CN101908906B - User channel satellite capture method based on WCDMA (Wideband Code Diversion Multiple Access) system - Google Patents

Abstract

A user channel on-board acquisition method based on the WCDMA system. Firstly, in the beam access time slot, the admitted users are screened out according to the signature information of the PRACH access preamble, and then the beam where the admitted user is located is determined to be the current beam or a cross beam. If it is this beam, then use the signature phase to determine the search start time and search interval of the DPCH channel corresponding to the admitted user, search for the single-path delay of the DPCH channel corresponding to the admitted user in this beam within the search interval, and then Perform scrambling code tracking on DPCH channel. If it is a cross-beam access user, it will allocate a DPCH channel in this beam, and use the reference time of this beam as a reference to determine the search start time and search time of the DPCH channel corresponding to the cross-beam access user in this beam. In the search interval, search for the single-path delay of the DPCH channel corresponding to the user across the beam in the current beam within the search interval, and then perform scrambling code tracking on the DPCH channel.

Description

A WCDMA System-Based Onboard Acquisition Method of User Channels

technical field

The invention belongs to the field of satellite communication, and relates to a user channel on-board acquisition method for 3G communication on-board reception based on the WCDMA system.

Background technique

Considering the characteristics of the GEO (Geosynchronous Earth Orbit) satellite mobile communication system, as well as the limitations of power consumption and volume on the satellite, the access processing method on the satellite is different from that of the ground system.

At present, there is no satellite communication system that adopts the WCDMA system and processes it on the satellite. In the terrestrial WCDMA mobile system, user channel acquisition includes PRACH (Physical random access channel) acquisition and DPCH (Dedicated Physical Channel downlink dedicated physical channel) acquisition, but there is no direct connection between the two acquisitions. Because for the ground, the channel environment is complex and changeable, the multipath effect is obvious, and the multipath delay spread is relatively large, so it is difficult to use the PRACH channel acquisition information for DPCH acquisition. Therefore, multiple separate acquisition methods are adopted in the terrestrial WCDMA mobile system, that is, PRACH and DPCH need to be acquired separately when establishing a communication link.

Compared with the channels of the land mobile communication system, the GEO satellite channel has its obvious characteristics: the Rice channel is the main channel, and the Rayleigh channel is very rare. The Ricean channel often contains a direct path (LOS), and the energy of the main path accounts for most of the signal energy. Therefore, multi-path processing becomes insignificant. If the method of multiple separate captures is adopted as in the ground mobile communication system, a complex capture structure and a large amount of redundant hardware resources will be introduced. It can be seen that the method of multiple separate captures is not suitable for the characteristics of satellite channels, and at the same time, it is not feasible due to the strict constraints of on-board power consumption and volume.

Contents of the invention

The problem solved by the technology of the present invention is: to overcome the deficiencies of the prior art, and provide an on-board user channel acquisition method based on the WCDMA system, which is easy to operate and fast in acquisition speed.

The technical solution of the present invention is: a kind of user channel satellite capture method based on WGDMA system, the steps are as follows:

(1) Obtain the signature information of the PRACH access preamble transmitted by the user equipment on the access slot of the beam, and filter out the admitted users according to the signature information, and the signature information includes the user channel signature energy, signature sequence and signature phase ;

(2) Determine the beam where the admitted user is located, if the beam where the admitted user is located is the own beam, then go to step (3), if the beam where the admitted user is located is a cross beam, then go to step (5), the said beam is satellite reception Beams being processed in each incoming beam signal, and the remaining beams are crossing beams;

(3) Utilize the signature phase of the admitted user channel to determine the search start time and search interval of the DPCH channel corresponding to the admitted user; search start time t _{DPCH_start_time} = t _{prach_delay} + T _FrameOffset + T _ChipOffset + Rx_Tx _delay , where t _{prach_delay} is the signature phase, T _FrameOffset is the frame offset, T _ChipOffset is the chip offset, Rx_Tx _delay is the fixed delay between the uplink physical channel frame and the downlink physical channel frame; The ratio of the user's changing distance L _interval relative to the satellite to the radio wave propagation distance L _signal/chip of each chip within a period of time, the unit is chip;

