KR100914562B1 - Power control for a wireless communication system utilizing orthogonal multiplexing - Google Patents

Abstract

The present invention relates to techniques for adjusting transmit power to reduce both intra-sector interference for a serving base station and inter-sector interference for adjacent base stations. The amount of intersector interference that a terminal can cause can be estimated roughly based on the total interference observed by each neighboring base station, channel gains for the serving base station and neighboring base stations, and the current transmit power level. The transmit power may be reduced if high interference is observed by neighboring base stations and may be increased in other cases. The transmit power may be adjusted by a larger amount and / or more often when the terminal is located closer to the adjacent base station that observes high interference and / or when the current transmit power level is higher and vice versa. In-sector interference is maintained within an acceptable level by limiting the received SNR for the terminal to be within a range of acceptable SNRs.

Description

POWER CONTROL FOR A WIRELESS COMMUNICATION SYSTEM UTILIZING ORTHOGONAL MULTIPLEXING}

Claiming Priorities in 35 U.S.C. §119

This patent application claims the priority of provisional application number 60 / 580,819 entitled “Reverse Link Power Control Algorithm”, filed June 18, 2004, which is assigned to the assignee of the present application and incorporated herein by reference. .

Reference to co-pending patent application

This patent application is related to the following co-pending US patent applications:

Document number 040404U1, filed on July 13, 2004, which is assigned to the assignee of the present application and incorporated herein by reference, "A robust erase detection and erase rate based closed loop power control" by Arak Sutivong et al.

TECHNICAL FIELD The present invention generally relates to communications, and more particularly to power control in wireless communication systems.

A wireless multiple access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations by transmissions on the forward and reverse links. The forward link (or down link) refers to the communication link from the base stations to the terminals, and the reverse link (or up link) refers to the communication link from the terminals to the base stations.

Multiple terminals can transmit simultaneously on the reverse link by multiplexing their transmissions to be orthogonal to each other. Multiplexing attempts to achieve orthogonality between multiple reverse link transmissions in time, frequency and / or code domain. If achieved, the transmission from each terminal does not interfere with transmissions from other terminals at the receiving base station due to full orthogonality. However, complete orthogonality between transmissions from different terminals is often not realized due to channel environments, receiver faults and the like. Due to the lack of orthogonality, each terminal generates some interference to other terminals communicating with the same base station. Also, transmissions from terminals communicating with different base stations are generally not orthogonal to each other. Thus, each terminal may cause interference to terminals communicating with adjacent base stations. The performance of each terminal is reduced by interference from all other terminals in the system.

Thus, there is a need for techniques that reduce the effects of interference so that improved performance is achieved.

1 illustrates a wireless multiple access communication system.

2 shows frequency hopping in the time-frequency plane.

3 shows a process for adjusting the transmit power in a probabilistic manner.

4 shows a process for adjusting the transmit power in a deterministic manner.

5 illustrates a power control mechanism for the data channel.

6 illustrates a power control mechanism for a control channel.

7 illustrates a terminal, a service base station, and a neighbor base station.

Disclosed herein are techniques for controlling transmit power for data transmission from a wireless terminal in a manner that reduces both "intra-sector" interference and "inter-sector" interference. The transmit power is within acceptable levels of both the amount of intersectoral interference that the terminal may cause for "serving" and the amount of intersectoral interference that the terminal may cause for "neighbor" base stations. Adjusted to maintain at. (The terminology used is described below.) The amount of intersector interference that a terminal may encounter is (1) the total interference observed by each neighboring base station, (2) the channel gains for the serving base stations and neighboring base stations, It can be estimated roughly based on (3) the current transmit power level used by the terminal, and (4) possibly other parameters. Each base station may broadcast a report (eg, a single bit) indicating the total interference observed by that base station. The channel gain for each base station can be estimated based on the pilot received from the base station. The transmit power may be adjusted in a probabilistic manner, in a deterministic manner, or in some other manner based on the other parameters.

In general, the transmit power can be reduced when high interference is observed by neighboring base stations and increased when low interference is observed. The transmit power may also be adjusted by a larger amount and / or more often when (1) the terminal is located adjacent to a neighbor base station that observes high interference and / or (2) when the current transmit power level is higher. . The transmit power may be adjusted by (1) a smaller amount and / or less frequently when the terminal is located closer to the serving base station and / or when the current transmit power level is lower. In-sector interference caused by the terminal is maintained within an acceptable level by limiting the received signal quality (SNR) for data transmission to be within a range of acceptable SNRs.

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

The features and characteristics of the present invention are explained with reference to the following drawings.

The term "exemplary" is used herein to mean "an example, case, or description." Any embodiment or design disclosed herein as "exemplary" need not be considered to be advantageous or desirable in other embodiments or designs.

1 illustrates a wireless multiple access communication system 100. System 100 includes a number of base stations 110 that support communication for a number of wireless terminals 120. Terminals 120 are generally distributed throughout the system, and each terminal may be fixed or mobile. A terminal may also be referred to as a mobile station, user equipment (UE), wireless communication device, or some other technical terminology. A base station is a fixed station used to communicate with terminals and may be referred to as an access point, a Node B, or some other terminology. System controller 130 is connected to base station 110, provides coordination and control for the base stations, and further controls the routing of data to terminals served by the base stations.

Each base station 110 provides communication coverage for an individual geographic area 102. A base station and / or its coverage area may be referred to as a "cell" depending on the context in which the term is used. To increase performance, the coverage area of each base station can be divided into multiple (eg, three) sectors 104. Each sector is serviced by a base station transceiver subsystem (BTS). The term “sector” may refer to a BTS and / or its coverage area depending on the context in which the term is used. For a sectorized cell, the base station for that cell generally includes the BTSs for all sectors of that cell. For simplicity, in the following description the term “base station” is used for both fixed stations serving cells and fixed stations serving sectors. A "service" base station or "service" sector is a base station or sector with which the terminal communicates. An "adjacent" base station or "adjacent" sector is a base station or sector with which the terminal does not communicate. For simplicity, in the following description each terminal communicates with one serving base station, but this need not be limited to the techniques described herein.

The power control techniques disclosed herein can be used for various wireless communication systems. For example, the techniques may be used for time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and the like. TDMA systems use time division multiplexing (TDM), and transmissions for different terminals can be orthogonalized by transmitting at different time intervals. FDMA systems use frequency division multiplexing (FDM), and transmissions for different terminals can be orthogonalized by transmitting in different frequency subbands. TDMA and FDMA systems use code division multiplexing (CDM). In that case, transmissions for multiple terminals are orthogonalized using different orthogonal (eg Walsh) codes, while transmitted in the same time interval or frequency subband. An OFDM system uses Orthogonal Frequency Division Multiplexing (OFDM), which efficiently partitions the overall system bandwidth into multiple (N) orthogonal frequency subbands. The subbands are referred to as tones, sub-carriers, bins frequency channels, and so forth. Each subband is associated with an individual sub-carrier that can be modulated with data. An OFDMA system uses any combination of time, frequency and / or code division multiplexing. For clarity, power control techniques are described below for an OFDMA system.

For an OFDMA system, multiple "traffic" channels are used for (1) each subband is used for only one traffic channel at any given time interval, and (2) for each traffic channel zero at each time interval, One, or multiple subbands can be defined that can be allocated. Traffic channels may include "data" channels used to transmit traffic / packet data and "control" channels used to transmit overhead / control data. Traffic channels may be referred to as physical channels, transport channels or any other terminology.

The traffic channels for each sector can be defined as orthogonal to each other in time and frequency, so that no two traffic channels use the same subband in any given time interval. The orthogonality prevents intrasector interference between multiple transmissions transmitted simultaneously on multiple traffic channels within the same sector. Loss of orthogonality can cause various effects such as, for example, intercarrier interference (ICI) and intersymbol interference (ISI). The loss of orthogonality results in intrasector interference. Traffic channels for each sector may be defined as pseudo-random with respect to traffic channels for neighboring sectors. This randomizes intersectoral interference or other sector interference caused by traffic channels in adjacent sectors by traffic channels in one sector. Randomized intrasector interference and intersector interference can be achieved in various ways. For example, frequency hopping can provide frequency diversity against adverse path effects as well as randomized intrasector and intersector interference.

