HK1186855B - Scheduling of beamformed data to reduce interference - Google Patents

Description

Scheduling of beamformed data for interference reduction

Cross Reference to Related Applications

This application claims benefit of U.S. provisional application No.61/362659 filed on 7/8/2010 and is related to U.S. provisional application No.61/329504 filed on 29/4/2010 (which provisional application is incorporated herein by reference). Both of these applications are incorporated herein by reference for all purposes.

Technical Field

The present invention relates generally to systems and methods for coordinating scheduling of beamformed data to reduce interference. Transmissions from base stations may be scheduled for lower interference levels and generally higher network efficiency based on various factors including interference levels from neighboring base stations, priority of reducing interference, and relative phase differences of neighboring base stations.

Background

A wireless communication system may employ transmit beamforming to increase the signal level seen at a predetermined receiver and to decrease the interference level seen at other receivers. The interference reduction capability of beamforming is advantageous in cellular wireless systems where high levels of interference can severely reduce the capacity of these systems.

Beamforming generally refers to a technique used in a wireless communication system, such as a radio frequency system, an optical frequency system, or an audio system, in which signals transmitted or received by multiple transmit or receive sensors are combined in some way to improve their overall gain or carrier-to-interference ratio. Beamforming employs at least two transmit or receive sensors.

Beamforming is commonly used in cellular wireless communication systems to increase the range over which a mobile device can communicate with a base station. An additional potential for using beamforming is the ability to reduce interference by selecting phases and signal amplitudes that can cause signals received or transmitted by another mobile station to cancel.

Beamforming typically utilizes multiple antennas in the base station and employs signal processing techniques to ensure that the signals are phase aligned with each other when arriving at the mobile device. In a system employing Time Division Duplexing (TDD), where the same set of frequencies is used for both downlink (base station to mobile) and uplink (mobile to base station) transmissions, the base station can utilize channel reciprocity to adjust the amplitude and phase of the transmissions at each antenna. For Frequency Division Duplex (FDD) systems, where downlink and uplink transmissions use different frequencies, feedback from the mobile station to the base station regarding the amplitude and phase of the signal received at the mobile station is typically required.

Cellular wireless beamforming systems typically use two to eight antennas. Since the cost of supporting beamforming in a base station product increases as the number of antennas increases, systems with more than eight antennas are generally considered cost prohibitive.

Fig. 1 illustrates a wireless beamforming system 100 using two transmit antennas at a base station to communicate with a mobile station 108 according to an embodiment of the present invention. The signal processing algorithms at the base station 102 select the appropriate phase and amplitude of the signals 104 and 106 for each base station transmit antenna to ensure that the combined signal received by the mobile station 108 has sufficient power to operate properly.

Fig. 2-5 show some examples of how the phase and amplitude differences between two signals 104 and 106 arriving at a mobile device (e.g., 108) or Customer Premises Equipment (CPE) can affect the combined signal seen by the receiver. The beamforming system (e.g., 100) can control the relative amplitude and phase at the transmitter so that the combined signal seen at the receiver (e.g., 108) can have an increased amplitude or can have a decreased amplitude.

Fig. 2A and 2B show graphs 202 and 204, respectively, of two equal power sinusoidal signals received at a mobile device (e.g., 108) with 0 ° and 180 ° phase differences, in accordance with an embodiment of the present invention. In the first graph 202, the two signals 104 and 106 are aligned exactly in phase with each other. The combined signal (indicated with triangles) is twice the amplitude of the respective signals. Referring to fig. 2B, in the second graph 204, the two signals are 180 ° out of phase with each other. In this case, the signals cancel each other completely, resulting in a combined signal with zero amplitude. In this case, the receiver (e.g., 108) does not detect any signal because the signals are completely cancelled by destructive interference.

Fig. 3A and 3B show graphs 302 and 304, respectively, of two unequal power sinusoidal signals received at a mobile device (e.g., 108) with a phase difference of 0 ° and 180 °, in accordance with an embodiment of the present invention. In this example, the two signals are not equal in power, and the first signal 104 is 3dB stronger than the second signal 106. Referring to fig. 3A, a first graph 302 plots two signals 104 and 106 that are precisely aligned in phase with each other, which results in a much stronger received combined signal. The second graph 304 shows the situation where the two signals 104 and 106 are 180 deg. out of phase with each other. In this case, the signals do not completely cancel each other out, but the combined signal at the receiver is still significantly attenuated when compared to the case where the two separate signals are precisely aligned with each other (e.g., in graphs 202 and 302 as shown in fig. 2A and 3A, respectively).

The signals arriving at the receiver do not necessarily have to be aligned exactly in phase to achieve a combining gain in signal strength. Likewise, the signals do not necessarily have to be exactly 180 ° out of phase with each other to achieve signal cancellation. Thus, fig. 4A and 4B show graphs 402 and 404, respectively, of two unequal power sinusoidal signals received at a mobile device (e.g., 108) with a phase difference of 45 ° and 160 °, in accordance with an embodiment of the present invention.

Fig. 4A and 4B show two signals (e.g., signals 104 and 106) with 3dB power difference as in fig. 3A and 3B, respectively, but here with 45 ° and 160 ° phase difference at the receiver (e.g., 108). In the case where the received signals have a phase difference of 45 ° (i.e., in graph 402), the combined signal at the receiver still exhibits significant gain and is not degraded much as compared to the case where the received signals have a phase difference of 0 ° as shown in graph 302 in fig. 3A. Similarly, when the received original signals are 160 ° out of phase with each other (as shown in graph 404), the level of the combined signal is still significantly reduced compared to the case where the received signals are 180 ° out of phase as shown in graph 304 in fig. 3B.

Fig. 5 shows a graph 500 of the power gain of a combined signal (also referred to as beamforming gain) as a function of the phase difference of two signals (e.g., signals 104 and 106) at a receiver (e.g., 108) in accordance with an embodiment of the present invention. Note that graph 500 assumes that the two received signals have equal amplitudes, similar to the signals depicted in fig. 2A and 2B. The beamforming gain is relative to a signal transmitted from one of the transmit antennas at a nominal level of 0 dB. The maximum gain (6 dB) is seen when the two signals are precisely aligned in phase (e.g., as in graph 202), while the minimum gain (in this case- ∞whenexpressed in dB) is seen when the signals have a phase difference of 180 ° (e.g., as in graph 204).

Modern wireless communication networks include many different network topologies, including heterogeneous mixes of macrocell, microcell, picocell, and femtocell resources. At the highest level of wireless coverage, a macrocell provides cellular service for a relatively large physical area, often in areas where network traffic density is low. In areas where traffic is more concentrated, the macro cell may act as a comprehensive service provider, primarily responsible for providing continuity for service area gaps between smaller network cells. In areas of increased traffic density, microcells are often used to increase network capacity and improve signal quality for smaller physical areas requiring increased bandwidth. The large number of pico and femto cells generally increases network capacity for even smaller physical areas in larger densely populated urban and residential areas of data communication networks.

This mix of larger and smaller cells can reduce the period of network congestion caused by conventional network architectures that previously prevented a large portion of regional user communications over a small number of larger network cells (e.g., macro or micro cells). Such congestion reduction techniques can improve the quality of service (QOS) of a service provider network and the collective quality of experience (QOE) of network service users within a particular portion of a data communications network. Negative effects associated with poor QOS and poor QOE (e.g., conditions largely caused by congestion and/or interference) may include: the negative effects of queuing delay, data loss, and congestion of new and existing network connections for certain network users can be mitigated by adding a large number of short-range wireless base station devices to the network infrastructure.

As the number of overlapping cells in a network (i.e., the number of macro, micro, pico, and femto cells in the network) increases, the management of air link resources shared by components in the network becomes increasingly important. For example, resources such as frequency channels, time slots, and spreading codes must be managed for each cell in the network, which can lead to increased interference and reduced overall network efficiency.

Conventional systems have attempted to employ beamforming techniques to manage transmissions from a base station to an intended mobile device to improve signal strength, similar to the techniques described in graphs 202, 302, and 402. Some conventional systems have attempted to reduce the level of unwanted interference using beamformed signal cancellation techniques similar to the techniques described in graphs 204, 304, and 404. However, these systems require relatively complex signal processing algorithms and communication between base stations to achieve interference suppression. It is therefore desirable to schedule transmissions in a wireless network such that signals received by a mobile device from a serving base station combine constructively at a mobile receiver, while signals arriving at the mobile base station from non-serving base stations combine destructively at the mobile receiver. Furthermore, it is desirable that the scheduling has a minimum resource-intensive property so that complicated scheduling can be easily performed.

Disclosure of Invention

The present invention relates generally to systems and methods for coordinating scheduling of beamformed data to reduce interference. A Customer Premises Equipment (CPE) uses a number of bits to quantize the phase angle of the beamformed data received by the CPE and reports it to its serving base station. The serving base station selects one of the phase adjustment angles based on bits received from the CPE for scheduling data transmission to the CPE. The phase adjustment angle is within "n" degree steps. In one embodiment, the phase angle reported by the CPE to its serving base station is quantized using two bits and four phase adjustment angles (i.e., in 90 degree steps) are used. Two bits allow quantization of the phase region into four different levels. Each phase angle adjustment is mapped to a single phase angle difference.

In one embodiment, the phase angle reported by the CPE to its serving base station is quantized using three bits and four phase adjustment angles (i.e., in 90 degree steps) are used. Three bits allow quantization of the phase regions into eight different levels instead of four. Each phase angle adjustment is mapped to two phase angle differences. Additional quantization bits are used to distinguish between the second optimal phase angle correction and the third optimal phase angle correction.

In one embodiment, a computer-implemented method for transmitting beamformed data to a mobile station includes receiving, at a first base station that transmitted a reference signal to a mobile station, quantized phase angle information of the reference signal from the mobile station. A first phase adjustment angle is selected based on the quantized phase angle information received from the mobile station. Transmitting a first beamformed signal having the first phase adjustment angle selected based on the received quantized phase angle information from the first base station to the mobile station. The reference signal may or may not be a beamformed signal.

In one embodiment, the first base station is a serving base station for the mobile station, and the mobile station receives an interfering signal from a second base station. The interfering signal may or may not be a beamformed signal. The first base station sends the first beamformed signal to the mobile station as part of a first data packet. Scheduling, at the first base station, a first data packet within a first radio resource with a first phase adjustment coordinated with an associated second phase adjustment of a second radio resource at a second base station.

In one embodiment, a computer-implemented method for receiving beamformed data from a base station includes receiving, at a mobile station, a first signal from a first base station. A first phase difference of the first signal is measured at the mobile station. The mobile station sends the quantized phase angle information of the first signal to the first base station that transmitted the first signal to the mobile station. A first beamformed signal having a first phase adjustment angle is received from the first base station. The first base station selects a first phase adjustment angle based on the quantized phase angle information transmitted by the mobile station. The first signal may or may not be a beamformed signal.

In another embodiment, a wireless communication system for coordinating scheduling of beamformed data to reduce interference is provided at a base station. The system includes a processor; a receiver; and a transmitter. Configuring the system to: the method includes transmitting a first signal to a mobile station, receiving quantized phase angle information of the first signal from the mobile station, selecting a first phase adjustment angle based on the quantized phase angle information received from the mobile station, and transmitting a first beamformed signal having the first phase adjustment angle selected based on the received quantized phase angle information to the mobile station. The first signal may or may not be a beamformed signal. The first signal may or may not be a beamformed signal.

