HK1151664B - Method and apparatus for interference control in a wireless communication system - Google Patents

Abstract

The present invention relates to a method and apparatus for interference control in a wireless communication system. The method comprises: a sector m estimates interference observed from terminals in neighbor sectors and obtains an interference estimate. Sector m may generate an over-the-air (OTA) other-sector interference (OSI) report and/or an inter-sector (IS) OSI report based on the interference estimate. Sector m may broadcast the OTA OSI report to the terminals in the neighbor sectors. These terminals may adjust their transmit powers based on the OTA OSI report. Sector m may send the IS OSI report to the neighbor sectors, receive IS OSI reports from the neighbor sectors, and regulate data transmissions for terminals in sector m based on the received IS OSI reports. Sector m may control admission of terminals to sector m, de-assign admitted terminals, schedule terminals in sector m in a manner to reduce interference to the neighbor sectors, and/or assign the terminals in sector m with traffic channels that cause less interference to the neighbor sectors.

Description

Interference control method and device in wireless communication system

The application is a divisional application of an invention patent application with the application number of 2006800160273 after the PCT application with the international application date of 2006, 3 and 15, the international application number of PCT/US2006/009550 and the invention name of interference control in a wireless communication system enters the China national phase.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from united states provisional patent application No. 60/662,176, filed on 3/15/2005 and incorporated herein by reference in its entirety.

Technical Field

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

Background

A wireless multiple-access communication system may communicate with multiple terminals on the forward and reverse links simultaneously. The forward 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. Multiple terminals may simultaneously transmit data on the reverse link and/or receive data on the forward link. This is often accomplished by multiplexing the transmissions on each link to be orthogonal to each other in the time, frequency, and/or code domain.

On the reverse link, transmissions from terminals communicating with different base stations are typically not orthogonal to each other. Thus, each terminal may generate interference to, and may also receive interference from, other terminals communicating with nearby base stations. Interference from other terminals communicating with other base stations degrades the performance of each terminal.

Accordingly, there is a need in the art for techniques to mitigate interference in a wireless communication system.

Disclosure of Invention

Techniques for controlling interference observed by each sector from neighboring sectors in a wireless communication system are described herein. The term "sector" can refer to a base station or a coverage area of a base station. Sector m estimates the interference observed from terminals in neighboring sectors and obtains an interference estimate. For user-based interference control, sector m generates an over-the-air (OTA) other-sector interference (OSI) report based on the interference estimate and broadcasts the OTA OSI report to terminals in neighboring sectors. These terminals may autonomously adjust their transmit power as necessary based on OTA OSI reports from sector m to reduce the amount of interference observed by sector m. The OTA OSI report may indicate one of a plurality of possible interference levels observed by sector m. Terminals in neighboring sectors may adjust their transmit powers by different amounts and/or at different rates depending on the interference level observed by sector m.

For network-based interference control, sector m may generate an inter-sector (IS) OSI report based on the interference estimate and send the IS OSI report to neighboring sectors. The IS OSI report may be the same as the OTA OSI report or may be more comprehensive. Sector m also receives IS OSI reports from neighboring sectors and adjusts data transmissions for terminals in sector m based on the received IS OSI reports. Sector m may adjust data transmission by: (1) controlling the admission of a new terminal to sector m; (2) de-assigning the admitted terminal; (3) scheduling terminals in sector m in a manner that reduces interference to neighboring sectors; and/or (4) assign traffic channels to terminals in sector m that cause less interference to neighboring sectors.

Various aspects and embodiments of the disclosure are described in further detail below.

Drawings

The features and nature of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout.

Fig. 1 shows a communication system with a base station and a terminal.

Fig. 2 shows a process for interference control performed by one sector.

Fig. 3 shows a process for interference control performed by one terminal.

Fig. 4 shows a process for adjusting transmission power in a deterministic manner.

Fig. 5 shows a process for adjusting transmission power in a probabilistic manner.

Fig. 6 shows a power control mechanism suitable for interference control.

Fig. 7 shows a block diagram of one terminal and two base stations.

Detailed Description

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

Fig. 1 shows 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 may also be referred to as an access point, a node B, or some other terminology. Each base station 110 provides communication coverage for a particular geographic area 102a, 102b, and 102 c. The term "cell" can refer to a base station and/or its coverage area depending on the context in which the term is used. To improve system capacity, the coverage area of a base station may be divided into multiple smaller areas, e.g., three smaller areas 104a, 104b, and 104 c. Each smaller area is served by a respective Base Transceiver 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 sectorized cell, the BTSs for all sectors of the cell are typically co-located within the base station for the cell. A system controller 130 couples to base stations 110 and provides coordination and control for these base stations.

A terminal may be fixed or mobile and may also be referred to as a mobile station, a wireless device, a user equipment, or some other terminology. Each terminal may communicate with zero, one, or multiple base stations at any given moment.

The interference control techniques described herein may be used for systems with sectorized cells and systems with unsectorized cells. In the following description, the term "sector" refers to (1) a conventional BTS of a system having a sectorized cell and/or its coverage area and (2) a conventional base station of a system having an unsectorized cell and/or its coverage area. The terms "terminal" and "user" are used interchangeably, and the terms "sector" and "base station" are used interchangeably. A serving base station/sector is a base station/sector that communicates with the terminals. A neighboring base station/sector is a base station/sector that does not communicate with the terminal.

Interference control techniques may also be used in various multiple access communication systems. For example, the techniques may be used for Code Division Multiple Access (CDMA) systems, Frequency Division Multiple Access (FDMA) systems, Time Division Multiple Access (TDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, Interleaved Frequency Division Multiple Access (IFDMA) systems, localized FDMA (lfdma) systems, Spatial Division Multiple Access (SDMA) systems, quasi-orthogonal multiple access systems, and so on. IFDMA is also known as distributed FDMA and LFDMA is also known as narrowband FDMA or traditional FDMA. OFDMA systems utilize Orthogonal Frequency Division Multiplexing (OFDM). OFDM, IFDMA, and LFDMA effectively divide the overall system bandwidth into multiple (K) orthogonal frequency sub-bands. These subbands are also referred to as tones, subcarriers, bins (bins), etc. Each subband is associated with a respective subcarrier that may be modulated with data. OFDM transmits modulation symbols in the frequency domain on all or a subset of the K subbands. IFDMA transmits modulation symbols in the time domain on subbands that are evenly distributed across K subbands. LFDMA transmits modulation symbols in the time domain and typically on adjacent subbands.

