design of rf transceivers for wireless sensor networks in hazardous applications

11
Design of RF transceivers for wireless sensor networks in hazardous applications Bo Zhao Pengpeng Chen Huazhong Yang Received: 10 October 2013 / Accepted: 27 January 2014 Ó Springer Science+Business Media New York 2014 Abstract Wireless sensor networks (WSN) have a great prospect in many applications, among which the monitoring of hazardous environments is becoming more and more important. The basic requirements of WSN design are low cost and low power consumption, and then a low-power system-on-chip implementation is an optimal solution for WSN nodes. However, the radio-frequency (RF) part of a node chip is usually power hungry and difficult to fully integrate, so many previous works have focused on the design of RF transceivers for WSN. Specifically, for haz- ardous applications, the communication range is required to be long enough to protect human from harmful environ- ments. So a long effective communication distance is also necessary for WSN transceivers in hazardous applications. In this paper, we give a survey and a classification of WSN transceivers. Furthermore, we analyze the advantages and disadvantages of three main WSN transceivers, i.e. on-off keying transceivers, ultra-wide band transceivers, and fre- quency shift keying transceivers; and then find out the one most suitable for hazardous applications. Keywords Wireless sensor network (WSN) Á Hazardous application Á Transceiver Á On-off keying (OOK) Á Ultra- wide band (UWB) Á Frequency shift keying (FSK) 1 Introduction With the fast developing of wireless sensor networks (WSN), more and more applications have appeared, such as military reconnaissance, medical care, environment monitoring, smart home, etc. Specifically, the monitoring of hazardous environments plays a very important part among all the WSN usages. The hazardous environments include underground mines, nuclear reactors, forest, under sea, etc., which are harmful for the body of human beings. Instead of artificial detection, WSN has a great advantage in hazardous applications. A WSN system usually contains a large amount of communication nodes distributing in or around the target environments. Nowadays, the system-on-chip (SoC) reali- zation is the most significant technology of WSN design. The basic architecture of a node chip is shown in Fig. 1, which includes one or several sensors, a multi-path analog- to-digital converter (ADC), a micro controller unit (MCU), a storage unit, a real-time clock (RTC) unit, a power man- agement unit, and a radio-frequency (RF) transceiver. Each part plays a special role in the node system. (1) The sensors detect and collect the physical quantities of environments, and then change them into analog electrical signals. (2) The ADC converts the analog signals into digital domain. (3) The MCU is used for system controlling and data process- ing. (4) The storage unit is used to store the data. (5) In some applications such as smart grid or intelligent transportation system, an accurate timing should be provided by a RTC module. (6) The power management unit controls the power supply of all the parts and optimizes the power consumption of each node. (7) The RF transceiver is adopted to com- municate with other nodes or base station. For the SoC implementation of a WSN node chip, the RF transceiver is the designing bottleneck because there B. Zhao (&) Á P. Chen Á H. Yang Department of Electronic Engineering, Tsinghua University, Beijing, China e-mail: [email protected] H. Yang e-mail: [email protected] 123 Analog Integr Circ Sig Process DOI 10.1007/s10470-014-0267-3

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Design of RF transceivers for wireless sensor networksin hazardous applications

Bo Zhao • Pengpeng Chen • Huazhong Yang

Received: 10 October 2013 / Accepted: 27 January 2014

� Springer Science+Business Media New York 2014

Abstract Wireless sensor networks (WSN) have a great

prospect in many applications, among which the monitoring

of hazardous environments is becoming more and more

important. The basic requirements of WSN design are low

cost and low power consumption, and then a low-power

system-on-chip implementation is an optimal solution for

WSN nodes. However, the radio-frequency (RF) part of a

node chip is usually power hungry and difficult to fully

integrate, so many previous works have focused on the

design of RF transceivers for WSN. Specifically, for haz-

ardous applications, the communication range is required to

be long enough to protect human from harmful environ-

ments. So a long effective communication distance is also

necessary for WSN transceivers in hazardous applications.

In this paper, we give a survey and a classification of WSN

transceivers. Furthermore, we analyze the advantages and

disadvantages of three main WSN transceivers, i.e. on-off

keying transceivers, ultra-wide band transceivers, and fre-

quency shift keying transceivers; and then find out the one

most suitable for hazardous applications.

