HK1069029B - Wireless local area network time division duplex relay system with high speed automatic up-link and down-link detection - Google Patents

Description

Wireless local area network time division duplex relay system with high speed automatic uplink and downlink detection

Technical Field

The present invention relates generally to wireless communication systems, and more particularly to Time Division Duplex (TDD) wireless relay systems.

Background

Wireless communication systems have base stations, or access points, from which radio signals are transmitted and propagated. These signals are then received by a mobile station, remote station, subscriber station, etc. (referred to herein as a station) to allow communication to continue. The station may be, for example, a computer with a wireless modem, such as a laptop computer (referred to herein as a wireless laptop) equipped with a Wireless Local Area Network (WLAN) card, a mobile phone, or a wireless personal digital assistant. A radio signal may only travel a certain distance and not be efficiently received until its power level falls below a certain threshold. The area around a network access point within which signals may be received is called a coverage area, sometimes referred to as a cell. When the station moves out of the coverage area, the signal cannot be received and communication is impossible. Therefore, it is generally desirable to implement a wireless system that generates as large a network coverage area as possible at a minimum cost.

One way to extend the network coverage area is to use a relay or repeater system. The repeater is a system that receives, amplifies, and retransmits a radio signal at a higher power level. The coverage area of the original signal is extended by placing a repeater at the edge of the coverage area that receives, amplifies, and retransmits the signal from a first coverage area to a second coverage area. An exemplary relay implementation is shown in fig. 1, where an original or first coverage area 101 is supplemented with a repeater or second coverage area 102.

Wireless communication systems typically provide two-way or duplex communication such that an access point can switch data or "talk" to a station, such as a wireless laptop, and the station can also "talk" to the access point. As a result, there are two independent radio links available for two signals to propagate, referred to as downlink and uplink, respectively, as shown in fig. 2.

Generally, the uplink and downlink are established on different frequencies. These schemes are known as Frequency Division Duplex (FDD) systems. In a commercial mobile telephone system, the downlink may use, for example, the 870-890MHz frequency band, while the uplink may use, for example, the 825-845MHz lower frequency band. The key to an FDD system is that the two signals are completely isolated in frequency and therefore do not interfere when simultaneous transmissions or "conversations" from the access point and the station occur. Fig. 3 shows an example of uplink and downlink frequency bands. It should be appreciated that the uplink and/or downlink frequency bands may be further divided into channels, such as frequency division channels defined in terms of sub-bands of the uplink and downlink frequency bands, time division channels defined in terms of time slices or bursts of uplink and downlink transmissions, code division channels defined in terms of orthogonal pseudo-random code spreading applied to uplink and downlink transmissions, and/or combinations thereof, to facilitate multiple access techniques such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). A disadvantage of FDD systems is that they require twice the frequency spectrum as some other systems for duplex communication.

An alternative method of separating the uplink and downlink signals is to use the same frequency band for both signals, but separate them in time. In other words, only downlink transmission occurs in one instant or time slot, and only uplink transmission occurs in the next instant or time slot. This is called Time Division Duplexing (TDD). Uplink and downlink cannot be transmitted simultaneously, but if the time slots are small enough and frequent enough, voice communications will appear to be simultaneous in both uplink and downlink. As with FDD described above, TDD may implement various channelization schemes within the TDD band, such as those based on frequency, time, and/or code division, for example, to provide multiple access techniques.

One important issue with all repeaters is that the feedback causes the system to oscillate. As shown in fig. 4, it can be observed that some of the signal from the transmitter is fed back to the receiver of the repeater. If these signals are thereafter amplified again, there is a circular path that causes the signals to grow stronger and stronger until oscillation or overload occurs. In order to maximize the coverage area combined by the repeater, the signal amplification provided by the repeater should be as high as possible. But the maximum amplification is limited by the isolation between the transmit and receive paths, antennas, etc. Therefore, very good isolation between the two antennas within the repeater system must be ensured so that the feedback path is not significant.

One important difference between TDD and FDD repeater systems is that the oscillation/feedback problem in TDD systems is usually more severe. This is due to the fact that in addition to the feedback problem described above, another feedback path also exists as shown in fig. 5. Because TDD systems use the same frequency for both uplink and downlink channels, uplink signals may be received at the downlink receiver in some cases, and vice versa. Furthermore, the signal is amplified in both uplink and downlink amplifiers. Thus, the gain in the feedback loop is doubled. To prevent feedback in TDD systems, the isolation between uplink and downlink channels typically needs to be greater than that of FDD systems to prevent feedback.