As shown in fig. 1, each sector can receive "desired" transmissions from terminals in the sector as well as "interfering" transmissions from terminals in other sectors. The total interference observed at each sector includes (1) intra-sector interference from terminals in the same sector and (2) inter-sector interference from terminals in other sectors. Inter-sector interference, also referred to as Other Sector Interference (OSI), results from transmissions in each sector that are not orthogonal to transmissions in other sectors. Both inter-sector interference and intra-sector interference have a large impact on performance and can be mitigated as described below.

Inter-sector interference may be controlled using various mechanisms, such as user-based interference control and network-based interference control. For user-based interference control, terminals are notified of inter-sector interference observed by neighboring sectors and their transmit powers are adjusted accordingly such that inter-sector interference is maintained within acceptable levels. For network-based interference control, each sector is informed of the inter-sector interference observed by neighboring sectors and adjusts its terminals' data transmissions such that the inter-sector interference is maintained within acceptable levels. The system may utilize only user-based interference control, or only network-based interference control, or both. Each interference control mechanism may be implemented in various ways, as described below.

Fig. 2 shows a process 200 performed by one sector m for inter-sector interference control. Sector m estimates interference observed from terminals in other sectors and obtains an interference estimate (block 210).

For user-based interference control, sector m generates an over-the-air (OTA) OSI report based on the interference estimate (block 212). The OTA OSI report conveys the amount of inter-sector interference observed by sector m and may be given in various forms, as described below. Sector m broadcasts the OTA OSI report to terminals in neighboring sectors (block 214). These terminals may adjust their transmit power as necessary based on OTA OSI reports from sector m to reduce the amount of inter-sector interference observed by sector m.

For network-based interference control, sector m generates an inter-sector (IS) OSI report based on the interference estimate (block 222). The IS OSI report and the OTA OSI report are two interference reports that may have the same or different formats. For example, the IS OSI report may be the same as the OTA OSI report. Alternatively, sector m may broadcast a simple OTA OSI report to terminals in the neighbor sectors and may send a more comprehensive IS OSI report to the neighbor sectors. Sector m may send an IS OSI report to the neighbor sector periodically or only when sector m observes excessive interference (block 224). Sector m may also receive IS OSI reports from neighboring sectors (block 226). The rate at which IS OSI reports are exchanged between sectors may be the same or different than the rate at which OTA OSI reports are broadcast to the terminals. Sector m adjusts data transmissions for terminals in sector m based on the IS OSI reports received from neighboring sectors (block 228). The blocks in fig. 2 are described in further detail below.

Sector m may estimate inter-sector interference in various ways. For systems utilizing orthogonal multiplexing, one terminal may transmit data or pilot on each subband in each symbol period. A pilot is the transmission of a symbol that is known a priori by both the transmitter and the receiver. The data symbols are modulation symbols for data, the pilot symbols are modulation symbols for pilot, and the modulation symbols are complex values for one point in a signal constellation, e.g., for M-PSK, M-QAM, etc.

Sector m may estimate interference on a given subband k in a given symbol period n based on the pilot received from terminal u as follows:

equation (1)

Wherein P is_u(k, n) are pilot symbols sent by terminal u on subband k in symbol period n;

is an estimate of the channel gain between sector m and terminal u;

R_m，u(k, n) are received symbols obtained by sector m from terminal u; and is

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

The quantity in equation (1) is a scalar quantity.

Sector m may also estimate the interference based on data received from terminal u, as follows:

equation (2)

WhereinIs an estimate of the data symbols transmitted by terminal u on subband k in symbol period n. Sector m may derive data symbol estimates by(1) For having channel estimation valueReceived symbol R of_m，u(k, n) performing data detection to obtain detected symbols; (2) deriving a hard decision based on the detected symbols; and (3) using the hard decision as a data symbol estimate. Alternatively, sector m may derive data symbol estimates by: (1) performing data detection on the received symbols; (2) decoding the detected symbols to obtain decoded data; and (3) re-encoding and symbol mapping the decoded data to obtain data symbol estimates.

Sector m may also perform joint channel and interference estimation to obtain both a channel response estimate and an interference estimate.

Interference estimation value I obtained from equation (1) or (2)_m(k, n) includes both inter-sector interference and intra-sector interference. Intra-sector interference can be maintained within acceptable levels through power control as described below and can be negligible compared to inter-sector interference.

Sector m may average the interference estimate over the frequency, spatial, and/or time domains. For example, sector m may average interference estimates over multiple receive antennas. Sector m may average the interference estimates for all subbands using any of the following averaging schemes:

equation (3)

And equation (4)

Equation (5)

Wherein I_m(n) is sector m in symbol period nAverage interference power, and P_nomRepresenting the nominal received power of each sub-band. I is_m(k, n) and I_m(n) is a linear unit in equations (3) to (5). Equation (3) is used for arithmetic averaging, equation (4) is used for geometric averaging, and equation (5) is used for SNR-based averaging. Using arithmetic averaging, several larger interference estimates may skew the average interference power. Geometric averaging and SNR-based averaging may suppress large interference estimates for several sub-bands.

Sector m may also filter the average interference power over multiple symbol periods to improve the quality of the interference estimate. The filtering may be implemented with a Finite Impulse Response (FIR) filter, an Infinite Impulse Response (IIR) filter, or some other type of filter. Sector m obtains measured interference I at each measurement period_meas，mThe measurement period may span one or more symbol periods.

