HK1140868A - Enhanced physical layer repeater for operation in wimax systems - Google Patents

Abstract

An exemplary method (500) and repeater (110, 210, 300) are described for repeating using a time division duplex (TDD) radio protocol. A signal is transmitted from a first station to a second station using a downlink and an uplink. The signal can be detected with detectors (309, 310, 855, 856) on the uplink or the downlink. The repeater can synchronize to time intervals associated with the detected signal that are measured during an observation period. The signal can be retransmitted from the second station to the first station if the signal is detected on the uplink and re-transmitted from the first station to the second station if the signal is detected on the downlink. A gain value associated with the downlink can be used to establish a gain value associated with the uplink.

Description

Enhanced physical layer repeater for operation in WiMAX systems

Technical Field

The present invention relates generally to wireless networks, and in particular to Time slot detection and Automatic Gain Control (AGC), synchronization, isolation, and operation in Time Division Duplex (TDD) repeaters as well as non-frequency translating repeaters.

Background

Several emerging protocols and/or specifications for wireless local area networks (often referred to as WLANs) or wireless metropolitan area networks (referred to as WMANs) are becoming increasingly popular, including protocols such as 802.11, 802.16d/e, and related protocols, also known by names such as "WiFi", "WiMAX", mobile WiMAX, time division synchronous code division multiple access (TDS-CDMA), broadband wireless access, or "WiBro" systems. Many of these protocols (e.g., WiBro) are becoming increasingly popular in developing countries as low cost alternatives for providing network access in WMANs or cellular infrastructures.

While specifications for products using the above standard wireless protocols typically dictate certain data rates and coverage, these performance levels are often difficult to achieve. Insufficient performance between actual and regulatory performance levels may have many reasons, including attenuation of the radiation path of the RF signal, which for 802.16d/e is typically associated with 10MHz channels in the 2.3 to 2.4GHz licensed band, although 802.16 may support transmission frequencies up to 66 GHz. Systems that operate using Time Division Duplex (TDD) protocols, such as WiBro mentioned above, are of particular interest, in part because of their wide acceptance in the global market.

A number of problems arise because structures that require wireless network support, such as buildings, may have floor plans (florplan), including partition wall placements, etc., and may have constructions based on materials that can attenuate RF signals, all of which may prevent adequate coverage. In addition, the data rate of devices operating using the above standard wireless protocols is largely dependent on signal strength. As the distance in the coverage area increases, the wireless system performance typically decreases. Finally, the structure of the protocol itself may affect the operating range.

Repeaters are commonly used in the wireless industry to increase the range and in-building penetration of wireless systems. However, a number of problems and complications arise because the system receiver and transmitter in any given device may operate within the allocated time slots, for example, in a TDD system. In such systems, difficulties may arise when multiple transmitters are operating simultaneously (as would occur in repeater operation). Some TDD protocols provide defined receive and transmit periods, and thus are resistant to collisions.

In TDD systems, the receive and transmit channels are separated by time rather than frequency, and in addition, some TDD systems, such as 802.16(e) systems, use predetermined times for specific uplink/downlink transmissions. Other TDD protocols (e.g., 802.11) do not use the constructed predetermined time slot. Receivers and transmitters intended for full-duplex repeaters operating in TDD systems may be isolated by any number of means, including physical separation, antenna patterns, frequency translation, or polarization isolation. An example of isolation using frequency translation can be found in international patent application No. PCT/US03/28558 entitled WIRELESS LOCAL AREA NETWORK with repeaters for enhanced NETWORK COVERAGE (WIRELESS LOCAL AREA NETWORK WITH REPEATER for NETWORK COVERAGE), attorney docket number WF02-05/27-003-PCT, and based on U.S. provisional application No. 60/414,888. It should be noted, however, that to ensure robust operation, a non-frequency translating repeater must be able to quickly detect the presence of a signal for efficient operation and to cooperate with the mac and overall protocol associated with a TDD system in which the repeating is performed in order to efficiently repeat transmissions over time slots.

Also of interest is the synchronization of the repeater with the transmission under TDD protocol and gain control. If excessive gain control is utilized, the modulation may be cancelled, resulting in distortion or signal loss. FOR further information on AUTOMATIC gain control, see international patent application No. PCT/US03/29130 entitled WIRELESS LOCAL AREA NETWORK repeater with AUTOMATIC gain control FOR extended NETWORK COVERAGE (autonomous NETWORK repeater REPEATER WITH), attorney docket No. WF02-04/27-008-PCT, and based on U.S. provisional application No. 60/418,288. In addition, the specific gain control approach must not negatively impact the system level performance of the base station to subscriber link and must not negatively impact network performance when many subscribers are operating in the system at the same time.

As will be appreciated by those skilled in the art, TDD systems according to 802.16(e) have designated subcarriers for the uplink and designated subcarriers for the downlink on designated channels having a certain bandwidth and multiple traffic slots, each of which may be assigned to one or more subscriber stations on a subcarrier within a prescribed bandwidth. For each connection established within a TDD system, operating under the 802.16 standards and protocols uses a known frequency channel for all timeslots, as will be appreciated. WiBro is one such profile of 802.16(e), which is described in the appendix filed herewith.

Disclosure of Invention

Thus, in various exemplary and alternative exemplary embodiments, the present invention extends coverage area in a wireless environment, such as a WLAN environment, and broadly, in any time division duplex system (including IEEE 802.16, IEEE802.20, PHS, and TDS-CDMA), with dynamic frequency detection methods and relaying methods that may be performed in systems that use predetermined uplink and downlink time slots or unscheduled random access (such as used in 802.11 based systems). Additionally, the exemplary repeater may operate in synchronous TDD systems (e.g., 802.16 and PHS systems), where uplink and downlink repeating directions may be determined by observation periods or by reception of broadcast system information. An exemplary WLAN non-frequency translating repeater allows two or more unsynchronized WLAN nodes or nodes that would normally communicate on a predetermined basis to communicate according to a synchronization scheme. Unsynchronized WLAN nodes typically generate unscheduled transmissions, while other nodes (e.g., subscriber units and base units) are synchronized and communicate based on scheduled transmissions.

Such units may communicate in accordance with the invention by synchronizing to a control slot interval or any regular downlink interval, e.g., on a narrowband downlink control channel (as in a PHS system), and relay a wider bandwidth set of carrier frequencies to a wideband relayed downlink. In other systems (e.g., in 802.16 systems), the control slot detection bandwidth will be the same as the relayed bandwidth. On the uplink side, the repeater preferably monitors one or more time slots by performing wideband monitoring to see transmissions on the subscriber side, and when an uplink transmission is detected, may repeat the received signal on an uplink channel towards the base station apparatus. According to various exemplary embodiments, the repeater will preferably provide a direct repeating solution, wherein the received signals are transmitted on substantially the same time slot including any repeater delays.

Drawings

The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.

Fig. 1 is a diagram illustrating an exemplary non-frequency translating repeater in accordance with various exemplary embodiments.

Fig. 2 is a diagram illustrating an exemplary non-frequency translating repeater environment including a subscriber side and a base station side.

Fig. 3 is a schematic diagram illustrating exemplary detection and repeater circuitry associated with an exemplary non-frequency translating repeater.

Fig. 4 is a diagram illustrating Orthogonal Frequency Division Multiple Access (OFDMA) frames associated with various embodiments of an exemplary non-frequency translating repeater.

Fig. 5 is a flow diagram illustrating repeater synchronization with a TDD interval associated with various embodiments of an exemplary non-frequency translating repeater.

Fig. 6 is a diagram illustrating a synchronization scheme associated with various embodiments of an exemplary non-frequency translating repeater.

Fig. 7 is a diagram illustrating a power control scheme associated with various embodiments of an exemplary non-frequency translating repeater.

Fig. 8 is a circuit diagram illustrating an exemplary repeater configuration associated with various embodiments of a non-frequency translating repeater.

Fig. 9 is a circuit diagram illustrating an exemplary detector associated with various embodiments of an exemplary non-frequency translating repeater.

