The concepts of network function virtualization and end-to-end network slicing are the two promising technologies empowering 5G networks for efficient and dynamic network/service deployment and management. In this paper, we propose a resource allocation model for 5G virtualized networks in a heterogeneous cloud infrastructure. In our model, each network slice has a resource demand vector for each of its virtual network functions. We first consider a system of collaborative slices and formulate the resource allocation as a convex optimization problem, maximizing the overall system utility function. We further introduce a distributed solution for the resource allocation problem by forming a resource auction between the slices and the data centers. By using an example, we show how the selfish behavior of non-collaborative slices affects the fairness performance of the system. For a system with non-collaborative slices, we formulate a new resource allocation problem based on the notion of dominant resource fairness and propose a fully distributed scheme for solving the problem. Simulation results are provided to show the validity of the results, evaluate the convergence of the distributed solutions, show protection of collaborative slices against non-collaborative slices and compare the performance of the optimal schemes with the heuristic ones.

Packet switched transport technologies have been suggested to be used in 5G front-haul networks. Front-haul bandwidth and packet latency are two major challenges to be addressed in these networks. This paper focuses on capacity planning for packet-based front-haul technologies considering the latency requirements of the 5G front-haul flows. More specifically, we answer three main questions for Constant Bit Rate (CBR) and Variable Bit Rate (VBR) packet front-haul networks: First, is statistical multiplexing gain always achievable in packet front-haul networks? Second, what is the minimum bandwidth required to accommodate a set of front-haul flows on a front-haul link? Third, what is the proper bandwidth allocation and the scheduling algorithm among the packets of different antennas to guarantee the latency requirements of the flows? It is shown that for CBR traffic no statistical multiplexing gain is achievable and the Earliest Deadline First (EDF) is the optimal packet scheduler. For VBR traffic, statistical multiplexing gain is achievable only when the latency requirement of at least one flow is greater than the packet inter-arrival time. The optimal bandwidth allocation is also determined for a Weighted Fair Queueing (WFQ) scheduler. Finally, simulation is used to validate the theoretical results for both CBR and VBR front-haul traffic.

In this paper, we propose Access Point Channel Capacity (ACC) as a Key Performance Indicator (KPI) for Radio Resource Management (RRM) algorithms in 802.11 Wireless Local Area Networks (WLANs). Introducing such a KPI is important especially for performance evaluation of 802.11 WLAN Self Organizing Networks (SON). ACC is a low complexity KPI that provides accurate per-AP estimate of the MAC layer potential throughput in the WLAN. The advantage of the proposed metric is that it can be derived directly from network statistics collected periodically from the access points. ACC is a vendor agnostic KPI since the required statistics are widely supported by all AP vendors and also TR-069 data model.

In Cognitive Radio (CR), secondary radios are allowed to use the spectrum allocated to primary radios (PR) only if the spectrum is sensed to be unused by the PR users. Cooperative spectrum sensing is a sensing methodology in which secondary users send their detection results to a central fusion node for global decision. It has been shown that for single node detection, SNR wall provides a hard threshold on the sensed SNR for robust signal detection. In this paper, asymptotic performance of cooperative spectrum sensing with Hard Decision Combining (HDC) will be studied under noise uncertainty. It is first shown that under noise uncertainty, SNR wall is yet a substantial constraint on the performance of the cooperative spectrum sensing when applying HDC. We then show that k-out-of-n fusion rule with finite k (e.g., “OR” rule) does not result in robust detection of the PR signal, even for SNR values greater than SNR wall. Finally, it is shown that for SNR values greater than the SNR wall, the PR signal can be robustly detected by the k-out-of-n fusion rule with finite n - k (e.g., “AND” rule).