In yet another embodiment, a wireless communication system for coordinating scheduling of beamformed data to reduce interference includes a first base station; a second base station; a data communication network for facilitating data communication between the first base station and the second base station; and a first mobile station. The first beamformed signal received by the first mobile station from the first base station is received as a communication. The second beamformed signal received by the first mobile station from the second base station is received as interference. Configuring the system to: the method includes transmitting a first signal to a mobile station, receiving quantized phase angle information of the first signal from the mobile station, selecting a first phase adjustment angle based on the quantized phase angle information received from the mobile station, and transmitting a first beamformed signal having the first phase adjustment angle selected based on the received quantized phase angle information to the mobile station. The first signal may or may not be a beamformed signal.

The present invention also includes a computer-readable medium encoded with computer-executable instructions for coordinating beamformed data for wireless transmission, which when executed perform a method comprising: scheduling, at a first base station, a first data packet into a first radio resource having a first phase adjustment coordinated with an associated second phase adjustment of a second radio resource at a second base station; and transmitting the first data packet as a first beamformed signal to a first mobile station.

Drawings

Embodiments of the invention will be described in detail below, by way of example, with reference to the accompanying drawings, in which:

fig. 1 illustrates a wireless beamforming system employing two transmit antennas at a base station to communicate with a mobile station in accordance with an embodiment of the present invention;

FIGS. 2A and 2B illustrate two equal power sinusoidal signals received at a mobile device with a phase difference of 0 and 180, according to an embodiment of the present invention;

FIGS. 3A and 3B illustrate two unequal power sinusoidal signals received at a mobile device with a phase difference of 0 and 180, in accordance with an embodiment of the present invention;

FIGS. 4A and 4B illustrate two unequal power sinusoidal signals received at a mobile device with a phase difference of 45 and 160, according to an embodiment of the present invention;

fig. 5 shows a graph of the power gain of the combined signal, i.e. the beamforming gain, as a function of the phase difference of the two signals at the receiver, according to an embodiment of the invention;

FIG. 6 illustrates a distributed data communications system according to an embodiment of the present invention;

FIG. 7 illustrates a block diagram of a base station in accordance with an embodiment of the present invention;

FIG. 8 shows a block diagram of a server computer according to an embodiment of the invention;

fig. 9 shows a block diagram of a mobile station according to an embodiment of the invention;

fig. 10 illustrates a mobile station receiving interference from neighboring sectors in accordance with an embodiment of the present invention;

FIG. 11 illustrates the coordination of four-level quantized beam scheduling according to an embodiment of the present invention;

FIG. 12 shows a table for mapping binary values to quantized phase differences according to an embodiment of the invention;

fig. 13 shows a graph of beamforming gain as a function of phase difference of two signals with 0dB branch imbalance at a receiver, wherein the phase difference corresponds to a quantized phase difference region, in accordance with an embodiment of the invention;

FIG. 14 shows a table illustrating the average gain of the combined signal of FIG. 13 relative to the signal transmitted from one of the antennas for each quantized phase region, in accordance with an embodiment of the present invention;

fig. 15 shows a graph of beamforming gain as a function of phase difference of two signals with 3dB branch imbalance at a receiver, where the phase difference corresponds to a quantized phase difference region, according to an embodiment of the invention;

FIG. 16 shows a table illustrating the average gain of the combined signal of FIG. 15 relative to the signal transmitted from one of the antennas for each quantized phase region, in accordance with an embodiment of the present invention;

fig. 17 shows a graph of beamforming gain as a function of phase difference of two signals with 10dB branch imbalance at a receiver, wherein the phase difference corresponds to a quantized phase difference region, in accordance with an embodiment of the invention;

FIG. 18 shows a table illustrating the average gain of the combined signal of FIG. 17 relative to a signal transmitted from one of the antennas for each quantized phase region, in accordance with an embodiment of the invention;

figure 19 shows a mobile station receiving an intended signal from a first base station and interference from an adjacent sector with varying phase adjustments, in accordance with an embodiment of the present invention;

FIG. 20 shows a phase adjustment diagram according to an embodiment of the invention;

fig. 21 illustrates frequency resources used at a base station according to an embodiment of the present invention;

fig. 22 shows a CPE phase management table at a base station with various mobile station transmissions and interference data according to an embodiment of the invention;

FIG. 23 shows a flow diagram depicting a process for scheduling transmissions at a base station, in accordance with an embodiment of the invention;

FIG. 24 shows a flow diagram depicting a process for scheduling transmissions at a base station, in accordance with an embodiment of the invention;

FIG. 25 shows an empty transmission schedule at base station A according to an embodiment of the invention;

fig. 26 shows a transmission schedule after processing first priority interference from base station B according to an embodiment of the invention;

fig. 27 shows a transmission schedule after handling first priority interference from base station C according to an embodiment of the invention;

fig. 28 shows a transmission schedule after processing first priority interference from base station D according to an embodiment of the invention;

fig. 29 shows a transmission schedule after processing second priority interference from a base station B according to an embodiment of the invention;

fig. 30 shows a transmission schedule after processing second priority interference from base station D according to an embodiment of the invention;

fig. 31 shows a transmission schedule after handling third-priority interference according to an embodiment of the invention;

fig. 32 shows a transmission schedule after processing fourth priority interference according to an embodiment of the invention;

FIG. 33 shows a flowchart depicting a process for scheduling transmissions at a base station, in accordance with an embodiment of the invention;

FIG. 34 shows a flowchart depicting a process for scheduling transmissions at a base station, in accordance with an embodiment of the invention;

FIG. 35 shows a table mapping a three-bit message to eight quantized phase angle regions/zones according to an embodiment of the invention;

fig. 36 shows a graph of beamforming gain as a function of phase difference of two signals with 0dB branch imbalance at a receiver, where the phase difference corresponds to a quantized phase difference region, in accordance with an embodiment of the invention;

FIG. 37 shows a table showing the average gain of the combined signal relative to the signal transmitted by one of the antennas for each quantized phase field in accordance with an embodiment of the invention;

FIG. 38 shows a table showing the best, sub-best, and third best phase adjustment steps to achieve the best signal combination for each phase difference measurement zone, in accordance with an embodiment of the present invention;

figure 39 shows a wireless system with a mobile station that is within the coverage area of a base station and that receives interference from a neighboring base station;

fig. 40 shows a wireless system similar to that of fig. 39 with the addition of an additional mobile station MS 2'; and

fig. 41-49 illustrate examples of how data transmissions between multiple base stations can be scheduled to reduce interference to neighboring base station sectors by coordinating the adjustment of the relative phase of the transmitted signals at each base station, according to embodiments of the invention.

Detailed Description

The present invention relates generally to systems and methods for coordinating scheduling of beamformed data to reduce interference. Transmissions of each base station in a cellular wireless system are coordinated to reduce interference levels at user devices, thereby reducing interference levels in the system. A Customer Premises Equipment (CPE) employs a plurality of bits to quantize the phase angle of the beamformed data received by the CPE and reports it to its serving base station. The serving base station selects one of the phase adjustment angles based on bits received from the CPE for scheduling data transmission to the CPE. The phase adjustment angle is within "n" degree steps. In one embodiment, the phase angle that the CPE reports to its serving base station is quantized using two bits and four phase adjustment angles (i.e., in 90 degree steps) are used. Two bits allow quantization of the phase region into four different levels. Each phase angle adjustment is mapped to a single phase angle difference.

In another embodiment, the phase angle that the CPE reports to its serving base station is quantized using three bits and four phase adjustment angles (i.e., in 90 degree steps) are used. Three bits allow quantization of the phase regions into eight different levels instead of four. Each phase angle adjustment is mapped to two phase angle differences. Additional quantization bits are used to distinguish between the second optimal phase angle correction and the third optimal phase angle correction.

FIG. 6 illustrates a networked computing system 600 including various wired and wireless computing devices, which may be used to implement any scheduling coordination processes associated with various embodiments of the present invention. The networked computing system 600 may include, but is not limited to: a set of remote base station devices 606a-c, any of which may be associated with a macrocell, microcell, or picocell base station, each of which may be a base station that is adjacent to one or more short-range base station devices 612 (e.g., femtocell or picocell devices) within a particular area of the networked computing system 600; a data communications network 602 including both a Wide Area Network (WAN) portion and a Local Area Network (LAN) portion; various wireless user equipment, including: cellular telephone or PDA devices 608a-c, 622, notebook or netbook computer 624, ebook device 626, and any other commonly used portable wireless computing device known in the art capable of communicating with data communication network 602 using one or more of remote base stations 606a-c, short-range base station device 612, or any other commonly used wireless or wired network communication technology (e.g.,handheld gaming devices, personal music players, video recorders, etc.); one or more gateway or switching devices 610 capable of facilitating data communication processes within the LANs and between LANs and WANs of the data communication network 602; a television device 616 (e.g., a high definition LCD or plasma television) is optionally connected to a multimedia device 614 (e.g., a set-top box, Digital Video Recorder (DVR), or Blu-Ray)^TMA player device); and a desktop computer 620 optionally connected to the external hard drive device 618.

In one embodiment, remote base station apparatuses 606a-c may represent individual base stations having a single antenna, individual base stations having antenna arrays configured to transmit beamformed signals, or base stations containing multiple sectors with multiple antenna arrays per sector. Further, remote base station devices 606a-c or short-range base station device 612 may represent base station 102 in FIG. 1.

In one embodiment, the remote base station apparatus 606a-c, the short range base station apparatus 612 (e.g., a femto cell or pico cell apparatus), or any user equipment (608 a-c, 614, 616, 618, 620, 622, 624, or 626) may be configured to run any well known operating system including, but not limited to:or any known mobile operating system, includingWindowsMobileAnd the like. In one embodiment, any of the remote base stations 606a-c may use any number of commonly used servers, desktops, notebooks, and personal computing devices.

In one embodiment, the user equipment (608 a-c, 622, 624, or 626) may include a common mobile computing device (e.g., notebook computer, netbook computer, cellular telephone, PDA, handheld gaming device, electronic book device, personal music player, MiFi) with the capability to wirelessly communicate using any common wireless data communication technology^TMDevice, video recorder, etc.), including but not limited to: GSM (Global System for Mobile communications)^TM、UMTS^TM、LTE^TM、LTEAdvanced^TM、Wi-Max^TM、Wi-Fi^TMAnd the like. Further, the user equipment (608 a-c, 614, 616, 618, 620, 622, 624, or 626) may represent the receiver 108 in fig. 1.

In one embodiment, the LAN portion or the WAN portion of the data communications network 602 in FIG. 6 may employ, but is not limited to, any of the following common communications techniques: optical fiber, coaxial cable, twisted pair cable, ethernet cable, and power line cable, as well as any wireless communication technology known in the art. In one embodiment, any of the remote wireless base stations 606a-c, wireless user equipment (608 a-c, 622, 624, or 626), and any other LAN connected computing devices (610, 614, 616, 618, or 620) may include data processing, data storage, and any standard computing software and hardware necessary for data communications with each other within the networked computing system 600. The computing hardware implemented by any network computing system 600 device (606 a-c, 608a-c, 610, 612, 614, 616, 620, 622, 624, or 626) may include, but is not limited to: one or more processors, volatile and non-volatile memory, user interfaces, transcoders, and wired and/or wireless communication transceivers, among others.

Further, any of the networked computing system 600 devices (606 a-c, 608a-c, 610, 612, 614, 616, 620, 622, 624, or 626) may be configured to include one or more computer-readable media (e.g., any of the commonly used volatile or non-volatile memory types) having a set of computer-readable instructions embodied thereon that, when executed, perform a portion of any short-range wireless communication optimization processes associated with the various embodiments of the present invention.