Detailed Description

Referring now to fig. 1, an exemplary non-frequency translating repeater 110 is shown. Repeater 110 may include a control terminal 111 connected to repeater 110 by a communication link, such as link 112, which may be an RS-232 connection or the like, for serial communication for various purposes, such as for configuring repeater 110, collecting various metrics, or the like. It will be appreciated that in a production model of the repeater 110, it would be unlikely that such a connection would be used, as the configuration would be done during manufacture, or the repeater 110 would be automatically configured under control of, for example, a microprocessor, controller, or the like. The repeater 110 system may also include an external antenna 120 for communicating with one side of the TDD repeater connection (e.g., base station 122) over a wireless interface 121. It will be appreciated that base station 122 may refer to any infrastructure node capable of serving multiple subscribers, such as WiBro protocol subset of 802.16(e), PHS Cell Station (CS), and so forth. The antenna 120 may be coupled to the repeater 110 by a connection 114, which connection 114 may be achieved using a direct coupling connection, such as by using a coaxial cable and SMA connector or other direct connections as will be appreciated by those skilled in the art.

Another antenna 130 may be used to communicate over a wireless interface 131 to the other side of the TDD repeater connection, such as subscriber terminal 132. Subscriber terminal 132 will be used herein to refer to a device configured to receive services from base station 122 (e.g., user entity, user equipment, terminal equipment), such as an 802.16(e) Subscriber Station (SS), a PHS Personal Station (PS), and so on. The antenna 130 may be coupled to the repeater 110 by a connection 115, which connection 115 may be achieved using a direct coupling connection, such as by using a coaxial cable and SMA connector (as mentioned above). The repeater 110 will be powered by a standard external DC power supply.

It will also be appreciated that in some embodiments, the antennas 120 and 130 may be directional antennas, and may also be integrated with repeater circuitry associated with the repeater 110 into a single package, such that one side of the package may be oriented in one direction (e.g., toward a base station) and the other side of the package or enclosure may be oriented in another direction (e.g., toward a subscriber or the like), such as when mounted in a window or exterior wall of a structure, for example. In addition, the antennas 120 and 130 may be directional or omnidirectional in their radiation pattern (radiation pattern). For Personal Internet (PI) repeaters, it is expected that one antenna will be installed outside a building and the other antenna will be located inside the building. PI repeaters may also be located inside the building. It will also be appreciated that many different form factors may be used to achieve proper placement and configuration. For example, transversely polarized antennas may be used, such as cross-polarized patch antennas, planar antennas, strip antennas, and the like, as will be appreciated by those skilled in the art. In addition, two such antennas may be used, one for input and one for output, or the like as will be appreciated. In a typical scenario, one of antennas 120 and 130 (in this example, antenna 120) may be defined as a "donor" antenna, i.e., an antenna coupled to base station 122.

According to some embodiments, repeater 110 may include unit 1110 a and unit 2110b, which may be connected by link 140 (e.g., a communication link, a data and control link, etc.). Unit 1110 a may be located to communicate with base station 122 and unit 2110b may be located to communicate with subscriber terminal 132. The units 1110 a and 2110b may communicate analog or digital information over the link 140, which link 140 may be a wireless link 141 or a wired link 142. The wired link may include coaxial cables, telephone lines, household power wiring circuits, fiber optic cables, and the like. The unit 1110 a and the unit 2110b may perform filtering (e.g., with matched filters) to ensure that no unwanted signals are passed on the core frequency being used for relaying. It will be appreciated that different frequencies may be used between the unit 1110 a and the unit 2110b in order to reduce the likelihood of interference. It will be appreciated that a protocol such as 802.11 may be used between the units, and in this case, signals communicated between the units over link 140 may be demodulated and passed between the units as 802.16 data in 802.11 packets, and re-encapsulated for relay purposes, such as for transmission to a base station or subscriber station. Alternatively, the 802.11 packet may contain digital samples, such as Nyquist samples of the relayed signal. Therefore, it is preferable to use an inter-unit synchronization protocol.

It will be appreciated that by dividing the exemplary repeater into multiple units, better isolation can be achieved. Alternatively, isolation may be achieved in a single unit repeater by antenna placement, use of directional antennas, and the like. In one or two-element embodiments, isolation of antennas operating at the same frequency is critical. Thus, to improve isolation, isolation measurements can be made, for example, by transmitting a known signal from one unit at a known time and measuring the known signal on another unit, or in the case of a single unit, transmitting the known signal from one antenna to another. It will be appreciated that the transmission of known signals may be cleared for transmission on the licensed band, or may be freely transmitted on the unlicensed band. The degree of isolation may be displayed, for example, using a series of LEDs or the like, or a single LED may be illuminated when the isolation is acceptable. In this manner, the installer can move or rearrange the units, or in the case of a single unit repeater, the donor and non-donor antennas, until the desired degree of isolation is achieved (as determined by observing the indicators).

For a better understanding of the operating environment of an exemplary repeater or repeater system according to various exemplary embodiments, please refer to fig. 2. A base station 222, for example, operated by a service provider of an 802.16, TDS-CDMA, PHS-based system, or similar system, may communicate with a subscriber terminal 232, which subscriber terminal 232 may be located, for example, inside a building. The directional antenna 220 may be located on the outer wall portion 202 of the wall 200, such as in a window, on an exterior surface, etc., and may be coupled to the non-frequency translating repeater 210 by a link 214. Packets transmitted between the subscriber terminal 232 and the base station 222 may be relayed in a manner to be described in more detail below.

It is important to note that in considering aspects of the physical structure of repeater 210, some basic assumptions about the system may be made. In this discussion, it is assumed that the repeater 210 operates in an environment consisting of a single base station and a single subscriber terminal 232, although it will be appreciated that in some embodiments multiple subscriber stations and/or base stations may be included. The frame duration, the receive/transmit transition gap (RTG/TTG) described in more detail below, and the percentage of time allocated to downlink subframes relative to the frame length are known in advance, and in some embodiments it is possible to adjust the variable frame duration. In a typical session, the expected frame duration is 5ms, and the expected RTG/TTG gap is from about 80 to 800 μ s in duration. A fixed split is expected between the uplink and downlink subframe portions of a frame and specifies a fixed frame duration. Notwithstanding such assumptions, repeater 210 will be required to autonomously synchronize with the start timing of the frame in a manner to be described below. In addition, the UL/DL subframe relationship may change from time to time, and the relay must adapt. In addition, such as in accordance with an exemplary 802.16-based embodiment, the service provider will know the operating channel or channels in the 2.3 to 2.4GHz transmission band (e.g., 8.75MHz, 10MHz, etc. operating channel) and can manually set the channel at repeater 210, for example, using a control terminal or the like. In case of WiBro, three synchronization channels can be simultaneously relayed, resulting in a total relaying bandwidth of 30 MHz.

It will be appreciated that repeater synchronization, as will be described in greater detail below, may be performed to ensure that the repeater operates in accordance with the timing requirements for the 802.16 protocol. The RSSI method as will be illustrated and described below may use power detection, correlation, statistical signal processing, etc.

In addition, according to an exemplary 802.16(e) based embodiment (e.g., a "WiBro" embodiment), it is possible that a typical base station 222 may support many frequency subcarriers (up to 1024) by Orthogonal Frequency Division Multiplexing (OFDM). The channels may be encoded and interleaved prior to transmission using, for example, an Inverse Fast Fourier Transform (IFFT). The subcarriers provide communication links between the base station 222 and a plurality of subscriber terminals 232. For each connection established within an 802.16 system, the uplink and downlink operate on dedicated uplink and downlink subcarriers occupying different time slots, as will be described in more detail in connection with, for example, fig. 6 and 7. It should also be noted that multiple subcarriers may operate simultaneously on different subcarriers within the same time slot. Furthermore, multiple Base Stations (BSs) may use the same technology to allow operation on the same time slot and channel but using different subcarriers.

