Frequency bandwidth is a limited resource, a fact made more apparent as the number of wireless communications users continues to grow. Various antennas and antenna beamforming techniques have been investigated to allow several users to communicate at the same time while employing the same frequency, including multiple-input, multiple-output (MIMO) antenna methods and distributed antenna beam forming. To explore the most efficient use of available bandwidth, Researchers from the Suranaree University of Technology in Nakhon Ratchasima, Thailand examined the use of orthogonal beamforming methods (OBFMs) for multiple wireless communications users operating at the same frequency.
Wireless technology has become more or less a technological fixture in the lives of many people, and that is expected to only grow with time; more and more people depend upon wireless devices for transferring and storing personal and business information on both fixed and mobile communications devices. The OBFM concept provides multiple-beam formation at the same time and at the same frequency for multiple-user communications. All of the signal beams operating at the same frequency are orthogonal to one another, ideally with maximum gain in the direction of desired users and beam nulls in the directions of other users.
The researchers developed an OBFM approach in which only signal direction-of-arrival (DOA) information on an incoming signal was needed for effective multiuser communications with conventional beamforming techniques. The DOA signal-processing portion of the solution is based on existing methods available from the technical literature.
A multiple-user wireless system based on this approach consists of each user having a wireless design with a single antenna element and a base station with a sufficiently large array antenna to handle the multiple users and their individual antenna elements. The researchers developed straightforward formulations for calculating the signal vectors of the individual users’ signals at the base station.
Users’ signals consist of line-of-sight (LOS) and non-line-of-sight (NLOS) signals which are modeled with Rayleigh fading effects to account for accurate signal characteristics, as observed at the base station. With the aid of software programs such as MATLAB from MathWorks, four omnidirectional antenna elements equally spaced by one-half wavelength (λ/2) at 2.4 GHz were arranged in a linear manner, thus achieving signals at directions of 30, 60, 90, and 120 deg.
Even though the beams exhibited relative high sidelobes, the researchers’ OBFM approach resulted in main beams with strong attenuation of interference effects from neighboring beams at the same frequency. A number of simulations were run with random beams within a 120-deg. sector, and the gain was maximized in the desired beam direction by using the proposed OBFM approach. All of the beams operating at the same frequency are orthogonal to one another so that beam nulls are pointed in the direction of another beam’s main energy for minimal interference.
See “Orthogonal Beamforming for Multiuser Wireless Communications,” IEEE Antennas & Propagation Magazine, Vol. 59, No. 4, August 2017, p. 38.