KR100547878B1 - Apparatus and Method for Effective Soft Handover in Orthogonal Frequency Division Multiplex / Wideband Code Division Multiple Access Mobile Communication System - Google Patents

Abstract

The present invention provides a user terminal in a handover area in a mobile communication system in which orthogonal frequency division multiplexing (OFDM) and wideband code division multiple access (WCDMA) coexist with multiple sub-channels. A method and apparatus for soft combining the same signals transmitted from multiple cells to effectively perform soft handover.

The present invention provides a process for a user terminal receiving reference signals including information for distinguishing the base station and the adjacent base station from the base station and the adjacent base station, and measuring the arrival time of the reference signal for each base station; Selecting base stations within a guard interval inserted to reduce inter-symbol interference in the first mobile communication scheme from the reference time using the measured arrival time; and indicating information indicating the selected base stations. Characterized in that the transmission to the base station controller.

OFDM, Handover, Channel Interference, Guard Interval

Description

TECHNICAL APPARATUS AND METHOD FOR IMPORTANT SOFT HANDLE OVEROVER IN A MULTIPLE ACCESS OF QUARTZED FREQUENCY SPLIT MULTI / WIDE-BAND CODE SPLIT MULTIPLE ACCESS MULTIPLEXING / WIDEBAND CODE DIVISION MULTIPLEXING ACCESS COMMUNICATION SYSTEM}             

1 is a diagram illustrating a system structure for supporting soft handover in an OFDM // WCDMA mobile communication system for applying the present invention.

2 is a diagram illustrating a structure of a guard interval in an orthogonal frequency division multiplex (OFDM) mobile communication system for applying the present invention.

3 is a diagram illustrating a structure for selecting some cells from among a plurality of cells in order to improve reception performance of a mobile communication system according to an embodiment of the present invention.

4 is a diagram illustrating a structure of a transmitting apparatus of a UE supporting soft handover in a mobile communication system in which OFDM / WCDMA scheme coexists according to a first embodiment of the present invention.

5 is a diagram illustrating a structure of a receiver of a UE supporting soft handover in a mobile communication system in which OFDM / WCDMA scheme coexists according to a first embodiment of the present invention.

FIG. 6 illustrates a process in which a UE selects Node Bs for supporting soft handover according to the first embodiment of the present invention. FIG.

7 is a flowchart showing operation of the UTRAN according to the first embodiment of the present invention.

8A, 8B, and 8C are diagrams illustrating a step-by-step calculation process of the reception time measuring device 100 for each Node B of FIG.

9 is a diagram illustrating a detailed structure of the reception time measuring device 100 for each Node B according to the present invention.

10 is a diagram illustrating a calculation process of a delay time 102 for each Node B according to the present invention.

11 illustrates a calculation process of a comparator 104 in accordance with the present invention.

Fig. 12 shows the operation of the selector 106 in accordance with the present invention.

FIG. 13 is a diagram illustrating a process in which a UTRAN selects Node Bs for supporting soft handover according to a second embodiment of the present invention. FIG.

The present invention relates to a mobile communication system using an orthogonal frequency division multiplexing / wideband code division multiple access scheme, and more particularly, an apparatus for soft combining the same downlink signal transmitted from a plurality of base stations by a user terminal existing in a handover region; It is about a method.                         

Orthogonal Frequency Division Multiplexing (hereinafter referred to as "OFDM"), which is recently used as a useful method for high-speed data transmission in wired / wireless channels, transmits a large amount of data using a plurality of carriers as subchannels. Technology. In this OFDM scheme, multi-carrier modulation is performed by converting symbol strings that are serially input in parallel, modulating each of them into a plurality of sub-carriers (Sub-Channels) having mutually orthogonal characteristics. (Multi Carrier Modulation: hereinafter referred to as "MCM") is a kind of method. The mobile communication system applying the MCM scheme was first applied to military high frequency wireless communications in the late 1950s, and the OFDM scheme overlapping a plurality of orthogonal subcarriers began to be developed since the 1970s, but is orthogonal among multiple carriers. Since the implementation of the modulation had to be solved, there was a limit to the practical application of the system. However, in 1971, Weinstein et al. Proposed the modulation and demodulation using the OFDM scheme using a discrete Fourier transform, and thus the technology for the OFDM scheme was rapidly developed. In addition, the known Guard Interval insertion scheme further reduces the negative effects of the OFDM mobile communication system on the multipath and delay spread.

Accordingly, the OFDM scheme includes digital audio broadcasting (DAB), digital TV, wireless local area network (WLAN), and wireless asynchronous transmission mode (Wireless). Asynchronous Transfer Mode (hereinafter referred to as "WATM") has been widely applied to digital transfer technologies.

Nevertheless, the OFDM scheme has not been widely used due to hardware complexity, and recently, the Fast Fourier Transform (hereinafter referred to as "FFT") and the Inverse Fast Fourier Transform (hereinafter referred to as "FFT") are not widely used. Various digital signal processing technologies, including IFFT " The OFDM scheme is similar to the conventional Frequency Division Multiplexing (FDM) scheme. However, the OFDM scheme maintains orthogonality among a plurality of subcarriers to achieve optimal transmission efficiency in high-speed data transmission. It has the characteristics to be able. In addition, since the frequency spectrum is superimposed, frequency use is efficient, and it is strong in frequency selective fading and multipath fading. In addition, since the protection interval may be used, it is possible to simply design the equalizer structure to reduce the influence of Inter Symbol Interference (hereinafter referred to as ISI) in hardware.

