Diversity branch delay alignment in radio base station

Abstract

A base station ( 28 ) included in a radio access network of a telecommunications system has two diversity antennas ( 44 A, 44 B) for a cell/carrier utilized in a sector served by the base station which are respectively involved in transmission of two branches of a radio link signal of the cell/carrier between the base station and a user equipment unit ( 30 ). Two branches of signal processing hardware respectively process the two branches of the radio link signal to yield two respective processed branches of the radio link signal. A rake receiver ( 62, 262 ) measures the delay difference between the two processed branches of the radio link signal, and uses the measured delay difference for various purposes. For example, some embodiments of the invention use the delay difference between the two branches as measured by the rake receiver to compensate for a delay difference which exists between the two processed branches of the radio link signal. When measuring the delay difference between the two branches of an uplink radio signal, a rake receiver ( 62 ) at the radio base station is employed. On the other hand, when measuring the delay difference between the two branches of a downlink radio signal, a rake receiver ( 262 ) at test user equipment unit ( 30 T) is employed.

1 . A method of operating a base station included in a radio access network of a telecommunications system, the method comprising: 
 (1) obtaining, for a cell/carrier utilized in a sector served by the base station, two branches of an uplink radio link signal respectively received by two diversity antennas situated at the base station;    (2) routing the two branches of the radio link signal through two respective branches of signal processing hardware subsequent to receipt of the two branches of the uplink radio link signal from the respective two diversity antennas;    (3) measuring a delay difference between the two branches of the radio link signal.    
   
   
       2 . The method of  claim 1 , further comprising using a rake receiver for measuring the delay difference between the two branches of the radio link signal.  
   
   
       3 . The method of  claim 1 , further comprising: 
 (4) using the delay difference to determine a delay alignment adjustment value for compensating for the delay difference between the two branches of the radio link signal.    
   
   
       4 . The method of  claim 2 , wherein the radio link signal is an uplink signal to the radio base station, and further comprising using a rake receiver at the base station for measuring the delay difference between the two branches of the radio link signal.  
   
   
       5 . The method of  claim 4 , further comprising: 
 (4) using the delay difference to determine a delay alignment adjustment value for compensating for the delay difference between the two branches of the radio link signal.    
   
   
       6 . The method of  claim 5 , further comprising: 
 performing steps (1)-(3) with respect to radio link signals involved in plural calls with plural user equipment units;    after step (3), determining an average of the plural delay difference values with respect to the plural cells; and    as step (4), using the average delay difference to determine the delay adjustment value.    
   
   
       7 . The method of  claim 6 , further comprising: 
 utilizing plural rake receivers for measuring delay difference values between the two branches of the radio link signals, at least one of the plural rake receivers being utilized for plural cell/carriers;    for each of the plural rake receivers, storing, in a memory, the average of the plural delay difference values measured for a specified cell/carrier by the rake receivers;    periodically accessing the memory to obtain the average of the plural delay difference values for each of the plural rake receivers for the specified cell/carrier for calculating the delay alignment adjustment value for the specified cell/carrier.    
   
   
       8 . The method of  claim 7 , further comprising: 
 for each of the plural rake receivers, storing for each of the plural cell/carriers, in a memory, an average of plural delay difference values measured by the rake receivers;    periodically accessing the memory to obtain the average of the plural delay difference values for each of the plural rake receivers on a per cell/carrier basis for calculating the delay alignment adjustment value for each of the plural cell/carriers.    
   
   
       9 . The method of  claim 5 , further comprising applying the delay alignment adjustment value to one of the two branches of signal processing hardware to compensate for the delay difference.  
   
   
       10 . The method of  claim 9 , further comprising applying the delay alignment adjustment value to a delay alignment buffer included in the one of the two branches of signal processing hardware to compensate for the delay difference.  
   
   
       11 . The method of  claim 1 , wherein the user equipment unit is a test user equipment unit which is situated essentially equidistantly between the two diversity antennas.  
   
   
       12 . The method of  claim 1 , further comprising: 
 (A) performing steps (1)-(3) with respect to a radio link signal received from a test user equipment unit which is situated essentially equidistantly between the two diversity antennas, and thereby obtaining a hardware delay value;    (B) performing steps (1)-(3) with respect to a radio link signal received from a non-test user equipment unit which utilizes the cell/carrier in the sector, and thereby obtaining a total delay value;    (C) using the total delay value and the hardware delay value to determine an angle of arrival for the radio link signal received from a non-test user equipment unit.    
   
   
       13 . The method of  claim 12 , wherein step (C) further comprises: 
 using the total delay value and the hardware delay value to determine a delay component attributable to the angle of arrival of the radio link signal from the non-test user equipment unit;    using the delay component attributable to the angle of arrival of the radio link signal from the non-test user equipment unit to determine an arrival delay component, the arrival delay component being represented by a projection of a distance separating the two diversity antennas on a direction of approach of the radio link signal from the non-test user equipment unit;    using the arrival delay component to determine the angle of arrival.    
   
   
       14 . The method of  claim 12 , further comprising: 
 performing step (B) and step (C) for plural non-test user equipment units which utilize the cell/carrier in the sector;    accumulating statistics pertaining to the angle of arrival of radio link signals received by the plural non-test user equipment units.    
   
