Check the attached articles. There is no optimal solution. It depends on the protocol used (802.15.4 or something else)

You need to review critically existing approaches and try to choose the best that suits your application.

Good luck !

Integrated Low-Power Communication System Design for Wireless Sensor Networks

http://www.eeweb.ee.ucla.edu/publications/journalGregoryPottiekaiser_ieeecomm-mag_dec04.pdf

Dear Sir,

This is a rather difficult question. I mean, there are many aspects to it.

Basically, for a WSN system, the power consumption falls into a number of categories:

(1.) The 'base' consumption when the system is operating. In this falls the dissipation

       of the VCO, the LNA, and the sleep consumption of all the digital and analog.

(2.) The consumption associated with the transmission of information.

To minimize consumption, there are now 2 competing criteria:

(1.) You want to transmit the stream as efficient as possible with the given modulation system.

(2.) You want to keep the ON time as short as possible (the duty cycle as low as possible) to cut down on 'base' consumption.

The best modulation to have maximum amount of bits per unit power transmitted is QPSK. To improve over raw QPSK, some coding gain can be introduced by adding an error corrector. (usually a Viterbi)

To keep the ON time as short as possible possible, the data rate should be as high as possible. If then the link budget is not enough, you could increase link budget by doing MIMO (multiple receive and transmit antenna.)(No standards do that yet.) (You can do MIMO to increase SNR, so multiple antenna single stream, or multiple antenna multiple streams.)

Note that that the 'sleep' dissipation is often also quite high. (the LNA and the VCO). In order to cut down on the VCO complexity and dissipation, in some codes (Bluetooth Low Energy to name one), frequency modulation is used instead of phase modulation. This loses a few db vs QPSK, but it is quite tolerant for VCO frequency drift on switch-on of the power amplifier, an effect that is quite difficult to control in single-chip systems.

This means that , excluding the VCO, 802.15.4 is superior to BTLE, but including the VCO, I dont think so, as BTLE is tolerant for Tx frequency drift, while 802.15.4 is not.

Cheers,

Henri.