WO2005117475A1

WO2005117475A1 - Structure of connecting re o' radio frequency unit in centralized basestation and method therefor

Info

Publication number: WO2005117475A1
Application number: PCT/CN2004/000578
Authority: WO
Inventors: Sheng Liu; Jing Fang; Yulin Li
Original assignee: Utstarcom Telecom Co., Ltd.
Priority date: 2004-05-31
Filing date: 2004-05-31
Publication date: 2005-12-08
Also published as: CN1954625A

Abstract

A structure of interconnecting channel processing main unit and multiple radio frequency units is disclosed, wherein the structure includes a line concentrator which is connected with a part or all of said multiple radio frequency units through a first link respectively and connected with said channel processing main unit through a second link, and wherein said line concentrator includes multiplex/demultiplex means for connecting said first and second links.

Description

Connected to the far end in a centralized base station

Structure of radio frequency unit and method thereof

The present invention relates to a centralized base station in a mobile communication system, and in particular, to a structure and a method for connecting a remote radio frequency unit in a centralized base station system that uses a radio frequency unit to be remote. technical background

In a mobile communication system, a base station (BTS) completes the transmission, reception, and processing of wireless signals. Traditional BTS mainly consists of a baseband processing subsystem, a radio frequency (RF) subsystem, and an antenna. A BTS can cover different antennas through multiple antennas. Cell (cell), as shown in Figure la; and each BTS communicates with the base station controller through a certain interface.

(BSC) or Radio Network Controller (RNC) to form a radio access network

(RAN), as shown in Figure lb.

FIG. 2 shows the system structure of another distributed base station, that is, a centralized base station that uses a radio frequency unit to extend the distance. Compared with traditional base stations, this centralized base station using radio frequency units has many advantages: it allows multiple micro cells to replace a macro cell based on a traditional base station, which can better adapt to different wireless environments and improve the system's Wireless performance such as capacity and coverage; The centralized structure enables soft handover to be completed with softer handover, thereby obtaining additional processing gain; the centralized structure also makes expensive baseband signal processing resources a resource pool shared by multiple cells, Thus, the benefits of statistical multiplexing are obtained, and the system cost is effectively reduced. PCT patent "WO9005432, communication system"; US patent "US5657374, cellular system with centralized base station and distributed antenna unit", "US6324391, cellular system with centralized control and signal processing"; Chinese patent application "CN1471331, mobile communication Base station system "; and US patent application" US20030171118, cellular wireless transmission equipment and cellular wireless transmission method ", etc. Reveals the implementation details of this technology.

As shown in FIG. 2, a centralized base station system (BTS) IO using a radio frequency unit is mainly composed of a centrally configured central channel processing main unit (MU) 15 and a remote radio frequency unit (RRU) 14, which are transmitted through broadband. The link or network 16 is connected, and the BSC / RNC interface unit 11 is responsible for completing the user plane and control plane signaling processing of the BTS 10 and the BSC RNC interface (not shown). Μϋ 15 is mainly composed of functional units such as channel processing resource pool 12 and signal routing allocation unit 13. Among them, channel processing resource pool 12 is formed by stacking multiple channel processing units 1-N to complete tasks such as baseband signal processing and signal routing allocation. The unit 13 dynamically allocates channel processing resources according to the traffic of each cell corresponding to the remote radio frequency unit 14 to achieve effective sharing of multi-cell processing resources. In addition to being implemented inside the MU 15 as shown in FIG. 2, the signal routing and distribution unit 13 may also be implemented outside the MU 15 as a separate device. The remote RF unit is mainly composed of functional units such as the RF power amplifier of the transmitting channel, the low noise amplifier of the receiving channel, the duplexer, and the antenna. The link between the central channel processing main unit and the remote antenna unit can typically use optical fiber, copper cable, microwave and other transmission media; the signal transmission method can be a sampled digital signal or a modulated analog signal; the signal can use baseband Signal, intermediate frequency signal or radio frequency signal.

