CN103152816B - Distributed beam forming system and carrier synchronization method of transmitting antennas at source end of distributed beam forming system - Google Patents

Abstract

The present invention is applicable to the technical field of wireless communication, and provides a distributed beamforming system and a carrier synchronization method for each transmitting antenna at the source end. In the present invention, the transmitting antenna at the source end can realize precise time slot control, and can control the received signal Perform frequency and phase estimation, and estimate phase offset information caused by channel delay. The present invention makes full use of the broadcast characteristics of the wireless link, and realizes the precise synchronization of the carrier frequency and phase of the distributed beamforming system through precise time slot control and channel estimation. Compared with the traditional carrier synchronization method, the present invention greatly reduces The synchronization overhead is reduced, and the time slot required for synchronization is reduced from 2M-1 to M (where M is the number of source base stations), thereby increasing the effective communication time of the system.

Description

Distributed beamforming system and its carrier synchronization method for each transmitting antenna at the source end

technical field

The invention belongs to the technical field of wireless communication, and in particular relates to a distributed beam forming system and a carrier synchronization method for each transmitting antenna at a source end.

Background technique

Distributed beamforming technology is a wireless communication technology that can significantly improve system power efficiency. It forms a virtual antenna array from independent antennas distributed in multiple cells (each antenna has its own crystal oscillator, and only Knowing its own local time), each antenna in the antenna array sends the same signal to the destination base station, where these signals are coherently combined. Due to the scalability and robustness of the virtual antenna array, the distributed beamforming technology can obtain higher directional transmission characteristics than the traditional antenna array, and can obtain a larger signal noise ratio (Signal Noise Ratio) than the single-antenna system. , SNR) gain, its application involves multi-cell cooperative network, multi-user wireless communication system, wireless sensor network (Wireless Sensor Network, WSN), orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM)-multiple input multiple output (Multiple -Input Multiple-Output, MIMO), 3G Long Term Evolution (Long Term Evolution, LTE) and many other fields. However, due to the heterogeneity of the source base stations in the network, that is, each source base station has an independent local oscillator, the location of the source base station, and the difference in channel transmission status, the phase shift occurs when the signals of each source base station arrive at the destination base station. Destroying the combination and recombination of the signal, therefore, the source must carry out synchronous processing on the transmitting carrier.

Carrier synchronization at the source is a key technology in distributed beamforming. Whether the carrier is synchronized or not determines the receiving performance of the destination. The less time taken for synchronization, the better the system performance. In the prior art, the open-loop methods applicable to the distributed beamforming technology and synchronizing the carriers mainly include the round-trip carrier synchronization method and the two-way carrier synchronization method based on time division duplexing. The former method transmits the received uplink signal back and forth in the base station at the sending end to estimate the phase information of each base station to achieve synchronization. The main disadvantages of this method are (1) more time slots are occupied. For M The system composed of root antennas needs 2M-1 time slots to realize the synchronization of all base stations. (2) This method can only realize the synchronization of the carrier phase, but cannot realize the precise synchronization of the carrier frequency. (3) This method is used before the antenna sends the signal Synchronization cannot be achieved, and synchronization must be started after receiving the uplink signal from the destination, which increases the delay of the system; the latter method uses the time-division two-way transmission of the synchronization signal between the base stations to estimate the phase of the received signal, thereby realizing the base station Carrier synchronization, but this method occupies a large number of time slots. For a system composed of M antennas, 2M-2 time slots are required to achieve synchronization of all base stations.

Contents of the invention

The first technical problem to be solved by the present invention is to provide a carrier synchronization method for each transmitting antenna at the source end of a distributed beamforming system, aiming at realizing the phase and frequency synchronization of the carrier waves of each transmitting antenna at the source end and reducing the time spent on synchronization Slot overhead.

The present invention is achieved in this way, a carrier synchronization method for each transmitting antenna at the source end of a distributed beamforming system, the distributed beamforming system includes a source end and a destination end, and the source end has multiple base stations, each The base station only covers the adjacent base stations on both sides, and the multiple base stations include a synchronization signal generation base station and an intermediate base station, the intermediate base station is the base station farthest from the synchronization signal generation base station, and the synchronization signal generation base station and the There are two signal transmission paths between the intermediate base stations; the carrier synchronization method includes the following steps:

Step A, the synchronization signal generation base station initializes the synchronization signal in the first time slot and broadcasts the synchronization signal to the adjacent base stations on both sides of the synchronization signal, and at the same time the adjacent base stations on both sides of the intermediate base station respectively estimate the channel distance between them and the intermediate base station phase offset;

