JP2010541300A - Method for allocating bandwidth from a radio frequency spectrum in a cellular network including a set of cells - Google Patents

Abstract

The method allocates bandwidth from a radio frequency spectrum in a cellular network including a set of cells.
Each cell includes a base station that serves a set of mobile stations in the cell. An area centered on each base station is divided into a central area and a boundary area. Each base station reserves bandwidth for use in the central region according to the inter-cell interference coordination (ICIC) protocol, and uses bandwidth within the boundary region according to the ICIC protocol and the base station cooperation (BSC) protocol. Reserve width. Next, according to the bandwidth reservation, when the mobile station communicates with the base station in the central region and the boundary region, bandwidth is allocated to the mobile station.
[Selection] Figure 1A

Description

  The present invention relates generally to dynamic radio resource allocation in a wireless cellular network, and more particularly to reducing inter-cell interference.

OFDMA
Orthogonal frequency division multiplexing (OFDM) is a modulation technique used in many wireless networks, such as the physical layer (PHY) of networks designed in accordance with the known IEEE 802.11a / g standard and IEEE 802.16 / 16e standard. It is. Orthogonal frequency division multiple access (OFDMA) is a multiple access protocol based on OFDM. In OFDMA, a separate set of orthogonal tones (subchannels or frequencies) and time slots are assigned by a base station (BS) to multiple transceivers or mobile stations (MS) so that multiple transceivers communicate simultaneously. be able to. OFDMA is widely used in many next generation cellular networks such as networked networks based on 3GPP Long Term Evolution (LTE) and IEEE 802.16m standards due to its efficiency and variability in radio resource allocation. Has been adopted.

OFDMA Resource Allocation Radio frequency (RF) can carry information by varying the combination of amplitude, frequency, and phase of radio waves within a frequency band. The use of radio spectrum is regulated through frequency allocation by many government agencies.

  As used and defined herein, bandwidth means a portion of the radio frequency spectrum. For example, IEEE 802.11a uses a bandwidth of 5 GHz U-NII frequency band, which provides 8 non-overlapping channels. IEEE802. g uses the bandwidth of the 2.4 GHz band as in IEEE 802.11b, but uses the same OFDM-based transmission scheme as IEEE 802.11a. IEEE 802.16a has been amended to IEEE 802.16 and uses a bandwidth between 2 GHz and 11 GHz for multipoint communication. IEEE 802.16e uses scalable OFDMA data and supports a channel bandwidth of 1.25 MHz to 20 MHz with up to 2048 subcarriers. IEEE 802.16m is expected to operate in RF bandwidths above 20 MHz.

  Bandwidth and time are two scarce resources in wireless communications, so an efficient allocation method is needed. With the rapid growth of wireless applications and subscriber transceivers, i.e. mobile stations (MS), there is a need for good radio resource management (RRM) methods that can increase network capacity and reduce deployment costs. As a result, developing an efficient radio resource allocation protocol for OFDMA is very important for wireless communications.

  The basic challenge is to allocate limited available RF spectrum bandwidth to a large number of transceivers (also known as users, nodes, or terminals) in a wide geographical area. Usually, base stations allocate resources. In other words, the same frequency spectrum can be used in multiple geographic regions or cells. This necessarily results in inter-cell interference (ICI) when transceivers or mobile stations (MS) in adjacent cells use the same spectrum at the same time. In fact, for wireless cellular networks, ICI has been found to be a major factor limiting performance.

  In order to maximize spectral efficiency, a frequency reuse factor of 1 is used in the OFDMA cell arrangement. That is, the same spectrum is reused simultaneously by the BS and MS. Unfortunately, this high spectral efficiency inevitably results in ICI. Therefore, a good ICI management protocol is needed.

  In the case of a single cell, most conventional allocation methods optimize power or throughput under the assumption that each MS uses a different subchannel to avoid intra-cell interference. That is, all MSs in the cell use separate subcarriers for transmitting and receiving signals. For this reason, interference cannot occur.

  Another important assumption in single cell resource allocation is that the BS obtains the signal to noise ratio (SNR) for the subchannel. In the downlink (DL) channel from the BS to the MS, the SNR is usually estimated by the MS and fed back to the BS. In the uplink channel from the MS to the BS, the BS can directly estimate the SNR based on the signal received from the MS.