One example of a prior attempt to provide an extended coverage area in a cellular TDD system is disclosed in U.S. patent No.5,812,933 to NiKi, the contents of which are incorporated herein by reference. In the embodiment disclosed by NiKi, separate amplifiers are used on the uplink and downlink. Therefore, to prevent oscillation, the signal paths associated with the amplifier must be sufficiently isolated, which is difficult to achieve in various embodiments. In particular, the NiKi amplifier requires strict isolation between the signals, which, as indicated above, is due to the fact that TDD systems may experience feedback paths related to using the same frequency carrier for the uplink and downlink paths, and additional effort is required to isolate the amplifier or control oscillation as the amplifiers operate simultaneously. One technique that may be used within the system of NiKi to avoid oscillations is the cellular protocol used within it, which explicitly defines when uplink and downlink transmissions occur. But if a protocol is used that allows uplink and downlink transmissions to occur simultaneously, such as the carrier sense multiple access/collision avoidance (CSMA/CA) protocol, the NiKi system will face an increased likelihood of oscillation.

One example of a prior attempt to provide an extended coverage area in a cellular FDD system is disclosed in U.S. patent No.4,849,963 to Kawano, the contents of which are incorporated herein by reference. In the embodiment disclosed by Kawano, the same amplifier is used on both the uplink and downlink. Isolation between the two signal paths has been provided by the protocol since the systems therein use different frequency bands in the uplink and downlink. Thus, the duplexer network used by Kawano separates the uplink and downlink signals and provides sufficient isolation to amplify the uplink and downlink signals without causing oscillations.

Therefore, there is a need for a system and method to extend the coverage area that does not require separate frequency allocations, so that efficient use of the spectrum, such as TDD, is provided. There is also a need for a system and method that can be economically implemented to extend the coverage area without causing harmful interference with existing coverage areas. There is also a need for a system and method that provides sufficient isolation between uplink and downlink channels to prevent unwanted oscillation of repeaters associated with extended coverage areas. The repeater should also be easy to use and operate automatically, and be self-contained, requiring no additional external control signals or special adjustments.

Disclosure of Invention

The present invention relates to a system and method in which a Time Division Duplex (TDD) repeater for a wireless communication system is implemented to extend coverage. The repeater may be implemented, for example, in a Wireless Local Area Network (WLAN) system, such as the systems described in IEEE 802.11 and HIPERLAN/1 and 2. The repeater of the preferred embodiment need not derive any additional frequency allocations. In addition, embodiments of the repeater implement a simple switching amplifier for transmitting in both uplink and downlink directions, which increases uplink and downlink isolation and minimizes deleterious feedback and oscillation tendencies. The single amplifier design also results in a lower cost implementation over conventional technology.

According to the present invention, there is provided a time division duplex repeater system comprising:

two antennas serving first and second coverage areas, the second coverage area being an extension of the first coverage area;

a switched directional amplifier coupled between the two antennas, wherein the switched directional amplifier is controlled to provide amplification of signals associated with the first or second coverage areas only at any particular time; and

control circuitry coupled to the switched directional amplifier and to the two antennas, the control circuitry being arranged to receive transmitted signals simultaneously from the first and second coverage zones and to apply control signals to the switched directional amplifier so as to control a signal path direction of an amplified signal provided by the switched directional amplifier based on a property of the transmitted signals received from the first and second coverage zones.

According to the present invention, there is also provided a time division duplex repeater system, comprising:

two antennas serving a first and a second coverage area, respectively, the second coverage area being an extension of the first coverage area;

a switched directional amplifier having a pair of cross-coupled, tri-state amplifiers coupled between the two antennas; and

a control circuit coupled to the amplifier and receiving the output of the antenna, the control circuit being arranged to receive a transmission signal from the coverage area and to apply a control signal to the amplifier to activate one of the pair of amplifiers at a time to control the direction of transmission of the amplified signal.

According to one embodiment of the invention, a time division duplex repeater system includes two antennas, a switched directional amplifier, and a control circuit. The antenna serves a first and a second coverage area, wherein the second coverage area is an extension of the first coverage area. The switched directional amplifier of this embodiment is coupled between the two antennas, preferably with a single amplifier. The control circuit is coupled to the switched directional amplifier and to a receive input of the antenna. The control circuit receives transmissions from the coverage area and applies control signals to the switched directional amplifier to control the direction of transmission.

The control circuit includes at least one power detection circuit coupled to a receive output of the antenna. The power detection circuit may output a power level signal, i.e. a percentage of the input power at the respective receiving input of the antenna, which may be used, for example, by the control circuit described above to determine the transmission direction of the repeater. The control circuit also outputs a gain control signal to a switching directional amplifier based on the power level signal. The control circuit may also mute a transmit amplifier based on the power level signal.

The repeater system may also incorporate one or more pre-amplifier stages between the output of each receive antenna and the switched directional amplifier. A power detection circuit is coupled to the output of each preamplifier stage. The determined power level may be used to bypass one or more amplification stages prior to transmission from the repeater. The antenna may be a yagi antenna or any other type of directional antenna or antenna configuration and may be mounted to the repeater using a rotating gantry or other adjustable gantry to facilitate selection of coverage areas associated therewith.

