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Dynamic spectrum access (DSA) is proposed to deal with the growing shortage of available leased spectrum for wireless communication. We investigate a subset of DSA referred to as Dynamic Spectrum Leasing (DSL). At its core, DSL allows spectrum lease holders and cognitive radios to cooperate in an effort to leverage spatial diversity to improve channel utilization for both parties. In this research,...
We consider cooperative relaying systems employing amplify-and-forward (AF) distributed space-time block codes (DSTBCs) in which only backward channel-state-information (CSI) is known at relays and destination. For such systems, we study the particular case where, in order to minimize overhead, each of N relays decide independently whether to join the cooperation with basis on the received signal...
In many half-duplex cooperative systems, the direct formulation of the problem of finding the jointly optimal power and channel resource allocation that maximizes a weighted sum of the achievable rates can be difficult to solve. In this paper, we provide an efficient algorithm to solve this problem for a class of systems with convex achievable rate regions. For those systems, we show that the weighted-sum-rate...
WiMAX with femto cells is a cost-effective next generation broadband wireless communication system. Cognitive Radio (CR) has recently emerged as a promising technology to improve spectrum utilization by allowing dynamic spectrum access. There will be large potential benefits by applying the CR technique to WiMAX with femto cells, which are barely explored in the literature. In this paper, we propose...
We consider a system with a single base station communicating with multiple users over orthogonal channels while being assisted by multiple relays. Several recent works have suggested that, in such a scenario, selection, i.e., a single relay helping the source, is the best relaying option in terms of the resulting complexity and overhead. However, in a multiuser setting, optimal relay assignment is...
In this paper, we study the joint power and channel resource allocation problem for a multiuser F/TDMA decode-and-forward (DF) relay network under per-node power constraints and a total channel resource constraint. Our goal is to maximize the total throughput achieved by the systems. To that end, we formulate a joint power and channel resource allocation problem. We develop an iterative optimization...
Cooperative diversity is a promising technology for future wireless networks. In this paper, we consider a cooperative communication system operating in an amplify-and-forward (AF) mode with an imperfectly-known relay fading channel. It is assumed that a pilot symbol assisted modulation (PSAM) scheme with linear minimum mean square estimator (LMMSE) is used for the channel estimation. A simple and...
In this paper, we consider the dynamic subchannel allocation problem in OFDMA-based selective relaying networks. Our goal is to maximize the total throughput under the constraint of total transmission power, while guaranteeing fairness on subchannel occupation by multiple destination nodes (users). Since the optimal solution to this optimization problem is extremely computationally complex to obtain,...
The network planning aims to allow the maximum number of users and throughput in a network. This imposes a demanding performance requirement on the new relay-based architecture for mobile WiMAX, in which the capacity estimation is complex. In the network design process, where interference avoidance plays an important role, WiMAX supports reconfiguration of the subchannel usage with some frequency...
A two-hop relaying system where a source communicates with its destination through multiple relay nodes is studied for capacity maximization. Amplify-and-forward (AF) relaying is adopted for its simplicity. Taking the independent channel transfer function of different subcarriers and links into consideration, we formulate a resource allocation optimization problem for joint subcarrier assignment,...
In this paper we consider an OFDM (orthogonal frequency division multiplexing) transmission scheme with a relay. Symbols sent by the source may or may not be retransmitted during a second time slot by the relay, which is assumed to be of the decode-and-forward (DF) type. For each relayed carrier the destination implements maximum ratio combining. Assuming perfect CSI (channel state information) knowledge...
This paper explores the attributes, layering models and objective functions in cross layer designs for mobile ad hoc wireless networks by taking all the statistical characteristics and constraints from the physical (PHY) layer, media access control (MAC) layer and network (NET) layer into consideration. This paper reviews the entire network optimization across all the PHY/MAC/NET layers. At the PHY...
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