Fig. 7 shows a block diagram of a base station apparatus 700 (e.g., a femto cell, pico cell, micro cell or macro cell apparatus) that may represent the base stations 606a-c and 612 in fig. 6. In one embodiment of the invention, the base station apparatus 700 may include, but is not limited to, baseband processing circuitry comprising at least one Central Processing Unit (CPU) 702. In one embodiment, CPU702 may include an arithmetic logic unit (ALU, not shown) to perform arithmetic and logical operations, and one or more control units (CU, not shown) to fetch instructions and memory contents from memory, then execute and/or process the instructions and memory contents, calling the ALU as needed during program execution. The CPU702 is responsible for executing all computer programs stored on the volatile (RAM) and non-volatile (ROM) system memories 704 and 726 of the base station apparatus 700.

Base station apparatus 700 may also include, but is not limited to, Radio Frequency (RF) circuitry to transmit and receive data to and from a network. The RF circuitry may include, but is not limited to, a transmit path including a digital-to-analog converter 710 for converting digital signals from the system bus 720 into analog signals to be transmitted, an upconverter 708 for setting the frequency of the analog signals, and a transmit amplifier 706 for amplifying the analog signals to be sent to an antenna 712 and transmitted as beamformed signals. Further, the RF circuitry may include, but is not limited to, a receive path including a receive amplifier 714 to amplify any individual signal or beamformed signal received by the antenna 712, a downconverter 716 to reduce the frequency of the received signal, and an analog-to-digital converter 718 to output the received signal onto the system bus 720. The system bus 720 facilitates data communication between all hardware resources of the base station apparatus 700. There may be any number of transmit/receive paths 730, 732, 734 that include multiple digital-to-analog converters, up-converters, and transmit amplifiers, as well as multiple analog-to-digital converters, down-converters, and receive amplifiers to implement transmission and reception as a beamforming base station. Further, antenna 712 may include multiple physical antennas for transmitting beamformed signals.

Base station apparatus 700 may also include, but is not limited to, a user interface 722; an operations and maintenance interface 724; a memory 726 that stores applications and protocol processing software; and a network interface circuit 728 that facilitates communication across the LAN and/or WAN portions of the data communication network 602 (i.e., the backhaul network).

In one embodiment of the present invention, the base station 700 may employ any modulation/coding scheme known in the art, such as binary phase shift keying (BPSK, with 1 bit/symbol), quadrature phase shift keying (with 2 bits/symbol), and quadrature amplitude modulation (e.g., 16-QAM, 64-QAM, etc., with 4 bits/symbol, 6 bits/symbol, etc.). Further, base station 700 can be configured to communicate with user devices (e.g., 608a-c, 622, 624, and 626) via any cellular data communication protocol, including any of the commonly used GSM, UMTS, WiMAX, and LTE protocols.

Fig. 8 illustrates a block diagram of a server computer 800, which may represent any of the teleservice provider devices 606a-c or base station 612 of fig. 6, base station 700 of fig. 7, or any other common network device known in the art (e.g., routers, gateways, and switching devices). The server computer 800 may include, but is not limited to, one or more processor devices including a Central Processing Unit (CPU) 804. In one embodiment, CPU804 may include an Arithmetic Logic Unit (ALU) (not shown) that performs arithmetic and logical operations, and one or more Control Units (CUs) (not shown) that fetch instructions and memory contents from memory, then execute and/or process the instructions and memory contents, calling the ALU as needed during program execution. The CPU804 is responsible for executing all computer programs stored on the volatile memory (RAM), non-volatile memory (ROM), and long-term storage system memories 802 and 810 of the server computer 800.

The server computer 800 may also include, but is not limited to, an optional user interface 820, the user interface 820 allowing a server administrator to interact with the software and hardware resources of the server computer 800, as well as displaying the capabilities and operation of the networked computing system 600; a software/database repository 810 comprising: a phase adjustment map 812 (e.g., statically or dynamically created phase adjustment map 2000 in fig. 20), which may include a list of neighboring wireless base stations and their instantaneous transmit phase adjustments; a scheduling unit 814 for generating CPE phase management tables (e.g., CPE phase management table 2200 in fig. 22 for a plurality of base stations) for transmitting data to mobile stations associated with a server computer or base stations; a beamforming unit 816 for generating a beamforming signal to be transmitted to a specific mobile apparatus; and a priority determination unit 818 for determining a priority level of interference associated with a neighboring interfering base station. Base station 700 may include components in software/database repository 810 to implement the systems and methods described herein.

Further, server computer 800 may include a modem 808 for formatting the data information prior to transmission; a transceiver 806 for transmitting and receiving beamformed network information between various network base stations, user equipment, and computing devices utilizing the data communication network 602 of the networked computing system 600; and a system bus 822 that facilitates data communication among all of the hardware resources of the server computer 800.

Fig. 9 illustrates a block diagram of a mobile station 900, which may represent any of the user devices (e.g., 608a-c, 622, 624, and 626) shown in fig. 6. Mobile station 900 may include, but is not limited to, components similar to those described above in connection with base station 700. Accordingly, mobile station 900 may include baseband processing circuitry 902 corresponding to the baseband processing circuitry in fig. 7, RF circuitry 904 corresponding to the RF circuitry in fig. 7, memory 906 corresponding to memory 726, system bus 908 corresponding to system bus 720, user interface 910 corresponding to user interface 722, operation and maintenance interface 912 corresponding to operation and maintenance interface 724, and phase difference measurement unit 914.

In one embodiment, the phase difference measurement unit 914 measures the phase difference between the signals received from each base station. For example, phase difference measurement unit 914 will determine a phase difference measurement for signals from a predetermined base station, and determine a phase difference measurement for signals received from neighboring base station sectors as interference. This measurement is needed at the mobile station 900 because the phase difference between the signals will vary because the signals will travel through different paths and arrive at the mobile station 900 with an offset phase difference. In addition, the phase difference measurement unit may measure and record signal characteristics of the predetermined signal and the interference signal, including power level, interference level (e.g., level of signal to interference plus noise ratio (SINR) or level of carrier to interference plus noise ratio (CINR)), or other characteristics.

Fig. 10-34 illustrate a system and method for using two bits to quantize the phase angle reported by a CPE to its serving base station to coordinate the scheduling of beamformed data to reduce interference according to one embodiment of the present invention. The serving base station selects one of four phase adjustment angles (in 90 degree steps) based on the bits received from the CPE for scheduling data transmission to the CPE. Two bits allow quantization of the phase region into four different levels. In this embodiment, each phase angle adjustment is mapped to a single phase angle difference.

According to one embodiment of the invention, a quantized phase angle report and a quantized phase angle adjustment are performed in order to reduce interference and increase the strength of the desired signal at the CPE. As described in more detail below, the mobile devices/CPEs (e.g., 108, 608a-c, 622, 624, 626, 900, MS1, and MS 2) measure the phase difference between the two signals that they receive from each base station transmitter (e.g., by phase difference measurement unit 914) and send the measurements back to their serving base station. This measurement is quantized into one of four values by rounding the measured difference to the nearest 90 degrees. For example, if the measured difference is 244 °, then the nearest 90 ° step is 270 °.

Fig. 10 shows a wireless system 1000 in accordance with one embodiment of the invention in which a mobile station MS1 receives interference 1004 from a neighboring sector. In the wireless system 1000, a mobile station MS1 communicates with a base station BS1 through beamformed transmissions 1002. In one embodiment, mobile station MS1 may represent mobile station 900 and base stations BS1 and BS2 may represent base station 700. When base station BS1 is communicating with mobile station MS1, the best signal is obtained from BS1 when BS1 transmits to MS1 with a 0 ° quantization phase adjustment (i.e., the signals arriving at MS1 from each BS1 transmit antenna are combined to provide the strongest signal when no adjustment is made to the relative phase of the signals transmitted by BS 1). An example of constructive interference at a receiving mobile station is seen in the combined signals in graphs 202 and 302.

When the mobile station MS1 receives the intended signal from the base station BS1, the mobile station MS1 also receives interference from the neighboring base station BS 2. In this case, the signal received by the MS1 from the BS2 can be maximally attenuated when the BS2 transmits with a quantization phase adjustment of 270 °. In other words, when BS1 transmits to MS1 with a phase adjustment of 0 ° and BS2 transmits to different mobile stations within its coverage area with a phase adjustment of 270 °, the best CINR or SINR will be obtained at MS 1.

Fig. 11 shows a radio system 1100 similar to the radio system 1000 in fig. 10, wherein a further mobile station MS2 is added. Furthermore, fig. 11 introduces the concept of coordinating the scheduling of four levels of quantized beams. In this case, the phase difference is quantized into four discrete regions corresponding to the phase differences of 0 °, 90 °, 180 ° and 270 °. This quantization reduces the amount of feedback from the mobile station to the base station that is required when communicating the phase difference information. The quantization also reduces computational overhead while still providing excellent control over the level of constructive or destructive interference. The four-level quantization will be further explained with reference to fig. 12-18.

The wireless system 1100 shows a BS2 transmitting to a mobile station MS2 within its coverage area. The best combination of signals arriving at MS2 from BS2 occurs when BS2 makes a 180 ° adjustment of the relative phase of its transmitted signals. However, sufficient performance can still be obtained at the MS2 if the BS2 employs a phase adjustment of 90 ° or 270 °. In this case, BS2 transmits to MS2 with a phase adjustment of 270 °, while BS1 transmits to MS1 with a phase adjustment of 0 °. The combined signal at MS2 is slightly degraded compared to the combination that can be achieved with a phase adjustment of 180 °. However, the improvement in CINR at MS1 with a phase adjustment of 270 ° instead of 180 ° is much greater than the loss in CINR at MS 2. Thus, this optimization takes into account the efficiencies obtained at each mobile station MS1 and MS2, while taking into account the overall system efficiency to obtain the best efficiency gain.

Next, fig. 12-18 describe four levels of quantization of the phase difference and the effect on the signal strength at the receiver. In an exemplary system implementing this coordination scheme (e.g., wireless beamforming system 100 and networked computing system 600), the relative phases of the signals (e.g., 104 and 106) transmitted by the base stations (e.g., 102, 606a-c, 612, and 700) are adjusted in 90 ° steps. The mobile device/CPE (e.g., 108, 608a-c, 622, 624, 626, 900, MS1, and MS 2) measures the phase difference between the two signals it receives from each base station transmitter (e.g., by phase difference measurement unit 914) and sends the measurement back to its serving base station. This measurement is quantized to one of four values by rounding the measured difference to the nearest 90 degrees. For example, if the measured difference is 244 °, then the nearest 90 ° step is 270 °.

Two-bit quantization may be performed at the mobile device and the quantized phase difference may be represented as two binary bits in the signaling message. For example, a mapping may be made between the two-bit message and the phase difference, as seen in fig. 12.

An advantage of quantizing the phase difference to one of four values is that the overhead of transmitting messages to the base station is reduced (e.g., nine binary bits are required to represent the phase difference quantized to 1 degree steps) compared to quantizing to a larger number of values. This aspect helps to promote efficiency goals while not being computationally burdensome to schedule.

When the base station (e.g., 102, 606a-c, 612, and 700) or server computer 800 receives the quantized phase differences, it can adjust the phase at a transmitter (e.g., in a transmit antenna in a beamforming antenna array) so that the phase difference of the beamformed signals arriving at the mobile station fall into a zone as shown in fig. 13.

