Distributed digital antenna system and communication method using the system

Distributed digital antenna system and communication method using the system

[0001] Related Application

[0002] This application claims priority to United States Provisional Application No. 60/430434, entitled "Distributed Digital Antenna System", filed on December 3, 2002, which is jointly assigned with this application and is incorporated by reference In this article.

[0003] Technical Field

[0004] The present invention generally relates to the field of communication, and more specifically, to communication through a distributed antenna system.

[0005] Background Art

[0006] Various types of wireless communication systems have been popularized all over the world. For example, cellular communication systems cover most major urban areas and major highways passing through remote areas. Cellular systems allow individuals with cellular phones to communicate with base stations connected to the Public Switched Telephone Network (PSTN) or some other communication network.

[0007] As in the case of any communication system, cellular systems may leave coverage "holes" where base station signals cannot reach. The vulnerability may be located in tunnels, valleys, city streets between high-rise buildings, or any other places where radio frequency (RF) signals are blocked.

[0008] It is not always feasible to install additional base stations where these coverage holes are located. Not only because of the cost of equipment, but also because of the cost of land occupation, the cost of setting up base stations is often very expensive. In addition, large base station antennas may not physically or aesthetically match the field area.

[0009] A solution to the coverage loophole is to use a small remote antenna where coverage is required but the installation of base stations is not guaranteed or is not expected to be installed. But the long-range antenna has a problem, that is, the coaxial cable cannot run for a long distance due to attenuation. Due to this attenuation problem, it is difficult to install remote antennas along highways or through tunnels. The use of transponders is also not a viable option, because it will only increase the cost and complexity of the system. Therefore, there is a need in the prior art for a distributed antenna system that is not bothered by attenuation problems.

[0010] Summary of the invention

[0011] The embodiments of the present invention cover a distributed digital antenna system, which has a main unit for converting radio frequency signals into digital optical signals and digital optical signals into radio frequency signals. The digital optical signals are transmitted to A plurality of remote units arranged in a daisy chain along the optical medium. Each remote unit sends an analog representation of a digital optical signal from the main unit and receives a radio frequency signal, which is converted by the remote unit into a digital optical signal for use by the main unit.

Brief introduction of the drawings

[0012] FIG. 1 illustrates an embodiment of a distributed digital antenna system according to the present invention in a block diagram.

[0013] FIG. 2 illustrates another embodiment of the distributed digital antenna system of the present invention with a block diagram.

[0014] FIG. 3 illustrates an embodiment of a remote unit according to the system shown in FIG. 1 in a block diagram.

[0015] FIG. 4 illustrates an embodiment of a remote unit according to the system shown in FIG. 2 in a block diagram.

[0016] Detailed description of the preferred embodiment

[0017] The embodiments of the present invention provide a digital distributed antenna system, which enables a communication system to fill coverage holes without having to pay for the cost of additional installation of base stations. The method is to distribute the optical fiber cables to pass through the area to be covered, and tap into the optical fiber at the desired antenna position.

CN 1745560 Β

[0018] The embodiment of the present invention relates to an optical fiber as a communication means between a remote unit and a main unit. However, any optical medium (such as a laser passing through the air) can be substituted for the optical fiber.

[0019] FIG. 1 illustrates an embodiment of a distributed digital antenna system according to the present invention in a block diagram. The system has a base station (100) that uses an antenna (110) to perform communication on an RF link. The base station uses any suitable air interface standard to communicate on the RF link. For example, the air interface standard includes one of the following: Advanced Mobile Phone System (AMPS), Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA) or Global System for Mobile Communications (GSM) or any other suitable air interface standard.

[0020] The RF link is constituted by a forward link used by the base station (100) to transmit to the subscriber unit wireless terminal (150). The subscriber unit (150) transmits back to the base station (100) through the reverse link. The subscriber unit (150) is a mobile station or a fixed station such as in a wireless local loop system.

[0021] The base station (100) has a transmitter and a receiver to allow the subscriber unit (150) to communicate with the public switched telephone network (PSTN) (130). In one embodiment, the base station also links the subscriber unit (150) to subscriber units that communicate with other base stations. In one embodiment, the base station (100) is connected to the PST through a mobile switching center that handles call switching with multiple base stations.

[0022] The main unit (101) is connected to the base station (100) through an RF link (115). In one embodiment, this link (115) is a coaxial cable. Other embodiments use other types of connections, such as an air interface or optical fiber carrying digital RF signals. U.S. Patent Application No. 09/619431 assigned to ADC Telecommunications Corporation discloses digital RF signals, which application is incorporated herein by reference.

