WO2006033094A2

WO2006033094A2 - A system and method for communicating between a cellular base station and a cell extender

Info

Publication number: WO2006033094A2
Application number: PCT/IL2005/000903
Authority: WO
Inventors: Shmuel Miller; Yosef Rockah
Original assignee: Celletra Ltd.
Priority date: 2004-09-22
Filing date: 2005-08-18
Publication date: 2006-03-30
Also published as: WO2006033094A3

Abstract

A communication system for communicating a cellular signal composed of separate sector signals between a base station and a cell extender, includes a transmitter which combines the separate sector signals onto different frequency bands on a common RF carrier prior to transmitting the sector signals to the receiving end. Preferably and optionally, the system includes a receiver which performs the opposite function of splitting a received RF signal carrying the separate sector signals, and recovering the sector signals. The transmitter includes a translator unit for translating each of the sector signals to a distinct frequency band, and a modulator unit for modulating the distinct frequency bands onto a transmit common carrier for communicating as a single RF signal. Modulation onto the RF carrier is performed in a manner that retains the separate sector signals within the single RF signal. The receiver includes a splitter, for splitting an RF carrier modulated with a plurality of sector signals at distinct frequency bands, and a restorer unit for restoring a separate sector signal from each of the split RF signals.

Description

A SYSTEM AND METHOD FOR COMMUNICATING BETWEEN A CELLULAR BASE STATION AND A CELL EXTENDER

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to cellular communication systems and, more particularly, but not exclusively to the uplink and downlink transfer of sector signals between a base station and a cell extender.

Conventional cellular networks employ an architecture which divides a geographical area unto coverage areas called cells. In each cell a base station (BTS) is placed at the center of the cell, to serve trie cellular traffic within the cell.

To increase the capacity (the total data throughput or the number of user served) the cell is further divided into sectors (typically 3), which are served by the same base station using dedicated baseband resources, transceivers and directional antennas per sector. The duplex traffic between the base station (BTS) and the mobile subscribers (MS) includes both downlink: (base to mobile) and uplink (mobile to base) communications .

In some cases, there is excess capacity in the cell, which can be used to extend the coverage of the cell. If neighbouring areas do not need the excess capacity it can be used to serve another remote cell. The base station then serves the original cell through its legacy antenna system, and trie additional cell through a second antenna system located at a distance from the base. The new remote cell could be a complete cell with 3 sectors, or a reduced cell with, only one or two sectors. To do so, a cell extender is used to relay the 3 -sector transmit signals (downlink) from the base station to the remote location, and to return the signals received from mobile stations at the remote antenna system to the base station (uplink). Reference is now made to Fig. 1, which illustrates a prior-art embodiment of a base station serving a local cell and a remote cell. Base station 110 is connected directly to local antenna system 120, and via cell extender 130 to remote antenna system 140. The base station can thus relay a signal to mobile station 150 using local antenna system 120, and to mobile station 160 using remote antenna 140. Cell extender 130 provides the capability to distribute the BTS resources and to place the antenna systems at different locations. This might also be advantageous to regular cellular networks, where the base station serves only its own (local) cell. The criteria for choosing the locations of the BTS and the antenna systems are different: The preferred location of the antenna depends on topography and coverage considerations, as well as on zoning regulations, while the base station location might depend on real estate availability and other cost considerations. Utilizing a cell extender the base station can be located in a remote location outside the cell coverage area. This flexibility allows a system architecture which has a cluster of BTSs located at a central depot ("BTS Farm") serving cells at different locations, at distances of few kilometers away. Fig. 2 illustrates a prior-art configuration in which a cluster of base stations in a central location serve cells at different (remote) locations. Base station "farm" 210, which is located at a central base station location, contains base stations 220.1 to 22O.n. Each base station, 220.x, is connected to a cell extender, 230.x, at the desired location. Cell extender 230.x is connected in turn to a remote antenna system 240.x. Thus BTS's 220.1 to 220.n can be clustered in a single location while antenna systems 240.1 to 240.n are dispersed geographically.

The basic building block for both scenarios, the shared configuration of Fig. 1 (where the BTS serves its original cell and a remote cell) and the BTS farm of Fig. 2 (where the BTS is remote from its own cell), is the cell extender.

