Patent Publication Number: US-8995361-B2

Title: Multi-channel, multi-modulation, multi-rate communication with a radio transceiver

Description:
RELATED APPLICATIONS 
     This application is a continuation of, and claims priority to, PCT International Application No. PCT/US12/23016, filed Jan. 27, 2012, which claims foreign priority to European Application No. 11188908.5, filed on Nov. 11, 2011, both of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Wireless networks are configured for many purposes. They may be configured in small areas, such as a residence, or larger areas such as an enterprise-wide network. In some cases, wireless networks extend over entire cities, states, continents, and the globe. 
     Generally, wireless networks include a plurality of nodes which communicate with each other on a same wireless channel (e.g., a predefined frequency range). The communication often includes transferring (e.g., transmitting) large amounts of data between two or more nodes. In some instances, two or more of the plurality of nodes wish to communicate on the channel at a same time. 
     In these networks, one or more of the plurality of nodes are often forced to wait to communicate on the network. For example, due to a limited channel number, a node may be forced to transfer data after another node finishes communicating on the channel. This waiting period may be lengthened when the other node is transferring a large amount of data which requires more communication time. 
     There is an increasing opportunity to transfer data in a wireless network in an efficient manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description refers to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical items. 
         FIG. 1  illustrates an exemplary architecture in which techniques described herein may be implemented. 
         FIG. 2  illustrates an exemplary control channel and exemplary data channels that may be utilized to transfer data between nodes of a network. 
         FIG. 3  illustrates an exemplary frequency hopping process to frequency hop a control channel over a plurality of channels. 
         FIG. 4  illustrates an exemplary request-to-send frame that may be communicated to request to send data to a node. 
         FIG. 5  illustrates an exemplary clear-to-send frame that may be communicated to indicate that data may be sent to a node. 
         FIG. 6  illustrates an exemplary process of sending a first message via a control channel indicating a request to send data, receiving a second message indicating a particular data channel, and sending the data via the particular data channel. 
         FIG. 7  illustrates an exemplary process of receiving a first message via a control channel indicating a request to send data, sending a second message via the control channel indicating a particular data channel that has been determined, and receiving data via the particular data channel. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure describes techniques for transferring (e.g., transmitting) data over a network having multiple nodes, including at least first and second nodes. In particular implementations, the techniques may be implemented in a multi-channel network in which a physical channel is divided into a control channel and multiple data channels. The first and second nodes may communicate one or more messages via the control channel that indicate a particular data channel from the multiple data channels that may be utilized to transfer data between the first and second nodes. The one or more messages may also indicate a modulation technique and/or a data rate that may be utilized when the data is transferred. In some cases, each of the one or more messages is shorter in length than the data (i.e., each of the one or more messages includes less bits and/or bytes than the data). 
     The first node and/or second node may determine the particular data channel that will be utilized to transfer data based at least in part on the one or more messages. The first node and/or second node may also determine the modulation technique and/or data rate that will be utilized. The first node and/or second node may switch to the particular data channel based on the determination. The first node may then send the data to the second node via the particular data channel. In some cases, the data is sent via the particular data channel based at least in part on the determined modulation technique and/or data rate. The first node and/or second node may switch back to the control channel after the data has been transferred. In some instances, the first node and/or second node each include a single radio frequency transceiver configured to implement a plurality of different modulation techniques and/or data rates. 
     The techniques described herein may allow data to be transferred in an efficient manner. For example, by specifying a control channel and multiple data channels, nodes may communicate via the control channel while other nodes transfer data via a data channel. In addition, by specifying multiple data channels, a first set of nodes may transfer data via a first data channel while a second set of nodes transfer data via a second data channel. This may allow a network to increase data throughput compared to techniques which utilize a single channel. Moreover, in some instances, a node may communicate via a single radio frequency transceiver configured to implement a plurality of different modulation techniques and/or data rates. Further, by communicating short messages on a control channel and transferring long data on a data channel, more nodes may communicate via the control channel compared to techniques which utilize a single channel for communicating short messages and long data. 
     The sections below are examples provided for the reader&#39;s convenience and are not intended to limit the scope of the claims, nor the proceeding sections. Furthermore, the techniques described in detail below may be implemented in a number of ways and in a number of contexts. One example implementation and context is provided with reference to the following figures, as described below in more detail. However, the following implementation and context is but one of many. 
     Illustrative Architecture 
       FIG. 1  illustrates an exemplary architecture  100  in which techniques described herein may be implemented. The architecture  100  includes a plurality of nodes  102 - 108  communicatively coupled to each other via communication paths  110 - 116 . Here, the nodes  102 - 108  are also configured to communicate with a central office  118  via a network(s)  120 . 
