| This dissertation primarily examines the performance of adaptive multielement-antenna decision feedback equalization (DFE) receiver structures for a narrowband, two-user space division multiple access (SDMA) system with a TDMA slot structure similar to that of DAMPS (Digital Advanced Mobile Phone Service). It is shown that performance lost in terms of degrees of diversity due to the addition of another, synchronous user, may be regained through the use of cross feedback (or coupling) between receiver sections for each user. It is verified that given a sufficient span of symbol decisions from another co-channel user, that there is the potential to remove the other user's interfering influence completely, and attain the performance of the same user operating in the system alone. These points are shown through simulation of the adaptive cross-feedback (XFB) receiver in the time-invariant channel, using correct decisions, and an extended training period. Mathematically, the complete removal and attaining of single user performance is shown in the appendix. Performance analysis of a single user DFE receiver is presented for purposes of comparison.;With the addition of actual decisions, as opposed to true (correct) decisions, the effect of errors from the user of interest (in conventional decision feedback) and the other user (in the cross feedback) is shown. Through this the importance of full-coupling, and the importance of proper ordering of the receiver according to each user's received power is demonstrated. It is observed that the full-coupling receiver structure is best used in situations where the received powers of the users are close, and that the half-coupled receiver structure is best used in situations where the received powers of the users are disparate. Ultimately, a slot-to-slot adaptively structured receiver is created which chooses full-coupled receiver structure or half-coupled receiver structure based on the ratio of the received powers. If the absolute value of this ratio taken in dB's is below a certain threshold, then the full-coupled receiver structure is chosen. If this ratio is above that threshold, then the half-coupled receiver structure is chosen. Once the structure is chosen, the processing of the users' received signals is ordered according to their received powers.;Lastly, the feasibility of receiving simultaneous transmissions from two users transmitting in the DAMPS format, using an adaptive receiver structure which utilizes the existing training sequence is demonstrated. At pedestrian transmitter speeds with a 900 MHz carrier frequency, this reception can be done with only two antennas. However, at vehicular transmitter speeds, the reception becomes more difficult, requiring the addition of two additional diversity antennas, which may be horizontally polarized for reasons of practicality. Under the worst case conditions of rapid fading and next tier interference, it is observed that the capacity of the uplink can be doubled 86% of the time. |
