This work focuses on angle of arrival estimation algorithms of massive MIMO LEO satellite-ground networks. In particular, the performance is investigated under pilot contamination effects caused by residual Doppler frequency shifts, a common phenomenon in non-stationary satellite communications, especially when operating in higher frequency bands. This study provides pertinent insights on such impairments and concludes on the suitability as well as shortcomings of these AoA estimation techniques with respect to the different system parameters of massive MIMO LEO satellite networks. Overall, results show that a larger number of antenna elements on-board the satellite provides a better estimation quality and aids to reduce the adverse effects of pilot contamination.

Abstract In this paper, a communication system with digital burst‐mode transmission and distributed reception in the presence of carrier frequency offset and Additive White Gaussian Noise (AWGN) is considered. The distributed receiver consists of distributed nodes and a fusion center. Data‐aided frequency estimation at a receiving node can be performed using a preamble. However, accurate frequency estimation may not be achievable at nodes with low signal‐to‐noise ratio (SNR). The problem can be alleviated by collaboration between nodes. Low‐SNR nodes can improve their data‐aided frequency estimation by fetching already decoded symbols from the fusion center. This paper investigates deterministic and data dependent criteria for selecting and fetching of additional symbols. The mean‐square error (MSE) of frequency estimation errors achieved by different criteria are numerically compared via Monte‐Carlo simulations. The Cramer–Rao Lower Bounds (CRLB) for frequency estimation under the considered criteria are presented. The bit‐error‐rates (BER) of the distributed receiver across different symbol fetching schemes are numerically compared.

We consider the problem of tracking, in realtime, an unstable autoregressive (AR) source over a discrete memoryless channel (DMC). We present computable achievable bounds on the optimal tracking error for general DMCs, and we particularize these bounds to the binary erasure, packet erasure, and binary symmetric channels. The achievable bounds in this paper are proved using a partially separatesource quantizationandchannel codingarchitecture. We do not use complete or strict separation in usual Shannon sense: 1) the quantiser’s resolution is optimized against the error-correction capabilities of the channel code and the channel code is optimized against anAR Hamming distortion functionmatched to the source (a weighted Hamming distortion function that provides unequal error protection to different parts of the AR source). The achievability results for general DMCs are proved by combining the AR Hamming distortion function with new realtime (streaming) versions of therandom coding unionanddependence testing bounds. When applied to erasure channels, these general bounds combine with simple converses to demonstrate that the channel’s cutoff rate plays an important role in realtime tracking.

Multi-hop relaying is well known to extend the range of wireless communications. However, the end-to-end performance of the multi-hop relaying channel degrades compared to that observed at the first hop. This performance degradation mainly arises due to: 1) half-duplex loss and 2) hopping or relaying loss. In this paper, we analyze the degradation in outage probability and ergodic capacity due to hopping loss in a multiple-input multiple-output (MIMO) dual-hop decode-and-forward relaying network over Rayleigh fading channels. In particular, we characterize analytically the performance degradation by deriving closed-form approximations of ergodic capacity and outage probability in the single-source single-relay single-user, single-source multiple-relay single-user, and single-source single-relay multiple-user topologies. These approximations also provide insights on how to overcome performance degradations due to hopping loss. Moreover, we show that cooperative relaying schemes can recover a significant portion of the hopping loss.

Anytime codes are known to be useful for tracking and controlling unstable systems over noisy channels. Although practical anytime codes have been developed for point-to-point communication, to date no practical code constructions and tractable analysis of anytime codes are known to exist for relay networks. In this paper, we study the design and theoretical analysis of anytime codes for a three-terminal relay network. We propose bilayer codes for anytime transmission over the relay network and consider two transmission schemes for the relay-destination link. For both schemes, we analytically derive the delay-exponents and show that they closely match the corresponding numerical results obtained from density evolution. Through simulation, we also show the finite-length performance of the proposed bilayer anytime code.

