KR100249333B1 - Communication service providing method and system in coverage hole - Google Patents

Abstract

The system providing communication service to the coverage hole 22 in the DS-CDMA cellular communication system 50 includes an OMC 52 that determines a transmitter in the cells 122-132 adjacent to the coverage hole 22. The OMC 52 places each transmitter 134-144 in the neighbor cells 122-132 into a power on request mode 92. The OMC 52 then selects at least one to increase power to the pilot channel but less than all transmitters 134-144. The selected transmitter (s) is selected based on one or more of the following factors: the unused power level of the transmitter, the disturbance level at the transmitter and the position of the transmitter.

Description

[Name of invention]

Method and system for providing communication service in coverage hall

[Field of Invention]

TECHNICAL FIELD The present invention generally relates to the field of communication systems, and more particularly, to a method and system for providing communication services in a coverage hole.

[Background of invention]

Cellular communication systems are generally designed to have spare parts so that communication services are not lost when a part fails. This margin requires an extra transceiver for every active transceiver, an extra power amplifier for every active amplifier, and an extra controller for every active controller, all of which spare parts significantly increase the manufacturing cost of a cellular communication system. Let's do it. Under current systems, if a transmitter or power amplifier fails, an extra transmitter is used until the failed transmitter is recovered. This margin also increases maintenance and repair costs. Both active and redundant transmitters require periodic calibration and maintenance. If the extra demand in the cellular system is reduced, the business cost of the cellular operator can be significantly reduced.

One concept proposed as a solution in direct sequence code division multiple access (DS-CDMA) cellular communication systems is cell breathing. This cell respiration concept is that when a transmitter (power amplifier) fails in a particular cell, adjacent cells expand to fill the coverage gap. Thus, no extra transmitter or power amplifier is needed. Adjacent cells fill the coverage gap until the failed transmitter (power amplifier) is recovered. This solution increases the interference of adjacent cells until the transmitter is recovered. The simulation shows that adjacent cells expand when the cell transmitter fails, but not enough to eliminate the coverage gap. 1 shows a simulation of a DS-CDMA cellular communication system 10. &Quot; X " 12 is base stations with omni-directional transmitter " o " 14 is an active mobile station (mobile device, subscriber unit). The simulator randomly located the mobile station in the cellular system 10. Line 16 defines a cell boundary and is a line at which the energy per chip Ec, or Ec / Io, divided by the total interference energy Io detected by the mobile station at that point is constant. Cell boundaries 16 overlap to form an area of soft handoff. 2 shows a phenomenon that occurs when a transmitter for the central base station 20 fails. As can be seen in FIG. 2, a coverage gap 22 exists around the central base station 20. There is a coverage gap 22 even when the peripheral cell boundary 16 is expanded.

The obvious solution to the coverage gap 22 left by the failed transmitter is to increase the power of the transmitter of adjacent cells. This solution results in increased self interference from all adjacent cell transmitters and does not fill the coverage gap 12.

Accordingly, what is needed is a method and system that can eliminate the need for redundant transmitters in cellular communication systems by providing communication services in the coverage gap.

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

[Brief Description of Drawings]

1 is a schematic diagram of a direct sequence code division multiple access (DS-CDMA) cellular communication system.

2 is a schematic diagram of a direct sequence code division multiple access (DS-CDMA) cellular communication system in which a transmitter of a central cell has failed.

3 is a block diagram of a cellular communication system.

4 is a chart showing two transmitter power strategies of a DS-CDMA cellular communication system.

5 is a schematic diagram of a direct sequence code division multiple access (DS-CDMA) cellular communication system in which a transmitter of a central cell has failed.

6 is a schematic diagram of a cellular communication system.

7 is a flowchart of a method for providing a communication service in a coverage hall.

8 is a flowchart of another method for providing a communication service in a coverage hall.

9 is a flowchart of another method for providing a communication service in a coverage hall.

10 is a schematic diagram of a direct sequence code division multiple access (DS-CDMA) cellular communication system in which a transmitter of a central cell has failed.

Detailed description of the invention

The present invention provides a method and system for providing communication in a coverage gap in a DS-CDMA cellular communication system. These methods and systems eliminate the need for redundant transmitters, reducing the acquisition and maintenance costs of DS-CDMA cellular communication systems.

3 is a block diagram of a typical cellular communication system 50. The Operation and Maintenance Center (OMC) 52 monitors and controls all points of the cellular communication system. The OMC 52 is connected to another part of the cellular communication system via a switching and control (routing) system 54. The switching and control system 54 is also connected to a public circuit switched telephone network (PSTN) 56 and a plurality of base station controllers (BSC) 58. The BSC 58 has a controller 60 and a number of transcoders (transcoder (XCDR) 62). Each BSC 58 is coupled to a number of base station transmitters (BTS) 64. The BTS 64 is generally located in the center of the cell and corresponds to "X" 12 in FIG. The BTS 64 has a controller 68, a plurality of transceivers (transmitter and receiver 70), a power amplifier (PA) 72, and an antenna 74. The OMC 52 constantly monitors the BTS 64, which constantly reports various information to the OMC 52, including whether the transmitter 70 or the power amplifier 72 has failed.