Step B, the synchronization signal is transmitted to the intermediate base station in the forward direction along the two signal transmission paths, and the transmission method is to transmit one station for each time slot, and during the entire forward transmission process, each base station is based on the received Performing carrier information estimation on the synchronization signal to obtain respective first carrier estimation information including carrier frequency and phase information;

In step C, the intermediate base station superimposes the synchronization signals transmitted on the two signal transmission paths, and then reversely transmits the superimposed synchronization signals along the two signal transmission paths respectively, and the adjacent base stations on both sides of the intermediate base station Extract the signal transmitted by the other party's path from the superimposed synchronous signal, and perform carrier information estimation according to the extracted signal, and obtain respective second carrier estimation information including carrier frequency and phase information; then both sides of the middle base station Adjacent base stations reversely transmit the extracted signals to the synchronization signal generation base station, and each base station in the same direction as the transmission path of the synchronization signal during the transmission process performs carrier information estimation according to the received extraction signals, and obtains the respective carrier information second carrier estimation information of frequency and phase information;

Step D, all base stations add the frequency in the first carrier estimation information and the frequency in the second carrier estimation information as the synchronized carrier frequency, and calculate the phase in the first carrier estimation information and the second carrier estimation The phases in the information are summed as the synchronized carrier frequency.

The second technical problem to be solved by the present invention is to provide a distributed beamforming system, including a source end and a destination end, the source end has multiple base stations, and each base station only covers adjacent base stations on both sides;

The multiple base stations include a synchronization signal generating base station and an intermediate base station, the intermediate base station is the base station farthest from the synchronization signal generating base station, and there are two signal transmission paths between the synchronization signal generating base station and the intermediate base station;

The synchronization signal generation base station is used to initialize the synchronization signal in the first time slot and broadcast the synchronization signal to adjacent base stations on both sides; the synchronization signal generation base stations on both sides of the base station are respectively along the two signal transmission paths The synchronization signal is forward broadcasted to the intermediate base station, and the transmission method is to transmit one station for each time slot; and the intermediate base station is used to superimpose the synchronization signals transmitted on the two signal transmission paths, and then superimpose The subsequent synchronization signals are then reversely transmitted to the synchronization signal generation base station along the two signal transmission paths respectively;

A phase offset estimating unit is included in the intermediate base station and the adjacent base stations on both sides thereof; the phase offset estimating unit is used for estimating the phase between the intermediate base station and its two sides when the synchronization signal generating base station starts broadcasting. The phase offset of the channel between adjacent base stations;

Each base station includes a first carrier information estimation unit, a second carrier information estimation unit, and a synchronization information calculation unit; the first carrier information estimation unit is used to, according to the received synchronization Carrier information estimation is performed on the signal to obtain respective first carrier estimation information including carrier frequency and phase information; the second carrier information estimation unit is used to extract the passed signal, and perform carrier information estimation according to the extracted signal to obtain Respective second carrier estimation information including carrier frequency and phase information; the synchronization information calculation units of all base stations are used to add the frequency in the respective first carrier estimation information and the frequency in the second carrier estimation information as the synchronized carrier frequency, adding the phase in the first carrier estimation information and the phase in the second carrier estimation information as the synchronized carrier frequency.

The present invention makes full use of the broadcast characteristics of the wireless link, and realizes the precise synchronization of the carrier frequency and phase of the distributed beamforming system through precise time slot control and channel estimation. Compared with the traditional carrier synchronization method, the present invention greatly reduces The synchronization overhead is reduced, and the time slot required for synchronization is reduced from 2M-1 to M (where M is the number of source base stations), thereby increasing the effective communication time of the system.

Description of drawings

Fig. 1 is a schematic diagram of the signal flow when there are an odd number of ring-shaped base stations at the source in the distributed beamforming system provided by the present invention;

Fig. 2 is a schematic diagram of signal flow when there are an even number of ring-shaped base stations at the source in the distributed beamforming system provided by the present invention;

Fig. 3 is a schematic diagram of signal flow when there are an odd number of base stations with a linear structure at the source in the distributed beamforming system provided by the present invention;

Fig. 4 is a schematic diagram of signal flow when there are an even number of base stations with a linear structure at the source in the distributed beamforming system provided by the present invention;

Fig. 5 is a schematic diagram of the architecture of the distributed beamforming system provided by the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

In the distributed beamforming system provided by the present invention, each base station at the source end has at least one antenna, and each antenna provides services in its own coverage area and has its own crystal oscillator, and each antenna uses its own local time Receiving and processing signals can realize precise time slot control, and estimate the frequency and phase of the received signal and the phase offset information caused by channel delay.

