We propose an efficient resource allocation (RA) scheme for downlink of relay-aided orthogonal frequency division multiple access systems. To mitigate excessive computational complexity of the centralized RA where the base station (BS) is responsible for resource allocation of the entire cell, we take a distributed RA strategy with which each relay station (RS) and BS perform resource allocation for their respective receivers by themselves. The proposed RA scheme is composed of two parts, RS resource allocation (RS-RA) and BS resource allocation (BS-RA). Considering that multiple RSs compete for radio resource in a distributive manner, we design the RS-RA scheme according to noncooperative game framework. The proposed RS-RA scheme aims at allocating less resource to two-hop transmission via RS so that more resource can be used for one-hop (direct) transmission. This RA strategy greatly heightens the system performance. Simulation results show that the proposed RA scheme provides the high cell throughput and the low outage probability. In addition, we devise a heuristic RA scheme that can lower the computational complexity further with much smaller reporting overhead and also suggest an iterative algorithm that can easily implement the proposed RA scheme.

This paper proposes a novel medium access control (MAC) scheme for multichannel cognitive radio (CR) ad hoc networks, which achieves high throughput of CR system while protecting primary users (PUs) effectively. In designing the MAC scheme, we consider that the PU signal may cover only a part of the network and the nodes can have the different sensing result for the same PU even on the same channel. By allowing the nodes to use the channel on which the PU exists as long as their transmissions do not disturb the PU, the proposed MAC scheme fully utilizes the spectrum access opportunity. To mitigate the hidden PU problem inherent to multichannel CR networks where the PU signal is detectable only to some nodes, the proposed MAC scheme adjusts the sensing priorities of channels at each node with the PU detection information of other nodes and also limits the transmission power of a CR node to the maximum allowable power for guaranteeing the quality of service requirement of PU. The performance of the proposed MAC scheme is evaluated by using simulation. The simulation results show that the CR system with the proposed MAC accomplishes good performance in throughput and packet delay, while protecting PUs properly.

In order to guarantee the high quality of service (QoS) even for cell edge users and deeply shadowed users, future cellular networks are expected to deploy relay stations (RSs). For fully exploiting the newly deployed RSs, the centralized scheduling at the base station (BS) have been widely studied due to its ability to provide optimal use of wireless resources and RSs. However, severe burden for channel reporting can be imposed by the centralized scheduling since the BS should collect every channel gain not only between BS and mobile stations (MSs) but also between each RS and MSs. To cope with this high overhead problem, we propose a distributed scheduling scheme which exploits the frequency reuse and provides high QoS to MSs, based on the game theoretic framework. The simulation results show that the proposed scheme can obtain higher throughput than the centralized scheme while the outage probability of the proposed scheme is similar to that of the centralized scheme.

For supporting the high quality of service (QoS) in relay network, this paper proposes a new scheduling scheme that can be adopted in the orthogonal frequency division multiple access (OFDMA) cellular systems. In relay-aided network, a relay station should receive data from base station for forwarding data to its serving mobile stations. In addition, since the channel quality of each hop cannot be the same, the transmission time of each hop should be adjusted to harmonize the achievable transmission rate on each hop. In this paper, we first formulate the optimal scheduling problem and suggest a simple and fast heuristic scheme that provides enough subchannels to each hop for guaranteeing QoS and also adjusts the transmission time of each hop. With the proposed scheme, the QoS of each mobile station can be guaranteed and the channel utilization is increased. By using the simulation, we show that the throughput of the proposed scheme is higher than that of the scheme with fixed transmission time and the scheme not using relay stations. Moreover, since the proposed scheme not only allocates subchannels adequately but also adjusts the transmission time of each hop, the lowest outage rate can be achieved.

It is expected for multi-channel ad hoc networks to adopt cognitive radio (CR) technology since the CR technology can provide enough channels for high speed data transmission. These CR ad hoc networks should maintain accurate channel state information not only for protecting primary users (PUs) but also for obtaining enough channels. To cope with this, we propose a novel dissemination scheme for channel state information and an adjustment scheme of sensing priorities. According to the proposed dissemination scheme, a CR node can inform the PU presence or a request for a temporary quiet period on a channel for its sensing. When a CR node receives the PU presence on a channel, the CR node adjusts the sensing priority of a channel in order to confirm the availability of the channel by its own sensing. With these schemes, CR nodes cooperate together to accurately maintain the channel state information while each CR node grasps available channels in its own location. Using a simulation, we show that the proposed scheme provides more channels while guaranteeing the right of PUs. Since the proposed scheme uses only two bit channel map for informing the channel status and sends it on top of control packets, the performance gain can be achieved by low overhead.

In cognitive radio (CR) systems, the channel sensing scheme for detecting the presence of primary user directly affects the quality-of-service of CR users and primary user. In this letter, we propose a sensing scheme that consists of a series of consecutive energy detections followed by feature detection, where the energy detection time is much shorter than the feature detection time. With the proposed scheme, multiple energy detections decrease the feature detection due to false alarm and the overall channel sensing time. The performance evaluation using Markov analysis shows that the proposed scheme can heighten the maximum channel utilization of CR users, while maintaining the detection delay of primary user under a predefined value.