Measurement-assisted dynamic frequency-reuse in cellular telecommuncations networks

DESCRIPTION

DYNAMIC FREQUENCY REUSE USING MEASUREMENT IN CELL TELECOMMUNICATION NETWORKS

TECHNICAL FIELD OF THE INVENTION

The invention relates generally to the field of telecommunications without. and, in particular, improvements in frequency reuse in cellular telecommunications.

BACKGROUND

Frequency reuse patterns are cell-based schemes for assigning available frequency channels within a specific cellular telecommunications system. The most basic unit of any frequency reuse pattern is a cell. Each cell within a frequency reuse pattern is assigned a number of frequency channels. A plurality of cells are then joined together and referred to as a cluster and use all available frequency channels for a particular cellular telecommunications system. Cluster groups are then used to provide a cellular coverage area within the cellular telecommunications system and the frequency channels allocated to a cluster.

ΡΕ2501703 are reused in other groupings. The scheme for recycling or reassigning the frequency channels throughout the service coverage area is referred to as a reuse plan. The distance between a first cell using a particular frequency channel within a first cluster and a second cell using the same frequency channel within a second cluster is also known as a reuse distance.

Reuse of the same frequency channels by a different number of cells implies that the cells may undergo co-channel interference. It is therefore desirable that the force received from the service carrier (C) within each cell is higher than the interference level of the total cochannel (J). As a result, the higher the carrier value for interference (C, / J), the better the voice quality. A higher C / I value is obtained partially by controlling the channel reuse distance. The longer the reuse distance between adjacent cells using the same frequency channels, the less cochanal interference created between these cells. The C / I ratio is also related to. a frequency reuse plan (N / F) where N indicates the number of sites included within a single cluster and F indicates the number of frequency groups. For example, the C / I ratio is directly related to the following equation: D_R= (3 * F) ^1/2'R where: D_K is the reuse distance; F is the number of frequency groups; and, R is the radius of a cell. Therefore,

ΡΕ2501703 the higher the F value, the longer the reuse distance. However, it is not always desirable to use a higher F value to increase the C / I ratio. Since the total number of available frequency channels (Γ) is fixed within a particular mobile network, if there are groups F, then each group will contain T / F channels. As a result, a higher frequency group number (F) would result in fewer channels per cell and lower call capacity. In addition, in a cellular packet data system (such as Evolved UTRA) packet transmission takes place via one. channel, where resources are shared by multiple users. This means that a very large number of users may have to compete for limited resources, reducing peak user bitrate and thus increasing packet delay transmission. 0 Increased packet delay is not desirable as it impairs the quality of service.

achieve a link quality value of

For most cell systems, capacity is not a big problem when the system initially goes into operation. Therefore, in order to high C / I and to improve mz, a high frequency (F / F) reuse plan, such as 9/27, is initially used. However, as capacity increases, the cellular telecommunications network has to resort to a smaller frequency reuse plan, such as a 7/21 or 4/12, to allocate more frequency channels per cell. In addition, the success of such systems requires that they be

502501703 Able to offer higher and lower bit rate pie during its initial implementation packet transmission delay.

In cellular communication there are generally two main modes of operation for uplink and downlink duplex transmission: Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD), with their use typically dependent on the frequency band used. . FDD uses paired bandwidth when uplink and downlink transmission occurs at different carrier frequencies. Generally, there is also a fixed relationship between a frequency band used for uplink and downlink transmission. TDD is used in unpaired bands where the common carrier frequency is used for uplink and downlink transmission. A potential advantage with TDD is that frequency bands are used more efficiently. Second, the total available radio resources that are defined in terms of uplink and downlink time slots can be dynamically exchanged. This means that asymmetric traffic between uplink and downlink can be better handled by adjusting uplink and downlink capability (ie, time slots).

tecnicu in a related technical field is disclosed in WO 03/005752 A1, which discloses a

An RNC method for controlling radio resources assigned to communication between a terminal and a radio network by applying spread spectrum and micro diversity, comprising an RNC and fixed transceivers. However, the features that are controlled are the active transceiver sets or the transmitter transmit power in the active sets. They are controlled to optimize the gain of micro diversity. In addition, the need to add or remove transceivers from active arrays or to adapt transmit power levels is assessed based on propagation channel parameter measurements that are used to determine the energy distribution across propagation paths in propagation profiles. . Measurements comprise power measurements made on pilot channels or signals.