Accordingly, the OFDM-based mobile communication system is currently adopted as a standard for high-capacity wireless communication systems, such as transmission of European digital broadcasting and IEEE 802.11a, IEEE 802.16a, and IEEE 802.16b.

When the OFDM scheme is applied to a current cellular mobile communication system, a user terminal (UE: User Element, hereinafter referred to as "UE") existing in a handover area has several Node Bs as compared to other mobile communication systems. It was not easy to perform soft combining by receiving the same downlink signal. This means that downlink signals arriving at the UE existing in the handover region have an arrival delay out of a guard time defined in the OFDM scheme, thereby acting as an interference between the signals. Because. Thus, a problem arises that degrades the performance of the received signal. That is, according to different arrival delays of the signals transmitted from each Node B, the signals do not act as channel gains when performing soft combining, but rather as interference of respective signals. There is a problem that the reception performance of the transmitted signal is reduced.

Therefore, in the OFDM / WCDMA type mobile communication system, when the UE exists in the soft handover region, the implementation gain of the system is increased, unnecessary signals are blocked, and signal interference between downlinks is reduced to reduce reception performance. An apparatus and method for increasing is provided.

Accordingly, the present invention proposes an apparatus and method for soft combining only signals having an arrival delay within a guard interval according to the OFDM scheme when the UE exists in the soft handover region in an OFDM / WCDMA scheme. do.

Accordingly, an object of the present invention is to select Node Bs capable of transmitting data through a downlink channel by a user terminal in a handover region in a mobile communication system in which OFDM and WCDMA systems exist together. To provide an apparatus and method.                         

Another object of the present invention is to provide an apparatus and method for selecting Node Bs capable of data transmission through a downlink channel in a mobile communication system in which an OFDM scheme and a WCDMA scheme exist together.

 Another object of the present invention is to provide an apparatus and method for soft combining the same signals transmitted from multiple cells by a user terminal in a handover region in a mobile communication system having both OFDM and WCDMA schemes. have.

A first embodiment of the present invention for achieving the above objects is a base station for a user terminal existing within a certain area in a mobile communication system in which a first mobile communication system and a second mobile communication system coexist, and occupied by the base station; A method for performing a handover when the user terminal is present in an area in which a plurality of base stations are shared, comprising a user terminal existing in an area of the base station and a base station controller for controlling a plurality of base stations. Receiving reference signals including information for distinguishing the base station and the adjacent base station from a base station and a neighboring base station, measuring the arrival time of the reference signal for each base station, and using the arrival times measured for each base station The difference in arrival time for each base station from time is significant in the first mobile communication system. The process and the information indicative of the selected base station for selecting the base station is within the guard interval is inserted to reduce interference between, it characterized in that it comprises the step of transmitting to the base station controller.

A second embodiment of the present invention for achieving the above objects is a base station that is in charge of a user terminal existing within a certain area in a mobile communication system in which the first mobile communication and the second mobile communication scheme coexists, and occupied by the base station; And a base station controller for controlling a plurality of base stations, wherein the user terminal exists in an area where a plurality of base stations are shared, wherein the base station controller performs the handover. Measuring a time of arrival for each base station by which a signal transmitted from a user terminal is received by each of the plurality of base stations, and using the arrival time measured for each base station, a difference of arrival time for each base station from the reference time is shifted to the first movement; To reduce the interference between symbols in the communication method, the base station within the guard interval inserted And a step of transmitting data for communicating with the user terminal to the selected base stations.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In 3GPP Release 6, a discussion is being made to use an OFDM mobile communication system together with a conventional W-CDMA mobile communication system. In this case, the OFDM mobile communication system communicates with signals transmitted from a plurality of cells by sharing channel information provided by WCDMA. That is, in the OFDM / WCDMA mobile communication system, the UE receives the arrival time information of the signals using a unique scrambling code and a training sequence indicating each cell through downlink channels transmitted from a plurality of Node Bs in the WCDMA manner. It is possible to select cells for performing soft handover.

Accordingly, a mobile communication system using a mobile communication system of the WCDMA method and the OFDM method can obtain the arrival time information of the data channel transmitted from each cell using a unique pilot channel transmitted through downlink in the WCDMA method. Can be.

That is, the mobile communication system for performing data communication through the OFDM scheme is not only the mobile communication system of the WCDMA scheme but also a mobile communication system capable of distinguishing signals transmitted from a cell to a UE and measuring arrival times of the signals; For example, the present invention can be applied to a mobile communication system such as CDMA2000.

As described above, the present invention is to provide an apparatus and method for using soft handover in a mobile communication system that performs data communication through an OFDM scheme by taking advantage of the benefits that can occur when different mobile communication systems exist at the same time. This means that in a mobile communication system performing data communication using the OFDM scheme, when signals transmitted from multiple cells come in simultaneously with a delay time within a guard time range, they can be combined with each other to obtain a transmission diversity gain. It is to use.

