The energy detection technology is adopted as the detection method of the unlicensed channel in LTE release 13. However, the detection may be imperfect in actual scenario due to the simplicity of the detection method. In order to eliminate the controversy over LTE licensed assisted access (LAA) scheme, the paper deeply investigates the performance of the scheme under imperfect spectrum sensing (ISS). Considering possible ISS during the enhanced clear channel assessment (eCCA), the LAA scheme is modeled as a new two dimensional discrete time markov chain. In order to capture ISS, different from the definition in Bianchi’s model, the discrete time scale is defined as the end of backoff slot time in the proposed model. The definition enables LAA small base stations to enter the defer state from backoff state when the channel is detected to be busy, and further possible ISS in the defer period and backoff slot time (BST) of eCCA can be considered. Based on the proposed model, the expressions of collision probabilities and throughput under three backoff mechanisms based LAA schemes are derived to deeply analyze their performance by comparisons. A large number of experimental and analytical results prove the validity of the proposed model. The analytical results also show that not only the backoff mechanisms but also ISS can greatly affect the network performance. In the respect of fairness (i.e. the impact on WiFi users), the WiFi collision probability always increases with the decrease of the false alarm probability (FAP). This means the WiFi collision probabilities under three LAA schemes may be higher than the baseline level for the graceful coexistence when FAP is very little. In this sense, the LAA schemes cannot be referred to as being graceful though they have been proven to be deterministic graceful coexistence schemes under perfect spectrum sensing (PSS). In the respect of throughput, LAA throughput always decreases and WiFi throughput increases with the growth of FAP, and total throughput always decreases. Therefore, based on the fixed SNR and sampling rate in actual scenario, the network performance can be tuned by energy threshold, as is consistent with the viewpoint in other literatures.

中文翻译：

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不完善的频谱感知对LTE授权辅助接入方案性能的影响

LTE release 13采用能量检测技术作为非授权信道的检测方法，但由于检测方法的简单性，在实际场景中检测可能不完善。为了消除LTE许可辅助接入（LAA）方案的争议，本文深入研究了该方案在不完善频谱感知（ISS）下的性能。考虑到增强型畅通信道评估 (eCCA) 期间可能存在的 ISS，LAA 方案被建模为新的二维离散时间马尔可夫链。为了捕获 ISS，与 Bianchi 模型中的定义不同，离散时间尺度被定义为所提出模型中退避槽时间的结束。该定义使 LAA 小基站在检测到信道忙时从退避状态进入延迟状态，并且可以考虑在 eCCA 的延迟期间和退避时隙 (BST) 中进一步可能的 ISS。基于所提出的模型，推导出了三种基于回退机制的LAA方案下碰撞概率和吞吐量的表达式，通过比较深入分析了它们的性能。大量的实验和分析结果证明了所提出模型的有效性。分析结果还表明，不仅退避机制而且 ISS 都会极大地影响网络性能。在公平性（即对WiFi用户的影响）方面，WiFi碰撞概率总是随着虚警概率（FAP）的降低而增加。这意味着当 FAP 非常小时，三种 LAA 方案下的 WiFi 冲突概率可能高于优雅共存的基线水平。从这个意义上说，虽然 LAA 方案已被证明是完美频谱感知 (PSS) 下的确定性优雅共存方案，但它们不能被称为优雅共存方案。在吞吐量方面，LAA吞吐量总是随着FAP的增长而下降，WiFi吞吐量随着FAP的增长而增加，总吞吐量总是在下降。因此，基于实际场景中固定的信噪比和采样率，可以通过能量阈值来调整网络性能，这与其他文献中的观点是一致的。