**2.2.1 Impact of LCD EMI analysis on 802.11g throughput[5]**

In a laptop, there are many interference sources which can be in the form of radiation or conduction. LCD noise is the major interference to the wireless performance. Figure 11 shows the frequency domain measurement setup and measured results for platform noise from LCD. The measurement setup is shown in Figure 11a and the test procedures are described as following:


Figure 11b shows the different antenna placements along the horizontal edge on top of a LCD panel. The measured results show that the noises at 2.400GHz, 2.450GHz, 2.490GHz ( harmonics of the pixel clock) are major interference sources that fall into WLAN band. We can obtain 2-5dB noise suppression by simply moving the antenna several millimeters away from its initial location. The comparison for different antenna measurements at different locations shows that the LCD noise might have an significant impact on desensitization to 802.11g. The measurement of antenna positioned towards the left 20mm serves as a reference to quantify the impact of antenna placement on the platform noise measurement. The noise picked up by antennas would desensitizes the receiver and reduced the throughput. Meanwhile, the throughput test procedure and test setup are as follows: the setup consists of an AP (access point), EUT (laptop) and Chariot console throughput software. The AP (access point) and EUT (laptop) are connected through path-loss attenuators to control RFI strength, and the communication traffic is controlled and monitored by a desktop using Ixia Chariot® software as shown in Figure 12a. The system

(a) Platform noise measurement setup for antenna port

(b) Comparison of the different antennas measurement at different locations on the LCD panle.

Fig. 11. LCD noise measured at antenna port in WLAN band.

802.11g. The measurement of antenna positioned towards the left 20mm serves as a reference to quantify the impact of antenna placement on the platform noise measurement. The noise picked up by antennas would desensitizes the receiver and reduced the throughput. Meanwhile, the throughput test procedure and test setup are as follows: the setup consists of an AP (access point), EUT (laptop) and Chariot console throughput software. The AP (access point) and EUT (laptop) are connected through path-loss attenuators to control RFI strength, and the communication traffic is controlled and monitored by a desktop using Ixia Chariot® software as shown in Figure 12a. The system

(a) Platform noise measurement setup for antenna port

(b) Comparison of the different antennas measurement at different locations on the LCD panle.

Fig. 11. LCD noise measured at antenna port in WLAN band.

path-loss includes cable loss, space loss and attenuators. The results in Figure 12b the real line and dotted line, clearly show that the sensitivity and the throughput decrease as the LCD interference is injected to the communication link between the AP and NIC card. It is found that there is about 10dB desensitization between the two throughput measurements for different locations. It is show that when the LCD noise increases the sensitivity is reduced and performance is also degraded. Moreover, it is again shown that the location of antenna placement is significant to wireless communication performance. Figure 12c shows the photograph of the antenna integrated into a laptop for investigation.

(a) The throughput test procedure and test setup

(b) Throughput comparison for in 802.11g antenna 2 and antenna 3 at two different positions.

(c) Photograph of the antenna integrate into a laptop.

Fig. 12. Throughput comparison in 802.11g for different locations on the LCD panel.