(4) According to the result of step (3), search for the single-path delay of the DPCH channel corresponding to the admitted user in the beam in the search interval, and then use the corresponding scrambling code and spreading code information to perform scrambling code tracking on the DPCH channel , to achieve despreading and demodulation;

(5) Allocate DPCH channels in this beam for cross-beam access users, and use the reference time of this beam as a reference to determine the search start time and search interval of the DPCH channel corresponding to the cross-beam access users in this beam; Search start time t _{DPCH_start_time} = t _{pre_T_cell} ±ΔT _{T_cell} , where t _{pre_T_cell} is the delay of the cross-beam access user under the original beam relative to the reference time of the original beam, and ΔT _{T_cell} is the beam time offset between the current beam and the original beam The absolute value of the difference between T _cells , if the time offset of the current beam is ahead of the original beam, take "+", otherwise take "-"; search radius N＞=2 ^* L _interval /L _sihnal/chip , the unit is chip;

(6) According to the result of step (5), search for the single-path delay of the DPCH channel corresponding to the cross-beam admission user in the search interval, and then use the corresponding scrambling code and spreading code information to scramble the DPCH channel Code tracking to realize despreading and demodulation.

进行匹配运算，得到不同时延时的相关值，其中PDP(n)为功率时延函数，S(k)为本地扰码，R(k)为波束输入的基带数字接收信号，^＊表示复数共扼，K为相关积分长度，对于步骤(4)中的搜索，K选取搜索范围的8～16倍，对于步骤(6)中的搜索，K选取搜索范围的4～8倍。The search method of the single-path delay in the step (4) or step (6) is: according to the formula

Perform a matching operation to obtain the correlation values of different time delays, where PDP(n) is the power delay function, S(k) is the local scrambling code, R(k) is the baseband digital receiving signal input by the beam, and ^* means complex total Concisely, K is the correlation integral length, for the search in step (4), K selects 8～16 times of the search range, and for the search in step (6), K selects 4～8 times of the search range.

The method for screening admitted users in the step (1) is: perform correlation or matching processing on the signature energy of the PRACH access preamble, then perform Hadamard transformation on the correlation or matching processing results, and finally make the signature energy meet the channel signature energy threshold value The user corresponding to the PRACH access preamble is used as the admitted user.

Compared with the prior art, the present invention has the advantages that: the acquisition method of the present invention takes into account the satellite channel characteristics and the constraints of the satellite platform, abandons the RAKE receiver mode, and for the users in the beam, accesses and captures through the PRACH preamble to realize user The coarse capture provides the search start time and search interval for the narrow search of the DPCH channel, and then realizes the fine capture through the narrow search, and then realizes the precise synchronization of the scrambling code through the scrambling code tracking. For users crossing beams, through wide search, fine acquisition of DPCH channels of users entering this beam from other beams is realized, and then precise synchronization of scrambling codes is realized through scrambling code tracking. In addition, the single-path search method is used in the search, which simplifies the on-board reception process compared to the multi-path search. The operation of the capture method of the invention greatly simplifies the capture search process and search range, and accelerates the capture speed.

Description of drawings

Fig. 1 is the flowchart of capture method of the present invention;

Fig. 2 is a schematic diagram of the time delay of PRACH search in the present invention;

FIG. 3 is a schematic diagram of time delay of DPCH search in the present invention;

FIG. 4 is a schematic diagram of capturing a PRACH access preamble in the present invention.