In the present invention, each base station at the source end only covers the adjacent base stations on both sides, which can be realized by setting an appropriate signal transmission distance, and a synchronization signal generation base station is included in multiple base stations, and the synchronization signal generation base station can be One (such as a ring structure), or two (such as a linear structure), see below for details.

The carrier communication method provided by the present invention comprises the following steps:

Step A, the synchronization signal generation base station initializes the synchronization signal in the first time slot and broadcasts the synchronization signal to the adjacent base stations on both sides of the synchronization signal, and at the same time the adjacent base stations on both sides of the intermediate base station respectively estimate the channel distance between them and the intermediate base station Phase offset.

Wherein, the intermediate base station is the base station farthest from the synchronization signal generating base station. When there are an odd number of base stations at the source end, there are two farthest base stations from the synchronization signal generating base station, and any one of them can be used as an intermediate base station. Assuming that the base stations in the system composed of M base stations are numbered, they are BS ₁ , BS ₂ , ..., BS _M in turn, in a certain time slot, any base station (assuming BS ₁ ) initializes the synchronization signal and broadcasts the synchronization signal to the surroundings. The synchronization signal can only be received by its two adjacent base stations. In this way, there are two signal transmission paths between the synchronization signal generation base station and the intermediate base station, and the adjacent base stations on both sides of the synchronization signal generation base station can transmit the synchronization signal forward broadcast to the intermediate base station along the two signal transmission paths. Among them, the synchronization signal received by the next base station is a period extension of the synchronization signal sent by the previous base station, which is specifically manifested in that the phase will be delayed, but the frequency will remain basically unchanged.

Because this method utilizes the broadcast characteristic of the wireless link, in the synchronization signal processing process, there will be a situation that the synchronization signals broadcast by two base stations arrive at the intermediate base station at the same time. The processing method at this time is that the three base stations involved estimate the phase offset information caused by the channel delay between the three base stations involved. After the synchronous signal, use the received signal to subtract the respective processed synchronous signal. The processed synchronous signal is the synchronous signal phase broadcasted in the previous time slot plus the channel delay phase as the new phase signal. The intermediate base station Do something similar. According to the parity of the number of base stations, the number of base stations that need to perform channel estimation is different, and the number of time slots occupied by channel estimation is also different. For the case where the number of base stations is greater than 6, the channel estimation can be performed by using the time slot that initially broadcasts the synchronization signal, thereby reducing the number of time slots occupied by the entire synchronization process; for the case where the number of base stations is not greater than 6, additional time is required to avoid interference. slots are used for channel estimation. When the number of base stations is M, according to the specific value of M, the number of time slots required are: (1) M>6, M time slots are required to achieve synchronization, (2) M≤6, approximately M+1 are required Time slots are synchronized.

Step B, the synchronization signal is transmitted to the intermediate base station in the forward direction along the two signal transmission paths, and the transmission method is to transmit one station for each time slot, and during the entire forward transmission process, each base station is based on the received Carrier information estimation is performed on the synchronization signal to obtain respective first carrier estimation information including carrier frequency and phase information.

As above, in a certain time slot, any base station (assuming BS1) initializes the synchronization signal and broadcasts the synchronization signal to the surroundings. This synchronization signal can only be received by its two adjacent base stations and used to estimate their respective carrier frequency and phase information. At this time, other base stations ignore this signal. In the next time slot, the two base stations broadcast and forward the synchronization signal received in the previous time slot, which is received by their respective adjacent base stations and used for carrier information estimation. This synchronization signal will be transmitted simultaneously along the path BS ₁ , BS ₂ , ..., BS _M/2 and the path BS _M , B _SM-1 , ..., BS _M/2 until it reaches the intermediate base station, at which point the signal transmission path The base station in the direction uses the received synchronization signal to estimate the frequency and phase information of the carrier to obtain the first carrier estimation information, while the base station in the opposite direction of the signal transmission path directly ignores the received synchronization signal.

In step C, the intermediate base station superimposes the synchronization signals transmitted on the two signal transmission paths, and then reversely transmits the superimposed synchronization signals along the two signal transmission paths respectively, and the adjacent base stations on both sides of the intermediate base station Extract the signal transmitted by the other party's path from the superimposed synchronous signal, and perform carrier information estimation according to the extracted signal, and obtain respective second carrier estimation information including carrier frequency and phase information; then both sides of the middle base station Adjacent base stations reversely transmit the extracted signals to the synchronization signal generation base station, and each base station in the same direction as the transmission path of the synchronization signal during the transmission process performs carrier information estimation according to the received extraction signals, and obtains the respective carrier information Secondary carrier estimation information for frequency and phase information.