Keywords Wireless sensor network (WSN) � Hazardous

application � Transceiver � On-off keying (OOK) � Ultra-

wide band (UWB) � Frequency shift keying (FSK)

1 Introduction

With the fast developing of wireless sensor networks

(WSN), more and more applications have appeared, such

as military reconnaissance, medical care, environment

monitoring, smart home, etc. Specifically, the monitoring

of hazardous environments plays a very important part

among all the WSN usages. The hazardous environments

include underground mines, nuclear reactors, forest, under

sea, etc., which are harmful for the body of human beings.

Instead of artificial detection, WSN has a great advantage

in hazardous applications.

A WSN system usually contains a large amount of

communication nodes distributing in or around the target

environments. Nowadays, the system-on-chip (SoC) reali-

zation is the most significant technology of WSN design.

The basic architecture of a node chip is shown in Fig. 1,

which includes one or several sensors, a multi-path analog-

to-digital converter (ADC), a micro controller unit (MCU), a

storage unit, a real-time clock (RTC) unit, a power man-

agement unit, and a radio-frequency (RF) transceiver. Each

part plays a special role in the node system. (1) The sensors

detect and collect the physical quantities of environments,

and then change them into analog electrical signals. (2) The

ADC converts the analog signals into digital domain. (3)

The MCU is used for system controlling and data process-

ing. (4) The storage unit is used to store the data. (5) In some

applications such as smart grid or intelligent transportation

system, an accurate timing should be provided by a RTC

module. (6) The power management unit controls the power

supply of all the parts and optimizes the power consumption

of each node. (7) The RF transceiver is adopted to com-

municate with other nodes or base station.

For the SoC implementation of a WSN node chip, the

RF transceiver is the designing bottleneck because there

B. Zhao (&) � P. Chen � H. Yang

Department of Electronic Engineering, Tsinghua University,

Beijing, China

e-mail: [email protected]

H. Yang

e-mail: [email protected]

123

Analog Integr Circ Sig Process

DOI 10.1007/s10470-014-0267-3

are several intrinsic contradictions between RF design and

the common requirements of WSN, as shown in Fig. 2.

Firstly, low cost is necessary because large quantities of

nodes are needed for a comprehensive monitoring task. In

this case, a complementary metal oxide semiconductor

(CMOS) full-integrated SoC is obviously a good candidate.

Unfortunately, the RF part usually has to use inductors and

capacitors, which occupy a large die area and are not easy

to integrate, and then the overall cost of the nodes will be

increased. Secondly, the distribution of communication

nodes is often irregular and flexible, and then the distance

between two nodes may be very long (several hundred

meters) or very short (several centimeters). So the input

signal amplitude of receiver may be very large (larger than

0 dBm) or very small (less than -100 dBm), which means

that each receiver should have a large dynamic range. As a

result, the receiver must contain a high-performance

automatic gain control (AGC) loop, which is a traditional

difficulty in CMOS analog design. Thirdly, reliability is

also an important issue, especially for the nodes in haz-

ardous environments, while the RF part is sensitive to the

variations of process, voltage, and temperature (PVT).

Fourthly, the RF part costs a much longer design period

when compared to the digital part, and this is inconsistent

with the ‘‘Easy to Design’’ requirement of WSN. Lastly,

power consumption is the most significant factor because

the WSN nodes are usually battery powered, while the RF

part usually consumes larger than 90 % power of a node

chip. Therefore, the RF transceiver design of a node chip is

a challenging research topic in the WSN field.

Several companies have developed series of commercial

chips for WSN. The basic specifications of these com-

mercial chips are shown in Table 1 [1], and there are some

common characters of these chips:

• Low data rate: In many WSN applications, the physical

quantities to be monitored are often temperature, voice,

or images with a low frame rate.

• Low power: The purpose is to extend the lifetime of

battery-powered nodes.

• High sensitivity: It’s used for long-distance communi-

cation to satisfy the WSN requirement on flexibility.

• Low emitting power: The multi-hop topology is usually

adopted [2, 3], and then the output power of transmitter

can be reduced to further reduce the power

consumption.

• Simple modulation schemes: Both the cost and design

difficulty can be reduced.

All the above characters are consistent with the

requirements of WSN, and they are also the trend of chip

design for modern WSN.

