Cell design program and apparatus for optimum arrangement of base station in railroad line

The present invention relates to a cell design program and device for optimally arranging a base station on a railroad track.

In recent years, many passengers in trains have come to send and receive e-mails or contents using terminals (or mobile phones) having a wireless communication function. These terminals communicate with radio base stations located on (or at some distance) the railroad tracks. In general, a base station that can be connected from inside a train is not exclusively installed at a terminal inside a train that runs on a railroad track. That is, the base station realizes communication with all terminals existing in the area covered by the base station.

On the other hand, in the future, due to the diversification of contents or the reduction of communication charges, the number of communication traffic transmitted and received using terminals having a wireless communication function may increase explosively. This also applies to terminals operated by passengers in the train.

<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2004-241799</text></patcit>

<p> In a base station existing outside the train, communication with a terminal in the train needs to be considered separately from a general terminal as a group movement model of traffic because the communication traffic source moves in a group. As for the line quality of terminals in trains, not only the moving speed of trains but also the line quality of terminals in trains fluctuates greatly with time due to changes in connectable base stations. In particular, in a CDMA (Code Division Multiple Access) system, an increase or decrease in the number of terminals also greatly affects the amount of interference.</p><p> For example, in a base station around a station, the amount of interference increases because the number of terminals simultaneously connected to the base station increases during a time zone when there are many users such as when commuting. In addition, the number of simultaneously connected terminals fluctuates sharply depending on the arrival and departure of trains. On the other hand, in a base station installed at a place away from the station, the number of simultaneously connected terminals fluctuates due to the traffic of trains, and the amount of interference also fluctuates greatly. Under such circumstances, it is difficult for the terminals in the train to ensure sufficient line quality with the conventional base station arrangement method, and the base stations that mainly communicate with the terminals in the train are separately railways. It also needs to be placed on the track.</p><p> Therefore, the present invention considers the amount of interference that varies depending on the number of terminals accommodated by each base station, and optimally arranges the base stations on the railroad track so that the line quality for the terminals in the train satisfies the desired value. It is an object of the present invention to provide a cell design program and a device for the purpose.</p>

