IQM Mitigation Algorithm with Channel Awareness for Upstream SC-FDMA Systems in the Context of Dual-Hop Broadcasts

A challenging issue for single carrier frequency division multiple access (SC-FDMA) transmissions is in-phase and quadrature-phase mismatch (IQM). There has been prior reporting on this issue; however, it has always been in the setting of single-hop broadcasts. This study explored the problem of IQM in multiple users upstream SC-FDMA networks within the framework of amplify-and-forward (AF) dual-hop transmissions. We got closer to realistic scenarios by supposing that each node in the network creates its own IQM. Moreover, we profited from the channel decoders that are included in most wireless standards to provide a valuable aid to the offered estimator. A mathematical analysis revealed that IQM originating from all nodes can be merged into channel coefficients to provide so-called effective channel coefficients. This eliminates the requirement for a chain of algorithms to be employed at each node to estimate and adjust for IQM, as well as the algorithms needed to evaluate channel coefficients between the base station and each node in the network. A theoretical investigation showed that the maximum likelihood (ML) solution to the effective channel coefficients estimation is too complicated to be applied in reality. Alternatively, we employed a simple methodology relying on the space-alternating generalized expectation maximization (SAGE) process to determine the ML predictions of the required parameters. The proposed approach incorporates a feedback loop in which the estimator and the channel decoder exchange information to boost one another’s efficiency. Furthermore, we detail how to execute data detection by making use of the predicted effective channel coefficients. The simulation results verify the effectiveness of the proposed approach and show that it outperforms the current methods.