Performance of Joint Iterative Detection and Decoding in Coherent Optical Channels

We propose a layered space time (LST) transceiver in a multiuser code division multiple access (CDMA) mobile communication system. In particular, we examine a multiuser iterative receiver with joint detection, channel estimation and decoding in a frequency selective fading channel. The iterative parallel interference canceller (PIC) with statistics combining is used as the multiuser detection scheme and a least mean square (LMS) adaptive algorithm is applied to estimate the multiple input and multiple output (MIMO) frequency selective fading channel. Simulation results are presented to demonstrate the performance of this receiver. It is shown that the performance of the receiver with iterative channel estimation is close to that of the receiver with perfect channel state information (CSI).

In this paper, we derive the exact input/output transfer functions of the optimal a-posteriori probability channel detector for a general ISI channel with erasures. Considering three channel impulse responses of different memory as an example, we compute the BP and MAP thresholds for regular spatially coupled LDPC codes with joint iterative detection and decoding. When we compare the results with the thresholds of ISI channels with Gaussian noise we observe an apparent inconsistency, i.e., a channel which performs better with erasures performs worse with AWGN. We show that this anomaly can be resolved by looking at the thresholds from an entropy perspective. We finally show that with spatial coupling we can achieve the symmetric information rates of different ISI channels using the same code.

In order to achieve the full potential of massive multiple-input multiple-output (MIMO) systems, joint iterative detection and decoding (JIDD) methods are often used. In addition, minimum mean-square-error parallel interference cancellation (MMSE-PIC) technique is usually employed for JIDD-based MIMO systems due to the good trade-off between complexity and performance. In spite of this, the operations of matrix inversion still bring great pressure to the complexity of the system. In this paper, we propose complexity reduced MMSE-PIC detection methods for JIDD schemes. The presented methods combine the Newton iteration method with MMSE-PIC for JIDD systems to reduce the computational complexity of matrix inversion. The simulation results reveal that the proposed methods can reduce the complexity without obvious performance degradation.

In TDD-CDMA, the detection method conventionally is MMSE-BDFE (minimum mean square error-block decision feedback equalization) based joint detection. MMSE-IC is an efficient detection algorithm in V-BLAST. To adopt the advantages of MMSE-IC (minimum mean square error-interference cancellation), we can embed MMSE-BDFE into MMSE-IC. Furthermore, we can postpone the interference cancellation after decoding, and joint detect the remained users' data from the remained signals in the next iteration. By the aid of interference cancellation after decoding, the decoding decision gain and interference cancellation gain can be obtained, so the performance is improved especially when the users' number is large. The experiments show that the proposed methods have better performance.

Iterative receiver algorithms for multi-user detection and decoding are a solution for mitigating multiple-access interference (MAI) in multiple access communication systems. After several iterations they outperform noniterative schemes, while maintaining modest complexity. In this paper, we present an iterative receiver for multiple-antenna systems in frequency selective fading. Channel knowledge is not assumed to be available at the receiver. We propose a comprehensive algorithm that performs channel estimation, multi-user detection and decoding in an iterative manner. The multipath channel is estimated using several pilot symbols and soft estimates of data symbols. The performance of the receiver is evaluated by simulations.

We propose a very fast-convergence joint iterative detection and decoding (JIDD) scheme for channel-coded sparse code multiple access (SCMA). In the conventional JIDD, all users’ channel decoding iterations are performed in parallel after all users’ variable nodes in the SCMA factor graph are updated. The proposed JIDD scheme, however, slices all channel decoding iterations into per-user channel decoding, and inserts them deeply into the factor graph. By doing this, message enhancement by channel decoding immediately propagates to the connected users’ messages in the factor graph, even within one message passing algorithm iteration, while maintaining the same total computational complexity per JIDD iteration. Numerical results confirm that in various link scenarios, the proposed scheme requires only two or three iterations for BER convergence, while the conventional JIDD scheme requires more than six iterations. In downlink scenarios, the proposed scheme achieves an even faster convergence rate. Moreover, in a uplink scenario with perfect power control, the converged BER of the proposed scheme is quite a bit lower than the conventional scheme, and the proposed scheme requires only two iterations to get the same BER level as the conventional scheme. Consequently, thanks to fast convergence, the proposed scheme dramatically reduces the overall computational complexity for achieving BER convergence. In addition, the fast convergence rate compensates for the multi-user detection latency issue, which is inherent in sequential algorithms, and the issue is further overcome by employing the group-wise sequential version of the proposed scheme.

Publication in the conference proceedings of EUSIPCO, Viena, Austria, 2004

This study evaluated the use of GFDM transmission in passive optical networks (PONs) by comparing the performance of coherent and non-coherent optical receivers using OptSim 2023.12sp2 and Matlab 2018b ®. The study concentrated on transmitting 10 Gb/s radio frequency signals over optical fiber, emphasizing the significance of high-speed fronthaul links for 5G networks. The findings demonstrated that coherent detection markedly enhances receiver sensitivity by approximately 3 dB compared to direct detection, thereby augmenting the capacity of optical fronthaul networks despite the elevated cost. Additionally, the study recommended investigating pre- and post-compensation techniques to mitigate signal dispersion in optical fibers for further performance optimization.