After the synchronization signal is broadcast to the intermediate base station, the intermediate base station broadcasts the sum of the superimposed synchronization signals from the two paths, and the signal is received and processed by the adjacent base station of the intermediate base station, and then follows the opposite path Simultaneous transmission, until the synchronization signal is broadcast back to the original base station, similar to before, the base station along the signal transmission path uses the received synchronization signal to estimate the frequency and phase information of the carrier to obtain the second carrier Estimate information, while the base station in the opposite direction of the signal transmission path simply ignores the received synchronization signal.

For the intermediate base station and the adjacent base stations on both sides, an additional channel estimation process is required, and the following steps C1 or C2 are performed according to the parity of the number of source base stations:

Step C1, when the number of source base stations is an odd number, for the adjacent base stations on both sides of the intermediate base station, after receiving the superimposed synchronization signals sent by the intermediate base station, use the superimposed synchronization signals as the subtracted The signal received in the last time slot delayed by 2 times the phase offset is used as a subtrahend to make a difference, and then the carrier information is estimated according to the difference, and the respective second carrier estimation information including carrier frequency and phase information is obtained. .

Step C2, when the number of source base stations is an even number, for the adjacent base stations on both sides of the intermediate base station, after receiving the superimposed synchronization signals sent by the intermediate base station, use the superimposed synchronization signals as the subtracted The signal received in the last time slot delayed by 2 times the phase offset is used as a subtrahend to make a difference, and then the carrier information is estimated according to the difference, and the respective second carrier estimation information including carrier frequency and phase information is obtained. (The reason for the phase offset of 2 times is because the signal is delayed twice between the corresponding two base stations). Then the adjacent base stations on both sides of the middle base station broadcast the extracted and processed signals in different time slots. The middle base station estimates the carrier information of the two extracted signals received at this time to obtain two phase estimates and two frequencies. The estimated value is to subtract the corresponding phase offset from the two phase estimated values as the first and second carrier phase estimation information, and the frequency estimated value is the first and second carrier frequency estimation information.

Step D, all base stations add the frequency in the first carrier estimation information and the frequency in the second carrier estimation information as the synchronized carrier frequency, and calculate the phase in the first carrier estimation information and the second carrier estimation The phases in the information are summed as the synchronized carrier frequency.

At this time, each base station has the first carrier estimation information and the second carrier estimation information (the base station that initially sends the synchronization signal has only one set of frequency and phase estimation information, and the other set of frequency and phase information is the frequency and phase of the initial transmission. ), and the three base stations in the middle also have phase estimation information. Each base station adds the two frequencies as the synchronized frequency, and the phase addition as the synchronized phase, so as to realize the carrier synchronization of all base stations in the system.

In order to illustrate the technical solutions in the embodiments of the present invention more clearly, three embodiments and four situations are described below.

Embodiment 1: An odd number of base stations at the source end forms a closed-loop structure, and the synchronization signal generating base station is any base station in the closed-loop structure, as shown in FIG. 1 . Step A specifically includes the following steps: Step A1, in the first time slot, the adjacent base stations on both sides of the intermediate base station respectively estimate the phase offset of the channel with the intermediate base station. In Fig. 1, the solid line represents the transmission process of the synchronization signal among the base stations. The signal transmitted each time is a periodic extension of the previous time slot signal, and the dotted line represents the channel estimation process. At this time, a time slot TS ₁ is needed for Channel estimation (respectively base station estimate and The channel phase between, estimate and The channel phase between), where TS _i represents the i-th time slot, BS _i represents the i-th base station, and the symbol " "Indicates rounding, the same below.

Embodiment 2: An even number of base stations at the source end forms a closed-loop structure, and the synchronization signal generating base station is any base station in the closed-loop structure, as shown in FIG. 2 . Step A specifically includes the following steps: Step A2, in the first time slot, the adjacent base stations on both sides of the intermediate base station respectively estimate the phase offset of the channel with the intermediate base station; in the second time slot, the intermediate base station estimates its The phase offset of the channel with the adjacent base station on one side; in the last time slot of the reverse broadcast transmission, the intermediate base station estimates the phase offset of the channel between it and the adjacent base station on the other side. In Fig. 2, the solid line represents the transmission process of the synchronization signal among the base stations. The signal transmitted each time is a periodic extension of the previous time slot signal. The dotted line represents the channel estimation process. At this time, three time slots are required for the channel Estimation (in TS ₁ time slot, BS _M/2 and BS _M/2+2 estimate the channel phase between them and BS _M/2+1 ; in TS2 time slot, BS _M/2+1 estimates their channel phase with BS _{M /2+2} ; in the TS _M slot, BS _M/2+1 estimates the channel phase between itself and BS _M/2 ).

