A Power-Efficient Scheme for Cellular Uplink with Inter-cell Interference.

We investigate Gaussian widely linear precoding well-known as improper Gaussian signaling for the cellular uplink with inter-cell interference (known as interference multiple access channel (IMAC)). This transmission scheme provides extra degrees of freedom by treating the real and imaginary components of the complex Gaussian signal differently. Since current standards mainly utilize proper Gaussian signaling, we highlight the benefits of joint improper Gaussian signaling and precoding over multiple temporal dimensions (symbol extension in time) in IMAC. This scheme achieves significantly high information rates at the expense of extra complexity at the transmission phase. We study the sum-power minimization problem under rate constraints. This problem is a difference of convex (DC) program, hence a non-convex problem. We derive a convex subset of the original non-convex set that belongs to its interior. The convex subset expands and approaches the original non-convex set from its interior iteratively. By numerical simulations, we observe the benefits of improper Gaussian signaling alongside symbol extension in power consumption for both single-antenna and multi-antenna base stations. Interestingly, we observe that at high interference scenarios, the efficiency of improper Gaussian signaling outperforms conventional proper Gaussian signaling at low rate demands. Moreover, in such scenarios the sum-power required for achieving particular rate demands is significantly reduced.