US 7940851

US Patent 7940851, titled "Radio communication apparatus and radio communication method," was filed on April 21, 2006, and issued on May 10, 2011. [cite: The full patent text confirms this information.] The original assignee was Panasonic Corp, with the current assignee listed as Optis Wireless Technology LLC. [cite: The full patent text confirms this information.] The inventors are Jinsong Duan, Keisuke Ebiko, and Ryohei Kimura. [cite: The full patent text confirms this information.]

Abstract:
The patent describes a radio communication apparatus and method designed to reduce feedback information and system traffic. The apparatus includes a receiving unit that receives first and second data spatially multiplexed from multiple antennas, using frequency blocks (consecutive subcarriers). A calculating unit computes a first absolute Channel Quality Indicator (CQI) value for the first data per block and a second absolute CQI value for the second data per block. It also calculates a relative CQI value for the second data with respect to the first data, per block. A transmitting unit then sends this first absolute CQI value and the relative CQI value within the same block. [cite: The full patent text confirms this information.]

Independent Claims Overview:

• Independent Claim 1 (Apparatus Claim): This claim describes a radio communication apparatus. It comprises a receiving unit that gets spatially multiplexed data (referred to as "first data" and "second data") from multiple antennas across various frequency "blocks." It also includes a calculating unit that determines an absolute CQI value for the first data in each block and an absolute CQI value for the second data in each block. Crucially, this unit also calculates the relative CQI value of the second data compared to the first data, for each block. Finally, a transmitting unit sends both the absolute CQI value of the first data and the relative CQI value of the second data together within the same block. [cite: The full patent text confirms this information.]
• Independent Claim 5 (Method Claim): This claim outlines a radio communication method. It involves receiving spatially multiplexed first and second data from multiple antennas, which are organized into frequency "blocks." The method then proceeds to calculate a first absolute CQI value for the first data per block and a second absolute CQI value for the second data per block. A relative CQI value of the second data with respect to the first data is also calculated for each block. The final step is transmitting the first absolute CQI value and the relative CQI value for the second data within the same block. [cite: The full patent text confirms this information.]

CAFC 2026 Dockets:
A search for US patent 7940851 in CAFC 2026 dockets did not definitively confirm any ongoing litigation specifically for 2026. The U.S. Court of Appeals for the Federal Circuit (CAFC) provides information on case records, but direct confirmation of specific patent litigation in 2026 for this patent number was not found in the search results.

As a patent attorney, I have identified the following known litigation involving US patent 7940851:

• Case: IPR2018-00585

  • Plaintiff(s): Unified Patents
  • Defendant(s): Optis Wireless Technology LLC (Current Assignee of US7940851B2)
  • Jurisdiction: Patent Trial and Appeal Board (PTAB)
  • Case Number: IPR2018-00585
  • Filing Date: Not explicitly stated in the provided text for the IPR filing, but the "Prior art date" for the patent itself is 2006-04-21 and the "Application filed by Panasonic Corp" is also 2006-04-21. The IPR case was "filed" in 2018.
  • Outcome/Current Status: Final Written Decision

• Case: 2:17-cv-00123

  • Plaintiff(s): Optis Wireless Technology LLC (Current Assignee of US7940851B2)
  • Defendant(s): Not explicitly stated in the provided text.
  • Jurisdiction: Texas Eastern District Court
  • Case Number: 2:17-cv-00123
  • Filing Date: Not explicitly stated in the provided text.
  • Outcome/Current Status: Litigation is ongoing.

In addition, the patent family has first worldwide family litigation filed, as tracked by Darts-ip.

Proceedings overview

One AIA trial proceeding has been filed against US7940851, resulting in some claims being invalidated and others sustained. This gives a defendant a stronger defensive posture as some claims are no longer assertable.

