Patent Application
20110090885
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
This disclosure relates in one exemplary aspect to interference mitigation in wireless networks such as local area networks (WLANs). At least some of the examples disclosed herein relate to a centralized interference measurement and mitigation method involving in one embodiment spectral sensing, beamforming, MIMO, power control, MAC scheduling using a cross-layer approach, and broadcast channel precoding, some or all of which can be employed towards performance enhancement of WLAN networks in presence of interference.
Over the few past years, the wireless technology (including e.g., local area network (WLAN) technology) has undergone tremendous evolution. For example, in the case of the WLAN, the evolution has been from low rate data infrared-based communications in first generation WLANs to the high throughput OFDM radios with sophisticated adaptive algorithms including MIMO. As the new technologies evolve, the need for integration of various applications and services become increasingly necessary. For example, today's IEEE 802.11n-based technologies are progressively integrated with the cellular third generation (3G) mobile communication systems to improve the coverage and capacity. It is anticipated that in the near future a superposition (and node co-location) of access networks of various architectures and topologies ranging from pico-cellular systems (such as WPANS) to large cell sized or macro-cellular systems (such as WCDMA and LTE or Long Term Evolution of the UMTS network) covering a wide range of user applications and services. This evolution of wireless networking towards heterogeneous architectures with ubiquitous coverage, imposes yet a higher degree of adaptively and flexibility that can affect the WLAN design and implementation.
In addition to the integration paradigm, due to the growing number of WLAN users on one hand, and the scarcity of spectrum on the other hand, it is anticipated that in the absence of some form of interference management, the interference level (including co-channel interference, adjacent channel interference, co-location interference, etc.) can potentially grow with the scale of future network deployments. Co-location interference is a potentially severe co-channel and/or adjacent interference that exists between co-located devices. Co-located devices are usually two mutually interfering transceivers integrated into a single device and may be co-located on the same circuit board. Co-channel interference in particular is of utmost importance as it can set limits to the performance and spectral efficiencies of wireless networks. This form of interference can be generated by other users belonging to the same network (termed self interference), adjacent uncoordinated networks, or other wireless devices sharing the spectrum in the WLAN's unlicensed bands. Control of co-channel interference is also very important to the network designers and service providers as it determines the size and number of access points in the network, which in turn affects the overall network deployment costs. In addition to co-channel interference, adjacent channel interference can be harmful in some wireless networks, which are sensitive to interference. For example, WLAN devices operating in the lower edge of the 5 GHZ band can interfere with Ultra Wideband (UWB) networks operating at higher edge of the 3.5-4.8 GHz band, especially if they are co-located in the same device. In fact, proper addressing of the adjacent channel interference in co-located radio terminals becomes an important issue that is already attracting the standards development bodies.
This radio channel agility and interference susceptibility along with the scarcity of wireless spectrum motivated a large body of work to optimize the performance of wireless networks. This effort, highly focused on optimization of physical (PHY) layer, resulted in a number of innovative and effective methods for performance improvement of wireless networks. In parallel, advancement in the IC design and integration technologies, resulted in the possibility of employment of complicated receiver algorithms that were initiated by the pioneering works in the 60's and the 70's, but were not feasible to implement until recently. Among the above advancements in the PHY-based radio link techniques, various types of advanced channel coding schemes such as turbo-codes, low-density parity-check codes (LDPC) and other efficient coding schemes have been proposed for WLAN, with a very narrow margin to Shannon capacity (see, e.g. References [1], [2], which are incorporated herein by reference in their entirety). The combination of OFDM (orthogonal frequency division multiplexing) and MIMO (multiple input multiple output)-based multiple antenna systems is yet another important example of highly robust and attractive PHY-based solutions for broadband radio networks (see References [3], [4], which are incorporated herein by reference in their entirety). On the other hand, the time variable nature of mobile wireless networks is effectively addressed by a PHY technique called adaptive modulation and coding (AMC) which dynamically allocates the modulation and coding resources to users, based on their channel condition (or channel state information) (see References [5], [6], which are incorporated herein by reference in their entirety). The interference problem is addressed by a number of MIMO based signal processing algorithms applicable to both uplink and downlink, in addition to the classic interference cancellation methods such as successive interference cancellation (SIC) (see Reference [7], which is incorporated herein by reference in its entirety). Finally a control mechanism that can significantly affect the performance of WLAN networks is the power control which is tightly coupled with both MAC and PHY layers.