4 shows two strategies for controlling the power amplifier 72 in a DS-CDMA cellular communication system. The first strategy is called constant power strategy 90. The second strategy is called power on demand strategy (92). The figure shows the total PA power out on the vertical axis. Dotted line 96 represents the maximum power output of the PA. In constant power strategy 90, three components make up the total power used by the PA. The first power group 98 is used in pilot channels, paging channels and sync channels. The second power group 100 is used in the actual traffic channel in use. The third power group 102 is used in the dummy traffic channel. The concept of powering a dummy traffic channel is to provide a "constant" cell boundary. In power on demand strategy 92, no power is used by the dummy traffic channel. FIG. 5 shows the effect of switching from the constant power mode shown in FIG. 2 to the power on demand mode. As can be seen by examining both figures, the coverage hole 22 is reduced but still exists.

6 shows a well-known hexagonal cell and an ideal cellular communication system with a transmitter in the center of the cell. Cell 120 is shown without a transmitter to indicate that the transmitter in cell 120 has failed. Multiple adjacent cells 122-132 having a coverage area adjacent to the coverage area of the failed transmitter have a transmitter (base station, BTS) 134-144. Cells 122 and 128 are considered opposite cells (BTS 134 and 140 are opposite BTS). Thus, cells 124 and 130 are opposing cells and cells 132 and 126 are opposing cells. Using this definition, the solution shown in FIG. 7 for providing a communication service in the coverage gap can be described. The process is initiated at block 200 where it is determined by the OMC that the transmitter has failed. Then, at block 202, the OMC determines the set of cells adjacent to the cell with the failed transmitter and sets the transmitters of all adjacent cells to the power on demand mode. Thereafter, at block 204 these adjacent cells are grouped into opposite pairs. At block 206, the combined interference level for each opposing pair is determined and the opposing pair having the lowest combined interference level is selected. The interference level is determined from the received signal strength indicator (RSSI) at the base stations. The interference level may be chosen to be the mean value of the RSSI or the variance value or other statistical dimension derived from the RSSI. Since the DS-CDMA cellular communication system is its own interference system, RSSI is an indicator of the level of interference in DS-CDMA. Channels of a DS-CDMA system share the same frequency spectrum. In step 208, the power of the pilot channel of the transmitters of the selected opposing pair is increased by 3 dB. The process described in FIG. 7 moves the mobile station in the coverage hole into two cells with the best reception, thus cells that can optimally accommodate more users. This process can provide communication services to the coverage hall because only a selected number of transmitters (cells) increase the pilot channel power. As the power of the pilot channel increases, the range of cells increases. A pilot channel is a channel that a mobile station looks for from its base station to determine if that base station can communicate.

8 is another process for selecting a pair of opposing transmitters to fill a coverage gap. This process selects adjacent transmitters with the highest amount of unused PA power. If the opposing transmitter has enough unused power to increase the pilot power by 3 dB, this transistor pair is selected to fill the coverage gap. The process begins at block 220. At block 222, the process waits until it is determined that the transmitter has failed. Then, at block 224, the OMC determines all adjacent cells of the cell where the transmitter failed. At block 226, the OMC puts all neighboring cells in constant power mode into power on demand mode. Then, at block 228, the OMC selects the adjacent cell (transmitter) with the maximum unused transmitter power. Then, at block 230, the OMC determines whether the cell opposite the selected cell has sufficient power to increase its pilot channel by 3 dB. If the opposing cell has sufficient power to increase the pilot channel by 3 dB, then at block 232, the selected transmitter pair increases the pilot channel's power by 3 dB. If the opposing cell does not have enough power to increase the pilot channel by 3 dB, then at block 234, the OMC determines whether all adjacent cells have been selected. In block 234, if not all cells have been selected, in step 236, the OMC selects the cell with the next maximum unused transmit power. The process then continues at block 230. If all adjacent cells have been selected at block 234, then at block 238 the OMC selects the cell pair with the highest combined unused power. The selected pair of transmitters then increases the power of those pilot channels at block 240.

