Frequency Hopping Technique Research Articles

Performance of packet-switched fiber-optic frequency-hopping multiple-access networks

A packet-switched frequency-hopping multiple-access (FO-FHMA) communication system based on bus topology is proposed and investigated. In this arrangement, access to the optical medium for the network subscribers is provided via frequency-hopping (FH). The proposed FH technique in this analysis takes advantage of the Reed-Solomon (RS) codes to encode information packets and, consequently, to combat possible burst errors at the receiver. At user locations, encoded subpackets are frequency-hopped with the aid of a phase modulator, using a preassigned FH pattern for transmission over the optical medium. At the receiver site, a balanced phase discriminator/detection device followed by a frequency-dehopping receiver is used to recover the desired information. An alternative receiver structure, where the received signal is heterodyned prior to dehopping, is also proposed. The implications of this coherent detection are consequently discussed. Performance measures in terms of throughput and probability of incorrect decoding for chip synchronous model with asynchronous transmission characteristic in the absence of side information are obtained to assess the viability of the proposed packet-switched fiber-optic multiple-access communication system. Numerical results are presented when short RS codes are utilized as FH assignment codes. >

Analysis of interconnect networks using complex frequency hopping (CFH)

With increasing miniaturization and operating speeds, loss of signal integrity due to physical interconnects represents a major performance limiting factor of chip-, board- or system-level design. Moment-matching techniques using Pade approximations have recently been applied to simulating modelled interconnect networks that include lossy coupled transmission lines and nonlinear terminations, giving a marked increase in efficiency over traditional simulation techniques. Nevertheless, moment-matching can be inaccurate in high-speed circuits due to critical properties of Pade approximations. Further, moment-generation for transmission line networks can be shown to have increasing numerical truncation error with higher order moments. These inaccuracies are reflected in both the frequency and transient response and there is no criterion for determining the limits of the error. In this paper, a multipoint moment-matching, or complex frequency hopping (CFH) technique is introduced which extracts accurate dominant poles of a linear subnetwork up to any predefined maximum frequency. The method generates a single transfer function for a large linear subnetwork and provides for a CPU/accuracy tradeoff. A new algorithm is also introduced for generating higher-order moments for transmission lines without incurring increasing truncation error. Several interconnect examples are considered which demonstrate the accuracy and efficiency in both the time and frequency domains of the new method. >

Hybrid slow frequency hopping/ direct sequence spread spectrum indoor communication systems with QPSK modulation

This paper analyses the performance of a spread-spectrum multiple access system based on hybrid direct sequence/slow frequency hopping techniques with QPSK modulation. The performance is analyzed considering multipath and multiple access interferences and an indoor channel having Rician distributed path gains. The system performance is investigated for 2 diversity techniques and compared, for given delay spread, bandwidth and bit rate, with the performance provided by bpsk modulation. It is shown that the larger symbol duration of QPSK is favorable to combat the effect of multipath propagation.

A class of frequency hop codes with nearly ideal characteristics for use in multiple-access spread-spectrum communications and radar and sonar systems

The problem of constructing frequency hop codes for use in multiuser communication systems such as multiple-access spread-spectrum communications and multiuser radar and sonar systems is addressed. Previous frequency hopping techniques are reviewed. The construction of a new family of frequency hopping codes called hyperbolic frequency hop codes is given. The concepts of multiple-access spread-spectrum communication systems and multiuser radar and sonar systems are reviewed, and it is shown that the hyperbolic frequency hop codes possess nearly ideal characteristics for use in both types of system. Specifically, in multiple-access communications the codes achieve minimum error probability, while in radar and sonar systems the codes have at most two hits in their auto- and cross-ambiguity function. Examples of address assignment for multiple-access communications systems and radar and sonar auto- and cross-ambiguity functions are also given. >

Frequency-Hopped Single-Sideband Modulation for Mobile Radio

A frequency-hopped single-sideband (SSB) modulation with pilot tone (FH-SSB-PT) transmission scheme is described for mobile radio. The single-sideband signal changes its carrier frequency every τ seconds, and the sequence of carrier frequencies is controlled by a suitable scrambling code. Co-channel cells using the same frequency band in the mobile radio system use different scrambling codes with the result that co-channel interference is altered from cross-talk to random noise if τ is small. In the presence of Rayleigh fading, frequency hopping improves reception for stationary vehicles, and does not degrade the performance for moving vehicles. Further, the technique of frequency hopping may offer communications privacy. Expressions for s/n are derived for SSB, SSB plus pilot tone, and FH-SSB-PT in the presence of Rayleigh fading. Co-channel interference effects are also considered.

Randomization Effect of Errors by Means of Frequency-Hopping Techniques in a Fading Channel

This paper describes the effective randomization of errors by means of frequency hopping (FH) in a selective Rayleigh fading channel. The major advantage of the randomization is the option to use random error-correcting codes in burst error channels, including the fading channel. Bit interleaving, which operates in the time domain, is very useful to randomize the errors, but equivalent operation is possible by FH in the frequency domain. That is based on low correlation between frequency chips, which is realized by hopping over a sufficiently wide bandwidth in selective fading channels. In this paper, bit error rates of FH with majority decision are analyzed to show the effect of randomization in various spread bandwidths. It is also shown that FH and interleaving are equivalent in the sense that spread bandwidth corresponds to interleaving degree with respect to its randomization effect.

The Jaguar V frequency-hopping radio

A new generation of secure tactical military radios has been developed utilising a frequency-hopping technique