Universal trellis codes for diagonally layered space-time systems

In broadcast scenarios or in the absence of accurate channel probability distribution information, code design for consistent channel-by-channel performance, rather than average performance over a channel distribution, may be desirable. Root and Varaiya's compound channel theorem for linear Gaussian channels promises the existence of universal codes that operate reliably whenever the channel mutual information (MI) is above the transmitted rate. This paper presents two-dimensional trellis codes that provide such universal performance over the compound linear vector Gaussian channel when demultiplexed over two, three, and four transmit antennas. The presented trellis codes, found by exhaustive search, guarantee consistent performance on every matrix channel that supports the information transmission rate with an MI gap that is similar to the capacity gap of a well-designed additive white Gaussian noise (AWGN)-specific code on the AWGN channel. As a result of their channel-by-channel consistency, the universal trellis codes presented here also deliver comparable, or, in some cases, superior, frame-error rate and bit-error rate performance under quasi-static Rayleigh fading, as compared with trellis codes of similar complexity that are designed specifically for the quasi-static Rayleigh-fading scenario

In the absence of accurate channel probability distribution information or in broadcast scenarios, code design for consistent channel-by-channel performance, rather than average performance, may be desirable. Root and Varaiya's compound channel theorem promises the existence of universal codes that operate with a consistent proximity to channel mutual information on any instance of the compound linear vector Gaussian channel that is similar to the capacity gap of an AWGN-specific code with similar complexity on the AWGN channel. This study presents single-dimensional trellis codes such that when multiplexed over two, three and four transmit antennas, provide universal performance over the compound linear vector Gaussian channel. As a result of their channel-by-channel consistency, the universal trellis codes presented here deliver comparable or in some cases superior frame-error-rate and bit-error-rate performance under quasistatic Rayleigh fading to trellis codes of similar complexity that are designed specifically for the quasistatic Rayleigh fading scenario.

For a single channel Shannon's classical capacity formula predicts a capacity increase of 1 bit/cycle for every 3 dB increase in signal to noise ratio (SNR). Consequently in multiple antenna arrays, the increase in capacity can be in the order of almost n more bits/cycle for each 3 dB increase in SNR. This tremendous gain in capacity exhibited by MIMO channels over single antenna systems illustrates the enormous potential in wireless communications systems. This paper provides an analysis of multi-element antenna systems in a wireless channel. A geometric model incorporating local scatterers around the fixed user is presented. This space-time model considers non-isotropic scattering using the von Mises pdf at the user. This space-time cross correlation function includes some key elements, such as antenna element spacing, degree of scattering, angle of arrival at user and array configuration in MIMO channels. The capacity of the MIMO fading channel with varying; number of antenna elements, the degree of isotropic scattering at receiver and the spacing between the antenna elements are investigated and presented for the chosen model

Previous studies have shown that a wireless system using n transmitting and n receiving antennas can achieve a capacity n times higher than a single-antenna system in an independent Rayleigh fading environment. We explore the capacities of multiple-element antenna arrays (MEAs) in a more realistic propagation environment simulated via the WiSE ray-tracing tool. We impose an average power constraint and collect statistics of the capacity with optimal power allocation, C/sub wf/, and the mutual information with an equal power allocation, I/sub eq/. In addition, we present expressions for the asymptotic growth rates C/sub wf//n and I/sub eq//n as n/spl rarr//spl infin/ for two cases: (a) independent fadings and (b) correlated fadings at different antennas. We find that C/sub wf//n and I/sub eq//n converge to constants C/sub wf/* and I/sub eq/*, respectively in case (a), and to C/sub wf//sup 0/and I/sub eq//sup 0/ in case (b). We observe that C/sub wf//sup 0/ and I/sub eq//sup 0/ predict very closely the slopes observed for simulated channels, even for moderate n (i.e., 16).

The use of the millimeter (mm) wave spectrum for next generation (5G) mobile communication has gained significant attention recently. The small carrier wavelengths at mmwave frequencies enable synthesis of compact antenna arrays, providing beamforming gains that compensate the increased propagation losses. In this work, we investigate the feasibility of employing multiple antenna arrays (at the transmitter and/or receiver) to obtain diversity/multiplexing gains in mmwave systems, where each of the arrays is capable of beamforming independently. Considering a codebook-based beamforming system (the set of possible beamforming directions is fixed a priori, e.g., to facilitate limited feedback), we observe that the complexity of jointly optimizing the beamforming directions across the multiple arrays is highly prohibitive, even for very reasonable system parameters. To overcome this bottleneck, we develop reduced complexity algorithms for optimizing the choice of beamforming directions, premised on the sparse multipath structure of the mmwave channel. Specifically, we reduce the cardinality of the joint beamforming search space, by restricting attention to a small set of dominant candidate directions. To obtain the set of dominant directions, we develop two complementary approaches: 1) based on computation of a novel spatial power metric; a detailed analysis of this metric shows that, in the limit of large antenna arrays, the selected candidate directions approach the channel's dominant angles of arrival and departure, and 2) precise estimation of the channel's (long-term) dominant angles of arrival, exploiting the correlations of the signals received across the different receiver subarrays. Our methods enable a drastic reduction of the optimization search space (a factor of 100 reduction), while delivering close to optimal performance, thereby indicating the potential feasibility of achieving diversity and multiplexing gains in mmwave systems.