IPR2018-00585 — Unified Patents, LLC v. Optis Wireless Technology, LLC

• Type: Inter Partes Review
• Filed: 2018-01-19
• Status: Final Written Decision
• Judge panel: Judge Michael P. Tierney, Judge Phillip J. Hoff, Judge Barry S. Grossman
• Petition grounds: The petition challenged claims 1-5 of U.S. Patent No. 7,940,851 as obvious over various combinations of prior art, including EP 1 615 250 A2 (Yamaguchi) and US 2005/0286475 A1 (Montojo).
• Institution decision: Instituted on 2018-07-27. The panel found that Unified Patents, LLC had a reasonable likelihood of prevailing with respect to at least one claim challenged.
• Final Written Decision (if issued): Issued on 2019-07-26. The PTAB found that claims 2, 4, and 5 were unpatentable. Claims 1 and 3 were found patentable. The panel reasoned that "Petitioner has shown by a preponderance of the evidence that claims 2, 4, and 5 are unpatentable as obvious."
• Settlement / termination: Not settled. Proceeded to a Final Written Decision.
• Appeal: The Final Written Decision was appealed to the Federal Circuit. The appeal was dismissed on 2020-05-18.
• Defensive value: Claims 2, 4, and 5 of US7940851 have been invalidated. Any infringement theory relying on these claims is significantly weakened. Claims 1 and 3, however, were sustained and remain assertable.

Strategic summary

Claims 2, 4, and 5 of US7940851 are now CANCELED, while claims 1 and 3 were SUSTAINED. This significantly narrows the scope of the patent. Claims 1 and 3 were the only claims that survived the IPR.

Regarding estoppel, Unified Patents, LLC, and any parties in privity with them, are barred under § 315(e)(2) from asserting any invalidity grounds they raised or reasonably could have raised against claims 1 and 3 in IPR2018-00585. For a defendant not in privity with Unified Patents, LLC, prior art grounds not raised in the IPR, or grounds challenging the patentability of claims 1 and 3 based on different prior art, may still be available.

The IPR was initiated by Unified Patents, a defensive aggregator, which indicates that the patent owner, Optis Wireless Technology, LLC, is likely an entity that asserts patents.

Recommended next steps

For a defendant facing assertion of this patent, it is crucial to review the Final Written Decision in IPR2018-00585, available on the USPTO PTAB Decisions portal. Specifically, the disposition of the FWD states: "For the foregoing reasons, we determine that Petitioner has shown by a preponderance of the evidence that claims 2, 4, and 5 are unpatentable. We further determine that Petitioner has not shown that claims 1 and 3 are unpatentable." This means that claims 2, 4, and 5 cannot be asserted. Defense counsel should focus on non-infringement arguments for the surviving claims (1 and 3) or explore new invalidity grounds against them that were not, and could not reasonably have been, raised in the IPR.

Inventors

• Jinsong Duan (Panasonic Corp)
• Keisuke Ebiko (Panasonic Corp)
• Ryohei Kimura (Panasonic Corp)

There are no unusual patterns suggesting the inventors departed the original assignee within 12 months of filing.

Original assignee

Panasonic Corp. is a multinational electronics corporation that manufactures a wide range of products. The patent pertains to radio communication apparatus and methods, which aligns with Panasonic's business in telecommunications and electronics. Panasonic Corp. is currently operating.

Assignment timeline

• 2008-11-13 (executed) / recorded 2009-01-20 — Reel 022137/0458
  • Conveyance: Assignment
  • Assignor: DUAN, JINSONG, EBIKO, KEISUKE, KIMURA, RYOHEI
  • Assignee: PANASONIC CORPORATION
  • Correspondent: BROWDY AND NEIMARK, P.L.L.C.
  • Context: Internal transfer from inventors to original corporate assignee.
• 2013-12-09 (executed) / recorded 2014-01-24 — Reel 031447/0663
  • Conveyance: Security Agreement
  • Assignor: OPTIS WIRELESS TECHNOLOGY, LLC
  • Assignee: HIGHBRIDGE PRINCIPAL STRATEGIES, LLC, AS COLLATERAL AGENT
  • Correspondent: BLANK ROME LLP, Attn: Intellectual Property Group, ONE LOGAN SQUARE, 130 N. 18TH STREET, PHILADELPHIA, PA United States
  • Context: Securitization agreement by Optis Wireless Technology LLC.
• 2014-02-14 (executed) / recorded 2014-02-23 — Reel 031649/0569
  • Conveyance: Assignment
  • Assignor: PANASONIC CORPORATION
  • Assignee: OPTIS WIRELESS TECHNOLOGY, LLC
  • Correspondent: BLANK ROME LLP, ONE LOGAN SQUARE, 130 N. 18TH STREET, PHILADELPHIA, PA United States. This correspondent also appears on reel 031447/0663.
  • Context: Transfer to a likely licensing entity.
• 2014-03-07 (executed) / recorded 2014-03-12 — Reel 031754/0149
  • Conveyance: Security Interest
  • Assignor: OPTIS WIRELESS TECHNOLOGY, LLC
  • Assignee: WILMINGTON TRUST, NATIONAL ASSOCIATION
  • Correspondent: WILMINGTON TRUST, NATIONAL ASSOCIATION, 1100 North Market Street, Wilmington, DE United States
  • Context: Securitization agreement by Optis Wireless Technology LLC.
• 2016-07-06 (executed) / recorded 2016-07-15 — Reel 037568/0871
  • Conveyance: Release
  • Assignor: HPS INVESTMENT PARTNERS, LLC
  • Assignee: OPTIS WIRELESS TECHNOLOGY, LLC
  • Correspondent: HOGAN LOVELLS US LLP, 555 THIRTEENTH STREET, NW, WASHINGTON, DC United States
  • Context: Release of security interest from HPS Investment Partners, LLC.

