Measuring angle of incidence in an ultrawideband communication system

Abstract

In an ultra-wideband (“UWB”) receiver, a received UWB signal is periodically digitized as a series of ternary samples. During a carrier acquisition mode of operation, the samples are continuously correlated with a predetermined preamble sequence to develop a correlation value. When the value exceeds a predetermined threshold, indicating that the preamble sequence is being received, estimates of the channel impulse response (“CIR”) are developed. When a start-of-frame delimiter (“SFD”) is detected, the best CIR estimate is provided to a channel matched filter (“CMF”). During a data recovery mode of operation, the CMF filters channel-injected noise from the sample stream. Both carrier phase errors and data timing errors are continuously detected and corrected during both the carrier acquisition and data recovery modes of operation. The phase of the carrier can be determined by accumulating the correlator output before it is rotated by the carrier correction. By comparing the carrier phases of two receivers separated by a known distance, d, the angle of incidence, θ, of the signal can be determined.

The invention claimed is: 
     
       1. In a radio frequency (“RF”) system comprising an RF transmitter, a first RF receiver having a first antenna, and a second RF receiver having a second antenna, the first and second antennas being separated by a predetermined distance, d, a method comprising the steps of:
 [1] in the first and second receivers receiver, using respective a first and second clock tracking loops loop to synchronize the carrier phase of said the first receiver to the transmitter and in the second receiver, using a second clock tracking loop to synchronize the carrier phase of the second receiver to the transmitter; 
 [2] in the transmitter, transmitting an ultra-wideband (“UWB”) signal having a predetermined carrier wavelength, λ; 
 [3] in the first receiver:
 [3.1] receiving the transmitted UWB signal; 
 [3.2] developing a first phase value as a function of the complex baseband impulse response of said received UWB signal; and 
 [3.3] correcting the first phase value by subtracting the phase of the first clock tracking loop; 
 
 [4] in the second receiver:
 [4.1] receiving the transmitted UWB signal; 
 [4.2] developing a second phase value as a function of the complex baseband impulse response of said received UWB signal; and 
 [4.3] correcting the second phase value by subtracting the phase of the second clock tracking loop; 
 
 [5] developing a phase difference value, α, as a function of difference between the corrected first and second phase values; and 
 [6] developing an angle of arrival, θ, of the transmitted UWB signal relative to the first receiver as a function of d, λ and α. 
 
     
     
       2. The method of  claim 1  wherein, if d is at least λ/2, step [6] is further characterized as:
 [6] developing a plurality of angles of arrival, θ, of the transmitted UWB signal relative to the first receiver according to the following: 
 
       
         
           
             
               
                 θ 
                 = 
                 
                   
                     sin 
                     
                       - 
                       1 
                     
                   
                   ⁢ 
                   
                     αλ 
                     
                       2 
                       ⁢ 
                       π 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       d 
                     
                   
                 
               
               ; 
             
           
         
       
       the method further comprising the step of:
 [8] in the first and second receivers, determining respective first and second times of arrival of the transmitted UWB signal; and 
 [9] selecting one of the plurality of angles of arrival as a function of the first and second times of arrival. 
 
     
     
       3. The method of  claim 1  wherein, if d is at least λ/2, step [6] is further characterized as:
 [6] developing a plurality of angles of arrival, θ, of the transmitted signal relative to the first receiver according to the following: 
 
       
         
           
             
               
                 θ 
                 = 
                 
                   
                     sin 
                     
                       - 
                       1 
                     
                   
                   ⁢ 
                   
                     αλ 
                     
                       2 
                       ⁢ 
                       π 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       d 
                     
                   
                 
               
               ; 
             
           
         
       
       the method further comprising the step of:
 [8] performing steps [1] through [6] using a first carrier wavelength λ 1 ; 
 [9] performing steps [1] through [6] using a second carrier wavelength Δ 2  different than the first carrier wavelength λ 1 ; and 
 [10] selecting one of the plurality of angles of arrival as a function of the first and second carrier wavelengths. 
 
     
     
       4. A non-transitory computer readable medium including executable instructions which, when executed in a processing system, cause the processing system to perform all of the steps of a method according to any one of  claims 1 ,  2  and  3 .