Probabilistic Analysis of Mutual Interference in Cognitive Radio Communications

Power allocation for secondary users (SUs) in cognitive networks is an important issue to ensure the SUs’ quality of service. When the mutual interference between the primary users (PUs) and the SUs is taken into consideration, it is wanted to achieve the conflict-free power allocation while synchronously maximizing the capacity of the secondary network. In this paper, the optimal power allocation problem is considered in orthogonal frequency division multiplexing cognitive networks. The single SU case is primarily formulated as a constrained optimization problem. On this basis, the multiple SUs case is then studied and simulated in detail. During the analysis, the mutual interference among the PUs and the SUs is comprehensively formulated as the restrictions on the SU’s transmission power and the optimization problems are finally resolved by iterative water-filling algorithms. Consequently, the proposed power allocation scheme restrains the interference to the primary network, as well as maximizing the capacity of the secondary network. Specifying the multiple-SUs case, simulation results are exhibited in a simplified scenario to confirm the efficiency of the proposed water-filling algorithm, and the influence of the mutual interference on the power allocation and the system capacity is further illustrated.

In this paper, we consider medium access control (MAC) protocol design for random-access cognitive radio (CR) networks. A two-level opportunistic spectrum access strategy is proposed to optimize the system performance of the secondary network and to adequately protect the operation of the primary network. At the first level, secondary users (SUs) maintain a sufficient detection probability to avoid interference with primary users (PUs), and the spectrum sensing time is optimized to control the total traffic rate of the secondary network allowed for random access when the channel is detected to be available. At the second level, two MAC protocols called the slotted cognitive radio ALOHA (CR-ALOHA) and cognitive-radio-based carrier-sensing multiple access (CR-CSMA) are developed to deal with the packet scheduling of the secondary network. We employ normalized throughput and average packet delay as the network metrics and derive closed-form expressions to evaluate the performance of the secondary network for our proposed protocols. Moreover, we use the interference and agility factors as the performance parameters to measure the protection effects on the primary network. For various frame lengths and numbers of SUs, the optimal performance of throughput and delay can be achieved at the same spectrum sensing time, and there also exists a tradeoff between the achievable performance of the secondary network and the effects of protection on the primary network. Simulation results show that the CR-CSMA protocol outperforms the slotted CR-ALOHA protocol and that the PUs' activities have an influence on the performance of SUs for both the slotted CR-ALOHA and CR-CSMA.

In this paper, we present an analytical study for the performance of a two-tier primary-secondary network based on IEEE 802.11 DCF mechanism. It is assumed that multiple primary users (PUs) and secondary users (SUs) coexist in the radio environment and share a single band such that the SUs are allowed to contend only if they sense the channel idle for a certain period of time. First, we derive the PUs' medium access delay in the presence of SUs. Then, assuming an exponential packet inter-arrival time for the primary network, and using M/G/1 queue modeling, we determine the collision probability and throughput for the primary and secondary networks, as well as the PUs' average total delay including the queuing delay. Numerical along with simulation results show how the performance in the primary network, with given packet arrival rate, can be affected as functions of the sensing time, packet payload size and population size of the SUs. The findings of this work can be used effectively to study the performance of any IEEE 802.11 based primary-secondary network, such as cognitive radio networks where SUs may exploit a primary channel opportunistically based on a predefined policy, as well as to optimize the performance of distributed cognitive radio MAC protocols.

Node density and connectivity of large-scale multi-channel cognitive radio networks (CRNs) are studied in this paper. Current existing researches on connectivity of CRNs are mainly conducted under the assumption of one licensed channel and ignore the spectrum sensing errors. Thus, in this paper, practical assumptions such as spatially varying spectrum holes for secondary users (SUs), multiple channels licensed for the primary network, correct detection and false alarm probabilities (Pd and Pf) are considered to derive the diluted density of SUs in closed-form for the secondary network. The sensing errors of SUs and amount of licensed channels of primary users (PUs) are found to have a significant impact on the density of active SUs. Increasing density of PUs considerably reduces the node density of active SUs. Sequentially connectivity of the secondary network is investigated by applying percolation theory and complex network. The critical condition for percolation of the secondary network coexisting with primary network is then estimated analytically. We study the impacts of node density, protection radius, amount of licensed channels of the primary network on connectivity of the secondary network. It is shown that more licensed channels can loosen the condition for SUs percolation. Also, sensing errors significantly affect the connectivity of SUs. However, we found that more accurate sensing carried by SUs (larger Pd and smaller Pf) does not necessarily bring better connectivity of the secondary network.

In cognitive radio (CR) networks, proper power controlling is of importance to ensure efficient operation of both primary and secondary networks. The previous work on power control in cognitive radios has mainly focused on the interactions among a set of secondary users while ignoring the influence of primary users. In [1], we introduced a new game model for power control in cognitive radios by incorporating the primary users into the player set of the game. In this new framework, the primary users are rewarded (for example, monetarily) for sharing their licensed spectrum with secondary users. In our proposed game formulation, they achieve this by setting a reasonable interference cap (IC) for the secondary users. However, the primary users are to be severely penalized if they do not meet their transmission quality. To ensure this, an exponential pricing term is incorporated into their utility function. Simultaneously, the secondary users aim to achieve energy efficient transmissions while not introducing too much interference to the primary as well as other secondary users. In this paper, we investigate the CR system design aspects based on our proposed new game theoretic spectrum sharing framework. In particular, the performance of the system is compared under different linear detector schemes at the secondary receiver, namely, the matched filter (MF) and the linear MMSE (LMMSE) receivers.