Detailed ways

As shown in Fig. 1, it is a flow chart of the capture method of the present invention. When there is user access in a certain beam, the satellite system will inform the acquisition unit on the satellite of the spreading code and scrambling code information corresponding to the DPCH channel of the user, and the acquisition unit will send a message to the user equipment (UE) on the access time slot of the beam. ) to perform correlation or matching calculations on the signature information of the PRACH access preamble transmitted, perform Hadamard transformation and threshold judgment on the calculation results, record the signature sequence, signature phase, and signature energy whose signature energy is greater than the threshold; determine whether the signature energy is greater than the signature energy threshold, If it is less than, return to the acquisition state and continue to process the signal with matched filtering; if it is greater than, allow access, and then further judge whether the user is the user of the beam according to the signature information, and if so, calculate the search start time and corresponding DPCH channel according to the formula In the narrow search interval, the scrambling code, spreading code and calculated search information allocated by the satellite system are assigned to narrow search, scrambling code tracking and despreading demodulation of DPCH channel single-path delay; if it is a cross-beam user, pass The satellite system allocates DPCH channels in this beam for cross-beam access users. Taking the reference time of this beam as a reference, calculate the search start time and search interval of the DPCH channel corresponding to the cross-beam access users in this beam according to the formula , assign the scrambling code, spreading code and calculated search information allocated by the satellite system to perform wide search of DPCH channel single-path delay, scrambling code tracking and despreading demodulation.

Compared with the channels of the land mobile communication system, the GEO satellite channel has its obvious characteristics: the Rice channel is the main channel, and the Rayleigh channel is very rare. The Ricean channel often contains a direct path (LOS), and the energy of the main path accounts for most of the signal energy. Therefore, on the satellite, the transmission delay from the UE to the satellite (equivalent to the Node B on the ground) is directly extracted from the PRACH, and these delays can be used for the reception of the traffic channel by using a narrow search for a little compensation; Under the command of the satellite (providing the delay value of the original beam), the users who cross the area between them use a wider range of search single paths to ensure that the communication of the users is not affected.

For the GEO satellite channel, the information captured by the preamble of the PRACH channel can be used for the capture of the DPCH channel. As shown in Figure 2, for the PRACH channel, the downlink transmission time of the access slot has a beam (cell) time offset (T _Cell ) relative to the base station system time (BFN), assuming that the satellite (base station) transmit radio frequency channel processing delay is T _Txd , the delay of the downlink signal transmission in the air is T _PropDelay , after the mobile station receives the access slot, it transmits the corresponding preamble sequence, the delay of the uplink signal transmission in the air is T _PropDelay , the satellite (base station) receives the radio frequency channel The processing delay is T _RXD , so the starting time of satellite (base station) search should be added T _Cell +T _Txd +T _RXD +2 ^* T _PropDelay on the basis of BFN, that is, relative to the base station system time (BFN ), the capture start time of the PRACH channel preamble is t _{prach_start} = T _Cell + T _Txd + T _RXD + 2 ^* T _PropDelay .

As shown in Figure 3, for the DPCH channel, the downlink transmission time has a beam (cell) time offset (T _Cell ) plus a frame offset (T _FrameOffset ) and a chip offset relative to the satellite (base station) system time (BFN) (T _ChipOffset ), assuming that the satellite (base station) transmission radio frequency channel processing delay is T _Txd , and the downlink signal transmission delay in the air is T _PropDelay , after the UE receives the downlink DPCCH/DPCH frame, it will be delayed by a fixed time Rx_Tx After _{the delay} , the corresponding uplink DPCCH/DPCH frame is transmitted, the delay of the uplink signal transmission in the air is T _PropDelay , and the processing delay of the satellite (base station) receiving radio frequency channel is T _RXD , so the starting time of the satellite (base station) search should be at Add T _Cell +T _Txd +T _RXD +2 ^* T _PropDelay +T _FrameOffset +T _ChipOffset +Rx_Tx _delay on the basis of BFN, that is to say, relative to the base station system time (BFN), the capture start time of the DPCH channel is t _{DPCH_start} =T _Cell +T _Txd +T _RXD +2 ^* T _PopDelay +T _FrameOffset +T _ChipOffset +Rx_Tx _delay .

