Comparison of Decentralized Time Slot Allocation Strategies for Asymmetric Traffic in TDD Systems

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Sohn, Illsoo; Lee, Kwang Bok; Choi, Young Sil
Issue Date
Institute of Electrical and Electronics Engineers (IEEE)
IEEE Trans. Wireless Commun., vol. 8, no. 6, pp. 2990-3003, Sep. 2005
TDDasymmetric traffictime slot allocationcrossed-slot interferenceWiBro/WiMAXIEEE802.16e
This paper was presented in part at the IEEE Consumer Communications and
Networking Conference (CCNC), Las Vegas, USA, Jan. 2006.
Recently, wireless multimedia services have been
growing because of the spread of various wireless applications.
Hence, time division duplex (TDD) systems and their crossed-slot
interference problems in a cellular environment have been attracting
growing interests. Considering large signaling overhead
between cells, decentralized time slot allocation (TSA) strategy is
suitable for practical implementation. Thus, Fixed-TSA strategy
which fixes the same ratio of uplink and downlink time slots in
all cells is adopted in commercial WiBro systems (IEEE802.16e
Mobile WiMax) to mitigate the crossed-slot interference. However,
the Fixed-TSA strategy reduces the flexibility in time
slot allocation due to a strong constraint set by a predefined
boundary. Moreover, the mathematical derivation of the optimal
value for the predefined boundary has not been presented yet. In
this paper, we propose two decentralized TSA strategies. The first
one is Enhanced Fixed-TSA strategy, which dynamically adapts
the predefined boundary of the conventional Fixed-TSA strategy
according to traffic conditions. The second one is REgion-based
Decentralized Time Slot Allocation (RED-TSA) strategy, which
utilizes partial location information of MSs to reduce crossedslot
interference. We fully analyze the proposed TSA strategies
in terms of new call blocking probability, average bit error
probability, and the overall system throughput. Numerical results
show that the proposed RED-TSA strategy provides the highest
system throughput by compromising both new call blocking performance
and average bit error performance, whereas it requires
additional location information and complicated computation.
On the contrary, the proposed Enhanced Fixed-TSA strategy
requires reasonable computational complexity while it provides
almost the same system throughput with that of the proposed
RED-TSA strategy. In a nutshell, the proposed Enhanced Fixed-
TSA strategy is more appropriate for the practical systems.
Moreover, it can be directly applied to the current commercial
WiMax/WiBro systems with minimum changes.
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Electrical and Computer Engineering (전기·정보공학부)Journal Papers (저널논문_전기·정보공학부)
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