<p> According to the present invention, a straight line from a predetermined start point to an end point on a railroad track is divided into equally spaced sections i (i = 1 to I), and bases arranged in section j for optimal placement of base stations. A cell design program that causes a computer to execute a computer so that a station determines whether or not to accommodate a terminal existing in a section i (i, j) (= 1,0). As an objective function, a base station Number Σ_{j = 1}^IIn order to minimize f (j), as a constraint condition, the desired wave reception power received from the base station j by one terminal in the train existing in the section i is interfered with by all the base stations with respect to the section i. Calculated using linear programming so that the ratio of the quantity to the sum of the amount of interference by all other terminals in the train in section i is greater than or equal to the minimum line quality Q required by the terminals in the train. It is characterized by having the computer run to have steps to do.</p><p> According to other embodiments of the present invention, the constraints are:<maths num="3"><img file="JP2007074241A_D0001.tif" /></maths>And dist (i) | i-j + 1 | + α (1-f (j)), | ij | α, where Q is the minimum line quality (power vs. noise) required by the terminal in the train. Density ratio), g (i, j) is the propagation loss from the base station located in section j to section i, and p (j) is the propagation loss from the base station located in section j to one terminal. N (k) is the number of simultaneously connected terminals in the section k, N is the number of simultaneously connected terminals in the train, G is the diffusion gain, and dist (i) is the interval. The distance between the terminal in the train existing in i and the base station to be connected, α is the maximum distance between the base station and the terminal, and the molecular formula is that one terminal in the train existing in section i is. , The desired wave reception power received from the base station located in section j, and the denominator left side formula is the sum of the interference power received from the traffic outside the train received by one terminal in the train existing in section i. It is also preferable that the right-hand side equation of the denominator causes the computer to be executed so as to be the sum of the interference power received by one terminal in the train existing in the section i from the traffic of the other terminals in the train.</p><p> Further, according to the present invention, a straight line from a predetermined start point to an end point on a railroad track is divided into equally spaced sections i (i = 1 to I), and the train starts from the start time t = 0 and arrives at the end point. A cell design that causes the computer to execute so as to decide whether or not to place the base station f (j) (= 1,0) in the section i for the optimum placement of the base station, assuming that the vehicle has traveled to t = T. It is a program, and as an objective function, the number of base stations Σ₁^IIn order to minimize f (j), as a constraint condition, the desired wave reception power r (t, i) received by one terminal in the train from the base station in the section i for the time t is set in the section i in the time t. Have the computer run to have steps to calculate using linear programming so that the ratio of interference from base stations other than the base station is greater than or equal to the minimum line quality Q required by the terminals in the train. It is a feature.</p><p> According to another embodiment of the present invention, for the step calculated using the linear programming method, the amount of interference from a base station other than the base station in the section i at time t is determined.<maths num="4"><img file="JP2007074241A_D0002.tif" /></maths>Q'is the minimum line quality (power to noise density ratio) required by the terminals in the train, and n (t, i) is the number of terminals simultaneously connected to the base station in section i for time t. M (t) is the section where the base station to which the terminal in the train is connected exists for time t, and r (t, m (t)) is the section where one terminal in the train is connected for time t. It is the power received from the base station existing in m (t), and the denominator formula is the amount obtained by subtracting the desired wave received power r (t, i) of the terminal from the received power from all the base stations. It is also preferable to run the computer in this way.</p><p> Further, according to another embodiment of the present invention, it is also preferable that the base station is arranged based on the CDMA system.</p><p> Further, according to the present invention, the cell design simulation device equipped with a computer is characterized in that the above-mentioned cell design program is executed by the computer.</p>

<p> According to the present invention, the minimum number of base stations is provided on the railroad track so that the amount of interference that varies depending on the number of terminals accommodated by each base station is taken into consideration and the line quality for the terminals in the train satisfies the desired value. Can be optimally placed.</p><p> According to the present invention, a straight line from a predetermined start point to an end point on a railroad track can be divided into equally spaced sections, and the optimum arrangement of base stations can be derived as a one-dimensional model. By treating it as a one-dimensional model, it can be derived with a relatively small amount of calculation by linear programming without considering complicated and diverse amounts of information.</p>

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

FIG. 1 is a first layout configuration diagram of a base station and a cell.

According to FIG. 1, the train 1 runs on the railroad track 2. A plurality of base stations 3 are arranged around the railroad track 2, and terminals in the train can communicate with these base stations. A straight line from a predetermined start point to an end point on a railroad track is divided into equally spaced sections i (i = 1 to I). According to Fig. 1, it is divided into 18 sections with I = 18. Further, it is assumed that a plurality of base stations for wireless communication of terminals in the traveling train are arranged near the railway line.

Whether or not a base station is arranged in the section j is represented by f (j). At most one base station is placed in one section (f (j) = 1), or no base station is placed (f (j) = 0). According to FIG. 1, base stations are arranged in section 3, section 7, section 12, and section 17, and are as follows. f (3) = f (7) = f (12) = f (17) = 1 f (1) = f (2) = f (4) = f (5) = f (6) = f (8) = f (9) = f (10) = f (11) = f (13) = f (14) = f (15) = f (16) = f (18) = 0

FIG. 2 is an explanatory diagram showing a section i accommodated by a base station arranged in the section j in the present invention.

