Absence Of Channel State Information Research Articles

Performance Analysis of an IRS-Aided Wireless Communication System With Spatially Correlated Channels

An intelligent reflecting surface (IRS) assisted wireless communication system, with statistically correlated channels between the transmitter and the IRS pair and between the IRS and the receiver pair, is studied in the absence of channel state information (CSI). Assuming the phases added by IRS elements to be deterministic, the closed-form analytical expression for the symbol error probability (SEP) and the upper bound on the channel capacity are derived, with the transmitter employing binary phase-shift keying (BPSK) modulation for data transmission. The asymptotic SEP expression is derived and the achievable diversity order of the system is shown to be independent of the number of IRS elements. A search based algorithm is proposed to obtain the optimal phase at IRS minimizing the average SEP, as a equal phase configuration. The optimal equal phase is also found to maximize the average channel capacity. Numerical results are presented for the case of channels following a practical IRS correlation model.

Error Probability Analysis for Rectangular Differential OFDM With Index Modulation Over Dispersive Channels

In this letter, a novel forgetting factor aided rectangular differential (RD) orthogonal frequency division multiplexing (OFDM) with index modulation (IM) is proposed for dispersive channels, which amalgamates the concept of RD coding for exploiting the benefits of OFDM-IM with the absence of channel state information (CSI). To be more specific, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> subcarriers are partitioned into <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${G}$ </tex-math></inline-formula> subblocks for IM mapping. By employing RD coding during two adjacent subblocks, non-coherent detection without CSI can be carried out at the receiver. To further improve the performance, a novel forgetting factor is exploited at the receiver, which can be optimized via a closed form without extra complexity. Based on the derived forgetting factor, the upper bound of the average bit error probability (ABEP) of the proposed RD-OFDM-IM scheme is derived and is validated by the simulation results. Both the theoretical and simulation results indicate that the proposed RD-OFDM-IM scheme is capable of providing a considerable performance gain over its conventional differential OFDM (D-OFDM) counterpart.

Multi-User Small Base Station Association via Contextual Combinatorial Volatile Bandits

We propose an efficient mobility management solution to the problem of assigning small base stations (SBSs) to multiple mobile data users in a heterogeneous setting. We formalize the problem using a novel sequential decision-making model named contextual combinatorial volatile multi-armed bandits (MABs), in which each association is considered as an arm, volatility of an arm is imposed by the dynamic arrivals of the users, and context is the additional information linked with the user and the SBS such as user/SBS distance and the transmission frequency. As the next-generation communications are envisioned to take place over highly dynamic links such as the millimeter wave (mmWave) frequency band, we consider the association problem over an unknown channel distribution with a limited feedback in the form of acknowledgments and under the absence of channel state information (CSI). As the links are unknown and dynamically varying, the assignment problem cannot be solved offline. Thus, we propose an online algorithm which is able to solve the user-SBS association problem in a multi-user and time-varying environment, where the number of users dynamically varies over time. Our algorithm strikes the balance between exploration and exploitation and achieves sublinear in time regret with an optimal dependence on the problem structure and the dynamics of user arrivals and departures. In addition, we demonstrate via numerical experiments that our algorithm achieves significant performance gains compared to several benchmark algorithms.

Low-Complexity Channel Allocation Scheme for URLLC Traffic

In this paper, we consider the downlink transmission of URLLC packets requiring very low latency and ultra-reliability. Because of the low latency constraint, the Base Station may not have enough time to acquire the instantaneous Channel State Information (CSI) of the corresponding device and has then to transmit urgent packets immediately in the absence of CSI. To enhance reliability, we explore frequency diversity where a packet can be simultaneously sent over multiple channels. Using a Markov Decision Process framework, we address the problem of dynamic channel allocation to the URLLC devices in absence of instantaneous CSI. More precisely, we define a multi-agent MDP wherein the state of each device is the packet loss rate experienced in the previous time slots and the decision variable is how to split the available orthogonal channels across the devices. We design a new low-complexity algorithm which avoids the exhaustive enumeration of all possible resource allocations and enables significant computational savings compared to the Value Iteration algorithm. We investigate the gap between our proposed low complexity algorithm and the Value Iteration policy. We provide numerical performance results and show that our algorithm can achieve more than 80% of the optimal reward with substantial computational complexity reduction.

