TCM Codes Research Articles

Performance analysis of OFDM based FSO communication system with TCM codes

Various channel coding schemes have been used over free space optical (FSO) links to alleviate the effects of turbulence induced fading. In this paper, performance analysis for TCM coded orthogonal frequency division multiplexing (OFDM) based FSO communication systems, operating over atmospheric turbulence channels. Analysis have been done in terms of bit error rate (BER) as a function of signal to noise ratio (SNR), considering the log-normal distribution model during weak turbulence and gamma-gamma distribution model for moderate and strong turbulence conditions. The integration of TCM with OFDM can solve bandwidth issue and bit rate degradation during wireless communication. Various modulation schemes have been studied for the said system keeping in mind different requirements such as band width and data rate etc. The simulation results and analysis have shown that the TCM coder with 16-QAM provides considerable coding gain as compared to uncoded system during all turbulence conditions. This system acts as high-performance wireless communication system (HPWCS) by providing BER of 10−9 which is necessary for stable operation on communication system.

Impact of Human Immunodeficiency Virus Infection on Takotsubo Cardiomyopathy Outcomes in a Large Nationwide Sample

Background/purposeTakotsubo cardiomyopathy (TCM) or stress-induced cardiomyopathy is characterized by transient wall-motion abnormalities often preceded by physical or emotional stress. Various baseline medical comorbidities were associated with worse outcomes, theoretically due to their effect on chronic stress exposure. The effect of concurrent human immunodeficiency virus (HIV) infection on outcomes of TCM has not been well-established. Methods/materialWe conducted a US-wide analysis of TCM hospitalizations from 2006 to 2014 by querying the National Inpatient Sample database for the International Classification of Diseases, Ninth Revision TCM code, baseline characteristics, and inpatient outcomes. TCM patients with HIV were compared to TCM patients without HIV. Multivariate regression models were constructed to account for potential confounders. ResultsWe identified 123,050 patients hospitalized with TCM; of those patients, 304 had positive HIV status. In an unadjusted analysis, in-hospital outcomes were worse in TCM patients with HIV infection in terms of development of acute kidney injury (16.8% vs 33.3%, P-value 0.002), use of invasive mechanical ventilation (18.3% vs 34.5%, P-value 0.003), and mortality (5.3% vs 17.1%, P-value <0.0001). After adjusting for age, gender, and comorbidities, there was no significant difference in the captured outcomes. ConclusionTCM patients with concurrent HIV had numerically worse outcomes. After adjusting for potential confounders, the statistical significance no longer existed, suggesting that statistical difference was primarily driven by difference in baseline sociodemographic parameters and coexisting comorbidities.

Abstract W P366: Increasing Utilization of Transitional Care Management (TCM) codes for Post-acute Stroke Care

Background and Issues: Stroke patients discharged home often are medically complex with decreased functional independence, especially during the initial transitional period after discharge. The Centers for Medicare and Medicaid Services has set transitional care requirements with new TCM coding that includes a 48 hour phone call from a licensed health professional and provider visit within 14 days after discharge. Process improvement methods can help determine the necessary staffing in order to efficiently meet these guidelines and increase utilization of these codes. Purpose: To review our post stroke transitional care program for TCM code utilization before and after addition of an RN to perform the follow-up phone calls. Methods: We performed a retrospective review of our hospital-supported transitional stroke care program. Our program initially consisted of 2 NPs on rotating schedules between inpatient service and outpatient ambulatory clinics to provide continuity of care during the transitional period after discharge, followed by 2 week hospital follow up visit focused on stroke education, caregiver support, recovery, and complications. The 2 nd phase included NPs performing high risk 48 hour phone calls after discharge thus allowing utilization of TCM codes. The 3 rd phase included addition of an RN to perform 48 hour phone calls and coordinating care between discharge and the stroke NP clinic visit. To assess the increased benefit of adding an RN for phone calls, we searched our EMR for TCM codes during the 3 month period before and 3 month period after RN phone calls were performed (February 2014 through July 2014). Results: A total of 95 patients were discharged home with a stroke or TIA in 6 months. In the first 3 months, 9 TCM codes were utilized. The last 3 months after the RN focused on 48 hour calls, 20 TCM codes were utilized. Conclusions: The a ddition of an RN to help provide 48 hour phone calls to patients after discharge increased the utilization of TCM coding. Further assessment of our transitional care program and use of TCM coding will be focused on effectiveness of decreasing readmission rates and improving outcomes.

