Efficiency–Throughput Trade-off of
Pulsed RF Waveforms in Simultaneous
Wireless Information and Power Transfer
Nachiket Ayir
Unit of Electrical Engineering
Tampere University, Finland
nachiket.ayir@tuni.fi
Taneli Riihonen
Unit of Electrical Engineering
Tampere University, Finland
taneli.riihonen@tuni.fi
Abstract—We study the receiver efficiency–throughput
trade-off in a realistic radio frequency (RF) simultaneous
wireless information and power transfer (SWIPT) system. Based
on the energy harvesting receiver characteristics, we propose a
continuously phase-modulated pulsed RF waveform to achieve
maximum receiver efficiency at any input RF power level. We
study the impact of varying the duty cycle of a pulsed RF
waveform on the receiver efficiency of wireless power transfer
along with the throughput of information transfer, and the
trade-off thereof. The experiments confirm that a phase-shift
keying (PSK) modulated pulsed RF waveform yields superior
receiver efficiency than other digital baseband modulations as
well as multisine signals despite they are designed particularly
for power transfer. However, the optimal efficiency is attained
at the expense of a significant loss in throughput due to pulsed
transmission, depending on the average input RF power level.
Index Terms—Continuous phase modulation, wireless
power transfer, efficiency–throughput trade-off, pulsed RF,
simultaneous wireless information and power transfer.
I. INTRODUCTION
Far-field radio frequency (RF) simultaneous wireless
information and power transfer (SWIPT) has received
significant research interest [1] due to its potential applications
in consumer and industrial Internet-of-Things (IoT). While RF
wireless power transfer (WPT) envisions providing IoT sensors
a replenishable energy source, the true technical challenge
lies in utilizing the same RF spectrum for delivering both
information and power to receivers.
The RF energy harvesting (EH) receiver and the information
receiver can either be co-located or separate (cf. Fig. 1)
depending on the network configuration, device complexity
and intended application. The concept of RF SWIPT can also
be extended to the networking paradigms of wireless powered
communication and backscatter networking. In these networks,
the energy is harvested in the downlink, stored momentarily
and then utilized to transmit information in the uplink [2].
While the transmitter side of an RF SWIPT system is similar
to that of an RF WPT system, the receiver architecture is
different and it plays a crucial role in the overall performance
This research was supported by the Finnish Cultural Foundation and by the
Academy of Finland under the grants 315858, 341489, and 346622.
Digital
baseband 
samples
PA
RF 
signal
generator
Power splitting
or
Time splitting
Information retriever
Energy harvester
Transmitter SWIPT Receiver
Information retriever
Energy harvester
Fig. 1: Block diagram of a typical RF SWIPT system.
of an RF SWIPT system. A SWIPT receiver with a co-located
information receiver and RF energy harvester employs either
power-splitting (PS) or time-splitting (TS) technique to direct
the received RF signal to the nodes (cf. Fig. 1). In PS approach,
a fraction (say α) of the total received RF power is directed
towards the RF energy harvester, whereas the remaining
1 − α portion of the power is supplied to the information
retriever. In this way, both the nodes can simultaneously
access the incoming RF signal. A power splitter is utilized
to distribute the incident RF power. In TS approach, the
RF EH receiver gets complete access to the incoming RF
signal for a part (say τ ) of the total transmission time (T ),
while the communication node receives the incident RF signal
for the remaining T − τ time duration. In practice, an RF
switch is employed to implement TS. These two schemes were
experimentally compared in [3] and the PS scheme was found
to be superior in the input power range relevant to RF EH.
Moving on to SWIPT test-beds, one based on software-
defined radios was presented in [3] to study the rate–energy
trade-off, while employing a multisine signal for WPT and
an orthogonal frequency-division modulation (OFDM) signal
for information transfer, which were superimposed by TS and
PS schemes. A SWIPT test-bed to evaluate the performance of
multitone frequency-shift keying signals was showcased in [4],
where the frequency spacing between the tones encodes the
information. More such test-beds are reviewed in [2].
In this paper, we explore the use of a single waveform,
a phase modulated pulsed RF signal, for both WPT and
information transfer, and study the efficiency–throughput
trade-off thereof. To the best of authors’ knowledge, this is
the first work in this regard.
II. PULSED RF MODULATION FOR RF SWIPT
In this section, we first present an overview of an RF SWIPT
system along with some eminent experimental observations.
Later, we study the performance of a digitally modulated
pulsed RF waveform for RF SWIPT and focus on the impact
of varying the duty cycle of the pulsed RF signal on the power
transfer efficiency of an RF EH receiver.
