  This paper proposes the first known universal interference alignment scheme
for general $(1\times{}1)^K$ interference networks, either Gaussian or
deterministic, with only 2 symbol extension. While interference alignment is
theoretically powerful to increase the total network throughput tremendously,
no existing scheme can achieve the degree of freedom upper bound exactly with
finite complexity. This paper starts with detailed analysis of the diagonality
problem of naive symbol extension in small $(1\times1)^3$ networks, a technique
widely regarded as necessary to achieve interference alignment with
insufficient diversity. Then, a joint bandpass noncoherent demodulation and
interference alignment scheme is proposed to solve the diagonality problem by
trading signal power for increased system diversity, which is further traded
for multiplexing improvement. Finally, the proposed noncoherent interference
alignment scheme is extended to general $(1\times{}1)^K$ cases and is proven to
achieve the degree of freedom upper bound exactly. Simulation results verify
the correctness and powerfulness of the proposed scheme and show significant
degree of freedom improvement compared to the conventional orthogonal
transmission scheme.
