Independent Subchannels Research Articles

Analysis of Precoder Decomposition Algorithms for MIMO System Design

ABSTRACT Wireless communication over Multiple Input and Multiple Output (MIMO) channel achieve increased transmission rate by dividing the input stream into a multitude of parallel data streams which are transmitted in parallel. Precoding at the transmitter aims to decompose the channel into an uncorrelated multiple subchannels using the channel decomposition technique so that data streams will be sent in parallel independent subchannels. The proposed analysis is to analyze the performances of the MIMO precoder using various channel decomposition algorithms are compared and its computational complexity is analyzed. The channel decomposition schemes considered are Singular Value Decomposition, Geometric Mean Decomposition, LDLH, LU, Schur, QR and Jordan decomposition. The simulation and analytical results confirm that precoding for the MIMO channel decomposed by the QR scheme outperforms all the other precoding methods based on channel decomposition in the light of Bit Error Rate performance and involves a relatively lesser number of Floating Point Operations.

Sparse Non-Orthogonal Frequency Division Multiplexing for Secure Transmission Over Broadcast Channels

We propose a novel transmission scheme for the parallel Gaussian broadcast channel with confidential messages (BCCM). In this model, The source node wishes to transmit a confidential message to each user over N independent sub-channels, where each sub-channel is degraded for one user than others. Our objective is to design a secure transmission technique that maximizes the sum secrecy rate under an average power constraint. The most common technique to tackle this problem in practice is orthogonal frequency division multiplexing (OFDM). Nevertheless, the OFDM-based BCCM suffers from excessive bandwidth utilization due to the sub-carrier orthogonality requirement. We propose a sparse non-orthogonal frequency-division Multiplexing (SNOFDM) transmission scheme. In SNOFDM, sub-carriers are generated by first selecting a subset of orthogonal sub-channels to reduce spectral resources. Then, the selected sub-channels are multiplexed in time to generate non-orthogonal sub-carriers. This, in effect increases, the spectral efficiency compared to OFDM. To overcome the interference introduced due to the non-orthogonality of sub-carriers, the transmitter sends the sparsest representation of the transmitted codeword. Furthermore, we provide a sub-carrier selection and power control procedures to maximize the sum rate of SNOFDM according to CSI fed back from receivers to source node. Our numerical results show that SNOFDM offers better spectral efficiency and a higher secrecy rate compared to OFDM. We provide extensive simulation results to study the effects of transmission parameters of SNOFDM on the achievable secrecy rate.

A Study of Discrete Multitone Modulation for Wireline Links Beyond 100 Gb/s

To overcome the severe losses beyond 28 GHz in low-cost electrical channels, 4-level pulse-amplitude modulation (4-PAM) wireline links targeting 112 Gb/s incorporate resource- or power-intensive equalization schemes such as decision-feedback equalizers (DFE) with many taps. Alleviating the timing constraints that cause DFEs to balloon in size and power, discrete multitone (DMT) modulation involves independent sub-channels that can be equalized in the frequency domain without feedback. DMT allows flexibility in assigning bits to each sub-channel, thereby potentially avoiding lossy parts of the frequency spectrum. This article presents behavioural modeling results and an experimental setup used to study DMT transceivers. Our simulations show 200 Gb/s operation at a bit error rate (BER) of less than ${10^{-5}}$ over an IEEE P802.3ck channel with 21 dB of loss at 50 GHz and assuming $150~\mathrm{fs_{rms}}$ of jitter, $1.26~{\mathrm{ mV}}_{\mathrm{ rms}}$ of noise at the receiver’s input, and 7-bit 80 GS/s data converters. An updated bit-loading algorithm led to BER values 1–2 orders of magnitude below our previous results. The estimated power and area of the associated digital signal processing are comparable to those of DFE. We also present an experimental DMT setup achieving 61.6 Gb/s at a BER of ${8.6 \times 10^{-4}}$ over a physical channel with severe notches that is very challenging for 4-PAM.

