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.
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