SAFH - Smooth Adaptive Frequency Hopping

In this paper we present the multi-frequency wireless communication protocol and adaptive frequency hopping algorithm that are designed specifically with the goal of increasing the reliability of the physiological data transmissions by medical body area networks (MBAN). We discuss the protocol structure and compare adaptive and non-adaptive frequency hopping algorithms used within the MAC protocol. We introduce the comprehensive simulation framework and provide the simulation results which clearly show the advantage of using adaptive frequency hopping in realistic hospital scenarios, dominated with inter-MBAN and Wi-Fi interferes.

In this paper, an adaptive and self-organizing spectrum allocation policy for ad hoc femtocells in two-tier networks based on usage of random frequency hopping is presented. As femto- and macrocells normally share the same frequency resources, the proposed approach is able to minimize InterCell Interference (ICI) in an adaptive manner. Each femto- and macrocell user chooses random carrier frequencies for transmission corresponding to a given probability density function (pdf). If the level of interference reaches a certain limit, which is typically the case for femtocell edge users, the probability density function of the carrier frequencies is changed in a way that it is quasi-orthogonal to the one of the macrocell users nearby. The changeover point between different probability density functions is realized in a self-organizing manner regarding the detected level of interference. Hence, the approach is able to adjust the trade-off between spectral efficiency and introduced interference during operation. We present analytical models for the Signal-to-Interference-and-Noise-Ratio (SINR), the Bit Error Ratio (BER) and the required transmission power of Orthogonal Frequency Division Multiple Access (OFDMA) femtocells applying adaptive random frequency hopping. The mobile radio channel is characterized by non-frequency selective Rayleigh fading and all results are verified by simulations implemented in MATLAB. In order to evaluate the improvements, the results are compared to systems using centralized orthogonal planning, systems using neither centralized nor distributed planning, and systems using static random frequency hopping. The comparison shows that adaptive random frequency hopping is capable of reducing the BER by a factor of 15 and the transmission power of femtocells by 17 dBm compared to systems where the macrocell user transmits in the same subbands as the femtocell user.

The authors propose an adaptive frequency hopping (AFH) algorithm, entitled robust adaptive frequency hopping (RAFH), for providing increased reliability of a wireless medical telemetry system (WMTS) under coexistence environment with non-medical devices. The conventional AFH scheme classifies channels into `good` or `bad` according to the threshold-based on`off decision by packet error rate (PER) measurement, and only uses good channels with a uniform hop probability. Unlike the conventional AFH scheme, RAFH is a novel technique, which solves a constrained entropy maximisation problem and assigns every channel a different hop probability as a decreasing function of the measured PER. The key novelty of RAFH over existing AFH schemes is that it reflects the relative channel condition by assigning non-uniform hop probabilities. By adopting constrained entropy maximisation, RAFH not only improves the average PER, but also reduces the PER fluctuation over time under a dynamic interference environment, both of which increase the reliability of WMTS. Through extensive simulation, we show that RAFH outperforms basic frequency hopping (FH) and the conventional AFH with respect to the PER under various scenarios of dynamic interference.

The main objective of this contribution is to introduce novel techniques for reducing the time taken from the reader to identify the frequency coded chipless radio frequency identification tags existed in the reader's interrogation region, system latency. The frequency scanning methodology, number of averaging for clutter removal, and hop duration are the 3 main parameters that significantly affect the overall system latency. Consequently, the adaptive frequency hopping (AFH) and adaptive sliding window (ASW) methodologies are proposed and proofed to be efficient for the chipless radio frequency identification systems from the latency and accuracy perspectives. Likewise, the performance of the designed AFH and ASW techniques are compared with the classical fixed frequency hopping methodology with a fine frequency step to validate the accuracy of the proposed methods. Moreover, 4 different coded frequency coded chipless tags are manufactured and used in the measurements. A real‐world testbed is designed including a software‐defined radio platform by which the proposed adaptive algorithms and traditional fixed frequency hopping methodology are implemented. All the measurements are performed in an indoor realized scenario, including the environmental effects. The experiments show that the proposed AFH combined with ASW algorithms significantly reduce the system latency by 58%.