A Novel Decoding Method for Non-Binary TCM Codes

A new non-binary decoding method, which is called Yaletharatalhussein decoding algorithm, is designed and implemented for decoding non-binary convolutional codes which is based on the trellis diagram representing the convolutional encoder. Yaletharatalhussein decoding algorithm outperforms the Viterbi algorithm and other algorithms in its simplicity, very small computational complexity, decoding reliability for high states TCM codes that suitable for Fourth-Generation (4G), decreasing errors with increasing word length, and easy to implement with real-time applications. The proposed Yaletharatalhussein decoding algorithm deals with non-binary error control coding of the convolutional and TCM codes. Convolutional codes differ from block codes in that a block code takes a fixed message length and encodes it, whereas a convolutional code can encode a continuous stream of data, and a hard-decision decoding can easily be realized using the Yaletharatalhussein algorithm. The idea of non-binary codes has been extended for symbols defined over rings of integers, which outperform binary codes with only a small increase in decoding complexity. The simulation results show that the performance of the nonbinary TCM-based Yaletharatalhussein algorithm outperforms the binary and non-binary decoding methods.

지상파 3D HDTV 전송을 위한 ATSC 전송 시스템의 확장 및 수정에 관한 연구

In this paper, we examined the possibility of the transmission capacity increase by an extension and a modification of ATSC 8-VSB transmission system[1] for broadcasting a 3D HDTV services through 6 MHz terrestrial channel. First we examined the performance and the limit of conventional ATSC 8-VSB transmission system. After that LDPC & BCH code are employed instead of conventional RS & TCM code and the transmission parameter is founded for the capacity increase with resonable TOV by varying the code-rates and increasing the modulation constellation. We do not consider the perfect backward compatibility for maximum transmission capacity increase like DVB-S2 system.

High-Speed Access over Copper: Rate Optimization and Signal Construction

This paper focuses on assessment and design of transmission systems for distribution of digital signals over standard Category-7A copper cables at speeds beyond 10 Gbps. The main contribution of this paper is on the technical feasibility and system design for data rates of 40 Gbps and 100 Gbps over copper. Based on capacity analysis and rate optimization algorithms, system parameters are obtained and the design implementation trade-offs are discussed. Our simulation results confirm that with the aid of a decision-feedback equalizer and powerful coding techniques, namely, TCM or LDPC code, 40 Gbps transmission is feasible over 50 m of CAT-7A copper cable. These results also indicate that 100 Gbps transmission can be achieved over 15 m cables.

Reduced-complexity algorithms for near-optimal decoding of turbo TCM codes

A reduced-complexity modified decoding algorithm for turbo trellis-coded modulation (TTCM) is proposed and evaluated in terms of complexity and bit error rate (BER) performance in an additive white Gaussian noise channel. The algorithm uses an optimal approximation of the Jacobian logarithm, used in the so-called Log-MAP decoding, by means of the max operation and three piecewise-linear terms. Further computational complexity savings are obtained by applying this approximation only to the two largest values within the decoding step. To improve performance, the algorithms are also investigated using a scaling factor for the extrinsic information. Computer-simulated BER performance evaluation results and complexity comparisons are reported showing the near-optimal performance as well as noticeable implementation advantages of the proposed algorithms with respect to the Log-MAP decoding.

