Wireless communication system having adaptive threshold for timing deviation measurement and method

Abstract

Apparatus and method of wireless communication that determines received signal timing deviation which is used to generate a timing advance for adjusting wireless transmit receive unit (WTRU) transmissions. An adaptive threshold for measuring the timing deviation is set based on the energy level of received WTRU signals. WTRU signal samples which exceed the threshold are evaluated to determine timing deviation.

1 . A wireless transmit receive unit (WTRU) configured to determine signal timing deviation comprising:
 a receiver configured to receive wireless signals; and   processing circuitry configured to process signals received from another WTRU and to set a threshold for measuring timing deviation of the signals received from the other WTRU based on an energy level of the received signals;   said processing circuitry configured to compare signal samples which exceed the threshold to determine timing deviation; and   a transmitter configured to transmit to the other WTRU a signal to control the other WTRU's transmission timing based on the determined timing deviation.   
   
   
       2 . The WTRU according to  claim 1  wherein the receiver is configured to receive wireless signals from the other WTRU in bursts designated for specific timeslots of system time frames and the processing circuitry is configured to compute an energy level of at least a portion of a received burst to determine the energy level used to set the threshold. 
   
   
       3 . The WTRU according to  claim 2  wherein the receiver is configured to receive wireless signals from the other WTRU in bursts that include a midamble and the processing circuitry is configured to compute an energy level of the midamble of a received burst to determine the energy level used to set the threshold. 
   
   
       4 . The WTRU according to  claim 3  wherein the processing circuitry is configured to define a reception window based on a type of burst received and a timeslot designated for reception, to sample burst midambles received within the defined window, to perform channel estimation to determine midamble channel impulse responses, to compute the energy level of the midamble of a received burst based on a selected combination of the midamble channel impulse responses and to determine timing deviation based on a relationship of midamble channel impulse responses to the threshold. 
   
   
       5 . The WTRU according to  claim 4  further wherein the receiver is configured to receive wireless signals from the other WTRU in bursts that have a predefined chip rate and the processing circuitry is configured to sample burst midambles at twice the chip rate, to perform channel estimation on even and odd samples of received midambles to produce oversampled midamble channel impulse responses, to compute the energy level of the midamble of a received burst based on a summation of squares of non-noise oversampled midamble channel impulse responses and to determine timing deviation based on oversampled midamble channel impulse responses whose square exceeds the threshold. 
   
   
       6 . The WTRU according to  claim 4  wherein the receiver is configured to receive wireless signals from the other WTRU in bursts that have a predefined chip rate and a midamble sequence of one of K shifts of a predetermined sequence, a number k, which is ≦K, of bursts are received within the same designated timeslot, each having a different midamble shift, and the processing circuitry is configured to sample the k received burst midambles at twice the chip rate, to perform channel estimation using the Steiner algorithm on even and odd samples of received midambles to produce oversampled midamble channel impulse responses for each of the k received midambles, to compute the energy level of the midamble of at least one of the k received bursts based on a summation of squares of oversampled midamble channel impulse responses for that burst and to determine timing deviation based on the oversampled midamble channel impulse responses for that burst whose squares exceeds the threshold. 
   
   
       7 . The WTRU according to  claim 6  wherein the processing circuitry is configured to use the determined timing deviation to generate a timing advance signal and the transmitter is configured to transmit the generated timing advance signal to the other WTRU. 
   
   
       8 . The WTRU according to  claim 7  wherein the processing circuitry is embodied in a Radio Network Controller (RNC) and the receiver and transmitter are embodied in a Node b. 
   
   
       9 . The WTRU according to  claim 1  configured as a UMTS Terrestrial Radio Access Network (UTRAN) of a Third Generation Partnership Project type system that communicates with other WTRUs configured as User Equipments (UEs) wherein:
 the receiver is configured to receive wireless signals from UEs in bursts that include a midamble;   the processing circuitry is configured to compute the energy level of the midamble of bursts received from respective UEs to determine the energy level used to set respective thresholds for measuring timing deviation of signals received from the respective UEs based on respective energy levels of the received signals;   the processing circuitry is configured to compare respective signal samples which exceed the respective threshold to determine timing deviation for the respective UEs; and   the transmitter is configured to transmit to the respective UEs a signal to control transmission timing based on the respective determined timing deviation.   
   
