VHF command system study

Solutions are provided to specific problems arising in the GSFC VHF-PSK and VHF-FSK Command Systems in support of establishment and maintenance of Data Systems Standards. Signal structures which incorporate transmission on the uplink of a clock along with the PSK or FSK data are considered. Strategies are developed for allocating power between the clock and data, and spectral analyses are performed. Bit error probability and other probabilities pertinent to correct transmission of command messages are calculated. Biphase PCM/PM and PCM/FM are considered as candidate modulation techniques on the telemetry downlink, with application to command verification. Comparative performance of PCM/PM and PSK systems is given special attention, including implementation considerations. Gain in bit error performance due to coding is also considered

The Gaussian assumption in second-order estimation problems in digital communications

This paper deals with the goodness of the Gaussian assumption when designing second-order blind estimation methods in the context of digital communications. The low- and high-signal-to-noise ratio (SNR) asymptotic performance of the maximum likelihood estimator - derived assuming Gaussian transmitted symbols - is compared with the performance of the optimal second-order estimator, which exploits the actual distribution of the discrete constellation. The asymptotic study concludes that the Gaussian assumption leads to the optimal second-order solution if the SNR is very low or if the symbols belong to a multilevel constellation such as quadrature-amplitude modulation (QAM) or amplitude-phase-shift keying (APSK). On the other hand, the Gaussian assumption can yield important losses at high SNR if the transmitted symbols are drawn from a constant modulus constellation such as phase-shift keying (PSK) or continuous-phase modulations (CPM). These conclusions are illustrated for the problem of direction-of-arrival (DOA) estimation of multiple digitally-modulated signals.Peer ReviewedPostprint (published version

Analysis of Single RF Performance on MIMO-OFDM System Using Turbo Code and V-BLAST MMSE Detection

Along with the passing time and recent technology, the advancement of information technology has been increased in the wireless technology. The common methods that are used in this wireless communication are MIMO (Multiple Input Multiple Output) and OFDM (Orthogonal Frequency Division Multiplexing). MIMO is a system stands for a couple antenna on the transmitter and receiver which are working on themultipath component. While OFDM (Orthogonal Frequency Division Multiplexing) is a transmission method using multicarrier technique, dividing spectrum frequency into a couple subcarrier. The combination of MIMO and OFDM results in a high-speed transfer data system. The Single RF has reduced the USAge of RF Front-End into a bigger matrix size in the conventional MIMO system. This final project will discuss about the Single RF system of MIMO-OFDM with the V-BLAST (Vertical Bell Laboratories Space-Time) and MMSE (Minimum Mean Square Error) detectionwhich is used to remove ISI (Intersymbol Interference) combined with theTurbo Code,where theTurbo Encoder that lies on the transmitter side is also theTurbo Decoder in the receiver side. MIMO-OFDM utilizesthe Single RF (Radio Frequency) basis. The test on this final project will include a Single RF antenna on the MIMO-OFDM system, MIMO-OFDM with the V-BLAST detector and MMSE MIMO-OFDM with the Turbo Code, by using 64 QAM modulation. The expected result is the analysis performance of the Single RF on the MIMO-OFDM system using Turbo Code and V-BLAST MMSEDetection. The system will be shown on theBit Error Rate (BER) toward the Signal to Noise Ratio (SNR)

Comparison of Intersymbol Interference Power Penalties for OOK and 4-PAM in Short-Range Optical Links

We present results of experimental and theoretical investigations of intersymbol interference in 4-PAM transmission in short-range optical communications links based on the power penalty. A test link comprised of a directly modulated 850 nm VCSEL with up to 200 m of multimode fiber and direct detection was used. The link bandwidth was below 10 GHz and the maximum achieved data rate with 4-PAM was 44 Gbps over 100 m of fiber. In the same case and at similar sensitivity, only 32 Gbps could be achieved with OOK. If typical forward error correction could be applied, the sensitivity of the 4-PAM system was improved by up to 4 dB, reaching -10 dBm at 25 Gbps

Design and Evaluation of the Efficiency of Channel Coding LDPC Codes for 5G Information Technology

