1 EE 499 Wireless Communications Project by Team 4: Arati NagarkarHemant Samtani Supriya HerwadkarChinmay Shete Shivani KaushalSalil Sawhney

2 Communication between 2 cars Design of a microwave communications link between 2 cars via a LEO Satellite in order to provide a useful data rate of 144 kbps.

3 Design Requirements  Data rate: 144Kbps  GSM system  Bandwidth: 200 KHz  Carrier Frequency: 3.8 GHz  Maximize Power efficiency (Eb/No)  LEO at 1000 Km

4 GSM specifications  Bandwidth (Uplink)/(Downlink) : 25MHz  200 KHz channels  GSM data rate : kbps  Spacing b/w corresponding Tx & Rx freq : 45 MHz  8 Users per carrier frequency.

5 Frequency Spectrum  Data rate of 144 Kbps in 200 KHz  Spacing of 45 MHz between transmit and receive frequencies as in GSM  Uplink and Downlink bands of 25 MHz GHz UPLINKUPLINK DOWNLINKDOWNLINK

6 Transmitter Section  QPSK Modulation --- IF frequency o/p : 70 MHz  Frequency Up-Converter --- i/p : 70 MHz --- o/p : 3.6 – 4.2 GHz  Variable Attenuator (PAD)  Preamplifier used for linearity  High Power Amplifier with max. gain of 40 dB.  Coaxial cable --- handles high Power of HPA --- loss negligible (7.5 dB/100 ft)

7 Receiver Section  Antenna --- Same Antenna for Tx & Rx --- Duplexer used to isolate Tx & Rx section --- Less bulky, sufficient gain  Low Noise Amplifier --- Front end of Rx section --- Very low Noise figure --- Sufficient gain  Frequency Down-Converter --- i/p : 3.8 GHz --- o/p : 70 MHz  QPSK Demodulator

8 Satellite Considerations  Regenerative Satellite used.  No Noise carried through the Satellite.  Uplink & Downlink budgets independent of each other.

9 Uplink Budget  Input to Tx : 0 dBm  EIRP should be necessarily of the order of a few watts.  Analysis and selection of Tx components done using 0 dBm as starting point and EIRP as finishing point.  Eb/No at the Satellite determined by amount of Power reaching the Satellite, Satellite Thermal Noise Power & Sky Noise Power.

10 Noise Considerations  Thermal Noise Power for Tx at 290 Kelvin  Total Noise Power for Tx : G T F T KTB  Total Noise Power of Tx reaching Satellite is negligible  Total Noise Power at the Satellite : sum of Thermal Noise Power of Satellite Transponder & Sky Noise Power.

11 CALCULATION OF LINK MARGIN  M = E b /N o (received) - E b /N o (required)  System Designed for maximizing power efficiency: E b /N o (received) = 12dB ( BER:10 -7 ) E b /N o (required) for system=9dB(BER:10 -4 )  Hence, Margin for our system=3dB  BER: => 1 bit in error in bits 14.4 bits in error in 144 kbps

12 DOWNLINK BUDGET  Reverse Link Analysis DEMODULATOR Eb/No=12dB RECEIVER ANTENNA  C/N (SNR) at demodulator input = (Eb/No)*(R/B)  Cascading NF for all components  C/N (SNR) after receiver antenna  Thermal Noise Power at receiver  EIRP at satellite

13 Design Tradeoffs And Future Scope…… Tradeoffs:  Size of the antenna Vs the antenna Gain  Simplicity of design Vs the data rate Possible Enhancements:  The incorporation of telephony in the design.  Scalability: Two users could simultaneously share the channel leading to the possible increase of the minimum SNR.