That is, in the present invention, in a mobile communication system in which an OFDM scheme using a plurality of subchannels and a WCDMA scheme for transmitting signals spread over a wide band coexist, the arrival time information obtained from the mobile communication system of the WCDMA scheme is used. The present invention provides an apparatus and method for performing a soft handover in a data communication through an OFDM scheme by a UE present in a handover region. Accordingly, an object of the present invention is to provide an apparatus and method for improving system performance at a UE and increasing capacity of a downlink channel.

1 is a diagram illustrating a structure for supporting soft handover in a mobile communication system in which an OFDM / WCDMA scheme for applying the present invention coexists.

Referring to FIG. 1, the mobile communication system includes a core network (CN) 10, a radio network controller (RNC) 12, A plurality of base stations (Node B, Node B1: 18-2, Node B2: 18-4, Node B3: 18-6) and UE22. The RNC12 operates as an SRNC for the UE22, and each Node B (Node B1: 18-2, Node B2: 18-4, Node B3: 18-6) is controlled by the RNC12. In addition, the cell (cell 14-2, cell 14-4, cell 14-6) is managed by the corresponding Node B (Node B1: 18-2, Node B2: 18-4, Node B3: 18-6). . If the UE22 exists in the cell 14-2, the UE22 is connected to the Node B1 18-2 to access the CN10. If the UE22 exists in a handover area (hatched area of FIG. 1), the UE22 is connected to and communicates with the Node B1 18-2, the Node B2 18-4, and the Node B3 18-6. Do this. In this case, the UE22 soft-combines signals transmitted from the plurality of Node B1 18-2, Node B2 18-4, and Node B3 18-6 to increase the gain of the received signal. In this case, the UE22 is about signals existing in the guard interval according to the OFDM scheme among the signals transmitted from the plurality of Node B1 (18-2), Node B2 (18-4), Node B3 (18-6). Soft combining is performed to increase the performance of the mobile communication system.

2 is a diagram illustrating a structure of a guard interval in an orthogonal frequency division multiplex (OFDM) mobile communication system for applying the present invention.

Referring to FIG. 2, a guard interval (hereinafter, referred to as a "GI") 24 used in an OFDM-based mobile communication system is a symbol interference between subchannels (hereinafter referred to as ISI) and a frame interference ( Inter Frame Interference (hereinafter referred to as IFI) is added to reduce the effects. Therefore, when soft combining the signals received outside the GI range and the signals arriving within the GI range, the signals received outside the GI range act as interference signals to each other, thereby degrading the performance of the mobile communication system. .

At this time, the GI range is selected in consideration of the channel impulse response (28). In this case, a form in which the last section of the OFDM symbol is copied and pasted as GI is called a cyclic prefix (hereinafter, referred to as "CP"). The cyclic prefix has the effect of maintaining orthogonality between the transmitted signals. Therefore, even if a predetermined frequency is superimposed, each frequency acts as an independent signal from each other, thus making efficient use of the frequency. When downlink signals are transmitted from a plurality of cells to the UE22 existing in a handover region in the OFDM mobile communication system, the UE22 receives a signal having the same information through various paths. Therefore, the transmitted signal has a unique delay time according to each communication path. Signal 26 indicates the format of the signal transmitted from the transmitting side. Signals 26-1, 26-2, 26-3 and 26-4 represent signals received through different paths. On the other hand, 26-5 represents a signal received through the shortest path. At this time, signals 26-1, 26-2, and 26-3 received through different paths are signals having a delay within a GI range defined by signal 26. Accordingly, soft combining is performed on the signals 26-1, 26-2, and 26-3 to perform channel gain of the received signal. On the other hand, 26-4 is a signal that does not exist in the GI and acts as an interference signal with respect to the signals 26-1, 26-2, and 26-3. That is, the signal 26-4 in which the delay time exceeds GI in the multipath signal is broken as orthogonality with the signals 26-1, 26-2, and 26-3 to act as an interference signal. It will degrade performance. UE22 performs soft combining on the signals present in the GI to reproduce a signal having the same format as the signal transmitted from the transmitter, such as signal 26-5.

3 is a diagram illustrating a structure in which some cells are selected from among a plurality of cells in order to improve reception performance of a mobile communication system according to an embodiment of the present invention.

Referring to FIG. 3, the UE22 receives signals transmitted through different paths from a plurality of cells (cell 14-2, cell 14-4, and cell 14-6). The signal transmitted from cell A14-2 is the signal arriving at the UE as the earliest and becomes a reference reception signal. The second, third, and fourth signals transmitted from cells B14-4 and A14-2 and C14-6 arrive at a delay within the GI range of the reference signal. On the other hand, the fifth, sixth, ... Nth signals transmitted from cell E or cell C have an arrival delay outside the GI range of the reference signal. Therefore, when performing soft combining including signals having an arrival delay outside the GI range from the cell E or the cell C, the reception performance of the UE22 is degraded.                     