In hazardous applications, the target environments are

harmful to humans. Therefore, long-distance communication

must be ensured for every nodes so that the humans can be

kept away from the dangerous environments. This results in

that the sensitivity performance of RF receivers becomes the

most significant factor among all the specifications.

The rest of our paper is organized as follows. Section 2

gives a survey of the transceivers suitable for WSN usages.

In Sects. 3–5, several common-used WSN transceivers are

classified, and then the advantages and disadvantages of

each type are analyzed; in addition, the transceivers most

suitable for hazardous applications are detailed in Sect. 5.

Section 6 concludes the paper.

2 Overview of WSN transceivers

The architectures of transceivers can be summarized into

super-heterodyne, zero-intermediate-frequency (zero-IF),

low-IF, slide-IF, super-regenerative, amplifier sequenced

hybrid, etc. A general transceiver adopts the low-IF or

zero-IF architecture, as shown in Fig. 3, which is known as

the software defined radio (SDR). The received signals

from the antenna is firstly amplified by a low-noise

amplifier (LNA), and then down-converted by in-phase/

quadrature-phase (I/Q) mixers. Additionally, a filter is used

Fig. 1 Basic architecture of WSN node

Fig. 2 Contradictions between RF design and WSN requirements

Analog Integr Circ Sig Process

123

to get rid of the image and interferences, and then the IF

signals are controlled by two AGC modules. The analog

signals are sampled by I/Q dual-path ADCs, and then the

demodulation, data decision, clock recovery, etc. can all be

done in digital domain. In the transmitting part, the base-

band data are converted to analog signals by I/Q digital-to-

analog converters, and then processed by a filter. Two

mixers is used as up-converters, and then the signals are

modulated onto a RF carrier. At last, the RF signals are

emitted through a power amplifier (PA).

To obtain high spectrum efficiency, we can adopt some

complex modulation schemes, such as orthogonal fre-

quency-division multiplexing, but these modulation

schemes often result in high cost and large power con-

sumption. For example, the SDR architecture can be used

for all the modulation schemes because the demodulation

can be easily done in digital domain even if the modulation

schemes are complicated. In many cases, the high cost of

complex circuit structure cannot be tolerated in some WSN

applications. Therefore, simpler modulation schemes are

more popular as the candidate of WSN, such as on-off

keying (OOK), frequency shift keying (FSK), etc.

There are some other modulation schemes suitable for

WSN. Compared to FSK, minimum shift keying has higher

spectrum efficiency, whereas the demodulation is more

complicated and frequency hopping cannot be realized. In

2003 IEEE issued the 802.15.4 standard [4], supporting

binary phase shift keying (BPSK) and offset quadrature

phase shift keying (O-QPSK). BPSK has stronger immu-

nity to interferences than that of FSK, whereas O-QPSK

has higher spectrum efficiency. However, the demodula-

tions of BPSK and O-QPSK cannot be done without ADCs,

which will result in large power and hardware cost.

It’s obvious that these simple modulation schemes are

widely used in commercial chips, as shown in Table 1.

Compared to the SDR transceiver in Fig. 3, the architecture

Table 1 Several commercial

chips for WSN applications [1]

a This indicates the power

consumption in transmitting/

receiving mode, respectively

Chips Frequency

(MHz)

Data rate

(kb/s)

Powera

(mW)

Sensitivity

(dBm)

Emitting power

(dBm)

Modulation

scheme

TR1000 916.5 115.2 14.4/36 -98 -1.2 OOK/ASK

TRF6903 300–1,000 19.2 60/111 -103 -12 to 8 FSK/OOK

CC1000 300–1,000 76.8 30/87.8 -107 -20 to 10 FSK

CC2420 2,400 250 33.8/31.3 -95 0 O-QPSK

nRF905 433–915 100 37.5/90 -100 -10 to 10 GFSK

nRF2401 2,400 0–1,000 75/39 -80 -20 to 0 GFSK

Fig. 3 Architecture of SDR transceiver

Analog Integr Circ Sig Process

123

for WSN transceivers can be simplified. In the following

sections, we mainly focus on three kinds of transceivers:

(1) OOK transceivers, (2) ultra-wide band (UWB) trans-

ceivers, and (3) FSK transceivers.