Fig. 13 shows a graph 1300 of beamforming gain versus phase difference for two signals with 0dB branch imbalance at a receiver according to an embodiment of the present invention, where the phase difference corresponds to a quantized phase difference region. If the base station makes adjustments to the phase such that the phase difference of the signals arriving at the user equipment falls within the 0 region, the signals combine to achieve the greatest increase in signal strength at the receiver. If the base station adjusts the phase such that the phase difference of the signals arriving at the user equipment fall within the 180 ° region, the signals combine to achieve the maximum reduction in signal strength at the receiver. If the signals are aligned such that the phase difference falls within the 90 or 270 region, then the combined signal will also have a gain or a slight drop in gain when compared to one of the originally transmitted signals.

Fig. 14 shows a table 1400 of one embodiment of the present invention showing the average gain of the combined signal of fig. 13 relative to the signal transmitted from one of the antennas for each quantized phase field. On average, the strongest signal strength will be achieved if the phase is adjusted such that the phase difference at the receiver falls within the 0 ° region. If the phase difference is adjusted such that it falls within the 90 ° or 270 ° region, the combined signal strength is, on average, 3dB lower than the average signal strength achieved in the 0 ° region. If the phase difference is adjusted such that it falls within the 180 ° region, the combined signal is attenuated by 14dB on average relative to the signal in the 0 ° region.

Fig. 15 shows a plot 1500 of beamforming gain for two signals with 3dB branch imbalance at a receiver as a function of phase difference, corresponding to a quantized phase difference region, according to an embodiment of the invention. In this graph 1500, the beamforming gain is relative to the stronger of the two received signals.

Fig. 16 shows a table 1600 according to an embodiment of the invention showing the average gain of the combined signal of fig. 15 relative to the stronger of the two received signals for each quantized phase field. The phase differences in the 0 °, 90 ° and 270 ° regions give the best average signal strength, while the phase differences falling within the 180 ° region give the best average combined signal attenuation.

Fig. 17 shows a graph 1700 of beamforming gain for two signals with 10dB branch imbalance at a receiver as a function of phase difference, corresponding to a quantized phase difference region, according to an embodiment of the invention. As in the case of fig. 15, the beamforming gain is relative to the stronger of the two received signals. Note that in this case, the gain in the 0 ° region is lower than the gains shown in fig. 13 and 15. Furthermore, the attenuation in the 180 ° region is lower than that achieved when the relative signal strength is such that the signals from the two transmit antennas are close to each other at the receiver.

Fig. 18 shows a table 1800 of one embodiment of the invention showing the average gain of the combined signal of fig. 17 relative to the stronger of the two received signals for each quantized phase region. As previously mentioned, the phase differences in the 0 °, 90 ° and 270 ° regions give the best average signal strength, while the phase differences falling within the 180 ° region give the best average attenuation of the combined signal.

Next, fig. 19 shows a mobile station receiving a desired signal from a first base station and receiving interference from an adjacent sector with varying phase adjustments according to one embodiment of the present invention. Referring to fig. 19 in conjunction with the phase adjustment diagram of fig. 20, it is apparent that the base station BSA communicating with the mobile station MS1 transmits a beamformed transmission signal 1902 with a 0 degree phase adjustment. Meanwhile, the neighboring base station BSB transmits the beamformed signals 1904 with 90 degree phase adjustment using the same radio resources (e.g., frequency, channel, time slot, etc.). Beamformed transmission signals 1904 are received at the MS1 as interference and not as communication content. In addition, base station BSC transmits beamformed signals 1906 with 180 degree phase adjustment and base station BSD transmits beamformed signals 1908 with 270 degree phase adjustment. Signals 1906 and 1908 are also received as interference at MS 1. Referring to fig. 19, 20 and 21, the transmit transients in fig. 19 correspond to the phase adjustments employed by base stations A, B, C and D as arranged in slot 1, column 1 of tables 2002, 2004, 2006 and 2008 in fig. 20.

Fig. 20-34 illustrate examples of how data transmission between multiple base stations can be scheduled to reduce interference to neighboring base station sectors by coordinating the adjustment of the relative phase of the transmitted signal of each base station (e.g., base stations BSA, BSB, BSC, and BSD in fig. 19). The following example assumes two transmitters per base station (e.g., similar to the dual transmitter beamforming antenna array 102 in fig. 1) and that the relative phases of the transmitted signals are adjusted in 90 ° steps (i.e., the phase differences are quantized according to the four-level quantization scheme shown in fig. 12).

Fig. 20 shows a phase adjustment diagram according to an embodiment of the invention. In this example, there are four base stations in the cluster: base stations A, B, C and D, similar to the topology shown in FIG. 19, but it is apparent that the systems and methods described herein can be applied to any number of base stations, servers, or mobile devices.

Also, in this example, there are ten mobile stations in communication with base station a: CPEID1-10 (see, e.g., CPEID1-10 in FIG. 22). This example also assumes that each CPE/mobile station is able to measure the phase difference between the signals arriving from its serving base station and the phase difference of the signals arriving from the interfering base stations. The phase difference may be measured by a pilot reference signal or other methods known in the art or by a phase difference measurement unit similar to phase difference measurement unit 914 in fig. 9. The present example also assumes that the mobile station/CPE reports this information to the serving base station or server computer for centralized scheduling. Note that in a Time Division Duplex (TDD) system, a base station may utilize channel reciprocity to determine the phase difference between signals arriving at a CPE served by the base station, perhaps without explicit feedback from the CPE. However, the CPE still must measure the phase difference between the signals arriving from the interfering base stations and their levels and report these phase difference and level values to the serving base station and/or server computer.

For fig. 20 and 21, the present example further assumes that an airlink frame structure has been defined that includes a plurality of time slots, each time slot containing a plurality of frequency slots. Many OFDM air link structures are similar (e.g., LTE or AMC permutation mode in WiMAX). In one embodiment, these systems and methods of coordinating the scheduling of beamformed data may be applied to any wireless technology, including but not limited to: GSM (Global System for Mobile communications)^TM、UMTS^TM、LTE^TM、LTEAdvanced^TM、Wi-Max^TM、Wi-Fi^TMAnd the like.

Consistent with the OFDM structure, in this embodiment, the radio resource is designed to have 32 frequency slots in one slot, and to be able to transmit data burst frames (databurst) in each slot/frequency slot (e.g., 32 data burst frames may be transmitted in a single slot — possibly one data burst frame to each of up to 32 mobile stations/CPEs). A frame structure in which one frame includes eight slots is also applied.

Turning to fig. 20, a phase adjustment diagram 2000 in accordance with an embodiment of the present invention is shown. In this example, the four base stations A, B, C and D are assigned a fixed phase transmission pattern in time slots 0-3. The 32 frequency slots in one time slot are divided into 4 groups of 8 frequency slots each (i.e., 8 frequency slots per group). Each set of frequency slots is assigned a fixed phase adjustment value. This frequency structure is shown in fig. 21 as a table 2100 illustrating frequency resources for a base station. Fig. 21 shows eight time slots used to allocate resources for beamforming scheduling. Further, the 32 frequency resources are equally divided into four groups as shown by columns 2102, 2104, 2106 and 2108. Thus, in fig. 21, it is clear that slot #1 corresponding to phase adjustment #2 refers to the set of frequencies (i.e., channels) numbered 8-15. Applying this frequency table to the phase adjustment diagram of fig. 20, it can be seen that, for example, base station B transmits with 180 degree phase adjustment for channels 8-15 in time slot # 1. Meanwhile, for the same timeslot/channel combination, base station a transmits with a 90 degree phase adjustment.

In fig. 20, for time slots 4-7, any phase may be transmitted in any frequency slot. These time slots will be used when coordination of scheduling cannot be done in the first four time slots, and for interference-independent transmissions. Thus, for transmissions where interference is not an issue, or where a guaranteed phase difference is not required, slots 4-7 may be considered "universal" slots.

Assigning phase adjustments to frequency slots and time slots in phase adjustment map 2000 may be accomplished in various ways. For ease of illustration, the phase adjustment map is shown using the fixed allocation of fig. 20. In one fixed allocation, the phase differences are pre-allocated using a reuse pattern, similar to the frequency reuse pattern typically employed in cellular radio systems. In a separate embodiment, the phase adjustment map may be dynamically determined based on phase difference measurements made by the mobile station. These measurements can be shared among the base stations, which can then agree on the appropriate phase adjustment map, or the measurements can be sent to a central processing server, which can then determine the appropriate phase adjustment map for each base station and send the maps to the base stations. In the dynamic determination of the phase adjustment map, the update rate of the phase adjustment map may be as fast as one update every one to five airlink frames, or may be relatively slow, on the order of one update every few seconds. In another embodiment, the phase adjustment may be determined based on historical data or transient factors, such as demand or interference levels.

Note also that it may not be necessary to attempt to reduce interference at all mobile stations/CPEs within the coverage area of the base station. Many mobile stations/CPEs have good CINR initially so they do not require special processing. In this example, data may be sent to such mobile stations/CPEs in "generic" time slots 4-7 or time slots 0-3 if the schedule can accommodate additional mobile stations.

Fig. 22 shows a CPE phase management table 2200 at base station a with various mobile station transmissions and interference data according to one embodiment of the invention. For this example, base station a (btsa) has 10 mobile stations/CPEs to which base station a will send data. The number of data blocks and the optimal phase adjustment angle to be used by the BTSA to transmit to the CPE are shown in table 2200. Also shown in the table are the optimal phase adjustment angles for the base stations interfering with each CPE to minimize the interference level. Looking at the data associated with CPE #1 in table 2200, CPE #1 receives the strongest signal from base station a when base station a transmits with 0 degrees phase difference. Further, CPE #1 receives minimal interference from base station B when base station B transmits to its associated CPE on the same wireless resource with a 180 degree phase adjustment.

In the CPE phase management table 2200, the entry in the interfering BTS phase adjustment unit has two numbers. The upper number is the phase adjustment angle, in degrees, of the base station causing the lowest level of interference at the mobile station served by the BTSA. The lower number is the priority assigned to each interferer, which indicates the relative priority of reducing the interference level. Continuing with CPE #1, the phase of the BTSB that causes the lowest level of interference at the mobile station CPE #1 is adjusted to 180 degrees, as described above. In addition, for CPE #1, the priority to reduce interference from base station B is 1. In this scheduling algorithm, the priority levels are 1 to 4, with 1 being the highest priority. Note that it is obvious to one of ordinary skill in the art that the number of priorities may be greater or less than 4. The priority may be set in various ways, for example, by setting the highest priority for reducing the interference of the strongest interferer seen by the CPE with the lowest CINR, or by setting the highest priority for the base station causing the highest level of interference to a particular CPE, or by using some other priority setting scheme. For example, in fig. 19, reducing interference from base station B may have the highest priority because the signal strength from base station B is the highest relative to other neighboring interfering base stations (e.g., due to the relative distance from the base station to mobile station MS 1).

Next, the coordinated scheduling algorithm will be generally described by way of example in connection with the flow diagrams in FIGS. 23 and 24, followed by specific scheduling examples given in FIGS. 25-32.

