Performance of concatenated Reed-Solomon trellis-coded modulation over Rician fading channels

A concatenated coding scheme for providing very reliable data over mobile-satellite channels at power levels similar to those used for vocoded speech is described. The outer code is a shorter Reed-Solomon code which provides error detection as well as error correction capabilities. The inner code is a 1-D 8-state trellis code applied independently to both the inphase and quadrature channels. To achieve the full error correction potential of this inner code, the code symbols are multiplexed with a pilot sequence which is used to provide dynamic channel estimation and coherent detection. The implementation structure of this scheme is discussed and its performance is estimated

An implementation of a reference symbol approach to generic modulation in fading channels

As mobile satellite communications systems evolve over the next decade, they will have to adapt to a changing tradeoff between bandwidth and power. This paper presents a flexible approach to digital modulation and coding that will accommodate both wideband and narrowband schemes. This architecture could be the basis for a family of modems, each satisfying a specific power and bandwidth constraint, yet all having a large number of common signal processing blocks. The implementation of this generic approach, with general purpose digital processors for transmission of 4.8 kilobits per sec. digitally encoded speech, is described

Data-aided fading estimation technique for shadowed mobile satellite fading channels

A novel data-aided fading estimation technique that employs both pilot and data symbols is proposed to significantly reduce the bandwidth redundancy of the pilot-symbol-aided (PSA) systems using receivers with low complexity and latency in the shadowed mobile satellite fading channels. The shadowed mobile satellite fading channels are modeled as the sum of a lognormally distributed direct component and a Rayleigh distributed multipath component, and the PSA system employs 16-ary quadrature-amplitude-modulation (16QAM) for transmission. Monte Carlo computer simulation has been used to assess the technique on the bit-error-rate (BER) performances of the system in the light shadowed, the average shadowed and the heavy shadowed Rician fading environments. The results have shown that the proposed technique requires a very low bandwidth redundancy to provide satisfactory BER performances, and can substantially lower the error floors of the PSA systems.postprin

Improved pilot symbol-aided transmission technique for hybrid satellite and terrestrial mobile systems

In the hybrid satellite and terrestrial mobile systems, robust transmission techniques are required to compensate the signal distortion introduced in the fading channels. Recently, the pilot symbol-aided techniques have been proved to be suitable for the transmission of digital signals over satellite mobile and terrestrial mobile channels. In this paper, an improved pilot symbol-aided transmission technique suitable for the hybrid systems is proposed. The proposed technique uses the distortion information in data symbols as well as in pilot symbols for the multipath fading compensation. Monte Carlo simulations have been carried out to investigate the effects of the proposed technique on the bit-error rate (BER) performances of 16PSK and 16QAM signals in satellite mobile and terrestrial mobile channels. Results have shown that, at high signal-to-noise ratios (SNRs), an improvement of more than two orders of magnitude in the BER performance can be obtained by the proposed technique, relative to those only using the pilot symbols.published_or_final_versio

MSAT voice modulation considerations

The challenge for Mobile satellite (MSAT) voice services is to provide near toll quality voice to the user, while minimizing the power and bandwidth resources of the satellite. The options for MSAT voice can be put into one of two groups: Analog and Digital. Analog, nominally narrowband single sideband techniques, have a shown robustness to the fading and shadowing environment. Digital techniques, a combination of low rate vocoders and bandwidth efficient modems, show the promise of enhanced fidelity, as well as easier networking to the emerging digital world. The problems and tradeoffs to designers are many, especially in the digital case. Processor speed vs. cost and MET power requirements, channel coding, bandwidth efficiency vs. power efficiency etc. While the list looks daunting, in fact an acceptable solution is well within the technology. The objectives are reviewed that the MSAT voice service must meet, along with the options that are seen for the future

Separable concatenated codes with iterative map decoding for Rician fading channels

Very efficient signalling in radio channels requires the design of very powerful codes having special structure suitable for practical decoding schemes. In this paper, powerful codes are obtained by combining comparatively simple convolutional codes to form multi-tiered 'separable' convolutional codes. The decoding of these codes, using separable symbol-by-symbol maximum a posteriori (MAP) 'filters', is described. It is known that this approach yields impressive results in non-fading additive white Gaussian noise channels. Interleaving is an inherent part of the code construction, and consequently, these codes are well suited for fading channel communications. Here, simulation results for communications over Rician fading channels are presented to support this claim

Multipath fading compensation technique using pilot and data bearing symbols in mobile radio channels

Conference Theme: The Global BridgeThe paper studies techniques for transmitting a 16-ary quadrature-amplitude modulated (16QAM) signal in different mobile radio environments. Conventional multipath fading compensation techniques using only the pilot symbols, incorporated with zeroth-order and first-order prediction methods, are studied. Novel techniques making use both the pilot symbols and the data symbols, together with the improved zeroth-order and first-order prediction methods, are proposed. A series of intensive Monte Carlo simulations has been carried out on these techniques and the results have shown that, at high signal-to-noise ratios (SNRs), the bit-error rate (BER) performance can be reduced by a factor of about 46 and 2 using the improved zeroth-order and first-order prediction respectively, relative to those obtained using the pilot symbols only.published_or_final_versionThe 1994 IEEE Global Telecommunications Conference (GLOBECOM '94), San Francisco, CA., 28 November-2 December 1994. In Globecom. IEEE Conference and Exhibition, 1994, v. 2, p. 1009-101

Combining PSA fading estimation techniques for TCM and diversity reception in Rician fading channels

In this paper, a novel pilot-symbol-aided (PSA) technique is proposed for fading estimation in the land mobile satellite fading channels. The proposed technique combines the fading estimates obtained from a bandwidth-efficient technique and a conventional technique according to the signal-to-noise ratios (SNRs) of the fading estimates. To enhance the transmission quality, trellis-coded modulation (TCM) and diversity reception are employed in the system, and the combined estimates are subsequently used to correct the channel fading effects, to weight the signals from different diversity branches, and to provide channel state information of the Viterbi decoder. Monte Carlo computer simulation has been used to study the bit-error-rate (BER) performance of the proposed technique on trellis-coded 16-ary quadrature amplitude modulation in the frequency non-selective Rician fading channels. Results have shown that the proposed PSA technique requires a very low bandwidth redundancy to provide satisfactory BER performance at low SNRs, and thus is suitable for use with TCM and diversity reception to achieve both bandwidth and power-efficient transmission.postprin

Performance of a Faded-Compensated 16QAM with Diversity Reception in Mobile radio Channels

The paper studies the bit-error-rate (BER) performance of a fade-compensated 16 QAM with two-branch postdetection selection combining diversity reception in the Rayleigh fading channels. A pilot symbol-aided (PSA) technique that uses both pilot symbols and data symbols is employed for fading compensation. Computer simulation results have shown that, the use of diversity reception technique can significantly improve the BER performance when the normalized delay between the signals at the two receivers is small. It is also shown that, the error-floor is sensitive to the normalized delay, but relatively less sensitive to the power ratio between the signals at the two receivers.published_or_final_versio