Obviousness

Obviousness Analysis under 35 U.S.C. § 103 for US Patent 7027426

This analysis assesses the obviousness of US Patent 7027426, "Multi-channel mobile ad hoc network," by identifying combinations of prior art references that would render the claimed invention obvious to a person having ordinary skill in the art (PHOSITA) at the time of the invention (priority date: August 5, 2002).

Person Having Ordinary Skill in the Art (PHOSITA)

A PHOSITA in this field would possess knowledge in wireless communication networks, particularly mobile ad hoc networks (MANETs), including routing protocols (e.g., AODV, DSR), Medium Access Control (MAC) layer protocols, network performance optimization, and Quality of Service (QoS) considerations.

Motivation to Combine Prior Art

The background of US7027426 explicitly identifies a problem with conventional mobile ad-hoc networks: they "assume that all nodes are on the same channel permanently," leading to "limited bandwidth" and "single channel operation" as a significant factor in bandwidth availability. [Description, BACKGROUND OF THE INVENTION] The patent states its object is to "provide a multichannel mobile ad hoc network to efficiently make use of a plurality of channels." [Description, SUMMARY OF THE INVENTION]

A PHOSITA, facing the known limitations of single-channel operation in MANETs, would be motivated to combine existing routing protocols with multi-channel communication techniques to improve network throughput, reduce contention, and enhance overall network efficiency. This motivation is explicitly addressed by the problems described in the '426 patent and the solutions proposed in the prior art.

Obviousness Combinations and Rationale

The independent claims (Claims 1, 8, and 18) of US7027426 focus on a mobile ad hoc network utilizing a plurality of electrically separate wireless channels for route discovery and selection, allowing routes to span multiple channels. This combination can be found obvious when considering the following prior art references:

Primary References for Combination:

1. Tseng et al., "A Multi-Channel MAC Protocol with Power Control for Multi-Hop Mobile Ad Hoc Networks," IEEE, pp. 419-424, 2001. (hereinafter "Tseng")
2. Johnson et al., "The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks (DSR)," Internet Engineering Task Force (IETF) MANET Working Group, Internet Draft, Nov. 21, 2001. (hereinafter "Johnson")
3. Perkins et al., "Ad hoc On-Demand Distance Vector (AODV) Routing," Internet Engineering Task Force (IETF) MANET Working Group, Internet Draft, Nov. 9, 2001. (hereinafter "Perkins AODV")

Secondary References for Known Elements:
4. Chakrabarti et al., "QoS Issues in Ad Hoc Wireless Networks," IEEE Communications Magazine, Feb. 2001, pp. 142-148. (hereinafter "Chakrabarti")
5. Perkins et al., "Quality of Service in Ad Hoc On-Demand Distance Vector Routing," Internet Engineering Task Force (IETF) MANET Working Group, Internet Draft, Jul. 2000. (hereinafter "Perkins QoS")

Combination: Tseng + Johnson/Perkins AODV + Chakrabarti/Perkins QoS

Rationale for Combination:
Tseng explicitly describes a "multi-channel MAC protocol with power control for multi-hop mobile ad hoc networks using multiple non-overlapping channels." It notes that "each mobile host is equipped with multiple half-duplex transceivers and can transmit/receive simultaneously on multiple channels," allowing "different nodes in a neighborhood to concurrently communicate on different channels, reducing both contention and the hidden terminal problem." This directly addresses the "plurality of electrically separate wireless channels" in a mobile ad hoc network, and the motivation to improve throughput, a problem identified by the '426 patent. [Description, BACKGROUND OF THE INVENTION]

Johnson and Perkins AODV represent well-known on-demand (reactive) routing protocols for mobile ad hoc networks, defining standard mechanisms for route discovery (Route Request, RREQ) and route reply (Route Reply, RREP). The '426 patent itself explicitly mentions DSR and AODV as types of on-demand routing protocols to which its method can be applied. [Description, DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS]

A PHOSITA, seeking to leverage the multi-channel capabilities described by Tseng at the MAC layer within an ad hoc network, would find it obvious to adapt an existing on-demand routing protocol like DSR (Johnson) or AODV (Perkins AODV) to utilize these channels for routing decisions. This adaptation would naturally involve extending the route discovery and selection processes to account for the multiple available channels.

Detailed Obviousness Analysis for Representative Claim 1:

Claim 1: "A method for operating a mobile ad hoc network comprising a plurality of wireless mobile nodes and a plurality of wireless communication links connecting the plurality of nodes together over a plurality of electrically separate wireless channels, the method comprising: at a source node, sending a route request over each of the plurality of electrically separate channels to discover routing to a destination node; at each intermediate node, determining whether the intermediate node can support the route requested and, if so, forwarding the route request to other intermediate nodes and the destination node over each of the plurality of electrically separate channels; at the destination node, upon receiving the route request, generating a reply to the source node for each discovered route; at the source node, selecting a route to the destination node on at least one of the plurality of electrically separate channels; and at the source node, sending a transmission to the destination node along the selected route."

1. "a mobile ad hoc network comprising a plurality of wireless mobile nodes and a plurality of wireless communication links connecting the plurality of nodes together over a plurality of electrically separate wireless channels": Tseng teaches a "multi-channel MAC protocol... for multi-hop mobile ad hoc networks using multiple non-overlapping channels." Non-overlapping channels are "electrically separate." This directly discloses a mobile ad hoc network operating over multiple channels.