Increase in the number of coexisting networks in license free Industrial, Scientific and Medical (ISM) band causes interferences for industrial automation, e.g., shop floors of manufacturing facilities. In order to ensure the reliability for automation networks, interference avoidance schemes are required. This paper proposes a novel Predefined Hopping Pattern (PHP) technique for frequency hopping in ISM band, which mitigates self-interferences and static interferers as well. This technique generates optimized frequency hopping sequences which ensure sufficient frequency diversity and frequency offset among the coexisting Bluetooth piconets and exploits transmission experiences for a particular frequency in eliminating interference. Simulation studies have shown that PHP has better collision avoidance rate than well known adaptive frequency hopping (AFH) and adaptive frequency rolling (AFR) schemes.

In wireless sensor networks, fault-tolerant and energy efficiency are two important topics. Some link failures may happen during data transmission. In this paper, we propose a fault-tolerant and energy efficient multipath-routing (FEEM) scheme aided with channel coding and interleaver, which is a cross-layer design approach. For multipath selection, we propose an energy and mobility-aware geographical multipath routing (EM-GMR) scheme, which is based on fuzzy logic system considering the remaining battery capacity, mobility, and distance to the destination node. Simulation results show that our EM-GMR scheme can extend the network lifetime longer than the original geographical routing scheme which only considers distance to the destination location, and this scheme can reduce the frame loss rate and link failure rate since mobility is considered. We demonstrate that even if certain paths have failures, our FEEM scheme is still able to recover the transmitted message from failure with very low bit error rate and frame error rate

A single-chip transceiver for wireless digital audio applications is realized in a 0.25 /spl mu/m BiCMOS process. To avoid the congested 2.4 GHz band and to achieve better penetration through walls, 863 and 915 MHz bands are adopted. The frame structure used in this design guarantees a low latency for streaming audio. Adaptive frequency hopping and antenna diversity ensure robust link management.

Increase in the number of coexisting networks in Industrial, Scientific and Medical (ISM) band cause interferences and demands for intelligent interference avoidance schemes. This paper proposes a novel Diversified Adaptive Frequency Rolling (DAFR) technique for frequency hopping in Bluetooth piconets which has the tendency to mitigate both the self and static interferences and ensures sufficient frequency diversity. Simulation studies validate the prospects for the proposed scheme to be used for frequency hopping networks against already existing techniques, Adaptive Frequency Hopping (AFH) and Adaptive Frequency Rolling (AFR).

Both research and practice have revealed that sensor devices running the 802.15.4 on their MAC layer may be competing for wireless communication on the 2.4 GHz ISM band with Wi-Fi, Bluetooth and other proprietary devices. Building upon a SunSPOT development platform, we evaluate the impact of channel hopping on interference mitigation in the 2.4 GHz ISM band and propose a channel hopping model that may be used to mitigate interference under different indoor WSN deployment scenarios. The results obtained by using a wireless sensor network where the sensor nodes are placed at different distances from an interference source and using different power levels agree with previous experimental works on interference in the 2.4GHz band and reveal that (1) channel hopping can improve the performance of WSNs when deployed in Wi-Fi collocating environments and (2) among the different parameters, the received signal strength indication (RSSI) is the most relevant for WSN performance evaluation in collocating Wi-Fi environments.

Subchannel allocation for the reverse link of multi-carrier code-division multiplex-access (MC-CDMA) system with adaptive frequency hopping (AFH) is investigated. An efficient allocation method that can be employed with the matched filter (MF) receiver as well as with multiuser detectors (MUDs) by exploiting the appropriate signal to interference and noise ratio (SINR) analysis is described. It is demonstrated that combined improved subcarrier allocation and the linear decorrelating detector (LDD) are very efficient in mitigating multiple-access interference (MAI), resulting in much larger system capacity than for a non-adaptive MC direct-sequence (DS)-CDMA system. This conclusion is confirmed for realistic fading channels with correlated subcarriers and imperfect channel state information (CSI) at the transmitter.