This paper studies the performance of iterative multiuser decoding, interference cancellation, and channel estimation techniques applicable to third generation WCDMA systems. The concept uses a posteriori probabilities of code symbols to enhance detection, decoding and channel estimation in an iterative fashion. The performance is analyzed in a multipath channel with simulations. It is seen that the proposed concept combats multiuser interference effectively and performs almost as well as single user systems.

The BER performance of iterative decoding systems and PRML systems in a perpendicular magnetic recording channel is experimentally investigated. A performance evaluation system consisting of a spinstand, a recording waveform generator, a digital storage oscilloscope and a personal computer was used. PR1ML, PR2ML, EPR3ML, E/sup 2/PR3ML and ME/sup 2/PR4ML systems are discussed as a PRML channel. The 8/9 and 16/17 iterative decoding systems consists of the encoder, with RSC encoder serially concatenated with preceded PR channels and the iterative decoder with APP modules using Max-log-MAP algorithm. The results show that EPR3ML and E/sup 2/PR3ML provide good BER performance in a perpendicular magnetic recording channel and that the iterative decoding system is also an efficient way to improve the BER performance in the channel.

An improved coherent optical receiver architecture that compensates for a random drift in the state of polarization (SOP) of both the signal and the local oscillator (LO) is presented for the first time. The proposed architecture comprises two conventional coherent optical receiver front-ends in tandem, where the SOP of the LO is first divided into its two orthogonal components and then distributed to each coherent optical receiver front-end module. Two distinct methods of polarization diversity recovery of the modulation based on the MRC technique and an eigenvalue-eigenvector decomposition of the covariance matrix have been used to effectively recover the transmitted signal. The concept is validated by numerical simulations, where a differential quadrature phase-shift keyed (DQPSK) modulated signal with a random time-varying SOP is first generated. After its mixing with a LO also possessing a random time-varying SOP, the algorithms that have been developed are provided with eight input variables to be digitally processed. The constellation diagrams corresponding to the recovered DQPSK modulation obtained using the two polarization diversity methods are presented.

This letter considers low-density parity-check (LDPC) coding of correlated binary sources and a novel iterative joint channel decoding without communication of any side information. We demonstrate that depending on the extent of the source correlation, additional coding gains can be obtained. Two stages of iterative decoding are employed. During global iterations, updated estimates of the source correlation are obtained and passed on to the sum-product decoder that performs local iterations with a predefined stopping criterion and/or a maximum number of local decoding iterations. Simulation results indicate that very few global iterations (2-5) are sufficient to reap significant benefits from implicit knowledge of source correlation. Finally, we provide analytical performance bounds for our iterative joint decoder and comparisons with sample simulation results.

Delivering geographically segmented local content remains one of the key challenges in Single Frequency Networks (SFNs). By leveraging Layered Division Multiplexing (LDM), Local Content Insertion (LCI) can be achieved through Geographically Segmented Localcasting (GSL) for both multimedia and datacasting applications. This paper introduces a solution where region-wide broadcast services are carried by the Core Layer (CL) of the LDM, while local content is transmitted through the Enhancement Layer (EL). This approach also benefits network design and transmitter deployment, as new transmitters can be positioned freely within the intended broadcast service area. Each additional site enhances the reception quality of the regional component (LDM CL) while simultaneously delivering geographically specific multimedia and datacasting services to its local coverage zone. Since the localcasting signal on the EL operates at a lower transmission power, co-channel interference among local transmitters is minimized. A co-channel interference mitigation technique, Iterative Joint Detection and Decoding (IJDD), is also introduced. The paper outlines a roadmap for deploying LCI/GSL systems. Leveraging LDM enables any terrestrial television platform to adopt this approach in SFN or High-Power High-Tower (HPHT) configurations while remaining compatible with existing receivers. Furthermore, any cell-based wireless systems (5G/6G) can exploit this method, efficiently integrating broadcast, multicast, and unicast service delivery.

We propose a self-reconfiguring constant modulus algorithm (CMA) using a constrained mode followed by an unconstrained mode for solving the singularity issue of CMA equalizers in polarization-division-multiplexed coherent receivers.

A highly integrated 40 Gbit/s coherent optical receiver is reported using a Costas loop as a homodyne optical phase locked loop (OPLL). A photonic IC, an electrical IC, and a hybrid loop filter are characterized, and the feedback loop system is fully analyzed to build a stable homodyne OPLL. All components are integrated on a single substrate within the compact size of 10 × 10mm(2), and a 1.1 GHz loop bandwidth and a 120 psloop delay are achieved. The binary phase-shift keying receiver exhibits error-free (BER<10(-12)) up to 35 Gbit/s and BER<10(-7) for 40 Gbit/s with no latency, and consumes less than 3 W power.