A key technology of the centralized base station system is the wireless signal transmission between the RU and the MU. In the existing technology, a scheme based on analog intermediate frequency or analog radio frequency signal transmission through a transmission medium such as optical fiber, copper winding, and microwave is typically used. . Although it is relatively easy to realize by analog signal transmission, analog lines will inevitably be mixed with interference components such as noise, and the signal modulation during transmission will also introduce non-linear distortion. Transmission media such as copper cables and microwaves also limit the effective transmission loss. Transmission distance. In addition, the analog transmission makes the transmission line utilization rate low, and it is not convenient to implement the large-capacity multiplexing technology. Therefore, it is difficult for analog transmission schemes to be used in Morocco networking.

For this reason, Chinese patent applications "CN1464666, a soft base station system based on optical fiber remote and its synchronization method", "CN1471331, a base station system for mobile communication, etc. are proposed In addition to the implementation of digital signal transmission, another cooperative organization called CPRI (Common Public Radio Interface) is also engaged in the standardization of digital baseband transmission between RRU and MU. Its technical specifications can be downloaded from the website http: 〃 www.cDri .info / spec.html download. However, these technologies all use special interface specifications, and it is difficult to use the mature broadband transmission resources existing in the existing telecommunication transmission network, thereby increasing the network construction cost. In addition, the existing digital transmission technology between the RRU and the MU also has problems such as inflexible networking and complicated maintenance management.

In response to the above-mentioned problems, the same applicant submitted to the Chinese Patent Office on April 9, 2004 and January-January 2004, entitled "Signal Transmission Method and System for Radio-Based Wireless Base Stations" (Agency Volume Number) IEE040020PCT), and "Multi-antenna signal transmission method and system in a radio remote radio base station," (Agent Volume IEE040024PCT) patent application, proposes a compatible with the existing telecommunications transmission network technology, can directly use the existing There are digital wireless signal transmission technologies between RRU and MU of SDH / OTN transmission network. Since the STM-N / OTM-n standard interface is directly adopted, digital wireless signal transmission between RRU and MU can be realized without a dedicated transmission network.

On the other hand, in the centralized base station system 10 shown in FIG. 2 where the radio frequency unit is remote, the MU 15 and the RRU 14 are directly connected through a broadband transmission link. If it is difficult to implement large-capacity multiplexing technology and an analog signal transmission scheme is adopted, its networking scheme is still more feasible. However, when a digital transmission scheme is adopted, such a network structure is not flexible enough in actual networking. For example, when there are multiple cells in a relatively geographically concentrated area (a typical case is a high-rise building, an airport, a shopping mall, etc.), if the MU capacity is large and the distance is far from the area, because the main transmission paths are the same, Therefore, directly connecting the corresponding RRU of each cell in the area to the MU will cause the cost of transmission line resources. The present invention proposes an effective remote radio frequency unit hub device and method for the above problems. Summary of the invention

It is an object of the present invention to provide an interconnection structure to overcome the above-mentioned drawbacks of the prior art.

According to an aspect of the present invention, a structure for interconnecting a channel processing main unit and a plurality of radio frequency units in a centralized base station system is provided, including a hub device, which is respectively connected to the plurality of radio frequency units through a first link. Part or all of them are connected, and are connected to the channel processing main unit through a second link, wherein the hub device includes a multiplexing / demultiplexing device for connecting the first and second links.

In one embodiment, the communication on the first link includes wireless signals and management control signaling related to a radio frequency unit connected to the hub device.

In another embodiment, the communication on the first link is in digital form. In another embodiment, the communication on each of the second links includes a wireless signal corresponding to a radio frequency unit connected to the second link and a management control signal related to the radio frequency unit.

In another embodiment, the communication on each of said second links is in analog form.

In another embodiment, the management control signal is transmitted through a dedicated line. In another embodiment, the hub device further includes a timing acquisition device, which is configured to provide a unified timing and frequency reference within the hub device.

In another embodiment, the timing is recovered from the first-link downlink digital wireless signal data stream;

In another embodiment, the timing is obtained from a GPS system.

In another embodiment, the hub device further includes a control device for controlling an operation of the multiplexing / demultiplexing device.

In another embodiment, the control device is further used for monitoring and management of the connected radio frequency unit.

