1,723,554 research outputs found
Mellin Transform Based Performance Analysis of FFH M-ary FSK Using Product Combining Against Partial Band Noise Jamming
No full textWe propose a novel bit error ratio (BER) analysis technique for fast frequency hopping (FFH) assisted M-ary frequency shift keying (MFSK) using product combining (PC), when the channel is contaminated by partial band noise jamming (PBNJ). Exploiting the fact that the Mellin transform of the product of independent random variables is the product of their Mellin transforms, we derive the probability density function (PDF) of the PC’s output, when communicating in uncorrelated Rayleigh fading channels contaminated by PBNJ. Derivation of the PDF thus allows computation of the system’s BER. It is shown that the Mellin transform substantially simplifies the analysis of the PC receiver and facilitates for the first time the analysis of FFH-MFSK PC receiver for modulation orders of M > 2
Mellin Transform Based Performance Analysis of Fast Frequency Hopping Using Product Combining
No full textAbstract—In this contribution, we analyze the bit error rate (BER) performance of fast frequency hopping (FFH) assisted M-ary frequency shift keying (MFSK) using product combining. Product combining constitutes an efficient yet low-complexity scheme that may be employed in FFH-MFSK receiver to combat the detrimental effects of interference or jamming. We propose a novel approach to the analysis of this receiver system, which is based on the Mellin transform. Using this approach, the probability density function (PDF) of the product combiner output is expressed in a closed form. Based on the resultant PDF, the BER of the FFH-MFSK product combining receiver operating in Rayleigh fading channel is evaluated analytically. It is shown that the Mellin transform simplifies the analysis of the product combining receiver
Successive Interference Cancellation in Clipped and Product Combining aided FFH Multi-User Systems
No full textAbstract—In this contribution, we propose two successive interference cancellation (SIC) schemes for a fast frequency hopping (FFH) multiple access (MA) system using M-ary frequency shift keying (MFSK) and invoking multi-user detection (MUD). One of the proposed schemes invokes clipped combining, while the other scheme employs both product combining and clipped combining. The SIC schemes are adapted from a scheme proposed by U.-C. Fiebig in 1996. The basic principle of the SIC schemes is that detection is carried out in multiple stages and during each stage, only the most reliable symbols are detected. In subsequent stages, the interference contributed by the already detected symbols may be removed. The performance of the proposed schemes is evaluated and compared to that of Fiebig’s scheme, when the FFH-MFSK system operates in a Nakagamim fading MA channel. The simulation results demonstrate that the proposed schemes attain a better bit error rate performance than Fiebig’s scheme
Fast Frequency-Hopping Dynamic Multiple-Access for Cognitive Radios: Detection and Performance
No full textThis paper proposes a fast frequency-hopping -ary frequency-shift keying dynamic multiple-access (FFH/MFSK DMA) scheme for application in cognitive radios (CRs). For characterising the performance of the FFH/MFSK DMA systems, primary users (PUs) are assumed to become active according to a Poisson process. In our FFH/MFSK DMA system, the noncoherent majority vote assisted single-user detector (MV-SUD) or noncoherent iterative interference cancellation assisted multiuser detector (IIC-MUD) is employed, in order to implement low-complexity detection. The bit error rate (BER) and throughput performance of the FFH/MFSK DMA systems are investigated, when assuming communications over Nakagami- fading channels. Our studies show that the FFH/MFSK DMA is a high-flexibility scheme for application in CRs. It is capable of attaining a substantial throughput without degrading the quality-of-service (QoS) of primary radios (PRs)
Iterative Detection of Three-Stage Concatenated FFH-MFSK
No full textSerially concatenated and iteratively decoded Irregular Variable Length Coding (IrVLC) combined with precoded Fast Frequency Hopping (FFH) M-ary Frequency Shift Keying (MFSK) is considered. We employ EXtrinsic Information Transfer (EXIT) charts to investigate the 3-stage concatenation of the FFH-MFSK demodulator, the rate-1 decoder and the outer IrVLC decoder. The proposed joint source and channel coding scheme is capable of operating at low Signal-to-Noise Ratio (SNR) in Rayleigh fading channels contaminated by Partial Band Noise Jamming (PBNJ). The IrVLC scheme is comprised of a number of component Variable Length Coding (VLC) codebooks employing different coding rates for encoding particular fractions of the input source symbol stream. These fractions may be chosen with the aid of EXIT charts in order to shape the inverted EXIT curve of the IrVLC codec so that it can be matched with the EXIT curve of the inner decoder. We demonstrate that using the proposed scheme an infinitesimally low bit error ratio may be achieved at low SNR values
