RF Circuits and Systems (EEE 6374 Spring 2013) Project Report; UFID#06078296 1

Abstract—Wireless Local Area Network (WLAN) are an

extension of Local Area Network (LAN) which are typically a

short ranged data communication network between portable

devices and an Access Point (AP). The end users or nodes,

communicate to this AP using a Network Adapter analogous to

Ethernet Connection. The mobility within transmission range

gives added advantage to being connected. Fast growing

requirement of Gigabit data rates, call for sophisticated network

architecture reform from PHY (MIMO-OFDM) to Transport

layer (Wireless TCPs) and high level modulation ensuring more

data rate, but it comes inherently with higher Bit Error Rate

(BER) and poorer EVM (Error Vector Magnitude-Signal

Constellation) at the transmitter. In this project, an RF wireless

Link has been designed which ensures to provide peak data rate

of 1 Gbps at 5 GHz band. High attenuation is expected since

frequency band is high; therefore the distance of transmission is

also a major concern. RF system design for transmitter and

receiver is presented, to keep EVM within 2% and BER within

10-5 which are the prescribed limits as mentioned in subsequent

sections.

Index Terms— Path Loss, Power Amplifiers, QAM, Signal

Constellation, Spectrum.

I. INTRODUCTION

IRELESS LAN RF module is the most important aspect

in a Digital Communication System, since it has a direct

impact on the quality of receiver signal. This part is

responsible to move the baseband data onto Radio Frequency,

in which it is transmitted. Since we operate in a wireless

medium, the received signal is typically attenuated and

distorted likewise due to Multi-paths caused by reflection and

refraction in the environment. High Level modulation schemes

such as QPSK, 16/64/256 QAM can be used which pumps

more bits per symbol, but these increase the Bit Error Rate

(BER) for a given SNR (we denote SNR as in digital

domain). The signal constellation gets crowded as we increase

the modulation level, thus making it vulnerable to decision

errors at the receiver decision device. If the transmitted power

is increased so as to increase the probability of the received

signal to be more than a threshold SNR, we tend to increase

the noise at the transmitted signal too along-with putting more

out of band emissions which might cause interference to the

adjacent channels. There are several such considerations

which are described in the following sections.

At the transmitted, we intend not to saturate the PA (Power

Amplifier) and IF Amplifier (Intermediate Frequency). This is

the reason for the OIP3 (3rd

Order Output Intermodulation

Product) to be kept on higher side, especially for the PA, since

chances of saturating PA is highest, as the available input

power to the PA faces high Gain (at each stage) till it reaches

PA. Major concern in designing the entire Wireless Link is the

Linearity and Noise Figure. So, the link budget is designed

using Syscalc 6.0, where we only calculate the receiver Noise

Figure of receiver circuit and check for linearity and path loss

through receiver, at the transmitter. An important thing to note

is, we have to consider the transmitter and receiver antenna to

be Isotropic (0 dB Gain) as per given problem statement.

For designing an RF module, we need to consider one

frequency band which can provide 1Gbps data rate. The center

frequency should be in the 5GHz band. Therefore 256 QAM

has been considered as a modulation scheme at the transmitter

and a channel bandwidth of 160 MHz as specified in IEEE

802.11ac standard has been used. The RF transmitter and

receivers has been designed using Agilent ADS 2012.08 using

heterodyne architecture because of several reasons which will

be explained throughout the flow of this work.

Section II consist a basic overview of the channel allocation

and band specification as mentioned in IEEE 802.11ac.

Section III presents the transmitter and receiver architecture.

This section explains all the modules being used and their

specification has been justified with the application point of

view. In section IV, Link budget analysis has been shown.

This has been implemented using Syscalc 6.0 and the values

has been used to manually calculate receiver sensitivity, since

it is observed, this software does not provide appropriate

Sensitivity. Section V concludes the work and followed by

acknowledgement in section VI.

II. CHANNEL ALLOCATION AND SPECTRUM SPECIFICATIONS –

IEEE 802.11ac

IEEE 802.11ac has been standardized in the IEEE 802.11

suite, which ensures to give a peak data rate of 3.4 Gbps

(single link). The FCC transmit spectrum mask has been

shown in fig.. . Essentially it uses MIMO spatial streams to

boost up the data rate. The channel allocation is shown in

fig.1. FCC UNII spectrum bands are shown in the following

figure. 802.11ac takes up the 160MHz band with the given

center frequency.

RF Architecture for 1 Gbps Wireless Link

WLAN.

Ankan Roybardhan, Department of Electrical and Computer Engineering,

University of Florida, Gainesville, FL(USA).

W

RF Circuits and Systems (EEE 6374 Spring 2013) Project Report; UFID#06078296 2

.

Fig.1. IEEE802.11 spectrum allocation from FCC-UNII

For our work, would consider the 160MHz band, and one

band would include one channel (Not considerable out-of-

band emission). The consideration is quite logical in the sense,

since we are not implementing sophisticated MIMO

techniques, for getting 1Gbps data rate we need to consider

huge bandwidth (160MHz X 8 bits per symbol for 256

QAM=1.2 Gbps).