Therefore, there is a need in the art for improved methods, and systems for employing such methods, to optimize frequency reuse in cellular communication systems.

To overcome the shortcomings of the prior art, the present invention discloses a method for dynamically distributing resources to a plurality of cell regions in a cellular communication network according to claim 1 and a corresponding first network node according to claim 16. Realization Templates

Models of

Preferred ΡΕ2501703 are disclosed in the appended claims. The new method may be implemented in a conventional radio network resource controller, such as a Radio Network Controller, or other node, in a Global Mobile Communications System (GSM) and Terrestrial Radio Access Network telecommunications network.

Universal Evolved (E-UTRAN). E-UTRAN will use Orthogonal Frequency Division Multiple Access (OFDMA) on downlink and

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<td>operations</td><td>duplexing</td><td>by division</td><td>not have</td><td>npo</td><td>(TDD) and</td>

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<td>c systems</td><td>om OFDMA base</td><td>and SC-FDMA,</td><td>the long</td><td>frog</td><td>of band</td>

The available data is subdivided into several resource blocks or units as defined, for example, in 3GPP TR 25.814:

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At present, a resource block size is 180KHz and 0.5ms in frequency and time domains, respectively. The bandwidth of the globad uplink and uplink transmission can be as large as 20MHz. The principles of the invention, however, are not limited to a particular technology standard, but are adaptable to most conventional wireless network technologies and topologies.

ΡΕ2501703

BRIEF DESCRIPTION OF DRAWINGS

A more complete understanding of the method and apparatus of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an exemplary cell having two frequency reuse regions;

FIG. 2 illustrates a first exemplary dynamic frequency reuse scheme;

FIG. 3 illustrates a second exemplary dynamic frequency reuse scheme;

FIGS. 4-Ά and 4-B illustrate exemplary scenarios for triggering frequency reuse reallocation;

5a and

-B illustrate simple iarioí relocation for r ί G u.

triggering frequency;

FIG. 6 illustrates a first network topology in which the principles of the invention may be implemented;

FIG. 7 illustrates a second network topology in which the principles of the invention may be implemented; and_f

FIG. 8 illustrates an exemplary method for relocating dynamic frequency reuse in accordance with the principles of the invention.

Reuse GG

ΡΕ2501703

DETAILED DESCRIPTION OF DRAWINGS

In a simple scenario, channel sets (ie, carrier frequencies) are assigned to each cell with a certain frequency reuse pattern. In this case, there is no partition within the cell in terms of channel assignment and the assigned carrier frequencies can be used throughout the cell. In another scenario, as illustrated in Figure 1, a cell may be divided into two (or more) regions. In the example illustrated in Figure 1, the two regions are concentric. In the inner region 101 of the cell, the frequency reuse is 1, while in the outer region 102 (region: en of the cell) the frequency reuse is k (k> l). In downlink to a given service, a user equipment (UE; eg, a wireless terminal) requires power transmitted from the lower base station in the interior region compared to that of the exterior (ie cell boundary region) of the cell. According to UE position and mobility profile, the transmitted power of the base station is generally controlled by dynamically compensating for loss due to distance and fading behavior. In uplink, power control can also be used; ie, a UE transmits with lower power when it is near the cell and with higher power when it is in the cell boundary region. The main advantage of this approach is that carriers are used more efficiently and interference at the cell boundary is minimized. In principle, a cell can be divided by

ΡΕ2501703 multiple frequency reuse regions. However, the most common and practical scenario is that of two partitions as illustrated in Figure 1. One problem with conventional frequency reuse schemes is that fixed resource allocation in different reuse regions leads to inefficient resource utilization. This is because charges in different regions (eg, cell interior and cell boundary regions) may vary over time, but resources are not reallocated between different regions on a dynamic basis.