According to another embodiment of the present invention, a method extends a coverage area of a signal. According to a preferred embodiment of the method, the first and second input signals are received via opposing directional antennas, wherein the directional antennas serve the respective first and second coverage areas. The direction of transmission may be determined based on power levels associated with the first and second input signals. One of the first and second input signals is amplified at a common amplifier based on the determined transmission direction, and the amplified input signals are output at the same frequency via opposing directional antennas.

A gain associated with amplifying an input signal may be controlled based on a power level of the input signal. The amplification may likewise be attenuated based on the input signal power level. The method may further comprise pre-amplifying the input signal at one or more stages. The method may further comprise bypassing one or more amplification stages based on the power level of the input signal.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.

Drawings

For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

the features and advantages of the invention described above may be more fully understood with reference to the accompanying drawings and detailed description, in which:

figure 1 shows a repeater for extending the coverage area.

Fig. 2 shows a mobile station associated with a repeater and a wireless access point, illustrating uplink and downlink transmission paths.

Fig. 3 illustrates a prior art embodiment of a communication system using separate uplink and downlink frequency bands.

Fig. 4 shows a feedback path within a Frequency Division Duplex (FDD) repeater.

Fig. 5 illustrates a feedback path within a Time Division Duplex (TDD) repeater.

Fig. 6 shows a functional block diagram of a repeater according to one embodiment of the present invention.

Figure 7 shows a repeater with switched directional amplifiers driven by preamplifiers associated with each antenna, according to one embodiment of the present invention.

Figure 8 shows a repeater including two preamplifiers used with one switched directional amplifier, according to one embodiment of the present invention.

Fig. 9 shows another embodiment of the invention incorporating a different implementation of a switched directional amplifier.

Figure 10 illustrates an implementation of a repeater that improves network coverage and performance according to one embodiment of the present invention.

Detailed Description

According to an embodiment of the present invention, a Time Division Duplex (TDD) repeater for a wireless communication system can be implemented as an extended coverage area. The repeater may be implemented, for example, in a Wireless Local Area Network (WLAN) system, such as the systems disclosed in IEEE 802.11 and HIPERLAN/1 and 2. The repeater in the preferred embodiment does not require the system to allocate any additional frequencies for its use. Furthermore, the repeater of the preferred embodiment implements a single switching amplifier to transmit in both the uplink and downlink directions, which increases uplink and downlink isolation and minimizes detrimental feedback and oscillation tendencies. In addition, the single amplifier design also results in a lower cost implementation over conventional techniques.

The repeater is also implemented to facilitate installation with minimal expertise. It is also possible to operate in an automatic and independent manner, so that no external control signals or adjustments are required or minimized. For example, according to one embodiment of the present invention, a control signal for selecting a downlink or uplink direction may be generated inherently by listening to normal communications between an access point and a station.

For CSMA/CA (carrier sense multiple access/collision avoidance) based protocols such as 802.11 and HIPERLAN, the protocol itself attempts to avoid collisions of signals between the access point and the station. Collisions occur when a station and an access point transmit at the same time such that neither of the signals can be processed by the repeater. However, collisions cannot be completely avoided and still occur from time to time such that the signals collide to a complete loss. However, the 802.11 and HIPERLAN protocols, as well as other CAMA/CA protocols, recognize the collision and attempt to retransmit the lost signal until there are no more collisions and the signal is successfully transmitted.

From the perspective of the repeater, these collisions appear as simultaneous uplink and downlink transmissions. Conventional TDD repeater configurations, such as those designed for cellular TDD telephony systems (where the protocols do not typically allow signal collisions to occur), may attempt to amplify both the uplink and downlink resulting in self-collisions. According to one embodiment of the invention, a single switching directional amplifier or multiple switching directional amplifiers operate such that only one link, either uplink or downlink, transmission is amplified and retransmitted. This automatically overcomes the oscillation problem.

Furthermore, the repeater may include logic for auto-calibrating itself so that the amplification is not so large as to cause self-oscillation and not so small as to render the repeater ineffective. The automatic self-calibration device simplifies and isolates repeater implementations. Thus, the repeater may incorporate logic for the self-calibration process. Alternatively, the repeater may utilize signals from a centralized control center to adjust the level of amplification applied at the repeater.

Fig. 6 shows a block diagram of a repeater 600 according to one embodiment of the invention. Referring to fig. 6, the repeater 600 includes a switched directional amplifier 610 controlled by a control circuit 620. The switching directional amplifier 610 of the illustrated embodiment is also coupled to an antenna 625 to transmit/receive (e.g., receive in the downlink direction and transmit in the uplink direction) within a first service area (e.g., service area 611) and to an antenna 630 to transmit/receive (e.g., receive in the uplink direction and transmit in the downlink direction) within a second service area (e.g., service area 612).

