Frequency-hopping Multiple-access Systems Research Articles

Optimal Low-Hit-Zone Frequency-Hopping Sequence Sets With Wide-Gap for FHMA Systems Under Follower Jamming

This letter is concerned with tackling both of the multi-access interference (MAI) and the follower jamming (FJ) in frequency-hopping multiple-access (FHMA) systems via novel FH sequence (FHS) design. We consider low-hit-zone (LHZ) FHS which provides lower MAIs in quasi-synchronous FHMA systems but suffers from FJ attack. We introduce an improved LHZ-FHS with wide-gap (i.e., WG-LHZ-FHS) for the neighboring carrier frequencies so as to combat the MAI and the FJ. We first present a general method to generate new WG-FHS sets and then construct the first known WG-LHZ-FHS sets with optimal periodic Hamming correlation (PHC) properties. Besides, the error-rate performance of the constructed WG-LHZ-FHS set imposed in an FHMA system under FJ is investigated. The numerical analysis and the system simulation results indicate that the proposed WG-LHZ-FHS set provides the better error-rate performance to combat the FJ as well as satisfactory capability of MAI suppression due to its combined merits of WG and LHZ.

Decimated m-sequences families with optimal partial Hamming correlation

In quasi-synchronous frequency-hopping multiple-access systems where relative delays are restricted within a certain zone, low hit zone frequency-hopping sequences (LHZ FHSs) with favorable partial Hamming correlation properties are desirable. In this paper, we present a new class of LHZ FHS sets with optimal partial Hamming correlation based on t-decimation of m-sequence.

Construction of optimal low-hit-zone frequency hopping sequence sets under periodic partial Hamming correlation

In practice, when a frequency-hopping sequence (FHS) set is applied in a frequency-hopping multiple-access (FHMA) system, its periodic partial Hamming correlation (PPHC) rather than its periodic Hamming correlation (PHC) within the whole period is used to evaluate the system performance. Moreover, FHS sets with low hit zone (LHZ) can be well applied in quasi-synchronous (QS) FHMA systems in which some relative time delay among different users within a zone around the origin can be allowed. Therefore, it is very urgent to conduct research on LHZ FHS sets with optimal PPHC property in depth. In this paper, we first derive a new tighter lower bound on the maximum PPHC of an LHZ FHS set. Then we present a new class of optimal one-coincidence FHS sets. Finally we have a construction of LHZ FHS sets which can be optimal with respect to our new lower bound.

Generalized methods to construct low-hit-zone frequency-hopping sequence sets and optimal constructions

In a quasi-synchronous frequency-hopping multiple-access system, relative time delay between different users within a zone around the origin can be allowed. Therefore, frequency-hopping sequence (FHS) sets with low-hit-zone (LHZ) have attracted great interest of many related scholars. Moreover, on account of the limited synchronous time or hardware complexity, the periodic partial Hamming correlation (PPHC) plays a major role in determining the synchronization performance. In this paper, we first present three new generalized methods to construct LHZ-FHS sets via Cartesian product. Meanwhile, we pay our attention to the maximum periodic Hamming correlation (PHC) of the constructed LHZ-FHS sets in the first generalized method, and to the maximum PPHC of the constructed LHZ-FHS sets in the rest generalized methods. In addition, we also introduce five new classes of optimal LHZ-FHS sets based on these three generalized methods.

New sets of optimal low-hit-zone frequency-hopping sequences based on m-sequences

In quasi-synchronous frequency-hopping multiple-access systems where relative delays are restricted within a certain correlation zone, low-hit-zone frequency-hopping sequences (LHZ-FHSs) are commonly employed to minimize multiple-access interferences. In this paper, we present two classes of optimal LHZ-FHS sets with respect to the Peng-Fan-Lee bound, which are obtained from an m-sequence and its decimated sequence, respectively. The parameters of these LHZ-FHS sets are new and flexible.

New Constructions of Optimal Frequency-Hopping Sequence Sets with Low-Hit-Zone

The frequency-hopping sequence set with low-hit-zone (LHZ FHS set) is useful for eliminating multiple-access interference in quasi-synchronous frequency-hopping multiple access systems. In this paper, basing on Cyclotomy, the discrete logarithm function and the Chinese remainder theorem, we construct two classes of LHZ FHS sets which have new parameters not covered in the literature. It is proved that proposed LHZ FHS sets are optimal respectively with respect to the Peng-Fan-Lee bounds.

Theoretical lower bound on average periodic partial Hamming correlations of frequency‐hopping sequence set

Owing to the limited synchronisation time and hardware complexity of frequency-hopping multiple access (FHMA) systems, partial Hamming correlation of the frequency-hopping sequence (FHS) set applied by the FHMA system plays an increasingly important role in measuring the performance of the system. A new lower bound on the average periodic partial Hamming correlation which is tighter than the existing one in a particular case is introduced. The new lower bound includes some earlier theoretical lower bounds on the average Hamming correlation of the FHS set as special cases. A necessary and sufficient condition for obtaining optimality with regard to the new bound is also presented.