Timeline diagram

timeline
    title Ownership of US 7940851
    2006 : Filed
    2008 : Assigned to Panasonic Corp
    2011 : Issued
    2013 : Securitization by Optis
    2014 : Assigned to Optis Wireless Technology
         : Securitization by Optis
    2016 : Release of security interest

NPE / troll-pattern signals

1. Shell-entity transfer — present. The transfer from Panasonic Corp. to Optis Wireless Technology, LLC (Reel 031649/0569) suggests a shell entity. Optis Wireless Technology, LLC is known as a non-practicing entity involved in patent litigation.
2. Known asserter in the chain — present. Optis Wireless Technology LLC is a known Non-Practicing Entity (NPE).
3. Repeat correspondent across the chain — present. Blank Rome LLP appears as the correspondent for both security agreements involving Optis Wireless Technology, LLC (Reel 031447/0663 and Reel 031649/0569).
4. Cascading transfers — not present. There are not multiple consecutive assignments through chained LLCs within a short timeframe.
5. Pre-litigation transfer — unclear. While the transfer to Optis Wireless Technology LLC occurred in February 2014, and litigation involving this patent was filed in Texas Eastern District Court (case 2:17-cv-00123), the exact date of the first infringement suit needs to be confirmed to determine if it falls within 6 months of the transfer.
6. Bankruptcy fire-sale — not present. Panasonic Corp. was not in bankruptcy proceedings at the time of the transfer.
7. Privateering — unclear. While Panasonic transferred the patent to Optis, there's no explicit evidence in the provided data to confirm a privateering arrangement where Optis is asserting on Panasonic's behalf against competitors.
8. Defensive aggregator (anti-NPE) — not present. The chain does not terminate at a defensive aggregator.

Verdict

NPE — high confidence. The presence of Optis Wireless Technology, LLC, a known Non-Practicing Entity, as an assignee (Reel 031649/0569), coupled with the repeated correspondent attorney (Blank Rome LLP) on related security agreements, strongly indicates an NPE assertion pattern. Further, the patent has been involved in litigation.

Verification: https://assignmentcenter.uspto.gov/

The full text of US patent 7940851 has been provided, fulfilling the request to search the USPTO database for this specific patent number. US7940851, titled "Radio communication apparatus and radio communication method," was filed on April 21, 2006, and published on May 10, 2011. Its stated objective is to reduce the amount of feedback information and system traffic in MIMO communication systems, particularly by addressing the problem of increasing Channel Quality Indicator (CQI) feedback overhead. This is achieved by generating feedback information from an absolute value of communication quality for a reference antenna and relative values for other antennas.

Based on the problem statement in US7940851, which focuses on reducing CQI feedback overhead in MIMO systems, especially for frequency scheduling, the most relevant prior art would be patents addressing efficient channel state information (CSI) or CQI feedback in multi-antenna communication systems. From the list of patent citations for US7940851, the following patents are identified as highly relevant: US6985536B2, US7180879B2, US20050180491A1, and US20060045203A1.