In parallel to the information theory-based technologies applied to PHY-based resource allocation, MAC-based resource allocation strategies has also been optimized using a handful of advanced networking techniques In particular an important design aspect of modern WLANs is the support of quality of service or QoS in the MAC. This demand triggered a new generation of MAC protocols in the IEEE 802.11 standards. More specifically, the IEEE 802.11 MAC was initially designed for best effort services, lacked a built-in mechanism for support of the QoS required for real time services such as VoIP, HDTV, online gaming, etc. In order to provide a guaranteed QoS, a new generation of MAC termed IEEE 802.11.e was introduced (see Reference [8], which is incorporated herein by reference in its entirety). This new MAC employs a so called Hybrid Coordination Function (HFC) with two medium access mechanisms and four classes of user priorities that facilitate implementation of a QoS-enabled MAC architecture.
Recently, further enhancement in the design of wireless networks has been enabled through introduction of a new design paradigm, the so-called cross-layer approach which aims at enhancement of the system performance by jointly designing multiple protocol layers (see References [9], [10], which are incorporated herein by reference in their entirety). The main benefit of this approach is that it allows upper layers to better adapt their strategies to varying link and network conditions resulting in extra flexibility helping to improve the network's end-to-end performance. Many recent cross-layer design concepts are based on exploiting multi-user diversity (MUD), the phenomenon of multiple users experiencing independent fading channels. The exploitation of MUD was initially based on the pioneering work presented in Reference [11], incorporated herein by reference in its entirety, for uplink of a single cell. The MUD concept is mainly based on maximizing the sum capacity (defined as the sum of simultaneous user capacities) by scheduling for each time instant, the user (or user group) that has the best channel condition. The gain achieved by this scheme is called MUD gain, which demands a power control law by applying more transmit power to the stronger channels. For downlink scenario a similar optimization concept is used by MUD; i.e., at each time instance the access point (or base station) scheduler assigns transmission to the user with the best channel. These cross-layer methodologies, in effect break the traditional isolation between PRY-based and MAC/DLC-based resource allocation strategies which were historically addressed by the information theory field and networking theory field respectively. This is achieved through a MAC resource allocation strategy supported by knowledge of the channel state information (CSI) provided by the PHY layer.
In addition to the conventional MUD, other degrees of diversity that might appear in a multi-user environment may be exploited to improve the system performance of a WLAN. In particular future networks are anticipated to have a high degree of heterogeneity which includes scenarios like multiservice supporting nodes, multi-standard supporting nodes, single antenna users sharing resources with multiple antenna users, etc. This results in terminals or nodes that require specific methods of exploiting channel conditions, leading to a concept of networks supporting heterogeneous multiuser diversity (HMUD).
These design concepts are particularly useful for supporting delay-constrained applications such as streaming video. However there are still a number of challenges left to be addressed, many of which related to running high QoS services over the unlicensed spectrum assigned to WLANs. For example, in densely populated residential areas such as apartment buildings, WLAN users set their networks completely independent from one another, while the networks can be at close enough proximity to cause severe interference problems. Although the users can select from a number of operating channels, it is still likely that two networks using the same RF frequency be close enough to interfere with each other. In such cases, it is possible that the hidden node problem is not completely addressed by the CSMA/CA and RTS/CTS handshaking mechanisms, resulting in significant throughput degradation. This problem is particularly significant when the radio link traffic has QoS requirements that impose extra sensitivity to each transmission SNR. High speed real time traffics involving image or motion picture communications (e.g. HDTV) are in particular very sensitive to the fading and interference disturbances observed in a wireless network. For example, studies have shown (see Reference [12], incorporated herein by reference in its entirety) that the throughput of the new generation of WLAN (802.11n) supporting live HDTV channels can be significantly reduced (to the extent that the application cannot be supported), if the SNIR is reduced beyond certain threshold (due to the fading and interference effects). In addition, in many scenarios it is known that the radius ratio of the interference region to the transmission region in a node is a function of minimum allowed SNIR, and as the SNIR requirements for specific services (e.g. HDTV) increase, the likelihood of having interference regions beyond the transmission region increases, resulting in the hidden node or uncoordinated interference problems. Interference region of a node can be defined as a region within which the node in receive mode can be interfered by e.g., an unrelated or uncoordinated interferer and suffer a performance loss. Transmission (or communication) region of a node can be defined as a region over which the node can correctly detect data in the absence of interference.
The latest research indicates the need for further optimization in WLAN architecture including strong network management capabilities. This ostensibly promises more efficient networks with access points, switches, and other clients to communicate and cooperate among themselves in an optimized manner by effectively adjusting to the dynamic channel conditions. This effort within the IEEE Part-11 standardization committee is focused on development an extension to 802.11 called 802.11v (see Reference [13], which is incorporated herein by reference in its entirety). The IEEE 802.11v amendment promises to optimize the next generation of WLAN in many aspects. The key elements of this extension include reduction of the radio power consumption through WLAN Network Management Sleep Mode and automatic reduction of the transmitter power when it is not being used. Other important features supported by 802.11v are timing synchronization among nodes, and real time location services (RTLS), which enables mobile device tracking. Finally, one of the most important new features of this extension is a network management approach targeted to improvement of the network reliability and throughput, while improving the co-location interference problem in co-located devices.
