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Method for high bit rate WLAN communications using MIMO-OFDM and SDMA-OFDM

IP.com Disclosure Number: IPCOM000124276D
Publication Date: 2005-Apr-14

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for high bit rate wireless local area network (WLAN) communications using multiple inputs multiple outputs (MIMO) orthogonal frequency division multiplexing (OFDM) and space division multiple access (SDMA) OFDM. Benefits include improved functionality, improved performance, and improved power performance

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Method for high bit rate WLAN communications using MIMO-OFDM and SDMA-OFDM

Disclosed is a method for high bit rate wireless local area network (WLAN) communications using multiple inputs multiple outputs (MIMO) orthogonal frequency division multiplexing (OFDM) and space division multiple access (SDMA) OFDM. Benefits include improved functionality, improved performance, and improved power performance.

Background

      Wireless communications by multiantenna systems with OFDM have become an active area of research for realizing higher throughputs. In the spatial domain, among multiantenna systems, MIMO provides greater capacity. In the time domain, the modulation method OFDM simplifies the equalization process by eliminating the intersymbol interference (ISI). With the combination of MIMO and OFDM, greater channel capacities could be realized with robustness to channel impairments like ISI through cyclic prefix (CP) and multipath fading through adaptive bit loading. As a result, the next generation WLAN is expected to dramatically increase throughputs without requiring additional transmission bandwidth but at the cost of higher complexity of multiple antennas, transmitters and receivers. A high-throughput WLAN (HT-WLAN) is a multiantenna system that uses OFDM as the modulation technique.

      Higher capacities by HT-WLAN based on MIMO require channel support for uncorrelated multipaths. The received multipath signals are independent and uncorrelated in space and time. As a result, MIMO can achieve a capacity equivalent to the capacity of a single antenna system multiplied by the number of receiving antennas when NT<NR. NT is the number of transmitting antennas and NR is the number of receiving antennas. The uncorrelated multipaths are possible when two stations communicate in a not-line-of-sight (NLOS) condition. It may not always be possible because the stations could be communicating in LOS condition, for example when two stations are positioned on the same floor. In LOS, very strong signal components exist in the direct paths between the stations. Very strong correlation occurs among the multipaths and

communication by MIMO-OFDM is not feasible.

      Next higher capacities can be achieved by spatially beamforming the signals in the strong direct path directions. Beamforming in spatial directions is called space division multiple access (SDMA).

General description

      The disclosed method includes exchanging capability and configuration information through control frames. The information includes ready-to-send (RTS), clear-to-send (CTS), and MIMO-OFDM or SDMA-OFDM transmission. The communication between stations using MIMO or SDMA capabilities may be changed dynamically when the stations are mobile, which sustains continued communication through variability of channel conditions.


Advantages

The disclosed method provides advantages, including:

•             Improved functionality due to enabling the dynamic selection of...