Accordingly, the UE 22 selects only the cell B14-4, the cell A 14-2, and the cell C14-6 which have transmitted the second, third, and fourth signals having arrival delays in the GI based on the reference received signal. The downlink signal is transmitted. Therefore, the interference signal between the signals received by the UE22 is reduced, when performing the soft combining the same signal transmitted from a plurality of cells, the performance of the received signal is increased.

4 is a diagram illustrating a structure of a transmission apparatus of a UE supporting soft handover in a mobile communication system in which OFDM / WCDMA scheme coexists according to a first embodiment of the present invention.

Referring to FIG. 4, the transmitter of the UE22 is a data transmitter 30 for an OFDM mobile communication system and index information of Node Bs fed back from a receiver (shown in FIG. 5 below). And an FBI information generator 60 for transmitting control data using a " FBI "

The data transmitter 30 includes a data generator 40, a channel encoder 42, a serial to parallel transform (S / P) 44, a signal mapper 46, and an inverse fast Fourier transformer according to an OFDM mobile communication system. Inverse Fast Fourier Transform (IFFT) 48, Parallel to Serial transform (P / S) 50, Protective section inserter 52, Digital to Analog converter (D / A) 54) and the antenna 56.

First, the data generator 40 inputs data to be transmitted and transmits it to the channel encoder 42. The channel encoder 42 performs channel encoding of the input data in a coding scheme preset in accordance with the OFDM mobile communication system. At this time, the channel-coded input data is input to S / P44. By the S / P44, serial data is arranged in parallel data and input to the signal mapper 46. The signal mapper 46 allocates data input in parallel to each sub channel and outputs the data. Data output from the signal mapper 46 is allocated to each sub channel and input to IFFT48. In this case, a pilot signal for measuring a transmission state of each subchannel may be input to the IFFT48. The IFFT48 performs inverse Fourier transform on the input data and outputs the data subchannels as P / S50. The P / S50 combines each data subchannel into a single data channel, and outputs the combined data channel to the guard interval inserter 52. The guard interval inserter 52 protects the data channel output from the IFFT48 to reduce the effects of symbol interference between the subchannels (hereinafter referred to as ISI) and frame interference (hereinafter referred to as IFI). Insert Guard Interval and output to Antenna 56. The antenna 56 propagates a single data channel received from the guard interval inserter 52 to the wireless channel. The pilots are pilot symbols set in the OFDM mobile communication system and inserted into a plurality of subchannels, that is, data symbols, output from S / P44. Here, the reason why the pilot symbols are inserted and transmitted together with the subchannel through which the data symbols are transmitted is for channel estimation of each subchannel, and therefore, the pilot symbols operate as a training sequence. The pilot subchannels have a predefined transmission position in the mobile communication system of the above scheme.                     

The FBI information generator 60 receives index information on the selected Node Bs and converts the index information into FBI information used for gain adjustment of a transmission antenna. The FBI information generator 60 transmits index information for Node Bs transmitted from a receiver of the UE22 (described in FIG. 5 below) to an uplink data channel 6442 such as a dedicated physical control channel of WCDMA. ) To UTRAN.

5 is a diagram illustrating a structure of a receiver of a UE supporting soft handover in a mobile communication system in which OFDM / WCDMA scheme coexists according to a first embodiment of the present invention.

Referring to FIG. 5, the receiver is largely comprised of a data receiver 34, a Node B searcher 36, and a controller 38 (same as the controller of FIG. 4). First, the data receiver 34 includes an antenna 80, an A / D82, a guard interval remover 84, S / P86, a fast Fourier transform (hereinafter referred to as "FFT") 88, an equalizer 90, a signal mapper 92, P / S94, channel predictor 96, channel compensator 98, and channel decoder 99. In this case, the antenna 80 is the same as the antenna 56 of FIG. 4, which is to distinguish and describe the transmitter of FIG. 4 and the receiver of FIG. 5.

UE22 receives data through the antenna 80. The received data is input to the guard interval remover 84. The guard section remover 84 removes the guard section inserted through the guard section inserter 52 of FIG. 4 from the received data. That is, the backward section remover 84 removes the inserted GI to reduce symbol interference and frame interference between subchannels. The received signal from which the GI is removed is input to S / P86. The S / P86 converts the serial reception signal into a parallel signal and outputs the same to the FFT88. The parallel received signals are Fourier transformed into a plurality of subchannel signals. The received signal converted into a plurality of sub channel signals by the FFT88 is output to the equalizer 90. The equalizer 90 restores the attenuated signal to its original form according to channel transmission. The recovered received signal is output to the signal mapper 92. The signal mapper 92 allocates and outputs a subchannel to each parallel data. P / S94 combines each data subchannel to form a single data channel. Channel predictor 96 predicts the single data channel and passes it to channel compensator 98. The channel compensator 98 compensates for the channel of the received signal. The received signal compensated by the channel compensator 98 is output to the channel decoder 99. The channel compensated received data passes through the channel decoder 99 and then is decoded. The channel decoder 99 is mainly used as a Viterbi decoder or a decoder using a MAP algorithm.

The Node B search unit 36 includes a reception time measuring device 100 for each Node B, a delay time calculator 102 for each Node B, a delay time and guard time comparator 104, and a Node B selector 106.