2 shows frequency hopping (FH) in the time-frequency plane 200 for an OFDMA system. In frequency hopping, each traffic channel is associated with a specific FH sequence that indicates the particular subband (s) used for that traffic channel at each time interval. The FH sequences for different traffic channels in each sector are orthogonal to each other, so no two traffic channels use the same subband in any time interval. The FH sequences for each sector are also pseudo random with respect to the FH sequences for adjacent sectors. Interference between two traffic channels in two sectors occurs whenever the two traffic channels use the same subband within the same time interval. However, intrasector interference is randomized due to the pseudo random nature of the FH sequences used for different sectors.

Data channels can be assigned to active terminals so that each data channel is used by only one terminal at any given time. To conserve system resources, control channels can be shared among multiple terminals, for example using code division multiplexing. If the data channels are orthogonal multiplexed only at frequency and time (not code), the data channels are less susceptible to loss of orthogonality due to channel conditions and receiver imperfections than control channels.

The data channels thus have some key characteristics suitable for power control. First, intracell interference in data channels is minimal due to orthogonal multiplexing in frequency and time. Secondly, intercell interference is randomized because adjacent sectors use different FH sequences. The amount of intercell interference generated by a given terminal is determined by (1) the transmission power level used by the terminal and (2) the location of the terminal relative to neighboring base stations.

For data channels, power control may be performed to allow each terminal to transmit at the highest power level possible while maintaining intra-cell interference and inter-cell interference within acceptable levels. A terminal located adjacent to a serving base station may be allowed to transmit at a higher power level because the terminal may cause less interference to neighboring base stations. Conversely, a terminal located away from the serving base station toward the sector edge may be allowed to transmit at lower power levels because the terminal may cause more interference to neighboring base stations. Controlling transmit power in this manner temporarily reduces the overall interference observed by each base station while allowing "suitable" terminals to achieve higher SNRs and higher data rates.

Power control for data channels may be performed in various ways to achieve the aforementioned goals. For clarity, certain embodiments of power control are described below. For this embodiment, the transmit power for the data channel for a given terminal can be expressed as follows:

P _dch (n) = P _ref (n) + ΔP (n), equation (1)

P _dch (n) is the transmit power for the data channel during update interval n,

P _ref (n) is the reference power level for update interval n,

ΔP (n) is the transmit power delta for the update interval n.

Power levels P _dch (n) and P _ref (n) and transmit power delta ΔP (n) are given in decibels (dB).

The reference power level is the amount of transmit power required to achieve the target signal quality for a designated transmission (eg, over a control channel). Signal quality (denoted SNR) may be defined by the signal-to-noise ratio, signal-to-noise and interference ratio, and the like. The reference power level and target SNR may be adjusted by the power control mechanism to achieve the required performance level for the designated transmission as described below. If the reference power level can achieve the target SNR, the received SNR for the data channel can be calculated as follows:

SNR _dch (n) = SNR _target + ΔP (n). Formula (2)

Equation (2) assumes that the data channel and the control channel have similar interference statistics. This is the case, for example, if control and data channels from different sectors can interfere with each other. The reference power level can be determined as follows.

The transmit power for the data channel is determined by (1) the amount of intersector interference that a terminal can cause to other terminals in adjacent sectors, (2) the amount of intrasector interference that a terminal can cause to other terminals in the same sector, and (2) the terminal. It may be set based on the maximum power level allowed for and (4) various factors, possibly other factors. Each of these factors is described below.

The amount of intersector interference that each terminal may occur may be determined in various ways. For example, the amount of intersector interference generated by each terminal may be estimated directly by each neighboring base station or may be transmitted to the terminal to adjust the corresponding transmit power. The individual interference report may require extensive overhead signaling. For the sake of simplicity, the amount of intersector interference that each terminal may generate is (1) the total interference observed by each neighboring base station, (2) the channel gains for the serving base station and the neighboring base station, and (3) by the terminal. It can be estimated briefly based on the transmit power level used. The amounts (1) and (2) are described below.

Each base station can estimate the total or average amount of interference observed by that base station. This can be accomplished by estimating the interference power in each subband and calculating the average interference power based on the interference power estimates for the individual subbands. Average interference power can be obtained using various average techniques such as, for example, arithmetic mean, geometric mean, SNR-based mean, and the like.

For an arithmetic mean, the average interference power can be expressed as:

Formula (3)

I _m (k, n) is an interference power estimate for sector m in subband k within time interval n,

I _{meas , m} (n) is the average interference power for sector m in time interval n.

The quantities I _m (k, n) and I _{meas , m} (n) are linear units in equation (3), but can be given in decibels (dB). Using the arithmetic mean, some large interference power estimates distort the average interference power.

For the geometric mean, the average interference power can be expressed as:

Formula (4)

The geometric mean suppresses large interference power estimates for some subbands so that the average interference power is lower than when using the arithmetic mean.

For SNR-based averages, the average interference power can be expressed as follows:

Formula (5)

P _nom denotes the nominal received power assumed for each subband. Equation (5) determines the theoretical performance of each subband based on the nominal received power, calculates the average performance for all N subbands, and determines the average interference power that provides the average performance. SNR-based averages (also called performance-based averages) suppress large interference power estimates for some subbands.

Regardless of the average technique used, each base station may filter the power estimates and / or average interference power in multiple time intervals to improve the quality of the interference measurement. Filtering can be accomplished using a finite impulse response (FIR) filter, an infinite impulse response (IIR) filter, or any other type of filter known in the art. The term “interference” may refer to filtered or unfiltered interference in the description herein.

Each base station may broadcast interference measurements for use by terminals in other sectors. Interference measurements may be broadcast in various ways. In one embodiment, the average interference power (or “measured” interference) is quantized into a predetermined number of bits transmitted over the broadcast channel. In another embodiment, the measured interference is broadcast using a single bit indicating whether the measured interference is above or below the nominal interference threshold. In another embodiment, the measured interference is broadcast using two bits. One bit represents the measured interference with respect to the nominal interference threshold. The other bit can be used as a fault / panic bit that indicates whether the measured interference exceeds the high interference threshold. Interference measurements may also be transmitted in other ways.

For simplicity, the following description assumes that the use of a single different center interference (OSI) is for providing interference information. Each base station may set its OSI bit (OSIB) as follows:

Formula (6)

The I _target is a nominal interference threshold.

Optionally, each base station can obtain a measured interference to thermal noise (IOT), which is the ratio of the total interference power to thermal noise power observed by the base station. The total interference power can be calculated as described above. Thermal noise power can be calculated by turning off the transmitter and measuring noise at the receiver. The specific operating point is selected for the system and is marked as an IOT _target . Higher operating point allows terminals to use higher transmit powers (on average) for data channels. However, a very high operating point may cause undesirable interference because the system allows interference to be limited, and in such situations an increase in transmit power does not change with an increase in the received SNR. In addition, very high operating points increase the likelihood of system instability. In any case, each base station may set its OSI bit as follows:

Formula (7)

IOT _{meas , m} (n) is the IOT measured for sector m within time interval n,

The IOT _target is the operating point required for the sector.

For both cases, the OSI bit can be used for power control as follows. Each terminal may estimate the channel gain (or propagation path gain) for each base station capable of receiving reverse link transmission from the terminal. The channel gains for each base station are processed over time (eg, hundreds of milliseconds) to process pilots received from the base station on the forward link, estimate received pilot strength / power, and remove the effects of fast fading. Can be estimated by filtering the pilot strength estimates (using a filter with a time constant). If all base stations transmit their pilots at the same power level, the pilot strength received for each base station indicates the channel gain between the base station and the terminal. The terminal has a channel gain ratio vector as Can form:

Formula (8)

remind Formula (9)

G _s (n) is the channel gain between the terminal and the serving base station,

g _ni (n) is the channel gain between the terminal and the adjacent base station i,

r _i (n) is the channel gain ratio for the adjacent base station i.

Since the distance is inversely proportional to the channel gain, the channel gain ratio g _s (n) / g _ni (n) is observed as a “relative distance” indicating the distance to the neighboring base station i and the distance to the serving base station relative to it. In general, the channel gain ratio r _i (n) for neighboring base stations decreases as the terminal moves toward the sector edge and increases as the terminal moves adjacent to the serving base station. Channel gain ratio vector Can be used for power control as follows.

