Error Performance of FH Wireless LANs in DS and Tone Interference

Frequency hopping systems have been widely used in military communications to prevent hostile jamming, interception and detection. In traditional frequency hopping (FH) systems, the transmitter hops in a pseudo-random manner among available frequencies according to a pre- specified algorithm, and the receiver operates accordingly in exact synchronization with the transmitter's hopping pattern. In multiple access systems, a collision may happen when more than one users transmit in the same frequency band simultaneously. Two major limitations with the conventional frequency hopping systems are: strict requirement on frequency acquisition/synchronization, and very low spectral efficiency due to inefficient utilization of the available bandwidth. In this paper, we introduce a new concept collision-free frequency hopping (CFFH). Based on the OFDM framework and the secure subcarrier assignment algorithm, the proposed CFFH system can achieve high information capacity through collision-free multiple access, and can successfully resolve the strict synchronization limitation. At the same time, as each user still transmits through a pseudo-random frequency hopping scheme, CFFH can maintain the inherent anti-jamming, anti-interception security features of the conventional FH system. The proposed CFFH scheme can be used for both civilian and military applications where secure high speed information transmission is needed.

Robust frequency hop (FH) waveforms perform forward error correction coding across multiple time-frequency slots (referred to as hops). The typical assumption for FH receivers is that only one signal per hop can be recovered by the demodulator. In terms of multiple-access interference (MAI), this typically leads to one of two design choices for FH systems. One option is to mitigate MAI statistically; namely, through the use of nonorthogonal hopping. With nonorthogonal hopping, from time to time multiple users' signals occupy the same hop. Because coding is performed across many hops, this interference does not necessarily preclude correct decoding, and the corresponding performance degradation may be deemed acceptable. The advantage of this approach is that one user's hopping sequence does not depend on the hopping sequence of one or more of the other users, which reduces the required level of coordination among the users. The second option is to completely avoid MAI through the use of orthogonal hopping sequences. Such sequences ensure that at most one user signal is present in each hop, which complements the capabilities of a single-user detector, but additional coordination is required among the users.

A new series of frequency hopping (FH) sequences, designated as n-order prime sequences, are constructed based on the multiplication of extension Galois fields GF(P n ) with P an odd prime and integer n≥2. The result provides more sequences, longer period and more families compared with prime sequences. And after partition, FH sequences in the same group show ideal Hamming auto- and cross-correlation properties.

Based on chaotic map, a new method for generating chaotic frequency-hopping (FH) sequences is proposed. The real-valued trajectory' of chaotic system is first encoded to binary sequences by means of a quantization function, and then we can obtain the chaotic FH sequences by reshaping bits of these binary sequences. Theory analysis and performance experiment results show that this sequence is Bernoulli sequence and its Hamming correlation is shown to be Poisson distributed. It is comparable to other FH sequences on the properties of uniform distribution, Hamming correlation and linear complexity when they have the same number of frequency slots and the same period, but its map iterative number has reduced largely. Consequently, more FH sequences can be generated by this method and they are suitable for FH code-division multiple-access systems.

Inter-vehicle communication is an essential part of any intelligent transportation system (ITS). It allows vehicles to share surrounding road traffic information to support safe driving and road traffic management. Current systems use spread spectrum (SS) techniques: direct sequence (DS) or frequency hopping (FH). This paper proposes an implementation of a hybrid system in which DSSS and FHSS techniques are combined to provide performance and scalability improvements over a system that uses either of the SS techniques. Also this paper presents a theoretical analysis showing the improvement in the overall system capacity of the proposed system and the results of the computer simulations conducted. The results show that given an equal bandwidth, the hybrid system out performed the DS or FH systems. It showed superior bit error rate (BER) performance and scalability.

In frequency hopping (FH) sequence design, the wide gap is an important performance indicator. In this paper, the average Hamming correlation of wide gap FH sequence (WG-FH sequence) sets with low hit zone, which has not yet been reported previously, is studied. A lower bound on the average Hamming auto-correlation and the average Hamming cross-correlation of low-hit-zone FH sequence sets is firstly derived. The new lower bound includes the bound for conventional FH sequence sets derived by Peng et al. as a special case. Then a construction of WG-FH sequence sets with multiple low hit zones is presented, which are optimal by the new bound for these low hit zones. Finally, another class of optimal WG-FH sequence sets with multiple low hit zones is presented, which have larger wide gap.

In this paper, we derive a new bound on maximum nontrivial Hamming correlation of frequency hopping (FH) sequences from the Singleton bound in error correcting code literature, and we discuss the relation between the new bound and the known ones on FH sequences. Further, we construct two classes of FH sequences from punctured Reed–Solomon codes and one class of FH sequences from polynomial functions, which meet the new bound.

