Smart WiMAX Delivering personal broadband

Summary
Wireless communications is becoming an inherent part of our everyday life. We expect to be able to make a phone call no matter where we are via a cellular phone. At the same time the Internet explosion has created a need for access to data and multimedia that is much more than simple voice communication. Moreover, we expect to be able to access these applications anywhere, any time on any device. The end result is personal broadband – a wireless broadband connection that belongs to an individual, like a cell phone.

Achieving the economics of a personal broadband network deployment is the real challenge for next generation wireless networks. Some believe that existing cellular networks and their evolution to 3G and LTE can address this need. However, cellular networks that were originally designed for outdoor have a challenging time reliably delivering indoor voice, let alone mediarich broadband content indoors and out. As personal broadband devices such as laptops, ultramobile computing platforms, PDAs, game devices, etc. proliferate; the expectation is to be able to access broadband content indoors as well as outdoors in a stationary or mobile context. Given such a requirement it is increasingly becoming clear that we need a different approach to the delivery of ubiquitous anytime, anywhere broadband. This paper outlines a solution, which Navini terms “Smart WiMAX” that delivers this promise.

Smart WiMAX is Navini’s next generation wireless broadband solution that is fully compliant with the IEEE 802.16e Mobile WiMAX standard, and focused on the delivery of personal and mobile broadband. Smart WiMAX refers to the combination of two key next-generation technologies --Adaptive Beamforming and MIMO (Multiple input multiple output). Both are supported by the IEEE 802.16e standard to deliver on the vision of personal broadband. Networks using the key innovations of Smart WiMAX are in commercial service today, providing profitable mobile personal broadband service in large and small cities and towns around the world.

We discuss Smart WiMAX and in particular, the impact of adaptive beamforming and MIMO on the delivery of personal broadband. We show that Navini’s adaptive beamforming can increase the signal power delivered to a device by as much as 64 times (18dB) thus making it possible to deliver plug and play non-line-of-sight (NLOS) broadband anywhere, anytime indoors or outdoors. We also show that combining adaptive beamforming and MIMO can significantly improve the performance and usability of MIMO significantly by increasing the delivered SNR by as much as 16.5dB (in different MIMO schemes) over simple MIMO. Smart WiMAX makes MIMO practical - more reliable over larger areas while delivering higher throughput.
Smart WiMAX is fully standards compliant, and will interoperate with WiMAX Forum Certified TM Wave 2 mobile stations after wave 2 certification.

Smart Beamforming
To address the fundamental power problem encountered in delivering personal broadband with high data rates, a technology Navini calls “Smart Beamforming,” based on advanced antenna system (AAS) has been included in the Mobile WiMAX standard. All customer devices must support beamforming as part of the wave 2 certification profiles whereas the BTS may include support for beamforming as an optional feature.

The main idea behind Smart Beamforming is to address the power problem using multi-signal processing techniques. The system sends multiple small signals (instead of sending one high powered signal) such that they combine effectively at the end user terminal but cancel each other out in other places. This process is similar to dropping multiple small pebbles in water such that all the different waves combine to form a much larger wave at the end user but do not combine in the same way anywhere else. This process is called beamforming: Multiple signals are
combined to form an RF beam to the user.

The most effective form of beamforming uses adaptive techniques to measure the RF environment, and use those measurements to provide the best possible signal delivered to the exact location of the user.

A useful analogy to highlight the difference between a non-beamforming system and a beamforming system is to compare the effectiveness of a light bulb and a flashlight in illuminating a particular area. While the light bulb is far more powerful and disperses light all around the broad area it is illuminating, the flashlight is lower powered but can shine a focused beam to a specific area. The light bulb uses more power to light up a given area since it must overcome the inefficiency of spreading the light in all directions. By focusing on a specific area, the flashlight only requires enough power to focus the beam and leaves the rest of the area in darkness. This translates into beamforming boosting the signal to a particular user by the focused “beam” and also reduces interference to other users.

Navini’s Smart Beamforming system forms such beams every 5msec (the frame length for a WiMAX 802.16e-based system) so that as the user moves, he/she always has a beam tailor-made at that instant in time. On the downlink, from the BTS to the customer device, the BTS uses multiple antennas to send multiple signals to the user with slight variations in phase and amplitude determined by the channel conditions and environment variables at that instant in time. A similar process takes place on the uplink where multiple copies of the signal from the user are received at the base station and are combined to deliver a much stronger signal.