     Each of the nodes  102 - 108  may be implemented as any one of a variety of conventional computing devices such as, for example, smart utility meters (e.g., electric, gas, and/or water meters equipped with two-way communications), sensors (e.g., temperature sensors, weather stations, frequency sensors, etc.), control devices, routers, regulators, servers, relays, switches, valves, or a combination thereof. In some instances, the nodes  102 - 108  form part of one or more networks, such as Autonomous Routing Area (ARA) networks, such as a Local Area Network (LAN), Personal Area Network (PAN), Home Area Network (HAN), Neighborhood Area Network (NAN), Wide Area Network (WAN), Metropolitan Area Network (MAN), etc. Further, in some aspects of this disclosure, the nodes  102 - 108  are implemented in a mesh networking environment where the nodes  102 - 108  transfer data between each other. 
     The node  102  is representative of each of the nodes  102 - 108  and includes a radio  122  and a processing unit  124 . The radio  122  may comprise a radio frequency (RF) transceiver configured to transmit and/or receive RF signals via one or more of a plurality of channels. In some instances, the radio  122  may implement one or more of a plurality of different modulation techniques, data rates (i.e., bit rates), protocols, signal strengths, and/or power levels. In some implementations, the radio  122  comprises a single RF transceiver configured to implement a plurality of different modulation techniques, data rates, protocols, signal strengths, and/or power levels. 
     Further, in some implementations, the radio  122  utilizes a modulation technique and/or data rate associated with a previously defined standard. In some instances, the modulation technique and/or data rate are associated with a standard defined by the Institute of Electrical and Electronics Engineering (IEEE), such as the IEEE 802.11 standard, the IEEE 802.15 standard, etc. In one example, the modulation technique and/or data rate are selected from the following non-exhaustive list:
         Frequency Shift Keying (FSK) modulation with a data rate of 50 or 150 kbps; channel spacing of 200 or 400 kHz; and/or a first channel starting at 902.2 or 902.4 MHz. FSK modulation may utilize convolutional code forward error correction (FEC).   Orthogonal Frequency-Division Multiplexing (OFDM) with physical modulations of binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), and/or quadrature amplitude modulation (QAM) (e.g., 16-QAM); a data rate of 50, 100, 200, 300, 400, 600, or 800 kbps; and/or channel spacing of 400 or 800 kHz. OFDM may utilize convolutional FEC with ½ or ¾ coding rate.   Direct-sequence spread spectrum (DSSS) modulation with a physical modulation of offset quadrature phase-shift keying (O-QPSK); a data rate of 31.25, 125, 250, or 500 kbps; and/or channel design based on a previously defined standard, such as the 802.15.4 standard. DSSS may utilize convolutional FEC.       

     Moreover, in further implementations, the radio  122  may utilize a customized modulation technique. In one example, the customized modulation technique is associated with a data rate of 6 or 10 kbps. 
     The radio  122  includes an antenna (not illustrated in  FIG. 1 ) providing input to an RF front end  126 . The RF front end  126  may provide transmitting and/or receiving functions. The RF front end  126  may include high-frequency analog and/or hardware components that provide functionality, such as tuning and/or attenuating signals provided by the antenna and obtained from one or more of the nodes  104 - 108 . The RF front end  126  may provide a signal to a baseband processor  128 . 
     All or part of the baseband processor  128  may be configured as a software (SW) defined radio. In one example, the baseband processor  128  provides frequency and/or channel selection functionality to the radio  122 . The SW defined radio may include components that might alternatively be implemented using analog components. For example, the SW defined radio may include mixers, filters, amplifiers, modulators and/or demodulators, detectors, etc., implemented in software executed by a processor or application specific integrated circuit (ASIC) or other embedded computing device(s). The SW defined radio may utilize a processor(s)  130  and software defined or stored in memory  132 . 
     Meanwhile, the processing unit  124  may include the processor(s)  130  communicatively coupled to the memory  132 . The processing unit  124  may also include a clock  134  configured to maintain a time. The clock  134  may also be configured to provide one or more count-up or count-down timers. Such timers may be used in frequency hopping a control and/or data channel. 
     The memory  132  may be configured to store one or more software and/or firmware modules, which are executable on the processor(s)  130  to implement various functionalities. While the modules are described herein as being software and/or firmware executable on a processor, in other embodiments, any or all of the modules may be implemented in whole or in part by hardware (e.g., as an ASIC, a specialized processing unit, etc.) which execute the described functions or instructions. 
     In the embodiment of  FIG. 1 , the memory  132  includes a communication module  136 , a channel determination module  138 , and a switching module  140 . The communication module  136  may cause one or more messages and/or data to be sent and/or received via a channel, such as a data or control channel. The channel determination module  138  may determine the channel to be utilized for sending and/or receiving the one or more messages and/or data. The switching module  140  may cause the channel to be switched. The memory  132  may also include a frequency hopping function  142  utilized during frequency hopping of a channel, such as a data channel or control channel. 
