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Trafc indication map (TIM) is one information element (IE) that is used to indicate the buffered frame status for the stations (STAs) and carried in the regularly transmitted beacons in the IEEE 802.11 based WLANs. To reduce the overhead of TIM signaling for the recent standardization of IEEE 802.11ah, which supports a large number of STAs and operates at the sub-1GHz frequency, a hierarchical structure...
The IEEE 802.11ah task group has been formed to develop the specification for sub-1GHz WLAN. Due to the low operating frequency, it is expected that the 802.11ah can support coverage up to 1km. Such large coverage is well-suited for machine-to-machine (M2M) or machine-type communication (MTC) applications like smart grid and sensor networks. These applications are characterized by large number of...
With the prior knowledge that the primary user is highly likely idle and the primary signals are digitally modulated, we propose an optimal Bayesian detector for spectrum sensing to achieve higher spectrum utilization in cognitive radio networks. We derive the optimal detector structure for MPSK modulated primary signals with known order over AWGN channels and give its corresponding suboptimal detectors...
We have derived the optimal cooperative sensing schemes for distributed sensors with time independent signals and shown that the optimal scheme is simply a linear combination of the normalized energies from all sensors. To avoid using the SNR information and simplify the decision process and threshold setting, some sub-optimal schemes have been analyzed and compared. In general, the proposed AOCS...
Analytical formulations of the throughput of cognitive multi-channel MACs with perfect and imperfect sensing are presented. Both imperfect concurrent sensing and imperfect sequential sensing schemes are considered. A discrete time Markov chain is used to model the number of communicating node pairs in the MAC protocols. The throughput of the MAC protocol with perfect sensing is expressed as a function...
Cooperative communication enables the nodes in wireless networks to transmit their packets to the next hops with the help of neighboring nodes. The design of cooperative MAC usually considers only the communication within one hop and current routing protocols have seldom been developed with the concept of cooperative communications. Envisaging the new challenge in cooperative wireless networks, we...
Based on the high probability that primary user is idle in cognitive radio networks, we propose an optimal Bayesian detector structure for spectrum sensing. Although the optimal detector by Neyman-Pearson theorem maximizes the detection probability for a given false alarm probability, Bayesian detector can achieve a higher overall spectrum utilization and SU throughput and at the same time the primary...
Analytical formulations of the throughput of multi-channel medium access control (MAC) protocols are presented. Both multi-channel multi-rate MAC and multi-channel CoopMAC protocols are considered. A discrete time Markov chain is used to model the number of nodes communicating with the AP in the multi-channel multi-rate MAC protocol, while another discrete time Markov chain is used to model the number...
In the cooperative wireless networks, the source node transmits its packets to the destination in one hop with the cooperation from the helper nodes. We design a TDMA-based cooperative MAC which can determine the cooperative cooperation opportunity, to maximize the expected reward, taking into consideration the gain of cooperative communication and network coding that are received from all of its...
In our paper, we propose a Multi-Rate IEEE 802.11b MAC protocol with network coding. The standard X-OR operation is used in the network coding. Two topologies of paired topology and random topology are considered. The analytical framework is formulated for n stations. The state transition diagram is modeled by a two-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the...
In this paper, we are interested in a cognitive secondary wireless local area network (WLAN) which operates in the same or overlapping spectrum and coverage with a primary wireless network. The protection of primary network is quantified by the detection time, which defines the number of superframes required for the secondary network to recognize the re-appearance of the primary network. We obtain...
In cooperative wireless networks, the source node transmits the packets to its destination with the help from the cooperative nodes. However, existing routing metrics in the literature do not take into account the cooperative gain in choosing the next hop in a multi-hop network. In this paper, we propose a new routing metric that accounts for the potential cooperative gain a candidate next hop may...
We propose a MAC for wireless ad hoc cognitive radio networks where secondary users employ cooperative spectrum sensing to mitigate the degradation of the channel between primary transmitter and secondary users. The sensing reports and fused decisions are transmitted based on random access of CSMA/CA and 802.11e EDCA on the control channel, whose access scheme determines the overall achievable throughput...
In cognitive radio networks, the secondary users (SUs) are allowed to use the spectrum originally allocated to primary users (PUs) as long as the PUs are not using it temporarily. This operation is called opportunistic spectrum access (OSA), and it is assisted through spectrum sensing. In distributed OSA, the SUs sense the channel independently; once the channel is available, they contend for channel...
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