superficial acoustic waves
S. V. Bogoslovskiy, G. A. Sapozhnikov
In the given¬ work two ways of coding are considered: time-item a way of coding; way of the co-ordinated filtration.
Distinguish the following versions of a way 1 connected with a kind of the probing impulse: sounding by a radio impulse with the fixed bearing frequency (as a rule, duration of probing impulses on frequency to 1 GHz does not exceed 50 nanoseconds); use of coding sequences, in particular, the fazo-kodo-modulated signals and the linearly-frequency-modulated signals.
Advantage of a way 1 is compactness (the size of a radio label for a frequency range to 1 GHz does not exceed 15 mm) and simplicity of realisation of topology and the input reader.
It is necessary to carry to lacks: small range (to 10); rather a small amount of various codes.
Coding by way 2 (the co-ordinated filtration) has following variants: fazo-code modulation; frequency modulation, in particular, linearly-frequency modulation; coding sequences (codes of Barker etc.); correlation ways; radio labels on the basis of resonators.
Advantage of the given way of coding is possibility of construction enough the big alphabet (not less than 100 elements) and, accordingly, increase in quantity of possible codes. Other advantage is possibility of increase in pulse capacity of the reflected signal of a radio label.
Lack is necessity of formation of several topology on one radio label, and also necessity of complication of the aerial of a radio label.
Let's estimate the achievable quantity of codes realised on each of ways.
Time-item a way of coding is characterised by following integrated parametres: duration of a probing radio impulse; admissible quantity of reflecting structures on a label; the maximum size of a delay; the minimum admissible time delay between two next reflected impulses; the minimum time step identified by system.
At coding by way of the co-ordinated filtration in the parametres defining possibilities of physical realisation, are: quantity of bats of the information (capacity of the alphabet) which can be generated one reflecting structure; in the elementary case it is defined by presence of the signals having mutual correlation functions at set level in relation to autocorrelation function; admissible quantity of the reflecting structures (topology) realising various signals, on one radio label.
As a rule, a way of the co-ordinated filtration in time-item in the way of coding complexities. At additional coding on frequency with use of the linearly-frequency-modulated probing impulses the quantity of the reflected signals having mutual correlation function at comprehensible level 0.3 and generated on different frequencies with use of one reflecting structure, usually makes not less than 100. Label coding in this case is carried out by means of a small number of chips, each of which is coded only to it by an inherent code. As the code of any of chips is defined by size of a delay and frequency of the impulse reflected by this chip capacity of the alphabet appears on some usages above, than at time-item a way of coding. The quantity of possible codes for radio labels is defined by number of possible variants of placing of had quantity of various chips in the places reserved for them on a label, and this quantity appears on some usages more than at time-item a way of coding. For realisation of such quantity of codes by means of standard paper stroke-coding the tape which length can appear in tens times more long a radio label can be demanded.