The Rate Adaptive Throughput Maximization in PAM-Modulated Overloaded System

The current high speed downlink packet access (HSDPA) system with the quadrature amplitude modulation (QAM) allocates equal data rates to multiple codes for link adaptation which causes large quantization loss in the total data rates. The 2 group allocation method proposed in significantly reduces the quantization loss by optimally adjusting the data rates over each channel for the QAM-modulated underloaded system. This paper applies this rate adaptive throughput maximization problem to the pulse amplitude modulated (PAM) overloaded systems. The proposed system uses complex Grass-mannian codes as the spreading sequences and a new complex conjugate concatenation technique for the receiver to further reduce the quantization loss. The numerical results show that the proposed PAM-modulated system employing the 2 group allocation scheme increases the total data rate approximately by 30 - 100% compared with the link adaptation method currently used in the HSDPA system.