     The memory  132  may comprise computer-readable media and may take the form of volatile memory, such as random access memory (RAM) and/or non-volatile memory, such as read only memory (ROM) or flash memory. Computer-readable media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data for execution by one or more processors of a computing device. Examples of computer-readable media include, but are not limited to, phase change memory (PRAM), static random-access memory (SRAM), dynamic random-access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information for access by a computing device. As defined herein, computer-readable media does not include communication media, such as modulated data signals and carrier waves. 
     In some implementations, information (e.g., a message, data, etc.) is transferred in the architecture  100  by means of a protocol data unit (PDU). A PDU may be based at least in concept on, for example, the Open Systems Interconnection (OSI) Model and may comprise, for example, a bit, a frame, a packet, a segment, etc. In some instances, one or more layers of the OSI model are utilized to transfer one or more PDUs between nodes. For example, the data link layer of the OSI model may be utilized to transfer PDUs between two or more of the nodes  102 - 108  in the architecture  100 . In particular implementations, the media access control (MAC) sub-layer of the data link layer is utilized to transfer PDUs between two or more of the nodes  102 - 108 . Further, in some implementations, an access method may be utilized to transfer PDUs, such as the carrier sense multiple access with collision avoidance (CSMA/CA) method, for example. 
     For ease of illustration, the following description will refer to transferring information in the context of transferring PDUs. As used herein, the term “message PDU” generally refers to a PDU associated with controlling and/or commanding the transfer of data. The message PDU may specify, for example, a data channel that may be utilized to transfer the data, a modulation technique that may be utilized on the data channel, and/or a data rate that may be utilized on the data channel. In some instances, the message PDU may be associated with an IEEE standard (e.g., IEEE 802.11, 802.15.4, etc.). Here, the message PDU may comprise, for example, a Request-to-Send (RTS) PDU, a Clear-to-Send (CTS) PDU, a Non-Clear-to-Send (NCTS) PDU, etc. 
     Meanwhile, the term “data PDU” is used herein to generally refer to a PDU associated with data that is transferred. For example, a data PDU may include data that is generated at and/or provided to a node to be transferred to another node. In some instances, a data PDU may be associated with an IEEE standard (e.g., IEEE 802.11, 802.15.4, etc.). Here, the data PDU may comprise, for example, Unicast Data and/or Broadcast Data. In some instances, a data PDU may include the same or similar information that is included in a message PDU. 
     A message PDU generally operates in combination with a data PDU. For instance, a message PDU may be transferred on a control channel to request that a data PDU be transferred on a data channel. In some instances, a data PDU is transferred on a data channel when a message PDU is shorter in length than the data PDU. That is, the message PDU includes less bits and/or bytes than the data PDU. In other instances, a data PDU is transferred on a control channel when a message PDU is equal or longer in length than the data PDU. Here, the data PDU may be transferred without transferring a message PDU. 
     In  FIG. 1 , the communication path  110  is representative of the communication paths  112 - 116  and includes a plurality of channels labeled  1 -N. Each of the plurality of channels may be defined by a frequency range which is the same or different for each of the plurality of channels. In some instances, the plurality of channels comprises RF channels. As illustrated, the plurality of channels may comprise a control channel  144  and multiple data channels  146 . In some instances, the control channel  144  is utilized for communicating one or more message PDUs between nodes to specify one of the data channels  146  to be utilized to transfer one or more data PDUs. Meanwhile, the data channels  146  may be utilized to transfer the one or more data PDUs between the nodes. 
     In some implementations, each of the nodes  102 - 108  divides the communication path  110  into the control channel  144  and the multiple data channels  146 . For example, the MAC sub-layer implemented in of each of the nodes  102 - 108  may divide a total number of physical RF channels of the communication path  110  into the control channel  144  and the multiple data channels  146 . 
     The network(s)  120 , meanwhile, may comprise a wireless or a wired network, or a combination thereof. The network(s)  120  may be a collection of individual networks interconnected with each other and functioning as a single large network (e.g., the Internet or an intranet). Examples of such individual networks include, but are not limited to, PANs, HANs, LANs, WANs, and MANs. Further, the individual networks may be wireless or wired networks, or a combination thereof. 
     The central office  118  may be implemented by one or more computing devices, such as servers, personal computers, laptop computers, etc. The one or more computing devices may be equipped with one or more processor(s) communicatively coupled to memory. In some examples, the central office  118  includes a centralized meter data management system which performs processing, analysis, storage, and/or management of data received from one or more of the nodes  102 - 108 . For instance, the central office  118  may process, analyze, store, and/or manage data obtained from a smart utility meter, sensor, control device, router, regulator, server, relay, switch, valve, and/or other nodes. Although the example of  FIG. 1  illustrates the central office  118  in a single location, in some examples the central office  118  may distributed amongst multiple locations and/or may be eliminated entirely (e.g., in the case of a highly decentralized distributed computing platform). 
       FIG. 2  illustrates an exemplary environment  200  for transferring one or more message PDU(s) and/or data PDU(s) between a first node  202  and a second node  204 . The first and second nodes  202  and  204  may be similar to or the same as the nodes  102 - 108  in  FIG. 1 . Here, the first node  202  and/or second node  204  may transfer the one or more message PDU(s) and/or data PDU(s) via a control channel  206  and/or data channels  208 - 212 . 
