Patent Application
20070280155
The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are provided with the same reference numerals. The present invention describes a system, device and method for optimizing communications in a wireless network. While the exemplary embodiment of the present invention will be described with reference to a wireless mesh network and optimizing wireless communications at nodes in the mesh, those of skill in the art will understand that the present invention may be utilized in any wireless environment and by any wireless device.
In the exemplary embodiment, the switch 10 may be deployed in an indoor environment (e.g., a building, warehouse, etc.), while the mesh nodes are deployed in an outdoor environment (e.g., a shipping yard, a parking lot, etc.). The switch 10 may be coupled to a server 12 and a communications network 14 (e.g., a LAN, an intranet, the Internet, etc.). The mesh 7 provides access to the communications network 14 for users of mobile computing units (MUs), e.g., MU 30 and MU 35, in the outdoor environment. Those of skill in the art will understand that the system 5 may be deployed wholly or partially in the indoor and/or outdoor environments.
The switch 15 may be an Ethernet switch/hub or a wireless switch and uses the root node 10 as a means for communicating with the nodes in the mesh 7, while the nodes utilize the root node 10 as a means for communicating with the switch 10. For example, all packets from the mesh 7 which are bound for the switch 10, the server 12 and/or the network 14 may be funneled through the root node 15.
Wireless communications in the mesh 7 may be executed according to a predetermined wireless communication protocol, e.g., an IEEE 802.1x protocol. As known by those of skill in the art, the 802.1x protocol defines a CSMA/CA mechanism to limit congestion on a radio frequency channel utilized for wireless communications. As describe above, in a conventional mesh network, all of the mesh nodes utilize a single channel for wireless communications. This may result in low throughput and interference in the mesh network. According to the exemplary embodiments of the present invention, the mesh nodes utilize channels on at least two frequency bands (e.g., 2.4 GHz and 5.2 GHz) for conducting wireless communications to increase throughput without interference.
As is known in the art, each of the mesh nodes transmits and receives wireless signals in a predetermined wireless coverage area. As shown in
In a conventional mesh network, a root node, upon gaining access to a channel, transmits a packet bound for a fringe node to an intermediate node. Upon receipt of the first packet, the intermediate node would attempt to transmit the first packet to the fringe node. However, the root node may still have control of the channel. Thus, the intermediate node must wait until the root node relinquishes control of the channel before attempting to transmit the first packet. Delay is introduced at the intermediate node, because it cannot transmit the packet to the fringe node or communicate with any MUs associated therewith. Additional delay is introduced for MUs associated with the root node which have packets to transmit thereto. Even if the intermediate node could retransmit the packet to the fringe node immediately upon receipt thereof, the additional delay may still be present. That is, the MUs associated with the root node would have to wait to transmit their packets, because the intermediate has control of the channel. As a result, in the conventional mesh network, throughput decreases as packets propagate through multiple nodes.
According to the exemplary embodiments of the present invention, throughput in the mesh 7 may be increased by utilizing mesh nodes which are capable of communicating simultaneously on channels of at least two different frequency bands (e.g., the 2.4 GHz band and the 5.2 GHz band). That is, each mesh node may utilize two transceivers, each of which is configured to communicate on a respective channel of a respective frequency band. As will be described below, each mesh node assigns a first channel on a first frequency band for communication with MUs and a second channel on a second frequency band for backhaul transfer (e.g., communication with other mesh nodes, the switch 10, etc.). The assignments may be designated manually by a system operator when, for example, deploying the mesh nodes, or may be designated automatically when the mesh node boots. When a mesh node receives a wireless signal, it selects one of the transceivers to retransmit the signal based on a destination thereof. That is, when the designations is an MU associated with the mesh node, it retransmits the signal on the first channel, and when the destination is another mesh node (or the switch 10) it transmits the signal on the second channel. The mesh node may store data indicative of destinations and the corresponding channel for communications.
