Interference control in a wireless communication system

DESCRIPTION

INTERFERENCE CONTROL IN A WIRELESS COMMUNICATION SYSTEM

BACKGROUND

I. Field

The present disclosure relates generally to communication, and more specifically to the control of interference in a wireless communication system.

II. Background

A wireless multiple access communication system can simultaneously communicate with multiple terminals on direct and reverse connections. The direct link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. Several terminals can simultaneously transmit data on the reverse link and / or receive data on the direct link. This is often achieved by multiplexing the transmissions on each link to be orthogonal to each other in the domain of time, frequency and / or code.

ΡΕ2265073

In the reverse connection, transmissions from terminals communicating with different base stations are typically not orthogonal to each other. Consequently, each terminal can cause interference to other terminals communicating with neighboring base stations and can also receive interference from those other terminals. The performance of each terminal is degraded by interference from the other terminals communicating with other base stations.

There is therefore a need in the art for techniques to mitigate interference in a wireless communication system.

SUMMARY

According to the present invention, a method and apparatus for controlling interference as defined in claims 1 and 10, respectively, are provided. Additional embodiments are claimed in the appended claims.

Techniques for controlling the interference observed by each sector from neighboring sectors in a wireless communication system are described here. A sector m calculates the observed interference from terminals in neighboring sectors and obtains an interference estimate or related measurements. For network-based interference control, sector m generates an intersectoral OSI report

ΡΕ2265073 (IS) based on the interference estimate and sends the OSI IS report to neighboring sectors via a physical link, eg a return transport channel. Sector m also receives OSI IS reports from neighboring sectors and regulates data transmissions to terminals in sector m based on the received OSI IS reports. Sector m can regulate data transmissions through (1) admission control of new terminals for sector m, (2) cancellation of terminals that had already been admitted, (3) programming of terminals in sector m in order to reduce the interference to neighboring sectors, and / or (4) assigning terminals in sector m to traffic channels that cause less interference to neighboring sectors.

Various aspects and embodiments of the invention are described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and nature of the present invention will become more evident from the detailed description presented below when considered together with the drawings in which equal references identify the same elements correspondingly throughout the presentation.

FIG. 1 illustrates a communication system with base stations and terminals.

ΡΕ2265073

FIG. 2 illustrates a process carried out by a sector to control interference.

FIG. 3 illustrates a process performed by an interference control terminal.

FIG. 4 illustrates a process for adjusting the transmission energy in a deterministic manner.

FIG. 5 illustrates a process for adjusting transmission energy in a probabilistic manner.

FIG. 6 illustrates an energy control mechanism suitable for interference control.

FIG. 7 illustrates a block diagram of a terminal and two base stations.

FIG. 8 illustrates an apparatus suitable for interference control.

FIG. 9 illustrates an apparatus suitable for providing interference control.

DETAILED DESCRIPTION serve

The word exemplary is used here to mean as an example, instance, or illustration.

Any realization model or project described here as

ΡΕ2265073 exemplary is not necessarily to be interpreted as preferred or advantageous over other embodiments or projects.

FIG. 1 illustrates a wireless communication system 100 with multiple base stations 110 and multiple terminals 120. A base station is generally a fixed station that communicates with the terminals and can also be called an access point, a Node B, or some other terminology. Each base station 110 provides communication coverage for a particular geographical area 102. The term cell can refer to a base station and / or its coverage area depends on the context in which the term is used. To improve the capacity of the system, the base station coverage area can be divided into multiple smaller areas, eg, three smaller areas 104a, 104b, and 104c. Each smaller area is served by a respective base transmitting subsystem (BTS). The term sector can refer to a BTS and / or its coverage area depending on the context in which the term is used. For a sectored cell, BTSs for all sectors of that cell are typically co-located within the base station for the cell. A system controller 130 connects to base stations 110 and provides coordination and control for these base stations.

A terminal can be fixed or mobile and can also be called a mobile station, a wireless device, user equipment, or any other terminology.

ΡΕ2265073

Each terminal can communicate with zero, one, or multiple base stations at any time.

The interference control techniques described here can be used for a system with sectored cells and a system with non-sectored cells. In the following description, the term sector refers to (1) a conventional BTS and / or its coverage area for a system with sectored cells (2) a conventional base station and / or its coverage area for a system with non-sectored cells. The terms terminal and user are used interchangeably, and the terms sector and base station are also used interchangeably. A base station / server sector is a base station / sector with which a terminal communicates. A neighboring base station / sector is a base station / sector with which the terminal is not in communication.

Interference control techniques can also be used for multiple multiple access communication systems. For example, these techniques can be used for a code division multiple access system (CDMA), a frequency division multiple access system (FDMA), a time division multiple access system (TDMA), a system orthogonal frequency division multiple access (OFDMA), an interleaved system (IFDMA), a localized FDMA system (LFDMA), a spatial division multiple access system (SDMA), a guasi-orthogonal multiple access system, and so on. IFDMA is also called distributed FDMA,

ΡΕ2265073 and LFDMA is also called narrowband FDMA or classic FDMA. An OFDMA system uses orthogonal frequency division multiplexing (OFDM). OFDM, IFDMA, and LFDMA effectively divide the bandwidth of the general system into multiple (K) orthogonal frequency sub-bands. These sub-bands can also be called tones, subcarriers, binaries, and so on. OFDM transmits modulation symbols in the frequency domain in all or a subset of the K subbands. IFDMA transmits modulation symbols in the time domain in subbands that are uniformly distributed throughout the K subbands. LFDMA transmits modulation symbols in the time domain and typically in the adjacent subbands.

As illustrated in FIG. 1 each sector can receive the desired transmissions from terminals within the sector as well as interference transmissions from terminals in other sectors. The total interference observed in each sector is composed of (1) intersector interference from terminals within the same sector and (2) intersector interference from terminals in other sectors. Intersectoral interference, which is also known as interference from another sector (OSI), results from transmissions in each sector not being orthogonal to transmissions in other sectors. Intersector interference and intrasector interference have a major impact on performance and can be mitigated as described below.

