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The Bluetooth radio chip uses GFSK Modulation. It is natural to assume that GFSK is quite like FSK Modulation, however the differences between the 2 are substantial in implementation and results (output)

Question 1
What are the physical Differences between an FSK & GFSK Modulator, and how do their results vary?
Answer 1
An FSK Modulator is much the same as a GFSK Modulator ,but GFSK uses a Gaussian filter as well. In a GFSK modulator everything is the same as a FSK modulator except that before the baseband pulses (-1, 1) go into the FSK modulator, it is passed through a gaussian filter to make the pulse smoother so to limit its spectral width.

Question 2
What is Gaussian Filtering?
Answer 2
Gaussian filtering is one of the very standard ways for reducing the spectral width, it is called Pulse Shaping. If we use -1 for fc-fd and 1 for fc+fd, once when we jump from -1 to 1 or 1 to -1, the modulated waveform changes rapidly, which introduces large out-of-band spectrum. If we change the pulse going from -1 to 1 as -1, -.98, -.93 ..... .96, .99, 1, and we use this smoother pulse to modulate the carrier, the out-of-band spectrum will be reduced.

Question 3
So, why is GFSK implemented in Bluetooth Radios , and not FSK , is it cheaper?
Answer 3
The spectral width for FSK is unlimited, comparatively, there is a limitation on GFSK. fc "climbs slowly" to fd in GFSK, However, in the case of FSK, fc "jumps sharply" to fd, which greatly decreases spectral efficiency.

GFSK is not implemented in the Bluetooth radio unit for cheaper chips (since you need to put an extra pulse-shaping filter in front of the modulator), but for spectral efficiency.

ps.
1. Gaussian filtering에 대해 자세히 알고 싶으면 아래 사이트를 참고할 것!
  http://homepages.inf.ed.ac.uk/rbf/HIPR2/gsmooth.htm
  http://www.fho-emden.de/~hoffmann/gauss25092001.pdf
2. FSK는 무선 랜에서 사용되는 변조 방식임.

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Bluetooth has been designed to operate in noisy radio frequency environments, and uses a fast acknowledgement and frequency-hopping scheme to make the link robust, communication-wise. Bluetooth radio modules avoid interference from other signals by hopping to a new frequency after transmitting or receiving a packet.
Compared with other systems operating in the same frequency band, the Bluetooth radio typically hops faster and uses shorter packets. This is because short packages and fast hopping limit the impact of microwave ovens and other sources of disturbances. Use of Forward Error Correction (FEC) limits the impact of random noise on long-distance links.

Considering the figure 1, one realizes that hopping out-and-into a continuous range of frequencies that are subject to noise gives the communications link a better chance to remedy transmission errors when out of the disturbed frequencies, than would have been the case if the transmission had stayed for several timeslots within the noisy frequency range. This argument does not hold true if the noise is spread over the whole frequency range in a random fashion, but sources of electro-magnetic noise usually give the pattern illustrated in figure 2.

Whenever a connection (a "piconet") is first established between 2 (or more) units, the Master-unit establishes a frequency-hopping scheme, which is communicated to the other units. This frequency selection scheme consists of two parts:

• selecting a sequence;
• mapping this sequence onto the hop frequencies.

The mapping from the input to a particular hop frequency is performed in the selection box. Basically, the input is the native clock and the current address. In the CONNECTION state, the native clock is modified by an offset to equal the master clock. Only the 27 MSBs of the clock are used. In the page and inquiry substates, all 28 bits of the clock are used. However, in the PAGE substate the native clock will be modified to the master estimate of the paged unit.

The frequency-hopping schemes

10 types of frequency-hopping sequences are defined ?5 for the 79-hop and 5 for the 23-hop system. These sequences are:

1. A page hopping sequence with 32 (16) unique wake-up frequencies, distributed equally over the 79 (23) MHz, with a period length of 32 (16).
2. A page response sequence covering 32 (16) unique response frequencies that are all in a one-to-one correspondence to the current hopping sequence. Master & Slave use different rules to obtain the same sequence.
3. An inquiry sequence with 32 (16) unique wake-up frequencies, distributed equally over the 79 (23) MHz, with a period length of 32 (16).
4. A inquiry response sequence covering 32 (16) unique response frequencies that are all in a one-to-one correspondence to the current inquiry hopping sequence.
5. A channel hopping sequence with very long period, which does not show repetitive patterns over a short time interval, but which distributes the hop frequencies equally.

크리에이티브 커먼즈 라이선스

이 저작물은 크리에이티브 커먼즈 코리아 저작자표시-비영리-동일조건변경허락 2.0 대한민국 라이선스에 따라 이용하실 수 있습니다.

1. http://www.bluetooth.com
BT에 관한 포탈 사이트와 비슷하다. BT에 대한 간단한 개념과 참여업체, 적용 제품에 관하여 설명하고 있는 잡지성(?) 사이트라고 볼 수 있다.

2. http://www.bluetooth.org
공식 멤버쉽 사이트로 기술적이 내용이 주를 이루고 있다. 스펙과 같은 개발에 관련된 문서를 구하려면 방문할 것!

3. http://www.csr.com
BT 솔루션 판매 업체로 정확하게 잘 모르겠지만 애플에서 이곳 칩셋과 API를 이용하는 것 같다. 외국에서 가장 많이 사용하는 칩셋으로 생각된다.

4. http://www.palowireless.com/bluetooth/
Bluetooth Resource Center라는 제목에 걸맞게 BT 입문자, 개발자, 마케팅 담당자, 온라인 상점 등 여러 분야에서 필요한 리소스의 링크를 가지고 있다.

5. http://www.bluez.org
리눅스에서 BT 프로토콜 스택을 구현하는 프로젝트인 BlueZ의 공식 사이트이다. 공개된 소스코드를 여기서 구할 수 있다.

6. http://www.holtmann.org/linux/bluetooth/
BT HOWTO 문서를 정리해 놓은 사이트로 특히 리눅스와 관련된 문서가 많다.

7. http://www.thewirelessreport.com/category/bluetooth/
BT에 관한 블로그로 잡지성 기사가 많다.

8. http://kde-bluetooth.sourceforge.net/
KDE에 BuleZ를 사용하여 BT 프레임워크를 만들기 위한 프로젝트

9. http://www.eng.tau.ac.il/~yash/shaked-wool-mobisys05/
BT PIN을 이용한 공격을 구현한 논문으로 보안 이슈를 중점적으로 다루고 있다. 참고문헌에 BT 보안에 관련된 링크가 많다.

10. http://www.korwin.co.kr/kor/
BT와 ZigBee 라이브러리를 개발하는 우리나라 업체로 한번 살펴볼만 하다.

11. http://www.sds.samsung.co.kr/support/epartner/itreview/data/epci001t/bluetooth1.pdf
삼성 SDS에서 만든 간단한 한글 보고서로 BT에 대해 쉽게 정리되어 있다.

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크리에이티브 커먼즈 라이선스

이 저작물은 크리에이티브 커먼즈 코리아 저작자표시-비영리-동일조건변경허락 2.0 대한민국 라이선스에 따라 이용하실 수 있습니다.