     In one example, the first node  202  and/or second node  204  listen to the control channel  206  for a message PDU that requests the first node  202  and/or second node  204  to exchange information (e.g., a message PDU, a data PDU, etc.). The first node  202  and/or second node  204  may listen to the control channel  206  by tuning to a frequency associated with the control channel  206 . The control channel  206  may be static or hop according to a predefined frequency hopping pattern. 
     When the first node  202 , for example, wishes to transfer a data PDU to the second node  204 , the first node  202  may send a first message PDU to the second node  204  via the control channel  206 . The first message PDU may indicate a request to send a data PDU from the first node  202  to the second node  204 . The first message PDU may comprise, for example, an RTS PDU. In response, the second node  204  may send a second message PDU to the first node  202  via the control channel  206  indicating that the first node  202  may send the data PDU to the second node  204 . The second message may comprise, for example, a CTS PDU. 
     In some instances, the first node  202  may send the first message PDU multiple times. Here, the first node  202  may send the first message PDU based on a first modulation technique. If a response (e.g., the second message PDU) from the second node  204  is not received within a predetermined time period, then the first node  202  may send the first message PDU again based on a second modulation technique (e.g., a modulation technique different than the first modulation technique) and/or different channel and/or different data rate. This process may be repeated any number of times until a response is received from the second node  204 . By doing so, the first node  202  may utilize different advantages of different modulation techniques. 
     In some aspects of this disclosure, the first modulation technique is associated with a different connectivity range, signal strength, signal-to-noise ratio, power level, data rate, etc. The connectivity range may refer to a distance at which a signal may be received. In some implementations, the second modulation technique is associated with a connectivity range that is greater than a connectivity range associated with the first modulation technique. Further, in some implementations, the second modulation technique is associated with a data rate that is less than a data rate associated with the first modulation technique. 
     Alternatively, or additionally, the first modulation technique and/or second modulation technique may include predefined techniques. To illustrate, the first modulation technique may utilize, for example, FSK modulation, while the second modulation technique may utilize OFDM or DSSS. 
     Meanwhile, the first message PDU and/or second message PDU may specify a particular data channel from the multiple data channels  208 - 212  that may be utilized to transfer a data PDU. The first message PDU and/or second message PDU may also specify a modulation technique and/or data rate that may be utilized on the particular data channel while transferring the data PDU. Further, the first message PDU and/or second message PDU may specify a number of data PDUs that may be transferred on the particular data channel. 
     In some implementations, the first message PDU and/or second message PDU specifies capabilities of one or more of the nodes  202  and  204 . The capabilities may include, for example, a maximum, minimum, preferred, and/or range of data channels, modulation techniques, and/or data rates. The capabilities may differ because of, for example, different device types (e.g., meter vs. cell router), generation of a device, model of a device, etc. To illustrate, the first node  202  may send a first message PDU that indicates that the first node  202  includes hardware and/or software resources to transmit and/or receive a data PDU at a particular data rate and/or with a particular modulation technique. The first message PDU may additionally, or alternatively, specify a preferred data channel from the multiple data channels  208 - 212  and/or a list of available data channels. 
     Based on the first message PDU and/or second message PDU, the first node  202  and/or second node  204  may determine a particular data channel that will be utilized to transfer a data PDU, a modulation technique that will be utilized on the particular data channel, and/or a data rate that will be utilized on the particular data channel. In some examples, the second node  204  may perform the determination after the second node  204  receives a message PDU from the first node  202 , while in other examples the first node  202  may perform the determination. 
     In some instances, a particular data channel is determined based on a plurality of data channels that may be available to the first node  202  and/or second node  204 . In one implementation, the second node  204  receives a first message PDU including a list of data channels that are available. Here, the second node  204  may select a particular data channel from the list and send a second message PDU to the first node  202  indicating that the particular data channel has been selected to transfer a data PDU. 
     Alternatively, or additionally, a particular data channel may be determined based on a preferred data channel specified in, for example, the first message PDU and/or second message PDU. In one implementation, the second node  204  receives a first message PDU from the first node  202  indicating a preferred data channel. Here, the second node  204  may select the preferred data channel and send a second message PDU to the first node  202  indicating that the preferred data channel has been selected. In the example of  FIG. 2 , the data channel  212  represents the particular data channel that is determined for transferring the data PDU. 
     In some instances, a particular data channel, modulation technique, and/or data rate may be determined based on capabilities of the first node  202  and/or second node  204 . For example, if the second node  204  receives a message PDU from the first node  202  that indicates capabilities of the first node  202 , then the second node  204  may compare these capabilities with capabilities of the second node  204 . Based on the comparison, the second node  204  may determine, for example, a modulation technique and/or data rate that is common to the first node  202  and second node  204 . That is, the comparison may identify the modulation technique and/or data rate that may be supported by hardware and/or software resources of the first node  202  and second node  204 . 
