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TRANSMISSION CHANNEL BANDWIDTH SELECTION FOR COMMUNICATIONS BETWEEN MULTI-BANDWIDTH NODES
The present invention relates generally to communications and more particularly to techniques for selecting a channel bandWidth for communicating data betWeen nodes in a Wireless communication netWork.
Wireless netWorks have experienced increased development in the past decades. TWo types of Wireless netWorks are infrastructure-based Wireless netWorks and ad hoc netWorks. An infrastructure-based Wireless netWork typically includes a communication netWork With fixed and Wired gateWays. Many infrastructure-based Wireless netWorks employ a mobile unit Which communicates With a base station that is coupled to a Wired netWork. The mobile unit can move geographically Wile it is communicating over a Wireless link to the fixed base station. When the mobile unit moves out of range of one base station, it may connect or perform a “bandover” to a neW base station and continue communicating With the Wired netWork though the neW base station.
In comparison to infrastructure-based Wireless netWorks, such as cellular netWorks, or satellite netWorks, ad hoc netWorks are self-forrning netWorks Which can operate in the absence of any fixed infrastructure, and in some cases the ad hoc netWork is formed entirely of Wireless nodes. An ad hoc netWork typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” Which are Wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). The nodes can communicate With each other over a Wireless media Without the support of an infrastructure-based or Wired netWork. Links or connections betWeen nodes can change dynamically in an arbitrary manner as existing nodes leave or exit the ad hoc netWork.
Nodes in an ad hoc netWork can utilize a Request-to-Send (RTS)/Clear-to-Send (CTS) protocol to reduce frame collisions introduced by a hidden node problem. According to this protocol, a transmitter node Wishing to send data can initiate the RTS/CTS protocol by transmitting a Request-to-Send (RTS) message. The RTS message can be a short frame (30 bytes) and may contain the duration of a CTS-Data-Ack exchange that may eventually folloW. A receiver node replies With a Clear-to-Send (CTS) message. The CTS message can be a frame contains the remaining duration of the data-ACK exchange that may folloW. Upon receipt of the CTS message the transmitter node begins transmission, and any other node receiving the CTS frame should refrain from sending data for a given time (solving the hidden node problem). The amount of time the node should Wait before trying to get access to the medium is included in both the RTS message and the CTS message. Any other node receiving the RTS frame but not the CTS frame is permitted to transmit to other neighboring nodes (solving the exposed node problem). The RTS-CTS protocol Was designed under the assumption that all nodes have the same transmission range.
BRIEF DESCRIPTION OF THE FIGURES
The accompanying figures, Where like reference numerals refer to identical or functionally similar elements throughout the separate vieWs and Which together With the detailed
description beloW are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance With the present invention.
FIG. 1 is a block diagram of an exemplary communication netWork;
FIG. 2 is a block diagram of an exemplary general purpose computing node;
FIG. 3 is a message floW diagram shoWing messages exchanged betWeen a transmitter/ source node and a receiver/ destination node according to one exemplary implementation of the present invention;
FIG. 4 is an exemplary frame structure of a Request-toSend (RTS) message according to one exemplary implementation of the present invention;
FIG. 5 is another exemplary frame structure of a Clear-toSend (CTS) message according to one exemplary implementation of the present invention;
FIG. 6 is a timing diagram shoWing the timing of messages exchanged betWeen a transmitter/ source node and a receiver/ destination node during a successful negotiation of a requested channel bandWidth according to one exemplary implementation of the present invention; and
FIG. 7 is a timing diagram shoWing the timing of messages exchanged betWeen a transmitter/ source node and a receiver/ destination node during a failed negotiation of a requested channel bandWidth according to one exemplary implementation of the present invention.
Skilled artisans Will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been draWn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
Before describing in detail embodiments that are in accordance With the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to dynamically selecting a channel bandWidth for transmitting a data packet over a Wireless communication link Which couples a transmitter node to a receiver node. Accordingly, the apparatus components and method steps have been represented Where appropriate by conventional symbols in the draWings, shoWing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure With details that Will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
It Will be appreciated that embodiments of the invention described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction With certain non-processor circuits, some, most, or all of the functions for dynamically selecting a channel bandWidth for transmitting a data packet over a Wireless communication link Which couples a transmitter node to a receiver node as described herein. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, poWer source circuits, and user input devices. As such, these functions may be interpreted as steps of a method for dynamically selecting a channel bandWidth for transmitting a data packet over a Wireless communication link Which couples a transmitter node to a receiver node. Alternatively, some or all functions could be implemented by
a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in Which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. Thus, methods and means for these functions have been described herein. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, When guided by the concepts and principles disclosed herein Will be readily designed to generate such software instructions and programs and ICs With minimal experimentation.