Antennas 625 and 630 may be any antennas with sufficient directional isolation from each other. One of the antennas is generally preferred to be directed towards the network to be extended. The other antenna is generally preferred to be directed to a device or other portion of the network that has an extended coverage area. For example, in the case of a wireless local area network, antenna 625 may be directed toward an access point (e.g., node 601) and antenna 630 may be directed toward a wireless station (e.g., node 602). When the relay station is implemented with two antennas, antennas 625 and 630 are preferably both implemented as bidirectional antennas. The repeater may also be implemented with four antennas-two on each side. In this embodiment, each antenna may transmit or receive. Of course, multiple antenna diversity configurations may additionally or alternatively be implemented in accordance with the present invention. Similarly, adaptive beamforming techniques and/or multi-beam arrays may be utilized in accordance with embodiments of the present invention.

The switched directional amplifier 610 may include an amplifier 640, switches 635 and 650, and a squelch circuit 645. The control circuit 620 of the illustrated embodiment provides control signals to the switching directional amplifier 610 to control the direction of transmission in the uplink or downlink direction. In some embodiments, the control signal also controls the level of amplification so that nearby mobile stations do not overload the repeater and cause distortion. The control of the amplification level may also be used to keep the total loop gain of the system below unity. In very rare configurations, antenna isolation may be reduced (perhaps the antenna is poorly or incorrectly positioned and/or a reflected path exists), so self-oscillation may occur if the loop gain is greater than one. The control of the amplification level thus also allows to prevent the self-oscillation in rare cases where the antenna isolation is not high enough.

Squelch circuit 645 may include, for example, an on-off switch that may be used to control power to the amplifier or to otherwise prevent coupling of transmit power to either of the antennas. Squelch circuit 645 may operate under the control of the control circuit.

Each switch 635 and 650 of the illustrated embodiment receives one or more control signals from the control circuit 620. The switch changes the direction of signal propagation and amplification between antennas 625 and 630. For example, the switch may be configured to couple a signal received from antenna 625 to an input of amplifier 640 and to couple an output of amplifier 640 to antenna 630 for downlink transmission. The switch may be configured to couple signals received from the antenna 630 to an input of the amplifier 640 and to couple an output of the amplifier 640 to the antenna 625 for uplink transmission. The control circuit configures the switched directional amplifier in this manner to transmit signals received from one coverage area to another at the same frequency.

Generally, the control circuit uses duty cycles for switches 635 and 650. The duty cycle may be configured such that uplink and downlink transmissions occur in non-overlapping time slots. When the repeater operates for an 802.11 WLAN system, the duty cycle may be determined entirely by the communication between the access point and the station. For example, if the station starts uplink communication, the control circuitry will thereafter detect the signal at antenna 630 and configure the switching directional amplifier 610 in the uplink direction. Alternatively, if downlink transmission begins, the signal at antenna 625 will be detected and switching directional amplifier 610 will be configured in the downlink direction. If there is no signal, the switching directional amplifier may be turned off. If uplink and downlink transmissions begin together, the control circuitry will select either the uplink or downlink direction, but not both, randomly or according to some hierarchical structure, such as giving priority on the access point station or giving priority to the transmitting node for a duration (last to transmit node). In this case, for example, the 802.11 protocol will automatically establish that collisions within the downlink and uplink transmissions have occurred, with the result that the station or access point will retransmit the information in a later time slot.

The control circuit 620 may also send a control signal to the amplifier 640 to control the gain of the amplifier 640. The amplifier 640 may be gain controlled to have low or high power levels, multiple discrete power levels, or selectable power levels over a continuous range, depending on the implementation. The control circuit may send control signals to the amplifiers to select a power level based on the power of a signal received from one of the antennas 625 or 630, or based on any other convenient criteria.

The single amplifier design shown in fig. 6 uses a single amplifier to amplify both the uplink and downlink. This reduces the amount of loop gain within the repeater system, thus reducing the sensitivity of the repeater feedback by approximately 50% compared to a common two amplifier design.

Still referring to fig. 6, each antenna 625 and 630 provides an input to the switching directional amplifier and control circuit 620. The inputs from antennas 625 and 630, as processed by control circuit 620, may each pass through a corresponding power detector (not shown) to analyze the received signal and switch the corresponding control of directional amplifier 610. For example, a power detector may be implemented that converts an RF signal to a DC signal power voltage that is proportional to the RF power level of the RF signal. The signal power voltage may thereafter be processed by control circuitry 620 to detect the signal transmission to be relayed and/or to determine an appropriate gain level for amplifier 640. For example, the signal power voltage may be used at an input of a comparator (not shown) having its input coupled to a corresponding voltage threshold (e.g., T1-T3). When the signal power voltage exceeds (or, depending on the implementation, is less than) a corresponding threshold T1-T3 at the comparator, the comparator may output a control signal. Based on the output of the comparator, the control circuit 620 may output a control signal to the switching directional amplifier to switch the amplifier on or off, thereby setting the amplifier to low amplification or high amplification and/or selecting amplification in the uplink or downlink direction. For example, if the input signal is above the threshold T1, a high control signal may be generated and provided to the amplifier 640. If the input signal is above the threshold T2, a low level control signal may be generated and provided to the amplifier 640. If the input signal is above the threshold T3, a control signal may be generated and provided to the on-off switch 645 to turn off the amplifier. Further, if the signal is below the threshold T1, a control signal may be generated and provided to cause circuit 645 to turn off the amplifier. Additionally or alternatively, the output of the comparator may be used to control uplink or downlink direction transmissions, for example the transmission direction may be determined based on signals received from two coverage areas served by the repeater 600 with a maximum power level.

