Co-Channel Interference Cancellation for Downlink Block Transmission with Cyclic Prefix

Performance analysis of multicell multiuser MIMO MC DS/CDMA system with MMSE user-ordered SIC technique

Multi carrier modulation is Orthogonal Frequency Division Multiplexing (OFDM), dividing the large band spectrum into small (narrow) band spectrum.OFDM offers flexibility in adaptation to time varying channel condition by adopting the parameters at each subcarrier accurately.Due to the multipath effect the OFDM system suffers Inter Symbol Interference (ISI).ISI can be reduced by introducing the guard band (cyclic prefix).Time-varying channel estimation is an important activity in next generation wireless communication.Channel estimation is required mainly for the significant signal processing operation in multiple input multiple output MIMO-OFDM systems.In this project DFT -based channel estimation based on block type arrangement is implemented in MAT Lab.The bit error rate (BER) of DFT (Discrete Fourier Transform)based channel estimation is less than the BER of LS (Least Square) and MMSE (Minimum Mean Square Error) based channel estimation with same signal to noise ratio (SNR).

The rapid growth of user density and heterogeneous service requirements in 5G and emerging 6G networks has intensified multi-user interference, particularly in power-domain non-orthogonal multiple access (PD-NOMA) systems. Conventional successive interference cancellation (SIC) techniques suffer from error propagation and performance degradation under imperfect channel conditions, limiting their reliability in practical deployments. This paper proposes a deep learning–based interference cancellation framework that combines Convolutional Neural Networks (CNNs) and Bidirectional Long Short-Term Memory (BiLSTM) networks for end-to-end signal detection in downlink NOMA systems. The proposed model exploits CNN layers to extract spatial interference features from complex-valued received signals, while BiLSTM layers capture bidirectional temporal dependencies caused by channel fading and symbol correlation. Unlike traditional SIC-based receivers, DL-NOMA-CancelNet directly reconstructs user signals without explicit channel estimation or manual interference subtraction. Simulation results obtained using MATLAB under Rayleigh fading and AWGN conditions demonstrate that our framework significantly outperforms conventional Least Squares (LS), Minimum Mean Square Error (MMSE), and single-network deep learning detectors. Specifically, this method achieves up to an 8–10× reduction in bit error rate (BER) across a wide signal-to-noise ratio (SNR) range, while maintaining low inference latency and moderate model complexity. These results confirm that our work provides a robust and scalable solution for interference mitigation in future 5G/6G downlink NOMA systems, particularly for ultra-reliable low-latency communications (URLLC) and massive machine-type communications (mMTC).

In orthogonal frequency division multiplexing (OFDM), Fourier Transform (FT) is used as a modulation technique. To avoid inter-symbol interference (ISI) in OFDM by a time dispersive channel, a cyclic prefix (CP) is used which also reduces its spectral efficiency. wavelet packet transform (WPT) as a modulation scheme has been proposed for wireless communication. In this paper, WPT based OFDM is presented and proposed using minimum mean square error (MMSE) equalizer. Equalization is a major factor in wavelets. MMSE is proposed for wavelet based OFDM (WOFDM) based on WPT and compared with zero forcing equalizer (ZFE). The performance is measured for arbitrary magnitude finite impulse response (FIR) channels in the presence of additive white Gaussian noise (AWGN) and impulse noise. Simulation results show a clear improvement in bit error rate (BER) for MMSE over ZFE equalization technique in the presence of noise.

This paper proposes an optimal training sequence framework for general block transmission systems over spatially correlated multiple-input multiple-output (MIMO) frequency selective channels. The pilot design is based on a formulation that minimizes the Bayesian Cramér-Rao bound (BCRB) for the mean squared error (MSE) of channel estimation, and is thus MSE optimal in nature. The novelty of the proposed work lies in development of a generic pilot design scheme applicable to all the four MIMO block transmission systems, namely single carrier cyclic prefix (SC-CP), single carrier zero padded (SC-ZP), multi-carrier zero padded (MC-ZP), and multi-carrier cyclic prefix (MC-CP) systems. Simulation results are presented to illustrate the superior performance of the proposed technique over the conventional pilot sequences, in terms of both MSE as well as bit error rate (BER).