We study the throughput and delay scaling laws of cognitive radio networks (CRN) with mobile primary and secondary users. They operate at the same time, space and share the spectrum. The primary users (PUs) have higher priority to access the spectrum while the secondary users (SUs) should access opportunistically. Furthermore, we consider a unique situation where both PUs and SUs move according to a General Heterogeneous Speed-restricted Mobility (GHSM) model. In this model, we define (h+1) heterogeneous moving patterns using a universal set T={T_i |0≤i≤h,A_i=n^(-i χ_0/h)}, where A_i determines the moving area of each pattern. The set of primary (secondary) moving patterns T^((p)) (T^((s) )) is a randomly and independently selected subset of T. We assign n (n^β, where β>1) primary (secondary) nodes to each moving pattern, and their initial positions are subject to a poisson point process. In addition, we have |T^((p) ) |~|T^((s) ) |=θ(h)= θ(logn). By proposing a cooperative routing strategy, we fully utilize the mobility heterogeneity of primary and secondary users and achieve near-optimal throughput and delay performance of order θ(poly log n) when χ_0≥β. In other cases, our transmission scheme shows advantages over [1] in delay performance of the primary network (PN) and over [2] in capacity of the secondary network (SN).

In this paper, we propose an adaptive spectrum access protocol for secondary users (SUs) be used to access licensed bands in cognitive radio networks. Specifically, if the primary network, which uses multicast communication to transmit data from one primary source to multiple primary destinations, satisfies a required system quality of service (QoS), SUs can access the licensed bands, follows an underlay spectrum sharing. Otherwise, a secondary base (SB) station must assist the primary network in obtaining the QoS so that it can find opportunities to use the bands, i.e., cooperation-based spectrum access. To enhance the performance for the secondary network, in terms of outage probability (OP), various best-user selection methods are proposed. Moreover, we take into consideration the impact of hardware impairments on the OP of both primary and secondary networks. We derive exact and asymptotic closed-form expressions of the OP over Rayleigh fading channel. From the analytical results, an optimal value of maximal interference threshold and an optimal fraction of the SBs' transmit power to the primary data are obtained when the secondary network operates on the underlay and the cooperation-based spectrum access modes, respectively. Finally, Monte Carlo simulations are performed to verify the theoretical derivations.

In cognitive radio networks, secondary users need to access the licensed spectrum while neither disturbing the transmissions of the primary users nor introducing much interference to other secondary users. Hence, proper power controlling is of paramount importance to ensure efficient system operation. The previous work on power control in cognitive networks mainly focuses on the interactions among a set of secondary users. The primary users' influence is rarely considered. In this paper, a new power control game model is formulated, by including the primary users into the player set of the game. The primary users are rewarded for sharing their licensed spectrum with secondary users by setting a reasonable interference cap for the secondary transmissions. However, we ensure a minimum required Quality of Service (QoS) for primary users by severely penalizing their utility if their required transmission quality is not met. Simultaneously, the secondary users achieve energy efficient transmissions while not introducing much interference to both the primary and other secondary users. We prove that the proposed cognitive power control game has a unique Nash equilibrium (NE). The numerical examples show that the proposed game theoretical power control algorithm can provide the secondary users with energy efficient transmissions and the primary users with reasonable monetary rewards, while not compromising their required QoS.

In this paper, we study the problem of jointing power and rate optimization in multi-channel Heterogeneous Cognitive Radio Networks (H-CRNs), where the Leader-Follower relationship between Primary Users (PUs) in macrocells and Secondary Users (SUs) in femtocells is modeled as a Stackelberg game. We formulate the problem of power allocation in primary networks as a Non-Cooperative Game, while formulating the jointing power and rate optimization in cognitive networks as a Market Competition Equilibrium problem. Furthermore, we propose a Primary networks and Cognitive networks Joint Resource Allocation (PCJRA) algorithm to maximize the utilities of SUs subject to the maximum rate requirements for PUs. Theoretical analysis and simulation results demonstrate both the feasibility of the multi-channel H-CRNs model and the effectiveness of the proposed PCJRA algorithm.

