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  Base station and method for selecting best transmit antenna(s) for signaling control channel informationUSPTO Application #: 20080051037Title: Base station and method for selecting best transmit antenna(s) for signaling control channel information Abstract: A base station is described herein which implements a method that uses different aspects of reported channel quality information (CQI) measurements to help select the “best” transmit antenna(s) on which to transmit control channel information to mobile terminal(s). The base station can also transmit a format indicator to communicate the assigned control channel transmit antenna(s) and the assigned data transmit antenna(s) to the mobile terminal(s). (end of abstract)
Agent: Ericsson Inc. - Plano, TX, US Inventors: Karl James Molnar, Tomas Sundin, David Astely USPTO Applicaton #: 20080051037 - Class: 455070000 (USPTO) Related Patent Categories: Telecommunications, Transmitter And Receiver At Separate Stations, With Control Signal, Receiver Control Signal Originates At Message Transmitter The Patent Description & Claims data below is from USPTO Patent Application 20080051037. Brief Patent Description - Full Patent Description - Patent Application Claims
CLAIMING BENEFIT OF PRIOR FILED U.S. APPLICATION [0001] This application is a continuation-in-part application of U.S. patent application Ser. No. 11/275,388, filed Dec. 29, 2005, and entitled "MIMO Control Channel with Shared Channelization Codes". TECHNICAL FIELD [0002] The present invention relates to the wireless communications field, and in particular, to a base station and method for selecting which transmit antenna(s) should be used to transmit control channel information to one or more receivers (mobile terminals). BACKGROUND [0003] The following abbreviations are herewith defined, at least some of which are referred to within the ensuing description of the prior art and the present invention. CQI Channel Quality Information HS-DSCH High-Speed Downlink Shared Channel HS-SCCH High-Speed Shared Control Channel LTE Long Term Evolution Mbps Megabits Per Second MCS Modulation and Coding Scheme MIMO-SCCH Multiple Input Multiple Output Shared Control Channel MMSE Minimum Mean-Square Estimation OFDM Orthogonal Frequency Division Multiplexing PARC Per-Antenna Rate Control SNR Signal-Noise-Ratio S-PARC Selective Per-Antenna Rate Control SIC Successive Interference Cancellation TTI Total Timeslot Interval NCDMA Wideband CDMA [0004] In the multi-antenna concept proposed for the HSDPA mode of a WCDMA cellular system, the selection of a subset of antennas by the base station from which to transmit data streams to mobile terminals is considered an extension of fast link adaptation for single-antenna systems. This multi-antenna approach leads to a transmission antenna mode that is closely matched to the existing propagation conditions between the base station and mobile terminals. In one case, the base station can utilize PARC which is a multi-antenna approach that provides high downlink data rates to mobile terminals (see, S. J. Grant et al. "Per-Antenna-Rate-Control (PARC) in Frequency Selective Fading with SIC-GRAKE Receiver" Los Angeles, September 2004). In this approach, the base station uses separate transmission rates for the data streams which are mapped to all of the transmit antennas. In another case, the base station can utilize S-PARC which is a multi-antenna approach that provides even higher downlink data rates to the mobile terminals (see, S. J. Grant et al. "System-Level Performance Gains of Selective Per-Antenna-Rate-Control (S-PARC)" published in the IEEE Spring Vehicular Technology Conference, May 2005). In this approach, the base station selectively adapts both the transmit antenna(s) and the transmission data rates which are to be used to transmit the data streams to the mobile terminals. [0005] As part of the fast link adaptation process, the mobile terminals measure the CQI and transmit the CQI measurements on the uplink to the base station so that the base station can use the CQI measurements to select the transmission data rate assignment and if needed the transmit antenna(s) assignment. Since the base station transmits signals concurrently from different transmit antennas these signals interfere with each other which means the estimated CQI is going to change for each combination of transmit antennas. Thus, the providing of CQI estimates for each transmit antenna under each combination of transmit antenna(s) is going to utilize a large amount of the available uplink resources when compared to single-antenna transmission. Moreover, the type of receivers employed in the mobile terminals may increase the number of CQI values that may be fed back on the uplink to the base station. For example, the mobile terminal may have a SIC receiver which places an ordering on the transmit antenna(s) so that there will be a separate CQI value for each permutation (rather than combination) of the transmit antenna(s). [0006] One approach that can be used to reduce the complexity of the CQI feedback from a mobile terminal that uses a SIC receiver and implements S-PARC was described in co-assigned U.S. patent application Ser. No. 10/841,911 filed on May 7, 2004 and entitled "Reduced CQI Feedback for MIMO HSDPA" (the contents of which are hereby incorporated by reference herein). In this approach, the base station that is considering transmission with one antenna will select the transmit antenna that provides the best rate and use that for a single-antenna transmission. In considering transmission with two antennas, the base station constrains the two-antenna subset to contain the best antenna previously found for the single-antenna transmission and the transmit antenna with the next-best rate. This scheme is repeated for the three-antenna subset, the four-antenna subset etc . . . , and in general is called the "subset property" when related to the transmit antenna selection. Thus, an order is given to the transmit antennas so that the first antenna has the greatest transmit rate while the last antenna has the lowest transmit rate. This ordering of antennas from lowest to greatest rates is the order that the SIC-receiver processes the received signals. As a result, a large number of antenna orderings can be avoided and the feedback on the uplink can be reduced by constraining the antenna order and antenna subset selection by using a CQI report with this subset property. Continue reading... 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