Channel sounding and estimation strategies for antenna selection in MIMO systems

#The present invention relates generally to wireless communication systems and, more particularly, to channel sounding and estimation techniques in wireless systems employing multiple antennas.

#Wireless communications continue to experience large growth in consumer demand and services. Wide coverage area systems such as cellular networks are commonplace, but increasingly so to are local area systems such as “WiFi,” IEEE 802.11a, and IEEE 802.11b systems. In fact, various wireless technologies are described in detail in the 802.11 IEEE Standards, including for example, the IEEE Standard 802.11a (1999) and its updates and amendments, the IEEE Standard 802.11g (2003), and the IEEE Standard 802.11n (Draft 3.0) now in the process of being adopted, all of which are collectively incorporated herein fully by reference. The later standards in particular have been or are in the process of being commercialized with the promise of 54 Mbps or more effective bandwidth, making them a strong competitor to traditional wired Ethernet and the more common “802.11b” or “WiFi” 11 Mbps mobile wireless transmission standard.

#Generally speaking, many wireless communications systems use multi-carrier modulation schemes for data transmission. Communication systems compliant with the IEEE 802.11a and 802.11g or “802.11a/g” as well as the 802.11n standards, for example, may use Orthogonal Frequency Division Multiplexing (OFDM) which is a digital multi-carrier modulation scheme that employs a large number of relatively closely spaced orthogonal sub-carriers or sub-channels. Each sub-carrier is modulated at a relatively low symbol rate using a modulation scheme such as quadrature amplitude modulation, phase shift keying, etc. Each frequency sub-band of an OFDM system may be viewed as an independent transmission channel within which to send data, thereby increasing the overall throughput or transmission rate of the communication system. Even though data on a particular sub-carrier is modulated at a low symbol rate, the large number of sub-channels provides an overall data rate similar to single-carrier modulation schemes that utilize the same bandwidth.

#FIG. 1 is a block diagram of a wireless communication configuration in which a MIMO transmitter and a MIMO receiver are able to communicate with each other;

#FIG. 2 is a diagram of an example antenna selection (ASEL) training procedure using consecutive sounding packets sent by the MIMO transmitter in a transmitter-based ASEL determination;

#FIG. 3 is a diagram of another example ASEL training procedure using consecutive sounding packets in a receiver-based ASEL determination;

#Described below are example channel sounding and estimation techniques that may be used in MIMO systems to improve ASEL. The techniques may be implemented in various types of MIMO systems, such as OFDM(A) (OFDM and Orthogonal Frequency Division Multiple Access) MIMO systems sending data over signals having a channelization bandwidth of 20 MHz divided into 56 sub-carriers as set forth in IEEE 802.11n, Draft 3.0, or 40 MHz divided into a larger number of sub-carriers as set forth in subsequent drafts. OFDM(A) MIMO systems may employ various digital modulation and mapping schemes including binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), 16 bit quadrature amplitude modulation (16-QAM), 64-QAM, or 256-QAM.

#Each transmitter and receiver in an MIMO system will have multiple antennas that are selected to produced desired beamforming and beamsteering and thereby optimize data transmission between the transmitter and receiver. As discussed further below, the transmitter, the receiver, or both may perform this antenna selection (ASEL). For example, the receiver may perform ASEL by knowing a pre-determined transmitter power level rule applied at the transmitter and then conducting appropriate scaling based on that transmit power level and a receiver gain factor. The transmitter may perform ASEL through a joint strategy with the receiver, where the receiver scales sub-channel estimates of the full-size channel appropriately and then feeds back channel state information (CSI) to the transmitter which then performs ASEL based on the CSI; or through a single device strategy in which transmitter adjusts its power levels based on a determination of the proximity of the receiver.

#FIG. 1 illustrates an example MIMO communication system 10 in block diagram form as generally including a single MIMO transmitter 12 having multiple antennas 14A-14M for communicating with a single MIMO receiver 16 having multiple antennas 18A-18M. The number of transmission antennas 14A-14M may be the same as, more than, or less than the number of receiver antennas 18A-18M. A controller 20 in the transmitter 12 and a controller 22 in the receiver 16 controller general operation of each MIMO wireless device, respectively. The controllers 20 and 22 may be implemented as one or more standard multi-purpose, programmable processors, such as micro-processors, application specific integrated circuits (ASICs), etc. or may be implemented using any other desired types of hardware, software and/or firmware.