A bandwidth efficient coding scheme for the Hubble Space Telescope

As a demonstration of the performance capabilities of trellis codes using multidimensional signal sets, a Viterbi decoder was designed. The choice of code was based on two factors. The first factor was its application as a possible replacement for the coding scheme currently used on the Hubble Space Telescope (HST). The HST at present uses the rate 1/3 nu = 6 (with 2 (exp nu) = 64 states) convolutional code with Binary Phase Shift Keying (BPSK) modulation. With the modulator restricted to a 3 Msym/s, this implies a data rate of only 1 Mbit/s, since the bandwidth efficiency K = 1/3 bit/sym. This is a very bandwidth inefficient scheme, although the system has the advantage of simplicity and large coding gain. The basic requirement from NASA was for a scheme that has as large a K as possible. Since a satellite channel was being used, 8PSK modulation was selected. This allows a K of between 2 and 3 bit/sym. The next influencing factor was INTELSAT's intention of transmitting the SONET 155.52 Mbit/s standard data rate over the 72 MHz transponders on its satellites. This requires a bandwidth efficiency of around 2.5 bit/sym. A Reed-Solomon block code is used as an outer code to give very low bit error rates (BER). A 16 state rate 5/6, 2.5 bit/sym, 4D-8PSK trellis code was selected. This code has reasonable complexity and has a coding gain of 4.8 dB compared to uncoded 8PSK (2). This trellis code also has the advantage that it is 45 deg rotationally invariant. This means that the decoder needs only to synchronize to one of the two naturally mapped 8PSK signals in the signal set

Golden Space-Time Trellis Coded Modulation

In this paper, we present a concatenated coding scheme for a high rate $2\times 2$ multiple-input multiple-output (MIMO) system over slow fading channels. The inner code is the Golden code \cite{Golden05} and the outer code is a trellis code. Set partitioning of the Golden code is designed specifically to increase the minimum determinant. The branches of the outer trellis code are labeled with these partitions. Viterbi algorithm is applied for trellis decoding. In order to compute the branch metrics a lattice sphere decoder is used. The general framework for code optimization is given. The performance of the proposed concatenated scheme is evaluated by simulation. It is shown that the proposed scheme achieves significant performance gains over uncoded Golden code.Comment: 33 pages, 13 figure

Trellis Coded Modulation Schemes Using A New Expanded 16-Dimensional Constant Envelope Quadrature-Quadrature Phase Shift Keying Constellation

In this thesis, the author presents and analyzes two 4-dimensional Constant Envelope Quadrature-Quadrature Phase Shift Keying constellations. Optimal demodulators for the two constellations are presented, and one of them was designed and implemented by the author. In addition, a novel expanded 16-dimensional CEQ2PSK constellation that doubles the number of points without decreasing the distance between points or increasing the peak energy is generated by concatenating the aforementioned constellations with a particular method and restrictions. This original 16-dimensional set of symbols is set-partitioned and used in a multidimensional Trellis-Coded Modulation scheme along with a convolutional encoder of rate 2/3. Effective gain of 2.67 dB over uncoded CEQ2PSK constellation with low complexity is achieved theoretically. A coding gain of 2.4 dB with 8 dB SNR is obtained by using Monte Carlo simulations. The TCM systems and demodulators were tested under an Additive White Gaussian Noise channel by using Matlab\u27s Simulink block diagrams

Trellis Coded Modulation Schemes Using A New Expanded 16-Dimensional Constant Envelope Quadrature-Quadrature Phase Shift Keying Constellation

In this thesis, the author presents and analyzes two 4-dimensional Constant Envelope Quadrature-Quadrature Phase Shift Keying constellations. Optimal demodulators for the two constellations are presented, and one of them was designed and implemented by the author. In addition, a novel expanded 16-dimensional CEQ2PSK constellation that doubles the number of points without decreasing the distance between points or increasing the peak energy is generated by concatenating the aforementioned constellations with a particular method and restrictions. This original 16-dimensional set of symbols is set-partitioned and used in a multidimensional Trellis-Coded Modulation scheme along with a convolutional encoder of rate 2/3. Effective gain of 2.67 dB over uncoded CEQ2PSK constellation with low complexity is achieved theoretically. A coding gain of 2.4 dB with 8 dB SNR is obtained by using Monte Carlo simulations. The TCM systems and demodulators were tested under an Additive White Gaussian Noise channel by using Matlab\u27s Simulink block diagrams

Bandwidth efficient CCSDS coding standard proposals

The basic concatenated coding system for the space telemetry channel consists of a Reed-Solomon (RS) outer code, a symbol interleaver/deinterleaver, and a bandwidth efficient trellis inner code. A block diagram of this configuration is shown. The system may operate with or without the outer code and interleaver. In this recommendation, the outer code remains the (255,223) RS code over GF(2 exp 8) with an error correcting capability of t = 16 eight bit symbols. This code's excellent performance and the existence of fast, cost effective, decoders justify its continued use. The purpose of the interleaver/deinterleaver is to distribute burst errors out of the inner decoder over multiple codewords of the outer code. This utilizes the error correcting capability of the outer code more efficiently and reduces the probability of an RS decoder failure. Since the space telemetry channel is not considered bursty, the required interleaving depth is primarily a function of the inner decoding method. A diagram of an interleaver with depth 4 that is compatible with the (255,223) RS code is shown. Specific interleaver requirements are discussed after the inner code recommendations