The data channels for each sector are multiplexed to be orthogonal to each other, but any loss of orthogonality can result in intercarrier interference (ICI), intersymbol interference (ISI), and the like. The loss of orthogonality results in intrasector interference. In order to mitigate intrasector interference, the transmit power of each terminal may be controlled such that the amount of intrasector interference that the terminal may experience to other terminals in the same sector is maintained within an acceptable level. This can be accomplished, for example, by requiring that the received SNR for each terminal's data channel be within a predetermined SNR range as follows:

SNR _dch (n) ∈ [SNR _min , SNR _max ], equation (10)

The SNR _min is the minimum allowable SNR for the data channel,

SNR _max is the maximum receive SNR allowable for the data channel.

The minimum received SNR ensures that, in particular, all terminals located adjacent to the sector edge can achieve the minimum performance level. Without such constraints, terminals located near the sector edge can transmit at very low power levels because they often provide a significant amount of intersector interference.

If the received SNRs for the data channels of all terminals are limited within the range [SNR _min , SNR _max ], then the amount of intersectoral interference generated by each terminal due to loss of orthogonality is assumed to be within an acceptable level. do. By limiting received SNRs within the SNR range, the received power spectral density between adjacent subbands is (SNR _max). SNR _min ) may be greater than the dB difference (similar inter-sector interference is observed in the subbands, for example, where control and data channels randomly hop so that control and data channels from different sectors may collide with each other. Assuming it is true). The small SNR range improves the robustness of the system in the presence of ICI and ISI. An SNR range of 10 dB is found to provide good performance in most operating scenarios. Other SNR ranges may also be used.

If the transmit power of the data channel is determined as shown in equation (1), then the received SNR for the data channel is limited to [SNR] by limiting the transmit power delta ΔP (n) to be within a corresponding range as follows. _min , SNR _max ]

ΔP (n) ∈ [ΔP _min , ΔP _max ], equation (11)

[Delta] P _min is the minimum allowable transmit power delta for the data channel and [Delta] P _{m ax} is the maximum allowable transmit power delta for the data channel.

In particular, ΔP _min = SNR _min -SNR _target , ΔP _max = SNR _max -SNR _target . In another embodiment, the transmit power P _dch (n) is limited to be within a range determined for example based on the received signal power for the data channel. This embodiment can be used, for example, when the interference power is statistically different between the subbands.

The transmit power for the data channel of each terminal can be adjusted based on the following parameters:

OSI bits broadcast by each base station;

Channel gain ratio vector calculated by the terminal ;

The range of allowable received SNRs for data channels [SNR _min , SNR _max ] or the range of allowable transmit power deltas [ΔP _min , ΔP _max ]; And

The maximum power level P _max that may be set by the power amplifier or system in the terminal and allowed by the terminal.

Parameters 1) and 2) relate to the intersectoral interference generated by the terminal. Parameter 3) relates to intrasector interference generated by the terminal.

In general, a terminal located adjacent to an adjacent sector reporting high interference transmits using a lower transmit power delta, so that the received SNR becomes a value adjacent to SNR _min . Conversely, a terminal placed adjacent to a serving base station can transmit with a high transmit power delta, so that the received SNR becomes a value adjacent to SNR _max . The reduction in received SNRs can be observed based on their proximity to the serving base stations for the terminals in the system. The scheduler at each base station can distribute the received SNRs to achieve high throughput while ensuring fairness for the terminal.

The transmit power for the data channel can be adjusted in various ways based on the four parameters described above. The power control mechanism does not need to maintain the same SNR, especially for all terminals in an orthogonal system similar to the OFDMA system, and terminals adjacent to the base station can transmit at higher transmit power without causing significant problems to other terminals. For clarity, specific embodiments for adjusting the transmit power are described below. For this embodiment, each terminal monitors the OSI bits broadcast by neighboring base stations, so that the vector Respond to the OSI of the strongest neighbor base station with the smallest channel gain ratio within. If the OSI bit of a given base station is set to '1' (due to the base station observed to be higher than the nominal intersector interference), the transmit power of the terminals having the base station as the strongest neighboring base station can be adjusted down. On the contrary, if the OSI bit is set to '0', the transmission power of the terminals having the base station as the strongest neighbor base station may be adjusted upward. For other embodiments, each terminal may adjust its transmit power based on one or more OSI bits obtained for one or more base stations (eg, service and / or neighbor base stations). .

Thus, the OSI bit determines the direction to adjust the transmit power. The amount of transmit power adjustment for each terminal may be determined according to (1) the current transmit power level (or current transmit power delta) of the terminal and (2) the channel gain ratio for the strongest neighbor base station. Table 1 lists some rules for adjusting transmit power based on transmit power delta and channel gain ratio for the strongest base station.

Table 1

OSI bit Transmit Power Regulation '1' (high interference level) A terminal with a smaller channel gain ratio (and thus adjacent) for a base station transmitting an OSI bit will generally have its transmit power delta compared to a terminal with a larger channel gain ratio (and thus farther away) for that base station. Decreases by a larger amount. A terminal with a larger transmit power delta generally reduces its transmit power delta by a larger amount compared to a terminal with a similar channel gain or smaller transmit power delta for the base station. '0' (low interference level) A terminal with a larger channel gain ratio (and thus farther away) for a base station transmitting an OSI bit will generally have its transmit power delta compared to a terminal with a smaller channel gain ratio (and thus adjacent) for that base station. Increase by a larger amount. Terminals with smaller transmit power deltas generally increase their transmit power deltas by a greater amount compared to terminals with similar channel gains or larger transmit power deltas for the base station.

The transmit power may be adjusted in a deterministic manner, probabilistic manner or any other manner. For deterministic adjustment, the transmit power is adjusted in a predefined manner based on the appropriate parameters. For stochastic adjustment, the transmit power has a certain probability of being adjusted, which probability is determined by appropriate parameters. Exemplary deterministic and probabilistic adjustment schemes are described below.

3 shows a flowchart of a process 300 for adjusting transmit power in a probabilistic manner. Process 300 may be performed by each terminal during each time interval in which OSI bits are transmitted. First, the terminal processes the OSI bit of the strongest neighbor base station (block 312). The terminal then determines whether the OSI bit is '1' or '0' (block 314).

If the 'I' indicates that the OSI bit is higher than the nominal interference level, the terminal determines the probability Pr _dr (n) for reducing the transmission power (block 322). Pr _dr (n) can be calculated as follows based on the current transmit power delta ΔP (n) and the channel gain ratio r _osib (n) for the strongest neighbor base station. The terminal then randomly selects a value x between 0.0 and 1.0 (block 324). In particular, x is a k random variable distributed uniformly between 0.0 and 1.0. If the randomly selected value x is equal to or less than the probability Pr _dr (n) as determined in block 326, then the terminal reduces its transmit power by [Delta] P _dn down step as follows (block 328):

ΔP (n + 1) = ΔP (n) _{−ΔP dn} . Formula (12)

Otherwise, if x is greater than Pr _dr (n), the terminal maintains the transmit power delta at the current level (block 330). From blocks 328 and 330, the process proceeds to block 342.

If at block 314 the '0' indicates that the OSI bit is below the nominal interference level, then the terminal may, for example, increase the transmit power based on ΔP (n) and r _osib (n) as described below. The probability Pr _up (n) is determined (block 332). The terminal then randomly selects the value x between 0.0 and 1.0 (block 334). If the randomly selected value x the probability as determined in block 336 Pr _up (n) and equal to or less than, the terminal is increased by △ P _up-up phase such as to the transmit power deltas (block 338):

ΔP (n + 1) = ΔP (n)-ΔP _up . Formula (12)

The step sizes for ΔP _up and ΔP _dn may both be set to the same appropriate value (eg, 0.25 dB, 0.5 dB, 1.0 dB, etc.). If x is greater than Pr _up (n) of block 336, then the terminal maintains the transmit power delta at the same level (block 330). From blocks 330 and 338, the process proceeds to block 342.

At block 342, the terminal is limited to a value in the transmit power delta △ P (n + 1) the allowable range ^{_{[△ P min,, △ P}} max]. The terminal then transmits the transmit power P _dch (n + 1) for the next time interval based on the transmit power delta ΔP (n + 1) and the reference power level P _ref (for the next time interval) as shown in equation (1). n + 1) (block 344). The terminal then limits the transmit power P _dch (n + 1) to be within the maximum power level (block 346) as follows.