  In a multi-cell scenario, the interference may come from BSs and MSs in multiple cells, due to various factors such as interferer distance, location, and occupied channel conditions that are not known prior to resource allocation. Because it relies on, signal to interference noise ratio (SINR) is difficult to obtain. This results in ICI interdependencies and complicates resource allocation problems. Therefore, a practical multi-cell resource allocation method that does not require global and complete knowledge of SINR is desirable.

Inter-cell interference adjustment (ICIC)
Inter-cell interference coordination (ICIC) is a protocol that can effectively reduce ICI in a region relatively far from the BS, that is, a region at a cell boundary. ICIC is achieved by allocating separate channel resources to MSs near cell boundaries that are associated with different cells. Since the boundary MS has a very strong tendency for high ICI, the overall ICI can be significantly reduced by adjusting the channel assignment between the boundary MSs. More specifically, ICIC reduces ICI interference by assigning the same resources to geographically distant MSs, thereby reducing path loss due to interference.

  However, ICIC based solely on avoiding resource collisions for the boundary MS provides only limited performance gains for DL communication. This is because ICIC does not take into account the interference caused by transmission from the BS to the MS in the cell center.

Space division multiple access (SDMA)
Spatial division multiple access (SDMA) provides multi-user channel connections by using multiple-input multiple-output (MIMO) techniques with precoding and multi-user scheduling. SDMA uses spatial information of the location of the MS in the cell. With SDMA, the radiation pattern of a signal obtains the highest gain in a specific direction. This is often referred to as beam forming or beam steering. Beamforming is a signal processing technique for directional signal transmission and reception. Beam forming uses interference to change signal directivity. When transmitting, the beamformer controls the phase and relative amplitude of the signal to produce a pattern of constructive and destructive interference. When receiving, information from different antennas is combined so that the expected radiation pattern is selectively observed.

  A BS that supports SDMA transmits signals simultaneously to multiple mobile stations using the same resource. Since SDMA enables spatial multiplexing, the network capacity can be increased. Nevertheless, ICI remains an important issue even when SDMA is used.

Base station cooperation (BSC)
Base Station Cooperation (BSC) allows multiple BSs to transmit signals simultaneously to a single MS using beamforming while sharing the same resources, ie time and frequency.

  The BSC uses SDMA techniques to allow the BS to transmit signals in coordination with the MS. The BSC is specifically used for a boundary MS that is within the transmission range of multiple BSs. In this case, the interference signal from another BS is now a useful signal part. Thus, BSC has two advantages: spatial diversity and ICI reduction.

Diversity Set Normally, each MS registers and communicates with one BS called an anchor BS or serving BS. However, in some scenarios such as handovers, simultaneous communication with multiple BSs can occur. A diversity set is defined in the IEEE 802.16e standard to serve this purpose. The diversity set keeps track of neighboring BSs that are within communication range of the anchor BS and the MS. Also, diversity set information is maintained and updated in the MS.

Macro diversity handover (MDHO)
During macro diversity handover (MDHO), multiple base stations transmit the same signal to a single MS in the handover (HO) region. Macro diversity increases received signal strength and reduces fading in the HO region. MDHO is used when the MS moves from one cell to another cell through the border region. This transition uses the BS to MS downlink (DL) to cause the BS to send multiple copies of the same information to the MS, thereby performing either RF combining or diversity combining at the MS Is achieved by allowing

  In the uplink from the MS to the BS (UL), the transition may cause two or more BSs to receive the same signal from the MS in the HO region so that the selected diversity uses the “best” uplink. This is achieved by making it possible. MDHO can reduce ICI even when the same resources are used for duplicate signals. That is, MDHO wastes resources. This is because the MS uses resources from more than one cell and this resource is otherwise available for use by other MSs.

  Embodiments of the present invention provide a method for allocating resources in a wireless network that incorporates an interference management protocol, namely inter-cell interference coordination (ICIC) and base station cooperation (BSC).

  The cell area is divided into a cell center region and a cell boundary region. The cell central area is near the base station, and the boundary area is far from the base station. The boundary area is further divided into a set of sectors, eg three. It is assumed that the base station has knowledge of the overall geometry of the area and the location of the mobile station (MS) within the area.

  In the central and boundary areas of the cell, a minimum bandwidth is reserved for bandwidth allocation to the MS. Thus, consuming all of the bandwidth is avoided and the MS is not unnecessarily denied access. The exact amount of bandwidth guaranteed depends on the actual design and can be adjusted accordingly.