As mentioned, the LED indicator will be able to visually inform when proper synchronization of the frame timing has been achieved, if desired. Additionally, a series of LED indicators (e.g., of different colors) may be provided to show relative signal strength in order to aid in placement of the antenna and/or repeater, as well as proper isolation at the donor and non-donor antennas. As mentioned above, an RS-232 connector may be provided to interface to a control terminal (e.g., a laptop computer) having repeater configuration software driven by a Graphical User Interface (GUI). The configuration software will be able to configure, for example, the operating channel, the frame duration, and may graphically observe key parameters of the repeater in operation. Once such parameters are determined, or once a scheme is determined for applying certain values under certain conditions, such operational control may be delegated to a microprocessor or the like having an operating program. The microprocessor/controller with associated software and/or firmware can then be used for parameter control in production repeaters, which can be reconfigured in manufacturing with the network information mentioned above.

According to various embodiments, a TDD format (e.g., as specified in the IEEE 802.16d/e Orthogonal Frequency Division Multiple Access (OFDMA) (TTA-PI korea) standard) should facilitate the development of exemplary non-frequency translating repeaters for commercial use in the global marketplace. Since the uplink and downlink frames will be synchronized between the various base stations of a given system, there is less chance that base station transmissions will occur at the same time as subscriber terminal transmissions. The use of synchronous and sophisticated BS-to-SS power control techniques serves to mitigate a variety of problems, such as near-near effects (near-far effects) and the fact that a typical base station 222 may transmit at an Effective Isotropic Radiated Power (EIRP) level significantly higher than that of a subscriber terminal 232.

To implement TDD relaying, the only modification to the radio signal by the repeater 210, in addition to the required signal amplification, is to add a propagation delay of about 1 mus. Since the additional delay of 1 mus is constant, symbol synchronization at the subscriber terminal 232 or the base station 222 is not an issue. The subscriber terminal 232 may receive signals from the base station 222 and the repeater 210 with little impact. Given the cyclic prefix time (CP) for the exemplary 802.16 configuration, the additional delay is relatively insignificant, and the OFDM subcarriers should remain orthogonal when the direct and repeated signals are received.

According to some protocols (e.g., 802.16), subscriber terminal 232 may periodically receive an OFDMA power control information element containing 8-bit quantized signed values, which indicate changes in power levels in 0.25dB increments, as will be appreciated. Due to the possibility of power control associated with the subscriber terminal 232, it is desirable to maintain the automatic gain control setting of the repeater 210 at a constant level between the UL and DL as much as possible. Any gain provided to the "input" antenna of the repeater 210 needs to be passed to the power amplifier in a consistent manner. In the case of 802.16(e) WiBro, it is preferable to use a specific power control method as discussed and described herein.

It will be appreciated that with OFDMA, multiple users and base stations may receive or transmit simultaneously on different subcarriers. The number of subcarriers allocated to each user and the total number of subcarriers being used for user traffic is variable from frame to frame. Thus, some variation in the received power level at the antenna input of repeater 210 may occur because all of the subcarriers are not allocated during each frame. However, due to the averaging formed by the large number of active users, and the operation of the AGC loop, frequency domain multiplexing of users should not be a significant problem for the repeater 210 compared to the frame duration. The present invention further alleviates any problems by allowing the gain provided by the AGC on the DL to be applied to the UL to maintain a "reciprocal channel," allowing open and closed loop 802.16 power control to operate transparently.

According to 802.16(e) and WiBro, several types of power control are defined to implement closed loop and open loop UL power control. Some are mandatory and some are optional. Both open loop UL power control and closed loop UL power control rely on assuming that the path loss on DL is equal to the path loss on UL with some adjustment to compensate for the non-TDD mode of operation. For TDD mode of operation, the path loss reciprocity remains tighter than for FDD/TDD mode.

For power control in TDD mode of operation, the preferred approach is to try to maintain the overall reciprocal path loss over the entire downlink and the entire uplink, so that the reciprocity of path loss is maintained as closely as possible. In the case where the path loss is not maintained due to various practical limitations, the closed loop power control mechanism will make an offset adjustment to compensate for the required difference in UL/DL. It should be noted that the difference in path loss may be due to local interference on one link, requiring additional received power to overcome. The difference may also be due to limitations in the output power or sensitivity of the repeater.

Therefore, a preferred approach to power control is as follows. On the DL, the gain will be set during the header (preamble) and kept constant for the duration of the DL subframe. The gain will be set such that the target output power is achieved according to a typical AGC approach that sets a constant output power, except that the gain is "frozen" after the initial setting is completed. The gain applied to the DL subframe is stored and retrieved for use on the UL. In addition to the above procedure, the repeater output target power set during the DL gain setting operation may be adjusted by some offset to affect the manner in which the SS gain procedure will operate, and thus to some extent, the transmission power level.

For UL gain control, the gain applied to DL transmissions is retrieved (as mentioned, the gain has been stored) and applied in conjunction with the UL, regardless of received power or transmission power, unless a particular limit is exceeded. For UL output power management, if the signal received from the SS is so strong that the gain must be reduced by some amount DELTA after the DL gain is applied in conjunction with the UL repeater mode, then the value DELTA should be included as an offset from the DL output power set point. The offset will be reflected in the DL AGC function as an increase in output power, which will affect power control in the SS to reduce TX power during UL operation, as typically occurs in the open loop and closed loop power control methods specified in 802.16 (e).

For UL receive power management, in contrast to the example above, if the repeater is receiving a low signal level from the SS, the offset to the DL AGC can be subtracted from the DL output power set point as-DELTA, causing it to decrease, such that the open loop power control will act to increase the output power from the SS, resulting in a stronger signal being received from the SS at the repeater during UL operation.

In conjunction with applying a DELTA or OFFSET TO the DL output power, the OFFSET TO the downlink power control may be referred TO as UL _ OFFSET _ TO _ DL _ TXPOWER _ SP. It should be noted that power control in conjunction with 802.16(e) is described in section 8.4.10.3.1 (closed loop power control) and section 8.4.10.3.2 (open loop power control) of section 16 "air interface for fixed broadband wireless access system" of IEEE standard 802.16-2004.

As will be appreciated by those skilled in the art, the repeater 210 may apply a fixed gain to the inbound and outbound signals and may operate on the same frequency on both the uplink and downlink time periods in duplex mode. To provide uplink power control, the uplink is set according to the measured power level on the downlink. This configuration is important to reduce gain adjustments caused by, for example, the base station's reaction to sensed downlink path loss that would result from system differences in gain levels due to factors such as placement of repeater units. If the repeater unit communicating with the subscriber is placed such that a strong signal is received from the subscriber, the repeater unit may report that a lower signal level is required, while the repeater communicating with the base station may have a different repeating environment where reducing the transmission power would be undesirable. Thus, by matching the uplink power level to the downlink power level, the perceived path loss can be minimized, thereby reducing the chance of power amplifier saturation due to power control settings being out of range. According to a preferred embodiment, on the downlink, the detection of the power level may be determined during an initial portion (e.g., header) of the downlink packet and then "frozen" for the remainder of the transmission of the downlink packet. The power level of the subscriber terminal 232 may be set to the same power level on the uplink, thus minimizing perceived path loss and establishing path reciprocity. In other words, the downlink gain is manipulated such that the transmission power level on the uplink and the resulting received power level at the repeater unit serving the subscriber are controlled. Thus, automatic gain control is used on the downlink to set the output power from the repeater, and the gain setting is applied to the uplink independently of the repeater uplink output power within limits.