The power detector described above may be implemented as an analog power detector or an analog-to-digital conversion is performed at the power detector to obtain a digital value representative of the power level of the RF signal. It should be appreciated that switching speed may be improved when an analog power detector is used in the control scheme, rather than an analog-to-digital converter, as described above.

Most cellular systems are used for voice communications requiring a lower switching speed. Therefore, embodiments with slower switching speeds are set for these applications. It can be implemented by performing uplink or downlink switching by measuring RF power of a signal output to the control circuit 620 and the microprocessor with D/a and a/D converters and applying a gain control signal to the amplifier 640.

Fig. 7 depicts another embodiment of the present invention in which a switched directional amplifier 700 is driven by a preamplifier 710 for each antenna. A preamplifier 710 is used at each antenna, for example to pre-process the signal for analysis and/or repeater amplification, but only one power amplifier 710 is used for repeater amplification and is controlled by a switch as above. The preamplifier 710 may improve the noise performance of the system and/or provide a power detector with higher sensitivity. The control circuit 730 may use the control signal to switch the directional amplifier 700 in the same manner as described in connection with fig. 6.

Fig. 8 depicts another embodiment of the present invention in which two preamplifiers are used with one switched directional amplifier 800. Referring to fig. 8, a low noise amplifier 820 is coupled to the receive output 810 of each antenna. The output of low noise amplifier 820 is coupled to the input of switch 830, which is controlled by control circuit 840. Switch 830 is used to controllably couple the output of low noise amplifier 820 to preamplifier 850 or a corresponding transmit antenna. The output of each preamplifier 850 is coupled to a switched directional amplifier 800 that provides additional gain and the same features described with reference to fig. 6.

In controlling the amplification and power level of the transmitted signal output by the repeater, control circuit 840 of the illustrated embodiment receives signals from the outputs of both low noise amplifier 820 and preamplifier 850. When the power level of the signal output by the low noise amplifier is determined to be too high by the corresponding power detection direction circuit of control circuit 840, the control circuit may cause switch 830 to bypass preamplifier 850. Alternatively, the control circuit may cause the gain of the preamplifier to be reduced.

Control circuit 840 additionally or alternatively monitors the power level of the output of preamplifier 850 and sends a gain control signal to switching directional amplifier 800 based on the power level to adjust the gain of the final gain stage. Thus, the embodiment of FIG. 8 allows the use of a power detector with a smaller dynamic range. By using multiple power detectors, each corresponding to a different amplification stage, the dynamic range of the power detector can be effectively increased.

Still referring to fig. 8, two power detectors (not shown) are implemented with respect to each receive antenna. A first of the power detectors may be coupled to an output of low noise amplifier 820. A second one of the power detectors may be coupled to an output of preamplifier 850. The comparator may have an input coupled to the output of the power detector and a threshold voltage (e.g., T1-T3). The power detector may convert the RF signal at the input into a DC signal power voltage proportional to the RF power level of the RF signal. When the signal power voltage exceeds (or, depending on the implementation, falls below) a corresponding threshold (TI-T3) at the comparator, the comparator may output a signal to a prompt of the control circuit 840. Based on the output of the comparator, control circuit 840 may output a gain control signal to the switched directional amplifier to set the amplification level of the amplifier 800. In addition, the control circuit 840 may output a control signal that subsequently controls the switch 830. Additionally or alternatively, the output of the comparator may determine whether the repeater is to transmit in the uplink or downlink direction and may cause a control signal to be sent to the switching directional amplifier 800 accordingly.

If the input signal is above the threshold T1, a high control signal may be generated by the control circuit 840 and provided to the amplifier of the switched directional amplifier 800. If the input signal is above the threshold T2, a low level control signal may be generated by the control circuit 840 and provided to the amplifier of the switched directional amplifier 800. If the input signal is above the threshold T3, a control signal may be generated by control circuit 840 and provided to switch 830 to bypass preamplifier 950. Additionally, if the signal is below the threshold T1, a control signal may be generated and provided to the switching directional amplifier 800 to turn off the amplifier.

