CAREER: Key Problems in Wireless Communications

这项研究可以分为两个主要的主题，由以下关键瓶颈的无线系统的动机：无线带宽的稀缺性，和接口的问题，固有的损耗无线链路与高速有线网络的损失发生mainlv由于拥塞。第一个研究主题是关于提高容量和性能的直接序列CDMA，这具有很大的希望作为一个强大的主力技术，为未来的无线系统。由于多址干扰对CDMA性能的主要限制，两种广泛的方法被认为是减轻其影响：分散式自适应接收和集中式多用户接收。我们的目标是进一步的理论发展，这两种方法，以期开发实用的接收器结构。解决的问题包括设计方法，使自适应干扰抑制工作在严重的时间变化的无线多址信道，支持多种类别的业务（因此多速率）使用直接序列CDMA，发明接近最佳的自适应非线性接收机，将天线分集以合理的复杂度纳入干扰抑制方案，以及对于自适应方法不适用的系统，基于多用户检测和估计原理导出接收机。 第二个研究主题是开发设计接口的理论，确保无线和有线网络之间的兼容性，同时最大限度地减少宝贵的无线带宽的使用。问题的配方，而更广泛的兴趣，是出于这样一个事实，即两个有线技术与无线网络必须兼容的是新兴的ATM网络和TCP/IP。考虑的问题包括制定服务保证在一个有损的无线链路和设计原则，实现它们，优化无线带宽的广播或多址无线信道通过使用传输控制的基础上看到的每个接收机的信道状态，通过无线接口操纵TCP/IP流控制和ATM速率控制所使用的反馈机制，以提供良好的端到端通信。终端性能的异构网络与无线和有线链路，以及流量控制机制的设计，不遭受TCP/IP的缺点。

This research can be classified into two major themes, motivated by the following key bottlenecks for wireless systems: the scarcity of radio bandwidth, and the problem of interfacing inherently lossy wireless links with high-speed wireline networks where loss occurs mainlv due to congestion. The first research theme is concerned with enhancing the capacity and performance of direct-sequence CDMA, which holds great promise as a robust workhorse technology for future wireless systems. Since multiple-access interference imposes a major limitation on CDMA performance two broad methodologies are considered for alleviating its effects: decentralized adaptive reception and centralized multi-user reception. The goal is to further the theoretical development of both these methodologies with a view to developing practical receiver structures. The issues addressed include devising methods for making adaptive interference suppression work over the severe time variations of a wireless multiple-access channel, supporting multiple classes of traffic (and hence multiple rates) using direct-sequence CDMA, inventing near optimal adaptive nonlinear receivers, incorporating antenna diversity into interference suppression schemes with reasonable complexity, and deriving receivers based on multi-user detection and estimation principles for systems to which adaptive methods do not apply. The second research theme is the development of a theory for designing interfaces that ensure compatibility between wireless and wireline networks while minimizing the use of precious wireless bandwidth. The problem formulations, while of broader interest, are motivated by the fact that two wireline technologies with which a wireless network must be compatible are the emerging ATM networks and TCP/IP. The problems considered include the formulation of service guarantees over a lossy wireless link and the design principles for implementing them, optimization of wireless bandwidth for a broadcast or multiple-access wireless channel by using transmission control based on the channel state seen by each receiver, manipulation of the feedback mechanisms used by TCP/IP flow control and ATM rate control by the wireless interface to provide good end-to-end performance over a heterogeneous network with both wireless and wireline links, and the design of a flow control mechanism that does not suffer from the shortcomings of TCP/IP.