Sector m generates an OTA OSI report based on the measured interference. In an embodiment, the measured interference is quantized to a predetermined number of bits, which are included in the OTA OSI report. In another embodiment, the OTA OSI report includes a single bit indicating whether the measured interference is above or below an interference threshold. In yet another embodiment, the OTA OSI report includes a plurality of bits that convey measured interference relative to a plurality of interference thresholds. For clarity, the following description is for embodiments in which OTA OSI reports convey measured interference relative to two interference thresholds.

In an embodiment, the OTA OSI report includes two binary OSI bits, referred to as OSI bit 1 and OSI bit 2. These OSI bits can be set as follows:

equation (6a)

Equation (6 b))

Wherein I_{nom_th}Is a nominal interference threshold, I_{high_th}Is a high interference threshold, and I_{high_th}＞I_{nom_th}. OSI bit 1 indicates whether the measured interference is above or below a nominal interference threshold. OSI bit 2 indicates whether the measured interference is above or below the high interference threshold. For this embodiment, it is considered that sector m is measuring interference below I_{nom_th}Low interference is observed, and interference measured at I_{nom_th}And I_{high_th}In between, and when the measured interference is greater than or equal to I_{high_th}Excessive interference is observed. OSI bit 2 can be used to indicate excess interference observed by the sector.

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

equation (7)

Three levels of OSI values can be transmitted using a signal constellation having three signal points. For example, the symbols 1+ j0 or e may be used^j0To transmit an OSI value of "0", the symbols 0+ j1 or e may be used^jπ/2The OSI value "1" is sent and the symbols-1 + j0 or e can be used^jπThe OSI value "2" is sent.

Alternatively, sector m may obtain a measured thermal Interference (IOT), which is the ratio of the total interference power observed by sector m to the thermal noise power. The total interference power may be calculated as described above. The thermal noise power can be estimated by switching off the transmitter and measuring the noise at the receiver. A particular operating point may be selected for the system. The higher operating point allows the terminal to transmit at an average higher power level. However, high operating points adversely affect the link budget and may be undesirable. For a given maximum transmission power and a given data rate, the maximum allowable path loss decreases as the IOT increases. A very high operating point is also undesirable because the system may become interference limited, which is a situation where an increase in transmit power does not translate into an increase in received SNR. In addition, the very high operating point increases the likelihood of system instability. In any case, sector m may set its three-level OSI value as follows:

equation (8)

Wherein IOT_{nom_th}Is a nominal IOT threshold, and IOT_{high_th}Is a high IOT threshold.

Hysteresis may also be used to generate OSI bits/values such that an indication of excessive interference is not triggered too frequently. For example, OSI bit 2 may only be for the first duration T when the measured interference exceeds the high threshold_W1(e.g., 50 milliseconds) and may only be set to "1" if the measured interference is below the high threshold for a second duration T_W2Is reset to "0". As another example, OSI bit 2 may only be if the measured interference exceeds a first high threshold I_{high_th1}Is set to "1" and may then only fall to the second high threshold I when the measured interference falls_{high_th2}Reset to "0" when I is_{high_th1}＞I_{high_th2}。

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

Sector m also sends its IS OSI report to neighboring sectors for network-based interference control. The IS OSI report may contain two OSI bits, a three-level OSI value, measured interference quantized to a predetermined number of bits, or some other information. Sector m may send an isisi report in each measurement period or only when excessive interference is observed or when some other criterion is met. Another sector q may also request sector m to send an IS OSI report when a terminal in sector q indicates that it cannot receive OSI bits from sector m. Each sector uses IS OSI reports from neighboring sectors to control data transmissions from terminals in its sector to mitigate inter-sector interference at neighboring sectors.

Network-based interference control may be implemented in various ways. Some embodiments of network-based interference control are described below.

In one embodiment, sector m schedules terminals in the sector based on the IS OSI reports received from neighbor sectors. For example, if one or more neighboring sectors observe excessive interference, sector m may reduce the transmission power used by disadvantaged terminals in sector m, such that these terminals generate less interference to other sectors. A disadvantaged terminal has a small channel gain (or large path loss) for the serving sector and needs to transmit at a high power level in order to achieve a given signal-to-noise-and-interference ratio (SNR) at the serving sector. A disadvantaged terminal is typically positioned closer to a neighboring sector, and a high transmission power level results in high inter-sector interference to this neighboring sector.

Sector m may identify the disadvantaged terminals based on various quality metrics such as channel gain, pilot strength, carrier-to-noise ratio (C/N), channel gain ratio, and so on. These quality metrics may be estimated based on pilot and/or other transmissions sent by the terminal. For example, the estimated channel gain for a terminal may be compared to a channel gain threshold, and the terminal may be considered an adverse terminal when its channel gain is below the channel gain threshold. Sector m may reduce the transmission power used by disadvantaged terminals by: (1) reducing a high transmission power limit applicable to the terminal; (2) lower transmission power limits applicable to the terminal are reduced; (3) assigning disadvantaged terminals with lower data rates that require lower SNR and thus lower transmission power; (4) not scheduling the unfavorable terminal for data transmission; or (5) using some other method or combination of methods.

In another embodiment, sector m uses admission control to mitigate inter-sector interference observed by neighboring sectors. For example, if one or more neighboring sectors observe excessive interference, sector m may reduce the number of active terminals in the sector by: (1) denying access to the new terminal for transmission of the request on the reverse link; (2) access to the disadvantaged terminal is denied; (3) de-assigning terminals to which access has been granted; (4) de-assigning the disadvantaged terminal; or (5) use some other admission control method. The rate at which a terminal IS de-assigned can also be a function of IS OSI reports from neighboring sectors (e.g., an observed interference level), the number of neighboring sectors that observe excessive interference, and/or other factors. Sector m may thus regulate loading of sectors based on IS OSI reports from neighboring sectors.

