Finite Blocklength Research Articles

Multi-Device Low-Latency IoT Networks With Blind Retransmissions in the Finite Blocklength Regime

In future wireless communications, the Internet of Things (IoT) is a promising paradigm which is expected to connect massive number of devices while satisfying ultra-reliable and low latency communications (URLLC). In this article, we consider a multi-device IoT network supporting URLLC, where the data transmission process from the devices perform blind Automatic Repeat-reQuest (ARQ) or Hybrid ARQ (HARQ) via shared radio resources. We leverage recent advances in the characterization of coding rates and error probability in the finite blocklength regime to investigate the reliability and goodput performances of such network with both ARQ and HARQ schemes. Furthermore, both reliability-oriented and goodput-oriented designs are proposed for ARQ and HARQ schemes, respectively. In particular, we provide the optimal solutions for the error probability minimization problem, while efficient sub-optimal solutions for the goodput maximization problem are introduced, which show a tight performance in comparison to exhaustive search. Via simulation, the analytical results are validated and the system performance for both schemes are evaluated under variant setups with respect to total resources, packet sizes and SNR.

Decode-and-Forward Short-Packet Relaying in the Internet of Things: Timely Status Updates

In this paper, a decode-and-forward (DF) short-packet relaying model is developed to achieve timely status updates for intelligent monitoring within the Internet of Things (IoT), where the status updates generated at an IoT device are delivered to a remote server with the aid of a relay in both half-duplex (HD) and full-duplex (FD) modes. To characterise the data freshness of status updates, we exploit the age of information (AoI) as a metric, which is defined as the time elapsed since the generation of the latest successfully decoded status update. The average AoI is formulated and minimised for both HD-DF and FD-DF relaying IoT networks in finite blocklength regime. For the HD-DF relaying, we introduce a perfect approximation of the average AoI to solve the problem of average AoI minimisation with the optimal blocklengths in two phases. For the FD-DF relaying, we propose an iterative algorithm to solve the problem of average AoI minimisation by optimising the relay’s transmit power and the blocklength. Illustrative numerical results not only substantiate the validity of our proposed algorithms, but also provide useful references for the IoT monitoring network design, specifically for the transmit power thresholds at the IoT device and the relay.

Three-Dimensional Placement and Transmit Power Design for UAV Covert Communications

This work tackles the joint optimization of a unmanned aerial vehicle's (UAV's) three-dimensional (3D) placement and transmit power for covert communications with the objective to maximize the communication covertness subject to a constraint on communication quality. We analytically prove that the optimal horizontal location of the UAV must be on the straight line connecting the legitimate receiver and the warden, while its optimal height is the minimum allowable flying altitude. Subsequently, we derive closed-form expressions to characterize the UAV's optimal 3D location and its optimal transmit power, taking into account the impact of finite blocklength coding. Our numerical results show that the developed optimal design can achieve a better covertness performance compared with an optimal two-dimensional (2D) UAV deployment, especially when the warden is close to the receiver. Besides, we show that, for a given requirement on the communication quality, communication covertness does not always improve as the number of channel uses increases.

Opportunistic Bits in Short-Packet Communications: A Finite Blocklength Perspective

In this paper, the concept of opportunistic bits (OBs) is developed in short-packet communications and investigated from a finite blocklength perspective. In the OB-based transmission, the data unit of a packet is divided into two parts: OBs and conventional bits (CBs). The OBs are not physically transmitted but used to indicate the index of the time slot (TS) when the packet containing CBs is transmitted. The loading of a bulk of OB-based packets into multiple TSs can be modelled as a Repeated Balls-into-Bins process with a multi-queue storage. If the bulk is not large enough, certain combination(s) of OBs will not appear, which leaves certain TS(s) empty and hence reduces the TS load efficiency. To evaluate the OB-based transmission performance, we formulate its maximal payload rate and TS load efficiency. With the aid of these two formulations, the energy gain, the goodput, and the latency of OB-based short-packet communications are derived and obtained in analytical forms. For achieving further insights, illustrative numerical results on the resource utilisation efficiency and the performance not only substantiate the advantages of the OB-based transmission over the conventional but also provide useful tools and specifications for its design in massive short-packet communications.

