CN1917388B - Distribution type antenna system, and communication method - Google Patents

Abstract

The invention relates to a distributed antenna system and a communication method thereof. The distributed antenna system is based on a cell structure, and each cell includes a central processing unit, multiple wireless access units and transmission links, and the multiple wireless access units are respectively connected to the central processing unit through their respective transmission links. Wherein, the wireless access unit includes a duplexer and an antenna on it, and the central processing unit includes a path loss estimator, a resource allocator, a sending processor, a wireless access unit selector, and a radio frequency link group. The distributed antenna system and communication method of the present invention can allocate the wireless access unit capable of realizing the largest system capacity to the same user, and can increase the system capacity while increasing the degree of freedom of space dimension for the user.

Description

Distributed antenna system and its communication method

technical field

The present invention relates to a multi-antenna system and its communication method, in particular to a distributed antenna system and its communication method. The distributed antenna system and communication method can select the optimal wireless access unit for a certain user, Thus providing the best system capacity.

Background technique

Future wireless communication systems need to support very high-speed data services, such as video conferencing, video on demand, interactive games, and so on. According to the requirements mentioned in the ITU-R M1645 document: for high-speed wireless services (High Mobility), it is necessary to support a rate up to 100Mbps; for low-speed (Low Mobility) or fixed wireless (Fixed wireless) services, it is necessary to reach 1Gbps rate. At the same time, as a wireless communication system, it must also ensure the coverage of the system and provide high data rate services for any user anywhere and at any time.

The analysis found that for such a high link rate, user coverage is a serious problem. Specifically, there are two reasons:

a. The rate to be supported by the future system is very high. Even if the existing technology can achieve high spectral efficiency, it still needs a relatively large bandwidth to support it. The current experimental system uses a bandwidth of 100MHz for the downlink and 40MHz for the uplink . In order to accommodate this system, a relatively high frequency band, such as 10GHz, has to be used. Compared with signals in lower frequency bands (for example, GSM, 1GHz; WCDMA, 2GHz), the path loss (Path Loss, hereinafter abbreviated as P1) of high-frequency signals is much larger. The transmission distance will be greatly reduced.

b. As the data rate of the system increases, the signal-to-noise ratio per bit (SNR/bit) that can be achieved with the same transmission power will decrease inversely. The performance of the user is directly related to the signal-to-noise ratio per bit. Of course, the same coverage can also be satisfied by increasing the transmission power of the system. However, considering the impact of radio waves on human health, the transmission power of the base station needs to be limited within a certain range. In this way, under the same limited power, the coverage of the signal will be greatly reduced. In the above situation, the traditional cellular system can only realize the coverage of the system through the method of cell division. In this case, on the one hand, it will cause a large increase in the system infrastructure, which will lead to an increase in investment, and on the other hand, due to the reduction of the cell area, it will cause users to switch between ordinary cells while moving.

To solve this problem, two new network structures are proposed. One is a network structure based on forwarding and multi-hop structure (Relay and Multi-Hop Structure), and the other is a network structure based on distributed antenna system (Distributed Antenna System, DAS). Here, since the present invention only focuses on the network structure based on the distributed antenna system, the network system based on the forwarding and multi-hop structure will not be described.

For distributed antenna systems, reference [1], "A.A.M.Saleh, A.J.Rustako, and R.S.Roman". Distributed antennas for indoor radio communications," IEEETrans.On Communications, Vol.35, pp.1245-1251, Dec .1987", revealing one of the earliest distributed antenna systems. Among them, the wireless signal is simply transmitted to a relatively distant place through a coaxial cable, and then sent out through one or more antennas, and these antennas can be connected in series on a coaxial cable at the same time. More often, it may be to lay a coaxial cable, and then set small openings for the cable at the corresponding places so that wireless signals can leak out. Here, these openings are equivalent to small antennas for transmitting wireless signals.

In this case, the transmitted signals of multiple antennas are actually the same signal, and its main function is to provide indoor signal coverage for the mobile system. Usually, this kind of distributed antenna system is called passive distributed antenna system (Passive DAS), and the system performance gain it can provide is very limited.