The reception time measuring device 100 for each Node B receives signals transmitted from cells in a handover region and measures arrival times of the signals. The arrival delay time of the signals of the Node Bs received through the multipath is to find the Node Bs within the guard period. First, the reception time measuring device 100 for each Node B uses a downlink channel shared by all UEs located in the same cell transmitted in a WCDMA mobile communication system. For example, in case of WCDMA, it may be Common Pilot Channel (CPICH). Therefore, the WCDMA system confirms arrival time information corresponding to each Node B by demodulating signals using a searcher looking for time information.

The delay time calculator 102 measures a time at which the downlink signals transmitted by the Node Bs arrive at the UE through the reception time measurer 100. The Node B delay time calculator 102 sets, as a reference signal, a signal first arriving at the UE22 among the same signals transmitted through the multipath. The arrival delay time of signals arriving from other cells is measured based on the reference signal. That is, the delay time calculator 102 has arrival time information corresponding to each Node B received from the reception time measuring device 100 for each Node B, and calculates arrival delay times of other Node Bs based on the Node B signal having the fastest arrival time. Measure

Comparator 104 compares the difference between the delay time of the reference signal and the signals transmitted from the respective Node Bs within the GI range. That is, the output of the delay calculator 102 is input to determine whether a difference in arrival delay time of the signals transmitted from each Node B based on the Node B signal having the fastest arrival time exists in the GI of the OFDM scheme.

If the difference in arrival delay time of the signals transmitted from each Node B based on the Node B signal having the fastest arrival time exists in the GI inserted for the orthogonality between the multiple carriers, the selector 106 determines that the delay time difference is the GI. Node Bs which have transmitted signals existing within are selected as cells supporting soft handover. That is, the selector 106 receives the output information of the comparator 104 and finally selects Node B to transmit downlink data to the UE existing in the handover region. The transmitter 108 transmits index information about the selected Node Bs to UTRAN, which is a higher system.

The controller 38 is the same as the controller of FIG. 4, and provides a control signal according to an actual data transmission / reception operation and adjusts a processing time of data transmitted / received to the upper system UTRAN.

FIG. 6 is a diagram illustrating a process in which a UE selects a Node B for supporting soft handover according to the first embodiment of the present invention.

Referring to FIG. 6, in step 120, after entering the handover region, the UE22 receives reference signals from a plurality of Node Bs. In this case, the reference signals are signals for distinguishing the plurality of Node Bs as a downlink common channel transmitted from the plurality of Node Bs. Therefore, in WCDMA, the signal includes a scrambling code, and in CDMA, the signal includes a pilot signal. In addition, training sequences are also available. The training sequence is a data sequence for checking the state of the channel between the UE22 and the plurality of Node Bs during data transmission, and it is possible to grasp the channel state and data rate of the receiving side.

In step 122, the UE22 receives reference signals for each Node B and performs channel demodulation. In step 124, the UE22 measures the arrival time of signals arriving from each Node B through the reception time meter 100. That is, the arrival time information corresponding to each Node B is confirmed through the channel demodulated signals. The arrival time information is stored in a separate storage device (not shown). In step 126, the UE22 measures the delay time according to the arrival of other reference signals based on the signal having the fastest arrival time among the reference signals transmitted from each Node B through the delay time calculator 102. That is, the arrival delay time of the signals transmitted from each Node B around the reference signal is measured. In step 128, the UE22 checks whether a difference in arrival delay time between the reference signal and the signals transmitted from the respective Node Bs is present in the GI of the OFDM scheme. Signals having an arrival delay time present in the GI may perform macro diversity like transmit antenna diversity. Signals that do not act as interference signals between channels having arrival delay time present in the GI can be combined into a single radio channel through soft combining. Accordingly, UE22 performs soft combining on the signals to increase reception performance. In step 130, the UE22 selects signals existing in the GI as Node Bs capable of soft handover support through a selector. In step 132, the UE22 identifies the index information of each Node B, which is identification information of the selected Node Bs, and generates FBI information. The FBI information generated in step 134 is transmitted to the UTRAN through an uplink channel. In step 136, the UTRAN checks the received FBI information and then transmits data to Node Bs corresponding to the FBI information. Accordingly, UE22 soft combines the signals transmitted from the selected Node Bs.

As described above, the UE22 selects only cells B that transmit signals arriving in the GI and transmits information of the cells B to the UTRAN, which is a higher system. Accordingly, the UE22 receives data from the selected cells Node B under the control of the UTRAN. In addition, by performing soft combining the signals transmitted from the selected cells (Node B) to improve the reception performance.

7 is a flowchart illustrating the operation of the UTRAN according to the first embodiment of the present invention.

Referring to FIG. 7, in step 140, the UTRAN receives the selected cell (Node B) index information from the UE22. That is, the UTRAN12 checks index information of Node Bs that have transmitted signals having arrival delay time in GI according to the OFDM scheme. In step 142, the UTRAN controls the selected Node Bs to perform data transmission on a downlink channel.

