Low Power Wide Area Networks (lpwan): Technology Review And Experimental Study on Mobility Effect

WEIGHTLESS-SIG

Weightless is both the name of technology and a group called Weightless Special Interest Group [66]. It is a proprietary standard developed for machine to machine communication. This standard aims to use the TV white spaces which are unused frequency bands which can be used by secondary devices without interfering with the function of the primary device. The group has presented three LPWAN standards which can function in both licensed as well as license-free spectrum. Each of these standards have different features, power consumption and communication range. While all the standards use symmetric key cryptography for network integrity and authentication. The following summarizes the pros and cons of Wightless.

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  Weightless-W: This standard has better signal propagation in TV white spaces compared to the other two standards. Weightless-W can transmit data packets of sizes up to 10 bytes at data rates between 1kbps and 10Mbps. Weightless-W supports a wide range of spreading factors and multiple modulation schemes like
  

DBPSK (Differential BPSK) and 16-QAM (16-Quadrature Amplitude Modulation). In order to achieve a longer battery life the end nodes communicate with the base station via a narrow band and lower power levels as compared to the base stations. The drawback of Weightless-W is that the shared access to white TV spaces is granted only for limited regions. To overcome this, Weightless-SIG introduces Weightless-P and Weightless-N which are available for shared access globally.

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  Weightless-N: This standard is the most power efficient when compared to Weightless W and Weightless-P. It is an ultra-narrow band standard which offers only one way communication from end devices to base station. This standard uses the Differential Binary Phase Shift Keying modulation scheme. The disadvantage of Weightless-N is that due to its one way communication characteristic, its can be used with restricted number of applications which do not need bi directional communication.
  
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  Weightless-P: This is a bidirectional standard which offers two way communication with fully acknowledged data transmission for reliability and capabilities for over the air firmware upgrades. It supports payload sizes up to 48 bytes and can achieve data rates from 0.625kbps to 100kbps. Weightless-P can operate in any frequency band but currently it is defined to operate in only license-exempt sub-GHz frequency bands. It uses Quadrature Phase Shift Keying (QPSK) and Gaussian Minimum Shift Keying (GMSK) to modulate the signals.
  

Pros:

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  Communication range from 2 to 5 plus km.
  
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  With advanced demodulation it can work with existing Radio Frequency technologies with minimal interference.
  
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  Weightless-W and Weightless-P offer bidirectional communication.
  
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  Low speed sensors can use Weightless-N while Weightless-P offers adaptive data
  

rate.
Cons:

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  Weightless requires a white space TV spectrum to work for Weightless-W.
  
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  Depending on the standard used, battery life can range from 2 to 10 years.
  

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