Physical-Layer Network Coding: An Efficient Technique for Wireless Communications

Analysis and scheduling of practical network coding in OFDMA relay networks

Fuzzy logic based cross-layer design to improve Quality of Service in Mobile ad-hoc networks for Next-gen Cyber Physical System

Consider a time slotted multiuser random access network where M users have access to a single channel and each user attempts to send packets in a particular time slot with a certain probability, according to a predetermined access scheme. This forms an interacting system of queues and in this study, the authors consider generic access schemes that satisfy a separability condition and obtain bounds for the stability region, directly using a Lyapunov-type analysis. They apply their results to the case of random access networks with partial conflicts where any particular user has collision conflicts with only a subset of the other users. Using conflict graphs to quantify the degree of such conflicts, they obtain bounds for the stability region for both deterministic and random conflict graphs that model, respectively, static and mobile networks.

This paper concerns the cross-layer design between physical layer and MAC (multiple access control) layer in asynchronous wireless random access network. The proposed cross-layer design consists of two parts: a MPR (Multiple Packet Reception) physical layer and a collision- aware MAC layer. In the physical layer design, different spreading codes are assigned to packets according to their frame types at the transmitter, and at the receiver, an enhanced synchronization method and MUD (Multi-user Detection) are utilized to synchronize the collided packets and recover packets. In order to reduce the computational complexity of the receiver, interference cancellation is performed at the receiver by utilizing the known preamble and the partially known frame header information. In the MAC layer design, collisions are divided into different types according to frame types and packet arrival time, and different operations are developed for different collision types to tactically access the channel. Simulation results show that the proposed cross-layer design can significantly improve the network throughput and reduce the transmission delay.

In this work, we study the finite-user stability region of a slotted ALOHA random access network with cooperative users. The network consists of multiple cooperating pairs where the users in each pair is allowed to cooperate by relaying each others' messages to the access point (AP). Spatial diversity gains are achieved since the packet of a cooperative user can be transmitted through independent fading channels, eg. the direct transmission path and the cooperative relaying path. Most works in the literature on cooperative communications focus on the physical layer aspects such as coding, modulation, transceiver signal processing etc. In this paper, we study the advantages of user cooperation from a MAC layer perspective and devise queueing strategies to exploit the cooperative diversity gains in a random access network. Extending upon our previous results for the two-user case, we study the stability of the finite-user cooperative system that consists of multiple cooperating pairs. By treating each cooperative pair as a transmission entity, we derive inner bounds for the finite-user stability region and propose a ranking system to characterize the transmission entities' relative tendency of being stable (or unstable).

The combination of orthogonal frequency division multiplexing (OFDM) and interleave division multiple access (IDMA), known as OFDM-IDMA, has been proposed as a promising multiple access scheme for wireless communications due to its low decoding complexity and potential of achieving high spectral efficiency. However, most of the work on OFDM-IDMA is in radio frequency (RF) communications scenarios and based on computer simulations. In this paper, we propose OFDM-IDMA over underwater acoustic (UWA) channels with experimental results. We also extend the original OFDM-IDMA to a multiple hydrophones scenario to improve the bit error rate (BER) performance. Experimental results show that with multiple hydrophones, the coded BER performance of OFDM-IDMA approaches zero after only a few iterations, validating the feasibility of our proposed approach over UWA channels.

Wiretap channel has caught a lot of attention recently in secured communications. A commonly adopted wiretap model is that the main channel is noiseless and the eavesdroppers channel is binary erasure channel (BEC). LDPC codes have been applied to achieve strong secrecy. However, it lacks design flexibility balancing on security and reliability, and cannot illustrate the fundamental tradeoffs among erasure rate, secrecy rate, and the security performance. In this paper, we propose a random complex field code (RCFC) design for such wiretap channels. The design of RCFCs is systematic and flexible for any secrecy rate. By using the proposed code design, the desired receiver can decode the confidential information without any error (in the absence of noise). Simultaneously, when the secrecy rate is below or equal to the secrecy capacity, we prove that the mutual information between the confidential message and the decoded message given by the eavesdropper converges to zero with the codeword length goes to infinity. Additionally, our RCFC design is the first one which provides a platform to tradeoff secrecy rate with the security performance.

