The Ins and Outs of the Signal Delivery Problem
Wi-Fi users have seen significant improvements in Wi-Fi radios in recent years. What hasn’t kept pace with these advances is Wi-Fi antenna technology. A better signal delivery system that optimizes the path between an access point and its client devices is needed more than ever to sustain the latest high-speed Wi-Fi data rates. Wi-Fi radios, when they first appeared on the market, used simple omni-directional antennas. Now, fifteen years later, most of the industry is still using the same omni antennas that are directly attached, or internal to access points. They indiscriminately radiate signals in all directions perpendicular to each antenna’s axis. If the AP and its antennas are mounted in a room with an outside wall, for example, a high percentage of the AP’s signal energy is scattered outside the building, wasting AP transmit power and making the wireless network more vulnerable to intrusion by “unfriendlies”. Or, at the very least, slows down the access point by forcing it to receive off-site interference from neighboring Wi-Fi APs and clients on the same channel.
How Signals Get Lost in Transit
Signals from an omni antenna transmitted toward adjacent rooms suffer significant loss in going through walls and office clutter in an attempt to reach clients. Each transit through solid objects, like sheet rock walls, furniture, book shelves, people, etc. absorbs a high percentage (typically 50 – 80%) of the signal during every occurrence like a series of sponges. Or if the object is metallic, the signal can be totally reflected and scattered back toward the access point. All of this lost signal strength is wasted when it could be used to illuminate many more user areas with high-level signals while concurrently decreasing external security risks and equipment costs. Furthermore, clients in the vicinity of an AP using omni antennas see tremendous signal “overkill” since any signal level significantly greater than a minimum needed to properly decode the highest desired data rate is simply wasted. The scale model office suite below shows these effects:
Light is used in this scale model to simulate radio frequency transmission from an access point at the end of a row of offices.
Note the “signal overkill” near the AP and the shadowing from metal wall studs, furniture and other objects.
The Ideal System
What’s needed is an efficient, low-loss method of distributing (and gathering) wireless signals from both nearby and distant clients. Signal attenuation in a transmission path is reciprocal, i.e. any improvement in signal level from an AP to a client is matched in gain of a client’s signal toward an AP. No matter which 802.11 standard is being used, or whatever signaling standard is being employed, “low signal strength equals low speed” always applies. Signals need to be preserved in strength and quality while being provided to multiple users at dispersed locations. These problems can be overcome by using an economical and efficient WE waveguide-based wireless distribution system that carries signals to dispersed areas in a building. This concept, when you think about it, isn’t much different than other distributed conveniences, like air conditioning, water outlets, and electrical sockets. The challenge is to devise an inexpensive system that can efficiently bypass radio frequency obstructions and provide high-quality signals to all users.
The Solution to the Problem
It has been known for many years that metallic waveguide is the most efficient medium for transporting radio signals. The signal loss per unit length is extremely low. WE has developed a low-loss, low-cost, waveguide-based DAS (distributed antenna systems) to transport and distribute high-quality signals throughout indoor facilities. Our waveguides at 2.4GHz, for example, have approximately 0.4dB loss per 100 feet. In comparison, a typical “low loss” coaxial cable that’s widely used in the wireless industry for transporting signals has approximately 6.7dB loss per 100 feet. Translated to signal power preservation, our waveguide maintains 83% of the original signal strength at 200 feet, while “low loss” coaxial transmission line will have less than 4.7% of its signal power remaining at the end of a 200ft section of cable. And our waveguide components are designed with materials that are fire-safety compatible for out-of-sight installation in HVAC plenum spaces. They require no maintenance after installation and can be moved and reinstalled at a later date.
Efficiency Gets the Job Done
Keep in mind that every percent of power lost in a transmission medium ultimately equates to a commensurate loss in percentage of coverage area, or in signal strength provided to each user in areas that are illuminated. The low loss in our waveguide system allows AP signals to be transported long distances (100’s of feet) and distributed with very little loss along the way. Coaxial systems are not as practical due to their high attenuation. And the loss in coaxial cable is much higher at 5GHz (802.11a,n,ac) where our waveguide loss remains very low. It is also well known that it is physically impossible to make a coaxial cable that has a loss per unit length that is as low as our waveguide at the same frequency.
Not the Old Way of Constructing Waveguide
Although it’s the best transmission medium, the historical problem with waveguide has been its high cost. It was originally developed for “high ticket” military radar and high-end commercial microwave systems that use expensive hardware. WE has developed practical, low-cost waveguides that now rival those in military-grade systems. Expensive waveguide components, such as precision launchers, choke flanges, and mode suppressors have been replaced with lower-cost equivalents that are easy to install and work very efficiently.
The Right Signals for All Locations
Coupling signals from a waveguide must be performed accurately. WE has solved this problem with patented, high-efficiency signal coupler designs. They minimize signal losses and reflections in both the waveguide and coupler, allow easy output adjustment over a 40dB (10,000/1signal power) range, and supply the correct signal level to each user-area antenna. Note the uniform signal distribution in all offices illuminated by a WE waveguide system:
Simulation of signals delivered and radiated into each office area over a WE waveguide system.
Full Coverage by Design
Signal distribution throughout a facility can best be performed with a Wireless Expressways waveguide system. Our systems provide controlled, specific, illumination to all users. Unlike simple omnidirectional antennas on scattered APs, or even local directional antennas, a WE waveguide system transports signals very efficiently from a transmitting AP to each user area in a large facility with very little signal loss. Signal couplers attached to the waveguide at each user area then feed pre-calculated amounts of signal power to local antennas for proper illumination of client locations. The result is high-strength, high-speed signals provided to clients everywhere. WE Wi-Fi systems go around and over signal-absorbing and reflecting objects to deliver excellent signals to all users in required areas. And more than one channel can be paralleled on the same waveguide for redundancy, separate applications, or wider total bandwidth.
Short Circuiting Problems While Lowering Costs
WE “short circuits” the harmful losses experienced with legacy transmission methods that try to penetrate walls in, e.g. offices, classrooms, hospitals, or products on rack shelves in warehouses in attempting to propagate signals to wireless clients. WE waveguide systems provide remarkably large coverage areas with far fewer access points. Any enterprise-grade APs with external antenna ports can be used. WE recovers what would normally be lost signal power and uses it to better serve all client areas. And fewer APs mean fewer switch or wireless controller ports, UTP runs to APs, and lower on-going maintenance for far better, more reliable, wireless communications.