Preliminary Design Review Team E – Shrey Bhatnagar, Ben Buyanovsky, Tamara Gaynes, Tim Reeb
Preliminary Design Review • Our goal is to build a cell phone signal amplifier • This will be used in the WellCar • Plan is to power via USB for versatility • Will place focus on Sprint’s bands but also work for universal applicability • Plan to use the LO band 806.2 to 894.2 MHz and HI band 1850.2 to 2570 MHz • This covers voice, 3G, and 4G for the four major carriers
Last Year’s Group • They used dual-band, we are using tri-band • One main problem they had was not enough gain in the system • Amplifiers did not work as expected • Maybe port mismatch?
Gain Explanation • Our team kept track of our signal strength in a number of different locations • How much power at “no bars” • How much power at “full bars” • The lowest signal power was -121 dBm • The highest found was -63 dBm • Needs to have an overall gain of approximately 60 dB so we can take the service from no bars to full bars Allen Fieldhouse
Technical Specifications Antennas
Technical Specifications Amplifiers
Technical Specifications Filters
Technical Specifications Splitters/Combiners
Interfacing • The signal from the cellular network will be divided into 3 bands, and each band separated into an uplink channel and a downlink channel. • Each of the six channels will be comprised of a filter followed by 3 amplifiers. • Powered splitter/combiners will handle the transition between bands and channels. Triplexers will handle the transition between the overall signal and the bands. • Beyond this, all other components, aside from power connectors, are off the board. • The amplifiers and the splitters are active components in this system and therefore will need to powered. Power will be delivered to the board via a car’s auxiliary power port. • These typically deliver 12 V DC, which will need to be stepped down for our setup, which requires 5 V DC individually and has a recommended operating current of 115 mA.
Test Plan • Antennas: Both antennas will need to be tested to ensure they are propagating the signal properly. Furthermore, the signal power for each antenna will need to be tested while operating independent to the device as well as when connected to the device. • Triplexers: These components will initially be tested independent of the system to check for proper band separation. Later, they will be tested with the amplifiers to ensure there is no signal loss. • Amplifiers: These components will initially be tested independent of the system to ensure proper amplification. Later they will be tested together as the design dictates, and with the triplexers, to check for signal degradation. • Uplink/downlink: Testing of the uplink and downlink of the cellular signal will ensure that the handling of the voice and data connections while connected to the network is achieved.
Test Plan • Cabling: All cables and connectors will be tested for signal loss and impedance. • Power: Initially, power to the system will be tested using a programmable power supply available in the lab. A kill-a-watt unit will be used to test power consumption. The goal is to simulate the power delivered to the unit from an automobile auxiliary port and ensure no loss in performance after transitioning to real world application. • Car: Once the device has been thoroughly tested in the lab, it will be transplanted into the WellCar project vehicle for field testing. This will entail driving out to remote locations and testing functionality, based on existing coverage data from Sprint.
Risk Mitigation - High • Durability: Need to be able to handle all weather conditions • Will weather-proof final packaging • Mutual Coupling: Possibility of the two close antennas becoming mutually coupled • Extra metal sheet between antennas to reduce risk • Have not yet been able to test with the antennas but once they are ordered we will test using a handheld NA • Testing Failure: If testing does not work as planned and parts need to be reordered or repaired, it will set the schedule behind a bit • Schedule leaves room for error
Risk Mitigation - Medium • Power Management : Power delivered to the device will be through a standard auxiliary power to USB connection • Consideration will be given to adding an additional port to the board and delivering power over two USB cables • Component Failure: Due to the nature of surface mount components; i.e. very small in size and rather fragile, there is a likelihood of damaging them during assembly and testing • One member of the group will be elected to study and practice surface mount soldering to reduce the chance of damaging a component • Triplexer Failure: The triplexer selected for the current design has very sparse specifications provided by the vendor • Although its application listed by the vendor meets our need; if the part fails to meet its functionality during testing a secondary design is already in place where the triplexer can be replaced by a splitter/combiner followed by a diplexer (for the 850 MHz and 1900 MHz band) and a filter (for the 2500 MHz band).
Risk Mitigation - Low • Noise: The primary source of power for the device will be an auxiliary or “cigarette lighter” port in an automobile, typically noisy • This noise will need to be filtered out to ensure the signals being transmitted and received are not affected. • Unsatisfactory Amplifiers Performance: The amplifiers identified for the design are chosen not only for their high gain and low gain flatness but also high reverse isolation (on the order of 45-60 dB). • Although a reverse isolation of 40 dB is considered adequate for most microwave applications, heavy testing of all the potential amplifiers will carried out to ensure their best performance. • Part Orders: If the parts ordered do not arrive as planned upon arrival to school from spring break, the team leader will call the companies that we have not received parts from. • This is to ensure the order was submitted correctly or find out what needs to be done to receive the parts sooner rather than later.