Fig. 23 shows a flow diagram 2300 depicting a process for scheduling transmissions at a base station, in accordance with an embodiment of the present invention. It should be appreciated that this process may be performed using one or more computer-executable programs stored on one or more computer-readable media on any of the base station apparatuses (e.g., 606a-c, 612, 700 and BS1 and BS2 of fig. 10 and 11) or in server computer 800 in fig. 8. In blocks 2302 and 2304, the process begins with scheduling transmissions at base station a with an empty schedule. Next, in block 2306, the process initializes a priority level YY = 1. Starting with priority level 1 may reduce the most severe interference before scheduling around the secondary (i.e., lower priority) interfering transmission. Next, in block 2308, the process initializes an interfering base station XX = B, wherein the interfering base station is selected from the group consisting of base stations B, C and D. It is also noted that process 2300 can accommodate any number of base stations, mobile devices, and priority levels. Next, in block 2310, the process processes priority YY radio frequency interference from interfering base station XX. Based on the initialization value, the algorithm processes priority 1 interference from base station B.

In block 2312, the process checks to see if the interference of each base station with the particular priority level has been handled. If not, the process moves to step 2314 where the algorithm processes the interference for the next base station in the set (e.g., continues processing interference for base station C after processing interference for base station B at step 2310). When the interference of each base station is processed at the specific priority level (e.g., "yes" at step 2312), the process moves to step 2316 to check whether all priority levels are processed. If not, the process moves to step 2318 where the priority level is increased (i.e., YY is increased) and the process returns to block 2310 to handle interference from neighboring base stations. Thus, process 2300 loops through an outer loop (handling interference for each priority level) and an inner loop at each priority level (handling interference for each base station at a particular priority level).

Fig. 24 shows a flow chart 2400 depicting a process for scheduling transmissions at a base station, in accordance with an embodiment of the present invention. This flow chart may be used alone or in conjunction with fig. 23 to illustrate the scheduling process. Further, it should be appreciated that this process may be performed using one or more computer-executable programs stored on one or more computer-readable media on any of the base station apparatuses (e.g., 606a-c, 612, 700 and BS1 and BS2 of fig. 10 and 11) or in server computer 800 in fig. 8. The scheduling process 2400 begins at block 2402 by determining the phase adjustments for the best and next best signal transmissions from base station a to each CPE served by base station a. This information is depicted as the column in fig. 22 entitled "phase adjustment to achieve optimal signal level". Next, in block 2404, the process determines the best phase adjustment to reduce the interference level of each interfering base station to each CPE served by base station a. Next, in block 2406, the process determines a priority level for reducing the interference level of each interfering base station to each CPE served by base station a. This information determined in blocks 2404 and 2406 is depicted in fig. 22 as the column entitled "best phase adjustment (in degrees) to reduce interference level and priority to reduce interference".

In block 2408, the process starts with the highest priority level and selects a CPEID for which to schedule transmissions. For the CPE selected in block 2408, the process determines the number of blocks to transmit to the CPE at base station a in block 2410. This information is depicted as the column in fig. 22 entitled "number of blocks to transmit".

Next, in block 2412, the process determines available radio resources in a phase adjustment map for base station a, which transmits with a phase adjustment that results in the selected CPE obtaining the best and next-best signal levels. The available radio resources that meet this requirement may be denoted as "set 1". For example, if the process is performing the actions in step 2412 for CPE #1 in fig. 22, the process will look up the time slots corresponding to 0 degree phase adjustment (for obtaining the best signal level) in table 2002 and look up the time slots corresponding to 90 and 270 degree phase adjustments (for obtaining the next best signal level) in table 2002. The set 1 is made up of the first, second, and fourth columns in the table 2002.

Next, in block 2414, the process determines a second set of radio resources corresponding to radio resources in the phase adjustment map of the base station with the highest priority level of reduced interference, wherein the interfering base station transmits with the best phase adjustment angle that results in the selected CPE obtaining the lowest interfering signal level. For example, as shown in fig. 22, the base station having the highest priority level for reducing interference to CPE #1 is base station B. Fig. 22 also states that the best phase adjustment employed for base station B transmission is 180 degrees. Looking up the phase adjustment map of base station B, table 2004, can find the radio resources that meet these requirements: column 1, slot 2; column 2, slot 1; column 3, slot 0; and column 4, slot 3. As described above, this is set 2.

In block 2416, the process schedules transmission at base station a to the selected CPEID within overlapping radio resources in set 1 and set 2, starting with the overlapping radio resource in set 1 providing the best signal level and continuing with the overlapping radio resources in set 1 in order of signal level provided to the CPE. For set 1 and set 2 in the above example, the best radio resources for base station a are column 1 and slot 2, when base station a transmits with 0 degree phase adjustment. The corresponding radio resource in the base station B is column 1 and slot 2, and at this time, the base station B performs transmission with 180-degree phase adjustment. Thus, by selecting this resource, transmissions to CPE #1 are scheduled to be transmitted under the conditions most favorable for receiving the largest signal from base station a, while transmitting within the same radio resource where the interference of the base station causing the largest interference is minimized. If there is not enough space in column 1, slot 2 to accommodate all transmissions to the selected CPEID, then the additional data sent to the CPE is scheduled into the radio resource (e.g., the resource in column 2, slot 1 or column 4, slot 3 of the phase adjustment maps 2002 and 2004) that causes the selected CPE to obtain a suboptimal signal level.

Next, in block 2418, the process continues with scheduling the remaining data blocks for transmission. If there are any blocks that could not be scheduled in the radio resource in the previous step, block 2418 may schedule the blocks in the resource where interference phase is not guaranteed and employ phase adjustment for best signal transmission by base station a, or block 2418 may queue the blocks, which remain in the queue for transmission in future air link frames. For example, if there is more data remaining to be scheduled for CPE #1 in the above example, the remaining blocks may be scheduled to be transmitted in time slots 4-7 of base station a or buffered for transmission in subsequent airlink frames. If the transmission is in a resource where the interference phase is not guaranteed, the base station a will transmit to CPE #1 with a 0 degree phase shift, which corresponds to "phase adjustment to get the best signal level" in fig. 22.

Finally, in block 2420, the scheduling process is repeated for the remaining CPEs communicating with base station a at the same priority level, and then repeated at a lower priority level until all data blocks to be transmitted are scheduled or until the schedule is full. Thus, the scheduling process schedules all priority 1 interference to CPEs #2-10, and then repeats the process again at the lower priority level until all transmissions are scheduled. Once a CPE is scheduled at a particular priority level, it does not have to be scheduled again at a lower priority level. Further, the present process schedules on each base station (e.g., base stations B, C and D) until all transmissions are scheduled.

For example, fig. 25-32 collectively schedule CPEs into the CPE phase management table shown in fig. 22 for scheduling data transmitted by base station a. Variations of the scheduling process can be readily derived and are intended to be within the scope of the present invention.

Thus, fig. 25 shows an empty transmission schedule at base station a according to one embodiment of the present invention. This is the start of the exemplary scheduling process, which may be referred to as step one.

Next, fig. 26 shows the transmission schedule after processing the first priority interference from the base station B according to an embodiment of the present invention, which may be referred to as step two. In fig. 26-32, the CPEs and the number of blocks to transmit are shown in the time slot and frequency diagrams. The number of blocks to be transmitted to the CPE is shown in brackets next to the CPEID. The CPE scheduled in each step is shown in bold.

In a second step of processing the first priority interference from base station B, the best scheduling location for CPE #1 is slot #2 on the frequency resource with zero degree phase adjustment for base station a. This optimum phase adjustment can be seen in fig. 22, where the phase adjustment map for base station a is table 2002. In slot #2, base station B is guaranteed to transmit to CPEs within its coverage area with a 180 degree phase adjustment on those same frequency resources (i.e., resources that base station a transmits with a zero degree phase adjustment).

Note that only eight data blocks can be transmitted in this time slot with this phase adjustment, since in this example only 8 channels are transmitted in this particular time slot with this phase adjustment, as shown in fig. 21. However, there are 14 blocks to send to CPE # 1. The remaining six data blocks to be sent to CPE #1 must then be scheduled on another set of time/frequency resources. Since the maximum gain is achieved by ensuring that transmissions to CPE #1 are scheduled to the time when base station B employs 180 degree phase adjustment, the scheduling algorithm should select the time/frequency resources that base station B transmits with 180 degree phase adjustment. The algorithm should also select a phase adjustment for base station a that is within +/-90 degrees of the optimal phase adjustment for base station a. The sub-optimal phase adjustment may correspond to a phase adjustment that achieves a sub-optimal signal level, as mentioned in block 2412 in fig. 24. In this case, it means 90 degrees or 270 degrees phase adjustment (i.e., +270 degrees phase adjustment is equivalent to-90 degrees phase adjustment). In this case, the remaining six blocks are scheduled into slot 1 on the frequency resource with base station a having a 90 degree phase adjustment and base station B having a 180 degree phase adjustment. This scheduling result can be seen in fig. 26, where eight data blocks to be sent to CPE #1 are scheduled into the first column, slot 2, and the remaining six data blocks are scheduled into the second column, slot 1.

Similarly, the best scheduling position for CPE #5 is slot #1 on the frequency resource with 180 degree phase adjustment for base station a (see, e.g., fig. 21, column entitled "phase adjustment to get best signal level"). Cross-referencing the phase adjustment map in fig. 20, it can be determined that base station B transmits with 270 degrees phase adjustment over the set of time/frequency resources. Since there are only 6 blocks to transmit to CPE #5, all blocks can be scheduled on these time/frequency resources. In addition, the scheduling result for CPE #5 can be seen in fig. 26, where six data blocks destined for CPE #5 are scheduled into the third column, slot 1.

Next, the remaining CPE with first priority interference of base station B (i.e., CPE # 10) is scheduled by the scheduling algorithm. CPE #10 transmission is scheduled to slot 0 in the frequency resource with 270 degree phase adjustment for base station a. Base station B will transmit on these resources with 270 degree phase adjustments to minimize the interference level seen by the CPE. Since CPE #10 has 10 blocks to transmit, 8 blocks are scheduled on these time/frequency resources and, in this example, the remaining blocks are scheduled in time slot 3 on the frequency resource with 0 degree phase adjustment for base station a and 270 degree phase adjustment for base station B. The updated schedule is shown in fig. 26.

Next, the scheduling algorithm processes interference from base station C with priority 1. The result of this scheduling step is shown in fig. 27, which may be referred to as step three. In processing interference from priority 1 of base station C, transmissions of CPE #3 and CPE #8 are scheduled in a similar manner to the transmissions in step two. 8 of the 12 data blocks to be sent to CPE #3 are scheduled to slot 2, 90 degree phase adjustment, which corresponds to 0 degree phase adjustment at base station C (see, e.g., phase adjustment maps 2002 and 2006). The remaining four data blocks for CPE #3 are scheduled to slot 0 with 0 degree phase adjustment at base station C and 0 degree sub-optimal phase adjustment at base station a.

Two data blocks for CPE #8 are scheduled on the best time/frequency resource on slot 3 with 270 degrees phase adjustment for base station a and zero degrees phase adjustment for base station C. The updated schedule is shown in fig. 27.

Next, the scheduling algorithm processes priority 1 interference from base station D. Fig. 28 shows the transmission schedule after processing priority 1 interference from base station D according to one embodiment of the present invention, which may be referred to as step four. Looking at table 2200 in fig. 22, it can be seen that only CPE #2 receives priority 1 interference from base station D. All 8 blocks for CPE #2 are scheduled to slot 1 with 0 degree phase adjustment for base station a and 270 degree phase adjustment for base station D.

