KR20070077579A - Apparatus and method for allocating of preamble pseudo noise code in broadband wireless communication system - Google Patents

Abstract

An apparatus and a method for allocating a preamble PN(Pseudo Noise) code in a broadband wireless communication system are provided to allocate a preamble PN code in consideration of allocation of an ID cell and a segment number together. A proximity determining unit(101) calculates proximity between all the base stations. A parameter repeated cost determining unit(103) determines an allocation priority level of each parameter constituting a PN code, and determines a cost when respective parameters of base stations are repeated according to the determined priority level. A parameter allocation cost calculating unit(105) selects a base station to which a PN code is to be allocated according to a current allocation state, and calculates an allocation cost with respect to the PN code of the selected base station by using the calculated proximity and the cost. A parameter allocating unit(107) allocates a PN code incurring a minimum allocation cost among the calculated allocation costs to the selected base station.

Description

Apparatus and method for allocating a preamble pseudo noise code in a broadband wireless communication system {APPARATUS AND METHOD FOR ALLOCATING OF PREAMBLE PSEUDO NOISE CODE IN BROADBAND WIRELESS COMMUNICATION SYSTEM}

1 is a block diagram showing an apparatus for allocation of a preamble pseudo noise code in a broadband wireless communication system according to the present invention; and

2 is a flowchart illustrating a procedure of a method for assigning a preamble pseudo noise code in a broadband wireless communication system according to an exemplary embodiment of the present invention.

The present invention relates to a wideband wireless communication system, and more particularly, to an apparatus and method for allocating a preamble pseudo noise code for identifying a base station.

The IEEE 802.16e system basically adopts a cellular method, and supports the frequency reuse factor 1 so that the same frequency can be used between adjacent cells. Accordingly, the terminal in the system should be able to distinguish between the base station to which it belongs and the adjacent base station among the base stations using the same frequency. To this end, each base station carries a Pseudo Noise code (hereinafter referred to as a 'PN code') unique to the base station in a preamble, which is the first symbol of every frame transmitted to the terminal.

The PN code is used for the transmission of system parameters as well as the division of the base station. Upon receiving the PN code, the terminal interprets the PN code to extract a parameter of the base station, that is, an ID cell (hereinafter referred to as IDcell) and a segment number. Here, the IDcell is a parameter used for subchannel permutation and randomization of modulation, and the segment number is used for frequency allocation of a preamble and randomization of modulation. Is a parameter.

There are 114 preamble PN codes defined in the IEEE 802.16e system standard. Each code has a code index of 0 to 113, and also has the IDcell and the segment number. Therefore, the terminal can determine the code index, IDcell, segment number of the base station by analyzing the preamble PN code. Here, the IDcell has 32 values of 0 to 31, and the segment number has 3 values of 0 to 2. Therefore, not all codes can have unique (IDcell, segment number) combinations. Only codes 0 through 95 of the 114 codes have unique (IDcell, segment number) combinations. Code 113 ~ overlaps existing code (IDcell, segment number) combination.

Meanwhile, when the code index, IDcell, and segment number, which are three components of the preamble PN code, are overlapped in adjacent cells, the following problem may occur.

First, when the code index is duplicated in an adjacent cell, when the same preamble PN code is used in two or more base stations located in close proximity, the terminal cannot distinguish the base station to which it belongs, and the terminal If the base station cannot be identified, all data communication between the terminal and the base station is impossible. Therefore, one base station must use a preamble PN code having a code index different from that of neighboring base stations.

In addition, the same IDcell may be used between base stations using different PN codes. For example, codes 0, 32, 64, and 96 in Table 309 of the IEEE 802.16e draft are all equal to 0 in IDcell. The IDcell is used for modulation randomization and subchannel exchange, and the problems that may occur when the IDcell is used in adjacent cells for each use are as follows.

First, the modulation randomization, the modulation of the base station is randomized by a unique pseudo-random bit sequence (hereinafter referred to as "PRBS") of the base station. Here, the initialization vector of the PRBS may be composed of 11 bits, for example, as shown below.

b0∼b4: Downlink-Partial Usage of Sub-Channels

                  : In the area below called 'PUSC', the IDcell or PermBase

                  Least Significant Bit (hereinafter referred to as 'LSB')

                  Called)