According to FIG. 2, the horizontal axis represents the section i = 1 to I (I = 18), and the vertical axis represents the section j (j = 3,7,12,17) in which the base station is arranged. The base station located in the section j either accommodates the terminals existing in the section i (h (i, j) = 1) or does not accommodate (h (i, j) = 0). .. According to Fig. 2, it is as follows. The table in Figure 2 is represented as a matrix for solving linear programming. It is assumed that the base station arranged in the section j = 3 accommodates the section i = 1,2,3,4. h (1,3) = h (2,3) = h (3,3) = h (4,3) = 1 The base station located in the section j = 7 is the section i = 5,6,7, Suppose that 8 and 9 are accommodated. h (5,7) = h (6,7) = h (7,7) = h (8,7) = h (9,7) = 1 The base station located in section j = 12 is the section i. = It is assumed that 10,11,12,13,14 are accommodated. h (10,12) = h (11,12) = h (12,12) = h (13,12) = h (14,12) = 1 The base station located in section j = 17 is the section i. = It is assumed that 15,16,17,18 are accommodated. h (15,17) = h (16,17) = h (17,17) = h (18,17) = 1 Other h (i, j) is 0.

FIG. 3 is a first flowchart of the present invention.

(S301) The straight line from the start point to the end point is divided into equally spaced intervals i. The present invention derives the optimum arrangement of base stations for a one-dimensional model.

(S302) Let f (j) = 0 and h (i, j) = 0 for all. (S303) Determine whether to consider existing base stations. By fixing the base stations already arranged in the section j, it is possible to determine only the arrangement of the base stations to be installed separately. (S304) When considering an existing base station, set f (j) = 1 and h (i, j) = 1 for the section of the arranged base station.

(S305) P (j), g (i, j), and n (k) are determined in advance as parameters for solving the linear programming method. g (i, j) is the propagation loss from the base station located in the section j to the section i. p (j) is the transmission power from the base station located in the section j to one terminal. n (k) is the number of simultaneously connected terminals in the interval k.

Once the location of the base station is determined, the propagation loss g (i, j) from that location to the section can be derived by actual measurement or a predetermined calculation formula. The received power received from the base station by the terminal in the train is the transmission power p (j) of the base station located in the section j and the propagation loss g (i) from the section j to the section i where the base station is located. Derived by multiplication with, j).

Further, the number of simultaneously connected terminals in the section k accommodated by the base station is also considered. The number of simultaneously connected terminals affects the amount of interference, and is therefore an important parameter in cell design. For example, in a base station around a station, the amount of interference increases because the number of terminals simultaneously connected to the base station increases during a time zone when there are many users such as when commuting. In addition, the number of simultaneously connected terminals fluctuates sharply depending on the arrival and departure of trains. On the other hand, in a base station installed at a place away from the station, the number of simultaneously connected terminals fluctuates due to the traffic of trains, and the amount of interference also fluctuates greatly. Therefore, the amount of traffic in the section k can be determined by simulation in consideration of the communication traffic in the train, which will increase in the future.

(S306) Solving linear programming, the number of base stations Σ_{j = 1}^IDetermine the section where the base station is placed so that f (j) is minimized. (S307) Finally, f (j) and h (i, j) for the optimum arrangement of base stations on the railway line are derived. The location of the new base station derived by the present invention is intended to accommodate the traffic traffic in the train, which will increase in the future, and therefore is targeted near the railway line.

According to the present invention, it is possible to receive radio waves of a predetermined quality or higher regardless of whether the terminal operated by the user is in the train and the train is in any section. On top of that, the purpose is to minimize the number of base stations to be installed. It is assumed that the terminal uses the nearest base station, and does not use a remote base station. In addition, one terminal communicates with only one base station, and communication with a plurality of base stations at the same time is not considered.

The linear programming method will be described in detail below.

The objective function is determined as follows. Minimize Σ₁^If (j)

The objective function is the number of base stations Σ over the entire railroad track._{j = 1}^IThe purpose is to minimize f (j). For example, according to Fig. 1, the number of base stations is Σ.₁¹⁸With f (j) = 4, the section accommodated by the base station is determined as shown in Fig. 2.

