Abstract
This paper studies time division duplex- (TDD-) specific interference issues in orthogonal frequency division multiple access- (OFDMA-) TDD cellular networks arising from various uplink (UL)/downlink (DL) traffic asymmetries, considering both line-of-sight (LOS) and non-LOS (NLOS) conditions among base stations (BSs). The study explores aspects both of channel allocation and user scheduling. In particular, a comparison is drawn between the fixed slot allocation (FSA) technique and a dynamic channel allocation (DCA) technique for different UL/DL loads. For the latter, random time slot opposing (RTSO) is assumed due to its simplicity and its low signaling overhead. Both channel allocation techniques do not obviate the need for user scheduling algorithms, therefore, a greedy and a fair scheduling approach are applied to both the RTSO and the FSA. The systems are evaluated based on spectral efficiency, subcarrier utilization, and user outage. The results show that RTSO networks with DL-favored traffic asymmetries outperform FSA networks for all considered metrics and are robust to LOS between BSs. In addition, it is demonstrated that the greedy scheduling algorithm only offers a marginal increase in spectral efficiency as compared to the fair scheduling algorithm, while the latter exhibits up to 20% lower outage.
Highlights
In the recent years, orthogonal frequency division multiplexing (OFDM) has been a subject of considerable interest for cellular systems of beyond third generation (3G)
The purpose of this paper is to explore interference aspects arising from cell-specific traffic asymmetry demands in OFDMA-time division duplex (TDD) cellular networks, while jointly considering channel allocation and user scheduling
Spectral efficiency is the achieved system throughput divided by the total bandwidth divided by the number of base stations (BSs), subcarrier utilization is the number of subcarriers used in the system, divided by the total number of subcarriers, and user outage is defined as the users not served as a fraction of the total number of users in the system
Summary
Orthogonal frequency division multiplexing (OFDM) has been a subject of considerable interest for cellular systems of beyond third generation (3G). Wong et al [1] show promising results for OFDM as a multiuser technique, focusing on the gains in using adaptive modulation. Results, presented by Keller and Hanzo in [2], highlight the solid benefits of employing adaptive modulation in OFDM systems. Yan et al [3] propose an adaptive subcarrier, bit, and power allocation algorithm for a multiuser, multicell OFDM system, which shows significant improvement in throughput when compared to an equal power allocation algorithm. The gains in combining OFDM with an adequate multiple access scheme have been thoroughly described in [4], emphasizing on the superiority of frequency division multiple access (FDMA)
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