Obviousness

Obviousness Analysis of US Patent 8139544 Under 35 U.S.C. § 103

This analysis identifies combinations of prior art references, publicly available before the priority date of US patent 8139544 (July 30, 2004), that would render the independent claims of the patent obvious to a person having ordinary skill in the art (PHOSITA).

Independent Claims Overview

The independent claims (Claims 1, 15, 24, and 25) of US Patent 8139544 primarily describe a receiving device's operations in a wireless communication system, involving:

1. Receiving first and second signals, each from a different transmit antenna, where each signal includes data and pilot subcarriers.
2. Separating the first set of data subcarriers from the second set of data subcarriers, and the first set of pilot subcarriers from the second set of pilot subcarriers, using a signal separating function based on channel estimates for the respective communication paths.
3. Match-filter combining at least one pilot subcarrier from the first set of pilot subcarriers with at least one pilot subcarrier from the second set of pilot subcarriers.

Identified Prior Art Combinations and Obviousness Rationale

The following combination of prior art references and common general knowledge would render the independent claims, and by extension the dependent claims, obvious.

Primary Reference: US6850481B2 to Nortel Networks Limited (Priority: September 1, 2000; Publication: February 1, 2005)

• Disclosure: This patent, titled "Channels estimation for multiple input—multiple output, orthogonal frequency division multiplexing (OFDM) system," explicitly teaches a receiver in a Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) system. It addresses the fundamental aspect of channel estimation in such an environment. This reference thus clearly teaches the reception of signals from multiple transmit antennas, with these signals comprising OFDM subcarriers (both data and pilot), and the necessity of estimating the communication channels for these paths.

Secondary Reference 1: US6785341B2 to Qualcomm Incorporated (Priority: May 11, 2001; Publication: August 31, 2004)

• Disclosure: This patent, "Method and apparatus for processing data in a multiple-input multiple-output (MIMO) communication system utilizing channel state information," provides methods and apparatus for utilizing channel state information (derived from channel estimates) to process data in MIMO communication systems.

Motivation to Combine US6850481B2 and US6785341B2:
A PHOSITA would be motivated to combine the teachings of US6850481B2 and US6785341B2. US6850481B2 establishes the context of channel estimation in MIMO-OFDM systems, while US6785341B2 provides general techniques for processing data using such channel state information in MIMO systems. It would be a natural engineering step to apply the principles of utilizing channel state information (from Qualcomm) to the specific problem of channel estimation in MIMO-OFDM (from Nortel) to effectively process the received signals.

Secondary Reference 2 (Common General Knowledge of Signal Separation Techniques): Zero Forcing (ZF) and Minimum Mean Squared Error (MMSE) algorithms.

• Disclosure: The patent US8139544 itself describes the signal separating function as performing "inversion (e.g., single coefficient inversion, such as minimum mean squared error (MMSE) techniques, zero forcing (ZF), etc.)". Both ZF and MMSE were well-established and widely known signal separation and equalization techniques in MIMO communication systems prior to the July 2004 priority date. These techniques are fundamental for separating spatially multiplexed signals, using channel estimates to de-correlate interference between streams.

Motivation for Incorporating ZF/MMSE:
A PHOSITA, having understood the need for channel estimation in MIMO-OFDM (from US6850481B2) and the use of channel state information for data processing (from US6785341B2), would find it obvious to employ known signal separation techniques like ZF or MMSE to separate the self-interfering data and pilot subcarriers corresponding to different transmit antennas. The choice between ZF and MMSE would be a routine design consideration based on factors like desired trade-offs between noise enhancement and interference cancellation.

Secondary Reference 3 (Common General Knowledge of Optimal Combining and Correlation Exploitation): Matched filter combining or Maximum Ratio Combining (MRC).

• Disclosure: Matched filter combining and Maximum Ratio Combining (MRC) are well-known optimal signal combining techniques used to improve the signal-to-noise ratio (SNR) in communication systems. MRC, in particular, weights and sums multiple received signal components based on their SNR to maximize the output SNR, and can be implemented as a form of matched filtering. US8139544 itself notes the use of "maximum ratio combining (MRC) logic 418" for pilot tones after initial signal separation. Furthermore, the patent describes how "information can be shared between PLLs of the post-signal processors 140 and 142" when phase noise jitter is highly correlated across transmit paths, suggesting combining information from different streams for improved estimation.

