A multiple-input multiple-output (MIMO) system can transmit on multiple antennas simultaneously and receive on multiple antennas simultaneously. Unfortunately, because a legacy 802.11a/g device is not able to decode multiple data streams, such a legacy device may “stomp” on a MIMO packet by transmitting before the transmission of the MIMO packet is complete. Therefore, MIMO systems and methods are provided herein to allow legacy devices to decode the length of a MIMO packet and to restrain from transmitting during that period. These MIMO systems and methods are optimized for efficient transmission of MIMO packets.

Multiple-input multiple-output system and method

The present invention relates to wireless communications and is particularly applicable to devices and modules for correcting errors introduced to a wireless signal after its transmission. An equalizer is provided which compensates for undesirable effects on received radio signals introduced by either signal processing or by the transmission medium. In operation, the equalizer multiples the complex received signal with a complex corrective signal that compensates for these effects. A tap corrective signal corrects for time-varying channel effects (i.e. channel distortions), a timing tracking signal corrects for carrier frequency offset errors, and a phase tracking signal corrects for sampling frequency offset errors.

Frequency domain equalizer for wireless communications system

A method and apparatus for radio resources control in a multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) communication system are disclosed. Channel metric is calculated for each of a plurality of transmit antennas. Sub-carriers are allocated to each transmit antenna in accordance with the channel metric of each transmit antenna. Signals are transmitted using the allocated sub-carriers at each antenna. Adaptive modulation and coding and transmit power control of each sub-carrier may be further implemented in accordance with the channel metric. Power control may be implemented per antenna basis or per sub-carrier basis. In performing power control, a subset of transmit antennas may be selected and waterpouring may be applied only to the selected antennas. Waterpouring may be based on SNR instead of channel response.

Method and apparatus for subcarrier and antenna selection in MIMO-OFDM system

A wireless device, method, and signal for use in communication of a wireless packet between transmitting device and a wireless receiving device via a plurality of antennas, wherein a signal generator generates wireless packet including a short-preamble sequence used for a first automatic gain control (AGC), a first long-preamble sequence, a signal field used for conveying a length of the wireless packet, an AGC preamble sequence used for a second AGC to be performed after the first AGC, a second long-preamble sequence, and a data field conveying data. The AGC preamble sequence is transmitted in parallel by the plurality of antennas.

Wireless transmitting and receiving device and method

A method for configuring a multiple input multiple output (MIMO) wireless communication begins by generating a first preamble for a first antenna of the MIMO communication, wherein the first preamble includes a carrier detect field, a first channel select field, a first signal field, and a second signal field. The method continues by generating a second preamble for at least one other antenna of the MIMO communication, wherein the second preamble includes the carrier detect field, a plurality of channel select fields, and the second signal field. The method continues by simultaneously transmitting the carrier detect field via the first antenna and the least one other antenna. The method continues by transmitting the first channel select field and the first signal field via the first antenna. The method continues by, subsequent to the transmitting the first channel select field and the first signal field via the first antenna, transmitting the plurality of channel select fields via the at least one other antenna. The method continues by simultaneously transmitting the second signal field via the first antenna and the at least one other antenna.

Configuring a MIMO communication

A method for estimating carrier frequency offset (CFO) and sampling frequency offset (SFO) in an Orthogonal Frequency Division Multiplexing (OFDM) system having a plurality of pilot tones. The absolute phase angle for each pilot tone is measured, and estimates of the CFO and the SFO are derived using a weighted least-squares methodology. More particularly, the phase of each pilot tone is measured for a number (n) of symbol times; for each of the pilot tones, the slope of a phase angle change from symbol time to symbol time is estimated using a best least-squares fit of the measured phases to a straight line; and a weighted least-squares best-fit straight line is determined to find an estimated phase angle differential value (α(i)) for each pilot tone; wherein a slope of the best-fit straight line yields an estimate of the SFO, and an intercept with the best-fit straight line yields an estimate of the CFO. The plurality of pilot tones may have frequencies which are symmetrically disposed about a reference frequency, and there may be four pilot tones. The OFDM communications system is suitably a wireless LAN (WLAN) implementing a standard such as IEEE 802.11a or HiperLAN/2. Corresponding apparatus is also described.

Estimating frequency offsets using pilot tones in an OFDM system

A method and apparatus for accurately estimating the carrier frequency offset and the carrier phase offset of a digitally modulated signal using a signal processing algorithm to initialize the state variables of a Phase-Locked Loop (PLL) is disclosed. A sequence of phase values is estimated from a received sequence of symbols and the angular effect due to the modulation format is removed from the sequence of phase values. A curve-fit algorithm based in one embodiment on the RLS algorithm is then applied to a sequence of unwrapped phase values to estimate the carrier frequency offset and the carrier phase offset.

Phase-locked loop initialization via curve-fitting

A method comprising encoding a plurality of signals according to a predetermined negation scheme and transmitting the plurality of signals, wherein each signal is transmitted by way of a wireless channel. The method further comprises receiving a signal, wherein the received signal is a combination of the plurality of transmitted signals, and interpolating between data in the received signal to generate a plurality of systems of equations. The method further comprises solving the plurality of systems of equations to determine a gain and phase shift applied to each of the plurality of transmitted signals by a corresponding wireless channel.

Scalable and backwards compatible preamble for OFDM systems

A method (300) for estimating carrier frequency offset (CFO) and sampling frequency offset (SFO) in an Orthogonal Frequency Division Multiplexing (OFDM) system which has a plurality of pilot tones. The absolute phase angle for each pilot tone is measured, and estimates of the CFO and the SFO are derived using a weighted least-squares method. More particularly, the phase of each pilot tone is measured for a number (n) of symbol times (302); for each of the pilot tones, the slope of a phase angle change from symbol time to symbol time is estimated using a best least-squares fit of the measured phases to a straight line (304,306); and a weighted least-squares best-fit straight line is determined, in order to find an estimated differential phase angle value (α(i)) for each pilot tone (308); wherein the slope of the best-fit straight line yields an estimate of the SFO (310), and an interception of the best-fit straight line yields an estimate of the CFO (310). The plurality of pilot tones may have frequencies which are symmetrically disposed about a reference frequency, and there may be four pilot tones. The OFDM communications system is suitably a wireless LAN (WLAN) implementing a standard such as IEEE 802.11a or HiperLAN/2. Corresponding apparatus is also described.

Estimation of offsets carrier and sampling frequency in a multicarrier receiver

This chapter considers the recently successful IEEE 802.11b standard for high-performance wireless Ethernet and a proposed extension that provides for 22 Mbit/s transmission. IEEE 802.11 sets standards for wireless Ethernet or wireless local area networks. The chapter describes the history of the IEEE 802.11 standards and the market opportunities in the wireless Ethernet field. The chapter gives a brief description of the Medium Access Control (MAC) layer and then presents details about the physical layer methods, including coding descriptions and performance evaluations. The chapter also discusses the role and limitations of spread spectrum communications in wireless Ethernet. A comparison in terms of range versus rate with several alternatives is presented.

Peter A. Murphy

Papers

Estimating frequency offsets using pilot tones in an OFDM system

Phase-locked loop initialization via curve-fitting

Scalable and backwards compatible preamble for OFDM systems

Estimation of offsets carrier and sampling frequency in a multicarrier receiver

Evolution of 2.4-GHz wireless LANs