Минимизации вероятности ошибки на бит в многоэтапной релейной MIMO-системе

This research is devoted to the investigation of the relay multi-stage relay MIMO (Multiple-Input Multiple-Output) of cellular communication with antenna arrays at each stage of transmission, in which parallel independent subchannels for data transmission are formed, are considered. The possibility of minimizing the error probability per bit of transmitted information is investigated while using the method of separate optimization of each transmission stage and the threshold method for selecting energetically strong subchannels. The presented simulation results in the case of a multipath channel with Rayleigh signal fading confirm the high efficiency of the proposed approach.

Full-Azimuth Beam Steering MIMO Antenna Arranged in a Daisy Chain Array Structure.

This paper presents a multiple-input, multiple-output (MIMO) antenna system with the ability to perform full-azimuth beam steering, and with the aim of realizing greater than 20 Gbps vehicular communications. The MIMO antenna described in this paper comprises 64 elements arranged in a daisy chain array structure, where 32 subarrays are formed by pairing elements in each subarray; the antenna yields 32 independent subchannels for MIMO transmission, and covers all communication targets regardless of their position relative to the array. Analytical results reveal that the proposed antenna system can provide a channel capacity of more than 200 bits/s/Hz at a signal-to-noise power ratio (SNR) of 30 dB over the whole azimuth, which is equivalent to 20 Gbps for a bandwidth of 100 MHz. This remarkably high channel capacity is shown to be due to two significant factors; the improved directivity created by the optimum in-phase excitation and the low correlation between the subarrays due to the orthogonal alignment of the array with respect to the incident waves. Over-the-air (OTA) experiments confirm the increase in channel capacity; the proposed antenna can maintain a constant transmission rate over all azimuth angles.

Continuity Pattern Structure of Target Scene in Support of Multiple-Channel ISAR Imagery

This paper presents a multiple-channel ISAR system for multiple air-targets imaging by illuminating a sequence of N narrow and high-gain signal beams over a wide area. Echoes are received by M channels and synthesized into N independent sub-channels using space-time processing technique. The ISAR imaging for each sub-channel is based on the continuity pattern structure technique. Comparing to the conventional ISAR imaging methods, the proposed method can reduce the computational complexity. The numerical results obtained from simulation and experiments demonstrate that the proposed multiple-channel ISAR system has the advantage in detecting multiple air-targets over a wide area and preserving the weak scatterer points comparing to conventional ISAR system.

Experimental Evaluation of the Tri-Polarized MIMO Channel Properties Based on a Compact Multimode Antenna

Based on a planar and compact antenna, extensive measurements are conducted to investigate the behavior of the colocated tri-polarized multiple-input multiple-output (MIMO) system working at 3.5 GHz. Several scenarios with different multipath distributions have been considered, including a reverberation chamber (RC) and also some line-of-sight (LOS) and obstructed LOS (OLOS) real-world indoor environments. Many channel parameters of the MIMO system are analyzed based on the measured data, including cross-polarization discrimination (XPD), Ricean K-factor, correlation coefficient (CC), MIMO channel capacity gain (CG), channel eigenvalues, and ellipticity statistic (ES). The results show that for a multi-polarized MIMO system, the effects of polarization coupling and transition depend strongly on the polarimetric scattering characteristic of the environments. Furthermore, in all the scenarios tested, three non-zero eigenvalues of the MIMO channel matrix are obtained, which indicates that three independent subchannels can be supported by the tri-polarized MIMO system.

Channel Diagonalization for Cloud Radio Access

The diagonalization of a conventional multiple-input multiple-output (MIMO) channel into parallel and independent subchannels via singular value decomposition (SVD) is a fundamental strategy that allows the MIMO channel capacity to be achieved using scalar channel codes. This letter establishes a similar channel diagonalization result for the uplink and the downlink of a cloud radio access network (C-RAN), in which a central processor is connected to a remote radio head (RRH) serving a single user via rate-limit digital fronthaul carrying the compressed baseband signal. Specifically, we show that the diagonalization of the MIMO channel between the RRH and the user via SVD and the subsequent independent and parallel quantization of scalar signals and channel coding in each of the subchannels is optimal. This letter establishes this fact using the majorization theory. Further, an uplink-downlink duality for the multiple-antenna C-RAN is identified for this single-user case.