ΡΕ2265073

Intersectoral interference can be controlled using various mechanisms such as user-based interference control and network-based interference control. For user-based interference control, the terminals are informed of the intersector interference observed by neighboring sectors and adjust their transmission energies accordingly in such a way that the intersector interference is kept within acceptable levels. For network-based interference control, each sector is informed of the intersectoral interference observed by neighboring sectors and regulates data transmissions to its terminals in such a way that the intersectoral interference is kept within acceptable levels. The system can use only user-based interference control, or only network-based interference control, or both. The interference control mechanisms, and their combinations, can be implemented in several ways, as described below.

FIG. 2 illustrates a process 200 performed by a sector m for controlling intersectoral interference. Sector m calculates the observed interference from the terminals in other sectors and obtains an interference estimate (block 210). Additionally,;

it needs to be the calculation of interference and constitute raw measurements and, or, thresholds obtained by sector m for terminals in other sectors.

generated information cannot

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For user-based interference control, sector m generates an OSI over-the-air (OTA) report based on the interference estimate (block 212). The OSI OTA report transmits the amount of intersectoral interference observed by the sector and can be given in several ways, as described below. Sector m transmits the OSI OTA report to terminals in neighboring sectors (block 214). These terminals can adjust their transmission energies based on the OSI OTA report for sector m, if necessary, to reduce the amount of intersectoral interference observed by sector m.

For network-based interference control, sector m generates an intersectoral OSI (IS) report based on the interference estimate (block 222). The OSI report

IS and the OSI OTA report are two interference reports that can have the same or different formats. For example, the OSI IS report can be the same as the OSI OTA report. Alternatively, the OSI IS report may consist of information related to interference thresholds, interference measurements, path losses, energy received from sector m terminals measured in other sectors, and / or any other information that can be used to determine the interference caused by the terminals of the sector m and the other sector of the OSI IS report is received. Sector m can send the OSI IS report to neighboring sectors periodically or only if sector m observes excessive interference (block 224). Sector m also receives OSI IS reports from the sectors

Vizinhos2265073 neighbors (block 226). The rate at which OSI IS reports are exchanged between sectors can be the same or different from the rate at which OSI OTA reports are broadcast to terminals. Sector m regulates data transmissions to terminals in sector m based on the OSI IS reports received from neighboring sectors (block 228). The blocks in FIG. 2 are described in more detail below.

Sector m can calculate intersectoral interference in several ways. For a system that uses orthogonal multiplexing, a terminal can transmit data or pilot on each sub-carrier in each symbol period. A pilot is a transmission of symbols that are known a priori by either a transmitter or a receiver. A data symbol is a modulation symbol for data, a pilot symbol is a modulation symbol for a pilot, and a modulation symbol is a complex value for a point in a signal constellation, eg, for M-PSK, M- QAM, and so on.

Sector m can calculate the interference of a given sub-carrier k in a given period of symbol n based on a pilot received from a terminal u, as follows:

I_m(k, n) - \ H_mu(k, n ') ·, Eq (l) where P_u (k, n) is a pilot symbol sent by terminal u on subcarrier k in the symbol period n;

ΡΕ2265073

Hm, u (k, n) is an estimate of the channel gain between the sector m and the terminal u;

kn, u (k, n) is a received symbol obtained by sector m from terminal u; and

I + (k, n) is an estimate of the interference observed by sector m.

The quantities in equation (1) are scalar.

sector m can also calculate interference based on data received from terminal u, as follows:

I_m(k, n) = \ H_mtU(k,_nbD_nhii(k, n) -R_ni4l(k, n ') \^Q

Eq (2) where D_m^_u(k, n) is an estimate of a data symbol transmitted by terminal u on subcarrier k in symbol period n. Sector m can deduce the estimates of data symbols D_m,_u (k, n) (1) performing data detection on received symbols R_mrU(k, n) with the Hm channel estimate,_u(k, n) to obtain detected symbols, (2) deducing rigid decisions based on the detected symbols, and (3) using rigid decisions as an estimate of the data symbol. Alternatively, sector m can derive the data symbol estimate (1) by performing data detection on the received symbols, (2) decoding the detected symbols to obtain decoded data, and (3) reΡΕ2265073 encoding and mapping symbols from the decoded data to get the data symbol estimate.

Sector m can also perform joint channel and interference estimation to obtain either an estimate of the channel response or an interference estimate.

The interference estimate I_m(k, n) obtained from equation (1) or (2) includes both intersectoral and intrasectoral interference. Intrasector interference can be maintained within acceptable levels through energy control, as described below, and can then be insignificant compared to intersector interference.

Sector m can average the interference estimate through the frequency, spatial, and / or time domains. For example, sector m can average the interference estimate through multiple receiving antennas. Sector m can average the interference estimate for all sub-bands using any of the following averaging schemes:

<img file="PT2265073E_D0001.tif" />

Eq (3)

<img file="PT2265073E_D0002.tif" />

L (») = W)

<img file="PT2265073E_D0003.tif" />

Eq (4)

ΡΕ2265073 ί Ρ ι 1 ^κ ί Ρ logl + - ^ - = _. £ log 1 + - ^ 4Eq (5) where Im (n) is the mean interference energy for sector m in symbol period ne P_mon indicates a nominal energy received for each sub-carrier. I_m(k, n) and I_m(n) are in linear units in equations (3) through (5). Equation (3) is for arithmetic mean, equation (4) is for geometric mean, and equation (5) is for mean based on SNR. With arithmetic averages, some extended interference estimates can distort the average interference energy. Geometric mean and SNR-based mean can suppress the extended interference estimate for a small set of sub-bands.

Sector m can also filter the average interference energy over multiple symbol periods to improve the quality of the interference estimate. Filtration can be achieved with a finite impulse response filter (FIR), an infinite pulse response filter (IIR), or some other type of filter. Sector m obtains an Imeas, ™ interference calculated for each measurement period, which can cover one or multiple symbol periods.

Interference sector interference m generates a calculated.

calculated OSI OTA report based on

In a realization model, it is quantified for the

a predetermined number of bits, which are included in the

ΡΕ2265073 OSI OTA report. In another embodiment, the OSI OTA report includes a single bit that indicates when the calculated interference is greater than or less than an interference threshold. In yet another embodiment, the OSI OTA report includes multiple bits that carry the calculated relative interference to multiple interference thresholds. For clarity, the following description is for an embodiment in which the OSI OTA report transmits the calculated interference relative to two interference thresholds.