Comparing Figure 2 and Figure 3, it can be seen that the search interval mainly includes: round trip delay (Round Trip Delay, RDT) caused by path propagation, satellite (base station) transmission radio frequency channel processing delay T _Txd and satellite (base station) reception Radio frequency channel processing delay T _RXD . Since the frame offset (T _FrameOffset ), the chip offset (T _ChipOffset ) and the beam (cell) time offset (T _Cell ) are all known, then the PRACH search value t _{prach_delay} obtained by PRACH capture search, After a series of known conditions (frame offset, chip offset, and uplink/downlink transmission fixed delay), it can be used for DPCH acquisition, as shown in the following formula: t _{DPCH_start_time} = t _{prach_delay} + T _FrameOffset + T _ChipOffset +Rx_Tx _delay .

In addition, after the PRACH access is captured, there is one or several radio frame intervals from the access of the DPCH channel in time. At this time, the spatial distance of the UE to the satellite (base station) may change, and the narrow search (based on the UE relative to the base station) may change. The feature selection of the satellite distance change), and the search correction is performed on the estimated search start time.

For the DPCH channel from adjacent beams, the signal strength will fluctuate due to beam gain fluctuations and pattern irregularities in the beam overlapping area. To accurately estimate the starting position and search interval of the search window, It is relatively difficult. Therefore, the present invention adopts a wide search method, which can increase the search probability and make the soft handover complete smoothly.

To sum up, in the satellite WCDMA mobile communication system, because the channel environment changes slowly and the on-board processing resources are very limited, the method of the present invention associates the acquisition of the PRACH channel with the acquisition of the DPDH channel, and the acquisition of the scrambling code adopts "PRACH Coarse acquisition, DPCH channel narrow search (wide search) fine acquisition and DPCH scrambling code tracking" scheme, which is suitable for satellite channel environment and can simplify the complexity of on-board implementation.

As shown in FIG. 4 , it is a schematic diagram of capturing a PRACH access preamble in the present invention. In the figure, the correlation or matching operation completes the descrambling, derotation and despreading of the preamble signal, and generates 16 input values of the 16-point Hadamard transformation; FHT is a fast Hadamard transformation; the scrambling code generator generates local scrambling codes, and The I and Q two-way scrambling codes generated by the pi/4 rotation of the real part of the code are used for correlation or matching operations; the scrambling code serial number is allocated to the scrambling code generator under the satellite system. The threshold judgment completes the judgment on the signature energy, and records the signature sequence, signature phase, signature energy and other information whose signature energy is greater than the threshold. The threshold threshold is calculated by the capture probability and false alarm probability required by the system, and is assigned to the threshold judgment device under the satellite system. .

The narrow search mainly compensates the change between the DPCH scrambling code and the calculated local scrambling code phase caused by the position change of the UE (user equipment) relative to the satellite (base station) during the period from the capture of the preamble to the reception of the DPCH, thereby Realize precise synchronization between DPCH channel and local scrambling code. The search range is the change distance/radio wave propagation distance per chip (the WCDMA air interface wireless transmission rate is 3.84Mchips/s, and the propagation speed of radio waves is 300000km/s, then the radio wave propagation distance per chip=300000km/s ^* ( 1chip/3.84Mchips/s)=78.125m). The range of the narrow search is related to the motion state of the UE, and the higher the speed of the UE, the larger the search range. For example, when the UE moves at a maximum speed of 200km/h, the time difference between its access preamble transmission time and the DPCH transmission time is generally on the order of seconds. If it is calculated in 5s, then the distance between the UE and the GEO satellite changes the most within 5s It is 277.8m (277.8=200000÷3600×5, that is, the UE maximum rate is multiplied by 5s), which is about 3.6 chips (277.8m/78.125m). At this time, on the basis of the search start time obtained through the signature phase, the chip value corresponding to the maximum distance from the UE to the satellite during the period from ±N chips (N>PRACH preamble capture to DPCH reception) can be calculated. Reference formula: UE maximum relative to satellite maximum speed ^* this period of time/radio wave propagation distance per chip, by correlating or matching the DPCH channel signal sent by the UE with the local scrambling code, calculating the correlation peak, and adjusting the local scrambling code phase, Realize fine acquisition.In other words, narrow search is to search for the DPCH single-path delay of the channel corresponding to the access preamble, and then perform despreading and demodulation of the DPCH channel in the beam.