In addition, the operation of the Node B search unit 36 of FIG. 5 may be described as, for example, an initial cell search and a multipath search of the WCDMA system. Particularly, in the case of initial cell search, code information about one Node B is finally output through a three-step cell search process that passes through steps 1, 2, and 3 described in FIGS. 8A, 8B, and 8C. In this case, code information about one or more Node Bs is finally output through the cell search process of steps 1 and 3 described with reference to FIGS. 8A and 8C. In only three steps of correlation, there may be slight differences depending on the initial cell search and the multipath search, but this does not add explanation because it is not related to the core of the present invention.

In the following, a calculation process of the Node B search unit 36 of FIG. 5 is shown in a schematic hardware block diagram. In the OFDM / WCDMA mobile communication system of the present invention, an operation for achieving synchronization of a specific Node B through a predetermined synchronization channel is required according to the WCDDMA scheme. The channel used for the Node B cell search in the downlink physical channel (DPCH) of the WCDMA system is called a primary synchronization channel (P-SCH). And Secondary Synchronization CHannel (hereinafter referred to as S-SCH). The P-SCH is a channel in which a sequence having a length of 256 chips is repeatedly transmitted during the first 256 chips of each slot (slot, 1 slot = 2560 chips). UE22 of the WCDMA system performs slot timing synchronization using the P-SCH. After the slot is synchronized, frames are synchronized through the second channel. Then, after identifying the information about the Node B through the above channels, the arrival time of the signal transmitted from the Node B is measured. This process will be described in more detail with reference to FIG. 8.

8A, 8B, and 8C are diagrams illustrating the operation of the reception time measuring device 100 for each Node B of FIG. 5 step by step. 8A is a diagram illustrating a process of detecting slot synchronization of the WCDMA mobile communication system as a first process of the reception time measuring device 100.

Referring to FIG. 8A, the receiving device of UE22 receives the first synchronization channel through the receiving antenna 38. The received first synchronization channel is output to the decimator 180. The decimator 180 decimates a signal input at 2N (N = 0, 1, 2,) times the chip speed into M signals. Thereafter, the decimated result is separated into an I channel and a Q channel and output to 2M correlators. The correlators 184, 186, ... 188, 190 obtain a correlation value with respect to the input signal, and then output the result to the calculation units 192, ..., 194. The calculation units 192,..., 194 obtain correlation energies with respect to correlation values of I and Q channels, respectively, output from the correlators 184, 186,..., 188, 190. In this case, the detector 196 detects a maximum energy value among the correlation energies output from the correlators 184, 186,..., 188, 190. In this case, a time point having a maximum value among the correlation energies becomes a synchronization point of the first synchronization channel. Accordingly, UE22 is synchronized with the slot. 8B illustrates a process of detecting frame synchronization of the WCDMA mobile communication system as a second operation process of the reception time measuring device 100.

A total of 64 code groups with slot synchronization include 8 cells each. That is, since there are eight scrambling codes in one code group, cell identification is possible by analyzing the correlations of the eight scrambling codes by checking the respective code groups. Accordingly, the UE22 receives the second synchronization channel through the reception antenna 38. The received second synchronization channel is output to the decimator 220. The decimator 220 decimates the received second synchronization channel with L scrambling codes. The decimated result is output to the frame boundary detector 222. The frame boundary detector 222 continuously selects correlation values for the L scrambling codes. (228, 230, 232, ...) The second detector 224 selects a code group having a valid value among the output columns of correlation values.

FIG. 8C illustrates a process of measuring arrival delay time of a signal transmitted from a code group having the valid value, or a process of measuring arrival delay time with scrambling code information about neighbor cells received from UTRAN. In the following description, a process of measuring arrival delay time with scrambling code information of neighbor cells received from UTRAN, that is, multipath search, will be described as an example.

Referring to FIG. 8C, a correlation value of scrambling codes for input signals and scrambling codes for neighboring cells received from the UTRAN may be obtained in all cases which may be included in an active set. Here, a method of taking correlation while moving at the window interval may be used.

Accordingly, signals input through the receive antenna 38 are input to the N correlators 272, 274, ..., 276. The descrambler 262 of each correlator 272, 274, ..., 276 calculates the scrambling codes for the I and Q channels generated by the received signal and the scrambling code generator 260 and outputs them to the calculator 264. The calculator 264 obtains a correlation energy for each correlation value and outputs the correlation energy to the third detector 266. The third detector 266 detects Node Bs belonging to an active set transmitting substantial data to the UE22 among the input signals.

Information about the detected cells is transmitted to the arrival time selector 266. Accordingly, the arrival time selector 268 detects arrival time information using the scrambling codes used for the common downlink channel transmitted from the selected Node Bs. The arrival time information transmitted from each Node B is stored in a separate storage device (not shown).

9 is a diagram illustrating a detailed structure of the reception time measuring device 100 for each Node B according to the present invention.