Concurrent genetic optimization for joint design of source and channel codes

A Cross Layered framework is an important concept in today’s world given the abundant usage of both single-path and multi path wireless network architectures. One of the important design issues in the development of a robust framework such as this is the design of an Optimization Agent or an OA. In recent days of wireless and wired ad-hoc networks, cross-layer design was brought about a few years back to explore attached optimization at different layers. In order to describe solutions in cross-layered design, the Open System Intercommunications model was employed. However, it is clear that no voice and reference mechanism exists to aid optimization, which could effectively halt effective adaptability and deployment of cross-layered solutions. In this study, we suggest some hypotheses regarding how to model and create cross-layer solutions using the OSI layered method. We use the aforementioned method to analyse and simulate a particular type of cross-layered solution, namely energy-aware routing protocols. We use a layered approach to examine two proposals that are accessible in the literature. The applied strategy leads to the creation of an energy- aware, one-of-a-kind solution that outperforms prior versions and provides interesting and clear insights into the function that each layer plays in the overall optimization process. The network throughput, utilization, and reliability have all increased practically rapidly in the last few years. With the emergence of broadband wireless and wired cellular networks, as well as mobile adhoc networks (MANETs) and improved computational capacity, a new generation of apps, especially real-time multimedia applications, has emerged. Delivering real-time multimedia traffic across a sophisticated network like the Internet could be a particularly difficult undertaking, as these applications have stringent bandwidth and other quality-of-service (QoS) requirements.

This paper analyzes the impact of error propagation on the achievable throughput and throughput-delay tradeoff in wireless networks. It addresses the particular class of multihop routing schemes for parallel unicast that achieve a throughput scaling of Θ(n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/2</sup> ) per node in a network of n nodes. It is shown that in the finite-block-length case, necessitated by finite decoding memory at the nodes, the guaranteed per-node throughput in the network cannot scale better than o (n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-r</sup> ) per node for any r > 0. This bound on the guaranteed per-node throughput is tighter than the O (1/n) bound shown previously. Instead of focusing on the probability of error for each link, which is intractable, an approach of bounding mutual information is employed to show tight results on the achievable throughput and throughput-delay tradeoffs. It is shown that for multihop transmission protocols, error propagation leads to significant changes in the tradeoff between the throughput T(n) and the delay D(n), compared to previous results. The best known scaling behavior is only D(n) = Θ (n (log n) T(n)) under maximum throughput scaling, where the block length required scales as Ω (log n). When decoding memory at nodes is constrained to be O (log log n), the achievable tradeoff worsens to D(n) = Θ (n (log n) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> T(n)).

The inherent nature of the physical setup and transmission mechanism in wireless ad hoc networks with random channel access, results in correlation between the link metrics of adjacent links, when considering path optimization problems. We identify a special structure inherent to the solution of Dynamic Programming (DP) problem arising in such an optimization over paths. According to this structure, the optimal policy tries to equalize the link metrics of adjacent links in a multi-hop route. We validate this structural property with simulations.

We consider a random access network in which the nodes need to optimize their channel access rates. The nodes are assumed to be rational and interested in their performance seen as a transmitter as well as a receiver. By casting this problem as a non-cooperative game, we derive conditions for the Nash equilibrium. We also show the existence of a Nash equilibrium when the nodes are constrained by their battery power (for this case, the constraints on the access rates of the nodes become coupled). For the special case where all nodes are each other's neighbors, we find that the equilibrium is given by the solution of a system of linear equations. An adaptive distributed scheme is then proposed for learning this equilibrium and its convergence is studied numerically.

In cooperative systems, users achieve spatial diversity and multihop gains by transmitting packets over multiple independent fading paths provided by their partners. Most previous works on cooperative communications focus on the physical layer aspects such as coding, modulation, and transceiver signal processing techniques. In this work, we study the advantages of user cooperation from a MAC layer perspective and devise queueing strategies to exploit cooperative gains in random access networks. Based on the conventional slotted ALOHA protocol, we propose a simple cooperative transmission mechanism for a two-user cooperative pair. We derive the two-user stability region of the proposed system and show the improvements compared to noncooperative systems. The benefits can be attributed to both physical layer cooperation, where users with good channels may relay for those with bad channels, and MAC layer cooperation, where system parameters can be chosen to enhance cooperation and reduce competition. Then, we extend the proposed strategy to a finite-user system that consists of multiple cooperative pairs. By treating each pair as a single transmission entity, we derive inner bounds for the finite-user stability region and propose a ranking system to characterize the transmission entities' relative tendency of being stable (or unstable).

Cooperative Communications in Random Access Networks

We study the age of information (AoI) in a random access network consisting of multiple source-destination pairs, where each source node is empowered by energy harvesting capability. Every source node transmits a sequence of data packets to its destination using only the harvested energy. Each data packet is encoded with finite-length codewords, characterizing the nature of short codeword transmissions in random access networks. By combining tools from bulk-service Markov chains with stochastic geometry, we derive an analytical expression for the network average AoI and obtain closed-form results in two special cases, i.e., the small and large energy buffer size scenarios. Our analysis reveals the trade-off between energy accumulation time and transmission success probability. We then optimize the network average AoI by jointly adjusting the update rate and the blocklength of the data packet. Our findings indicate that the optimal update rate should be set to one in the energy-constrained regime where the energy consumption rate exceeds the energy arrival rate. This also means if the optimal blocklength of the data packet is pre-configured, an energy buffer size supporting only one transmission is sufficient.