         Uplink-IDcell's 5-Bit LSB

b5 ～ b6: Downlink-Segment Number + 1

         Uplink-0b11, i.e. all bits are 1

b7-b10: Downlink-0b1111, that is, all bits are 1

                 Uplink-4 bit LSB of frame number

In the case of the downlink, since there are 32 PermBase or IDcells and three segment numbers, 96 initialization vectors are generated. In the case of the uplink, the initialization vector is generated by IDcell and frame number. When these frame numbers are synchronized, 32 initialization vectors are generated. That is, the number of PRBSs that can be generated in the uplink is 32, and therefore, the probability that two or more base stations in the adjacent distance perform the same randomization is about three times higher than in the case of the downlink. When the two or more base stations in the near distance have the same randomization, constellation mapping between the base stations is the same. As such, if the constellation mapping between the base stations is the same, the terminal cannot distinguish which of the received signals is its own signal and which is interference, which causes a serious failure in demodulation, for example, a pilot ( Estimation performance of the pilot can be greatly degraded. In addition, the base station can not distinguish between the signal of the terminal belonging to itself and the signal of the terminal belonging to the neighboring base station. Therefore, it is preferable that one base station uses an IDcell different from the neighboring base station.

Next, referring to the subchannel exchange, the subchannel of the IEEE 802.16e system is configured by a complex exchange rule to minimize interference between the subchannels in an adjacent base station, and a parameter for distinguishing the subchannel exchange is PermBase. to be. In other words, if the PermBase is the same between base stations, since the same subchannel exchange is applied, interference between subchannels increases, thereby increasing the error of the subchannels. Here, the IDcell is obliged to be used as a PermBase of the first PUSC area, and may be used as the PermBase in other areas depending on the operation method.

In addition, the same segment number may be used between base stations using different PN codes. For example, codes 0 through 31, 96, 99, 102, 105, 108, and 111 in Table 309 of the IEEE 802.16e draft all have the segment number 0. same. The segment number is used for modulation randomization together with the IDcell in downlink, and when the segment number is overlapped in an adjacent base station, the number of cases of the randomization is reduced to 32.

As described above, since various problems occur when PN codes overlap between base stations in the IEEE 802.16e system, the allocation of the preamble PN codes may significantly affect the performance of the system. However, there is no specific allocation method of the preamble PN code. Accordingly, there is a need for a preamble PN code allocation method that is suitable for the characteristics of the IEEE 802.16e system.

An object of the present invention is to provide an apparatus and method for the assignment of a preamble pseudo noise code in a broadband wireless communication system.

Another object of the present invention is to provide an apparatus and method for differently assigning a preamble pseudo noise code between base stations in close proximity in a broadband wireless communication system.

Another object of the present invention is to provide an apparatus and method for allocating a preamble pseudo noise code in consideration of the allocation of an IDcell and a segment number in a broadband wireless communication system.

Another object of the present invention is to provide an apparatus and method for allocating a preamble pseudo noise code used for identifying a base station in a broadband wireless communication system to a base station in consideration of priority of each parameter and proximity between base stations.

According to an exemplary embodiment of the present invention, a method for allocating a preamble pseudo noise code in a broadband wireless communication system includes a pseudo noise code (hereinafter referred to as a 'PN code') in the system. Check whether there is an assigned base station, and when there is a base station to which the PN code is assigned, select one of the base stations adjacent to the base station, and when there is no base station to which the PN code is assigned, a base station in the system Selecting one of the base stations, calculating an allocation cost for a predetermined number of PN codes of the selected base station, and selecting a PN code having a minimum allocation cost among the calculated allocation costs. It characterized in that it comprises a process for assigning.

According to an embodiment of the present invention, an apparatus for allocating a preamble pseudo noise code in a broadband wireless communication system includes: a proximity calculation unit for calculating proximity between all base stations and a pseudo noise code; (Pseudo Noise code: hereinafter referred to as 'PN code') Determining the priority of allocation between the parameters constituting, the parameter overlapping cost determining unit for determining the cost when each parameter overlaps between base stations according to the priority determined above And selecting a base station to which a PN code is to be allocated according to a current allocation state, and assigning the PN code of the selected base station by using a cost of overlapping all the calculated base stations and the respective parameters between the determined base stations. A parameter allocation cost calculation unit for calculating a cost, and a PN code which takes the minimum allocation cost among the calculated allocation costs It characterized in that it comprises a parameter assignment unit for assigning to the selected base station.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, an apparatus and method for allocating a preamble pseudo noise code in a broadband wireless communication system will be described.

1 is a block diagram illustrating an apparatus for assigning a preamble pseudo noise code in a broadband wireless communication system according to the present invention. The apparatus for allocating the preamble pseudo noise code includes an adjacent base station determining unit 101, a parameter overlapping cost determining unit 103, a parameter allocation cost calculating unit 105, a parameter allocation unit 107, and a current allocation state storage. It comprises a unit 109.