     In some implementations, a determined data rate may be a maximum common data rate from among a plurality of data rates that may be supported by the first node  202  and second node  204 . Alternatively, or additionally, the determined data rate may be a rate that is proposed in the first message PDU and/or second message PDU. Meanwhile, the determined modulation technique may be a common modulation technique which is associated with, for example, a maximum data rate and/or maximum connectivity range from among a plurality of modulation techniques that may be implemented by the first node  202  and second node  204 . 
     In some instances, the determined modulation technique and/or data rate are different than those which are utilized on the control channel, while in other instances the determined modulation technique and/or data rate are the same. For example, the determined modulation technique may be a technique which provides a longer or shorter connectivity range than the modulation technique utilized on the control channel. Meanwhile, the determined data rate may be greater than, equal to, or less than a data rate implemented on the control channel. In some instances, the determined modulation technique and/or data rate may be one that is less susceptible to interference than other modulation techniques and/or data rates available to the first and second nodes  202  and  204 . 
     Further, in some instances, the determined modulation technique and/or data rate may be based on a distance between the first and second nodes  202  and  204 . For example, if the distance is greater than a threshold, then a particular modulation technique and/or data rate may be selected that is more suited for communicating a signal a long distance (e.g., a distance greater than the threshold). 
     After a particular data channel, modulation technique, and/or data rate are determined, the first node  202  and/or second node  204  may switch from the control channel  206  to the particular data channel. The first node  202  and/or second node  204  may switch by tuning to a frequency associated with the particular data channel. As noted above, the data channel  212  in  FIG. 2  represents the particular data channel that is determined. 
     The first node  202  and second node  204  may then transfer a data PDU via the particular data channel. Here, the first node  202 , for example, may send a data PDU to the second node  204  via the data channel  212 . In some examples, the first node  202  and second node  204  transfer the data PDU based on the modulation technique and/or data rate determined from the first message PDU and/or second message PDU. As noted above, the data PDU may be, in some instances, transferred via the particular data channel when the data PDU is longer in length than the first message PDU and/or second message PDU transferred on the control channel  206 . 
     After the data PDU has been transferred, the first node  202  and/or second node  204  may switch from the data channel  212  to the control channel  206 . In some instances, the first node  202  and/or second node  204  switch in response to receiving or sending an acknowledgment PDU indicating that the data PDU was received. The acknowledgement PDU may comprise, for example, an Acknowledgement (ACK) signal defined in an IEEE standard, such as the IEEE 802.15.4 standard. The acknowledgement PDU may be sent via the data channel  212 . In other instances, the first node  202  and/or second node  204  may switch to the control channel  206  after a predetermined time has passed since the data PDU was received and/or sent. 
     As discussed above, in some implementations, the first node  202  and/or second node  204  are each equipped with an RF transceiver configured to implement a plurality of different modulation techniques, data rates, protocols, signal strengths, and/or power levels. In particular implementations, each RF transceiver comprises a single RF transceiver. 
     Meanwhile, in some cases, while the nodes  202  and  204  utilize the data channel  212 , other nodes may utilize the control channel  206  and/or one of the other data channels  208 - 210 . That is, while the nodes  202  and  204  transfer the data PDU on the data channel  212 , two or more other nodes may specify a particular data channel via the control channel  206  and switch to the particular data channel to transfer data. The particular data channel may be a different data channel than that utilized by the first and second nodes  202  and  204 , such as the data channel  208  or  210 . This may allow multiple nodes on a network to utilize a common control channel. Further, this may allow first nodes to transfer data on a first data channel while second nodes simultaneously/concurrently transfer data on a second data channel. In some cases, this may increase data throughput of the network in comparison to networks which do not utilize a control channel and/or multiple data channels, such as networks with a single channel. 
     Further, in instances where a data PDU is longer in length than a first message PDU and/or second message PDU, a common control channel may be utilized by transferring short message PDUs on the control channel and transferring long data PDUs on one or more data channels. This may further increase data throughput of the network in comparison to networks which do not utilize a control channel and/or multiple data channels. 
     Although the techniques described herein illustrate transferring a PDU to one node at a time, the PDU may be alternatively, or additionally, transferred to more than one node at a time. For example, the PDU may be transferred to a plurality of nodes at the same time by, for example, broadcasting the PDU to the plurality of nodes. Here, the PDU may be broadcast via, for example, a control channel and/or a particular data channel which are previously specified to the plurality of nodes. Further, in some instances, when transferring a PDU to a single node, one or more other nodes in the vicinity of the single node may overhear (e.g., receive) the transmission. 
