Space-Time Trellis and Space-Time Block Coding Versus Adaptive Modulation and Coding Aided OFDM for Wideband Channels

Abstract—The achievable performance of channel coded spacetime trellis (STT) codes and space-time block (STB) codes transmitted over wideband channels is studied in the context of schemes having an effective throughput of 2 bits/symbol (BPS) and 3 BPS. At high implementational complexities, the best performance was typically provided by Alamouti’s unity-rate G2 code in both the 2-BPS and 3-BPS scenarios. However, if a low complexity implementation is sought, the 3-BPS 8PSK space-time trellis code outperfoms the G2 code. The G2 space-time block code is also combined with symbol-by-symbol adaptive orthogonal frequency division multiplex (AOFDM) modems and turbo convolutional channel codecs for enhancing the system’s performance. It was concluded that upon exploiting the diversity effect of the G2 space-time block code, the channel-induced fading effects are mitigated, and therefore, the benefits of adaptive modulation erode. In other words, once the time- and frequency-domain fades of the wideband channel have been counteracted by the diversity-aided G2 code, the benefits of adaptive modulation erode, and hence, it is sufficient to employ fixed-mode modems. Therefore, the low-complexity approach of mitigating the effects of fading can be viewed as employing a single-transmitter, single-receiver-based AOFDM modem. By contrast, it is sufficient to employ fixed-mode OFDM modems when the added complexity of a two-transmitter G2 scheme is affordable

Analysis and Simulation of the Signals Transmission in the DVB-H/SH Standards

Tato disertační práce se zabývá analýzou, simulací a měřením zpracování a přenosu signálů digitální televize pro příjem mobilního TV vysílání ve standardech DVB-H a DVB-SH. Tyto standardy vycházejí z předpokladu, že příjem signálu je charakterizován modely přenosových kanálů s vícecestným šířením. Tyto, tzv. únikové kanály, jsou charakterizovány hlavně zpožděním a ziskem jednotlivých cest. V závislosti na dalších parametrech (rychlost přijímače, Dopplerovské spektrum), je možné rozdělit únikové kanály do třech hlavních skupin: mobilní, přenosné a fixní. Dá se předpokládat, že v různých modelech kanálů bude přenášený signál různě ovlivněn. Proto je potřebné najít optimální parametry systémů (DVB-H/SH) pro kvalitní příjem vysílaných služeb mobilní televize, což je hlavním cílem této disertační práci. Pro tento účel byly vytvořeny dvě vhodné aplikace (jedna pro DVB-H a jedna pro DVB-SH) s GUI v prostředí MATLAB, které umožňují simulovat a analyzovat míru zkreslení signálu v případě mobilních, přenosných a fixních scénářů přenosu. Navíc, tyto aplikace obsahují i druhý samostatný simulátor pro nastavení a modifikaci parametrů jednotlivých přenosových cest. Díky tomu je možné zhodnotit vliv parametrů celého systému a kanálových modelů na dosaženou chybovost (BER a MER) a kvalitu přenosu. Ve všech přenosových scénářích (v závislosti na poměru C/N) byly získané, vyhodnocené a diskutované zkreslení signálů. Navíc, u standardu DVB-H, všechny získané výsledky ze simulací byly ověřeny měřením. Rozdíly mezi dosaženými výsledky (simulace a měření) byly rovněž podrobeny diskuzi. Tuto disertační práci je možné rozdělit do čtyř hlavních částí. První část disertační práce se zabývá rešerší současného vývoje v oblasti digitálního televizního vysílání na mobilní terminály ve standardech DVB-H/SH. Na konci této části jsou jasně popsány cíle této disertační práce. Druhá část práce je zaměřená na stručný popis blokového diagramu vysílačů v obou standardech DVB-H/SH. Dále jsou stručně popsány modely přenosových kanálů, které se používají pro modelování přenosu signálu. Stručný popis vytvořených aplikací, i s vývojovým diagramem, které jsou vhodné pro simulaci a analýzu přenosu v DVB-H/SH, jsou popsány v třetí části práce. Čtvrtá a nejdelší část této disertační práce se zabývá vyhodnocením získaných výsledků ze simulací a měření.This dissertation thesis deals with the analysis, simulation and measurement of the signal processing and transmission in DVB-H and DVB-SH standards. These standards are based on the assumption that signal reception is characterized by the transmission channels with echoes. These, so called fading channels, are mainly characterized by the path delays and path losses. Depending on the other, additional features (speed of the receiver, Doppler spectrum, etc.), it can be possible divided these channels onto three main groups: mobile, portable and fixed. Of course, signal transmission in different transmission channel models are affected differently. Therefore, it is needed found the optimal system parameters in both, DVB-H and DVB-SH standards, for the quality reception of the broadcasted mobile TV services, which is the main goal of this thesis. For this purpose, two appropriate applications (one for DVB-H and one for DVB-SH) with GUI were created in MATLAB, which enable simulated and analyzed the signal distortions in mobile, portable and fixed transmission scenarios. Moreover, these applications also contain a second application with GUI for the easy set and modification of the parameters of the used channel models. Therefore, it is possible to evaluate the effect of parameters of whole system and channel models on the achieved error rate (BER and MER) and quality of the transmission. In all mentioned transmission scenarios, the signal distortions (depending on the Carrier-to-Noise ratio) were obtained, evaluated and discussed in this dissertation thesis. Furthermore, in case of DVB-H, all obtained results from the simulations, were verified by the measuring. Differences between the obtained results (simulation and measuring) are also discussed. This dissertation thesis can be divided into four main parts. The first part of this dissertation thesis, after the short introduction, deals with present state-of-the-art and literature survey in mobile broadcast DVB-H/SH standards. At the end of this part are clearly outlined the main aims of this dissertation thesis. Second part is focused on the brief description of the functional block diagram of transmitters in both, DVB-H/SH standards. Furthermore, there are briefly described the transmission fading channel models, which are commonly used for the modeling of the signal transmission. The brief description of program applications with flowcharts, appropriate for the simulation of the transmission in the DVB-H/SH standards, are presented and described in the third part of this thesis. Finally, the fourth and longest part of this thesis is focused on the evaluation and comparison of obtained results from the simulations and measurements.