3 OOK transceivers

A significant advantage of OOK transceivers is that a high

data rate can be realized. Recently, many OOK transceivers

have been focusing on GHz-carrier high-speed wireless

communication in a very short range [5–8]. In addition, the

OOK transceivers is low in complexity, and then the

designers can minimize both hardware cost and power

consumption.

A typical OOK transceiver is shown in Fig. 4 [9]. In the

receiver, the received signals are filtered by a surface

acoustic wave (SAW) filter, and then processed by a LNA

to obtain suitable amplitude. The OOK demodulation is

realized by the composition of an envelope detector, a gain

controller, and a low-precision ADC. In the transmitter, a

SAW resonator is adopted to control an oscillator for car-

rier generation. Then, the data from digital baseband

modulate the carrier by a mixer to achieve OOK signals. At

last, the modulated signals are amplified by a PA with an

antenna. Generally, the 1 Mb/s data rate in this work is

quite adequate for most WSN usages, and the power con-

sumption is less than 12 mW. Moreover, the startup time is

only 2.5 ls, so fast settling is another advantage of OOK

transceivers. However, the sensitivity of the receiver is

only -65 dBm, which seriously limits the communication

distance and not suitable for hazardous applications. The

integration level is also poor because the off-chip compo-

nents such as the SAW filter and the SAW resonator are

necessary, and then the cost will be considerably increased

when a large number of nodes are utilized.

Ultra-low power consumption can be realized for OOK

transceivers, and some work adopts an OOK receiver for

wake-up usages, as shown in Fig. 5 [10]. The signals are

filtered by a SAW filter, and then down-converted by a

mixer. The local oscillating (LO) signals of mixer are gen-

erated by an oscillator, whose resonant frequency is cali-

brated by off-chip components. Nevertheless, the output

frequency of oscillator will still be deviated since there is no

phase-locked loop (PLL). Therefore, a wide-band amplifier

follows mixer for the tolerance of IF offsets caused by the

free oscillator. In addition, an energy detector is used for

OOK demodulation and wake-up controlling. This wake-up

receiver consumes only 52 lW at a 2 GHz carrier frequency

and a 100 kb/s data rate. However, the sensitivity is also poor,

and only the receiving signals with large than -72 dBm can

be detected. The same with the OOK transceiver in Fig. 4,

off-chip components are also required here, so the sim-

plicity structure is at the cost of low integration level.

Besides the above two typical OOK transceivers, other

OOK chips have the similar features. The chip in [11]

reduced the power consumption to less than 60 pJ/bit at

1 Mb/s data rate, but the sensitivity was only -55 dBm. A

5 Mb/s super-regenerative OOK transceiver was reported

in [12], with a boosted energy efficiency of 0.363 nJ/bit;

but the high efficiency was also at the cost of several off-

chip components.

In brief, the superiorities of OOK transceivers can be

summarized:

• High data rate at Mb/s level;

• Low power consumption at mW or lW level;

• Low complexity;

• Fast settling in several ls.

Nevertheless, there are some disadvantages:

• Short communication range induced by poor

sensitivity;

Fig. 4 An 1 Mb/s 916.5 MHz OOK transceiver [9]

Analog Integr Circ Sig Process

123

• High cost caused by low integration level.

As a result, the OOK transceivers are suitable for short-

range high-speed communications, such as wireless body

area networks (WBAN), but it’s not a reasonable choice for

hazardous applications because the short communication

range usually cannot protect human from the harmful

environments.

4 UWB transceivers

UWB is defined as a signal whose bandwidth is larger than

500 MHz or larger than 20 % of the carrier frequency.

With such a large bandwidth, UWB transceivers can

achieve an ultra-high bit rate. Although the OOK modu-

lation scheme can be adopted in UWB transceivers, the

UWB data rate can even be much higher than normal OOK

transceivers.

There is a common used UWB approach named impulse

radio (IR) UWB, modulating the baseband data onto short

impulses, and then the duty cycle is often very small. As a

result, IR-UWB equipment can work in an intermittent

mode to further reduce the power consumption, and then

such IR-UWB transceiver is consistent with the low-power

requirements of WSN. A typical structure of IR-UWB

transceivers is shown in Fig. 6 [13]. The receiver consists

of a LNA and a correlator, which is composed of a mixer, a

pulse generator, a delay controller, an integrator, and a

comparator. Specially, the transmitting part contains only a

PA and an impulse generator, which can be realized by all-

digital architecture, as shown in Fig. 7. Then, the power

consumption can be reduced to about 1 mW for 1 Mb/s

data communication since the LNA operates intermittently.

