Bit-error rate performance of a two-user CDMA receiver with fixed point arithmetic

Fixed point arithmetic (FIPA) effects on the bit-error rate (BER) of a joint demodulation scheme for the uplink of a mobile radio system with direct sequence code-division multiple access are investigated. Results from Monte-Carlo simulations indicate that the robustness of the scheme against multiple-access interference being achieved for floating-point arithmetic operation can be preserved for FIPA at the expense of an increased BER for low interference levels. For a given word length in the FIPA operation, a threshold effect in the BER is observed if overflow is not suppressed. The threshold depends on the relative interference level and the adopted overflow handling. In moderate near-far scenarios, the performance can be improved by reducing the total dynamic range and increasing the accuracy of the decision variable of the weak signal