According to another aspect of the present invention, a channel in a centralized base station system is provided. A method for processing a communication between a main unit and a plurality of radio frequency units, the centralized base station system further includes a hub device, which is connected to a part or all of the plurality of radio frequency units through a first link, and A second link is connected to the channel processing main unit, and the method includes:

In the downlink direction, the hub device receives the downlink signal stream sent from the channel processing main unit; the hub device demultiplexes the received downlink signal stream into downlink sub-signal streams respectively for the corresponding radio frequency unit; and each downlink The sub-signal stream is forwarded to the corresponding radio frequency unit,

In the uplink direction, the hub device receives the uplink sub-signal stream sent by each radio frequency unit; the hub device multiplexes the received uplink sub-signal stream into an uplink signal stream; and sends the uplink signal stream to the channel processing main unit. BRIEF DESCRIPTION OF THE DRAWINGS

The following describes embodiments of the present invention with reference to the accompanying drawings, where:

Figure la is a schematic diagram of a traditional BTS structure;

FIG. 1b is a schematic diagram of a structure of a radio access network;

Fig. 2 is a block diagram showing the structure of a centralized base station system using a radio frequency unit;

FIG. 3 illustrates a distributed multi-cell remote radio frequency unit and a network structure according to an embodiment of the present invention;

FIG. 4 is a block diagram of a main structure of a hub unit;

Figure 5 is a block diagram of the main structure of the RF front-end module. detailed description

According to the present invention, in a centralized base station system that uses a radio frequency unit to remotely, when a digital transmission scheme between a MIMO and RRU that supports digital multiplexing technology is adopted, a distributed multi-cell remote radio frequency unit and group The network structure is shown in Figure 3, where Mϋ The link between 15 and hub unit 21 is a broadband digital transmission link. The antenna corresponding to each cell is directly connected to the corresponding radio frequency front-end module 22. Each radio frequency front-end module 22 and hub unit 21 transmit analog radio frequency signals. The cables are connected. The radio frequency front-end module 22 mainly finishes transmitting and receiving radio frequency signals. The concentrating unit 21 is responsible for completing the processing of the broadband digital transmission interface with the M15, which typically includes the multiplexing and demultiplexing of digital wireless signals of multiple cells and data streams of corresponding management control signaling, and wireless Signal clock recovery, ADC / DAC (analog-to-digital conversion / digital-to-analog conversion), frequency conversion, centralized management and control of each RF front-end module and other functions.

In fact, the hub unit proposed by the present invention first effectively utilizes the transmission line resources with the MU. At the same time, because of the structure, the common unit can be used to collectively execute the wideband digital signals with the MIMO that were originally completed by each remote radio frequency unit. Transmission interface, wireless signal clock recovery, ADC / DAC, centralized management and control of the RF front-end module, so the complexity of the RF front-end module is effectively reduced, and the overall cost is compared with multiple RRUs with the same accuracy. obvious advantage. Therefore, the technology proposed by the present invention can be well combined with the digital transmission technology between MIMO and RRU supporting digital multiplexing technology, which can effectively reduce system cost and networking complexity.

1. Structure of hub unit and RF front-end module

FIG. 4 is a block diagram showing the main structure of the concentrating unit 21. The hub unit 21 includes a downstream digital interface 31, a down conversion unit 32, a clock recovery unit 33, a frequency synthesizing unit 34, an uplink digital interface 35, and an up conversion unit 36. The downstream digital interface 31 includes a digital broadband interface 37 and a demultiplexing unit 38. The down conversion unit 32 includes a plurality of down conversion paths, each of which corresponds to a radio frequency front-end module, and includes a DAC unit 39 and an up conversion unit 40. The upstream digital interface 35 includes a digital broadband interface 41 and a multiplexing unit 42. The up-conversion unit 36 includes several up-conversion paths, each of which corresponds to a radio frequency front-end module, and includes an ADC unit 43 and a down-conversion unit 44.