In one embodiment, the OSI OTA report includes two binary OSI bits, which are known as OSI bit 1 and OSI bit 2. These OSI bits can be set as follows:

OSI bit

<img file="PT2265073E_D0004.tif" />

<img file="PT2265073E_D0005.tif" />

Ϊ .....&gt; T

Bit OSI 2! ' 'I' j * í ~ Warhead «[0, if 'where I_no th is a nominal interference threshold, Ihigh th is a high interference threshold, and Ihigh_th&gt; Inom_th · Bit OSI 1 indicates when the calculated interference is above or below the nominal interference threshold. OSI bit 2 indicates

ΡΕ2265073 if the calculated interference is above or below the high interference threshold. For this realization model, sector m is considered to observe low interference if the calculated interference is below I_{at the}m th, high interference if the calculated interference is between I_no th and Ihígh th, and excessive interference if the calculated interference is greater than or equal to I_High th · OSI 2 bit can be used to indicate excessive interference being observed by the industry.

In another embodiment, the OSI OTA report includes a single OSI value having three levels. The OSI value can be defined as follows:

OSI value ”2 '* 1 * híW3 $₍W

S_Ú) h

Ϊ&gt; 1&gt; 1 • Miíí * A · * · βΚ «Β, SH - '

XmKox.m · 1 OSI value a constellation For example, a 1 + symbol sent with a '2' can be of three levels can be transmitted using a signal having three signal points, an OSI value of '0' can be transmitted be sent with a

OJ or e³°, an OSI value of '1' can be a symbol of O + Jl or e ^^{n / 2}, and an OSI value sent with a symbol of -1 + JO or e^jn.

Alternatively, sector m can obtain a calculated thermal interference (IOT), which is the ratio

ΡΕ2265073 of the total interference energy observed by sector m for the thermal noise energy. The total energy of the interference can be calculated as described previously. Thermal noise energy can be estimated by turning the transmitter off and measuring the noise at the receiver. A specific operating point can be selected for the system. A higher operating point allows terminals to transmit at higher energy levels on average. However, a high operating point has a negative impact on the connection cost and may be undesirable. For a given maximum transmission energy and a given data rate, the maximum tolerable path loss decreases with increasing IOT. A very high operating point is also undesirable since the system can become limited by interference, which is a situation in which an increase in transmission energy does not translate into an increase in received SNR. In addition, a very high operating point increases the likelihood of system instability. In any case, sector m can define its three-level OSI value as follows:

í ισί '&gt; iqt,

Values:

do&gt; .x&gt; í stssas. ss r, «&gt;; oT_m„.,&gt; IOT, l ιοτ„_Λ„&lt;Ιοτ ^, where IOT_no-th is a nominal IOT threshold and IOThigh _th is a threshold

High IOT.

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The OSI bits / value can also be generated using hysteresis so that an indication of excessive interference does not change very often. For example, OSI bit 2 can be set to '1' only if the calculated interference exceeds the high threshold in the first duration of time T_W1 (eg, 50 milliseconds) and can be reset to '0' only if the calculated interference is below the high threshold in a second duration of time T_w2. As another example, bit OSI 2 can be set to '1' only if the calculated interference exceeds a first high threshold Ihigh thi θ can then be reset to '0' only if the calculated interference falls below a second high threshold Ihigh_th2z Where - The Ihigh_th2 ·

Sector m transmits its OSI OTA report, which may contain the two OSI bits or the three-level OSI value, for user-based interference control. Sector m can disseminate the OSI OTA report in several ways. In an embodiment, sector m transmits the OSI OTA report for each measurement period. In another embodiment, sector m transmits the OSI bit 1 in each measurement period and transmits the OSI bit 2 only if this bit is set to '1'. Sector m can also broadcast OSI reports from other sectors to terminals within sector m for better OSI coverage.

Sector m also sends its OSI IS report to neighboring sectors for network-based interference control. The OSI IS report can contain two OSI bits; O

ΡΕ2265073 OSI value of three levels; the calculated interference quantified, or not quantified, for a predetermined number of bits; IOT_nom_thz IOThigh_thz θ IOT_meaSí Inom_thz Ihigh_th and Imeas, loss of path; energy received from terminals in sector m calculated in other sectors; any other information; and their combinations. Sector m can send the OSI IS report for each measurement period, or only if excessive interference is observed, or if any other criteria are met. Another sector q can also request sector m to send the OSI IS report if the terminals in sector q indicate that they cannot receive sector OSI bits. Each sector uses the OSI IS report from neighboring sectors to control data transmissions from the terminals in its sector to mitigate intersectoral interference in neighboring sectors.

Network-based interference control can be achieved in several ways. Some models of performing network-based interference control are described below.

In a realization model, sector m schedules terminals in the sector based on the OSI IS reports received from neighboring sectors. For example, if one or more neighboring sectors experience excessive interference, then sector m can reduce the transmission energies used by disadvantaged terminals in sector m so that these terminals cause less interference to other sectors. A disadvantaged terminal has a small channel gain (or a large loss of path) for the server sector and

ΡΕ2265073 needs to transmit at a high energy level in order to achieve a given signal-to-noise and interference (SNR) ratio in the server sector. The disadvantaged terminal is typically located closer to a neighboring sector, and the high level of transmission energy results in high intersectoral interference for this neighboring sector.

Sector m can identify disadvantaged terminals based on various quality indicators such as channel gain, pilot strength, carrier-to-noise ratio (C / N), channel gain ratio, and so on. These quality indicators can be estimated based on the pilot and / or other transmissions sent by the terminals. For example, the estimated channel gain for a terminal can be compared to a channel gain threshold, and the terminal can be considered to be a disadvantaged terminal if its channel gain is below the channel gain threshold. Additionally, disadvantaged terminals can be identified in the OSI IS report together with their calculated values, eg IOT_meas,_ffl or calculated received energy. In addition, in some cases, the OSI IS report can provide information such as how to identify the terminals without further ado to allow the use of the different approaches described below.