It should be noted that if a portion of the output signal externally or internally arrives at the input with sufficient gain, an input-to-output oscillation condition (similar to that which may occur in some types of CDMA repeaters) may occur, significantly degrading system performance. The amount of internal and external isolation correspondingly limits the amount of amplification that the repeater 210 can provide. Thus, providing 75dB of gain requires that the antenna-to-antenna isolation of the repeater 210 and the antenna-to-antenna isolation of a particular installation be 10dB or 85dB higher than the maximum applied gain. To achieve the required internal isolation, careful attention to leakage and EMI related issues must be considered in circuit design, especially in input signal and feedback path design. To achieve the required external isolation, it is assumed that (at least) a directional antenna will be used for the link 221 to the base station 222, for example. It can also be assumed that the antenna 220 serving the link 221 to the base station 222 will be on the outer wall 202 of the wall 200 with the field connection line as close as possible to the base station 222. Assume that link 231 from repeater 210 to subscriber terminal 232 uses an omni-directional antenna, which would typically be installed inside a building or structure. If signal oscillations continue to occur, repeater 210 may detect the signal oscillations and reduce the amount of gain to link 231 until better antenna-to-antenna isolation is achieved, either by further separating antennas or by optimizing the orientation or placement there.

For proper TDD operation, such as in the exemplary PHS and exemplary 802.16 embodiments, repeater 210 needs to determine whether to amplify signals in the uplink or downlink direction by determining the start and end timing of uplink and downlink subframes associated with the relevant TDD protocol. For example, on a downlink subframe, a signal arriving at a directional antenna 220 (also referred to as a donor port) facing a base station 222 needs to be amplified and output at a directional antenna 230. On an uplink subframe, signals arriving at directional antenna 230 from subscriber terminal 232 need to be amplified in the opposite direction and output at directional antenna 220 to base station 222.

It should be noted that according to 802.11 TDD relaying, the presence of a packet on one of the two antennas is detected and the amplification direction is dynamically changed. Other techniques for TDD amplification (e.g., TDD remote amplifiers) may clip the beginning of the packet because the amplifier is disabled before the presence of the waveform is detected. If the headers of the waveforms are not clipped, then the 802.11 TDD repeaters may be cascaded in series to obtain deeper in-building penetrations. While cascading and associated detection techniques work well for 802.11 systems, some form of uplink/downlink synchronization must be used, where multiple subscribers can transmit. Multiple subscribers may confuse repeater 210 if no more system information is used.

According to various exemplary embodiments, several methods may be used to determine TDD framing. Thus, the repeater 210 may use a number of strategies to accurately determine the direction in which signal amplification should occur. The techniques described herein are not affected by timing differences due to factors such as propagation distance from the repeater 210 and unwanted signals arriving from neighboring cell sites that may arrive after the end of the sub-frame in which the signal is transmitted.

The method for determining the direction of amplification may involve a combination of metrics, such as gating and latching the repeater 210 using the first signal arrival. It should be noted that since, through normal system operation according to various protocols, the base station 222 will decide whether to advance or delay transmissions from different subscribers so that packet transmissions arrive at the same time, the repeater 210 may be configured to latch on the first arriving signal and ignore any other channel detections for that packet.

It will be appreciated that a statistical analysis of the received power level as a function of time may also be used to determine the direction of amplification. It is expected that the received power into the directional antenna 220 facing the base station 222 will have distinct characteristics during the downlink sub-frame. Known transmission characteristics associated with signals from the base station 219 may further be used for or to assist synchronization.

Additional features associated with timing may include defined gaps and control channel slots that appear consistently on the downlink on a periodic basis, such as FCH, DL-MAP, and UL-MAP data. Thus, consistency and periodicity can be used along with known system information such as uplink and downlink slot parameters to identify and synchronize with the timing of the base station.

Feature detection (as described above) may include detailed statistical analysis of the signal from the base station 222 to identify known features and timing characteristics of the signal. Thus, the repeater 210 may use three exemplary steps to determine the direction of amplification of the wireless signal. First, the locations of the transmission transition gap and the reception transition gap (TTG/RTG) may be determined, in part, by monitoring the directional antenna 220 during initialization (as will be described below). Second, the start timing and duration of a downlink subframe within a 5ms IEEE 802.16 frame may be determined. Finally, the transmission and reception timing between the uplink and downlink subframes may be adjusted at a rate of once per frame.

In some 802.16(e) systems, modem-based synchronization is used to explicitly receive signaling information about the timing of uplink and downlink subframes and apply this information for synchronization. However, such systems are expensive and complex. The present system greatly reduces cost and complexity by eliminating the need for expensive modems by providing synchronization through the use of power detectors, correlators, and the like.

According to one exemplary embodiment, the repeater 210 looks and functions in a manner similar to a cdma2000 RF-based repeater, but with certain differences (as will be described and as will be appreciated by those skilled in the art). A typical repeater system as described above consists of an outdoor directional antenna with a gain of perhaps 10dBi, with several feet of coaxial cable connected to an indoor repeater module. The repeater module will be powered by an external DC power supply. The repeater will also be connected to an indoor omnidirectional antenna with a gain of perhaps 5dBi, which amplifies the signals destined for the various rooms of the subscriber's house, work area, etc. The indoor antenna may also be directional, as long as proper antenna-to-antenna isolation is achieved.

It will be appreciated that technical support personnel may be necessary to mount the directional antenna 220 to the exterior wall portion 202 of the wall 200 of the building and route the cable to the interior of the building. However, the arrangement of the indoor repeater will not require any special configuration, and it is possible for a residential customer to determine the direction of the indoor antenna according to a particular preference without assistance. It should also be noted that the personal repeater may contain one or more LEDs to indicate RSSI levels, antenna isolation, synchronization, etc., in order to aid in the placement of the repeater 210, the orientation and placement of the directional antennas 220 and 230, and to indicate when the repeater 210 has properly synchronized to the timing of the TDD uplink and downlink subframes.

Alternatively, as shown, repeater 210 may include two units, such as repeater unit 210a and repeater unit 210 b. The units may be coupled using a link 240, and the link 240 may be a wireless link 241 or a wired link 242 as described above in connection with fig. 1.

According to other exemplary embodiments, the purpose of the non-frequency translating repeater service is to provide high capacity internet service in service areas that were previously difficult to access, such as subway service or in-building service. For example, an in-building repeater may be configured as a small indoor unit having, for example, one antenna for outdoor or near outdoor placement and another antenna for indoor placement, as described above. Other repeater models would be more suitable for self-installation.

It IS envisioned that the exemplary repeater will have specifications similar to existing repeaters, such as for IS-2000 systems. Repeaters may take various forms including, for example, indoor repeaters of the same frequency, outdoor infrastructure repeaters, which are high power repeaters used to fill in poor or problematic coverage areas in outdoor installations (e.g., in alleys) or to selectively extend coverage outside the current coverage area. Outdoor infrastructure repeaters may be deployed on top of buildings, cell towers, etc. In addition, exemplary repeaters may include indoor distribution systems where a repeater must span a significant distance from an antenna coupled to a base station for use in subways and parking garages. Further, exemplary repeaters may include fiber optic repeater systems having relatively short fiber distances to achieve "deep" in-building coverage. However, long fiber distances may cause system-level problems, where the operation of the repeater system described herein depends on factors such as latency.

A block diagram of an exemplary repeater 300 is shown in fig. 3. Antenna 301 and antenna 302 are coupled to transmit/receive (T/R) switches 303 and 304, respectively. Initially, each of T/R switch 303 and T/R switch 304 is arranged to feed a signal from each of antenna 301 and antenna 302 into a corresponding Low Noise Amplifier (LNA)305 and LNA 306. The amplified signal is then down-converted using mixers 307 and 308 and may be further passed into corresponding signal detectors, such as detector 309 for antenna 201 and detector 311 for antenna 302. The first antenna for detecting a signal is set as an input antenna by configuring one of the T/R switch 303 or the T/R switch 304, and the other antenna is set as an output antenna by configuring the other of the T/R switch 303 or the T/R switch 304. It should be noted that in typical applications, such as 802.16 applications, the detection process takes about 500ns and the delay in setting the transmit switch is about 200 ns. Transmit switch 315 passes the signal from the input antenna delayed by the amount of delay added in one of delay element 310 or delay element 312 into power amplifier 316, which power amplifier 316 feeds the amplified signal into one of antenna 301 or antenna 302, which is designated as the output antenna as described above, by operation of the other transmit switch 317. It will be appreciated that the amount of delay should not exceed or even approach the timeout value associated with the protocol. Additionally, if the TDD protocol requires synchronization (as in the case of 802.16 (e)), there may be no need to compensate for detection delays. The microcontroller 313 and combinational logic circuit 314 can be used to increase the reliability of the detection process and perform additional procedures such as system maintenance, control, etc., as will be appreciated by those skilled in the art, and execute some software to enhance, augment, or control the operation of the repeater 300. It will also be appreciated that in some embodiments, at least one of the connections between antennas 301 and 302 may be coupled to an exemplary repeater module using fiber optic cables.

