Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L12/00—Data switching networks
  • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W72/00—Local resource management
  • H04W72/20—Control channels or signalling for resource management

Definitions

• the present invention generally relates to wireless networks and more particularly relates to separating control and data in wireless networks.
• Users have access to an ever increasing variety of devices which can be utilized for an ever increasing variety of purposes.
• the user may talk on a wireless phone, schedule appointments using a personal digital assistant, edit documents on a personal computer (PC), play games on a game console, watch recorded television programming from a digital video recorder, and so on.
• PC personal computer
• the personal digital assistant may be communicatively coupled to the desktop PC to share a schedule.
• each of these devices may have peripheral devices which further increase the functionality of the device.
• a headset may be utilized with the wireless phone
• a global positioning system (GPS) receiver may be utilized with a personal digital assistant
• a printer may be utilized with the personal computer
• another game console may be attached to the game console so that players can play "head-to-head", and so forth.
• GPS global positioning system
• Wireless communication techniques are described in which control and data are separated.
• a method is described which includes sending data packets on one or more wireless channels and sending control data relating to the data packets on at least one other wireless channel having a data rate that is lower than a data rate of the one or more wireless channels.
• the one or more wireless channels may operate at frequencies about 900 MHz while the at least one channel operates at a frequency below 900 MHz.
• a method which includes sending a set of data packets on one or more wireless channels and sending control data on at least one other wireless channel during the sending of the set of data packets.
• the control data is configured to reserve a time on the one or more wireless channels to send another set of data packets.
• a method which includes sending a set of data packets on one or more wireless channels and sending contention control data relating to another set of data packets on at least one other wireless channel simultaneously during sending of the set of data packets.
• FIG. 1 is an illustration of an environment in an exemplary implementation that is operable to employ a wireless protocol having split data and control channels.
• FIG. 2 is an illustration of data transfer in an exemplary implementation which may be performed using the data channel and the control channel of FIG. 1.
• FIG. 3 is an illustration of data transfer in an exemplary implementation which may be performed using the data channel arid the control channel of FIG. 1 without an advance reservation technique.
• FIG. 4 is an illustration of data transfer in an exemplary implementation which may be performed using the data channel and the control channel of FIG. 1 in conjunction with an advance reservation technique.
• FIG. 5 is a flow diagram depicting a procedure in an exemplary implementation in which data and control information are simultaneously communicated on respective data and control channels.
• Radio spectrum allocated for use in unlicensed wireless networks is typically distributed across non-contiguous frequency bands, hereinafter also referred to as “slices”, “slivers” and “channels”.
• Traditional Medium Access Control (MAC) protocols e.g., IEEE 802.11, however, only operate in contiguous bands, which is inefficient and results in decreased data transfer bandwidth.
• MAC Medium Access Control
• a split-channel protocol is described that improves the capacity of a wireless infrastructure and multi-hop wireless network by utilizing a sliver of unused spectrum in the lower frequency band for control purposes which was previously deemed unsuitable for data transfer.
• the protocol may increase throughput by moving contention resolution overheads to a separate low-rate channel (e.g., at or below 900 MHz) than a data channel which is to be utilized for transfer of data received from a "higher layer", e.g., an application.
• the protocol may incorporate a variety of techniques for separate transfer of control and data. For example, the protocol may allow simultaneous channel contention and data transmission by incorporating "advance reservation" on the control channel and "data aggregation" on the data channel, and so on, further discussion of which may be found in relation to the following sections.
• FIG. 1 is an illustration of an environment 100 in an exemplary implementation that is operable to employ a wireless protocol having split data and control channels.
• the environment includes a first client 102(1) and a second client 102(2) which are communicatively coupled, one to another, using a wireless architecture 104.
• the clients 102(1), 102(2) may be configured in a variety of ways for communicating via the wireless architecture 104.
• one or more of the clients 102(1), 102(2) may be configured as a computing device, such as a desktop computer, a mobile station, an entertainment appliance, a wireless phone, a game console, and so forth.
• one or more of the clients 102(1), 102(2) may be configured as a peripheral device, such as a wireless printer.
• the clients 102(1), 102(2) may range from full resource devices with substantial memory and processor resources (e.g., personal computers, game consoles) to low-resource devices with limited memory and/or processing resources (e.g., peripheral devices).
• the clients 102(1), 102(2) may also be referenced as "nodes" in the wireless architecture 104.
• the wireless architecture 104 is further illustrated as including a plurality of protocol components on each of the clients 102(1), 102(2), respectively, which as illustrated include data aggregation protocols 106(1), 106(2), channel reservation and contention resolution protocols 108(1), 108(2), and data train management protocols 110(1), 110(2).
• Data aggregation protocols 106(1), 106(2) are representative of functionality which is responsible for aggregating packets to a particular destination into a train of packets.
