The next generation cellular network, 5G, is expected to far exceed the current LTE network in many aspects including user density, latency, and network speed. Physical Random-Access Channel (PRACH) and Scheduled Request (SR) schemes are based on an Analog Bloom Filter for 5G networks. The User Equipment (UE) needs to inform the base station about its intention for initiating a connection or data transmission. In the LTE network, each base station has 64 orthogonal sequences, and a UE randomly picks a sequence to transmit on the PRACH channel. As the number of sequences is limited, the probability of collision, i.e., two UEs picked a same sequence, is high.
This procedure uses PRACH and SR, when the UE is in the disconnected mode or the connected mode, respectively. With PRACH, a UE can transmit multiple signals (sequences), to the base station, instead of only one sequence with the LTE systems. The advantage of this scheme is that the collision probability (probability that two UEs picked exactly the same signal to transmit) is dramatically reduced, because the number of different combinations of sequences (2048), is much more than the number of sequences (64) for an LTE base station. A new decoding algorithm copes with the unique challenges in the signal generated with ZC sequences, such as peak shifting and multiple peaks. The new scheme allows the UE to piggyback approximately three (3) bits of information along with the signal. Evaluation shows that the new scheme outperforms the existing PRACH of LTE by more than an order of magnitude making it a good candidate for 5G networks.