Oversampling Based Analog Beamforming for Initial Access With a Large Number of Receive Antennas

Beamforming can provide huge array gains in large-scale antenna systems under the condition that the channel state information (CSI) has been obtained by training signals. During the initial access, no CSI is available at the receiver because the communication link between the transmitter and the receiver has not been established. This paper considers the problem of obtaining the beamforming gain for receivers with the analog beamforming architecture in the initial access, assuming that a fixed beam pattern is employed. We present the necessary and sufficient condition to obtain the receive beamforming gain in the absence of CSI, and then derive the upper bound of the receive beamforming gain for different antenna spacings. It is shown that oversampling in space is needed at the receiver to obtain a non-trivial beamforming gain without CSI, since the total received signal power is proportional to the number of receive antennas. We also design the beamformer that can achieve the upper bound. Numerical results demonstrate the effectiveness of the proposed beamformer in the scenarios of downlink synchronization and random access in millimeter-wave systems.

Outage and Average Rate Performances of Full-Duplex Multiuser AF Relay Systems With Time-Selective Fading

The outage and average rate performances are studied for a multiuser amplify-and-forward two-way relay system, where all the users are assumed to be mobile, and the effect of mobility is modeled using a first-order autoregressive process. The absolute and normalized channel-power-based scheduling schemes are adopted when channel state information (CSI) is available at the relay node. In the absence of CSI, we consider the random scheduling scheme, where user pairs are selected randomly. To characterize the residual self-interference (RSI) at the full-duplex relay and user nodes, the fading-channel-based approach is used, and RSI is modeled as a Rician-distributed random variable. Using the Gaussian–Chebyshev approximation, expressions for the outage probability and the average rate are derived for the adopted scheduling schemes, and their performance is compared with the hybrid scheduling scheme assuming independent and nonidentically distributed channels. The analytical results are validated through simulations. This article reveals the impact of key parameters, such as user mobility, channel estimation errors, and RSI, on the performance of the considered full-duplex two-way relaying system.

On Achievable Distortion in Sending Gaussian Sources over a Bandwidth-Matched Gaussian MAC with No Transmitter CSI

This paper investigates the minimum mean square error (MMSE) of communicating a pair of Gaussian sources over a a bandwidth-matched Gaussian multiple-access channel with block Rayleigh fading in the absence of channel state information (CSI) at the transmitters. The achievable MMSE is not known. To this end, we derive several upper-bounds to the minimum achievable average MMSE as a function of the transmitter powers, the average channel fading power-to-noise ratio, and the correlation coefficient of the two sources. To derive nontrivial upper bounds which improve on those of separate source-channel coding and uncoded transmission, we incorporate ideas from joint source-channel coding and hybrid digital–analog coding to construct specific coding schemes for which the achievable MMSE can be determined.

Blind Sparse Estimation of Intermittent Sources Over Unknown Fading Channels

Radio frequency sources are observed at a fusion center via sensor measurements made over slow flat-fading channels. The number of sources may be larger than the number of sensors, but their activity is sparse and intermittent with bursty transmission patterns. To account for this, sources are modeled as hidden Markov models with known or unknown parameters. The problem of blind source estimation in the absence of channel state information is tackled via a novel algorithm, consisting of a dictionary learning (DL) stage and a per-source stochastic filtering (PSF) stage. The two stages work in tandem, with the latter operating on the output produced by the former. Both stages are designed so as to account for the sparsity and memory of the sources. To this end, smooth LASSO is integrated with DL, while the forward-backward algorithm and Expectation Maximization (EM) algorithm are leveraged for PSF. It is shown that the proposed algorithm can enhance the detection and the estimation performance of the sources, and that it is robust to the sparsity level.