Compared to the OOK transceivers in Fig. 4 [9] and Fig. 5

[10], this IR-UWB transceiver is fully integrated. However,

with 0.1 % bit error rate, the range for data communication

is only 1 m, which is too short for hazardous application.

Many works adopt UWB transceivers for high-speed

applications. An IR-UWB transceiver with an 112 Mb/s

data rate for RF identification (RFID) is designed as in

Fig. 8 [14]. A super-regenerative oscillator is shared by

both transmitting and receiving modes, and it generates the

transmission pulse as well as supplies the gain for receiver

assisted by quench signals. In addition, a peak detector and

a comparator are adopted to demodulate the receiving

signals. Moreover, all the modules are on-chip except the

antenna, and then full integration is also realized. This

transceiver can operate in a full-duplex mode at the

7.9 GHz UWB frequency band, and the power consump-

tion is about 58 and 48pJ/b. Nevertheless, this chip also has

an extremely short communication distance since it’s

designed for wireless non-volatile memory (NV-Memory)

applications.

The advantages of UWB transceivers can be summa-

rized into the following aspects:

• High data rate reaching several 100 Mb/s;

• Low power consumption;

• Low cost with high integration level.

The spectrum density is very low because of the ultra-

wide frequency band, and then the communication is very

sensitive to interferences, so there is a fatal defect of UWB

transceivers:

• Very short communication distance (usually less than

5 m).

Therefore, with low cost and a high data rate, UWB

transceivers can be used for short-range high-speed moni-

toring, such as wireless high definition, but not suitable for

hazardous applications.

5 FSK transceivers

For a FSK signal, only the zero-crossing points contain

data information, so the gain control is easy to realize for

FSK receivers. In addition, both the cost and power con-

sumption is low since the modulation-demodulation cir-

cuits are simple. Furthermore, FSK transceiver can achieve

a long communication distance since both the spectrum

efficiency and immunity to interferences are better than

that of OOK. Moreover, frequency hopping is supported by

FSK, and then the immunity to interferences can be further

enhanced.

Fig. 5 A 2 GHz 52 lW OOK

receiver for wake-up usages

[10]

Analog Integr Circ Sig Process

123

A typical FSK transceiver is shown in Fig. 9 [15, 16].

With a direct-conversion architecture, the receiver has a RF

front-end composed of a LNA, I/Q mixers, and filters. The

FSK IF signals are amplified by two limiting amplifiers,

and then demodulated by a demodulator, which can be

realized by analog circuits or simple digital modules.

Compared to the SDR structure shown in Fig. 3, neither the

AGC loop nor the ADCs are required, and then the cost and

power consumption can be reduced. The defect is that the

receiving chain seems more complex when compared to

OOK receivers or UWB receivers. For the transmitting

part, the I/Q LO signals are mixed with the transmitting

data from baseband, and then the modulated signals are

emitted through a PA. It can be seen that two mixers are

needed in this FSK transmitter, and then the power con-

sumption of transmitter became as large as 25 mW.

According to the character of FSK signal, the transmitter

architecture can be simplified, as shown in Fig. 10 [17],

where the PLL based FSK modulation is adopted [18, 19].

Then, the complexity of transmitter is considerably reduced

because only a PLL can be adequate for the data modula-

tion. In addition, the LO signals can be generated by a

poly-phase network [20], a quadrature VCO [21], or a

frequency divider [22].

According to the FSK modulation method proposed in

[19], PLL has three forms of implementation: (1) open-

loop modulation, (2) offset modulation, and (3) closed-loop

modulation. Next, we give a brief description of these three

kinds of circuits.

The open-loop modulation is shown in Fig. 11(a) [19],

where the traditional charge-pump structure is taken as an

example. The charge-pump PLL is composed of a phase-

frequency detector, a charge pump, a loop filter (LF), a

VCO, and a divider. The VCO is set to a fixed frequency by

the loop, and then the loop is split at the VCO’s controlling

port where the baseband data is then input for frequency

tuning. This way the PLL falls into an open-loop state

when the modulation is executed, so there will be a drift of

the VCO’s resonant frequency. As a result, the modulation

precision will be depressed.