Optimization and Implementation of a Viterbi Decoder Under Flexibility Constraints

This paper discusses the impact of flexibility when designing a Viterbi decoder for both convolutional and TCM codes. Different trade-offs have to be considered in choosing the right architecture for the processing blocks and the resulting hardware penalty is evaluated. We study the impact of symbol quantization that degrades performance and affects the wordlength of the rate-flexible trellis datapath. A radix-2-based architecture for this datapath relaxes the hardware requirements on the branch metric and survivor path blocks substantially. The cost of flexibility in terms of cell area and power consumption is explored by an investigation of synthesized designs that provide different transmission rates. Two designs are fabricated in a digital 0.13-mum CMOS process. Based on post-layout simulations, a symbol baud rate of 168 Mbaud/s is achieved in TCM mode, equivalent to a maximum throughput of 840 Mbit/s using a 64-QAM constellation.

Improving Wireless TCP Throughput by a Novel TCM-Based Hybrid ARQ

A novel hybrid ARQ (HARQ) scheme using a concatenated two-state trellis-coded modulation (CT-TCM) code is proposed for improving wireless TCP throughput. A distinguished feature of the proposed scheme is that the heavily punctured TCM codes are used for retransmissions of the corrupted data block, which are combined at the receiver with the previously received sequences of the same data block for decoding. By this method, significantly improved coding gain and efficient spectrum utilization can be achieved with very low complexity. A Markov model is developed to evaluate TCP throughput over the proposed HARQ in wireless link. By both analysis and simulation, we demonstrate that compared with other existing TCM-based ARQ schemes, significant improvement of TCP throughput over wireless links is achieved by the proposed CT-TCM HARQ while smaller buffer size is required at the access point.

High-Speed Turbo-TCM-Coded Orthogonal Frequency-Division Multiplexing Ultra-Wideband Systems

One of the UWB proposals in the IEEE P802.15 WPAN project is to use a multiband orthogonal frequency-division multiplexing (OFDM) system and punctured convolutional codes for UWB channels supporting a data rate up to 480 Mbps. In this paper, we improve the proposed system using turbo TCM with QAM constellation for higher data rate transmission. We construct a punctured parity-concatenated trellis codes, in which a TCM code is used as the inner code and a simple parity-check code is employed as the outer code. The result shows that the system can offer a much higher spectral efficiency, for example, 1.2 Gbps, which is 2.5 times higher than the proposed system. We identify several essential requirements to achieve the high rate transmission, for example, frequency and time diversity and multilevel error protection. Results are confirmed by density evolution.

Space – time ring TCM codes for QAM over fading channels

A new joint channel estimation with ST-ring TCM codes suitable for QAM modulation is proposed. The signal-to-point mapping is carefully studied and methods for further improving performance of QAM ST codes are investigated. The criteria for the design of ST codes are developed to include other factors and results of an a priori computer search to find good QAM ST-ring TCM codes are provided.

Minimal and systematic convolutional codes over finite Abelian groups

Convolutional codes over Abelian groups provide an effective theoretical framework for the analysis of some classes of TCM codes. The encoder synthesis for this class of codes is not as simple as in the binary case, since minimal encoders in the group case might be necessarily nonlinear. In this contribution an algorithmic method testing whether a convolutional code over an Abelian group admits a systematic or a minimal homomorphic encoder is provided. This test consists in verifying whether a subgroup splits in a group. Through this method, the class of codes admitting systematic encoders and the class of codes admitting minimal encoders can be compared. Finally this test is applied to some examples of practical relevance.

Neural network space diversity combination and ring coding for multicarrier CDMA over fast fading channels

Multicarrier CDMA is a major candidate to fulfil the requirements of 3G mobile systems. A novel scheme is developed combining modulo-S ring TCM with RNN-based adaptive space diversity for multicarrier CDMA systems with single-antenna transmitter and multiple-antenna receiver. The nonlinear RTRL algorithm for antenna diversity combining combats the distortive effects of the communication channel and reduces the interference. Ring TCM channel coding and RNN space diversity are evaluated in 16-QAM multicarrier CDMA systems transmitting over Rician and Rayleigh fast fading channels with a maximum Doppler frequency of 96 Hz. Modulo-4 ring TCM codes of 16 and 64 states have been designed. The RNN system is shown to be superior to the linear algorithms in channels dominated by multipath fading, inter-symbol interference and multiple access interference. The complexity of the RNN structure is comparable to that of the linear techniques. The joint utilisation of RNN based diversity, ring TCM and binary TCM coding schemes has been implemented. Whereas coding and space diversity do not provide sufficient benefit separately, the combination of both produces an increase in performance.

