Scalable real-time channel simulation for wireless network emulation

Wireless network emulators are valuable tools for evaluating the performance of a wireless network in a realistic and controlled environment. In hardware based wireless network emulators, the antenna ports of radios are attached to a real-time hardware channel simulator which produces a multipath channel between each pair of nodes. As the number of nodes in a network increases the number of paths increases quadratically. Hardware channel simulators often operate in the time domain, but for a large number of multipath channels, hardware simulation is more efficient in the frequency domain. The problem with frequency domain emulation is that the FFT and IFFT operations introduce a large latency into the channel which may not be acceptable for emulating networks with time sensitive protocols. This thesis presents a frequency domain simulation technique that can greatly extend the length of the channel without increasing the channel latency with only a small increase in hardware. The technique uses a feedback loop in the frequency domain to simulate a long multipath channel and is referred to as the feedback channel extender (FCE). An 11 node frequency domain emulator system was built with an FCE on each channel. The new emulator system is shown to produce the FCE channels without significant distortion from hardware. The FCE is able to extend the length of the channel, but the statistics of the resulting channel will stray from typical channel models. When properly designed, the FCE is able to produce a wide sense stationary, uncorrelated scattering (WSS-US), Rayleigh fading channel with an exponential power delay profile. The theoretical performance of a narrowband radio and a wideband radio with MIMSE equalization are all studied for the FCE channel. The validity of the FCE was also tested with 802.11b and 802.11g radios in the emulator. From the theoretical analysis and experimentation, the performance of the radios in the FCE channels is shown to be similar to the performance in channels created by a traditional channel simulator with many more hardware resources. Therefore, the FCE can be used to simulate channels with long delay spreads when hardware resources are scarce.