Method and apparatus for beam pattern stabilisation

Abstract

Methods and apparatuses for beam pattern stabilisation are provided. A method may include processing an output of a gyroscopic sensor to generate a plurality of first phase corrections for a first time interval and a plurality of second phase corrections for a second time interval. The method may further include measuring respective signal propagation characteristics between each antenna element of the array and each of a first and second subscriber module for the first time interval. The method may further include forming, based on the measured respective signal propagation characteristics, the plurality of first phase corrections, and the plurality of second phase corrections, a MU-MIMO beam pattern for the second time interval having a main lobe towards the first subscriber module and a null towards the second subscriber module, whereby to correct for a change in orientation of the array between the first time interval and the second time interval.

What is claimed is: 
     
         1 . A method of stabilising at least one Multi User Multiple Input Multiple Output MU-MIMO beam pattern formed by an array of antenna elements at an access point of a point to multi-point wireless communication network comprising a plurality of subscriber modules, the method comprising:
 processing an output of a gyroscopic sensor to generate a plurality of first phase corrections for a first time interval and to generate a plurality of second phase corrections for a second time interval;   measuring respective signal propagation characteristics between each antenna element of the array and each of a first and second subscriber module for the first time interval; and   forming, based on the measured respective signal propagation characteristics, based on the plurality of first phase corrections and based on the plurality of second phase corrections, a MU-MIMO beam pattern for the second time interval having a main lobe towards the first subscriber module and a null towards the second subscriber module,   whereby to correct for a change in orientation of the array between the first time interval and the second time interval.   
     
     
         2 . A method according to  claim 1 , wherein:
 the plurality of first phase corrections comprises a respective first phase shift value for each antenna element of the array; and   the method comprises correcting each measured respective signal propagation characteristic by the respective first phase shift value.   
     
     
         3 . A method according to  claim 2 , wherein:
 the plurality of second phase corrections comprises a respective second phase shift value for each antenna element of the array; and   said forming the MU-MIMO beam pattern comprises:   generating a first weightset for a beamforming weights matrix based on the corrected measured respective signal propagation characteristics; and   correcting the first weightset by applying the respective second phase shift value for each element of the array.   
     
     
         4 . A method according to  claim 3 , comprising:
 applying respective correction factors to each output of the beamforming weights matrix to correct for respective signal transmission characteristics between each respective output of the beamforming weights matrix and the respective antenna element,   wherein said correcting the first weightset comprises correcting each output of the beamforming weights matrix for the respective second phase shift value by applying each respective second phase shift value to the respective correction factor.   
     
     
         5 . A method according to  claim 4 , comprising:
 generating the respective correction factors by measuring respective signal propagation characteristics between each respective output of the beamforming weights matrix and the respective antenna element by a process comprising:   coupling a sample from each signal transmitted from each output of the beamforming weights matrix to each respective antenna element;   removing the respective second phase shift from each coupled sample; and   updating the respective correction factors on the basis of the coupled samples with the respective second phase shift removed.   
     
     
         6 . A method according to  claim 2 , wherein said processing an output of a gyroscopic sensor comprises:
 generating the first phase shift values and the second phase shift values based on a single approximation factor relating a change in array orientation to a change in radiofrequency phase.   
     
     
         7 . A method according to  claim 1 , wherein said forming the MU-MIMO beam pattern comprises:
 correcting each measured respective signal propagation characteristic for a change in orientation of the array between the first time interval and the second time interval based on the plurality of first phase corrections and the plurality of second phase corrections; and   forming the MU-MIMO beam pattern based on the corrected measured respective signal propagation characteristics.   
     
     
         8 . A method according to  claim 1 , wherein the array of antenna elements is an integral part of the access point, and the gyroscopic sensor is mounted within the access point. 
     
     
         9 . A method according to  claim 8 , wherein the access point comprises a calibrated integrated module comprising transmit chains and the array of antenna elements. 
     
     
         10 . A method according to  claim 8 , wherein the access point is mounted on an antenna tower and said change in orientation of the array is due to wind. 
     
     
         11 . A method according to  claim 10 , wherein said change in orientation of the antenna array is a change in azimuth angle. 
     
     
         12 . A method according to  claim 1 , wherein the gyroscopic sensor is a rate gyro, and said output of the gyroscopic sensor is an angular rotation rate. 
     
     
         13 . A method according to  claim 12 , wherein processing the output of the gyroscopic sensor comprises:
 integrating an angular rotation rate and removing a mean value to determine an azimuth angle; and   determining a respective phase shift value for each antenna element of the array from the azimuth angle and from stored data regarding the geometry of the array.   
     
     
         14 . A method according to  claim 1 , wherein the first time interval is a first time division duplex period and the second time interval is a subsequent time division duplex period. 
     
     
         15 . An access point for a point to multi-point wireless communication network comprising a plurality of subscriber modules, the access point comprising:
 an array of antenna elements;   a digital beamforming weights matrix for applying a weightset to one or more signals streams;   a respective transmit chain for each antenna element;   a gyroscopic sensor; and   a processor configured to:
 process an output of the gyroscopic sensor to generate a plurality of first phase corrections for a first time interval and to generate a plurality of second phase corrections for a second time interval; 
 measure respective signal propagation characteristics between each antenna element of the array and each of a first and second subscriber module for the first time interval; and 
 form, based on the measured respective signal propagation characteristics, the plurality of first phase corrections and the plurality of second phase corrections, a Multi User Multiple Input Multiple Output MU-MIMO beam pattern for the second time interval having a main lobe towards the first subscriber module and a null towards the second subscriber module, 
 whereby to correct for a change in orientation of the array between the first time interval and the second time interval. 
   
     
     
         16 . An access point according to  claim 15 , wherein each respective transmit chain is connected to the array of antenna elements using printed conductors. 
     
     
         17 . An access point according to  claim 16 , wherein the circuit design and physical layout of a radio frequency transmission path for each transmit chain to the respective antenna element is the same for each antenna element. 
     
     
         18 . An access point according to  claim 17 , wherein the physical layout of the access point provides a fixed spacing between the radio frequency transmission paths for each antenna element. 
     
     
         19 . An access point according to  claim 15 , wherein a radio frequency isolation between each antenna element is at least 30 dB at an operating frequency of the antenna element.