In frequency-hopped (FH) code-division multiple-access (CDMA) systems, a number of users can transmit their packets simultaneously by using quasi-orthogonal FH patterns (codes). In applications where time is unslotted, the symbol-error probability is not the same for each symbol because the number of interfering users varies throughout the packet duration. Packet-error probability for such systems is evaluated by first enumerating all possible interference states and then averaging the packet-error probability associated with each of these states. The use of Reed-Solomon error-control coding is assumed. The computational task for this evaluation is enormous. Therefore, upper bounds and an alternate less-detailed approximate model are developed for easier computation. This approximate model generates results that are very close to those obtained using the authors' first model (1988) for the cases in which those results are computable. The conclusions of this study confirm the observation, originally made elsewhere, that the widely used threshold-based model for other-user interference is not an accurate one.>

In some multiuser radio systems the receiver is not allowed to transmit feedback information to the senders. In other applications, the transmitters cannot receive feedback information sent by the receiver. For these cases, a multiple-access protocol is needed that maintains satisfactory performance in the absence of feedback. Such a protocol is introduced and an exact analysis and performance evaluation of it is provided. The protocol, which uses an unconventional reservation mechanism, exploits the capability of interference rejection that code-division multiple access (CDMA) provides.>