In this paper, we study multiple-input multiple-output (MIMO) systems with a large number of antennas at a base station serving a number of users in a cell. The antennas at the base station are assembled into multiple antenna arrays (MAA), which are well separated to keep independence between the arrays, but in each array, antennas are densely installed. The MAA can be viewed as a flexible configuration of multiple antennas to reduce the space for installing the antennas and benefit from beamforming. In order to determine how dense the MAA can be designed, we define antenna area efficiency, that is the ratio of the achievable rate and the 2-D space required for installing the antennas. Then, we analyze the achievable rate of the massive MIMO system with K uplink users and NM antenna elements at the base station placed in N square arrays and each array having √M × √M antennas densely deployed. Specifically, the analytical uplink sum rate is first derived. Then, the sum rate in the low-SNR and highSNR regimes is studied. A case study is provided to show how dense MAA can be designed in a massive MIMO system. Our analytical and simulations results show that, for ten users in low SNR, a single dense antenna array with 11 ×11 antennas in a square requires only 1/200 of the area of conventional 100 independent antennas to achieve the same rate. For ten users in high SNR, we find that two 8 × 8 square arrays can achieve the highest antenna area efficiency in comparison with one 16 × 16 antenna array, four 5 × 5 antenna arrays, and 100 independent antennas.

The High Performance Waveform (HPW) was developed before parallel concatenated codes (PCCC) and serial concatenated codes (SCCC) were in wide use and so it makes sense to take advantage of the advancements in communication theory and processor computation speed that have taken place since its inception. In its current form, HPW transmits a Raised-Cosine Continuous Phase Modulation (1RC CPM) modulation with a trellis code that is designed to provide, with the use of a Cyclic Redundancy Check Code error detection (CRC), error free transmission over a single, narrowband UHF satellite communications channel. In this paper we present an additional set of coding and modulation schemes which take advantage of serial concatenated code (SCCC) technology to simultaneously improve throughput at the lower end of the signal-to-noise ratio (SNR) range while increasing the highest throughput at the highest SNR available on UHF satellites. The overall bit error rate and throughput of each individual modulation type is analyzed and the framework for the adaptive modulation protocol is provided. To provide for a gradual release of a newer revision of HPW, a framework for a PHY layer is provided which will allow a heterogeneous network of legacy and updated radio terminals.

An enhanced transmission is presented in a multiple‐input‐multiple‐output (MIMO) dense‐wavelength division multiplexed (DWDM) free‐space‐optical (FSO) communication link using diversity coding techniques under the effect of turbulent weather phenomenon. The findings show good performance with an (8 channels × 2.5 Gbps data rate/channel) 20 Gbps 1500 m transmission distance. The bit‐error‐rate (BER), outage probability (OP), and signal‐to‐noise ratio (SNR) of the diversity combining techniques using maximum‐ratio combining (MRC), selection combining (SC), and equal‐gain combining (EGC) technique are evaluated in this work. The obtained results illustrate that Alamouti, space‐time coding (STC), space‐time block coding (STBC), space‐time trellis code (STTC), orthogonal STBC (O‐STBC), and quasi‐orthogonal STBC ( QO‐STBC ) on the minimum mean‐square‐error, and MRC are worth implementing on the DWDM‐FSO wireless communication systems. The mitigation of atmospheric turbulence is achieved using MIMO diversity combining techniques coding. The simulation results for diversity coding techniques using QO‐STBC/STTC and SC/MRC in the MIMO‐DWDM FSO communication system can improve BER performance, OP, and SNR. The MRC exhibits the lowest OP and BER when compared with the SC and EGC. The numerical results demonstrate that the FSO communication link using DWDM QO‐STBC/STTC improves the power penalty at both BER values under varying atmospheric turbulence conditions for ST, MT, and WT, in comparison to FSO systems without DWDM QO‐STBC/STTC diversity coding techniques.

We propose a new overloaded multiple access scheme based on Turbo Trellis Coded Modulations (TTCM) which, thanks to the high gain provided by turbo coded schemes, exhibits improved performance with respect to other solutions based on Trellis Coded Modulation (TCM). Turbo Trellis Coded Multiple Access (TTCMA) performs simultaneous transmission of multiple turbo-encoded and modulated data streams intended for users experiencing similar Signal-to-Noise Ratios (SNR). Stream-specific permutations are employed in turbo code interleavers to enable stream identification and separation at the receiver. An efficient solution for the generation of sets of such permutations is also provided. TTCMA overcomes known limitations of previous TCM-based schemes, achieving a high aggregate spectral efficiency even at low SNR by exploiting the large coding gains provided by parallel concatenated schemes when the size of the transmitted information words is large.