Channel model proposal for indoor relay‐assisted power line communications

Due to its tree-like topology, the point-to-point (P2P) indoor power line communication (PLC) channel exhibits a similar broadcasting property as the wireless propagation channel shows. However, after relay nodes are introduced, the relay-assisted PLC (RaPLC) channel shows some notable differences compared with its wireless counterpart. A lot of results about the relay-assisted wireless channel can be found in the literature, but the work of modelling RaPLC channel has rarely been discussed in detail. As the first attempt to fill this gap, we apply the ABCD method to compute the channel transfer function (CTF) of the RaPLC channel. It has been clarified that, in general, the CTF of RaPLC channel cannot be obtained as a cascade of two independent P2P PLC sub-channels located on two sides of the relay node. Also, it is shown that the challenge of generating CTF of the RaPLC channel can be transformed into a group of equivalent P2P PLC channel modelling tasks. Under the time-division duplexing constraint, the relay node changes its working mode from the receiving phase to the transmitting phase, which shows that the RaPLC channel is abruptly time-varying in nature. Following the hybrid bottom-up approach, a statistical channel model with a simple six-segment indoor power grid topology has been developed for simulation. Practical measurements and numerical examples verify our results.

Scalable Content Delivery With Coded Caching in Multi-Antenna Fading Channels

We consider the content delivery problem in a fading multi-input single-output channel with cache-aided users. We are interested in the scalability of the equivalent content delivery rate when the number of users, $K$ , is large. Analytical results show that, using coded caching and wireless multicasting, without channel state information at the transmitter, linear scaling of the content delivery rate with respect to $K$ can be achieved in some different ways. First, if the multicast transmission spans over $L$ independent sub-channels, e.g., in quasi-static fading if $L = 1$ , and in block fading or multi-carrier systems if $L>1$ , linear scaling can be obtained, when the product of the number of transmit antennas and the number of sub-channels scales logarithmically with $K$ . Second, even with a fixed number of antennas, we can achieve the linear scaling with a threshold-based user selection requiring only one-bit feedbacks from the users. When CSIT is available, we propose a mixed strategy that combines spatial multiplexing and multicasting. Numerical results show that, by optimizing the power split between spatial multiplexing and multicasting, we can achieve a significant gain of the content delivery rate with moderate cache size.

Coding for Parallel Gaussian Bidirectional Relay Channels: A Deterministic Approach

We study the capacity region of the parallel Gaussian bidirectional relay channel with $L$ independent sub-channels and propose efficient coding schemes for approaching the capacity limit within a constant gap. A two-step approach is considered. First, the corresponding finite field linear deterministic model is studied, for which linear network coding across sub-channels is shown to achieve the capacity region of the channel. Next, based on the insight obtained, a lattice-based compute-and-forward scheme together with simple linear network coding across sub-channels is proposed and is shown to achieve the capacity region of the Gaussian model to within $L$ bits per user regardless of the channel parameters. Even though coding across different sub-channels is necessary for approaching the capacity region, it is shown that this can be realized through a simple linear network coding scheme (across different sub-channels) at the relay.

Analysis of Frequency Channel Division Strategy for CSMA/CA with RTS/CTS Mechanism

Abstract In this work we study the collision probability, saturation throughput and statistical delay for the carrier sense multiple access collision avoidance (CSMA/CA) protocol with request to send and clear to send (RTS/CTS) mechanism in the case of frequency channel division. We propose in this paper a modified version of CSMA/CA-RTS/CTS to be compatible with the channel repartition technique and we prove that an important gain is introduced in terms of system performance especially for loaded networks. Simulations highlight that dividing the channel into independent sub-channels reduces drastically the RTS collision probability. Moreover, a gain in terms of saturation throughput and delay is shown especially in dense networks.

