The time variance of a channel is exploited in interference alignment techniques. However, in the case of static channels, these interference alignment techniques do not hold, specifically for single-antenna systems. In this paper, we introduce simple data processing techniques that enable us to create the effect of a time varying channel from the underlying static channel. We call this channel the shadow channel. We exploit the time-varying nature of the relative channels introduced by the shadow channel for interference alignment. We demonstrate the throughput benefits of this interference alignment technique for different topologies. This technique can be thought of as operating over the two dimensions of the complex space of typical communication systems. In this paper, we present the feasibility of interference alignment techniques for single antenna nodes in static channel. We establish bound on the throughput gain due to this technique. Finally, we implement interference alignment over the shadow channel on the NI PXIe 1082 based software defined radio. We achieve throughput gains of upto 1.44X over TDMA systems using this interference alignment technique and upto 1.61X when this technique is coupled with interference cancellation.

We implement a passive remote keystroke detection mechanism using only changes in the wireless channel. The detection algorithm does not require the user to wear any active devices nor does it require a change in the user's wireless transmission technique. The receiver system is implemented with five antennas. We cancel the signals received on multiple antennas. The key insight to realizing a fine-grained localization system is to exploit the extremely high sensitivity of cancellation performance (interference cancellation in full-duplex for example) to exact amplitude and phase matching. The receiver design introduces a delay mismatch between the received signal streams to guarantee imperfect cancellation across the transmission bandwidth except at one in-band frequency resulting in a trough in the cancellation spectrum. We detect keystrokes by forming an array of observed trough frequency across different antenna pairs.

Global synchronization across time and frequency domains significantly benefits wireless communications. Multi-Cell (Network) MIMO, interference alignment solutions, opportunistic routing techniques in ad-hoc networks, OFDMA etc. all necessitate synchronization in either time or frequency domain or both. This paper presents sysname, a system that exploits the easily accessible and ubiquitous power line infrastructure to achieve synchronization in time and frequency domains across nodes distributed beyond a single-collision domain. sysname uses the power lines to transmit a reference frequency tone to which each node locks its frequency. sysname exploits the steady periodicity of delivered power signal itself to synchronize distributed nodes in time.