   
       15 . A base station included in a radio access network of a telecommunications system and comprising: 
 two diversity antennas for a cell/carrier utilized in a sector served by the base station from which are respectively obtained two branches of an uplink radio link signal transmitted between the base station and a user equipment unit;    two branches of signal processing hardware at the base station which respectively process the two branches of the uplink radio link signal respectively recevied by the two diversity antennas of the base station either before or after transmission between the user equipment unit and the base station; and    a rake receiver which measures a delay difference between the two processed branches of the uplink radio link signal.    
   
   
       16 . The apparatus of  claim 15 , further comprising a processor which uses the delay difference to determine a delay alignment adjustment value.  
   
   
       17 . The apparatus of  claim 16 , further comprising: 
 plural rake receivers which, with respect to radio link signals involved with plural calls with plural user equipment units, measure delay difference values between the two branches of the plural radio link signals, at least one of the plural rake receivers being utilized for plural cell/carriers;    a local memory for each of the plural rake receivers in which is stored an average of plural delay difference values measured for a specified cell/carrier by the rake receivers;    wherein the processor periodically accesses the local memory to obtain the average of the plural delay difference values for each of the plural rake receivers for the specified cell/carrier for calculating the delay alignment adjustment value for the specified cell/carrier.    
   
   
       18 . The apparatus of  claim 17 , wherein each rake receiver is situated on a board which has a board processor which computes the average of plural delay difference values measured for the specified cell/carrier; and 
 wherein the processor which periodically accesses the local memory is a main processor which is distinct from the board processor.    
   
   
       19 . The apparatus of  claim 18 , further comprising an array of rake receivers each having a board processor which is periodically accessed by the main processor.  
   
   
       20 . The apparatus of  claim 17 , wherein the processor periodically accesses the local memories for the plural rake receivers to obtain the average of the plural delay difference values for each of the plural rake receivers on a per cell/carrier basis for calculating the delay alignment adjustment value for each of the plural cell/carriers.  
   
   
       21 . The apparatus of  claim 18 , wherein each rake receiver is situated on a board which has a board processor which computes the average of plural delay difference values measured for the specified cell/carrier; and 
 wherein the processor which periodically accesses the local memory is a main processor which is distinct from the board processor.    
   
   
       22 . The apparatus of  claim 16 , wherein the delay alignment adjustment value is applied to one of the two branches of signal processing hardware.  
   
   
       23 . The apparatus of  claim 22 , wherein the delay alignment adjustment value is applied to a delay alignment buffer included in the one of the two branches of signal processing hardware.  
   
   
       24 . A radio access network of a telecommunications system comprising: 
 a base station having two diversity antennas for a cell/carrier utilized in a sector served by the base station;    a test user equipment unit situated essentially equidistantly with respect to the two diversity antennas, two branches of an uplink radio link signal received from the test user equipment unit being received respectively by the two diversity branches;    the base station further comprising: 
 two branches of signal processing hardware which respectively process the two branches of the radio link signal;  
 a rake receiver which measures a delay difference between the two branches of the uplink radio link signal.  
   
   
   
       25 . The apparatus of  claim 24 , further comprising a processor which uses the delay difference to determine a delay alignment adjustment value.  
   
   
       26 . The apparatus of  claim 25 , further comprising: 
 a local memory for the rake receiver in which is stored an average of plural delay difference values measured for the cell/carrier by the rake receiver;    wherein the processor periodically accesses the local memory to obtain the average of the plural delay difference values for calculating the delay alignment adjustment value for the cell/carrier.    
   
   
       27 . The apparatus of  claim 26 , wherein the rake receiver is situated on a board which has a board processor which computes the average of plural delay difference values measured for the cell/carrier; and 
 wherein the processor which periodically accesses the local memory is a main processor which is distinct from the board processor.    
   
   
       28 . The apparatus of  claim 25 , wherein the delay alignment adjustment value is applied to one of the two branches of signal processing hardware.  
   
   
       29 . The apparatus of  claim 28 , wherein the delay alignment adjustment value is applied to a delay alignment buffer included in the one of the two branches of signal processing hardware.  
   
   
       30 . The apparatus of  claim 24 , further comprising: 
 a non-test user equipment unit which utilizes the cell/carrier in the sector, wherein the two branches of signal processing hardware respectively process the two branches of the radio link signal received from the non-test user equipment unit;    wherein the rake receiver measures a delay difference between the two branches of the radio link signal for the non-test user equipment unit to obtain a total delay value;    wherein the delay difference between the two branches of the radio link signal measured by the rake receiver for the test user equipment unit is used as a hardware delay value; and further comprising    an angle of arrival determination unit which uses the total delay value and the hardware delay value to determine an angle of arrival for the radio link signal received from the non-test user equipment unit.    
   
   
       31 . The apparatus of  claim 30 , wherein the angle of arrival determination unit executes the steps of: 
 (A) using the total delay value and the hardware delay value to determine a delay component attributable to the angle of arrival of the radio link signal from the non-test user equipment unit;    (B) using the delay component attributable to the angle of arrival of the radio link signal from the non-test user equipment unit to determine an arrival delay component, the arrival delay component being represented by a projection of a distance separating the two diversity antennas on a direction of approach of the radio link signal from the non-test user equipment unit;    (C) using the arrival delay component to determine the angle of arrival.    
   
   
       32 . The apparatus of  claim 31 , wherein the angle of arrival determination unit performs step (B) and step (C) for plural non-test user equipment units which utilize the cell/carrier in the sector; and accumulates statistics pertaining to the angle of arrival of radio link signals received by the plural non-test user equipment units