Sector m can reduce the transmission energies used by disadvantaged terminals (1) by lowering a high transmission energy limit that is applicable

ΡΕ2265073 to terminals, (2) lowering a lower transmission power limit that is applicable to terminals, (3) assigning lower data rates to disadvantaged terminals that require

Lower SNRs consequently lower transmission energies, (4) not programming disadvantaged terminals for data transmission, or (5) using any other method or combination of methods.

In another embodiment, sector m uses admission control to mitigate intersectoral interference observed by neighboring sectors. For example, if one or more neighboring sectors experience excessive interference, then sector m can reduce the number of active terminals in sector (1) by denying access to new terminals by asking to transmit on the reverse link, (2) denying access to disadvantaged terminals, (3) reassigning terminals that have already been granted access, (4) reassigning disadvantaged terminals, or (5) using some other admission control methods. The terminal reassignment rate can also be made a function of OSI IS reports from neighboring sectors (eg, the levels of observed interference), the number of neighboring sectors to observe excessive interference, and / or other factors. Sector m can thus adjust the sector load based on the OSI IS reports from neighboring sectors.

In yet another realization model, sector m assigns traffic channels to terminals in the sector in a

62265073 to mitigate the intersectoral interference observed by neighboring sectors. For example, each sector can be assigned a set of traffic channels which in turn can be assigned to terminals in the sector. Neighboring sectors can also share a common set of traffic channels that are orthogonal to the set of traffic channels assigned to each sector. If one or more neighboring sectors observe excessive interference, then sector m can assign disadvantaged terminals in sector m to traffic channels in the common set. These disadvantaged terminals will then not cause interference to neighboring sectors since the traffic channels in the common set are orthogonal to the traffic channels assigned to neighboring sectors. As another example, each sector can be assigned a set of traffic channels that can be assigned to strong terminals that can tolerate high levels of interference. If one or more neighboring sectors experience excessive interference, then sector m can assign disadvantaged terminals in sector m to the traffic channels assigned to strong terminals in neighboring sectors.

A combination of one or more of the above approaches can also be used to provide flexibility or for other reasons.

To make it more clear, a lot is for a sector m.

of description

Each sector in the

62265073 system can perform interference control as described above for sector m.

User-based interference control can also be achieved in several ways. In one embodiment, user-based interference control is achieved by allowing terminals to autonomously adjust their transmission energies based on the OSI OTA report received from neighboring sectors.

It should be noted that while FIG. 2, depicts using either network based interference control or user based interference control, only an approximation can be used. For example, blocks 212 and 214 can be omitted and all interference control can be provided using only network based interference control, eg as discussed with respect to blocks 222-228.

FIG. 3 illustrates a process 300 performed by an u terminal for interference control. Terminal u receives an OSI OTA report from a neighboring sector (block 312). A determination is then made as to whether the neighboring sector observes excessive interference, eg, whether the OSI bit 2 is set to '1' (block 314). If the answer is 'Yes', then terminal u reduces its transmission energy with a larger descending step size and / or at a faster rate (block 316). Otherwise, a determination is made as to whether the neighboring sector observes interference

ΡΕ2265073 raised, eg, if the OSI bit 1 is set to '1' and the OSI bit 2 is set to '0' (block 318). If the answer is 'Yes', then terminal u reduces its transmission energy with a nominal downward step size and / or at a nominal rate (block 320). Otherwise, terminal u increases its transmission energy with a nominal upward step size and / or at a nominal rate (block 322).

FIG. 3 illustrates an implementation model in which the OSI OTA report conveys the intersectoral interference observed by the neighboring sector at three possible levels: reduced, elevated, and excessive. Process 300 can be extended to cover any number of levels of interference. In general, the transmission energy to terminal u can be (1) reduced by a downward step that is related to the amount of interference observed by the neighboring sector (eg, higher downward step for higher interference) when the calculated interference is above a given threshold and / or (2) increased through an ascending step that is inversely related to the amount of interference observed by the neighboring sector (eg, higher ascending step for lower interference) when the calculated interference is below the given threshold. The step size and / or the adjustment rate can also be determined based on other parameters such as, for example, the level of current transmission energy to the terminal, the channel gain for the neighboring sector relative to the channel gain

62265073 for the server sector, previous OSI OTA reports, and so on.

Terminal u can adjust its transmission energy based on the OSI OTA report from one or multiple neighboring sectors. Terminal u can calculate the channel gain for each sector based on a pilot received from the sector. Terminal u can then derive a channel gain ratio for each neighboring sector as follows:

ζ («) = ^ 7 ^, Eq (9) where g_ns, i (n) is the channel gain between terminal u and neighboring sector i;

g_ss(n) is the channel gain between the u terminal and the server sector; er₂(n) is the channel gain ratio for neighboring sector i.

In a realization model, terminal u identifies the strongest neighbor sector with the highest channel gain ratio. Terminal u then adjusts its transmission energy based on the OSI OTA report only from this stronger neighboring sector. In another embodiment, terminal u adjusts its transmission energy based on OSI OTA reports from all sectors in an OSI set. This OSI set can contain (1) stronger neighboring sectors T, where T&gt; 1, (2) neighboring sectors with channel gain ratios exceeding the threshold of the

ΡΕ2265073 channel, (3) neighboring sectors with channel gains exceeding a channel gain threshold, (4) neighboring sectors included in a list of neighbors disseminated by the server sector, or (5) any other group of neighboring sectors. Terminal u can adjust its transmission power in several ways based on the OSI OTA report from multiple neighboring sectors in the OSI suite. For example, terminal u can decrease its transmission energy if any neighboring sector in the OSI set experiences high or excessive interference. As another example, terminal u can determine an adjustment of the transmission energy for each neighboring sector in the OSI set and can then combine the adjustments for all neighboring sectors in the OSI set to obtain an adjustment of the overall transmission energy.

In general, adjustment of the transmission energy for interference control can be carried out in conjunction with various energy control schemes. To clarify, a specific energy control scheme is described below. For this energy control scheme, the transmission energy for a traffic channel assigned to terminal u can be expressed as:

^Pdch («) = P_ref(n) + AP (n),

Eq (10) where P_dch (n) is the transmission energy for the traffic channel to update interval n;

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P_ref (n) θ a reference energy level for n interval update; and

ΔΡ (n) is a delta transmission energy for n interval update.