[0023] The main unit (101) is responsible for converting the RF signal from the base station (100) into an optical signal for transmission on an optical medium. The main unit (101) also converts the received optical signal into an RF signal for transmission to the base station (100). In other embodiments, the main unit (100) also performs additional functions.

[0024] One or more remote units (105T08) are connected to the main unit (101) through optical media in a daisy-chain arrangement, such as optical fiber lines (120 and 125). The remote units (105-108) are located where additional signal coverage is needed due to lack of coverage by the base station (100). These remote units (105-108) communicate with subscriber units in the coverage area of a particular remote unit through the RF link provided by the remote unit antennas (135-138).

[0025] For illustrative purposes, four remote units (105-108) are shown in the figure. However, alternative embodiments may employ other numbers of remote units. If only a small geographic area needs to be covered, as few as one remote unit (105) can be used. If the highway in the remote area requires additional coverage, usually more than four remote units are used.

[0026] The embodiment of FIG. 1 uses a separate optical fiber line for each communication direction. Each fiber carries a different wavelength. For example, the optical fiber line (120) from the main unit (101) to the remote unit (105-108) carries the wavelength λ_1οThe optical fiber line (125) from the remote unit (105-108) to the main unit (101) carries the wavelength λ_2ΟIn alternative embodiments, each optical fiber can carry the same wavelength.

[0027] The optical fiber line (120) from the main unit (101) to the remote unit (105-108) carries digital optical signals for the remote unit (105-108) to transmit. The digital optical signal carried by the optical fiber line (125) starting from the remote unit (105-108) contains the sum of the signals received from each remote unit (105-108). Then we discuss how to generate the sum signal of the remote unit.

[0028] FIG. 2 illustrates another embodiment of the distributed digital antenna system of the present invention with a block diagram. This system is similar to the embodiment shown in Fig. 1, except that the remote unit (205-208) is connected to the main unit (201) through a single optical medium (220).

[0029] The system shown in FIG. 2 has a base station (200) that uses an antenna (210) to communicate via an RF link. The base station

CN 1745560 Β

Any air interface standard can be used to communicate over the RF link. For example, the above-mentioned air interface standard may be Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Global System for Mobile Communications (GSM).

[0030] The RF link is constituted by a forward link used by the base station (200) for transmission to the subscriber unit (250). The subscriber unit (250) transmits back to the base station (200) through the reverse link. The subscriber unit (250) can be a mobile station or a fixed station such as in a wireless local loop system.

[0031] The base station (200) has a transmitter and a receiver, which allow the subscriber unit (250) to communicate with the public switched telephone network (PSTN) (230). The base station can also link the subscriber unit (250) to subscriber units that are communicating with other base stations. In one embodiment, the base station (200) is connected to the PSTN through a mobile switching center, which handles call switching with multiple base stations.

[0032] The main unit (201) is connected to the base station (200) through an RF link (215). In one embodiment, this link (215) is a coaxial cable. Other embodiments use other types of connections, such as air interfaces or optical cables carrying digital RF signals.

[0033] The main unit (201) is responsible for converting the RF signal from the base station (200) into a digital optical signal for transmission on an optical medium. The main unit (201) is also responsible for converting the received optical signal into an RF signal for transmission to the base station (200). In other embodiments, the main unit (201) also performs additional functions.

[0034] One or more remote units (205-208) are connected to the main unit (201) through an optical medium configured in a daisy chain, such as an optical fiber line (220). The remote units (205-208) are located where additional signal coverage is needed due to lack of coverage by the base station (200).

[0035] For illustrative purposes, four remote units (205-208) are shown in the figure. However, alternative embodiments may employ other numbers of remote units.

[0036] The embodiment of FIG. 2 uses a single fiber optic line (220) for communication to and from remote units (205-208). This is achieved by a single fiber (220) carrying multiple wavelengths. For example, the optical fiber line (220) uses the wavelength λ for the digital signal from the main unit to the remote unit (205-208)_1οThe optical fiber line (220) also carries the digital and signal using the wavelength. The digital sum signal is the sum of the signals received from the remote unit (205-208). Then we will discuss how to generate this sum signal of the remote unit.

[0037] FIG. 3 illustrates an embodiment of the remote unit (105) shown in FIG. 1 in a block diagram. Each remote unit (105-108) of the embodiment shown in Fig. 1 is basically the same in functional composition.

