose the digital signal transmitted by the upper-level radio frequency unit and the digital signal obtained by local sampling according to the identifiers of the M signal channels.

Main advantages and characteristics of the present invention are as follows:

1. The coverage radius of each RRU is maintained, and the coverage capability of the cell can be expanded in the case of unlimited capacity, and at the same time, the demand for BBU processing capability is reduced to achieve the purpose of saving costs. Compared with the method of partition coverage by power divider, it has the advantage of coverage radius. At the same time, the digital signal processing between different RRU signals in the uplink direction avoids the noise introduced by the combiner, and the digital signal transmission in the downlink direction avoids the noise introduced by the power divider. noise and attenuation.

2. Mirrored RRU is also suitable for some special networking scenarios, such as highway/railway coverage scenarios to reduce handover call drops, and indoor coverage scenarios to support more coverage areas with fewer BBU channels wait.

3. In future network construction, changing the mirrored RRU to the main RRU, and independently processing the signals of the RRU in the BBU can achieve the purpose of capacity expansion.

Description of drawings

FIG. 1 is a schematic diagram of an existing smart antenna in road coverage;

Figure 2 is a schematic diagram of existing indoor coverage based on BBU+RRU;

Fig. 3 is the system structural diagram that utilizes mirror image RRU to realize partition coverage that the present invention proposes;

FIG. 4 is a schematic diagram of a multi-mirror RRU according to Embodiment 1 of the present invention;

FIG. 5 is a schematic diagram of the application of the mirrored RRU described in Embodiment 2 of the present invention to expressway coverage;

FIG. 6 is a schematic diagram of the application of the mirrored RRU described in Embodiment 3 to indoor coverage in the present invention.

Detailed ways

Referring to FIG. 3 , the method and system for implementing partition coverage by using mirrored RRU proposed by the present invention are described.

In the downlink direction, the BBU transmits a downlink digital signal to the cascaded RRUs, and each RRU independently obtains and converts the downlink digital signal into an analog signal and sends it to the corresponding coverage area through the antenna. Here, the master RRU and the mirror RRU obtain the same downlink data from the same signal transmitted from the BBU.

In the uplink direction, each cascaded RRU converts the signal received by the antenna from the corresponding coverage area from analog signal to digital signal, superimposes the digital signal transmitted by the upper RRU and the digital signal obtained by local sampling, and sends the The next level of transmission is finally transmitted to the BBU for unified processing, where only one uplink digital signal is transmitted to the BBU. Here, the superposition can adopt the method of saturated superposition, that is, to judge whether the sum of the digital signal transmitted by the upper RRU and the digital signal obtained by local sampling exceeds the maximum threshold. If it exceeds, the superposition result is the maximum threshold. If it does not exceed Then the superposition result is the actual sum of the digital signals. Since digital signals are superimposed, the bandwidth of data transmission in the uplink and downlink directions has nothing to do with the number of RRUs.

For the case where multiple antennas are used on each RRU, each antenna connected to each RRU can achieve independent power calibration, and the mirrored RRU technology can also be used in combination with traditional multi-channel technology. At this time, each RRU implements independent antenna calibration. It is beneficial to the application of smart antennas. The solution after combining mirroring RRU technology with multi-channel technology is as follows:

In the downlink direction, the BBU transmits the downlink digital signals from each signal channel to the cascaded RRUs, and each RRU independently converts the downlink digital signals into analog signals and sends them to the corresponding coverage area. In the uplink direction, each cascaded RRU performs analog-to-digital conversion on the corresponding signal channels of the signals received by multiple antennas from the corresponding coverage area, and digital signals transmitted by the upper-level RRU according to the signal channel The identification is bit-superimposed and transmitted to the next level until the last-level mirroring RRU transmits the digital signal after bit superimposition to each corresponding signal channel in the BBU for baseband processing.

In the scheme of combining mirror RRU technology with multi-channel technology, the digital signal is composed of branch signals on each signal channel, and the processing of each branch signal is the same as the processing of the above-mentioned signal, so each RRU samples locally The obtained digital signal and the digital signal transmitted by the upper-level RRU are superimposed in parallel between different channels, while saturation superposition can be performed on the same channel. This kind of superimposition is beneficial to the use of smart antennas, but it will introduce a certain amount of uplink noise, which will amplify the thermal noise in the RRU coverage area where the user is located, thus having a certain negative impact on the system capacity, but the introduced interference sources are relatively few , so it is suitable for occasions where the capacity is not limited.