In yet another embodiment, sector m assigns traffic channels to terminals in the sector in a manner that mitigates inter-sector interference observed by neighboring sectors. For example, each sector can be assigned a set of traffic channels, which in turn can assign the set of traffic channels to terminals in the sector. Neighboring sectors may also share a common set of traffic channels that are orthogonal to the set of traffic channels assigned to each sector. Sector m may assign a traffic channel in the common set to a disadvantaged terminal in sector m if one or more neighboring sectors observe excessive interference. These disadvantaged terminals will then not cause any interference to the neighboring sectors because the traffic channels in the common group are orthogonal to the traffic channels assigned to the neighboring sectors. As another example, each sector can be assigned a set of traffic channels that the sector can assign to stronger terminals that can tolerate high interference levels. If one or more neighboring sectors observe excessive interference, sector m may assign a traffic channel assigned to a stronger terminal in the neighboring sector to a disadvantaged terminal in sector m.

For clarity, most of the above description is for one sector m. Each sector in the system may perform interference control as described above for sector m.

User-based interference control may also be implemented in various ways. In an embodiment, user-based interference control is achieved by the admitting terminal autonomously adjusting its transmit power based on OTA OSI reports received from neighboring sectors.

Fig. 3 shows a process 300 performed by one terminal u for interference control. Terminal u receives an OTA OSI report from a neighboring sector (block 312). A determination is then made as to whether the neighboring sector observes excessive interference, e.g., whether OSI bit 2 is set to "1" (block 314). If the answer is "yes," then terminal u decreases its transmission power in larger step sizes and/or at a faster rate (block 316). Otherwise, it is determined whether the neighboring sector observes high interference, e.g., whether OSI bit 1 is set to "1" and OSI bit 2 is set to "0" (block 318). If the answer is "yes," then terminal u decreases its transmission power in a nominal down step size and/or at a nominal rate (block 320). Otherwise, terminal u increases its transmission power by the nominal up-step size and/or at the nominal rate (block 322).

Fig. 3 shows an embodiment in which OTA OSI reports convey inter-sector interference observed by neighboring sectors at one of three possible levels (low, high, and excessive). Process 300 may be extended to cover any number of interference levels. In general, the transmission power of terminal u may be: (1) decreasing a step down related to an amount of interference observed by neighboring sectors when the measured interference is above a given threshold (e.g., a larger step down for higher interference); and/or (2) increase an up step inversely related to an amount of interference observed by neighboring sectors when the measured interference is below a given threshold (e.g., a larger up step for lower interference). The step size and/or adjustment rate can also be determined based on other parameters such as, for example, the current transmit power level of the terminal, the channel gain of the neighboring sector relative to the channel gain of the serving sector, previous OTA OSI reports, and the like.

Terminal u may adjust its transmit power based on OTA OSI reports from one or more neighboring sectors. Terminal u may estimate the channel gain for each sector based on the pilot received from the sector. Terminal u may then derive the channel gain ratio for each neighboring sector as follows:

equation (9)

Wherein g is_ns，i(n) is the channel gain between terminal u and neighbor sector i;

g_ss(n) is the channel gain between terminal u and the serving sector; and is

r_i(n) is the channel gain ratio of the neighboring sector i.

In one embodiment, terminal u identifies the strongest neighbor sector with the largest channel gain ratio. Terminal u then adjusts its transmit power based on the OTA OSI report from only this strongest neighbor sector. In another embodiment, terminal u adjusts its transmit power based on OTA OSI reports from all sectors in the OSI group. This OSI group can contain: (1) t strongest adjacent sectors, wherein T is more than or equal to 1; (2) an adjacent sector having a channel gain ratio exceeding a channel gain ratio threshold; (3) neighboring sectors having a channel gain exceeding a channel gain threshold; (4) neighbor sectors included in a neighbor list broadcast by the serving sector; or (5) some other group of neighboring sectors. Terminal u can then adjust its transmit power in various ways based on OTA OSI reports from multiple neighboring sectors in the OSI group. For example, terminal u may reduce its transmit power when any neighboring sector in the OSI group observes high interference or excessive interference. As another example, terminal u may determine a transmission power adjustment for each neighbor sector in the OSI group, and may then combine the adjustments for all neighbor sectors in the OSI group to obtain a total transmission power adjustment.

In general, transmission power adjustment for interference control may be performed in conjunction with various power control schemes. For clarity, specific power control schemes are described below. For this power control scheme, the transmission power of the traffic channel assigned to terminal u can be expressed as:

P_dch(n)＝P_ref(n) + Δ P (n), equation (10)

Wherein P is_dch(n) updating the transmission power of the traffic channel in time interval n;

P_ref(n) is the reference power level in the update time interval n; and is

Δ p (n) is the transmission power increment in the update time interval n.

Transmission power level P_dch(n) and P_ref(n) and the transmission power increment Δ p (n) are given in decibels (dB).

Reference power level P_ref(n) is the amount of transmit power required to achieve the target SNR for a given transmission, which may be signaled by terminal u on a control channel or some other transmission. The reference power level and the target SNR may be adjusted to achieve a desired level of performance for a given transmission, such as 1% Packet Error Rate (PER). Received SNR for a data transmission if similar noise and interference characteristics are observed for the data transmission and a designated transmission on a traffic channel_dch(n) can be estimated as:

SNR_dch(n)＝SNR_target+ Δ p (n). Equation (11)

The transmission power delta Δ p (n) may be adjusted in a deterministic manner, a probabilistic manner, or in some other manner based on OTA OSI reports from neighboring sectors. The transmission power may be adjusted (1) by different amounts for different interference levels using deterministic adjustments; or (2) use probabilistic adjustments to adjust at different rates for different interference levels. Exemplary deterministic and probabilistic transmission power adjustment schemes are described below. For simplicity, the following description is directed to transmit power adjustment for OSI bits received from one neighbor sector. This OSI bit may be OSI bit 1 or 2.