     Illustrative Frequency Hopping 
       FIG. 3  illustrates an exemplary frequency hopping process  300  to frequency hop a control channel  302  over a plurality of channels. As illustrated, the control channel  302  is hopped over channels  1 -N such that the control channel  302  is located at a channel  1  at a time t 0 , a channel  3  at a time t 1 , and at a channel N−1 at a time t 2 . The channels  1 -N are each defined by a frequency range. For instance, the channel  1  is defined between a frequency f 0  and f 1 . 
     The frequency hopping may be associated with a frequency hopping sequence. This sequence may be transmitted to one or more nodes of a network that may utilize the channels  1 -N. In some instances, the sequence is transmitted from a particular node in the network that will initiate the frequency hopping. The particular node may comprise, for example, a coordinator of the network, such as a PAN coordinator. 
     In some instances, data channels of the network are also hopped over the channels  1 -N as the control channel  302  is hopped. For example, when the control channel  302  is located at channel  1 , the data channels may be defined from channels  2 -N. Thereafter, when the control channel  302  is located at channel  3 , the data channels may be defined from the channels  1 ,  2 , and  4 -N. Further, in some cases, the frequency hopping is implemented by MAC sub-layers of the nodes of the network. 
     In some implementation, frequency hopping may be implemented to reduce or mitigate radio interference which may affect communication on a network. 
     It should be appreciated that the frequency hopping illustrated in  FIG. 3  is an exemplary implementation, and that the frequency hopping may be implemented in other manners and/or based on other hopping sequences. For example, although the example of  FIG. 3  utilizes a hopping sequence that hops the control channel  302  from channel  1  to channel  3 , and then from channel  3  to channel N−1, a different hopping sequence may be utilized to hop the control channel  302  to any of the channels  1 -N in any order. 
     Illustrative Protocol Data Units 
       FIGS. 4-5  illustrate exemplary PDUs which may be transferred via a control channel and/or data channel. In particular,  FIG. 4  illustrates an example request-to-send (RTS) frame  400  that may be used to indicate that a node wishes to send data to another node, while  FIG. 5  illustrates an example clear-to-send (CTS) frame  500  that may be used to indicate that a node is available to receive data. In some examples, upon receiving an RTS message, a node may respond (if available) by sending a CTS message. In this example, the RTS and CTS frame structures are defined by the IEEE 802.15.4 standard. However, in other examples other PDU structures may be used for the RTS messages, CTS messages, or other communications conveying information associated with a multi-channel communication network. 
     Referring to  FIG. 4 , the example RTS frame  400  may be used to inform neighboring nodes that a node wishes to send data and will not be available for another transmission, and to negotiate a particular data channel and one or more physical (PHY) parameters (e.g., data rate and/or modulation technique) with an intended recipient node. As shown in  FIG. 4 , the RTS frame includes the following fields: frame control (FC), sequence number, destination personal area network (PAN) identifier, destination address, source PAN identifier, source address, auxiliary security header, payload, and frame check sequence (FCS). Details of the foregoing fields of the RTS frame other than the payload are well known to those skilled in the art and are not described in detail herein. The payload of the RTS frame  400 , however, is customized to implement the techniques described above, as well as other functionalities. The payload may be variable in size and may include, for example, one or more of the following fields:
         Type: This field indicates a type of the frame, e.g., RTS, CTS, not-clear-to-send (NCTS), etc. In the example of  FIG. 4 , this field indicates that the frame is an RTS frame.   HW: This field indicates a type of hardware of a node sending the RTS frame. The type may include, for example, a version or generation of device, and/or any other information usable to determine capabilities of the node (e.g., battery powered, modulation techniques and/or data rates that are supported by the node).   Rank: This field indicates a routing protocol for low power and lossy networks (RPL) rank (if known) of the node which is sending the RTS frame. This field may be utilized by a receiving node for routing consistency detection at the MAC sub-layer.   DODAG_ID: This field is a Destination Oriented Directed Acyclic Graph (DODAG) identifier (ID), which identifies a DODAG root (e.g., a network border router, cellular router, relay, etc.), through which the node sending the RTS is connected to a backhaul network, such as the Internet, for communication with a central office or other network computing device. In the context of the architecture  100  of  FIG. 1 , the node  104  is an example of a DODAG root which is in communication with network(s)  120 , which may comprise a backhaul network(s). The DODAG_ID allows a node which receives the RTS frame to accept or reject the RTS frame by verifying routing consistency conditions at the MAC sub-layer.   Duration: This field indicates a total expected time for exchanging data frame(s) specified in the RTS. The duration may include time to transmit the specified data frames, waiting times such inter-frame spacing (IFS) (e.g., SIFS, GIFS, etc.) between frames, and acknowledgment (ACK) or non-acknowledgement (NACK) responses. The duration field may be used to determine a duration that a node will be busy communicating with another node and therefore unavailable to receive.   Ch. On: This field includes a flag indicating whether the RTS includes a channels list.   