• the data aggregation protocols 106(1), 106(2) for instance, may maintain a separate queue for each neighboring node to support per-destination aggregation.
• Channel reservation and contention resolution protocols 108(1), 108(2) are representative of functionality to resolve contention and reserve time on a data channel 112 for a packet train received from the data aggregation protocols 106(1), 106(2) by exchanging "request-to-send” (RTS) and "clear-to-send” (CTS) packets on a control channel 114.
• RTS request-to-send
• CTS clear-to-send
• Data train management protocols 110(1), 110(2) are representative of functionality in the wireless architecture 104 that manages respective buffers 116(1), 116(2) at the respective clients 102(1), 102(2).
• the buffers 116(1), 116(2) may be utilized to buffer packets which were transmitted or received utilizing a respective transmitter/receiver 118(1), 118(2), e.g., radios.
• the data train management protocol 110(1), 110(2) may also selectively send an acknowledgement packet (ACK) for the received packets in the trains and support retransmission of lost packets.
• ACK acknowledgement packet
• the data aggregation protocols 106(1), 106(2) may be utilized to build a train of packets which has a total size greater than a specified threshold, and transmit the train using a single reservation on the control channel 114.
• the data aggregation protocol 106(1), 106(2) may be configured such that the control channel 114 does not become a bottleneck to performance because each reservation on the control channel 114 may reserve time for relatively "large" packets, e.g., packet trains.
• the RTS-CTS exchange reserves the data channel 112 for communication between a sender and one receiver.
• the packets in the train have a common destination.
• successive packets from a higher layer e.g., the application modules 120(1), 120(2)
• the data aggregation protocol 106(1), 106(2) may be utilized to separately aggregate packets for each destination.
• the data aggregation protocol 106(1), 106(2) may maintain a queue for each known neighbor, e.g., another client. Whenever a packet is received from the higher layer to a destination for which that are no packets pending, the data aggregation protocol 106(1), 106(2) may assemble a new packet train. When the size of the packet train is equal to the threshold (hereinafter referred to as an "aggregation limit"), which is a parameter of the data aggregation protocol 106(1), 106(2), the packet train is transferred to the channel reservation and contention resolution protocol 108(1), 108(2) for scheduling and subsequent transmission.
• the threshold hereinafter referred to as an "aggregation limit”
• the data aggregation protocol 106(1), 106(2) may utilize another parameter called "aggregation timeout", which specifies a maximum time a partially built packet train may wait for a new packet. Thus, even when multiple packets to a single destination are not available, the packet is sent as specified by the aggregation timeout parameter.
• the average size of data transmitted for each contention resolution attempt is sufficiently large to achieve significant performance improvements be aggregating packets into a train of packets and reserving the data channel for the whole train with the single contention resolution operation.
• the size of the packet train effectively increases the size of the "packets" communicated on the data channel.
• the data aggregation protocols 106(1), 106(2) may be utilized such that the average packet train size is larger than a threshold, such that an improvement in the throughput of the data channel 112 is larger than the data rate of the control channel 114.
• Channel reservation and contention resolution protocol may include two parts, a reservation protocol and a contention protocol.
• the reservation protocol exchanges control packets between a sender and a receiver (e.g., RTS and CTS packets) for reservation of the data channel.
• the reservation protocol has a parameter "reserve ahead limit" that indicates a maximum number of packet trains that may be reserved for transmission at any time, i.e., advance reservation.
• a new reservation is initiated. Otherwise, the packet train is buffered (e.g., via a respective buffer 116(1), 116(2)) until a reservation opportunity arises later.
• Each channel reservation and contention resolution protocol 108(1), 108(2) on the respective clients 102(1), 102(2) may also maintain a reservation table to tracks reservation already scheduled for communication on the data channel 112.
• a sender initiating the reservation first computes a time "T" utilized for transmitting the associated packet train and receiving an acknowledgement (ACK).
• the sender then examines the reservation table for an earliest time "E", starting from an estimated end of the RTS-CTS exchanges, when the data channel is continuously free for T duration.
• the pair (E, T) is sent in the RTS.
• the receiver also examines its reservation table to check if the duration (E, T) is indeed free. If the channel is free during (E, T), then (E, T) is sent back in the CTS.
• E a next possible time after E (denoted as "El") is chosen, for which, the channel is free for duration T and (El, T) is sent back in the CTS.
• the receiver adds the pair sent in the CTS to its reservation table.
• the sender receives a CTS with some pair (E, T) it checks if this pair conflicts with an entry in the reservation table. If there is no conflict, then the reservation is successful, and (E, T) is added to the reservation table. Otherwise, a new reservation attempt is initiated.
• RTS or CTS packets may be lost due to errors or collisions. Therefore, the reservation protocol may use a retransmission procedure which doubles a contention window when encountering a collision.