A variable-rate modulation and coding scheme for low earth orbit satellites

Low Earth Orbit (LEO) satellites are increasingly being used for a wide variety of communications applications. These satellites have to operate in widely varying channel conditions. These conditions are often significantly better than the 'worst case' situations that are experienced and thus a single rate transmission scheme is clearly suboptimal. The objective of the thesis is to suggest and test a method of modulation/coding that can take advantage of better signal strength conditions in order to improve data transmission rates. In order to provide the goal of approximately 50kbps transmission in a 10kHz Frequency Division Multiple Access (FDMA) channel it was necessary to consider spectrally efficient, rather than power efficient, modulations. The proposed modulation scheme makes use of an eight-dimensional trellis coded modulation system. Multiple signal constellation sets are used in conjunction with this coding in order to provide different transmission rates, depending on the signal to noise ratio and the channel state. To enhance the suitability of the modulation scheme for the channel, it was combined with Reed-Solomon Coding and interleaving in an inner/outer code arrangement. Various means of determining when to switch between coding rates were discussed briefly, but an in-depth treatment of the subject fell outside of the scope of the thesis. Various combinations of these codes were tested in gaussian noise conditions and various degrees of Rician and Rayleigh fading. In order to make use of the higher rate QAM constellations, it was necessary to provide the decoder with channel state information. The tested system achieved its purpose of providing a variable rate coding scheme resulting in good performance over a range of channel conditions. It is fairly flexible and can be adapted to specific channel requirements

Four-dimensional modulation and coding: An alternate to frequency-reuse

Four dimensional modulation as a means of improving communication efficiency on the band-limited Gaussian channel, with the four dimensions of signal space constituted by phase orthogonal carriers (cos omega sub c t and sin omega sub c t) simultaneously on space orthogonal electromagnetic waves are discussed. "Frequency reuse' techniques use such polarization orthogonality to reuse the same frequency slot, but the modulation is not treated as four dimensional, rather a product of two-d modulations, e.g., QPSK. It is well known that, higher dimensionality signalling affords possible improvements in the power bandwidth sense. Four-D modulations based upon subsets of lattice-packings in four-D, which afford simplification of encoding and decoding are described. Sets of up to 1024 signals are constructed in four-D, providing a (Nyquist) spectral efficiency of up to 10 bps/Hz. Energy gains over the reuse technique are in the one to three dB range t equal bandwidth

Error control techniques for satellite and space communications

Shannon's capacity bound shows that coding can achieve large reductions in the required signal to noise ratio per information bit (E sub b/N sub 0 where E sub b is the energy per bit and (N sub 0)/2 is the double sided noise density) in comparison to uncoded schemes. For bandwidth efficiencies of 2 bit/sym or greater, these improvements were obtained through the use of Trellis Coded Modulation and Block Coded Modulation. A method of obtaining these high efficiencies using multidimensional Multiple Phase Shift Keying (MPSK) and Quadrature Amplitude Modulation (QAM) signal sets with trellis coding is described. These schemes have advantages in decoding speed, phase transparency, and coding gain in comparison to other trellis coding schemes. Finally, a general parity check equation for rotationally invariant trellis codes is introduced from which non-linear codes for two dimensional MPSK and QAM signal sets are found. These codes are fully transparent to all rotations of the signal set

A novel high-speed trellis-coded modulation encoder/decoder ASIC design

Trellis-coded Modulation (TCM) is used in bandlimited communication systems. TCM efficiency improves coding gain by combining modulation and forward error correction coding in one process. In TCM, the bandwidth expansion is not required because it uses the same symbol rate and power spectrum; the differences are the introduction of a redundancy bit and the use of a constellation with double points. In this thesis, a novel TCM encoder/decoder ASIC chip implementation is presented. This ASIC codec not only increases decoding speed but also reduces hardware complexity. The algorithm and technique are presented for a 16-state convolutional code which is used in standard 256-QAM wireless systems. In the decoder, a Hamming distance is used as a cost function to determine output in the maximum likelihood Viterbi decoder. Using the relationship between the delay states and the path state in the Trellis tree of the code, a pre-calculated Hamming distances are stored in a look-up table. In addition, an output look-up-table is generated to determine the decoder output. This table is established by the two relative delay states in the code. The thesis provides details of the algorithm and the structure of TCM codec chip. Besides using parallel processing, the ASIC implementation also uses pipelining to further increase decoding speed. The codec was implemented in ASIC using standard 0.18ƒÝm CMOS technology; the ASIC core occupied a silicon area of 1.1mm2. All register transfer level code of the codec was simulated and synthesized. The chip layout was generated and the final chip was fabricated by Taiwan Semiconductor Manufacturing Company through the Canadian Microelectronics Corporation. The functional testing of the fabricated codec was performed partially successful; the timing testing has not been fully accomplished because the chip was not always stable