The standards [7][8] shows the maximum transmitted power

should not exceed +30 dBm, which is the case we get in our

simulation. The transit mask should follow the following-

Fig.2. Transit Spectrum Mask

Center frequency is considered to be 5.25GHz (5170+80

MHz). Channel BW is 160 MHz and so the band 160 MHz as

it is a wide band channel and we typically follow 802.11ac

standard. In addition to it, since the channel allocation is not

contiguous as in fig.1, we would consider one single channel

as a whole because a part of the 2nd

channel has weather

forecast communications.

III. RF SYSTEM ARCHITECTURE

Heterodyne architecture has been considered for this design

process because the circuit simplicity. We are essentially

operating at 5GHz band, so chances of LO leakage, and DC

offset may come up which may produce a zero frequency

component and ultimately saturate the high speed ADC, if

homodyne system had been implemented. It is better to go for

atleast one stage down-conversion to the baseband before we

demodulate or put any kind of filtering (higher operating

frequency will give high Q filter which is costly).

Following are architectures explained for the Wireless

transmission system-

A) Transmitter RF architecture

Modulation-256 QAM : 8 bits per symbol.

The Intermediate Frequency (IF) is 290 MHz because the IF

should be more than the receiver band (160 MHz) and the

practical blocks/modules in transmitter are available in market

for this IF frequency. Symbol rate is 125 MHz (1 Gbps/8 bits

per symbol). Inside the SUC_AMUFA has

been shown below –

Fig.4. IF-RF Composite Block with Channel Select Filter

Following are the list of the components used in the

architecture-

Block/Components Gain

(dB)

Noise Figure

(dB)

OIP3

(dBm) F_center

Filter

Passband

IF Amplifier 21.9 3.7 34.6

Mixer 0.8ǂ 13.2* 24

LO =4.9GHz;

and IF =

290 MHz

Bandpass

Filter1_chebyshev -2.5** 2.5 5.25 GHz 225 MHz

Power Amplifier

(PA) 32 3.01 42.636

Duplexer

Filter_Elliptic*** -2.5** 2.5 5.25 GHz 225 MHz

*NFSSB=NFDSB-3dB=16.2-3 dB.

**Gain= - Insertion Loss.

*** Elliptical filter gives the optimal response amongst all IIR filter classes. ǂ Mixer has conversion Gain only. ConvGain.

The band selected is 225 MHz. This is because of the fact

that it is wide band system and it operates on higher frequency

band 5GHz, which is not crowded much with ISM equipment

or other part 15 equipment, the filter response can be relaxed.

This relaxation is used to meet/adjusted to meet the EVM

requirement of maximum 2%.

B) Receiver RF Architecture.

Fig.5. Receiver RF architecture

The main idea here is, we would emulate the received signal

constellation as shown in the above figure. by a 256 QAM

system with a given RF Power calculated equal to sensitivity.

f1=79 MHz

f2=81 MHz

f3=160 MHz

f4=240 MHz

Fig.3. Transmitter RF architecture

RF Circuits and Systems (EEE 6374 Spring 2013) Project Report; UFID#06078296 3

Though the constellation received will be poor at the receiver,

but this is only way we can consider having the received

signal at the receiver’s input. The received power which is set

to -52.32 dBm is calculated by the sensitivity equation as

explained in section IV. Here we use, Lower Side Band (LSB)

receiver circuit, so the LO_frequency is set to 5.54GHz such

that different between LO and RF should be IF=290 MHz. The

block SDC_AMFA is enlarged as following –

Fig.6. Receiver RF architecture

Following are the list of the components used in the

architecture-

Block/Components Gain

(dB)

Noise

Figure (dB)

OIP3

(dBm) F_center

Filter

Passband

Duplexer

Filter_SAW 21.9 3.7 34.6

Low Noise

Amplifier 24.43 1.86 23

Mixer 0.8 16.3* 24

LO

=5.54GHz; and IF =

290 MHz

Bandpass Filter1_chebyshev

-1.3 1.3 290 MHz 225 MHz

IF Amplifier 21.9 3.7 34.6

*Here we do Single Side band. So NF will be 3 dB worse

IV. LINK BUDGET ANALYSIS

Fig. 7a. SysCalc Linearity Check for Transmitter

1) BER is given as 10-5

; Eb/N0 =22.4dB

( )

**T=290K; KT=-174 dBm/Hz.

2) Maximum transmission range

By frii’s free space equation - ( ) ( ) ( ) ( ) ( )

Since, Pt =19dBm from the simulation result as below of the transmitter circuit

and the P input for this transmitter is from syscalc Pin-

Fig.7b. Power Amplifier Pin v/s Pout 1st and 3rd order IMP

3) PA Modeling

Fig. 8. Power Amplifier Pin v/s Pout 1st and 3rd order IMP

The point has been shown for the 1dB compression for the

1st and 3

rd order Intermodulation Product.

