Hopping Pattern Research Articles

Multitone-Hopping CDMA Using Feedback-Controlled Hopping Pattern for Decentralized Multiple Access

We propose multitone-hopping code-division multiple access (MH-CDMA) using a feedback-controlled hopping pattern (FCHP) (FCHP/MH-CDMA). In the FCHP/MH-CDMA, part of the filter coefficients of an adaptive finite-duration impulse response (FIR) filter receiver are fed back to a transmitter, in which they are used as an updated hopping pattern. Each chip of the updated hopping pattern consists of plural tones. As a result, it is shown that the FCHP/MH-CDMA provides us with an excellent asynchronous, decentralized multiple-access performance over time-invariant multipath channels.

A wind density model to quantify the airborne spread of Culicoides species during north-western Europe bluetongue epidemic, 2006

Increased transport and trade as well as climate shifts play an important role in the introduction, establishment and spread of new pathogens. Arguably, the introduction of bluetongue virus (BTV) serotype 8 in Benelux, Germany and France in 2006 is such an example. After its establishment in receptive local vector and host populations the continued spread of such a disease in a suitable environment will mainly depend on movement of infected vectors and animals. In this paper we explore how wind models can contribute to explain the spread of BTV in a temperate eco-climatic setting. Based on previous work in Greece and Bulgaria filtered wind density maps were computed using data from the European Centre for Medium-Range Weather Forecasts (ECMWF). Six hourly forward wind trajectories were computed at pressure levels of 850 hPa for each infected farm as from the recorded onset of symptoms. The trajectories were filtered to remove wind events that do not contribute to possible spread of the vector. The suitable wind events were rastered and aggregated on a weekly basis to obtain weekly wind density maps. Next to this, cumulated wind density maps were also calculated to assess the overall impact of wind dispersal of vectors. A strong positive correlation was established between wind density data and the horizontal asymmetrical spread pattern of the 2006 BTV8 epidemic. It was shown that short (<5 km), medium (5–31 km) and long (>31 km) distance spread had a different impact on disease spread. Computed wind densities were linked to the medium/long-distance spread whilst short range spread was mainly driven by active Culicoides flight. Whilst previous work in the Mediterranean basin showed that wind driven spread of Culicoides over sea occurred over distances of up to 700 km, this phenomenon was not observed over land. Long-distance spread over land followed a hopping pattern, i.e. with intermediary stops and establishment of local virus circulation clusters at distances of 35–85 km. Despite suitable wind densities, no long range spread was recorded over distances of 300–400 km. Factors preventing spread Eastwards to the UK and Northwards to Denmark during the 2006 epidemic are discussed. Towards the east both elevation and terrain roughness, causing air turbulences and drop down of Culicoides, were major factors restricting spread. It is concluded that the proposed approach opens new avenues for understanding the spread of vector-borne viruses in Europe. Future developments should take into consideration both physical and biological factors affecting spread.

An EM approach to multiple-access interference mitigation in asynchronous slow FHSS systems

In this paper, we apply the EM algorithm for mitigation of multi-access interference (MAI) in asynchronous slow frequency-hop spread spectrum (FHSS) systems that employ binary frequency-shift keying (BFSK) modulation. MAI occurs if the hopping patterns of the users are not orthogonal. We show that when FSK signals arrive asynchronously, the time offset exposes portions of the desired and interfering signals in a way that can be exploited to improve the decoder performance. We develop an iterative detection, estimation, and decoding scheme to recover the desired signal in the presence of MAI. We compare the performance of this algorithm with that of a conventional noncoherent BFSK transceiver and show that the EM-based algorithm is particularly effective in the presence of strong interfering signals and allows more users in a FHSS system.

Sequence hopping cell search scheme for OFDM cellular systems

OFDM has been a widely accepted technology in high rate and multimedia data service systems, such as 3G Long Term Evolution (3G LTE) system in the 3rd Generation Partnership Project (3GPP). In this paper, we propose a new cell search scheme based on the frequency domain sequence hopping of synchronization channel symbols. The assigned hopping pattern provides frame boundary information as well as cell identification (cell ID) to a mobile station (MS). The proposed synchronization channel structure allows MS to acquire OFDM symbol/frame timing, cell ID and frequency offset estimates in the initial cell search stage. The cell search in MS is composed of 2 steps; OFDM symbol synchronization step, frequency offset correction and cell ID/frame boundary detection step. We evaluate the performance of proposed scheme under various channel environments. The impacts of multipath fading, vehicular speed and frequency offset on the performance are investigated. We also compare the performance of proposed scheme with 3G LTE cell search scheme.

