The present invention relates to a wireless base station device and path search method and, more particularly, to a wireless base station device that communicates with a mobile device via an advance base station, detects multipath from the mobile device to the advance base station, and synthesizes and processes signals received from each of these paths, and to a path search method of the wireless base station device.
In mobile communications, random amplitudes and phase variations and fading with a maximum frequency that is determined according to the frequency of the carrier wave and the speed of the moving body arise and, as a result, stable reception is extremely difficult in comparison with fixed wireless communications. The spectrum spreading communication method is effective in alleviating degradation caused by the effects of such frequency selective fading. This is because, even when a decrease in the received field strength occurs in a certain specific frequency range because a signal of narrow bandwidth is transmitted after being spread to a high bandwidth, information can be recovered from the other bandwidths with very errors. For this reason, DS-CDMA (Direct Sequence Code Division. Multiple Access) technology has been adopted in Third Generation digital cellular wireless communication systems. With DS-CDMA, transmission information of a plurality of channels (users) is multiplexed by means of spread code and then transmitted via a transmission path such as a wireless line.
Furthermore, in mobile communications, when the same fading as that above is produced as a result of the peripheral environment of the receiver due to a delayed wave from a high-rise building or mountain, or the like, a multi-fading environment then exists. In the case of DS, because the delayed wave constitutes interference with respect to the spread code, degradation of the reception characteristic is induced. As one method that is actively used to improve the characteristic of the delayed wave, the RAKA reception method (Rake reception method) is known. This is a method that performs de-spreading for each of the delay waves arriving via each path of the multipath and synthesizes the delay waves by arranging the respective delay times.
The backbone base station device 1 sends and receives a wireless signal to and from each mobile station within the cell via each antenna. For example, the backbone base station device 1 is able to communicate by receiving a signal from mobile station 5 by means of antenna 43, computing the correlation between the received signal and the desired signal, creating a delay profile corresponding with the cell radius R, detecting multipath from the mobile station 5 to the backbone base station device 1 on the basis of the peak of the delay profile, and receiving radio waves from all the mobile devices in the arriving signals via each path.
When a direct spreading signal that is affected by multipath is inputted to the matched filter 6a, same performs a self-correlation calculation for the desired signal contained in the received signal and a delay profile (
The fingers 71, 72, 73 corresponding with each path have the same constitution and each comprise a de-spreading circuit 7a, a demodulation circuit 7b, and a delay circuit 7c. Each de-spreading circuit 7a performs de-spreading processing on the received Ich signal and Qch signal by using the de-spread code of its own channel at the timings (t1 to t3) indicated by the path search portion 6. The demodulation circuits 7b demodulate the original data by using I symbol data DI′ and Q symbol data DQ′ that are obtained by means of the de-spreading and the delay circuits 7c apply delays corresponding to the periods (D1 to D3) indicated by the path search portion 6 and output the delayed signals. As a result, each finger performs de-spreading at the same times as for the mobile device spread code, adjusts the delay time in accordance with the path, inputs the signal to the Rake synthesis portion 7d with the phase in step, whereupon the Rake synthesis portion 7d synthesizes and outputs the input signals.
The cell constitution of
In the case of the cell constitution in
However, in conventional product groups, delay profile generation processing that takes the advance distance and cell radius, and so forth into account is not performed and, with the cell constitution in
For example, a send/receive sequence between the base station device 1 and a mobile device 5 in cell 10a according to the W-CDMA method is shown in
After sending the downlink signal, the base station device 1 starts the reception operation starting from time T12 at which the fixed timing offset period tC has elapsed as shown in
The prior art includes a spectrum spreading communication system (see claims 1 and 13 of JP2000-50338A, for example) that makes it possible to perform rapid signal demodulation in a mobile device or handover destination base station instead of performing a wide-range path search.
According to the prior art of JP2000-50338A, when a mobile device performs handover, the reception timing difference between the handover-source base station and the handover destination base station is stored and a period of a predetermined time interval is established as the reception timing by considering the stored reception timing difference, whereby the path search range is narrowed and the signal demodulation processing load is lightened. However, the prior art does not prevent an increase in the path search range that arises from the delay time that corresponds with the advance distance and cell radius, and so forth in a cell constitution comprising advance base stations.