It should further be noted that the detector 311 may be used by itself to enable relaying, or may be used in conjunction with synchronized uplink or downlink frame timing. Alternatively, the detector 311 may be used only to maintain uplink and downlink synchronization. For example, once synchronized, the detector 311 on a given antenna will cause a relay from that antenna to another antenna. However, if detector 311 detects a signal in a time slot that is not defined as an active repeater time slot for a given antenna, detector 311 will not repeat the information.

NMS (as mentioned above) for the repeater 300 may be implemented in some cases, for example, in conjunction with in-building distributed repeaters and infrastructure repeaters. However, due to the additional cost of the modem, microprocessor and memory, it is not expected that an NMS option will exist for typical personal use repeaters. The NMS may include remote gain adjustment, remote firmware upgrade, and may be developed in coordination with vendors from Customer Premise Equipment (CPE) vendors.

Referring again to fig. 3, it should be noted that according to an exemplary embodiment, repeater 300 may delay the input radio frequency signal, if desired, by an amount equal to the time it takes to determine the direction in which signal amplification needs to occur, for example, as described above. All transmit and receive switches (e.g., T/R switches 302, 303 and TX switches 315, 317) are set to the correct direction just before the delayed input signal arrives in the PA 316, and thus never clip any portion of the signal. The amplification direction will be known based on the defined slots and the synchronized framing. Thus, the above techniques may be used in combination to achieve relaying. For example, there must be synchronization and detection on a particular antenna port to enable relaying. In other words, relaying will only be achieved when a signal should be present (e.g. during an active uplink or downlink time slot according to the synchronization) is detected on a given antenna port.

Active RF repeaters are advantageous over store-and-forward repeaters because of improved delay, improved throughput, and reduced complexity. Furthermore, RF-based repeaters are used to maintain the integrity of the data security scheme since no encryption keys are required, resulting in reduced complexity and management. The delay of an RF repeater is below 1 microsecond and may be several hundred nanoseconds, while the delay of a store-and-forward repeater is greater than the frame time, which is 5ms for IEEE 802.16. A delay increase of this magnitude is intolerable for many delay sensitive applications. It will be appreciated that a bottleneck in the bit rate of the store-and-forward repeater occurs, as the achieved bit rate is limited by the bit rate of the slowest point-to-point link. Since it is not always possible to place the repeater exactly halfway between the subscriber and the base station, improvements in throughput and range can be quite limited. Also, as table 1 indicates, the improvement in bit rate is greatest for smaller block sizes and is reduced for larger block sizes. Because each packet needs to be sent twice, store and forward repeaters may reduce cell throughput in the case of R3/416-QAM and 64QAM modulation. Finally, store and forward repeaters are inherently complex because additional processing must occur in order to recover and retransmit the packet, thereby increasing repeater price and increasing its power consumption. Practical limitations in the protocol related to security, quality of service (QoS) and installation costs, and network management may prevent widespread adoption of store and forward repeaters.

As mentioned below, table 1 shows receiver SNR and uncoded block size for the IEEE 802.16 Signal Constellation (IEEE 802.16 Signal Constellation), as well as block size improvement rate with 9dB SNR improvement.

Modulation	Encoding rate	Receiver SNR (dB)	Uncoded block size	Block size improvement ratio
					QPSK	1/2	9.4	24	3
QPSK	3/4	11.2	36	2
					16-QAM	1/2	16.4	48	2.25
16-QAM	3/4	18.2	72	1.5
					64-QAM	2/3	22.7	96	1.125
64-QAM	3/4	24.4	108	0

It should be noted that if multiple simultaneous transmissions occur in different OFDM subchannels, as permitted by, for example, IEEE 802.16OFDMA, IEEE 802.16O FDMA permits multiplexing to occur in both the time and frequency domains, the transmissions to the various users may occupy different subcarriers simultaneously. Since the exemplary repeater will synchronize to the beginning of the uplink and downlink subframes regardless of how many users are transmitting in these subframes, the repeater will be able to amplify the multiple simultaneous transmissions without any problem. However, different numbers of occupied subcarriers can cause fluctuations in AGC input power, but the gain control algorithm should provide sufficient accuracy margin.

To better understand the structure of a typical frame scenario 400 according to 802.16(e), please refer to fig. 4, wherein the structure of logical subchannels is depicted with respect to time and corresponding OFDMA symbol numbers 401. Within the Downlink (DL) frame structure 410 and the Uplink (UL) frame structure 420, various frame components are shown, including a header and DL map portion in the DL frame structure 410 and various UL burst portions in the UL frame structure 420, as will be appreciated. The UL frame structure 420 and the DL frame structure 410 are separated in time by a Transmission Transition Gap (TTG)402, while the end of the frame and the beginning of the next frame portion 430 are separated by a Reception Transition Gap (RTG)403, the placement of which is also shown in fig. 4. It should be noted that the DL frame structure 410 is composed of a header portion, a DL map, a UL map, and several data regions that can be considered as two-dimensional resource allocation. The first resource dimension is a group of consecutive logical subchannels and the second resource dimension is a group of consecutive OFDMA symbols 401. The DL frame structure 410 is divided into a plurality of data regions or "bursts". Each burst is mapped in time with a first slot occupied, for example, by the lowest numbered subchannel using the lowest numbered OFDMA symbol. Subsequent slots may be mapped according to increasing OFDMA symbol indices. The edge of the burst indicates continuation of the mapping in the next subchannel and return to the lower OFDMA symbol index. In a typical OFDMA frame, there may be 128 subchannels.

The UL frame structure 420 includes a burst region occupying the entire UL subframe. Within a UL burst, slots may be numbered starting from the lowest subchannel corresponding to the use of the first OFDMA symbol. Subsequent slots are mapped according to the increased OFDMA symbol index. When the burst edge is reached, the mapping may be incremented to the next subchannel, returning to using the lowest numbered OFDMA symbol for the UL "zone". The UL burst consists of consecutive time slots. The UL frame structure can be considered one-dimensional because a single parameter (e.g., burst duration) is required to describe the UL allocation, significantly reducing the UL mapping size.

It will be appreciated that the above-mentioned configuration may impose buffering requirements, as UL and DL bursts may span the entire duration of a subframe. For example, a UL burst spans the entire UL frame, while a DL burst may span the entire DL frame. In both DL frame structure 410 and DL frame structure 420, the burst may span the entire bandwidth, or in other words, the entire number of subchannels. The maximum buffer size should therefore be equal to the entire sub-frame.

To better understand the operation of an exemplary TDD repeater in accordance with various embodiments, a flow diagram of an exemplary procedure 500 is presented in fig. 5. The program 500 includes, for example, synchronized operations in accordance with the present invention. After starting at 501, a configuration can be read from a memory, such as a non-volatile memory, at 502. The configuration may include the duration of the Transmission Transition Gap (TTG) and the Reception Transition Gap (RTG), the frame duration, and any other network parameters for operation. Once repeater operation begins, at 503, the signal on the donor antenna may be observed and the set of statistical frequencies may be populated with values associated with the detected signal, such as Received Signal Strength Indicator (RSSI) level, correlation level, power level, and the like. The signal may be observed, for example, during an observation period that may be established to have a duration of from one to a few frames or many frames, depending on factors such as reliability desired. An observation period of duration, for example, around 30 seconds, may yield acceptable results in many situations. As will be appreciated, the accumulated values in the set of frequencies may be processed according to a single-pole Infinite Impulse Response (IIR) filtering process using a processor or controller, such as a high performance processor, signal processor, or the like. It should be noted that the particular set of frequencies to be padded will be incremented for each power measurement. The number of frequency groups will correspond to the duration of an 802.16 frame and the frequency groups are updated cyclically. The values input to a particular set of frequencies will occur at the frame rate and use a weighted average, IIR filtering, or other common techniques known to those skilled in the art.

