Q2.1 Consider the single-sender CDMA example in Kurose & Ross (see Figure 6.5: ‘

Question

Q2.1 Consider the single-sender CDMA example in Kurose & Ross (see Figure 6.5: ‘A simple CDMA example’). What would be the sender's output (for the 2 data bits shown), if the sender's CDMA code were (1, -1, 1, 1, -1, -1, 1, -1)?

Q2.2 Suppose an 802.11 b station is configured to always reserve the channel with the RTS/CTS sequence. Suppose this station suddenly wants to transmit 1,000 bytes of data, and all other stations are idle at this time. As a function of SIFS and DIFS, and ignoring propagation delay and assuming no bit errors, calculate the time required to transmit the frame and receive the acknowledgment.

Explanation / Answer

1) Output corresponding to bit
d1 = [-1,1,-1,1,-1,1,-1,1]
Output corresponding to bit
d0 = [1,-1,1,-1,1,-1,1,-1]
2)A frame without data is 32 bytes long. Assuming a transmission rate of 11 Mbps, the time to
transmit a control frame (such as an RTS frame, a CTS frame, or an ACK frame) is (256
bits)/(11 Mbps) = 23 usec. The time required to t
ransmit the data frame is (8256 bits)/(11 Mbps)
= 751
DIFS + RTS + SIFS + CTS + SIFS + FRAME + SIFS + ACK
= DIFS + 3SIFS + (3*23 + 751) usec = DIFS + 3SIFS + 820 usec

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