Multi-Carrier Index Keying for Next Generation Gigabit Wireless Communications

在过去的几十年里，移动数据流量呈指数级增长。这一趋势将持续下去，预计到2020年将增长1000倍。未来的无线通信承诺通过利用不断增加的频谱来提供所需的数据速率。多载波调制（MCM）技术在大多数现代无线通信系统中得到了应用，由于其对多径衰落具有很强的固有抗扰性，可以显著提高数据速率。MCM有效地将频率选择性衰落信道转换为平行的平坦衰落信道，极大地简化了接收机的数据恢复过程。然而，这些好处是以能量效率的损失为代价的，因为有限的功率分配给多载波信号，增加了对频率偏移和多普勒频移的灵敏度，以及由MCM信号的非恒定功率比引起的传输非线性。MCM的这些缺点挑战了它在5G系统中的直接应用，5G系统要求数据速率增加1000倍（例如，每秒100千兆比特），而4G系统的理想峰值速率为每秒100兆比特。此外，移动客户端有限的电力可用性加上这些传输速率需求提出了挑战，可以通过在较短范围内增加带宽来解决；5G的规模是现在4G的250倍。由于无线信道的时变特性，需要周期性地传输训练序列以进行信道估计。对于如此大带宽的信道估计，训练序列所带来的过载可能是显著的，特别是对于功率有限的设备应用。功率限制传输和大频谱调制的挑战必须同时解决。本课题介绍了一种简单、低成本的基于索引键控的多载波系统在分散信道中的映射方法。关键概念涉及一个特殊的索引映射函数，称为MCIK（多载波索引键控）。在每次传输中，只有几个随机的子载波是有效的，以提高能效，同时，有效/非活跃子载波的索引有助于在没有额外功率的情况下传输额外的信息位。这种MCIK概念有望在低功耗下有效传输大数据量，特别是在大带宽和实际色散信道上。我们的目标是为MCIK的成功实施提供理论参考和指导，从而产生重大的进步；我们的初步结果表明，与传统的多载波传输相比，它可以节省50%的电力，并且可能达到每秒数十千兆比特的速率。MCIK适用于调制大量多载波的有限功率系统。它提供了一种实现分集和复用的机制，从而提高了能量效率和频谱效率。我们还建议设计一个线性处理的MCIK系统，以促进低成本的数据恢复过程，从而实现更高的频谱效率多载波系统。为了有效地克服当前正交频分多址（OFDMA）传输中的载波频偏和多用户干扰问题，我们提出了一种新的多址技术，该技术可以很容易地实现实际性能限制和所需的性能，并展示了MCIK特性如何与多用户多输入多输出系统相结合。我们的工作重点是研究MCIK中“索引键控”过程的特殊性质，这些性质被其他人所忽视。我们的目标是在多载波索引调制、检测和估计以及多址设计的背景下利用这些特性。这是为了在可承受的计算复杂度下获得未来无线通信的最佳性能。

An exponential increase in mobile data traffic has been observed in the last decades. This will continue and a 1000-fold increase by 2020 has been forecasted. Future wireless communications promise to provide the required data rate by an utilisation of the increasing spectrum.Multicarrier Modulation (MCM) techniques have found application in the majority of modern wireless communication systems, due to strong inherent immunity to multipath fading, which allows for a significant increase in the data rate. MCM effectively transforms a frequency selective fading channel into parallel flat fading channels which immensely simplifies the data recovery process at the receiver. However, these benefits come at the cost of a loss of energy efficiency due to the distribution of finite power to multicarrier signals, an increased sensitivity to frequency offset and Doppler shift as well as transmission nonlinearity caused by the non-constant power ratio of MCM signals. Such drawbacks of MCM challenges its direct application to 5G systems that request a 1000-fold increase in the data rate (e.g., 100 gigabits per second), compared to 4G system that has its ideal peak rate of 100 megabits per second. Additionally, the limited power availability at the mobile client coupled with these transmission rate demands present challenges which can be solved by increasing bandwidth over shorter ranges; about 250 times larger than today 4G is considered in 5G. Due to the time-varying nature of wireless channels, training sequences need to be transmitted periodically for the purpose of channel estimation. The overload imposed by training sequences for channel estimation of such a large bandwidth can be significant, especially for power-limited device applications. Power-limited transmission and large spectrum modulation challenges must be simultaneously tackled.This project introduces a simple and low-cost mapping method for index keying based multicarrier systems in dispersive channels. The key concept involves a special index mapping function named MCIK (multicarrier index keying). At every transmission, only a few random sub-carriers are active for high energy-efficiency and, simultaneously, index of the active/inactive sub-carriers helps inherently to transmit extra information bits with no extra power. This MCIK concept is promising to effectively transmit big data volumes at low-power, especially on the large bandwidth and realistic dispersive channels. Our goal is to provide theoretical references and guidelines for a successful MCIK implementation that can produce significant advance; our preliminary results show 50% power savings and a potential rate of tens of gigabits per second over classical multicarrier transmission. MCIK is suitable for a power limited system modulating a large number of multicarrier. It provides a mechanism for attaining both diversity and multiplexing so that the energy efficiency and the spectral efficiency are increased. We also propose to design a linearly processed MCIK system to facilitate a low-cost data recovery process, resulting in higher spectral efficient multicarrier system. In order to effectively overcome carrier frequency offset and multiuser interference problems in the current orthogonal frequency division multiple access (OFDMA) transmissions, we propose a new multiple access technique which can allow the practical performance limits and needs for the desired performance to be easily obtained and show how MCIK features should be combined with multiuser multiple-input multiple-output systems. Our emphasis in this work will be on the study of special properties of 'index keying' process in MCIK which have been overlooked by others. We aim to leverage these properties in the context of multicarrier index modulation, detection and estimation, and multiple access design. This is to attain optimal performance with affordable computational complexity, for future wireless communications.