  ICIC is used for MS in the central region. Two interference management protocols, ICIC and BSC, are supported for MSs in the border region. A fixed bandwidth is allocated for ICIC and a variable bandwidth is allocated for BSC. The variability in BSC bandwidth can adapt to changes in traffic load, ie the number of MSs being served. Optionally, if it is necessary to switch the BSC bandwidth partially or entirely to the use of ICIC, this can be done.

  However, adaptation in the BSC bandwidth may result in spectral overlap in sectors that are not involved in the same BSC, and thus ICI may occur. However, this effect is minimal in this particular resource allocation protocol due to sector division of the cell boundary region that separates non-BSC associated sectors.

1 is a schematic diagram of a radio resource allocation protocol according to an embodiment of the present invention. FIG. FIG. 6 is a schematic diagram of ICIC spectrum allocation performed in a neighboring cell according to an embodiment of the present invention. FIG. 6 is a schematic diagram of BSC spectrum allocation performed in a neighboring cell according to an embodiment of the present invention. 1 is a schematic diagram of bandwidth reuse design according to an embodiment of the present invention. FIG. FIG. 6 is a schematic diagram of an alternative bandwidth reuse design according to an embodiment of the present invention. FIG. 6 is a schematic diagram of an alternative bandwidth reuse design according to an embodiment of the present invention. 1 is a schematic diagram of a cellular network having two mobile stations and two base stations for an ICIC scenario according to an embodiment of the invention. FIG. 1 is a schematic diagram of a cellular network having two mobile stations and two base stations for the BSC protocol according to an embodiment of the present invention. FIG. FIG. 3 is a schematic diagram of cell division according to an embodiment of the present invention. 5 is a flowchart of a resource allocation method according to an embodiment of the present invention.

Resource Allocation FIG. 1A shows a radio resource allocation structure according to an embodiment of the present invention. FIG. 1A shows seven cells 100 of a cellular network. To simplify the illustration, the serviced area in each cell is shown having a hexagonal shape 100. It is understood that this is an approximation of the cell shape, and other shapes are possible depending on, for example, the geography within the cell, the topology, and a building such as a building.

  A base station 110 exists in the approximate center of each cell. The base station serves a mobile station (MS) 111 in the cell. It is understood that the BSs can coordinate with each other using the network infrastructure 400 or backbone as known in the prior art and as shown in FIG.

  The configuration of FIG. 1A can be generalized to more than eight cells. Here, the frequency reuse factor is 1. That is, each cell uses the entire bandwidth allocated to the network. Regarding cell 1 to cell 7, each cell area is geographically divided into a cell central region (D) 101 and a plurality of cell boundary regions 102.

  As defined herein, a cell area is associated with an entire cell, and a region is a division of the area. In the illustrated embodiment, the cell area is divided into a central region and a plurality of cell boundary regions (eg, three). However, it should be understood that other divisions are possible. In this document, various partitions for bandwidth allocation purposes are effectively applied to base stations and mobile stations in the region.

  Since the cell center region 101 is farther from the neighboring cell, there is less inter-cell interference (ICI) for mobile stations in neighboring cells caused by transmission to mobile stations in the cell central region. In contrast, because cell boundary region 102 touches the boundary region of an adjacent cell, transmission to mobile stations within the boundary region can cause stronger ICI and the transmission can be subject to stronger ICI.

  In other words, resource allocation (to the mobile station) in the border region should be managed more carefully so that ICI is reduced. ICI can be reduced by implementing planning for border areas in combination with ICI management protocols such as ICIC or Base Station Cooperation (BSC).

  Specifically, ICIC achieves by allocating non-overlapping bandwidth resources to adjacent cell boundary regions, eg, A1, A2, and A3; or B1, B6, and B7; or C1, C4, and C5 mobile stations. Is done. FIG. 1B shows non-overlapping resources, and different hatched patterns represent non-overlapping bandwidth allocation.

  In comparison, BSC is achieved by allocating the same bandwidth resources to multiple mobile stations that exist in the neighboring cell boundary region and participate in the same BSC operation. This is illustrated in FIG. 1C. It should be noted that both ICIC and BSC management protocols can be used simultaneously by the radio resource allocation protocol according to the present invention.

Bandwidth Allocation FIGS. 2A-2C illustrate an exemplary bandwidth allocation protocol according to an embodiment of the present invention. As used and defined herein, bandwidth means a portion of the radio frequency spectrum. In these figures, the horizontal axis shows the available bandwidth and the vertical axis shows the central region (D) and the border region (ABC). When describing bandwidth allocation for multiple regions, it is understood that it means that reserved bandwidth is allocated for communication between base stations and mobile stations in each region.

