This paper proposes an OFDM mobile radio packet system that employs a new protocol of automatic repeat request (ARQ) for nonlinear multiuser detection (MUD) with log likelihood ratio combining (LC) on the appropriate bits. The conventional metric combining (MC) MUD separates collided packets by using nonlinear MUD, accumulates the Euclidian distance metrics of the received subcarrier symbols in the packets, and then achieves throughput improvement. However, when MC-MUD detects a packet error, it makes user terminals retransmit the same packets so as to reproduce the collision of the same packets. The proposed LC-MUD scheme simplifies the ARQ protocol and requires no reproduction of the same packet collision. The computer simulations demonstrate the superior throughput of LC-MUD to that of MC-MUD, and further improvement due to adaptive modulation and coding (AMC) optimized for the nonlinear MUD in LC-MUD.

This paper proposes an OFDM mobile packet transmission scheme that increases throughput by using nonlinear multiuser detection (MUD) and automatic repeat request (ARQ) with metric-combining. The scheme identifies users by detecting user identification (ID) symbols located at the head of a packet, and can separate packets that have collided by using MUD. It also forces the respective transmitters to retransmit the same packets so as to reproduce the collision if the cyclic redundancy check (CRC) detects some errors, and it uses metric-combining to decrease the number of retransmissions. The results of computer simulations show that the proposed scheme can provide twice the throughput of the conventional schemes.

This paper proposes a new correction technique for a linear amplification with nonlinear components (LINC) transmitter. The technique, which is based on the minimum mean squared error (MMSE) criterion, estimates the gain and phase imbalance between the two amplifier branches. With information on the estimation, the imbalance is offset by controlling the amplitude and phase of the input signal that is fed into one of the two amplifiers. Computer simulations with a DS-CDMA system demonstrate that this method can compensate for the imbalance and sufficiently suppress the out-of-band distortion spectrum.