Joint computation and power allocation for NOMA enabled MEC networks in the finite blocklength regime

This paper investigates the reliable computation offloading in non-orthogonal multiple access enabled mobile edge computing networks, where the short-packet technique is adopted to meet the stringent latency requirements of delay-sensitive computing services. To characterize the reliability of computation offloading with finite blocklength coding, a novel analytical framework is developed to approximate the average overall block error probability (AOBEP) by using a double-case linearization. With the derived approximate expression for AOBEP, the joint optimization of computation workload and transmit power is further investigated, in order to minimize the AOBEP under the computation/communication delay constraints. To tackle the non-convexity of the formulated problem, the formulated problem is first decomposed into the computation workload problem and the transmit power allocation problem. For the computing workload problem, a closed-form solution is derived. Then, by applying the derived workload allocation, the power allocation is transformed into the convex form through some approximations and solved by the successive convex approximation technique. Finally, simulation results are provided to demonstrate the reliability enhancement of computation offloading and reveal the relationship between the workload/power allocation and the communication/computation delay.

Information Age-Delay Correlation and Optimization With Finite Block Length

Both information age and delay are critical performance metrics of emerging time-sensitive applications. However, their inherent correlation in the finite block length (FBL) regime has remained uninvestigated as it is affected by block length and update rate in a complex manner. In this paper, closed-form expressions for average age of information (AoI), peak AoI (PAoI) and delay are derived for an FBL Last-Come First-Served system with retransmission and non-preemption policies, based on which a comprehensive analysis of the relationship among the three metrics in the FBL regime is presented. It is proved that there exists a strong tradeoff between delay and AoI/PAoI given a block length, and that AoI, PAoI and delay have positive correlation given an update rate, regardless of the weight. With the goal of minimizing delay and AoI simultaneously, the weighted sum of delay and PAoI (upper bound on AoI) is formulated and proved to be convex with respect to block length and update rate. A low-complexity optimization algorithm is developed with a closed-form expression of the optimal update rate, whose performance approaches the Pareto boundaries of the PAoI-delay and the AoI-delay regions, at much lower complexity than exhaustive search.

Cognitive D2D Finite Blocklength Transmissions With the Presence of Time-Selective Interference

In this paper, we study an underlay device-to-device (D2D) communication system where the secondary D2D transmitter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$D_{Tx}$</tex-math></inline-formula> ) communicates with D2D receiver ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$D_{Rx}$</tex-math></inline-formula> ) under ultra-reliable low-latency communication (URLLC) constraints. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$D_{Tx}$</tex-math></inline-formula> attempts to send the mission-critical information to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$D_{Rx}$</tex-math></inline-formula> with fixed and proportional power constraints in order to prevent interference at the mobile primary cellular user (CU). We demonstrate the performance of the considered D2D URLLC system in terms of the block error rate and system goodput in the finite blocklength regime. Our analysis reveals the key insights related to the impact of mobility of primary CU, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$D_{Tx}$</tex-math></inline-formula> transmission power, blocklength, and packet size on the reliability and throughput performance of the cognitive network. The theoretical results are validated using Monte-Carlo simulations.

AoI-Driven Statistical Delay and Error-Rate Bounded QoS Provisioning for mURLLC Over UAV-Multimedia 6G Mobile Networks Using FBC

Massive ultra-reliable and low latency communications (mURLLC) has emerged as new and dominating 6G-standard services to support statistical quality-of-services (QoS) provisioning for delay-sensitive data transmissions. To measure the freshness of updated information, age of information (AoI) has recently formed as the new dimension of QoS metric. Since status updates usually consist of a small number of information bits but warrant ultra-low latency, integrating AoI with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">finite blocklength coding</i> (FBC) creates an alternative promising solution for mURLLC. On the other hand, to solve the massive connectivity issues imposed by mURLLC, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">unmanned aerial vehicle</i> (UAV) has been developed to significantly enhance the line-of-sight (LOS) coverage while guaranteeing various QoS requirements. However, how to efficiently integrate the above new techniques for statistical delay and error-rate bounded QoS provisioning in UAV systems has been neither well understood nor thoroughly studied. To overcome these challenges, we propose FBC based statistical delay and error-rate bounded QoS provisioning schemes which leverage AoI as a key QoS provisioning technique for mURLLC over UAV mobile networks. First, we develop FBC based UAV system models. Second, we build up AoI-metric based modeling frameworks to upper-bound peak AoI violation probability using FBC. Third, we formulate and solve FBC based peak AoI violation probability minimization problem. Forth, we jointly optimize peak AoI violation probability and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\epsilon $ </tex-math></inline-formula> -effective capacity and characterize their tradeoffs. Finally, our simulations validate and evaluate our developed schemes.

