Abstract
In this paper, we propose a new scheme to improve the performance of an LDPC-coded OFDM based cognitive radio (CR) link by applying adaptive power weights. To minimize estimation errors of detected signals in all the CR subcarriers, power weights are allocated to the CR subcarriers at the secondary transmitter. Some constraints for the power weights are considered, such as keeping the interference power introduced by the CR to primary users below a given interference threshold and also keeping sum of transmission powers in all CR subcarriers within a total transmission power. The LDPC decoder applies these power weights in the Log Likelihood Ratios (LLRs) used in message passing scheme at the secondary receiver to achieve more reliable communications. So, the received signal in each CR subcarrier will be decoded with the knowledge of transmission power weights, which come from the cognitive feedback channel without additional cost. Simulation results demonstrate that our proposed scheme achieves a lower bit error rate and a higher transmission rate compared with those of the same scheme without applying power weights.
Highlights
Transmission of data over wireless communication systems grows rapidly
We propose a new scheme to improve the performance of an Low Density Parity Check (LDPC)-coded Orthogonal Frequency Division Multiplexing (OFDM) based cognitive radio (CR) link by applying adaptive power weights
We propose an iterative scheme for message passing in the LDPC decoder, while in the secondary transmitter, power weights for each OFDM subcarrier is considered to improve both bit error rate (BER) and throughput of the CR
Summary
Transmission of data over wireless communication systems grows rapidly. Cognitive Radio (CR) systems have made it feasible to utilize the frequency spectrum, dynamically and efficiently. LDPC codes can improve bit error rate (BER), considerably in fading channels by applying appropriate decoders [3]. Use of message passing scheme for decoding of LDPC codes is considered jointly with cooperative spectrum sensing, which is discussed in [6]. We propose an iterative scheme for message passing in the LDPC decoder, while in the secondary transmitter, power weights for each OFDM subcarrier is considered to improve both BER and throughput of the CR. Since there is a cognitive feedback channel between secondary transmitter and secondary receiver, we apply these power weights in the LDPC decoder as used in the secondary transmitter This causes improvement in the performance of the CR for error corrections.
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