Orthogonal beamforming

Orthogonal Beamforming Serves Multiple Users

Orthogonal beamforming techniques can provide reliable communications to multiple users on the same frequencies at the same time.

Wireless communications networks must handle ever-increasing numbers of users with growing demands for bandwidth in the form of transmitted and received voice, video, and data. Conventionally, base stations can transmit data to a number of users at the same frequency at the same time by using a feedback channel, although this adds to the complexity of the communications channel and system.

However, by using multiple antenna elements to create a number of beams in predefined directions at the same time and the same frequency, and keeping the beams orthogonal to one another—using a process known as orthogonal beamforming (OBFM)—it is possible to communicate large amounts of information to multiple users at the same time, with minimal interference among the users.

Various methods are used to support multiple users on the same frequency, including multiple-input, multiple-output (MIMO) techniques and several forms of beamforming approaches, but often a feedback channel is required to minimize interference among the different beams. However, by making use of beam direction-of-arrival (DOA) information, it is possible to use multiple beams at the same frequency while also minimizing interference and delivering excellent bit-error-rate (BER) performance.

Researchers from the School of Telecommunication Engineering, Suranaree University of Technology, Nakhon Ratchasima, Thailand propose a system model in which multiple users are operating at the same frequency with a single antenna element. In their design, however, the wireless basestation uses multiple linearly aligned antenna elements to differentiate the different signal vectors of the received beams, including multipath signals from users.

Using simulations of beam patterns at 30, 60, 90, and 120 deg. with an experimental signal-processing algorithm developed with MATLAB mathematical software from MathWorks (www.mathworks.com), high gain was achieved with the main beams with strong suppression of sidelobes, resulting in high signal-to-interference-plus-noise ratio (SINR). The OBFM approach shows great promise for achieving high data throughput with multiple wireless users, provided that DOA estimation errors for the multiple beams can be minimized (through the use of effective DOA algorithms).

See “Orthogonal Beamforming for Multiuser Wireless Communications,” IEEE Antennas & Propagation Magazine, Vol. 59, No. 4, August 2017, p. 39.

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