Introduction to Software Radio Concepts
The Need for Software Radios
With the emergence of new standards and protocols, wireless communications is developing at a furious pace. Rapid adoption of the wireline-base Internet has led to demand for wireless Internet connectivity but with added capabilities, such as integrated services that offer seamless global coverage and user-controlled quality of service (QoS). The challenge in creating sophisticated wireless Internet connectivity is compounded by the desire for future-proof radios, which keep radio hardware and software from becoming obsolete as new standards, techniques, and technology become available. The concept of integrated seamless global coverage requires that the radio support two distinct features: first, global roaming or seamless coverage across geographical regions; second, interfacing with different systems and standards to provide seamless services at a fixed location. Multimode phones that can switch between different cellular standards like IS-95 and Global System Mobile (GSM) fall in the first category, while the ability to interface with other services like Bluetooth or IEEE 802.11 networks falls in the second category. Further, the rate of technology innovation is accelerating, and predicting technological change and its ramifi-cations to business is especially problematic. As a result, to keep their systems up to date, wireless systems manufacturers and service providers must respond to changes as they occur by upgrading systems to incorporate the latest innovations or to fix bugs as they are discovered. Many manufacturers tell horror stories of releasing hundreds of thousands of defective phones that had to be recalled and discarded. Since frequent redesign is expensive, time-consuming, and inconvenient to end users, interest is increasing in future-proof radios.
Existing technologies for voice, video, and data use different packet structures, data types, and signal processing techniques. Integrated services can be obtained with either a single device capable of delivering various services or with a radio that can communicate with devices providing complementary services. The supporting technologies and networks that the radio might have to use can vary with the physical location of the user. To successfully communicate with different systems, the radio has to communicate and decode the signals of devices using different air-interfaces. Furthermore, to manage changes in networking protocols, services, and environments, mobile devices supporting reconfig-urable hardware also need to seamlessly support multiple protocols, such as IP (Internet Protocol) and MExE (Mobile Execution Environment). Such radios can be implemented efficiently using software radio architectures in which the radio reconfigures itself based on the system it will be interfacing with and the functionalities it will be supporting.
Second-generation (2G) wireless technology consists of a handful of incompatible standards, and the goal behind the development of third-generation (3G) standards is compatibility among these standards within and between different generations' standards. Even if cellular standards globally converge, 3G systems require multimode operation and automatic mode selection. With fourth-generation (4G) and possibly 3G systems, the user's application will likely have the ability to control the quality of service and obtain a higher QoS for a higher cost. Higher QoS can be achieved through priority scheduling of packets, changes in data packaging, improved protection coding, better channel equalization techniques, implementation of smart antennas, and so on. The mobile subscriber must have the ability to select the network provider as well as the services needed.