In step 205, the root node 15 assigns a first channel (e.g., channel 1) on a first frequency band (e.g., the 2.4 GHz band) and for communication with MUs (e.g., the MU 30) associated with the root node 15. Thus, when the root node 15 and the MU 30 have packets to transmit to each other, they would both contend for access to the first channel. In a similar manner and also in step 205, the root node 15 assigns a second channel (e.g., channel 36) on a second frequency band (e.g., the 5.2 GHz band) for backhaul communications, i.e., with other mesh nodes, with the switch 10, etc. Thus, when the root node 15 and the intermediate node 25 both have packets to transmit to each other, they would both contend for access to the second channel. Each node in the mesh 7 may perform a similar assignment process when being deployed and/or after booting. Those of skill in the art will understand that the selection of a channel on a particular frequency band is based on activity on other channels of the band.
In an exemplary embodiment in which the mesh node automatically assigns channels for communications, the mesh node may, upon powering up, scan the channels on the frequency bands for activity. For example, when the fringe node 20 is deployed, it may scan the channels on the 2.4 GHz and 5.2 GHz bands. In the exemplary embodiment, the fringe node 20 detects activity on channel 36 of the 5.2 GHz band (i.e., communications between the root and intermediate nodes) and, potentially, activity on one or more channels of the 2.4 GHz band if the intermediate node 25 is communicating with any MUs associated therewith or other mesh nodes. As shown in
In step 210, the root node 15 receives a packet addressed to the fringe node 20. The packet may have been transmitted from the MU 30, the switch 10 or a mesh node communicatively coupled to the root node 15. Those of skill in the art will understand that for each packet received by the root node 15 it may determine a destination of the packet and select a corresponding channel for the transmission of the packet. That is, for a packet addressed to the MU 30, the root node 15 may take steps (similar to those described below for transmitting on the second channel) for transmitting the packet to the MU 30 on the first channel on the first frequency band, e.g., channel 1 of 2.4 GHz band.
In step 215, the root node 15 contends for access to the second channel using, for example, the conventional methods implemented in the CSMA/CA mechanism. Because only the intermediate node 25 (and other mesh nodes who communicate with the root node 15 on the second channel and have coverage areas which overlap the coverage area 40) may be contending for the second channel, access thereto may be gained relatively quickly. For example, the intermediate node 25 may be transmitting a packet to the root node 15 on the second channel when the root node 15 attempts to gain access thereto.
In step 220, the root node 15 gains access to the second channel and transmits the packet to the intermediate node 25. In step 225, the root node 15 may maintain control of the second channel and transmit remaining packets in the series of packets to the intermediate node 25. As described above with reference to the conventional mesh network, the intermediate node 25 would have to wait for the root node 15 to relinquish control of the second channel before forwarding the packet to the fringe node 20.
According to the present invention, as shown in step 230, the intermediate node 25 may, simultaneously with step 225, forward the packet to the fringe node 20 and receive the remaining packets from the root node 15. The intermediate node 25 may utilize a third channel (e.g., channel 11) on the first frequency band to communicate backhaul transfer with the fringe node 20. Because the root node 15 is communicating with the MU 30 on the channel 1 of the 2.4 GHz band, the intermediate node 25 selects the channel 11 of the 2.4 GHz band so that there is no interference between transmissions by the root node 15 to/from the MU 30 and the intermediate node 25 to/from the fringe node 20—same frequency band, different channel. In addition, there will not be any interference between transmission by the root node 15 to/from the MU 30 and the root node 15 to/from the intermediate node 25—different frequency band.
As shown in
Simultaneous use of channels on at least two different frequency bands increases throughput in the mesh 7. That is, in a conventional wireless network in which all of the mesh nodes utilize only a single frequency channel, all mesh nodes contend for access to the single channel. Thus, after the root node transmits the packet to the intermediate node, both nodes would contend for access to the single channel (decreasing throughput), and, when one node gets access to the single channel, the other node (and MUs associated with the root and intermediate nodes) must wait until the channel is free (causing a further decrease in throughput). According to the present invention, the intermediate node 25 (and any other mesh node and/or wireless device) may utilize at least two channels on two frequency bands to eliminate or substantially reduce the delays existent in the conventional networks.
The present invention has been described with reference to an exemplary embodiment. One skilled in the art would understand that the present invention may also be successfully implemented, for example, in alternative embodiments. Accordingly, various modifications and changes may be made to the embodiments without departing from the broadest spirit and scope of the present invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.