If, for example, it is determined at 504 that the observation period is complete, a power envelope sliding correlation or windowing function may be performed on the frequency bin content at 505 to determine where the timing window exists based on statistical analysis. If the observation period is not complete, the frequency groups will continue to be populated during the observation period. The contents of the uplink and downlink frame windows may be certified at 506, and if it is determined that the contents are properly certified and aligned, the downlink transmission window timing may be established at 507 based on known parameters such as frame rate. It will be appreciated that the procedure of steps 503-505 may be repeated during operation at 508 in a tracking period, rather than an observation period, to maintain synchronization and alignment. Although the procedure is indicated as ending at 509, it will be appreciated that the procedure may be invoked whenever repeater startup is performed, may be performed periodically, or may only be performed whenever recalibration or adjustment in synchronization is required. As will be appreciated, such selections for the repetitive synchronization procedure and other operations and parameters may be implemented, for example, in a software or firmware configuration, or may be partially or fully implemented in an integrated hardware device, such as an integrated circuit chip.

An exemplary synchronization scenario 600 according to various embodiments may be better understood with reference to fig. 6. Where the Received Signal Strength Intensity (RSSI) over the donor antenna 601 and the non-donor antenna 602 are shown in graphs 603 and 604, respectively, versus time. It should be noted that, for example, the durations of the TTG and RTG and possibly other timing relationships are not shown to scale for illustrative purposes. It will be appreciated that information obtained from the various steps and procedures described, for example, in connection with fig. 5 above, may be used to modify the detection threshold in the uplink/downlink transmission selection process of an exemplary repeater, which equates to an a priori detection algorithm that dynamically modifies the uplink and downlink detection thresholds based on the known synchronization of the uplink and downlink timeslots. There is no air activity on the uplink or downlink during the TTG and RTG, which are typically specified to be at least 87.2 μ s and 744 μ s in duration, respectively. Simple RSSI detection or a windowing function associated with, for example, RSSI, can be used to identify the location of these gaps.

In the drawings, a typical frame is shown, such as the frame shown and described in connection with fig. 4. During a Downlink (DL) interval, such as DL interval 610, DL transmission windows, such as DL windows 612 and 613, may be established, and during an Uplink (UL) interval 620, UL transmission windows, such as UL windows 624 and 625, are shown to provide synchronization for the reception and transmission of information in accordance with the timing requirements of the 802.16(e) protocol. It is important to note that the timing window must be tracked to ensure that alignment and synchronization are maintained during repeater operation. As previously mentioned in connection with fig. 5, the detection values may be placed in the frequency groups represented by the dotted column regions in the UL intervals 610 and 630 and the DL intervals 620 and 640. Each column or group of frequencies represents a signal sample at an appropriate fraction of the required resolution. In this example, a 10 to 20 musec sampling interval should be sufficient to accurately determine the timing of the signal edges during the DL, UL, RTG, and TTG intervals of graphs 603 and 604, which are represented in the figure as regions B612, E624, a 633, and D632 for the donor antenna 601, and regions C613, F625, a 633, and D632 for the non-donor antenna 602. As discussed and described above, the set of frequencies is updated in a cyclic manner with a period equal to the frame duration, e.g., during an observation period, etc.

As will be appreciated, UL/DL timing may be tracked, that is, the value may be determined by performing one or more of the following: a preamble correlator, a matched filter or a simple RSSI value is used. In addition, known TTG timing, frame timing, RTG timing may be used as parameters in the process of evaluating the contents of the frequency group or the like. An average, histogram, threshold or other statistical approach may be used to determine or improve the "slot" or symbol occupancy for a fraction of the frame timing and (most likely) a fraction of the symbol or slot timing.

According to further embodiments, the rising edge of the DL TX subframe content 611 may be tracked (shown at zone B612 in graph 603) and always occupied by the header, FCH, DL _ MAP message and data content. The falling edge of the DL TX subframe content 611 may also be tracked, although it is not guaranteed to be always occupied by content and tends to merge with transmission gaps. The rising edge of the UL subframe may be tracked with the corresponding frequency group filled with user data 621, user data 622, or user data 623 (in other words, any subscriber data transmitted on either the donor antenna 601 or non-donor antenna 602). It will also be appreciated that other activity on the donor antenna 601 and non-donor antenna 602 is shown, for example, as user data 631, 632, 641, 642, and 643.

In other embodiments, or to augment existing embodiments, the RTG gap 633 and/or TTG gap 632 may be observed between successive transmissions on the donor antenna 601 or the donor antenna 601 and the non-donor antenna 602. It should be noted that if there are no subscribers inside the structure in which the repeater configuration is located, any outdoor subscriber transmissions can be observed on the donor antenna and the TTG or RTG gaps observed and used for synchronization.

Additionally, the average RSSI over several frequency sets during each of zones B612, C613, E624, F625, and a 633 and D632 may be integrated and compared to the detection threshold shown as a dashed line in fig. 6. Multiple metrics from multiple integrations may be used to generate final timing and detection decisions and may include TTG, RTG, preamble correlation, integrated DL subframe power, and the like. Consider the example of DL timing where the average set of frequencies for the DL subframe duration is integrated. The value of the 10 x integral RTG gap may then be subtracted, and the timing of the resulting "envelope matched filter" may be slid by 1 frequency bin, generating a metric for each time alignment with an incremental frequency bin offset. The time alignment with the maximum value may be selected as the correct timing alignment and the UL/DL TX enable window may be adjusted accordingly.

Alternatively, the timing may be based on header/symbol correlation, with RSSI used to determine the UL/DL subframe ratio in a manner similar to that described above. As an alternative to averaging the RSSI or correlation values in each frequency bin, a non-linear or linear weighted combination of the values may be used to generate each frequency bin value for use in the envelope matched filter analysis technique. A simple example of an envelope matched filter may be expressed as the output (frequency bin) — 100 × P (rtg) + P (DL-donor) -100 × P (ttg) -P (DL-non-donor), where the function P (x) is the integration of the power over many pre-processed time-frequency bins and may include correlation power, RSSI power, etc. In addition, the pre-processing may include simple averaging, IIR or FIR filter structures, or non-linear processing of individual measurements in the respective frequency groups that are higher than subsequent measurements and updated at the frame rate. As mentioned, when the output is plotted as a function of the set of frequencies, the "match" in the correlation filter described above will include a peak to indicate the best alignment. The alignment associated with the peaks will provide a relative adjustment to the timing such that the desired frequency bins are aligned and the DL/UL TX-enable window is aligned with the correct frequency bin and UL/DL subframe timing. It should be noted that the foregoing example assumes that the frame time, UL/DL subframe duration, RTG and TTG are all known.

Therefore, by using the above-described program and circuit, relay in various protocol environments requiring non-regenerative physical layer (PHY) TDD type relay can be accomplished. As illustrated in fig. 7, a relay scenario 700 is illustrated in which a certified relay is used that utilizes a synchronized relay direction enable window and AGC control.

With the various examples shown in the figures, AGC control according to the present invention may be better understood, particularly in view of the description provided in connection with fig. 6. Consider a downlink interval, such as DL 750 from a Base Station (BS) to a Subscriber Station (SS) using an exemplary repeater. At a 1701, a signal received at a donor antenna of a repeater exceeds a threshold, such as a repeater detection threshold shown as a horizontal dashed line in the figure. The baseband signal 710 at B704 may be generated in the repeater. At a 2702, donor antenna signal detection logic may be activated with a logic value indicating detection. At a 3703, transmission is enabled on the non-donor transmitter of the repeater. If (donor signal detection is true) and (DL TX window is true), then the transmitter is enabled, meaning that the downlink transmission window is established and synchronized and is currently active on DL so that an end-to-end relay link 711 can be established. Once the transmitter is enabled according to the above, the transmit power of the DL may be determined based on the AGC procedure. Thus, a power set point may be output and a value of the downlink gain DL _ gain may be stored. The power set point is shown in the figure as the horizontal dashed line repeater DL AGC output power set point.

