Multiple access schemes for Cognitive Radio networks: A survey

In this paper, we develop and analyze a novel performance metric, called interference efficiency, which shows the number of transmitted bits per unit of interference energy imposed on the primary users (PUs) in an underlay cognitive radio network (CRN). Specifically, we develop a framework to maximize the interference efficiency of a CRN with multiple secondary users (SUs) while satisfying target constraints on the average interference power, total transmit power, and minimum ergodic rate for the SUs. In doing so, we formulate a multiobjective optimization problem (MOP) that aims to maximize ergodic sum rate of SUs and to minimize average interference power on the primary receiver. We solve the MOP by first transferring it into a single objective problem (SOP) using a weighted sum method. Considering different scenarios in terms of channel state information (CSI) availability to the SU transmitter, we investigate the effect of CSI on the performance and power allocation of the SUs. When full CSI is available, the formulated SOP is nonconvex and is solved using augmented penalty method (also known as the method of multiplier). When only statistical information of the channel gains between the SU transmitters and the PU receiver is available, the SOP is solved using Lagrangian optimization. Numerical results are conducted to corroborate our theoretical analysis.

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Interference Efficiency: A New Metric to Analyze the Performance of Cognitive Radio Networks

In this paper, we aim to minimize the average file transmission delay via bandwidth allocation and cache placement in two-tier heterogeneous networks with limited storage capacity, which consists of cache capacity and buffer capacity. For average delay minimization problem with fixed bandwidth allocation, although this problem is nonconvex, the optimal solution is obtained in closed form by comparing all locally optimal solutions calculated from solving the Karush-Kuhn-Tucker conditions. To jointly optimize bandwidth allocation and cache placement, the optimal bandwidth allocation is first derived and then substituted into the original problem. The structure of the optimal caching strategy is presented, which shows that it is optimal to cache the files with high popularity instead of the files with big size. Based on this optimal structure, we propose an iterative algorithm with low complexity to obtain a suboptimal solution, where the closed-from expression is obtained in each step. Numerical results show the superiority of our solution compared to the conventional cache strategy without considering cache and buffer tradeoff in terms of delay.

Cache Placement in Two-Tier HetNets with Limited Storage Capacity: Cache or Buffer?

Physical layer network coding (PNC) has been studied to serve wireless network MIMO systems with much lower backhaul load than approaches such as Cloud Radio Access Network (Cloud-RAN) and coordinated multipoint (CoMP). In this paper, we present a design guideline of engineering applicable PNC to fulfil the request of high user densities in 5G wireless RAN infrastructure. We show that the proposed design criteria guarantee that: 1) the whole system operates over binary system; 2) the PNC functions utilized at each access point overcome all singular fade states; and 3) the destination can unambiguously recover all source messages, while the overall backhaul load remains at the lowest level. We then develop a two-stage search algorithm to identify the optimum PNC mapping functions which greatly reduces the real-time computational complexity. The impact of estimated channel information and reduced number of singular fade states in different QAM modulation schemes are studied in this paper. Numerical results show that the proposed schemes achieve low outage probability with reduced backhaul load.

/pdf/physical-layer-network-coding-in-network-mimo-a-new-design-1vyf9ovn9k.pdf

Physical Layer Network Coding in Network MIMO: A New Design for 5G and Beyond

This paper investigates the resource allocation problem for a multiuser underlay cognitive system where the secondary system is allowed to transmit and cooperate with the primary system. In this scenario, the secondary users are subject to two main constraints in the presence of the primary user: their total power budget and the allowable interference threshold at the primary receiver. Power and subcarrier allocation problems are detailed in order to maximize the system sum rate. In this work, we highlight the benefits of the proposed multiuser adaptive algorithm which encompasses three phases. The first step includes the adaptive selection of the decoding strategy at the secondary receiver which is either treating interference as noise or performing successive interference cancelation or superposition coding. The second step describes the subcarrier allocation among the different users. Finally, the third step details the optimal distribution of the available power budget on the users. The problem is first treated assuming perfect channel state information (CSI). The simulation results show that our proposed scheme achieves higher secondary and sum rates compared to existing approaches with perfect CSI. The robustness of the proposed algorithm when the secondary user has only partial information about channel gains is also derived.

/pdf/resource-allocation-for-ofdm-based-multiuser-cooperative-3uivx4bwq4.pdf

Resource allocation for OFDM-based multiuser cooperative underlay cognitive systems

A novel probabilistic radio resource allocation algorithm is proposed for code-division multiple-access cognitive radio networks. Our method incorporates a sensing-based hybrid access- and interference-limited spectrum sharing strategy to maximize the achievable spectral efficiency of cognitive users (CUs) while guaranteeing the quality-of-service (QoS) requirements of licensed services. Specifically, the enhanced performance for CUs is achieved through optimal joint power and rate adaptation to the time-varying multiuser interference and frequency-selective fading channel conditions. We show that this scheme can improve the average spectral efficiency of CUs, while satisfying the peak and average received-interference constraints at the primary receiver.