Later, due to the in-depth research on the multiple-input multiple-output system (MIMO), an active distributed antenna system (Active DAS) was proposed, please refer to the reference [2], "Troels B. Sorensen, "Intelligent Distributed Antenna System." Ph.D thesis, 2003". In this distributed antenna system, multiple antennas at the system end are not installed centrally on a central base station, but are respectively installed on small base stations evenly distributed in different places within a cell. The radio frequency signal to be transmitted/received by each antenna is received/sent from the base station signal processing unit through the optical fiber.

Figure 1 shows a schematic diagram of an active distributed antenna system. In order to be different from the traditional network structure, the small base station installed with the antenna module is called the radio access unit (Radio Access Unit, RAU), and the signal processing module is called the central processing unit (Central Unit, central processing unit). Multiple independent antennas can be installed on each wireless access unit. For such a system, the wireless access unit only needs to have a duplexer, a photoelectric converter for radio frequency signals, and a power amplifier for transmitting radio frequency signals. All other base station units including, for example, up/down converters, encoders, modulators, space-time processors, etc. are concentrated in the central processing unit. The study found that, compared with the Centralized Antenna System (CAS), the distributed antenna system can complete the system signal coverage well, and can greatly reduce the signal transmission power.

FIG. 1 is a schematic structural diagram of a cell in a distributed antenna system. For such a system, there is a problem to be solved: when a user wants to access the system, which wireless access units should be selected to communicate with it.

For the uplink, as long as the wireless access unit can receive the user's signal, no matter how low the energy of the signal is, it is useful to improve the system performance theoretically.

As for the downlink, under the condition of maintaining the same transmit power, selecting more radio access units to serve a user may not necessarily improve the performance of the system. This is because: for the central antenna system, adding transmit antennas can increase the performance of the system, but the premise is that the path loss of each transmit antenna to the user is the same. But for the distributed antenna system, since the antennas are distributed in different places, the distance between each wireless access unit and the user is different, resulting in different path losses.

Taking Figure 2 as an example, when the distance between the wireless access unit and the user (such as d1 and d2) is relatively large, adding a wireless access unit can increase the degree of freedom of the space dimension, but the effective transmission power Sex will be greatly reduced. If the performance increase caused by the increased space dimension and the path loss introduced by the wireless access unit cannot be compensated, adding the wireless access unit 2 to transmit signals to the user may not necessarily increase the performance of the system. In such a distributed antenna system, the problem is how to select the wireless access unit to send signals to the users so that the system performance is the best.

Reference [3], "Tao Xiaofeng, Ni Li, Dai Zuojun, Liu Baoling, Zhang Ping, "Intelligent group handover mode in multicell infrastructure", PIMRC 2003, Vol.1, Sept.7-10, 2003", in A concept of group handover is mentioned, and its basic idea is to set a threshold value, and all wireless access units whose path loss is smaller than the threshold value are selected.

Reference [4], "Wan Choi, Jeffrey G. Andrews, and Chaehag Yi, "The capacity of multicellular distributed antenna networks," WirelessCom2005, Jun12-16, 2005", mentioned another method, which chooses A fixed number of L wireless access units transmit data for one user. In this way, L radio access units with the minimum path loss will be selected.

The two methods mentioned above are actually based on the absolute value of the path loss to select the wireless access unit, and neither of them can guarantee the maximum channel capacity of the system. To maximize the system capacity, the selection of wireless access units should be related to the relative value of the path loss between them and users. That is, when the user is very close to the wireless access unit, selecting the nearest wireless access unit can completely maximize the capacity, and there is no need to allocate power to other wireless access units for data transmission.

Contents of the invention

In order to overcome the above problems, the present invention proposes a distributed antenna system and a communication method thereof, which can maximize system capacity when selecting wireless access units for users.

