Position location using phase-adjusted transmitters

Abstract

Systems and methods are provided for determining position location information in a wireless network. In one embodiment, timing offset information is communicated between multiple transmitters and one or more receivers. Such information enables accurate position or location determinations to be made that account for timing differences throughout the network. In another embodiment, transmitter phase adjustments are made that advance or delay transmissions from the transmitters to account for potential timing differences at receivers. In yet another embodiment, combinations of timing offset communications and/or transmitter phase adjustments can be employed in the wireless network to facilitate position location determinations.

1 . A system in a wireless network, comprising:
 at least three base stations, wherein:
 each of the base stations are configured to determine a time difference between a future transmission time of the base stations and a common clock in the wireless network; 
 at least one of the base stations is further configured to regulate an effective channel delay spread, as perceived by at least one receiver, by advancing or delaying transmission timing of future transmission of the at least one base station relative to the common clock; and 
 each of the base stations are further configured to regulate cyclically shifting a signal based on a determined time difference, wherein the signal is cyclically shifted according to a cyclic convolution; and 
 each of the base stations are further configured to transmit the cyclically shifted signal to the at least one receiver at the future transmission time, wherein a position of the at least one receiver is determined based at least on a linear convolution of a channel with the transmitted signal, from the at least three base stations, that is processed as the cyclic convolution based on the delay spread of the channel being less than a cyclic prefix employed by the signal. 
   
     
     
         2 . The system of  claim 1 , wherein each of the base stations are further configured to generate at least two timing offsets denoted as d a  and d b . 
     
     
         3 . The system of  claim 2 , wherein each of the base stations are further configured to determine a first parameter τ′ a  that is an actual delay perceived by a line of sight propagation component based on a distance between a first base station A and the at least one receiver, and determining a second parameter τ′ b  that is an actual delay that is perceived by a line of sight component from a second base station B to the at least one receiver. 
     
     
         4 . The system of  claim 3 , wherein at least a first and second base station of the base stations are further configured to process additional delays d a  and d b  at the first and second base stations based on a delay spread τ′ b −τ′ a  exceeding a cyclic prefix. 
     
     
         5 . The system of  claim 4 , wherein the receiver is configured to process the following equation:
 y(n)=h a (n)*x a (n−d a )+h b (n)*x b (n−d b )+w(n), where y(n) represents a signal received at the receiver, h a (n) and x a (n) are a channel and a signal with respect to the first base station A, * represents a linear convolution operation, w(n) is noise added at the receiver.   
     
     
         6 . The system of  claim 5 , wherein the receiver is further configured to process the following equation:
 y(n)=h a (n−d a )*x(n)+h b (n−d b )*x(n)+w(n), where a perceived channel delay spread is given by (τ′ a −d b )−(τ′ a −d a ) and controlled by introducing timing offsets at the first base station A.   
     
     
         7 . The system of  claim 5 , wherein the receiver is further configured to determine a cyclic convolution based on an effective delay spread being less than a cyclic prefix as in the following equations:
     y ( n )= h   a ( n )   x   a ( n−d   a )+ h   b ( n )   x   b ( n−d   b )+ w ( n ),     or       y ( n )= h   a ( n−d   a )   x   a ( n )+ h   b ( n−d   b )   x   b ( n )+ w ( n )   
       where   denotes circular convolution. 
     
     
         8 . The system of  claim 7 , wherein at least one base station of the base stations is further configured to delay transmissions from transmitters thereby meeting length requirements of cyclic prefix. 
     
     
         9 . The system of  claim 7 , wherein at least one base station of the base stations is further configured to employ a long cyclic prefix to enable an estimation of delay from weak transmitters that are far away. 
     
     
         10 . The system of  claim 9 , further comprising means for undoing an effect of physical delays by a cyclic shift of a positioning signal, where x a,p (n) is an intended positioning signal from the first base station A with timing delay d a , and a transmitter sends a cyclically shifted version given by x a,p (n+d a ). 
     
     
         11 . The system of  claim 10 , further comprising processing the following equation:
     y ( n )= h   a ( n )   x   a,p ( n )+ h   b ( n )   x   b,p ( n )+ w ( n ).   
     