New Classes of Optimal Low-Hit-Zone Frequency-Hopping Sequence Sets by Cartesian Product

In quasi-synchronous frequency-hopping multiple-access systems where relative delays between different users are restricted within a zone around the origin, low-hit-zone frequency-hopping sequences (LHZ-FHSs) are employed as spreading sequences. In this paper, we study LHZ-FHS sets obtained from the Cartesian product of some FHS sets. We first derive an upper bound on the Hamming correlation of FHSs constructed by the Cartesian product. We also give a general method to construct LHZ-FHS sets by the Cartesian product. We then present four new classes of optimal LHZ-FHS sets. The first three classes of sets are obtained from the product of Solomon's FHS sets and Kumar's FHS sets. The last one is constructed by the product of FHS sets based on interleaving techniques. These LHZ-FHS sets have new parameters not covered in the literature.

New frequency-hopping sequence sets with optimal average and good maximum Hamming correlations

In frequency-hopping multiple-access systems, the average Hamming correlation (AHC) among frequency-hopping sequences (FHSs) as well as the maximum Hamming correlation (MHC) is an important performance measure. Moreover, each FHS is required to be balanced for its robustness against jamming or fading environments. In this study, the authors investigate FHS sets with optimal AHC and (near-)optimal MHC, whose FHSs are balanced. The authors first show that any uniformly distributed FHS set has optimal AHC with respect to the Peng-Niu-Tang bound. The authors also present two classes of FHS sets with optimal AHC and (near-)optimal MHC, whose FHSs are (perfectly) balanced. The authors then analyse the AHC of FHS sets constructed by interleaving techniques, and present some new FHS sets with optimal AHC and MHC, whose FHSs are perfectly balanced.

Performance of a Novel MFSK/FHMA System Employing No-Hit Zone Sequence Set over Rayleigh Fading Channel

To further suppress the multiple-access interference (MAI) in frequency-hopping multiple-access (FHMA) system, a novel kind of FH sequence set named as no-hit-zone (NHZ) sequence, is proposed for an FHMA system with M-ary FSK modulation (MFSK/FHMA) in this paper. Expressions for the decision variables are derived for the asynchronous MFSK/FHMA system with NHZ sequence set (MFSK/FHMA-NHZ) under a slow Rayleigh-fading channel model. For the special case of M=2, accurate analytic bit error rate (BER) is derived as a function of maximum relative delay D and the number of users K by a characteristic function method. The theoretical results validated by Monte Carlo simulations are used to investigate the dependence of the average BER on D and K. Comparison with the MFSK/FHMA system with Markov hit pattern (MFSK/FHMA-Markov) shows that MFSK/FHMA-NHZ system performs better than Markov hit pattern system as long as D is restricted in a certain range and further, the gain in the performance increases with increase in the value of K.

Performance Analysis of a Coherent FH-MA System Based on Latin Squares

Frequency hopping (FH) combined with coding is a popular technique in wireless communication applications. Motivated by the commercial system outlined in [1], this paper investigates the performance of a coherent FH multiple access (FH-MA) cellular system, where hopping patterns are constructed from latin squares. Some of the patterns carry pilot symbols, which the users track to estimate the channel on the data patterns and perform coherent detection. The latin squares construction enables us to analytically evaluate the bit error probability (BEP) over each data pattern, when convolutional codes are employed for error protection. The focus of our work is to precisely determine the effect that frequency and interference diversity, ensuing from FH, have on the coded performance. Regarding frequency diversity, it is shown that the performance can vary widely for different latin squares. Moreover, under pilot-assisted channel estimation, a performance tradeoff is observed, as an increasing frequency selectivity results in more diversity, but also more inaccurate channel state information. With respect to interference diversity, we analyze the performance when the interference power variations are perfectly known or ignored by the receiver. Our results confirm that interference tracking is important in harnessing the error correcting power of convolutional coding.

Performance Study of Asynchronous FFH/MFSK Communications using Various Diversity Combining Techniques with MAI Modeled as Alpha-Stable Process

In this paper, we present analytical bit-error probability expressions of an asynchronous fast frequency-hopped multiple-access system over fading channels with multiple-access interference modeled as alpha-stable noise. Various diversity-combining receivers over both Rician fading and Rayleigh fading channels are analyzed based on the Fourier-Bessel series. Numerical results under various environments show that the two non-linear diversity-combining methods significantly outperform the linear-combining receiver

Multicarrier On-Off Keying for Fast Frequency Hopping Multiple Access Systems in Rayleigh Fading Channels

We study multicarrier on-off keying (MCOOK) for fast frequency-hopping (FFH) multiple-access systems. The performance of a sub-optimum receiver is analyzed for Rayleigh fading channels and a closed form expression for bit error rate (BER) has been derived for the binary case. We find that the number of chips per symbol required to optimize the perfor- mance of the system varies from system to system. Comparison with FFH M-ary frequency shift keying (MFSK) shows that in the interference-limited region (large MAI), MCOOK performs better than MFSK and further, the gain in the performance increases with increase in the value of modulation index M.