The distributed antenna system of the present invention is based on cell structure, and each cell includes a central processing unit, a plurality of wireless access units and transmission links, and the plurality of wireless access units communicate with the central processing unit through respective transmission links connect. Wherein, each wireless access unit includes a duplexer, and the duplexer is used to receive user's uplink information through its antenna and send downlink information from the central processing unit. The central processing unit includes: a path loss estimator, configured to estimate the uplink information from the above-mentioned multiple wireless access units, obtain the path loss between each wireless access unit and the user, and store each path loss correspondingly and the serial number of the wireless access unit; the resource allocator obtains resource allocation information according to the path loss stored above and the serial number of the wireless access unit, and the resource allocation information includes the wireless access unit adopted by the user; the sending processor, According to the above resource allocation information, the user data of the user is correspondingly processed to transmit signals, and the baseband signal flow for each wireless access unit in the wireless access unit adopted by the user is generated; the wireless access unit selector, according to For the above resource allocation information, select the corresponding wireless access unit among all the wireless access units connected to the central processing unit to transmit the above-mentioned baseband signal streams processed by the sending processor; and, the radio frequency link group, the wireless The baseband signal streams output by the access unit selector are respectively subjected to frequency up-conversion processing, and the up-converted baseband signal streams are sent as downlink information to corresponding wireless access units through transmission links.

The communication method of the present invention comprises the steps of:

Step 1, the wireless access unit respectively receives the uplink information of the same user, and sends the uplink information to the central processing unit;

Step 2, the central processing unit estimates the path loss of the user's uplink information from each wireless access unit, and stores the path loss and the number of the wireless access unit correspondingly;

Step 3, according to the stored path loss and the serial number of the wireless access unit, obtain resource allocation information, the resource allocation information includes the wireless access unit used by the user;

Step 4: According to the resource allocation information above, perform corresponding signal processing on the user data of the user, and generate baseband signal streams for each of the wireless access units used by the user;

Step 5, according to the above resource allocation information, select the corresponding wireless access unit for sending each baseband signal flow, to send each baseband signal flow respectively; and

Step 6, performing upconversion processing on each baseband signal stream, and transmitting the upconverted baseband signal streams to corresponding wireless access units as downlink information; and

In step seven, each wireless access unit sends downlink information to the same user.

The resource allocation process in the above step 3 includes the following steps:

i) find the minimum value of the path loss from the above path loss;

ii) Find out the corresponding wireless access unit according to the minimum value, and use it as the wireless access unit for transmitting the user data of the user;

iii) find the minimum value of the path loss from the remaining other path losses;

iv) Find out the corresponding wireless access unit according to the minimum value, and calculate whether the addition of the wireless access unit increases the system capacity. When the addition of the wireless access unit reduces the system capacity, the resource allocation ends. When When the addition of the wireless access unit increases the system capacity, it is used as a wireless access unit for transmitting user data, and then steps iii and iv are repeated until the resource allocation ends.

Compared with the prior art, the distributed antenna system and communication method of the present invention can allocate the wireless access unit that can realize the maximum system capacity to the same user, and can increase the degree of freedom of the space dimension for the user while increasing the system capacity. capacity.

Description of drawings

FIG. 1 is a schematic diagram of an active distributed antenna system.

Fig. 2 is a schematic diagram of a distributed antenna system with path loss differences.

FIG. 3 is a schematic diagram of the distributed antenna system of the present invention.

FIG. 4 is a specific block diagram of the distributed antenna system of the present invention.

FIG. 5 is a flow chart of the resource allocation process of the communication method of the distributed antenna system of the present invention.

Detailed ways

The distributed antenna system of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 3 is a schematic diagram of the distributed antenna system of the present invention. Figure 3 shows multiple cells (indicated by dotted circles), and each cell includes at least one central processing unit and multiple wireless access units. For ease of description, a central processing unit CU and multiple wireless access units are uniformly set in each cell in Figure 3, but in an actual system, the number and distribution of wireless access units can be set according to the conditions of the cell situation.

In each cell, the wireless access unit is connected to the central processing unit. On the one hand, each wireless access unit receives uplink information from users in the cell and transmits the uplink information to the central processing unit after processing. On the one hand, each wireless access unit receives the downlink information from the central processing unit, processes the downlink information, and sends it to users in the cell through its transmitting antenna.

Fig. 4 is a specific structural diagram of the distributed antenna system of the present invention, in which only the central processing unit and the wireless access unit in one cell are shown. For generality of description, therefore, here it is assumed that the number of wireless access units in the cell is nT. At the same time, for the convenience of description, only one central processing unit is used as an example for illustration, and the example of using multiple central processing units in the same cell can be derived from it.