To facilitate simple and independent operation of the repeater, the amplifier may be self-calibrated so that its gain is not so large as to cause self-oscillation, nor so low as to render the repeater ineffective. Still referring to fig. 8, self-calibration may be implemented within control circuit 840, for example. The control circuit 840 may apply a calibration signal of known amplitude to the input 810 of the preamplifier and amplifier chain or any other point at all times or during the configuration mode. The control circuit 840 may measure the amplification result of the calibration signal when it is output from the directional amplifier. It is possible to measure the amplitude total gain through the amplifier chain at the control circuit and then adjust it in any convenient way. The adjustment may be by using the amplifier control signal described above. Alternatively, the control signal may be applied to the amplifier to adjust the amplifier gain in any convenient manner. One such convenient method is to use a programmable amplifier. In addition, a control circuit may be incorporated that can detect an overload condition of the amplifier so that the amplifier gain can be reduced when an overload occurs. The automatic self-calibrating device simplifies and isolates repeater use and tends to make the repeater transparent to the network protocol of the network within which it is implemented. In an alternative embodiment of the present invention, control circuit 840 may correspond to a calibration control signal transmitted by an access point or station to the repeater.

Another important aspect affecting the performance of a repeater system according to embodiments of the present invention is how it handles channel processing within the frequency band provided for signal repeating. In general, all channels can be handled or processed together in the same way. But the relaxation in the system specification may be to allow the repeater to focus on only the active channel and adjust the system to meet the specification for that channel only. In some embodiments, this allows for simplified circuitry.

Fig. 9 depicts an embodiment of the present invention that introduces a different implementation of a switched directional amplifier and which may operate according to the CSMA/CA TDD protocol used in 802.11 and HIPERLAN WLAN systems. In this embodiment, two amplifiers 910 are implemented in a cross-coupled tri-state implementation within the switched directional amplifier 900. On/off control may be provided for each amplifier under the control of control circuit 920, which may be used to ensure that only one or none of the amplifiers is operating at any particular time. Preferably, any form of magnification does not occur in both directions simultaneously. This helps to prevent self-oscillation that would otherwise occur if a collision occurred within the CSMA/CA protocol. An advantage of this embodiment is that the switch can be removed and replaced by a control signal that switches the corresponding amplifier on or off, instead of switching the input and output signals with the switch. Because one or more of the amplifiers are always off, the loop gain is equal to one of the amplifier chains, rather than two as in prior art systems.

The duty cycle of this embodiment of the switched directional amplifier is similar to the other embodiments when the repeater is operating for an 802.11 WLAN system. That is, the duty cycle may be determined by the communication between the access point and the station. For example, if the station starts uplink transmission, control circuitry 920 detects the signal at antenna 930 and configures switching directional amplifier 900 for uplink transmission. Alternatively, if downlink transmission begins, the signal at antenna 925 is detected and switching directional amplifier 900 is configured to transmit in the downlink direction. If there is no signal, the switching directional amplifier 900 may be turned off. If uplink and downlink transmissions begin together, the control circuitry 920 preferably selects either the uplink or downlink direction, but not both. This may be done randomly for uplink or downlink transmissions, according to priority, or according to a set of rules or any other convenient criteria. For example, when a collision occurs, the 802.11 protocol will automatically establish that a collision has occurred within the downlink and/or uplink transmissions, with the result that the station or access point will retransmit the information in a subsequent time slot.

To increase the isolation between the uplink and downlink transmission paths stimulated in TDD, an antenna isolation feature may be implemented. In general, the uplink and downlink antennas may be isolated using orientation, polarization, placement, and configuration. For example, two directional antennas may be implemented in a back-to-back configuration to generate isolation between the uplink and downlink paths. The antenna may be, for example, a yagi antenna incorporating a folded dipole element. Alternatively, the antenna may be any directional antenna, such as a patch array, dielectric resonator, disk, spiral, cone, horn, cavity or any other directional antenna that provides directional isolation from each other. The antenna may be secured within or on the repeater housing using a gimbal or rotating mount to allow for easy pointing and positioning of the antenna.

In addition, the antenna may have orthogonal polarizations such as vertical and horizontal polarizations to increase isolation. Left and right circular polarizations may alternatively be used. In general, the directional antennas may be oriented such that the uplink antenna is directed toward the access point and the downlink antenna is directed toward or includes the ideal coverage area for the device. The orientation and placement of the antennas allows for reflective objects and other obstructions within the coverage area.

Each of the characteristics of the antenna, i.e. cross polarization, high gain and reflector, contributes to increased isolation. With a yagi antenna incorporating folded dipole elements, an isolation of about 60dB can be achieved.

Fig. 10 illustrates an embodiment of a repeater within a Wireless Local Area Network (WLAN). The WLAN may implement any convenient protocol. In general, access point 1010 is coupled to a network, such as the network 1000 shown. Network 1000 may be any interconnected network of computers, routers, bridges, switches, and other network elements, including local area networks, wide area networks, interconnected computer networks known as the internet, and/or any other network. The access points may include electrical, optical, or other interfaces to the network 1000 to switch data with the network 1000 according to any convenient protocol, including IP, HTTP, UDP, POP, SMTP, and any other convenient network protocol.

