The introduction of cable television (CATV) in the 1940s and 1950s has significantly influenced
communications technology. Originally supplying only one-way television programming,
the CATV industry recognized the potential of two-way communications. Starting with the introduction of pay-per view services in the 1980s, two-way communications over
CATV networks eventually expanded into supplying internet access services. The increased demand for CATV services, and thus the increased demand for CATV equipment, has led the
CATV industry to develop interoperability standards. The primary standard now used by the CATV industry is the Data Over Cable Service Specification (DOCSIS). DOCSIS defines both the upstream (data towards the CATV provider) and downstream (data towards the CATV customer) transmission channels. This includes specifications for the modulators and
demodulators used in these channels.
The number of manufacturers of CATV modulators and demodulators has greatly increased over the last twenty years and continues to do so. As the number of competitive CATV equipment suppliers increases, these manufacturers must look to ways to remain competitive
by reducing time-to-market and costs associated with equipment design, as well as allowing their designs to be flexible so that they may adapt to the improvements in DOCSIS.
In the past, manufacturers have primarily used Application Specific Integrated Circuits (ASICs) to implement digital hardware designs for CATV equipment. ASICs have a very high initial setup cost and do not allow for system modifications without a complete redesign.
Recently, Field Programmable Gate Array (FPGA) technology has been introduced that allows manufacturers to both modify their designed digital hardware structures without a complete physical hardware redesign, as well as providing a reduced initial setup cost.
Although in the long term, ASICs provide a cheaper alternative to FPGAs when produced in quantity, FPGAs provide quicker time-to-market in new product development and allow changes to made after initial release. This ability to change designs after release and the quicker time-to-market has led manufacturers to adopt FPGAs in new products.
A critical component in the upstream channel of a DOCSIS compliant system is the Quadrature Amplitude Modulated (QAM) receiver. The data received at the QAM receiver have undergone several impairments including additive noise, timing offset, and frequency and phase mismatches between the transmitted modulated signal and the signal received at the demodulator. It is the function of the front-end of the receiver to correct for these impairments.
This thesis presents methods for, and an example of, the design and implementation of a DOCSIS compliant QAM receiver front-end that corrects for timing, phase and frequency impairments experienced in the upstream communication channel when additive noise is
present. The circuits presented are designed and implemented to reduce hardware costs when using FPGA technology. In addition, the circuits designed do not use proprietary logic, which gives designers more flexibility when implementing their own demodulator front-end
circuitry.
The FPGA implementation presented in this thesis achieves an average MER of 54.3 dB in a no-noise channel and close to 31 dB MER in a 25 dBc AWGN channel. The overall design uses 65 dedicated 18-bit by 18-bit multipliers and 2,970 bytes of RAM to implement
the digital front-end of the receiver