Referring to FIG. 9, all scrambling codes capable of data transmission from the plurality of correlators of FIG. 8 to the UE 22 existing in the handover region, that is, scrambling codes of neighbor cells received from the UTRAN Receive a correlation value. That is, the UE22 existing in the handover region receives the correlation values for all available scrambling codes and stores the correlation values corresponding to the respective scrambling codes. That is, the correlator 1 266-2 stores the correlation value 1 and the first correlation energy for the first scrambling code. The correlator N 266-6 stores the correlation value N and the Nth correlation energy for the Nth scrambling code. At this time, the scrambling code selector 266-8 selects valid values among correlation values corresponding to the respective scrambling codes and outputs scrambling code identification information ID having the correlation values or index information of the Node Bs. . That is, values from the correlation value 1 (266-2) corresponding to the scrambling code 1 to the correlation value N (266-6) corresponding to the scrambling code N are stored and output to the scrambling code selector 266-8. In this case, the scrambling code selector 266-8 selects valid exchange values among the correlation values of the scrambling code received, and ID or index information Scr_Idx_1, Scr_Idx_2, .. Scr_Idx_i, and i = 1, of the selected scrambling code. 2 ... N) is outputted to the arrival time selector 268.

Arrival time selector 268 stores arrival time information 1 for the first scrambling code from arrival time information 1 for the first scrambling code i (268-2) (Arr_Time_for_Scr_Idx_1, Arr_Time_for_Scr_Idx_2, Arr_Time_for_Scr_Idx_N) to the arrival time selector 268-4. Output In this case, the arrival time selector 268-4 receives the Node B index information Scr_Idx_1, Scr_Idx_2, .., Scr_Idx_i, and i = 0,1... Only the arrival times (Arr_Time_for_Scr_Idx_1, Arr_Time_for_Scr_Idx_2, ..., Arr_Time_for_Scr_Idx_i, and i = 1, 2 ... N) for the code are selected.

10 is a diagram illustrating a calculation process of the delay time 102 for each Node B according to the present invention.

Referring to FIG. 10, the delay time measurer 102 sets the earliest arrival signal among the arrival time information output from the reception time measurer 100. At this time, the arrival time of the signals corresponding to each scrambling code is compared with the arrival time of the reference signal. That is, the delay time measuring unit 102 refers to the information having the earliest arrival time among the arrival time information Arr_Time_for_Scr_Idx_1, Arr_Time_for_Scr_Idx_2, Arr_Time_for_Scr_Idx_i, and i = 0,1 ... N, which are output from the reception time measuring device 100. Set to time (Arr_Time_for_Scr_Idx_n_Ref). Delay difference (Arr_Time_for_Scr_Idx_i_Ref-Arr_Time_for_Scr_Idx_i, i = 1, 2, ..., N) of the respective scrambling codes is measured based on the reference time Arr_Time_for_Scr_Idx_n_Ref. Accordingly, delay information (Delay_Time_for_Scr_Idx_1, Delay_Time_for_Scr_Idx_2, ..., Delay_Time_for_Scr_Idx_i, and i = 1, 2 ... N) for each scrambling code is output to the comparator 104 through the multiplexer 102-8.

11 is a diagram illustrating a calculation process of the comparator 104 according to the present invention.

Referring to FIG. 11, the comparator 104 checks whether delay information output from the delay time measurer 102 of FIG. 10 exists within a GI range. If the delay information is present in the GI, a corresponding scrambling code is selected. The comparator 104 determines the difference between the delay information and the GI according to each scrambling code (Guard_Time-Delay_Time_for_Scr_Idx_1, Guard_Time-Delay_Time_for_Scr_Idx_2, ..., Guard_Time-Delay_Time_for_Scr_Idx_i, and i) in 104-2, 104-4, and 104-6. Calculate = 1,2 ... N). The calculation result (Diff_Time_for_Scr_Idx_1, Diff_Time_for_Scr_Idx_2, ..., Diff_Time_for_Scr_Idx_i, and i = 1, 2 ... N) is output to the selector 106 through the multiplexer 104-8.

12 is a diagram illustrating a calculation process of the selector 106 according to the present invention.

Referring to FIG. 12, the comparator 106-2 checks the information on the GI and the delay time (Diff_Time_for_Scr_Idx_1, Diff_Time_for_Scr_Idx_2, ... Diff_Time_for_Scr_Idx_i) of the scrambling code. The selector 106-4 selects only the information arriving in the GI from the information output from the comparator 106-2, that is, information having Diff_Time_for_Scr_Idx_i> 0. Accordingly, the selector 106-4 selects only scrambling codes corresponding to information arriving in the GI. Accordingly, when the UE 22 exists in the handover region, Node Bs for data transmission are selected through downlink. (Selected_node-B_Idx_1, Selected_node-B_Idx_2,, Selected_node-B_Idx_j, and j = 1,2. ..N)

FIG. 13 is a diagram illustrating a process in which a UTRAN selects Node Bs for supporting soft handover according to a second embodiment of the present invention.                     

Referring to FIG. 13, when the UE22 enters the handover region, a plurality of Node Bs that can receive the same signal from the UE22 measures the arrival time of the signal transmitted from the UE22. Each of the Node Bs transmits the measured arrival time information to the RNC12. In step 162, the RNC12 sets the Node B signal having the fastest arrival time as the reference signal among the arrival time information received from the Node Bs. The delay time for each Node B is measured by calculating the difference in arrival times of other Node Bs based on the set reference arrival time. In step 164, the RNC12 checks whether a difference in delay time for each Node B based on the reference arrival time exists in the GI according to the OFDM scheme. Signals that do not act as interference signals between channels having arrival delay time existing in the GI around the reference signal can be combined into a single wireless channel through soft combining. Therefore, in step 166, the RNC12 checks the delay time, and selects Node Bs capable of receiving signals in the GI as Node Bs capable of soft handover support. In step 168, the RNC12 transmits downlink data to the selected Node Bs. Accordingly, the Node Bs receiving the downlink data from the RNC12 in step 168 transmit the data to the UE22 located in the handover area.

