近年來，因為預期可以找到有效的方法來提升頻譜的使用以及解決無線電裝置異質性的問題，感知無線電的技術已經引起了很多研究人員的注意。我們研究多重速率感知無線電網路，其中每個不同種類的使用者有著不同頻寬的需求。我們有一種主要使用者，PU，以及兩種次要使用者，SU1與SU2。我們考慮兩種連結允入控制方案：CAC1以及CAC2，其中PU新連結對於正在進行的SU1與SU2連結具有使用佔先優先權(preemptive priority)，且一些子通道會保留給SU1新連結，但不讓SU2新連結使用。此外，在CAC1之下，SU1交遞連結可以佔用正在進行中的SU2連結之子通道，反之，在CAC2之下，SU1交遞連結不可以佔用正在進行的SU2連結之子通道。這個系統可以被塑模成一個三維馬可夫程序。我們提出一個疊代演算法去找到穩態機率分佈以及計算效能指標。我們感興趣的效能指標包括新連結阻塞機率，強迫中斷機率以及成功送達率。在使用相同的系統參數之下，首先，無論使用CAC1或CAC2，PU、SU1、以及SU2的新連結阻塞機率皆是一樣的。第二，如果使用CAC1，除了PU服務時間很小或是SU2服務時間很大以外，SU1的強迫中斷機率小於SU2的強迫中斷機率。如果使用CAC2，除了SU1服務時間很大以及SU2服務時間很小以外，SU1的強迫中斷機率大於SU2的強迫中斷機率。第三，無論使用CAC1或CAC2，SU1以及SU2的成功送達率幾乎是一樣的。除了SU1到達速率很小以外，SU1的成功送達率高於SU2的成功送達率。最後但並非最不重要的，我們利用模擬程式來驗證我們數學解析結果的準確性，而電腦模擬是以visual C++來撰寫。在大部分的研究情形當中，數學解析結果都合理的接近電腦模擬結果。

In the past few years, the technology of cognitive radios has captured the attention of many researchers in that it promises an effective way of enhancing spectrum usage and solving the problem of heterogeneity of radio devices. We study the multirate cognitive radio networks where the users of each class have a different bandwidth requirement. There are one class of primary users, PU, and two classes of secondary users, SU1, and SU2. We consider two call admission control policies: CAC1 and CAC2, where PU new calls have the preemptive priority over ongoing SU1 and SU2 calls, and some sub-channels are reserved for SU1 against SU2 new calls. Furthermore, under CAC1, SU1 handoff calls can preempt SU2 ongoing calls, whereas under CAC2, SU1 handoff calls cannot preempt SU2 ongoing calls. The system can be modeled as a three-dimensional Markov process. We propose an iterative algorithm to find the steady state probability distribution and compute the performance measures. The performance measures of interest are new call blocking probability, forced termination probability, and throughput.
With the same system parameters, first, it is shown that the new call blocking probabilities of PU, SU1, and SU2 calls remain the same no matter CAC1 or CAC2 is enforced. Second, the forced termination probability of SU1 calls is lower than that of SU2 calls under CAC1, except for small PU service rates or large SU2 service rates. The forced termination probability of SU1 calls is higher than that of SU2 calls under CAC2, except for large SU1 service rates or small SU2 service rates. Third, the throughput of SU1 (SU2) calls remains almost the same no matter CAC1 or CAC2 is enforced. The throughput of SU1 calls is higher than that of SU2 calls except for small SU1 arrival rates. Last but not least, we verify the accuracy of the analytical results by the simulation program written by visual C++. In most cases studied, the analytical results are reasonably close to the simulation results.

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