Performance Analysis of Orthogonal-Code Hopping Multiplexing Systems With Repetition, Convolutional, and Turbo Coding Schemes

In orthogonal-code hopping multiplexing (OCHM) systems, hopping-pattern (HP) collisions may degrade system performance. Previous studies on the effect of HP collisions in OCHM systems were based on computer simulations, and there was no mathematical analysis of the bit-error-rate (BER) performance. The HP collisions in OCHM systems differ from hits in frequency-hopping systems or intracell interference in direct-sequence code-division multiple-access (DS/CDMA) systems because they can effectively be controlled through synergy and perforation techniques. In this paper, we introduce a received-signal model for OCHM systems called a perforation-only model and analyze the BER performance for OCHM systems in both uncoded and coded environments. Repetition, convolutional, and turbo codes are considered in coded environments. Through the analysis of BER performance, OCHM systems can more clearly be characterized, and the allocated power at the base station (BS) can be estimated for OCHM systems. Furthermore, the user capacity is analyzed for a given channel coding scheme. The results show that the uncoded BER is saturated by the perforation probability, and the coded BER is degraded as the perforation probability increases. We investigate the allocated power at the BS according to the perforation probability and compare the user capacities of OCHM systems using the three different types of coding schemes.

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.

Clustering and Coupled Gating Modulate the Activity in KcsA, a Potassium Channel Model

Different patterns of channel activity have been detected by patch clamping excised membrane patches from reconstituted giant liposomes containing purified KcsA, a potassium channel from prokaryotes. The more frequent pattern has a characteristic low channel opening probability and exhibits many other features reported for KcsA reconstituted into planar lipid bilayers, including a moderate voltage dependence, blockade by Na(+), and a strict dependence on acidic pH for channel opening. The predominant gating event in this low channel opening probability pattern corresponds to the positive coupling of two KcsA channels. However, other activity patterns have been detected as well, which are characterized by a high channel opening probability (HOP patterns), positive coupling of mostly five concerted channels, and profound changes in other KcsA features, including a different voltage dependence, channel opening at neutral pH, and lack of Na(+) blockade. The above functional diversity occurs correlatively to the heterogeneous supramolecular assembly of KcsA into clusters. Clustering of KcsA depends on protein concentration and occurs both in detergent solution and more markedly in reconstituted membranes, including giant liposomes, where some of the clusters are large enough (up to micrometer size) to be observed by confocal microscopy. As in the allosteric conformational spread responses observed in receptor clustering (Bray, D. and Duke, T. (2004) Annu. Rev. Biophys. Biomol. Struct. 33, 53-73) our tenet is that physical clustering of KcsA channels is behind the observed multiple coupled gating and diverse functional responses.

Interference mitigation study for UWB radio using template waveform processing

Ultra-wideband (UWB) is an effective technique that enables coexistence with other radio systems using very short pulses and spread spectrum. However, there are potential interferences among those using the same frequency bands. This paper discusses the effects of interference between pulse-based UWB (p-UWB) and other systems: continuous wave, binary phase-shift keying signal, IEEE802.11a wireless LAN using a 5-GHz band, and multiband orthogonal frequency-division multiplexing (MB-OFDM). The MB-OFDM is inferentially proposed for personal area networks, as is p-UWB. The FCC has stated that both p-UWB and MB-OFDM systems will use the same band from 3.1 to 10.6 GHz. The bit-error-rate performance is shown assuming that p-UWB and the other systems are utilized at close range. To mitigate the effects of interference to p-UWB from other radio systems, a multicarrier template wave technique is proposed. The multicarrier template wave is approximated with an ordinary pulse waveform by Gabor transform formula and is composed of several subband pulses without interfering bands. The proposed UWB receiver for MB-OFDM interferences can detect their hopping pattern without a priori knowledge from the MB-OFDM transmitter. These techniques are shown to be effective for the systems to coexist.

A new family of 2-D optical orthogonal codes and analysis of its performance in optical CDMA access networks

A new family of two-dimensional optical orthogonal code (2-D OOC), one-coincidence frequency hop code (OCFHC)/OOC, which employs OCFHC and OOC as wavelength hopping and time-spreading patterns, respectively, is proposed in this paper. In contrary to previously constructed 2-D OOCs, OCFHC/OOC provides more choices on the number of available wavelengths and its cardinality achieves the upper bound in theory without sacrificing good auto-and-cross correlation properties, i.e., the correlation properties of the code is still ideal. Meanwhile, we utilize a new method, called effective normalized throughput, to compare the performance of diverse codes applicable to optical code division multiple access (OCDMA) systems besides conventional measure bit error rate, and the results indicate that our code performs better than obtained OCDMA codes and is truly applicable to OCDMA networks as multiaccess codes and will greatly facilitate the implementation of OCDMA access networks.