A. A Practical RF SWIPT System
A realistic RF SWIPT system consists of a digital
transmitter, an external power amplifier (PA) and the receiver
side comprising a communication node and an RF energy
harvester. Depending on the network configuration, the
communication node and the RF energy harvester could be
co-located or separate. Likewise, the network may contain
multiple such transmitters and/or receivers. We consider a
generic single-input multiple-output system, as depicted in
Fig. 1, with atleast one receiver capable of information
retrieval as well as RF EH. Nonetheless, the analysis in the
sequel holds for any RF SWIPT network configuration.
At the transmitter, the digital baseband samples are
converted to an analog signal to modulate an RF carrier.
The internal amplification of the RF signal generator is
insufficient for wireless transmission, and thus an external PA
is required. The amplified signal is then propagated wirelessly
through an antenna. At the receiver, the signal captured by
the antenna is available either for information decoding or RF
EH, or both, based on the PS or TS receiver architecture.
The efficiency of RF WPT is determined in terms of the
RF-to-direct current (DC) efficiency of the receiver while the
efficacy of information transfer is evaluated in terms of the
transmission bit-rate (ρ), the receiver bit error rate (BER) and
the corresponding throughput (Γ), which is defined as
Γ = ρ× (1− BER) (1)
In practice, the receiver sensitivity of a communication node
is much lower (< −80 dBm) than an RF EH receiver
(−30 to −15 dBm for commercial energy harvesters) [3],
[5], [6]. Consequently, in the power range that is relevant
to RF EH (even with the PS scheme), the BER for
a communication receiver is practically zero [3]. We
confirmed the same through wireless measurements for
varying transmitter–receiver separation relevant to RF SWIPT.
Thus, the throughput in (1) is effectively equal to ρ. This
implies that Γ in RF SWIPT could be maximized by
transmitting an information carrying waveform.
Therefore, we shall next focus on determining the
information carrying waveforms that can maximize the
receiver RF WPT efficiency (η) as well.
B. Continuous Phase-Modulated Pulsed RF Waveform
Let us examine the receiver RF EH efficiency while
employing only an information carrying signal, instead of
using separate signals for RF WPT and information transfer.
We do so by employing the test-bed shown in Fig. 2.
National
Instruments
PXIe-5645R
Powercast P211XXCSR
wideband RF energy harvester
Keysight
 MSOX4104A
vector
signal transceiver 
Digital baseband
waveform samples data
PA RF energy
harvester Oscilloscope
Fig. 2: Block diagram of the RF WPT test-bed utilized for
evaluating the receiver efficiency for varying PRFin .
1) Test-bed: The test-bed is similar to the RF EH part of
the RF SWIPT block diagram in Fig. 1, with the exception
that here we use a wired medium to have a precise control
over the average RF input power (PRFin ) at the input port
of the RF energy harvester. This allows us to determine η
accurately at each PRFin . Here, a computer generates the digital
baseband waveform samples and sends it to a vector signal
transceiver for analog RF transmission. The RF signal, on
amplification by an external PA, is transmitted towards the
RF energy harvester, comprising a matching network and a
diode-based rectifier network. The oscilloscope measures the
DC root mean square voltage (V DCout) across a load capacitor CL
and a load resistor RL. The computer retrieves the V DCout value
from the oscilloscope and computes the average harvested DC
power (PDCout ) and the corresponding η, which is given as
η =
PDCout
PRFin
=
(V DCout)
2
RL PRFin
(2)
2) Proposition: We begin by experimentally evaluating
η for a continuous wave (CW). In accordance with the
observation in [7], our measurements reveal that an M -level
phase-shift keying (PSK) modulated RF waveform (M = 2n,
n ∈ P) yields the same η as a CW. This result can be attributed
to the fact that an M -PSK modulated RF signal is still a CW,
with phase transitions at symbol rate. The aforementioned
experimental observation can be further extended to any
continuously phase-modulated RF signal, where the envelope
of the RF signal does not change with time. We further
improvise this concept and apply it to a pulsed RF signal
with duty cycle δ. We propose that: given a continuously
phase-modulated RF signal (δ = 1) with P RFin = P¯
RF
in
and corresponding receiver efficiency η, a continuous phase
modulated pulsed RF signal with duty cycle δ achieves the
same η, albeit at a lower P RFin = δ P¯
RF
in . The reasoning is as
follows. A pulsed RF signal with duty cycle δ and input power
δ P¯RFin has the same amplitude as a CW with input power P¯
RF
in .
Consequently, the pulsed wave signal, during its absolute pulse
duration, attains the same V DCout as a CW, at a lower P
RF
in . As
a result, the pulsed signal yields the same efficiency as a CW,
at a lower PRFin depending on its duty cycle δ.
