Obviousness

Obviousness Analysis under 35 U.S.C. § 103 for US Patent 8891347

This analysis examines the obviousness of claims 1, 8, and 15 of US Patent 8891347 under 35 U.S.C. § 103, based on the prior art explicitly described and distinguished within the patent itself.

Claims Under Consideration

The independent claims defining the scope of the invention are:

• Claim 1 (Method): A method for wireless communication involving transmitting a first signal, performing channel estimation to obtain path parameter information, sending this information back to the transmitter, and then predistorting a second signal at the transmitter in the time, frequency, and spatial domains according to the received channel estimation, before transmitting and receiving the predistorted signal.
• Claim 8 (System): A wireless communication system configured to perform the method of Claim 1, with a receiver adapted to perform channel estimation and send path parameter information, and a transmitter adapted to predistort a second signal in the time, frequency, and spatial domains based on this information.
• Claim 15 (Base Station): A base station comprising a transmitter, computing device, and computer-readable storage medium with instructions to perform the transmitting of a first signal, receiving channel estimation, predistorting a second signal in the time, frequency, and spatial domains, and transmitting the predistorted signal.

The core distinguishing feature across these claims is the predistortion of a signal at the transmitter in the time domain, a frequency domain, and a spatial domain, based on detailed path parameter information (e.g., delay, Doppler frequency, direction of arrival, direction of departure).

Hypothetical Person of Ordinary Skill in the Art (POSITA)

A person of ordinary skill in the art in 2011 (the patent's filing date) would be a wireless communication engineer or researcher familiar with concepts such as channel modeling, equalization techniques, precoding, beamforming, multi-path propagation, and adaptive wireless systems.

Prior Art Combination and Motivation

The patent itself describes and distinguishes various known techniques, which serve as foundational prior art for an obviousness argument:

1. Primary Prior Art Reference: Systems employing channel estimation, feedback, and transmitter-side precoding/pre-equalization.
The patent explicitly discusses "conventional precoding techniques" which "make use of simplified representations of channel, e.g. in terms of code-book". It also refers to "pre-equalization techniques" that "usually rely on the structure of finite impulse response (FIR) filter" and "aims at removing the inter-symbol-interferences (ISI) in the frequency and spatial domains". These descriptions establish that the general concept of channel estimation at the receiver, feedback to the transmitter, and subsequent transmitter-side pre-compensation (predistortion/precoding) was known in the art. Furthermore, the patent describes CoMP systems in 3GPP LTE-Advanced, which use "joint processing (JP)" and "coherent adding" where signals are constructively combined at the receiver, and notes this is "an extension of the standard channel equalization techniques". This demonstrates the known goal of constructive signal combination through channel compensation.

2. Secondary Prior Art Reference: Techniques for obtaining and utilizing detailed propagation path parameters.
The patent extensively lists numerous "channel estimation algorithms" that were known and could be used to obtain "estimates of the delay τ, the Doppler frequency u, direction of arrival Ω 1 , direction of departure Ω 2 , and complex amplitude α for each of the propagation paths". These include:

• Spectral-based methods (Bartlett beamformer, Capon beamformer, MUSIC)
• Subspace-based techniques (root-MUSIC, ESPRIT, Propagator method, Unitary-ESPRIT)
• Approximations of maximum-likelihood methods (EM, SAGE, RiMAX)
• LSE (Least-Square-Error) principles (LMMSEE, covariance matrix fitting)
• Tracking algorithms (Kalman filtering, enhanced Kalman filtering, particle filtering, particle-filter based SAGE)
  The patent also mentions Geometrical Stochastic Channel Models (GSCM) that characterize "multiple paths by delay, Doppler, directions and polarizations" to reproduce time-variant channels. This demonstrates that the detailed path parameters and methods for acquiring them were well-known in the art. The patent itself highlights that its "full-dimensional parametric description of the channel can be much more accurate than using the codebooks", thereby acknowledging the known benefit of more detailed channel information.

3. Motivation to Combine (Problem Solved and Benefits Achieved):
The patent explicitly identifies a significant problem with conventional equalization techniques: "One problem with these techniques... is that they require that channel equalization be performed at the receiver, meaning that the receiver have additional resources in order to perform the equalization". This statement provides a clear and compelling motivation for a POSITA to seek alternative solutions that reduce receiver complexity.

The patent then states its "user-focusing technique adds pseudo “distortion” before the signals are transmitted at the transmitter 110 . These “pre-distorted” signals are then transmitted in such a way that the signal distortion can be successfully removed while propagating". It further emphasizes that a "conventional equalization process in the conventional receiver is not needed anymore, because the pre-distortion can be removed automatically by the propagation channel, i.e. the channel itself works as an equalizer". These statements articulate the motivation to shift the equalization burden from the receiver to the transmitter and the expected benefit of doing so.

Reasoning for Obviousness

A POSITA, motivated by the recognized problem of high computational requirements for channel equalization at the receiver, would have sought ways to offload this complexity to the transmitter. Knowing that transmitter-side precoding/pre-equalization already existed, even in simplified forms like codebook-based approaches or FIR-filter based pre-equalization, the POSITA would naturally consider improving the accuracy and effectiveness of such transmitter-side compensation.

Given the widespread knowledge of various channel estimation algorithms capable of providing highly detailed path parameter information (delay, Doppler frequency, direction of arrival, direction of departure, complex amplitude) for individual propagation paths, and the acknowledged benefit that "full-dimensional parametric description of the channel can be much more accurate than using the codebooks", it would have been obvious to a POSITA to replace the "simplified representations" or FIR filter structures of conventional precoding/pre-equalization with this more detailed and accurate path parameter information.

Applying these detailed path parameters to the transmitter's predistortion logic would inherently lead to compensation across the time, frequency, and spatial domains:

• Time Domain: Compensation for delay τ and Doppler frequency u directly addresses time-domain characteristics and time-variance of the channel.
• Frequency Domain: Compensation for delay τ and Doppler frequency u (which impacts signal phase over time and frequency) would also effectively address frequency domain distortions. The patent's own formula α i *exp(−j 2π(f−u i )τ i ) c Tx *(Ω 1,i ) {circle around (x)}c Rx *(Ω 2,i ) u (f) explicitly shows how frequency (f), Doppler (u), and delay (τ) are used in the predistortion.
• Spatial Domain: Compensation for direction of departure Ω 1 and direction of arrival Ω 2 (using c Tx *(Ω 1,i ) and c Rx *(Ω 2,i ) in the patent's formula) directly addresses spatial selectivity and enables directional energy focusing.

The patent's distinction from prior pre-equalization, which it states removes ISI "in the frequency and spatial domains" but is "only applicable in the fixed wireless, wireless local loop systems" and not "time-variant cases", further points to the obviousness of extending compensation to the time domain for time-variant channels. The detailed path parameters, particularly Doppler frequency, are precisely what is needed to address time-variance. Thus, for a POSITA seeking to improve performance in time-variant channels, incorporating these parameters into a transmitter-side predistortion would be a logical and obvious design choice.

The expected outcome of this combination would be a wireless communication system that achieves improved signal quality, reduced receiver complexity, and effective signal "focusing" at the receiver, precisely the benefits claimed by the patent. Therefore, the combination of known channel estimation and feedback mechanisms with the existing concept of transmitter-side pre-compensation, driven by the motivation to reduce receiver complexity and improve signal focusing by employing more detailed and accurate channel parameter information across time, frequency, and spatial domains, renders claims 1, 8, and 15 obvious.