Embodiment 3: Multiple base stations at the source end can form a linear structure, and the synchronization signal generating base stations are base stations at both ends of the linear structure. At this time, it can be an odd number of base stations as shown in Figure 3, or an even number of base stations as shown in Figure 4 The difference between the base station and the ring structure is that the synchronization signals generated by the two ends of the base station can be the same or different. Step A specifically includes the following steps: Step A3, in the first time slot, the adjacent base stations on both sides of the intermediate base station respectively estimate the phase offset of the channel with the intermediate base station. For the situation in Figure 3, the thin solid line represents the transmission process of the synchronization signal among the base stations. The signal transmitted each time is a periodic extension of the previous time slot signal. The thick solid line represents the channel estimation process. At this time, it takes a time Slot TS ₁ is used for channel estimation (respectively base station estimate and The channel phase between, estimate and between the channel phase), the dotted line indicates the base station and Separate two time slots to broadcast and transmit synchronization signals around. When one base station broadcasts the signal, the other base station is in the listening state but does not do any processing, thus preventing the signal from reaching the intermediate base station at the same time. For the situation in Figure 4, the thin solid line represents the transmission process of the synchronization signal between the base stations. The signal transmitted each time is a periodic extension of the previous time slot signal. The thick solid line represents the channel estimation process. At this time, it takes a time Slot TS ₁ is used for channel estimation (respectively base station estimate and The channel phase between, estimate and The channel phase between), the dotted line indicates that the intermediate base station receives the synchronization signals from the two adjacent base stations respectively.

It should be noted that for the case of linear odd numbers, when the base stations are linearly distributed, BS ₁ and BS _M initialize synchronization signals at the same time and broadcast them to the surrounding space. The frequency and phase of these two synchronization signals are not necessarily equal, and when When the base stations are distributed in a ring, only the base station BS ₁ initializes the synchronization signal and broadcasts it to the surrounding space, that is, the adjacent base stations on both sides of the middle base station respectively broadcast and transmit the synchronization signal in two different time slots.

To sum up, the present invention makes full use of the broadcast characteristics of the wireless link, and realizes the precise synchronization of the carrier frequency and phase of the distributed beamforming system through precise time slot control and channel estimation. The path is divided into two, and then the base stations on the two paths record and save the phase delay information of the other path, and exchange the local time information of the base stations through the transmission of synchronization signals between the base stations, so as to realize the global synchronization of the system carrier. After the system carrier achieves global synchronization, each base station subtracts the phase of the uplink signal from the synchronized phase. This difference is used as the phase of the downlink signal, and the frequency after synchronization is subtracted from the frequency of the uplink signal. This difference is used as the downlink signal frequency. The frequency of the signal (generally, the frequency after synchronization is approximately twice the frequency of the uplink signal), so that when the downlink signal reaches the terminal, it is always synchronized. Compared with the traditional carrier synchronization method, the present invention greatly reduces the synchronization overhead and reduces the time slot required for synchronization from 2M-1 to M (wherein M is the number of source base stations), thereby increasing the effective communication time of the system.

Fig. 5 shows the structural principle of the distributed beam forming system provided by the present invention, and for the convenience of description, only the parts related to the present invention are shown. FIG. 5 is only described by taking an odd number of base stations arranged in a ring at the source end as an example. It should be understood that the principles of the remaining even number of base stations arranged in a ring and odd and even base stations in a linear arrangement are the same.

Referring to FIG. 5 , the distributed beamforming system includes a source end and a destination end. The source end has multiple base stations BS ₁ to BS _M , and each base station only covers adjacent base stations on both sides. A plurality of base stations include a synchronization signal generating base station BS ₁ and an intermediate base station. In the present invention, the intermediate base station is the base station farthest from the synchronization signal generating base station. There are two signal transmission paths between the synchronization signal generating base station BS ₁ and the intermediate base station , in the present invention, when the source end has an odd number of base stations, there are two farthest base stations from the synchronization signal generation base station BS ₁ , any one of which can be used as an intermediate base station, and BS _{(M/2)+ 2} as an intermediate base station. Synchronization signal generation base station BS ₁ is used for initializing synchronization signal in the first time slot and broadcasting synchronization signal to its adjacent base stations on both sides; Synchronization signal generation base station BS ₁ and its intermediate base station BS _(M/2)+2 have two two signal transmission paths, the synchronous signal generation base station BS ₁ on both sides of the adjacent base station BS ₂ and BS _M respectively transmit the synchronous signal forward broadcast to the intermediate base station BS _(M/2)+2 along the two signal transmission paths, and The transmission method is to transmit one station for each time slot; and the intermediate base station BS _(M/2)+2 is used to superimpose the synchronization signals transmitted on the two signal transmission paths, and then the superimposed synchronization signals are respectively passed along the two The first signal transmission path is reversely transmitted to the synchronization signal generating base station BS ₁ .

