Survey on coexistence of heterogeneous wireless networks in 2.4 GHz and TV white spaces <s> Coexistence under presence of PUs <s> Spectrum sensing plays a critical role in cognitive radio networks (CRNs). The majority of spectrum sensing algorithms aim to detect the existence of a signal on a channel, i.e., they classify a channel into either busy or idle state, referred to as a two-state sensing model in this paper. While this model works properly when there is only one CRN accessing a channel, it significantly limits the potential and fairness of spectrum access when there are multiple co-existing CRNs. This is because if the secondary users (SUs) from one CRN are accessing a channel, SUs from other CRNs would detect the channel as busy and hence be starved. In this paper, we propose a three-state sensing model that distinguishes the channel into three states: idle, occupied by a primary user, or occupied by a secondary user. This model effectively addresses the fairness concern of the two-state sensing model, and resolves the starvation problem of multiple co-existing CRNs. To accurately detect each state of the three, we develop a two-stage detection procedure. In the first stage, energy detection is employed to identify whether a channel is idle or occupied. If the channel is occupied, the received signal is further analyzed at the second stage to determine whether the signal originates from a primary user or an SU. For the second stage, we design a statistical model and use it for distance estimation. For detection performance, false alarm and miss detection probabilities are theoretically analyzed. Furthermore, we thoroughly analyze the performance of throughput and fairness for the three-state sensing model compared with the two-state sensing model. In terms of fairness, we define a novel performance metric called all-level fairness for all(ALFA) to characterize fairness among CRNs. Extensive simulations are carried out under various scenarios to evaluate the three-state sensing model and verify the aforementioned theoretical analysis. <s> BIB001 </s> Survey on coexistence of heterogeneous wireless networks in 2.4 GHz and TV white spaces <s> Coexistence under presence of PUs <s> Cognitive radio is viewed as a disruptive technology innovation to improve spectrum efficiency. The deployment of coexisting cognitive radio networks, however, raises a great challenge to the medium access control (MAC) protocol design. While there have been many MAC protocols developed for cognitive radio networks, most of them have not considered the coexistence of cognitive radio networks, and thus do not provide a mechanism to ensure fair and efficient coexistence of cognitive radio networks. In this paper, we introduce a novel MAC protocol, termed fairness-oriented media access control (FMAC), to address the dynamic availability of channels and achieve fair and efficient coexistence of cognitive radio networks. Different from the existing MACs, FMAC utilizes a three-state spectrum sensing model to distinguish whether a busy channel is being used by a primary user or a secondary user from an adjacent cognitive radio network. As a result, secondary users from coexisting cognitive radio networks are able to share the channel together, and hence to achieve fair and efficient coexistence. We develop an analytical model using two-level Markov chain to analyze the performance of FMAC including throughput and fairness. Numerical results verify that FMAC is able to significantly improve the fairness of coexisting cognitive radio networks while maintaining a high throughput. <s> BIB002
As mentioned in the previous section, in TVWSs, a particularity that makes the coexistence of CR networks challenging is the presence of PUs, whose transmission may not necessarily follow a predictable pattern. Hence, coordination among heterogeneous secondary networks under the presence of PUs consists of an importance design. We point out that although the PUs issue is mentioned in a number of CR coexistence standards (e.g. TVWSs database in IEEE 802.19.1 19 ), the problem of how to react when PUs arrive has not been specified. For example, in IEEE 802.19.1, it is mentioned that a PU list in TVWSs database can provide PU information to CMs to manage spectrum hopping of the coexisting networks, but the problem of coexistence under the presence of PUs is not specified. Zhao and colleagues BIB002 BIB001 develop a solution to this problem. However, their solution requires that the locations of PUs are prior known to the coexisting networks and are fixed. Such assumptions may be too strong although impractical in many cases. Even in the cases where the assumptions hold, their solution may not be effective or even fail to work if PUs are geographically close to cognitive nodes, which makes it difficult to distinguish the primary signal from secondary signal. Given the above argument, a primary building block enabling coexistence of CR networks with the presence of PUs is the detection of primary signals. Once the primary signal is detected, distributed mechanisms should be devised to let cognitive nodes react and coordinate the spectrum access among them. We illustrate the challenge in this phase via the following example. Two CR networks (A and B) operate on a band of 30 MHz. A occupies first 20 MHz and B occupies last 20 MHz with an overlapped 10-MHz band in the middle part that they share. The event that a PU arrives at first 10 MHz will not only trigger A to relocate its spectrum but also probably impact B who might need to adapt its operation band.