This paper discusses two approaches of reliability-based HARQ, adapting the packet size of a retransmission in a 3GPP Long Term Evolution (LTE) system. We focus on the adaptation of the retransmission size in terms of physical resources by using information 1) of the channel, namely the signal-to-noise ratio (SNR) or 2) reliability information from the decoder output, taking the overall transmission into account. Both approaches will be compared to the HARQ system used
in LTE in terms of throughput performance. Link level simulations will be performed with single bit feedback and 2 bit multilevel ACK/NAK. This work takes realistic impairments such as channel estimation, signal-to-noise ratio (SNR) estimation and implementation of a Turbo en- and decoder into regard.