Multi-carrier Equalization by Restoration of RedundancY (MERRY) for Adaptive Channel Shortening in Multi-carrier Systems

Abstract This paper proposes a new blind adaptive channel shortening approach for multi-carrier systems. The performance of the discrete Fourier transform-DMT (DFT-DMT) system is investigated with the proposed DST-DMT system over the standard carrier serving area (CSA) loop1. Enhanced bit rates demonstrated and less complexity also involved by the simulation of the DST-DMT system. Keywords DFT, DMT, DST. 1. I NTRODUCTION Multi carrier modulation, particularly Discrete Multi-tone (DMT) modulation, is one of the most prominent modulation methods for high-speed digital communications. For the channel in the DMT system separated into self- regulating sub-channels. The full amount of bits transmitted over the channel would be the total amount of the bits transmitted in each sub-channel. The binary input data are passed onto a set of parallel, independent sub-channels, each of which is assigned a fixed number of bits during startup or system initialization. Given the measured SNR of each sub-channel during startup, the number of bits for each sub-channel is then determined [1]. Each sub-channel is encoded into a quadrature amplitude modulation (QAM) constellation of the appropriate size. For example, if four bits are assigned to tone

CSI Usage over Parallel Fading Channels under Jamming Attacks: A Game Theory Study

Consider a parallel channel with M independent flat-fading subchannels. There exists a smart jammer which has possession of a copy of perfect channel state information (CSI) measured and sent back by a receiver to its transmitter. Under this model, a class of two-person zero-sum games is investigated where either achievable mutual information rate or Chernoff bound is taken as the underlying pay-off function with the strategy space of each player determined by respective power control and hopping functions. More specifically, we have tackled and answered the following three fundamental questions. The first one is about whether the transmitter and jammer should hop or fully use all degrees of freedom over the entire parallel channels given the full CSI available to both of them, i.e. to hop or not to hop. The second question is about the impact of sending back CSI on system performance considering that the smart jammer can exploit CSI to further enhance its interference effects, i.e. to feedback or not to feedback. The last question is about whether the amount of feedback information can be reduced given the mutual restrictions between transmitter and jammer, i.e. when to feedback and when not to.

Fading Cognitive Multiple-Access Channels With Confidential Messages

The fading cognitive multiple-access channel with confidential messages (CMAC-CM) is investigated, in which two users (users 1 and 2) wish to transmit a common message to a destination and user 1 also has a confidential message intended for the destination. The two users transmit to the destination via a multiple access channel, and user 2 also receives noisy channel outputs. Such channel outputs potentially help user 2 to learn user 1's confidential information (although they are not exploited by user 2 for channel transmission). Hence, user 1 views user 2 as an eavesdropper and wishes to keep its confidential message as secret as possible from user 2. A parallel CMAC-CM with independent subchannels is first studied. The secrecy capacity region of the parallel CMAC-CM is established, which yields the secrecy capacity regions of the parallel CMAC-CM with degraded subchannels and the parallel Gaussian CMAC-CM. These results are then applied to study the fading CMAC-CM, in which both the user-to-user channel and the user-to-destination channel are corrupted by multiplicative fading gain coefficients in addition to additive white Gaussian noise. The channel state information (CSI) is assumed to be known at both the users and the destination. With the CSI, users can dynamically change their transmission powers with the channel realization to achieve the optimal performance. The closed-form power allocation function that achieves every boundary point of the secrecy capacity region is derived.

A Subspace-Based Optimization Strategy for Downlink Systems with Ill-Conditioned MIMO Channels

We propose an innovative and practically attainable downlink multi-cell MIMO system with distributed transmit beamforming design. The proposed system is referred to as the MIMO-MAP system which is aimed to mitigate the rank deficiency problem of those MIMO wireless channels that can not support high-order multiplexing gains. In the MIMO-MAP system, each mobile station is allowed to receive several independent data streams from multiple access points at the same time and the same frequency. To do this, a set of noise-subspace-based receive beamformers are employed to suppress the interference among the data streams from different access points. On the other hand, if we consider each receive beamformer as part of its associated wireless channel, we virtually reduce the antenna array at each receive mobile station to a single antenna. With this arrangement, we may have the transmit signal dimension high enough to pre-cancel the inter-stream-interferences at each transmit access point. As a result, the MIMO-MAP channel can be decomposed into a large number of independent subchannels which significantly increase the channel capacity.

