The File - Dec 1, 2008 - (Page 5)

In Focus | Mobile handsets Mobile handsets integrate WLAN By N. Venkatesh Chief Wireless Architect Redpine Signals, Inc. The growth of wireless networks based on the IEEE 802.11 wireless LAN (WLAN) family of standards has been one of the most outstanding success stories of the industry in recent years. The initial growth of WLAN, commonly referred to as WiFi—thanks to the certification efforts of the Wi-Fi Alliance—was in its intended role of providing a wireless data networking capability to replace a wired LAN connection. But as its capabilities grew to offer higher data rates, better quality of service and special modes such as power-save, it quickly became an integral part of a large variety of devices including phones, gaming devices, music players, sensors, and other consumer electronics. In this article, we look at the factors to be considered when integrating WLAN into mobile handsets. The handsets utilise WLAN connectivity for a wide array of purposes, including Voiceover-Wi-Fi (VoWiFi) calls, web browsing, email, data download, audio and video streaming, and file synchronisation. Integration issues The most common method of bringing in WLAN functionality into a handset is through the integration of a self-contained WLAN module offering a low load on the host processor. This approach minimises integration effort, as we elaborate further on. Figure 1 shows the typical constituent blocks of such a WLAN module. The Host Interface is usually SDIO or SPI, or sometimes a memorymapped interface or USB. The module shares a frequency reference with the handset’s communication blocks, and also a low frequency clock used in sleep modes. There are several considerations influencing the integration Figure 1: Components of a WLAN module. of this module into the handset, as listed: • Physical and electrical considerations—Size and weight are primary concerns because of their influence on a consumer’s choice of a mobile phone. State of the art WLAN modules are typically smaller than 10mm by 10mm. The high level of integration within the WLAN module drives a need for several voltages. To cater to this, and to the stringent power-save considerations, the modules include a full-featured powermanagement block. • Coexistence—Since the modern full-featured handset in- • transmission and reception are spaced apart in time and frequency. With some bands of the cellular spectrum being relatively close to the WLAN operational frequencies, handsets also require a measure of filtering in front of the WLAN module to curb mutual interference between the cellular RF and the WLAN RF. Software integration—The WLAN module is expected to take care of the majority of protocol specific tasks. The host application processor normally integrates a network driver that configures the WLAN hardware and provides for command and control • • cation risk on the platform; Minimum time-to-market; and Potentially simple upgrade path. “The most common method of bringing in WLAN functionality into a handset is through the integration of a self-contained WLAN module offering a low load on the host processor.” cludes a myriad of functional blocks, with many of them communicating wirelessly— via GPS, Bluetooth, FM radio, etc.—coexistence issues become prominent. Among these, Bluetooth requires special handling since it occupies the same frequency band of 2.4 GHz as WLAN. Bluetooth coexistence is handled usually by exchanging hardware signals in real time with the Bluetooth module, through which it is ensured that their functionality. The host may also include a supplicant taking care of enterprise mode authentication requirements. In summary, the integration of WLAN via a self-contained module is the preferred approach for the following reasons: • No WLAN-related protocol load in the host processor; • No critical RF design and integration necessary; • Independently Wi-Fi certified, which means lower re-certifi- Performance, power issues Power consumption is the primary consideration when integrating WLAN into handsets. Since the WLAN functionality would be used for a variety of purposes, each of the applications would require a separate analysis of performance requirements and power consumption. We explain this for two key applications, as follows: • Voice calls—VoWiFi is a potential “killer application” in mobile handsets. The widespread availability of WLAN connectivity in public places, at home and in the office means that a potentially large percentage of voice communication can take place through low-cost VoIP services. For the user to experience a satisfactory call quality, the WLAN connection would need to ensure performance in terms of low jitter, low packet loss and low latency. Meeting these requires the provision of standards-compliant QoS mechanisms, in addition to basic wireless performance. Furthermore, the WLAN client would have to implement a robust and quick roaming mechanism to ensure that voice calls are carried over smoothly when the client roams from one access point (AP) to another. continued on page 5 EE Times-India | December 1-15, 2008 | www.eetindia.com http://www.eetindia.co.in/SEARCH/SUMMARY/technical-articles/DATE/WLAN.HTM?ClickFromNewsletter_081201 http://www.eetindia.co.in/SEARCH/SUMMARY/technical-articles/DATE/WLAN.HTM?ClickFromNewsletter_081201 http://www.eetindia.co.in/SEARCH/SUMMARY/technical-articles/RELEVANCE/Wi~%40~Fi.HTM?ClickFromNewsletter_081201 http://www.eetindia.co.in/SEARCH/SUMMARY/technical-articles/RELEVANCE/Wi~%40~Fi.HTM?ClickFromNewsletter_081201 http://www.eetindia.co.in/SEARCH/SUMMARY/technical-articles/Bluetooth.HTM?ClickFromNewsletter_081201 http://www.eetindia.co.in/SEARCH/SUMMARY/technical-articles/%22access point%22.HTM?ClickFromNewsletter_081201 http://www.eetindia.com/STATIC/REDIRECT/Newsletter_081201_EETI02.htm?ClickFromNewsletter_081201

Table of Contents for the Digital Edition of The File - Dec 1, 2008

EETimes India - December 1, 2008
Contents
National Semiconductor
WiMAX Goes Beyond Mobile Devices
Mobile Handsets Integrate WLAN
Meet WiMAX Power Amp Challenges
NGSA - 08, Energy INDIA, ICDCIT 2008, REA-2008, ICON 2008, ICPCM 2008

The File - Dec 1, 2008