Sequence detection offers improved error-rate performance over conventional symbol-by-symbol detection when channel knowledge is not available at the receiver end. However, maximum-likelihood (ML) noncoherent sequence detection is proven to be notoriously intractable in many communication settings. In this work, we develop a new ML sequence detector for pulse-amplitude modulation (PAM) or quadrature-amplitude modulation (QAM) transmissions in unknown Rayleigh fading. Our detector identifies the ML sequence with overall polynomial complexity. This is possible via an auxiliary-angle approach that unlocks a low-rank property of the ML detection problem, reduces the exponential-size set of solution sequences to a polynomial-size set of candidates, and guarantees that the ML sequence is always contained in this substantially smaller set.

Blind sequence detection offers significant gains over conventional symbol-by-symbol detection when channel knowledge is not available at the receiver. However, maximum-likelihood (ML) blind sequence detection is often intractable due to exponential complexity in the sequence length. In this work, we develop a polynomial-time ML blind sequence detector for pulse-amplitude modulation (PAM) transmissions in Rayleigh fading. Our detector follows an auxiliary-angle approach that reduces the exponential-size space of solution vectors to a polynomial-size set of candidate sequences; we prove that this significantly smaller set always contains the ML PAM sequence. Hence, with overall polynomial complexity the proposed detector solves the problem of identifying the ML PAM sequence in unknown Rayleigh fading.

In this paper, we present a machine to machine (M2M) communication scheme, where the source communicates with the corresponding destination node with the help of one or more relay nodes. The objective is to minimize the total consumed power at the relays under specific performance constraints, while also considering the individual power limitations of each relay. In order to solve the original problem, we transform into an equivalent convex optimization problem. Simulations results are provided to validate the theoretical analysis and to illustrate the desired tradeoff between error performance and total energy consumption.