KR20020051498A - Digital LMDS System - Google Patents

Abstract

PURPOSE: A digital LMDS(Local Multipoint Distribution System) is provided to embody a hub system only with an antenna and an RF module by locating an up-converter at a head end and to apply an RF optical transmission method from the head end to the hub. CONSTITUTION: A digital LMDS consists of a head end(50), a hub(51), an LNB(Low Noise Block down-converter)(52), and a set-top box(53). The head end(50) makes and outputs a 950-2050MHz IF signal through digital modulation for a signal supplied from a program supplier. The hub(51) receives the IF signal from the head end(50), upconverts it into a signal of 26.7-27.5GHz, and transmits the upconverted signal to a subscriber in a sectionalized square lattice-structured cell. The LNB(52) receives the RF signal from the hub(51) and downconverts its frequency band. The set-top box(53) transmits the received digital signal to a subscriber's telephone, PC or television.

Description

Digital LMDS System {Digital LMDS System}

The present invention relates to a mobile communication system, and more particularly, by using a transmission method from the headend to the hub of a digital LMDS (Local Multipoint Distribution System) system as an RF method, it is possible to realize a small size, light weight, and ease of installation of a hub. A digital LMDS system.

In general, due to the development of wireless communication technology and the development of the millimeter wave band, a broadband wireless subscriber network (B-WLL), which is advantageous in terms of ease of network construction, scalability, and economics, has been in the spotlight.

In order to realize the broadband wireless subscriber network (B-WLL), Korea announced the frequency in the 20 GHz band, and similar systems include the Canada's Local Multipoint Communication System (LMCS) and the US Regional Multipoint. Distributed Services (LMDS) and ATM Wireless Access (AWA) in Japan are being studied.

Standardization in relation to broadband wireless subscriber networks (B-WLL) is most prominent in the work of the Digital Audio Visual Council (abbreviated as DAVC).

DAVC releases the 1.0 specification up to the 1.3 specification, and proposes the only specific standard for the broadband wireless subscriber network (B-WLL). In DAVC, we talk about down time division multiplexing (TDM), up time division multiple access (TDMA), and downlink, uplink frame structure, and media access control protocol. have.

In addition, MMDS, a broadband wireless subscriber network that provides wireless cable television service or high-speed Internet service using subscriber line frequencies in the millimeter wave band (2.535 GHz to 2.655 GHz) for subscribers within a radius of about 30 to 50 km. Standards are also presented in the DAVC 1.3 specification.

In DAVC, wireless cable television (CATV) is classified into a multichannel multipoint distribution service (MMDS) below 20 GHz and an LMDS above 20 GHz depending on the frequency band used.

In Korea, Ministry of Information and Communication Announcement No. 1997-49 designates the frequency for the subscriber line of the broadband wireless subscriber network (B-WLL), which allocates 2 하향 down from 25.5 ㎓ to 27.5 하향 for two-way broadband service in the 20 ㎓ band. Upwardly, 500 MHz of 24.25 Hz to 24.75 Hz was allocated. Of these, the 800 MHz band of 26.7 GHz to 27.5 GHz was temporarily designated for cable television (CATV) transmission.

As such, ultra-high-speed broadband multimedia service using subscriber line frequency in the millimeter wave band (2MHz downwards 25.5㎓-27.5㎓ and 500MHz upwards 24.25㎓24.75㎓) for subscribers within a radius of about 2-5km. An LMDS system that provides is a system developed to deliver multi-channel TV programs to subscribers as a competition for wirelines in the cable television market.

Early LMDS system was mainly used for distribution of cable TV operated by unidirectional CATV broadcasting by adopting analog modulation and demodulation method, but gradually developed into two-way digital system. Bidirectional digital LMDS system with LocalLoop service is under development. Services that can be provided by two-way high-speed wireless communication system include voice telephone service, data communication service, interactive video service, multimedia service combined with voice / data / video, and private line service. It has a subscriber type such as subscriber and public network transmission relay.

In the digital local multipoint distribution system (LMDS) system, a set-box network from a hub is implemented as a high-frequency wireless network with a cell concept. In addition to the existing CATV service, telephone and VOD are provided as additional services. Provides interactive services such as internet and satellite broadcasting.

A general LMDS system having a configuration of such a bidirectional digital LMDS system will be described with reference to the drawings.

1 is a block diagram of a general digital LMDS system (Local Multipoint Distribution System).

