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US 7486720
Added 9/23/2026, 5:45:48 PM
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Patent summary
Title, assignee, inventors, filing/issue dates, abstract, and a plain-language overview of the claims.
US 7486720 — Training Frames for MIMO Stations
Title: Training frames for MIMO stations
Patent number: US 7486720 B2
Application number: US 11/127,006
Inventors: Andreas F. Molisch, Jianxuan Du, Daqing Gu
Assignee: Mitsubishi Electric Research Laboratories, Inc. (original and current, per listing)
Priority/filing date: 2005-05-11
Publication date: 2009-02-03
Legal status (as listed, not a legal conclusion): Expired – Fee Related; adjusted expiration 2026-08-19
Other version: US 20060274847 A1; PCT publication WO 2006120865 A1
Source: https://patents.google.com/patent/US7486720/en
Purpose. The invention addresses antenna/beam selection in MIMO systems, where reducing radio-frequency (RF) chains via selection preserves capacity and diversity gains. The problem: selection depends on fading (frequency-dependent) or path angles of arrival, and the channel observed in transmit versus receive mode differs, so station A and station B may independently select different antenna/beam submatrices, severely degrading performance. Explicit PHY/MAC signaling to reconcile selections is described as undesirable due to practical limitations.
Plain-language scope. Station B transmits a long sequence of training frames to station A over the MIMO channel (number of frames at least the ceiling of N_B·N_A / N_A_SS; optionally in response to a "request for full training"). Station A estimates complete channel characteristics, selects a subset of antennas or beams, then transmits a short sequence of training frames back to station B, which estimates partial channel characteristics and selects its own subset. The stations then exchange data frames using the selected antennas/beams. Selection matrices F_A and F_B (identity submatrices for antenna selection; unitary-matrix columns for beam selection) are applied, with transformation possible in the RF domain using Butler matrix, phase shifters, attenuators/amplifiers, and combiners/switches.
What the excerpt does not establish. It does not provide the actual wording of the claims, the complete specification, prosecution history, measured results, or any validity/prior-art analysis. It also does not give the exact closed-form expressions for the frame counts (partially truncated) or the full FIG. 1–3 description.
Generated 10/1/2026, 9:43:18 PM
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