Noise-Loop Multiple Access for wireless communications

A fundamental problem for signal processing in wireless communications is the separation multiple signals/users from their mixture. The problem would be simpler if they are non-overlapping in either time domain or frequency domain. Two signals may be overlapping in both time and frequency, but they still can be easily separated if they are uncorrelated (orthogonal), like in Code Division Multiple Access system (CDMA). It may be interesting to know that two signals may be overlapping in both the frequency and time domain and also are not orthogonal to each other, but they can still be separated if each autocorrelation function at the receiver is separable in the domain of time-lags. In this paper, we will show how the Noise-Loop (NL) modulation, originally thought to produce security at physical layer, can be used to effectively separate uncoordinated/unorthogonal users sharing the same time and frequency band. In order to show the potential of noise-loop multiple access (NLMA) scheme, the theoretical solution is derived as well as numerical semi-analytical simulations. It can be shown that the NLMA is able to distinguish the bit stream of the users. This feature together with the intrinsic security make the NL an interesting scheme for wireless technology.