Using two different reuse partitions in a cell significantly reduces inter-cell interference at the cell boundary. There is, however, performance degradation due to fixed resource allocation on different partitions. The present invention recognizes that efficient performance of variable dynamic or semi-dynamic frequency reuse requires measurement reports from radio base stations, or access points, and possibly user terminal measurements. Conventional measurements, such as cell load, transmit power, received power, and Block Error Rate (BLER), however, are not sufficient for a dynamic frequency reuse scheme.

In accordance with the principles of the invention, certain measurements made by radio access points or user terminals are reported to a controller periodically or in response to a radio event.

ΡΕ2501703 default trigger. Based on the reported measurements (eg, resource activity), the controller dynamically distributes resources among differently reused cell regions. The controller can further improve resource allocation in different regions by using other measurements, such as transmitted power statistics above a predefined threshold or channel quality statistics on neighboring cells above a threshold.

Referring now to Figure 2, a first exemplary dynamic frequency reuse scheme is illustrated. In this example, each cell is partitioned into two regions 201, 202 for resource allocation purposes. The cell boundary region 202 of each cell may be defined by any prior art technique, such as those based on the received signal strength or received quality measurement reports measured by a user terminal on a common pilot signal. In this example, allow Ge {Ci, C₂,. . . ,Ç_N} be the group of channels available (eg, frequency carriers / frequency chunks / frequency frequency resource block) that will be assigned by a resource controller 203 to each cell with two partitions; In this example, resource controller 203 is a Radio Network Controller (RNC) in a Global Mobile System (GSM) cellular network. Set G is divided into two subsets of resources: H and S, where set

He {Ci, C₂, ---, Ç_M} is initially assigned to the region of the

ΡΕ2501703 interior cell 201 with reuse-1 and set If {C_K+ i, C_N} is initially assigned to the boundary region of cell 202 with k-reuse. RNC 203 then directs each network node, such as a radio base station, associated with the cell region, or a wireless terminal communicating via said region of the cell for measuring and reporting radio resource related data (211) as mentioned below. The RNC 203 then receives measurement reports from network nodes or wireless terminals of radio resource related data. In response, RNC 203 then dynamically reallocates resource allocation between cell regions as a function of radio resource related data.

<td>r on</td><td>account that</td><td>assignment</td>

<td>regions</td><td>of cells</td><td>Can be</td>

<td>for</td><td>1 channels</td><td>SCIENCE OF SC</td>

r downlink is performed. The interference ratio may be different for uplink channels than for downlink channels. In addition, cell regions other than concentric cells may be an alternative, as illustrated in Figure 3. In the example shown in Figure 3, each cell includes one subregion per neighboring cell, and S is divided into a 3-reuse with Sl, S2 and S3. However, only one of the sets S is used in adjacent areas of surrounding cells to achieve lower uplink interference for the other two sets.

ΡΕ2501703

In order to dynamically exchange radio resources between different cell regions, the radio access point (eg, radio base station) associated with the cell, and / or a wireless terminal communicating through the cell, makes certain measurements. radio resource related data that is reported to a radio network resource controller. Radio resource related data may be: (1) resource activity per channel, where resource activity per channel is defined as the ratio of time over which a channel is programmed for the measurement period; (2) Channel group aggregate resource activity, where channel group aggregate resource activity is defined as the average or xth percentile of resource activity for all channels in a group over a measurement period ; (3) the number of transmitted power samples exceeding a limit over a measurement period; and (4) channel quality samples per channel in a region of the neighboring cell that exceeds a quality limit over a measurement period.

For resource activity by channel data, the

<td>controller</td><td>in</td><td>feature of</td><td>T-cd-G</td><td>radio directs a point</td>

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<td>appeal by</td><td>Cc</td><td>mal (μ) in</td><td>C 3. ó â</td><td>. region of the cell where the</td>

channel resource activity (μ) is defined as the ratio of time over which a channel (eg, time-frequency resource block, frequency chunk) is programmed (T_s) for the measurement time period (T_ia). 0 measurement period I_1S can be set by the resource controller of the

