On the performance analysis of asynchronous FH-SSMA communications (original) (raw)
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On the Multiple Access Interference in a DS/FFH Spread Spectrum Communication system
1994
This paper describes the influence of Multiple Access (MA) interference on the performance of a hybrid Direct Sequence Fast Frequency Hopping SSMA Communication system. MA-interference plays an important role in determining the total interference in a Spread Spectrum system, especially in a non-cellular environment where Power Control is hardly possible. A cross correlation factor which is directly responsible for this interference is derived. Using this factor a comparison between slow and fast frequency hopping (both in combination with direct sequence) is made. At the end two sets of Kasami codes are selected which offer a good performance. 1 Introduction In recent years there has been much publications in the field of Spread Spectrum Communications, and more specific about Multiple-Access Interference ([1, 2] and others) . In this paper we deal with a hybrid Direct Sequence, Fast Frequency Hop system in a non-cellular environment. Therefore the correlation function changes and a...
IEEE Transactions on Vehicular Technology, 1999
In this paper, a multiple-access spread-spectrum communication system using binary frequency shift keying (BFSK) or M-ary frequency shift keying (MFSK) and noncoherent demodulation is considered. In contrast to previous work typically assuming that the frequency shift keying (FSK) tones are nonoverlapping after direct-sequence (DS) spreading, here we consider a spread-spectrum multiple-access (SSMA) system under the assumption that the DS spread signals of different FSK tones are only orthogonal over the information symbol duration. Consequently, the frequency band of a spread FSK tone may be fully or partially overlapping with the other spread signals. An estimate of the variance of the multiple-access interference is obtained by assuming that the phase angles and time delays of the received signals are mutually independent random variables, provided that random signature sequences are employed for spreading. On the basis of the above assumptions, the bit error rate (BER) of our DS spread-spectrum multiple-access (DS-SSMA) and that of our hybrid DS slow frequency-hopping spread-spectrum multiple-access (DS-SFH SSMA) systems using FSK modulation is analyzed, when the channel impairments are constituted by a combination of additive white Gaussian noise (AWGN) and multiple-access interference. From our analysis and the numerical results, we concluded that, for a given system bandwidth and for a certain value of M, the system's BER performance can be optimized by controlling the amount of overlapping and that the systems with optimized overlapping outperformed the systems using no overlapping. Index Terms-Frequency shift keying (FSK), slow frequency hopping, spread-spectrum multiple access. I. INTRODUCTION S PREAD-SPECTRUM multiple-access (SSMA) schemes have received considerable attention and have been proposed for use in a wide variety of applications, in order to mitigate the different problems encountered over different communications media [1], [2]. In addition to its multipleaccess potential, SSMA is also capable of combating various types of interferences. The most commonly used forms of SSMA are direct-sequence SSMA (DS-SSMA) [3], [4], frequency hopping SSMA (FH-SSMA) [5], [6], and hybrid DS slow frequency-hopping SSMA (DS-SFH SSMA) [7]-[11].
Exact Performance Analysis of Synchronous FH-MFSK Wireless Networks
IEEE Transactions on Vehicular Technology, 2000
In this paper, a new approach is presented to derive the exact bit-error-rate (BER) performance of frequency-hopping spread-spectrum (FHSS) wireless networks with noncoherent M-ary frequency-shift keying (MFSK) in additive white Gaussian noise (AWGN) and Rayleigh fading channels. The new approach has enabled an exact evaluation of the BER, regardless of the modulation order M or the number of interferers. Theoretical results validated by simulations have shown that system performance is dominated by the first two hits, which lead to an accurate and computationally efficient approximation for the AWGN channel case. The exact and approximated results are compared with the simulation and semianalytic results presented in the literature.
