Obviousness

Obviousness Analysis of US Patent 7359437 under 35 U.S.C. § 103

A person having ordinary skill in the art (POSITA) at the time of the invention (priority date September 12, 2001) would have found the claimed encoding method and system obvious, considering combinations of existing prior art references. The core inventive concepts of US7359437 involve selecting a robust subset of code words to reduce inter-symbol interference (ISI), utilizing these robust code words as guard bands, and transmitting auxiliary data during blanking intervals on serial links, particularly TMDS-like links. These concepts, when viewed through the lens of the existing knowledge and motivations in the field of high-speed serial data transmission, appear to be within the grasp of a POSITA.

Combination 1: ISI-Reduced Code Word Subset and DC Balancing

References: Conventional Transition Minimized Differential Signaling (TMDS) links, U.S. Pat. No. 5,999,571, U.S. Pat. No. 6,151,334, and general engineering principles regarding data transmission reliability.

Analysis:
The patent identifies a primary problem as "reducing the bit error rate resulting from inter-symbol interference or other error-causing effects during transmission" over serial links, especially for "very long conductors or under other conditions in which there would otherwise be a high risk of error due to ISI during transmission".

Conventional TMDS links, as described in the patent, already employ encoding that aims for "transition minimized" words and "DC balanced" words to ensure signal integrity and reduce voltage drift. This demonstrates a clear recognition in the prior art of the importance of specific bit patterns for reliable serial transmission. U.S. Pat. No. 5,999,571 explicitly teaches the use of "transition minimized code words (indicative of video data) transmitted over a TMDS link".

A POSITA, motivated to further reduce ISI and improve bit error rates (BER) in high-speed serial links, would naturally look for ways to optimize existing encoding schemes. Given that TMDS already strives for "transition minimization" (which inherently seeks to avoid long runs of identical bits), a POSITA would understand that certain bit patterns are more robust against ISI than others. The patent states that the inventive code words "are selected to be those whose serial patterns (during transmission) have fewer contiguous zeros and ones (e.g., on the average), and thus are less susceptible to ISI during transmission". This is a direct extension of the known principle of transition minimization.

The patent acknowledges the trade-off: "By reducing the ratio of M to N...lower bit-error rates (BER) can be achieved in accordance with the invention at the cost of reducing the rate at which the source data can be transmitted". This fundamental engineering trade-off between data rate and reliability (or error rate) is well-known to a POSITA. Therefore, deliberately selecting a subset of code words that are even more robust against ISI, even if it means sacrificing some data rate (i.e., using M-bit source words encoded into L-bit code words where M<N, when the full set could encode N-bit source words), would be an obvious design choice for applications where reliability is prioritized over maximum throughput.

Furthermore, maintaining DC balancing for the selected subset, as already a feature of conventional TMDS encoding, would be an obvious requirement for a POSITA to ensure overall signal integrity and prevent voltage drift over time.

Combination 2: Use of Inventive Code Words as Guard Bands

References: U.S. Pat. No. 5,999,571, U.S. Pat. No. 6,151,334, and the ISI-reduced code word subset from Combination 1.

Analysis:
The patent claims the use of "guard band" words from the inventive code word subset to identify the start or end of data bursts.

Prior art clearly establishes the practice of using special words for synchronization and data burst delineation:

• U.S. Pat. No. 5,999,571 teaches "synchronization words (distinguishable from the transition minimized code words) can be transmitted over the link during 'preamble' periods" and advocates for "several (e.g., three) repetitions of a synchronization word...to allow the decoder...rapidly and accurately to identify a specific transition".
• U.S. Pat. No. 6,151,334 teaches the transmission of "data stream separation' word that is transmitted before or after a burst of data and is indicative of the start or end of a burst and the type of data transmitted during the burst". It also describes "isochronous data transfer' word" to indicate the type of blanking interval. These control words are sometimes "transition maximized" and "distinguishable from transition minimized code words indicative of data".

A POSITA would be motivated to ensure the robustness of these critical synchronization and delineation markers. Having identified an ISI-reduced subset of code words (as discussed in Combination 1), it would be an obvious step to select guard band words from this robust subset. This would inherently improve the reliability with which the receiver can identify the transitions and boundaries of data bursts, directly addressing the patent's goal that "each guard band word should have a bit pattern which allows the receiver to more reliably identify the relevant transition". The patent's example of choosing a pre-data auxiliary guard band word with a first bit "1" after a previous "0," or a video guard band with "00" after "11," demonstrates a specific design choice to enhance detectability, consistent with the prior art's motivation for reliable synchronization. The repetition of guard band words, as taught by U.S. Pat. No. 5,999,571, would also be an obvious design choice for improved robustness against data shift errors.

Combination 3: Transmitting Auxiliary Data in Blanking Intervals using Inventive Code Words

References: Conventional TMDS links, U.S. Pat. No. 6,151,334, and Combination 1 & 2.

Analysis:
The patent claims transmitting "alternating bursts of encoded video data and encoded auxiliary data", with auxiliary data typically transmitted during "blanking intervals between the active video periods".

Conventional TMDS links transmit video data during "active video periods" (DE high) and control/synchronization signals during "blanking intervals" (DE low). The patent explicitly identifies these blanking intervals as providing "an opportunity...for auxiliary data to be transported, and they represent unused bandwidth".

U.S. Pat. No. 6,151,334 further supports this by teaching "data of the data burst (transmitted in the vertical blanking interval)", indicating that the concept of transmitting data (not just control signals) during blanking intervals was known. The patent broadly defines "auxiliary data" to include audio, keyboard signals, still images, etc..

A POSITA, motivated to efficiently utilize the available bandwidth of a serial link and knowing that blanking intervals offer an opportunity for auxiliary data transmission, would combine this knowledge with the ISI-reducing encoding scheme from Combination 1. If auxiliary data (such as audio) is critical or sensitive to errors, encoding it with the specially selected robust subset of code words would be an obvious step to achieve a "lower bit-error rate during transmission" for this data type. The natural consequence of transmitting auxiliary data during blanking intervals and video data during active periods is the "alternating bursts" described in the claims.

Combination 4: Video Guard Band Word Serving a Dual Purpose

References: Combination 2 & 3.

Analysis:
The patent claims that in some implementations, "at least one of the guard band words is also used for a second purpose: to encode auxiliary data". Specifically, a "video guard band word...is also used for a second purpose: to encode auxiliary data".

Given that a POSITA would have already developed an ISI-reduced set of code words (Combination 1) and designated certain ones as guard bands (Combination 2) for marking different types of data bursts (Combination 3), optimizing the use of these limited robust codes would be an obvious design consideration. If a specific guard band word (e.g., a video guard band) is part of the robust subset and can effectively serve both its role as a burst delimiter and simultaneously represent a particular value of auxiliary data without introducing ambiguity or compromising functionality, a POSITA would be motivated to assign such a dual purpose. This is a matter of efficient code word assignment within the established framework, not a novel inventive concept.