The integrated design for both radar and anonymous communication has drawn more attention recently since wireless communication system appeals to enhance security and reliability. Given the frequency hopping (FH) communication system, an effective way to realize integrated design is to meet the spectrum compatibility between these two systems. The paper deals with a unimodular sequence design technique which considers optimizing both the spectrum compatibility and peak sidelobes levels (PSL) of auto-correlation function (ACF). The spectrum compatibility requirement realizes anonymous communication for the FH system and provides this system lower probability of intercept (LPI) since the spectrum of the FH system is hidden in that of the radar system. The proposed algorithm, named generalized fitting template (GFT) technique, converts the sequence optimization design problem to a iterative fitting process. In this process, the power spectrum density (PSD) and PSL behaviors of the generated sequences fit both PSD and PSL templates progressively. Two templates are established based on the spectrum compatibility requirement and the expected PSL. As noted, in order to ensure the communication security and reliability, spectrum compatibility requirement is given a higher priority to achieve in the GFT algorithm. This algorithm realizes this point by adjusting the weight adaptively between these two terms during the iteration process. The simulation results are analyzed in terms of bit error rate (BER), PSD, PSL, and signal-interference rate (SIR) for both the radar and FH systems. The performance of GFT is compared with SCAN, CAN, FRE, CYC, and MAT algorithms in the above aspects, which shows its good effectiveness.

This paper makes preliminary steps at exploring a novel application of cognitive radios (CRs) for reliable satellite communications. We propose the use of dynamically adjusted frequency hopping (FH) sequences for satellite transmissions. Such sequences are more robust against smart eavesdropping and targeted interference than fixed FH sequences. In our approach, FH sequence is adjusted according to the outcome of out-of-band sensing, carried out by a CR module that resides in the satellite itself or at the receiving ground station. Our protocol, called OSDFH, relies on exploiting the spectrum sensing capabilities of CRs for proactive detection of channel quality. We analyze the characteristics of the proposed OSDFH using a finite state Markov chain (FSMC) framework. Level crossing rate (LCR) analysis is used to determine the transition probabilities of the Markov chain. These probabilities are then used to measure the "channel stability," a metric that reflects the freshness of sensed channel interference. We use simulations to study the effects of different system parameters on the performance of our proposed protocol.

The past decades of development of underwater acoustic communications (acomms) have produced many advances in physical layer algorithms, in hardware and firmware capabilities tailored to the underwater environment, and in concepts for networked sensors. In general, most deployed systems and most conceptual networks have assumed a strictly half duplex channel wherein all links must be shared over a bandwidth-constrained channel. This has led to an almost universal insistence on avoiding collisions among receptions, which might be achieved by TDMA schemes or by adapting other network concepts derived from (RF) mobile communications technology. For long duration deployment of underwater systems, any requirement for tight TDMA access forces the modem developer to use power-hungry high accuracy clocks, thus quickly draining precious battery resources. While networked acknowledgements at the speed of light make perfect sense, the latency of the acoustic channel demands excessive consumption of time to enable the network simply to know that a message has ultimately been received. There are many studies which attempt to devise minimally intrusive ARQ approaches, but ultimately acknowledgements in some form are necessary. In this paper we revisit some older technology, combine it with new capabilities in hardware, and add some signal processing insights to support discussion of a back channel providing asynchronous, multi-access command and control of a network, with supervised use of a second acoustic channel for high data rate, priority, and/or large data volume transfer. The two contending modulation schemes for asynchronous signalling have long been frequency hopping and direct sequence (DS), both of which are (typically) non-coherently processed spread spectrum methods. For a given bandwidth and data rate in additive white Gaussian (AWGN) the performance of the two is virtually identically. However, in a dynamic, multipath-rich environment, the well-recognized requirement for power control for DS signalling, given the constraint of channel latency, makes FH signalling the preferred choice. Justification for this is found throughout the development of the (NATO) JANUS underwater protocol, which itself is a frequency hopping scheme. In the context of power control, it is possible to transfer the burden of interference mitigation from the multiple transmitters to the receiver at a single modem by judicious spectral whiting and clipping of too loud interference. This not only compensates for variable strength transmissions, but for external sources of interference. Our anecdotal experience shows that a single modem operating this way in an 8 kHz band at a center frequency of 39 kHz can readily accommodate asynchronous reception of at least five messages from irregularly-spaced transmitters. Hardware is now available to support integration of two or more modems into a single system, especially to provide dual frequency acomms. From the hardware/system perspective the main constraint is providing sufficient spectral isolation between the two channels. In our experience, this requires physical separation and spectral filtering between the transducers to overcome high power sidelobe interference which is at best 50 dB below the level of the primary channel. However, given that these constraints are accommodated, we are positioned to consider development of media access control (MAC) and networking systems that benefit from this full duplex approach. We describe an FH signal as defined for the JANUS application and show how it can be used in multi-access applications. We provide an overview of the physical infrastructure we deploy to accommodate the two frequency bands, and we describe a possible network infrastructure utilizing these capabilities. Our goal is to promote discussion of alternatives to conventional half duplex TDMA and conflict avoidance acomms schemes.