Channels List: This field includes a channels list including a list of channels that are available to a node sending the RTS frame. A node receiving the RTS frame may select a channel from the available channels and specify this chosen channel inside a CTS frame. In some examples, the channel list may include less than all channels that are available to a node. For example, if a DSSS modulation is employed, the channel list may be limited to 13 channels in the 915 MHz Industrial, Scientific, and Medical (ISM) band. The channel list may comprise, for example, a list of qualified channels between the node that sent the RTS and the node that received the RTS. The list of qualified channels may be maintained in memory of the node that sent the RTS and/or the node that received the RTS.   Data Rate (DR) parameters: This field indicates a maximum data rate supported and/or proposed by a node sending the RTS frame. A node receiving the RTS frame may utilize this field to determine a data rate of which both the sending and receiving nodes are capable. The determined data rate may be sent to the sending node using a CTS frame. The determined data rate will be set to at most the maximum data rate of a slower of the two nodes. Thus, if the RTS proposes a data rate higher than the receiving node is capable of, the receiving node will set a lower data rate (at most the maximum data rate of the receiving node) when sending the CTS frame.   Data_ID: This field includes an ID of a data packet. This ID may be present inside the RTS frame. This field may be utilized if, for example, the data packet was received by a particular node but an acknowledgement was not received at a node which sent the data packet. In this case, the node which sent the data packet with Data_ID may assume that the data packet was not received and may reseed an RTS frame for the same Data_ID. In some cases, when the particular node keeps track of a number of last Data IDs received, the particular node may respond with an ACK frame instead of a CTS frame, and thus avoid a retransmission of the data packet.   F_ID: This field includes a MAC frame ID of the RTS frame and may be utilized to detect duplicate RTS frames. The receiving node of the RTS frame may copy this F_ID into the CTS frame when answering the RTS frame. When a node sending the RTS frame receives a CTS frame, the node may use the F_ID in the CTS frame to determine if the CTS frame is the expected frame (e.g., the CTS frame is an answer to the RTS frame the node sent previously).   NP: This field indicates a number of packets to be exchanged with a node receiving the RTS frame. This field tells the receiving node how many packets to listen for on a specified data channel before switching back to listen on the control channel. This field may also be useful in determining availability of articular channels.   Pre_Ch: This field indicates a channel that a node prefers to utilize for exchanging data frames. By default, the recipient of the RTS frame may select this channel for data exchange, if possible. However, if this channel is busy or is otherwise not available to the receiving node, the recipient node may designate a different channel in the CTS.   DIR: This field indicates whether traffic is from a root or is to be sent to the root. Traffic sent from a root toward a leaf is said to be “downstream,” while all communications sent toward the root are said to be “upstream.” The field may be set to 1 for upstream traffic and 0 for downstream traffic, for example.       

       FIG. 5 , meanwhile, illustrates an example CTS message  500  in the form of a frame that may be communicated to indicate that a node is available to receive data. The CTS frame  500  may include, for example, PHY parameters and a data channel selected by the first node. In some instances, the CTS frame  500  is utilized to inform neighboring nodes that the node sending the RTS frame and the node sending the CTS frame will be unavailable and that the selected data channel will be busy during a specified time period. In the example of  FIG. 5 , the CTS frame  500  includes the following fields: FC, sequence number, destination PAN identifier, destination address, source PAN identifier, source address, auxiliary security header, payload, and FCS. Details of the foregoing fields of the CTS frame  500  other than the payload are well known to those skilled in the art and are not described in detail herein. The payload of the CTS frame  500 , however, is customized to implement the techniques described above, as well as other functionalities. The payload of the CTS frame  500  may be variable in size and may include, for example, one or more of the following fields:
         Type: This field may indicate information similar to that described above in reference to  FIG. 4 . In the example of  FIG. 5 , this field indicates that the frame is a CTS frame.   HW: This field includes hardware parameters (e.g., type of device, version or generation of device, etc.) of a node that received the RTS frame (i.e., the node that will send the CTS frame).   Rank: This field is analogous to the corresponding field of the RTS frame, but as applied to the CTS frame. This field may be used in ranking communication paths according to their relative quality.   DODAG_ID: This field is analogous to the corresponding field of the RTS frame, but as applied to the CTS frame. Specifically, this field is a DODAG identifier providing a choice for a node which receives the CTS frame to accept or reject by verifying routing consistency conditions at a MAC sub-layer.   Duration: This field is analogous to the corresponding field of the RTS frame, but as applied to the CTS frame, and may be used in determining availability and duration of availability.   Channel: This field indicates a data channel selected by the node that received the RTS frame.   DR: This field indicates a data rate selected by the node that received the RTS frame. The data rate may be the same (if the receiving node is capable of the data rate) or different than the data rate specified in the RTS (if the receiving node is not capable of the data rate specified in the RTS). This data rate may be implemented to transfer data on a data channel.   F_ID: This field includes a MAC frame ID of the CTS frame, which may be identical to a F_ID of an RTS frame.       