Formula (14)

The terminal uses the transmit power P _dch (n + 1) for the next time interval.

The probabilities Pr _dn (n) and Pr _up (n) may be a function of the transmit power delta ΔP (n) and the channel gain ratio r _osib (n) for the strongest base station. Various functions can be used for Pr _dn (n) and Pr _up (n). Each function can have different effects on various power control characteristics such as (1) the convergence rate of transmit power regulation and (2) the distribution of transmit power deltas for terminals in the system.

In one embodiment, the probabilities Pr _dn (n) and Pr _up (n) can be defined as follows:

Formula (15a)

Formula (15b)

remind Formula (15c)

Formula (15d)

Pr _ΔP (n) is the probability associated with the transmit power level,

Pr _gain (n) is the probability associated with the channel gain ratio for the strongest neighbor base station,

r _max and r _min normalize the selected constants to achieve the required power control characteristics,

Pr _{up , min} is the minimum probability for up-regulation of the transmit power,

Pr _{dn , min} is the minimum probability for down regulation of the transmit power.

For the embodiment shown by equation set 15, Pr _dn (n) and Pr _up (n) are joint probabilities determined by the transmit power level and channel gain ratio for the strongest neighbor base station. The minimum probabilities Pr _{up , min} and Pr _{dn , min} improve steady state characteristics and promote some movement to points in extremes (eg, with very high or very low channel gain values). The probabilities Pr _dn (n) and Pr _up (n) derived as shown in equation set 15 follow the general transmit power adjustment rules given in Table 1. Probabilities Pr _dn (n) and Pr _up (n) can be derived using any other functions, which are within the spirit of the present invention.

4 shows a flow diagram of a process 400 for adjusting transmit power in a deterministic manner. Process 400 may also be performed by each terminal for each time interval over which OSI bits are transmitted. The terminal processes the OSI bit of the strongest neighbor base station (block 412) and determines whether the OSI bit is '1' or '0' (block 414). If the OSI bit is '1', the terminal determines the amount of decrease DELTA P _dn (n + 1) for the next time interval (block 422). The variable down step size may be determined based on the current transmit power delta ΔP (n) and the channel gain ratio r _osib (n) for the strongest base station. The terminal then decreases the transmit power delta by [Delta] P _dn (n + 1) (block angle 424). Otherwise, if the OSI bit is '0', the terminal determines, for example, the transmission power increase ΔP _up (n + 1) for the next time interval based on ΔP (n) and r _osib (n). (Block 432). The terminal then increases the transmit power delta by [Delta] P _up (n + 1) (block 434). After blocks 424 and 434, the terminal limits the transmit power delta ΔP (n + 1) to be within an acceptable range [ΔP _min , ΔP _max ] for the next time interval (block 442) The transmit power for the interval is calculated and defined to be a value within the maximum power level (blocks 444 and 446).

The variable step sizes ΔP _dn (n + 1) and ΔP _up (n + 1) are functions represented by equation set 15 based on a predetermined function of ΔP (n) and r _osib (n). Can be determined similarly. The variable step sizes may be defined as being proportional to _ΔP (n) and inversely proportional to r _osib (n). The adjustment probabilities and variable step sizes may be determined based on different probabilities and variable lookup tables for different ΔP (n) and r _osib (n) values or by any other means. .

3 and 4 illustrate exemplary embodiments for adjusting transmit power in a probabilistic and deterministic manner, respectively. For the probabilistic embodiment shown in FIG. 3, the adjustment probability is determined based on the parameters ΔP (n) and r _osib (n), and fixed-size increase and down steps are used for transmission power adjustment. . For the deterministic implementation shown in FIG. 4, the adjustment probability is fixed at 1.0, and the increase and down step sizes are determined based on the parameters ΔP (n) and r _osib (n). Various modifications may be made to the above embodiments. For example, variable increase and down step sizes may be used for the stochastic embodiment. As another example, fixed-size increase and down steps may be used for the critical embodiment.

The power delta ΔP (n) for the data channel is adjusted based on the OSI bit, channel gain, previous power delta ΔP (n-1), allowable power delta range and maximum power level for the terminal, as described above. Can be. In general, the power delta ΔP (n) may be adjusted based on any parameter or combination of any parameters. Other parameters that can be used to adjust ΔP (n) include the current transmit power P _{dch (n)} , the peak-to-average backoff factor ΔP _bo , a "designated" base station set that can temporarily observe high interference from the terminal. And so on. The peak-to-average backoff factor may be determined by the number of subbands used by the terminal for transmission, and higher values may be used for ΔP _bo when more subbands are used for transmission. The transmit power for the data channel may be less than P _max minus the backoff factor, or may be P _dch (n) ≦ (P _{max −ΔP bo} ).

The transmit power for the terminal may be adjusted based on the OSI bits transmitted by multiple base stations (eg, service and / or neighbor base stations). The transmit power may be adjusted in the same or different ways for the serving base station and the neighboring base station. The terminal may be orthogonal to other terminals communicating with the serving base station, but may cause some interference to the other terminals if full orthogonality is not achieved. The transmit power for the terminal can be adjusted lower if the OSI bit for the serving base station is set to '1'. The amount of transmit power adjustment due to OSI bits from the serving base station can be determined based on computational simulation, empirical measurements, etc. to achieve good performance.

The transmit power for the terminal can be adjusted based on other parameters, criteria and information. For example, the terminal may only consider OSI bits from base stations in the designated set. The terminal considers a given base station for transmission power adjustment based on the channel gain and / or other parameters for that base station. The terminal may adjust the transmission power by different amounts and / or in different ways based on all the information available to the base station (s) to be considered for transmission power adjustment.

5 illustrates a power control mechanism 500 that may be used to adjust the transmit power for terminal 120x in system 100. Terminal 120x communicates with serving base station 110x and may interfere with neighboring base stations 110a through 110m (but by different amounts). The power control mechanism 500 includes a reference loop 510 and a second loop 520. Reference loop 510 operates between terminal 120x and serving base station 110x. Second loop 520 operates between terminal 120x and adjacent base stations 110a through 110m and possibly serving base station 110x. For simplicity, FIG. 5 shows only a portion of the loops 510 and 520 residing in terminal 120x.

The reference loop 510 adjusts the transmit power for the control channel (or any other traffic channel) and makes the received SNR for the control channel as close to the target SNR as possible as measured at the serving base station 110x. Try to keep For the reference loop 510, the serving base station 110x estimates the received SNR for the control channel and compares the received SNR with the target SNR and transmit power control (based on the comparison results as described below). TPC) instructions. Each TPC command may be (1) an UP command to increase transmit power for the control channel or (2) a DOWN command to reduce transmit power. The serving base station 110x sends a TPC command to the terminal 120x over the forward link (cloud 570).

Terminal 120x receives and processes forward link transmissions from serving base station 110x and provides " received " TPC commands to TPC command processor 542. Each received TPC command is a different version of the TPC command sent by the serving base station 110x. The processor 542 detects each received TPC command so that either (1) an UP decision is received if the received TPC command is considered to be an UP command or (2) a DOWN decision is considered that the received TPC command is a DOWN command. Obtain a "TPC decision" that can be made. The control channel transmit (TX) power adjustment unit 544 adjusts the transmit power P _cch (n) for the control channel based on the TPC decisions from the TPC command processor 542. For example, unit 544 increases P _cch (n) by ΔP _{cch, up} for each UP determination and decreases P _cch (n) by ΔP _{cch, dn} for each DOWN determination. . TX data processor / modulator 560 sets the transmit power for the control channel to P _cch (n) indicated by unit 544. Transmission on the control channel is sent to the serving base station 110x.

Due to path loss, fading, and multipath effects on the reverse link (form 540) that change over time for the mobile terminal, the received SNR for the control channel continues to fluctuate. The reference loop 510 attempts to keep the received SNR at or near the target SNR if the reverse link channel environment changes.

