Use of Homodyne Methods of Microwave Phase Measurements in a Task of Precision Indoor Positioning

1. Summary Microwave indoor propagation offers a good opportunity for object positioning. The use of the pulse radar method for measuring distances and angles are quite unsuitable for indoor applications. The resolution of this method is too low and there is a minimal distance requirement of the pulse radar measurement that is usually higher than the room size. In this paper the phase method of multipoint distance measurements is presented. The microwave phase progression was used for these measurements. The resolution of the phase method of distance measurements is determined by the microwave length. Depending on the wavelength one can reach an accuracy of 10 mm and better [1] and [2]. No doubts, the phase method causes an ambiguity because the phase measurements can only have values in an interval between 0-2π. In this paper the way of bypassing this problem is shown. 2. Approach to a problem Realizing the homodyne method of microwave phase measurements and consequently distances determination, we offer to place the radio beacons in the corners of a room or in the middle of an extended wall. The transponder is placed on the object that is to be located. The positioning of object is characterized by the distances i d from the object to each of beacons. The beacon radiates the microwave signal that can be described as () ,-The microwave, propagated along the distance i d , obtains the attenuation i A and phase progression i kd () ,-, where 2  π λ k is propagation constant, λ is the wavelength. The transponder receives this signal, shifts the frequency and phase of the received microwave signal on values  and φ LF by means of a controlled phase shifter () ,()-, and reradiates this frequency-phase transformed microwave signal back in direction of the beacon. The secondary microwave signal that is received in the beacon will be () ,()-, where 1 k takes into account the frequency shift 0  ω. If the frequency shift  is much lower than the initial frequency 0 ω , then 1  kk. This secondary received signal is mixed with the original microwave signal and at the mixer's output the low-frequency signal of difference is selected and amplified up to a certain limit. This low-frequency signal will be () ,-. 444 The initial frequency and initial phase of origin microwave signal both are subtracted in a mixer. The …