[0038] The remote unit (105) transmits and receives RF signals through the antenna (135). Both the receiving and transmitting circuits are connected to the antenna (135) through a duplexer (301) ο

[0039] Alternative embodiments may also use other numbers of antennas. For example, in one embodiment, three antennas are used to cover three different sectors in the area.

[0040] The analog signal received on the antenna (135) is separated by the duplexer (301) and then transmitted to the analog-to-digital converter (305). The analog-to-digital converter (305) digitizes the received analog signal by periodically sampling the signal. The sampling operation generates a digital representation of the received analog signal.

[0041] The digitized received signal is input to the adder (315) so as to be added with the digitized signal from the preceding remote unit in the daisy chain. Therefore, the input of the adder (315) is coupled to the output of the previous remote unit. The output of the adder (315) is a sum signal, which is coupled to the input of the subsequent remote unit or the main unit. Therefore, the main unit receives the sum signal of the sum of all signals received by the remote units (105-108) of the system.

[0042] The digital signal of the main unit is coupled to a digital-to-analog converter (310). Analog-to-digital converter (310) takes the number of analog signals

CN 1745560 Β

The word is expressed and converted into an analog signal for transmission through the antenna (135).

[0043] The photoelectric converters (320-323) are provided at the optical ports (330 and 335) of the remote unit (105). Each optical port (330 and 335) has its own input and output coupled to the photoelectric converter (320-323).

[0044] Because the remote unit (105) processes the electrical signal represented by the optical signal entering through the optical ports (330 and 335), the photoelectric converter (320-323) is responsible for converting the optical signal into an electrical signal for the remote unit (105) Treatment. The photoelectric converter (320-323) is also responsible for converting the received electrical signal from the electrical representation to the optical representation for transmission on the optical fiber.

[0045] FIG. 4 illustrates an embodiment of the remote unit (205) shown in FIG. 2 in a block diagram. Each remote unit (205-208) of the embodiment shown in Fig. 1 is basically the same in functional composition.

[0046] The remote unit (205) transmits and receives RF signals through the antenna (435). Both the receiving and transmitting circuits are connected to the antenna (435) through a duplexer (401) ο

[0047] Alternative embodiments may also use other numbers of antennas. For example, in one embodiment, three antennas are used to cover three different sectors in the area.

[0048] The analog signal received on the antenna (435) is separated and transmitted to the analog-to-digital converter (405) by the duplexer (401). The analog-to-digital converter (405) digitizes the received analog signal by periodically sampling the signal. The sampling operation generates a digital representation of the received analog signal.

[0049] The digitized received signal is input to the adder (415) so as to be added with the digitized signal from the preceding remote unit in the daisy chain. Therefore, the main unit receives the sum signal of the sum of all signals received by the remote units (205-208) of the system.

[0050] The digital signal of the main unit is coupled to a digital-to-analog converter (410). The analog-to-digital converter (410) takes the digital representation of the analog signal and converts it into an analog signal for transmission through the antenna (435).

[0051] The photoelectric converters (420-423) are provided at the optical ports (440 and 445) of the remote unit (205). Each optical port (440 and 445) has its own input and output coupled to the photoelectric converter (420-423).

[0052] Because the remote unit (205) processes the electrical signals represented by the optical signals entering through the optical ports (440 and 445), the photoelectric converters (420-423) are responsible for converting the optical signals into electrical signals for remote Unit (205) processing. The photoelectric converter (420-423) is also responsible for converting the received electrical signal from the electrical representation to the optical representation for transmission on the optical fiber.

[0053] A wavelength division multiplexer (WDM) (430 and 431) is provided at each optical port (440 and 445)_o WDM (430 and 431) performs the optical processing functions required to combine multiple optical signals with multiple wavelengths. WDM (430 and 431) also performs the optical demultiplexing function required to separate multiple wavelengths of a single fiber into their corresponding signal paths.

[0054] In summary, the distributed digital antenna system of the present invention provides a plurality of antennas linked in a daisy chain manner on a single medium such as an optical fiber. The optical fiber can be lapped multiple times anywhere above its length, thereby providing economical radio coverage in areas where base stations are not allowed due to cost.

[0055] According to the above principles, various modifications and changes can be made to the present invention. Therefore, it is clear that within the scope of the appended claims, the present invention can be implemented in a manner different from the above.

CN 1745560 Β