In the prior art, a cell extender is composed of multiple sector repeaters (typically three), where each repeater relays the BTS transmit signal of one sector (downlink) to its correponding sector antenna subsytem, and the MS's received signals of the sector (uplink) from the antenna subsystem to the corresponding BTS system. Typically, each sector repeater uses a duplex fiber link or microwave link, altogether three links. The cell extender may also include full two-channel receive diversity cappabilities (in the uplink).

Fig. 3 is a simplified block diagram of a typical embodiment of a prior art downlink cell extender connected to a base station with three fiber optic links. Base station 310 provides three sector transmit signals (TxA, TxB and TxC). Each sector transmit signal is independently modulated onto a fiber-optic link 330 by a respective EO modulator, 320.x. The fiber optic link 330 may be implemented by three parallel optical fibers, as shown in the diagram. Alternately, the three optical signals may be transferred over a single fiber using WDM techniques. WDM is an optical transmission technique in which several baseband-modulated channels are transmitted along a single fiber, with each channel located at a different wavelength. Each channel is modulated by onto the optical fiber by a separate laser. At the cell extender end, the optical signal is provided in parallel to three EO detectors, 340.1 to 340.3, which convert the optical signal into an electrical signal which can be amplified for transmission by power amplifiers (PA), 350.1 to 350.3. Similarly, Fig. 4 is a simplified block diagram of a typical embodiment of a prior art uplink cell extender connected to a base station with three fiber optic links. Three sector signals are received by antennas A, B, and C respectively. Each of the received sector signals is provided to a respective low noise amplifier (LNA), 410.1 to 410.3, which amplify the received sector signals prior to modulation into optical frequencies. Each received sector signal is independently modulated onto a fiber¬ optic link 430 by a separate EO modulator, 420.x. At the base station end, the optical signal is provided in parallel to three EO detectors, 440.1 to 440.3, which convert the optical signals into electrical signals RxA, RxB and RxB, which are provided to base station 450. A typical embodiment of a prior art downlink cell extender connected to a base station with microwave links is depicted in Fig. 5. The primary difference between the systems of Fig. 3 and Fig. 5, is that in Fig. 5 EO modulators 320.1-320.3 are replaced by microwave transmitters, and EO detectors 320.1-320.3 are replaced by microwave receivers. Each microwave transmitter consists of a mixer 520.x which modulates the sector transmit signal onto a microwave carrier, a bandpass filter (BPF) 530.x which filters the modulated microwave signal, and a power amplifier (PA) 540.x which amplifies the microwave signal for transmission to the remote antenna system. Each microwave receiver consists of an LNA 550.x which provides low- noise amplification of the received microwave signal, a mixer 560.x which translates the microwave signal down to cellular frequencies, a bandpass filter (BPF) 570.x which filters the sector signal, and a power amplifier (PA) 580.x which amplifies the sector signal for transmission to the mobile stations. It is seen that in all the configurations shown in Figs. 3 to 5, there is a significant duplication of hardware. Each sector is provided with a dedicated modulator/transmitter and with a dedicated detector/receiver. This duplication leads to increased manufacturing costs, as well as greater power, space, and cooling requirements.

There is thus a widely recognized need for, and it would be highly advantageous to have, a method for communicating sector signals between a base station and a cell extender devoid of the above limitations.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a communication system for communicating a cellular signal composed of separate sector signals between a base station and a cell extender. The system includes a transmitter which combines the separate sector signals onto different frequency bands on a common RF carrier prior to transmitting the sector signals to the receiving end. The transmitter includes a translator unit for translating each of the sector signals to a distinct frequency band, and a modulator unit for modulating the distinct frequency bands onto a transmit common carrier for communicating as a single RF signal. Modulation onto the RF carrier is performed in a manner that retains the separate sector signals within the single RF signal, such as FDM. The system further includes a receiver which includes a splitter, for splitting an RF carrier modulated with a plurality of sector signals at distinct frequency bands, and a restorer unit for restoring a separate sector signal from each of the split RF signals. Preferably, a frequency of the transmit common carrier and a frequency of the receive common carrier are equal.

Preferably, a frequency of the transmit common carrier and a frequency of the receive common carrier are different.

Preferably, the system is a component of the cell extender. Preferably, the system is a component of the base station.

