Negative Acknowledgement of RACH in UMTS
15 June 2003
This paper investigates the performance of the UMTS frequency-division duplex (FDD) Random Access Channel (RACH). The 3GPP standards provide an option for the Node B to send a negative acknowledge (NACK) when a RACH preamble is detected. Typically, the Node B sends a NACK when it detects a RACH preamble but does not have sufficient resources to process the subsequent RACH message. The user equipment (UE) reaction when a NACK is received from the Node B is that it will stop sending preambles and will back-off for a certain time. The main objective of this paper is to investigate the effect on the RACH performance and the network when a Node B sends a NACK or not.