Motivation for Match-Filter Combining Separated Pilot Subcarriers:
After separating the pilot subcarriers originating from different transmit antennas using ZF or MMSE, a PHOSITA would be motivated to further process these separated pilot signals to enhance the accuracy and robustness of channel estimations or phase noise tracking. The background of US8139544 explicitly highlights the use of pilot tones for "compensating for distortions in the received signal" such as "jitter phase noise". If common impairments like phase noise are correlated across the different transmit paths as seen at the receiver (as recognized by US8139544), then combining the separated pilot information from each transmit path using a known optimal combining technique, such as match-filter combining (or MRC), would provide a more robust and accurate estimate of these common channel characteristics. This would directly lead to improved system performance by reducing distortion.

Conclusion on Independent Claims

Based on the above, the independent claims (1, 15, 24, 25) of US8139544 would be obvious. The combination of US6850481B2 (teaching MIMO-OFDM channel estimation) with the common general knowledge of ZF/MMSE for signal separation and the common general knowledge of matched filter/MRC for optimal combining of related signals (motivated by improving channel impairment estimation from separated pilot streams), would lead a PHOSITA to the claimed invention. Such a combination represents a logical extension of known techniques to improve the performance of MIMO-OFDM communication systems.

Obviousness of Dependent Claims

If the independent claims are rendered obvious by the above combination, the dependent claims would also be obvious for the following reasons:

• Claims 2, 23 (Channel estimate based on preamble): Using preambles or training sequences for initial channel estimation in OFDM systems is standard practice and would be obvious to a PHOSITA in conjunction with US6850481B2.
• Claims 3, 26 (Separating data from pilot subcarriers): This is a fundamental step in any communication system employing pilot subcarriers for channel estimation/tracking, as described in the background of US8139544.
• Claims 4, 16 (ZF function): This is explicitly part of the common general knowledge regarding MIMO equalization techniques.
• Claims 5, 16 (MMSE function): This is also explicitly part of the common general knowledge regarding MIMO equalization techniques.
• Claims 6, 18, 29 (Correcting phase and jitter distortions): The primary purpose of pilot tones, as stated in the background of US8139544, is to compensate for such distortions. Applying the derived estimates to correct for these distortions is the intended use and would be obvious.
• Claims 7, 19, 28 (Combining and phase-lock looping of pilot subcarriers): This describes standard phase tracking loops (PLLs) applied to processed pilot signals. The patent itself depicts MRC logic (418) and PLLs (420) operating on separated pilot streams.
• Claims 8, 20 (MRC or simple combining): MRC and simple summing are both well-known combining techniques, and MRC is explicitly mentioned in US8139544 as an option.
• Claims 9, 10 (Multi-receiver/single transmitter configurations): These describe common communication system architectures (MIMO with multiple receive antennas or potentially distributed receivers) that do not add inventive subject matter to the core separation and combining techniques. The setup in FIG. 1 shows a single transmitter and single receiver with multiple antennas.
• Claims 11, 27 (Generating channel matrix and computing matrix inverse): These describe the mathematical implementation details of ZF/MMSE equalization, which is common general knowledge in MIMO channel equalization.
• Claims 12, 13 (Channel matrix based on amplitude/phase): Channel matrix elements fundamentally represent the amplitude and phase characteristics of the communication paths, as explicitly stated in US8139544. This is basic channel modeling.
• Claim 14 (Subcarrier frequencies): This describes the standard allocation of data and pilot subcarriers within an OFDM symbol, as illustrated in US8139544 (FIGS. 3A-3B).
• Claims 21, 22 (Implementation in hardware/software/firmware/circuitry): The choice of implementing communication system components in hardware, software, firmware, or a combination, and using digital or analog circuitry, represents routine engineering choices well within the skill of a PHOSITA. [0067-0069]