Link Design and HD Signal Research

Each member of the team was designated an aspect of the project to further research. It is important that each individual understand each component thoroughly, but in the interest of detailed research, we have concentrated on specific areas. David and Richie were asked to research the Bulter matrix concept. Chris and Max were asked to research the link budget and the HD signal, and in addition, Max will study antenna design.

The majority of my research on link design is sourced from Professor Grbic's lecture 11 & 12 notes. The following summary contains the points that I felt are necessary to understanding before we start design.

Noise depends on the noise temperature of the receiver system and the receiver noise bandwidth, where the bandwidth is determined by the data rate of transfer (or channel capacity) and the type of modulation coding. Modulation is a technique used to manipulate a message signal by using the message to vary the amplitude, phase frequency, or polarization of a certain carrier wave. Demodulation is the procedure of extracting the message signal by a receiver system from the received modulated carrier wave.

Due to environmental factors and noise from channel or circuit, we will notice a certain amount of error in the received signal. Error coding is the attempt to undo the error between the intended transmit message and the error filled message seen by the receiver. The process of error coding is achieved by using mathematics to formulate the message into an encoded set of bits, allowing the receiver to identify error, or undesired contamination, and in the best case, the receiver system can strip the signal of error. There is a tradeoff between decreasing the bit error rate and increasing the bandwidth of reception or similarly decrease the channel capacity. Examples of encoding methods are binary phase shift keying, quadriphased phase shift keying, binary frequency shift keying, multiple frequency shift keying, and binary amplitude shift keying.

We can measure the signal to noise ratio for a digital communication system by taking the ratio of the amount of energy received for a bit to the noise spectral density, and this ratio must pass a certain threshold to ensure the signal can be demodulated correctly. We can plot the bit error rate to the signal to noise ratio described above to give the designer the ability to choose the best performance for the digital link for a given amount of radio frequency power. We can use a certain strategy to find the amount of transmit power required to demonstrate an effective and error minimized link. The strategy is to first determine the maximum bit error rate that is allowed, then to find the signal to noise ratio for the digital link based on the type of modulation, and finally to factor in path loss to determine the minimum amount of transmit power required.