ΡΕ2501703 radio network or may be a default value. 0 time during which a channel is programmed T_s is measured at the radio access point by a programmer. The radio access point can measure the resource activity (μ) of all channels used in both downlink and uplink. The radio network resource controller may specify a number of parameters and events for the radio access point for the purpose of activity measurement reports eg the radio access point reports resource activity (μ certain threshold (μ> χι ); report ati¹ is below a certain limit (μ <χ2); or report resource activity (μ) on carriers / fuses whose quality is above a minimum signal quality level (γ_{! ΕΐΩ}) over time T1, the parameters x₂, x₂,

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<td>lade</td><td>in</td><td>resource</td><td>(μ)</td><td>if</td>

and Ti can be set by the radio network resource controller or can be default values ​​used by the radio access point. Using the same principles as noted above, the radio network resource controller may also request a radio access point to report aggregate resource activity by channel group. This indicates the overall activity of the K channels (K> 1). A channel group is one. set of at least two or more contiguous or non-contiguous channels in the frequency domain. A group may also comprise all channels used in a region of the cell; In this embodiment, the measurement would describe the state of global resource utilization of several or all channels in a region of the cell. THE

ΡΕ2501703 main advantage of poa aggregate resource activity

<td>group of</td><td>channel</td><td>is that requires</td><td>smaller</td><td>overload</td><td>in</td>

<td>signal</td><td>ux</td><td colspan="2">channel programming</td><td>(eg, block</td><td>in</td>

<td>feature of</td><td>time-</td><td>frequency, piece)</td><td>for</td><td>the users</td><td>S Θ</td>

<td>fulfilled</td><td>for one</td><td>programmer what</td><td>al es</td><td>it's located</td><td>at</td>

base station. Therefore, the base station can easily measure resource activity on both uplink and downlink channels and report the results to the network controller. The radio access point report corresponds to one resource activity per channel resource identification (ID) to the radio network resource controller. Similarly, the radio access point reports channel resource aggregate resource activity and a corresponding resource group identification (GID) or region ID to the radio network resource controller. Measurement reporting can either be triggered by an event, where an event is specified by system parameters, or it can be periodic. The event triggering approach reduces signaling overheads between the radio access point and the radio network resource controller. Based on resource activity reports, the radio network resource controller can then reallocate channels in different cell regions.

For transmitted power samples that exceed a limit over a data measurement period, the radio network resource controller directs a radio access point or wireless terminal to measure and

ΡΕ2501703 report the number of transmitted power samples that are above a certain threshold, measured per channel, over a measurement period (T_1B). Measurement is performed by a wireless terminal for uplink transmission power statistics and a radio access point for uplink transmission power statistics. In either case, the radio network resource controller sets the power limit and measurement period. Sample data of transmitted power may also be aggregated, in which case power statistics are collected for all channels used in a cell region during the measurement period. A wireless terminal will report this measurement only for channels allocated to it, while a radio access point can collect power statistics for all downlink channels.

For channel quality samples, per channel in a neighboring cell region that exceeds a quality limit over a measurement period, the radio network resource controller directs a wireless terminal to measure and report the number of samples. channel quality that are above a certain threshold, measured per channel in a neighboring cell over a measurement period (T_m). Criteria for calculating channel quality may be based on the total power received on the channel, the carrier-to-interference ratio (CIR); and, received signal strength indication (RSSI), radio link level block error rate (BLER), packet loss rate, etc. 0

ΡΕ2501703 radio network resource controller specifies boundaries, measurement period, and neighboring cells. Channel quality sample data can also be aggregated, in which case channel quality statistics are collected for all channels used in a neighboring cell during the measurement period. The measurement is performed by a wireless terminal for uplink channels and a radio access point for uplink channels.