     
         12 . The system of  claim 1 , wherein timing information is available offline. 
     
     
         13 . The system of  claim 12 , wherein pseudo ranges are measured. 
     
     
         14 . The system of  claim 13 , wherein each of the base stations are further configured to receive the pseudo ranges. 
     
     
         15 . A method in a wireless network, comprising:
 determining, by each of at least three base stations, a time difference between a future transmission time of the base stations and a common clock in the wireless network;   regulating, by at least one base station of the base stations, an effective channel delay spread, as perceived by at least one receiver, by advancing or delaying transmission timing of future transmission of the at least one of the base stations relative to the common clock;   regulating cyclically shifting, by each of the base stations, a signal based on a determined time difference, wherein the signal is cyclically shifted according to a cyclic convolution; and   transmitting the cyclically shifted signal, by each of the base stations, to the at least one receiver at the future transmission time, wherein a position of the at least one receiver is determined based at least on a linear convolution of a channel with the transmitted signal, from the at least three base stations, that is processed as the cyclic convolution based on the delay spread of the channel being less than a cyclic prefix employed by the signal.   
     
     
         16 . The method of  claim 15 , further comprising:
 generating, by each of the base stations, at least two timing offsets denoted as d a  and d b .   
     
     
         17 . The method of  claim 16 , further comprising:
 determining, by each of the base stations, a first parameter τ′ a  that that is an actual delay perceived by a line of sight propagation component based on a distance between a first base station A and the at least one receiver; and   determining, by each of the base stations, a second parameter τ′ b  that is an actual delay that is perceived by a line of sight component from a second base station B to the at least one receiver.   
     
     
         18 . The method of  claim 17 , further comprising:
 processing additional delays d a  and d b  at the first and second base stations based on a delay spread τ′ b −τ′ a  exceeding a cyclic prefix.   
     
     
         19 . The method of  claim 18 , further comprising:
 processing the following equation:   y(n)=h a (n)*x a (n−d a )+h b (n)*x b (n−d b )+w(n), where y(n) represents a signal received at the receiver, h a (n) and x a (n) are a channel and a signal with respect to the first base station A, * represents a linear convolution operation, w(n) is noise added at the receiver.   
     
     
         20 . The method of  claim 19 , further comprising:
 processing the following equation:   y(n)=h a (n−d a )*x(n)+h b (n−d b )*x(n) +w(n), where a perceived channel delay spread is given by (τ′ b −d b )−(τ′ a −d a ) and controlled by introducing timing offsets at the first base station A.   
     
     
         21 . The method of  claim 19 , further comprising:
 determining a cyclic convolution based on an effective delay spread being less than a cyclic prefix as in the following equations:
     y ( n )= h   a ( n )   x   a ( n−d   a )+ h   b ( n )   x   b ( n−d   b )+ w ( n ), 
   or 
     y ( n )= h   a ( n−d   a )   x   a ( n )+ h   b ( n−d   b )   x   b ( n )+ w ( n ) 
   
       where   denotes circular convolution. 
     
     
         22 . The method of  claim 21 , further comprising:
 delaying transmissions from transmitters thereby meeting length requirements of cyclic prefix.   
     
     
         23 . The method of  claim 21  further comprising:
 employing a long cyclic prefix to enable an estimation of delay from weak transmitters that are far away. 
 
     
     
         24 . The method of  claim 23 , further comprising:
 undoing an effect of physical delays by a cyclic shift of a positioning signal, where x a,pp (n) is an intended positioning signal from the first base station A with timing delay d a , and a transmitter sends a cyclically shifted version given by x a,p (n+d a ).   
     
     
         25 . The method of  claim 24 , further comprising:
 processing the following equation:
     y ( n )= h   a ( n )   x   a,p ( n )+ h   b ( n )   x   b,p ( n )+ w ( n ). 
   
     
     
         26 . The method of  claim 15 , wherein timing information is available offline. 
     
     
         27 . The method of  claim 26 , further comprising:
 measuring pseudo ranges.   
     
     
         28 . The method of  claim 27 , further comprising:
 receiving, by each of the base stations, the pseudo ranges.