Equivalent Capacity in Carrier Aggregation-Based LTE-A Systems: A Probabilistic Analysis

In this paper, we analyze the user accommodation capabilities of LTE-A systems with carrier aggregation for the LTE users and LTE-A users, respectively. The adopted performance metric is equivalent capacity (EC), defined as the maximum number of users allowed in the system given the user QoS requirements. Specifically, both LTE and LTE-A users are divided into heterogeneous user classes with different QoS requirements, traffic characteristics and bandwidth weights. Two bandwidth allocation strategies are studied, i.e., the fixed-weight strategy and the cognitive-weight strategy, where the bandwidth weights of different user classes are prefixed under the former and dynamically changing with the cell load conditions under the latter. For each strategy, closed-form expressions of ECs of different user classes are derived for LTE and LTE-A users, respectively. A net-profit-maximization problem is further formulated to discuss the tradeoff among the bandwidth weights. Extensive simulations are conducted to corroborate our analytical results, and demonstrate an interesting discovery that only a slightly higher spectrum utilization of LTE-A users than LTE users can result in a significant EC gain when the user traffic is bursty. Moreover, the cognitive-weight strategy is shown to outperform considerably the fixed-weight one due to stronger adaptability to the cell load conditions.