After handling the priority 1 interference of base stations B, C and D, the scheduling algorithm will then schedule priority 2CPE on base station B. The scheduling is shown in fig. 29, which illustrates a transmission schedule after processing second priority interference from base station B according to an embodiment of the present invention. This step may be referred to as step five. The 8 blocks for CPE #7 are scheduled to be in the best position in slot #1 while the remaining two blocks are scheduled to slot 2 where the phase adjustment for base station B is still the best 0 degrees and the phase adjustment for base station a is sub-optimal but still within +/-90 degrees of the best value, which represents the sub-optimal phase adjustment for the serving base station. The updated schedule is shown in fig. 29.

In a sixth step, the scheduling algorithm will schedule priority 2CPE on base station C. However, there are no CPEs to schedule, so the algorithm moves to the next step (see, e.g., fig. 22).

In a seventh step, the algorithm processes the priority 2CPE associated with base station D. Fig. 30 shows a transmission schedule after processing priority 2 interference from base station D according to an embodiment of the present invention. The best scheduling position for CPE #4 is on slot 1 on the frequency resource with 90 degree phase adjustment for base station a and 0 degree phase adjustment for base station D. Since six data blocks are already scheduled on these resources and only eight such resources are available, only two data blocks for CPE #4 can be transmitted on these resources. The remaining four blocks are transmitted on slot 3 with 180 degrees of phase adjustment for base station a (i.e., with sub-optimal phase adjustment) and 0 degrees of phase adjustment for base station D.

For step eight, only one priority 3CPE is scheduled. Fig. 31 shows a transmission schedule after processing third-priority interference according to an embodiment of the present invention. In this example, the best position for transmission to CPE #6 has a 180 degree phase adjustment of base station a, which corresponds to the radio resource in the third column of phase adjustment map 2002. As for the interference received by CPE #6, there are two priority 3 interference sources, the first from base station B and the second from base station D (see, e.g., fig. 22). Referring to fig. 22, it can be seen that the optimal phase adjustment for interference reduction from base stations B and D is 0 degrees. Cross-referencing the phase adjustment map 2002 and the phase adjustment maps 2004, 2008 (corresponding to base stations B and D) can determine that there are two best time slots in the transmission schedule. In this case, the algorithm can schedule the block for CPE #6 into slot 2, column 3 (where interference from base station B will be reduced), or onto slot 3, column 3 (where interference from base station D will be reduced). In this case, it is assumed that the algorithm chooses to schedule four resource blocks to be transmitted on slot 3 and two resource blocks to be transmitted on slot 2. The updated schedule after the eighth step is shown in fig. 31.

In the ninth step, there is one priority 4CPE to schedule, namely CPE #9 (see, e.g., fig. 22). The CPE has the lowest scheduling priority level. Since the best signal for this CPE has a 270 degree phase adjustment of base station a, the algorithm schedules the transmission to this CPE within the available time/frequency resources with this phase adjustment. Thus, fig. 32 shows the transmission schedule after handling priority 4 interference according to one embodiment of the present invention.

In the above scheduling example, the example shows how all CPEs are scheduled. In some cases, it may not be possible to match all CPE transmissions to a perfectly ideal set of phase adjustments from the serving and interfering base stations, or to a sub-optimal, sub-ideal set of phase adjustments (i.e., optimal for the interfering base station and +/-90 degrees from optimal for the serving base station). In these cases, the CPE transmission may be scheduled on time slots 4-7 where no phase adjustment is guaranteed for any base station. However, the serving base station may still use beamformed transmissions to optimize the downlink to the mobile while transmitting in slots 4-7. Alternatively, blocks to be sent to the CPE may be buffered for scheduling in subsequent airlink frames.

Although scheduling of transmissions to mobile devices/CPEs served by base stations B, C and D is not shown in the above example, these transmissions are scheduled in a manner similar to that of transmissions at base station a. Scheduling of a particular CPE into certain time/frequency slots can be performed independently at each of the base stations B, C and D as long as they adjust their phases according to the previously agreed-upon phase adjustment map.

Fig. 33 and 34 illustrate another embodiment of the scheduling process. Fig. 33 shows a flow diagram 3300 of a scheduling process for transmissions at a base station in accordance with an embodiment of the present invention. This flowchart may be used alone or in conjunction with the scheduling process shown in fig. 23 and 24 to illustrate the scheduling process. Further, it should be appreciated that this process may be performed using one or more computer-executable programs stored on any one of the base station apparatuses (e.g., 606a-c, 612, 700 and BS1 and BS2 in fig. 10 and 11), or in server computer 800 in fig. 8, or on one or more computer-readable media in wireless user devices 608a-c, 622, 624, 626. The scheduling process 3300 begins at block 3302 by measuring, at a first mobile station, a first phase difference of a first beamformed signal from a first base station. In one example, the measurement may be performed by the phase difference measurement unit 914. In block 3304, the process measures, at the first mobile station, a second phase difference of a second beamformed signal from the second base station.

Next, in block 3306, the process determines a first phase adjustment for the first beamformed signal based on the first phase difference measurement. The phase adjustment may be a four-level quantized phase adjustment and may be determined at the CPE, at the base station, or at a central server computer. This first phase adjustment may correspond to "phase adjustment to obtain the optimum signal level" in fig. 22. In block 3308, the process schedules, at the first base station, a first data packet into a first radio resource having a first phase adjustment coordinated with an associated second phase adjustment of a second radio resource at a second base station. The present scheduling process may be performed in accordance with the scheduling algorithm described in fig. 20-32. Finally, in block 3310, the process transmits the first data packet as a first beamformed signal to the first mobile station.

Fig. 34 shows another flow diagram of a scheduling process for transmissions at a base station in accordance with an embodiment of the present invention. This flowchart may be used alone or in conjunction with the scheduling process shown in fig. 23, 24, and 33 to illustrate the scheduling process. Additionally, it should be appreciated that this process may be performed using one or more computer-executable programs stored on any one of the base station apparatuses (e.g., 606a-c, 612, 700 and BS1 and BS2 of fig. 10 and 11), or in server computer 800 in fig. 8, or on one or more computer-readable media in wireless user equipment 608a-c, 622, 624, 626.

Referring to fig. 34, a scheduling process 3400 begins at block 3402 by measuring, at a mobile station, a first phase difference of a first beamformed signal from a first base station. Next, in block 3404, the process measures, at the mobile station, a second phase difference of a second beamformed signal from a second base station. Next, in block 3406, the process determines a first phase adjustment for the first beamformed signal based on the first phase difference measurement to increase a gain of the first beamformed signal at the mobile station. The first phase adjustment may correspond to "phase adjustment to obtain an optimum signal level" in fig. 22. In block 3408, the process determines an optimal phase adjustment for the second beamformed signal to reduce the gain of the second beamformed signal when received by the mobile station. This second phase adjustment may correspond to the "best phase adjustment (in degrees) to reduce the interference level and priority to reduce interference" in fig. 22. Next, in block 3410, the process continues with locating a radio resource in a phase adjustment map at the first base station, the radio resource corresponding to a first phase adjustment of the first beamformed signal and a second phase adjustment of the second beamformed signal. Finally, at block 3412, a first data packet is transmitted as a first beamformed signal to the first mobile station within the located wireless resource. Thus, by increasing the gain of the desired signal and decreasing the gain of the second signal, the SINR of the signal directed to the desired mobile station is greatly increased, thereby improving the signal quality of the end user.

Fig. 35-49 illustrate a system and method for coordinating the scheduling of beamformed data to reduce interference according to another embodiment of the present invention that employs more than two bits (e.g., three bits) to quantify the phase angle reported by a CPE to its serving base station. A Customer Premises Equipment (CPE) uses three bits to quantize the phase angle of the beamformed data received by the CPE and reports it to its serving base station. The serving base station selects one of the phase adjustment angles based on the bits received from the CPEs to coordinate data transmission scheduling to the CPEs. The phase adjustment angle is in "m" degree steps (e.g., in 90 degree steps). Three bits allow quantization of the phase region into eight different regions compared to four regions when two bits are used. The third bit is used to distinguish between the second optimal phase angle adjustment and the third optimal phase angle adjustment. In this embodiment, the phase adjustment angles are within 90 degree steps, so each phase angle adjustment is mapped to two phase angle regions.

According to one embodiment of the invention, quantized phase angle reporting and quantized phase angle adjustments are made to reduce interference at the CPE and increase the strength of the desired signal. As described in more detail below, the mobile devices/CPEs (e.g., 108, 608a-c, 622, 624, 626, 900, MS1, and MS 2) measure the phase difference between the two signals that they receive from each base station transmitter (e.g., by phase difference measurement unit 914) and send the measurements (which may also be referred to as "phase difference/phase angle information" or "quantized phase difference/phase angle information") back to their serving base stations. This measurement is quantified to one of 8 values by rounding the measured difference to the nearest angle having the form 22.5 ° + n × 45 ° (where 0 ≦ n ≦ 7).

Fig. 35 shows a table 3500, according to an embodiment of the invention, that maps 3-bit messages (or quantized phase angle information) into 8 quantized phase angle regions/zones. Each of the 3-bit binary values is mapped to a quantized phase difference, a phase difference range, and a region name. For example, the binary value "000" is associated with a quantized phase difference of 337.5 °, a range of phase differences of 315 ° to 360 °, and a lower area name of the 0 ° zone. The binary value "001" is associated with a quantization phase difference of 22.5 °, a phase difference range of 0 ° to 45 °, and a 0 ° zone high end zone name.

Fig. 36 shows a plot 3600 of beamforming gain for two signals with 0dB branch imbalance at a receiver as a function of phase difference, where the phase difference corresponds to a quantized phase difference region, according to an embodiment of the invention. The 8 zones in fig. 36 correspond to the 8 zones listed in table 3500.

Referring to fig. 35 and 36, according to one embodiment of the invention, quantized phase angle reporting and quantized phase angle adjustments are made in order to reduce interference and improve the strength of the desired signal at the CPE. The mobile device/CPE 608a-c, for example, measures the phase difference between the two signals it receives from each base station transmitter and sends the measurement back to its serving base station. The mobile quantifies this measurement to one of the eight values in table 3500 by rounding the measured difference to the nearest angle having the form 22.5 ° + n x 45 ° (where 0 ≦ n ≦ 7). Transmitting the quantized phase difference information as 3 binary bits to a serving base station in a signaling message.

An advantage of quantizing the phase difference to one of eight values is that the overhead of transmitting messages to the base station is reduced compared to quantizing to a larger number of values (e.g., nine binary bits are required to represent the phase difference quantized to 1 degree steps). This helps efficiency while not being computationally burdensome to schedule.

When the serving base station (or server computer 800) receives the quantized phase difference, it can adjust the phase on one of the transmitters (e.g., in one of the transmit antennas in the beamforming antenna array) so that the phase difference of the beamformed signals arriving at the mobile station fall within one of the 8 zones. In the present embodiment, only four phase adjustment angles are employed: 0 degrees, 90 degrees, 180 degrees, and 270 degrees (= -90 degrees). In other embodiments more than four phase adjustment angles may be employed.

If the measured phase difference falls within one of the zero degree zones, then the optimum phase is adjusted to zero degrees. If the phase measurement falls within one of the 90 degree zones, then the optimal phase is adjusted to 90 degrees. This will cause the signal arriving at the CPE to have a phase difference between 315 degrees (i.e. -45 degrees) and 45 degrees, which will provide maximum gain. Similarly, the best phase adjustments for signals having phase measurements falling within the 180 and 270 degree regions are 180 and 270 degrees, respectively. The second optimal phase adjustment/correction depends on where the phase measurement falls in the given zone.