Power transmission levels P_dch(n) and P_ref (n) and the delta transmission energy ΔΡ (n) are given in units of decibels (dB).

reference energy level P_ref(n) is the amount of transmission energy needed to reach a target SNR for a designated transmission, which can be signaling sent by terminal u on a control channel or some other transmission. The reference energy level and the target SNR can be adjusted to achieve a desired performance level for the designated transmission, eg, 1% packet error rate (PER). If the data transmission on the traffic channel and the designated transmission observe similar noise and interference characteristics, then the received SNR for data transmission, SNR_dch(n), can be estimated as:

SNR_dch(n) = SNR ^ + ΔΡ (η).

Eq (ll)

The delta transmission energy ΔΡ (n) can be adjusted in a deterministic way, in a probabilistic way, or in some other way based on OSI OTA reports from neighboring sectors. The transmission energy can be adjusted (1) by quantities

ΡΕ2265073 different for different interference levels using deterministic adjustment or (2) at different rates for different interference levels using probabilistic adjustment. Examples of deterministic and probabilistic transmission energy adjustment schemes are described below. For simplicity, the following description refers to adjusting the transmission power to an OSI bit received from a neighboring sector. This OSI bit can be OSI bit 1 or 2.

FIG. 4 illustrates a process 400 for adjusting the transmission power of terminal u in a deterministic manner. Initially, terminal u processes an OSI OTA report from a neighboring sector (block 412) and determines whether the OSI bit is '1' or '0' (block 414). If the OSI bit is Ί ', which indicates that the observed interference exceeds an interference threshold, then the terminal u determines the amount of reduction in the transmission energy, or a size of the descending step of the AP size_dn(n) (block 422). AP_dn(n) can be determined based on the delta transmission energy for the previous update interval, ΔΡ (η-Ι), and a channel gain ratio for the neighboring sector, r_ns(n). Terminal u then decreases the delta transmission energy via AP_dn(n) (block 424). On the other hand, if the OSI bit is '0', then terminal u determines the amount of increase in transmission energy, or an upward step of size ΔΡ_υρ(η) (block 432). ΔΡ_υρ(η) can also be determined based on ΔΡ (η-Ι) er_ns(n). Terminal u then increases the

ΡΕ2265073 delta transmission through ΔΡ_υρ(η) (block 434). The transmission power adjustments in blocks 424 and 434 can be expressed as:

âP (n -1) + (n), «« OSI bit '0', ®

ΛΡίη-ΙΙ-ΔΡ ^ η), if OSI bit = T.

Eq (12)

After blocks 424 and 434, terminal u limits the delta transmission energy ΔΡ (n) to be within the allowed delta transmission energy range (block 442), as follows:

ΔΡ («) ε [Δίν ,, ΔΡ ^], Eq (13) where AP_min is the minimum allowed delta transmission energy for the traffic channel, and AP_max is the maximum delta transmission energy allowed for the traffic channel. Restricting delta transmission energy to all terminals in a sector within a delta transmission energy range, as shown in equation (13), can keep intrasector interference within acceptable levels. The minimum delta transmission power AP_mi_n it can be adjusted by a control cycle to ensure that each terminal can meet the requirements for a quality of service (QoS) class to which the terminal belongs. AP_min for different QoS classes it can be adjusted at different rates and / or with different step sizes.

ΡΕ2265073

Terminal u then calculates the transmission energy P_dch(n) for the traffic channel based on the delta transmission energy ΔΡ (n) and the reference energy level Pref (-n), as illustrated in equation (10) (block 444). Terminal u can limit transmission power P_dch(n) to be within the maximum energy level P_max (block 446), as follows:

. ptóOO,^ss * _n l Skv&gt; contrary

Terminal u uses the transmission energy to transmit data on the traffic channel.

In one embodiment, the sizes of the steps

P_dch(n) for

<td>AP_dn(n) and ΔΡ_υρ(η) are</td><td>calculated as:</td><td></td>

<td>W ·</td><td>~ 0t ^ 00 »&amp; &lt;£ s)! ®</td><td>Eq (15a)</td>

<td>ΔΡ («·</td><td> ~1)_? r „₅(h), k_The?) ,</td><td>Eq (15b)</td>

where AP_drimmine and ΔΡ_{υΡίΓα1η} are minimum values ​​for AP_dn(n) and ΔΡ_υρ(η), respectively;

k_dn ek_up are scale factors for AP_dn(n) and ΔΡ_υρ(η), respectively; and

ΡΕ2265073 b_dn () and b_up () are functions to calculate AP_dn(n) and ΔΡ_υρ(η), respectively.

-F function_dn () can be defined as hP_dn(n) is related to either ΔΡ (η-Ι) or r_ns(n). If a neighboring sector experiences high or excessive interference, then (1) a higher channel gain for the neighboring sector results in an AP_dn(n) greater and (2) a greater value of AP (nl) results in an AP_dn(n) greater. Function b_up () can be defined as ΔΡ_υρ(η) is inversely proportional to either AP (nl)

<td>want to</td><td>r_ns (n). If the</td><td>sector</td><td>neighbor notes</td><td>interference</td>

<td>low,</td><td>then (1) one</td><td>gain</td><td>largest channel</td><td>for the sector</td>

<td>neighbor</td><td>results in</td><td>ΔΡ_υρ (n)</td><td>smaller and</td><td>(2) a value</td>

greater than ΔΡ (η-Ι) results in a ΔΡ_υρ(η) smaller.

FIG. 4 illustrates the process for an OSI bit from a neighboring sector. A higher value can be used for AP_dn(n) when the neighboring sector observes excessive interference. A smaller value can be used for AP_dn(n) when the neighboring sector observes high interference. Different sizes of descending steps can be obtained, eg, using different scale factors k_dnlek_dn2 for high and excessive interference, respectively.

FIG. 5 illustrates a process 500 for adjusting the transmission power of terminal u in a probabilistic manner. Terminal u initially processes an OSI OTA report from a neighboring sector (block 512)

ΡΕ2265073 and determines whether the OSI bit is '1' or '0' (block 514). If the OSI bit is Ί ', then terminal u determines the probability to decrease the transmission energy, Pr_dn(n), eg, based on ΔΡ (η-Ι) er_ns(n) (block 522). Terminal u then randomly selects an x ​​value between 0.0 and 1.0, where x is a random variable uniformly distributed between 0.0 and 1.0 (block 524). If x is less than or equal to Pr_dn(n), as determined in block 526, then terminal u decreases its delta transmission energy through AP_dn (block 528). Otherwise, if x is greater than Pr_dn(n), then terminal u maintains the delta transmission energy at the current level (block 530).