Accordingly, an object of the present invention is to reduce unnecessary data reception, processing, and the like by removing the delay time corresponding with the advance distance, cell radius, and so forth from the data reception timing.
A further object of the present invention is to narrow the time interval of the delay profile, that is, the path search range, by shortening the data reception period and thus lighten the processing load.
Yet another object of the present invention is to reduce unnecessary data reception, processing, and the like by considering the delay time corresponding with the advance distance and cell radius specific to each cell, even during handover.
The present invention achieves the above objects by means of a wireless base station device that communicates with a mobile device via an advance base station, and a path search circuit and path search method of the wireless base station device.
The wireless base station device of the present invention comprises a reception timing determination portion that determines the reception timing of data that is transmitted by a mobile device that exists in a cell of the advance base station on the basis of the distance between the wireless base station device and the advance base station and the cell radius of the advance base station; a data reception portion that receives data from the mobile device by performing a reception operation at the reception timing; a delay profile creation portion that creates a delay profile on the basis of the received data; a path detection portion that detects paths from the mobile device on the basis of the delay profile; and a demodulation portion that demodulates data from signals received via the detected paths. The advance base station also comprises advance base stations that are cascade-connected in sequence to the advance base station.
The wireless base station device further comprises a handover control portion that controls handover in accordance with movement of the mobile device, wherein the reception timing determination portion determines, on the basis of control by the handover control portion, the reception timing of data transmitted by the mobile device via each of the cells associated with the handover; the delay profile creation portion creates delay profiles on the basis of data received from the cells at the respective reception timings; and the path detection portion detects paths of large power from all of the delay profiles thus created.
In this case, the handover control portion references the respective reception timings and calculates the difference between the timing at which the very first delay profile was generated and the timing at which another delay profile was generated and, when the difference is equal to or more than a set value, implements control to shorten the total processing time for delay profile creation and path detection. Further, the handover control portion manages the channels of all the cells of the mobile device undergoing handover and detects the paths from the mobile device for which the delay profiles of all the channels have been gathered.
The path search circuit of the wireless base station device of the present invention comprises a reception timing determination portion that determines the reception timing of data that is transmitted by a mobile device that exists in a cell of the advance base station on the basis of the distance between the wireless base station device and the advance base station and the cell radius of the advance base station; a data reception portion that receives data from the mobile device by performing a reception operation at the reception timing; a delay profile creation portion that creates a delay profile on the basis of the received data; and a path detection portion that detects paths from the mobile device on the basis of the delay profile.
The path search circuit comprises a handover control portion that controls handover in accordance with movement of the mobile device, wherein the reception timing determination portion determines, on the basis of control by the handover control portion, the reception timing of data transmitted by the mobile device via the cells associated with the handover; the delay profile creation portion creates delay profiles on the basis of data received from each cell at the respective reception timings; and the path detection portion detects paths of large power from all of the delay profiles thus created.
In this case, the handover control portion references the respective reception timings and calculates the difference between the timing at which the delay profile was generated first and the timing when another delay profile was generated and, when the difference is equal to or more than a set value, implements control to shorten the total processing time for delay profile creation and path detection. Further, the handover control portion manages the channels of all the cells of the mobile device undergoing handover and detects the paths from the mobile device for which the delay profiles of all the channels have been gathered.
The path search method of the present invention is a path search method of a wireless base station device that communicates with a mobile device via an advance base station, detects paths from the mobile device to the advance base station, and demodulates data from signals received via the paths, comprising the steps of: determining the reception timing of data that is transmitted by a mobile device that exists in a cell of the advance base station on the basis of the distance between the wireless base station device and the advance base station and the cell radius of the advance base station; receiving data from the mobile device by performing a reception operation at the reception timing; creating a delay profile on the basis of the received data; and detecting multipath from the mobile device on the basis of the delay profile.
