Non-Continuous OFDM Research Articles

Peak-to-Average Power Ratio Analysis for OFDM-Based Mixed-Numerology Transmissions

In this paper, the probability distribution of the peak to average power ratio (PAPR) is analyzed for the mixed numerologies transmission based on orthogonal frequency division multiplexing (OFDM). State of the art theoretical analysis implicitly assumes continuous and symmetric frequency spectrum of OFDM signals. Thus, it is difficult to be applied to the mixed-numerology system due to its complication. By comprehensively considering system parameters, including numerology, bandwidth and power level of each subband, we propose a generic analytical distribution function of PAPR for continuous-time signals based on level-crossing theory. The proposed approach can be applied to both conventional single numerology and mixed-numerology systems. In addition, it also ensures the validity for the noncontinuous-OFDM (NC-OFDM). Given the derived distribution expression, we further investigate the effect of power allocation between different numerologies on PAPR. Simulations are presented and show the good match of the proposed theoretical results.

Throughput Optimization in Cognitive Radio Networks Ensembling Physical Layer Measurement

Wireless networks are developed under the fashion of wider spectrum utilization (e.g., cognitive radio) and multi-hop communication (e.g., wireless mesh networks). In these paradigms, how to effectively allocate the spectrum to different transmission links with minimized mutual interference becomes the key concern. In this paper, we study the throughput optimization via spectrum allocation in cognitive radio networks (CRNs). The previous studies incorporate either the conflict graph or SINR model to characterize the interference relationship. However, the former model neglects the accumulative interference effect and leads to unwanted interference and sub-optimal results, while the work based on the latter model neglects its heavy reliance on the accuracy of estimated RSS (receiving signal strength) among all potential links. Both are inadequate to characterize the complex relationship between interference and throughput. To this end, by considering the feature of CRs, like spectrum diversity and non-continuous OFDM, we propose a measurement-assisted SINR-based cross-layer throughput optimization solution. Our work concerns features in different layers: in the physical layer, we present an efficient RSS estimation algorithm to improve the accuracy of the SINR model; in the upper layer, a flow level SINR-based throughput optimization problem for WMNs is modelled as a mixed integer non-linear programming problem which is proved to be NP-hard. To solve this problem, a centralized (1 − e)-optimal algorithm and an efficient distributed algorithm are provided. To evaluate the algorithm performance, the real-world traces are used to illustrate the effectiveness of our scheme.

Synchronization Sequence Generated by Modified Park Algorithm for NC-OFDM Transmission

The traditional schemes for the synchronization in the OFDM transmission, such as the Schmidl&Cox, Minn and Park algorithms, utilize the only every second or fourth subcarriers of the preamble symbol. This regular subcarrier occupation pattern does not meet the requirement of Non-Continuous OFDM (NC-OFDM) with the arbitrary spectrum holes free from the interference with the primary users. In this letter, a special synchronization sequence with non-continuous spectrum is constructed and can be evaluated at the receiver with a modified version of the Park algorithm. Our new synchronization concept not only complies with the traditional Park algorithm, but also has the considerable smaller sidelobes in the correlation function evaluated for the time synchronization, so that a higher synchronization detection probability is obtained.

A Novel Approach for PAPR Reduction of NC-OFDM System

Although Non-continuous OFDM (NC-OFDM) has the unique advantage of eliminating interference to authorized user in cognitive radio context, it also confronts a difficulty of reducing peak to average power ratio (PAPR) like other OFDM techniques. In this paper, carrier interferometry is proposed to apply in NC-OFDM system in order to reduce its PAPR using the construction feature of CI code itself. The coding principle of CI code is analyzed at first. Then NC-OFDM base-band system based on carrier interferometry (CI/NC-OFDM) is modeled. Theoretical analysis and matlab simulation results indicate that CI code can bring 3 dB lower PAPR reference with the same probability of exceeding some PAPR reference, compared with traditional NC-OFDM system. This method is effective and feasible and gets better BER performance as well.

A Novel Approach for PAPR Reduction of NC-OFDM System

Although Non-continuous OFDM (NC-OFDM) has the unique advantage of eliminating interference to authorized user in cognitive radio context, it also confronts a difficulty of reducing peak to average power ratio (PAPR) like other OFDM techniques. In this paper, carrier interferometry is proposed to apply in NC-OFDM system in order to reduce its PAPR using the construction feature of CI code itself. The coding principle of CI code is analyzed at first. Then NC-OFDM base-band system based on carrier interferometry (CI/NC-OFDM) is modeled. Theoretical analysis and matlab simulation results indicate that CI code can bring 3 dB lower PAPR reference with the same probability of exceeding some PAPR reference, compared with traditional NC-OFDM system. This method is effective and feasible and gets better BER performance as well.

Cognitive Non-Continuous Carrier Interferometry Orthogonal Signal Division Multiplex Transmission In Autonomous Vehicular Communications

In order to provide autonomous broadband communications among mobile vehicles, especially in an environment without fixed terrestrial vehicular base stations, a Cognitive Non-Continuous Carrier Interferometry Orthogonal Signal Division Multiplexing (Cognitive NCI-OSDM) transmission system is proposed in this paper. Specifically, Orthogonal Signal Division Multiplexing (OSDM) provides the system with high transmission capacity and good adaptability to variable mobile speeds. Carrier Interferometry (CI) codes make a system with limited Peak to Average Power Ratio (PAPR) of the transmitted signal. The incorporation of adaptive OSDM scheme provides an efficient approach to control Inter-Carrier Interference (ICI). Moreover, the non-continuous scheme is quite suitable in cognitive radio applications. Compared with traditional broadband OFDM-based transmission, such as Non-Continuous OFDM (NC-OFDM) in IEEE802.22, Cognitive NCI-OSDM has advantages of higher transmission capacity and spectrum efficiency, lower ICI, limited PAPR, adaptability to its cognitive environment and variable mobile speed. In this paper, the application system and the structure of Cognitive NCI-OSDM transmission is proposed for autonomous vehicular communications. Furthermore, the performance is evaluated, including the Bit Error Rate (BER), throughput, PAPR and Power of Inter-Carrier Interference (PICI). Finally, the system complexity, which is considered as the potential drawback when compared with an OFDM-based system, is investigated and confirmed to be controllable. The results reported in this paper show the promise of the proposed cognitive NCI-OSDM system and identify some possibilities for its future application in autonomous vehicular communications.