Space-time ring TCM codes for QPSK on time-varying fast fading channels

Space-time codes based on rings of integers suitable for QPSK constellations are presented for time-varying flat Rayleigh fast fading channels. Furthermore, a comparison between space-time ring TCM codes and the best known space-time codes for time-varying channels has revealed that the former offers a significantly better trade-off between coding gain and decoder complexity.

Shaping the power spectrum of TCM codes using wavelet packet modulation

Many TCM codes do not shape the power spectrum. It is desirable to shape the power spectrum of the coded modulation to compensate for the linear filtering effect of the channel, in order to maximise the data transmission rate. A technique is proposed whereby several independent TCM codes are used to encode different subbands of the available transmission bandwidth such that they can all be decoded efficiently in a single decoder.

Design of efficient codes for the AWGN channel based on decomposable binary lattices

This work is concerned with the use of binary decomposable lattice codes over the QAM Gaussian channel. First, we investigate the structure of such class of lattices: we derive consistency conditions for the binary codes appearing in their decomposition and express their nominal coding gain and some bounds for their error coefficient in terms of the parameters of the component codes. Then we describe a general multistage bounded‐distance decoding algorithm with low complexity and we evaluate its performance. Finally, we develop a design example and report the corresponding simulation results; as a reference some comparisons with standard TCM codes are also presented.

Design of TCM codes and interleaving process for fading channels using genetic algorithms

Design of TCM codes and interleaving process for fading channels using genetic algorithms

Practical 8-PSK block-coded modulation with convolutional codes and soft decision block codes for packet networks

The design and performance of a class of practical rate 2/3, 8-PSK block-coded modulation (BCM) (also referred to as multilevel modulation codes) schemes are presented. These BCM schemes utilise both convolutional codes and block codes, and have block lengths that are matched with relatively short packet lengths to satisfy requirements in packet-wireless networks. Decoding issues such as optimum signal metrics and soft-decision decoding of block codes are addressed. Performance is evaluated and simulated. It is found that these BCM schemes exhibit a coding gain comparable to 16, 32 and 64 state Ungerboeck TCM codes, but require less complexity to decode.

A Performance Analysis of Pragmatic MPSK TCM

The performance of 8-PSK, 16-PSK and 32-PSK TCM are examined in the additive white gaussian noise (AWGN), Rician fading and Rayleigh fading channels. The TCM is implemented using the ’’Pragmatic Approach‘‘ to TCM based on the common rate ½, constraint length 7, 64-state convolutional code. The analytic performance model has been enhanced to account for the unencoded bit(s) resulting from implementation of TCM using the ’’Pragmatic Approach‘‘. Averaging of the Euclidean error weight profiles is also employed. The results provide an improved upper bound on published data from simulations and measurements. The results are then employed to facilitate the evaluation of a concatenated Reed-Solomon (RS) MPSK TCM code, as well as, TCM with diversity in the form of symbol repetition.

A matrix algorithm for computing the free space distance of TCM signal sequences

In this paper, the problem of computing the free distance of TCM code sequences has been discussed. A new algorithm, the matrix algorithm, is proposed, and the step-number estimation problem for state transmission to compute the free distance of the TCM code sequences has been theoretically solved. The matrix algorithm is derived from the Viterbi algorithm, and is an implementation of the Viterbi algorithm in the form of a matrix. Compared with other algorithms, the matrix algorithm has two advantages: (1) the explicit solution, and its relatively lower complexity, (2) its more reflexible ability to signal space distance variation. As examples, the results of some TCM code sequences on an AWGN channel and fading channels have been presented.