In orthogonal frequency division multiplexing (OFDM) systems, a proper channel estimation algorithm can better improve the accuracy of information received at the receiver. Aiming at the problem that the traditional discrete fourier transform (DFT) channel estimation algorithm can not effectively suppress the internal noise of the cyclic prefix (CP), we propose an improved DFT channel estimation algorithm. This algorithm eliminates the internal noise by setting a new threshold inside the cyclic prefix (CP), and improves the accuracy of channel estimation. The simulation results show that the proposed algorithm is superior to the LS algorithm as well as the traditional DFT algorithm. It has a lower computation complexity, which can further improve the system performance and reduce the system bit error rate(BER).

In this paper, a new scheme of downlink co-channel interference (CCI)\ncancellation in OFDM cellular networks is introduced for users at the\ncell-edge. Coordinated symbol transmission between base stations (BS) is\noperated where the same symbol is transmitted from different BS on different\nsub-carriers. At the mobile station (MS) receiver, we introduce a soft decision\nmaximum likelihood CCI canceler and a modified maximum ratio combining (M-MRC)\nto obtain an estimate of the transmitted symbols. Weights used in the combining\nmethod are derived from the channels coefficients between the cooperated BS and\nthe MS. Simulations show that the proposed scheme works well under\nfrequency-selective channels and frequency non-selective channels. A gain of 9\ndB and 6 dB in SIR is obtained under multipath fading and flat-fading channels,\nrespectively.\n

The WiMax (Worldwide Interoperability for Microwave Access) is a technology in<strong> </strong>broadband wireless access, which employs OFDM (Orthogonal Frequency Division Multiplexing) as an alternative transmission to enable high speed data in communication system. This research aim is to analyze the performance system of the OFDM-Based WiMAX, which used the cyclic prefix. The model was designed in four schemes of simulation method, the BPSK (Binary Phase Shift Keying, QPSK (Quadrature Phase Shift Keying), 16 QAM (Quadrature Amplitude Modulation) and 64 QAM. Each scheme was investigated BER (Bit Error Rate) on AWGN (Additive White Gaussian Noise) channel and multipath Rayleigh fading channel, which had applied the cyclic prefix. By simulation of the cyclic prefix was produced the modulation measurement of the BPSK, QPSK, 16 and 64 QAM. The performance result of Eb/No 15 dB was obtained the BER of BPSK and QPSK of 1.11E-11, the BER of 16 QAM and 64 QAM of 8.69E-06 and 0.00333 respectively. Those results indicated much smaller BER value than EbNo 0 dB which BPSK and QPSK of 1 BER, 1.5 and 1.75 BER for 16 QAM and 64 QAM respectively. In conclusion, a higher value of EbNo, hence the BER value would be lower.

Satellite communications are expected to collaborate with 5G techniques in the future. In this paper, a detector based on the minimum mean square error (MMSE) criterion is designed at the receiver of a LEO satellite system to cancel co-channel interference (CCI) in a predetermined order successively, which is called ordered successive interference cancellation (OSIC). In order to make the detector have stronger ability to mitigate interference, low density parity check (LDPC) coding and soft demodulation schemes are applied with the OSIC jointly to improve our proposed MMSE-OSIC detector's performance. In the simulation analysis, we present the bit error rate (BER) performance of our proposed detector in an AWGN channel. Numerical results show that compared to the results of the conventional detection in existing literatures, the MMSE-OSIC detector can reduce the BERs for fixed signal-to-noise ratio (SNR) values. It means our proposed detector can be employed at the receiver with high service availability and reliability guaranteed.

Filter bank based multicarrier systems (FBMC) offer a number of benefits over conventional orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP). One benefit is the improved spectral efficiency by not using a redundant CP and by having much better control of out-of-band emission. Another advantage is the ease of accommodating multiple users in an FDMA fashion especially in the uplink, i. e. the multiple access channel (MAC). On the other hand, more elaborate equalization concepts are needed compared to the single-tap per-subcarrier equalizer sufficient in the OFDM with CP case. In this contribution we will present an efficient linear minimum mean square error (MMSE) equalization concept. Since FBMC systems employ offset-quadrature-amplitude-modulation (OQAM), a fractionally spaced per-subcarrier equalizer will be derived, which takes into account the inter-subcarrier interference due to frequency selective multipath fading. Still this is handled with decoupled per-subcarrier equalizers. Simulation results will show that OQAMFBMCs allow for savings in transmit power which have to be paid with a practicable amount of computational overhead.