Joint hop timing and frequency estimation for collision resolution in FH networks

With the rapid growth of frequency-hopped (FH) wireless networks, interference due to frequency collisions has become one of the main performance-limiting challenges. This paper proposes a novel multiuser detection method for joint hop timing and frequency estimation, which is capable of unraveling and demodulating multiple FH transmissions in the presence of collisions and unknown hop patterns without retransmission. The method is based on the principle of dynamic programming (DP) coupled with two-dimensional harmonic retrieval (2-D HR) or low-rank trilinear decomposition, and it remains operational even with multiple unknown hop rates, frequency offsets, and asynchronism. The model is based on frequency-shift keying (FSK) and phase-shift keying (PSK) modulation, but the algorithms are also evaluated with Gaussian minimum-shift keying (GMSK) modulation and shown to be robust.

MIMO Frequency Hopping Spread Spectrum Multi-Carrier Multiple Access: A Novel Uplink System for B3G Cellular Networks

In this paper, we propose and give the performance of a novel uplink system based on the combination of multi-carrier (MC), code division multiple access (CDMA) and multiple input multiple output (MIMO) techniques. First, we describe the interests of spread-spectrum multi-carrier multiple access (SS-MC-MA) scheme for uplink, especially compared to MC-CDMA. Classically, with SS-MC-MA, each user spreads its data symbols on a specific subset of adjacent or multiplexed subcarriers, to facilitate the channel estimation and reduce complexity at the reception. In order to compensate for the lack of frequency diversity of SS-MC-MA with adjacent subcarriers, we first combine it with an orthogonal space-time block code (STBC) and demonstrate the resulting spatial diversity gain. Then, we propose to allocate the subsets to the different users by applying a frequency hopping pattern (FH). In that case, each user benefits from the frequency diversity linked to the total bandwidth as with the multiplexed subcarriers solution, while keeping the advantages of the adjacent subcarriers solution. The gain provided by the use of the frequency hopping is stressed on. Finally, the performance of this scheme is evaluated over realistic MIMO channel with channel turbo coding for systems offering asymptotic spectrum efficiency of 1, 2, 3 and 4.5 bit/s/Hz. Thus, the efficiency of the novel proposed STBC FH SS-MC-MA system as a very promising multiple access and modulation scheme for the uplink of the future wideband wireless networks is successfully demonstrated.

Coordination and stability of one-legged hopping patterns in patients with anterior cruciate ligament reconstruction: preliminary results

Objective. To investigate whether the intralimb coordination of the lower extremity during one-legged hopping in patients with anterior cruciate ligament reconstruction is different and less stable compared to control subjects. Design. Measures of coordination dynamics are applied to study the coordination and stability of movement patterns of the knee and ankle in patients and control subjects. Background. Due to several factors, such as loss of proprioceptive function and muscle weakness, the intralimb coordination of the lower extremity might be altered. Methods. Seven patients and 13 healthy control subjects were instructed to hop in place on one leg for 10 seconds at a comfortable frequency for each leg separately. Results and conclusions. The one-legged hopping movement pattern of patients with anterior cruciate ligament reconstruction one-year post-operative is different and less stable compared to healthy subjects, and thus is still impaired. Relevance This paper shows that patients, one year after reconstruction of the anterior cruciate ligament, have a different coordination pattern of the lower limb compared to a matched control group. Intersegmental coordination and stability, features that are often observed by eye during a rehabilitation process, are objectified in this study.

Multicarrier DS/SFH-CDMA systems

Multicarrier direct-sequence/slow-frequency-hopping (MC DS/SFH) code-division multiple-access (CDMA) systems are proposed, in which multiple carriers are modulated by the same DS waveform and hopped in frequency according to a random hopping pattern. The receiver dehops the received signal with the same pattern, provides RAKE receivers for each carrier, and combines the outputs with a maximal ratio combiner (MRC). The performance of the proposed system is investigated over a frequency-selective Rayleigh-fading channel and compared to that of the MC DS-CDMA systems. It is shown that for the same diversity order, the MC DS/SFH-CDMA systems are superior in reducing multiple-access interference (MAI) while preserving the good capability of narrowband interference suppression, when the system parameters are selected properly.

Multimedia applications using optical FFH‐CDMA communication systems

AbstractIn this Letter multimedia transmission in an optical‐fiber network using a fast frequency hopping–code division multiple access scheme is discussed. The multirate one coincidence variable length frequency hop patterns have been generated and their auto‐ and cross‐correlation properties are studied. A series of multiple Bragg gratings in a single optical fiber has been proposed to implement the encoder and decoder. Bit‐error‐rate analysis assuming Gaussian approximation for the error probability has been carried out. The results of the numerical analysis reveal that this system can support up to 30 simultaneous users with two different data rates (e.g., 500 Mbps and 2 Gbps). It can be concluded from the results that the fast frequency hopping–optical code division multiple access system is capable of supporting multimedia applications. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 259–263, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10432

