Obviousness

To analyze the obviousness of US patent 8027326 under 35 U.S.C. § 103, we identify key features of the independent claims and consider how a person having ordinary skill in the art (PHOSITA) in WLAN communications, at the time of the invention (priority date January 12, 2004), would have been motivated to combine existing prior art references.

Key Features of the Independent Claims (1, 12, 19, 20):

The independent claims describe a system and method for increasing data rates in WLANs by:

1. Channel Concatenation/Bonding: Generating and transmitting/receiving two adjacent Orthogonal Frequency Division Multiplexing (OFDM) signals over two separate, adjacent wireless channels that are separated by a frequency gap, thereby forming an expanded bandwidth channel (Claim 1, 12, 19, 20).
2. Gap-Filling Subcarriers: At least one of the OFDM signals includes additional subcarriers that fill at least a portion of the frequency gap between the two channels (Claim 1, 12, 19, 20).
3. Reuse of Legacy Hardware (Dual-Chain): The system implicitly or explicitly aims to achieve this expanded bandwidth operation while reusing existing single-channel radio designs, particularly for reception using parallel receive chains (Claim 12, 20, and supported by the patent's overall objective and figures like FIG. 7).
4. Adaptive Anti-Aliasing: Applying adaptive anti-aliasing techniques to mitigate aliasing due to adjacent channel waveform effects during reception, especially when decomposing the wideband signal into two received signals (Claim 19, 20).

Prior Art References and Common Knowledge (from the patent text and general PHOSITA knowledge):

1. IEEE 802.11a/g Standards: These standards define WLAN operations using OFDM modulation over 20 MHz (802.11a at 5 GHz) and 25 MHz (802.11g at 2.4 GHz) wide channels, with data rates up to 54 Mbps. The patent explicitly states, "A radio configured in accordance with IEEE 802.11a or 802.11g standards employs Orthogonal Frequency Division Multiplexing (OFDM) modulation in which a stream of data is transmitted over multiple small frequency sub-channels."
2. Orthogonal Frequency Division Multiplexing (OFDM): A widely known and employed modulation scheme for transmitting data over multiple sub-channels, used in 802.11a/g.
3. IEEE 802.11n Standard (proposed/emerging): At the time of filing, 802.11n was being developed with the goal of achieving significantly higher throughput (at least 100 Mbits/second) and requiring backward compatibility with legacy 802.11a/g deployments.
4. Channel Bonding/Aggregation: The general concept of combining multiple narrower frequency channels to form a wider channel and increase data throughput was a known technique in telecommunications. The patent itself mentions "channel bonding with OFDM" as an embodiment for increasing data rate.
5. Adjacent Channel Interference (ACI) and Aliasing: These are well-understood problems in wireless communications, particularly when operating multiple channels in close proximity or when processing wideband signals with filters designed for narrower bandwidths.
6. Adaptive Signal Processing Techniques: Adaptive filters and interference cancellation techniques (e.g., Least Mean Squared (LMS) algorithms) were well-established in signal processing for mitigating various forms of interference and distortion in communication systems. The patent references these, stating "Various adaptation techniques may be implemented. For example, the least-mean-squared (LMS) technique may be used."

Obviousness Analysis under 35 U.S.C. § 103:

A PHOSITA, motivated by the recognized need for higher data rates in WLANs (driven by the emerging 802.11n standard) and the desire for backward compatibility with existing 802.11a/g equipment, would have been motivated to combine the known prior art elements as follows:

Combination 1: IEEE 802.11a/g + Channel Bonding + Motivation for 802.11n Data Rates + Reuse of Legacy Hardware