In this paper, we present the performance analysis of a multibeam high throughput satellite (HTS) system with optical feeder link. We consider the forward link, or downlink, with a fixed gain transparent satellite payload, where the optical feeder link, i.e. the link between gateway and satellite, is impaired by turbulence fading and the RF user link, i.e. the link between satellite and user terminals, is degraded by rain fading. In multibeam HTS systems, frequency re-use in the user link creates interbeam interference which needs to be mitigated to avoid performance degradation. For this purpose, we consider our recently proposed novel zero-forcing (ZF) precoder that does not require channel state information at the gateway and compare its performance with the conventional ZF precoder. We derive statistics of the end-to-end signal-to-noise ratio to approximate performance measures including outage probability, average bit error rate and ergodic capacity. These approximations provide valuable insights into the system analysis. Monte Carlo simulations are used to validate the accuracy of our analysis.

In this paper, we present an analytical framework for detecting optical unipolar orthogonal frequency-division multiplexing (U-OFDM) signals. We derive analytical expressions for time-domain signal estimates based on different schemes including maximum likelihood, maximum a-posteriori and minimum mean-square error (MMSE) estimation. These schemes are compared with state-of-the-art U-OFDM detection schemes in terms of uncoded bit-error rate (BER). Numerical results show that the MMSE estimate-based scheme exhibits the least BER performance in the low signal-to-noise ratio (SNR) regime. Furthermore, we consider coded systems and reveal that the coded BER performance of the MMSE scheme is superior to previously proposed receivers. Finally, we propose an iterative-decoding scheme with soft-symbol estimation to further improve the performance of coded U-OFDM.

It is well-known that relaying can extend the communication range. However, the performance of the relaying network is inferior compared to a single-hop system where the destination is placed hypothetically at the relay. The gap between the single-hop and relay network, dubbed the multi-hopping or relaying loss, is studied in this paper. In particular, we investigate the increase in outage probability and the degradation in ergodic capacity incurred due to the multi-hopping loss in a dualhop multiple-input multiple-output decode-and-forward relaying network operating in the single-source single-relay single-user topology. Moreover, we show that a cooperative relaying scheme, called the best relay scheme, in the single-source K-relays single-user topology can recover a significant portion of the multi-hopping loss. In both topologies, we derive closed-form approximations for the outage probability and ergodic capacity using the well-known Gaussian approximation.

Multibeam satellite communication (SatCom) with full or aggressive frequency re-use is one of the most promising candidates for next-generation high throughput satellite systems. However, frequency re-use creates interbeam interference which needs to be managed using multiuser precoding techniques in the forward link and multiuser detection techniques in the reverse link. This work considers the forward link of multibeam Sat-Com systems and proposes a novel zero-forcing (ZF) precoding technique that makes use of users' physical location and antenna radiation pattern available at the gateway. Contrary to conventional precoding techniques in multibeam SatCom systems, the proposed precoding technique does not require feedback from user terminals. Numerical results show that the proposed ZF precoder achieves higher ergodic capacity than the conventional ZF precoder. We provide a closed-form approximation for the ergodic capacity of the proposed ZF precoder under rain fading. We also provide a closed-form approximation for computing the moments of the rain fading attenuation which enables us to derive high and low signal-to-noise ratio (SNR) expressions of the ergodic capacity in closed-form. Furthermore, an upper bound on the ergodic capacity is obtained. Monte Carlo simulations are used to validate the accuracy of our analysis.

This paper presents the design and analysis of spatially coupled low‐density parity‐check (SC‐LDPC) codes for Gaussian multiple access channel (GMAC). For two‐user GMAC, we consider that each user encodes their messages by SC‐LDPC codes while joint belief propagation decoding is considered at the receiver. We present low complexity density evolution analysis of SC‐LDPC GMAC codes and show simple optimisation procedure. For the asymptotic case, we observe that SC‐LDPC code‐based GMAC code outperforms existing irregular LDPC code‐based GMAC code.

Anytime transmission has been shown to be an effective means of stabilizing an unstable system over noisy channels. A crucial issue in implementing anytime transmission strategies is the design of anytime codes that offer good finite-length performance and asymptotic anytime properties. This paper introduces an efficient anytime code derived from protograph-based low-density parity-check convolutional codes known as extended S-LDPCC (XS-LDPCC) codes. The asymptotic anytime properties of XS-LDPCC codes over both the binary erasure channel (BEC) and the binary-input additive white Gaussian noise (BIAWGN) channel are demonstrated through density evolution. By means of certain observations verified by simulations, we provide accurate estimates of the delay exponents of XS-LDPCC codes over the BEC and the BIAWGN channel. Through simulations, the finite-length performance of XS-LDPCC codes and the effects of different code design parameters are quantified.