This paper proposes a result of an investigation of a topical problem and the development of models for efficient coding in information networks based on codes with a low density of parity check. The main advantage of the technique is the presented recommendations for choosing a signal-code construction is carried out taking into account the code rate and the number of iterations decoding for envisaging the defined noise immunity indices. The noise immunity of signal-code constructions based on low-density codes has been increased by combining them with multi position digital modulation. This solution eventually allowed to develop a strategy for decoder designing of such codes and to optimize the code structure for a specific information network. To test the effectiveness of the proposed method, MATLAB simulations are carried out under for various Information channels binary symmetric channel (BSC), a channel with additive white Gaussian noise (AWGN), binary asymmetric channel (BAC), asymmetric channel Z type. In addition, different code rates were used during the experiment. The study of signal-code constructions with differential modulation is presented. The efficiency of different decoding algorithms is investigated. The advantage of the obtained results over the known ones consists in determining the maximum noise immunity for the proposed codes. The energy gain was on the order of 6 dB, and an increase in the number of decoding iterations from 3 to 10 leads to a gain in coding energy of 5 dB. Envisaged that the results obtained can be very useful in the development of practical coding schemes in 5G networks

Digital transmission systems operating over high frequency radio channels

Imperial Users onl

Bit Loading and Peak Average Power Reduction Techniques for Adaptive Orthogonal Frequency Division Multiplexing Systems

In a frequency-selective channel a large number of resolvable multipaths are present which lead to the fading of the signal. Orthogonal frequency division multiplexing (OFDM) is well-known to be effective against multipath distortion. It is a multicarrier communication scheme, in which the bandwidth of the channel is divided into subcarriers and data symbols are modulated and transmitted on each subcarrier simultaneously. By inserting guard time that is longer than the delay spread of the channel, an OFDM system is able to mitigate intersymbol interference (ISI). Significant improvement in performance is achieved by adaptively loading the bits on the subcarriers based on the channel state information from the receiver. Imperfect channel state information (CSI) arises from noise at the receiver and also due to the time delay in providing the information to the transmitter for the next data transmission. This thesis presents an investigation into the different adaptive techniques for loading the data bits on the subcarriers. The choice of the loading technique is application specific. The spectral efficiency and the bit error rate (BER) performance of adaptive OFDM as well as the implementation complexity of the different loading algorithms is studied by varying any one of the parameters, data rate or BER or total transmit power subject to the constraints on the other two. A novel bit loading algorithm based on comparing the SNR with the threshold in order to minimize the BER is proposed and its performance for different data rates is plotted. Finally, this thesis presents a method for reducing the large peak to average power ratio (PAPR) problem with OFDM which arises when the sinusoidal signals of the subcarriers add constructively. The clipping and the probabilistic approaches were studied. The probabilistic technique shows comparatively better BER performance as well as reduced PAPR ratio but is more complex to implement

Iterative Equalization Using Improved Block DFE for Synchronous CDMA Systems

Iterative equalization using optimal multiuser detector and trellis-based channel decoder in coded CDMA systems improves the bit error rate (BER) performance dramatically. However, given large number of users employed in the system over multipath channels causing significant multiple-access interference (MAI) and intersymbol interference (ISI), the optimal multiuser detector is thus prohibitively complex. Therefore, the sub-optimal detectors such as low-complexity linear and non-linear equalizers have to be considered. In this paper, a novel low-complexity block decision feedback equalizer (DFE) is proposed for the synchronous CDMA system. Based on the conventional block DFE, the new method is developed by computing the reliable extrinsic log-likelihood ratio (LLR) using two consecutive received samples rather than one received sample in the literature. At each iteration, the estimated symbols by the equalizer is then saved as a priori information for next iteration. Simulation results demonstrate that the proposed low-complexity block DFE algorithm offers very good performance gain over the conventional block DFE

Digital receiver study and implementation

Computer software was developed which makes it possible to use any general purpose computer with A/D conversion capability as a PSK receiver for low data rate telemetry processing. Carrier tracking, bit synchronization, and matched filter detection are all performed digitally. To aid in the implementation of optimum computer processors, a study of general digital processing techniques was performed which emphasized various techniques for digitizing general analog systems. In particular, the phase-locked loop was extensively analyzed as a typical non-linear communication element. Bayesian estimation techniques for PSK demodulation were studied. A hardware implementation of the digital Costas loop was developed