Optimal Power Allocation and Power Constraint in OFDM-Based Cognitive Radio Systems
Nguyen Van Vinh,
Pham Ngoc Thang
Issue:
Volume 3, Issue 4, August 2014
Pages:
49-55
Received:
29 July 2014
Accepted:
15 August 2014
Published:
30 September 2014
Abstract: Cognitive Radio (CR), which aims to improve spectrum utilization by accessing the spectrum originally licensed to a primary system, is a promising concept. In cognitive radio system based on orthogonal frequency division multiplexing (OFDM), the optimized algorithms for sub-carrier power allocation share the problems of complex iterative calculation and difficult realization. In this case, a sub-optimal power allocation algorithm based on power function distribution is proposed, to allocate power of in-band subcarrier of cognitive user according to the numerical characteristics of the power function by using a convex optimization numerical method under linear constraint. This algorithm has the advantages of fast calculation speed and easy realization, and reduces the interference for the authorized user brought by the power leakage of the in-band subcarrier of cognitive user appears in the out-of-band. MALAB simulation results show that the proposed scheme maximizes the in-band channel capacity of the cognitive user under the interference threshold of the authorized user and the comparison model the optimal relationship between the limited and unlimited transmit power capacity. Meanwhile, the maximum transmission rate of the existing power allocation scheme is increased within the same condition.
Abstract: Cognitive Radio (CR), which aims to improve spectrum utilization by accessing the spectrum originally licensed to a primary system, is a promising concept. In cognitive radio system based on orthogonal frequency division multiplexing (OFDM), the optimized algorithms for sub-carrier power allocation share the problems of complex iterative calculatio...
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Signal Shaping to Achieve OOK and PSK Co-Existence for Improved Optical Access Network Performance
Yasuyuki Okumura,
Maki Kato,
Katsuyuki Fujii
Issue:
Volume 3, Issue 4, August 2014
Pages:
56-62
Received:
28 September 2014
Accepted:
13 October 2014
Published:
20 October 2014
Abstract: This paper proposes a novel symbol mapping that uses signal shaping to alleviate the BER problem in constellation sharing with the use of phase information. This mapping solves one of the most critical problems; the small Euclid distance of the PSK symbols in the constellation sharing of OOK and PSK in Passive Optical Networks (PONs). Constellation sharing enables next generation PONs to overlay existing PONs with the use of an advanced modulation format based on the Digital Signal Processing (DSP) technology that well supports migration of the access network. The modulation format of Amplitude Shift Keying (ASK), Phase Shift Keying (PSK), and Quadrature Amplitude Modulation (QAM) can co-exist with the existing PONs, which utilize On-off Keying (OOK). The proposed mapping is designed to maximize the symbol distance assuming the co-existence of OOK and PSK. This paper shows the configuration, operation principles, and performance of the proposed signal mapping for OOK and PSK. It also shows that constellation sharing improves the BER characteristics of OOK and PSK in conjunction with an existing PON and the next generation technology.
Abstract: This paper proposes a novel symbol mapping that uses signal shaping to alleviate the BER problem in constellation sharing with the use of phase information. This mapping solves one of the most critical problems; the small Euclid distance of the PSK symbols in the constellation sharing of OOK and PSK in Passive Optical Networks (PONs). Constellation...
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