Maximum Multiflow in Wireless Network Coding

In a multihop wireless network, wireless interference is crucial to the maximum multiflow (MMF) problem, which studies the maximum throughput between multiple pairs of sources and sinks. In this paper, we observe that network coding could help to decrease the impacts of wireless interference, and propose a framework to study the MMF problem for multihop wireless networks with network coding. Firstly, a network model is set up to describe the new conflict relations modified by network coding. Then, we formulate a linear programming problem to compute the maximum throughput and show its superiority over one in networks without coding. Finally, the MMF problem in wireless network coding is shown to be NP-hard and a polynomial approximation algorithm is proposed.Comment: 5 pages, 3 figures, submitted to ISIT 201

A Novel Cooperative Strategy for Wireless Multihop Backhaul Networks

The 5G wireless network architecture will bring dense deployments of base stations called {\em small cells} for both outdoors and indoors traffic. The feasibility of their dense deployments depends on the existence of a high data-rate transport network that can provide high-data backhaul from an aggregation node where data traffic originates and terminates, to every such small cell. Due to the limited range of radio signals in the high frequency bands, multihop wireless connection may need to be established between each access node and an aggregation node. In this paper, we present a novel transmission scheme for wireless multihop backhaul for 5G networks. The scheme consists of 1) {\em group successive relaying} that established a relay schedule to efficiently exploit half-duplex relays and 2) an optimized quantize-map-and-forward (QMF) coding scheme that improves the performance of QMF and reduces the decoding complexity and the delay. We derive an achievable rate region of the proposed scheme and attain a closed-form expression in the asymptotic case for several network models of interests. It is shown that the proposed scheme provides a significant gain over multihop routing (based on decode-and-forward), which is a solution currently proposed for wireless multihop backhaul network. Furthermore, the performance gap increases as a network becomes denser. For the proposed scheme, we then develop energy-efficient routing that determines {\em groups} of participating relays for every hop. To reflect the metric used in the routing algorithm, we refer to it as {\em interference-harnessing} routing. By turning interference into a useful signal, each relay requires a lower transmission power to achieve a desired performance compared to other routing schemes. Finally, we present a low-complexity successive decoder, which makes it feasible to use the proposed scheme in practice.Comment: Parts of this paper will be presented at GLOBECOM 2015. arXiv admin note: text overlap with arXiv:1003.5966 by other author

Network Coding with Two-Way Relaying: Achievable Rate Regions and Diversity-Multiplexing Tradeoffs

This paper addresses the fundamental characteristics of information exchange via multihop network coding over two-way relaying in a wireless ad hoc network. The end-to-end rate regions achieved by time-division multihop (TDMH), MAC-layer network coding (MLNC) and PHY-layer network coding (PLNC) are first characterized. It is shown that MLNC does not always achieve better rates than TDMH, time sharing between TDMH and MLNC is able to achieve a larger rate region, and PLNC dominates the rate regions achieved by TDMH and MLNC. An opportunistic scheduling algorithm for MLNC and PLNC is then proposed to stabilize the two-way relaying system for Poisson arrivals whenever the rate pair is within the Shannon rate regions of MLNC and PLNC. To understand the two-way transmission limits of multihop network coding, the sum-rate optimization with or without certain traffic pattern and the end-to-end diversity-multiplexing tradeoffs (DMTs) of two-way transmission over multiple relay nodes are also analyzed.Comment: 27 pages, 7 figures, submitted to IEEE trans. on wireless communication

