In this paper, a multiple-input-multiple-output (MIMO) extension for a third-generation (3G) wireless system is described. The integration of MIMO concepts within the existing UMTS standard and the associated space-time RAKE receiver are explained. An analysis is followed by a description of an actual experimental MIMO transmitter and receiver architecture, both realized on digital signal processors (DSPs) and FPGAs within a precommercial OneBTS base station. It uses four transmit and four receive antennas to achieve downlink data rates up to 1 Mb/s per user with a spreading factor of 32 and the UMTS chip rate of 3.84 MHz. Furthermore, different MIMO detectors are evaluated, comparing their performance and complexity. System performance is evaluated through simulations and indoor over-the-air measurements. Capacity and bit-error rate measurement results are presented.

Federal Communications Commission (FCC) mandates locating wireless phones that are in an emergency 911 call and many technologies were proposed and developed to meet that requirement. We review these techniques here because geolocation will have an even greater future role as a basis for value-added services and applications that integrate positioning and wireless multimedia. We explore in more detail one of the geolocation technologies, Assisted GPS, which has exceptional accuracy and cost-effectiveness. We also show how the SAMPS (System Assisted Mobile Positioning through Satellite) geolocation standard for TDMA wireless networks, based on assisted GPS, enables positioning-based services and enhances the performance of GPS receivers built into wireless handsets.

Packet error probability is the key parameter in evaluating the performance of ARQ schemes, in terms of waiting time to receive a data packet, and system throughput. The authors present an analysis of the packet error probability for two modulation schemes, BFSK and BPSK, when uncoded packets are transmitted over the meteor burst channel using a fixed data rate. They show that the optimum transmission rate, minimizing the waiting time to receive a packet correctly, is independent of the initial SNR of the trail and the modulation used. The results were derived analytically, and are in excellent agreement with exact numerical calculations. They also present simple approximations to the exact calculations, and lower bounds on the packet error rate which are tight in the neighborhood of the optimum transmission rate.>