Fig. 4 shows a process 400 for adjusting the transmission power of terminal u in a deterministic manner. Initially, terminal u processes the OTA OSI report from the neighboring sector (block 412) and determines whether the OSI bit is "1" or "0" (block 414). If the OSI bit is "1", indicating that the observed interference exceeds the interference threshold, the terminal u determines the reduction in the transmission power, or the step down Δ P_dn(n) (block 422). Transmission power delta deltaP (n-1) and channel gain ratio r of neighboring sectors, which may be based on a previous update time interval_ns(n) to determine Δ P_dn(n) of (a). Terminal u then decreases the transmission power increment by Δ P_dn(n) (block 424). Conversely, if the OSI bit is "0", terminal u determines the increase in transmission power, or the step up Δ P_up(n) (block 432). Can also be based on Δ P (n-1) and r_ns(n) determining Δ P_up(n) of (a). Terminal u then increases the transmission power increment by Δ P_up(n) (block 434). The transmission power adjustment in blocks 424 and 434 may be expressed as:

equation (12)

After blocks 424 and 434, terminal u limits the transmission power delta Δ p (n) to within the allowable transmission power delta range (block 442), as follows:

ΔP(n)∈[ΔP_min，ΔP_max]equation (13)

Wherein Δ P_minIs allowable for use in industryA minimum transmission power increment of a traffic channel, and

ΔP_maxis the maximum transmission power increment allowable for the traffic channel.

Limiting the transmission power increment for all terminals in a sector to within the transmission power increment range as shown in equation (13) can maintain intra-sector interference within acceptable levels. The minimum transmission power increment delta P can be adjusted by the control loop_minTo ensure that each terminal can meet the requirements of the quality of service (QoS) class to which the terminal belongs. Δ P for different QoS levels may be adjusted at different rates and/or in different steps_min。

Terminal u then bases on the transmission power increment Δ P (n) and the reference power level P_ref(n) calculating the transmission power P of the traffic channel_dch(n), as shown in equation (10) (block 444). Terminal u may transmit power P_dch(n) limiting to a maximum power level P_maxInner (block 446), as follows:

equation (14)

Terminal u uses transmission power P_dch(n) data transmission on the traffic channel.

In one embodiment, Δ P_dn(n) and Δ P_up(n) the step size is calculated as:

ΔP_dn(n)＝f_dn(ΔP_dn，min，ΔP(n-1)，r_ns(n)，k_dn) And equation (15a)

ΔP_up(n)＝f_up(ΔP_up，min，ΔP(n-1)，r_ns(n)，k_up) Equation (15b)

Wherein Δ P_dn，minAnd Δ P_up，minAre respectively Delta P_dn(n) and Δ P_up(n) minimum value;

k_dnand k_upAre respectively Delta P_dn(n) and Δ P_upA scaling factor of (n); and is

f_dn() And f_up() Respectively, calculating Δ P_dn(n) and Δ P_up(n) as a function of (n).

A function f can be defined_dn() So that Δ P_dn(n) with Δ P (n-1) and r_ns(n) both relate to each other. If high or excessive interference is observed by neighboring sectors, then (1) larger channel gain for neighboring sectors results in larger Δ P_dnLarger values of (n) and (2) Δ P (n-1) result in larger Δ P_dn(n) of (a). A function f can be defined_up() So that Δ P_up(n) with Δ P (n-1) and r_ns(n) both are inversely related. If the neighboring sector observes low interference, then (1) a larger channel gain for the neighboring sector results in a smaller Δ P_upLarger values of (n) and (2) Δ P (n-1) result in smaller Δ P_up(n)。

Fig. 4 shows processing for one OSI bit from one neighbor sector. Larger values may be used for Δ P when excessive interference is observed by neighboring sectors_dn(n) of (a). When high interference is observed by neighboring sectors, smaller values may be used for Δ P_dn(n) of (a). By using different scaling factors k, e.g. for high and excessive interference, respectively_dn1And k_dn2To obtain different step sizes of descent.

Fig. 5 shows a process 500 for adjusting the transmission power of terminal u in a probabilistic manner. Initially, terminal u processes the OTA OSI report from the neighboring sector (block 512) and determines whether the OSI bit is "1" or "0" (block 514). If the OSI bit is "1", then terminal u is based on, for example, Δ P (n-1) and r_ns(n) to determine a probability Pr for reducing the transmission power_dn(n) (block 522). Terminal u then randomly selects a value x between 0.0 and 1.0, where x is a random variable evenly 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 transmission power increment by Δ P_dn(block 528). Otherwise, if x is greater than Pr_dn(n)，Then terminal u maintains the transmit power delta at the current level (block 530).

If the OSI bit is "0" in block 514, then terminal u is based on, for example, Δ P (n-1) and r_ns(n) determining the probability Pr for increasing the transmission power_up(n) (block 532). Terminal u then randomly selects a value x 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 transmission power increment by Δ P_up(block 538). Otherwise, if x is greater than Pr_up(n), then terminal u maintains the transmission power increment at the current level (block 530). The transmit power adjustment in blocks 528, 530, and 538 may be expressed as:

equation (16)

ΔP_dnAnd Δ P_upMay be the same value (e.g., 0.25dB, 0.5dB, 1.0dB, etc.) or may be different values.

After blocks 528, 530, and 538, terminal u limits the transmit power increment as shown in equation (13) (block 542). Terminal u then bases on the transmission power increment Δ P (n) and the reference power level P_ref(n) calculating the transmission power P_dch(n), as shown in equation (10) (block 544), and transmit power P_dch(n) is further limited to the maximum power level as shown in equation (14) (block 546). Terminal u uses transmission power P_dch(n) data transmission on the traffic channel.

In one embodiment, the probability is calculated as follows:

Pr_dn(n)＝f′_dn(Pr_dn，min，ΔP(n-1)，r_ns(n)，k_dn) And equation (17a)

Pr_up(n)＝f′_up(Pr_up，min，ΔP(n-1)，r_ns(n)，k_up) Equation (17b)

Wherein Pr_dn，minAnd Pr_up，minAre respectively Pr_dn(n) and Pr_up(n) minimum value;

and f'_dn() And f'_up() Respectively calculating Pr_dn(n) and Pr_up(n) as a function of (n).