According to the present invention, unnecessary data reception and processing, and so forth, can be reduced following removal of the delay time corresponding with the advance distance and the cell radius, and so forth, from the data reception timing.
According to the present invention, because the delay period corresponding with the advance distance and cell radius, and so forth, is removed from the data reception timing, the data reception timing can be shortened and the time interval of the delay profile, that is, the path search range, can be narrowed whereby the processing load can be lightened. As a result, the path detection processing can be lightened and an increase in the circuit scale, a reduction in the number of accommodated channels, and so forth, can be prevented.
The present invention is able to reduce unnecessary data reception, processing, and the like, by considering the delay time corresponding with the advance distance and cell radius specific to each cell, even during handover, meaning that the processing load can be lightened and it is possible to prevent an increase in the circuit scale and a reduction in the number of accommodated channels, and so forth.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings.
During handover, the reception timing determination portion 12 determines the reception timings of data that are transmitted by a mobile device via cells that are associated with the handover on the basis of control by the handover control portion 18, whereupon the delay profile creation portion 14 creates delay profiles on the basis of data that is received from each of the cells at the respective reception timings and the path detection portion 15 detects paths with a large amount of power from all of the delay profiles thus created.
In the wireless base station device 11, an O/E conversion portion 21 captures signals by converting fiber-optic signals that are inputted via the fiber-optic cables 611 to 616 into electrical signals and converts digital data inputted from a modulation portion (not shown) into fiber-optic signals before sending same to the fiber-optic cables.
An advance distance measurement portion 22 measures the cable lengths between the wireless base station device 11 and each of the advance base stations 511 to 516 as the advance distance di on the basis of a well-known method (TDR method or OTDR method, or the like) that is widely used for cable length measurement, and stores the cable lengths in an advance distance storage memory 23. The measurement of the advance distances is performed at fixed intervals and the advance distance storage memory 23 is updated continually with the latest values. A base station constitution parameter storage memory 24 stores base station installation information (the cell radius of each of cells CL1 to CL6, the reception start timings of each channel, and the current number of users of each cell, and the like).
An MPU 25 performs control to determine the data start timings and handover control, and so forth. The reception timing determination control portion 25a of the MPU 25 uses the advance distances, cell radii, and the channel reception start timings when the data start timings are determined to calculate the reception timing and range (reception timing intervals) for each channel of each cell. Now, supposing that the reception timing of channel 1 that is allocated to the mobile device 711 which exists in first cell CL1 is T11, the advance distance (round-trip) of the first cell CL1 is d1, and the cell radius (round-trip) is CELL1, the actual reception start timing Tstart11 and reception end timing Tend11 can be calculated by means of the following equations:
Tstart11=T11+t(d1) (1)
Tend11=T11+t(d1)=t(CELL1) (2),
where t(d1) is a function that converts the advance distance d1 into a delay time and t(CELL1) is a function that converts the cell radius CELL1 into the delay time. The characters “11” appended to each variable indicate that this is the parameter of the first channel of the first CL1. When the MPU 25 finds the reception start timing Tstart11 and the reception end timing Tend11, the MPU 25 sends these times together with cell information and channel information to a reception timing adjustment portion 26. The reception timing adjustment portion 26 starts data reception for channel 1 of the first cell CL1 on the basis of the reception start timing Tstart11 thus calculated by the MPU 25 and ends data reception on the basis of the reception end timing Tend11 before storing the received data in a region of channel 1 of the received data storage memory 271 of the first cell CL1. Similarly, the MPU 25 determines the reception timings for all the channels of all the cells and controls the storage of the received data in the received data storage memories 271 to 276.