A phase offset estimation unit is included in the intermediate base station BS _(M/2)+2 and its adjacent base stations BS _(M/2)+1 and BS _(M/2)+3 on both sides; The quantity estimation unit is used to estimate the intermediate base station BS _(M/2)+2 and the adjacent base stations BS _(M/2)+1 and BS _(M/2)+3 on both sides when the synchronization signal is generated and the base station starts broadcasting The phase offset between the channels.

Each base station includes a first carrier information estimation unit, a second carrier information estimation unit, and a synchronization information calculation unit; the first carrier information estimation unit of each base station is used for receiving Carrier information estimation is performed on the received synchronization signal to obtain respective first carrier estimation information including carrier frequency and phase information; the second carrier information estimation unit of each base station is used to extract the handed over signal, and perform Estimating carrier information to obtain respective second carrier estimation information including carrier frequency and phase information. The synchronization information calculation units of all base stations are used to add the frequency in the respective first carrier estimation information and the frequency in the second carrier estimation information as the synchronized carrier frequency, and calculate the phase in the first carrier estimation information and the second carrier estimation information The phase addition of the two carrier estimation information is used as the synchronized carrier frequency.

Further, multiple base stations at the source end can form a closed-loop structure, and the synchronization signal generating base station can be any base station in the closed-loop structure. When the number of base stations at the source end is an odd number, in the first time slot, the adjacent base stations BS _{(M/2) +1 and BS (M/2) +3 on both sides of the intermediate base station BS (M/2)+2} The phase offset estimating unit of , respectively estimates the phase offset of the channel with the intermediate base station BS _(M/2)+2 . When the number of base stations at the source end is an even number, in the first time slot, the adjacent base stations BS _{(M/2) +1 and BS (M/2) +3 on both sides of the intermediate base station BS (M/2)+2} The phase offset estimating unit of estimating the phase offset of the channel between the intermediate base station and the intermediate base station respectively; in the second time slot, the phase offset estimating unit in the intermediate base station BS _(M/2)+2 estimates its and The phase offset of the channel between the adjacent base stations BS _(M/2)+1 and BS _(M/2)+3 on one side; the phase offset in the intermediate base station in the last time slot of the reverse broadcast transfer The amount estimating unit estimates the phase shift amount of the channel between it and the adjacent base station on the other side.

Further, _a plurality of base stations at the source end can form a linear structure, and the synchronous signal generation base station is the base station at both ends of the linear structure; in the first time slot, the adjacent base stations BS ₍ The phase offset estimation units in _M/2)+1 and BS _(M/2)+3 respectively estimate the phase offset of the channel with the intermediate base station.

Further, when the number of base stations at the source end is an odd number, the adjacent base stations BS _{(M/2) +1} and BS _{(M/2)+3 on both sides of the intermediate base station BS (M/2)+2} are respectively in the two Different time slots are used for broadcast transmission of synchronization signals.

Further, when the number of source base stations is an odd number, the second carrier information estimation units in the adjacent base stations on both sides of the intermediate base station respectively receive the superimposed synchronization signals sent by the intermediate base station, and calculate the superimposed The synchronous signal of is used as the subtrahend, and the signal received in the last time slot delayed by 2 times the phase offset is used as the subtrahend to make a difference, and then the carrier information is estimated according to the difference, and the respective carrier frequency and phase information are obtained. The second carrier estimation information of . When the number of source base stations is an even number, the second carrier information estimation units in the adjacent base stations on both sides of the intermediate base station receive the superimposed synchronization signals sent by the intermediate base station respectively, and output the superimposed synchronization signals to As the subtrahend, the signal received in the last time slot delayed by 2 times the phase offset is used as the subtrahend to make a difference, and then the carrier information is estimated according to the difference, and the respective second signals containing the carrier frequency and phase information are obtained. Carrier estimation information; then the adjacent base stations on both sides of the middle base station broadcast the extracted and processed signals in different time slots, and the middle base station estimates the carrier information of the two extracted signals received at this time to obtain two phase estimation values and two frequency estimation values, using the two phase estimation values to subtract the corresponding phase offsets as the first and second carrier phase estimation information, and the frequency estimation values are the first and second carrier frequency estimation information.

