High -speed access over copper wiring
This dissertation focuses on conceptual design, development and demonstration of a 40 Gigabits per second (Gbps) transmission system for distribution of a digital signal over Ethernet copper cables serving ultra high-speed interconnection in e.g. data centers, local area networks (LAN), consumer multimedia, teleconferencing, telemedicine, and many others. Although the actual implementation may not be feasible at the time of writing this dissertation due to technology limitations and high production costs, we have been trying to address the analysis, modeling and design of sub-systems in a framework leading to a practical implementation of beyond 10G, namely 40Gbps, in a not too distant future with the ever increasing speed of technology advances.
In the commercial market, a new challenge is the extension of fiber into the access network in small business and dense metropolitan areas. It has long been known that a major bottleneck in delivering multimedia services to the computer users is the low-capacity of LANs. With ever-increasing demand for higher capacities, the need for broadband access is transformed from a convenience into a necessity. So far, data communication has been the main driving force behind increased traffic on the communications networks. To keep up with this explosive growth, ultra high-capacity networks were required, and thus optical networks with terabit capacities dominated the network core. To enable the end user to take full advantage of this core, reliable high-speed LAN access is required. Providing service in a broadband access LAN, using a copper cable approach, has the advantages of the network being highly-dependable and cost-effective. This will benefit the providers of service over campus settings like hospitals, industry compounds or universities with facilities spread over several buildings that a quick service upgrade could extend new service offerings. Also, within server farms and data centers, short copper connectors are preferable.
After release of the 10GBASE-T, which supports data rates of 10Gbps up to a distance of 100 meters (for connecting work areas to a telecommunications room), many IEEE members recognized the potential for higher speed and are currently thinking of ways to deliver tens of Giga bits per second over copper cables. Researchers have started to study the technical feasibility, broad market potential, and economic feasibility of speeds beyond 10Gbps over copper. In this dissertation, we evaluate the possibility of 40Gbps data transmission (40GBASE-T) over horizontal balanced CAT-7A cables up to a distance of 50 meters. The objective of IEEE 40GBASE-T is to create an application that is capable of transporting data at a rate of 40Gbps over at least 10 meters of copper cable. Our capacity analysis of this cable shows that 40Gbps transmission is practical up to 50m over this cable at the cost of elaborate digital signal processing and complex coding schemes. Besides, the data center geography statistics show that 80∼90% of links are shorter than 45m. Accordingly, by the aid of upcoming new fast and low power CMOS technologies, we consider designing a system for 40Gbps transmission over 50m CAT-7A cable.
From a signal processing standpoint, 40Gbps applications on copper have two main disadvantages: (1) Computational complexities are substantially increased. (2) Circuits require significant innovations in analog mixed-signal design, and DSP design. In this dissertation, we discuss methods and algorithms that can contribute to alleviate these problems. The main contribution of this dissertation is in the technical feasibility assessment and system design for a data rate of 40Gbps over copper wire. We start by multi-input multi-output (MIMO) modeling and present formulas for capacity bounds. These bounds are good performance measures for a channel impaired by background noise and crosstalk signals. We also prove, by means of multiple access channel theorem, that single-input single-output (SISO) implementation will perform as well as MIMO implementation and this is due to low far-end crosstalk (FEXT) level in CAT-7 cables. We used the specification of CAT-7A cable, an enhanced version of CAT-7 with a better performance and engineering design, to analyze, model and finally optimize the parameters for the given system requirements. We also consider a more elaborate pulse shaping filter than regular zero-ISI raised-cosine filters. Different equalization and precoding methods are evaluated. Finally multi-dimensional trellis and Low-density parity-check codes are considered as potential candidates for channel coding. We designed a low-power, low-latency LDPC assisted coded modulation which can provide coding gains up to 6dB, sufficient to satisfy the required constraints in terms of system margin and error probability. With some optimization algorithms, we came up with an idea to substantially reduce the power through multichannel data transmission.