Preferably, the transmitter is a component of the cell extender and the receiver is a component of the base station. Preferably, the receiver is a component of the cell extender and the transmitter is a component of the base station.

Preferably, the translator unit comprises a respective mixer and band-pass filter for each of the separate sector signals. Preferably, the modulator unit is configured to use frequency division multiplexing (FDM).

Preferably, the distinct frequency bands are separated by guard bands.

Preferably, the translator unit is further operable to translate a control signal to a distinct control frequency band, for provision to the modulator unit. Preferably, the restorer unit comprises a respective mixer and band-pass filter for each of the split RF signals.

Preferably, the restorer unit is further operable to restore a control signal modulated onto the receive common carrier at a control frequency band.

Preferably, the system further comprises an electro-optical (EO) modulator. Preferably, the EO modulator comprises a single transmission laser.

Preferably, the system further comprises an EO detector.

Preferably, the system further comprises a microwave transmitter.

Preferably, the system further comprises a microwave receiver.

Preferably, the transmitter further comprises a power amplifier (PA). Preferably, the receiver further comprises a low-noise amplifier (LNA).

According to a second aspect of the present invention there is provided a communication system for transmitting a cellular signal composed of separate sector signals between a base station and a cell extender. The transmitter combines the separate sector signals onto different frequency bands on a common RF carrier prior to transmitting the sector signals to the receiving end. The transmitter includes a translator unit for translating each of the sector signals to a distinct frequency band, and a modulator unit for modulating the distinct frequency bands onto a transmit common carrier for communicating as a single RF signal. Modulation onto the RF carrier is performed in a manner that retains the separate sector signals within the single RF signal.

According to a third aspect of the present invention there is provided a method for transmitting a cellular signal composed of separate sector signals between a base station and a cell extender. The method includes the following steps. First, each of the sector signals is translated to a distinct frequency band. Then the distinct frequency bands are modulated onto a transmit common carrier for communicating as a single RF signal. Modulation is performed in a manner that retains the separate sector signals within the single RF signal.

The method preferably includes the further steps of demodulating an RF signal comprising a receive common carrier modulated with a plurality of sector signals at distinct frequency bands, splitting the demodulated signal to provide a respective split signal for each sector, and translating each of the split signals to the appropriate frequency, in order to restore the respective sector signal.

The present invention successfully addresses the shortcomings of the presently known configurations by combining the separate sector signals into a single RF signal, prior to providing the sector signal to the EO modulator (or microwave transmitter). Thus only a single transmitter/receiver pair is required in order to transfer the sector signal either uplink or downlink, and the duplication of hardware for each of the sector signals is avoided.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the patent specification, including definitions, will control, hi addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

Implementation of the method and system of the present invention involves performing or completing selected tasks or steps manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of preferred embodiments of the method and system of the present invention, several selected steps could be implemented by hardware or by software on any operating system of any firmware or a combination thereof. For example, as hardware, selected steps of the invention could be implemented as a chip or a circuit. As software, selected steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In any case, selected steps of the method and system of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings:

Fig. 1 illustrates a prior-art embodiment of a base station serving a local cell and a remote cell. Fig. 2 illustrates a prior-art configuration in which a cluster of base stations in a central location serve cells at different (remote) locations.

Fig. 3 is a simplified block diagram of a typical embodiment of a prior art downlinJk cell extender connected to a base station with three fiber optic links.

Fig. 4 is a simplified block diagram of a typical embodiment of a prior art uplink cell extender connected to a base station with three fiber optic links.

Fig. 5 is a simplified system diagram of a typical embodiment of a prior art downlinJk cell extender connected to a base station with microwave links.

Fig. 6a is a simplified block diagram of a transmitter, according to a preferred embodiment of the present invention. Fig. 6b shows sector frequency bands on the RF carrier with guard bands between, the sectors. Fig. 6c is a simplified block diagram of a receiver according to a preferred embodiment of the present invention.

Fig. 6d is a simplified block diagram of a system for communicating a cellular signal composed of separate sector signals between a base station and a cell extender, according to a preferred embodiment of the present invention.

Fig. 7 is a simplified system diagram of a downlink system (three sectors) using a single fiber link, according to a first preferred embodiment of the present invention.

