Abstract
Relay deployment in orthogonal frequency division multiple access (OFDMA) based cellular networks helps in coverage extension and/or capacity improvement. To quantify capacity improvement, blocking probability of voice call is typically calculated using Erlang B formula. This calculation is based on the assumption that all users require same amount of resources to satisfy their rate requirement. However, in an OFDMA system, each user requires different number of subcarriers to meet its rate requirement. This resource requirement depends on the signal to interference ratio (SIR) experienced by a user. Therefore, the Erlang B formula can not be employed to compute blocking probability in an OFDMA network. In this paper, we determine an analytical expression to compute the blocking probability in a relay based cellular OFDMA network. We determine an expression of the probability distribution of the user’s resource requirement based on its experienced SIR. Then, we classify the users into various classes depending upon their subcarrier requirement. We consider the system to be a multi-dimensional system with different classes and evaluate the blocking probability using the multi-dimensional Erlang loss formulas. This model is useful in the performance evaluation, design, planning of resources and call admission control in a relay based cellular OFDMA networks like long term evolution.
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Notes
In a practical cellular system, it is ensured that RS does not receive from BS and transmit to MS simultaneously in order to eliminate the relay transmitter causing interference to its own receiver. For example, in LTE, specific subframes known as the Multicast/Broadcast Single Frequency Network (MBSFN) subframes [20] are utilized to create gaps in the RS–MS transmission, during which transmission on only BS–RS link happens. Though we have not specifically considered this scenario, our system model captures such transmission scenario if we consider resource sharing at the subframe level. Note that the analytical results remain unaffected with this consideration.
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This work was performed while the authors—Mahima Mehta and Ranjan Bala Jain were with Department of Electrical Engineering, IIT Bombay.
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Mehta, M., Jain, R.B. & Karandikar, A. Analysis of Blocking Probability in a Relay-Based Cellular OFDMA Network. Wireless Pers Commun 84, 2467–2492 (2015). https://doi.org/10.1007/s11277-015-2715-5
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DOI: https://doi.org/10.1007/s11277-015-2715-5