A delay profile data generation portion 28 uses received data of a jth channel of an ith cell (where i=1 to 6, j=1 to ui, and ui is the number of users of the ith cell) that is stored in each of the received data storage memories 271 to 276 to create a delay profile and inputs the delay profile to a path search portion 29. The path search portion 29 detects a predetermined number of (=number of fingers) peaks at or more than the threshold value as multipath from the inputted delay profile and inputs path information (path times and so forth) to the demodulation portion (not shown). The path search portion 29 calculates the average interference power level of the delay profile when performing path detection, subtracts the average interference power level from each peak power level and selects a predetermined number of peaks with a peak power level equal to or more than the threshold value in order of size, whereby multipath is established. Further, the path search portion 29 calculates the latest average interference power level of each cell and stores these values in the interference power level storage memory 30.
The advance distance measurement portion 22 measures the cable lengths between the wireless base station device 11 and each of the advance base stations 511 to 516 as the advance distance di (where i=1 to 6), and the reception timing determination control portion 25a of the MPU 25 measures the delay time t(d1) that corresponds with the advance distance di (step 102), computes the reception start timing Tstartij and reception end timing Tendij of the jth channel of the ith cell (where i=1 to 6, j=1 to uj and ui is the number of users of the ith cell) by means of Equations (1) and (2) (step 103), and sets the computation result in the reception timing adjustment portion 26 (step 104).
The reception timing adjustment portion 26 starts data reception on the basis of the reception start timing Tstartij for the jth channel of the ith cell, ends data reception on the basis of the reception end timing Tendij and stores the received data in a region that corresponds with channel j in the received data storage memory 27i of cell i. Likewise, the reception timing adjustment portion 26 determines the reception timing for all of the channels of all the cells and performs control to store the received data in the received data storage memories 271 to 276 (step 105).
The delay profile data generation portion 28 creates a delay profile by using received data of the jth channel of the ith cell that is stored in each of the received data storage memories 271 to 276 (step 106) and the path search portion 29 detects multipath on the basis of the delay profile inputted thereto (step 107) and inputs path information (path times, and the like) to a demodulation portion (not shown).
According to the first embodiment example, after the delay period corresponding with the advance distance, cell radius, and so forth, has been removed from the data reception timing, the data reception period can be shortened and the delay profile time interval, that is, the path search range, can be narrowed to lighten the processing load. As a result, path detection processing can be lightened and an increase in the circuit scale, a reduction in the number of accommodated channels, and so forth, can be prevented.
The first embodiment example involves path search control during normal reception but requires path search control during handover that is somewhat different from path search control during normal reception. This is because the path search portion 29 must detect multipath by considering all the cells that are associated with the handover (movement source cell and movement destination candidate cell). That is, the path search portion 29 creates delay profiles by receiving transmission data from a mobile device that is undergoing handover from all the cells that are associated with the handover and must detect multipath by considering all of the delay profiles created.
For example, when the mobile device 711, which is communicating in the first cell CL1, is approaching the boundary between the first cell CL1 and sixth cell CL6, commonly known handover control begins and the cell numbers of the cells that are associated with the handover and the channel numbers allocated to the mobile device 711 in the cells are communicated to the MPU 25. As a result, the handover control portion 25b of the MPU 25 communicates the cell numbers of the cells (first and sixth cells) that are associated with the handover of the mobile device 711 and the channel numbers to the path search portion 29 (step 201). Thereafter, the reception timing determination control portion 25a of the MPU 25 calculates the timings at which data transmitted by the mobile device 711 is received from each of the first cell CL1 and the sixth cell CL6 on the basis of equations (1), (2) and sets the respective reception timings in the reception timing adjustment portion 26 (step 202).
The reception timing adjustment portion 26 receives data on the basis of the respective reception timings of the channels allocated to the mobile device 711 in the first cell and the channel allocated to the mobile device 711 in the sixth cell and stores the received data in regions that correspond with the channels of the received data storage memories 271 and 276 (step 203).
The delay profile data generation portion 28 creates respective delay profiles by using the received data for the channels of the mobile device 711 that is stored in each of the memories 271 and 276 (step 204).
The path search portion 29 checks whether the creation of delay profiles for the channels of the mobile device 711 in the first and sixth cells communicated in step 201 is complete (step 205). If delay profile creation is complete, the path search portion 29 detects multipath on the basis of two delay profiles (step 206) and inputs path information (path times and so forth) to the demodulation portion (not shown). The path detection control above is performed until handover is complete.
