This book provides the engineer and manager with a very good understanding of the processes needed to effectively perform the system design for broadband communication systems and home networking approaches. It is ideal for all engineers that design and analyze wireless, spread spectrum and basic broadband communication systems and are involved with the design of basic networking systems. It provides a good intuitive approach starting from basic telephony to satellite communications.
Inspec keywords: telephony; home networks; modems; broadband networks; digital communication
Other keywords: broadband communications; home networking technologies; homes; digital modulation; data distribution; networking solutions; telephony; orthogonal signals; high-speed digital communications; small offices; modems
This chapter reviews the basic principles of telephony and points of interest to aid a basic understanding of how the telephone operates and how the emerging new technologies affect telephony today. Discussed are telephony circuitry, the basic infrastructure, and alternatives to running the signals to the home.
High-speed modems and standards have been developed to meet the user demands for high-speed data information and faster communications with the Internet. DSL modems have been successful in reaching a large population because of the low cost structure, reliability, and high-speed data rates. ADSL and versions of ADSL, such as G.lite addressed a need in the market for many users. Hybrids using ISDN and ADSL have been produced, and high speed DSL such as HDSL and VDSL are reaching even greater modem speeds. Cable modems are rapidly becoming a solution for high-speed information to the home and office. Many new standards for bringing voice, data, and video to the home are being established as higher speeds and the number of users continue to grow.
Digital modulation waveforms are used extensively in broadband communications and home networking. BPSK is the simplest form of phaseshift keying; it shifts the carrier 0 or 180 degrees. QPSK is used to increase data rates or to provide for multiple channels. Differential techniques are used to provide simpler demodulation methods and are acceptable with all types of modulations. OQPSK is used to minimize amplitude modulation by eliminating the 180-phase shift possibility and provides another method to generate MSK and GMSK. Higher order PSK systems can be analyzed much the same way only with more phase states and phase transitions. However, the more phase shift possibilities, the harder it is to detect and resolve the different phase states. Therefore, there is a limit on how many phase states can be sent for good detection. This limit seems to grow with better detection technology, but caution must be given to the practicality of how many phase states can be sent out for standard equipment. Amplitude modulation points are combined with phase states to produce a hybrid QAM to further increase the data capacity for the bandwidth channel. FSK is another method of encoding data using two frequencies. Minimum spacing provides another method of producing MSK. TDMA, CDMA, FDMA are techniques to allow multiple users. Parallel systems can be implemented to increase the data rate, which is dependent on the number of parallel channels used. OFDM is a way to transmit parallel overlapping channels for bandwidth efficiency. OFDM can also be used to allow multiple users to operate in an FDM mode, with more users for a given bandwidth. Spread spectrum techniques are used to provide process gain to reduce the effects of jammers and allow more efficient use of the spectrum for multiple users.
Orthogonal signals are used extensively in communications because they can be received and demodulated as separate data streams with very little interference between the orthogonal signals. Quadrature demodulation is used to eliminate the ambiguity of the phase of the incoming signal, but also is used to provide a means of either sending more data or providing two separate data streams that can be demodulated separately. Antenna polarization is used to allow two channels to operate on the same frequency in quadrature. This can be either horizontal/vertical or LHCP/RHCP GSOs can be used to reduce the effects of jamming signals. The jammer and the signal are forced to be orthogonal so that the jammer can be eliminated and the signal be detected. GSOs are based on the inner product of orthogonal signals being equal to zero. Therefore, if they are orthogonal and the inner product is zero, then the desired signal can be easily detected in the presence of an unwanted signal or jammer. This approach assumes that the jammer signal level is much higher than the desired signal level. The basic GSO uses two inputs: one of the inputs contains more signal than jammer. This applies to having two antennas with one directed towards the signal providing higher power. The error signal for feedback in updating the weight value is produced by subtracting the weighted reference input signal from the received signal which contains the higher level of desired signal. When the weight has converged, the jamming signal is suppressed. OFDM is a method used in many communication applications where high-speed data or multiple users are desired. OFDM provides an optimal, spectrally efficient system for use with multiple users or the combination of parallel frequency channels for overall high data rates used for broadband communications and home networking.
