Method and apparatus for accessing an uplink random access channel in a single carrier frequency division multiple access system

Abstract

A method and apparatus for accessing a contention-based uplink random access channel (RACH) in a single carrier frequency division multiple access (SC-FDMA) system are disclosed. A wireless transmit/receive unit (WTRU) randomly selects a RACH subchannel and a signature among a plurality of available RACH subchannels and signatures. The WTRU transmits a preamble using the selected signature via the selected RACH subchannel at a predetermined or computed transmission power. A base station monitors the RACH to detect the preamble and sends an acquisition indicator (AI) to the WTRU when a signature is detected on the RACH. When receiving a positive acknowledgement, the WTRU sends a message part to the base station. If receiving a negative acknowledgement or no response, the WTRU retransmits the preamble.

1 . In a single carrier frequency division multiple access (SC-FDMA) wireless communication system including a wireless transmit/receive unit (WTRU) and a base station, a method for accessing a contention-based uplink random access channel (RACH), the method comprising: 
 the WTRU randomly selecting a RACH subchannel among a plurality of available RACH subchannels;    the WTRU randomly selecting a signature among a plurality of available signatures; and    the WTRU transmitting a preamble using the selected signature via the selected RACH subchannel at a transmission power level that is sufficient to guarantee successful decoding of the preamble by the base station.    
   
   
       2 . The method of  claim 1  further comprising: 
 the WTRU selecting an access service class (ASC) among a plurality of available ASCs, the available signatures and the available RACH subchannels being given for each of the ASCs, whereby the WTRU selects the RACH subchannel and the signatures based on the selected ASC.    
   
   
       3 . The method of  claim 1  wherein the WTRU initializes a retransmission counter at an initial transmission of the preamble, increments the retransmission counter by one each time the WTRU retransmits the preamble, and transmits the preamble only if the retransmission counter does not exceed a retransmission limit.  
   
   
       4 . The method of  claim 1  further comprising: 
 the WTRU performing a persistence check before transmission of the preamble, whereby the WTRU transmits the preamble only if the transmission of the preamble is allowed based on the persistence check.    
   
   
       5 . The method of  claim 4  further comprising: 
 the WTRU waiting for a next random access interval if the transmission of the preamble is not allowed based on the persistence check.    
   
   
       6 . The method of  claim 1  further comprising: 
 the base station monitoring the RACH subchannels to detect the preamble;    the base station sending an acquisition indicator (AI) to the WTRU on an acquisition indicator channel (AICH) when a signature is detected on the RACH, the AI being one of a positive acknowledgement (ACK) and a negative acknowledgement (NACK);    the WTRU monitoring an AICH to detect an AI; and    if an ACK is detected, the WTRU sending a message part to the base station.    
   
   
       7 . The method of  claim 6  wherein the AICH is multiplexed with downlink shared control channel.  
   
   
       8 . The method of  claim 6  further comprising: 
 the base station determining whether there is a preamble transmitted by another WTRU on the selected RACH subchannel; and    the base station sending an ACK if there is no preamble transmitted by another WTRU on the selected RACH subchannel.    
   
   
       9 . The method of  claim 8  further comprising: 
 the base station computing a power adjustment based on a received power level of the preamble; and    the base station sending the power adjustment to the WTRU along with the AI, whereby the WTRU adjusts transmit power level of the message part based on the power adjustment.    
   
   
       10 . The method of  claim 8  further comprising: 
 the base station computing a timing and frequency correction based on the preamble; and    the base station sending the timing and frequency correction to the WTRU along with the AI, whereby the WTRU adjusts timing and frequency based on the timing and frequency correction.    
   
   
       11 . The method of  claim 8  further comprising: 
 if there is at least one preamble transmitted by another WTRU on the selected RACH subchannel, the base station determining whether a signature used in the preamble transmitted by another WTRU is the same to the selected signature; and    if so, the base station sending a NACK to the WTRUs.    
   
   
       12 . The method of  claim 11  further comprising: 
 if the signature used by another WTRU is different from the selected signature, the base station sending an ACK to a WTRU whose signal-to-noise ratio (SNR) meets a required SNR and sending nothing to a WTRU whose SNR does not meet the required SNR.    
   