UAV-Relayed Covert Communication Towards a Flying Warden

Owing to the ever increasing of information privacy requirement, covert communication has gained more and more attention, whose effective range is limited by the trade-off between the covertness and the transmit power. Benefiting from the high mobility and easy deployment, unmanned aerial vehicles (UAVs) can be utilized to expand the range of covert networks. Thus, we propose a UAV-relayed covert communication scheme with finite blocklength to maximize the effective transmission bits from the transmitter to the legitimate receiver against a flying warden. The transmitter adopts the maximum ratio transmission and the relay performs Gaussian signalling transmission to cause uncertainty at the warden. First, the optimal detection thresholds are derived at the warden towards the transmitter and the relay, respectively. Then, the hovering location of the warden is optimized to maximize the summation of relative entropies from the transmitter and the relay, which can greatly threaten the covertness. With this worst covert situation, the blocklength and transmit power at the transmitter and the relay are jointly optimized under the constraint of the end-to-end error detection probability to maximize the effective transmission rate from the transmitter to the legitimate receiver. Numerical results are provided to demonstrate the effectiveness of the proposed UAV-relayed covert communication scheme.

Average Rate and Error Probability Analysis in Short Packet Communications Over RIS-Aided URLLC Systems

In this paper, the average achievable rate and error probability of a reconfigurable intelligent surface (RIS) aided systems is investigated for the finite blocklength (FBL) regime. The performance loss due to the presence of phase errors arising from limited quantization levels as well as hardware impairments at the RIS elements is also discussed. First, the composite channel containing the direct path plus the product of reflected channels through the RIS is characterized. Then, the distribution of the received signal-to-noise ratio (SNR) is matched to a Gamma random variable whose parameters depend on the total number of RIS elements, phase errors and the channels' path loss. Next, by considering the FBL regime, the achievable rate expression and error probability are identified and the corresponding average rate and average error probability are elaborated based on the proposed SNR distribution. Furthermore, the impact of the presence of phase error due to either limited quantization levels or hardware impairments on the average rate and error probability is discussed. The numerical results show that Monte Carlo simulations conform to matched Gamma distribution to received SNR for sufficiently large number of RIS elements. In addition, the system reliability indicated by the tightness of the SNR distribution increases when RIS is leveraged particularly when only the reflected channel exists. This highlights the advantages of RIS-aided communications for ultra-reliable and low-latency systems. The difference between Shannon capacity and achievable rate in FBL regime is also discussed. Additionally, the required number of RIS elements to achieve a desired error probability in the FBL regime will be significantly reduced when the phase shifts are performed without error.

Achieving Extremely Low-Latency in Industrial Internet of Things: Joint Finite Blocklength Coding, Resource Block Matching, and Performance Analysis

To enable a number of emerging applications, efforts from industry and academia have started to focus on defining 6G systems, in which more stringent requirements than those imposed on 5G systems are being considered. In particular, some 6G applications may require extremely low-latency on the order of 0.1ms, through which practical designs of channel coding can be investigated based on Finite-Blocklength Coding (FBC). In this paper, we focus on a joint FBC scheme over multi-user downlinks in the Industrial Internet of Things (IIoT), in which only several symbol durations are available for users within a requirement of extremely low-latency. Since a higher coding rate is obtained by enlarging the blocklength of FBC, we jointly encode users’ data bits over their allocated resources, through which an enlarged blocklength is attained. Specifically, we first formulate the multi-user joint encoding design with a matrix-based method. Then, we present the optimal power-constrained throughput within the extremely low-latency requirement by formulating a nonlinear bipartite matching problem. We finally demonstrate the benefit resulting from the joint FBC in terms of each user’s maximum obtainable distance. With the distance to each user varying, we also perform an analysis of the variation of the optimal power-constrained throughput.