The paper presents a novel cooperative coding scheme using punctured serial concatenated convolutional codes (SCCC). We evaluate its performance in terms of frame error rate (FER) under two cooperation protocols: a decode-and-forward protocol in conjunction with automatic repeat request (ARQ), by which the relay sends an acknowledge bit (ACK) back to the source to indicate whether its data packet is correctly decoded; an adaptive amplify-and-forward protocol, where the amplifying relay node cooperates to forward the message only when the inter-user link gain is above a certain threshold. In both cases, the destination makes the decision on each transmitted bit after appropriately combining signals and performing iterative decoding. Simulation results show that SCCC-based cooperative coding achieves full spatial diversity and exhibits a similar FER performance to that using parallel concatenated convolutional codes (PCCC). At the price of channel feedback, the adaptive decode-and-forward algorithm demonstrates a relatively lower FER than the adaptive amplify-and-forward scheme. Amplified cooperation experiences severe performance degradation due to the inefficiency of repetition coding and error propagation, especially when the quality of the source-relay link deteriorates; however, if the threshold for carrying cooperation is carefully selected, the adaptive amplify-and-forward protocol can perform comparably to the decode-and-forward protocol.

Recently, low-density parity-check (LDPC) codes have attracted much attention especially in mobile communication system as a good simple error correcting codes achieving the data throughput near Shannon limit with lower complexity. In this paper, we design some regular LDPC codes with very low bit error rate (BER) and frame error rate (FER) according to the downlink parameters in TD-SCDMA system. We construct the downlink physical layer emulation model with matlab according to TD-SCDMA system's baseband signal disposing flow chart, and execute the link simulation with the performance analysis for some available channel codes and the designed regular LDPC codes based on the proposed emulation model. Passing the simulation, we obtain some conclusions that the regular LDPC codes are better than the convolutional codes or turbo codes in error rate performance.

In this paper, we propose a slotted adaptive frequency hopping and rolling (SAFHR) scheme to realize the dynamic spectrum access for cognitive radio (CR). First, based on the CR spectrum sensing result and the quadratic prime code, an adaptive frequency hopping scheme is designed to avoid the frequency static interference due to primary user (PU). Secondly, adaptive frequency rolling scheme is incorporated to combat the frequency dynamic interference in the presence of multiple CR nets. As a whole, the SAFHR algorithm aims to maximize the frequency spectrum utilization and frequency diversity for each CR user, and to accommodate as many CR users as possible. By employing a so called Instruments-in-MATLAB software defined radio (IM-SDR) platform, experimental results of the SAFHR scheme is demonstrated under the scenario with two CR nets, five CR nodes, and one PU.

As the wireless personal area network (WPAN) gets utilized by more individuals, the interference that collocated WPANs cause to each other, termed self-interference, will be one of the major sources that degrade WPAN's communication performance. The conventional adaptive frequency hopping (AFH) strategies avoid frequency-static interference by reducing the hopset, but this deteriorates the performance if there is also self-interference. In this paper, we propose dynamic AFH (DAFH) mechanisms that are concurrently employed by collocated WPANs in order to avoid the self-interference. With DAFH, WPAN adaptively self-allocates a subset of frequency channels to be hopped, such as to minimize the experienced interference. The packet error rate is the only input to the proposed mechanisms, which enables DAFH to also avoid interference from frequency-static interferer. The optimization of the throughput should not be the sole target of the DAFH because WPAN operates in unlicensed spectrum and arbitrary adaptation of the FH pattern may be harmful to proximate non-WPAN devices. Therefore, we define and adopt an etiquette rule to characterize the behavior of the collocated WPANs with DAFH as a single collective entity that produces interference. The operation of DAFH is robust and adaptive to the dynamic changes in the environment and to the noise errors in the channel. Simulation results show that DAFH significantly increases the throughput of the WPANs in presence of both self-interference and frequency-static interference, while the WPANs employ best effort to minimize changes in the overall interference pattern

Interference among different wireless devices operating in the same frequency band in a given region is always a problem. The prominent type of it is the interference between Wireless Local Area Network (WLAN) and Wireless Personal Area Network (WPAN) devices operating in the 2.4-GHz unlicensed band. Various techniques such as Adaptive Frequency Hopping (AFH) were proposed recently to deal with this interference. When wireless devices are deployed on plant-floors, the approach required to mitigate the interference can be slightly different so that the proposed techniques should be able to support data prioritisation in addition to managing the interference. This will allow the important data through even if the interference levels are higher than expected. For this to take place, channel assessment should be done first, to find out which channels are suffering interference, to what levels and how often. This aspect of channel assessment is considered here, for different combinations of interferers and power levels.