For each wireless access unit, it includes a duplexer 11 , an antenna 12 located on the duplexer 11 , a receiving power amplifier 13 , an electrical-to-optical converter 14 , a transmitting power amplifier 15 and an optical-to-optical converter 16 . Here, the receiving power amplifier 13 and the transmitting power amplifier 15 are optional units. It can also be omitted when the power of the distributed antenna system is large and the signal-to-noise ratio is good.

Meanwhile, the central processing unit CU includes a photoelectric converter 21 , a path loss estimator 22 , a resource allocator 23 , a sending processor 24 , a wireless access unit selector 25 , a radio frequency link group 26 and an electro-optic converter 27 .

Before establishing a communication between a user and the distributed antenna system, the user will determine the cell to be accessed according to the downlink channel information it receives. For example, for the GSM system, the user decides the cell to access according to the energy of the channel frequency of each cell, and for the WCDMA system, the user determines the cell to access according to the energy of the scrambling code of each cell.

After determining the cell to access, the user will send a communication request to the cell.

In the distributed antenna system of the present invention, in the uplink direction, for each wireless access unit, the duplexer 11 uses the antenna 12 on it to receive uplink information (radio frequency signal, which can be the above-mentioned communication request) from the user. , can also be other information), and power amplifies the received radio frequency signal through the receiving power amplifier 13, which can be a low noise power amplifier. The electro-optic converter 14 performs electro-optic conversion on the amplified radio frequency signal to obtain a corresponding optical signal, and sends it to the central processing unit CU through the optical fiber link between the wireless access unit and the central processing unit CU.

For the central processing unit, the photoelectric converter 21 receives optical signals from all nT wireless access units in the cell via optical fiber links, and converts the optical signals from each wireless access unit into corresponding radio frequency signals. The path loss estimator 22 estimates the path loss between the user and each wireless access unit in the cell according to the radio frequency signal, and stores the obtained path loss and the corresponding wireless access unit. For example, the path loss and the corresponding wireless access units can be stored in ascending order, for example, in the manner shown in Table 1, assuming {Pl ₁ , Pl ₂ , Pl ₃ , ... Pl _nT } , where Pl ₁ represents the minimum path loss value. Table 1 is just a storage method, and the present invention is not limited thereto, and may also be stored in descending order or out of order, but it is necessary to establish the corresponding relationship between the path loss and its corresponding wireless access unit.

Table 1 RAU ₁ RAU ₂ RAU ₃ ... _wxya Pl ₁ Pl ₂ Pl ₃ ... lm _w

The resource allocator 23 performs resource allocation according to the path loss estimated by the path estimator 22 and its corresponding wireless access unit. As shown in Figure 5, the resource allocation process of the resource allocator is as follows:

Step 1, finding the minimum value of the path loss from the path loss estimated by the path estimator 22;

Step 2, find out the corresponding wireless access unit according to the minimum value, and use it as the wireless access unit for transmitting the user data of the user;

Step 3, find the minimum value of the path loss from the remaining other path losses;

Step 4, find out the corresponding wireless access unit according to the minimum value, and calculate whether adding the wireless access unit increases the system capacity. When the addition of the wireless access unit reduces the system capacity, resource allocation ends. When the addition of the wireless access unit increases the system capacity, it is used as the wireless access unit for transmitting user data, and then steps 3 and 4 are repeated until the resource allocation ends.

In the above resource allocation process by the resource allocator 23, the selection of the wireless access unit that realizes the maximum system capacity can be performed by formula (1).

Among them, Ce represents the expected value of the channel capacity, E represents the operation of finding the expectation, I _nR is the unit matrix of nR*nR dimension, nR represents the number of antennas of the user, H and H ^* are the channel matrix and its transpose matrix respectively, Q _L is a correlation matrix of transmitted signals, and L represents the number of radio access units selected from nT radio access units when the system capacity is the largest.

Above-mentioned H and Q _L are shown in formula (2), (3) respectively:

H _w is a random equation of nT*nR dimensions, each element of which is a Gaussian random variable with zero mean and unit variance. in, Indicates the channel gain between the user and the nTth wireless access unit.