It is seen that Interpolated Output Power (P1dB,out dBm), gain

(dBm) and Gain Compression (dB) are 30.976, 31.014 and

0.962 respectively. Which means by P1dB,out=P1dB,in+G-0.962,

P1dB,in =0.962 dBm where in actual, the input power to PA is

(19.87 dBm+2.5(due to filter)-32(gain of PA)=-9.63 dBm), so

the PA will not saturate with this input Power to the PA.

4) Signal Constellation – Transmitter

Fig.9. Transmitter EVM

RF Circuits and Systems (EEE 6374 Spring 2013) Project Report; UFID#06078296 4

5) Signal Constellation-Receiver

Fig.10. Receiver Signal Constellation

The constellation is degraded due to free space propagation

losses. This is intuitive, since for such a higher QAM system,

the constellation should have degraded this much. Efficient

Coding schemes and MIMO techniques are applied at PHY to

mitigate this effect.

6) Spectrum at receiver

Fig.11. Receiver Signal Spectrum

The receiver spectrum is shown as above. The out of band

emissions are pretty low around the center frequency.

V. CONCLUSION

The prime concern in design of this RF WLAN link was to

observe the Non Linearity at different points. The output of

the transmitter is 19.87 dBm which will push the range of

transmission to a maximum of around 21 mtrs. We had

detailed modeling of the Power Amplifier since its 3rd

order

Non Linearity is important as the available input power is high

enough to drive it saturation. At the receiver end, the LNA

should have the low Noise Figure (being the 1st stage) i.e. 1.5

dB which is good enough. The filter BW is not so strict for the

fact that spectrum is not much crowded as traditional 2.45

GHz band. The EVM is perfectly satisfied with 1.8% and the

sensitivity is around -53dBm. The part 15 FCC rules has been

satisfied by that fact that out of band emission is lower than

20dB @ 81MHz from center frequency. The constellation at

the receiver has degraded because of considerable SNR

degradation when passing through the medium. The Insertion

Loss and Stop band attenuation are the key factors for filter

selection. That has been satisfied by the filters found in

market.

VI. ACKNOWLEDGEMENT

This project is a partial requirement towards completion of

the course, EEE6374 RF Circuits and Systems. We thank Dr.

Jenshan Lin and the Mr. Taesong Hwang (TA) for guiding us

with every little details about the work and providing valuable

inputs throughout the time of working on this project.

VII. REFERENCES

[1] Shairi, N.A.; Rahman, T.A.; Abd Aziz, M.Z.A., "RF transmitter system

design for Wireless Local Area Network bridge at 5725 to 5825 MHz," Computer and Communication Engineering, 2008. ICCCE 2008. International

Conference on , vol., no., pp.109,112, 13-15 May 2008.

[2] Zhongming Shi; Rofougaran, R., "A single-chip and multi-mode 2.4/5GHz RF transceiver for IEEE 802.11 wireless LAN," Microwave and Millimeter

Wave Technology, 2002. Proceedings. ICMMT 2002. 2002 3rd International

Conference on , vol., no., pp.229,232, 17-19 Aug. 2002. [3] Shairi, N.A.; Ibrahim, I.M.; Rahman, T.A., "Third order intermodulation

distortion effect on the constellation error in RF transmitter of IEEE 802.11a

WLAN system," Industrial Electronics and Applications (ISIEA), 2011 IEEE Symposium on , vol., no., pp.223,226, 25-28 Sept. 2011.

[4] Office of Engineering and Technology - Federal Communications

Commission, UNDERSTANDING THE FCC REGULATIONS FOR LOW-POWER, NON-LICENSED TRANSMITTERS, USA.

[5] Pozer, D.M., Microwave and RF Design of Wireless Systems, John Willey

& Sons, Inc. NY. [6] Razavi, B., RF Microelectronics, Prentice Hall Communications and

Emerging Technologies Series, NJ.

[7]http://www.mhprofessional.com/downloads/products/0071701524/0071701524_chap02.pdf-WLAN standard

[8]http://www.litepoint.com/whitepaper/80211ac_Whitepaper.pdf-IEEE

802.11ac standard white paper. [9] Jenshan Lin, Lecture notes, Spring 2013.

VIII. COMPONENT LISTING

Component Make Power

Consumption

Parameters

Pricing

Tx_Rx_IF

Amplifier

MiniCircuits-

CMA 63+

0.725 W $ 4.95

Tx_Mixer Analog Devices ADL5801

0.161W $ 6.18

Tx_Chebyshev MiniCircuits-

VBF 7200+

2.01W $34.95

Tx_Power Amplifier

Skyworks – SE5003L-1*

0.3W $11.00

Tx_Duplex_filt

er.

MiniCircuits-

VBF 7200+

2.01W $34.95

Rx_Duplex_filter.

MiniCircuits-VBF 7200+

2.01W $34.95

Low Noise

Amplifier (LNA)

Skyworks-

SKY65404_31_201512I*

0.302W

Tx_Mixer Analog Devices

ADL5801

0.161W $6.18

Rx_BPF_Chebyshev Filter

MiniCircuits-RBP-253+

$15.95

*The component has been specially designed for 802.11ac radios.