The intra-and/or inter-cell interference have been the major obstacle that constrain the performance of cellular systems. In this regard, there have been approaches to mitigate the inherent interference in the cellular systems, which support multiple user equipments (UEs) distributed in multiple adjacent cells. However, the previous approaches to cancel the interference at the receiver were mostly available at the cost of additional system information of the interference from the neighboring cells. In this paper, we propose an advanced receiver algorithm that efficiently suppresses interferences by utilizing statistical characteristics of interference signals, hence no need for additional information to detect the interference. It is shown that the proposed receiver suppresses inter-cell interference well and outperforms conventional receivers when applied to typical LTE systems.

With the increase of the cell loadings, the interference among the adjacent cells becomes severer acting as the limiting factor for the cell-edge user performance. In this regard, there have been many standard activities in 3GPP (3rd Generation Partnership Project) to mitigate the ICI (Inter-Cell Interference). The eNB (Enhanced Node-B)-centric ICI mitigation having its own limit, the recent approaches incorporate the interference cancellation of a dominant interference from the adjacent cell at the receiver. However, for the LTE (Long Term Evolution) uplink, the SC-FDMA (Single-Carrier Frequency Division Multiple Access) structure prohibited the eNB to use a similar interference cancellation scheme as for the OFDMA (Orthogonal Frequency Division Multiple Access) UE (User Equipment) receiver. In this paper, we propose a blind interference cancellation receiver for LTE eNB, which performs ICI cancellation blindly without prior information of the adjacent cell interferences. It is shown that the proposed blind interference cancellation receiver for SC-FDMA provides significant performance gain against the conventional receiver.

Multitone‐frequency and quadrature‐amplitude modulation (MFQAM) is a combination of multitone frequency‐shift keying and quadrature‐amplitude modulation (QAM). In this study, the authors consider MFQAM with active subcarriers grouped in balance, where the active subcarriers are divided into a specified number of groups and the same QAM symbol is conveyed by every subcarrier in each group. This grouping may make MFQAM have frequency diversity in itself. They first derive the joint probability density function of the correlator outputs of an MFQAM receiver. They then compute the channel capacity of a coded modulation (CM) system employing MFQAM over Rayleigh fading channels. As a result, they demonstrate that for a moderate code rate between 1/3 and 2/3, its normalised throughput is close to the channel capacity limit in the low signal‐to‐noise ratio region, contrary to a CM system employing the conventional modulation. They also evaluate the frame error rate (FER) performance of a CM system employing MFQAM when a non‐binary error‐correcting code is employed. Numerical results demonstrate that the normalised throughput of the CM system computed via the FER shows a similar trend to that obtained via the channel capacity.

In cellular systems, the interference has been the most critical issue that practically limits the performance of overall networks. Furthermore, the distribution of the inter-cell interference (ICI) in conventional cellular networks employing orthogonal frequency-division multiple-access (OFDMA) with quadrature amplitude modulation (QAM) tends to approach a Gaussian distribution, which is known to be the worst-case distribution of the ICI as additive noise resulting in poor channel capacity. Thus, a dramatic enhancement of the channel capacity for the cellular network is expected when the ICI could be designed properly so that it has a non-Gaussian distribution. In this context, a cellular OFDMA system with a novel modulation scheme, frequency and quadrature-amplitude modulation (FQAM), is proposed in this paper. The statistical distribution of the ICI is shown to deviate far from the Gaussian distribution for the proposed FQAM-based system. Accordingly, it is shown that the non-Gaussian distribution of the ICI incurred with FQAM results in significantly improved transmission rates for the cell-edge users. Also, from the measurement results using practically implemented FQAM-based OFDMA systems, it is verified that the transmission rate for the cell-edge users could be increased significantly over the conventional QAM-based OFDMA system.

The distribution of the intercell interference (ICI) in conventional cellular networks employing orthogonal frequency-division multiple-access (OFDMA) with quadrature-amplitude modulation (QAM) tends to approach a Gaussian distribution when all available subcarriers in each cell are fully loaded. Recently, it has been also shown that the worst-case distribution of the ICI as additive noise in wireless networks with respect to the channel capacity is Gaussian. Thus, the channel capacity in cellular networks is expected to be further enhanced when the ICI could be designed properly so that it has a non-Gaussian distribution. This observation motivates us to propose, in this paper, a downlink cellular OFDMA network employing a modulation scheme called frequency and QAM (FQAM). We also derive maximum-likelihood metrics for the binary or non-binary error-correcting codes employed in the proposed network and propose their practical sub-optimal versions. Numerical results demonstrate that the distribution of the ICI in the proposed network deviates far from the Gaussian distribution. As a result, the transmission rates for the cell-edge users in the proposed network are significantly improved. In addition, the measurement results using practically implemented FQAM-based OFDMA systems verify that the transmission rates for the cell-edge users can dramatically increase, compared with the conventional QAM-based OFDMA network.

In this paper, we analyze the performance of soft decision decoded, synchronous, fast frequency-hopping spread-spectrum multiple-access networks using M-ary frequency shift keying in Rayleigh fading channels under the assumption that the number of frequency hopping slots is sufficiently large. The joint probability density function (pdf) of the absolute values of the correlator outputs is derived to compute the channel capacity and evaluate the soft decision decoding performance of the 3GPP Turbo and convolutional codes. Results indicate that soft decision decoding based on the derived pdf drastically outperforms traditional decoders based on the Gaussian approximation of the effect of the multiple access interference (MAI). The sensitivity of the derived soft decision decoder to estimation errors in system parameters and the required computational complexities of the derived soft decision decoding metrics are also investigated.