Rearch On Constellation Rotation Of Two-user Gaussian Channels

Gaussian Multiple Access Channel (GMAC) and Gaussian Interference Channel (GIC)are widely used in wireless communications. The maximum sum rates of GMAC andGIC are achieved by continuous and Gaussian distributed inputs of the channels. Inpractice, this continuous and unbounded Gaussian code-book is not suited. Transmittersin practical communication systems are based on constellations with finite size. Withthe fast speed development of wireless communication, the demand of channel capacityand transmission rate has been increased. Thus, how to enlarge capacity region ofconstellation based multi-user channel has become a hot research topic in recent years.This thesis focuses on discussing the influence of constellation rotation on capacityregion of constellation based2-GMAC and2-GIC.We analyse how rotation of constellation points could enlarge sum rates of2-GMAC with M-PSK and M-QAM. Optimal angles of rotation which maximize sumrates are calculated. We extend the idea of rotating all constellation points with the sameangle to two-angle rotation for M-QAM when M is more than4. We assume that thisrotation method could introduce more relative distance between two constellation setsthan one-angle rotation so that the capacity regions could be enlarged further more.For2-GIC and2-Z-GIC with strong interference, interference coefficient ofchannel would affect sum rate and capacity region of channel. One-angle rotation cannot only enlarge sum rate but also eliminate the influence of the phase of interferencecoefficient on sum rate. However, two-angle rotation is more significant than one-anglerotation in2-GIC and2-Z-GIC when angle of interference coefficient is the same asoptimum angle of one-angle rotation. In this case, there is no enlargement of sum ratewith one-angle rotation. However, two-angle rotation does not be affected by this factor.For2-GIC with weak interference, only sum rate can be calculated not thecomplete capacity region. One-angle and two-angle rotation could enlarge the sum rate.Moreover, this thesis proposes a constellation design to obtain optimum constellationpoints in2-GIC with weak interference, which can achieve largest sum rate with samechannel coefficients other than traditional M-QAM.