A function f 'may be defined'_dn() So that Pr is_dn(n) with Δ P (n-1) and r_ns(n) both relate to each other. If high interference or excessive interference is observed by neighboring sectors, then (1) greater channel gain for neighboring sectors results in greater Pr_dnLarger values of (n) and (2) Δ P (n-1) result in larger Pr_dn(n) of (a). Greater Pr_dn(n) results in a higher probability of reducing transmission power. A function f 'may be defined'_up() So that Pr is_up(n) with Δ P (n-1) and r_ns(n) both are inversely related. If the neighboring sector observes low interference, then (1) a larger channel gain for the neighboring sector results in a smaller Pr_upLarger values of (n) and (2) Δ P (n-1) result in smaller Pr_up(n) of (a). Smaller Pr_up(n) results in a lower probability of increasing the transmission power.

Fig. 5 shows processing for one OSI bit from one neighbor sector. Larger values may be used for Pr when an adjacent sector observes excessive interference_dn(n) of (a). When high interference is observed by neighboring sectors, a smaller value can be used for Pr_dn(n) of (a). E.g. by using different scaling factors k for high and excessive interference, respectively_dn1And k_dn2To obtain different probabilities of droop and thus different rates of power adjustment.

In general, Δ P may be calculated using various functions_dn(n) and Δ P_up(n) step size and Pr_dn(n) and Pr_up(n) probability. The function may be defined based on various parameters such as current transmit power, current transmit power delta, current OTA OSI report, previous OTA OSI report, channel gain, and so on. Each function may have different power control characteristics, such as the rate of convergence of transmission power adjustments and the distribution of transmission power increments for terminals in the systemThe influence of (c). The step size and probability may also be determined based on a look-up table or by some other method.

The transmission power adjustment and/or admission control described above may also be performed based on QoS level, user priority level, etc. For example, terminals using emergency services and policing terminals may have a higher priority and may be able to adjust transmission power at a faster rate and/or in larger steps than normal priority users. As another example, a terminal transmitting voice traffic may adjust the transmission power at a slower rate and/or in smaller steps.

Terminal u may also change the way transmission power is adjusted based on previous OTA OSI reports received from neighboring sectors. For example, terminal u may reduce its transmit power at a particular step down and/or at a particular rate when neighboring sectors report excessive interference, and may reduce transmit power at a larger step down and/or at a faster rate when neighboring sectors continue to report excessive interference. Alternatively or additionally, terminal u may ignore Δ P in equation (13) when the neighboring sector reports excessive interference or when the neighboring sector continues to report excessive interference_min。

Various embodiments of power control to mitigate inter-sector interference have been described above. Interference and power control may also be performed in other ways and this is within the scope of the invention.

In an embodiment, each sector broadcasts its OTA OSI report to terminals in neighboring sectors, as described above. The OTA OSI report can be broadcast with sufficient transmit power to achieve the desired coverage in the neighboring sector. Each terminal may receive OTA OSI reports from neighboring sectors and process these OTA OSI reports in a manner that achieves a sufficiently low false detection rate and a sufficiently low false alarm probability. False detection refers to detecting a failure of a transmitted OSI bit or value. False alarm refers to the detection of an error in a received OSI bit or value. For example, if the OSI bits are transmitted using BPSK, the terminal may announce the received OSI bits: (1) OSI bit < -B if detected OSI bit is below first threshold_thThen is "0"; (2) if detected OSI bitAbove the second threshold, OSI bit > + B_thThen is "1"; and (3) in other cases, + B_thOSI bit ≧ B_thAnd is empty. The terminal can typically trade off false detection rates against false alarm probabilities by adjusting the threshold for detection.

In another embodiment, each sector also broadcasts OTA OSI reports generated by neighboring sectors to terminals within its sector. Each sector thus acts as a proxy for neighboring sectors. This embodiment may ensure that each terminal may reliably receive OTA OSI reports generated by neighboring sectors because the terminal may receive these OTA OSI reports from the serving sector. This embodiment is well suited for asymmetric network layouts where the sector coverage size is not equal. Smaller sectors are typically transmitted at lower power levels and OTA OSI reports broadcast by these smaller sectors may not be reliably received by terminals in neighboring sectors. The smaller sector would then benefit from having its OTA OSI report broadcast by the neighboring sectors.

In general, a given sector m may broadcast OTA OSI reports generated by any number of other sectors and any of them. In an embodiment, sector m broadcasts an OTA OSI report generated by a sector in sector m's neighbor list. The proximity list may be formed by a network operator or in some other manner. In another embodiment, sector m broadcasts an OTA OSI report generated by all sectors in the terminal's active set contained in sector m. Each terminal may maintain an active set that includes all sectors in communication with the terminal. Sectors may be added to or removed from the active set as terminals handoff from one sector to another. In yet another embodiment, sector m broadcasts an OTA OSI report generated by all sectors in the candidate set for the terminal contained in sector m. Each terminal may maintain a candidate set that includes all sectors with which the terminal may communicate. Sectors may be added to or removed from the candidate set, e.g., based on channel gain and/or some other parameter. In yet another embodiment, sector m broadcasts an OTA OSI report generated by all sectors in the OSI group of terminals contained in sector m. The OSI group for each terminal may be defined as described above.

As described above, the system may utilize only user-based interference control or only network-based interference control. User-based interference control may be easier to implement because each sector and each terminal may act autonomously. Network-based interference control may provide improved performance because interference control is performed in a coordinated manner. The system may also utilize both user-based and network-based interference control. The system may also utilize user-based interference control at all times and may invoke network-based interference control only when excessive interference is observed. The system may also invoke each type of interference control for different operating conditions.