• the packet train is scheduled for transmission on the data channel at time E. This protocol will be described in greater detail in the following discussion.
• Advance reservation can be utilized to "hide" variations in contention resolution and data transfer durations.
• advance reservation may provide loose synchronization among nodes through specifying an item in a control packet relative to reception of that packet.
• the reservation interval may be set sufficiently large such that an amount of time utilized to transmit a data train accounts for propagation delay, but is not so long as to encounter clock drift errors.
• the reserve ahead limit may be set to equal a duration utilized to transmit a limited multiple of data packets, and thereby prevent data packet collisions resulting from two transmissions overlapping each other.
• the data train management protocol 110(1), 110(2) may be utilized to transmit a burst of packets during a single transmission opportunity. However, because the underlying data channel may not be error free, some of the packets in a packet train may be lost or corrupted. Therefore, these packets are retransmitted.
• a selective acknowledgment technique is employed in which a single acknowledgement packet (ACK) is utilized at the end of a packet burst.
• the acknowledgement packet for instance, may utilize a bit map to indicate which packets were correctly received. Based on the received acknowledgement packet, the lost and/or corrupted packets of a packet train are assembled into a new packet train and retransmitted after obtaining a reservation from the reservation protocol as previously described. In an instance in which an acknowledgement packet is not received at the end of a packet train transmission, the packet train may be retransmitted.
• each packet train is retransmitted a number of times that is below a specified threshold, which is referred to as a "retransmission threshold".
• a packet train may have a sequence number, and individual packets within the packet train may be identified by a number relative to the packet train.
• the packet train transmission management may be implemented without sending a separate acknowledgement (i.e., ACK) for each individual packet, but rather a single acknowledgement that may be sent which describes a plurality of packets in a packet train.
• the received packets are communicated to a higher layer (e.g., the application modules 120(1), 120(2)) in order.
• a higher layer e.g., the application modules 120(1), 120(2)
• the received packets may be buffered. After the missing packet is received following a retransmission, each of the buffered packets is communicated in order, one to another.
• a timeout may be associated with the buffer to ensure that if one or more packets in a train are never received, then subsequently received packets are transferred to the higher layer out of order after the timeout expires.
• FIG. 2 is an illustration of data transfer 200 in an exemplary implementation which may be performed using the data channel 112 and the control channel 114 of FIG. 1.
• the protocol as previously described, provides separate data and control channels 112, 114.
• the protocol may utilize Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) for controlling access to the channel and using control packets, e.g., request to send (RTS) and clear to send (CTS), for channel reservation.
• CSMA/CA Carrier Sense Multiple Access with Collision Avoidance
• RTS request to send
• CTS clear to send
• the contention resolution phase on the control channel 114 is performed in parallel (i.e., simultaneous) with data transfer on the data channel 112, as shown in the exemplary data transfer 200 of FIG. 2. While packet "i" is being transferred on the data channel 112 (which is illustrated by the data transfer packet (i) 202 in FIG. 2), contention resolution for the "i + 1" packet is performed on the control channel 114, which is illustrated as "contention resolution of packet (i + 1) 204" in FIG. 2.
• the data transfer may be performed on a relatively high-bandwidth data channel while contention resolution is performed on a relatively low-bandwidth data channel that was not previously utilized for control or data transfer.
• FIG. 3 is an illustration of data transfer 200 in an exemplary implementation which may be performed using the data channel 112 and the control channel 114 of FIG. 1 without an advance reservation technique. If contention resolution for packet "i + l" on the control channel 114 does not complete by the end of transmission of packet "i" on the data channel, then the data channel 112 may stay idle 302 until completion of contention resolution.
• FIG. 4 is an illustration of data transfer 400 in an exemplary implementation which may be performed using the data channel 112 and the control channel 114 of FIG. 1 in conjunction with an advance reservation technique.
• Advance reservation is a technique which allows each node (e.g., clients 102(1), 102(2)) to "reserve ahead" for "k" packets, where "k” is a protocol parameter. Therefore, a node transmitting packet "i" on the data channel can reserve the data channel for up to "k” additional packets using modified RTS-CTS packets exchanged on the control panel.
• advance reservation may be utilized to decouple contention resolution and data transfer in time through use of the separate channels.
• the data channel 112 when advance reservation is not used, if the contention resolution for packet "i + 2" takes longer than average, then the data channel 112 will be idle until contention resolution for packet "i + 2" is completed.
• the data transfer for packet "i” takes longer than contention resolution for packet "i + 1"
• the idle time on the control channel cannot be utilized unless advance reservation is used as shown in the data transfer 400 of FIG. 4.
• the advance reservation technique may utilize a carefully chosen value for "k” that ensures that the control channel is not a bottleneck to performance as along as the average duration for contention resolution is smaller than the average duration for data transfer.
