基于机会约束规划的高效自适应正交频分多址接入技术研究

Thanks to the rapid development of wireless technologies, 4G broadband wireless services are just around the corner. Various 4G technologies such as WiMax and LTE have converged to the use of OFDMA (Orthogonal Frequency Division Multiple Access) in the physical layer. One major advantage of OFDMA is that it provides a high degree of flexibility for adaptively allocating radio resources to exploit channel and multiuser diversity. Research has shown that such adaptive allocation schemes, referred to as adaptive OFDMA, is a powerful technique to provide higher data rates, lower latency, and better services to users compared with conventional static radio resource allocation.Despite years of investigative efforts, however, adaptive OFDMA is still too "expensive" to be practically implemented in real systems. A high cost component is the fast adaptation of resource allocation, which requires an optimization problem to be solved every time the wireless channel changes. Moreover, once resources are re-allocated, a control signaling message that contains the allocation decision needs to be sent to all mobile stations. In practice, wireless channel varies in the order of milliseconds, resulting in frequent re-optimization and signaling. There is an urgent need to revisit, rethink and even discard some of the basic designs of adaptive OFDMA to make such promising technique practical.In this project, we propose an entirely new concept, namely "slow" adaptive OFDMA. In contrast to conventional approaches that adapt resource allocation every time wireless channel changes, slow adaptive OFDMA updates resource allocation in a much slower timescale than that of channel fluctuation. The computational cost and signaling overhead can therefore be significantly reduced. A key challenge with slow adaptation is how to allocate resources such that the capacity gain of fast adaptation is also largely achievable by slow adaptation. Another challenging issue is how to satisfy users' QoS requirements defined in both large and small time scales, given that resource allocation is only performed in a large (slow) time scale. We address the challenges by leveraging on recent advances in stochastic optimization techniques. In particular, we will focus on (i) mathematical formulation of slow adaptive OFDMA; (ii) efficient solution methods that solve the formulated problems with low computational cost; and (iii) practical algorithms that cope with real-world situations such as unknown channel distribution and user mobility. The successful completion of this project will fundamentally solve the practicality issue of adaptive OFDMA in a new and effective way that has never been explored before.

随着OFDMA在下一代宽带移动通信系统中被广泛应用，高效的OFDMA系统设计对于未来无线通信系统的服务质量和效益成本都有着举足轻重的作用。 现行OFDMA利用不同子载波间频率选择性衰弱的独立性高度灵活地自适应分配无线资源，从而获得最大的信道容量。然而，这项极具前景的技术在实际应用中面临巨大障碍, 其中一个重要原因在于系统需要对毫秒级的速率极快地调整子载波分配。通信系统因此需要具备高速的硬件计算能力，从而大大提高了运营成本。基于这些考虑，本项目提出了一种全新的低复杂度OFDMA技术，称为慢速自适应OFDMA。相比于传统的OFDMA技术，慢速自适应OFDMA在保证高效频谱利用率的基础上，大大降低了用户到子载波的再分配速率，从而极大程度上降低了计算量。更为重要的是，本项目所采取的机会约束规划方法无论在现今的应用数学或是通信工程领域都极具前沿地位，相信可为本领域研究打开崭新的一页。

随着新一代移动通信技术的深入发展，OFDMA（正交频分复用多址接入）已成为下一代宽带无线通信系统，如LTE和LTE-Advanced的首选接入方案。OFDMA的一大优势在于其允许用户间的子载波分配根据信道状态进行自适应优化，从而大幅提高系统的信道容量。然而，这项极具前景的技术在实际应用中面临巨大障碍，即其需要以毫秒级的速度极快地调整子载波分配，从而造成极高的计算复杂度，远非当前的硬件系统所能承受。高效的OFDMA系统设计对于未来无线通信系统的服务质量和效益成本都有着举足轻重的作用。现有的系统为了降低复杂度，往往采用次优的算法，所获信道容量远低于系统最优性能。综合上述考虑，本项目致力于设计一种全新的子载波分配机制，即慢速自适应OFDMA。此项设计在极大降低计算复杂度之余保存了子载波分配的最优化，从而提供OFDMA低成本高效率的最佳解决方案。更为重要的是，本项目所采取的机会约束规划方法无论在现今的应用数学或是通信工程领域都极具前沿地位，相信可为本领域研究打开崭新的一页。..允许用户间根据信道状态进行自适应子载波优化分配的OFDMA（正交频分复用多址接入）因为能大幅度提高系统的通信速率而被各种通信协议广泛接受，并已成为未来无线系统的首选接入方案。然而，这项极具前景的技术至今未能在实际系统中得以应用，其中最大的障碍在于系统的资源分配需要频繁地对毫秒级的信道变化作出相应的调整。如此快速的自适应方式需要极高的计算复杂度和大量的控制信令，而这些远非当前的硬件系统所能承受。针对这一点，本项目将致力于设计一种全新的子载波分配机制——慢速自适应OFDMA。与传统设计不同，我们的设计具有如下优势：（1）在远慢于信道变化的时间尺度上进行子载波分配，从而极大降低计算复杂度和控制信号开销；（2）采用最新的机会约束规划方法对分配决策进行优化，以一种更贴近工程应用的方式来满足用户的服务质量(QoS)。更为重要的是，本项目的成功完成将为推动下一代无线通信系统的发展铺平道路。