Fig. 6 shows a power control mechanism 600 that may be used to adjust the transmission power of terminal 120x in system 100. Terminal 120x is in communication with serving sector 110x and may generate interference to neighboring sectors 110 a-110 l. Power control mechanism 600 includes: (1) a reference loop 610 that operates between terminal 120x and serving sector 110 x; and (2) a second loop 620 that operates between terminal 120x and neighboring sectors 110a through 110 l. The reference loop 610 and the second loop 620 may operate simultaneously but may be updated at different rates, with the reference loop 610 being a faster loop than the second loop 620. For simplicity, fig. 6 shows only the portion of loops 610 and 620 that reside at terminal 120 x.

The reference loop 610 adjusts the reference power level P_ref(n) such that the received SNR for a given transmission measured at serving sector 110x is as close as possible to the target SNR. For reference loop 610, serving sector 110x estimates the received SNR for a given transmission, compares the received SNR to a target SNR, and generates Transmit Power Control (TPC) commands based on the comparison. Each TPC command may be: (1) an UP command commanding an increase in the reference power level; or (2) command a DOWN command with a reduced reference power level. Serving sector 110x transmits TPC commands on the forward link (cloud 670) to terminal 120 x.

At terminal 120x, a TPC command processor 642 detects the TPC commands transmitted by serving sector 110x and provides TPC decisions. Each TPC decision may be taken when a received TPC command is treated as an UP commandAn UP decision, or a DOWN decision, when the received TPC command is considered a DOWN command. The reference power adjustment unit 644 adjusts the reference power level based on the TPC decision. Unit 644 may determine P for each UP decision_ref(n) increasing the step size of the rise and P for each DOWN decision_ref(n) decreasing the step of decreasing. A Transmit (TX) data processor 660 scales the designated transmission to achieve the reference power level. Terminal 120x sends a designated transmission to serving sector 110 x.

Due to path loss, attenuation, and multipath effects (typically varying over time) on the reverse link (cloud 640), and especially for mobile terminals, the received SNR for a given transmission continuously fluctuates. The reference loop 610 attempts to maintain the received SNR for a given transmission at or near the target SNR when there is a change in reverse link channel conditions.

Second loop 620 regulates the transmission power P of the traffic channel assigned to terminal 120x_dch(n) such that as high a power level as possible is used for the traffic channels while keeping the inter-sector interference within acceptable levels. For the second loop 620, each neighboring sector 110 receives transmissions on the reverse link, estimates the inter-sector interference that the neighboring sector observes from terminals in other sectors, generates OTA OSI reports based on the interference estimates, and broadcasts OTAOSI reports to terminals in other sectors.

At terminal 120x, OSI report processor 652 receives the OTA OSI report broadcast by the neighboring sector and provides the detected OSI report to transmit power delta adjustment unit 656. Channel estimator 654 receives pilots from the serving 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 ratio for the neighboring sector and further adjusts the transmit power delta ap (n) based on the detected OSI report and the channel gain ratio, as described above. Unit 656 may implement processes 300, 400, and/or 500 shown in fig. 3-5. Transmission power calculation unit 658 based on the reference transmission level P from unit 644_ref(n), the transmit power delta ap (n) from unit 656, and possibly other factors, calculate the work of transmissionRate P_dch(n) of (a). TX data processor 660 uses transmit power P_dch(n) data transmission to serving sector 110 x.

Fig. 6 shows an exemplary power control mechanism that may be used for interference control. The interference control may also be performed in other ways and/or with different parameters than those described above.

Fig. 7 shows a block diagram of an embodiment of a terminal 120x, a serving base station 110x, and a neighboring base station 110 y. For clarity, the following description assumes the use of the power control mechanism 600 shown in fig. 6.

On the reverse link, at terminal 120x, a TX data processor 710 encodes, interleaves, and symbol maps Reverse Link (RL) traffic data and control data and provides data symbols. A modulator (Mod)712 maps the data symbols and pilot symbols onto the appropriate subbands and symbol periods, performs OFDM modulation as applicable, and provides a sequence of complex-valued chips. A transmitter unit (TMTR)714 conditions (e.g., converts to analog, amplifies, filters, and frequency upconverts) the chip sequence and generates a reverse link signal, which is transmitted via an antenna 716.

At serving base station 110x, multiple antennas 752xa through 752xt receive the reverse link signals from terminal 120x and the other terminals. Each antenna 752x provides a received signal to a respective receiver unit (RCVR)754 x. Each receiver unit 754x conditions (e.g., filters, amplifies, frequency downconverts, and digitizes) its received signal, performs OFDM demodulation if applicable, and provides received symbols. An RX spatial processor 758 performs receiver spatial processing on the received symbols from all receiver units and provides data symbol estimates as estimates of the transmitted data symbols. RX data processor 760x demaps, deinterleaves, and decodes the data symbol estimates and provides decoded data for terminal 120x and other terminals currently served by base station 110 x.

The processing for forward link transmissions may be performed similar to that described above for the reverse link. The processing of transmissions on the forward and reverse links is typically specified by the system.

For interference and power control, at serving base station 110x, RX spatial processor 758x estimates the received SNR for terminal 120x, estimates the inter-sector interference observed by base station 110x, and estimates SNR and interference (e.g., measured interference I) for terminal 110x_meas，m) To the controller 770 x. Controller 770x generates TPC commands for terminal 120x based on the SNR estimate for the terminal and the target SNR. Controller 770x may generate an OTA OSI report and/or an IS OSI report based on the interference estimate. Controller 770x may also receive IS OSI reports from neighboring sectors via a communication (Comm) unit 774 x. The TPC commands, OTA OSI reports for base station 110x, and possibly OTA OSI reports for other sectors, are processed by a TX data processor 782x and a TX spatial processor 784x, conditioned by transmitter units 754xa through 754xt, and transmitted via antennas 752xa through 752 xt. An IS OSI report from base station 110x can be sent to a neighboring sector via communication unit 774 x.