Optimizing Frequency Hopping in GSM Cellular Phone Networks

The mobile telephony market has been undergoing a dramatic increase in the volume of demand as well as in the quality requirements. The limiting resource in this highly competitive market is the available frequency spectrum. In GSM networks, frequency reuse has been the basic tool for optimizing the spectrum management. This method is sometimes insufficient, however, for the most congested networks. Frequency Hopping (FH) is a method that allows one to expand the available capacity of mobile networks or to improve the quality of service through interference averaging and frequency diversity. Current implementations of FH are based on Random or Cyclic Hopping patterns. In this paper, we propose to optimize FH. We describe a simple heuristic algorithm for allocating frequencies to cells and scheduling the frequency hopping for each mobile. The performance of the proposed approach in a synchronized network is compared to Random and Cyclic FH and to the optimized static frequency reuse implementations. We show that hopping algorithms that use some form of controlled optimization beyond random and cyclic hopping could significantly improve the quality of service and achieve interference averaging, should the telecommunications equipment manufacturers decide to implement such a feature or to allow the operators to control frequency hopping by using their own algorithms.

Improving performance of multi-user OFDM systemsusingbit-wise interleaver

A new bit-wise interleaver is introduced for multi-user orthogonal frequency division multiplexing systems using frequency hopping. In addition to placing adjacent bits (belonging to one complex I/Q symbol) onto different subcarriers, they can be placed at different timeslots or different blocks. Furthermore, the interleaver can be adjusted adaptively based on the corresponding hopping pattern. The performance gain is investigated by simulations.

Slow frequency-hopping multicarrier DS-CDMA for transmission over Nakagami multipath fading channels

A novel multiple access scheme based on slow frequency hopping multicarrier direct-sequence code division multiple access (SFH/MC DS-CDMA) is proposed and investigated, which can be rendered compatible with the existing second-generation narrowband CDMA and third-generation wideband CDMA systems. The frequency hopping patterns are controlled by a set of constant-weight codes. Consequently, multirate communications can be implemented by selecting the corresponding sets of constant-weight codes having the required weights controlling the SFH patterns invoked. Two FH schemes, namely random and uniform FH, are considered and their advantages as well as disadvantages are investigated. We assume that the system operates in a multipath fading environment and a RAKE receiver structure with maximum ratio combining (MRC) is used for demodulation. The system's performance is evaluated over the range of multipath Nakagami (1960) fading channels, under the assumption that the receiver has all explicit knowledge of the associated frequency-hopping (FH) patterns invoked. Furthermore, the performance of the SFH/MC DS-CDMA system is compared to that of the conventional single-carrier (SC) DS-CDMA system and that of the conventional MC DS-CDMA system, under the assumptions of constant system bandwidth and of constant transmitted signal power.

On the detection of a class of fast frequency-hopped multiple access signals

The capacity of a fast frequency-hopped multiple access (FHMA) system is dictated by two major related design concerns: the hopping pattern and the receiver structure. This paper studies the impact of these two factors. We present a maximum likelihood (ML) diversity combiner for detecting asynchronous FHMA multilevel PSK (MPSK) signals in Rician fading channels and analyze the performance of a close approximation of the ML receiver. We compare systems using random hopping patterns and those using optimal hopping patterns of Einarsson (1980). Performance comparisons between chip-synchronous and chip-asynchronous systems are made as well. We propose and examine the effectiveness of a two-stage multiuser detector, in which the first stage makes an initial decision while the second stage tries to reduce multiple access interference (MAI) and resolve the ambiguity left by the first stage detector. The MAI caused by undesired users is constituted by a cochannel interference (CCI) contribution and an interchannel interference (ICI) contribution. This detector is of modest complexity and is capable of removing most of the CCI and part of the ICI. Two methods for mitigating MAI are also examined.

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.

MFSK/FH-SSMA wireless systems with double-media services over fading channels

The application of multilevel frequency-shift keying/frequency-hopping spread-spectrum multiple access (MFSK/FH-SSMA) to wireless systems has been receiving much attention. Most studies on MFSK/FH-SSMA wireless systems so far assume to support only one type of medium. A flexible support of multimedia services in future wireless systems is expected. However, the use of conventional "fixed-length" FH patterns alone cannot serve these multirate multimedia wireless systems. A family of double-length fixed-weight generalized prime hopping patterns is reviewed. These FH patterns have cross correlations of no greater than one in order to minimize mutual interference and are well suited for wireless systems with double-media services. The performances of the prime hopping patterns and conventional random hopping patterns in MFSK/FH-SSMA wireless systems over Rayleigh fading and additive white Gaussian noise (AWGN) channels are analyzed and compared for one type of medium first and extended to two types of media. Our results show that the proposed scheme performs better than the conventional one with random hopping patterns in both nonfading and fading channels.