Outage Effective Capacity of Buffer-Aided Diamond Relay Systems Using HARQ-IR

In this paper, transmission over buffer-aided diamond relay systems under statistical quality of service (QoS) constraints is studied. The statistical QoS constraints are imposed as limitations on delay violation probabilities. In the absence of channel state information (CSI) at the transmitter, truncated hybrid automatic repeat request-incremental redundancy (HARQ-IR) is incorporated to make better use of the wireless channel and the resources for each communication link. The packets that cannot be successfully received upon the maximum number of transmissions will be removed from buffer, i.e., outage occurs. The outage effective capacity of a communication link is defined as the maximum constant arrival rate to the source that can be supported by the goodput departure processes, i.e., the departure that can be successfully received by the receiver. Then, the outage effective capacity for the buffer-aided diamond relay system is obtained for HARQ-IR incorporated transmission strategy under the end-to-end delay constraints. It is shown that HARQ-IR can achieve the same performance as the one achieved with the decode-and-forward protocol with perfect CSI at the transmitters under certain delay constraints.

Sum-Rate Analysis for High Altitude Platform (HAP) Drones With Tethered Balloon Relay

High altitude platform (HAP) drones can provide broadband wireless connectivity to ground users in rural areas by establishing line-of-sight links and exploiting effective beamforming techniques. However, at high altitudes, acquiring the channel state information (CSI) for HAPs, which is a key requirement to perform beamforming, is challenging. In this paper, by exploiting an interference alignment (IA) technique, a novel method for achieving the maximum sum-rate in HAP-based communications without CSI is proposed. In particular, to realize IA, a multiple-antenna tethered balloon is used as a relay between multiple HAP drones and ground stations (GSs). Here, a multiple-input multiple-output X network system is considered. The capacity of the considered $M \times N$ X network with a tethered balloon relay is derived in closed-form. Simulation results corroborate the theoretical findings and show that the proposed approach yields the maximum sum-rate in multiple HAPs-GSs communications in absence of CSI. The results also show the existence of an optimal balloon’s altitude for which the sum-rate is maximized.

Blind Interference Alignment for the &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$K$&lt;/tex-math&gt; &lt;/inline-formula&gt;-User MISO BC Under Limited Symbol Extension

In this paper, we study the achievable degrees of freedom (DoFs) for $K$ -user multiple-input single-output broadcast channel (BC) in the absence of channel state information at the transmitter under the finite channel coherent time. For the considered $K$ -user BC, a transmitter is equipped with multiple conventional antennas, and receivers are equipped with a reconfigurable antenna that is capable of dynamically modifying the receiving beam radiation pattern. In this system, we propose a blind interference alignment scheme that is able to allocate an asymmetric number of information symbols to each user, which is essentially required to improve DoFs under limited symbol extension. A generalized systematic construction method of transmit beamforming vectors and receiving mode selection patterns to deal with such asymmetric allocation is established. As a consequence, for a broad class of network configurations and symbol extension constraints, the proposed scheme attains an improved sum DoF compared to the previous works, allowing only for the same number of information symbols for all users.

Chinese Remainder Theorem-Based Sequence Design for Resource Block Assignment in Relay-Assisted Internet-of-Things Communications

Terminal relays are expected to play a key role in facilitating the communication between base stations and low-cost power-constrained cellular Internet of Things (IoT) devices. However, these mobile relays require a mechanism by which they can autonomously assign the available resource blocks (RBs) to their assisted IoT devices in the absence of channel state information (CSI) and with minimal assignment conflicts. To address this problem, in this paper, we develop an autonomous sequence-based RB assignment scheme that dispenses with CSI. The sequences underlying the proposed scheme are designed using the Chinese remainder theorem (CRT). In particular, the CRT is used to combine the cyclic sequences generated by simple cyclic group structures into longer ones. The combining process introduces additional degrees of freedom in sequence generation, thereby enriching the set of RB assignment sequences. Simulation results show that the sequences generated by the proposed CRT-based scheme outperform those generated by currently available autonomous ones.