In the downstream direction (from the MU to the hub unit), the digital broadband interface 37 and the demultiplexing unit 38 of the downstream digital interface complete the broadband digital transmission with the MU. The processing of the input interface restores the downlink digital wireless signals of each cell and the corresponding management control signaling data flow. The downlink digital wireless signal is then converted into an analog signal by the DAC unit 39 of the corresponding path in the down conversion unit 32, and finally converted into a radio frequency signal by the up conversion unit 40 and transmitted to each radio frequency front-end module through a radio frequency cable. In the upstream direction (from the hub unit to Mϋ), the uplink RF signal from the RF front-end module is first converted into a zero intermediate frequency (baseband) or low intermediate frequency signal by the down conversion unit 44 of the corresponding path in the uplink conversion unit 36, and then passed through the ADC unit 43 is converted into a digital signal, and finally transmitted to the remote via the multiplexing unit 42 and the digital broadband interface 41 of the upstream digital interface 35 together with the corresponding management control signaling data stream generated by a control unit (described later) not shown here. MU. Depending on the digital broadband interface technology used, the digital broadband interface 37 and the demultiplexing unit 38 in the downstream digital interface 31, and the digital broadband interface 41 and the multiplexing unit 42 in the upstream digital interface 35 may be A set of functional units can also be two independent functional units.

At the same time, the clock recovery unit 33 recovers the data stream clock of the digital wireless signal according to the clock information provided by the digital interface 31 below. This clock is used by the digital broadband interface 41 and the multiplexing unit 42 in the uplink digital interface 35 for uplink transmission. The clock also provides the frequency synthesis unit 34 with a high-precision reference frequency. The frequency synthesizing unit 34 is responsible for generating various frequency signals required by the DAC / ADC and the up / down conversion unit. When the MIMO and RRU use a global common clock, typically when GPS (Global Positioning System) is used, the clock recovery unit 33 is not needed, and the system timing reference and frequency reference can be obtained from GPS by components known in the art. It should be noted that the functions of the clock recovery unit and the frequency synthesis unit may be implemented by separate devices, or may be implemented by an integrated device.

In addition, in addition to the modules shown in the functional block diagram of FIG. 4, the hub unit also includes a control unit. The control unit is typically a microprocessor-based unit, which mainly completes processing of management control signaling of the interface with the MU, where the management control signaling includes information about the link between the RRU and the MU. Build, modify, maintain, content Control signaling such as error, rate negotiation, data format and working mode negotiation, as well as RRU operation and maintenance messages. At the same time, the control unit is also responsible for the control and management of the entire hub unit and each RF front-end module.

FIG. 5 shows the main structural block diagram of the RF front-end module 22. It can be seen that the RF front-end module 22 mainly includes functions such as a downstream RF power amplifier 51, an upstream low-noise amplifier 52, a duplexer 53, and an antenna 54. The unit is composed of a duplexer 53 for an FDD (Frequency Division Duplex) system, and a duplexer 53 for a TDD (Time Division Duplex) system.

The hub unit is connected to each RF front-end module through a RF cable. Since the RF front-end module mainly completes the front-end amplification of the signal uplink / downlink RF signals, it does not require a highly stable frequency reference signal. However, since the control and management of the corresponding RF front-end unit by each hub unit is completed by the control unit in the hub unit, the control and management signals need to be transmitted between the hub unit and the corresponding RF front-end module, including by the hub. The control information sent by the line unit to the RF front-end module, and the alarm, monitoring results and other data sent by the RF front-end module to the hub unit. For this reason, according to the present invention, two methods can be used to transmit the control management signal between the above-mentioned hub unit and each RF front-end module: One is to use FSK (frequency shift keying) and other technologies to modulate the control management signal to a certain frequency In order to mix with wireless radio frequency signals for transmission; another method is to use a dedicated control line, typically such as direct transmission based on RS-232, RS-488> RS-485 and other twisted pairs, current loop, etc. At this time This dedicated control line is routed simultaneously with the RF cable.

2. Multi-channel sharing of functional units in hub units

As previously mentioned, the distributed multi-cell remote radio frequency unit provided by the present invention has obvious advantages compared with multiple RRUs of the same size in terms of overall cost, because the structure makes it compatible with MIMO's wideband digital transmission interface, wireless It is possible to share functional units such as signal clock recovery, ADC / DA (, centralized management and control of RF front-end modules, etc.).

According to the structure of the above-mentioned hub unit, the broadband digital transmission interface and wireless The signal clock recovery, the frequency synthesizing unit, and the control unit all realize multi-cell sharing, which is conducive to reducing system costs. In addition, a functional unit that may implement multi-cell sharing or integration is the ADC DAC unit. Due to factors such as improved integration and better consistency when the same functional units are implemented in the same integrated circuit, multiple parallel ADC or DAC units can be integrated on one integrated circuit, which is conducive to reducing the number of peripheral circuits. Complexity and effectively reduce system costs.

