1. What is the typical application of the communication technology that you choose to study? Give some examples and pictures. What products use this technology?
Answer: Wireless LAN.
2. What is the frequency band allocated by FCC for this technology?
Answer: 5Ghz for 802.11a and 2.4GHz for 802.11g
3. Who is the standard body? Where can one find the documents of the standard?
Which part of the document is about physical layer?
Answer: IEEE, http://www.ieee802.org/11/
Page 3 of the IEEE document entitled
"Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)
specifications" talks about Physical layer.
4. Show/draw and explain system block diagrams that process information bits,
perform error control encoding, and modulation.
Answer: 802.11a System Description
Figure 1: 802.11a Transmitter block diagram
Figure 2: 802.11a Receiver Block Diagram
5. What error control codes are used? (Convolutional codes, turbo codes, LDPC codes,
Reed-Solomon codes, etc.)
Answer: Convolution Encoding
Figure 3. Rate 1/3 non-recursive, non-systematic convolution encoder with constraint length 3
To convolutionally encode data, start with k memory registers, each holding 1 input bit. Unless otherwise specified, all memory registers start with a value of 0. The encoder has n modulo-2 adders, and n generator polynomials -- one for each adder (see figure above). An input bit m1 is fed into the leftmost register. Using the generator polynomials and the existing values in the remaining registers, the encoder outputs n bits. Now bit shift all register values to the right (m1 moves to m0, m0 moves to m-1) and wait for the next input bit. If there are no remaining input bits, the encoder continues output until all registers have returned to the zero state.
The figure above is a rate 1/3 (m/n) encoder with constraint length (k) of 3. Generator polynomials are G1 = (1,1,1), G2 = (0,1,1), and G3 = (1,0,1). Therefore, output bits are calculated as follows:
n1 = mod2 (m1 + m0 + m-1)
n2 = mod2 (m0 + m-1)
n3 = mod2 (m1 + m-1)
6. What constellations (BPSK, QPSK, 8PSK, 16-QAM, etc.) are used?
Answer: The modulation parameters dependent on the data rate used is set according to
Table 1. below.
7. IQ modulation used? What is in the I part of the base band complex signal and
what is the Q part of the base band complex signal?
Answer:
Figure4: BPSK, QPSK, 16-QAM, and 64-QAM constellation bit encoding
8. What kind of pulse shape is used? Can you show a picture of the pulse shape?
Where can one find the pulse shape in a document of the standard?
Answer:
9. What multi-access and broadcast technologies are used? (TDM(A), CDM(A),
FDM(A), OFDM(A), etc.)
How do they work? (Multi-access, or uplink, means that multiple users send signals
to the base station. Broadcast, or downlink, means that a base station sends different
signals to different users.)
Answer: OFDM for 802.11a, OFDM + DSSS for 802.11g
10. Does it use multi-antenna technology? How?
Answer: Single Omnidirectional Antenna
11. Is the standardization on-going? Which companies are the major players?
Answer: No,
Some a few companies are Cisco, Seimens, Alcatel, Nortel Network, etc.
References:
http://www.vocal.com/white_paper/80211a_wp1pdf.pdf 4
http://www.Stanford.edu/class/ee360/lecture7.ppt 4
http://ieeexplore.ieee.org/iel5/7152/19253/00891003.pdf 5
http://grouper.ieee.org/groups/802/15/pub/2003/Mar03/03151r1P802-15_TG3a-Wisair-CFP-Presentation.ppt 8
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