.NET ANSI/AIM Code 128 for .NET

Wireless LANs and personal-area networks using none tomake none on web,windows¨¬???qr I R bps convol. encoder interleaver QAM Q fc IFFT output barcode image generator Figure 12.7 Simpli ed OFDM transmitter, IEEE 801.11a and g checksum code39 c# (Examples of puncturing w none none ill be discussed below.) An interleaver is then used to spread out the punctured output stream, and the resultant bit stream stored the appropriate number of bits to provide a QAM symbol. Each QAM-symbol interval the QAM-constellation complex number corresponding to the set of input bits received in the QAM interval is stored until 48 such complex numbers, represented by a sequence of I (inphase) and Q (quadrature) numbers in a 3.

2 msec interval, are accumulated for input to the IFFT calculator. These complex numbers are represented by the symbols I and Q in Fig. 12.

7. These 48 numbers, corresponding to the data to be transmitted, are augmented by four numbers corresponding to the four pilot signals. A 64-point IFFT is used, with 16 of the IFFT input coef cients set equal to zero.

The IFFT output is then used to modulate the system carrier as shown. Two examples suf ce to describe the operation of this transmitter:. 2 of 5 interleaved free Example 1 Consider the 6 Mbps case rst. At this bit rate 24 bits are accumulated every 4 msec. The rate-1/2 encoder produces 48 bits in this same interval.

There is no puncturing in this case. With PSK modulation used, 48 binary numbers, either +1 or 1, are inputted to the IFFT calculator every 4 msec. Example 2 Now consider the maximum bit rate case of 54 Mbps.

Here 216 bits appear at the encoder input every 4 msec. For this bit rate, one-third of the encoder output bits are punctured or dropped, with 288 bits appearing at the output every 4 msec. The effective encoder rate is thus 3/4.

64-QAM is used in this case, as noted earlier, with the interleaved bits, taken six at a time, used to determine which one of 64 possible complex numbers is to be stored for IFFT processing. Note that 48 such complex numbers (288/6) are stored every 4 msec..

qr code url type .net c# Other input bit rates are none none processed in a similar manner, all producing the required 48 complex numbers to be inputted to the IFFT calculator every 4 msec. It is left to the reader to show that the QAM values and effective encoder rates shown in Table 12.1 all produce the 48 complex numbers required to carry out the IFFT calculation every 4 msec.

Throughput performance analysis We have described the physical-layer protocols for the various 802.11 implementations in the preceding two paragraphs. We also noted that the MAC-layer 802.

11 CSMA/CA access procedures described earlier in this section are essentially the same for all the 802.11 schemes. In this paragraph we return to the access procedures and describe a throughput performance analysis applicable to all the implementations.

We provide numerical examples of the analysis for the original 1 Mbps 802.11 scheme and the 802.11b, Wi-Fi, scheme only, however.

. c# gs1 datamatrix separati??onn Mobile Wireless Communications free generate qr code Table 12.1 Data rate parameters, IEEE 802.11a/g .NET Windows Forms 2/5 industrial maker on .net Data rate (Mbps) 6 9 12 1 8 24 36 48 54 QAM type PSK PSK QPSK QPSK 16-QAM 16-QAM 64-QAM 64-QAM Encoder rate. Embed 3 of 9 for .net /2 3 /4 1 /2 3 /4 1 /2 3 none none /4 2 /3 3 /4. Recall that there are two mechanisms used to carry out the MAC-layer CSMA/CA procedure. These are the basic access and virtual access techniques summarized in Figs. 12.

1 and 12.3 respectively. The throughput performance of each technique is measured by how effectively it utilizes the wireless channel capacity.

To answer this question we turn to analytical work, backed by simulation, carried out by Bianchi (2000). He has determined the maximum channel utilization obtainable for both access mechanisms as a function of the number of users, for various maximum contention window values. Interestingly, he models the access attempts using a p-persistent strategy similar to the strategies adopted for the various PRMA-type schemes described in the previous chapter.

Related work in determining the throughput performance of 802.11 systems appears in Ho and Chen (1996) and Cali et al. (1998), as well as other papers cited in all of these references.

The channel utilization or normalized throughput obtainable using the two CSMA/CA access procedures is de ned as the fraction of time the channel is used to successfully transmit the information portion of data frames, assuming each user station always has data packets ready to be transmitted. The normalized throughput to be determined is then referred to as the saturation throughput, the maximum possible system throughput under stable conditions (Bianchi, 2000). To determine this performance measure, begin at some randomly chosen slot time and consider a long interval of time following, long enough to cover many data frames being transmitted, as well as collisions incurred in attempting to transmit.

The length of time in this long interval used to actually transmit information divided by the full interval, i.e., the fraction of time in which information is transmitted, is then the desired channel utilization.

Equivalently, the average length of time following a randomly chosen slot time used to transmit user information divided by the average length of time required to transmit that information provides the desired channel utilization. This is the approach, following Bianchi, to be used here (Bianchi, 2000). Denote the information.

Bianchi, G. 2000. Perfor none none mance analysis of the IEEE 802.

11 distributed coordination function, IEEE Journal on Selected Areas in Communications, 18, 3 (March), 535 547. Ho, T.-S.

and K.-C. Chen.

1996. Performance analysis of 802.11 CSMA/CA medium access control protocol, IEEE PRMC, Taipai, Taiwan, October, 407 411.

Cali, F. et al. 1998.

IEEE 802.11 wireless LAN: capacity analysis and protocol enhancement, IEEE Infocom 98, San Francisco, CA, March..

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