Although the latest advancements in WLAN optimization try to further address the interference problem through signaling over network management frames (IEEE 802.11v), they still falls short of addressing the co-channel interference problem globally across a network (or multitudes of networks). This is mainly due to the fact that this standard focuses on the interference from a radio co-location aspect and not directly based on the co-channel interference that may have a different location than the victim radio terminal. On the other hand, it is based on a per-device (e.g., STA) distributed approach, which has two main drawbacks. Firstly, the interference sensing mechanism and accuracy may be limited by the capabilities of the STA, which is relatively restricted. In addition, since it does not follow a centralized approach, the interference scenario is not observed at a global level, and as such is not optimal.
Multiple embodiments of the present invention are directed toward systems and methods for further improvement of the throughput and capacity of a wireless communications network. This may be accomplished by, e.g., focusing upon reduction of the interference and in particular the co-channel interference, including the interferences scenarios that are not sufficiently addressed by a standard WLAN network.
In one exemplary aspect, a centralized approach to interference mitigation is disclosed. In one embodiment, the approach introduces a specific node that greatly facilitates the interference measurements and channel state communications to the nodes. Various embodiments detect the receiving or transmitting node interference (i.e. the interference affecting the receiver performance or cause a transmission back off after carrier sensing) at a single node or a set of dedicated nodes in order to avoid or reduce its effect at the victim node. This specialized node, termed Interference Controller Node or ICN, has in some variants communication capabilities with the STAs and AP's, and can be a dedicated access point. This interference detection can be as simple as spectral sensing constituting power measurement and/or can be more sophisticated such as measurements of interference parameters and statistics including bandwidth, duty cycle, hopping sequence, etc, as well as, estimating the link budget of the victim link.
In another aspect of the invention, a method for interference mitigation in a wireless network through use of at least one dedicated node is disclosed. In one embodiment, the at least one node is responsible for addressing the interference within the network, and the method comprising utilizing an interference detection mechanism at the at least one dedicated node.
In one variant, if a victim node's reception and/or transmission are affected by one or more cells of the same network, the method implements an interference correction mechanism.
In another variant, the correction mechanism comprises adjusting one or more parameters of a transmitter of the one or more cells based at least in part on at least one of: (i) one or more interference measurements performed at the dedicated node, and/or (ii) the transmission requirements of the one or more cells.
In yet another variant, the correction mechanism comprises adjusting the transmitter parameters of a node that is then transmitting to the victim node based at least in part on at least one of (i) one or more interference measurements at the dedicated node, and/or (ii) the transmission requirements of the transmitting node.
In still a further variant, the correction mechanism comprises adjusting one or more of the victim node's receiver parameters based at least in part on one or more interference measurements obtained at the dedicated node (e.g., one or more interference mitigation parameters).
In still another variant, if a victim node's reception and/or transmission are affected by one or more nodes of a network other than the network (or by an environmental or non-network based interferer such as a microwave oven or the like), the method implements the interference correction mechanism.
In another variant, the one or more nodes of the other network implement a protocol that the dedicated node supports, and the interference correction mechanism comprises adjusting one or more transmitter parameters of the one or more nodes based at least in part on at least one of: (i) the interference measurements at the dedicated node, and/or (ii) transmission requirements of the one or more nodes.
In a further variant, the interference correction mechanism comprises adjusting the transmitter parameters of a node that is transmitting to the victim node based at least in part on the interference measurements at the dedicated node and transmission requirements of the transmitting node.
In yet another aspect of the invention, apparatus for interference mitigation in a wireless network is disclosed. In one embodiment, the apparatus is disposed at a dedicated node of the network responsible for addressing the interference within the network, and the apparatus comprises apparatus configured to utilize an interference detection mechanism at the at least one dedicated node.
In one variant, the apparatus further comprises: logic configured to, if a victim node's reception and/or transmission are affected by one or more cells of the same network, implement an interference correction mechanism; and apparatus for interference correction.
In another variant, the apparatus for correction comprises apparatus configured to cause adjustment of one or more parameters of a transmitter of the one or more cells based at least in part on at least one of (i) one or more interference measurements performed at the dedicated node, and/or (ii) the transmission requirements of the one or more cells.
In still a further variant, the apparatus for correction comprises apparatus configured to cause adjustment of one or more of the transmitter parameters of a node that is then transmitting to the victim node based at least in part on at least one of (i) one or more interference measurements at the dedicated node, and/or (ii) transmission requirements of the transmitting node.
In another variant, the apparatus for correction comprises apparatus configured to cause adjustment of one or more of the victim node's receiver parameters based at least in part on one or more interference measurements obtained at the dedicated node.
In yet another variant, the apparatus further comprises logic configured to, if a victim node's reception and/or transmission are affected by one or more nodes of a network other than the network, implement the interference correction mechanism.