Among the RRUs that can be independently maintained, the farthest RRU is called the master RRU, and each RRU cascaded to the master RRU is a mirror RRU. In the uplink direction, each RRU includes an antenna unit and an uplink signal conversion unit, and each mirror image RRU includes a digital synthesis unit; in the downlink direction, each RRU includes a downlink signal conversion unit. in:

The antenna unit on each RRU is used to receive signals in the corresponding coverage area and consists of one or more antennas;

The uplink signal conversion unit on each RRU is used to convert the signal received by the antenna unit from an analog signal to a digital signal. The uplink signal conversion unit may be composed of an analog-to-digital converter (A/D converter), A/D conversion The number of devices is equal to the number of signal channels;

The digital synthesis unit on each mirrored RRU is used to superimpose the digital signal transmitted by the upper RRU and the digital signal obtained by local sampling. The digital synthesis unit can be composed of adders or similar devices. The number of adders is the same as The number of signal channels is equal;

The downlink signal conversion unit on each RRU is used to convert the digital signal transmitted by the BBU into an analog signal. The downlink signal conversion unit may be composed of a digital-to-analog converter (D/A converter), and the D/A converter The number is equal to the number of signal channels.

The scheme of using mirrored RRUs in the present invention to realize partition coverage can meet the requirements of the network for cell coverage and some special scenarios. In the following, the technical features and functional features of the present invention will be further described in detail through three embodiments.

Embodiment 1 is a scenario where the technical solution of the present invention is applied to one cell covering multiple areas to reduce network construction costs, as shown in FIG. 4 . Antennas in N independent areas are respectively connected to respective RRUs.

In the downlink direction, the BBU transmits the baseband digital domain signal that needs to be sent to the RRU. Therefore, the signals sent by N RRUs are exactly the same; in the uplink direction, the RRU independently processes the received signal of the antenna and outputs the baseband digital domain signal. The signal transmitted by the RRU and the local sampling signal are digitally superimposed according to the identification of the signal channel, and finally the BBU performs baseband processing on the superimposed signal.

At the same time, the RRU independently performs power calibration in its coverage area, so that one cell can cover N different coverage areas, thereby achieving the purpose of wide coverage, reducing the demand for BBU processing capacity, and saving network construction costs . If network expansion is required, the digital signals output by the RRUs are independently input to their respective BBU processing units for separate processing, and at the same time, the transmission bandwidth between the BBU and the RRU is appropriately increased, so that N different coverage areas belonging to the same cell can be split into N or less than N different cells achieve the purpose of increasing network capacity. Therefore, the mirrored RRU technology has good scalability.

Embodiment 2 is a scene where the technical solution of the present invention is applied to expressway coverage, as shown in FIG. 5 . Taking TS-SCDMA technology as an example, it is assumed that each group includes two sets of linear array smart antennas with M antennas, facing two directions of the highway respectively, and each group of smart antennas is connected to one RRU.

The same function as the existing RRU is that the RRUs perform power calibration and antenna correction on their respective smart antennas. The difference from the existing RRU function is: in the downlink direction, the digital baseband signal output by the BBU is transmitted to the cascaded RRU at the same time, and the two RRUs obtain the same baseband signal and perform subsequent downlink signal processing; in the uplink direction, each RRU pair The signals received by the M antennas are independently processed in the corresponding M signal channels, and the baseband data of the M antennas are obtained by sampling. The mirror RRU converts the digital signals transmitted by the upper-level RRU and the local sampling signals according to the signal channels. The IDs are superimposed and transmitted to the next-level RRU, and finally the BBU performs the baseband signal processing of the M channel, including the processing related to the smart antenna.

It can be seen from Figure 5 that the smart antenna array composed of M antennas, because the data input by the RRU channel is exactly the same, makes the two sets of downlink beamforming exactly the same, that is, mirror beamforming. When the user passes through the intersection of two sectors, the main beams of the two sets of beams are directed to the same position. Since the two sectors belong to the same cell, the user does not switch between cells, which avoids the excessive movement of the user that is used for switching. Insufficient time leads to the problem of call drop rate. This technical solution is also applicable to the coverage of high-speed railways.

