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New technologies have paved the way for portable computers operating at low power levels with extended battery duration. Computer manufacturers now offer portables using 3.3 Volt techniques, LCD displays and pen interfaces [6]. The AT&T Personal Communicator [7] is a first step towards a small sized personal communication device combining computation and communication.
Still users have to face the fact that even if they have sufficient computational power in their hands they have insufficient communication capabilities. Applications requiring mobile and wireless communication channels suffer from the low bandwidth offered (less than 20 kbit/sec). Current wireless LAN interfaces offer high data rates (0.5 - 2Mbit/sec) but consume too much power and space to fit into a portable computer.
Some of these wireless data networks are based on standards such as DECT or products like NCR WaveLan [4], and Motorola Altair [2]. While these systems replace cables in office environments efficiently, they are not suitable for supporting a large number of mobile users. DECT is a connection oriented network where a mobile user can send up to 400kbit/sec while fixed networks such as Ethernet offer 10Mbit/sec in a connectionless fashion. The NCR WaveLan product offers spread spectrum technology but lacks power control and does not support cell hand-overs well (due to its inability to listen with more than one spreading code sequence). Moving from one cell to another in the Altair system requires new synchronization to a control module and selection of one out of 36 possible antenna configurations.
The Walkstation II project will not only investigate wireless networks but a complete radio based cellular system for interactive mobile multimedia applications including aspects of VLSI design, radio communication, network protocols and mobile application services.
We will develop a device for mobile internet routing (MINT). It will have sufficient computational power to perform all necessary communication protocol operations, including access to TCP/IP networks. The MINT hardware has been developed in a pre-project phase in conjunction with HP Labs (Palo Alto). Initially commercial components and self-designed infrared transceivers will be used in an early testbed called ERIC (Electrum Radio based network for Interactive multimedia Communication). This gives possibilities for parallel research on distributed applications, radio link and network protocols as well as for network measurements. Later the refined solutions will be integrated in custom designed VLSI chips.
The second phase of the ERIC testbed will test new designs using recent advances in DSP systems [1] to realize high data rate digital spread spectrum modems with 2-10 Mbit/sec for radio communication at 2GHz. Special attention will be given to low power consumption.
In order to provide robust, low power, wireless Local Area Networks (LAN) we must seek new solutions for radio spectrum resource management and radio system architectures. Problem areas include the design of channel access protocols and point diversity schemes ("handoff"), multicasting and error control procedures. Research will focus on overall radio system design and performance/feasibility studies (performance bounds) leading to the proposal of actual algorithms/protocols for the ERIC testbed.
The integration of the mobile LAN into fixed environments must be transparent to the user who should see no difference when using mobile or fixed computers except some performance reduction due to different link rates. The Mobile*IP [3] network implementation developed at Columbia University, USA will act as a starting point. Network performance measurements with at least 50 to 100 users and network simulations will give further directions for improvements and network management. In cooperation with Stockholm Gigabit Network (SGN) we will also examine the use of ATM as a high-speed backbone technology.