In this document, relational terms such as first and second, front and last, beginning and end, and the like may be used solely to distinguish one entity or action from another entity or action Without necessarily requiring or implying any actual such relationship or order between such entities or actions. The use of these relational terms and the like in the description and the claims may be used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, designed to operate in sequences other than those illustrated or otherwise described herein.
FIG. 1 is a block diagram of an exemplary communication network 100 which comprises a source node 120 and a destination node 130 which communicate with one another over a link or channel 110. The link 110 can be wired or wireless. The receiver/destination node 130 is assumed to be within communication range of the transmitter/ source node 120. The nodes 120, 130 can generally be devices designed to receive packetized audio, video and/or data information. The nodes can exchange information as data packets transmitted over one or more communication channels. Some of the components in an exemplary node, such as an exemplary processor, transmitter, receiver and antenna, are described below with reference to FIG. 2. In one implementation, the source node 120 and destination node 130 can be nodes in a wireless network (e.g., a communication device and base station or vice-versa) and can communicate information packets over a communication medium in accordance with a multiple access scheme. Alternatively, in another implementation, the source
node 120 and destination node 130 can be nodes in an ad hoc communication network where the nodes each have repeater and routing capability.
As used herein, the term “transmitter/ source node 120” is defined to be the source of the transmission, not necessarily the source of a particular packet. As used herein, the term “receiver/destination node 130” is defined to be the destination for the transmission, not necessarily the final destination for a particular packet. The term “receiver/destination node 130” can refer to a neighbor node or a next hop node from the transmitter/ source node 120. In some situations, the receiver/ destination node 330 can be the actual destination of a packet transmitted from the transmitter/ source node 120.
In some operating environments (e.g., in outdoor urban environments), channel quality of the communication link between the transmitter and receiver nodes can vary considerably. Depending on the delay spread conditions, in some cases it is beneficial for nodes belonging to a particular network to use a relatively narrow channel bandwidth if the delay spread conditions are particularly bad. For example, an IEEE 802.11 network which operates on a single 10 MHz channel in the 4.9 GHz public safety band has proven to be a useful configuration to deal with harsh delay spread conditions which can occur in some channels in outdoor urban environments.
It wouldbe desirable to provide a wireless network (e.g., ad hoc network or other wireless network) comprising multibandwidth nodes which are designed to communicate at alternate channel bandwidths depending on integrity and quality of the channel or link between two nodes. For instance, it would be desirable to increase the channel bandwidth in some cases and decrease the channel bandwidth in other cases.
Techniques and technologies are described herein for allowing each node in a wireless network (e.g., ad hoc network or other wireless network) to select its desired transmission bandwidth for each data frame in a dynamic fashion. These techniques and technologies can be used, for example, to dynamically select one of a default channel bandwidth and a alternate channel bandwidth for transmitting a packet over a wireless communication link which couples a multi-bandwidth transmitter node to a multi-bandwidth receiver node in a wireless network (e.g., ad hoc network or other wireless network). In one implementation, each node can dynamically select one of a default channel bandwidth, a higher channel bandwidth and a lower channel bandwidth for transmitting a data packet over a wireless communication link which couples a transmitter (or source) node to a receiver (or destination) node in an ad hoc network. For instance, applying these techniques and technologies to the exemplary network 100 shown in FIG. 1, the transmitter/ source node 120 and the receiver/destination node 130 can transmit and receive at a default channel bandwidth (e.g., 10 MHz) and at least one of or each of a second channel of higher channel bandwidth (e.g., 20 MHz), a third channel of lower channel bandwidth (e.g., 5 MHz), and the like. These techniques and technologies provide a way to dynamically use higher or lower bandwidth channels for communication in situations where links will likely not be adversely affected by the harshest delay spread conditions, while also maintaining Media Access Control (MAC) integrity and not violating air interface standards.
Before further describing exemplary implementations of the invention, a brief overview of some conceptual components in a node will be provided with reference to FIG. 2.