In another variant, the one or more nodes of the other network implement a protocol that the dedicated node supports, and the interference correction mechanism comprises logic to cause adjustment of one or more transmitter parameters of the one or more nodes based at least in part on at least one of: (i) the interference measurements at the dedicated node, and/or (ii) transmission requirements of the one or more nodes.
In another aspect of the invention, an interference-mitigating wireless network architecture is disclosed. In one embodiment, the architecture comprises: at least one dedicated node responsible for addressing the interference within the network; at least one interference detection mechanism at the at least one dedicated node; and an interference correction mechanism in communication with the at least one detection mechanism. The detection and correction mechanisms cooperate to mitigate interference at a victim node within the network.
In another aspect of the invention, a computer-readable apparatus is disclosed. In one embodiment, the apparatus comprises a storage medium with at least one computer program disposed thereon, the at least one program configured to detect and cause mitigation of interference within one or more other nodes of the network.
In another aspect of the invention, a method of operating a wireless network is disclosed. In one embodiment, the method comprises designating one or more nodes within the network as interference mitigation nodes, and operating these nodes so as to detect and cause mitigation of interference at other “victim” nodes within the network by controlling at least one parameter at one or more interfering nodes within or external to the network.
These and other aspects of the invention shall become apparent when considered in light of the disclosure provided herein.
The invention described herein, is detailed with reference to the following figures. The attached drawings are provided for purposes of illustration only and only depict examples or typical embodiments of the invention. It should be noted that the illustrated regions are just examples and regions can take any shape. Also, it should be noted although illustrations are shown in 2D; in general, the zones are three dimensional. It also should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.
This invention is targeted at inter alia addressing the harmful effect of interference, and in one particular aspect, co-channel interference when implementation of the conventional methodologies are not possible, not effective, inefficient and/or insufficient (e.g. for support of the application's QoS requirements, etc.), or whenever the effectiveness of these techniques can be further enhanced. There are in fact a number of likely implementation scenarios that could result in these situations.
As used herein, the STA (station) is used to refer to a device that has the capability to use the IEEE 802.11 protocol including MAC and PHY (e.g. a PC, a laptop, PDA etc.). However, from the network topology point of view, the Station is the infrastructure mode of the wireless device which enables connection with the Access Point. A Station, a node, and a client may be used interchangeably depending on the context. Note however that the invention is in no way limited to 802.11 networks or equipment, or even WLANs for that matter. The WLAN embodiments described herein are merely exemplary of the broader principles of the invention.
The interference mitigation process can be divided into two steps:
Indirect Interference Detection: In this approach (
Combined Interference Detection: Some embodiments may use a combined interference detection approach (
Interference Correction: Once the interference is detected and its parameters of interest are verified, the ICN can deploy either or both of the following strategies:
In some embodiment the whole network or a part of the network (represented by a number of cells in a cellular network) is served by the ICN. We name this configuration as “inter-cell interference mitigation”. In some other embodiments the ICN is dedicated to the interference reduction in a set of networks in a specific geographical area. We name this configuration as “inter-network interference mitigation”. The following gives detail examples of the apparatus and its connectivity, as well as an implementation of some of the above interference mitigation methodologies in a WLAN environment.
Apparatus Example Block Diagram:
Examples of Interference Mitigation Scenarios Using a Centralized Strategy.
Note that without loss of generality, in the above examples, we assume that the IEEE 802.11v network management standard [13] is running over the distribution system (DS). When this standard protocol is used, the interference profiles (e.g. combination of the interference profiles measured by the ICN and the co-located interference) can be easily communicated across the network STAs using especial fields proposed for co-located interference. These fields transmitted on the so called interference frame [13] include many informative fields including interference report period, interference type (index or identifier), frequency domain fields (including interference level, power, bandwidth, carrier frequency, etc), time domain fields (such as interference period, start time), etc.
It will be recognized that while certain aspects of the invention are described in terms of a specific sequence of steps of a method, these descriptions are only illustrative of the broader methods of the invention, and may be modified as required by the particular application. Certain steps may be rendered unnecessary or optional under certain circumstances. Additionally, certain steps or functionality may be added to the disclosed embodiments, or the order of performance of two or more steps permuted. All such variations are considered to be encompassed within the invention disclosed and claimed herein.
While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the invention. The foregoing description is of the best mode presently contemplated of carrying out the invention. This description is in no way meant to be limiting, but rather should be taken as illustrative of the general principles of the invention. The scope of the invention should be determined with reference to the claims.
All references listed below are incorporated by reference herein in their entirety.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/252,088 entitled “METHODS AND APPARATUS FOR CENTRALIZED AND COORDINATED INTERFERENCE MITIGATION IN A WLAN NETWORK” filed Oct. 15, 2009, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61252088 | Oct 2009 | US |
