Paul S. Henry

WiFi: what's next?

WiFi, also known as 802.11b, has become the preferred technology for wireless local area networking in both business and home environments. Even though it was designed primarily for private applications, WiFi is also being deployed in public places to create so-called hotspots, where WiFi-capable users can obtain broadband Internet access. This new domain of application could be the major future market opportunity for WiFi, but in order to take advantage of it, several key challenges, both technical and business-related, must be overcome. We outline these challenges and discuss approaches to solutions.

Radio resource allocation in fixed broadband wireless networks

We consider use of fixed broadband wireless networks to provide packet services for telecommuting and Internet access. Each cell is divided into multiple sectors, each of them served by a sector antenna colocated with the base station (BS), and user terminals also use directional antennas mounted on the rooftops of homes or small offices and pointed to their respective BS antennas. To support a target data rate of 10 Mb/s, a bandwidth of several MHz is required. Since radio spectrum is expensive, the bandwidth needs to be reused very aggressively. Thus, efficient strategies for frequency reuse and managing cochannel interference are critically important. We propose several algorithms for dynamic radio-resource allocation in the fixed wireless networks. In particular, a method to be referred to as the staggered resource allocation (SRA) method uses a distributed scheduling algorithm to avoid major sources of interference while allowing concurrent packet transmission and meeting signal-to-interference objectives. The performance of the method is studied by analytic approximations and detailed simulation. Our results show that the combination of directional antennas plus the SRA method is highly effective in controlling cochannel interference. For reasonable system parameters, the SRA method delivers a throughput in excess of 30% per sector while permitting a given frequency band to be reused in every sector of every cell. It also provides satisfactory probability of successful packet transmission. In addition, a simple control mechanism can be applied in the method to improve performance for harsh radio environments.

Interference characteristics of broadband power line communication systems using aerial medium voltage wires

The promise of broadband power line (BPL) communications - broadband access to virtually every home in the United States - remains unfulfilled if the radio emissions from these systems cause significant harmful interference to other users of the wireless spectrum. This article presents an elementary analysis of the physical mechanisms underlying these emissions, from which the interference characteristics of BPL systems can be derived. Numerical models are evaluated for idealized systems using overhead medium-voltage wires, a configuration that is of particular interest for U.S. deployments. The central conclusions of the analysis are: (i) BPL interference is governed primarily by two parameters: signal power and electrical balance of system excitation; (ii) interfering emissions are typically confined to the immediate vicinity of the BPL wire, but long-range effects cannot be neglected; and (iii) measurements on an installed BPL system suggest that it is operating within, but very close to, the limits set by rules recently adopted by the Federal Communications Commission.

Design and optimization of fiber optic small-cell backhaul based on an existing fiber-to-the-node residential access network

As the number of wireless users and per-user bandwidth demands continue to increase, both the vendor and carrier communities agree that wireless networks must evolve toward more dense deployments. So-called heterogeneous networks are a commonly proposed evolution, whereby existing macrocellular networks are supplemented with an underlay of small cells. The placement of new small-cell sites is typically determined based on various location-dependent factors such as radio propagation calculations, user densities, and measurements of congestion and demand. The backhaul network, which can account for a significant portion of the total cost of the deployment, is then designed in reaction to the placement of small cells. In contrast, we describe a design method that first considers the locations of existing fibered and powered facilities that might be leveraged to provide inexpensive backhaul. Naturally, such a method is only feasible if the carrier has a legacy local fiber network. This article describes an efficient fiber backhaul strategy for a small-cell network, which leverages facilities associated with an existing FTTN residential access network. Once potential small-cell sites are determined from among all FTTN remote terminals, optimization techniques are used to choose the most efficient subset of sites for maximum coverage, and to design the fiber backhaul architecture.

The AT&T Labs broadband fixed wireless field experiment

We describe an ongoing broadband fixed two-way wireless field experiment conducted by AT&T Laboratories-Research in Monmouth County, New Jersey. Our experiment, which is one of the first two-way broadband fixed wireless systems offers an end-to-end broadband packet access service, with telecommuting as the primary application for our employee users. It operates in the 2.6 GHz MMDS spectrum, and is based on cable modem technology. We have developed a Web-based network monitoring/management tool that greatly enhances the ability to manage, diagnose, and optimize the system. The lengthy period of operation has allowed us to make observations about user behavior, weather-related channel impairments, and equipment performance. We have identified several design issues related to the application of cable modem technology to the fixed wireless environment. Also, we have measured a significant path loss effect arising from a combination of rain and foliage.

