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WLAN implementations should optimize certain basic performance parameters within the context and constraints of the application. These parameters include the reach or range of WLAN signaling, the data throughput rate supported by the WLAN implementation and its robustness when it comes to overcoming various sources of interference in the environment. In addition, the selection of a WLAN chipset solution as well as the software environment and tools supported by the WLAN solution are also important considerations.
Reach, Rate and Robustness
The effective reach or range of WLAN signaling is often determined by the specific requirements of the application. Some stationary CE systems require "whole house" coverage, while others do not. The effective reach of WLAN signaling is affected by the system's transmit output power and the sensitivity of the WLAN receivers. For stationary CE systems, which usually have access to a constant supply of power, output power can be adjusted upward somewhat to achieve greater range. Receiver sensitivity is an inherent capability of the WLAN chipset, and so careful attention should be paid to this feature. A general rule of thumb is that for every 6 dBm increase in receiver sensitivity, there is roughly double the linear range in free space. For example, a WLAN subsystem that has a sensitivity of -76 dBm at 54O FDM has roughly twice the linear range and 4 times the coverage area (in free space) as a chipset that has a sensitivity of -70 dBm at 54O FDM.
G++ Technology
G++ Technology
High data throughput speeds are certainly important for some stationary CE applications, as is the ability to connect at large distances. System-level design decisions and the throughput rate of the WLAN chipsets have a decided impact on these factors.
Robustness of a WLAN implementation can be of particular importance in stationary CE systems which are often subjected to several sources of adjacent channel and in-band interference. The sources of interference commonly found in homes include microwave ovens, cordless telephones and other WLAN networks in close proximity. The inherent capabilities of the WLAN chipset as well as antenna placement and other design considerations can increase or decrease the robustness of a stationary CE product with WLAN capabilities.
Chipset Selection
The processing requirements of the host processor demanded by the WLAN chipset will have significant effects on the overall performance of the stationary CE system. Some chipsets require very little intervention on the part of the system's host CPU, but others involve host CPU processing cycles in the execution of WLAN operations. "Stealing" processing cycles from the host CPU for WLAN operations effectively removes those cycles from other tasks that may be more essential to the functionality of the CE product. By doing so, the performance of the primary function of the product in the eyes of users is diminished.
Software Environment
A comprehensive and flexible software environment will accelerate development time and free programming resources for application-critical projects. Such a software environment should include a full-function driver and the flexibility to port the driver to another operating system (OS) should it be required by the manufacturer, an easily integrated driver architecture that can be quickly customized, standard APIs to ease application-specific integration as well as software development in general, security capabilities and a well-defined interface to the networking stack.
To ensure acceptable performance of a host system with a WLAN subsystem, interference between the two must be minimized. This requires adequate forethought and planning in the design of the motherboard and the daughtercard. The overall objective is to minimize the effects of noise sources from the DaVinci or DM-based system board on the WLAN subsystem and to optimize the WLAN subsystem's performance within the application. Because the sensitivity of the receivers in TI's WLAN chipsets is very high, steps should be taken to minimize radiated and conducted emissions from the motherboard that might otherwise degrade the performance of the WLAN subsystem.
TI provides a reference design of a WLAN subsystem, the PCA-171, for stationary CE applications. Implemented on a MiniPCI daughtercard, the PCA-171 WLAN offers several antenna configuration options, including single, dual and triple antenna architectures should additional antenna variations be needed. TI stationary design guides define the pin-outs for the MiniPCI connector to the motherboard.
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