This paper studies the bilayer codes for anytime reliable transmission over three terminal relay networks. We propose an anytime code structure and provide a theoretical analysis of bilayer anytime transmission when uncoded relaying takes place over the relay-destination channel. Through asymptotic analysis, we show the anytime characteristics of the proposed relaying scheme. We find the theoretical delay exponent through the mathematical induction technique and compare it with the delay exponent obtained from numerical results. Through simulation results, we also show the finite-length performance of the proposed bilayer anytime code.

In this paper, an efficient anytime code derived from protograph-based low-density parity-check convolutional (P-LDPCC) code is proposed. Density evolution technique is applied to demonstrate the anytime properties of the P-LDPCC code over the binary erasure channel (BEC). Through simulation, the finite-length performance is evaluated and the effects of code design parameters are observed. The delay exponent is evaluated using the density evolution functions and simulations of finite-length codes. The simulation results show that P-LDPCC code outperforms existing LDPCC anytime codes.

We propose a rate-adaptive error-correction coding framework for transmission over finite-length block-fading channels, with causal channel state information at the transmitter. A dynamic programming optimization approach can be use to obtain the optimal rate adaptation strategy. A suboptimal rate adaptation strategy is developed for sequential random codes. Numerical results show that significant performance gains are achievable with the proposed adaptation scheme.

Anytime transmission was previously shown to be necessary and sufficient for tracking and controlling an unstable plant over a noisy channel. In this paper, we propose an efficient channel coding scheme for anytime transmission. We design this coding scheme based on spatially coupled codes and investigate its performance over binary erasure channels (BEC) and binary input additive white Gaussian noise (BIAWGN) channels. Through density evolution analysis, we asymptotically show the desired anytime properties of the proposed code. For the BEC, we derive the corresponding delay-exponent and numerically predict the finite-length performance of the proposed anytime code. We also propose adaptive window decoding techniques to ensure low complexity anytime receivers.

In this paper, we study the design and the delay-exponent of anytime codes over a three terminal relay network. We propose a bilayer anytime code based on anytime spatially coupled low-density parity-check (LDPC) codes and investigate the anytime characteristics through density evolution analysis. By using mathematical induction technique, we find analytical expressions of the delay-exponent for the proposed code. Through comparison, we show that the analytical delay-exponent has a close match with the delay-exponent obtained from numerical results.

Lossless coding for streaming sources is studied under a delay-constrained point-to-point setup. A variant of random binning, known as variable-length sequential random (VLSR) binning, is proposed for this setup. The performance of this binning scheme is evaluated by its delay exponent, which measures the asymptotic rate at which the decoding error probability decays with the delay. An achievable delay exponent is derived for VLSR binning, and numerical results show that the proposed binning achieves a better delay exponent than the existing fixed-length sequential random binning.

In this paper, we study the performance of finite-length LDPC codes in the waterfall region. We propose an algorithm to predict the error performance of finite-length LDPC codes over various binary memoryless channels. Through numerical results, we find that our technique gives better performance prediction compared to existing techniques.

We propose a decode-forward protocol for streaming over a relay network using sequential random tree codes. An achievable bound on the end-to-end error performance is derived. The bound is parameterised by the number of errors occuring at the relay, which is the sum of correlated Bernoulli processes. The bound is useful for determining the achievable delay-exponent as well as for designing finite-delay relaying schemes. For a wide range of conjectured correlation models, the proposed scheme can achieve the delay-exponent of full source-relay cooperation.

We study compress-and-forward relaying for delay-universal transmission over a three-terminal network. An important performance measure of delay-universal transmission is the delay-exponent. Two achievable bounds of the delay-exponent are derived. The delay-exponent achieved by a suboptimal message-truncating decoder is inferior to that achieved by an approximate maximum-likelihood (ML) decoder in most cases. However, ML decoding is not analytically tractable when source compression is employed at the relay terminal. Therefore, the system with the message-truncating decoder performs better when signal compression is essential, for e.g. when the source-relay link is non-symmetric and the relay-destination link is noisy.