The second loop 520 adjusts the transmit power for the data channel (or any other traffic channel), so that as high a power level as possible maintains the data channel while inter-sector and intra-sector interference is maintained within acceptable levels. To be used. For the second loop 520, the OSI bit processor 552 receives and processes the OSI bits sent by the adjacent base stations 110a-110m and possibly the serving base station 110x. The OSI bit processor 552 provides the OSI bits detected from the base stations to the transmit power delta adjustment unit 556. Channel estimator 554 receives pilots from the service and neighbor base stations, calculates the channel gain for each base station and provides the unit 556 with the channel gains calculated for all base stations. Unit 556 determines the channel gain ratios for the neighbor base stations to identify the strongest neighbor base station. Unit 556 also adjusts the transmit power delta ΔP (n) for the data channel based on the detected OSI bit and channel gain ratio for the strongest neighbor base station as described above. Unit 556 executes process 300 or 400 and adjusts ΔP (n) in a probabilistic or deterministic manner. In general, unit 556 may determine the transmit power delta ΔP (n) based on the detected OSI bits and / or other suitable information for any number of base stations, which may include service and / or neighbor base stations. I can regulate it.

The data channel transmit power calculation unit 558 receives the control channel transmit power P _cch (n) and the transmit power delta ΔP (n) used at the reference power level P _ref (n). Unit 558 calculates the transmit power P _dch (n) for the data channel based on P _cch (n) and ΔP (n). Unit 560 sets the transmit power for the data channel to P _dch (n) indicated by unit 558. Transmission for the data channel is sent to the serving base station 110x. Transmissions over data and control channels can interfere with adjacent base stations 110a through 110m.

Each base station 110 receives the transmissions from the terminals on the reverse link, calculates the interference observed by the base station, compares the measured interference with a nominal interference threshold, and calculates OSI bits based on the comparison result. And broadcasts OSI bits on the forward link.

The reference loop 510 and the second loop 520 can operate simultaneously but can be updated at different rates using the loop 510, which is a loop faster than the loop 520. Update rates for the two loops can be selected to achieve the desired power control performance. For example, the reference loop 510 may be updated at a rate of 150 times per second, and the second loop may be updated at a rate of 10 to 20 times per second. The reference loop 510 and the second loop 520 may operate in transmissions transmitted over the control channel and the data channel, respectively. Control and data channels are assigned different subbands in each hop period as shown in FIG. In this case, the reference loop 510 and the second loop 520 can operate simultaneously in transmissions transmitted on different subbands. The control channel may also be multiplexed using data channels (eg, using TDM and / or CDM) and transmitted on the same subbands.

6 illustrates a power control mechanism 600 that may be used for the control channel. The power control mechanism 600 (which may be used for the reference loop 510 of FIG. 5) includes an inner loop 610, an outer loop 620, and a third loop 630. Inner loop 610 attempts to keep the received SNR for the control channel as close as possible to the target SNR. For inner loop 610, SNR estimator 642 estimates the received SNR for the control channel at serving base station 110x and provides the received SNR to TPC command generator 644. Generator 644 compares the received SNR with a target SNR and generates TPC commands based on the comparison results. The serving base station 110x sends TPC commands to the terminal 120x over the forward link (cloud form 570). Terminal 120x receives and processes TPC commands from serving base station 110x and adjusts the transmit power for the control channel as described above with respect to FIG.

Data may be sent in blocks over a control channel, and each data block may be coded using a block code to obtain a corresponding code word (or coded data block). The error detection code can be used for the control channel. In that case, the serving base station may perform erasure detection for each received codeword to determine whether the codeword is erased or non-erased. The erased codeword is considered unreliable and is therefore processed (e.g. deleted). Erasure detection may be performed by calculating a metric for each received codeword, comparing the calculated metric with an erase threshold, and declaring that the received codeword has been erased or not erased based on the comparison result.

Outer loop 620 adjusts the target SNR so that the target erase rate Pr _erasure is achieved for the control channel. The target erase rate indicates the probability (eg, 10%) required to declare the received codeword as erased. The metric calculation unit 652 calculates a metric for each received codeword. The erase detector 654 performs erase detection for each received codeword based on the calculated metric and the erase threshold, and determines the state of the received codeword (erased or not erased) by the target SNR adjustment unit 656. ) Unit 656 then adjusts the target SNR for the control channel as follows:

Formula (16)

The SNR _target (k) is a target ANR for the outer loop update interval k,

ΔSNR _up is the up step size for the target SNR,

ΔSNR _dn is the down step size for the target SNR.

△ SNR _up And [Delta] SNR _dn step sizes can be set based on the following equation:

Formula (17)

The third loop 630 adjusts the erase threshold so that the target condition error rate Pr _error is achieved for the control channel. The target condition error rate indicates the required probability of being decoded into an error when the received codeword is considered to be non-erased. Small Pr _error (eg 1%) corresponds to high reliability in decoding results for non-erased codewords. Other terminals in communication with terminal 110x and / or serving base station 110x may transmit known codewords periodically or when triggered via a control channel. Units 652 and 654 perform erase detection on each received known codeword in the same manner as for received codewords. For each received known codeword that is considered non-erased, decoder 662 decodes each received known codeword to determine whether the decoded data block is correct or error. Decoder 662 provides the status of each received known codeword that may be erased, "good" or "bad". A good codeword is a received known codeword that is considered to be unerased or correctly decoded. Bad codewords are received known codewords that are unerased but considered to be errors. The erase threshold adjustment unit 664 adjusts the error threshold based on the state of each known codeword received as follows:

Formula (18)

TH _erasure (l) is an erase threshold for a third loop update interval l,

ΔTH _up is the up step size for the erase threshold,

ΔTH _dn is the down step size for the erase threshold.

Equation (18) assumes that a lower erase threshold increases the likelihood that a received codeword is declared erased.

ΔTH _up and ΔTH _dn step sizes may be set based on the following equation:

Formula (19)

Inner loop 610, outer loop 620 and third loop 630 are generally updated at different rates. Inner loop 610 is the fastest of three loops, and the transmit power for the control channel can be updated at a particular rate (eg, 150 times per second). Outer loop 620 is the next fast loop, and the target SNR can be updated each time the codeword is received over the control channel. The third loop 630 is the slowest loop and the error threshold can be updated whenever a known codeword is received over the control channel. The update rates for the three loops can be selected to achieve the power control for the control channel and the performance required for erase detection. The power control mechanism 600 is also disclosed in a jointly-acquired US patent application number [document number 040404 U1] entitled “Robust Error Detection and Error Rate Based Closed Loop Power Control,” filed July 13, 2004. have. The transmit power for the control channel can be updated at a certain rate (eg, 150 times per second).

For clarity, certain embodiments have been described above for various aspects of power control. Various other embodiments may also be derived based on the description provided herein. Some examples are given below.

The allowable transmit power delta same range of _{[△ P min, △ P max} ] may be used for all terminals in the system. Different ranges of [ΔP _min , ΔP _max ] may be used for different terminals, for example based on their locations. For example, terminals with smaller channel gain ratios for the strongest neighbor base stations may have a smaller range of transmit power deltas (eg, the same ΔP _min or Smaller ΔP _max ) is used.

The reference power level P _ref (n) used to derive the data channel transmit power P _dch (n) may be set to the transmit power for another power control channel as described above. The reference power level may be obtained in other ways, for example as estimated based on the channel gain for the serving base station. The data channel transmit power can be adjusted directly instead of through the transmit power delta. The serving base station may provide feedback to inform the terminal if the data channel transmit power is within an acceptable range.

The terminal may respond only to the OSI bits of the strongest neighbor base station as described above. The terminal may adjust the transmit power based on the OSI bits of the multiple neighbor base stations. For example, the terminal performs a process 300 or 400 on one base station at a time for S strongest neighbor base stations, where S > The channel gain ratio for each neighboring base station may take into account the adjustment probability (for process 300) or variable step sizes (for process 400).

A single OSI bit can be used to indicate the interference observed by each base station as described above. Multiple bits can also be used to report interference. This may allow terminals to adjust their transmit powers faster and / or more efficiently. In turn, this improves overall system stability and performance. For example, each base station can report information about how far the measured interference is from the nominal interference threshold. As another example, each base station may broadcast additional bits (fault / panic bits) that may be set to '1' when the interference level exceeds a high interference threshold. The high threshold may have a value that is significantly higher than the nominal threshold (eg, a standard deviation of 2 to 3 higher). Rapidly rising or unusually high interference levels are often an indication of an unstable system. When observing the panic bit set, each terminal sets the transmit power delta to the minimum value ΔP _min and maintains the transmit power level until the panic bit is reset to '0'. The mechanism may be efficient when calibrating system stability.