The purpose of this paper is to introduce the basic concepts of code division multiple access (cdma) to those who are not familiar with the subject area. It briefly covers the two most important forms of spread spectrum modulation, frequency hopping (fh) and direct sequence (ds), before concentrating on cdma based on ds. The jamming margin equation is developed to give an estimate of spectral efficiency in a single-cell environment. Then the improvements in spectral efficiency based on coding and voice activation are discussed. The main advantages of cdma over more conventional access techniques in the cellular environment are discussed. Finally, the main limiting factors on cdma capacity, i.e. hand-off and power control are discussed.

Chapter 16 - Special Purpose Receivers

In application, frequency-hopping (FH) communication system often suffers various interferences, such as single frequency narrow-band interference, partial band blocking interference and tracking interference, and so on. For all that, by using optimal Wide-Gap (WG) FH sequences, FH communication system can significantly improve the anti-interference performances. In this paper, the relations between WG FH sequence theoretic bounds published in the journal IEEE Access (Peihua Li et al., 2019) are first made clear, and then five types of generalized methods are presented to design new classes of WG FH sequence sets. It is shown that all designed WG FH sequence sets are optimal according to the bound derived by Peihua Li <italic>et al.</italic> And by selecting appropriate original sequence sets, many of the optimal WG FH sequence sets can be obtained by our methods. Most importantly, these WG FH sequence sets have new parameters that are not covered in the literature.

We propose a new spread spectrum (SS) system based on continuous phase modulations (CPMs). The main idea is to exploit the sequence of modulation indices of a multi-h CPM as a frequency hopping (FH) sequence. We will show how the sequence of indices impacts on the CPM signal bandwidth and power spectral density (PSD). Spectral spreading, flatness and smoothness can be easily achieved by an appropriate choice of the maximum value of the modulation index and of the length of the index sequence. We will show that a CPM-based spread spectrum system achieves an overall spectral efficiency larger than that of a single-user single-h CPM signal even when a single-user detector is employed at the receiver.

Differential frequency hopping communication system as a new concept of communication systems has become an important development direction of the current shortwave confidential communications. In this paper, on the DFH communication mechanism based on the establishment of a function, the function design m sequences designed based on HHT transform DFH signal detection design, experimental results show that this scheme can effectively achieve DFH Signal generation and detection of a communication system. KEYWORD: DFH; G function; HHT transform; detection International Conference on Social Science, Education Management and Sports Education (SSEMSE 2015) © 2015. The authors Published by Atlantis Press 710 unknown Research hopping signal detection method differential signal parameters under the conditions. 2 BASIC PRINCIPLE OF DFH The concept stems from a DFH enhanced 1995 Sandes company developed Spread Spectrum (Correlated Hopping Enhanced Spread Spectrum, called CHESS) system, CHESS radio with DFH (Differential Frequency Hopping, referred DFH) as the core technology to achieve high-speed frequency hopping, hopping speed up to 5000 hops / sec transfer rate up to 19.2kbit / s, and anti-jamming, strong anti-fading capability. DFH has two key technologies, namely signal detection technology design technology and the receiving end of a differential frequency hopping pattern. DFH system uses a new technology system, its design is based on the hopping pattern called a mathematical relationship of G function, at the sending end, the frequency value of the current time n f is by the frequency value 1 n f  and the current time data symbols n X decision. An implicit difference equation is expressed as [8]: ) , ( 1 n n n X f G f   (1) G(∙)indicates a function transform relations, referred to function. Its frequency, data transformation relationship can be expressed in the form of a diagram of transformation function in Figure 1. Fig.1 The G function transform Differential frequency hopping communication system, the receiver uses a variety of new technology to receive broadband, digital signal processing. At the receiving end, by the broadband receiving digitized, characterized by the FFT analysis of all signals within the bandwidth of the frequency hopping, 1 n f  and n f is determined. Restore the data transmitting side by the inverse transform function, namely: ) , ( 1 1 n n n f f G X    (2) Wherein G -1 denotes inverse transform function of G, which requires the function G must have reversible. Its inverse transform relationship can be expressed in the form of a diagram 2. Fig.2 The inverse G function transform 3 G FUNCTION ALGORITHM PRINCIPLE In the differential frequency hopping, G function is a specific frequency transfer function, can be seen as a directed graph, directed graph node represents a frequency point of each frequency set, each node separates 2 f  branches, BPH representative of the number of bits per hop transmission, also called the fan-out coefficients. Are marked on each bifurcation current information symbols to the set of frequencies containing frequencies of 64, for example, when each hop transmission 1bit, each node has two bifurcated (0,1). BPH transmission bit stream bits per symbols constituting a transmission symbol stream according to a given differential frequency hopping sequence with a frequency corresponding to the generated map. 3.1 1 bit G function design G function design approach are many, including those based on the theory of congruence G function design, based on the state of the shift register design function G, G function m-sequence-based design and so on. In this selection of designs based on G function m sequences. Algorithm is described as follows: Step1 First reads the data n X to be transmitted, the data is encoded, the encoded data n d is calculated.