Access point 1010 may also include an antenna for wireless transmission to couple wireless stations, such as station 1050, to network 1000 through the access point. Access points are well known and may operate in accordance with any wireless network protocol, including the well-known IEEE 802.11 protocol and HIPERLAN/1 and 1 protocols.

Access point 1010 generates a signal having a coverage area 1020. When an access point is located within a building as shown in fig. 10, a repeater of the present invention may be positioned within coverage area 1020 to extend coverage area 1020 to other portions of the building, such as coverage area 1040. As shown, repeater 1030 includes two directional antennas that are directed to an access point and a station 1050 within a coverage area 1040, respectively. Coverage area 1040 extends network access to stations within coverage area 1040, such as station 1050. During use, station 1050 switches data with network 1000 through relay 1030 and access point 1010. The repeater receives uplink transmissions from station 1050 via a first directional antenna and retransmits the transmissions to access point 1010 via a second directional antenna. The access point 1010 then forwards the data to the network 1000. In the downlink direction, access point 1010 transmits data to relay 1030, and relay 1030 receives the transmission on the second antenna. The repeater then retransmits the data to station 1050. When station 1050 and access point 1010 transmit simultaneously, the conflict is resolved as described above.

While particular embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the spirit and scope of the invention. For example, although an exemplary analog embodiment of the control circuit is described, it should be understood that the analog-to-digital conversion may be performed at any point in the signal processing associated with receiving the antenna input signal. Any digitized values may be processed, for example, by a microprocessor or other controller that may generate control signals to control switching of the directional amplifier, preamplifier, switch, or any other unit of the repeater system. A microprocessor, discrete logic, or other integrated circuit chip may thus implement the control circuit, and may provide other functions to control the repeater, including functions for turning the repeater on or off in response to a remote control signal or an input signal level falling below a particular threshold.

The microprocessor and memory may also be used to store configuration values that determine, for example, the frequency at which the repeater operates, the duty cycles associated with the uplink and downlink signaling paths, and any other variables used to control the operation of the repeater portion.

It should also be understood that the power detection circuit may be implemented in a variety of forms in both analog and digital implementations. For example, one power detection circuit may be used to receive inputs from two receive antennas rather than two separate circuits. Other similar changes may be made to the control circuit shown and described based on well known design choices and considerations.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims (32)

1. A time division duplex repeater system, comprising:

two antennas serving first and second coverage areas, the second coverage area being an extension of the first coverage area;

a switched directional amplifier coupled between the two antennas, wherein the switched directional amplifier is controlled to provide amplification of signals associated with the first or second coverage areas only at any particular time; and

control circuitry coupled to the switched directional amplifier and to the two antennas, the control circuitry being arranged to receive transmitted signals simultaneously from the first and second coverage zones and to apply control signals to the switched directional amplifier so as to control a signal path direction of an amplified signal provided by the switched directional amplifier based on a property of the transmitted signals received from the first and second coverage zones.

2. The repeater system according to claim 1, wherein the control circuit includes:

circuitry for determining a signal strength relationship between a signal received by a first antenna of the two antennas and a signal received by a second antenna of the two antennas, wherein the control circuitry selects the signal path direction as a function of the determined signal strength relationship.

3. The repeater system according to claim 2, wherein the determined signal strength relationship includes a stronger received signal of the signals received by the first antenna and the signals received by the second antenna, and the selection of the signal path direction selects the signal path direction associated with the stronger received signal.

4. The repeater system according to claim 2, wherein the circuitry for determining a signal strength relationship between a signal received by a first antenna of the two antennas and a signal received by a second antenna of the two antennas further comprises:

at least one power detection circuit coupled to the two antennas, the at least one power detection circuit arranged to output a power level signal proportional to a received signal power of a signal received by a first antenna of the two antennas and a power level signal proportional to a received signal power of a signal received by a second antenna of the two antennas, wherein the control circuit determines the transmission direction based on the lower level signal.

5. The repeater system according to claim 1, wherein the control circuit outputs a gain control signal to the switching directional amplifier, wherein the gain control signal is a function of a signal received by the control circuit from at least one of the two antennas.

6. The repeater system according to claim 1, wherein the control circuit outputs a squelch control signal, wherein the squelch control signal is an analysis result of a signal received by the control circuit from at least one of the two antennas.

7. The repeater system according to claim 1, further comprising:

a first stage amplifier coupled between one of the two antennas and the switched directional amplifier.

8. The repeater system according to claim 7, wherein the control circuit includes:

at least one first power detection circuit coupled to the first stage amplifier, the first power detection circuit being arranged to output at least one power level signal proportional to the signal power of the first stage amplifier.