After the above resource allocation process, it is assumed that the resource allocator 23 has selected L wireless access units at this time, and these wireless access units are used to send the user data of the user and can satisfy the maximum system capacity. At the same time, it can be concluded that the user data of the user should be divided into L paths for transmission. That is, the resource allocation information generated by the above resource allocation process includes: the wireless access unit used by the user.

In the downlink direction, the transmission processor 24 performs transmission signal processing on the user data of the user according to the resource allocation information to generate an L-subgrade band signal. The processing here includes spatial signal processing, coding, modulation, etc., which can be passed through the user during communication. determined by the communication request issued.

The radio access unit selector 25 selects L radio access units for sending the user data according to the resource allocation information to send L channels of user data. In the figure, L indicates the number of selected wireless access units, nT indicates that there are nT wireless access units in total, and the unselected wireless access units do not send the user data of the user.

The transmitting radio frequency link group 26 performs up-conversion processing on the nT baseband signals output from the wireless access unit selector 25 (only the baseband signals corresponding to the selected L wireless access units transmit the user data of the user) , to obtain the corresponding radio frequency signal.

The electro-optic converter 27 performs electro-optical conversion on the nT channels of radio frequency signals output by the sending radio frequency link group 26, thereby obtaining the corresponding nT channels of optical signals, and transmits them to the corresponding wireless access unit through the optical fiber link.

The photoelectric converter 16 receives an optical signal from the central processing unit CU through an optical fiber link, and converts the optical signal into a corresponding radio frequency signal. After the radio frequency signal is amplified by the transmitting power amplifier 15 , it is sent to the user via the antenna 12 via the duplexer 11 .

It can be seen from the above that by allocating the wireless access unit that can realize the maximum system capacity to the user in the central processing unit, the system capacity can be increased while increasing the degree of freedom of the space dimension for the user.

The above is only a preferred embodiment of the present invention, and it is mainly aimed at the situation that the distance between the wireless access unit and the central processing unit is far away, so an optical fiber link is used to transmit data between the wireless access unit and the central processing unit. Signal. For this reason, it requires corresponding photoelectric converters and electro-optical converters on the wireless access unit and the central processing unit to realize mutual conversion between optical signals and electrical signals (radio frequency signals).

However, for the situation where the distance between the wireless access unit and the central processing unit is relatively close, a cable link can be used instead of an optical fiber link, so that the process of converting electrical signals into optical signals and optical signals into electrical signals can be omitted, and then , the distributed antenna system does not need to use electro-optical converters and photoelectric converters.

Further, since the distance between the wireless access unit and the central processing unit can be set according to the actual situation, therefore, for a relatively short distance, a cable link can be used to transmit signals, and for a relatively long distance, a cable link can be used fiber optic link to transmit the signal.

It is worth noting that although only one antenna is shown on each wireless access unit in Figure 4, for an actual distributed antenna system, there may be multiple antennas, and the maximum system capacity can be satisfied. In some cases, the central processing unit may allocate (all or part of) these antennas to the same user at the same time, and similarly, the user also has multiple antennas. At this time, the radio frequency link group multiplexes the user data transmitted by different antennas on the same wireless access unit with a multiplexer, and transmits them to the wireless access unit through an optical fiber link or a cable link. At the same time, the wireless access unit also needs multiple sets of units in FIG. 4 as well as multiplexers (uplink direction) and demultiplexers (downlink direction) to realize the transmission and reception of multiple signals. That is, each wireless access unit is equivalent to multiple wireless access units, which share a transmission link after using a multiplexer and a demultiplexer.

Claims (7)