A Model of Interference in Frequency Hopping Wireless Multiple Access
2006
We analyze the channel blocking effect of multiple sources that access a shared pool of frequency channels in a fixed frequency hopping wireless system. One source is seen as the subject of interference from all the others who occupy a number of the available channels at any particular time, thus denying its use by the interfered one. The effect is quantified in terms of the probability that more than a specified number of channels are blocked at any time, given the numbers of available channels and interfering sources
Frequency Hopping Spread Spectrum: An Effective Way to Improve Wireless Communication Performance
Advanced Trends in Wireless Communications, 2011
To improve the performance of short-range wireless communications, channel quality must be improved by avoiding interference and multi-path fading. Frequency hopping spread spectrum (FHSS) is a transmission technique where the carrier hops from frequency to frequency. For frequency hopping a mechanism must be designed so that the data can be transmitted in a clear channel and avoid congested channels. Adaptive frequency hopping is a system which is used to improve immunity toward frequency interference by avoiding using congested frequency channels in hopping sequence. Mathematical modelling is used to simulate and analyze the performance improvement by using frequency hopping spread spectrum with popular modulation schemes, and also the hopping channel situations are investigated. In this chapter the focus is to improve wireless communication performance by adaptive frequency hopping which is implemented by selecting sets of communication channels and adaptively hopping sender's and receiver's frequency channels and determining the channel numbers with less interference. Also the work investigates whether the selected channels are congested or clear then a list of good channels can be generated and in practice to use detected frequency channels as hopping sequence to improve the performance of communication and finally the quality of service. The Fourier transform mathematical modules are used to convert signals from time domain to frequency domain and vice versa. The mathematical modules are applied to represent the frequency and simulate them in MATLAB and as result the simulated spectrums are analysed. Then a simple two-state Gilbert-Elliot Channel Model (Gilbert, 1960; Elliott, 1963) in which a two-state Markov chain with states named "Good" and "Bad" is used to check if the channels are congested or clear in case of interference. Finally, a solution to improve the performance of wireless communications by choosing and using "Good" channels as the next frequency hopping sequence channel is proposed. 2. Review of related theories 2.1 Spread spectrum Spread spectrum is a digital modulation technology and a technique based on principals of spreading a signal among many frequencies to prevent interference and signal detection. As
Diversity combining considerations for incoherent frequency hopping multiple access systems
IEEE Journal on Selected Areas in Communications, 1995
This paper studies the problem of diversity combining for frequency-hopped multiple access (FHMA) systems that operate in a mobile satellite environment characterized by frequency-nonselective Rician multipath fading. The modulation scheme considered is the incoherent 3f-ary frequency-shift keying (MFSK). The optimal diversity combining rule is derived under the assumptions that the number of active users (IC) in the system is known, all users are chip (hop)-synchronous, and each user employs a random FH address. We suggest practical implementations that are close approximations of the optimal rule and examine the effects of various system parameters on the resulting receivers. The bit error probability performance is analyzed and numerical examples are provided. The effects of the diversity order (L) , the signaling size (31) and unequal received powers are examined and related system design concerns such as system capacity and spectral efficiency are evaluated as well. I. INTRODUCTION REQUENCY-HOPPED multiple access (FHMA) tech-F niques have attracted considerable interests over the past two decades [1]-[13]. Cooper and Nettleton [ l ] first proposed an FHMA system with differential phase shift-keyed (DPSK) signaling for mobile communication applications. At about the same time Viterbi [3] initiated the use of MFSK for low-rate multiple access (MA) mobile satellite systems. Performance of FHMADPSK and MFSK systems in Rayleigh fading channels was analyzed by Yue [SI, [6]. Using the same Rayleigh fading assumption, Goodman er al. [4] studied the system capability of a fast FHMAMFSK system with a hard-limited diversity combining receiver. Bounds and approximations for the bit error probability of an asynchronous slow FHMA system with memoryless random hopping pattern were obtained by Geraniotis and Pursley [ 7 ]. The effect of unequal user power levels was analyzed by Geraniotis [8]. Assuming Markov hopping pattern, Cheun and Stark [9] analyzed the performance of both synchronous and asynchronous slow FHMA systems with BFSK signaling. Agusti [ 101 used a numerical integration method to evaluate the performance of both slow and fast asynchronous FHMA/BFSK communications. Recently, Fiebig [ 1 11 evaluated the spectrum
Performance Improvement of Wireless Communications Using Frequency Hopping Spread Spectrum
Int'l J. of Communications, Network and System Sciences, 2010
To improve the performance of short-range wireless communications, channel quality must be improved by avoiding interference and multi-path fading. Frequency hopping spread spectrum (FHSS) is a transmission technique where the carrier hops from frequency to frequency. For frequency hopping a mechanism must be designed so that the data can be transmitted in a clear channel and avoid congested channels. Adaptive frequency hopping is a system which is used to improve immunity toward frequency interference by avoiding using congested frequency channels in hopping sequence. In this paper mathematical modelling is used to simulate and analyze the performance improvement by using FHSS with popular modulation schemes, and also the hopping channel situations are investigated.
Efficient evaluation of the error probabilities of spread-spectrum multiple-access communications
IEEE Transactions on Communications, 1997
In this paper, we consider the performance of codedivision multiple-access (CDMA) communications. In particular, we will illustrate the use of a semianalytical approach which is combined with importance sampling for the efficient evaluation of the average bit-error rates (BER's) of asynchronous directsequence (DS) based CDMA systems employing binary phase shift keying (BPSK) modulation along with specific signature sequences for a variety of system parameters.