Method and apparatus for uplink synchronization in wireless communications

Abstract

A method and system for uplink (UL) synchronization of an uplink transmission from a plurality of wireless transmit/receive units (WTRUs) to a Node-B in a code division multiple access (CDMA) system. A Node-B receives a transmission including a UL synchronization (SYNC_UL) sequence from a WTRU. A sampler samples the transmission at a sampling rate which is higher than a chip rate. The samples are down-sampled and the SYNC_UL sequence is detected at a lower rate. A first significant path location of the detected SYNC_UL sequence is determined, and based on the first significant path location, a final significant path location is determined. The final significant path location is quantized and UpPCH POS is transmitted to the WTRU to adjust a UL transmission timing.

1 . A Node-B for synchronizing uplink (UL) transmission of a wireless transmit/receive unit (WTRU) in a code division multiple access (CDMA) wireless communication system, the Node-B comprising: 
 a receiver for receiving a transmission including a UL synchronization (SYNC_UL) sequence from a WTRU;    a sampler for generating samples of the transmission at a sampling rate;    a down-sampler for down-sampling the samples at a down-sampling rate;    a first processing unit for detecting a SYNC_UL sequence in the transmission by processing down-sampled samples at the down-sampling rate, and determining an initial first significant path location of the detected SYNC_UL sequence;    a second processing unit for determining a final first significant path location of the SYNC_UL sequence in the transmission at the sampling rate using the detected initial first significant path location; and    a transmitter for transmitting a UL synchronization adjustment message generated based on the final first significant path location to the WTRU to adjust a UL transmission timing of the WTRU.    
   
   
       2 . The Node-B of  claim 1  wherein the sampling rate is eight (8) times the chip rate of the WTRU transmission.  
   
   
       3 . The Node-B of  claim 1  wherein the down-sampling rate is equal to the chip rate of the WTRU transmission.  
   
   
       4 . The Node-B of  claim 1  wherein the sampling rate is inversely proportional to the resolution of the UL synchronization sequence that is defined by the standards by which the WTRU is operating.  
   
   
       5 . The Node-B of  claim 1  wherein detecting the presence of a SYNC_UL sequence comprises generating correlation results for each SYNC_UL sequence assigned to a Node-B.  
   
   
       6 . The Node-B of  claim 1  wherein a SYNC_UL sequence is detected when the average signal power of a SYNC_UL sequence exceeds a predetermined noise threshold.  
   
   
       7 . The Node-B of  claim 1  wherein the final first significant path location is determined with a resolution of one eighth of the chip rate of the WTRU transmission.  
   
   
       8 . The Node-B of  claim 1  wherein the first final significant path location is quantized for transmission.  
   
   
       9 . The Node-B of  claim 1  wherein the first final significant path location is quantized to the closest multiple of one eighth of the chip rate of the WTRU transmission.  
   
   
       10 . A code division multiple access (CDMA) wireless communication system wherein at least one Node-B synchronizes the uplink (UL) transmissions of at least one wireless transmit/receive unit (WTRU), the system comprising: 
 a. at least one WTRU comprising: 
 i. a transmitter for transmitting an uplink synchronization (SYNC_UL) sequence through an UL pilot channel (UpPCH);  
 ii. a receiver for receiving an UL synchronization adjustment message; and  
 iii. means for adjusting UL transmission timing in response to said UL synchronization adjustment message; and  
   b. at least one Node-B comprising: 
 i. a receiver for receiving a transmission including a SYNC_UL sequence from at least one of said WTRUs;  
 ii. a sampler for generating samples of the transmission at a sampling rate;  
 iii. a down-sampler for down-sampling the samples at a down-sampling rate;  
 iv. a first processing unit for detecting a SYNC_UL sequence in the transmission by processing down-sampled samples at the down-sampling rate, and determining an initial first significant path location of the detected SYNC_UL sequence;  
 v. a second processing unit for determining a final first significant path location of the SYNC_UL sequence in the transmission at the sampling rate using the detected initial first significant path location; and  
 vi. a transmitter for transmitting a UL synchronization adjustment message generated based on the final first significant path location to the at least one of said WTRUs to adjust a UL transmission timing of the at least one of said WTRUs.  
   
   
   
       11 . The system of  claim 10  wherein the sampling rate is eight (8) times the chip rate of the WTRU transmission.  
   
   
       12 . The system of  claim 10  wherein the down-sampling rate is equal to the chip rate of the WTRU transmission.  
   
   
       13 . The system of  claim 10  wherein the sampling rate is inversely proportional to the resolution of the UL synchronization sequence that is defined by the standards by which the WTRU is operating.  
   
   
       14 . The system of  claim 10  wherein detecting the presence of a SYNC_UL sequence comprises generating correlation results for each SYNC_UL sequence assigned to a Node-B.  
   
   
       15 . The system of  claim 10  wherein a SYNC_UL sequence is detected when the average signal power of a SYNC_UL sequence exceeds a predetermined noise threshold.  
   
   
       16 . The system of  claim 10  wherein the final first significant path location is determined with a resolution of one eighth of the chip rate of the WTRU transmission.  
   
   
       17 . The system of  claim 10  wherein the final first significant path location is quantized for transmission.  
   
   
       18 . The system of  claim 10  wherein the final first significant path location is quantized to the closest multiple of one eighth of the chip rate of the WTRU transmission.