**3.2 External modulation problem**

192 Wireless Communications and Networks – Recent Advances

(2112.4MHz) -105.44 -114.74

(2140MHz) -103.74 -113.12

(2167.6MHz) -106.32 -115.03 (a) WCDMA Band1

(871.4MHz) -102.37 -110.63

(881.6MHz) -104.26 -112.17

(891.6MHz) -104.24 -112.56 (b) WCDMA Band5

Due to the increasing add-on functions demand for consumer electronics, currently multiradios, such as WLAN, WWAN, GPS, Bluetooth, and even DVB-H modules, have all been crowdedly embedded and highly integrated in a tiny space of wireless communications platform. Therefore the wireless devices usually have been equipped with more than one antennas, the purpose is to fit for different communication system such as cellular mobile communications, wireless local area networking, and personal area networking. Under this situation, the performance of various kinds of wireless communications is usually degraded by the mutual coupling and interference of closely arranged antennas inside the mobile device. Since the RF modules co-existence has become a critical design problem for wireless

Platform noise usually raises the RF receiver noise floor and dramatically degrades system performance by push the Eb/N0 to the margin when there in-band or out-of-band interference exists. A frequent cause of poor sensitivity on a single channel, or a small number of channels, is due to receiver's in-band noise from broadband digital noise or spurious signals from other coexistent transmitters. We describe in this section the potential coexistence problem for multimode and multiband RF modules, and also illustrate below in Figure 16 the example of isolation required for various RF systems to achieve better service.

(dBm)

(dBm)

NFS (dBm)

NFS (dBm)

WCDMA 1 TIS

WCDMA 5 TIS

CH10562

CH10700

CH10838

CH4357

CH4408

CH4458

**3. RF coexistence problems on product performance [7]** 

communications, we will discuss the RF coexistence problems in this section.

Table 2. Measured TIS on WCDMA bands of Netbook.

**3.1 Isolation required for RF coexistence** 

Even the low-speed digital I/O traces or cables in TP may induce GFSK modulation current, when they are nearby Bluetooth module operating at 2.4GHz. The non-linear ON/OFF switching of digital signal would also play a role as pulse modulation and generate magnetic field through those traces or cables to interfere the DCS and PCS systems. Some extreme case would also happen to WCDMA. The external modulation phenomenon can't be measured by network analyzer until the TP is activated as shown in Figure 17. We also illustrate in this section how the external modulation effect could be found in the final design stage of product with WWAN and BT RF modules ready, however the re-design is needed when platform and TP operate in their normal mode.

Fig. 17. External Modulation Effect.