2. "at a source node, sending a route request over each of the plurality of electrically separate channels to discover routing to a destination node": Johnson (DSR) and Perkins AODV describe source-initiated route discovery via flooding RREQs. Given Tseng's disclosure of multiple available channels and nodes with multiple transceivers, a PHOSITA would find it obvious to extend the conventional RREQ flooding mechanism to "each of the plurality of electrically separate channels" to discover all possible paths, including those spanning different channels. This is a logical adaptation to fully exploit the multi-channel capability. The '426 patent itself describes this as the source node sending "the route request RREQ over all the existing channels that the network is currently operating on to reach all nodes... within one-hop." [Description, DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS]

3. "at each intermediate node, determining whether the intermediate node can support the route requested and, if so, forwarding the route request to other intermediate nodes and the destination node over each of the plurality of electrically separate channels": The concept of an intermediate node determining "support" for a route request relates to QoS considerations, which were well-known in MANETs prior to the '426 patent. Chakrabarti discusses "QoS Issues in Ad Hoc Wireless Networks," and Perkins QoS describes "Quality of Service for Ad hoc On-Demand Distance Vector Routing." Forwarding the RREQ to other intermediate nodes and the destination node is a standard feature of DSR (Johnson) and AODV (Perkins AODV) route discovery. In a multi-channel environment enabled by Tseng, a PHOSITA would find it obvious to forward these requests over "each of the plurality of electrically separate channels" to continue path discovery across all available channels.

4. "at the destination node, upon receiving the route request, generating a reply to the source node for each discovered route": This is standard behavior for on-demand routing protocols like DSR (Johnson) and AODV (Perkins AODV), where the destination node responds to route requests with route replies. The need to generate a reply "for each discovered route" would be obvious if multiple distinct routes, potentially involving different channels, reached the destination.

5. "at the source node, selecting a route to the destination node on at least one of the plurality of electrically separate channels": DSR (Johnson) and AODV (Perkins AODV) involve route selection after receiving route replies. Given the multi-channel discovery, the source node would receive replies detailing various paths, some potentially utilizing multiple channels. The selection of a route "on at least one of the plurality of electrically separate channels" is an obvious outcome of choosing from these discovered multi-channel paths. The '426 patent explicitly mentions that the selected route "may include more than one of the plurality of channels" and "may be wholly, or in part, on a different channel than the source node." [Description, DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS]

6. "at the source node, sending a transmission to the destination node along the selected route": Once a route is selected, sending data traffic along that route is the ultimate purpose of any routing protocol (Johnson, Perkins AODV). The multi-channel nature of the selected route would be handled by the underlying multi-channel MAC protocol (Tseng).

Obviousness of Dependent Claims and Other Features:

Many features described in the dependent claims of US7027426 are likewise obvious extensions or existing elements in the prior art:

• Sequential sending of route requests (Claims 2, 13, 23): While the '426 patent states "the route request may be sent over each of the plurality of channels sequentially," [Abstract] this is an implementation detail for flooding on multiple channels, an obvious design choice for managing transceiver activity or avoiding self-interference, if applicable.
• Route request including a source node channel identifier (Claims 3, 14, 24): In a multi-channel network, including channel information in routing messages is an obvious modification to allow nodes to understand the channel context of a received message and to reconstruct multi-channel paths.
• Sending reply back in reverse (Claims 4, 11, 21): This is a well-known characteristic of many on-demand routing protocols, including DSR and AODV, where the path traversed by the RREQ is reversed to form the RREP path.
• Prioritizing discovered routes and using metrics (Claims 5, 6, 15, 16, 25, 26): Chakrabarti and Perkins QoS both teach the importance of QoS in ad hoc networks and discuss various metrics for route selection, such as "available bandwidth, error rate, end-to-end delay, end-to-end delay variation, hop count, expected path durability, and priority." These are precisely the metrics listed in the '426 patent. [Description, DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS] A PHOSITA would readily apply these known metrics to prioritize routes in a multi-channel environment.
• Selected route includes more than one channel (Claims 7, 17, 27): This is the direct result of enabling multi-channel route discovery as described by the combination of Tseng with DSR/AODV, where paths are no longer constrained to a single channel.

Obviousness of Claim 8 (Simplified Method) and Claim 18 (System):

Claim 8, which is a simplified method claim, omits intermediate node processing and reply generation steps but retains the core of multi-channel route request and selection at the source node. The arguments for these steps remain the same as for Claim 1.

Claim 18 describes a system with hardware units (communications device, controller, route discovery unit, route selection unit) to implement the method. The implementation of a method into hardware components is well within the skill of a PHOSITA. A "route discovery unit" configured to transmit RREQs over "each of the plurality of electrically separate channels" and a "route selection unit" to select a route on "at least one of the plurality of electrically separate channels" are straightforward functional descriptions of the method steps, which a PHOSITA would know how to implement given the underlying multi-channel MAC (Tseng) and the adapted routing protocol (Johnson/Perkins AODV).

Conclusion

Based on the combination of Tseng et al. with established on-demand routing protocols like DSR (Johnson et al.) or AODV (Perkins et al.), and considering the known applications of QoS routing (Chakrabarti et al., Perkins et al. QoS), a PHOSITA would have been motivated to combine these references to create a multi-channel mobile ad hoc network with routing capabilities across multiple channels. The resulting claimed invention in US7027426 represents an obvious adaptation of existing technologies to solve a known problem (limited bandwidth and contention in single-channel MANETs) using well-understood principles of network design and protocol extension.