Turbo-Coded Adaptive Modulation Versus Space-Time Trellis Codes for Transmission over Dispersive Channels

Decision feedback equalizer (DFE)-aided turbocoded wideband adaptive quadrature amplitude modulation (AQAM) is proposed, which is capable of combating the temporal channel quality variation of fading channels. A procedure is suggested for determining the AQAM switching thresholds and the specific turbo-coding rates capable of maintaining the target bit-error rate while aiming for achieving a highly effective bits per symbol throughput. As a design alternative, we also employ multiple-input/multiple-output DFE-aided space–time trellis codes, which benefit from transmit diversity and hence reduce the temporal channel quality fluctuations. The performance of both systems is characterized and compared when communicating over the COST 207 typical urban wideband fading channel. It was found that the turbo-coded AQAM scheme outperforms the two-transmitter space–time trellis coded system employing two receivers; although, its performance is inferior to the space–time trellis coded arrangement employing three receivers. Index Terms—Coded adaptive modulation, dispersive channels, space–time trellis codes

Burst-by-Burst Adaptive Decision Feedback Equalised TCM, TTCM and BICM for H.263-Assisted Wireless Video Telephony

Decision Feedback Equaliser (DFE) aided wideband Burst-by-Burst (BbB) Adaptive Trellis Coded Modulation (TCM), Turbo Trellis Coded Modulation (TTCM) and Bit-Interleaved Coded Modulation (BICM) assisted H.263-based video transceivers are proposed and characterised in performance terms when communicating over the COST 207 Typical Urban wideband fading channel. Specifically, four different modulation modes, namely 4QAM, 8PSK, 16QAM and 64QAM are invoked and protected by the above-mentioned coded modulation schemes. The TTCM assisted scheme was found to provide the best video performance, although at the cost of the highest complexity. A range of lower-complexity arrangements will also be characterised. Finally, in order to confirm these findings in an important practical environment, we have also investigated the adaptive TTCM scheme in the CDMA-based Universal Mobile Telecommunications System's (UMTS) Terrestrial Radio Access (UTRA) scenario and the good performance of adaptive TTCM scheme recorded when communicating over the COST 207 channels was retained in the UTRA environment