Fig. 8 is a simplified system diagram of a downlink system (three sectors) using a microwave link, according to a second preferred embodiment of the present invention.

Figs. 9 and 10 are simplified system diagrams of uplink systems (three sectors) using an optical and microwave link respectively, according to further preferred embodiments of the present invention. Fig. 11 is a simplified system diagram of a system including a control channel, according to a preferred embodiment of the present invention.

Fig. 12 is a simplified block diagram of a method for transmitting a cellular signal composed of separate sector signals between a base station and a cell extender, according to a preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present embodiments teach a system and method for communicating between a base station and a cell extender which can be used to to replace the multiple sector repeaters required for parallel communication links by a single fiber-optic or microwave link. Specifically, the present embodiments teach modulating of the separate sector signals at the transmission end, using FDM techniques, onto a common RF carrier, prior to translation to optical/microwave frequencies. At the receiving end, the received signal is split at optical/microwave frequencies and each of the split signals is translated down to the required sector frequencies. Thus all the sector signals are transmitted as a single optical/microwave signal. The resulting system is less expensive in both money and resources than using several RF channels or 3 -WDM technology.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. The present preferred embodiments are of a transmitter which combines the sector signals in RP and transmits the combined signals over a single communication link. The transmitted signal is later received and processed at the receiving end as described below, however the present invention is not limited to systems containing both a transmitter and a receiver. In the following the general descriptions of a transmitter and receiver are presented separately below, followed by more detailed examples of systems which include both a receiver and a transmitter.

The term "transmission end" refers herein to the portion of the system which provides the sector signal, that is the base station for downlink and the cell extender for uplink. Likewise the "receiving end" refers herein to the portion of the system which receives the sector signal, that is the cell extender for downlink and the base station for uplink.

The principles and operation of a cell extender and base station communication technique according to the present invention may be better understood with reference to the drawings and accompanying descriptions. Fig. 6a is a simplified block diagram of a transmitter according to a preferred embodiment of the present invention. Transmitter 600 includes translator unit 610 and modulator unit 620. Translator unit 610 inputs sector signals 1-n, and translates each of the sector signals to a distinct frequency band, F_A to F>j. The transmit signal of sector A is translated in frequency to frequency FA. Similarly, the transmit signals of sectors B and C are translated to frequencies F_B and Fc- Preferably, frequencies F_A, F_B and Fc are chosen so that each sector occupies a distinct frequency band with some guard bands (GB) between the sectors (see Fig. 6b). Modulator unit 620 modulates the distinct frequency bands onto a transmit common carrier, preferably by frequency division multiplexing (FDM). Transmitter 600 thus serves to combine the separate sector signals into a single RF signal. The separate sector signals are recoverable from the RF signal using demodulation techniques known in the art. In the preferred embodiment, translator unit 610 translates each of the sector signals to the appropriate frequency band using a dedicated mixer and band-pass filter (see Figs. 7-11 below). Each sector signal is translated independently of the others, and the translated sector signals are conveyed in parallel to modulator unit 620.

After the separate sector signals have been combined into a single RF signal by modulator unit 620, the RF signal is transmitted to the receiving end of the system. In a first preferred embodiment, transmitter 600 includes an EO modulator which modulates the RF signal onto an optical carrier. Preferably, the EO modulator utilizes a single transmission laser. This is in contrast with the prior-art WDM transmission discussed above, which requires a separate laser for each sector signal. In a second preferred embodiment, transmitter 600 includes a microwave transmitter which conveys the RF signal to the receiving end at microwave frequencies.

In the preferred embodiment, transmitter 600 is part of a system which further includes a receiver for receiving the transmitted signal and recovering the sector signals therefrom. Reference is now made to Fig. 6c, which is a simplified block diagram of a receiver according to a preferred embodiment of the present invention. Receiver 630 includes splitter 640 and restorer unit 650. At the receiving end, an RF signal containing sector signals modulated onto a receive common carrier is input to splitter 640. As discussed above, the multiple sector signals are located on the RF carrier at separate frequency bands. Splitter 640 splits the RF signal into several independent RF signals, which are provided to restorer unit 650. Restorer unit 650 restores a separate sector signal from each of the split RF signals, preferably translating the RF signal to the appropriate frequencies, and by filtering the translated signal to isolate a single sector (see examples below). Each sector signal may then be amplified and transmitted from the appropriate antenna. In a first preferred embodiment, the transmission is received over an EO link, and receiver 630 includes an EO detector which receives the optical transmission and extracts the RF signal. In a second preferred embodiment, the transmission is received over a microwave link, and receiver 630 includes a microwave receiver which receives the microwave transmission and extracts the RF signal.