Fig. 37 shows a table 3700 showing the average gain of the combined signal relative to the signal transmitted by one of the antennas for each quantized phase field according to an embodiment of the present invention. The table 3700 has a first column 3702 that lists the phase field, a second column 3704 that lists the average gain of the signal received by the mobile device for a particular phase field, and a third column 3706 that lists the difference from the 0 degree phase field average gain.

On average, the strongest signal strength can be achieved if the phase is adjusted such that the phase difference at the receiver falls within one of the 0 regions (i.e., the low end of the 0 region or the high end of the 0 region). If the phase difference is adjusted to fall within the 90 deg. or 270 deg. region, the combined signal strength is, on average, 3dB lower than the average signal strength achieved in the 0 deg. region. If the phase difference is adjusted such that it falls within the 180 ° region, the combined signal is attenuated by 14dB on average relative to the signal in the 0 ° region. However, if the phase can be adjusted to fall within the 90 ° low end or 270 ° high end, the combined signal strength is only 1.4dB lower on average than the optimal adjustment in which the phase difference will fall within the 0 ° zone low end (or 0 ° zone high end). Since the phase adjustment is performed in 90-degree steps in the present embodiment, the second optimum phase adjustment depends on whether the phase difference detected by the moving means falls at the low end or the high end of the phase measurement region.

Fig. 38 illustrates a table 3800 showing the best, sub-best, and third best phase adjustment steps to achieve the best signal combination for each phase difference measurement zone in accordance with one embodiment of the present invention. In the present embodiment, the phase adjustment is performed in 90-degree steps. The phase adjustment is performed by subtracting the phase measurements to obtain an adjusted phase difference. For example, a 90 degree phase adjustment means that 90 degrees should be subtracted from the phase difference measurement to obtain the final phase after adjustment.

The optimal phase adjustment places the adjusted signal in the low end of the 0 ° zone or in the high end of the 0 ° zone. The second optimum phase adjustment places the adjusted signal in the lower end of the 90 ° region or in the upper end of the 270 ° region. The third optimum phase adjustment places the adjusted signal in the high end of the 90 ° region or the low end of the 270 ° region. For example, if the mobile device measures the signal phase difference and sends a signal to the serving base station that is being received at the low end of the 0 ° zone, the optimal phase is adjusted to 0 °, thereby placing the signal being received within the low end of the 0 ° zone. The second optimum phase is adjusted to 270 deg., thereby placing the signal being received in the lower end of the 90 deg. region. The third optimum is adjusted to 90 deg., so that the signal being received is placed in the lower end of the 270 deg. region. The average gain difference between the second optimal adjustment and the third optimal adjustment is 3.5dB as shown in table 3700. Quantizing the phase region into 8 regions using 3 bits by the mobile device enables the serving base station to identify the second and third best phase adjustments.

For an interfering signal, the greatest reduction in interfering signal strength is obtained when the phase of the interfering signal is adjusted so that it falls within the low end of the 180 ° region or the high end of the 180 ° region. A second best case for interference suppression will be obtained when the interfering signal is phase adjusted so that it falls within the high end of the 90 deg. region or the low end of the 270 deg. region. Unless the phase of the interfering signal can be adjusted to fall within one of the 180 ° regions, the interfering signal cannot be significantly reduced and may actually have some gain. The average interference level jumps from an average of-8.2 dB when the phase adjustment results in a signal falling within the best interference rejection zone (i.e., within the 180 ° zone) to an average of 0.9dB when the phase adjustment results in a signal falling within the second best interference rejection zone (i.e., within the high end of the 90 ° zone or the low end of the 270 ° zone). It is therefore desirable to schedule data transmissions from the base station to the mobile station in a manner such that the transmissions occur when the phase adjustment of the interfering base station causes the interfering signal phase to fall within a 180 ° region at the mobile station.

Fig. 39 shows a wireless system 3900 having a mobile station MS1', a mobile station MS1' is within the coverage area of a base station BS1 'and receives interference 3904 from a neighboring base station BS 2'. The mobile station MS1 'communicates with the base station BS1' through beamforming transmission 3902. In one embodiment, mobile station MS1' may represent mobile station 900 and base stations BS1' and BS2' may represent base station 700. The phase difference of the reference signals received by MS1 'from BS1' is quantified as 8 discrete regions corresponding to phase differences of 337.5 ° (or the lower 0 ° region end), 22.5 ° (or the upper 0 ° region end), 67.5 ° (or the lower 90 ° region end), 112.5 ° (or the upper 90 ° region end), 157.5 ° (or the lower 180 ° region end), 202.5 ° (or the lower 180 ° region end), 247.5 ° (or the upper 270 ° region end), and 292.5 ° (or the lower 270 ° region end). This quantization reduces the amount of feedback from the mobile station to the base station required when transmitting the phase difference information. The quantization also reduces computational overhead while still providing excellent control over the level of constructive or destructive interference.

In wireless system 3900, the phase difference of the reference signals received by MS1 'from BS1' falls within the 180 ° zone high end (i.e., the phase difference is in the range of 180 ° to 225 °). When BS1 'transmits to MS1' with a 180 ° phase adjustment made to the signal transmitted to MS1', the best signal from BS1' will be obtained. The signal received by MS1' from BS2' is attenuated most when BS2' makes a 270 ° adjustment to the relative phase of its transmissions. In other words, when BS1 'transmits to MS1' with 180 ° phase adjustment and BS2 'transmits to a different CPE within its coverage area with 270 ° phase adjustment, an optimal CINR is achieved at MS 1'.

Fig. 40 shows a wireless system 4000 similar to the wireless system 3900 in fig. 39 with the addition of a further mobile station MS 2'. The wireless system 4000 shows the BS2 'transmitting with 270 phase adjustment to the mobile stations MS2' within its coverage area. The best CINR is obtained at MS1' when BS1' transmits to MS1' with 180 ° phase adjustment because the phase difference falls within the high end of the 180 ° zone. See table 3800. If BS1' transmits with 270 phase adjustment, a second best CINR will be achieved. If BS1' transmits with a 90 phase adjustment, a third optimal CINR will be achieved. In one embodiment, the BS1 'coordinates its data transmission to the MS1' by selecting the time slots associated with the 180 ° phase adjustment, the 270 ° phase adjustment, and the 90 ° phase adjustment.

Fig. 41-49 illustrate an example of how data transmissions between multiple base stations can be scheduled to reduce interference to neighboring base station sectors by coordinating the adjustment of the relative phase of each base station's transmitted signal, according to an embodiment of the present invention. The systems and methods disclosed herein for coordinating scheduling of beamformed data may be applied to any wireless technology, including but not limited to: GSM (Global System for Mobile communications)^TM、UMTS^TM、LTE^TM、LTEAdvanced^TM、Wi-Max^TM、Wi-Fi^TMAnd the like.

The present example assumes that an airlink frame structure has been defined that includes eight time slots, each containing multiple frequency slots, as in the previous example with two-bit quantization. See fig. 20 and phase adjustment diagram 2000. Four base stations A, B, C and D are assigned a fixed phase transmission pattern in time slots 0-3. The 32 frequency slots within one time slot are divided into four groups of eight frequency slots. A fixed phase adjustment value is assigned to each set of frequency slots. For time slots 4-7, any phase may be transmitted in any frequency slot. These slots will be used when coordination of scheduling cannot be done in the first four slots, and for interference-independent transmissions. Thus, for transmissions where interference is not an issue, or where a guaranteed phase difference is not required, slots 4-7 may be considered "universal" slots.

Assigning phase adjustments to frequency slots and time slots in the phase adjustment map may be accomplished in various ways, e.g., fixed assignment or dynamic determination as illustrated in the previous examples. In fixed allocation, the phase difference is pre-allocated using a reuse pattern, similar to the frequency reuse pattern typically employed in cellular radio systems. In dynamic allocation, the phase adjustment map is dynamically determined based on phase difference measurements made by the mobile station.

Fig. 41 shows a CPE phase management table 4100 at base station a with various mobile station transmissions and interference data according to one embodiment of the invention. For this example, base station a (btsa) has 10 mobile stations/CPEs to which base station a will send data. The number of data blocks and the zone in which the measured base station reference signal falls are shown in table 4100. The optimal phase adjustment angle employed by the BTSA to transmit to the CPE is also shown in table 4100, along with the second and third optimal phase adjustments. In addition, the table shows the optimal phase adjustment angle that the base station should employ to minimize the interference level, which causes interference to the CPE.

The entry in the interfering BTS phase adjustment unit has two numbers. The upper entry is the phase adjustment in degrees for a given interfering BTS that will produce the lowest level of interference at the mobile station when receiving signals from that interfering BTS. The lower entry is the priority assigned to each interferer, which indicates the relative importance of reducing the interference level. In this embodiment, the priority level is 1 to 4, with 1 being the highest priority, and interference reduction is most desirable. The priority may be assigned in various ways depending on the implementation. For example, the highest priority is set for reducing the interference of the strongest interferer seen by the CPE with the lowest CINR, or the highest priority is set for the base station causing the highest level of interference to a particular CPE, or the priority is set using some other priority setting scheme.

Fig. 42-47 illustrate a process for coordinating the scheduling of beamformed data to reduce interference according to one embodiment of the present invention. Fig. 42 shows an empty transmission schedule 4200 at base station a at the beginning of the scheduling process.

Fig. 43 shows a transmission schedule 4300 for handling first priority interference (or priority 1 interference) from base station B according to one embodiment of the invention. The CPE and the number of blocks to be transmitted are shown in the time slot and frequency diagram. The number of blocks to be transmitted to the CPE is shown in brackets next to the CPEID. The CPE scheduled in each step is shown in bold.

In the step related to the schedule table 4300, the best scheduling position of CPE #1 is slot #2 on the frequency resource with zero degree phase adjustment of base station a. In slot #2, base station B is guaranteed to transmit to CPEs within its coverage area with 180 degree phase adjustment on those same frequency resources.

There are 14 data blocks to transmit to CPE # 1. Since only 8 time/frequency resources are available in this example, only 8 out of 14 data blocks can be transmitted in slot #2 with zero degree phase adjustment. The remaining six data blocks must be transmitted to CPE #1 using another set of time/frequency resources. Since the best gain is achieved by ensuring that transmissions to CPE #1 are scheduled to the time when base station B employs 180 degree phase adjustment, the scheduling process should select the time/frequency resources that base station B transmits with 180 degree phase adjustment. The scheduling procedure should also select the second best phase adjustment from base station a. In this case, that means 90 degree phase adjustment (see table 4100). The remaining six blocks are scheduled into slot #1 on a frequency resource with base station a having a 90 degree phase adjustment and base station B having a 180 degree phase adjustment.

Similarly, the best scheduling position for CPE #5 is slot #1 on the frequency resource with 180 degree phase adjustment for base station a. Base station B transmits on the set of time-frequency resources with a phase adjustment of 270 degrees. Since there are only 6 blocks to transmit to CPE #5, all blocks can be scheduled on these time/frequency resources.

There are 22 data blocks to be transmitted from base station a to CPE # 10. Ideally, all of these blocks should be scheduled for transmission in slot #0 in the frequency resource with a phase adjustment of 270 degrees. Base station B will transmit on these resources with 270 degree phase adjustment to minimize the interference level seen at CPE # 10. Only 8 of the 22 blocks can be scheduled on these time/frequency resources. 8 additional blocks may be scheduled into the second best choice for CPE #10 in slot #3 on the frequency resource with 0 degree phase adjustment for base station a (see table 4100).

