Software-Defined Radio for Wireless Local-Area Networks

New wireless communications standards do not replace old ones, instead the number of standards keeps on increasing and by now an abundance of standards exists. Moreover there is no reason to assume that this trend will ever stop. Therefore, the software-radio concept is emerging as a potential pragmatic solution: a software implementation of the user terminal able to dynamically adapt to the radio environment in which the terminal is located. For manufacturers this could result in shorter development time, cheaper production due to higher volumes. Furthermore software radio has advantages for consumers because it enables only software updates for new functionality without new hardware. Because of the analog nature of the air interface, a software radio will always have an analog front-end. In an ideal software radio, the analog-to-digital converter (ADC) and the digital-to-analog converter (DAC) are positioned directly after the antenna. Such an implementation is not feasible due to the power that such a device would consume and other physical limitations. It is therefore a challenge to design a system that preserves most properties of the ideal software radio while being realizable with current-day technology. Such a system is called a software-defined radio (SDR). A flexible, all-standard radio will consume more energy than a dedicated radio for a single standard. The first flexible radio could be an application where power consumption is less an issue; an example being a flexible radio in a notebook. This thesis presents such a radio with the focus on wireless LAN standards. These standards use phase modulation or OFDM in the $2.4$ GHz or $5$ GHz frequency band, so we decided in our project to combine a receiver of a phase modulation standard (Bluetooth) with an OFDM receiver (HiperLAN/2) first. In our view SDR is an implementation technology: the HiperLAN/2 hardware is that complex to the Bluetooth hardware that the Bluetooth receiver may be added to the HiperLAN/2 one at limited costs. In this thesis we describe how the physical layer of the OSI model of a phase-modulation receiver can be combined with an OFDM receiver at a functional level. The second goal of this research is to investigate whether this combined receiver can be implemented in software running on a General Purpose Processor (GPP) and estimate the costs of such an implementation with respect to power consumption and computational power requirements. For this reason, a testbed has been developed where all baseband physical layer functions have been successfully mapped on a Pentium 4 processor. This has been tested in combination with a CMOS-integrated wideband analog SDR front-end, containing a low noise amplifier, down-conversion mixers and filters. The testbed can be extended to other standards, because the only limitations in our testbed are the maximal channel bandwidth of $20$ MHz, the dynamic range of the wideband SDR analog front-end and the processing capabilities of the used PC. In 1999, Bose showed for second-generation mobile standards that it is possible to perform most baseband functions of the physical layer on a GPP processor. In his research, I/O was one of the main bottlenecks. In thesis we have identified that this is no longer true for current-day computers. Nowadays, an important bottleneck is the latency of the operating system, because wireless standards require fast response times. Major contributions of this thesis to the field of SDR research are extending the work of Bose for wireless LAN standards and developing a functional SDR receiver architecture that is capable of receiving standards that use OFDM or phase modulation