11. spread spectrum communications: spread spectrum techniques - FH

(FYI) chap 5. AM, FM, and digital modulated systems: spread spectrum systems: FH system

참조 포스팅에서 다루고 있는 내용 및 접근방식은 기본적으로 본 포스팅의 내용과 맥락을 함께 한다.
the SS signal is

 where the complex envelope is function of both

 and

. in most cases, a product function is used, so that

.^[각주:1]

(FYI) 2. spread spectrum techniques: frequency hopping

TEXT: spread spectrum systems with commercial applications / Robert C. Dixon 에서 FH processing에 접근하는 방식은 조금 차이가 있다. BFSK 방식의 modulation tech에서 응용이 된, multiple-frequency, code-selected, FSK 로 설명한다. it is nothing more than FSK that the set of frequency choices is greatly expanded.

11.4.2 frequency hopping (FH) modulation


mathematical expression of signal 

• modulating signal,
  
   and its complex envelope,
  

FH modulation is traditionally used with multiple-frequency-shift-keyed (MFSK) information signal, which have the complex form

where

 is an M-level digital waveform. it has frequency duration,

 per symbols.

• 수식에 의해서, information signal
  
  에 의해서 변화되는 것은 frequency 라는 것을 알 수 있다.

 

• spreading signal,
  
   and its complex envelope,
  

 is formed by nonlinearly modulating a train of pulses with a sequence of pseudorandomly generated frequency shifts set. it has the complex form,

where pulse has a duration

, called the hop time.

• spread spectrum signal, FH/MFSK

FH/MFSK signal is formed by complex multiplying the MFSK signal by

, resulting in the real transmitted signal,

FH system block diagram

• transmission processing

FH/MFSK signal,

 (here, above figure

) is obtained by applying the sequence of pseudorandom frequency shifts

 directly to the frequency synthesizer that generates the carrier frequency

.
Q)

 의 경우 spread signal

 와 관련된 variable이며,

 는 information signal

와 관련된 variable이다. 그런데, 

와

 모두 PRN generator에 의해 생성되는 것인가?

successive (not necessarily disjoint)

 segments of a PN sequence drive a frequency synthesizer, which hops the carrier over

 frequencies. 

 

• receiving processing

the sum of the transmitted FH/MFSK signal and the channel interference is multipled by the identical FH modulation (known as dehopping). it returns the FH/MFSK signal to its original MFSK form, and the real interference singal became the wideband (in the average sense) signal.

the exact relation between

 (spread spectrum bandwidth),

 (pulse duration, hop time),

 (frequency duration) and the number of frequency shifts in the set

 will be discussed in the following posting.

1. chap 5. AM, FM, and digital modulated systems: spread spectrum systems, http://worthatry.tistory.com/448 [본문으로]