The third best option for transmitting to CPE #10 is for base station a to be phase adjusted to 180 degrees and base station B to be phase adjusted to 270 degrees. It is located in slot # 1. However, six of the eight frequency resources with these phase adjustments are already used for CPE #5 transmission, so only two of the remaining six data blocks for CPE #10 can be scheduled onto these resources. The remaining four data blocks for CPE #10 are scheduled into slot # 4. In this case, the transmit phase adjustment for the transmission is set to the 270 degree optimum from base station a. Note that the phase adjustment employed by base station B on these resources will not be guaranteed.

Fig. 44 shows a transmission schedule 4400 for handling first priority interference from a base station C according to an embodiment of the invention. In processing the first priority interference from base station C, transmissions for CPE #3 and CPE #8 are scheduled in a similar manner as transmissions for CPE # 10. 8 of the 12 data blocks to be sent to CPE #3 are scheduled to slot 2 with a 90 degree phase adjustment corresponding to a 0 degree phase adjustment at base station C. The remaining 4 data blocks for CPE #3 are scheduled on slot #0 with 0 degree best phase adjustment at base station C to achieve interference minimization and 0 degree suboptimal phase adjustment at base station a to achieve desired signal combining.

Two data blocks for CPE #8 are scheduled to the best time/frequency resource on slot #3 with 270 degrees phase adjustment from base station a and zero degrees phase adjustment from base station C.

Fig. 45 shows a transmission schedule 4500 according to an embodiment of the present invention after handling first priority interference from the base station D. All eight blocks for CPE #2 are scheduled to slot #1 with 0 degree phase adjustment from base station a and 270 degree phase adjustment from base station D.

Fig. 46 shows a transmission schedule 4600 for handling second priority interference (or priority 2 interference) from base station B according to one embodiment of the invention. Priority 2 interference is processed after priority 1 interference of base station B, C, D is processed. Eight blocks for CPE #7 are scheduled into the best position in slot #1 while the remaining two blocks are scheduled into slot #2, in which slot the phase adjustment of base station B is still the best 0 degrees and 180 degree best phase adjustments from base station a are achieved.

Fig. 47 shows a transmission schedule 4700 for handling second priority interference from base station D according to an embodiment of the invention. The scheduling process continues to handle priority 2 interference from base station D because there are no remaining blocks with priority 2 interference from base station C that need to be scheduled. The best scheduling position for CPE #4 is on slot #1 on the frequency resource with 90 degree phase adjustment from base station a and 0 degree phase adjustment from base station D. Since six data blocks are already scheduled on these resources and only eight such resources are available, only two data blocks for CPE #4 can be transmitted on these resources. The remaining four blocks are transmitted on slot #3 with 180 degree best phase adjustments from base station a and zero degree phase adjustments from base station D.

Fig. 48 illustrates a transmission schedule 4800 for handling priority 3 interference according to one embodiment of the invention. Only one priority 3 interference is to be handled. The best position for CPE #6 has a 180 degree phase adjustment from base station a. In this case, there are two priority 3 interferers, which come from base station B and base station D. The scheduling process can schedule the block for CPE #6 into slot #2, in which interference from base station B will be reduced, or onto slot #3, in which interference from base station D will be reduced. Four resource blocks are transmitted in slot #3 and two resource blocks are transmitted in slot # 2.

Fig. 49 illustrates a transmission schedule 4900 for handling priority 4 interference according to one embodiment of the invention. There is a priority of 4 to schedule, i.e., CEP # 9. The CPE has the lowest scheduling priority level. Since the best signal for a CPE has 270 degrees phase adjustment from base station a, the process schedules transmissions to that CPE within the available time/frequency resources with 270 degrees phase adjustment.

The above scheduling example describes how to schedule transmissions from base station a to CPE as described by embodiments of the present invention. Transmissions to CPEs served by base station B, C, D are scheduled in a similar manner. In some cases, it may not be possible to match all CPE transmissions to the best, sub-best, or third best phase adjustments. In these cases, CPE transmissions are scheduled onto time slots #4 through #7 with the best transmit phase adjustment from the serving base station, but without guaranteeing phase adjustment from any interfering base stations.

Although several embodiments of the present invention have been illustrated and described herein, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by any of the disclosed implementations. Rather, the scope of the invention should be determined from the following claims.

Claims (25)

1. A computer-implemented method for transmitting beamformed data to a mobile station, the method comprising:

receiving, at a first base station that transmitted a reference signal to a mobile station, quantized phase angle information of the reference signal from the mobile station;

selecting a first phase adjustment angle based on the quantized phase angle information received from the mobile station; and

transmitting a first beamformed signal having the first phase adjustment angle selected based on the received quantized phase angle information from the first base station to the mobile station,

wherein the quantized phase angle information is obtained by rounding a phase difference value of the reference signal to a nearest 90 ° step.

2. The method of claim 1, wherein the received quantized phase angle information is associated with one of eight quantized phase angle bins, wherein the reference signal is a beamformed signal.

3. The method of claim 1, wherein the quantized phase angle information is received by the first base station from the mobile station in the form of three bits of information.

4. The method of claim 1, wherein the first base station is a serving base station for the mobile station, the mobile station receives an interfering signal from a second base station, and

wherein the first base station transmits the first beamformed signal to the mobile station as part of a first data packet.

5. The method of claim 4, further comprising:

scheduling, at the first base station, the first data packet into a first radio resource having the first phase adjustment coordinated with an associated second phase adjustment of a second radio resource at the second base station.

6. The method of claim 5, wherein the received quantized phase angle information is associated with one of eight quantized phase angle bins, and the first phase adjustment angle is associated with one of four phase adjustment angles.

7. The method of claim 6, wherein the reference signal is a beamformed signal.

8. The method of claim 5, further comprising:

scheduling, at the first base station, a second data packet into a second radio resource having a third phase adjustment coordinated with an associated second phase adjustment of the second radio resource at a second base station; and

scheduling, at the first base station, a third data packet into a third radio resource having a fourth phase adjustment coordinated with a related second phase adjustment of a second radio resource at the second base station,

wherein the first phase adjustment is a best phase angle correction, the third phase adjustment is a second best phase angle correction, and the fourth phase adjustment is a third best phase angle correction.

9. The method of claim 5, wherein the first radio resource at the first base station corresponds to a first time slot associated with at least one frequency, and

wherein the second radio resource at the second base station corresponds to the first time slot associated with the at least one frequency of the first base station.

10. The method of claim 5, wherein the first phase adjustment is a quantized phase adjustment that determines an amount of constructive interference in the first beamformed signal received by the mobile station; and is

Wherein the second phase adjustment is a quantized phase adjustment that determines an amount of destructive interference in an interference signal received by the mobile station.

11. The method of claim 5, wherein the first data packet is transmitted within the first wireless resource such that a second phase adjustment related to an interference signal transmitted by the second base station is selected to cause an interference signal to be received at a mobile device as destructive interference.

12. The method of claim 5, wherein the first phase adjustment and the second phase adjustment are related by a first phase adjustment map related to the first base station and a second phase adjustment map related to the second base station, the first phase adjustment map and the second phase adjustment map aligning the first radio resource and first phase adjustment with the second radio resource and second phase adjustment.

13. A computer-implemented method for receiving beamformed data from a base station, the method comprising:

receiving a first signal at a mobile station from a first base station;

measuring a first phase difference of the first signal at the mobile station;

transmitting quantized phase angle information of the first signal based on the first phase difference measured by the mobile station to a first base station that transmitted the first signal to the mobile station; and

receiving a first beamformed signal having a first phase adjustment angle from the first base station,

wherein the first base station selects a first phase adjustment angle based on the quantized phase angle information transmitted by the mobile station,

wherein the quantized phase angle information is obtained by rounding the phase difference value of the first signal to the nearest 90 ° step.

14. The method of claim 13, wherein the received quantized phase angle information is associated with one of eight quantized phase angle bins, and wherein the first signal is a beamformed signal.

15. The method of claim 13, wherein the quantized phase angle information is received by the first base station from the mobile station in the form of three bits of information.

16. The method of claim 13, wherein the first base station is a serving base station for the mobile station, the mobile station receives an interfering signal from a second base station,

wherein the first base station transmits the first beamformed signal to the mobile station as part of a first data packet, and

scheduling, at the first base station, the first data packet into a first radio resource having the first phase adjustment coordinated with an associated second phase adjustment of a second radio resource at the second base station.

17. The method of claim 16, wherein the received quantized phase angle is associated with one of eight quantized phase angle bins, and the first phase adjustment angle is associated with one of four phase adjustment angles.

18. The method of claim 16, wherein the first signal is a beamformed signal.

19. The method of claim 16, further comprising:

receiving a second data packet and a third data packet from the first base station,

wherein the first base station schedules the second data packet into a second radio resource with a third phase adjustment coordinated with a related second phase adjustment of the second radio resource at the second base station, and

wherein the first base station schedules the third data packet into a third radio resource with a fourth phase adjustment coordinated with a related second phase adjustment of a second radio resource at the second base station,

wherein the first phase adjustment is a best phase angle correction, the third phase adjustment is a second best phase angle correction, and the fourth phase adjustment is a third best phase angle correction.

20. The method of claim 16, wherein the first radio resource at the first base station corresponds to a first time slot associated with at least one frequency, and

wherein the second radio resource at the second base station corresponds to the first time slot associated with the at least one frequency of the first base station.

21. The method of claim 16, wherein the first phase adjustment is a quantized phase adjustment that determines an amount of constructive interference in the first beamformed signal received by the mobile station; and is

Wherein the second phase adjustment is a quantized phase adjustment that determines an amount of destructive interference in an interference signal received by the mobile station.

22. The method of claim 16, wherein the first data packet is transmitted within the first wireless resource such that a second phase adjustment associated with an interference signal transmitted by a second base station is selected to cause an interference signal to be received at a mobile device as destructive interference.

23. The method of claim 16, wherein the first and second phase adjustments are related by a first phase adjustment map associated with a first base station and a second phase adjustment map associated with a second base station, the first and second phase adjustment maps aligning the first wireless resource and first phase adjustment with the second wireless resource and second phase adjustment.

24. A wireless communication system provided at a base station for coordinating scheduling of beamformed data to reduce interference, the system comprising:

a processor;

a receiver; and

a transmitter;

wherein the transmitter transmits a first signal to a mobile station, the receiver receives quantized phase angle information of the first signal from the mobile station, the processor selects a first phase adjustment angle based on the quantized phase angle information received from the mobile station, and the transmitter transmits a first beamformed signal to the mobile station with the first phase adjustment angle selected based on the received quantized phase angle information,

wherein the quantized phase angle information is obtained by rounding the phase difference value of the first signal to the nearest 90 ° step.

25. A wireless communication system for coordinating scheduling of beamformed data to reduce interference, the system comprising:

a first base station;

a second base station;

a data communication network that facilitates data communication between the first base station and the second base station; and

the first mobile station is a mobile station that is,

wherein a first beamformed signal received by the first mobile station from the first base station is received as a communication; and is

Wherein a second beamformed signal received by the first mobile station from the second base station is received as interference;

wherein the system is configured to:

a first signal is transmitted to the mobile station,

receiving quantized phase angle information of the first signal from the mobile station,

selecting a first phase adjustment angle based on quantized phase angle information received from the mobile station, and transmitting a first beamformed signal having the first phase adjustment angle selected based on the received quantized phase angle information to the mobile station,

wherein the quantized phase angle information is obtained by rounding the phase difference value of the first signal to the nearest 90 ° step.