Key Priorities For Sub Ghz Wireless Deployment
To build an advanced wireless system, most developers will end up choosing between two industrial
, scientific and medical (ISM) radio band options2.4GHz or sub-GHz frequencies. Pairing one or the other with the systems highest priorities will provide the best combination of wireless performance and economy.
These priorities can include:
Range
Power consumption
Data rates
Antenna size
Interoperability (standards)
Worldwide deployment
Wi-Fi, Bluetooth and ZigBee technologies are heavily marketed 2.4GHz protocols used extensively in todays markets. However, for low-data-rate applications, such as home security/automation and smart metering, sub-GHz wireless systems offer several advantages, including longer range, reduced power consumption and lower deployment and operating costs.
Sub-GHz radios
Sub-GHz radios can offer relatively simple wireless solutions that can operate uninterrupted on battery power alone for up to 20 years. Notable advantages over 2.4GHz radios include:
Range The narrowband operation of a sub-GHz radio enables transmission ranges of a kilometer or more. This allows sub-GHz nodes to communicate directly with a distant hub without hopping from node to node, as is often required using a much shorter-range 2.4GHz solution. There are three primary reasons for sub-GHz superior range performance over 2.4GHz applications:
1.As radio waves pass through walls and other obstacles, the signal weakens. Attenuation rates increase at higher frequencies, therefore the 2.4GHz signal weakens faster than a sub-GHz signal.
2.2.4GHz radio waves also fade more quickly than sub-GHz waves as they reflect off dense surfaces. In highly congested environments, the 2.4GHz transmission can weaken rapidly, which adversely affects signal quality.
3.Even though radio waves travel in a straight line, they do bend when they hit a solid edge (like the corner of a building). As frequencies decrease the angle of diffraction increases, allowing sub-GHz signals to bend farther around an obstacle, reducing the blocking effect.
The Friis Equation demonstrates the superior propagation characteristics of a sub-GHz radio, showing that path loss at 2.4GHz is 8.5dB higher than at 900MHz.
Path Loss = 20*log10 [(4*pie*d)/wavelength] {dB}
This translates into 2.67x longer range for a 900MHz radio since range approximately doubles with every 6dB increase in power. To match the range of a 900MHz radio, a 2.4GHz solution would need greater than 8.5dB additional power.
Low interference The airways are crowded with colliding 2.4GHz signals from various sources, such as home and office Wi-Fi hubs, Bluetooth-enabled computer and cell phone peripherals and microwave ovens. This traffic jam of 2.4GHz signals creates a lot of interference. Sub-GHz ISM bands are mostly used for proprietary low-duty-cycle links and are not as likely to interfere with each other. The quieter spectrum means easier transmissions and fewer retries, which is more efficient and saves battery power.
Low power Both power efficiency and system range are functions of the receiver sensitivity plus the transmission frequency. The sensitivity is inversely proportional to channel bandwidth, so a narrower bandwidth creates higher receiver sensitivity and allows efficient operation at lower transmission rates.
For example, at 300MHz, if the transmitter and receiver crystal errors (XTAL inaccuracies) are both 10 ppm (parts per million), the error is 3kHz for each. For the application to efficiently transmit and receive, the minimum channel bandwidth is two times the error rate, or 6kHz, which is ideal for narrowband applications. The same scenario at 2.4GHz requires a minimum channel bandwidth of 48kHz, which wastes bandwidth for narrowband applications and requires substantially more operating power.
In general, all radio circuits running at higher frequencies, including low-noise amplifier, power amplifier, mixer and synthesizer, need more current to achieve the same performance as lower frequencies.
Range, low interference and low power consumption are basic advantages of sub-GHz applications over 2.4GHz apps. One of the disadvantages often cited is that the antennas are larger than those used in 2.4GHz networks. The optimal antenna size for 433MHz applications, for instance, can be up to seven inches. However, antenna size and frequency are inversely proportional. If node size is an important design consideration, developers can raise the frequency (up to 950MHz) in order to employ a smaller antenna.
by: Chris Bartik
The Ease Of Using A Wireless Adapter How much Fun with Wireless Keyboard Wireless Burglar Alarms - 5 Reasons To Cut The Wires Use Of A Wireless Cooking Thermometer In Cooking An Overview Of A Wireless Cooking Thermometer Wireless Connectivity - How To Set Up A Netgear Wireless N Router Advantage of Having Kindle Wireless Reading Device RFID Handheld Device features reliable Wireless Date Transmission Wireless Reading Device on the Net Why You Must Use A Wireless Cooking Thermometer To Cook Meat Linksys Wireless Router Configuration in 3 Steps Going Wireless GPS Wireless Clock System