Turbo Trellis-Coded Differential Chaotic Modulation

In this brief, a novel turbo trellis-coded differential chaotic modulation (TTC-DCM) system is proposed, where parallel concatenated trellis codes are combined with the M-ary differential chaotic shift keying (M-ary DCSK) scheme. An extrinsic information transfer chart is employed to analyze the convergence over additive white Gaussian noise channel and multipath Rayleigh channels. Simulation results show that the new scheme can obtain considerable coding gains without impairing the bandwidth efficiency in comparison with the M-ary DCSK scheme and the trellis-coded differential chaotic modulation scheme. Moreover, compared to the direct-sequence spread-spectrum turbo trellis-coded modulation scheme, TTCDCM has lower complexity and better robustness in the absence of channel state information over multipath Rayleigh channels. Overall, because of the merits of promising performance, high bandwidth efficiency, robustness to poor channel conditions, and an easy-to-implement property, the TTC-DCM scheme is suitable for bandlimited communication applications under poor channel conditions.

A Novel Self-Interference Cancellation Scheme for Channel-Unaware Differential Space-Time Two-Way Relay Networks

This paper considers channel-unaware two-way relay networks in which two single-antenna nodes exchange information via multiple non-regenerative relays, each with multiple antennas. A novel self-interference cancellation scheme for distributed differential space-time signalling is developed. Despite the absence of channel-state information, this scheme enables self-interference to be completely eliminated, thereby maximizing the signal-to-interference-plus-noise-ratio of the nodes. First, we obtain a lower bound on the pairwise error probability (PEP) under residual self-interference and we show that this bound approaches a non-zero constant at high signal-to-noise ratios (SNRs), indicating a zero diversity order and an asymptotic error floor. Second, we derive a necessary and sufficient condition for the proposed scheme to eliminate self-interference perfectly. Proper operation of this scheme requires the relays to have an even number of active antennas and for relays with odd number of active antennas, such a scheme does not exist. Third, we show that, when self-interference is cancelled perfectly, the error floor vanishes and an upper bound on the PEP approaches zero at high SNRs. In this case, it is shown that the diversity gain is equal to the number of relays and is independent of the number of antennas per relay. Finally, it is shown that the coding gain increases with increasing the number of antennas per relay and converges to a constant as the number of relay antennas becomes large.

On the Capacity of Wireless Powered Communication Systems Over Rician Fading Channels

In this paper, we consider a point-to-point multi-input multi-output wireless-powered communication system, where the source S is powered by a dedicated power beacon (PB) with multiple antennas. Employing the time splitting protocol, the energy constrained source S first harvests energy through the radio-frequency signals sent by the PB and then uses this energy to transmit information to the destination D. Unlike several prior works, we assume that the energy transfer link is subjected to Rician fading, which is a real fading environment, due to relatively short range power transfer distance and the existence of a strong line of sight path. We present a comprehensive analysis of the achievable ergodic capacity in two scenarios, depending on the availability of channel state information (CSI) at PB, namely, the absence of CSI and partial CSI . For the former case, equal power allocation is used, while for the later one, energy beamforming is used to enhance the energy transfer efficiency. For both the cases, closed-form expressions for the upper and lower bounds of the ergodic capacity are derived. Furthermore, the optimal time split is discussed, and the capacity in the low and high signal-to-noise ratio regimes is studied through simple closed-form expressions. Numerical results and simulations are provided to validate the theoretical analysis. The results show that the Rician factor $K$ has a significant impact on the ergodic capacity performance, and this impact strongly depends on the availability of the CSI at the PB.

Linear Degrees of Freedom for $K$ -user MISO Interference Channels With Blind Interference Alignment

In this paper, we characterize the degrees of freedom (DoF) for $K$ -user $M \times 1$ multiple-input single-output interference channels with reconfigurable antennas, which have $N$ -preset modes at the receivers, assuming linear coding strategies in the absence of channel state information at the transmitters, i.e., blind interference alignment. Our linear DoF converse builds on the lemma that if a set of transmit symbols is aligned at their common unintended receivers, those symbols must have independent signal subspace at their corresponding receivers. This lemma arises from the inherent feature that channel state’s changing patterns of the links towards the same receiver are always identical, assuming that the coherence time of the channel is long enough. We derive an upper bound for the linear sum DoF, and propose an achievable scheme that exactly achieves the linear sum DoF upper bound when both of the ${n^{*}}/{M}=R_{1}$ and ${MK}/{n^{*}}=R_{2}$ are integers, where $n^{*}$ denotes the optimal number of preset modes out of $N$ preset modes. For the other cases, where either $R_{1}$ or $R_{2}$ is not an integer, we only give some guidelines how the interfering signals are aligned at the receivers to achieve the upper bound. As an extension, we also show the linear sum DoF upper bound for downlink/uplink cellular networks.