  Initially, during planning, base stations can communicate with each other and determine their geographical relationships and various regions. Bandwidth reservations determined during this planning phase can then be assigned to those MSs when the mobile station later enters and exits various regions.

  In each cell shown in FIG. 2A, the entire available network bandwidth is divided into two parts. The first part is reserved for mobile stations in the cell central area 201 and the second part is reserved for mobile stations in the cell boundary area 202.

  The ratio between these two parts depends on the traffic load and can be adjusted dynamically as the load varies. Here, an equal bandwidth reservation is shown for the cell boundary region and the cell center region such that the ratio is 1: 1. The cell center region uses bandwidth D for all cells. The cell center region is geographically separated so that ICI is not a problem.

  Allocations for mobile stations within the cell boundary region of different cell areas are carefully designed to achieve ICIC or enable BSC or both.

  As shown in FIG. 2A, bandwidth allocation to the cell boundary region according to the present invention allows the use of both protocols, namely ICIC (fixed) 203 and BSC (variable) 204.

  In FIG. 2A, mobile stations within the areas shown in the same column are assigned the same bandwidth. To achieve ICIC 203, mobile stations in adjacent sectors are assigned a separate frequency band to reduce ICI. For example, regions A1 (205), A2 (206), and A3 (207) are physically contiguous regions, and mobile stations in these regions are assigned separate frequency bands. The same is true for regions Bl, B6, B7 and regions Cl, C4, C5.

  To achieve BSC 204, mobile stations in adjacent regions, eg, A1 205, A2 206, A3 207, are assigned the same bandwidth to enable the BSC protocol.

  As shown in FIG. 2A, the size of the assignable frequency band can be dynamically adapted to the traffic load in each different region. In extreme cases where there is no traffic load using BSC, for example, mobile stations in regions Al (251), A2 (252), and A3 (253) may affect other regions as shown in FIG. 2B. It is possible to switch from BSC to ICIC without giving. This variability is highly desirable because the BSC protocol requires multiple antennas, while ICIC does not require multiple antennas. Therefore, in this embodiment, ICIC can be regarded as the main means for interference management, while BSC is an auxiliary means.

  FIG. 2C shows another allocation possibility. The difference from FIG. 2A is in the ICIC bandwidth allocation for the cell boundary region. Specifically, bandwidth is initially allocated to the cell boundary region so that any neighboring cells, eg, cells 1, 2, and 3, have separate bandwidths. By doing so, the mobile stations with the strongest interference, eg, mobile stations in regions A1 271, A2 272, A3 273 communicate on separate frequency bands. Next, any remaining bandwidth is allocated to the cell center area (internal mobile station).

ICIC Scenario FIG. 3 shows a network for an ICI scenario with two BSs 301 and 302 and two MSs 303 and 304. In FIG. 3, one cell boundary MS 303 is in communication with the BS 301 of the MS, and the other cell boundary MS 304 is in communication with the BS 302 of the MS. Due to the proximity of the MSs, interferences 306 and 307 can be caused by the MSs 303 and 304 if they use the same frequency band at the same time. Thus, the ICIC protocol separates these two interfering signals onto different frequency bands so as to minimize their interference.

BSC Scenario FIG. 4 shows a BSC scenario with two MSs and two BSs. In the non-BSC case, the two cell border MSs (403 and 404) communicate individually with their BS (401 and 402, respectively). By using BSC, potentially interfering signals 405-408 are turned into useful signals, thereby reducing ICI by allowing the MS to communicate simultaneously with two BSs.

  The two MS, two BS network shown in FIG. 4 can operate in the same time and frequency resources as long as the base station has multiple antennas that can support BSC operation.

Single Cell Division FIG. 5 shows a single cell area 501 and a cell central region 502 of the cell area. The size of the cell center region 502 affects the bandwidth allocation between the cell center region 201 and the cell boundary region 202 shown in FIG. 2A.

  As shown in FIG. 1A, when the MSs are distributed almost evenly in the cell and each mobile station has a similar traffic load, the bandwidth ratio (BR) of the cell central region 502 to the total network bandwidth is It is proportional to the ratio of the size of 502 to the size of the cell area 501. Some exemplary values r and a and the resulting BR are listed in Table A below.