As described above, when the UE exists in the handover region in the mobile communication system using the OFDM scheme, when the same data is received from the selected Node Bs having a delay in the guard period, soft combining is performed. As a result, the reception performance is increased. In addition, in supporting a handover in a mobile communication system using an OFDM scheme, the downlink data transmission capacity is increased by setting a guard interval in consideration of an arrival delay time, even though the downlink channel is reduced. Have In addition, since data is transmitted from the selected Node Bs, interference between channels due to downlink data transmission is reduced.

Claims (13)

In the mobile communication system in which the first mobile communication system and the second mobile communication system coexist, a base station for controlling a user terminal existing in a certain area, a user terminal existing in an area occupied by the base station, and a plurality of base stations are controlled. In the method comprising a base station controller, when the user terminal is present in an area where a plurality of base stations are shared, Receiving, by the user terminal, reference signals including information for distinguishing the base station from the adjacent base station from the base station and the adjacent base station, and measuring the arrival time of the reference signal for each base station; Selecting base stations within a guard interval in which a difference in arrival time for each base station from a reference time is inserted to reduce inter-symbol interference in the first mobile communication scheme by using the arrival time measured for each base station; And transmitting information indicating the selected base stations to the base station controller. The method of claim 1, The first mobile communication method is an orthogonal frequency division multiplexing method, and the second mobile communication method is a WCDMA method or a CDMA method is used. The method of claim 1, The reference time is characterized in that the best arrival time of the arrival time measured for each base station. The method of claim 1, And causing the base station controller to transmit data for communicating with the user terminal to the base stations corresponding to the information indicating the selected base stations. The method of claim 1, The reference signal is a signal comprising a scrambling code for distinguishing the base station and the adjacent base station. The method of claim 1, Wherein the reference signal is a signal including a training sequence for identifying a channel state between the base station receiving communication with the user terminal and the adjacent base station. In the mobile communication system in which the first mobile communication system and the second mobile communication system coexist, a base station for controlling a user terminal existing in a certain area, a user terminal existing in an area occupied by the base station, and a plurality of base stations are controlled. In the method comprising a base station controller, when the user terminal is present in an area where a plurality of base stations are shared, Measuring, by the base station controller, an arrival time for each base station from which a signal transmitted from the user terminal is received by each of the plurality of base stations; Selecting a base station within a guard interval inserted by the base station in order to reduce inter-symbol interference in the first mobile communication scheme by using the arrival time measured for each base station; And transmitting data for communicating with the user terminal to the selected base stations. The method of claim 7, wherein The first mobile communication method is an orthogonal frequency division multiplexing method, and the second mobile communication method is a WCDMA method or a CDMA method is used. The method of claim 7, wherein The reference time is characterized in that the best arrival time of the arrival time measured for each base station. In the mobile communication system in which the first mobile communication system and the second mobile communication system coexist, a base station for controlling a user terminal existing in a certain area, a user terminal existing in an area occupied by the base station, and a plurality of base stations are controlled. An apparatus comprising a base station controller and performing a handover when the user terminal exists in an area where a plurality of base stations are shared, A reception time measuring unit for receiving reference signals including information for identifying a base station from the plurality of base stations and measuring arrival times of the signals transmitted from the plurality of base stations for each base station; The base station selector selects the base stations within the guard interval inserted to reduce the inter-symbol interference in the first mobile communication scheme by using the arrival time measured by each base station. Said device. The method of claim 10, wherein the base station selection unit Delay time calculator for calculating the delay time for each base station using the reference time, A comparator for comparing whether the delay time for each base station exists within the guard period; And a base station selector configured to select a base station having a delay time for each base station within the guard period. The method of claim 11, wherein the reception time measuring device A scrambling code identification information corresponding to the valid correlation energy is obtained by obtaining a correlation energy by using a correlation value corresponding to a scrambling code of each of the reference signals transmitted from the base station and the neighboring base stations, and selecting valid values from the correlation energy. With a scrambling code selector for outputting And an arrival time selector which receives scrambling code identification information corresponding to the valid correlation energy from the scrambling code selector and selects an arrival time of the reference signal transmitted from a corresponding base station and an adjacent base station. In a mobile communication system in which orthogonal frequency division multiplexing (OFDM) and wideband code division multiple access are coexisting, a base station for a user terminal existing within a certain area, a user terminal existing in an area occupied by the base station, and a plurality of In the apparatus for performing a handover, comprising a base station controller for controlling the number of base stations, when the user terminal is present in an area where a plurality of base stations are shared, A data transmitter for transmitting and receiving a signal according to the orthogonal frequency division multiplexing scheme; And a feedback information (FBI) generator for generating selection information for base stations for communicating with the user terminal.

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