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

未来的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，随时随地都不需要有线。由于频谱资源的匮乏，用户数量和数据速率的需求日益增长，这就对无线通信系统提出了更高的要求。在发射机和接收机上使用多个天线(称为MIMO天线)和正交频分多路复用(Ofdm)(当前在IEEE802.11a和HiperLANII无线局域网标准中使用的传输方案)最近已被证明是为低移动性用户提供空中高速服务的最杰出的技术。MIMO天线技术和ofdm技术结合了空间和频率维度的使用来提高传输速度，被认为是无线系统未来成功的关键。本项目的目标是在发射机向许多用户(例如，从一个接入点到许多移动终端，可以是笔记本电脑或手机)发送独立的高速数据的下行链路场景中，设计一种用于空频传输的最佳资源分配方法。设计的目的是充分利用可用的系统资源(即带宽和功率)，以达到用户所要求的服务质量。文献中没有关于联合空频多用户分配的设计方面的研究，这主要是因为必须在正交信道上执行自适应资源分配，而传统的空频传输技术不能以正交方式容纳多用户下行链路设置的信号。不幸的是，将自适应信道资源分配的思想结合到具有MIMO处理的OFDM中要困难得多，因为信道资源单元变成了二维空频信道。由于同频道信号(共享同一无线频道的信号)现在可以通过使用多个天线从它们的空间特征中区分出来，所以这个额外的空间维度允许用户在空间中被多路复用。因此，所使用的频道通常将承载一个以上的同频道信号，其可能属于几个不同的用户。要支持的用户和支持的用户的空间信道数量决定了在每个频率可用的信道资源量，这也需要在问题中进行优化。另一个困难是，尽管用户可以通过天线(或空分复用)在空间上分割，但传统的MIMO技术不能以正交的方式发送同信道信号。因此，在移动终端，不希望的同频信号不会被完全消除，因为在移动终端上不太可能有大量的天线阵列。结果是资源通道实际上是彼此耦合的，这导致难以获得逐步分配方法。因为当尝试将更多功率分配给特定信道时，它往往会影响其他资源信道的信号质量。因此，能够在下行链路中垂直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，并最终能够针对每个频率最佳地确定要被服务的用户、被服务用户的空间维度数目、功率、发送的数据量和传输的编码率。这项研究的结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，该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系统的吞吐量将远远超过目前正在使用的系统。

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.