  The capacity gain for BSC for MS in the cell boundary region increases as r / a increases. 2A, 2B, and 2C use a BR of 0.5, which roughly corresponds to the case where r / a is equal to 2/3.

  FIG. 6 shows the steps of the overall method for reserving and allocating bandwidth in a cellular network.

  During the planning phase, the base station 601 uses the infrastructure 605 to determine the topology of the network.

  The topology is divided into areas for each base station (620), and each area is further broken down into a central area 621 and a boundary area 622. The boundary area can be further divided into sets of sectors.

  Bandwidth for each central region is reserved for use according to the ICIC protocol (630), while the border region reserves bandwidth for use according to the ICIC protocol and the BSC protocol (640). The bandwidth reserved for ICIC is fixed, while the bandwidth reserved for BSC is variable.

  After bandwidth resources 645 are reserved, those bandwidth resources can be allocated to the mobile station as the mobile station 602 enters various areas of the network. Reserved resources 645 can be dynamically updated (660) and reassigned to suit changing traffic loads and network topologies.

  Although the invention has been described by way of examples of preferred embodiments, it is to be understood that various other adaptations and modifications can be made within the spirit and scope of the invention. Accordingly, it is the object of the appended claims to cover all modifications and variations that fall within the true spirit and scope of the invention.

Claims (18)

A method of allocating bandwidth from a radio frequency spectrum in a cellular network including a set of cells, each cell comprising a base station serving a set of mobile stations in the cell;
Dividing an area centered on each base station into a central area and a boundary area;
Reserving bandwidth at each base station for allocation within the central region according to an inter-cell interference coordination protocol;
In each base station, reserving bandwidth for allocation in the boundary region according to the inter-cell interference coordination protocol and the base station cooperation protocol;
Allocating a reserved bandwidth to the mobile station when the mobile station in the central region and the boundary region communicates with the base station, from a radio frequency spectrum in a cellular network including a set of cells How to assign. The method of claim 1, wherein the dividing step uses an infrastructure of the cellular network. The method of claim 1, wherein a bandwidth reserved for the central region and a bandwidth reserved for the border region are separate. The method of claim 1, wherein a bandwidth for the inter-cell interference coordination protocol in the boundary region and a bandwidth for the base station cooperation protocol in the boundary region of the same cell are separate. The method of claim 1, wherein a bandwidth reserved for the central region of a particular cell and a bandwidth reserved for the border region of neighboring cells are separate. The bandwidth reserved for the inter-cell interference coordination protocol in the central region of a particular cell overlaps with the bandwidth reserved for the inter-cell interference coordination protocol in the border region of a neighboring cell. Item 2. The method according to Item 1. The method of claim 1, wherein a bandwidth reserved for the base station cooperation protocol in the boundary region is also used for the inter-cell interference coordination protocol. Further comprising dividing each boundary region into a set of sectors;
Reserving and allocating separate bandwidth for adjacent boundary regions in different cells when the mobile station uses the inter-cell interference coordination protocol;
The method of claim 1, further comprising reserving and allocating the same bandwidth for adjacent boundary regions in different cells when the mobile station uses the base station cooperation protocol. The method of claim 8, wherein the bandwidth reserved for the central region of a particular cell and the bandwidth reserved for the set of sectors of the same cell are separate. 9. The bandwidth reserved for the inter-cell interference coordination protocol for the set of sectors and the bandwidth reserved for the base station cooperation protocol for the set of sectors in the same cell are separate. The method described. The method of claim 8, wherein the bandwidth reserved for the central region and the bandwidth reserved for the set of sectors in the border region of neighboring cells are separate. The bandwidth reserved for the inter-cell interference coordination protocol in the central region overlaps with the bandwidth reserved for the inter-cell interference coordination protocol in the border region of an adjacent cell. Method. The method of claim 8, wherein a bandwidth reserved for the base station cooperation protocol for the set of sectors in the boundary region is also used for the inter-cell interference coordination protocol. The method according to claim 1, wherein a bandwidth reserved for the inter-cell interference coordination protocol is fixed, and a bandwidth reserved for the base station cooperation protocol is variable. The method of claim 1, wherein a ratio of bandwidth reserved for the central region and bandwidth reserved for the border region depends on traffic load. The method of claim 15, wherein the ratio is dynamically adjusted as the traffic load varies. The method according to claim 15, wherein the ratio is determined according to a size of the central region and the boundary region. The method according to claim 1, wherein the mobile station is mobile between the central region and the boundary region of the set of cells, and the assignment is dynamically updated.

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