UWB technology in home and cable TV networks

Ultra-wideband technology UWB (Ultra Wideband) began in the 1960s with pulse communication technology, which uses ultra-short pulses with extremely wide spectrum to communicate, also known as baseband communication and carrierless communication. Due to its low power consumption, high bandwidth, high transmission rate, low complexity, strong multipath resistance, low power spectral density of transmitted signals, and high security, UWB technology is expected to be closely related to people's lives in the next few years. Popularized in digital home appliances and consumer network devices, it will be widely used in cable TV networks and home networks.

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First, the basic principle of ultra-wideband technology

In February 2002, the US Federal Communications Commission (FCC) revised the 15th standard to define UWB signals as signals with a relative bandwidth (signal bandwidth to center frequency ratio) greater than 0.2, or an absolute bandwidth of not less than 500 MHz at any time during transmission. The signal bandwidth is defined as the bandwidth between the cutoff frequencies of 10 dB below the highest transmit power. The FCC also stipulates that UWB uses a frequency range of 3.1 to 10.6 GHz and its transmission power must be below 1 mW.

Compared with traditional communication systems, ultra-wideband systems have their own unique features. From the time domain, the general communication system performs signal modulation by transmitting the RF carrier, while UWB directly uses the time domain pulse (tens of nanoseconds) of the start and fall points to realize the modulation, and the ultra-wideband transmission puts the modulation information process. It is performed over a very wide frequency band and the frequency range occupied by the bandwidth is determined by the duration of the process. In the frequency domain, ultra-wideband is different from traditional narrowband and wideband, and its frequency band is wider. Narrowband refers to a bandwidth called less than 1%, a relative bandwidth of between 1% and 25%, called a wideband, a relative bandwidth of more than 25%, and a center frequency greater than 500 MHz is called ultra-wideband.

Second, the application of ultra-wideband technology in the home network

Home network

The home network system is composed of a wired system and a wireless system. Among them, the cable system adopts the international digital interface standard IEEE 1394b. On the basis of IEEE 1394b, the home network wireless system introduces a spectrum-efficient ultra-wideband pulse radio technology, which provides broadband wireless access with flexibility and mobility. The direct-spread sequence ultra-wideband home network seamlessly extends the mobile high-speed, high-performance wireless network to the wired 1394 backbone.

2. Direct sequence ultra-wideband communication subnet technology

The DS-UWB system with single-band system is an ideal solution for home networks. DS-CDMA recommends a dual-band (3.1 to 5.15 GHz plus 5.825 to 10.6 GHz) method of transmitting data in very short time pulses in each frequency band exceeding 1 GHz, also known as pulse radio. The structure of the DS-UWB wireless communication system is shown in Figure 1.

The home network structure integrated with the wireless 1394 bridge supports IEEE1394 fixed connection and DS-UWB wireless connection. The topology of the wireless UWB bus system is star-shaped, the HUB position is not fixed, and all the sub-stations hanging on the wireless bus are managed, which is responsible for maintaining the frame structure and allocating the periodic timing information. To monitor the status of the substation registered in the bus, broadcast the communication quality information between the substation and the substation, display the time slot arrangement of the synchronization and isochronous mode substation, control the multiple access process, and ensure that the output power is at a certain level. under. The transmission of data streams is a mode of peer-to-peer communication in an ad hoc network. When a direct link between a pair of substations is blocked, the substation and the HUB can also assume the function of relaying multiple pieces of data.

The physical layer of the direct sequence UWB system uses a binary phase shift keying modulation technique to receive signals using a RAKE receiver in order to avoid the effects of multipath fading. Its multiple access technology uses direct spread code division multiple access technology. Due to the particularity of the UWB signal generation, its pulse shaping technique is a very narrow Gaussian single-cycle pulse and is encoded using space-time coding. The typical Gaussian single-cycle pulse width is 0.2 to 2.0 ns, the pulse interval is 10 to 100 ns, and the pulse positions may be equally spaced, random or pseudo-random intervals.

The data link control layer (DLC) of the direct sequence UWB system is composed of a series of DLC frames whose frame length is several times the 1394 period, and the frame is composed of a management area, a data area, a random area, and the like. The data link control layer divides the resource into two parts, namely the reserved bandwidth for the isochronous time slot and the dynamic bandwidth for the synchronous time slot. The structure of the UWB bus protocol stack is shown in Figure 2.

The Direct Sequence Ultra Wideband 1394 Convergence Layer (CL) contains the IEEE 1394 Specific Service Convergence Sublayer (SSCS) and the Common Part Convergence Sublayer (CPCS), which is similar to the IEEE 1394 b link layer and is responsible for the 1394 transaction layer and the UWB low level. Mapping.