1. A distributed antenna system, which is based on a cell structure, and each cell includes a central processing unit, a plurality of wireless access units and a transmission link, and the plurality of wireless access units communicate with the central processing unit through respective transmission links unit connection, where, Each wireless access unit includes a duplexer, and the duplexers of the above-mentioned multiple wireless access units receive the uplink information of the same user through the antennas thereon and send the downlink information from the central processing unit to the user, The central processing unit includes: A path loss estimator, configured to estimate the uplink information from the above-mentioned multiple wireless access units, obtain the path loss between each wireless access unit and the user, and store each path loss and the wireless access unit correspondingly serial number; The resource allocator obtains resource allocation information according to the stored path loss and the serial number of the wireless access unit, and the resource allocation information includes the wireless access unit used by the user; The sending processor performs corresponding sending signal processing on the user data of the user according to the resource allocation information, and generates a baseband signal flow for each of the wireless access units used by the user; The wireless access unit selector selects a corresponding wireless access unit among all the wireless access units connected to the central processing unit according to the above resource allocation information to transmit the above-mentioned baseband signal streams processed by the sending processor; and The radio frequency link group performs up-conversion processing on the baseband signal streams output by the wireless access unit selector, and transmits the up-converted baseband signal streams as downlink information to the corresponding wireless access units through the transmission link. 2. The distributed antenna system according to claim 1, wherein the wireless access unit further comprises: a transmit power amplifier, configured to amplify the power of the downlink information from the central processing unit, and transmit the amplified downlink information to the duplexer; and The receiving power amplifier is used to amplify the power of the uplink information received by the duplexer, and transmit the amplified uplink information to the central processing unit through the transmission link. 3. The distributed antenna system as claimed in claim 1, wherein, The wireless access unit further includes: An electro-optical converter (14), used to convert the uplink information received by the duplexer into a corresponding optical signal, and transmit the optical signal to the central processing unit through a transmission link; and A photoelectric converter (16), used to convert the downlink information from the central processing unit into a corresponding electrical signal, and send the electrical signal through the antenna on the duplexer, and, The central processing unit further includes: an optical-to-electrical converter (21), used to convert the optical signals from each transmission link into corresponding electrical signals, and transmit them to the path loss estimator respectively; and The electro-optic converter (27) is used to convert each path of downlink information from the radio frequency link group into corresponding optical signals, and send them to corresponding wireless access units through corresponding transmission links. 4. The distributed antenna system as claimed in claim 2, wherein, The wireless access unit further includes: An electro-optical converter (14), which is used to convert the uplink information amplified by the receiving power amplifier into a corresponding optical signal, and transmit the optical signal to the central processing unit through the transmission link; and A photoelectric converter (16), used to convert the downlink information from the central processing unit into a corresponding electrical signal, and transmit the electrical signal to the transmitting power amplifier, and, The central processing unit further includes: an optical-to-electrical converter (21), used to convert the optical signals from each transmission link into corresponding electrical signals, and transmit them to the path loss estimator respectively; and The electro-optic converter (27) is used to convert each path of downlink information from the radio frequency link group into corresponding optical signals, and send them to corresponding wireless access units through corresponding transmission links. 5. The distributed antenna system according to claim 2 or 4, wherein the receiving power amplifier is a low noise power amplifier. 6. A communication method of a distributed antenna system, wherein the distributed antenna system has a central processing unit, a plurality of wireless access units and a transmission link, the method comprising steps: Step 1, the wireless access unit respectively receives the uplink information of the same user, and sends the uplink information to the central processing unit; Step 2, the central processing unit estimates the path loss of the user's uplink information from each wireless access unit, and stores the path loss and the number of the wireless access unit correspondingly; Step 3, according to the stored path loss and the serial number of the wireless access unit, obtain resource allocation information, the resource allocation information includes the wireless access unit used by the user; Step 4: According to the resource allocation information above, perform corresponding signal processing on the user data of the user, and generate baseband signal streams for each of the wireless access units used by the user; Step 5, according to the above resource allocation information, select the corresponding wireless access unit for sending each baseband signal flow, to send each baseband signal flow respectively; and Step 6, performing upconversion processing on each baseband signal stream, and transmitting the upconverted baseband signal streams to corresponding wireless access units as downlink information; and In step seven, each wireless access unit sends downlink information to the same user. 7. The communication method according to claim 6, wherein the resource allocation process in the above-mentioned step 3 comprises the following steps: i) find the minimum value of the path loss from the above path loss; ii) Find out the corresponding wireless access unit according to the minimum value, and use it as the wireless access unit for transmitting the user data of the user; iii) find the minimum value of the path loss from the remaining other path losses; iv) Find out the corresponding wireless access unit according to the minimum value, and calculate whether the addition of the wireless access unit increases the system capacity. When the addition of the wireless access unit reduces the system capacity, the resource allocation ends. When When the addition of the wireless access unit increases the system capacity, it is used as a wireless access unit for transmitting user data, and then steps iii and iv are repeated until the resource allocation ends.

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