Near/Far Resistant Receivers for DS/SSMA Communications
Abstract
In Code-Division Multiple-Access (CDMA), each transmitter is assigned a fixed, distinct signature waveform which he uses to modulate his message in the same fashion as in single-user communication. Then the information sent by each user can be demodulated by correlating the received signal with each of the signature waveforms. This demodulator, whose use is widespread in practice, is referred to as the conventional single-user detector. As is well-known, when the channel output is corrupted by additive white Gaussian noise, the conventional single-user detector minimizes the probability of error in a single-user channel, i.e., in the absence of interfering users. The fact that this is no longer true in the multiple-access channel is the raison d'etre of the area of multiuser detection. The performance of the conventional single-user detector is acceptable provided that the energies of the received signals are not too dissimilar and that the signature waveforms are designed so that their crosscorrelations are low enough (this depends on the desired maximum number of simultaneous users). In practice, low crosscorrelations are usually achieved employing Spread-Spectrum Pseudonoise sequences of long periodicity. If the received signal energies are indeed dissimilar, i.e., some users are very weak in comparison to others, then the conventional single-user detector is unable to recover the messages of the weak users reliably, even if the signature waveforms have very low crosscorrelations.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 27, 1990
- Accession Number
- ADA228147
Entities
People
- Sergio Verdú
Organizations
- Princeton University