A multistage multiuser detector (MMD) is presented for frequency-hopping/code-division multiple access (FH/CDMA.) The MMD reduces the bit-error rate (BER) over the conventional detector by exploiting prior knowledge of the addresses and energies of the user signals. This detector is a conservative multiuser detector which is robust to unknown users and has a complexity that is only linear in the number of users. The performance analysis of the synchronous MMD includes both theoretical and simulation BERs for the noiseless case as well as simulation results that include the presence of noise. The MMD is then extended to the fully asynchronous case which makes this work the first to propose an FH/CDMA multiuser detector for asynchronous communications. This asynchronous MMD is compared via simulation to the conventional detector.

We present three detector/estimators (DEs) which allow multiuser detection and parameter estimation without a side channel in a dynamic asynchronous code-division multiple-access (CDMA) system in which users are entering and leaving the system. These DEs optimally detect a new user given only the chip rate and the spreading factor of the new user. Two of these DEs, the maximum-likelihood detector/estimator (MLDE) and the generalized maximum-likelihood detector/estimator (GMLDE), produce maximum-likelihood estimates of the new user's signature sequence, delay, and amplitude, which are then incorporated into a multiuser detector. The third DE, the cyclic detector/estimator (CDE), is the most computationally efficient of the three processors. This DE detects the new user by testing for cyclostationarity and then uses suboptimal schemes to estimate the new user's signature sequence, delay, and amplitude. Simulations indicate that all three DEs reliably detect a new user for an E/sub s///spl sigma//sup 2/ (symbol-energy-to-noise ratio) of 5 dB. The MLDE and GMLDE produce signature sequence and delay estimates with probability of error less than 0.07 for an E/sub s///spl sigma//sup 2/ of 10 dB, and the CDE produces signature sequence and delay estimates with probability of error less than 0.13 for an E/sub s///spl sigma//sup 2/ of 15 dB.

The problem of binary hypothesis testing is revisited in the context of distributed detection with feedback. Two basic distributed structures with decision feedback are considered. The first structure is the fusion center network, with decision feedback connections from the fusion center element to each one of the subordinate decisionmakers. The second structure consists of a set of detectors that are fully interconnected via decision feedback. Both structures are optimized in the Neyman-Pearson sense by optimizing each decision-maker individually. Then, the time evolution of the power of the tests is derived. Definite conclusions regarding the gain induced by the feedback process and direct comparisons between the two structures and the optimal centralized scheme are obtained through asymptotic studies (that is, assuming the presence of asymptotically many local detectors). The behavior of these structures is also examined in the presence of variations in the statistical description of the hypotheses. Specific robust designs are proposed and the benefits from robust operations are established. Numerical results provide additional support to the theoretical arguments.>