The problem of joint resource allocation and relay selection is studied for bidirectional LTE-advanced relay networks. The bidirectional communication between user equipment (UE) and eNodeB (eNB) is performed via direct transmission, co-operative relaying (CoR), or a combination of network coding (NC) and CoR (NC/CoR). In this paper, an enhanced three-time-slot per cycle time-division duplexing (TDD) scheme is proposed for LTE-Advanced frame architecture to accommodate a hybrid transmission scheme. More specifically, we formulate the problem of joint resource assignment, relay selection, and bidirectional transmission scheme selection as a combinatorial optimization problem with the objective to maximize the total product of backlog and rate (back-pressure principle). Two approaches are considered to solve our combinatorial optimization problem. First, a graph-based framework is proposed in which the problem is transformed into a maximum weighted Clique problem (MWCP). In addition, our problem is also transformed into a three-dimensional assignment problem (3DAP) which is solved using a hybrid ant colony optimization (ACO) algorithm. Using simulations, it is concluded that the hybrid transmission scheme outperforms all conventional nonhybrid schemes. Moreover, the simulation results confirm that while the two proposed solutions provide similar results, the ACO algorithm is faster due to its lower complexity.

In this paper, we study the problem of optimal resource allocation in relay-assisted bidirectional LTE-Advanced networks. The bidirectional network consists of User Equipment (UE), Base Station or eNodeB (eNB) and a Relay Node (RN). We model the network by using a Two-Way Relay Channel (TWRC) in which UE and eNB can choose between different transmission schemes: direct transmission, pure CoR (CoR scheme), or via the combination of Network Coding and Cooperative Relaying (NC/CoR scheme). In this paper, an enhanced three-time-slot per cycle time-division duplexing (TDD) transmission scheme is proposed for LTE-Advanced frame architecture to accommodate the hybrid transmission scheme. We formulate the joint problem of subcarrier assignment, relay selection, and bidirectional transmission scheme selection as a combinatorial optimization problem to maximize the system total product of backlog and rate (backpressure principle). The problem is then transformed into a three-dimensional assignment problem which is solved using a hybrid ant colony optimization (ACO) algorithm. The simulation results show that our optimization algorithm significantly outperforms conventional schemes for both SISO and MIMO systems.

In cooperative wireless networks, relay nodes are employed to improve the performance of the network in terms of throughput and reliability. However, the presence of malicious relay nodes in the network may severely degrade the performance of the system. When a relay node behaves maliciously, there exists a possibility that such a node refuses to cooperate when it is selected for cooperation or deliberately drops the received packets. Trust establishment is a mechanism to detect misbehaving nodes in a network. In this paper, we propose a trust establishment method for cooperative wireless networks by using Bayesian framework. In contrast with the previous schemes proposed in wireless networks, this approach takes the channel state information and the relay selection decisions into account to derive a pure trust value for each relay node. The proposed method can be applied to any cooperative system with a general relay selection policy whose decisions in each cooperative transmission are independent of the previous ones. Moreover, it does not impose additional communication overhead on the system as it uses the available information in relay selection procedure. Copyright © 2012 John Wiley & Sons, Ltd.

Cooperative relaying (CoR) and network coding (NC) are two promising techniques for improving the performance of next generation LTE-Advanced networks. In this paper, a dynamic resource allocation scheme is proposed in relay-assisted LTE-Advanced networks which consists of three nodes: User Equipment (UE), Base Station or eNodeB (eNB) and an intermediate Relay Station (RS). In such a network, LTE UEs and eNB can choose between different transmission schemes: direct transmission, pure CoR (CoR scheme) using an intermediate relay station, or via the combination of Network Coding and Cooperative Relaying (NC/CoR scheme). We study the achievable rate regions for direct transmission, CoR and NC/CoR and it is noticed that NC/CoR does not always achieve better performance than CoR or direct transmission. Therefore, a hybrid transmission scheme with adaptive resource allocation is proposed to dynamically choose the best transmission scheme among NC/CoR, CoR or direct transmission. The proposed hybrid scheme determines the best transmission strategy and the optimal resource allocation decision at each bidirectional transmission time-frame based on the system channel information as well as the queue length information. The simulation results show that the hybrid algorithm significantly outperforms conventional schemes for both SISO and MIMO systems.