The invention is applicable to the technical field of wireless communication, and particularly relates to carrier synchronization of a distributed time division duplex system, a multi-cell communication system, a cooperative communication system, and a distributed adhoc/mesh network.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. A carrier synchronization method for each transmit antenna at the source end of a distributed beamforming system, characterized in that, the distributed beamforming system includes a source end and a destination end, and the source end has a plurality of base stations, each base station Only the adjacent base stations on both sides are covered, and the plurality of base stations include a synchronization signal generation base station and an intermediate base station, and the intermediate base station is the base station farthest from the synchronization signal generation base station, and the synchronization signal generation base station and the intermediate base station There are two signal transmission paths between the base stations; the carrier synchronization method includes the following steps: Step A, the synchronization signal generation base station initializes the synchronization signal in the first time slot and broadcasts the synchronization signal to the adjacent base stations on both sides of the synchronization signal, and at the same time the adjacent base stations on both sides of the intermediate base station respectively estimate the channel distance between them and the intermediate base station phase offset; Step B, the synchronization signal is transmitted to the intermediate base station in the forward direction along the two signal transmission paths, and the transmission method is to transmit one station for each time slot, and during the entire forward transmission process, each base station is based on the received Performing carrier information estimation on the synchronization signal to obtain respective first carrier estimation information including carrier frequency and phase information; In step C, the intermediate base station superimposes the synchronization signals transmitted on the two signal transmission paths, and then reversely transmits the superimposed synchronization signals along the two signal transmission paths respectively, and the adjacent base stations on both sides of the intermediate base station Extract the signal transmitted by the other party's path from the superimposed synchronous signal, and perform carrier information estimation according to the extracted signal, and obtain respective second carrier estimation information including carrier frequency and phase information; then both sides of the middle base station Adjacent base stations reversely transmit the extracted signals to the synchronization signal generation base station, and each base station in the same direction as the transmission path of the synchronization signal during the transmission process performs carrier information estimation according to the received extraction signals, and obtains the respective carrier information second carrier estimation information of frequency and phase information; Step D, all base stations add the frequency in the first carrier estimation information and the frequency in the second carrier estimation information as the synchronized carrier frequency, and calculate the phase in the first carrier estimation information and the second carrier estimation The phases in the information are summed as the synchronized carrier frequency. 2. carrier synchronization method as claimed in claim 1, is characterized in that, a plurality of base stations of described source end can form a closed-loop structure, and described synchronization signal generation base station is any one base station in closed-loop structure; When the number of base stations at the source end is an odd number, step A specifically includes the following steps: step A1, in the first time slot, the adjacent base stations on both sides of the intermediate base station respectively estimate the phase offset of the channel between them and the intermediate base station; When the number of base stations at the source end is an even number, step A specifically includes the following steps: step A2, in the first time slot, the adjacent base stations on both sides of the intermediate base station respectively estimate the phase offset of the channel between them and the intermediate base station; In the second time slot, the intermediate base station estimates the phase offset of the channel between it and the adjacent base station on one side; The phase offset of the channel between base stations. 3. carrier synchronization method as claimed in claim 1, is characterized in that, a plurality of base stations of described source end can form a linear structure, and described synchronous signal generation base station is the base station of two ends of linear structure; Step A specifically includes the following steps: Step A3, in the first time slot, the adjacent base stations on both sides of the intermediate base station respectively estimate the phase offset of the channel between them and the intermediate base station. 4. The carrier synchronization method according to claim 3, wherein when the number of base stations at the source end is an odd number, the adjacent base stations on both sides of the intermediate base station broadcast the synchronization signal in two different time slots respectively. 5. The carrier synchronization method according to claim 1, wherein said step C comprises the following steps C1 or C2: Step C1, when the number of source base stations is an odd number, for the adjacent base stations on both sides of the intermediate base station, after receiving the superimposed synchronization signals sent by the intermediate base station, use the superimposed synchronization signals as the subtracted The signal received in the last time slot delayed by 2 times the phase offset is used as a subtrahend to make a difference, and then the carrier information is estimated according to the difference, and the respective second carrier estimation information including carrier frequency and phase information is obtained. ; Step C2, when the number of source base stations is an even number, for the adjacent base stations on both sides of the intermediate base station, after receiving the superimposed synchronization signals sent by the intermediate base station, use the superimposed synchronization signals as the subtracted The signal received in the last time slot delayed by 2 times the phase offset is used as a subtrahend to make a difference, and then the carrier information is estimated according to the difference, and the respective second carrier estimation information including carrier frequency and phase information is obtained. ; Then the adjacent base stations on both sides of the intermediate base station broadcast the extracted and processed signals separately in different time slots, and the intermediate base station estimates the carrier information of the two extracted signals received at this time to obtain two phase estimation values and two For the frequency estimation value, the corresponding phase offset is subtracted from the two phase estimation values respectively as the first and second carrier phase estimation information, and the frequency estimation value is the first and second carrier frequency estimation information. 