Referring to FIG. 1, the proximity determining unit 101 calculates proximity of all base station-base station pairs. Here, the adjacency may be calculated in various ways. For example, when using a network planning tool, the total amount of interference that the base station j has on the base station i may be defined as the proximity of the base station j and the base station i. In addition, when there is only distance information between base stations, a path loss value between base station i and base station j may be defined as the proximity.

The parameter overlapping cost determining unit 103 determines the priority of allocation among the parameters constituting the PN code, determines the cost of overlapping each parameter between base stations according to the determined priority, and determines the determination result. The parameter allocation cost calculation unit 105 outputs the result. Here, the parameters constituting the PN code may be a PN code index, an IDcell, and a segment number, and the priority between the parameters may be determined by PN code index> IDcell> segment number. At this time, the cost when each parameter is duplicated between the base stations, that is, the cost (C1) when the PN code index is duplicated between the base stations, the cost (C2) when the IDcell is duplicated between the base stations and the segment number between the base stations The cost C3 when duplicated may be determined by the size of C1> C2> C3 according to the allocation priority between the parameters.

The parameter allocation cost calculator 105 selects a base station to which a PN code is to be allocated according to a current allocation state input from the current allocation state storage unit 109, and allocates the PN codes 0 to 113 of the selected base station. Calculate the cost. In this case, the allocation cost for the PN codes 0 to 113 is determined by the proximity of all base station-base station pairs calculated by the inter-base station proximity determining unit 101 and the parameter overlapping cost determining unit 103. The calculation is based on the cost of overlapping each parameter between the determined base stations.

The parameter allocator 107 assigns a PN code having a minimum allocation cost among the PN codes to the selected base station, and outputs the allocation result to the current allocation state storage unit 109.

The current allocation state storage unit 109 stores the parameter allocation result input from the parameter allocation unit 107, and outputs the stored result to the parameter allocation cost calculation unit 105.

2 is a flowchart illustrating a procedure of a method for allocating a preamble pseudo noise code in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the preamble pseudo noise code allocation apparatus determines allocation priority between parameters constituting the PN code in step 201, and determines the cost of overlapping each parameter between base stations according to the determined priority. do.

Here, the parameters constituting the PN code are a PN code index, an IDcell, and a segment number. The first purpose of the PN code is to classify base stations, and since the communication with the base station is impossible when the terminal cannot distinguish the base stations, the parameter having the highest allocation priority is the code index. In addition, when the modulation is randomized, the IDcell is used in both the downlink and the uplink, whereas the segment number is used only in the downlink, and the IDcell is used in the subchannel exchange. The IDcell has a high priority. In addition, since the segment number is only three of 0, 1, and 2, there is a high possibility of overlapping, and therefore, duplication of the IDcell should be prevented. Accordingly, the priority of the allocation between parameters may be determined by PN code index> IDcell> segment number.

In addition, the overlapping cost of the parameters is the cost when the PN code index is duplicated between the base stations (hereinafter referred to as 'C1'), the cost when the IDcell is duplicated between the base stations (hereinafter referred to as 'C2'), between the base stations It can be defined as the cost (hereinafter, referred to as 'C3') when the segment number is overlapped, and the defined costs can be determined by the size of C1> C2> C3 according to the determined priority.

In operation 203, the preamble pseudo noise code allocation apparatus calculates proximity of all base station-base station pairs. When the proximity of the base station j is defined as P _ij from the standpoint of the base station i, the P _ij may be calculated in various ways. For example, when using a network planning tool, the total amount of interference that base station j has on base station i may be defined as P _ij . If only distance information between base stations exists, base station i and base station A path loss value between j may be defined as P _ij .

In operation 205, the preamble pseudo noise code assignment apparatus checks whether there is a base station to which a PN code is assigned in the system. If there is no base station to which a PN code is currently assigned in the system, the preamble pseudo noise code assignment apparatus randomly selects one base station among the base stations in the system in step 207. When there is a base station to which a PN code is currently assigned in the system, the preamble pseudo noise code assignment apparatus randomly selects one base station adjacent to the base station to which the PN code is assigned among the base stations in the system in step 209.

