Abhinav End Sem Presentation Software Defined RadioPresentation Transcript
Presented By Abhinav Kumar Tyagi M.Tech II Year IIT Kharagpur Under the Guidance of Prof R V Raja Kumar E&ECE Department, IIT Kharagpur
Introduction to Software Defined Radio
Problems with Ideal Architecture implementation
Existing Software Defined Radio
Introduction to SDR
First introduced by J.Mitola in 1991
Refers to a technique in which all the processing is done in software
The processing mentioned include mixing, filtering, demodulation etc
The software can be used to implement different demodulation scheme and different standards can be implemented in the same device.
The software can be updated so the device doesn’t become obsolete with time.
SDR EXPLAINED Software Defined Radio Hardware Radio
IDEAL SDR Low Pass Filter Analog to Digital Converter Digital Signal Processor Antenna Block Diagram of Ideal SDR Receiver
Requires High Sampling Rate ADC
Costly, Power Hungry
High Speed Processor to Process High Sample Rate
Much Costly, Huge Power Consumption
Thus a non feasible solution for commercial applications!
PRACTICAL SDR ARCHITECTURE
Analog RF Front-End still required:
Digital-analog conversion, DAC/ADC
RF, IF Filtering
Mixing IF RF
TMDSSFFSDR, from Texas Instruments in 360-960 MHz range.
SDR-1000 from Flex-Radio System ; a commercial SDR; useful for amateur radio operators; 12KHz to 60MHz.
SDR-3000 & SDR-4000 from FlexComm , useful for tactical military communication system.
MULTI MODE RADIO GSM Chipset CDMA chipset Processor Software Hardware Most of Mobile phone that work in more than one standards are based on this principle
OBJECTIVE OF THE PROJECT
To develop a ‘Single Wideband’ RF Front end from 400MHz to 3.4 GHz.
This will cover all the existing/future standards like
GSM 850/900/1800, IS95, IS136, UMTS, WiFi, Wimax etc.
The design should have low cost and power efficient
Targets on reconfigurability and reusability.
No Single Wideband solution been reported till now!
The project involves development of complete system as a whole.
SDR is an emerging technology
It is very promising. SDR aims at
Providing multifunctionality to same device.
It supports Global Mobility
Ensures Compactness and Power Efficiency
Upgrades are easy with update of software
Evolution of new standards doesn’t make the device obsolete when compared to conventional multimode radios.
Architecture of RF Front End Digital to Analog Converter DAC5687 Baseband Processor Baseband Processor Analog to Digital Converter ADC08200 ADC08200 ADC8369 ADC8369 AD 8347 MGA665P8 TRF3761 FREQUENCY SYNTHESIZER I/Q MODULATOR TRF3703 MwT-17Q3 RF Front End Baseband Section Architecture of RF Front End Tx Ant Rx Ant
WORK DONE …
Study of basic receiver architectures
Study of TRF3761 Frequency Synthesizer Chip
Calculation of data words for programming TRF3761
Filter Design for Phased Lock Loop
Frequency Synthesizer PCB designed
Design of hardware required to program the chip
Testing of frequency synthesizer and reference oscillator
Non Linear modeling of LNA and Mixer
The basic receiver architectures are
Direct Conversion Receiver
Low IF Receiver
Direct Conversion Receiver LO frequency is equal to RF carrier frequency Converts RF signal to Zero frequency and hence called as Zero IF Receiver Simple Low Pass filter is used Image reject filter is not required Well suited for integration whole receiver ON-CHIP.
Low IF receiver
LO frequency is slightly different from RF carrier frequency.
Converts RF Signal to a very low IF frequency near to dc.
Have advantages of both Zero IF and Hetrodyne architectures but requires image reject mixer which is quite challenging for wideband applications
Less popular compared to Zero IF Architecture.
Converts RF signal to lower IF signal
Requires additional intermediate stages such as IF filter
Consumes more power
High Q IF filter are bulky compared to simple LPF for direct conversion type
Least popular architecture for On Chip solution
Study of TRF3761 Frequency Synthesizer Block Diagram
Assembled Board Top and Bottom Side of Frequency synthesizer board with components mounted
Output of 20 MHz Reference Oscillator
Frequency Synthesizer Output
Modeling of LNA and Mixer
Non Linear models of LNA and Mixer developed for the calculation of Intermodulation Products arising due to Simultaneous transmissions of two carriers.
The current can be expressed as
I (v) = c 0 + c 1 V + c 2 V 2 +c 3 V 3
Where V=A (Cos (w1t) + Cos (w2t)) represents input signal
DC and fundamental terms amplitude is given by
[c 0 + c 2 A 2 ]+ [ c 1 A + (9/4)c 3 A 3 ] [Cos (w1t) + Cos (w2t)] … (E1)
Third order intermodulation terms are given as
(3/4 c 3 A 3 ) [Cos (w1+2w2) t + Cos (w1-2w2) t
+ Cos (2w1+w2) t + Cos (2w1-w2) t] …. (E2) _
Since w1 and w2 are closer, 2w1-w2 and 2w2-w1 lies closer to w1 and w2
Equation E1 Shows gain compression with increase in level of input signal and is characterized by 1 dB compression point.
Equation E2 shows that 3 rd order distortion increases as cube of amplitude of the applied signal or 3 times in dB. The amplitude of input signal where IMD and Desired signal are equal is known as IIP3 or Input referred third order intercept point.
using IIP3 and P1dB data, the model is extracted for MGA665P8 from Avago Technologies.
y = 5.3088 Vin-16.882 V 3 ;
The model is implemented in Matlab
Modeling of Mixer
The mixer is a non linear device and can be represented by a non linear polynomial of fourth degree to consider up to 3rd order IMD
The coefficients c i for above can be calculated by analyzing the output for known signal. The parameters taken into consideration to compute the model include LO to IF leakage, RF to IF leakage, Third order intercept point IIP3 and Conversion Loss.
The values of c1, c2, c3, c4 are respectively 0.15263, 0.9142, -0.6, 0.0077
The mixer is implemented in Matlab.
LNA and Mixer stages are cascaded and the output at each stage is shown.
Output Obtained from Non Linear Models of LNA & Mixer
Considering two transmissions received at 935, 935.2 MHz with
-25 dBm level of each signal
LNA Input Two Signals at 935 & 935.2 MHZ, -25 dBm each.
Output of LNA The Intermodulation products are observed at 934.8 and 935.2 MHz
Output of Mixer
Considering GSM and WiFi transmission from 1805-1890 MHz and 2400-2420 MHz , the signal at different stages is shown in figure
Mixer Output 1 Down converted GSM Signal 2 Down converted WiFi Signal 1 2 3 Third Order Intermodulation Products of WiFi and LO 3 4 Third order intermodulation product of LO and GSM signal along with RF to IF leakage 4 5 RF to IF leakage of WiFi 5 6,7 Upconverted GSM and WiFi Signals 6 7
The RF band from 400 MHz to 3.4 GHz is to be partitioned into different sub bands to avoid intermodulation products arising from mixing. Major concern is third order intermodulation products.
Types of filters to be used: Wideband RF filter or narrowband tunable filters is to be examined for suitability and compact size implementation.
RF switches used for switching modules for the above mentioned bands is to be done.
The frequency synthesizer hardware is to be finalized.
Wideband matching of LNA is to be done over whole band.
Analysis and implementation of other subsystems of the receiver and finally combining all the modules for final receiver system.