• Motivation: The primary motivation would be to achieve the high data rates (100+ Mbps) targeted by 802.11n while minimizing costs and ensuring backward compatibility. A straightforward approach to increasing data rate in OFDM systems is to increase the usable bandwidth.
• Combination: A PHOSITA would find it obvious to take two existing 802.11a/g single-channel OFDM systems and operate them concurrently on adjacent channels to effectively double the bandwidth and thus the data rate. This is a direct application of the known principle of channel bonding/aggregation. The patent itself states that "An embodiment of the present invention increases the data rate using channel bonding with OFDM using two or more channels at once."
• Reuse of Legacy Hardware: Given the economic motivation to avoid designing entirely new wideband transceivers (as explicitly highlighted by the patent), a PHOSITA would be motivated to reuse existing single-channel 802.11a/g radio designs. The "dual-chain wideband radio" described and illustrated in FIG. 7, which uses "multiple radios in a box" with individual LPFs, ADCs, and FFTs for each channel, represents an obvious architectural choice for combining legacy hardware to process an expanded bandwidth signal. This approach utilizes already available 6th order filters with normal Q factors, as opposed to requiring more complex 10th or 12th order filters for a single wideband channel.

Combination 2: Combination 1 + Spectrum Optimization (Gap Filling)

• Motivation: Once the decision is made to bond adjacent 802.11a/g channels, a PHOSITA, seeking to maximize data throughput within the combined spectrum, would naturally look for ways to efficiently use any unused frequency portions.
• Combination: Standard 802.11a/g channels have guard bands and unused subcarriers. When two such channels are placed adjacently, a frequency gap may exist between their active subcarrier regions. To further increase data rate, it would be an obvious optimization for a PHOSITA to fill this internal frequency gap with additional OFDM subcarriers, provided it adheres to spectral mask requirements and does not introduce unacceptable Adjacent Channel Interference (ACI). The patent describes this as the "filled-gap OFDM approach" (FIG. 4, Case 2) that permits "greater information over the bandwidth" and is 802.11n friendly. The very discussion in the patent distinguishing between 802.11n-friendly gap-filling and non-friendly approaches (e.g., filling outer boundaries that violate the spectral mask) indicates that the underlying motivation to fill all available spectrum for data was well-understood, and the engineering challenge was doing so within regulatory constraints.

Combination 3: Combination 2 + Adaptive Anti-Aliasing for Foreseeable Interference

• Motivation: Combining adjacent channels, especially with gap-filling subcarriers, and processing them with parallel receive chains designed for narrower, single channels (as in the reuse of legacy hardware) would foreseeably introduce significant adjacent channel interference and ADC sample-rate aliasing. The patent itself explicitly states: "ADC sample-rate aliasing may occur when a wide signal is received by multiple, parallel receive chains designed to receive a single narrow signal." A PHOSITA would be motivated to address these known problems to ensure reliable data reception.
• Combination: To mitigate these foreseeable interference issues, a PHOSITA would apply known adaptive signal processing techniques. Adaptive anti-aliasing or interference cancellation methods (e.g., using feedback error techniques, LMS algorithms, frequency domain or time domain adaptive filters) are standard tools for improving signal quality in noisy or interfering environments. The patent describes various adaptive anti-aliasing techniques, including those that involve applying the interfering signal component to subtract or cross-compare with the desired signal to remove distortion. This is a predictable application of known adaptive filtering principles to a known problem arising from the combination of channels.

Conclusion on Obviousness:

Based on the above, the independent claims of US8027326 appear to be obvious under 35 U.S.C. § 103. A person having ordinary skill in the art, motivated by the recognized need for higher data rates (802.11n) and the practical desire to reuse existing 802.11a/g hardware for backward compatibility, would have been led to combine known wireless communication techniques (OFDM, channel bonding of adjacent channels) and to optimize spectrum utilization within these combined channels (by filling frequency gaps with additional subcarriers). Recognizing the foreseeable challenges of increased adjacent channel interference and aliasing that would result from such combinations, especially when reusing narrower legacy receive chains, the PHOSITA would have been motivated to apply known adaptive anti-aliasing or interference cancellation techniques to ensure reliable data reception. The specific implementations described in the patent, such as the dual-chain architecture and various adaptive anti-aliasing methods, represent predictable engineering choices and optimizations of known techniques to solve these problems within the context of the overall system.