If the OSI bit is '0' in block 514, then terminal u determines the probability to increase the transmission energy, Pr_up(n), eg, based on ΔΡ (η-Ι) er_ns(n) (block 532). Terminal u then randomly selects an x ​​value between 0.0 and 1.0 (block 534). If x is less than or equal to Pr_up(n), as determined in block 536, then terminal u increases its delta transmission energy through ΔΡ_υρ (block 538). Otherwise, if x is greater than Pr_up(n), then terminal u maintains the delta transmission energy at the current level (block 530). The transmission power adjustments in blocks 528, 530, and 538 can be expressed as:

ΡΕ2265073 | ΔΡ («-1) - Δίς, if OSI bir = Τ AND χ &lt;PçJ»),

ΔΡ (η) = &lt;ΔΡ (η -1) + ΔΡ ^ .., if OSI bit = Ό 'AND χ £ Pf_B(((n), Bq (16) 'j _y ..

[ΔΡ (? Ί —I), otherwise

AP_dn and ΔΡ_υρ can have the same value (eg, 0.25 dB, 0.5 dB,

1.0 dB, and so on) or can have different values.

After blocks 528, 530, and 538, terminal u limits the delta transmission energy, as illustrated in equation (13) (block 542). Terminal u then calculates the transmission energy P_A.Dh (n) based on the delta transmission energy ΔΡ (n) and the reference energy level P_ref (n), as shown in equation (10) (block 544), and further limits the transmission energy Pdch (-n) to be within the maximum energy level, as illustrated in equation (14) (block 546). Terminal u uses Pdch transmission energy (-n) to transmit data on the traffic channel.

In an embodiment, the probabilities are calculated as follows:

^Prdn («) = (Pr_dn,, ΔΡ (η -1), r_lls (n),), Eq (17a)

Pru_P(«) = ZÍ, (Pr_up.mi_n. ΔΡ (π-Ι), rjn), k_up) ,

Eq (17b)

ΡΕ2265073 where Pr_dn,_min and P_rup, min are minimum values ​​for Pr_dn(n) and Pr_up(n), respectively; eb '_dn() and f '_up() are functions to calculate Pr_dn(n) and Pr_up(n), respectively.

Function b '_dn() can be defined as Pr_dn(n) is related to either ΔΡ (η-Ι) or r_ns(n). If a neighboring sector experiences high or excessive interference, then (1) a higher channel gain for the neighboring sector results in a Pr_dn(n) greater and (2) a greater value of ΔΡ (η-Ι) results in a Pr_dn(n) greater. 0 Pr_dn(n) greater results in a greater likelihood of reducing transmission energy. Function f '_up () can be defined as Pr_up (n) is inversely proportional to either ΔΡ (η-Ι) or air_ns(n). If the neighboring sector experiences low interference, then (1) a higher channel gain for the neighboring sector results in a Pr_up(n) smaller and (2) a larger value of ΔΡ (η-Ι) results in a Pr_up(n) minor. 0 Pr_up(n) smaller results in a lesser probability of increasing the transmission energy.

FIG. 5 illustrates the process for an OSI bit from a neighboring sector. A larger value can be used for Pr_dn(n) when the neighboring sector observes excessive interference. A smaller value can be used for Pr_dn(n) when the neighboring sector observes high interference. Different low probabilities and therefore different rates of energy adjustment can be obtained, eg, using different scaling factors k_dnl ek_dn2for high and excessive interference, respectively.

ΡΕ2265073

In general, several functions can be used to calculate the size of AP steps_dn(n) and ΔΡ_υρ (n) and the probabilities of Pr_dn(n) and Pr_up(n). A function can be defined based on various parameters such as the current transmission energy, the current delta transmission energy, the current OSI OTA report, previous OSI OTA reports, channel gains, and so on. Each function can have a different impact on various energy control characteristics such as the convergence rate of the transmission energy adjustment and the distribution of the delta transmission energies to the terminals in the system. 0 step size and probabilities can also be determined based on lookup tables or by some other means.

Adjustment of transmission energy and / or control of admissions described above can also be performed based on the QoS class, user priority class, and so on. For example, a terminal using an emergency service and a police terminal may have a higher priority and may be able to adjust transmission power at a faster rate and / or with a step size larger than a priority user. normal. As another example, a terminal sending voice traffic can adjust the transmission energy at a slower rate and / or with the size of the smaller steps.

Terminal u can also vary the way the

62265073 transmission power is adjusted based on reports

OSI OTA previously received from neighboring sectors. For example, terminal u can reduce its transmission energy through a specific downward step size and / or at a specific rate if a neighboring sector reports excessive interference and can reduce transmission power through a larger downward step size. and / or at a faster rate if the neighboring sector continues to report excessive interference. Alternatively or additionally, terminal u can bypass the AP_min in equation (13) if a neighboring sector reports excessive interference, or if the neighboring sector continues to report excessive interference.

Several models of carrying out energy control to mitigate intersectoral interference have been previously described. Energy interference and control can also be carried out in other ways, and this is within the scope of the invention.

In a realization model, each sector disseminates its OSI OTA report to terminals in neighboring sectors, as previously described. The OSI OTA report can be broadcast with enough transmission power to achieve the desired coverage in neighboring sectors. Each terminal can receive OSI OTA reports from neighboring sectors and process these OSI OTA reports in order to achieve a sufficiently low detection failure rate and a sufficiently low probability of false alarm. Detection failure refers to

ΡΕ2265073 a failure to detect an OSI bit or value that has been transmitted. False alarm refers to an erroneous detection of a received bit or OSI value. For example, if an OSI bit is transmitted using BPSK, then a terminal can declare a received OSI bit as (1) a '0' if the detected OSI bit is below a first threshold, OSI bit &lt;B_thz (2) a '1' if the detected OSI bit exceeds a second threshold, OSI bit&gt; + B_thz and (3) an otherwise null bit, + B_th - OSI bit b -B_th · The terminal can typically compensate for the detection failure rate with the probability of false alarm by adjusting the thresholds used for detection.