• Directional communication may be utilized for improving capacity of a wireless network.
• the protocol may be utilizing with omnidirectional as well as with direction antennas to take advantage of directional communication.
• an omnidirectional RTS-CTS technique may be utilized in which RTS and CTS packets are sent omnidirectionally, and data and acknowledge packets are exchanged directionally.
• directional RTS-CTS technique may be utilized in which RTS and CTS packets are sent directionally.
• the direction to be used for communication may be discovered a priori.
• spatial reuse increases.
• directional RTS- CTS may result in poor performance in certain topologies due to a problem know as "deafness", an example of which is described as follows.
• the range of omnidirectional RTS-CTS of the control channel 114 is at least as large as a range of directional transmission on the data channel 112. It should be noted that when the control channel 114 operates at a lower frequency than the data channel 122 as previously described, the control channel 114 may support a correspondingly greater range. Additionally, if additional range is desired, the transmission power on the control channel may be suitably increased, further discussion of which may be found in relation to the following section.
• the data and control channels 112, 114 are also likely to have different ranges. While the exact difference in the range depends on several factors such as power levels and environmental factors, it is likely that the range of the control channel will be greater than the range of the data channel.
• the control channel is expected to be located in a lower frequency band, and consequently, for fixed transmission power, the control channel experiences a smaller path loss, resulting in reducing the effect of hidden terminals.
• the range up to which transmission may interfere with another transmission i.e., the "interference range"
• the control channel range is close to the interference range of the data channel, each node in the interference region may be notified of an impending transmission, thereby preventing data packet collisions and also permitting maximum spatial use.
• the control channel range is significantly greater than the data channel range, the control channel may reserve an unnecessarily large area, reducing spatial reuse.
• RTS-CTS transmission is performed on a different channel for the DATA-ACK transmission.
• RTS- CTS transmission will not interfere with data transmission on the data channel.
• a control channel with longer range is also beneficial when using directional antennas as previously described.
• FIG. 5 is a flow diagram depicting a procedure 500 in an exemplary implementation in which data and control information are simultaneously communicated on respective data and control channels.
• Data is received at a protocol layer from a higher layer for communication over a wireless network (block 502).
• the wireless architecture 104 may be implemented at the protocol level and the application modules 120(1), 120(2) are not aware of the particulars as to how the data is communicated.
• the data received from the higher layer is formed into one or more packet trains, each having a plurality of packets (block 504).
• the data aggregation protocol may be utilized to form a plurality of packets, and then form those packets into the one or more packet trains as previously described.
• Control data is sent on a control channel to perform advance reservation and contention resolution for the communication of at least one of the packet trains (block 506).
• a sender may send a RTS packet over the control channel which is utilized by a receiver to confirm scheduling of a particular time, during which, the packet train is to be communicated.
• a response is received via the control channel indicating a particular time, during which, the at lease one packet train is to be communicated (block 508).
• the sender may receive a CTS packet over the control channel which confirms the particular time, proposes a different time, and so on.
• the at least one packet train is sent over a data channel at the particular time, the data channel being separate from the control channel (block 510).
• the packet train may be sent on the data channel 112 configured to have a frequency about 900MHz, while the control channel 114 has a frequency below 900 MHz.
• the data channel 112 may have a higher data throughput rate than that of the control channel 114.
• control data is sent on the control channel to perform advance reservation and contention resolution for the communication of another one of the packet trains (block 512).
• the other one of the packet trains may be formed from the data received from the "higher" layers by the protocol layer (block 502).
• the reception of the data which forms the other packet train may be performed before and/or during the sending, receiving, and sending previously described (i.e., blocks 506-510).
• a response is received indicating another particular time, during which, the other packet train is to be communicated (block 514).
• the other packet train is then sent at the other particular time over the data channel (clock 516).
• This procedure 500 may be repeated as additional data is received from the higher layer for transfer over the wireless network.
• any of the functions described herein can be implemented using software, firmware (e.g., fixed logic circuitry), manual processing, or a combination of these implementations.
• the terms "module,” “functionality,” and “logic” as used herein generally represent software, firmware, or a combination of software and firmware.
• the module, functionality, or logic represents program code that performs specified tasks when executed on a processor (e.g., CPU or CPUs).
• the program code can be stored in one or more computer readable memory devices.
• the protocol splits and IEEE 802.11 protocol be operating a control portion over a low-frequency, low-data rate channel and a data portion over a high- frequency, high-data rate channel. Contention resolution occurs on the lower-rate channel (i.e., the "data channel") is used for exchanging data packets.
• the protocol may also be utilized to perform advance packet reservation and data aggregation to ensure that the control channel does not become a bottleneck to the data channel. Further, the protocol may perform channel arbitration and data transmission simultaneously.

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• 2005
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