Let’s take this opportunity to talk about wireless co-existence, an issue that begins to draw broad attention in the mobile communication industry, an issue that will help shape the system and architecture design of mobile device and infrastructure for years to come.As we know, wireless technologies operate in designated frequencies (or bands), assigned by regulatory bodies such as the FCC in the United States. Not only frequency but transmission power or power emission is also regulated so as to avoid interference between different wireless technologies. The rules and policies, for the most part, were designed for wireless systems feet or meters apart. When radios are forced into tight space, those regulations lose efficacy in avoiding interference. The military knew this when installing multiple radars in the front pod or the belly of a reconnaissance aircraft during the cold war. However, the co-existence issue only became front and center thanks to the proliferation of personal mobile devices such as cell phones, notebook computers and the merging Mobile Internet Devices (MID). Different wireless technologies are designed for different purposes; they work in different range distances and have different characteristics. As these mobile devices increasingly become indispensable, if not fashionable, in everyday life, multiple usages via wireless start to gravitate toward these device. For example, if a person wants to make phone calls, download songs, listen through headsets, check location, listen to talk shows and watch sportscasts, all on a MID, then wireless WAN (cellular or WiMAX), high-speed wireless LAN (WiFi), short-range wireless (Bluetooth), GPS, FM and mobile TV, all need to be installed on that MID. And it’s not hard to imagine some of these radios will operate at the same time. As mobile devices get ever smaller, thinner, and lighter (think about the first generation mobile phone that looked and weighed like a brick), all these radios are being squeezed into a space where a few millimeters distance is all that separates one from another. These radios will start to interfere with each other through co-channel interference, out-of-band emission, harmonic frequency interference, etc. If not designed well, there will be noticeable performance degradation under various scenarios rendering user experience anywhere between annoying to intolerable. Wireless co-existence is not limited to personal devices. As different flavors of the 3G technologies are assigned bands next to each other, base stations would run into similar types of interference when they are deployed on the same tower (to save real estate expense). Therefore, wireless co-existence is also a crucial factor in network infrastructure co-deployment. Back to personal devices, another trend is emerging in radio design that further complicates wireless co-existence, and that is radio integration. As the quest for reducing the cost and size of mobile devices continues, multiple radios start to be integrated into the same silicon package, and they start to share components such as antenna and RF components. Consequently, not only can radios interfere with each other through frequencies, their operations will further conflict each other by competition over the shared components. By now, I hope you have come to realize that wireless co-existence is an essential design issue for future mobile devices that are compact and multi-functional. Unfortunately, most radio technologies were developed and standardized without putting much thought into co-existence with other technologies. Co-existence issues are often discovered as an afterthought and dealt with as an inconvenience. The industry has begun to realize the necessity of systematic approach in incorporating co-existence methodology in designing future wireless devices and technology. Next time, let’s walk through some of those methodologies and solutions that are appearing on the horizon.
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