Simulation of Third Generation CDMA Systems - Virginia Tech

IT+ τT + τi i i I iτ iτ iiiz = h( t-τ ) d ( t- τ ) dt + Re{ I ( t)} C ( t-τ) dtIIT + τi I ii+ Re{ n ( t)} C ( t-τ) dtτii I i(3.22)Here T is the symbol period. If we assume that the magnitude response of the channelremains constant for the symbol interval, we getI IT + τT + τi i i I iτ iτ iiiz = Th K+ Re{ I ( t)} C ( t- τ ) dt+ Re{ n ( t)} C ( t-τ) dti I i(3.23)Here K can be either 1 or –1 depending on the transmitted symbol. The second termin equation (3.22) is ISI. Because of the processing gain, the ISI is pretty small compared thefirst tem of the equation (3.22). The third term here is the noise term.The above analysis can be extended to take the presence of MAI into account.Equation (3.22) will be modified as a fourth term corresponding to MAI will be added.3.3 Downlink SimulatorAt the downlink, the mobile station receiver receives the signal transmitted by thebase station transmitter. The MS receives the desired signal along with signals transmitted bythe base station for other mobile stations at the system. The block diagram of the downlinksimulator is shown in Figure 3.17.The downlink simulator differs from the uplink simulator in the generation of MAI.The frame structure and the spreading and modulation are a also modified from the up link.47