Once the net power levels at the peaks of all the delay profiles have been found, a predetermined number (=number of fingers) of power levels are chosen in order of size from among the net power levels A11 to A13 and A21 to A23 and paths are detected with the timings at the peaks corresponding with the chosen power levels constituting the multipath times.
According to the second embodiment example, unnecessary data reception and processing, and so forth, can be reduced by considering delay times that correspond with the advance distances and cell radii that are specific to each cell, even during handover, whereby the processing load can be lightened and an increase in the circuit scale, a reduction in the number of accommodated channels, and the like, can be prevented.
In a cell constitution in which advance base stations are installed, during a handover, as illustrated in the second embodiment example, paths with favorable S/N must be sequentially selected from all the cells that are associated with the handover. As a result, unless the delay profile data of all cells have been gathered, the path detection processing cannot be started. That is, the path search portion 29 performs path detection after the delay profiles of all the cells that are associated with the handover have been gathered. However, because the data reception timings from the cells are different, it takes time to gather all of the delay profile data. In particular, in cases where there is a large difference in the delay times determined from the advance distance and cell radius, it takes a long while to gather all of the delay profiles. For example, when handover processing is performed between the first cell 1T1 and the sixth cell CL6, supposing that the advance distance of the first cell CL1 is greater than that of the sixth cell CL6, equations (1) and (2) yield a difference at the timing when generation of the delay profile data is complete and the timing at which the path information is ultimately handed over to the demodulation portion is dependent on the first cell with a long advance distance. Therefore, meanwhile, the path search portion 29 is unable to perform processing of the other channels and the operating efficiency drops. Therefore, when there is a large difference in the delay times, control is required to shorten the time required for the generation of delay profile data and path detection, and so forth, of the larger delay times in order to reduce the hardware occupancy ratio per channel.
In the third embodiment example, the respective reception timings are referenced and the difference between the timing at which the very first delay profile is generated and the timing at which another delay profile is generated is computed and, when this difference is equal to or more than a set value, control is performed to shorten the total processing time for delay profile creation and path detection. More specifically, when this difference is equal to or more than the set value, for larger delay times:
(1) the delay profile computation time is shortened by reducing the number of oversamples; and
(2) the path search computation time is shortened by using values in the interference power level storage memories without calculating the average interference power level in a path search. Further, if the number of users in the cells is substantially the same, the average interference power level does not change significantly.
The delay profile data generation portion 28 performs control of the number of oversamples if the number of oversamples is halved, the time taken by the delay profile creation processing can be halved. Further, the path search portion 29 controls usage of the stored interference power level values. The path search portion 29 normally calculates the average interference power level from the delay profile data. However, the path detection time can be shortened by using the interference power level values stored in the interference power level storage memory 30 by indicating such values.
However, if the delay profile creation and path search processing time is shortened by means of (1), (2) above during handover, as shown in
A first shift register 28c with 256 stages stores in-phase components I of received data of 256 bits while shifting the data one bit at a time and a second shift register 28d with 256 stages stores quadrature components Q of the received data of 256 bits while shifting the data one bit at a time. A de-spread code generation portion 28e generates de-spread code of 256 chips and a multiplication portion 28f multiplies 256-chip spread code and 256 in-phase components I, and multiplies and outputs 256-chip spread code and 256 quadrature components Q. A synthesis portion 28g synthesizes the multiplication results of the 256 spread codes and 256 in-phase components I and performs conversion to electrical power by means of the electrical power conversion portion 28i. Further, a synthesis portion 28h synthesizes the result of multiplying the 256 spread codes and the 256 quadrature components Q and performs conversion to electrical power by means of the electrical power conversion portion 28j. Delay profile data of a time at which an adder 28k has added the outputs of each of the power conversion portions 28i and 28j are then outputted.
Therefore, the delay profile data can be created by performing the above-mentioned computation while the in-phase and quadrature components of the received data are shifted one bit at a time by the first and second shift registers 28c and 28d respectively. Thereafter, the delay profile computation time can be halved by reducing the number of oversamples from a multiple of eight to a multiple of four.