Mellin-Transform-Based Performance Analysis of FFH -ary FSK Using Product Combining for Combatting Partial-Band Noise Jamming
No full textMolecular dynamics simulations reveal structural coordination of Ffh-FtsY heterodimer
No full textMolecular dynamics simulations reveal structural coordination of Ffh-FtsY heterodime
Synthesis Report for Female Food Heroes (FFH) Engagement Strategy in Nigeria & Ethiopia
No full text
This synthesis report consolidates findings from two external evaluations of Oxfam’s Female Food Heroes (FFH) initiative in Nigeria and Ethiopia, conducted in 2024–2025. Since its launch in 2012, the program has celebrated and empowered women smallholder farmers, enhancing their leadership, visibility, and contributions to food security, gender justice, and rural livelihoods. The evaluations found that FFH has positively impacted awardees by improving self-confidence, economic opportunities, and policy engagement, while also challenging stereotypes about women in agriculture.
However, the report highlights persistent gaps that undermine the long-term sustainability and collective impact of the initiative. These include weak alumni engagement structures, limited staffing and financial resources, underdeveloped monitoring, evaluation and learning (MEL) systems, and entrenched cultural and structural barriers that restrict women’s leadership in agriculture. The program’s reliance on spotlighting individual champions has not been sufficient to overcome systemic inequalities without stronger collective action and gender-transformative approaches.
The report calls for a revitalized FFH model that invests in formal alumni networks, dedicated staffing, flexible funding, gender-transformative strategies, and robust MEL systems. Scaling up media engagement and linking alumni voices to national and regional policy dialogues are also key to sustaining impact. By embedding these recommendations, FFH can evolve into a more resilient, scalable, and transformative platform that empowers women farmers, strengthens inclusive food systems, and advances gender equality across Africa.
You can find case study on Nigeria here and the case study on Ethiopia here. 
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Iterative Decoding and Soft Interference Cancellation in Fast Frequency Hopping Multiuser System Using Clipped Combining
No full textIterative decoding (ID) aided fast frequency hopping (FFH), M-ary frequency shift keying (MFSK) using clipped combining in multiple access (MA) channels is investigated. All users’ data are convolutionally encoded and the encoded bits are interleaved and converted to M-ary symbols, which are transmitted using FFH-MFSK modulation. The soft metrics to be passed from the demodulator to the decoder are derived assuming a Rayleigh fading channel. We also propose a novel multiuser detection (MUD) scheme which employs joint soft decoding as well as successive interference cancellation (SIC), the receiver exploiting the soft information fed back by the decoder to the demodulator in order to cancel the interference imposed by reliable symbols. Our simulation results show that the proposed scheme is capable of combatting multiuser interference and outperforms the conventional ID by about 3dB
Fast Frequency-Hopping Dynamic Multiple-Access for Cognitive Radios: Suboptimum Noncoherent Maximum-Likelihood Multiuser Detection
Full text linkWe propose a novel dynamic multiple-access (DMA) scheme for application in cognitive radios (CRs). This DMA scheme is implemented by fast frequency hopping with -ary frequency-shift keying (FFH/MFSK) associated with suboptimum noncoherent maximum-likelihood multiuser detection (ML-MUD). In our studies, we assume that the primary users (PUs) and the cognitive radio users (CRUs) are operated in the interweave paradigm. The PUs activate to communicate according to a Poisson process and the duration of an activation obeys exponential distribution. The bit error rate (BER) and throughput performance of the dynamic FFH/MFSK systems are investigated by simulations, when assuming communications over Rayleigh fading channels. Our studies and simulation results demonstrate that the dynamic FFH/MFSK with suboptimum noncoherent ML-MUD constitutes one of the promising candidates for DMA in CRs. It has low-complexity and employs high-flexibility for DMA and seamless transition between different frequency bands
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