A computer program was used to test Wong's coevolution theory of the genetic code. The codon correlations between the codons of biosynthetically related amino acids in the universal genetic code and in randomly generated genetic codes were compared. It was determined that many codon correlations are also present within random genetic codes and that among the random codes there are always several which have many more correlations than that found in the universal code. Although the number of correlations depends on the choice of biosynthetically related amino acids, the probability of choosing a random genetic code with the same or greater number of codon correlations as the universal genetic code was found to vary from 0.1% to 34% (with respect to a fairly complete listing of related amino acids). Thus, Wong's theory that the genetic code arose by coevolution with the biosynthetic pathways of amino acids, based on codon correlations between biosynthetically related amino acids, is statistical in nature.

This paper considers the implementation of multiple element antenna arrays for MIMO wireless systems for use with multiple wireless standards operating at different frequencies. The capacity of such systems for a realistic channel model is considered, and it is shown that it is not generally worthwhile to reduce element spacing below 0.4 wavelengths, and proposes an array topology using a mixture of multi-band and single band elements to maximise the benefit of MIMO while minimising the hardware requirements. Some examples of multi-band elements are given.

We consider distributed estimation in wireless sensor networks (WSNs). Using linear minimum mean squared error (LMMSE) estimator, we derive mean squared error (MSE) to measure the quality of estimation. We introduce a global signal to noise ratio (SNR), where we can derive capacity of data collection in terms of mutual information as reciprocity of MSE. Based on the global SNR, we derive equal power allocation and optimal power allocation in orthogonal multiple access channel (MAC) models. We also derive asymptotic behavior of the global SNR when the power and the number of sensors become unlimited. We minimize MSE as well as maximize mutual information by considering total and individual power constraints. We show that MSE and mutual information of equal power allocation outperforms optimal power allocation. Moreover, system with individual power constraint is worse than the system without that because the suggested power to be allocated is constrained by maximum transmit power of the sensors.

In this chapter, the genetic code seems to be a universal code. The universal code has a specific arrangement of the codons that is definitely not random. There are at least three major concepts of the origin and the evolution of the universal genetic code: Firstly, there is the stereochemical theory stating that the assignments of codons are determined by the physicochemical affinity of the amino acids and the cognate codons (synonymously referred to as anticodons); secondly, the co-evolution theory stating that the structure of the code structure coevolved with the biosynthesis process of amino acids; and thirdly, the error minimization theory stating that there is a selection pressure minimizing the negative effects of point mutations and errors in translation were the main factor of code development. These theories are not contradictory and are also in line with the frozen accident hypothesis, such as the idea that the standard code may not have any special properties, but is simply determined by the fact that all existing life forms have a common ancestor, whereby later alterations to the code are generally excluded by the detrimental effect of codon reallocation. The mathematical examination of the structure and potential evolutionary trajectories of the code reveals that the code is highly resistant to translation errors, although there are numerous more resistant codes, suggesting that the standard code could emerge from a random code through a short sequence of rearrangements of series of codons. A large proportion of the evolution leading to the standard code seems to be a mixture of a frozen collision with a selection for error minimization, even though it cannot be excluded that the code co-evolves along with metabolic pathways due to weak affinities between amino acids and nucleotide triplets. These scenarios for code evolution, nonetheless, are founded on formal patterns with uncertain relevance to real primordial evolution. A true comprehension of code origins and developments is probably only possible in connection with a plausible script for the development of the coding scheme and the translation tool itself.

We propose a general channel model for mobile Ricean multiple-input multiple-output (MIMO) channels, which is characterized by parameters that are readily obtainable from measurements. To this end, a moment-based channel decomposition is derived. For the case of statistical channel state information (CSI) at the transmitter (TX) and instantaneous CSI at the receiver, we derive an approximation of the achievable rate, i.e., the mutual information (MI), which is only a function of the channel parameters of the proposed channel model and thus gives insight into the parameters that influence the MI. Finally, we evaluate the MI for a 4 × 4 MIMO system based on channel measurements at 2.53 GHz for two low-complexity TX strategies, i.e., a beamforming (BF) and a spatial multiplexing (SM) strategy. We find that the proposed channel model and the approximate evaluation of the MI are both accurate for realistic signal-to-noise ratio (SNR) values. The approximate evaluation is able to reproduce crossing points between the MI of the considered TX strategies; it thus reflects the SNR at which one should switch from the BF to the SM strategy.

Wireless channels with multiple transmit/receive antennas are known to provide a high spectral efficiency both when the channel is known to the receiver, and when the channel is not known to the receiver if the signal-to-noise ratio (SNR) is high. Here we analyze such systems at low SNR, which may find application in sensor networks and other low-power devices. The key point is that, since channel estimates are not reliable, it is often not reasonable to assume that the channel is known at the receiver at low SNR. In this unknown channel case, we show that for sensible input distributions, in particular all practical modulation schemes, the capacity is asymptotically quadratic in the SNR, /spl rho/, and thus much less than the known channel case where it exhibits a linear growth in /spl rho/. We show that under various signaling constraints, e.g., Gaussian modulation, unitary space-time modulation, and peak constraints, that mutual information is maximized by using a single transmit antenna. We also show that at low SNR, sending training symbols leads to a rate reduction in proportion to the fraction of training duration time so that it is best not to perform training. Furthermore, we show that the per-channel use mutual information is linear in both the number of receive antennas and the channel coherence interval.