Reference is now made to Fig. 6d, which is a simplified block diagram of a system for communicating a cellular signal composed of separate sector signals between a base station and a cell extender, according to a preferred embodiment of the present invention. Such a system includes both a receiver and a transmitter. Fig. 6d contains both uplink and downlink paths, and illustrates several possible system configurations. Possible configurations include:

a) Both transmitter and receiver are components of cell extender 660 -

Transmitter 600.1 and Receiver 630.1 b) Both transmitter and receiver are components of base station 670 — Transmitter 600.2 and Receiver 630.2 c) The transmitter is a component of the cell extender and the receiver is a component of the base station - Transmitter 600.1 and Receiver 630.2 d) The receiver is a component of the cell extender and the transmitter is a component of the base station - Transmitter 600.2 and Receiver 630.1

When the transmitter and receiver are located at opposite ends of lirJk 665 (i.e. configurations c and d), the frequencies of the receive and transmit common carriers are equal, since the RF carrier frequency is not affected by transmission through link 665. However, when the transmitter and receiver are located at the same end of the system (i.e. a and b), the frequencies of the transmit and receive common carriers may differ since the receiver and transmitter are not communicating with each other but rather with separate components at the opposite end of the system. Note that as discussed above, additional preferred embodiments do not necessarily include a receiver.

EXAMPLES Reference is now made to the following examples, which together with the above descriptions illustrate the invention in a non-limiting fashion. Parts that are the same as those in previous figures are given the same reference numerals and are not described again except as necessary for an understanding of the present embodiment.

Reference is now made to Fig. 7 which is a simplified system diagram of a downlink system (three sectors) using a single fiber link, according to a first preferred embodiment of the present invention. At the base station (left side of link 740) three sector signals, TxA, TxB and TxC, are input to translator unit 705. Translator unit 705 has three parallel branches, each including a mixer 710.x and a BPF 720.x that is appropriate for multicarrier operation. Mixer 710.1 translates TxA (the transmit signal of sector A) in frequency using a local oscilator LOA. The translated signal is then filtered by bandpass filter 720.1. Similarly, TxB and TxC (the transmit signals of sectors B and C) are translated in frequency, using local oscillators LOB and LOC respectively, and then filtered. The translating frequencies F_A, F_B and Fc are chosen so that each sector occupies a distinct frequency band with some guard bands (GB) between the sectors (see Fig. 6b). The three signals are then combined by modulator unit 725 to form a single RF signal. The RF signal is amplified by amplifier 730, converted into an electro-optical signal (using E/O modulator 735), and then transmitted to the over a single fiber link 740, to the cell extender (right side of link 740).

At the cell extender, the signal is received over fiber optic link 740 by E/O detector 745 which extracts the RF signal. The RF signal is amplified by LNA 750, and input to splitter 755. The split signals are fed in parallel to restorer unit 759, which has three parallel branches, one for each sector, each branch including a mixer 760.x and BPF 765.x. Each split signal is translated back to a different sector signal, which is transmitted to the mobile stations by the remote antennas, A, B and C. Reference is now made to Fig. 8 which is a simplified system diagram of a downlink system (three sectors) using a microwave link, according to a second preferred embodiment of the present invention. Translator unit 705, modulator unit 725, splitter 755, and restorer unit 759 are configured to operate as in Fig. 7. However the present system includes a microwave transmitter and receiver. At the base station, the modulated RF carrier is input to mixer 810 which converts the RF signal to microwave frequencies. The microwave signal is filtered by BPF 820, amplified by PA 830, and transmitted by microwave antenna 840. At the cell extender, the microwave signal is received at microwave antenna 850. The received microwave signal is amplified by LNA 860 and translated back to RF by mixer 870. After filtering by BPF 880, the RF signal is input to splitter 755.