The offset modulation is shown in Fig. 11(b) [18]. The

I/Q baseband data is converted to an IF signal by a mod-

ulator, and a mixer is added to the feedback path of PLL to

up-convert the IF signal to a RF signal. The offset modu-

lation is widely used because the wide-band noise of IF

signal is filtered out by PLL loop. However, a high-

Fig. 6 An UWB transceiver for

range finding [13]

a

Fig. 7 An all-digital UWB impulse generator [13]

Fig. 8 An 112 Mb/s full-

duplex UWB transceiver for

RFID [14]

Analog Integr Circ Sig Process

123

performance mixer is needed, and another PLL is required

to generate LO signal, so both the complexity and power

consumption will be large.

The closed-loop modulation is based on a sigma-delta

PLL shown in Fig. 11(c) [19]. The baseband data is shaped

by a digital filter, and then input into a sigma-delta mod-

ulator, which controls the divider of PLL. Then, the output

frequency of PLL is changed according to the dividing

ratio of divider. The realization of closed-loop modulation

is simpler than both open-loop and offset modulations, so it

will benefit from low cost and low power. Nevertheless, the

data rate is limited by the loop bandwidth. Although a pre-

compensation filter can be adopted [19], the mismatch

problem is difficult to overcome. For WSN usages, a low

data rate at 1–100 kb/s is often adequate; therefore, the

closed-loop modulation may be the best choice for WSN.

Many previous works have been focused on FSK

transceivers, and some of them are listed in Table 2. In

recent years, there have been many research progresses.

Such as in 2011, an injection-locked demodulation tech-

nique was proposed to enhance the data rate of FSK

transceivers to 5 Mb/s [23]. However, it’s at the cost of

-37 dBm sensitivity [23], which was similar to OOK

receivers. The chip in [24] was compatible to both IEEE

802.15.6 and BlueTooth LE, with the receiver sensitivity

reaching -104 dBm.

In summary, the common features of FSK transceivers

can be concluded as follows:

Fig. 9 A typical FSK transceiver [15, 16]

Fig. 10 A FSK transceiver adopting the PLL based modulation [17]

Analog Integr Circ Sig Process

123

• Low carrier frequency: To achieve a relatively long

communication distance, most works set the carrier

frequency below 1 GHz. Although the frequency band

in [25] was higher, it’s used for the pressure monitoring

of tires, where a few meters’ communication distance

was enough.

• Low data rate: This is adequate for most WSN usages.

Although the data rate reached 2–10 Mb/s in [23, 26–

28] or even 1 Gb/s [29], the cost was that the

communication distance was greatly decreased. E.g.

the communication range was only 1.8 m in the work

[28], and even 1 m in [29]. As a result, these short-

range communications are suitable for the applications

such as WBAN, but not hazardous environments.

• Low power consumption: This is because the modula-

tion and demodulation of FSK are easy to implement.

In the early years, the FSK transceivers usually

consumed large power [30–32], but the power was

significantly reduced as the developing of design

technologies and process. In recent years, some FSK

transceivers still appeared large power consumption,

but they were often designed for multi-mode applica-

tions [17, 24], large transmission power [33], or a high

carrier frequency [25].

• High sensitivity: This also aims at the realization of a

long communication distance. Although the designs in

[34] and [23] had relatively poor sensitivity, it’s

designed for ultra-low power consumption.

• Low emitting power: Multi-hop networks are often

adopted, and then the emitting power is often lower

than 10 dBm. Paper [17] showed relatively high output

amplitude, but the power consumption was as high as

85.5 mW.

The advantages of FSK transceivers can be summarized

as follows:

(a)

(b)

(c)

Fig. 11 Three implementations

of pll based FSK modulation: aopen-loop modulation [19], boffset modulation [18], and cclosed-loop modulation [19]

Analog Integr Circ Sig Process

123

• Low power consumption (Although the power of FSK

transceivers is often larger than that of OOK and UWB

ones, it’s also adequate for most WSN applications.);

• Low cost with high integration level;

• Long communication distance.

At the same time, FSK transceivers have some defects:

• Relatively low data rate at 1–100 kb/s level;

• Larger power than OOK and UWB transceivers;

• Higher cost than UWB transceivers.