Differential Space Time Frequency Codes for MIMO OFDM Systems

In general coherent detection, channel estimation requires huge number of symbols for transmission in Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra Wide Band (UWB) system, due to this bandwidth efficiency reduces. The proposed Differential Space-Time-Frequency Code (DSTFCs) for multiband-OFDM Ultra-WB communications is increases the efficiency of bandwidth. DSTFC system does not require Channel State Information (CSI). Due to this, the system bandwidth efficiency is possible to increase with DSTFCs. The proposed DSTFCs are derived both coding and decoding algorithms for 64 QAM (Quadrature Amplitude Modulation). The Simulation outcomes show that the use of DSTFCs can improve the coherent MB-OFDM (without STFC), differential MB-OFDM (without OFDM) bit error performance. The performance of DSTFCs almost reaches the STFCs performance even in the absence of channel state information.

A MIMO Relay With Delayed Feedback Can Improve DoF in $K$- User MISO Interference Channel With No CSIT

This paper studies the impact of a multiple-input-multiple-output (MIMO) relay on the K-user multiple-input-single-output (MISO) interference channel (IC) when the relay has delayed feedback (i.e., delayed channel state information (CSI) or delayed channel output feedback) from each receiver, yet each transmitter has no knowledge about CSI. We first develop a new relay-aided retrospective interference alignment (r-RIA) and characterize the optimal sum degrees of freedom (DoFs) for the K-user MISO IC with a MIMO relay by providing a new matching outer bound. It is shown that the sum DoF does not decrease, even in the absence of direct links between transmitters and receivers, as long as K is sufficiently large. We next show that a MIMO relay can provide a sum-DoF gain in the K-user MISO IC with delayed feedback to the relay in the absence of CSI at transmitter (CSIT), whereas relaying is shown to be not useful with instantaneous CSIT from the DoF perspective.

Distributed Bi-Directional Training of Nonlinear Precoders and Receivers in Cellular Networks

Joint optimization of nonlinear precoders and receive filters is studied for both the uplink and downlink in a cellular system. For the uplink, the base transceiver station (BTS) receiver implements successive interference cancellation, and for the downlink, the BTS station pre-compensates for the interference with Tomlinson-Harashima precoding (THP). Convergence of alternating optimization of receivers and transmitters in a single cell is established when filters are updated according to a minimum mean squared error (MMSE) criterion, subject to appropriate power constraints. Adaptive algorithms are then introduced for updating the precoders and receivers in the absence of channel state information, assuming time-division duplex transmissions with channel reciprocity. Instead of estimating the channels, the filters are directly estimated according to a least squares criterion via bi-directional training: Uplink pilots are used to update the feedforward and feedback filters, which are then used as interference pre-compensation filters for downlink training of the mobile receivers. Numerical results show that nonlinear filters can provide substantial gains relative to linear filters with limited forward-backward iterations.

A hybrid TIM-NOMA scheme for the Broadcast Channel

Future mobile communication networks will require enhanced network efficiency and reduced system overhead. Research on Blind Interference Alignment and Topological Interference Management (TIM) has shown that optimal Degrees of Freedom can be achieved, in the absence of Channel State Information at the transmitters. Moreover, the recently emerged Non-Orthogonal Multiple Access (NOMA) scheme suggests a different multiple access approach, compared to the orthogonal methods employed in 4G, resulting in high capacity gains. Our contribution is a hybrid TIM-NOMA scheme in K-user cells, where users are divided into T groups. By superimposing users in the power domain, we introduce a two-stage decoding process, managing inter-group interference based on the TIM principles, and intra-group interference based on Successful Interference Cancellation, as proposed by NOMA. We show that the hybrid scheme can improve the sum rate by at least 100% compared to Time Division Multiple Access, for high SNR values.