This paper demonstrates the advantages of using on-line arithmetic for traditional and advanced detection algorithms for communication systems. Detection is one of the core computationally-intensive physical layer operations in a communication receiver and determines the communication data rates. Detection algorithms typically involve hard decisions} (sign based testing) to find the sign of the transmitted information bit. This results in extraneous computations in a conventional number system as the sign is obtained only at the end due to the Least Significant Digit First (LSDF) nature of computations. On-line arithmetic, based on a signed digit number representation, provides Most Significant Digit First (MSDF) computation. Hence, the computations can stop after the first non-zero MSD (sign) is computed and additional computations for the successive digits can be avoided. Back-conversion to a conventional number system is not required as the sign of the digit represents the detected bit. A comparison of a radix-4 serial digit on-line multiuser detector with an 8-bit parallel conventional arithmetic multiuser detector shows a decrease in latency by 1.95X, a 3X increase in throughput, and possible savings in area.