The constraints are as follows. It is determined whether or not the base stations need to be installed so that the number of base stations is the minimum as in the objective function and the line quality of the terminals in the train satisfies the desired value in all sections.<maths num="5"><img file="JP2007074241A_D0003.tif" /></maths>

Q is the minimum line quality (power to noise density ratio) required by terminals in trains. N is the number of simultaneously connected terminals in the train. G is the diffusion gain. dist (i) is the distance between the terminal in the train existing in the section i and the base station connected to it. α is the maximum distance (number of sections) in which the base station and the terminal can be connected. For example, let α = 4.

Σ_{j = 1}^IWhen f (j) 1, it means that there is always one or more base stations. Σ_{j = i-α}^{i + α}h (i, j) = 1 means that at most one base station is installed in one section. h (i, j) f (j) and i-α j i + α mean that only one base station covers one section.

The following molecular formula is the desired wave reception power received by one terminal in the train existing in the section i from the base station arranged in the section j.<maths num="6"><img file="JP2007074241A_D0004.tif" /></maths>

For example, consider the desired wave reception power from a desired base station received by one terminal in a train existing in section i = 2. Assuming α = 4, base stations arranged in the sections j = (2-4) to (2 + 4) = 1 to 6 are targeted. Further, if the base stations arranged in the section 3 accommodate the sections 1 to 4, it will be as follows. h (2,3) = 1 h (2,1) = h (2,2) = h (2,4) = h (2,5) = h (2,6) = 0

Then, the molecular formula is as follows. G · {h (2,1) p (1) g (2,1) + h (2,2) p (2) g (2,2) + h (2,3) p (3) g (2) , 3) + h (2,4) p (4) g (2,4) + h (2,5) p (5) g (2,5) + h (2,6) p (6) g ( 2,6)} = G {h (2,3) p (3) g (2,3)} = G p (3) g (2,3)

p (3) means the transmission power from the base station arranged in the section 3 to one terminal. g (2,3) means the propagation loss between interval 3 and interval 2. Then, p (3) g (2,3) means the desired wave reception power received from the base station arranged in the section 3 by one terminal in the train existing in the section 2.

G means diffusion gain. In the spread coded communication system (CDMA), the spread code does not cause excessive interference. Therefore, by multiplying the received power of one terminal in the train by the diffusion gain G, it is possible to increase the resistance to the interference amount of the denominator and calculate the communication quality of the terminal.

The following denominator left-hand side formula is the sum of the interference power received from the traffic outside the train received by one terminal in the train existing in the section i.<maths num="7"><img file="JP2007074241A_D0005.tif" /></maths>

P (j) g (i, j) in the left-hand side equation of the denominator represents the received power from the base station j in the section i. Assuming α = 4, the interval from k = (3-4) to (3 + 4) = 1 to 7 is the target. Further, if the base stations arranged in the section 3 accommodate the sections 1 to 4, the following is obtained. h (1,3) = h (2,3) = h (3,3) = h (4,3) = 1 h (5,3) = h (6,3) = h (7,3) = 0

Then, the number of terminals connected to the base station at the same time is as follows. h (1,3) n (1) + h (2,3) n (2) + h (3,3) n (3) + h (4,3) n (4) + h (5,3) n (5) + h (6,3) n (6) + h (7,3) n (3) = h (1,3) n (1) + h (2,3) n (2) + h (3,3) n (3) + h (4,3) n (4)

By multiplying the received power from the base station j in the section i by the number of simultaneously connected terminals, the interference power received by the terminals in the train existing in the section i is represented. For example, the received power p (3) g (2,3) from the base station arranged in the section 3 to the section 2 is multiplied. p (3) g (2,3) h (1,3) n (1) + p (3) g (2,3) h (2,3) n (2) + p (3) g (2, 3) h (3,3) n (3) + p (3) g (2,3) h (4,3) n (4)

The right-hand side equation of the denominator is the sum of the interference powers received by one terminal in the train existing in the section i from the traffic of the other terminals in the train.<maths num="8"><img file="JP2007074241A_D0006.tif" /></maths>

N represents the amount of traffic in the train (the number of terminals connected at the same time). N-1 is the amount of traffic in the train with the traffic for the one terminal removed. That is, the amount of interference due to the traffic of other terminals in the train is derived.