NOMA-based UAV system under finite blocklength regime with analysis in Rician fading channel

The finite blocklength (FBL) communication has been studied for quite some time for the fifth generation of cellular networks (5G). Though, the research in FBL is still in early stage due to the fact that 5G requires high reliability of almost 99.9999% with latency of less than 1 ms, simultaneously. The FBL has been worked upon to reduce latency such that Shannon's capacity expression is no longer applicable. The 5G claims to provide connectivity everywhere, hence to increase the coverage to remote places Unmanned Ariel Vehicle (UAV) has gained attention due to its low cost, mobility, and air time. In this paper, a scenario where a UAV relays data from a base station (BS) to remote users (RU), which are otherwise not in direct contact, is analyzed. All the communications among BS, UAV, and RU's are considered to be non-orthogonal multiple access (NOMA) based with Finite blocklength (FBL). An exact closed form expression for end-to-end average block error rate (BLER) is derived for above mentioned scenario and verified by extensive simulations. In addition, an asymptotic BLER for remote users at high transmission Signal to noise ratio is also derived. Further, the BLER is minimized to jointly optimize the power allocation coefficients, position of UAV and Blocklength for the communication system. The effects of different parameters on average BLER, position, and power are studied and the coverage provided by UAV for given probability of error is presented.

Improved Atomic Norm Based Time-Varying Multipath Channel Estimation

In this paper, improved channel gain delay estimation strategies are investigated when practical pulse shapes with finite block length and transmission bandwidth are employed. Pilot-aided channel estimation with an augmented atomic norm based approach is proposed to promote the low rank structure of the time-varying narrowband leaked channel. All the channel parameters, i.e., delays, Doppler shifts, and channel gains are recovered. Design choices which ensure unique estimates of channel parameters for rectangular, Gaussian, and root-raised-cosine pulse shapes are examined in the noiseless case, respectively. Furthermore, a perturbation analysis is conducted to measure the impact of noise and further design choices for parameters are proposed to mitigate the effects of noise. Finally, numerical results verify the theoretical analysis and show performance improvements over the previously proposed method.

Finite Blocklength Covert Communications With Random Selection of Channel Use

This letter investigates the finite blocklength covert communications where transmitter Alice randomly chooses channel use according to probability <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> in the transmission block. To minimize the decoding error probability of a receiver Bob subject to the covert constraint on a detector Willie, we consider a new scheme that is changing the selection probability <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> . A proof is given for the first time that although Alice randomly chooses channel use for transmission, the received signal of each channel use at Willie in the transmission block satisfies the condition of independent and identical distribution (i.i.d). Subsequently, we examine the effect of channel use selection probability <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> on decoding error probability of Bob. By adjusting <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> , the decoding error probability can be decreased without changing the covert constraints.

Covert communication with beamforming over MISO channels in the finite blocklength regime

Covert communication with beamforming over MISO channels in the finite blocklength regime

Performance Analysis of Fountain Coded Non-Orthogonal Multiple Access With Finite Blocklength

Driven by the increasing demand for high reliability and low latency, finite blocklength communications have recently become the focus of the communication research field. In this letter, to achieve high reliability and low latency communication, we propose the cross-layer design of fountain coded two-user non-orthogonal multiple access (NOMA) system with finite blocklength. Specifically, the message for each user is firstly encoded by an application-layer fountain code at the base station (BS). Then, each fountain-coded packet for each user is encoded by a physical-layer channel code into a frame. Finally, the BS sends the frames to these two users by using superposition modulation. Under the reliability constraints of two users, the relationship among the application-layer code rate, the physical-layer data rate, and the optimal power allocation coefficient is derived to minimize the transmission latency. The numerical analysis and simulation results show that the message transmission latency of the proposed cross-layer scheme is much lower than that of the scheme which only adopts physical-layer channel codes in the finite blocklength NOMA system.