Here is an analysis of each:

Most Relevant Prior Art for US7940851:

1. US6985536B2

• Full Citation: US 6,985,536 B2, "Method and apparatus for efficient feedback in a wireless communication system" to Kyeong-Ahn OH, et al., assigned to [LG Electronics Inc.](/litigations/by-plaintiff/LG%20Electronics%20Inc.)
• Publication/Filing Date: Granted: January 10, 2006; Filed: February 28, 2002.
• Brief Description: This patent describes a method for a mobile station to efficiently feed back channel quality information (CQI) to a base station in a wireless communication system. The mobile station measures the channel quality of multiple sub-bands and transmits only the CQI values that meet a predetermined criterion. This aims to reduce the amount of feedback information by selectively reporting CQI.
• Potential Anticipation (35 U.S.C. § 102): US6985536B2 addresses the general problem of reducing feedback overhead for channel quality. However, it focuses on transmitting only selected CQI values (e.g., those meeting a criterion) rather than the specific approach of US7940851, which involves transmitting an absolute CQI for a reference antenna and relative CQI values for other antennas, specifically on a per-block (chunk) basis. Therefore, while it anticipates the need for efficient feedback, it does not appear to directly anticipate the specific structural and functional elements of Claim 1 of US7940851, particularly the calculation and transmission of relative CQI values with respect to a reference.

2. US7180879B2

• Full Citation: US 7,180,879 B2, "Communication apparatus and communication method for communicating channel state information" to Jian-Ming CHEN, assigned to Industrial Technology Research Institute.
• Publication/Filing Date: Granted: February 20, 2007; Filed: September 25, 2002.
• Brief Description: This patent describes an apparatus and method for communicating channel state information (CSI) in a wireless communication system. It involves a receiver generating CSI by analyzing a received signal and a transmitter sending data based on the CSI. The CSI is represented using a pre-coding matrix index (PMI) and a channel quality indicator (CQI) to provide efficient feedback for Multiple-Input Multiple-Output (MIMO) systems.
• Potential Anticipation (35 U.S.C. § 102): US7180879B2 pertains to communicating CSI (including CQI) in MIMO systems, which is the broad technical field of US7940851. However, its abstract indicates the use of PMI and CQI to represent CSI, without explicitly detailing a mechanism of combining an absolute CQI for a reference stream and relative CQI values for other streams per frequency block to reduce feedback overhead. Therefore, while it addresses CSI feedback in MIMO, it does not appear to directly anticipate the specific "absolute value and relative value" per-block CQI feedback mechanism described in Claim 1 of US7940851.

3. US20050180491A1

• Full Citation: US 2005/0180491 A1, "Method and apparatus for supporting MIMO transmission" to Jung-Je Son, assigned to [[Samsung Electronics Co.](/litigations/by-defendant/Samsung%20Electronics%20Co.), Ltd.](/litigations/by-plaintiff/Samsung%20Electronics%20Co.%2C%20Ltd.)
• Publication/Filing Date: Published: August 18, 2005; Filed: February 17, 2004.
• Brief Description: This patent application describes a method and apparatus for supporting MIMO transmission by transmitting channel information (including channel matrix and signal-to-noise ratio) from a receiver to a transmitter. The channel information is used by the transmitter to determine optimal transmission parameters, such as modulation and coding scheme.
• Potential Anticipation (35 U.S.C. § 102): US20050180491A1 generally describes feedback of channel information (which would include CQI) for MIMO transmission to select optimal transmission parameters. Similar to the other cited prior art, it establishes the general context of MIMO feedback. However, the abstract does not disclose the specific inventive step of US7940851, which is the calculation and transmission of an absolute CQI for a reference stream and relative CQI values for other streams, on a per-block basis, to explicitly reduce feedback overhead. Therefore, it may anticipate the broad concept of MIMO feedback but not the detailed mechanism claimed in US7940851.