In order to process the end of transmission on the DL from the BS to the SS via the relay, the following procedure may be used for explanation. At C1705, it is determined that the signal received at the donor antenna is below a threshold. The end of the baseband signal 710 is reached. At C2706, the donor antenna signal detection logic exits operation. At C3707, the transmitter is deactivated on the non-donor antenna according to the logic mentioned above.

Now consider the UL from SS to BS using an exemplary repeater after TTG 751 at, for example, 87.2 musec. At D1721, the signal at the non-donor antenna of the repeater receiver exceeds the detection threshold and generates baseband signal 724. At D2722, non-donor antenna signal detection logic is activated with a logic value indicating detection. At D3723, the transmitter is enabled on the donor antenna according to the following logic. If (non-donor signal detection true) and (UL TX window true), then the transmitter is enabled. Thus, an end-to-end relay link 725 is established.

Finally, to determine the transmission gain on the UL, the stored DL _ gain from the last DL frame arriving on the uplink is applied. The power on the uplink may be calculated from pout (ul) ═ rssi (ul) + DL _ gain. The gain is applied to achieve min (Pout, Pout max). If the value of Pout is greater than the maximum value of Pout, then the gain reduction value required to reduce the power is calculated, gain _ reduction. The DL output power set point is then decreased by the value gain _ decrease. If UL detection has not occurred, then the DL output power set point can be incrementally increased, but cannot exceed DL _ Pout _ Max. In this way, the UL transmission gain can be maintained within a desired range by manipulating the DL output power set point. A similar procedure may be followed for the relay of baseband signal 730 on DL 754 after RTG 753 of 744 musec, for example, and baseband signal 740 on UL 756 after TTG 755, which may be 87.2 musec, for example, as described above in connection with TTG 751.

A circuit diagram of an exemplary repeater configuration 800 is shown in fig. 8. With further reference to the configuration shown in fig. 3, for example, a Variable Gain Amplifier (VGA) controller and state machine (hereinafter "VGA 820") and detectors 855 and 856 are shown for carrying out the various procedures as described herein. Signals may be received and transmitted using antennas 801 and 802, which, as will be appreciated, may be oriented toward various donor and non-donor portions of the relay environment. Each of the antennas 801 and 802 may be equipped with a Band Pass Filter (BPF)803 and 804, and antenna switches 811 and 812 for placing the antennas in a transmit or receive mode. As will be appreciated, antenna switch 810 may direct a transmit signal to one or the other of antenna switches 811 or 812. During receive evolution on antenna 801, after an incoming signal passes through BPF 803 and switch 811, it will be amplified with Low Noise Amplifier (LNA)805 and downconverted in mixer 807, which mixer 807 mixes the received signal with local oscillator frequency LO 1809. The resulting Intermediate Frequency (IF) signal may be passed to splitter 851 where the signal instances may be passed to delay unit 853 and detector 855. For receive evolution on antenna 802, after an incoming signal passes through BPF 804 and switch 812, it will be amplified with Low Noise Amplifier (LNA)806 and downconverted in mixer 808, which mixer 808 mixes the received signal with local oscillator frequency LO 1809. The resulting Intermediate Frequency (IF) signal may be passed to a splitter 852, where the signal instances may be passed to a delay unit 854 and a detector 856.

When a signal is detected in either of detectors 855 and 856, the samples 857 may be passed to processor 850 for, e.g., statistical processing, etc., as described above. Detectors 855 and 856 can also provide RSSI measurements 858, which can be passed to VGA 820 for gain control and transmit power adjustment, also as described. Processor 850 may be configured to control VGA 820 through control line 827, which control line 827 may be a line, port, bus, etc., as will be appreciated. Processor 850 and VGA 820 may be configured to access control registers, which are substantially located in processor 850. The VGA 820 may access control registers through a line 828, which line 828 may be a line, port, bus, etc., as will be appreciated. In an exemplary scenario, a signal received on yet another antenna may be transmitted on the other antenna after a delay period, e.g., generated by delay units 853 and 854. Depending on the receive and retransmit directions, signals may be directed through the operation of TX select switch 823, switch 822, and VGA 824, which may be controlled by VGA 820 through control lines, as will be appreciated. The output of VGA 824 may be passed to mixer 825 for mixing with LO 1809 for upconversion. The output of mixer 825 is directed to power amplifier 826. The transmission signal will be directed to the opposite side of reception by switch 810. For example, if a signal is received on antenna 802, switch 810 will direct the relayed signal through switch 811 to antenna 801.

It should be noted that VGA 820 can be configured with control registers through line 828, which registers contain, for example, a DL power set point, a UL MAX power output level, a UL MIN power output level, and the like. VGA 820 may be used to perform AGC functions as described herein. For example, DL gain values may be stored in VGA 820 for application to UL subframes (as described herein) in order to enable power control during transmission. The UL power setpoint may be limited so as not to exceed UL MAX power output. VGA 820 can further manage the UL/DL transmit enable window by delaying or advancing the sliding window based on processor input and input from the frequency bin analysis as described above. VGA 820 can also perform logical operations on the remaining portions of the repeater and other controls (e.g., configuration of transmit switches, etc.), such as transmit combining control described above, through operation of, for example, a state machine, etc., based further on the UL/DL transmit enable window and detected power (e.g., correlated power or RSSI power).

The processor 850 may be configured to perform UL/DL timing management, filtering functions, and any other calculations, as described herein. Processor 850 may further manage the operation of VGA 820 state machine by control signals coupled to VGA 820 state machine. The processor 850 may further set configuration parameters and perform any other functions that require processor capabilities. It will be appreciated that most or all of the processor functionality may be implemented by executing program instructions carried on a computer readable medium such as a memory device, ROM, disk or other medium including a connection medium such as a wired or wireless network connection. Alternatively, the instructions may be integrated into a processor in the form of an Application Specific Integrated Circuit (ASIC) or the like.

To perform functions such as synchronization as described above, an exemplary detector, such as the detector shown in fig. 8, is required. One such embodiment of an exemplary detector is shown in fig. 9. The detector may be configured as shown, such as a detector amplifier 910 for generating RSSI values 903 based on detector inputs 901, which detector inputs 901 may be input signals such as Radio Frequency (RF) signals, e.g., IF signals from a receive antenna as described above with reference to fig. 8, etc. The output of the detector amplifier 910 may be passed to a correlator 911, which correlator 911 may be optionally included depending on the level of performance desired for the repeater. Thresholds, such as RSSI threshold 902 and correlator threshold setting 904, may be input to digital-to-analog converter DAC 912 and DAC 914, respectively, for use in generating correlated power detection and RSSI threshold detection using analog comparators 913 and 915. Additionally, an analog-to-digital converter (ADC)917 may be used to generate a digital value for the RSSI value and an ADC 916 is used to generate the correlator output value.

Those skilled in the art will recognize that, as mentioned above, various techniques may be used in the present invention to determine different signal detector configurations and set detection thresholds, etc. In addition, the various components (e.g., the functionality of the detector elements 309 and 311, the combinational logic element 314, and the microcontroller 313 and other elements) may be combined into a single integrated device. Other changes and modifications to the specific components and the interconnections thereof may be made by those skilled in the art without departing from the scope and spirit of the present invention.

Claims (34)

1. A method for relaying a signal transmitted from a first station to a second station using a relay configured according to a Time Division Duplex (TDD) protocol, the first station communicating to the second station on a downlink and the second station communicating to the first station on an uplink, the method characterized by:

detecting a presence of the signal on one of the uplink and the downlink;

synchronizing the repeater to one or more time intervals associated with the detected signal, the one or more time intervals being measured during an observation period to form one or more measurement time intervals;

if the signal is detected on the uplink, then rebroadcasting the signal from the second station to the first station; and

if the signal is detected on the downlink, then the signal is relayed from the first station to the second station,

wherein a first gain value associated with the downlink is used to establish a second gain value associated with the uplink.