Another third process is shown in FIG. 9, incorporating the process portions of FIGS. At block 260, once the transmitter fails, at block 262, the OMC determines adjacent cells and sets the transmitters to power on demand mode. Then, at block 264, an adjacent transmitter with the maximum amount of unused transmitter power is selected. Then, at block 266, the OMC determines if the transmitter opposite the selected transmitter has sufficient power to increase the pilot channel by 3 dB. If the transmitter opposite the selected transmitter has sufficient power to increase the pilot channel by 3 dB, then at block 268, the OMC determines whether both the selected transmitter and the opposing transmitter have an interference level below a predetermined threshold. If both the selected transmitter and the counter transmitter have an interference level below a predetermined threshold, then at block 270, the selected transmitter and the counter transmitter increase the pilot channel power by 3 dB. If either of the selected transmitter and the opposing transmitter has an interference level above (or equal to) the predetermined threshold, at block 272, the OMC selects the transmitter with the next maximum unused transmitter power. The process then returns to block 266. If the transmitter opposite the selected transmitter has no power to increase the pilot channel by 3 dB, then at block 274, the OMC determines whether all adjacent transmitters have been selected. If not all adjacent transmitters have been selected at block 274, the process continues at block 272. Once all adjacent transmitters have been selected at block 274, at block 276 the OMC selects the opposing transistor pair with the maximum combined unused power. The process continues at block 270.

10 is a simulation of the process of FIG. As can be seen from the figure, the coverage holes 22, which are evident in FIGS. 2 and 5, are covered. Accordingly, the present invention provides a method and system for providing communication at a coverage hole in a DS-CDMA cellular communication system. The present invention enables cellular operators to reduce their initial capital investment and maintenance costs by eliminating the need for redundant transmitters and power amplifiers.

Although the present invention has been described in connection with specific embodiments, various modifications will be possible to those skilled in the art in light of the above description. For example, although the invention has been described using an omni-directional transmitter, it can be easily modified to operate as a sectorized transmitter. Although the present invention has been described in the context of a DS-CDMA cellular system, it may equally be applied to frequency hopping or spread spectrum cellular systems. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations without departing from the spirit and scope of the appended claims.

Claims (9)

In the method for providing a communication service in a coverage hole, (a) determining a plurality of base stations having coverage areas adjacent to the coverage hole; (b) setting a power amplifier associated with the plurality of base stations adjacent to the coverage hole to a power on demand mode; (c) selecting a selected base station from one of the plurality of base stations with coverage areas adjacent to the coverage hole based on the amount of unused transmitter power; (d) determining whether the opposite base station has a sufficient amount of unused transmitter power; And (e) increasing pilot channel power of the selected base station and the opposite base station when the opposite base station has a sufficient amount of unused transmitter power. The method of claim 1, (f) if the opposite base station does not have the sufficient amount of unused transmitter power, base the other base station from one of the plurality of base stations with coverage areas adjacent to the coverage hole based on the amount of unused transmitter power. Selecting as the selected base station; And (g) repeating step (d). The method of claim 1, wherein step (e) comprises: (e) if the opposing base station has the sufficient amount of unused transmitter power and the interference level of both the selected base station and the opposing base station is below a threshold, Increasing the pilot channel power of the selected base station and the opposing base station. CLAIMS 1. A cellular communication system capable of providing coverage to a coverage hole created by a failure of a transmitter, comprising: a plurality of spread spectrum transmitters; And an Operation and Control Center (OMC) coupled to a plurality of base stations to monitor the plurality of base stations to determine whether any of the plurality of spread spectrum transmitters have failed. Transmit a signal for transitioning any of the adjacent base stations in power from the constant power mode to the power on demand mode, and the OMC determines a combined interference level at all of the plurality of adjacent base stations Means for selecting at least one spread spectrum transmitter from a list having a combined interference level less than a threshold among adjacent base stations of the apparatus, and transmitting a signal to increase power of a pilot channel of selected base stations adjacent to the failed spread spectrum transmitter; And the number of selected base stations is broken spectrum transmission A cellular communication system, characterized in that less than the number of base stations adjacent to the. 5. The cellular communication system of claim 4, wherein the selected base stations are determined before one of the plurality of spread spectrum transmitters fails. 5. The cellular communication system of claim 4, wherein the OMC signals the selected base stations based on the unused power capacity of a power amplifier to increase the power of the corresponding pilot channel. 5. The method of claim 4, wherein the OMC ranks each base station according to unused power amplifier power in the set of adjacent base stations and selects a base station to increase the power of a pilot channel in the set based on the rank of the base stations. Characterized by a cellular communication system. 5. The apparatus of claim 4, wherein the OMC includes means for determining a subset having a combined interference level below a threshold of the set of adjacent base stations and increasing the power of at least one pilot channel of the subset of the set of adjacent base stations. And a cellular communication system. 5. The method of claim 4, wherein (f) if the interference level of either of the selected base station or the opposite base station is above the threshold, the other base station is removed from one of the plurality of base stations with coverage areas adjacent to the coverage hole. Selecting as the selection base station based on the amount of unused transmitter power; And (g) further comprising repeating step (d).