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We consider a set of cognitive nodes cooperatively sensing the activities of a primary system. Two cooperative protocols are proposed, where cognitive nodes opportunistically transmit to each others, and finally each node makes a decision based its own observations. In the first protocol (Protocol~1), a node relays the signal received from the primary to the other nodes only if the signal energy is...
A distributed space-time block code (STBC) based on a decode-and-forward (DF) protocol is proposed for two-path successive relaying. By making the two relay nodes transmit and listen in turn, the proposed distributed STBC can achieve not only full rate but also full diversity when the relay nodes can correctly decode the information symbols from the source node and when the inter-relay channels are...
SIP-based systems inherently have NAT traversal and QoS problems because of the limited IPV4 addresses and the best-effort service on the Internet. Using relay server to relay media stream can solve NAT traversal in SIP systems, but have less scalability. In this paper, we propose a SIP+P2P architecture for SIP-based systems to solve the above problems. In this novel architecture, light weighted SIP...
This paper discusses channel estimation in a cooperative orthogonal frequency-division multiplexing (OFDM) network in the presence of frequency offsets. Both the amplify- and-forward (AF) and decode-and-forward (DF) relaying modes are analyzed. In order to eliminate the multiple access interference (MAI), the maximum number of active AF and DF relays are [N/2L-1] and [N/L], respectively, where N is...
In wireless relay networks, the use of multiple antennas at both the source and destination can increase the capacity linearly with the number of antennas. In this paper, we investigate amplify-and-forward dual-hop MIMO relay networks without channel state information at the relay nodes, i.e., noncoherent case. In contrast to the conventional approach where the available power is equally distributed...
A distributed space-frequency (SF) coded cooperative technique is proposed for broadband wireless ad-hoc networks, where both the channels from the source node to relay nodes and from the relay nodes to the destination node are characterized by frequency-selective fading. Using an SF coding at the source node and a circular shift at each relay node, we propose a scheme that can achieve both cooperative...
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