Methods and Apparatus for Power Control in Multi-carier Wireless Systems

• US 20080039129A1
• Filed: 06/29/2005
• Published: 02/14/2008
• Est. Priority Date: 06/30/2004
• Status: Active Grant

• Current Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Original Assignee: Neocific Incorporated
• Inventors: Lo, Titus, Huang, Haiming, Li, Xiaodong, Li, Kemin, Meng, Jun
• Granted Patent: US 8,031,686 B2
• Time in Patent Office: Days
• US Class Current: 455/522
• CPC Class Codes: H04B 17/309 Measuring or estimating channel quality parameters
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0019 in which mode-switching is based on a statistical approach
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 5/0073 Allocation arrangements that take into account other cell interferences for intercell interference mitigation or co-ordination in orthogonal multiplex systems H04J11/005
• CPC Class Codes: H04L 5/14 Two-way operation using the same type of signal, i.e. duplex
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 52/24 using SIR [Signal to Interference Ratio] or other wireless path parameters
• CPC Class Codes: H04W 52/241 taking into account channel quality metrics, e.g. SIR, SNR, CIR, Eb/lo
• CPC Class Codes: H04W 52/242 taking into account path loss
• CPC Class Codes: H04W 52/262 taking into account adaptive modulation and coding [AMC] scheme AMC per se H04L1/0001
• CPC Class Codes: H04W 52/343 taking into account loading or congestion level

Abstract

Methods and apparatus disclosed maximize the capacity of serving cells and minimize inter-cell interferences due to power emission from serving cells in a multi-carrier, multi-cell communication system. The control methods and apparatus take into account various factors such as cell configuration, frequency reuse, geometry and path-loss information, transmission priority, subchannel configuration, feedback from other cells, or any combination thereof, and produce signals that control the transmission power levels and the modulation and coding of transmitted signals.

Claims

1. A method of controlling transmission power of signal transmitters and modulation and coding of transmitted signals in a multi-cell wireless communication system for increasing service capacity of a cell and decreasing inter-cell interference with nearby cells, the method comprising:

arranging a communication channel into multiple subchannels, wherein each subchannel consists of at least one subcarrier; and

adaptively controlling the modulation and coding of transmitted signals and signal transmission power, wherein the adaptive control is based on rules and constraints derived from system parameters and direct or indirect performance measurements, and wherein a selected transmission power level satisfies a Rise over Thermal (RoT) threshold requirement, and wherein the adaptive control comprises;

a first process wherein an achievable Channel Quality Information (Q_new) at the receiver is updated by;

Q_new=Q_current+P_max−

P_current, where Q_current denotes a recent measured CQI (Channel Quality Information) at a receiver, P_max denotes a maximum transmission power available at a transmitter, and P_current denotes a recent transmission power at the transmitter;

in a case where a primary criteria is to maximize throughput while controlling transmission power;

if Q_new exceeds CQI requirement for a highest MCS (modulation and coding scheme) in a protocol, the highest MCS is selected and P_new is set as the transmission power level for that MCS with a certain margin;

if Q_new is lower than the CQI requirement for the highest MCS, the maximum transmission power (P_new) is selected to derive a corresponding MCS based on the value of Q_new; and

if Q_new is lower than the CQI requirement for the lowest MCS in the protocol, transmission may be denied and outage process may start;

in a case where the primary criteria is to minimize transmission power while meeting a data rate requirement;

if Q_new exceeds the CQI requirement for a given MCS in the protocol, a necessary transmission power level is set for the given MCS with a certain margin; and

if Q_new is lower than the CQI requirement for the given or lowest MCS, transmission is denied; and

a second process wherein an RoT check is performed and, if needed, the power is adjusted to meet the RoT threshold, the second process comprising;

R_new R_current+P_new−

P_current, where R_new denotes a new RoT resulting from the first process computations, and R_current denotes an RoT measurement before application of P_new, and wherein;

if R_new is less than the RoT threshold, decisions made during the first process concerning the transmission power level and MCS are maintained; and

if R_new exceeds the RoT threshold, the transmission power level is reduced to meet the RoT threshold requirement; and

a new transmission power level is calculated as;

P_new=P_current+R_threshold−

R_currents

and a new achievable CQI is calculated as;

Q_new=Q_current+R_threshold−

R_current,

where R_threshold denotes the RoT threshold and an appropriate MCS is selected based on Q_new.