In this paper, we propose a cooperative spectrum sharing protocol for cognitive radio networks (CRNs) which operate in underlay mode with an automatic repeat-request (ARQ)-based primary user (PU) including primary transmitter (PT) and primary receiver (PR) and a bidirectionally communicating secondary user (SU) which consists of the nodes S1 and S2. In ARQ-based PU, ACKnowledgement/Negative-ACKnowledgement (ACK/NACK) messages are sent from PR to PT and listened by S1 and S2 to control the PU's packet success. Si (i=1 or 2) alerts both PT and PR if its reception from PT is successed or failed and PR considers the link from Si or PT, respectively. PU transmits its packet by accessing the spectrum alone or by cooperating with SU or under an interference caused by SU. If PT transmits alone its packet successfully, in the next time slot it transmits a new packet in underlay mode during which SU access the spectrum simultaneously with a tolerable interference level to improves the PU's performance. Conversely, if PT fails to transmit alone its packet and at least one of the nodes S1 and S2 success to decode it, then S1 or S2 cooperates with PT attending as a relay to enhance the PU's throughput in the next time slot during which PT stays silent. If both of S1 and S2 fail to decode PT's packet, PT retransmits its packet in underlay mode. When the first transmission of PT's packet is failed in underlay mode, PT retransmits this packet alone. We derive analytical expressions for the throughputs of PU and SU and show that the proposed protocol significantly improves the PU's throughput compared to non-CR scheme while stabilizing the SU's throughput at high SNR values.

In this paper, we investigate users’ performance under the hybrid spectrum access model in the massive cognitive radio network (CRN), where multiple primary users (PUs) and secondary users (SUs) transmit on the same channel simultaneously. SUs first detect the state of the channel via channel sensing and select an appropriate channel access scheme (either underlay or overlay) for their transmissions based on the outcome of the channel sensing. When at least one PU is active, SUs transmit under the underlay channel access scheme by employing the power control technique to ensure that the interference generated in the primary network is below the pre-defined interference threshold. In the absence of PU, SUs transmit with full transmit power under the overlay channel access scheme, thereby maximizing their throughput. Using the tool of stochastic geometry, we obtained tractable analyses for important metrics such as success probability, throughput, and the average age of information (AoI) in both primary and secondary networks, while capturing the interference between the two networks. The obtained analyses offer an efficient way to understand the metrics of AoI, throughput and success probability in the hybrid spectrum access-based CRN. We further compared users’ performance under the hybrid spectrum access scheme with performances under overlay and underlay spectrum access schemes. The outcome of the numerical simulations shows that the hybrid spectrum access scheme can significantly improve the performance of users in the network, while also capturing more key features of real-life systems.

A novel protocol for transparent and simultaneous spectrum access between the secondary user and the primary user in cognitive radio networks

In recent years, cognitive radio (CR) has received a great attention due to the ability to improve the spectrum utilization. It allows the secondary user (SU) in the CR network to opportunistically access the licensed spectrum of the primary user (PU). For this end, quality of service (QoS) requirements for both the PU and the SU should be guaranteed at the same time. These QoSs can be respectively translated into the interference temperature at the primary receiver and the received signal- to-interference-plus-noise-ratio (SINR) of the secondary receiver. In such a CR network, a power control can increase the energy efficiency by keeping the transmission power of the SU as low as possible within the QoS requirements. In this paper, we propose an autonomous distributed power control scheme for CR networks that considers the QoS requirements of the PU and the SU simultaneously. Since the transmission power of each SU is constrained so that the interference temperature at the primary receiver caused by all SUs does not exceed the interference tolerance of the PU, the QoS requirement for the PU is always guaranteed. Through the simulation results, we demonstrate that the proposed scheme never exceed the interference tolerance of the PU.

The cooperation among the secondary users or among the secondary users and the primary users have proven to bring many benefits to both primary and secondary users in cognitive radio networks. In this paper, cooperative relaying in cognitive radio networks is studied for rateless coding error-control mechanism. For a pair of primary transmitter and receiver, we find the region in which any secondary or cognitive user can cooperate with the primary user in a constructive way. A queueing theoretical model is employed to describe the underlying system parameters and to create a mathematical framework for the analysis. The throughput performance of the secondary users is maximized based on the input traffic of the primary users. Using the unique properties of rateless codes, a low-complexity relay selection mechanism is also introduced. Through the experimental analysis, we show that the proposed rateless-coding-based cooperative mechanism can perform similar to the more complicated and more costly selective-repeat automatic repeat request algorithm. The numerical analysis using the Rapid Analysis of Queueing Systems (RAQS) software package is provided to support the findings.

In this paper we have studied the subcarrier and optimal power allocation strategy for OFDM-based cognitive radio (CR) networks. Firstly, in order to protect the primary user communication from the interference of the cognitive user transmissions in fading wireless channels, we design an opportunistic power control scheme to maximize the cognitive user capacity without degrading primary user's QoS. The mathematical optimization problem is formulated as maximizing the capacity of the secondary users under the interference constraint at the primary receiver and the Lagrange method is applied to obtain the optimal solution. Secondly, in order to limit the outage probability within primary user's tolerable range we analyze the outage probability of the primary user with respect to the interference power of the secondary user for imperfect CSI. Finally, in order to get the better tradeoff between fairness and system capacity in cognitive radio networks, we proposed an optimal algorithm of jointing subcarrier and power allocation scheme among multiple secondary users in OFDM-based cognitive radio networks. Simulation results demonstrate that our scheme can improve the capacity performance and efficiently guarantee the fairness of secondary users.