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WLAN System Capacity Zahid Iqbal. WLAN Technologiess IEEE802.11a IEEE802.11b IEEE802.11g.

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Presentation on theme: "WLAN System Capacity Zahid Iqbal. WLAN Technologiess IEEE802.11a IEEE802.11b IEEE802.11g."— Presentation transcript:

1 WLAN System Capacity Zahid Iqbal

2 WLAN Technologiess IEEE802.11a IEEE802.11b IEEE802.11g

3 1EEE802.11a Operates on 5GHz band Uses a Radio Transmission called Orthogonal Frequency Division Multiplexing (OFDM) Data Transmission rates from 6Mbps to 54Mbps Use Carrier Sense Multiple Access with collision avoidance (CSMA/CA) for access method

4 Channels and Capacity 300MHz GHz GHz GHz Low band with maximum power output of 50mW Middle band with maximum power output of 250mW High band with maximum power output of 1W

5 Channels and Capacity a standard has 12 non-overlapping channels spread across 3 bands 8 of the channels are restricted to indoor use 4 channels can be used indoor or outdoors

6 Channels and Capacity Maximum Wireless Capacity (Mbps) = Rate*# of Non Overlapping Channel Maximum a Capacity = 54*12 = 648Mbps

7 IEEE b Operates on 2.4GHz (ISM) band Uses a Radio Transmission called Direct Sequence Spread Spectrum (DSSS) Data Transmission rates from 1Mbps to 11Mbps Use Carrier Sense Multiple Access with collision avoidance (CSMA/CA) for access method

8 Channels and Capacity Total 11 channels are available in the US 3 non-overlapping channels for use (Channela 1, 6,11) Max b Capacity = 11*3 = 33Mbps

9 IEEE g Operates on 2.4GHz (ISM) band Uses a Radio Transmission called Orthogonal Frequency Division Multiplexing (OFDM) Data Transmission rates upto 54Mbps

10 IEEE g Provides backword compatability with b Use Carrier Sense Multiple Access with collision avoidance (CSMA/CA) for access method

11 Channel and Capacity Total 11 channels are available in the US 3 non-overlapping channels for use (Channela 1, 6,11) Max g Capacity = 54*3 = 162Mbps

12 Capacity and Performance of

13 Coverage and Throughput Performance Free space path loss

14 Coverage and Throughput Performance Free space path loss of 2.4GHz and 5GHz with distance 10m:

15 Coverage and Throughput Performance

16 The multipath effect is modeled as a Rayleigh fading channel with a 50 ns delay spread. The shadow fading can be modeled as a log- normal distributed random variable with an 8 dB standard deviation.

17 Coverage and Throughput Performance For indoor radio environments, a two-slope path loss model with a breakpoint is used. The break point is related to the first Fresnel zone clearance, antenna height, and the transmitted frequency.

18 Coverage and Throughput Performance a802.11b802.11g Data Rate (Mbps) Distance (Feet) Data rate (Mbps) Distance (Feet) Data rate(Mbps) Distance (feet)

19 Coverage and Throughput Performance

20 For a cell radius of 65 feet, more than four b cells would have to be overlaid on top of each other to achieve the same average throughput of a single a cell.

21 Impact of co-channel Interfenece on System Capacity b/g has 3 non-overlapping channels

22 Impact of co-channel Interfenece on System Capacity

23 Mechanism to model the effect of co-channel interference Clear Channel Assesment Method Hidden Cells

24 Impact of co-channel Interfenece on System Capacity Co-channel interference immunity (CCI) CCA Threshold Practical CCA threshold

25 Impact of co-channel Interfenece on System Capacity

26 Conclusion a can provide coverage comparable to b upto 225 feet in a typical office environment The data rate of a is approximately 2 to 5 times better than b within the coverage distance.

27 Conclusion g can provide coverage comparable to b as well. The data rate of g in a single cell is higher than a because of the better frequency dependant path loss.

28 References James C. Chen, PhD., Jeffrey M. Gilbert, PhD, “Measured Performance of 5-GHz a Wireless LAN Systems” Proxim Corporation, “A Detailed examination of the environment and protocol parameters that affect g network performance “


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