Adaptive space and frequency modulations for high-quality high-speed wireless LANs

未来无线通信的目标是支持高质量的高速服务，如互联网，视频会议和文件传输，在任何时间任何地点没有电线。由于频谱资源的有限性，满足日益增长的用户数量和数据传输速率的需求是一个挑战。在发射器和接收器两者处使用多个天线（称为MIMO天线）和正交频分复用（OFDM）（当前在IEEE802.11a和HiperLAN II无线局域网标准中使用的传输方案）最近已被证明是通过空中为低移动性用户提供高速服务的最杰出的技术。MIMO天线技术与OFDM技术结合使用空间和频率维度来提高传输速度，已被认为是未来无线系统成功的关键。本项目的目标是设计一种用于下行链路空频传输的最佳资源分配方法，其中发射机向多个用户发送独立的高速数据（例如，从接入点到许多移动的终端，这些终端可以是膝上型计算机或蜂窝电话）。该设计旨在最好地利用可用的系统资源（即，带宽和功率）以实现用户所请求的服务质量。在文献中没有对联合空频多用户分配方面的设计进行研究，主要是因为自适应资源分配必须在正交信道上执行，然而传统的太空-频率传输技术不能以正交方式适应多用户下行链路设置的信号。由于信道资源的单位变为二维空频信道，因此更加艰巨。由于同信道信号（共享相同无线电信道的信号）现在可以通过使用多个天线与它们的空间特征区分开，因此该额外的空间维度允许用户在空间中被复用。结果，所使用的频率信道通常将携带多于一个的共信道信号，这些共信道信号可能属于几个不同的用户。要支持的用户和用于所支持的用户的空间信道的数量决定了在每个频率处可用的信道资源的量，并且这也需要在问题中被优化。另一个困难是，尽管用户在空间上可被天线分割（或空分复用），但是传统的MIMO技术不能以正交方式发送同信道信号。因此，在移动的终端处，不希望的同信道信号没有被完全消除，因为在移动的终端处的大天线阵列实际上是不可能的。结果是资源信道实际上彼此耦合并且导致难以获得逐步分配方法。当试图向特定信道分配更多功率时，它往往会影响其他资源信道的信号质量。因此，能够在下行链路中正交地发送同信道信号的天线处理是至关重要的。为了实现我们的目标，我们需要克服上述挑战，并最终能够最佳地确定每个频率的用户，所服务的用户的空间维度的数量，功率，发送的数据量和传输的编码速率。本研究的成果是一种适用于支持MIMO的无线局域网的自适应资源分配算法，可以以最有效的方式使用可用资源。预计联合空-频-时分集可以使系统的吞吐量远远超过目前使用的系统。

Future wireless communication aims to support high-quality high-speed services such as Internet, video conferencing, and file transfer, at anytime anywhere without wires. Due to the paucity of frequency spectrum, it is challenging to meet the ever-increasing demand of the number of users and data-rate requirement. Ultilising multiple antennas at both transmitter and receiver (known as MIMO antenna) and orthogonal frequency-division multiplexing (OFDM) (the transmission scheme currently used in IEEE802.11a and HiperLAN II wireless LANs standards) have recently been demonstrated as the most outstanding techniques to providing high-speed services over the air for low mobility users. The MIMO antenna technology together with OFDM combines the use of the space and frequency dimensions to enhance the transmission speed and has been recognised as the key to the future success of wireless systems.The objective of this project is to devise an optimal resource allocation method for space-frequency transmission in a downlink scenario where a transmitter is sending independent high-speed data to many users (e.g., from an access point to many mobile terminals which can be a laptop or cell phone). The design aims to make the best use of available system resources (i.e., bandwidth and power) for achieving the requested Quality-of-Service of the users. None of research has been done in the literature on the design in the respect of joint space-frequency multiuser allocation mainly because adaptive resource allocation has to be performed on orthogonal channels, yet conventional space-frequency transmission technique is unable to accommodate signals in an orthogonal manner for a multiuser downlink setting.Incorporating the idea of adaptive channel resource allocation into OFDM with MIMO processing is unfortunately much more arduous, as the unit of channel resource becomes a two dimensional space-frequency channel. Since the cochannel signals (the signals that share the same radio channel) can now be distinguished from their spatial signatures by using multiple antennas, this additional spatial dimension allows users to be multiplexed in space. As a result, a used frequency channel will usually carry more than one co-channel signals, which may belong to several different users. The users to be supported and the number of spatial channels for the supported users dictate the amount of channel resources available at each frequency, and this needs to be optimised in the problem as well.Another difficulty is that though users are spatially divisible by the antennas (or space-division multiplexing), conventional MIMO technique is unable to transmit co-channel signals in an orthogonal manner. Therefore, at the mobile terminal, undesired co-channel signals are not completely eliminated as a large array of antennas at the mobile terminal is unlikely in practice. The consequence is that the resource channels are actually coupled each other and that causes a step-by-step allocation method difficult to obtain. As when trying to assign more power to a particular channel, it tends to affect the signal quality of other resource channels. Antenna processing capable of sending co-channel signals orthogonally in the downlink is thus crucial.To accomplish our objective, we need to overcome the above-mentioned challenges and in the end be able to optimally determine, for every frequency, the users to be served, the number of spatial dimensions of the served users, power, the amount of data being sent and the coding rate of the transmissions. The outcome of this research is an adaptive resource allocation algorithm for MIMO-enabled wireless LANs that can use the available resources in the most efficient way. It is anticipated that the joint space-frequency-time diversity can excel the system throughput far exceeding systems in use today.