Broadband Indoor Wireless System with In-Cell Frequency Reuse Based on Sectored Antennas

Abstract

This paper investigates a new multiple access system for broadband indoor wireless communications based on sectored antennas. Unlike previous sectored antenna indoor systems, this system incorporates the capability of reusing spectrum in different antenna sectors of the base station. It is shown that portable terminals located in different sectors of the indoor microcell may transmit/receive simultaneous data packets on the same frequency if their mutual interference is below a threshold level (or capture threshold) that guarantees an acceptable packet error rate. However, this requires careful scheduling of packet transmissions in order to avoid transmitting packets that would jam each other during the same time slot. When trying to transmit more than two packets per time slot, the optimum scheduling problem, the one that maximizes the number of packets transmitted per frame, is in the NP-complete class of problems, so it can not be solved in real time. Therefore, a sub-optimum algorithm named First Fit Algorighm is proposed for the frame scheduling problem. The problem is investigated experimentally for a sectorization level of ten (using ten antenna sectors in the base station). A statistical model of multipath propagation is used to extend the results to other levels of sectorization. The proposed system can significantly increase capacity when compared with systems that can transmit a single data packet per time slot. For example, while previous systems can transmit only one packet at a time, the proposed system can transmit on average close to three packets per time slot when operating with a capture threshold of 10 dB and ten antenna sectors in a closed indoor location with internal walls of concrete blocks.