Third, the application of ultra-wideband technology in cable TV networks

1. Cable TV network and high definition television technology

The cable television network is an efficient and cheap integrated network. It has the advantages of wide frequency bandwidth, large capacity, multi-function, low cost, strong anti-interference ability, and support for connecting multiple businesses to thousands of households. Its development has laid the foundation for the development of the information superhighway. The foundation. The cable TV network has become the most popular multimedia channel for families, but it still uses coaxial cable to deliver TV programs to users, and it is still at the analog level. High-definition television, the highest standard of digital TV, has the best video and audio effects. It is different from the traditional TV system that currently uses analog signal transmission, and uses digital signal transmission. Since high-definition television is digitalized from the collection and production of TV programs to the transmission of TV programs, and the reception to the user terminals, it brings us a high degree of clarity. In addition, the signal noise immunity is also Greatly strengthened. Digital TV has the advantages of high-definition picture, high-fidelity stereo sound, TV signal storage, multimedia system with computer, and full utilization of frequency resources. It has become the main force of home theater.

2. Ultra-wideband technology application in cable TV network

Interactive TV on demand systems and high definition television services have high code rates and large amounts of data, which require large bandwidth and network resources, and a large number of users cause a shortage of resources. In order to solve the bandwidth problem of the cable television network, the ultra-wideband technology is introduced because it uses the carrierless structure, the network configuration cost is low, and only the corresponding device needs to be added at the front end and the user side of the system, so that the existing cable television network structure can be changed without changing. The UWB data stream is transmitted on a base.

UWB technology has a noise-like characteristic. When transmitting data, it generates a pulse signal with a very short duration in the time domain. When the carrier signal transmitted in the cable TV system is interfered by external noise and other signals, the available bandwidth of the system and the transmission of the wired network. The capacity will be greatly affected. UWB's short pulse signal will not interfere with the carrier signal, so the coexistence of UWB pulse signal and other frequency domain signals is realized in the common transmission medium of cable TV network.

The inherent problem of using UWB technology in cable television networks is that the natural frequency loss of the cable television network itself changes the shape and amplitude of the UWB pulse signal. To solve this problem, a pre-compensation method can be used. UWB data is pre-compensated before entering the cable television network, so that the signal can easily pass through the coaxial cable system. At the same time, the UWB signal has pseudo-random characteristics, and the noise level of the hybrid optical fiber coaxial cable network is higher than its power spectral density, and the signal transmission Will not be affected.

When the cable TV network transmits the UWB signal, the data is first divided into video, audio and data streams. The channel modulator distributes each signal with the RF frequency and assigns a number. After the RF signal enters the mixer, the mixer combines the signals into An output signal, the other video data stream is modulated into a radio frequency signal and mixed with a common program output by the mixer, and then converted into an optical signal and transmitted through the optical fiber. At the receiving end, the system extracts the UWB signal from the mixed signal while the video and audio data are demodulated by the demodulator. A distinguishing feature of this technology is the addition of UWB signal modems to existing cable television networks without major changes to the cable television network. The UWB signal is extended to the 50MHz to 1GHz frequency range, and the signal energy at any frequency can be lower than the noise level at that frequency band. Ordinary cable television systems or hybrid fiber-optic coaxial cable networks generally use a maximum frequency range of 870MHz, but the system still has a bandwidth of about 1GHz, so that UWB narrow pulses can be reliably transmitted in coaxial cable, at the same time. Send more data.

4. Connection of cable TV network and home network using UWB technology

Applying UWB technology to cable TV networks, making full use of its technical advantages, basically does not interfere with existing TV channels, and does not occupy or seldom occupy channel resources. At the same time, UWB's multiple access method can realize a large number of concurrent users. Cable TV network service providers can make full use of existing resources to provide various broadband access services without upgrading the network. The IEEE 1394b will occupy an important position in home networks and other high-speed communication applications due to its low price, simple operation and stable application fields. The home network based on IEEE 1394b and direct sequence ultra-wideband combines the two technologies reasonably. UWB is a new wireless home network access mode, and its dynamic mesh network allows each device in the home network to act as a network. One of the users can also be used as a part of the network infrastructure to achieve full house coverage. By connecting the wireless home network using UWB technology and the cable TV network transmitting UWB signals, and taking advantage of the broadband advantages of UWB technology, the information level of life will be greatly improved, and people can fully enjoy the broadband convenience brought by UWB technology.

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