   
       13 . The method of  claim 12  further comprising: 
 the base station computing a power adjustment based on a received power level of the preamble of the WTRU whose SNR meets the required SNR; and    the base station sending the power adjustment to the WTRU, whereby the WTRU adjusts transmit power level of the message part based on the power adjustment.    
   
   
       14 . The method of  claim 13  wherein the power adjustment is implicitly carried in resource allocation information in a response to the preamble.  
   
   
       15 . The method of  claim 12  further comprising: 
 the base station computing a timing and frequency correction based on the preamble of the WTRU whose SNR meets the required SNR; and    the base station sending the timing and frequency correction to the WTRU along with the AI, whereby the WTRU adjusts timing and frequency based on the timing and frequency correction.    
   
   
       16 . The method of  claim 6  further comprising: 
 if no AI is detected, the WTRU waiting until a next available random access interval to retransmit the preamble.    
   
   
       17 . The method of  claim 6  further comprising: 
 if a NACK is detected, the WTRU setting a backoff timer to retransmit the preamble upon expiration of the backoff timer, wherein a transmit power for retransmission of the preamble is not increased.    
   
   
       18 . The method of  claim 17  wherein the backoff timer is set to an integer multiple of 10 ms, which is randomly selected between minimum and maximum backoff periods.  
   
   
       19 . The method of  claim 18  wherein the minimum and maximum backoff periods are set equal.  
   
   
       20 . The method of  claim 18  wherein the minimum and maximum backoff periods are set to zero.  
   
   
       21 . The method of  claim 1  wherein the RACH subchannels are defined by at least one subcarrier over at least one time slot.  
   
   
       22 . The method of  claim 1  wherein the RACH subchannels are defined by at least one subcarrier block including a plurality of subcarriers over at least one time slot.  
   
   
       23 . The method of  claim 22  wherein the subcarrier block is one of a distributed subcarrier block and a localized subcarrier block.  
   
   
       24 . The method of  claim 1  wherein the RACH subchannels are defined by at least one subcarrier over at least one time slot with at least one spreading code.  
   
   
       25 . The method of  claim 1  wherein the transmission power level of the preamble is predetermined.  
   
   
       26 . The method of  claim 1  wherein the transmission power level of the preamble is computed by the WTRU.  
   
   
       27 . In a single carrier frequency division multiple access (SC-FDMA) wireless communication system including a wireless transmit/receive unit (WTRU) and a base station, a WTRU for accessing a contention-based uplink random access channel (RACH), the WTRU comprising: 
 a RACH processor configured to randomly select a RACH subchannel among a plurality of available RACH subchannels and a signature among a plurality of available signatures; and    a transmitter configured to transmit a preamble using the selected signature via the selected RACH subchannel at a transmission power level that is sufficient to guarantee successful decoding of the preamble by the base station.    
   
   
       28 . The WTRU of  claim 27  wherein the RACH processor is configured to select an access service class (ASC) among a plurality of available ASCs, the available signatures and the available RACH subchannels being given for each of the ASCs, whereby the RACH processor selects the RACH subchannel and the signatures based on the selected ASC.  
   
   
       29 . The WTRU of  claim 27  further comprises: 
 a retransmission counter for tracking the number of retransmissions of the preamble, whereby the transmitter transmits the preamble only if the retransmission counter does not exceed a retransmission limit.    
   
   
       30 . The WTRU of  claim 27  wherein the RACH processor is configured to perform a persistence check before transmission of the preamble, whereby the transmitter transmits the preamble only if the transmission of the preamble is allowed based on the persistence check.  
   
   
       31 . The WTRU of  claim 30  wherein the RACH processor waits for a next random access interval if the transmission of the preamble is not allowed based on the persistence check.  
   
   
       32 . The WTRU of  claim 27  wherein the RACH processor monitors an acquisition indicator channel (AICH) to detect an acquisition indicator (AI) and sends a message part to the base station if a positive acknowledgement (ACK) is detected.  
   
   
       33 . The WTRU of  claim 32  wherein the AICH is multiplexed with downlink shared control channel.  
   
   
       34 . The WTRU of  claim 32  wherein if no AI is detected, the RACH processor waits until a next available RACH to retransmit the preamble.  
   