A wide search is performed on user DPCH channels handed over from adjacent beams. The wide search here is based on the search start time, and its search range is larger than that of the narrow search. The calculation of the search range is mainly related to the characteristics of the overlapping area of the beams, which can be obtained from empirical data. Generally, it is twice the narrow search range of the user in the original beam, and is informed by the system allocation instruction information. However, there are fluctuations in the signal strength in the beam overlapping area. If the upper layer switches too hastily, it will increase the difficulty of wide search reception. It is recommended that the upper layer perform switching instructions when the signal strength is stable.

For the user DPCH channel that crosses the beam and is about to enter the beam, the search start time under the new beam is calculated according to the delay of the user under the original beam relative to the time reference of the physical channel, as shown in the following formula:

t _{DPCH_start_time} =t _{pre_T_cell} ±ΔT _{T_cell}

Wherein, t _{pre_T_cell} is the delay of the user under the original beam relative to the time reference of the original beam, and ΔT _{T_cell} is the absolute value of the beam time offset (T _Cell ) difference between the current beam and the original beam. If the time offset of the current beam is ahead of the original beam, take "+", otherwise take "-".

It should be noted that, for any uplink DPCH channel, no matter whether it undergoes narrow search reception or wide search reception, the scrambling code acquisition process is as follows: the rough acquisition of the uplink DPCH channel is realized through the acquisition of the PRACH preamble, and the narrow (wide) search Fine capture is carried out, and the despreading and demodulation unit performs tracking, so as to realize the precise synchronization of the scrambling code.

The basic principle of wide (narrow) search is that according to the autocorrelation of PN sequence, the receiver can obtain different correlation values from the correlation operation of the local sequence and the received sequence. When the receiver starts to receive the transmitted spread spectrum signal, adjust and select the phase of the local spread spectrum sequence of the receiver. When the phase error between the local sequence and the received sequence is within a small range, the obtained correlation value is sharper. By setting an appropriate correlation value threshold, it can be preliminarily judged whether the receiving end has reached phase synchronization. In the actual system, the synchronization of the PN code is realized through a similar method.

In the existing multipath search algorithm, the scrambling code and the received signal are used for sliding correlation integration to obtain the complex correlation function CRF (Complex Relation Function) of the desired user, and then the sum of the squares of the real and imaginary parts of the complex correlation function is obtained to obtain the power Delay function PDP (Power Delay Profile), the power delay function is actually the square of the modulus of the coherence function between the scrambling code and the received signal. Then find out the peak position with a larger function value (that is, a larger correlation value and a larger power) or a value greater than a certain threshold from the power time delay function, and consider it as the position of the multipath time delay. This method can be found in the following documents: "Modern Mobile Communication System" edited by Qi Yusheng and Shao Shixiang (People's Posts and Telecommunications Press), "CDMA: Principies of Spread Spectrum Communication" (Addision_Wesley Publishing Company) by A.J.Viterbi, etc.

As mentioned above, due to the characteristics of GEO satellite channels, the Rice channel is the main channel, while the Rayleigh channel is very rare. The Ricean channel often contains a direct path (LOS), and the energy of the main path accounts for most of the signal energy, so the path with weak energy can be discarded during the search and the main path can be searched directly.

Searching for the main path is to search for the single-path delay of the received signal, through the local scrambling code S(k) and the baseband digital received signal R(k) input by the beam, according to the formula The matching operation is performed to obtain the relevant values of different time delays, that is, the power delay function PDP(n). Among them, K is the correlation integral length, that is, the number of sampling points, and " ^* " means complex conjugate. The larger the value of K, the higher the signal-to-noise ratio of the PDP, but the calculation amount becomes larger, so a compromise is required. In wide search, K can select 8 to 16 times of the search range, and in narrow search, K can select 4 to 8 times of the search range.