Each base station can broadcast the interference information to all terminals if the interference observed by the base station is randomized using, for example, frequency hopping. If the base stations have more specific interference information, the transmit powers of the terminals can be adjusted in such a way as to use the information. For example, each terminal may be assigned one or more specific subbands for data transmission (without frequency hopping). The base station can then observe different amounts of interference on different subbands. Terminals generating a large amount of interference can in particular be identified based on their assigned subbands, and the transmission powers of the terminals can be reduced accordingly.

The supported data rate for each terminal is determined by the SNR received for the data channel. For the foregoing embodiments the received SNR is determined according to (1) the target SNR associated with the reference power level and (2) the transmit power delta ΔP (n) used by the terminal. The transmit power delta can be adjusted independently by the terminal without any input from the serving base station as described above. The terminal may transmit a transmit power delta, an SNR received for the data channel, a supported data rate for the data channel, or equivalent information for the serving base station. The terminal can also send the maximum number of subbands N _{sb, max} (n) that the terminal can support the current transmit power delta, required quality of service (QoS), buffer size and the like. To reduce the amount of signaling, the terminal may send ΔP (n) and N _{sb, max} (n) every few update intervals via in-band signaling over the data channel.

The scheduler at / for the serving base station may use all the information reported by the terminal to schedule the terminal for data transmission on the reverse link and to allocate resources to the terminal. The scheduler may allocate the N _{sb, max} (n) subbands, or less than N _{sb, max} (n) subbands than N _{sb, max} (n) subbands terminal. If the scheduler allocates more than N _{sb, max} (n) subbands, the terminal can adjust the transmit power delta accordingly. If 2N _{sb, max} (n) subbands are allocated, ΔP (n) may be adjusted down by a factor of two.

Power control may be performed by each terminal based on various portions of information that the terminal obtains from the serving base station and neighboring base stations as described above. Power control may also be performed by each base station for all terminals communicating with the base station. For example, each base station can obtain an interference report (eg, OSI bit) for each neighboring base station via, for example, signaling between the base stations and these transmissions from terminals. Each base station may obtain channel gains determined by each terminal for the service and neighbor base stations. Each base station may then calculate a transmit power delta for each terminal based on the interference reports and the channel gains applicable for that terminal, and transmit the transmit power delta to the terminal. Each terminal may adjust its transmit power using the transmit power delta received from the serving base station. Optionally, each base station can calculate and transmit the transmit power for each terminal. The availability of transmit power deltas for all terminals communicating with each base station may facilitate scheduling terminals.

The power control techniques disclosed herein may be used for various kinds of wireless communication systems. The techniques are particularly suitable for systems with small sector interference, such as, for example, OFDMA, TDMA and FDMA systems.

The techniques disclosed herein may be used for power control of various kinds of traffic channels (eg, data and control channels). The techniques are also suitable for hybrid automatic retransmission (H-ARQ) schemes. Using H-ARQ, each coded packet is divided into multiple (Nbl) subblocks, and one subblock is transmitted at one time for the coded packet. As each subblock for a given coded packet is received on the reverse link, the serving base station decodes and reconstructs the packet based on all received subblocks, thus moving away from the packet. The serving base station may include residual information that the subblocks use to decode when the received SNR is low, but may reconstruct the packet based on the partial transmission since it may not be required when the received SNR is high. The serving base station transmits an acknowledgment (ACK) when the packet is correctly decoded, and the terminal may terminate the transmission of the packet before receiving the ACK.

Using H-ARQ, each coded packet can be sent in varying amounts of time until correctly decoded. Conventional power control mechanisms adjust the received SNR for the data channel based on the packet error rate (PER) and reduce the transmit power for the data channel to a lower level so that the target PER is transmitted for each coded packet. All are accomplished using Nbl subblocks. This hardly reduces system throughput. The techniques disclosed herein allow high transmit power levels to be used with variable periods of transmission supported by H-ARQ.

7 shows a block diagram of one embodiment of a terminal 120x, a serving base station 110x and a neighbor base station 110A. On the reverse link, at terminal 120x, TX data processor 710 processes (eg, codes, interleaves, and modulates) reverse link (RL) traffic data to provide modulation symbols for the traffic data. TX data processor 710 processes the control data (eg, channel quality indicator) from controller 720 to provide modulation symbols for the control data. Modulator (MOD) 712 processes the modulation symbols and pilot symbols for traffic and control data to provide a sequence of complex values of chips. Processing by the TX data processor 710 and modulator 712 is system dependent. The modulator 712 performs OFDM modulation when the system uses OFDM. The transmitter unit (TMTR) 714 processes (eg, converts to analog, amplifies, filters, and frequency upconverts) a sequence of chips to generate a reverse link signal, which is routed through a duplexer (D; 716). And transmitted via antenna 718.

At service base station 110x, the reverse link signal from terminal 120x is received by antenna 752x, routed through duplexer 754x, and provided to receiver unit (RCVR) 756x. Receiver unit 756x processes (eg, filters, amplifies, and frequency downconverts) the received signal, and further digitizes the processed signal to obtain a stream of data samples. Demodulator (DEMOD) 758x processes the data samples to obtain symbol estimates. A receive (RX) data processor 760x processes (eg, deinterleaves and decodes) the symbol estimates to obtain decoded data for terminal 120x. RX data processor 760x also performs erase detection to provide controller 770x with the status of each received codeword used for power control. The processing by demodulator 758x and RX data processor 760x is complementary to the processing performed by modulator 712 and TX data processor 710, respectively.

Processing for the forward link transmission may be performed similar to that described above for the reverse link. Processing for transmission on the forward and reverse links is defined by the system.

For reverse link power control, at service base station 110x, SNR estimator 774x estimates the received SNR for terminal 120x and provides the received SNR to SNR command (cmd) generator 776x. Generator 776x also receives the target SNR to generate TPC commands for terminal 120x. TPC commands are processed by TX data processor 782x and modulator 784x, processed by transmitter unit 786x, routed through duplexer 754x, and sent to terminal 120x via antenna 752x. . At neighbor base station 110a, interference estimator 774a estimates the interference observed by the base station and provides the measured interference to OSI bit generator 776a. Generator 776a also receives a nominal interference threshold to generate OSI bits for base station 110A. OSI bits are processed and broadcast to terminals in the system. Generator 776a generates a panic bit or any other form of interference report.

At terminal 120x, forward link signals from the service and neighboring base stations are received by antenna 718. The received signal is routed through duplexer 716, digitized by receiver unit 740, processed by demodulator 742 and RX data processor 744 to obtain received TPC commands and received OSI bits. do. The channel estimator in demodulator 742 estimates the channel gain for each base station. The TPC processor 742 detects the received TPC commands and obtains TPC decisions used to update the transmit power for the control channel. The TPC processor 724 also determines transmit power for the data channel based on the OSI bits received for the neighbor base stations, channel gains for the service and neighbor base stations, and transmit powers for the data and control channels. Adjust. The TPC processor 724 (or the controller 720) may execute the process 300 of FIG. 3 or the process 400 of FIG. 4. Processor 724 provides transmit power adjustment controls for the control and data channels. Processor 710 and / or modulator 712 receive controls from TPC processor 724 to adjust the transmit powers for the control and data channels.

Controllers 720, 770x, and 770a supervise the operation of various processing units within terminal 120x and base station 110x and 110a, respectively. The controllers may perform various functions for power control on the reverse link. For example, controllers 720 and 770x may execute the processing units shown for terminal 120x and base station 110x in FIGS. 5 and 6, respectively. Memory units 722, 722x and 722a store data and program codes for controllers 720, 770x and 770a, respectively. Scheduler 780x schedules terminals for data transmission to / from serving base station 110x.

The power control techniques disclosed herein may be implemented by various means. For example, the techniques may be implemented in hardware, software, or a combination thereof. For hardware implementation, the processing unit used to perform power control includes one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic. Implementation in devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions disclosed herein, or a combination thereof Can be.

For software implementation, power control techniques may be implemented using modules (eg, procedures, functions, etc.) that perform the functions disclosed herein. The software codes may be stored in a memory unit (eg, memory unit 722 of FIG. 7) and executed by a processor (eg, controller 720). The memory unit may be implemented within the processor or external to the processor and is communicatively connected to the process via various means as is known in the above case.