Embodiment 3 is a scenario where the technical solution of the present invention is applied to indoor coverage, as shown in FIG. 6 . Taking WCDMA technology as an example, it is assumed that each antenna covers a different area, and each antenna is connected to one RRU.

In the downlink direction, the digital baseband signal output by the BBU is transmitted to all cascaded RRUs. Each RRU obtains the same baseband signal and performs subsequent downlink signal processing; in the uplink direction, each RRU processes the signal received on the antenna independently. And sample the baseband data of the antenna port, then saturate and superimpose the data transmitted by the previous RRU with the sampled data of the local antenna, and pass it to the next RRU, and the last RRU transmits the superimposed data to the BBU for baseband processing.

It can be seen that by using mirrored RRU technology in multiple unrelated areas, multiple coverage zones of the same cell can be obtained, which meets the network's coverage requirements, reduces the need for processing capabilities of the baseband processing unit, and reduces network construction costs. In addition, the mirrored RRU is also suitable for some special networking scenarios, such as highway/railway coverage scenarios to reduce handover call drops, and indoor coverage scenarios to support more coverage areas with fewer BBU channels wait.

The present invention has been disclosed with the foregoing preferred embodiment, which is only for clearly illustrating that the technical solution is not intended to limit the present invention, and any person skilled in the art, without departing from the spirit and scope of the present invention, the modifications made include within the scope of this application.

Claims (10)

1. one kind is utilized mirror-image radio frequency unit to realize the method that subregion covers, and it is characterized in that:

In the radio frequency unit of cascade, the independent signal that at least one antenna is received from the respective coverage areas territory of each radio frequency unit is a digital signal by analog signal conversion, wherein the digital signal that obtains of mirror-image radio frequency unit digital signal that the upper level radio frequency unit is sent and local sampling superposes and transmits to next stage, transmits step by step in the signalling channel that digital signal after a mirror-image radio frequency unit will superpose is sent to Base Band Unit and carries out Base-Band Processing.

2. the method for claim 1 is characterized in that:

Described Base Band Unit transmits descending digital signal to the radio frequency unit of described cascade, and each radio frequency unit independently is converted to described descending digital signal analog signal and sends to corresponding overlay area.

3. the method for claim 1 is characterized in that described stack is saturated stack.

4. as claim 1,2 or 3 described methods, it is characterized in that described digital signal comprises the shunting sign on each signalling channel.

5. method as claimed in claim 4 is characterized in that:

The described mirror-image radio frequency unit digital signal that to be digital signal that the upper level radio frequency unit is sent obtain with local sampling is carried out the contraposition stack according to the sign of each signalling channel and is transmitted to next stage.

6. one kind is utilized mirror-image radio frequency unit to realize the system that subregion covers, it is characterized in that this system comprises the radio frequency unit and the Base Band Unit that is connected on the described cascaded RF unit of a plurality of cascades, the radio frequency unit of described cascade comprises main radio frequency unit and mirror-image radio frequency unit, wherein:

Described main radio frequency unit and mirror-image radio frequency unit comprise antenna element, are used to receive the signal in the respective coverage areas territory;

Described main radio frequency unit and mirror-image radio frequency unit comprise the upward signal converting unit, and the signal from analog conversion of signals that is used for antenna element is received is a digital signal;

Described mirror-image radio frequency unit comprises digital synthesis unit, is used for digital signal that the upper level radio frequency unit is sent and the digital signal that local sampling obtains and superposes.

7. system as claimed in claim 6 is characterized in that:

Described main radio frequency unit and mirror-image radio frequency unit also comprise the downstream signal converting unit, are used for the descending digital signal of described Base Band Unit transmission is converted to analog signal.

8. system as claimed in claim 6 is characterized in that described stack is saturated stack.

9. system as claimed in claim 6 is characterized in that:

Described antenna element comprises M antenna, and described upward signal converting unit comprises M analog to digital converter, and described digital synthesis unit comprises M adder.

10. system as claimed in claim 9 is characterized in that:

Described digital synthesis unit is to be used for digital signal that the upper level radio frequency unit is sent and the digital signal that local sampling obtains to carry out the contraposition stack according to the sign of M signalling channel.

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