9. The repeater system according to claim 8, wherein the control circuit further comprises:

at least one second power detection circuit coupled to at least one of the two antennas, the power detection circuit being arranged to output at least one power level signal proportional to the received signal power.

10. The repeater system according to claim 1, further comprising:

first and second stage amplifiers coupled in series between one of the two antennas and the switched directional amplifier.

11. The repeater system according to claim 10, wherein the control circuit includes:

a first power detection circuit coupled to an output of the first stage amplifier; and

a second power detection circuit coupled to an output of the second stage amplifier.

12. The repeater system according to claim 11, further comprising:

a switchable circuit coupled between the first and second stage amplifiers.

13. The repeater system according to claim 12, wherein the control circuit provides a control signal to the switchable circuit to control whether an input signal bypasses the second stage amplifier.

14. The repeater system according to claim 1, wherein said two antennas comprise at least one antenna selected from the group consisting of: yagi, patch, dielectric resonator, truncated paraboloid, helix, tapered slot, horn and cavity antenna.

15. A repeater system according to claim 1, wherein the repeater is part of a wireless LAN network.

16. The repeater system according to claim 1, wherein the control circuit includes:

a calibration signal generation circuit; and

a gain measurement circuit arranged to measure an amplification of the calibration signal as it is injected into the switched directional amplifier, wherein the control circuit outputs a gain control signal to the switched directional amplifier, wherein the gain control signal is a function of the calibration signal amplification measured by the gain measurement circuit.

17. The repeater system according to claim 1, wherein the two antennas are mounted to a housing of the repeater system using adjustable mounts.

18. The repeater system according to claim 1, further comprising:

means for determining a retransmission direction based on signal properties of a first received signal associated with the first coverage zone and a second received signal associated with the second coverage zone; and

means for configuring an amplifier circuit to amplify a selected one of the first and second receive signals in relation to the determined retransmission direction.

19. The repeater system according to claim 18, wherein the signal attribute includes a signal level.

20. The repeater system according to claim 18, further comprising:

means for muting said amplifier circuit based on a determination that said signal property associated with each of said first and second received signals satisfies a particular threshold.

21. The repeater system according to claim 20, wherein the threshold comprises a low signal level threshold.

22. The repeater system according to claim 18, wherein the means for configuring the amplifier circuit to amplify a selected one of the first and second receive signals associated with the determined retransmission direction further comprises:

a first switching circuit coupling a first antenna and the amplifier circuit;

a second switching circuit coupling a second antenna and the amplifier circuit, wherein the first switching circuit is to couple the first antenna to an input of the amplifier circuit when the second switching circuit is to couple the second antenna to an output of the amplifier circuit, and the first switching circuit is to couple the first antenna to the output of the amplifier circuit when the second switching circuit is to couple the second antenna to the input of the amplifier circuit.

23. The repeater system according to claim 18, wherein said means for determining a retransmission direction based on signal properties of a first received signal associated with said first coverage area and a second received signal associated with said second coverage area further comprises:

means for determining a signal level associated with the first received signal;

means for determining a signal level associated with the second received signal; and

means for comparing a signal level associated with the first received signal to a signal level associated with the second received signal.

24. A time division duplex repeater system, comprising:

two antennas serving a first and a second coverage area, respectively, the second coverage area being an extension of the first coverage area;

a switched directional amplifier having a pair of cross-coupled, tri-state amplifiers coupled between the two antennas; and

a control circuit coupled to the amplifier and receiving the output of the antenna, the control circuit being arranged to receive a transmission signal from the coverage area and to apply a control signal to the pair of cross-coupled, tri-state amplifiers to activate one of the pair of cross-coupled, tri-state amplifiers at a time to control the direction of transmission of the amplified signal.

25. The repeater system according to claim 24, wherein the control circuit further comprises:

at least one power detection circuit coupled to the receive inputs of the antennas, the power detection circuit being arranged to output at least one power level signal proportional to the input power received in at least one of the antennas; and

wherein the control circuit determines the transmission direction based on the power level signal.

26. The repeater system according to claim 25, wherein the control circuit outputs a gain control signal to the amplifier based on the at least one power level signal.

27. The repeater system according to claim 25, further comprising first and second stage amplifiers coupled in series between an input of each of said antennas and said switched directional amplifier.

28. The repeater system according to claim 27, where a plurality of power detection circuits are implemented, one of the plurality of power detection circuits being coupled to an output of the amplifier stage.

29. The repeater system according to claim 28, further comprising a switching circuit coupled between the first and second stage amplifiers.

30. The repeater system according to claim 29, wherein the control circuit provides a control signal to the switching circuit to control whether the input signal bypasses the second stage amplifier.

31. The repeater system according to claim 30, wherein the two antennas include at least one antenna selected from the group consisting of yagi, patch, dielectric resonator, truncated paraboloid, helix, tapered slot, horn, and cavity antenna.

32. A repeater system according to claim 24, wherein the repeater is part of a wireless LAN network.