This paper studies the asymptotic outage performance of incremental redundancy automatic-repeat-request (INR-ARQ) transmission over multiple-input multiple-output (MIMO) block-fading channels with discrete input constellations. We first show that transmission with random codes using a discrete signal constellation across all transmit antennas achieves the optimal outage diversity given by the Singleton bound. The optimal SNR-exponent and outage diversity of INR-ARQ transmission over the MIMO block-fading channel are then analysed. We show that a significant gain in outage diversity is obtained by providing more than one bit feedback at each ARQ round. Thus, the outage performance of INR-ARQ transmission can be remarkably improved with minimal additional overhead. A practical feedback-and-power-adaptation rule is proposed for MIMO INR-ARQ, demonstrating the benefits provided by multibit feedback. Although the rule is sub-optimal in terms of outage performance, it achieves the optimal outage diversity.

We study the error probability of LDPC codes in delay-limited block-fading channels with channel state information (CSI) at the transmitter and the receiver. We derive the optimal power allocation algorithms for LDPC codes with specific degree distributions using multi-edge-type density evolution error boundaries. The resulting performance approaches the outage probability for a number of power constraints. Furthermore, we adapt the algorithm for finite-length codes and show that the proposed algorithm enables gains larger than 10 dB over uniform power allocation. The method is valid for general, possibly correlated, fading distributions. This represents the first analysis of specific LDPC codes over block-fading channels with full CSI.

We study hybrid free-space optical (FSO) and radio-frequency (RF) communications, whereby information is conveyed simultaneously using both optical and RF carriers. We consider the case where both carriers experience scintillation, which is a slow fading process compared to typical data rates. A parallel block-fading channel model is proposed, that incorporates differences in signalling rates, power scaling and scintillation models between the two carriers. Under this framework, we study the outage probability in the large signal-to-noise ratio (SNR) regime. First we consider the case when only the receiver has perfect channel state information (CSIR case) and obtain the SNR exponent for general scintillation distributions. Then we consider the case when perfect CSI is known at both the receiver and transmitter, and derive the optimal power allocation strategy that minimises the outage probability subject to peak and average power constraints. The optimal solution involves non-convex optimisation, which is intractable in practical systems. We therefore propose a suboptimal algorithm that achieves the same diversity as the optimal one and provides significant power savings (on the order of tens of dBs) over uniform allocation.

We study the outage diversity of the multiple-input multiple-output (MIMO) Rayleigh block-fading channel when causal channel state information (CSI) is available at the transmitter (CSIT). Within this setting, we consider the optimal power allocation for blocks b = 1, ..., B given perfect CSIT for blocks 1, ..., b-u only, subject to a long-term power constraint. The parameter 0 ≤ u ≤ B is a fixed arbitrary integer that determines the delay in acquiring perfect knowledge of the CSI at the transmitter. Without explicitly solving the optimal power allocation problem, we derive the outage diversity of the system. For general 0 ≤ u ≤ B, we derive a simple recursive expression for computing the outage diversity. For the special case u = 0, it is shown that the outage diversity is infinite, coinciding with previously known results. For 1 ≤ u ≤ B, the outage diversity becomes finite and for the special case of u = 1, 2 it can be expressed in simple closed form.

Reliable communication over delay-constrained multiple-input multiple-output (MIMO) block-fading channels with discrete inputs and mismatched (imperfect) channel state information at the transmitter (CSIT) is studied. The CSIT mismatch is modeled as Gaussian random variables, whose variances decay as a power of the signal-to-noise ratio (SNR). A special focus is placed on the large-SNR decay of the error and outage probabilities when power control with long-term power constraints is used. Without explicitly characterizing the corresponding power allocation algorithms, we derive the outage exponent as a function of the system parameters, including the CSIT noise variance exponent and the exponent of the peak power constraint. It is shown that CSIT, even if noisy, is always beneficial and leads to important gains in terms of exponents.

Power allocation is studied for fixed-rate transmission over block-fading channels with arbitrary continuous fading distributions and perfect transmitter and receiver channel state information. Both short- and long-term power constraints for arbitrary input distributions are considered. Optimal power allocation schemes are shown to be direct applications of previous results in the literature. It is shown that the short- and long-term outage exponents for arbitrary input distributions are related through a simple formula. The formula is useful to predict when the delay-limited capacity is positive. Furthermore, this characterization is useful for the design of efficient coding schemes for this relevant channel model.

