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Got 11n?

By N. Venkatesh

One of the most valuable commodities in the world is frequency spectrum. Like land, they aren’t making any more of this either, but even more importantly, available spectrum is a key factor in the growth of the technology industry. Computers, electronic devices and machines all talk to each other exchanging volumes of information in a variety of scenarios. More than just communicate with each other, these devices form a vast, IP-based network, what is now being called ‘the Internet of Things’.

Spectrum may be scarce and expensive, but there are bands of frequencies that are available ‘license free’ for use by anyone adhering to certain guidelines. This has primarily been responsible for enabling the pervasiveness of wireless communications today. However, this spectrum is becoming increasingly crowded, potentially limiting the applications that can make use of wireless data transfer in a given area. The wireless community is therefore constantly at work creating ways in which the limited spectrum can be used with improved efficiency.

The IEEE 802.11n standard is one such endeavor – it has defined the physical layer and MAC layer characteristics to significantly increase the end-user throughput that can be achieved in a given frequency channel. Because of this ‘high throughput’ thrust, the 802.11n standard is largely associated with high speed communications between high performance computing platforms. Lesser known, but equally significant, is that it enables a much more efficient use of available spectrum. However, the benefits of 802.11n are realized fully only when all nodes on the wireless network are capable of communicating using 802.11n methods or are compatible with 11n. The presence of legacy 802.11a/b/g nodes in a network forces the other 802.11n nodes to resort to the use of protection mechanisms to preserve network integrity, thereby reducing overall network capacity by 30 percent or more.

Small embedded devices, with low data throughput needs, are particularly prone to being equipped with legacy WLAN transport – potentially being major network disrupters. Their wireless needs are apparently simple and legacy 802.11b/g WLAN modules do satisfy many or all of these needs – but with the major drawback of not being 802.11n compatible and thus future-proof. Commonly available 802.11n chipsets and modules, with two-stream MIMO capability and multiple antennas, would neither be small nor low power, and are more suited to systems such as laptops. The ideal choice for these embedded systems is a single-stream, self-contained, 802.11n module, which must meet hardware and software integration considerations to ensure system level performance with minimal design or integration effort.

The WLAN module should be fully self-contained. Wireless performance is influenced not only by the core MAC, Baseband and RF components, but also by other components such as the frequency reference, RF front-end, and antenna or antenna connector. For ensuring design performance, all the required hardware should be available in a pre-tested and calibrated module, with commonly used host interfaces such as UART or SPI. An added benefit of using a self-contained module is the possibility of utilizing its modular FCC certification, since the module would be integrated largely in its certified form.

Embedded systems are characterized by low memory usage and the use of low complexity microcontrollers; and the addition of a WLAN subsystem should not alter these characteristics. This is achieved by the WLAN module incorporating its own processor running the 802.11 functions, the wireless configuration and the entire networking stack. Only a few kilobytes of code should be added to the host processor to facilitate the WLAN interface.

Modules that meet these requirements are available today. New embedded designs therefore can be uniformly equipped with 802.11n connectivity at the same or lesser cost and lower power consumption than legacy WLAN transport, satisfying the communication needs of the users as well as preserving network throughput in the ubiquitous wireless networks of tomorrow.

N. Venkatesh is the vice president of advanced technologies at Redpine Signals, and has over 24 years of engineering and management experience in wireless system design, chip design, telecommunications, optical networking and avionics. At Redpine, Mr. Venkatesh’s responsibilities include leading the development of wireless systems at the company’s development center in Hyderabad, and their application into diverse industry areas. Mr. Venkatesh holds a Masters Degree in Electrical Engineering from the Indian Institute of Technology, Madras, India.