Pulse-Coding Techniques for Incoherent-Scatter Radar Vikki Howells RAL

Constraints on I.S. Measurements Monostatic measurements cannot transmit and receive at the same time Height resolution < Scale Height Chosen pulse must give good SNR Lag spacing small enough to define ACF accurately ACF sampled to correct length Sample spacing matched to filter width Filter width appropriate to spectrum

Constraints on Measurements

Farley Diagram

Range-Time diagram for a single pulse τ τ Range Time cτ R Lag 1 Lag 4

τ τ Range Time The Power Profile

Multipulse Time Range (km)

5-Pulse Multipulse T 1 st lag 2 nd lag 3 rd lag 4 th lag 5 th lag 6 th lag 7 th lag 8 th lag t 9 th lag 11 th lag

Multipulse Codes Time Range (km) Height 1 Height 2

Alternating Codes A single pulse of length τ T is divided into 8 or 16 sub-pulses of length τ, transmitted continuously. Each sub-pulse is modulated with a relative phase of 0° or 180°. When echoes from the transmitted coded pulse are sampled in the receiver, at any instant the echoes from a range cτ T /2 are combined. The echoes from the different sub-pulses are scrambled together and no decoding can unscramble the data.

Alternating Codes When a full sequence of pulses are transmitted, with each pulse coded in a different way according to a predetermined pattern (Walsh Codes), then when the echoes are decoded correctly and the results added in the correlator memory, every lag at every height cancels out exactly except for one selected lag at one selected height. If the same data stream is then decoded in a different way a different lag is determined or the same lages at a different height.

Alternating Codes (x) (-x) (x) (-x) (x) Alternating code1 st lag Multiply by (x) (-x) (x) (-x) (x) (-x) (x) (-x) Multiply by st Range 2 nd Range

Alternating Codes Alternating code nd lag Multiply by (x) (-x) (x) (-x) Multiply by (x) (-x) (x) (-x) (x) (-x) (x) st Range 2 nd Range

Random Codes x (1) x (-1) …

Barker Codes t Range

Barker Codes 2 bit+ - 3 bit bit bit bit bit bit bit EISCAT – 13 bit

Pulse-to-Pulse Range Time

Pulse-to-Pulse Range Time 1 st lag 2 nd lag 3 rd lag