In summary, the FSK transceivers are most suitable for

hazardous applications because of long communication

distance, although the hardware cost and power consump-

tion are not perfect.

6 Conclusion

The design of RF transceivers is the bottleneck of SoC

implementation for WSN. To meet the requirements of low

cost and low power consumption for WSN usages, simple

modulation schemes are usually adopted. For hazardous

applications, FSK transceivers have great advantages over

other kinds because of its longer communication distance.

Nevertheless, there are also some shortcomings of FSK

transceivers: (1) The architecture is more complex than

OOK and UWB ones; (2) the data rate is usually not high;

and (3) the power consumption is often relatively larger

than OOK and UWB ones.

Acknowledgments This work was supported by the National Nat-

ural Science Foundation of China (NSFC) under Grant 61204032.

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Table 2 Performance summary

of several typical FSK

transceivers

a The power consumption in

receiving/transmitting mode,

respectivelyb The unit of sensitivity in the

references [34, 30, 31] is lV

rms, whereas it’s dBm in other

worksc The maximum emitting power

of transmitter

References Process

(nm)

Carrier

frequency

(MHz)

Data rate

(kb/s)

Powera

(mW)

Sensitivityb

(lV rms/dBm)

Output

powerc

(dBm)

JSSC’98 [30, 31] 1,000 900 160 360/300 1.2 13

RFIC’01 [32] 250 868 30 30.8/56 -95 10

JSSC’01 [15, 16] 500 434 24 1/25 -95 10

RFIC’02 [35] 250 902 128 N/A -105.5 2

JSSC’04 [17] 250 433/868/915 9.6 59.1/85.5 -112.8 14

ISSCC’05 [33] 180 433/868 25 2.1/32.3 -111 10.5

RFIC’08 [36] 180 400 128 2/1.7 -93 -12

JSSC’08 [37] 130 862/902 50 2.1/2.6 -102 -7

RFIC’09 [38] 130 868/915 45 2.4/2.7 -89 -6

VLSI’09 [34] 180 402 250 0.49/0.4 80 -2

JSSC’10 [25] 130 2,100 50 23.2/12 -90 1

JSSC’11 [23] 180 920 5,000 0.5/3.8 -37 -11.4

JSSC’13 [24] 130 2,360 600 4.8/5.9 -104 5

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Bo Zhao received his B.S. degree

in Electronic Engineering Depart-

ment of Southeast University

in 2006, and then PhD degree in

Electronics Engineering Depart-

ment, Tsinghua University, Bei-

jing, China in 2011, supervised by

Prof. Huazhong Yang and Prof.

Hui Wang. Dr. Zhao is now an

assistant professor in Electronic

Engineering Department of Tsing

hua University. His research

mainly focuses on radio-frequency

integrated circuits (RFIC) design.

Dr. Zhao has published a series of

papers about RFIC design on TCAS-I, ESSCIRC, ISCAS, etc. He has been

granted by nine China patents. He is now the principal investigator of the

National Natural Science Foundation of China (NSFC) and he also takes

part in some other projects, e.g. National Science and Technology Major

Project and National High Technology Research and Development

Program of China (863 Program).

Pengpeng Chen received his

B.S. degree in Tsinghua Uni-

versity, Beijing, China in 2009.

Now he is doing his Ph.D.

research in Electronics Engi-

neering Department, Tsinghua

University, supervised by Pro-

fessor Bo Zhao and Professor

Rong Luo. His Ph.D. research is

mainly focused on radio-fre-

quency integrated circuits

(RFIC) design for wireless sen-

sor networks (WSN) and wire-

less body area networks

(WBAN).

Huazhong Yang received B.S.

degree in microelectronics in

1989, M.S. and Ph.D. degree in

electronic engineering in 1993

and 1998, respectively, all from

Tsinghua University, Beijing. In

1993, he joined the Department

of Electronic Engineering

Department of Tsinghua Uni-

versity, where he is a full pro-

fessor since 1998. Dr. Yang is a

specially-appointed professor of

the Cheung Kong Scholars Pro-

gram. His current interest

includes wireless sensor net-

works, data converters, parallel circuit simulation algorithms, nonvol-

atile processors, and energy-harvesting circuits. Dr. Yang has authored

and co-authored over 300 technical papers and 70 granted patents.

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