The foregoing 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 apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the present invention. Accordingly, the invention is not limited to the described embodiments but is to be accorded the widest scope indicated in the principles and novel features disclosed herein.

Claims (69)

A method of performing power control for a wireless terminal in a wireless communication system, Each of at least one base station-each of the at least one base station is a neighboring base station not designated to receive a data transmission sent by the wireless terminal or a service base station designated to receive the data transmission sent by the wireless terminal For, obtaining an indication of interference observed by the base station; And Adjusting a transmit power for the data transmission based on at least one indication obtained for the at least one base station, The indication for each of the at least one base station includes a first bit indicating whether the interference observed by the base station is above or below a first interference threshold, The indication for each of the at least one base station further comprises a second bit indicating whether the interference observed by the base station exceeds a second interference threshold that is greater than the first interference threshold. Way. The method of claim 1, Limiting the adjusted transmit power for the data transmission to fall within a predetermined range. The method of claim 1, Estimating a received signal quality (SNR) for the data transmission at the serving base station; And Limiting the transmit power for the data transmission based on the estimated received SNR for the data transmission. delete delete The method of claim 1, A plurality of interference indications are obtained for a plurality of neighboring base stations, and the transmit power for the data transmission is adjusted based on the indication obtained for a single neighboring base station selected from the plurality of neighboring base stations. How to perform control. The method of claim 6, And wherein the single neighbor base station is a neighbor base station having a minimum path loss to the wireless terminal among the plurality of neighbor base stations. The method of claim 1, Only indications of interference for base stations within a specified set of base stations are considered for adjustment of the transmit power for the data transmission. A method of performing power control for a wireless terminal in a wireless communication system, Each of at least one base station-each of the at least one base station is a neighboring base station not designated to receive a data transmission sent by the wireless terminal or a service base station designated to receive the data transmission sent by the wireless terminal With respect to-obtaining an indication of the interference observed by the base station; And Adjusting a transmit power for the data transmission based on at least one indication obtained for the at least one base station, Adjusting the transmission power for the data transmission, For each base station to be considered in adjusting the transmit power, an indication of the interference obtained for the base station, a current transmit power level for the data transmission, a range of allowable transmit power deltas, a maximum transmit power for the terminal, Adjusting the transmit power for the data transmission based on a peak-to-average backoff factor, or a combination thereof. A method of performing power control for a wireless terminal in a wireless communication system, Each of at least one base station-each of the at least one base station is a neighboring base station not designated to receive a data transmission sent by the wireless terminal or a service base station designated to receive the data transmission sent by the wireless terminal With respect to-obtaining an indication of the interference observed by the base station; And Adjusting a transmit power for the data transmission based on at least one indication obtained for the at least one base station, Adjusting the transmission power for the data transmission, For each base station to be considered in adjusting the transmit power, Reducing the transmit power if the interference observed by the base station exceeds a first interference threshold; And Increasing the transmit power if the interference observed by the base station is less than the first interference threshold, Adjusting the transmission power for the data transmission, For each base station to be considered for adjusting the transmit power, setting the transmit power to a predetermined low power if the interference observed by the base station is greater than or equal to a second interference threshold greater than the first interference threshold. A method for performing power control, characterized in that. delete A method of performing power control for a wireless terminal in a wireless communication system, Each of at least one base station-each of the at least one base station is a neighboring base station not designated to receive a data transmission sent by the wireless terminal or a service base station designated to receive the data transmission sent by the wireless terminal With respect to-obtaining an indication of the interference observed by the base station; And Adjusting a transmit power for the data transmission based on at least one indication obtained for the at least one base station, Estimating a channel gain for the serving base station; And For each neighbor base station to be considered in adjusting the transmission power, estimating a channel gain for the neighbor base station, an indication obtained for the neighbor base station and the estimated channel gain for the neighbor and serving base stations Adjusting the transmit power for the data transmission based on the transmission rate; For each adjacent base station to be considered in adjusting the transmit power, Determining a probability of adjusting the transmission power up or down based on the channel gains for the adjacent and serving base stations, and Adjusting the transmit power for the data transmission based on the indication obtained for the neighboring base station and the probability determined for the neighboring base station. The method of claim 12, Wherein the channel gains for the neighbor and serving base stations are estimated based on pilots received from the neighbor and serving base stations, respectively. delete 13. The method of claim 12, wherein the probability is further determined based on a current level of the transmit power for the data transmission. 13. The method of claim 12, wherein the transmit power is adjusted in a fixed sized step according to the determined probability. 13. The method of claim 12, for each neighboring base station to be considered in adjusting the transmit power, Determining a step size for adjusting the transmit power based on the estimated channel gains for the neighboring and serving base stations; And Adjusting the transmit power for the data transmission based on the indication obtained for the neighbor base station and the step size determined for the neighbor base station. The method of claim 17, And said step size is further determined based on a current level of said transmit power for said data transmission. The method of claim 3, wherein The transmit power for the data transmission is determined by a reference power level and a transmit power delta, wherein the transmit power delta is adjusted based on the at least one indication obtained for the at least one base station. How to perform control. The method of claim 19, Adjusting the reference power level such that a received SNR for a second transmission sent by the wireless terminal to the serving base station is maintained at a target SNR, wherein the received SNR for the data transmission is determined by the second transmission. 2 is estimated based on the target SNR for transmission. The method of claim 20, And wherein the second transmission is for a control channel transmitted by the terminal to the service base station. The method of claim 3, wherein And wherein the transmit power for the data transmission is defined such that the received SNR for the data transmission is within a range of received SNRs that are acceptable for the data transmission. The method of claim 3, wherein Limiting the transmit power for the data transmission to be at or below the maximum power level allowable for the wireless terminal. The method of claim 1, Acquiring the at least one interference indication observed by the at least one base station and adjusting the transmit power for the data transmission are performed by the wireless terminal. The method of claim 1, Acquiring the at least one interference indication observed by the at least one base station and adjusting the transmit power for the data transmission are performed by the serving base station. The method of claim 25, And the at least one indication is obtained through signaling exchanged between the at least one base station. The method of claim 25, Obtaining an estimate of channel gain between the wireless terminal and the serving base station; For each neighboring base station to be considered in adjusting the transmission power, obtaining an estimate of channel gain between the wireless terminal and the neighboring base station and in the indication obtained for the neighboring base station and the neighboring and serving base stations. Adjusting the transmit power for the data transmission based on the estimated channel gains for the power control. The method of claim 1, And wherein said data transmission is transmitted using hybrid automatic retransmission (H-ARQ), which allows early termination of transmission of a correctly decoded packet by a base station designated to receive said data transmission. The method of claim 1, And wherein said wireless communication system is an Orthogonal Frequency Division Multiple Access (OFDMA) system. The method of claim 1, And wherein said wireless communication system is a time division multiple access (TDMA) system. The method of claim 1, And wherein said wireless communication system is a frequency division multiple access (FDMA) system. An apparatus operative to perform power control for a wireless terminal in a wireless communication system, comprising: Each of at least one base station-each of the at least one base station is a neighboring base station not designated to receive a data transmission sent by the wireless terminal or a service base station designated to receive the data transmission sent by the wireless terminal -A processor operative to obtain an indication of the interference observed by the base station; And An adjustment unit operative to adjust transmission power for the data transmission based on at least one indication obtained for the at least one base station, The regulating unit may, for each base station to be considered for adjusting the transmit power, an indication of the interference obtained for the base station, a current transmit power level for the data transmission, a range of allowable transmit power deltas, to the terminal. And adjust the transmit power for the data transmission based on a maximum transmit power, a peak-to-average backoff factor, or a combination thereof. The method of claim 32, A calculating unit operable to estimate a received signal quality (SNR) for the data transmission at the serving base station and to limit the transmit power for the data transmission based on the estimated received SNR for the data transmission; Apparatus further comprising. delete An apparatus operative to perform power control for a wireless terminal in a wireless communication system, comprising: Each of at least one base station-each of the at least one base station is a neighboring base station not designated to receive a data transmission sent by the wireless terminal or a service base station designated to receive the data transmission sent by the wireless terminal Means for obtaining an indication of the interference observed by the base station; And Means for adjusting a transmit power for the data transmission based on at least one indication obtained for the at least one base station, For each base station to be considered in adjusting the transmit power, the transmit power for the data transmission is an indication of the interference obtained for the base station, the current transmit power level for the data transmission, and the range of allowable transmit power deltas. And adjust based on a maximum transmit power for the terminal, a peak-to-average backoff factor, or a combination thereof. The method of claim 35, wherein Means for estimating a received signal quality (SNR) for the data transmission at a serving base station designated to receive the data transmission; And Means for limiting the transmit power for the data transmission based on the estimated received SNR for the data transmission. delete A method of performing power control in a wireless communication system, Confirming the interference observed by the first base station not designated to receive the data transmission sent by the wireless terminal to the second base station; Adjusting a transmit power for the data transmission based on the interference observed by the first base station; And Limiting the transmit power for the data transmission to maintain interference due to the data transmission at the second base station below a predetermined level, The interference observed by the first base station is dependent upon the measurement report sent by the first base station, the current level of the transmit power used for the data transmission, the estimated distance to the first base station, or a combination thereof. And performing power control. delete 39. The method of claim 38, wherein limiting the transmit power for the data transmission comprises: Estimating a received signal quality (SNR) for the data transmission at the second base station, and And limiting the transmit power for the data transmission such that the received SNR for the data transmission is within a range of received SNRs that are acceptable for the data transmission. 