The primary advantage of adopting a phase-modulated
pulsed RF signal is that the RF EH receiver could be operated
at the maximum η for any given PRFin , by varying just δ of
-30 -25 -20 -15 -10 -5 0 5 10 15 20
 Pin
RF
 (dBm)
0
10
20
30
40
50
60
70
80
90
R
ec
ei
ve
r e
ffi
cie
nc
y 
(%
)
 = 1  M-PSK
 = 0.5  M-PSK
 = 0.25  M-PSK
 = 0.1  M-PSK
 = 0.01  M-PSK
Fig. 3: Receiver efficiency of the RF energy harvester for
M -PSK modulated RF signal and phased RF signals, for
varying PRFin and different duty cycles, with RL = 10 kΩ. The
solid lines represent the predictions of the proposition, while
the markers represent measurements. The discontinuities in the
measurements at low PRFin are due to resolution limitations of
the oscilloscope.
the transmitted pulsed wave. The benefit of operating at an
enhanced η, however, comes with an efficiency–throughput
trade-off. We present these in more detail in the next section.
III. MEASUREMENT RESULTS AND DISCUSSION
In this section, we first present measurement results that
corroborate the proposition in Section II-B2 and also compare
the performance of a phase-modulated pulsed RF signal with
other RF WPT and information transfer signals. Later, we
discuss the associated efficiency–throughput trade-off.
We evaluated the BER using Universal Software Radio
Peripheral (USRP) transceivers at 915 MHz and 2.45 GHz in
the ISM and WiFi frequency bands, respectively and found the
BER to be effectively zero at PRFin levels relevant to RF WPT.
The BER of phase-modulated pulsed RF signals would, thus,
also be zero since for a given PRFin , the pulsed RF signals have
higher amplitude, and therefore higher signal-to-noise ratio.
Next, the hardware configuration of the test-bed utilized to
determine η is depicted in Fig. 2. The oscilloscope probes with
≈ 15 pF capacitance act as CL without an external capacitor,
while we employ external 3.3 kΩ and 10 kΩ resistors as RL.
The receiver efficiency is evaluated for frequency band 3 of
the Powercast multiband energy harvester [5] at 915 MHz
center frequency, by varying PRFin from −30 dBm to 20 dBm in
one decibel steps. The M -PSK signal, henceforth, represents
4-PSK and 8-PSK modulations in the results.
A. Receiver Efficiency of Phase-Modulated Pulsed RF Signal
for Varying Duty Cycle
We begin by measuring η for an M -PSK modulated RF
wave (δ = 1) for different PRFin . Then using piecewise
-30 -25 -20 -15 -10 -5 0 5 10 15 20
 Pin
RF
 (dBm)
0
10
20
30
40
50
60
70
80
90
R
ec
ei
ve
r e
ffi
cie
nc
y 
(%
)
 = 1/8  M-PSK
8-Multisine
 = 1  M-PSK
SC 64-QAM
OFDM
Fig. 4: Comparison of receiver efficiency of a M -PSK
modulated pulsed RF signal with a WPT-specific multisine
signal and other information carrying signals, for varying PRFin
and RL = 10 kΩ. The markers represent measurements, while
the solid lines represent estimates based on the proposition for
the continuously phase-modulated pulsed waveforms.
interpolation, we obtain a continuous estimate for η in terms
of PRFin and use this as a benchmark to access the efficacy of
our proposition. The results are shown in Fig. 3. It is apparent
that the estimate accurately matches with the measurements
for all δ values. It is evident in Fig. 3 that the plots for
δ = 0.5, 0.25 and 0.1 are similar (minor variations due to
measurement inaccuracies) to the plot for δ = 1, but shifted
to left by 10 · log10δ. This corroborates our proposition in
Section II-B2. The proposition also allows us to estimate η for
lower values of δ such as 0.01, for which the measurements
are not reliable due to PA limitations.1
Moreover, it is evident in Fig. 3 that reducing δ also reduces
the PRFin at which the peak η occurs. The peak η corresponds to
the PRFin that yields receiver saturation (diode breakdown). As
δ is reduced, the peak instantaneous input voltage for a given
PRFin increases. It implies that the peak voltage corresponding
to receiver saturation is achieved at a lower PRFin by reducing δ
which explains the observation. The results presented in Fig. 3
are valid for any given load resistor (RL = 10 kΩ in this case).
It is possible to attain the peak η at a different PRFin with the
same M -PSK signal by varying RL. For example, a low duty
cycle M-PSK signal can attain the peak η at a higher PRFin if
a low value RL is connected as the load.
B. Comparison with Multisines and Other Information Signals
We compare the η performance of an M -PSK modulated
pulsed RF signal with multisine signals (2, 4, 8, 16-multisine)
since these are considered to be optimal, specifically for RF
WPT [2], and with information carrying (δ = 1) single-carrier
1The proposition is also valid for other rectifier circuits (i.e., matching
networks and diodes), other load resistors and other frequency bands [8].