Several algorithms are known in the prior art that can be used by a radio network resource controller to reallocate resources as a function of radio resource related data included in measurement reports in accordance with the principles of the invention. Measurements can be used to assist the

<td>controller</td><td>of r «</td><td>course of</td><td>network</td><td>radio on</td><td>assignment</td>

<td>dynamic, or</td><td>semi-</td><td>dynamics.</td><td>of channels</td><td>in regions</td><td>of cells</td>

<td>many different.</td><td>The</td><td>resources</td><td colspan="2">assigned may</td><td>so be</td>

<td>used</td><td>fur</td><td colspan="2">programmer for</td><td>the region</td><td>of the cell</td>

<td>corresponden</td><td>you.</td><td></td><td></td><td></td><td></td>

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<td colspan="2">p 9 X. ' 9 ΓΘ 3. Χ. OC 3 Ç 3 O</td><td>from reut</td><td>ili zation</td><td colspan="2">frequency by</td>

triggering. As illustrated in these figures, channel resource activity reports (μ) indicate to the radio network resource controller that there is an overload situation in the outer cell region (4-A) in the inner cell region (4- B). 0 controller

The ΡΕ2501703 radio network feature can then dynamically reallocate radio resources between these cell regions to balance the load.

Figures 5-A and 5-B illustrate additional exemplary scenarios for triggering frequency reuse reallocation. As illustrated in these figures, if resource activity is high (5-A) or reduced (5-B) in both the cell interior and cell exterior regions, the radio network resource controller can still reallocate resources. between regions of different cells. In such cases, carrier reassignment may, for example, be based on the quality level. For example, the carrier whose quality is above a certain limit (γι) or below another limit (γ₂) can be assigned to the cell boundary region, or vice versa. The γ parameters₂ and γ₂ can be set either by the radio network resource controller or they can have default parameters.

Figure 6 illustrates a first network topology in which the principles of the invention may be implemented. In this embodiment, the radio access network architecture is characterized by a central radio network resource controller, such as a Radio Network Controller (RNC) 603 in a Global System for Mobile Communications (GSM) network. ), which controls a plurality of radio access points 601, such as

ΡΕ2501703 as GSM Radio Base Stations (RBS). In principle, however, the principles of the invention may also be implemented in a distributed architecture without a central controller, wherein one or more nodes function as the radio network resource controller; Such a network is illustrated in Figure 7. In this embodiment, measurements are exchanged directly between the radio access points. Measurements can also be exchanged between radio access points via wireless terminals (not shown) by measuring:

for all

In such embodiments, reports from a radio access point may be broadcast wirelessly or directly transmitted to one or more specific terminals. Wireless terminals can then pass this information to other neighboring radio access points or to other wireless terminals in a neighboring cell, which can then link to their own wireless access points.

The wireless access points that mutually support different cells.

may thus decide to be allocated in regions of

Finally, reference is made to Figure 8, which summarizes the exemplary method described here for relocating

<td>reuse</td><td>in</td><td colspan="2">frequency</td><td>dynamics.</td><td>In step 8 01.,</td><td>one</td>

<td>controller</td><td>in</td><td>resource</td><td>gives</td><td>network</td><td>rdirect</td><td>one</td>

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or a wireless terminal communicating through the first region of the cell to measure and report radio resource related data. Related data

Recurso2501703; radio resources are selected from the grur ryi .e consists of: (1) resource activity by channel, where resource activity by channel is defined as the ratio over which channel is projected and measurement period; (2) aggregate resource activity by channel group is defined as the average or xth percentile of resource activity for all channels in a group over a measurement period; (3) the number of transmitted power samples exceeding one limit over one. measurement period; and (4) channel quality samples per channel in a neighboring cell region that exceed a quality limit over a measurement period. Then, at step 802, the radio network resource controller receives at least one measurement report of the radio resource related data. At step 803, the radio network resource controller, as a function of the radio resource related data in the first cell region, dynamically reallocates the resource distribution between the first cell region and at least one second cell region.

Uplink and downlink cell regions are not necessarily equal in size. Also, depending on the type of services in operation, the traffic load may be asymmetric in both uplink and downlink directions. In FDD mode, measurements are performed independently on the uplink and downlink radio resources. This means that in FDD the mitigation of

ΡΕ2501703 interference based on measurements shall be made independently of uplink and downlink. In TDD mode, separate measurements must also be made on uplink and downlink radio resources (ie, on uplink and downlink periods). But since radio resources (time slots) are shared between uplink and downlink, interference mitigation will require efficient and dynamic coordination between time domain uplink and uplink channel allocation in the step 803 (ie, increase uplink and decrease downlink times, or vice versa).

Good, M