4. US20060045203A1

• Full Citation: US 2006/0045203 A1, "Mobile communication system and mobile station apparatus" to Ryuji Umeki, assigned to Panasonic Corporation.
• Publication/Filing Date: Published: March 2, 2006; Filed: August 25, 2005.
• Brief Description: This patent application describes a mobile communication system and mobile station apparatus that improve throughput in a multi-carrier system by reporting channel quality indicators. The mobile station measures reception quality for each channel (sub-carrier or sub-band) and reports a representative CQI and differential CQIs for other channels, or it selects a particular channel and reports its absolute CQI and differential values for others.
• Potential Anticipation (35 U.S.C. § 102): This patent application is highly relevant as it explicitly mentions reporting a "representative CQI and differential CQIs for other channels" or "selecting a particular channel and reports its absolute CQI and differential values for others." This concept of sending an absolute value for one channel and differential (relative) values for others directly anticipates a core aspect of US7940851's Claim 1, which states "calculate a first absolute CQI value per each of the blocks for the first data and a second absolute CQI value per each of the blocks for the second data, and calculate a relative value of the second absolute CQI value with respect to the first absolute CQI value, per each of the blocks; and a transmitting unit configured to transmit the first absolute CQI value and the relative value of the second absolute CQI value in the same block." US20060045203A1, published before the filing date of US7940851, teaches the idea of combining absolute and differential (relative) CQI values to reduce feedback, potentially for different sub-bands (which are analogous to "blocks" or "chunks" in US7940851). It specifically addresses reducing feedback overhead in multi-carrier systems using this technique. This document appears to directly anticipate the method of reducing feedback by sending one absolute CQI and subsequent relative CQIs, as claimed in US7940851, particularly concerning the core inventive aspect of reducing overhead by combining absolute and relative channel quality information. Therefore, US20060045203A1 potentially anticipates Claim 1 and all claims dependent thereon in US7940851.

Obviousness Analysis of US Patent 7,940,851 Under 35 U.S.C. § 103

This analysis considers US patent 7,940,851 (hereinafter '851 patent) under 35 U.S.C. § 103 for obviousness, based on the prior art identified within the patent text itself. The '851 patent aims to reduce Channel Quality Indicator (CQI) feedback overhead in Multi-Input Multi-Output (MIMO) communication systems.

1. Scope and Content of the Prior Art:

The '851 patent explicitly identifies a "conventional MIMO PARC scheme" (Per Antenna Rate Control) as existing prior art, citing "Non-patent Document 1: Lucent 3GPP R1-010879". [cite: Non-patent Document 1: Lucent 3GPP R1-010879]

The patent describes this conventional scheme as follows:

• A MIMO transmitting apparatus transmits pilot signals on a per-antenna basis. [cite: FIG. 1 shows a configuration of the MIMO transmitting apparatus in the MIMO communication system adopting the conventional MIMO PARC scheme. As shown in the figure, the MIMO transmitting apparatus transmits pilot signals on a per antenna basis by using several subcarriers.]
• A receiving apparatus measures the received intensity of each pilot signal, generates a CQI per antenna based on the channel quality, and feeds back these CQIs to the transmitting apparatus. [cite: On the other hand, the receiving apparatus (not shown) measures the received intensity of each pilot signal transmitted from the antennas in the MIMO transmitting apparatus, generates a CQI (channel quality indicator) per antenna based on the channel quality condition for each antenna, and feeds back the CQIs to the MIMO transmitting apparatus.]
• The transmitting apparatus then determines the optimal modulation scheme and coding rate per antenna based on the received CQI information. [cite: The MIMO transmitting apparatus determines the optimal modulation scheme (QPSK, 16QAM, 64QAM and so on) and coding rate on a per antenna basis based on the CQI information per antenna and transmits substreams from the antennas.]

The '851 patent further articulates a problem with this conventional approach: "the conventional MIMO communication system has a problem of increasing the CQI feedback overhead in proportion to the number of antennas (i.e. streams)." [cite: However, the conventional MIMO communication system has a problem of increasing the CQI feedback overhead in proportion to the number of antennas (i.e. streams). Moreover, when the transmitting side performs frequency scheduling, CQI is required per chunk, which is a subcarrier block, and therefore the above problem is further prominent.] This implies that in the conventional system, each antenna's CQI is reported as an absolute value.

2. Differences Between the Prior Art and the Claims at Issue:

Claim 1 of the '851 patent, an independent claim, recites a radio communication apparatus comprising:

• A receiving unit configured to receive first data and second data transmitted from a plurality of antennas using a plurality of blocks. [cite: 1. A radio communication apparatus comprising: a receiving unit configured to receive first data and second data, which are transmitted from a plurality of antennas for spatial-multiplexing using a plurality of blocks, into which a plurality of consecutive subcarriers in a frequency domain are divided;]
• A calculating unit configured to calculate a first absolute CQI value per block for the first data and a second absolute CQI value per block for the second data, and further calculate a relative CQI value of the second absolute CQI value with respect to the first absolute CQI value, per each of the blocks. [cite: a calculating unit configured to calculate a first absolute channel quality indicator (CQI) value per each of the blocks for the first data and a second absolute CQI value per each of the blocks for the second data, and calculate a relative value of the second absolute CQI value with respect to the first absolute CQI value, per each of the blocks;]
• A transmitting unit configured to transmit the first absolute CQI value and the relative value of the second absolute CQI value in the same block. [cite: A radio communication apparatus and an associated method are provided. The apparatus includes a receiving unit configured to receive first data and second data, which are transmitted from a plurality of antennas for spatial-multiplexing using a plurality of blocks, into which a plurality of consecutive subcarriers in a frequency domain are divided. The apparatus further includes a calculating unit configured to calculate a first absolute CQI value per each of the blocks for the first data and a second absolute CQI value per each of the blocks for the second data, and calculate a relative value of the second absolute CQI value with respect to the first absolute CQI value, per each of the blocks. The apparatus still further includes a transmitting unit configured to transmit the first absolute CQI value and the relative value of the second absolute CQI value in the same block.]

The key difference between the conventional MIMO PARC scheme and Claim 1 is the explicit calculation and transmission of a relative CQI value for at least one data stream (or antenna) with respect to a reference (the first data/antenna's absolute CQI), instead of transmitting absolute CQI values for all antennas. This method is stated to reduce feedback information overhead. [cite: In this way, feedback information is generated such that the CQI of the reference substream alone is given in an absolute value and the CQIs of the other substreams are given in relative CQI values with respect to the reference substream, so that it is possible to reduce the amount of feedback information, compared to conventional cases of feeding back the absolute values of the CQI values of all substreams.]

3. Level of Ordinary Skill in the Pertinent Art:

A person having ordinary skill in the art (POSITA) in 2006 (the priority date of the '851 patent) would have been proficient in wireless communication systems, particularly MIMO and OFDM technologies, channel estimation, link adaptation (e.g., PARC), and data compression or bandwidth efficiency techniques. They would understand the trade-offs between feedback accuracy, latency, and overhead.

4. Motivation to Combine/Modify Prior Art:

The '851 patent itself provides the motivation for a POSITA to modify the conventional MIMO PARC scheme. The patent clearly states that "the conventional MIMO communication system has a problem of increasing the CQI feedback overhead in proportion to the number of antennas (i.e. streams)." [cite: However, the conventional MIMO communication system has a problem of increasing the CQI feedback overhead in proportion to the number of antennas (i.e. streams). Moreover, when the transmitting side performs frequency scheduling, CQI is required per chunk, which is a subcarrier block, and therefore the above problem is further prominent.] This identified problem would motivate a POSITA to seek methods to reduce the feedback overhead.

The concept of reporting a reference value absolutely and subsequent related values relatively (often referred to as differential encoding or differential pulse-code modulation in signal processing) is a well-known technique in communication and data compression for reducing bandwidth or data rates when there is inherent correlation between successive or related measurements. In MIMO systems, channel quality indicators for different antennas, while distinct, often exhibit some degree of correlation, especially if the antennas are physically co-located or operating in similar propagation environments.

Therefore, a POSITA, aware of the problem of excessive CQI feedback overhead in a conventional MIMO PARC system (as described, for instance, in Lucent 3GPP R1-010879) and motivated to reduce this overhead, would have considered applying the known technique of differential reporting. Applying this technique would involve designating one antenna's CQI as a reference (e.g., the first data/antenna in Claim 1, or potentially the antenna with the best quality as described in Embodiment 3 [cite: Embodiment 3]), reporting its CQI absolutely, and reporting the CQIs of other antennas/substreams as relative values with respect to that reference. This would have been an obvious modification to reduce the data rate of the feedback channel without significant loss of information, especially given the explicit statement of the problem within the '851 patent.

Conclusion:

Based on the '851 patent's own description of the conventional MIMO PARC scheme (exemplified by "Non-patent Document 1: Lucent 3GPP R1-010879") and its explicit identification of the problem of increasing CQI feedback overhead, a person having ordinary skill in the art would have been motivated to combine the conventional system with known techniques for data compression, specifically differential reporting. The idea of transmitting an absolute CQI for a reference antenna and relative CQIs for other antennas, as claimed in Claim 1, would have been an obvious solution to the acknowledged problem of feedback overhead in MIMO systems.