Networking devices in the home and small office/home office (SOHO) that provide one complete network that can be controlled from a central location have become increasingly popular. Many companies are providing the link from the providers to the user using twisted pair wire, coax cable, fiber optics, wireless and satellite with the objective to increase the bandwidth for both high-speed connections and provide this bandwidth to an increasing number of users. Networks have been in use for some time; however in the recent years and with the increase in the number of users and computers, the Internet, and all of the different ways that information is being brought to the home, networking and distribution are in high demand. The technologies that are under consideration for home distribution include wireless, power line, and phone line communications. Wireless will be the most successful technology because it affords networking in the home without requiring wires and a new infrastructure.
Power line communications is a viable medium for sending and receiving information, which includes voice, data, music, video, Internet access, networking, and many other applications. PLC uses an already existing infrastructure, the A/C power lines, for distribution of these types of signals without adding new wiring to the home or small office. Because of the existing infrastructure and lack of high frequency RF components or antennas, this method for sending and receiving information appears offer the lowest cost and the best coverage at the present time. Nearly all types of modulation schemes can be used for sending and receiving signals over the power line; however, for high speed, reliability, and security, digital modulation is the preferred method. These digital modulation schemes along with parallel OFDM type techniques provide the demands for broadband communications and home and small office networking. Standards regarding the interoperability of multiple devices are in place to prevent interference and jamming between users. These standards are being modified and upgraded as the technology and higher data rates are being incorporated. Different frequency bands are being used for different purposes; spread spectrum and adaptive systems are being designed in order to co-exist and for interoperability. The advantages of a power line communication system far outweigh the disadvantages.
Telepone lines provide an already existing infrastructure in the home that can be utilized for broadband communications and home networking. A communications node can be connected to every telephone outlet in the house to provide a network through the telephone lines. However, most homes are not wired adequately to provide ubiquitous connections in the home. Some homes may only have one telephone outlet in the entire house. Therefore, the telephone line networking system is limited in coverage. One of the ways to increase the coverage and still use the telephone lines for networking is to combine the telephone network with either power line communications, wireless communications, or all three methods. This hybrid provides excellent coverage throughout the home and small office.
RF communications is the only true wireless technology to connect high-speed communications to and throughout the home and to provide a network that is both portable and mobile. Several standards are in existence or are being created to accommodate the tremendous technology growth curve to provide higher data rates and more universal home networks. There is an accelerating need to bring and distribute high-speed information in the home including voice, data, audio and video for applications such as providing an Internet gateway, feature rich telephony, CD quality music, shopping, games, file sharing and print sharing, memory storage, appliance and environmental controls, security systems, movies and television including HDTV and many more future devices. Four standards that are well on their way in establishing true wireless connections include IEEE 802.11 standard, Bluetooth, HomeRF, and HIPERLAN. The RF communications systems will investigate other technologies such as Home PNA and PLC to try and bridge the gap to provide a complete networking system for the home. The RF communication systems will provide wireless networking in the home that would interconnect many types of peripheral devices and provide mobility and portability.
The "last mile" specifies the connection from the local distributor of the signal to the end user or home. Several companies are providing different methods to connect and provide services of voice, data, music, video, and all other communications. They include wired solutions PSTN, cable, and fiber optics, and wireless solutions, fixed wireless, power line, and satellite. Also, many of these technologies are combined to provide new methods of bringing the communications signals to the home, including hybrid fiber/copper, hybrid fiber/coax, and wireless/wired systems. Many wireless systems in multiple bands compete for the "last mile." Methods considered include point-to-point, point-to-multipoint, and multipoint-to-multipoint for bringing broadband communications information and provide networking capabilities amongst the end users. The basic requirement for all of these methods is to bring high-speed information to the home and office environments.
Satellite communications allows the most remote places to receive Internet, telephones, faxes, video and telecommunications via satellite connections. The infrastructure, bandwidth, and availability of satellite communications, and the possibility of combining satellite communications with other types of communications systems makes this method an ideal candidate for providing ubiquitous communications to everyone worldwide.