In another embodiment, each sector also disseminates OSI OTA reports generated by neighboring sectors to the terminals within its sector. In this way, each sector represents a proxy for neighboring sectors. This realization model can guarantee that each terminal can reliably receive OSI OTA reports generated by neighboring sectors since the terminal can receive these OSI OTA reports from the server sector. This realization model is well suited for the development of an asymmetric network in which the sector's coverage sizes are not the same. Smaller sectors typically transmit at lower energy levels, and OSI OTA reports disseminated by these smaller sectors may not be reliably received by terminals in neighboring sectors. Smaller sectors will then benefit from having their OSI OTA reports disseminated to neighboring sectors.

ΡΕ2265073

In general, a given sector m can broadcast OSI OTA reports generated by any number and by any of the other sectors. In a realization model, sector m broadcasts OSI OTA reports generated by sectors from a list of neighbors for sector m. The list of neighbors can be formed by a network operator or in any other way. In another embodiment, sector m disseminates OSI OTA reports generated by all sectors that are included in the active sets of terminals in sector m. Each terminal can maintain an active set that includes all sectors with which the terminal is in communication. Sectors can be added to or removed from the active set as the terminal is passed from sector to sector. In yet another realization model, sector m disseminates OSI OTA reports generated by all sectors that are included in candidate sets of terminals in sector m. Each terminal can maintain a candidate set that includes all sectors with which the terminal can communicate. Sectors can be added or removed from the candidate set, eg, based on channel gain and / or some other parameter. In yet another embodiment, sector m disseminates OSI OTA reports generated by all sectors that are included in the OSI sets of terminals in sector m. The OSI set for each terminal can be defined as described previously.

As mentioned earlier, the system can use only user-based interference control or only interference control based on

Rede2265073 network. User-based interference control can be simpler to implement since each sector and each terminal can act autonomously. Network-based interference control can provide improved performance since interference control is performed in a coordinated manner. The system can also use interference control both based on the user and based on the network at the same time. 0 The system can also always use user-based interference control and can invoke network-based interference control only when excessive interference is observed. The system can also invoke each type of interference control for different operating conditions.

FIG. 6 illustrates a power control mechanism 600 that can be used to adjust transmission power to a 120x terminal on the 100 system. Terminal 120x communicates with a HOx server sector and can cause interference to neighboring sectors 110a through 1101. Control mechanism Power 600 includes (1) a reference cycle 610 that operates between terminal 120x and the HOx server sector and (2) a second cycle 620 that operates between terminal 120x and neighboring sectors 110a through 1101.

Reference cycle 610 and second cycle 620 can act simultaneously but can be updated at different rates, with reference cycle 610 being a faster cycle than the second cycle 620. For simplicity, FIG. 6

62265073 illustrates only the portion of cycles 610 and 620 that reside in terminal 120x.

Reference cycle 610 adjusts the reference energy level P_ref(n) such that the SNR received for the designated transmission, as measured in the HOx server sector, is as close as possible to the target SNR. For the 610 reference cycle, the HOx server sector estimates the received SNR for the designated transmission, compares the received SNR with the target SNR, and generates transmission power control (TPC) commands based on the comparison results. Each TPC command can either be (1) an UP command to drive an increase in the reference energy level or (2) a DOWN command to drive a decrease in the reference energy level. The HOx server sector transmits the TPC commands on the direct link (cloud 670) to the 120x terminal.

At the 120x terminal, a TPC 642 command processor detects the TPC commands transmitted by the HOx server sector and provides TPC decisions. Each TPC decision can be an UP decision if a received TPC command is considered to be an UP command or a DOWN decision if the received TPC command is considered to be a DOWN command. A reference energy adjustment unit 644 adjusts the reference energy level based on TPC decisions. 644 unit can increase P_ref (n) by an ascending step for each UP decision and decreasing P_ref (n) by a descending step for each DOWN decision. A data processor

ΡΕ2265073 transmission (TX) 660 scales the designated transmission to reach the reference energy level. The 120x terminal sends the designated transmission to the IlOx server sector.

Due to loss of path, fading, and multi-path effects on the reverse link (cloud 640), which typically varies over time and especially for a mobile terminal, the SNR received for the designated transmission fluctuates continuously. Reference cycle 610 attempts to maintain the received SNR for the designated transmission at or near the target SNR in the presence of changes in the reverse link channel conditions.

Second cycle 620 adjusts Pd transmission power_Çh (n) for a traffic channel assigned to terminal 120x in such a way that an energy level that is as high as possible is used for the traffic channel while maintaining intersectoral interference within acceptable levels. For the second cycle 620, each neighboring sector 110 receives transmissions on the reverse link, estimates the intersectoral interference observed by the neighboring sector from the terminals in other sectors, generates an OSI OTA report based on the interference estimate, and disseminates the OSI OTA report to terminals in other sectors.

At the 120x terminal, an OSI 652 report processor receives the OSI OTA reports broadcast by neighboring sectors and provides detected OSI reports to a delta 656 transmission power computing unit.

ΡΕ2265073

A 654 channel estimator receives pilots from the server and neighboring sectors, estimates the channel gain for each sector, and provides the estimated channel gains for all sectors to unit 656. Unit 656 determines the channel gain ratios for the neighboring sectors and also adjusts the delta transmission energy ΔΡ (n) based on the detected OSI reports and channel gain ratios, as previously described. Unit 656 can implement processes 300, 400 and / or 500 illustrated in FIGS. 3 to 5. A transmission power computing unit 658 calculates the transmission energy Pd_Çh (n) based on the reference transmission level P_ref(n) from unit 644, the delta transmission energy ΔΡ (n) from unit 656, and possibly other factors. TX 660 data processor uses Pd transmission power_Çh (n) for data transmission to the IlOx server sector.

FIG. 6 illustrates an example of an energy control mechanism that can be used for interference control. Interference control can also be performed in other ways and / or with parameters different from those previously described.

FIG. 7 illustrates a block diagram of an embodiment of the 120x terminal, IlOx server base station, and neighboring base station HOy. For clarity, the following description assumes the use of the energy control mechanism 600 illustrated in FIG. 6.