In operation 211, the preamble pseudo noise code allocation apparatus calculates an allocation cost for PN codes 0 to 113 of the selected base station. In this case, the allocation cost for the PN codes 0 to 113 is calculated on the basis of the calculated proximity of all the base station-base station pairs and the cost when each parameter between the determined base stations overlaps. Here, when there are N base stations in the system, the equation for obtaining the allocation cost C _i ^x for the preamble PN code x of the base station i may be expressed as Equation 1 below.

Here, x has a value of 0 to 113.

In operation 213, the preamble pseudo noise code allocation apparatus selects and assigns a PN code having the minimum allocation cost among the PN codes to the base station. Here, when there are a plurality of PN codes having the same price, one of the codes is randomly selected and assigned to the base station.

In operation 215, the preamble pseudo noise code assignment apparatus checks whether a base station to which the PN code should be allocated remains in the system. When there is a base station to which the PN code is to be allocated, the preamble pseudo noise code allocation apparatus returns to step 209 to randomly select one of the base station to which the PN code is assigned and the adjacent base station. When there is no base station to which the PN code should be allocated, the preamble pseudo noise code assignment apparatus terminates the PN code assignment algorithm according to the present invention.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the present invention assigns a preamble pseudo noise code used for classification of base stations in a broadband wireless communication system to the base station in consideration of the priority of each parameter and the proximity between the base stations. There is an advantage to improve the problem that can not be distinguished, and to prevent the increase of the demodulation error.

Claims (11)

A method for allocating a preamble pseudo noise code in a broadband wireless communication system, If there is a base station assigned a pseudo noise code (hereinafter referred to as a 'PN code') in the system, and if there is a base station to which the PN code is assigned, one of the base stations adjacent to the base station is checked. Selecting, when there is no base station to which the PN code is assigned, selecting one of the base stations in the system; Calculating an allocation cost for a predetermined number of PN codes of the selected base station; And selecting a PN code having a minimum allocation cost among the calculated allocation costs and allocating the PN code to the base station. The method of claim 1, The predetermined number of PN codes is characterized in that the 0 to 113 114 PN codes. The method of claim 1, Determining an allocation priority between parameters constituting the PN code and determining the cost of overlapping each parameter between base stations according to the determined priority; The method of claim 1 further comprising the step of calculating the proximity (Proximity) between all base stations. The method of claim 3, wherein The allocation priority between parameters constituting the PN code is determined by PN code index> IDcell> segment number. The method of claim 4, wherein The cost of overlapping each parameter between base stations is the cost of overlapping PN code indexes between base stations> the cost of overlapping IDcells between base stations> the cost of overlapping segment numbers between base stations. How to determine the size of. The method of claim 3, wherein Proximity between the base stations is calculated as the total amount of interference between base stations using a network planning tool (Network planning tool).  The method of claim 3, wherein The proximity between the base stations (Proximity) is characterized in that to calculate the path loss value (path loss) between base stations using the distance information between base stations. The method of claim 3, wherein The allocation cost for the PN code of the selected base station is calculated using the cost of overlapping between the calculated base station and the respective parameters between the determined base station. The method of claim 8, The equation for calculating the allocation cost for the PN code of the selected base station is represented by the following Equation 2.

Here, C _i ^x denotes an allocation cost for the preamble PN code x of the base station i when there are N base stations in the system, and P _ik denotes the proximity of the base station k in the position of the base station i. In addition, the C ₁ means the cost when the PN code index is duplicated between the base stations, the C ₂ is the cost when the IDcell is duplicated between the base stations, the C ₃ is the segment number (segment number) between the base stations ) Is the cost of overlapping. An apparatus for allocating a preamble pseudo noise code in a broadband wireless communication system, Proximity calculation unit for calculating the proximity between all base stations, Determination of allocation priority between parameters constituting a pseudo noise code (hereinafter referred to as 'PN code'), and parameter duplication determining the cost when each parameter is duplicated between base stations according to the determined priority. With a cost determination department, The base station to which the PN code is to be allocated is selected according to the current allocation state, and the allocation cost for the PN code of the selected base station is determined using the cost of overlapping all calculated base stations and the respective parameters between the determined base stations. A parameter allocation cost calculation unit to calculate, And a parameter allocator for allocating a PN code for the minimum allocation cost among the calculated allocation costs to the selected base station.  The method of claim 10, The parameter allocation cost calculator which selects a base station to which a PN code is to be allocated according to a current allocation state input from a current allocation state storage unit; The parameter allocator for outputting the allocation result to the current allocation state storage unit; And a current allocation state storage unit for storing the parameter allocation result inputted from the parameter allocation unit and outputting the stored result to the parameter allocation cost calculating unit.

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