39. The base station of claim 38, wherein the first base station is a base station having the strongest received signal at the wireless terminal among at least one base station received by the wireless terminal, and is a base station not designated to receive the data transmission. Characterized in that the power control method. A method of performing power control for a wireless terminal in a wireless communication system, Transmit power for the first transmission transmitted by the terminal on a first set of at least one frequency subband to a service base station designated to receive a first transmission, the transmit power for the first transmission being the service base station Adjusting at to achieve a target received signal quality (SNR) for the first transmission; And Transmit power for a second transmission transmitted by the terminal to the serving base station via a second set of at least one frequency subband, the transmit power for the second transmission being the transmit power for the first transmission and Adjusting based on a transmit power delta. 43. The method of claim 42, wherein the first and second sets comprise different frequency subbands. 44. The method of claim 43, wherein the first set of at least one frequency subband is the same as the second set of the at least one frequency subband. The method of claim 42, wherein For each of the at least one base station, obtaining an indication of the interference observed by the base station, wherein the transmit power for the second transmission is at least one obtained by the at least one base station. And control based on the indication. The method of claim 45, The transmit power for the second transmission is channel gain for each of the at least one base station, current transmit power level for the first transmission, range of allowable transmit power deltas, maximum transmit power for the terminal, peak And further adjusted based on the mean versus backoff factor, or a combination thereof. The method of claim 42, wherein And wherein the first transmission is for signaling transmitted through a control channel, and the second transmission is for data transmitted through a data channel. The method of claim 42, wherein And wherein the transmit power for the first transmission and the transmit power for the second transmission are adjusted at different rates. A method of performing power control for a wireless terminal in a wireless communication system, Obtaining a reference power level corresponding to a target received signal quality (SNR) for the first transmission at a serving base station designated to receive the first transmission from the terminal; Setting transmit power for a second transmission from the terminal to the serving base station based on the reference power level and transmit power delta; And Adjusting the transmit power delta based on at least one parameter. The method of claim 49, The at least one parameter is an indication of interference observed by each of the at least one base station, a channel gain for each of the at least one base station, a current transmit power level for the first transmission, an acceptable range of transmit power deltas. And a maximum transmit power for the terminal, a peak to average backoff factor, or a combination thereof. A method of reporting interference in a wireless communication system, Estimating the interference observed at the base station; Forming an interference report for the estimated interference; And Broadcasting the interference report via a wireless channel, Comparing the estimated interference with a first interference threshold; And Setting a first bit based on whether the estimated interference is above or below the first interference threshold, wherein the interference report includes the first bit, Comparing the estimated interference with a second interference threshold higher than the first interference threshold; And And setting a second bit based on whether the estimated interference is above or below the second interference threshold, wherein the interference report comprises the second bit. The method of claim 51, And wherein the interference includes signal power received for terminals transmitting to the base station. delete delete The method of claim 51, wherein estimating the interference observed at the base station comprises: Obtaining an interference estimate for each of a plurality of subbands at the base station, and Deriving the estimated interference based on the plurality of interference estimates for the plurality of subbands. 56. The method of claim 55 wherein the estimated interference is an arithmetic mean of the plurality of interference estimates for the plurality of subbands. 56. The method of claim 55 wherein the estimated interference is a geometric mean of the plurality of interference estimates for the plurality of subbands. 56. The method of claim 55 wherein the estimated interference is obtained based on a performance-based average of the plurality of interference estimates for the plurality of subbands. A device of a wireless communication system, An interference estimator operative to estimate interference observed at the base station; A controller operative to form an interference report for the estimated interference; And A data processor operative to process the interference report for broadcasting over a wireless channel, The controller is operative to compare the estimated interference with a first interference threshold and set a first bit based on whether the estimated interference exceeds or falls below the first interference threshold, and the interference report is configured to include the first interference threshold. Contains 1 bit, The controller is operative to compare the estimated interference with a second interference threshold higher than the first interference threshold and set a second bit based on whether the estimated interference exceeds or falls below the second interference threshold. And the interference report comprises the second bit. delete A device of a wireless communication system, Means for estimating the interference observed at the base station; Means for forming an interference report for the estimated interference; And Means for broadcasting the interference report over a wireless channel, Means for comparing the estimated interference with a first interference threshold; And Means for setting a first bit based on whether the estimated interference is above or below the first interference threshold, wherein the interference report comprises the first bit, Means for comparing the estimated interference with a second interference threshold higher than the first interference threshold; And Means for setting a second bit based on whether the estimated interference is above or below the second interference threshold, wherein the interference report comprises the second bit. delete A method of scheduling data transmission in a wireless communication system, At a base station, a transmission power level supported by the wireless terminal for data transmission to the base station, the transmission power level being indicative of the interference observed by each of at least one neighboring base station not designated to receive the data transmission. Determined based on; And Scheduling data transmission of the wireless terminal for data transmission based on the transmission power level supported by the wireless terminal, The transmit power level for the data transmission is determined by a reference power level and a transmit power delta, wherein the transmit power delta is adjusted based on an indication of the interference obtained for each of the at least one neighboring base station. Scheduling method. The method of claim 63, wherein Adjusting a reference power level for the wireless terminal to achieve a target signal quality (SNR) for a second transmission from the wireless terminal to the base station, wherein the transmit power level is in accordance with the reference power level. The scheduling method, characterized in that further determined based on. The method of claim 63, wherein At the base station, obtaining, by the wireless terminal, a specific number of subbands supported at the transmit power level, wherein the wireless terminal is further added to the specific number of subbands supported at the transmit power level. Scheduling for the data transmission based on the scheduling. A device of a wireless communication system, Transmit power level supported by the wireless terminal for data transmission to a base station, the transmit power level being determined based on an indication of interference observed by each of at least one neighboring base station not designated to receive the data transmission; A processor operative to obtain a processor; And A scheduler operative to schedule data transmission of the wireless terminal for the data transmission based on the transmission power level supported by the wireless terminal, The transmit power level for the data transmission is determined by a reference power level and a transmit power delta, wherein the transmit power delta is adjusted based on an indication of the interference obtained for each of the at least one neighboring base station. Device. The method of claim 66, And a controller operative to adjust a reference power level for the wireless terminal to achieve a target signal quality (SNR) for a second transmission from the wireless terminal to the base station, wherein the transmit power level is the reference power. And the device is further determined based on the level. A device of a wireless communication system, Transmit power level supported by the wireless terminal for data transmission to a base station, the transmit power level being determined based on an indication of interference observed by each of at least one neighboring base station not designated to receive the data transmission; Means for obtaining; And Means for scheduling data transmission of the wireless terminal for the data transmission based on the transmission power level supported by the wireless terminal, The transmit power level for the data transmission is determined by a reference power level and a transmit power delta, wherein the transmit power delta is adjusted based on an indication of the interference obtained for each of the at least one neighboring base station. Device. The method of claim 68, wherein Means for adjusting a reference power level for the wireless terminal to achieve a target signal quality (SNR) for a second transmission from the wireless terminal to the base station, wherein the transmit power level is the reference power level. And the device is further determined based on.