The filtering threshold is calculated by using the statistical characteristics of the PDP value such as the maximum value, the minimum value and the average value. The maximum function value greater than the threshold is the main path, and the corresponding delay is the time delay. This delay is used for delay adjustment when despreading and tracking, so as to realize accurate synchronization between local scrambling code and received signal.

The content that is not described in detail in the description of the present invention belongs to the well-known technology of those skilled in the art.

Claims (3)

1. one kind based on catching method on the user channel satellite of WCDMA system, it is characterized in that step is following:

(1) on the access slot of wave beam, obtain the signing messages of the PRACH access lead of subscriber equipment emission, and filter out the access user according to signing messages, described signing messages comprises subscriber channel signature energy, signature sequence and signature phase place;

(2) confirm that the access user belongs to wave beam; If belonging to wave beam, access user is this wave beam then change step (3); If access user belongs to wave beam for crossing over wave beam then change step (5); Described wave beam be satellite receive respectively import the wave beam that is being processed in the beam signal, all the other wave beams are for crossing over wave beam;

(3) utilize the signature phase place of access subscriber channel to confirm the search zero-time and the region of search of the DPCH channel corresponding with this access user; Search zero-time t _{DPCH_start_time}=t _{Prach_delay}+ T _FrameOffset+ T _ChipOffset+ Rx_Tx _Delay, t wherein _{Prach_delay}Be signature phase place, T _FrameOffsetBe vertical shift, T _ChipOffsetBe chip offset, Rx_Tx _DelayBe the constant time lag between uplink physical channel frame and the down physical channel frame; Search radius is to receive in this time period the user with respect to the variation distance L of satellite to DPCH behind the pilot capture _IntervalWith each chip radio range L _Signal/chipRatio, unit is chip;

(4) according to the result of step (3), single footpath retardation of the DPCH channel of access user correspondence in this wave beam of search utilizes corresponding scrambler and spreading code information that the DPCH channel is carried out the scrambler tracking then in the region of search, realizes despread-and-demodulation, finishes;

(5) in this wave beam, distributes the DPCH channel for crossing over wave beam access user, with fiducial time of this wave beam be reference, confirm search zero-time and the region of search of DPCH channel in this wave beam of this leap wave beam access user correspondence; Search zero-time t _{DPCH_start_time}=t _{Pre_T_cell}± Δ T _{T_cell}, t wherein _{Pre_T_cell}For cross over wave beam access user under original wave beam with respect to the time-delay of fiducial time of original wave beam, Δ T _{T_cell}Be wave beam time migration T between current wave beam and the original wave beam _CellThe absolute value of difference, if the time migration of current wave beam is ahead of primary beam, then get "+", otherwise get "-"; Search radius N＞=2*L _Interval/ L _Signal/chip, unit is chip;

(6) according to the result of step (5), in the region of search, search for single footpath retardation of the DPCH channel corresponding with said leap wave beam access user, utilize corresponding scrambler and spreading code information that the DPCH channel is carried out the scrambler tracking then, realize despread-and-demodulation.

2. according to claim 1 a kind of based on catching method on the user channel satellite of WCDMA system; It is characterized in that: the searching method of single footpath retardation is in said step (4) or the step (6):

carries out matching operation according to formula; Correlation when obtaining different delay; Wherein PDP (n) is the power time delay function, and s (k) is local scrambler, and R (k) receives signal for the base-band digital of wave beam input; * represent complex conjugate; K is a correlation intergal length, and for the search in the step (4), K chooses 8～16 times of hunting zone; For the search in the step (6), K chooses 4～8 times of hunting zone.

3. according to claim 1 a kind of based on catching method on the user channel satellite of WCDMA system; It is characterized in that: screening access user's method is in the said step (1): the signature energy to the PRACH access lead is correlated with or matching operation; Then relevant or matching operation result are carried out the Hadamard conversion, the energy of will signing at last satisfies the pairing user of PRACH access lead of channel signature energy threshold as the access user.

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