On the Performance of Optimized Dense Device-to-Device Wireless Networks

We consider a D2D wireless network where $n$ users are densely deployed in a squared planar region and communicate with each other without the help of a wired infrastructure. For this network, we examine the 3-phase hierarchical cooperation (HC) scheme and the 2-phase improved HC scheme based on the concept of {\em network multiple access}. Exploiting recent results on the optimality of treating interference as noise in Gaussian interference channels, we optimize the achievable average per-link rate and not just its scaling law. In addition, we provide further improvements on both the previously proposed hierarchical cooperation schemes by a more efficient use of TDMA and spatial reuse. Thanks to our explicit achievable rate expressions, we can compare HC scheme with multihop routing (MR), where the latter can be regarded as the current practice of D2D wireless networks. Our results show that the improved and optimized HC schemes yield very significant rate gains over MR in realistic conditions of channel propagation exponents, signal to noise ratio, and number of users. This sheds light on the long-standing question about the real advantage of HC scheme over MR beyond the well-known scaling laws analysis. In contrast, we also show that our rate optimization is non-trivial, since when HC is applied with off-the-shelf choice of the system parameters, no significant rate gain with respect to MR is achieved. We also show that for large pathloss exponent the sum rate is a nearly linear function of the number of users $n$ in the range of networks of practical size. This also sheds light on a long-standing dispute on the effective achievability of linear sum rate scaling with HC. Finally, we notice that the achievable sum rate for large $\alpha$ is much larger than for small $\alpha$. This suggests that HC scheme may be a very effective approach for networks operating at mm-waves.Comment: Revised and resubmitted to IEEE Transactions on Information Theor

Distributed Cross-layer Dynamic Route Selection in Wireless Multiuser Multihop Networks

In wireless ad-hoc networks, forwarding data through intermediate relays extends the coverage area and enhances the network throughput. We consider a general wireless multiuser multihop transmission, where each data flow is subject to a constraint on the end-to-end buffering delay and the associated packet drop rate as a quality of service (QoS) requirement. The objective is to maximize the weighted sum-rate between source destination pairs, while the corresponding QoS requirements are satisfied. We introduce two new distributed cross-layer dynamic route selection schemes in this setting that are designed involving physical, MAC, and network layers. In the proposed opportunistic cross-layer dynamic route selection scheme, routes are assigned dynamically based on the state of network nodes' buffers and the instantaneous state of fading channels. In the same setting, the proposed time division cross layer dynamic route selection scheme utilizes the average quality of channels instead for more efficient implementation. Detailed results and comparisons are provided, which demonstrate the superior performance of the proposed cross-layer dynamic route selection schemes.Comment: Submitted to IEEE Transaction on Wireless Comunication

Cooperative Relaying for Large Random Multihop Networks

In this paper, we propose a new relaying protocol for large multihop networks combining the concepts of cooperative diversity and opportunistic relaying. The cooperative relaying protocol is based on two diversity mechanisms, incremental redundancy combining and repetition combining. We assume that nodes in the large multihop network are modeled by a homogeneous Poisson Point Process and operate under Rayleigh fading and constant power transmission per node. The performance of the proposed relaying protocol is evaluated through the progress rate density (PRD) of the multihop network and compared to the conventional multihop relaying with no cooperation. We develop an analytic approximation to the PRD based on the concept of decoding cells. The protocol parameters are optimized to maximize the PRD of network. We show that the cooperative relaying protocol provides significant throughput improvements over conventional relaying with no cooperation in a large multihop network. It is also shown that incremental redundancy combining provides a higher gain in PRD relative to repetition combining. The gain in PRD has near constant value at all values of the path loss exponent and is monotonic in diversity order.Comment: 30 pages, 5 figures, IEEE SPAWC 2013 and IEEE WCNC 2016 submitte

Performance Evaluation of Flow Allocation with Successive Interference Cancelation for Random Access WMNs

In this study we explore the performance gain that can be achieved at the network level by employing successive interference cancelation (SIC) instead of treating interference as noise for random access wireless mesh networks with multi-packet reception capabilities. More precisely we explore both the throughput and the delay of a distributed flow allocation scheme aimed at maximizing average aggregate flow throughput while also providing bounded delay combined with SIC. Simulation results derived from three simple topologies show that the gain over treating interference as noise for this scheme can be up to $15\%$ for an SINR threshold value equal to $0.5$. For SINR threshold values as high as $2.0$ however, this gain is either insignificant or treating interference as noise proves a better practice. The reason is that although SIC improves the throughput on a specific link, it also increases the interference imposed on neighboring receivers. We also show that the gain of applying SIC is more profound in cases of a large degree of asymmetry among interfering links.Comment: arXiv admin note: text overlap with arXiv:1406.630