Resource Allocation for Parallel Gaussian MIMO Wire-tap Channels

Wire-tap channels are able to provide perfect secrecy when a receiver exhibits a better channel than its wire-tapping opponent. In this letter, we extend the perfect secrecy principle to parallel Gaussian multiple input multiple output (MIMO) wire-tap channels with independent sub-channels. Assuming N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ≥ N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> ≥ N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> , mathematical derivations show that a sub-optimal solution can be given in closed-form considering either secrecy rate maximization subject to a total power constraint or power minimization subject to a secrecy rate constraint. Although sub-optimal for MIMO systems, simulation results show that the proposed algorithm allows to reach higher secrecy rates with substantial gains in power consumption compared to the single input single output (SISO) system.

Opportunistic Communication (Cognitive Radio) over Primary Discarded Subchannels by Applying a Double Power Distribution

This paper proposes the establishment of a simultaneous cognitive radio communication based on a subdistribution of power made over unselected subchannels which were discarded by the primary user through an initial optimal power allotment. The aim of this work is to show the possibility of introducing an opportunistic communication into a licensed transmission where the total power constraint is shared. The analysis of the proposed transmission scheme was performed by considering 128 and 2048 independent subchannels affected byRayleighfading, over 10,000 channel realizations, and three different signal-to-noise ratios (8 , 16 , and 24 ). From the system evaluation it was possible to find the optimal power allotment for the primary user, the subdistribution of power for the secondary user, as well as the attenuation and the capacity per subchannel for every channel realization. Moreover, thePDFandCDFof the total obtained capacities, as well as the generation of empirical capacity regions, were estimated as complementary results.

Bit-interleaved coded modulation for hybrid RF/FSO systems

In this paper, we propose a novel architecture for hybrid radio frequency (RF)/free-space optics (FSO) wireless systems. Hybrid RF/FSO systems are attractive since the RF and FSO sub-systems are affected differently by weather and fading phenomena. For example, while 60-GHz RF systems are susceptible to rain, fog is detrimental to FSO systems. We show that a hybrid system robust to these impairments is obtained by joint bit-interleaved coded modulation (BICM) of the bit steams transmitted over the RF and FSO sub-channels. An asymptotic performance analysis reveals that a properly designed convolutional code can exploit the diversity offered by the independent sub-channels. Furthermore, we develop code design and power assignment criteria and provide an efficient code search procedure. The cut-off rate of the proposed hybrid system is also derived and compared to that of hybrid systems with perfect channel state information at the transmitter. Simulation results show that hybrid RF/FSO systems with BICM outperform previously proposed hybrid systems employing a simple repetition code and selection diversity.

Maximizing the Average Spectral Efficiency of Dual-Branch MIMO Systems With Discrete-Rate Adaptation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The capacity of multiple-input–multiple-output (MIMO) systems with perfect transmitter and receiver channel state information (CSI) can be attained by decoupling the MIMO channel into a set of independent subchannels and distributing the power among these subchannels in accordance with the <emphasis emphasistype="boldital"> water-filling</emphasis> solution. Implementation of this scheme on a time-varying channel, however, requires continuous-rate adaptation and is not feasible in any such practical system. In this paper, we show how to maximize the average spectral efficiency (ASE) of dual-branch MIMO systems (either two transmit or two receive antennas) with perfect transmitter and receiver CSI when using a fixed number of codes (discrete-rate adaptation). This maximum ASE is compared with the system's ergodic capacity and with the maximum ASE that can be attained if the available power is distributed among the different subchannels in accordance with the water-filling solution although only discrete-rate adaptation is possible. We assume that capacity-achieving codes for additive white Gaussian noise (AWGN) channels are available and that the power available to the transmitter to transmit the <formula formulatype="inline"><tex>$i$</tex></formula>th symbol frame is fixed and independent of the frame index <formula formulatype="inline"><tex>$i$</tex></formula>. </para>