As shown, Figure 1 (a) is a diagram showing a hub from the program provider of the LMDS system, that is, the transmission and reception base station, Figure 1 (b) shows a configuration in which the subscriber's indoor TV, PC, telephone is connected to the hub As shown in the figure, a headend device 10 for digitally modulating a signal supplied from the program provider 9 into an intermediate frequency (IF) signal in the 950 to 2050 MHz band, and outputting the same; 10) receives an optically modulated IF signal from the optical cable 11 to the hub 12, and receives an intermediate frequency (IF) signal from the headend 10 and up-converts to a frequency band of 26.7-27.5 GHz. A hub 12 for transmitting to a subscriber located in a cell of a zoned square lattice structure, the antenna 13 of the subscriber receiving the transmitted signal, and the signal received through the antenna 13. 95 to 2050 MHz Subscriber RF module 14 for inverse down-conversion, and network interface unit (NIU) for converting the indoor-transmitted signal for transmitting the down-converted signal into a baseband signal and digital demodulating (NIU) ( 15) and a set-top box 16 for transmitting the digital demodulated signal to a subscriber's telephone 17, a personal computer (PC) 18, or a television 18. .

In FIG. 1 (a), the subscriber and the hub are shown in a square lattice diagram of a sectorized cell, where the subscriber is located in the cell of the zoned lattice structure and the hub 12 is located at the center portion thereof.

In the general bidirectional digital LMDS system configured as described above, bidirectional flow is established between the subscriber and the hub.

First, the flow of information from the service provider to the subscriber proceeds in the order described above.

Secondly, the upstream flow from which the subscriber signals to the hub is in the reverse order described above. That is, the baseband signal is converted into an IF signal of 200 to 700 MHz by the network interface device (NIU) 15, and then up-converted into a high frequency signal of 24.25 to 24.75 GHz by the subscriber RF module 14 to the hub 12. send.

Since the LMDS system configured as described above uses a high frequency in the 24-27 GHz band, the LMDS system uses an IF signal from the head end to each base station, and sometimes uses a point-to-point link.

2 is a block diagram of a digital LMDS according to the prior art.

As shown, a head end 20 for digitally modulating a signal supplied from a program provider (not shown) to produce an intermediate frequency (IF) signal in the 950 to 2050 MHz band, and outputting the intermediate frequency from the head end. A hub 21 for receiving an (IF) signal and up-converting it to a frequency band of 26.7-27.5 GHz and transmitting it to a subscriber located in a cell of a zoned square lattice structure, and a high frequency signal transmitted from the hub. Receiving antenna and Low Noise Block Down-Converter (LNB) 22 for receiving and down-converting the frequency band, and set-top for transmitting the received digital signal to a subscriber's telephone, personal computer (PC) or television. It consists of a box (Stop-Top Box) 23.

The headend 20 includes a modulator 20-1 and a demodulator 20-2 for modulating and demodulating a signal between a program provider and each subscriber, and an intermediate frequency suitable for the modulated or demodulated signal, that is, an IF signal. IF module 20-3 and Optic module 20-4, which is a matching device for carrying the IF signal on an optical cable and transmitting the same.

In addition, the hub 21 is an RF high-frequency signal for transmitting and receiving a signal from the RF module 21-2 through the optics module 21-1, which is a matching device with the optical cable, the IF signal received from the headend. Is converted.

On the other hand, the signal received from the antenna and the LNB 22 is converted into an intermediate frequency signal in the IF module 23-3 of the set-top box, the signal is demodulated in the demodulator 23-1 is connected to the TV or telephone.

The LNB (Low Noise Block Down-Converter) is a frequency converter, and is a device for converting the high frequency electromagnetic waves collected at one point of the receiving antenna to a low-noise amplification to convert to a frequency of 1GHz band that is convenient for processing.

However, the conventional technique as described above has a problem in that the base station installed in each hub is responsible for converting the IF signal into the RF signal, which makes it difficult to reduce the size and weight of the base station.

Therefore, the present invention has been proposed to solve the above problems according to the prior art,

An object of the present invention is to apply the RF optical transmission method from the head end to the hub by placing the up converter installed in the digital LMDS (Local Multipoint Distribution System) system from the head end, to implement the system in the hub system only antenna and RF module To provide a digital LMDS system.

Features of the digital LMDS system according to the present invention for achieving the above object,

In a digital LMDS system having a program provider, a head end, a hub, and a subscriber set-top box,

The RF module is connected to the output of the IF module in the headend, and the RF signal is transmitted to the hub by up-converting the intermediate frequency signal digitally modulated by the IF module to the RF high frequency signal for radio transmission and reception. A headend for directly transmitting;

And a hub for directly radiating the RF signal directly received through the optical fiber connected to the headend to the sectorized region through the antenna.

In addition, the hub in the digital LMDS system according to the present invention for achieving the above object is characterized in that the RF signal is transmitted and received from the head end to the hub consists of only the antenna and the RF module.