2. The method of claim 1, wherein service capacity is the capacity to communicate data, voice, video, or any combination thereof.

3. The method of claim 1, wherein at an initial stage of network entry, a mobile station can estimate an uplink CQI and RoT based on an observed path-loss from a downlink message and choose an appropriate transmission power and MCS, and a certain margin to account for the estimation error.

4. In a multi-carrier, multi-cell wireless communication system, a process of controlling transmission power of signal transmitters and modulation and coding of transmitted signals, the process comprising:

configuring a communication channel into multiple subchannels, wherein each subchannel consists of at least one subcarrier; and

adaptively controlling modulation and coding of the transmitted signals and signal transmission power to substantially achieve a balance between maximizing a capacity of a serving cell and minimizing interference with other cells due to power emission from the serving cell, wherein the adaptive control is based on rules and constraints derived from system parameters and performance measurements.

5. The process of claim 4, wherein:

the process is applicable to downlink, uplink, or both;

the multi-carrier system comprises OFDM, or Multi-Carrier Code Division Multiple Access (MC-CDMA); and

a Time Division Duplexing (TDD) or a Frequency Division Duplexing (FDD) technique is employed.

6. The process of claim 4, wherein a total transmission power of a base station is controlled and a maximum allowable level is set relatively high for large cells, isolated cells, or cells with large frequency reuse factors, and wherein the total transmission power of the base station is set relatively low for small cells, congested cells, or cells with small frequency reuse factors, and wherein the total transmission power is adjusted either by changing a power density of each subcarrier/subchannel or changing a number of utilized subcarriers/subchannels.

7. The process of claim 4, wherein a performance measurement is SINR (signal-to-interference-plus-noise ratio), BER (bit error rate), PER (packet error rate), or any combination thereof, and wherein the performance measurement is a single number or a statistical indicator.

8. The process of claim 4, wherein modulation and coding requirements are pre-stored in a table based on system simulation or measurement, or the quality requirements are dynamically adjusted.

9. The process of claim 4, wherein a selected transmission power level requires to satisfy a Rise over Thermal (RoT) threshold, and wherein:

a central control method is adapted and;

a network-wide coordination among adaptive controllers globally optimizes the RoT threshold to achieve high overall performance; and

a central processor, based on information from base stations, determines the RoT threshold with which the network capacity on a particular subchannel is optimized;

or

a distributed method is adapted and;

the RoT threshold is computed for each data link; and

an RoT threshold Calculator resides within or outside of a controller, wherein inputs to the Calculator include one or more of the following factors;

cell configuration, frequency reuse factor, geometry/path loss information, transmission priority, subchannel configuration, and feedback from other cells or other users and an output of the Calculator is the RoT threshold value.

10. In a multi-carrier, multi-cell communication system wherein a communication channel is configured into multiple subchannels and each subchannel includes multiple subcarriers, an apparatus for controlling transmission power and modulation and coding of transmitted signals, the apparatus comprising:

at least one controller configured to process input information and generate output signals for controlling transmission power, modulation and coding, or both, wherein the controller uses a part or all of the inputs to generate the output signals, and wherein the output signals are sent to and employed by the transmitter in a next transmission; and

wherein the input information to the controller comprises;

direct or indirect performance measurements, wherein the performance measurements are frequently varying and repeatedly updated; and

system parameters and requirements, wherein the system parameters are stable and infrequently updated.

11. The apparatus of claim 10, wherein the AMCP controller (a) selects a transmission power level that satisfies the Signal to Noise Ratio (SNR) or Rise over Thermal (RoT) threshold requirement and that achieves the highest modulation and coding scheme (MCS) for applications with adaptive MCS schemes, and (b) selects the corresponding MCS.

12. The apparatus of claim 10, wherein the SNR or RoT threshold is calculated using the cell configuration, frequency reuse factor, geometry and path-loss information, transmission priority, subchannel configuration, feedback from other cells, or any combination thereof;

and wherein;

the SNR or RoT threshold is set relatively low if

the cell size is relatively small;

the configuration is relatively congested;

the frequency reuse factor is small;

the path-loss delta is relatively small;

or

the transmission priority is low; and

the SNR or RoT threshold is set relatively high if

the cell size is relatively large;

the configuration is relatively isolated;

the frequency reuse factor is large;

the path-loss delta is relatively large;

or

the transmission priority is high.