First, the MPU 25 calculates the timing for receiving the data (reception start timing, reception end timing) of a mobile device that is undergoing handover from each cell that is associated with the handover from the equations (1), (2) (step 301). Thereafter, the MPU 25 calculates the time difference ΔTi between the reception end timing Tend (min) of the cell for which the delay profile data was generated first and the reception end timing Tendi of the other cells by means of the following equation:
ΔTi=Tendi−Tend(min) (step 302).
The MPU 25 then checks whether a cell for which ΔTi is equal to or more than a threshold value exists (step S303) and ends the processing if no such cell exists. On the other hand, if an ith cell for which ΔTi is equal to or more than the threshold value exists, the MPU 25 determines the processing time for delay profile creation and path detection for the channel allocated to the mobile device in the ith cell be shortened and communicates this fact to the delay profile data generation portion 28 and the path search portion 29 (step 304). As a result, the delay profile data generation portion 28 reduces the number of oversamples for the channel of the ith cell from a multiple of eight to a multiple of four and the path search portion 29 uses a value that is stored in the interference power level storage memory 30 as the average interference power level value.
According to the third embodiment example, the speed of the data processing time during handover between advance base stations can be increased, whereby the hardware occupancy ratio per channel can be lowered.
The fourth embodiment example manages the channels undergoing handover and the response of the cells that are associated with the handover and performs path detection when the delay profiles of all the channels associated with a predetermined handover have all been gathered.
The MPU 25 stores data that has flowed to each cell from the delay profile data generation portion 28 in a vacant channel region of the profile data storage memories 29a1 to 29a6 and, if the data is that of a mobile device undergoing handover, manages the link with the channels associated with the handover (cell 1: ch1 and cell 5: ch8, and so forth, for example). Further, the MPU 25 monitors whether the delay profile data of all the channels associated with the handover have been gathered and transfers the delay profile data from all the gathered channels to the path detection portion 29b, whereupon the path detection portion 29b executes path detection by using the plurality of delay profile data thus transferred.
According to the fourth embodiment example, the occupancy ratio per channel of the path search portion can be lowered.
If a plurality of the advance base stations, that is, cells, is arranged in the form of a straight line within a tunnel, the number of users per channel in each cell can be estimated. However, in reality, this does not mean that there is that number of users and full usage cannot be considered at first. Further, the optical fiber cables must then be laid in parallel, which is wasteful. In addition, a case where the desire exists to arrange the cells in series, not only within a tunnel, but also along a road and to arrange the cells in series in stages within a high-rise building, and so forth, is similar.
A fifth embodiment example makes active use in this case of the resources of the wireless backbone base station device 11 by cascade-connecting advance base stations 511, 512, 513 . . . by means of fiber-optic cables 611, 612, 613 . . . , as shown in
If downlink data is received from the wireless backbone base station device 11, the O/E conversion portion 53 of each of the advance base stations captures the downlink data and transmits same by means of an antenna, sending the downlink data through to the advance base station of the next stage. Further, if uplink data is received from a lower order advance base station, the O/E conversion portion 53 of the advance base station then sends the uplink data as is through to the wireless backbone base station device 11.
As detailed above, if a plurality of advance base stations is cascade-connected, the number of users corresponding with one cell is covered by a plurality of advance base stations. Therefore, the resources of the wireless backbone base station 11 are not wasted. Further, supposing that three advance base stations can be cascade-connected and six advance base stations can be connected in series to the wireless backbone base station device 11, substantially 18 advance base stations can then be installed. As a result, one advance base station can then be installed in each floor of the building, for example.
In the above embodiment example, the present invention was applied to a Rake receiver that performed a multipath search and retrieved and synthesized desired signals from the signals received via the respective paths. The present invention can also be applied to a case where one path is detected and data is demodulated by means of a signal that is received via this path.
As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.
Number | Date | Country | Kind |
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JP 2004-286301 | Sep 2004 | JP | national |