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Communications Baseband

The Baseband Project at Rochester Institute of Technology is designed to enhance students' practical understanding of communication systems. Under the guidance of esteemed professors and experienced advisors, the project involves modulating and demodulating signals using various methods, including Amplitude Modulation, Frequency Modulation, and Pulse Code Modulation. Students will design and implement systems for both analog and digital signals, focusing on real-world applications while assessing feasibility, compliance, and system integration.

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Communications Baseband

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  1. Communications Baseband Project 05500

  2. Members • Advisors: • Dr. Joe Delorenzo • Dr. Eli Saber • Dr. Sohail Dianat • Team Members: • Leland Smith (Team Leader) • Jason Riesbeck (Chief Engineer) • Jonathan Hutton

  3. Introduction • Communications Baseband is a project created by several professors in order to stimulate student’s practical understanding of communication systems. • Sponsor: Rochester Institute of Technology Department of Electrical Engineering

  4. Project Overview • Modulate/Demodulate using Amplitude Modulation, Frequency Modulation, and Pulse Code Modulation • Receive analog or digital transmission approximately a classrooms distance and demodulate • Output original signal to see/hear successful recovery

  5. Team Work Breakdown

  6. Fundamental Design Objectives

  7. Preliminary Design Concept #1 Universal AM/FM/ASK/FSK System • Digital data rate • Not truly PCM • Usefulness • Two distanced RF channels • Digital and analog signals utilize common modulators   • Versatile

  8. Preliminary Design Concept #2 Analog Voice and Wireless RS232 • Not a PCM solution • Requires extra lab equipment • Duplex communication • Analog AM and FM maintained • Serial link established   • Reasonable Bandwidth

  9. Preliminary Design Concept #3 Analog Voice and Wireless USB • Difficult to implement • Requires extra lab equipment • Duplex communication • Analog AM and FM maintained • USB link established   • Impressive Bandwidth • 1.5 - 450 Mbps

  10. Preliminary Design Concept #4 Analog Voice and Streaming PCM Audio •All modulations have independent communication systems •All schemes have a common audio source ◦Impressive Bandwidth ◦Comparison of modulation schemes ◦No external equipment 

  11. Concept Analysis

  12. System Development •Divided into 12 subsystems •Specification developed for each

  13. Feasibility • Assessed at a subsystem level. • Depends on the resources available • To maintain feasibility, subsystems should: • Satisfy design objectives • Economical • Comply with time constraints

  14. FCC Considerations Unlicensed Bands (FCC 15.247.b.4) Antenna gain can be as much as 6dB. All other bands 100mW or less

  15. Audio Subsystem • Block Diagram

  16. Anti-Aliasing Filter • Specifications: • 0-5V Input • Pass-band 20 kHz • Stop-band 22 kHz • Attenuation 20 dB • Butterworth Filter • Elliptical Filter

  17. Low Pass Filter -17dB 22.1 kHz

  18. AM Modulation • Concept Development • Discrete Parts • IC • Transceiver IC • Feasibility Assessment

  19. Design Objectives and Synthesis • Clock Oscillator • 1 MHz Sine Wave • RLC Filter

  20. Clock Oscillator

  21. AM Receiver • AM Receiver • Demodulates Signal • Amplifies the Signal by 18 dB

  22. FM Systems • Complicated to engineer • Could take months in industry Transmitter Receiver

  23. Radio IC’s • A simple and effective solution

  24. Choosing an FM IC

  25. FM Feasibility • Meets design requirements • •Able to be complete in allotted time • •Low cost

  26. FSK Systems • Similar to analog FM systems • Also very complicated

  27. FSK Feasibility • Nordic NRF2401 • Transmits data at 1Mbps • 2.4GHz ISM band

  28. FSK Link Analysis • NRF2401 Specification ○ 0dBm output power ○ -80dBm receiver sensitivity • Link Budget Analysis ○ 60dB of attenuation at 10m (with 0dB antenna gain)

  29. FSK Feasibility •Meets project needs •Only $4 with few external parts •Reasonable time budget

  30. PCM and Control Subassembly • Transmit Side • Conversion of Analog to Digital • Apply Protocol to Digital Data • Manage Memory and Data Flow to FSK Chip • Receive Side • Provide Control to FSK Chip • Receive and Manage FSK Chip Data • Control and Send Data to DAC

  31. Interface Specifications • Rail to rail (0-3.3V) analog signal input • Desire ~44 kHz Sample Rate • 1 Mbps transmit rate to FSK chip • Send samples to Digital to Analog Converter at sample rate

  32. Microcontroller Specifications • At least 10 I/O pins • UART (clocked serial data transfer) • Support 1 Mbps

  33. Solutions • PICmicro Microcontroller • Analog Devices DAC • 10-bit • No overhead bits • Serial

  34. Capabilities • PIC offers 10-bit AD • PIC provides I/O ports • USART (Synchronous/Asynchronous Communications) • Many I/O Ports for control lines • Provides 1MHz USART • Data storage and management

  35. System Diagram

  36. Communications Protocol • PIC must manage data from 10-bit samples to exact 1 Mbps output • USART sends 8-bit words • Start and Stop bit • Must hold at least 2 samples in PIC memory to transfer

  37. IN  PIC  OUT • Known: What goes in must come out – and at the same rate. • Therefore: The rate the PIC can sample at is governed by the FSK communications protocol. • Sampling rate must be some integer number of the outgoing packet rate

  38. Protocol Options

  39. Synchronous Option

  40. Asynchronous Option 1

  41. Asynchronous Option 2

  42. Choice Protocol • Asynchronous – 1 Sample per 2 Frames

  43. The Plan for May • Purchase all components • Build systems to spec • Test individual systems • Integrate Systems

  44. Preliminary Cost Analysis

  45. Possible Upgrades

  46. Questions?

  47. Preliminary System Design

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