2. The method of claim 1, wherein the detecting the presence of the signal comprises detecting using a power detector.

3. The method of claim 1, wherein the detecting the presence of the signal comprises detecting using a correlator.

4. The method of claim 1, wherein the detecting the presence of the signal comprises detecting using a matched filter.

5. The method of claim 1, wherein the synchronizing comprises:

measuring one of a Received Signal Strength Indicator (RSSI) value and a correlation value associated with a sample of the signal during the one or more measurement time intervals to form one or more measurement values; and

populating one or more sets of signal processing frequencies with ones of the one or more measurements associated with the one or more measurement time intervals such that the one or more measurement time intervals are established by processing the one or more sets of signal processing frequencies using a statistical procedure after the observation period expires.

6. The method of claim 5, wherein the statistical procedure comprises a power envelope sliding correlation function.

7. The method of claim 5, wherein the detecting comprises detecting one or more gaps between an uplink interval and a downlink interval using a windowing function.

8. The method of claim 1, wherein the TDD protocol comprises an IEEE 802.16 protocol.

9. The method of claim 1, wherein the TDD protocol comprises an IEEE802.20 protocol.

10. The method of claim 1, wherein the TDD protocol comprises an IEEE 802.16(d) protocol.

11. The method of claim 1, wherein the TDD protocol comprises an IEEE 802.16(e) protocol.

12. The method of claim 1, wherein the TDD protocol comprises an IEEE 802.16(d/e) protocol.

13. The method of claim 1, wherein the TDD protocol comprises a Personal Handyphone System (PHS) protocol.

14. The method of claim 1, wherein the TDD protocol comprises a time division synchronous code division multiple access (TDS-CDMA) protocol.

15. The method of claim 1, wherein the first station comprises a base station and the second station comprises a subscriber terminal.

16. The method of claim 1, wherein the first gain value comprises a first Automatic Gain Control (AGC) level for the downlink and the second gain value comprises a power control value for the uplink.

17. The method of claim 1, further characterized by measuring an isolation between the uplink and the downlink, and providing an indication of the isolation.

18. The method of claim 1, wherein the repeater is divided into a first unit and a second unit, and wherein the method further comprises communicating between the first unit and the second unit via a communication link.

19. A repeater that repeats a signal transmitted from a first station to a second station, the repeater configured according to a Time Division Duplex (TDD) protocol, the first station communicating to the second station on a downlink and the second station communicating to the first station on an uplink, the repeater characterized by:

an antenna;

a detector coupled to the antenna, the detector configured to detect a presence of the signal in an interval associated with one of the uplink and the downlink; and

a processor coupled to the antenna and the detector, the processor configured to:

measuring one or more time intervals during an observation period associated with the detected signal, the one or more time intervals being measured during an observation period to form one or more measurement time intervals;

synchronizing the relay to the one or more time intervals such that a first one or more of the measurement time intervals correspond to one or more uplink intervals and a second one or more of the measurement time intervals correspond to one or more downlink intervals.

20. The repeater according to claim 19, further characterized by a transmitter coupled to the antenna and the processor,

wherein the processor comprises a gain controller, the processor further configured to:

if the signal is detected on the downlink, then rebroadcasting the signal from the first station to the second station using the transmitter on one of the one or more downlink intervals, the gain controller controlling a first gain value of the rebroadcast signal;

if the signal is detected on the uplink, then the signal is relayed from the second station to the first station using the transmitter over one of the one or more uplink intervals, the gain controller controlling a second gain value,

wherein the second gain value is established using the first gain value.

21. The repeater according to claim 19, wherein the detector includes a power detector.

22. The repeater according to claim 19, wherein the detector includes a correlator.

23. The repeater according to claim 19, wherein the detector includes a matched filter.

24. The repeater according to claim 19, wherein the processor further comprises a signal processor, and wherein the processor, in synchronizing the repeater, is further configured to:

measuring one of a Received Signal Strength Indicator (RSSI) value and a correlation value associated with the signal at a sampling interval to form a measurement value; and

one or more sets of signal processing frequencies are populated with values associated with the one or more measurement time intervals such that one or more timing intervals are established by processing the one or more sets of signal processing frequencies using a statistical procedure after the observation period expires.

25. The repeater according to claim 24, wherein the statistical procedure includes a power envelope sliding correlation function.

26. The repeater according to claim 19, wherein the detector and the processor are configured to detect one or more gaps between an uplink interval and a downlink interval using a windowing function.

27. The repeater according to claim 19, wherein the TDD protocol includes one of an IEEE 802.16 protocol, an IEEE802.20 protocol, an IEEE 802.16(d) protocol, an IEEE 802.16(e) protocol, an IEEE 802.16(d/e) protocol, a Personal Handyphone System (PHS) protocol, and a time division synchronous code division multiple access (TDS-CDMA) protocol.

28. The repeater according to claim 20, wherein the first gain value includes a first Automatic Gain Control (AGC) level for the downlink and the second gain value includes a power control value for the uplink.

29. The repeater according to claim 19, wherein the processor is further configured to:

measuring an isolation between the uplink and the downlink; and

providing an indication of the isolation.

30. A repeater that repeats a signal transmitted from a first station to a second station, the repeater configured according to a Time Division Duplex (TDD) protocol, the first station communicating to the second station on a downlink and the second station communicating to the first station on an uplink, the repeater characterized by:

a first unit comprising:

a donor-side antenna;

a first transmitter;

a first detector coupled to the donor-side antenna, the detector configured to detect a presence of the signal in an interval associated with the downlink;

a first transmitter; and

a first processor coupled to the donor-side antenna, the first detector, and the first transmitter, the first processor configured to:

measuring a first one or more time intervals during an observation period associated with the detected signal, the first one or more time intervals being measured during a first observation period to form a first measurement time interval;

synchronizing the relay to the first one or more time intervals such that a first one or more of the first measurement time intervals correspond to one or more downlink intervals associated with the downlink; and

a second unit coupled to the first unit by a communication link, the second unit comprising:

a receptor-side antenna;

a second detector coupled to the receptor-side antenna, the second detector configured to detect a presence of the signal in an interval associated with the uplink;

a second transmitter; and

a second processor coupled to the receptor-side antenna, the second detector, and the second transmitter, the second processor configured to:

measuring a second one or more time intervals during an observation period associated with the detected signal, the second one or more time intervals being measured during the observation period to form a second measurement time interval;

synchronizing the repeater to the second one or more time intervals such that a second one or more of the second measurement time intervals correspond to one or more uplink intervals associated with the uplink.

31. The repeater according to claim 30, wherein:

the first unit is further configured to:

communicating the signal from the first station to the second unit via the communication link in one of the one or more downlink intervals if the signal is detected on the downlink, a first gain value associated with relaying the signal being set by the second unit; and

the second unit is further configured to:

retransmitting the signal to the second station with the first gain value in the one of the one or more downlink intervals.

32. The repeater according to claim 30, wherein:

the second unit is further configured to:

communicating the signal from the second station to the first unit via the communication link in one of the one or more uplink intervals if the signal is detected on the uplink, a second gain value associated with relaying the signal being set by the first unit; and

the first unit is further configured to:

retransmitting the signal to the first station with the second gain value in the one of the one or more uplink intervals.

33. The repeater according to claim 30, wherein the TDD protocol includes one of an IEEE 802.16 protocol, an IEEE802.20 protocol, an IEEE 802.16(d) protocol, an IEEE 802.16(e) protocol, an IEEE 802.16(d/e) protocol, a Personal Handyphone System (PHS) protocol, and a time division synchronous code division multiple access (TDS-CDMA) protocol.

34. The repeater according to claim 31, wherein the first gain value includes a first Automatic Gain Control (AGC) level for the downlink and the second gain value includes a power control value for the uplink.