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摘要
This paper describes the development of a fast adaptable FPGA-based wideband channel sounder with signal bandwidths of up to 200ˋMHz and channel sampling rates up to 5.4ˋkHz. The application of FPGA allows the user to vary the number of real-time channel response averages, channel sampling interval, and duration of measurement. The waveform, bandwidth, and frequency resolution of the sounder can be adapted for any channel under investigation. The design approach and technology used has led to a reduction in size and weight by more than 60%. This makes the sounder ideal for mobile time-variant wireless communication channels studies. Averaging allows processing gains of up to 30ˋdB to be achieved for measurement in weak signal conditions. The technique applied also improves reliability, reduces power consumption, and has shifted sounder design complexity from hardware to software. Test results show that the sounder can detect very small-scale variations in channels. 1. Introduction Channel sounders are used to study wideband signal transmission channels [1]. Although simple to design, in theory, they are complex to build and hence, expensive to purchase. Most channel sounders are developed using bespoke electronic systems. Although the use of wideband wireless communication systems is widespread and is expected to continue to grow, research into the channels that support these high data rate transmissions is limited, in most part, to simulations [2, 3]. Many wideband channel studies involve the use of general purpose instruments such as a vector network analyzer that can only be used for short-range investigations and are not suitable for fast channel sampling and mobile measurements [4, 5]. Compared to narrow band systems, channel sounders have to measure all frequencies within the bandwidth in a very short time during which the channel is assumed to be stationary [6]. For any given bandwidth, the Nyquist sampling criterion must be met. Channel probing signals that are widely used include Pseudorandom Binary Sequence (PRBS) and chirp [7]. Since the frequency spectra of these signals are not perfectly rectangular, the sampling frequency ( ) must be more than twice the signal bandwidth ( ). This generates large volumes of data in a short time and transferring this data from a sampling system for storage presents a unique challenge. To facilitate further studies into the causes and impact of high-speed channel variations on wireless communication, an adaptive and fast channel sampling sounder was required. The objective was ※to developed a very compact,