ΡΕ2265073

On the reverse link, at the 120x terminal, a TX 710 data processor encodes, merges, and symbol maps reverse link (RL) data traffic and control data and provides data symbols. A modulator (Mod) 712 maps the data symbols and pilot symbols to the appropriate sub-bands and symbol periods, performs OFDM modulation if applicable, and provides a sequence of complex value chips. A transmitter unit (TMTR) 714 conditions (eg, converts to analog, amplifies, filters, and converts a higher frequency) the chip sequence and generates a reverse link signal, which is transmitted through an antenna 716.

At the HOx server base station, multiple 752x antennas through 752xt receive the reverse link signals from terminal 120x and other terminals. Each 752x antenna provides a received signal to a respective 754x receiver unit (RCVR). Each 754x receiver unit conditions (eg, filters, amplifies, converts to a lower frequency and digitizes) its received signal, performs OFDM demodulation if applicable, and provides received symbols. An RX 758 space processor performs spatial receiver processing on symbols received from all receiver units and provides data symbol estimates, which are estimates of transmitted data symbols. An RX 760x data processor unmap, deinterleaves, and decodes the data symbol estimates and provides decoded data to the 120x terminal and

ΡΕ2265073 other terminals currently served by the base station

IlOx.

The process for direct link transmission can be carried out in a similar manner to that described previously for reverse link. The process for transmissions on direct and reverse links is typically specified by the system.

For interference and power control, on the IlOx server base station, space processor RX 758x estimates the received SNR for the 120x terminal, estimates the intersector interference observed by the IlOx base station, and provides an SNR estimate for the IlOx terminal and an estimate interference (eg, the measured interference Imeas, ™) for a 770x controller. Controller 770x generates TPC commands for the 120x terminal based on the SNR estimate for the terminal and the target SNR. 770x controller can generate an OSI OTA report and / or an OSI report

IS based on the interference estimate. 0 controller

770x can also receive OSI IS reports from neighboring sectors via a 774x communication unit (Comm). TPC commands, the OSI OTA report for IlOx base station, and possibly OSI OTA reports for other sectors are processed by a TX 782x data processor and a TX 784x space processor, conditioned by 754x transmitter units via 754xt, and transmitted through antennas 752x through 752xt. 0 OSI IS report of the IlOx base station can be

ΡΕ2265073 sent to neighboring sectors via the 774x communication unit, eg via a return transport channel or other wired communication link.

At the neighboring base station HOy, a space processor RX 758y estimates the intersector interference observed by the base station HOy and provides an interference estimate for the 77Oy controller. Controller 770y can generate an OSI OTA report and / or an OSI IS report based on the interference estimate. The OSI OTA report is processed and broadcast to the terminals in the system. The OSI IS report can be sent to neighboring sectors via a 774y communication unit.

At the 120x terminal, antenna 716 receives the direct link signals from the base server and neighbor base stations and provides a received signal to a receiver unit 714. The received signal is conditioned and digitized by the receiver unit 714 and further processed by a demodulator (Demod) 742 and an RX 744 data processor. Processor 744 provides the TPC commands sent by the HOx server base station to the 120x terminal and broadcasts OSI OTA reports to neighboring base stations. A channel estimator within demodulator 742 estimates the channel gain for each base station. Controller 720 detects received TPC commands and updates the reference power level based on TPC decisions. Controller 720 also adjusts the power of

ΡΕ2265073 transmission to the traffic channel based on OSI OTA reports received from neighboring base stations and channel gains to server and neighboring base stations. Controller 720 provides the transmission power for the traffic channel assigned to the 120x terminal. Processor 710 and / or modulator 712 scales the data symbols based on the transmit energy provided by the controller 720.

720, 770x, and 770y controllers direct the operations of various process units at the 120x terminal and HOx and 110y base station, respectively. These controllers can also perform various functions for interference and power control. For example, controller 720 can implement any of the units or all units 642 to 658 illustrated in FIG. 6 and / or processes 300, 400 and / or 500 illustrated in FIGS. 3 to 5.

Controller 770 for each base station 110 can implement the entire process or a process part 200 in FIG. 2. Memory units 722, 772x, and 772y store data and program codes for controllers 720, 770x, and 770y, respectively. A 780x scheduler schedules terminals for communication with the HOx base station and also assigns traffic channels to the scheduled terminals, eg, based on OSI IS reports from neighboring base stations.

FIG. 8 illustrates an apparatus suitable for interference control. The apparatus includes means 800 for

ΡΕ2265073 receive an OSI IS report (s) and 802 means to regulate data transmissions to terminals in the sector based on the received OSI IS reports.

FIG. 9 illustrates an apparatus suitable for providing interference control. The apparatus includes means 900 for generating an OSI IS report (s) and means 902 for transmitting the OSI IS reports to one or more sectors. In certain cases, the means to generate may include means to generate a different OSI IS report for each sector and the means to transmit may be coupled to a physical link, eg a return transport channel.

The interference control techniques described herein can be implemented by various means. For example, these techniques can be implemented in hardware, software, or a combination of them. For a hardware implementation, the processing units used to perform interference control at a base station can be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), signal processing devices (DSPDs), programmable logic devices (PLDs), network of programmable logic gates (FPGAs), processors, microcontrollers, microprocessors, electronics, other electronic units designed to perform the functions described above, or a combination of controllers, devices between them. The processing units used for

62265073 performing interference control at a terminal can also be implemented within one or more ASICs, DSPs, processors, electronic devices, and so on.

For a software implementation, interference control techniques can be implemented with modules (eg, procedures, functions, and so on) that perform the functions described here. The software codes can be stored in a memory unit (eg, memory unit 722, 772x, or 772y in FIG. 7) and executed by a processor (eg, controller 720, 770x, or 77Oy). The memory unit can be implemented inside the processor or outside the processor.

The foregoing description of the disclosed embodiments is provided to enable anyone skilled in the art to make or use the present invention. They will be readily apparent. Various modifications for these embodiments to those who are experts in the art, and the generic principles defined herein can be applied to other embodiments without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments illustrated here, but should be granted the broadest scope consistent with the principles and new features described here.

Lisbon, November 4, 2014

ΡΕ2265073