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Throughput (MSps)
0
10
20
30
40
50
60
70
80
90
R
ec
ei
ve
r e
ffi
cie
nc
y 
(%
)
 Pin
RF
 = -30 dBm
 Pin
RF
 = -20 dBm
 Pin
RF
 = -10 dBm
 Pin
RF
 = 0 dBm
(a) for a 10 kΩ load resistor
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Throughput (MSps)
0
10
20
30
40
50
60
70
80
90
R
ec
ei
ve
r e
ffi
cie
nc
y 
(%
)
 Pin
RF
 = -25 dBm
 Pin
RF
 = -15 dBm
 Pin
RF
 = -5 dBm
 Pin
RF
 = 5 dBm
(b) for a 3.3 kΩ load resistor
Fig. 5: Efficiency–throughput trade-off for M -PSK modulated pulsed RF waveforms in a SWIPT system. Along with the
throughput, the horizontal axis also represents the corresponding duty cycle of the pulsed RF waveform.
(SC) 64 quadrature amplitude modulation (QAM), and OFDM
M -PSK and OFDM 64-QAM signals. The results are depicted
in Fig. 4. We showcase the measurements for an 8-multisine
signal and compare it with δ = 1/8 M -PSK pulsed RF, since
these two signals have the same peak-to-average-power-ratio
of 16. It is clear that the M -PSK pulsed RF signal clearly
outperforms the multisine signal. For PRFin > 0 dBm, where
the 8-multisine has higher η than the 1/8M -PSK pulsed RF,
we can opt for a higher δ value to obtain greater efficiency than
the 8-multisine. This holds true for all the multisine signals.
Next, it is evident in Fig. 4 that the M -PSK signal also
yields higher η than SC 64-QAM and OFDM signals (the
receiver efficiency of OFDM signal is found to be independent
of the underlying baseband modulation). In fact, so long as the
M -PSK modulated RF signal has the highest η (≈ 71% for
frequency band 3) amongst all signals at some PRFin = Pˆ
RF
in ,
the M -PSK pulsed RF signal can yield the same maximum
η at any PRFin < Pˆ
RF
in by varying just the duty cycle δ. The
M -PSK pulsed RF signal, thus, outperforms multisine signal
as well as other information signals at all PRFin levels.
C. Receiver Efficiency–Throughput Trade-off
In a realistic SWIPT system employing phase-modulated
pulsed RF waveforms, the transmitter would initially transmit
a CW signal to the receiver, in order to receive a feedback
about the PRFin level at the receiver input. The transmitter
then varies δ accordingly (but not necessarily chooses δ that
maximizes η) and transmits a phase-modulated pulsed RF
signal towards the receiver for SWIPT. Let us now discuss the
trade-off that needs to be dealt with while employing phase
modulated pulsed RF waveforms with the aid of Fig. 5.
In Fig. 5, we showcase the receiver efficiency–throughput
trade-off for different PRFin . When the duty cycle of a phase
modulated pulsed RF signal reduces by a factor δ, the
throughput also reduces by the same factor since there is
no transmission for 1 − δ portion of the time period of
the signal. We observe in Fig. 5 that an increase in the
throughput (due to an increase in δ) results in a decrease
in η. This implies that the transmitter needs to prioritize
either η gain or throughput. For example, in the case of
IoT SWIPT sensors that require extremely low throughput,
the transmitter could reduce δ as much as possible to attain
higher η or even the maximum. Furthermore, we observe
that for PRFin ≥ −10 dBm, the efficiency initially increases
with throughput, reaches a maximum value and then starts
reducing. In such scenarios, the transmitter would reduce the
duty cycle only until the peak efficiency is achieved, since
any further reduction in δ would reduce both efficiency and
throughput. The efficiency–throughput trade-off provides a
scope for developing scheduling protocols depending on the
SWIPT network type or configuration.
IV. CONCLUSION
This paper experimentally studies the receiver efficiency of
phase-modulated pulsed RF waveforms for RF SWIPT. We
show that a phase-modulated pulsed RF signal can achieve
the same receiver efficiency as a phase-modulated continuous
wave, albeit at a lower input RF power level that is determined
by the duty cycle of the pulsed waveform. The experimental
results showcase that a phase-modulated pulsed RF signal
attains higher receiver efficiency than multisines as well as
other information signals, while effectively maintaining a zero
bit error rate. The analysis of the efficiency–throughput reveals
that while reducing the duty cycle of a phase-modulated pulsed
RF signal enhances the receiver efficiency, it is detrimental
to the throughput of the RF SWIPT system. This trade-off
could be utilized to develop application-specific scheduling
algorithms for an RF SWIPT system.
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