Joint precoding and equalization design for reduced-CP OTFS based on the compact input–output model

In a companion paper, we have studied the zero-forcing (ZF) transceiver with decision feedback equalizer (DFE) over slowly time-varying narrowband multiinput multioutput (MIMO) channels. The space-time generalized triangular decomposition (ST-GTD) was used for the design of ZF-DFE transceivers. The space-time geometric mean decomposition (ST-GMD) ZF transceiver minimizes both the arithmetic mean square error (MSE) at the feedback detector and the average uncoded bit error rate (BER) in moderate high signal-to-noise ratio (SNR). This paper addresses the design problem of DFE transceiver without zero-forcing constraint. In the first part, a channel independent temporal precoder is superimposed on the conventional block-wise GMD-based minimum mean square error (MMSE) DFE transceiver to take advantage of the temporal diversity. In the second part, ST-GTD is applied for the design of MMSE DFE transceivers. With accurate channel prediction and space-time powerloading, the proposed ST-GMD MMSE transceiver minimizes the arithmetic MSE at the feedack detector, and maximizes Gaussian mutual information. For practical applications, the ST-GTD MMSE transceiver which does not require channel prediction but shares the same asymptotic BER performance with the ST-GMD MMSE system is also developed. In the convex region, our analysis shows that the proposed MMSE transceivers has better BER performance than the conventional GMD-based MMSE transceiver; the average BERs of the proposed systems are nonincreasing functions of the ST-block size. The superior performance of ST-GMD MMSE transceiver over the ST-GMD ZF transceiver is also verified analytically.

On the basis of analyzing the principle of multicarrier CDMA (MC-CDMA) technique and space–time coding technique, using the optimized complex wavelet packet as multicarrier modulation, a novel MC-CDMA system based on complex wavelet packet and space–time block codes is proposed. The bit error rate (BER) performance of the system is investigated in Rayleigh fading channel, and the corresponding BER expression is derived in detail. The system can overcome the decrease of spectrum efficiency of conventional MC-CDMA due to inserting cyclic prefix (CP). Moreover, the application of space–time coding technique strengthens the capability against fading channel significantly and perfects the system performance. Theoretical analysis shows that the proposed system with 2-transmitter antenna and 2-receiver antenna space–time block codes performs four times better than the single-antenna MC-CDMA system based on complex wavelet packet (CWP-MC-CDMA); the same conclusion is also reached by the simulation results in fading channel. As a result, the performance of the proposed CWP-MC-CDMA system outperforms a conventional MC-CDMA system based on DFT, it is close or superior to that of the conventional MC-CDMA with CP. Especially, the CWP-MC-CDMA system with space–time coding has superior ability to combat spatial fading and multi-access interference, and it slightly outperforms conventional MC-CDMA with CP and space–time coding.

Orthogonal Frequency Division Multiplexing (OFDM) underpins modern wireless communication due to its resilience against multi-path fading and computationally efficient implementations. However, on one hand, in scenarios with time-frequency doubly selective fading channels, OFDM systems face significant challenges, as channel variation induces inter-carrier interference (ICI) that disrupts subcarrier orthogonality. On the other hand, the limited length of the cyclic prefix (CP), often constrained to a fraction of the symbol duration, may be insufficient to fully mitigate inter-symbol interference (ISI) in scenarios with large time spreads. Extending CP length would reduce spectral efficiency and increase latency, making it incompatible with the demands of high-efficiency, low-latency systems. In this paper, we propose an autoencoder based OFDM architecture integrating adaptive pulse shaping with an equalization neural network (PS-EQNet) that jointly addresses ISI caused by insufficient CP and ICI due to channel dynamics through learnable time-frequency filters. Additionally, we introduce a detection network tailored for simplified channels, which reduces computational complexity compared to existing schemes while maintaining robust performance. Simulation results confirm that the proposed PS-EQNet OFDM system significantly relaxes CP requirements, enhances spectral efficiency (SE), and achieves reliable bit error rate (BER) performance in time-frequency selective channels, establishing a flexible trade-off among SE, BER, and computational complexity.

With the wireless communications growing rapidly, we need great-performance and high-efficiency channel estimation. An estimation method based on the quadri-phase complete complementary sequences (CCs) is proposed for the Multiple-Input and Multiple-Output (MIMO) systems. A time slot structure that using CCs with optimal periodic autocorrelations as cyclic prefix (CP) and zero padded (ZP) suffix is investigated. With the pilot blocks of CCs, optimal least square (LS) estimation in the minimum mean square error (MMSE) is got. In addition, with the appropriate length CCs, higher accuracy channel estimation will be achieved. To reduce the waste of frequency spectrum that pilot blocks usage, the same blocks would include the training sequences and the data. Analytical and simulation results demonstrate that the method is available and obtainable.