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ABSTRACT: The Non-Contiguous (NC) OFDM is a promising candidate transmission scheme in cognitive radio (CR) system. However, the NC available sub-carriers bring new challenges on system design. The pattern of known signals in frequency domain, such as preamble and pilots is vulnerable by NC subcarriers. Several recent researches have studied synchronization issues for NC-OFDM. In this paper, we study the comb-type pilot channel estimation and interpolation for NC-OFDM transmission. Firstly, three types of channel estimation strategies are revealed. And then, we proposed the Shift Pilot (SP) scheme by inserting some punched pilots on other available sub-carriers of data at transmitter. A preprocessor is introduced between channel estimation and interpolation at receiver to estimate channel values of punched pilots. The enhanced strategy achieves better performance with a reasonable complexity in NC-OFDM.
Wireless Communications, Networking and Mobile Computing, 2009. WiCom '09. 5th International Conference on; 10/2009
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ABSTRACT: To avoid interferences, network-wide quiet periods (QPs) are usually scheduled for the purpose of channel sensing in cognitive radio (CR) networks. The recent IEEE 802.22 draft standard requires that adjacent base stations (BSs) should synchronize their QP in scheduling. However, we find that the current design is incomplete in handling the dynamic of synchronized QP. The problem is that BSs cannot handle the decreasing of synchronized QP duration. This can cause the wastage of network resources. To solve the problem, we propose a synchronization counter (SC)-based method in this paper. With the method, the BSs can accurately synchronize the QP when the duration varies. It makes the synchronization more accurate and thus saves the network resources. We have verified the proposed scheme with simulation and provide the performance results that reveal the basic features of network-wide QP synchronization.
Wireless Communications, Networking and Mobile Computing, 2009. WiCom '09. 5th International Conference on; 10/2009
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ABSTRACT: Cognitive radios can significantly improve spectrum efficiency by using locally available spectrum. The efficiency, however, depends heavily on their transceiver design. In particular, being able to use non-contiguously aligned spectrum bands simultaneously is a critical requirement. Prior work in this area requires a control channel so that transmitter/receiver pairs can synchronize on their spectrum usage patterns. However, this approach can suffer from high cost and control congestion. In this paper, we propose an in-band solution for informing receivers the spectrum usage patterns. By judiciously designing packet preambles, we embed the spectrum usage patterns in each data packet. Using the legacy 802.11 preamble structure, we focus on choosing the appropriate preamble sequences to maintain reliable packet detection in the presence of noise and interference. We verify our design using simulation and show that it can lead to reliable packet transmissions comparable to those of contiguous spectrum usage. We also identify the impact of interference on our design and propose refinements to choose the preamble sequence using information on the interference.
Wireless Communications and Networking Conference, 2009. WCNC 2009. IEEE; 05/2009