Turbo-detected unequal protection audio and speech transceivers using serially concatenated convolutional codes, trellis coded modulation and space-time trellis coding

The MPEG-4 TwinVQ audio codec and the AMR-WB speech codec are investigated in the context of a jointly optimised turbo transceiver capable of providing unequal error protection. The transceiver advocated consists of serially concatenated Space-Time Trellis Coding (STTC), Trellis Coded Modulation (TCM) and two different-rate Non-Systematic Convolutional codes (NSCs) used for unequal error protection. A benchmarker scheme combining STTC and a single-class protection NSC is used for comparison with the proposed scheme. The audio and speech performance of both schemes is evaluated, when communicating over uncorrelated Rayleigh fading channels. An $E_b/N_0$ value of about 2.5 (3.5)~dB is required for near-unimpaired audio (speech) transmission, which is about 3.07 (4.2)~dB from the capacity of the system

Optimum Linear LLR Calculation for Iterative Decoding on Fading Channels

On a fading channel with no channel state information at the receiver, calculating true log-likelihood ratios (LLR) is complicated. Existing work assume that the power of the additive noise is known and use the expected value of the fading gain in a linear function of the channel output to find approximate LLRs. In this work, we first assume that the power of the additive noise is known and we find the optimum linear approximation of LLRs in the sense of maximum achievable transmission rate on the channel. The maximum achievable rate under this linear LLR calculation is almost equal to the maximum achievable rate under true LLR calculation. We also observe that this method appears to be the optimum in the sense of bit error rate performance too. These results are then extended to the case that the noise power is unknown at the receiver and a performance almost identical to the case that the noise power is perfectly known is obtained.Comment: This paper will be presented in IEEE International Symposium on Information Theory (ISIT) 2007 in Nice, Franc

TTCM-aided rate-adaptive distributed source coding for Rayleigh fading channels

Adaptive turbo-trellis-coded modulation (TTCM)-aided asymmetric distributed source coding (DSC) is proposed, where two correlated sources are transmitted to a destination node. The first source sequence is TTCM encoded and is further compressed before it is transmitted through a Rayleigh fading channel, whereas the second source signal is assumed to be perfectly decoded and, hence, to be flawlessly shown at the destination for exploitation as side information for improving the decoding performance of the first source. The proposed scheme is capable of reliable communications within 0.80 dB of the Slepian-Wolf/Shannon (SW/S) theoretical limit at a bit error rate (BER) of 10-5. Furthermore, its encoder is capable of accommodating time-variant short-term correlation between the two sources

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

Interleaving Gains for Receive Diversity Schemes of Distributed Turbo Codes in Wireless Half–Duplex Relay Channels

This paper proposes the interleaving gain in two different distributed turbo-coding schemes: Distributed Turbo Codes (DTC) and Distributed Multiple Turbo Codes (DMTC) for half-duplex relay system as an extension of our previous work on turbo coding interleaver design for direct communication channel. For these schemes with half-duplex constraint, the source node transmits its information with the parity bit sequence(s) to both the relay and the destination nodes during the first phase. The relay received the data from the source and process it by using decode and forward protocol. For the second transmission period, the decoded systematic data at relay is interleaved and re-encoded by a Recursive Systematic Convolutional (RSC) encoder and forwarded to the destination. At destination node, the signals received from the source and relay are processed by using turbo log-MAP iterative decoding for retrieving the original information bits. We demonstrate via simulations that the interleaving gain has a large effect with DTC scheme when we use only one RSC encoder at both the source and relay with best performance when using Modified Matched S-Random (MMSR) interleaver. Furthermore, by designing a Chaotic Pseudo Random Interleaver (CPRI) as an outer interleaver at the source node instead of classical interleavers, our scheme can add more secure channel conditions