6. A distributed beamforming system, comprising a source end and a destination end, the source end has a plurality of base stations, and each base station only covers adjacent base stations on its two sides; it is characterized in that: The multiple base stations include a synchronization signal generating base station and an intermediate base station, the intermediate base station is the base station farthest from the synchronization signal generating base station, and there are two signal transmission paths between the synchronization signal generating base station and the intermediate base station; The synchronization signal generation base station is used to initialize the synchronization signal in the first time slot and broadcast the synchronization signal to adjacent base stations on both sides; the synchronization signal generation base stations on both sides of the base station are respectively along the two signal transmission paths The synchronization signal is forward broadcasted to the intermediate base station, and the transmission method is to transmit one station for each time slot; and the intermediate base station is used to superimpose the synchronization signals transmitted on the two signal transmission paths, and then superimpose The subsequent synchronization signals are then reversely transmitted to the synchronization signal generation base station along the two signal transmission paths respectively; A phase offset estimating unit is included in the intermediate base station and the adjacent base stations on both sides thereof; the phase offset estimating unit is used for estimating the phase between the intermediate base station and its two sides when the synchronization signal generating base station starts broadcasting. The phase offset of the channel between adjacent base stations; Each base station includes a first carrier information estimation unit, a second carrier information estimation unit, and a synchronization information calculation unit; the first carrier information estimation unit is used to, according to the received synchronization Carrier information estimation is performed on the signal to obtain respective first carrier estimation information including carrier frequency and phase information; the second carrier information estimation unit is used to extract the passed signal, and perform carrier information estimation according to the extracted signal to obtain Respective second carrier estimation information including carrier frequency and phase information; the synchronization information calculation units of all base stations are used to add the frequency in the respective first carrier estimation information and the frequency in the second carrier estimation information as the synchronized carrier frequency, adding the phase in the first carrier estimation information and the phase in the second carrier estimation information as the synchronized carrier frequency. 7. The distributed beamforming system according to claim 6, wherein the plurality of base stations at the source end can form a closed-loop structure, and the synchronization signal generating base station is any one of the base stations in the closed-loop structure; When the number of base stations at the source end is an odd number, in the first time slot, the phase offset estimation units in the adjacent base stations on both sides of the intermediate base station respectively estimate the phase offset of the channel with the intermediate base station; When the number of base stations at the source end is an even number, in the first time slot, the phase offset estimation units in the adjacent base stations on both sides of the intermediate base station respectively estimate the phase offset of the channel with the intermediate base station; time slot, the phase offset estimation unit in the intermediate base station estimates the phase offset of the channel between it and the adjacent base station on one side; in the last time slot transmitted by the reverse broadcast, the phase offset in the intermediate base station The shift amount estimation unit estimates the phase shift amount of the channel between it and the adjacent base station on the other side. 8. The distributed beam forming system as claimed in claim 6, wherein a plurality of base stations at the source end can form a linear structure, and the synchronization signal generating base stations are base stations at both ends of the linear structure; In the first time slot, the phase offset estimation units in the adjacent base stations on both sides of the intermediate base station respectively estimate the phase offset of the channel with the intermediate base station. 9. The distributed beamforming system according to claim 8, wherein when the number of base stations at the source end is an odd number, the adjacent base stations on both sides of the intermediate base station perform broadcast transmission of synchronization signals in two different time slots respectively . 10. The distributed beamforming system according to claim 6, wherein when the number of source base stations is an odd number, the second carrier information estimation units in the adjacent base stations on both sides of the intermediate base station respectively receive the intermediate After the superimposed synchronization signal sent by the base station, the superimposed synchronization signal is used as the subtrahend, and the signal received in the previous time slot delayed by 2 times the phase offset is used as the subtrahend to make a difference, and then according to Perform carrier information estimation on the difference to obtain respective second carrier estimation information including carrier frequency and phase information; When the number of source base stations is an even number, the second carrier information estimation units in the adjacent base stations on both sides of the intermediate base station receive the superimposed synchronization signals sent by the intermediate base station respectively, and output the superimposed synchronization signals to As the subtrahend, the signal received in the last time slot delayed by 2 times the phase offset is used as the subtrahend to make a difference, and then the carrier information is estimated according to the difference, and the respective second signals containing the carrier frequency and phase information are obtained. Carrier estimation information; then the adjacent base stations on both sides of the middle base station broadcast the extracted and processed signals in different time slots, and the middle base station estimates the carrier information of the two extracted signals received at this time to obtain two phase estimation values and two frequency estimation values, using the two phase estimation values to subtract the corresponding phase offsets as the first and second carrier phase estimation information, and the frequency estimation values are the first and second carrier frequency estimation information.