   
       10 . The UTRAN according to  claim 9  wherein said processing circuitry is configured to define respective reception windows based on a type of burst received and a timeslot designated for reception, to sample burst midambles received within the defined windows, to perform channel estimation to determine midamble channel impulse responses, to compute energy levels of the midambles of received bursts based on a selected combination of midamble channel impulse responses and to determine respective timing deviation based a relationship of midamble channel impulse responses to the respective threshold. 
   
   
       11 . The UTRAN according to  claim 10  wherein the receiver is configured to receive wireless signals from the respective UEs in bursts that bursts have a predefined chip rate and the processing circuitry is configured to sample respective burst midambles at twice the chip rate, to perform channel estimation on even and odd samples of respective received midambles to produce respective oversampled midamble channel impulse responses, to compute respective energy levels of the midamble of received bursts based on a summation of the squares of respective non-noise oversampled midamble channel impulse responses and to determine respective timing deviation based on respective oversampled midamble channel impulse responses whose square exceeds the respective threshold. 
   
   
       12 . The UTRAN according to  claim 11  wherein said processing circuitry is configured to set the respective thresholds at a value equal to the respective computed energy level multiplied by a constant. 
   
   
       13 . The UTRAN according to  claim 12  wherein said processing circuitry is embodied in a Radio Network Controller (RNC) and the receiver and transmitter are embodied in a Node B. 
   
   
       14 . A method of wireless communication to determine signal timing deviation and to facilitate signal timing adjustment comprising:
 receiving a wireless signal from a wireless transmit receive unit (WTRU);   setting a threshold for measuring the timing deviation based on an energy level of signal received from the WTRU;   evaluating signal samples which exceed the threshold to determine timing deviation; and   transmitting to the WTRU a signal to control transmission timing of the WTRU based on the determined timing deviation.   
   
   
       15 . The method according to  claim 14  wherein the receiving of wireless signals from the WTRU includes receiving signals in bursts designated for specific timeslots of system time frames and the setting a threshold includes computing an energy level of at least a portion of a received burst to determine the energy level used to set the threshold. 
   
   
       16 . The method according to  claim 15  wherein the receiving of wireless signals from the WTRU includes receiving signals in bursts that include a midamble and an energy level of the midamble of a received burst is computed to determine the energy level used to set the threshold. 
   
   
       17 . The method according to  claim 16  further comprising defining a reception window based on type of burst received and a timeslot designated for reception, sampling burst midambles received within the defined window and performing channel estimation to determine midamble channel impulse responses wherein the energy level of the midamble of a received burst is computed based on a selected combination of elements of the midamble channel impulse responses and the timing deviation is determined based on a relationship of midamble channel impulse responses to the threshold. 
   
   
       18 . The method according to  claim 17  wherein the receiving of wireless signals from the WTRU includes receiving signals in bursts that have a predefined chip rate, the sampling of burst midambles is at twice the chip rate, the channel estimation is performed on even and odd samples of received midambles to produce oversampled midamble channel impulse responses, the energy level of the midamble of a received UE burst is computed based on a summation of squares of non-noise oversampled midamble channel impulse response elements and the timing deviation is determined based on oversampled midamble channel impulse responses whose square exceeds the threshold. 
   
   
       18 . The method according to  claim 16  wherein the receiving of wireless signals from the WTRU includes receiving signals in bursts that have a predefined chip rate and a midamble sequence of one of K shifts of a predetermined sequence, a number k, which is ≦K, of bursts are received within the same designated timeslot, each having a different midamble shift, the sampling of the k received burst midambles is at twice the chip rate, the channel estimation is performed using the Steiner algorithm on even and odd samples of received midambles to produce oversampled midamble channel impulse responses for each of the k received midambles, the energy level of the midamble of at least one of the k received bursts is computed based on a summation of squares of non-noise oversampled midamble channel impulse responses for that burst and the timing deviation is determined based on the oversampled midamble channel impulse responses for that burst whose squares exceeds the threshold. 
   
   
       19 . The method according to  claim 18  further comprising using the determined timing deviation to generate a timing advance signal and transmitting the generated timing advance signal to the WTRU. 
   
   
       20 . A method of wireless communication to determine signal timing deviation and to facilitate signal timing adjustment comprising:
 receiving a wireless signal from a plurality of wireless transmit receive unit (WTRUs);   setting respective thresholds for measuring timing deviation based on respective energy levels of signals received from the respective WTRUs;   evaluating respective signal samples which exceed the respective thresholds to determine respective timing deviations; and   transmitting to the respective WTRUs respective signals to control transmission timing of the respective WTRUs based on the respective determined timing deviation.