Figs. 9 and 10 are simplified system diagrams of uplink systems (three sectors) using an optical and microwave link respectively, according to further preferred embodiments of the present invention. In Figs. 9 and 10, translator unit 905 and modulator unit 925 are located at the cell extender (left side of link 940) whereas splitter 955 and restorer unit 959 are located at the base station (left side of link 940). The uplink systems operate essentially as described for the downlink examples. High performance and efficient network operation requires an effective monitoring and control, including monitoring and controlling the cell extender parametrs, such as gain, transmit power etc. The monitoring and/or control signals are usually communicated between the cell extender and base station using dedicated links, which could be fiber, microwave or a dedicated channel in the cellular or PCS network itself, when applicable. In a further preferred embodiment, the control/monitoring signals are treated similarly to a sector signal, by translating the control signal in frequency, using its own local oscillator and adding the result to the combined RF signal.

Reference is now made to Fig. 11, which is a simplified system diagram of a system including a control channel, according to a preferred embodiment of the present invention. Control channel 1110 translates the control signal in frequency, using its own local oscillator, and adds the translated control signal to the combined RF signal. At the receiver, the control signal is extracted from the received RF signal in a similar manner to the sector signals. The control channel may alternately or additionally be used for transferring a monitoring signal. Note that the configuration of the present example is equally relevant to a system containing a microwave link. Reference is now made to Fig. 12, which is a simplified block diagram of a method for transmitting a cellular signal composed of separate sector signals between a base station and a cell extender, according to a preferred embodiment of the present invention. In step 1210 each of the sector signals is translated to a distinct frequency band. In step 1220, the distinct frequency bands are modulated onto a transmit common carrier in a manner, such as FDM, which retains the separate sector signals within the single RP signal. Preferably, the distinct frequency bands are separated by guard bands to promote sector signal recovery at the receiver.

Preferably, the RF signal is prepared for transmission (by modulating onto an optical or microwave carrier) and transmitted in step 1230. Preferably, the present method further includes steps 1240-1260 which together process the received signal to recover the separate signals. In step 1240 the transmitted signal is received over the microwave or EO link and downconverted to RP. In step 1240 the RF signal is split into to provide a respective RP signal for each sector. In step 1250 each of the split signals is translated by the appropriate frequency to restore the respective sector signal.

In the preferred embodiment, the method includes one or more of the following steps: a) Filtering a translated sector signal with a band-pass filter b) Upconverting the RF signal for transmission over a microwave link or modulating the RP signal for transmission over an EO link. c) Filtering a restored sector signal with a band-pass filter d) Amplifying the RF and/or sector signals

By first modulating the separate sector signals onto a common carrier, the abovedescribed system and method enable the communication of the sector signals over a single communication link. As it is not necessary to provide separate channels for each sector signal, the duplication of hardware seen in prior-art systems is avoided.

It is expected that during the life of this patent many relevant base stations, cell extenders, transmission methods, cellular network configurations, and modulation and demodulation techniques will be developed and the scope of the parallel term is intended to include all such new technologies a priori.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

Claims

WHAT IS CLAIMED IS:

1. A communication system for communicating a cellular signal composed of separate sector signals between a base station and a cell extender, said system comprising: a transmitter comprising: a translator unit for translating each of said sector signals to a distinct frequency band, and a modulator unit associated with said translator, for modulating said distinct frequency bands onto a transmit common carrier for communicating as a single RF signal, such as to retain said separate sector signals within said single RF signal, and a receiver comprising: a splitter, for splitting a single received RF signal, said received RF signal comprising a receive common carrier modulated with a plurality of sector signals at distinct frequency bands; and a restorer unit associated with said splitter, for restoring a separate sector signal from each of said split RF signals.

2. The system of claim 1 , wherein a frequency of said transmit common carrier and a frequency of said receive common carrier are equal.

3. The system of claim 1 , wherein a frequency of said transmit common carrier and a frequency of said receive common carrier are different.

4. The system of claim 1, wherein said system is a component of said cell extender.

5. The system of claim I₅ wherein said system is a component of said base station.

6. The system of claim 1, wherein said transmitter is a component of said cell extender and said receiver is a component of said base station.

7. The system of claim 1, wherein said receiver is a component of said cell extender and said transmitter is a component of said base station.

8. The system of claim 1, wherein said translator unit comprises a respective mixer and band-pass filter for each of said separate sector signals.