13. The apparatus of claim 12, wherein a common SNR or RoT threshold is first set for all active links in one direction to control the interference with close-by cells, and wherein the common SNR or RoT threshold is used as a constraint in the calculation of individual SNR or RoT thresholds for each link.

14. The apparatus of claim 12, wherein information pertaining to interference occurrences within a network is used by the base station to compute the SNR or RoT threshold.

15. The apparatus of claim 10, wherein the path-loss for a mobile station to its serving and/or adjacent base stations is determined from strength of downlink or uplink signals from and to the base station, wherein:

each base station sends a unique downlink preamble signal or a pilot pattern and the mobile station scans through these preamble signals or pilot patterns using correlation or other signal processing methods, and wherein a result of a correlation indicates the path-loss to each base station, and wherein the path-loss information is fed back by the mobile station to its serving base station;

or

the mobile station sends a unique ranging signal to a target base station and from the strength of such uplink signals the base station, and other close-by base stations that also detect such uplink signal, measure the corresponding path-loss.

16. The apparatus of claim 10, wherein the inputs and outputs of the controller correspond to an individual subchannel in case each subchannel uses a modulation and coding and a power control different from those of other subchannels or correspond to a set of subchannels in case the set of subchannels use the same modulation and coding and power control to reduce the control overhead.

17. An apparatus for controlling transmission power of signal transmitters and modulation and coding of transmitted signals in a multi-cell wireless communication system for increasing service capacity of a cell and decreasing inter-cell interference with nearby cells, the apparatus comprising:

a means for arranging a communication channel into multiple subchannels, wherein each subchannel consists of at least one subcarrier;

a means for adaptively controlling the modulation and coding of the transmitted signals and the signal transmission power, wherein the adaptive control operation is based on rules and constraints derived from system parameters and direct or indirect performance measurements, and wherein the selected transmission power level satisfies a Rise over Thermal (RoT) threshold requirement; and

a means for calculating the RoT threshold, wherein the means for calculating calculates the RoT threshold by applying at least one of the following factors;

cell configuration, frequency reuse factor, geometry/path loss information, transmission priority, subchannel configuration, and feedback from other cells or other mobile users.

18. A base station in a multi-cell wireless communication network capable of controlling transmission power and modulation and coding of transmitted signals, the base station comprising:

a transceiver;

a facility, coupled to the transceiver, for adaptively controlling the modulation and coding of transmitted signals and signal transmission power, wherein the adaptive control is based on boundaries derived from system specifics and direct or indirect performance indicators, and wherein the selected transmission power level satisfies a Rise over Thermal (RoT) or a Signal to Noise Ratio (SNR) threshold requirement;

a facility for calculating the RoT threshold based on cell configuration, frequency reuse factor, geometry/path loss information, transmission priority, subchannel configuration, feedback from other cells or other remote units, or any combination thereof;

a configuration where information pertaining to interference occurrences within the network is used by the base station to compute the RoT threshold; and

a configuration wherein the path-loss for a mobile station to the base stations is determined from strength of downlink or uplink signals from and to the base station.

19. The base station of claim 18, wherein the total transmission power of the base station is controlled and a maximum allowable level is set relatively high for large cells, isolated cells, or cells with large frequency reuse factors, and wherein the total transmission power of the base station is set relatively low for small cells, congested cells, or cells with small frequency reuse factors, and wherein the total transmission power is adjusted either by changing a power density of each subcarrier/subchannel or changing a number of utilized subcarriers/subchannels.

20. The base station of claim 18, wherein the path-loss for a mobile station to the base stations is determined in the following manner:

each base station sends a unique downlink preamble signal or a pilot pattern and the mobile station scans through these preamble signals or pilot patterns using correlation or other signal processing methods, and wherein a result of a correlation indicates the path-loss to each base station, and wherein the path-loss information is fed back by the mobile station to its serving base station;

or

the mobile station sends a unique ranging signal to the base station and from the strength of such uplink signals the base station, and other close-by base stations that also detect such uplink signal, measure the corresponding path-loss.