Cognitive radio (CR) is a new intelligent wireless technology that aims at improving spectrum utilization by allowing opportunistic access to the underutilized licensed spectrum. Wireless CR operating environment is typically characterized by its unreliable and unpredictable channel conditions and time availability due to fading and the randomness of primary radio (PR) activities. In such environment, packet fragmentation is needed to enhance the probability of success/packet delivery and reduce the needed number of packet re-transmission attempts. Specifically, the quality and availability of the PR channels along with the data packet size should be considered when designing communication protocols for CR networks (CRNs) such that the packet success probability is improved. Based on the quality and availability of the PR channels, an optimal-packet size metric is derived, which is defined as the packet size that can be transmitted over a selected channel while guarantying a predefined probability of success. In this paper, we propose three fragmentation-based channel assignment algorithms: fixed-fragment size algorithm, first-fit algorithm and near-exact fit algorithm. The first algorithm divides the packet equally over the selected channels while the other algorithms use variable fragment size. The main objectives of the algorithms are to enhance network throughput, decrease the number of dropped packets and reduce the average number of retransmission attempts. This preserves more channels for potential future CR transmissions, resulting in higher network throughput with less energy consumption. Simulation results show that the proposed algorithms significantly outperform existing CRN channel assignment algorithms with no fragmentation.

认知无线电（CR）是一种新的智能无线技术，旨在通过允许机会性访问未充分利用的许可频谱来提高频谱利用率。无线CR操作环境的典型特征是由于衰落和主要无线电（PR）活动的随机性，其不可靠且不可预测的信道状况和时间可用性。在这样的环境中，需要分组分段以增加成功/分组传送的可能性并减少所需的分组重发尝试次数。具体而言，在设计用于CR网络（CRN）的通信协议时应考虑PR信道的质量和可用性以及数据包大小，从而提高包成功概率。根据PR渠道的质量和可用性，推导最佳分组大小度量，该最优分组大小度量被定义为可在保证预定的成功概率的同时在选定信道上发送的分组大小。本文提出了三种基于分片的信道分配算法：固定分片大小算法，初拟合算法和准精确拟合算法。第一种算法在所选通道上平均分配数据包，而其他算法使用可变的片段大小。该算法的主要目标是提高网络吞吐量，减少丢弃的数据包数量并减少平均重传尝试次数。这为将来的潜在CR传输保留了更多的信道，从而以更少的能耗获得更高的网络吞吐量。