tailieunhanh - Introduction to Smart Antennas - Chapter 6

Beamforming Fundamentals Với sự chỉ đạo của các tín hiệu đến được biết đến hoặc ước tính, bước tiếp theo là sử dụng các kỹ thuật chế biến không gian để cải thiện hiệu suất tiếp nhận của các mảng ăng-ten nhận được dựa trên thông tin này. Một số các kỹ thuật xử lý không gian được gọi là beamforming bởi vì họ có thể hình thành các beampattern mảng để đáp ứng các yêu cầu quyết định bởi hệ thống không dây. Với một 1D mảng tuyến tính của các yếu tố và một đầu sóng tác. | 87 CHAPTER 6 Beamforming Fundamentals With the direction of the incoming signals known or estimated the next step is to use spatial processing techniques to improve the reception performance of the receiving antenna array based on this information. Some of these spatial processing techniques are referred to as beamforming because they can form the array beampattern to meet the requirements dictated by the wireless system. Given a 1D linear array of elements and an impinging wavefront from an arbitrary point source the directional power pattern P e can be expressed as 59 125 P e a x e-jpd x e dx where a x is the amplitude distribution along the array ỊÌ is the phase constant and d x e is the relative distance the impinging wavefront with an angle of arrival e has to travel between points uniformly spaced a distance x apart along the length of the array. The exponential term is the one that primarily scans the beam of the array in a given angular direction. The integral of can be generalized for two- and three-dimensional configurations 59 . Equation is basically the Fourier transform of a x along the length of the array and is the basis for beamforming methods 125 . The amplitude distribution a x necessary for a desired P e is usually difficult to implement practically 59 . Therefore realization of most of the times is accomplished using discrete sources represented by a summation over a finite number of elements 59 . Thus by controlling the relative phase between the elements the beam can be scanned electronically with some possible changes in the overall shape of the array pattern. This is the basic principle of array phasing and beam shaping. The main objective of this spatial signal pattern shaping is to simultaneously place a beam maximum toward the signal-of-interest SOI and ideally nulls toward directions of interfering signals or signals-not-of-interest SNOIs . This process continuously changes to accommodate the incoming SOIs and SNOIs. The