The problem of assignment of K identical servers to a set of N symmetric parallel queues is investigated in this paper. The parallel queueing system is considered to be time slotted and the connectivity of each queue to each server is varying randomly over time and following Bernoulli distribution with a given parameter. Each server is capable of serving at most one packet per time slot (if it is connected and assigned to a queue). At any time slot, each server can serve at most one queue and each queue can be served by at most one server. We assume that the service of a scheduled packet by a connected server fails randomly with a certain probability. The packet arrival processes to the queues are assumed to be i.i.d. and follow Bernoulli distribution with a fixed parameter. For such a symmetric system, i.e., with the same arrival, connectivity and service failure parameters for all the queues, we show that Maximum Weighted Matching (MWM) server assignment policy is delay optimal. More specifically, using stochastic ordering and dynamic coupling techniques we prove that MWM minimizes, in stochastic ordering sense, a broad range of stochastic cost functions of the queue lengths including total queue occupancy (or equivalently average queueing delay).

In this paper, we characterize the stability region of multi-queue multi-server (MQMS) queueing systems with stationary channel and packet arrival processes. Toward this, the necessary and sufficient conditions for the stability of the system are derived under general arrival processes with finite first and second moments. We show that when the arrival processes are stationary, the stability region form is a polytope for which we explicitly find the coefficients of the linear inequalities which characterize the stability region polytope.

Cooperative communication makes use of the broadcast nature of the wireless medium where adjacent nodes overhear the message transmitted by the source and assist in the transmission by relaying the overheard message to the destination. Although cooperative communication brings in significant benefits, it also raises serious security issues to wireless mobile networks. For example, there exists a possibility that a node refuses to cooperate when it is selected for cooperation or deliberately drop the received packets. In wireless mobile networks with cooperative communication, trust management is an important mechanism to monitor such networks for violations of security. In this paper, we propose a trust management method for wireless mobile networks with cooperative communications. Conventional Bayesian methodology is insufficient for the cooperative communication paradigm, as it is biased by the channel conditions and relay selection decision processes. Therefore, we modify the conventional trust management method by incorporating not only the relay selection policy but also the dynamic wireless channel conditions among the source, relays and destination. Simulation results are presented to show the effectiveness of the proposed scheme.

Availability of multiple channels and multiple radio interfaces can lead to substantial improvements in the performance of wireless access networks. The optimal allocation of available channels to the users with multiple interfaces however is not a trivial problem especially in a dynamically varying system. In this paper, we will consider the problem of channel and radio interface management in multi-channel multi-interface wireless access networks. In our model, there is a set of orthogonal channels which is shared among several users. Furthermore, each user is equipped with a fixed number of radio interfaces through which it can communicate with the access point. We also consider exogenous stochastic packet arrivals for each user which may be queued for future transmissions. We introduce a general modelling for multi-channel multi-interface wireless access networks for which we propose a throughput optimal channel/interface allocation policy that stabilizes the system for all the arrival rates strictly inside the stability region. We show that the optimal policy determination is equivalent to finding the maximum weighted matching in a bipartite graph at every time slot. Finally, we characterize the stability region for specific cases of the proposed model. Simulation is used to compare the performance of the optimal policy with some other policies in terms of average total queue occupancy.

Network capacity region of multi-queue multi-server queueing system with random connectivities and stationary arrival processes is studied in this paper. Specifically, the necessary and sufficient conditions for the stability of the system are derived under general arrival processes with finite first and second moments. In the case of stationary arrival processes, these conditions establish the network capacity region of the system. It is also shown that AS/LCQ (Any Server/Longest Connected Queue) policy stabilizes the system when it is stabilizable. Furthermore, an upper bound for the average queue occupancy is derived for this policy.

A greedy scheme called Greedy Codeword Assignment Scheme (GCAS) is proposed to assign D-ary codewords to the given code-lengths ¿1,¿2,...,¿n, so that they satisfy the fix-free property. This scheme guarantees that a D-ary fix-free code can be obtained whenever ¿i=1nD-¿¿ ¿(D), where ¿(D) is equal to 5/8 for D even and very close to 5/8 for D odd. This result can be regarded as an extension of Yekhanin's theorem on the existence of binary fix-free codes. In the special case D=2 , the greediness of GCAS enables us to prove that if mini ¿i= 2, the inequality ¿i=1n2-¿i¿ 21/32 implies the existence of a binary fix-free code with code-lengths ¿1,¿2,...,¿n.