Telemetering and telecommunications research

The research center activities during the reporting period have been focused in three areas: (1) developing the necessary equipment and test procedures to support the testing of 8PSK-TCM through TDRSS from the WSGT; (2) extending the theoretical decoder work to higher speeds with a design goal of 600MBPS at 2 bits/Hz; and (3) completing the initial phase of the CPFSK Multi-H research and determining what subsets (if any) of these coding schemes are useful in the TDRSS environment. The equipment for the WSGT TCM testing has been completed and is functioning in the lab at NMSU. Measured results to date indicate that the uncoded system with the modified HRD and NMSU symbol sync operates at 1 to 1.5 dB from theory when processing encoded 8PSK. The NMSU pragmatic decoder when combined with these units produces approximately 2.9 dB of coding gain at 10(exp -5) BER. Our study of CPFSK with Multi-H coding has reached a critical stage. The principal conclusions reached in this activity are: (1) no scheme using Multi-H alone investigated by us or found in the literature produces power/bandwidth trades that are as good as TCM with filtered 8PSK; (2) when Multi-H is combined with convolutional coding, one can obtain better coding gain than with Multi-H alone but still no better power/bandwidth performance than TCM and these gains are available only with complex receivers; (3) the only advantage we can find for the CPFSK schemes over filtered MPSK with TCM is that they are constant envelope (however, constant envelope is of no benefit in a multiple access channel and of questionable benefit in a single access channel since driving the TWT to saturation in this situation is generally acceptable); and (4) based upon these results the center's research program will focus on concluding the existing CPFSK studies

On the Power Spectral Density of the GSM Signaling Scheme

In this paper, the Power Spectral Density of encoded Gaussian Minimum Shift Keying (GMSK) which is the Signaling Scheme of the Global System for Mobile Communication (GSM) is derived by a combined approach of the autocorrelation method and Markov Process. In the analysis, the Amplitude Modulated Pulse decomposition proposed by P. Laurent is employed to ease computation. Encoding of the message data utilizes Convolutional Code of rate1/2. Results are for both the uncoded and coded waveform comparing variation in power spread over a range of frequency

A B-ISDN-compatible modem/codec

Coded modulation techniques for development of a broadband integrated services digital network (B-ISDN)-compatible modem/codec are investigated. The selected baseband processor system must support transmission of 155.52 Mbit/s of data over an INTELSAT 72-MHz transponder. Performance objectives and fundamental system parameters, including channel symbol rate, code rate, and the modulation scheme are determined. From several candidate codes, a concatenated coding system consisting of a coded octal phase shift keying modulation as the inner code and a high rate Reed-Solomon as the outer code is selected and its bit error rate performance is analyzed by computer simulation. The hardware implementation of the decoder for the selected code is also described

An improved algorithm for evaluating trellis phase codes

A method is described for evaluating the minimum distance parameters of trellis phase codes, including CPFSK, partial response FM, and more importantly, coded CPM (continuous phase modulation) schemes. The algorithm provides dramatically faster execution times and lesser memory requirements than previous algorithms. Results of sample calculations and timing comparisons are included

Permutation Trellis Coded Multi-level FSK Signaling to Mitigate Primary User Interference in Cognitive Radio Networks

We employ Permutation Trellis Code (PTC) based multi-level Frequency Shift Keying signaling to mitigate the impact of Primary Users (PUs) on the performance of Secondary Users (SUs) in Cognitive Radio Networks (CRNs). The PUs are assumed to be dynamic in that they appear intermittently and stay active for an unknown duration. Our approach is based on the use of PTC combined with multi-level FSK modulation so that an SU can improve its data rate by increasing its transmission bandwidth while operating at low power and not creating destructive interference for PUs. We evaluate system performance by obtaining an approximation for the actual Bit Error Rate (BER) using properties of the Viterbi decoder and carry out a thorough performance analysis in terms of BER and throughput. The results show that the proposed coded system achieves i) robustness by ensuring that SUs have stable throughput in the presence of heavy PU interference and ii) improved resiliency of SU links to interference in the presence of multiple dynamic PUs.Comment: 30 pages, 12 figure

Modulation and coding technology for deep space and satellite applications

Modulation and coding research and development at the Jet Propulsion Laboratory (JPL) currently emphasize Deep Space Communications Systems and advanced near earth Commercial Satellite Communications Systems. The Deep Space Communication channel is extremely signal to noise ratio limited and has long transmission delay. The near earth satellite channel is bandwidth limited with fading and multipath. Recent code search efforts at JPL have found a long constraint, low rate convolutional code (15, 1/6) which, when concatenated with a ten bit Reed-Solomon (RS) code, provides a 2.1 dB gain over that of the Voyager spacecraft - the current standard. The new code is only 2 dB from the theoretical Shannon limit. A flight qualified version of the (15, 1/6) convolutional encoder was implemented on the Galileo Spacecraft to be launched later this year. An L-band mobile link, use of the Ka-band for personal communications, and the development of subsystem technology for the interconnection of satellite resources by using high rate optical inter-satellite links are noted

Self-concatenated code design and its application in power-efficient cooperative communications

In this tutorial, we have focused on the design of binary self-concatenated coding schemes with the help of EXtrinsic Information Transfer (EXIT) charts and Union bound analysis. The design methodology of future iteratively decoded self-concatenated aided cooperative communication schemes is presented. In doing so, we will identify the most important milestones in the area of channel coding, concatenated coding schemes and cooperative communication systems till date and suggest future research directions