1 is a block diagram of a general digital LMDS system;

2 is a block diagram of a digital LMDS according to the prior art,

3 is a block diagram of a digital LMDS according to the present invention;

4 is a block diagram showing the configuration of a hub in FIG.

<Explanation of symbols for the main parts of the drawings>

10: headend device

15: Network Interface Unit (NIU)

22: Low Noise Block Down-Converter

53: set top box

Hereinafter, a preferred embodiment of a digital LMDS system according to the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram of a digital LMDS according to the present invention.

As shown, a head end 50 for digitally modulating a signal supplied from a program provider (not shown) to produce an intermediate frequency (IF) signal in the 950 to 2050 MHz band, and outputting the intermediate frequency from the head end. Hub (51) for receiving the (IF) signal and up-converted to the frequency band of 26.7-27.5 GHz and transmitting it to the subscriber located in the cell of the zoned square lattice structure, and the high frequency signal transmitted from the hub. Receiving side antenna and Low Noise Block Down-Converter (NBN) 52 for receiving and down-converting the frequency band, and set-top for transmitting the received digital signal to a subscriber's telephone, personal computer (PC) or television. A box (Stop-Top Box) 53 is configured.

The headend 50 includes a modulator 50-1 and a demodulator 20-2 for modulating and demodulating a signal between a program provider and each subscriber, and an intermediate frequency suitable for the modulated or demodulated signal, that is, an IF signal. An IF module 50-3, an RF module 50-4 for converting the IF signal into an RF signal which is a high frequency signal, and an optical device that is a matching device for transmitting the converted RF high frequency signal on an optical cable It consists of the module 50-5.

In addition, the hub 51 is provided with an Optic module 51-1, in which an IF signal received from the headend is a matching device with an optical cable, and receives an RF signal received by the Optic module 51-1. RF module 51-2 which is a device for processing.

On the other hand, the signal received from the antenna and the LNB 52 is converted into an intermediate frequency signal in the IF module 53-3 of the set-top box, the signal is demodulated in the demodulator 53-1 is connected to the TV or telephone.

In the above configuration, the headend receives a program from a broadcast program provider, modulates a predetermined frequency channel, and then performs IF / RF conversion. The RF signal produced at the head end of the LMDS system is transmitted to each hub using an optical cable.

When using the optical transmission as described above, not only can use the broadband characteristics of the optical fiber, but also has a small volume and light weight, and has the advantage of reducing power loss and error rate. In the prior art, the RF upconversion is performed at the hub, but according to the present invention, the RF upconversion is performed at the headend instead of the hub, and the hub is an upconversion function required in the LMDS system of the conventional IF transmission method. Since the RF signal received from the headend through the optical fiber is satisfied by the amplifier, bandpass filter, etc., the system specification is satisfied, and then the signal is radiated to the sectorized region or omnidirectionally through the antenna.

In addition, the subscriber receiving apparatus installs a reception antenna and a low noise block down-converter (LBN) in a home, and a set-top box is installed indoors to demodulate received RF signals and connect them to a TV, a computer, a telephone, and the like.

FIG. 4 is a block diagram showing the configuration of a hub in FIG. 3. As shown in FIG. 4, the optical connection unit 70 includes an optical connection unit 70, an antenna connection unit 71, and an antenna 76. A photo detector 74 and an optical modulator 74 are provided to provide a matching function between the signal output from the headend and the antenna connection unit.

As described above, since the frequency is up-converted to the hub at the headend and arrives at the hub, there is no further conversion, and there are a plurality of amplifiers 73 and bandpass inside the hub to meet the transmission standard of the LMDS system. There is a filter 72, a power controller 77, and the like. That is, the 27 GHz frequency mixer required for upconversion in IF transmission according to the prior art is mounted on the headend without being provided in the hub according to the present invention. Therefore, since all hubs (remote base stations) receive the same RF signal from the headend, the headend directly transmits an RF signal of 27 GHz band, and each hub receives an RF signal directly from the headend to receive an RF signal through an antenna. It will only be responsible for the transmission function.

As described above, the digital LMDS system according to the present invention transmits the RF up-conversion function installed in a plurality of hubs through the RF method from the headend to the hub, thereby realizing a compact and lightweight base station system. There is an advantage in reducing costs and in an easier base station system, i.e., a hub.

Claims (1)

In a digital LMDS system having a head end and a hub consisting of a modulator, a demodulator, an optics module, and an IF module, An RF module which receives the intermediate frequency output from the IF module and converts the RF frequency up to an RF high frequency signal necessary for wireless transmission and reception directly to the hub; And a hub for directly radiating an RF signal received through an optical fiber connected to the headend through an antenna.