Consider interval i = 2. If α = 4, then j = (2-4) ~ (2 + 4) = 1 ~ 6. (N-1) {h (2,1) p (1) g (2,1) + h (2,2) p (2) g (2,2) + h (2,3) p (3) ) g (2,3) + h (2,4) p (4) g (2,4) + h (2,5) p (5) g (2,5) + h (2,6) p ( 6) g (2,6)} = (N-1) {h (2,3) p (3) g (2,3)} = (N-1) p (3) g (2,3) )

dist (i) | i-j + 1 | + α (1-f (j)), | ij | α ignores the nearest base station and communicates with a base station farther away. It means that there is no such thing. For | i-j + 1 |, the section where the base station exists is 1, and the value increases as the distance increases. α (1-f (j)) is 0 if the base station exists, and α if the base station does not exist. The distance between the base station and the terminal is shorter than the maximum connectable distance α.

In the first embodiment described above, the amount of interference that fluctuates according to the number of terminals accommodated by each base station is taken into consideration without considering the traveling time t of the train, and the line quality for the terminals in the train is a desired value. The optimum location of the base station on the railroad track can be derived on a section-by-section basis so as to satisfy the above conditions.

FIG. 4 is a second layout configuration diagram of the base station and the cell.

Compared with FIG. 1, FIG. 4 considers the elapsed time 0 &lt;t &lt;T from the departure time of the train. m (t) represents a section in which a base station with which a terminal in the train can communicate exists at time t.

According to FIG. 4, it is assumed that the train is currently traveling in section 11 at time t. The terminal existing in the train uses the received power r (t, 12) from the base station C arranged in the section 12 at the time t as the desired wave received power. On the other hand, in the terminal, the received power from the base stations A, B and D acts as an interference power.

The interference power from the base station B arranged in the section 7 at time t is the received power r (t, 12) from the base station B and the number of terminals n (t, 7) simultaneously connected to the base station B. Calculated from multiplication with. Further, the interference power from the base station D arranged in the section 17 at time t is the received power r (t, 17) from the base station D and the number of terminals n (t, t, 17) simultaneously connected to the base station D. Calculated from multiplication with 17). Further, the interference power from the base station A arranged in the section 3 at time t is the received power r (t, 3) from the base station A and the number of terminals n (t, t, 3) simultaneously connected to the base station A. Calculated from multiplication with 3).

FIG. 5 is a second flowchart of the present invention.

(S501) The straight line from the start point to the end point is divided into equally spaced intervals i. The present invention derives the optimum arrangement of base stations for a one-dimensional model.

(S502) Set f (i) = 0 for all. (S503) Determine whether to consider existing base stations. By fixing the base stations already arranged in the section i, it is possible to determine only the arrangement of the base stations to be installed separately. (S504) When considering an existing base station, set f (i) = 1 for the section of the arranged base station.

(S505) R (t, i) and n (t, i) are determined in advance as parameters for solving the linear programming method. r (t, i) represents the received power received by one terminal in the train from the base station arranged in the section i at time t. n (t, i) represents the number of terminals connected to the base station arranged in the section i at time t. These parameters may be actual measurement values or simulation values derived from a predetermined calculation formula.

(S506) Solving linear programming, the number of base stations Σ_{j = 1}^IDetermine the section where the base station is placed so as to minimize f (i). (S507) Finally, f (i) for the optimum placement of base stations on the railroad track is derived.

The linear programming method will be described in detail below.

The objective function is determined as follows. Minimize Σ₁^If (i) f (i) = {0,1}, 1 j I

The left-hand side equation of the objective function is the number of base stations Σ over the entire railway line._{j = 1}^IThe purpose is to minimize f (i).