9. The system of claim 1, wherein said modulator unit is configured to use frequency division multiplexing (FDM).

10. The system of claim 1, wherein said distinct frequency bands are separated by guard bands.

11. The system of claim 1 , wherein said translator unit is further operable to translate a control signal to a distinct control frequency band, for provision to said modulator unit.

12. The system of claim 1, wherein said restorer unit comprises a respective mixer and band-pass filter for each of said split RF signals.

13. The system of claim 1, wherein said restorer unit is further operable to restore a control signal modulated onto said receive common carrier at a control frequency band.

14. The system of claim 1, further comprising an electro-optical (EO) modulator.

15. The system of claim 14, wherein said EO modulator comprises a single transmission laser.

16. The system of claim 1, further comprising an EO detector.

17. The system of claim 1, further comprising a microwave transmitter.

18. The system of claim 1, further comprising a microwave receiver.

19. The system of claim 1, wherein said transmitter further comprises a power amplifier (PA).

20. The system of claim 1, wherein said receiver further comprises a low- noise amplifier (LNA).

21. A communication system for transmitting a cellular signal composed of separate sector signals between a base station and a cell extender, the system comprising: a translator unit for translating each of said sector signals to a distinct frequency band, and a modulator unit associated with said translator, for modulating said distinct frequency bands onto a transmit common carrier for communicating as a single RP signal, such as to retain said separate sector signals within said single RF signal.

22. The system of claim 21, wherein said translator unit comprises a respective mixer and band-pass filter for each of said separate sector signals.

23. The system of claim 21, wherein said modulator unit is configured to use frequency division multiplexing (FDM).

24. The system of claim 21, further comprising an electro-optical (EO) modulator.

25. The system of claim 24, wherein said EO modulator comprises a single transmission laser.

26. The system of claim 21, further comprising a microwave transmitter.

27. The system of claim 21, wherein said distinct frequency bands are separated by guard bands.

28. The system of claim 21 , wherein said translator unit is further operable to translate a control signal to a distinct control frequency band, for provision to said modulator unit.

29. The system of claim 21, further comprising a receiver, wherein said receiver comprises: a splitter, for splitting a single received RF signal, said received RP signal comprising a receive common carrier modulated with a plurality of sector signals at distinct frequency bands; and a restorer unit associated with said splitter, for restoring a separate sector signal from each of said split RF signals.

30. The system of claim 29, wherein said restorer unit comprises a respective mixer and band-pass filter for each of said split RF signals.

31. The system of claim 29, wherein said restorer unit is further operable to restore a control signal modulated onto said receive common carrier at a control frequency band.

32. The system of claim 29, wherein said system is a component of said cell extender.

33. The system of claim 29, wherein said system is a component of said base station.

34. The system of claim 29, wherein said system is distributed between said cell extender and said base station.

35. The system of claim 21, further comprising an EO detector.

36. The system of claim 29, further comprising a microwave receiver.

37. A method for transmitting a cellular signal composed of separate sector signals between a base station and a cell extender, the method comprising: translating each of said sector signals to a distinct frequency band, and modulating said distinct frequency bands onto a transmit common carrier for communicating as a single RF signal, such as to retain said separate sector signals within said single RF signal.

38. The method of claim 37, further comprising filtering a translated sector signal to limit the bandwidth of said translated sector signal.

39. The method of claim 37, wherein said distinct frequency bands are separated by guard bands.

40. The method of claim 37, further comprising upconverting said RF signal for transmission over a microwave link.

41. The method of claim 40, further comprising receiving said transmitted signal over said microwave link, and downconverting said received signal to RF.

42. The method of claim 37, further comprising modulating said RF signal for transmission over an EO link.

43. The method of claim 37, further comprising transmitting said modulated RF signal with a single-laser EO modulator.

44. The method of claim 37, further comprising receiving said transmitted signal over said EO link, and demodulating said received signal to RF.

45. The method of claim 37, further comprising the steps of: demodulating an RP signal comprising a receive common carrier modulated with a plurality of sector signals at distinct frequency bands, splitting said demodulated signal to provide a respective split signal for each sector, and for each of said split signals, translating said split signal to restore the respective sector signal.

46. The method of claim 45, further comprising filtering a restored sector signal to provide bandwidth limitation.