At neighboring base station 110y, multiple antennas 752ya through 752yt receive the reverse link signals from terminal 120x and other terminals. Each antenna 752y provides a received signal to a respective receiver unit (RCVR)754ya through 754 yt. Each receiver unit 754y conditions (e.g., filters, amplifies, frequency downconverts, and digitizes) its received signal, performs OFDM demodulation if applicable, and provides received symbols. An RX spatial processor 758y estimates the inter-sector interference observed by base station 110y and provides an interference estimate to a controller 770 y. RX data processor 760y demaps, deinterleaves, and decodes the data symbol estimates and provides decoded data for terminal 120x and other terminals currently served by base station 110 y. Controller 770y may generate an OTA OSI report and/or an IS OSI report based on the interference estimate. The OTA OSI report is processed and broadcast to the terminals in the system. The IS OSI report can be sent to the neighboring sector via communication unit 774 y. OTA OSI reports for base station 110y and possibly other sectors are processed by TX data processor 782y and TX spatial processor 784 y.

At terminal 120x, an antenna 716 receives forward link signals from the serving and neighboring base stations and provides a received signal to a receiver unit 714. The received signal is conditioned and digitized by a receiver unit 714 and further processed by a demodulator (Demod)742 and a RX data processor 744. Processor 744 provides TPC commands for terminal 120x that are sent by serving base station 110x and OTA OSI reports that are broadcast by neighboring base stations. A channel estimator within demodulator 742 estimates the channel gain for each base station. Controller 720 detects the received TPC commands and updates the reference power level based on the TPC decisions. Controller 720 also adjusts the transmit power of the traffic channel based on the OTA OSI reports received from the neighboring base stations and the channel gains of the serving and neighboring base stations. Controller 720 provides the transmission power for the traffic channel assigned to terminal 120 x. Processor 710 and/or modulator 712 scales the data symbols based on the transmit power provided by controller 720.

Controllers 720, 770x, and 770y direct the operation of various processing units at terminal 120x and base stations 110x and 110y, respectively. The controllers may also perform various functions for interference and power control. For example, controller 720 may implement any or all of units 642-658 shown in fig. 6 and/or processes 300, 400, and/or 500 shown in fig. 3-5. Controller 770 of each base station 110 may implement all or a portion of process 200 in fig. 2. Memory units 722, 772x, and 772y store data and program codes for controllers 720, 770x, and 770y, respectively. Scheduler 780x schedules terminals for communication with base station 110x and also assigns traffic channels to the scheduled terminals, e.g., based on IS OSI reports from neighboring base stations.

The interference control techniques described herein may be implemented by various methods. For example, these techniques may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units used to perform interference control at a base station may be implemented within one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, electronic devices, other electronic units designed to perform the functions described herein, or a combination thereof. The processing units used to perform interference control at the terminal may also be implemented within one or more ASICs, DSPs, processors, electronic devices, and so on.

For a software implementation, the interference control techniques may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit (e.g., memory unit 722, 772x, or 772y in fig. 7) and executed by a processor (e.g., controller 720, 770x, or 770 y). The memory unit may be implemented within the processor or external to the processor.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A method for interference control, comprising:

estimating interference observed by a sector from terminals in neighboring sectors and obtaining an interference estimate therefrom;

generating an over-the-air (OTA) Other Sector Interference (OSI) report based on the interference estimate;

broadcasting the over-the-air (OTA) Other Sector Interference (OSI) report to the terminals of the neighboring sectors;

generating an inter-sector (IS) OSI report based on the interference estimate, wherein the IS OSI report IS more comprehensive than the OTA OSI report;

sending the IS OSI report from the sector to the neighboring sector;

receiving interference reports from the neighboring sectors; and

adjusting data transmissions for terminals on the sector based on the interference reports received from the neighboring sectors.

2. The method of claim 1, further comprising:

obtaining a plurality of interference estimates; and

averaging the plurality of interference estimates over a plurality of receive antennas and thereby obtaining an average of the plurality of interference estimates;

wherein the over-the-air (OTA) Other Sector Interference (OSI) report is generated based on the average of the plurality of interference estimates.

3. The method of claim 1, wherein at least one of the OTA OSI report and the IS OSI report indicates whether the interference estimate IS greater than or less than a threshold.

4. The method of claim 1, wherein at least one of the OTA OSI report and the IS OSI report conveys the interference estimate relative to a plurality of thresholds.

5. The method of claim 1, further comprising broadcasting the interference report received from the neighboring sector to the terminals on the sector.

6. An apparatus for interference control, comprising:

means for estimating interference observed by a sector from terminals in neighboring sectors, and obtaining an interference estimate therefrom;

means for generating an over-the-air (OTA) Other Sector Interference (OSI) report based on the interference estimate;

means for broadcasting the over-the-air (OTA) Other Sector Interference (OSI) report to the terminal of the neighboring sector;

means for generating an inter-sector (IS) OSI report based on the interference estimate, wherein the IS OSI report IS more comprehensive than the OTA OSI report;

means for transmitting the inter-sector (IS) OSI report from the sector to the neighboring sector;

means for receiving interference reports from the neighboring sectors; and

means for adjusting data transmissions for terminals on the sector based on the interference reports received from the neighboring sectors.

7. The device of claim 6, further comprising:

means for obtaining a plurality of interference estimates; and

means for averaging the plurality of interference estimates over a plurality of receive antennas and thereby obtaining an average of the plurality of interference estimates;

wherein the over-the-air (OTA) Other Sector Interference (OSI) report is generated based on the average of the plurality of interference estimates.

8. The apparatus of claim 6, wherein at least one of the OTA OSI report and the IS OSI report indicates whether the interference estimate IS greater than or less than a threshold.

9. The apparatus of claim 6, wherein at least one of the OTA OSI report and the IS OSI report conveys the interference estimate relative to multiple thresholds.

10. The device of claim 6, further comprising means for broadcasting the interference report received from the neighboring sector to the terminals on the sector.