Probabilistic Radio Resource Allocation Over CDMA-Based Cognitive Radio Networks

In this paper, we consider a CDMA-based Cognitive Radio (CR) system that involves joint optimization of Outer Loop Power Control (OLPC) and rate control of a cognitive user using Variable Spreading Factors (VSFs) which enhances the average spectral efficiency (ASE) of these users. The cognitive radio system in this paper consists of a number of licensed (primary) users and a cognitive (secondary) user. The bandwidth of the licensed user is allowed to be accessed by the cognitive user under limited interference constraint. Primary and cognitive users employ Code-Division Multiple-Access (CDMA) technology. Considering Nakagami-m flat-fading channels we optimize the system throughput in terms of cognitive user's ASE under average transmission power constraint and pre-defined interference limit on primary receiver. Numerical results affirm that by using joint-optimization of rate and OLPC in the CR system, the cognitive user's throughput in high SNRs achieves considerable gain compared to a system that does not employ OLPC.

Joint optimization of rate and outer loop power control for CDMA-based cognitive radio networks

Radio resource allocation (RRA) algorithms are developed to enhance the spectral efficiency of downlink adaptive modulation and coding (AMC)-based orthogonal frequency-division multiple access (OFDMA) cognitive radios (CRs) under average transmit and peak interference power constraints. We consider the practical case of noisy channel-state-information (CSI) between cognitive transmitter (CTx) and primary receiver (PRx), and design novel interference management techniques to model and control the CR-inflicted interference on licensed spectrum. An expression for the cumulative density function (cdf) of the CRs' received signal-to-interference-plus-noise ratio (SINR) is developed to evaluate the resultant average spectral efficiency. Simulation results reveal that by adopting the joint resource allocation and interference management framework a considerable performance gain in the AMC-based OFDMA CR network is achieved over the conventional optimization methods.

Resource Allocation and Interference Management for Adaptive Modulation and Coding-Based OFDMA Cognitive Radio Networks

In this paper we consider a multiuser CDMA/CDMA cognitive radio system that involves joint optimization of outer loop power control (OLPC) SNR-target and variable spreading factor of the secondary service, based on the number of active primary and cognitive users (CUs). Optimality is in the sense of maximizing average spectral efficiency (ASE) of the reference CU in the presence of multiple access interference (MAI), whilst maintaining an average transmit power constraint during the time when the licensed spectrum is used and when the secondary frequency band is exploited. The cognitive service employs access-bounded opportunistic spectrum access (AB-OSA) technique to exploit the under-utilized primary bandwidth. In the AB-OSA scheme, CUs' access to the primary user's spectrum is limited based on activity of the primary users. Considering frequency-selective fading channels, we optimize ASE of the reference CU where a coherent RAKE receiver is used with maximum ratio combining (MRC). Numerical results confirm that by using our joint optimization scheme in the cognitive radio system, considerable gain is achieved compared to a system that does not exploit optimum OLPC and subsequently the optimal SNR-target.

https://ieeexplore.ieee.org/iel5/6287113/6296540/06296555.pdf

Impact of primary users activity on achievable average spectral efficiency of CDMA-based cognitive radio networks

A cross-layer design framework, in the sense of maximizing sum-throughput, is proposed for a multi-service network of heterogeneous traffic. Considering different prescribed target packet loss rates and maximum automatic repeat request (ARQ) delays for the services in the data link control (DLC)-layer, we derive the respective optimum signal-to-interference-plus-noise ratio (SINR)-targets and variable spreading factor (VSF)s of the services in the physical (PHY)-layer, analytically as functions of the multi-user interference (MUI) and fading fluctuations. A multi-dimensional Markov chain is employed to model the packet traffic characteristics in the network. Performance of the proposed optimized cross-layer system is demonstrated and compared to state-of-the-art universal mobile telecommunication system (UMTS) standard, with conventional power, rate, and error control, for various practical system settings using theoretical and simulation results. Considerable improvement in sum-throughput performance of the multi-service mobile communication network is achieved through joint optimization of PHY-layer and DLC-layer parameters, whilst satisfying unique quality of service (QoS) constraints of different traffic types.

Mohammad Mirtavoosi Mahyari

Papers

Probabilistic Radio Resource Allocation Over CDMA-Based Cognitive Radio Networks

Joint optimization of rate and outer loop power control for CDMA-based cognitive radio networks

Resource Allocation and Interference Management for Adaptive Modulation and Coding-Based OFDMA Cognitive Radio Networks

Impact of primary users activity on achievable average spectral efficiency of CDMA-based cognitive radio networks

Cross-layer radio resource allocation for multi-service networks of heterogeneous traffic