Further combinatorial constructions for optimal frequency-hopping sequences

Frequency-hopping multiple-access (FHMA) spread-spectrum communication systems employing multiple frequency shift keying as data modulation technique were investigated by Fuji-Hara, Miao and Mishima [R. Fuji-Hara, Y. Miao, M. Mishima, Optimal frequency hopping sequences: A combinatorial approach, IEEE Trans. Inform. Theory 50 (2004) 2408–2420] from a combinatorial approach, where a correspondence between frequency-hopping (FH) sequences and partition-type cyclic difference packings was established, and several combinatorial constructions were provided for FHMA systems with a single optimal FH sequence. In this paper, by means of this correspondence, we describe more combinatorial constructions for such optimal FH sequences. As a consequence, more new infinite series of optimal FH sequences are obtained.

Generation and upper bound of one-coincidence sequences in frequency-hopping multiple-access systems

In frequency-hopping one-coincidence sequences, a specified distance between two adjacent symbols is usually employed to reduce the interference among sequences. We propose a new algorithm to construct one-coincidence sequence sets satisfying distance constraints. Compared to the conventional method, our approach provides a more flexible and general way to generate one-coincidence sequences of variable lengths. We also obtain a tighter upper bound for one-coincidence sequences of odd length, which is independent of code lengths.

Optimal Frequency Hopping Sequences: A Combinatorial Approach

Frequency hopping multiple access (FHMA) spread-spectrum communication systems employing multiple frequency-shift keying (MFSK) as data modulation technique are investigated from a combinatorial approach. A correspondence between optimal frequency hopping (FH) sequences and partition-type difference packings is first established. By virtue of this correspondence, FHMA systems with a single optimal FH sequence each are constructed from various combinatorial structures such as affine geometries, cyclic designs, and difference families. Combinatorial recursive constructions are also presented. Many new infinite series of optimal FH sequences are thus obtained. These new FH sequences are also useful in ultra wideband (UWB) communication systems.

A novel receiver for FHMA systems

A novel FH/MFSK receiver with additional partial correlators is proposed by means of side information for asynchronous frequency-hopping multiple-access (FHMA) systems in the presence of Rayleigh fading. Performance analysis is carried out and compared for both the novel and conventional receivers. One hop per symbol and Reed-Solomon (RS) coding are used in the FHMA systems. It is shown that the novel receiver performs much better than the conventional receiver for a wide range of signal to noise ratio. The capacity of the FHMA system with novel receivers is almost as twice as that of the system with conventional receivers.

Performance of one-hop/symbol FHMA for cellular mobile communications

This paper is concerned with the bit-error rate (BER) performance of a cellular one-hop/symbol frequency-hopping multiple-access (FHMA) system operating through a multipath Rayleigh fading channel. M-ary frequency shift keying modulation with noncoherent square-law envelope demodulation and Reed-Solomon (RS) coding is considered. The multiple-access and adjacent cell interference of the cellular FHMA system has been studied. In order to illustrate how sensitive both systems are to the near/far problem, performance of the FHMA system is compared with that of a direct-sequence code-division multiple-access system for an equal system bandwidth. Also, this paper investigates the effect of the values of frequency reuse factor (N) on the system capacity of the cellular frequency-hopping system.

Iterative multiuser detection for turbo-coded FHMA communications

An iterative receiver structure Is proposed for turbo-coded frequency-hop multiple access (FHMA) systems. In FHMA systems, the adjacent channel interference (ACI) is the major contributor of multiple access interference (MAI) if orthogonal hopping patterns are used. The ACI is a function of the tone spacings of the adjacent subchannels and the rolloff factor of the pulse-shaping filter. The calculation of the ACI for a square-root raised-cosine pulse-shaping filter in an FHMA system is presented in this paper. In addition, a low complexity iterative multiuser detector is developed to mitigate the degradation caused by ACI in the FHMA systems. The iterative receiver structure is based on a modified turbo decoding algorithm which makes use of the a posteriori log-likelihood ratio (LLR) information of the systematic bits to obtain the a posteriori information of the turbo-encoded parity bits. Iterations of the receiver/decoder are used as the mechanism to estimate and mitigate the MAI in the FHMA system. The properties of both soft and hard interference suppressors based on the modified turbo decoding algorithm are examined and an efficient recursive implementation is derived. Compared to maximum-likelihood multiuser detection, the proposed system is more practical and its complexity is only a linear function of the number of users. Simulation results show that the proposed iterative receiver structure offers significant performance gain in bandwidth efficiency and the required signal-to-noise ratio (SNR) for a target bit-error rate (BER) over the noniterative receiver structure. Moreover, the single user performance can be achieved when imperfect power control exists.

Difference threshold test for asynchronous BFSK frequency-hopped multiple access systems over Rician channels

A new side information generating mechanism, the difference threshold test (DTT), is proposed to improve the capacity of asynchronous frequency-hopped multiple access systems with binary frequency shift keying (BFSK) signalling over Rician fading channels. By adjusting the threshold in the DTT decision logic, optimum capacity can be obtained. This technique has proven to be advantageous compared with the conventional hard decision technique. For systems with signal-to-noise ratio ranging from 10 to 13 dB, this improvement can be >13%.