Dynamic Radio Resource Management for Random Network Coding: Power Control and CSMA Backoff Control

Resource allocation in wireless networks typically occurs at PHY/MAC layers, while random network coding (RNC) is a network layer strategy. An interesting question is how resource allocation mechanisms can be tuned to improve RNC performance. By means of a differential equation framework which models RNC throughput in terms of lower layer parameters, we propose a gradient based approach that can dynamically allocate MAC and PHY layer resources with the goal of maximizing the minimum network coding throughput among all the destination nodes in a RNC multicast. We exemplify this general approach with two resource allocation problems: (i) power control to improve network coding throughput, and (ii) CSMA mean backoff delay control to improve network coding throughput. We design both centralized algorithms and online algorithms for power control and CSMA backoff control. Our evaluations, including numerically solving the differential equations in the centralized algorithm and an event-driven simulation for the online algorithm, show that such gradient based dynamic resource allocation yields significant throughput improvement of the destination nodes in RNC. Further, our numerical results reveal that network coding aware power control can regain the broadcast advantage of wireless transmissions to improve the throughput.Comment: 28 pages, 9 figures. Submitted to IEEE Transactions on Wireless Communication

Diversity-Multiplexing Tradeoff of Network Coding with Bidirectional Random Relaying

This paper develops a diversity-multiplexing tradeoff (DMT) over a bidirectional random relay set in a wireless network where the distribution of all nodes is a stationary Poisson point process. This is a nontrivial extension of the DMT because it requires consideration of the cooperation (or lack thereof) of relay nodes, the traffic pattern and the time allocation between the forward and reverse traffic directions. We then use this tradeoff to compare the DMTs of traditional time-division multihop (TDMH) and network coding (NC). Our main results are the derivations of the DMT for both TDMH and NC. This shows, surprisingly, that if relay nodes collaborate NC does not always have a better DMT than TDMH since it is difficult to simultaneously achieve bidirectional transmit diversity for both source nodes. In fact, for certain traffic patterns NC can have a worse DMT due to suboptimal time allocation between the forward and reverse transmission directions.Comment: 7 pages, 4 figures, to appear in the Proceedings of Allerton Conference on Communication, Control and Computing, September 200

FiWi Access Networks Based on Next-Generation PON and Gigabit-Class WLAN Technologies: A Capacity and Delay Analysis (Extended Version)

Current Gigabit-class passive optical networks (PONs) evolve into next-generation PONs, whereby high-speed 10+ Gb/s time division multiplexing (TDM) and long-reach wavelength-broadcasting/routing wavelength division multiplexing (WDM) PONs are promising near-term candidates. On the other hand, next-generation wireless local area networks (WLANs) based on frame aggregation techniques will leverage physical layer enhancements, giving rise to Gigabit-class very high throughput (VHT) WLANs. In this paper, we develop an analytical framework for evaluating the capacity and delay performance of a wide range of routing algorithms in converged fiber-wireless (FiWi) broadband access networks based on different next-generation PONs and a Gigabit-class multi-radio multi-channel WLAN-mesh front-end. Our framework is very flexible and incorporates arbitrary frame size distributions, traffic matrices, optical/wireless propagation delays, data rates, and fiber faults. We verify the accuracy of our probabilistic analysis by means of simulation for the wireless and wireless-optical-wireless operation modes of various FiWi network architectures under peer-to-peer, upstream, uniform, and nonuniform traffic scenarios. The results indicate that our proposed optimized FiWi routing algorithm (OFRA) outperforms minimum (wireless) hop and delay routing in terms of throughput for balanced and unbalanced traffic loads, at the expense of a slightly increased mean delay at small to medium traffic loads.Comment: Technical Report, School of Electrical, Computer, and Energy Eng. Arizona State University, Temp