   
       35 . The WTRU of  claim 32  further comprises a backoff timer, whereby if a NACK is detected, the RACH processor sets the backoff timer to retransmit the preamble upon expiration of the backoff timer, wherein a transmit power for retransmission of the preamble is not increased.  
   
   
       36 . The WTRU of  claim 35  wherein the backoff timer is set to an integer multiple of 10 ms, which is randomly selected between minimum and maximum backoff periods.  
   
   
       37 . The WTRU of  claim 36  wherein the minimum and maximum backoff periods are set equal.  
   
   
       38 . The WTRU of  claim 36  wherein the minimum and maximum backoff periods are set to zero.  
   
   
       39 . The WTRU of  claim 27  wherein the RACH subchannels are defined by at least one subcarrier over at least one time slot.  
   
   
       40 . The WTRU of  claim 27  wherein the RACH subchannels are defined by at least one subcarrier block including a plurality of subcarriers over at least one time slot.  
   
   
       41 . The WTRU of  claim 40  wherein the subcarrier block is one of a distributed subcarrier block and a localized subcarrier block.  
   
   
       42 . The WTRU of  claim 27  wherein the RACH subchannels are defined by at least one subcarrier over at least one time slot with at least one spreading code.  
   
   
       43 . The WTRU of  claim 27  wherein the transmission power level of the preamble is predetermined.  
   
   
       44 . The WTRU of  claim 27  wherein the transmission power level of the preamble is computed by the WTRU.  
   
   
       45 . In a single carrier frequency division multiple access (SC-FDMA) wireless communication system including a wireless transmit/receive unit (WTRU) and a base station, a base station for processing contention-based uplink random access channel (RACH) transmissions, the base station comprising: 
 a preamble detector configured to detect a preamble transmitted by a WTRU on a RACH; and    an acquisition indicator channel (AICH) processor configured to send an acquisition indicator (AI) via an AICH to the WTRU when a preamble is detected on the RACH, the AI being one of a positive acknowledgement (ACK) and a negative acknowledgement (NACK).    
   
   
       46 . The base station of  claim 45  wherein the preamble detector determines whether there is a preamble transmitted by another WTRU on the selected RACH subchannel and the AICH processor sends an ACK if there is no preamble transmitted by another WTRU on the selected RACH subchannel.  
   
   
       47 . The base station of  claim 46  further comprising: 
 a transmit power controller configured to compute a power adjustment based on a received power level of the preamble, wherein the AICH processor sends the power adjustment to the WTRU and the WTRU adjusts transmit power level of the message part based on the power adjustment.    
   
   
       48 . The base station of  claim 47  wherein the power adjustment is implicitly carried in resource allocation information in a response to the preamble.  
   
   
       49 . The base station of  claim 46  further comprising: 
 a timing and frequency controller configured to compute a timing and frequency correction based on the preamble, wherein the AICH processor sends the timing and frequency correction to the WTRU along with the AI, and the WTRU adjusts timing and frequency based on the timing and frequency correction.    
   
   
       50 . The base station of  claim 46  wherein if there is at least one preamble transmitted by another WTRU on the selected RACH subchannel, the preamble detector is configured to determine whether a signature used in the preamble transmitted by another WTRU is same to the selected signature and if so, the AICH processor sends a NACK to the WTRUs.  
   
   
       51 . The base station of  claim 50  wherein if the signature used by another WTRU is different from the selected signature, the AICH processor sends an ACK to a WTRU whose signal-to-noise ratio (SNR) meets a required SNR and sending nothing to a WTRU whose SNR does not meet the required SNR.  
   
   
       52 . The base station of  claim 51  further comprising: 
 a transmit power controller configured to compute a power adjustment based on a received power level of the preamble of the WTRU whose SNR meets the required SNR, wherein the AICH processor sends the power adjustment to the WTRU along with the AI, and the WTRU adjusts transmit power level of the message part based on the power adjustment.    
   
   
       53 . The base station of  claim 51  further comprising: 
 a timing and frequency controller configured to compute a timing and frequency correction based on the preamble of the WTRU whose SNR meets the required SNR, wherein the AICH processor sends the timing and frequency correction to the WTRU along with the AI, and the WTRU adjusts timing and frequency based on the timing and frequency correction.    
   
   
       54 . The base station of  claim 45  wherein the AICH is multiplexed with downlink shared control channel.