The train starts at the start point and reaches the end point T hours later. The line quality of terminals in trains is expressed as the carrier power (Interference) ratio (C / I value). The constraints are as follows. The necessity of installing base stations is determined so that the number of base stations is the minimum as in the objective function and the line quality of the terminals in the train satisfies the desired value in all sections.

<maths num="9"><img file="JP2007074241A_D0007.tif" /></maths>

Q': Line quality (C / I value) required by the terminal in the train m (t): Section where the base station with which the terminal in the train communicates exists at time t n (t, i): Section at time t Number of terminals to which i base stations are connected at the same time r (t, i): At time t, received power r (t, m (t)): time received by one terminal in the train from the base station in section i At t, the received power received by one terminal in the train from the base station located in the section m (t).

The denominator formula represents the amount of interference from a base station other than the base station that transmits the desired wave at time t.<maths num="10"><img file="JP2007074241A_D0008.tif" /></maths>

The value obtained by multiplying the received power from the base station arranged in the section i to one terminal by the number of terminals simultaneously connected to the base station is defined as the amount of interference from the base station. The denominator left-hand side formula calculates the sum of the amounts of interference from all base stations. f (3) r (t, 3) n (t, 3) + f (7) r (t, 7) n (t, 7) + f (12) r (t, 12) n (t, 12) The + f (17) r (t, 17) n (t, 17) denominator formula is the left-hand side formula of the denominator, which indicates the amount of interference from all base stations, minus the desired wave reception power at time t. The amount of interference from a base station other than the desired base station.

In the second embodiment described above, the traveling time t of the train is taken into consideration, the amount of interference that fluctuates according to the number of terminals accommodated by each base station is taken into consideration, and the line quality for the terminals in the train satisfies the desired value. As described above, the optimum location of the base station on the railway line can be derived on a section-by-section basis.

Finally, the simulation results in the first embodiment described above will be described. Simulations were performed for three patterns under the following conditions. Line length: 5km Section interval: 100m α: 1km p (j): 30dBm 30dBm = 10 logx logx = 30/10 x = 10^30/10= 1000 g (i, j):<maths num="11"><img file="JP2007074241A_D0009.tif" /></maths> G: 20dB Q: 7dB 7dB = 10^0.7=5.012

FIG. 6 shows the simulation results when N = 10 people and n (k) = 2 people. According to Fig. 6, the minimum number of base stations was 26, and the calculation time took 51 minutes.

FIG. 7 shows the simulation results when N = 1 person and n (k) = 2 people. According to Fig. 7, the minimum number of base stations was 10, and the calculation time took 21 minutes.

FIG. 8 shows the simulation results when N = 1, 16 people every n (k) = 1 km, and 0 people (96 people in total) in the other sections. According to Fig. 8, the minimum number of base stations was 11, and the calculation time took 3 minutes.

In Figures 6 to 8, I = 50 section, and * is shown in the section where the base station is located. In addition, --- indicates the range covered by one base station. It can be seen that all q's are 7 dB (5.012) or more, and that the minimum line quality required by the terminals in the train is satisfied in all sections.

According to the various embodiments of the present invention described above, those skilled in the art can easily make various changes, modifications and omissions in the technical idea and the scope of the present invention. The above explanation is just an example and does not attempt to restrict anything. The present invention is limited only to the scope of claims and their equivalents.

<figref num="1">It is a 1st layout block diagram of a base station and a cell.</figref><figref num="2">It is explanatory drawing which shows the section i which the base station arranged in the section j in this invention accommodates.</figref><figref num="3">It is a 1st flowchart in this invention.</figref><figref num="4">It is a 2nd arrangement block diagram of a base station and a cell.</figref><figref num="5">It is a 2nd flowchart in this invention.</figref><figref num="6">It is a simulation result of the first pattern in this invention.</figref><figref num="7">It is a simulation result of the second pattern in this invention.</figref><figref num="8">It is a simulation result of the third pattern in this invention.</figref>

Code description

1 train 2 railroad track 3 base station