Abstract: A CDMA wireless communication system for communicating with wireless terminals. The system comprises a channel estimator for determining characteristics of the wireless channels of the wireless terminals. The channel characteristics are used by a code optimizer to assign spreading codes to the wireless terminals. In one embodiment, the code optimizer utilizes an iterative code optimization algorithm and maintains a processing set of wireless terminals. The code optimizer chooses target wireless terminals and performs a random code search in order to find an improved code for the target wireless terminal. The improved code found in the random code search is further improved by performing a gradient search of codes in the signal space in the vicinity of the improved code and by performing a gradient search of transmission delays. The improved codes are transmitted to the wireless terminals for use in reverse link communication.

Abstract: Wireless communications for frequency-selective fading channels is realized by employing a system including orthogonal frequency division multiplexing (OFDM) in combination with an at least two antenna transmit diversity arrangement. Specifically, OFDM converts a multipath channel into a plurality of narrowband subchannels each having flat fading. Then, the signals on the same frequency subchannels of the at least two antennas are grouped together. Considering a first frequency subchannel, during a first OFDM time interval, a first signal and a second signal are transmitted on the first frequency subchannel from a first antenna (0) and from a second antenna (1), respectively. During a second OFDM time interval, a reverse sign (?) complex conjugate of the second signal and a complex conjugate of the first signal are transmitted from the first antenna and the second antenna, respectively.

Abstract: We describe a method for CDMA transmission of sets of data symbols to users that are organized into one or more user groups. Each user group is paired with a group of spreading codes, referred to as a “code group.” Each set of data symbols that are destined for respective users of a given user group is transmitted in the form of two or more distinct signal sequences. Each such signal sequence is transmitted from a respective one of two or more transmitting antennas. Each signal sequence is a linear combination of spreading code sequences belonging to the corresponding code group. Within each of these linear combinations, each spreading code sequence that appears has a scalar coefficient. Each of these scalar coefficients is a linear combination of pertinent data symbols (i.e., data symbols destined for users in the given user group) or of complex conjugates of pertinent data symbols.

Abstract: Linear space-time multiuser detectors are described that combine array processing, rake detection, and multiuser detection and that satisfy a minimum mean-squared error criteria. Both embodiments can be implemented adaptively so as to account for unknown sources of interference. The adaptive implementation of the first embodiment of a linear space-time detector requires explicit estimates of the channel coefficients. On the other hand, the adaptive implementation of the second embodiment does not require these estimates since they can be adaptively obtained. Both of these detectors provide significant performance advantages over single-user space-time detectors and over multiuser detectors which do not account for CDMA interference from unknown sources.