     In some instances, one or more of the above fields included within the RTS frame  400  of  FIG. 4  and/or the CTS frame  500  of  FIG. 5  may be utilized by one or more nodes to determine a particular data channel from multiple data channels, a modulation technique to be utilized on the particular data channel, and/or a data rate to be implemented on the particular data channel. 
     For instance, a first node may send an RTS frame to a second node requesting to transfer data with the second node. The RTS frame may include one or more of the fields noted above, such as HW, Ch. List, DR, and/or Pre CH. Based on one or more of these fields the second node may determine the particular data channel, modulation technique, and/or data rate. The second node may then send a CTS frame to the first node indicating the particular data channel, modulation technique, and/or data rate that have been selected to transfer data. 
     As discussed above, the RTS and CTS frames  400  and  500  are merely examples of some PDUs that may be used to implement the techniques described herein. In other embodiments various other PDUs may be employed to implement the described techniques. 
     Illustrative Processes 
       FIGS. 6-7  illustrate exemplary processes  600  and  700  of communicating one or more messages via a control channel and transferring data via a particular data channel. The processes  600  and  700  (as well as each process described herein) are illustrated as a logical flow graph, each operation of which represents a sequence of operations that can be implemented in hardware, software, or a combination thereof. In the context of software, the operations represent computer-executable instructions stored on one or more computer-readable storage media that, when executed by one or more processors, perform the recited operations. Generally, computer-executable instructions include routines, programs, objects, components, data structures, and the like that perform particular functions or implement particular abstract data types. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described operations can be combined in any order and/or in parallel to implement the process. 
     In  FIG. 6 , the process  600  may be performed by a node that will send data (e.g., a data PDU). While in  FIG. 7 , the process  700  may be performed by a node that will receive the data. In  FIGS. 6 and 7 , the term “sending node” refers to the node that will send the data, and the term “receiving node” refers to the node that will receive the data during a given exchange of data. However it should be understood that every node can function as both a sending node and a receiving node as needed. 
     As illustrated in  FIG. 6 , the process  600  includes an operation  602  for specifying a control channel and multiple data channels from a plurality of channels. In some instances, the operation  602  is performed at a MAC sub-layer. The operation  600  also includes an operation  604  for sending a first message via the control channel indicating a request to send data. The first message may be sent to a receiving node. 
     The process  600  also includes an operation  606  for receiving a second message via the control channel. The second message may be received from the receiving node. In some instances, the second message indicates a particular data channel of the multiple data channels, a modulation technique to be utilized on the particular data channel, and/or a data rate of the particular data channel that was determined at the receiving node to transfer the data. The process  600  may then proceed to an operation  608  for switching to the particular data channel. The operation  608  may be performed based on the particular data channel that is indicated in the second message. 
     The process  600  also includes an operation  610  for sending the data via the particular data channel to, for example, the receiving node. In some instances, the data is sent based on the modulation technique and/or data rate indicated in the second message. The process  600  includes an operation  612  for receiving an acknowledgement indicating that the data has been received. The acknowledgement may be received from, for example, the receiving node. 
     The process  600  also includes an operation  614  for switching to the control channel. In some instances, the operation  614  is performed in response to receiving the acknowledgement, while in other instances the operation  614  is performed after a predetermined time period has expired. The process  600  includes an operation  616  for listening on the control channel for a message that requests a further operation to be performed by, for example, the sending node. 
     Meanwhile, the process  700  in  FIG. 7  may be performed by a receiving node. The process  700  includes an operation  702  for specifying a control channel and multiple data channels from a plurality of channels. In some instances, the operation  702  is performed at a MAC sub-layer. The process  700  includes an operation  704  for receiving a first message via the control channel indicating a request to send data. The first message may be received from a sending node. Further, the process  700  includes an operation  706  for determining a particular data channel of the multiple data channels, a modulation technique to be utilized on the particular data channel, and/or a data rate of the particular data channel based at least in part on the first message. The process  700  includes an operation  708  for sending a second message via the control channel to, for example, the sending node. In some implementations, the second message specifies the particular data channel, modulation technique, and/or data rate determined in the operation  706 . 
     The process  700  also includes an operation  710  for switching to the particular data channel determined in the operation  706 . The operation  710  may be performed in response to sending the second message. The process  700  also includes an operation  712  for receiving the data via the particular data channel. In addition, the process  700  includes an operation  714  for sending an acknowledgement indicating that the data has been received. The operation  714  may be performed after the data has been received. 
     Moreover, the process  700  includes an operation  716  for switching to the control channel. The operation  716  may be performed in response to sending the acknowledgment. Alternatively, or additionally, the operation  716  may be performed after a predetermined time period has expired since the data, or a portion thereof, has been received and/or since switching to the particular data channel. Here, the expiration of the predetermined time period may be based on a timer. The process  700  includes an operation  718  for listening on the control channel for a message that requests a further operation to be performed by, for example, the receiving node. 
     CONCLUSION 
     Although embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the disclosure is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed herein as illustrative forms of implementing the embodiments.