Another situation where multi-cell sharing or integration is possible is to use digital IF technology in the up-down conversion unit. For a detailed introduction to digital IF technology, please refer to "Software Radio Principles and Applications, Yang Xiaoniu, Lou Caiyi, Xu Jianliang, Electronic Industry Press, February 2001". When digital IF technology is used, digital up-conversion and digital down-conversion functions are implemented using digital circuits. Because digital circuits are easy to integrate on a large scale, multi-channel signal processing can be implemented on the same integrated circuit, which is beneficial to reduce The complexity of small peripheral circuits effectively reduces system costs.

3. Digital multiplex transmission scheme for interface with MU

As mentioned above, the present invention requires a digital transmission scheme between MIMO and RRU to support digital multiplexing. As a preferred example, the applicant may submit to the China Patent Office on April 9, 2004 Submitted entitled "Signal Transmission Method and System for Radio Frequency-Based Wireless Base Stations" (Agent Volume IEE040020PCT), and entitled "Multi-antenna Signal Transmission Method and System in Radio Frequency-Remote Wireless Base Stations," The technology proposed in the patent application No. IEE0400 ²⁴ PCT) is applied to the realization of multiplexed digital transmission between the hub unit and the MU in the distributed multi-cell remote radio frequency unit proposed by the present invention.

Claims

A structure for interconnecting a main channel processing unit and a plurality of radio frequency units in a centralized base station system, comprising a hub device, which is connected to some or all of the plurality of radio frequency units through a first link, respectively; and Connected to the channel processing main unit through a second link,

Wherein the hub device includes a multiplexing I demultiplexing device for connecting the first and second links.

2. The structure according to claim 1, wherein the communication on the first link comprises wireless signals and management control type signaling related to a radio frequency unit connected to the hub device.

3. The structure according to claim 2, wherein the communication on the first link is in digital form.

4. The structure according to claim 1, wherein the communication on each of the second links includes a wireless signal corresponding to a radio frequency unit connected to the second link and a management control signal related to the radio frequency unit.

5. The structure according to claim 4, wherein the communication on each of said second links is in analog form.

6. The structure according to claim 4, wherein the management control signal is transmitted through a dedicated line.

7. The structure according to claim 1, wherein the line concentrating device further comprises:

A timing acquisition device is used to provide a unified timing and frequency reference in the hub device.

8. The structure according to claim 7, wherein the timing is recovered from the first-link downlink digital wireless signal data stream.

9. The structure of claim 7, wherein the timing is obtained from a GPS system.

10. The structure according to claim 1, wherein the line concentrating device further comprises: A control device, configured to control an operation of the multiplexing / demultiplexing device.

11. The structure according to claim 10, wherein the control device is further used for monitoring and management of a connected radio frequency unit.

12. A communication method between a channel processing main unit and a plurality of radio frequency units in a centralized base station system, the centralized base station system further comprising a hub device, which respectively communicates with the plurality of radio frequency units through a first link Part or all of the connections are connected, and the channel processing main unit is connected through a second link, and the method includes:

In the downward direction,

The hub device receives the downlink signal flow sent from the channel processing main unit; the hub device demultiplexes the received downlink signal flow into downlink sub-signal flows respectively for the corresponding radio unit; and

Forward each downlink sub-signal stream to the corresponding radio frequency unit,

In the up direction,

The hub device receives the uplink sub-signal stream sent by each radio frequency unit;

The hub device multiplexes the received uplink sub-signal stream into a uplink signal stream; and sends the uplink signal stream to a channel processing main unit.

13. The method of claim 12, wherein the upstream and downstream signal flows include wireless signals and management control-type signals related to a radio frequency unit connected to the hub device.

14. The method according to claim 13, wherein the upstream and downstream signal flows are in digital form.

15. The method according to claim 12, wherein the uplink and downlink sub-signal streams include a wireless signal of a corresponding radio frequency unit and a management control signal related to the radio frequency unit.

16. The method according to claim 15, wherein the uplink and downlink sub-signal streams are in analog form.

17. The method according to claim 15, wherein the management control signal is transmitted through a dedicated line.

18. The method according to claim 12, further comprising monitoring and managing a radio frequency unit connected to the hub device.