ITR: Collaborative Research: 'Free' Bits: The Challenge of the Wireless Internet

第二代和第三代无线系统主要是为语音设计的，因此它们是面向连接的，对延迟敏感的，并提供固定的比特率。此外，由于需要“随时随地”提供服务，因此这些系统必须提供无处不在的覆盖。这种覆盖是通过相对统一的蜂窝站点网格来实现的，这些网格的放置是为了控制干扰和最小化中断，而不是最大化整个。因此，这种系统提供较低的比特率，并且在用于大量信息时相对昂贵。与此同时，与互联网的有线连接鼓励了依赖于比特几乎“免费”的使用（和用户）。我们认为，有线和无线接入之间的“经济”不匹配是无线互联网急剧增长的主要障碍。解决方案可能在于专门为无线数据设计系统，认识到数据服务通常是无连接的，延迟不敏感的，并且没有特定的比特率要求。这些差异表明，无处不在（随时/任何地点）的覆盖范围并不是无线数据网络的严格要求，并且使小的、分离的覆盖区域能够在几分之一秒内传输兆字节的数据的系统成为可能，而与传统的无处不在的覆盖范围相关的成本只是其中的一小部分。通信理论和简单的链路预算计算告诉我们，建立这样的系统是可能的，但是信号处理的挑战是众多的，并且与面向连接的无线服务提供的历史挑战不同。当移动用户经过Infostation时，将有一个机会窗口，可能只有几分之一秒，在此期间用户将访问高速通信通道。关键任务是确定该窗口并以适当的速率传输。移动设备必须根据对宽带无线电信道的测量来做出这些决定，其中在衰落和干扰中存在频率选择性和时间变化。在Infostations系统的具体背景下，我们计划将我们的研究分为四个部分：无线电信道建模：典型Infostation无线电信道的表征。收发器设计：单载波和多载波系统的收发器分析和性能评估。无线电资源管理根据接收机测量得出的发射机功率和速率自适应策略。算法开发试验台采用DSP和FPGA技术对收发算法进行实际评估的平台。该项目的活动将包括新泽西州的三个研究机构（新泽西理工学院、普林斯顿大学、罗格斯大学），由新泽西州无线电信中心（NJCWT）主持。NJCWT是一个机构间的研究和教育组织，由新泽西州科学技术委员会赞助和资助。该中心的重点是在计算、通信和信息系统的数字无线电技术方面的多年努力。这项工作支持并将加强目前提议的无线网络项目。

Second and third generation wireless systems have been designed primarily for voice, so they are con-nection oriented, delay sensitive, and provide fixed bit rates. Additionally, since service is desired "any-time/anywhere," these systems must provide ubiquitous coverage. This coverage is achieved through rela-tively uniform grids of cell sites, which are placed to control interference and minimize outage rather than to maximize throughout. As a result, such systems deliver low bit rates and are relatively expensive when used for large amounts of information. At the same time, wireline connection to the Internet has encouraged uses (and users) that depend upon bits being virtually "free." We contend that this "economic" mismatch between wired and wireless access is the primary obstacle to the dramatic growth of a wireless Internet. The solution may lie in designing systems specifically for wireless data, recognizing that data services are often connectionless, delay insensitive and have no specific bit rate requirements. These differences suggest that ubiquitous (anytime/anywhere) coverage is not a strict requirement for wireless data networks and makes possible systems in which small, separated coverage areas facilitate transfers of megabytes of data in fractions of a second, and for a fraction of the cost associated with conventional ubiquitous coverage. Communication theory and simple link budget calculations tell us that it is possible to build such sys-tems, but the signal processing challenges are numerous and distinct from the historical challenges offered by connection-oriented wireless services. When a mobile user passes an Infostation, there will be a window of opportunity, perhaps as short as a fraction of a second, in which the user will have access to a high-rate communication channel. A key task is to identify that window and transmit at an appropriate rate. The mobile must make these decisions based on measurements of a wideband radio channel in which there is frequency selectivity and time variation in the fading as well as in the interference. In the specific contextof an Infostations system, we plan to divide our research into four components: Radio Channel Modeling: The characterization of typical Infostation radio channels. Transceiver Design: The analysis and performance evaluation of transmitters and receivers for both single carrier and multicarrier systems.Radio Resource Management Transmitter power and rate adaptation policies derived from receiver measurements.Algorithm Development Testbed A platform employing DSP and FPGA technology for the practical evaluation of transmitter and receiver algorithms. The activities of this project will encompass three research institutions in New Jersey (New Jersey In-stitute of Technology, Princeton University, Rutgers University) under the auspices of the N.J. Center for Wireless Telecommunications (NJCWT). The NJCWT is an inter-institutional research and educational or-ganization sponsored and funded by the N.J. Commission on Science and Technology. The focus of the center is a multi-year effort in Digital Radio Technology for Computing, Communications and Information Systems. This effort is supportive of and will enhance the present proposed project in wireless networks.