A subjective survey of user experience for data applications for future cellular wireless networks

We present results from a subjective survey of user experience for data applications in future cellular wireless networks. Using a network emulator, we tested various computing scenarios with different channel sharing schemes (dedicated and shared bandwidth), computing models (local processing with remote files and thin-client server based computing), applications (Web browsing, MS Word, and MS Power Point), and devices (laptops and palm devices). Subjective quality ratings (1 to 5) from 100+ users were collected to obtain an average quality score for the user experience in each scenario. They are used to generate a set of utility curves based on channel rate and number of users sharing the system. Our survey results show that, with laptop-type devices, the preferred computing model changes with the application, and may also change as the available bandwidth changes. For palm devices, the ability to handle general computing tasks is primarily limited by the display and is not sensitive to the wireless channel conditions.

A common password method for protection of multiple accounts

This paper proposes a common password method for users who need to protect multiple accounts using passwords. It requires a user to remember only one password, called a common password, to access any of his/her accounts. Each account is protected by a different password, called a specific password. It is generated by a one-way hash function of an account-specific random number that is stored at the account server or a proxy in an encryption form, where the encryption key is derived from the common password. Compared with a convenient but insecure practice of using one or several passwords to protect multiple accounts, the common password method is convenient and secure. It assures that compromising one specific password does not reveal the common password and any other specific password. A Web-based implementation for the common password method is also presented in this paper. It employs a Web server to store every users account identifiers and encrypted random numbers, and to supply them to the user in a Web page that contains a password calculator written in JavaScript. The user can compute a specific password using a Web browser on his/her computer for any application that requires password authentication.

Off-the-record email system

In the flood of communications now carried via email, it frequently happens that users want to keep some casual or sensitive exchanges off the record, just as in ordinary telephone conversations. Within the system architectures commonly in use today, however, virtually all email transmissions leave a permanent record behind-a paper trail-that is extremely difficult to obliterate. Even after an email is deleted by both the sender and the recipient, a copy will likely remain in backup storage at one or more of the email servers that handled the message during its lifetime. Encryption does not solve the problem, because the message can be recovered if the decryption key is revealed, perhaps under court order, or for some other reason. To ensure email privacy, an off-the-record email system is proposed. In this system, the email stays in the senders computer and is read by the recipient through a Web browser over a secure connection. The message content cannot be recovered from an encrypted copy even with the help of both parties private keys. Further, the email has a limited lifetime. After it is deleted from the senders computer, it cannot be recovered from any remaining backup records. The new system is completely compatible with current email implementations. Using existing tools, email users can conduct secure, off-the-record communications. Two practical implementations are given to demonstrate how to deploy off-the-record email both in an intranet as well as on the Internet.

Seamless mobility management based on proxy servers

We devise an integrated wireless network architecture using proxy servers to support mobility management. The technique takes advantage of the existing functionalities of proxy servers to provide mobility support for applications such as Web browsing and ftp, without modifying the IP protocol stack of the mobile host. The architecture uses proxy servers to force all packets originating from mobile hosts to a close-by mobility-aware router so that the latter can maintain active data connections during handoffs across different networks. By deploying multiple proxy and mobility-aware router pairs and by assigning mobile hosts to proxy servers dynamically, the proposed architecture provides efficient mobility management functionalities, and is inherently scalable.

Internet roaming: a WLAN/3G integration system for enterprises

This paper proposes an enterprise-oriented WLAN/3G network integration solution, called the Internet Roaming system. Differing from other operator-oriented WLAN/3G network integration solutions, the Internet Roaming system is a practical IP-based corporate network architecture that provides seamless internetworking across office WLAN, home WLAN, public WLAN, and 2.5G/3G cellular network for corporate wireless data users. An Internet Roaming system may have four building blocks. They are IRC (Internet Roaming Client), SMG (secure mobility gateway), SIA (Secure IP Access) gateway, and VSA (virtual single account) server. The IRC is a special client tool (software or hardware) installed on a wireless data device. It provides a secure mobile IP connection from the wireless data device to the corporate network transparent to the operating system of the wireless data devices. The SMG is a mobile IPsec gateway installed on the corporate core network facing the Internet. It works with the IRC to maintain a secure mobile IP connection when the wireless data device is connected on the Internet through a home WLAN, a public WLAN, or a cellular network. The SIA server is a special IPsec gateway installed on the corporate intranet where office WLAN is installed. It works with the IRC to assure the security of office WLAN while improving the routing efficiency for users computers. The VSA server manages the IRC, SMG, and SIA servers.