We consider improving the outage performance of incremental-redundancy automatic repeat request (INR-ARQ) transmission over the multiple-input multiple-output (MIMO) block-fading channel by allowing multi-bit receiver feedback. We show that multi-bit feedback offers significant gain in outage diversity when power adaptation is employed. A suboptimal feedback and power adaptation rule is proposed, illustrating the benefits provided by multi-bit feedback.

We study the hybrid free-space optical (FSO) and radio-frequency (RF) channel from an information theoretic perspective. Since both links operate at vastly different carrier frequencies, we model the hybrid channel as a pair of parallel channels. Moreover, since the FSO channel signals at a higher rate than the RF channel, we incorporate this key feature in the parallel channel model. Both channels experience fading due to scintillation, which is slow compared to typical signalling rates. Under this framework, we study the fundamental limits of the hybrid channel. In particular, we analyse the outage probability in the large signal-to-noise ratio (SNR) regime, and obtain the outage diversity or SNR exponent of the hybrid system. First we consider the case when only the receiver has perfect channel state information (CSIR case), and obtain the exponents for general scintillation distributions. These exponents relate key system design parameters to the asymptotic outage performance and illustrate the benefits of using hybrid systems with respect to independent FSO or RF links. We next consider the case when perfect CSI is known at both the receiver and transmitter, and derive the optimal power allocation strategy that minimises the outage probability subject to peak and average power constraints. The optimal solution involves non-convex optimisation, which is intractable in practical systems. We therefore propose a suboptimal algorithm that achieves significant power savings (on the order of tens of dBs) over uniform power allocation. We show that the suboptimal algorithm has the same diversity as the optimal power allocation strategy.

We consider power allocation strategies for arbitrary input channels with peak, average and peak-to-average power ratio (PAPR) constraints. We are focusing on systems with a fixed and finite input constellation, as encountered in most practical systems. Generalizing previous results, we derive the optimal power allocation scheme that minimizes the outage probability of block-fading channels with arbitrary input constellations, subject to PAPR constraints. We further show that the signal-to-noise ratio exponent for any finite peak-to-average power ratio is the same as that of the peak-power limited problem, resulting in an error floor. We also derive the optimal power allocation strategies that maximize the ergodic capacity for arbitrary input channels, subject to average and PAPR constraints.We show that capacities with peak-to-average power ratio constraints, even for small ratios, are close to capacities without peak-power restrictions. For both delay-limited and ergodic block-fading channels, the optimal power allocation strategies rely on the first derivative of the input-output mutual information, which may be computationally prohibitive for efficient practical implementation. To overcome this limitation, we develop suboptimal power allocation schemes that resemble the traditional water-filling technique. The suboptimal power allocation schemes significantly reduce computational and storage requirements, while enjoying minimal performance losses as compared to optimal schemes.

Power allocation with peak-to-average power constraints over Nakagami-m block-fading channels with arbitrary input distributions is studied. In particular, we find the solution to the minimum outage power allocation scheme with peak-to-average power constraints and arbitrary input distributions, and show that the signal-to-noise ratio exponent for any systems with a finite peak-to-average power ratio constraint is the same as that of systems with peak-power constraints, resulting in an error floor.

We characterize the asymptotic outage performance of power allocation techniques for systems with average power constraints. We show that the outage diversity of a system with average power constraints can be obtained from the diversity of the corresponding system with peak power constraints. The characterization is therefore useful since the asymptotic performance of systems with peak power constraints is well known in the literature.

In this paper, we propose a tight lower bound to the outage probability of Nakagami-m block-fading channels. The approach permits an efficient method for numerical evaluation of the bound, providing an additional tool for system design. The optimal rate-diversity trade-off for the Nakagami-m block-fading channel is also derived and a tight upper bound is obtained for the optimal coding gain constant.

In this correspondence, a tight lower bound to the outage probability of discrete-input Nakagami-$m$block-fading channels is proposed. The approach permits an efficient method for numerical evaluation of the bound, providing an additional tool for system design. The optimal rate-diversity tradeoff for the Nakagami-$m$block-fading channel is also derived and a tight upper bound is obtained for the optimal coding gain constant.