Statistical Delay and Error-Rate Bounded QoS Provisioning for SWIPT Over CF M-MIMO 6G Mobile Wireless Networks Using FBC

As a new and dominating type of time-sensitive traffic over 6G wireless networks, massive ultra-reliable and low latency communications (mURLLC) has attracted considerable research attention, while raising several new challenges, including massive connectivity, ultra-low latency, super-reliability, and high energy efficiency. Several promising 6G enablers, including statistical delay and error-rate bounded quality-of-service (QoS) provisioning, cell-free (CF) massive multi-input multi-output (m-MIMO), simultaneous wireless information and power transfer (SWIPT), etc., have been developed to support mURLLC. Specifically, CF m-MIMO can significantly enhance QoS performance of SWIPT by boosting data rate and energy efficiency. On the other hand, finite blocklength coding (FBC) has been proposed to support various massive access techniques while reducing access latency and guaranteeing stringent QoS. However, how to efficiently integrate SWIPT with CF m-MIMO using FBC for statistical delay and error-rate bounded QoS to support mURLLC has posed many new challenges not encountered before. To overcome these difficulties, in this paper we develop FBC based statistical delay and error-rate bounded QoS provisioning schemes over SWIPT-enabled CF m-MIMO 6G wireless networks. First, we establish SWIPT-enabled CF m-MIMO system models using FBC. Then, we optimize the tradeoffs between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\epsilon$</tex-math></inline-formula> -effective capacity and harvested energy for our proposed statistical QoS provisioning. Finally, our simulated results validate and evaluate our developed schemes.

Delay-Sensitive NOMA-HARQ for Short Packet Communications.

This paper investigates the two-user uplink non-orthogonal multiple access (NOMA) paired with the hybrid automatic repeat request (HARQ) in the finite blocklength regime, where the target latency of each user is the priority. To limit the packet delivery delay and avoid packet queuing of the users, we propose a novel NOMA-HARQ approach where the retransmission of each packet is served non-orthogonally with the new packet in the same time slot. We use a Markov model (MM) to analyze the dynamics of the uplink NOMA-HARQ with one retransmission and characterize the packet error rate (PER), throughput, and latency performance of each user. We also present numerical optimizations to find the optimal power ratios of each user. Numerical results show that the proposed scheme significantly outperforms the standard NOMA-HARQ in terms of packet delivery delay at the target PER.

NOMA for Next-Generation Massive IoT: Performance Potential and Technology Directions

Broader applications of the Internet of Things (loT) are expected in the forthcoming 6G system, although massive loT is already a key scenario in 5G, predominantly relying on physical layer solutions inherited from 4G LTE and primarily using orthogonal multiple access (OMA). In 6G loT, supporting a massive number of connections will be required for diverse services of the vertical sectors, prompting fundamental studies on how to improve the spectral efficiency of the system. One of the key enabling technologies is non-or-thogonal multiple access (NOMA). This article consists of two parts. In the first part, finite block length theory and the diversity order of multi-user systems are used to show the significant potential of NOMA compared to traditional OMA. The supremacy of NOMA over OMA is particularly pronounced for asynchronous contention-based systems relying on imperfect link adaptation, which are commonly assumed for massive loT systems. To approach these performance bounds, in the second part of the article, several promising technology directions are proposed for 6G massive loT, including linear spreading, joint spreading and modulation, multi-user channel coding in the context of various techniques for practical uncoordinated transmissions, cell-free operations, and so on, from the perspective of NOMA.

A New Achievable Rate-Distortion Region for Distributed Source Coding

In this work, lossy distributed compression of a pair of correlated sources is considered. Conventionally, Shannon’s random coding arguments — using randomly generated unstructured codebooks whose blocklength is taken to be asymptotically large — are used to derive achievability results. However, in some multi-terminal communications scenarios, using random codes with constant finite blocklength in certain coding architectures leads to improved achievable regions compared to the conventional approach. In other words, in some network communication scenarios, there is a finite optimal value in the blocklength of the randomly generated code used for distributed processing of information sources. Motivated by this, a coding scheme is proposed which consists of two codebook layers: i) the primary codebook which has constant finite blocklength, and ii) the secondary codebook whose blocklength is taken to be asymptotically large. The achievable performance is analyzed in two steps. In the first step, a characterization of an inner bound to the achievable region is derived in terms information measures which are functions of multi-letter probability distributions. In the next step, a computable single-letter inner-bound to the achievable region is extracted. It is shown through an example that the resulting rate-distortion region is strictly larger than the Berger-Tung achievable region.