Patent Application
20130143483
1. Field
This disclosure generally relates to repeaters in wireless communication systems, and in particular, to a method for maintaining repeater stability in a multi-repeater scenario.
2. Background
Wireless communication systems and techniques have become an important part of the way we communicate. However, providing coverage can be a significant challenge to wireless service providers. One way to extend coverage is to deploy repeaters.
In general, a repeater is a device that receives a signal, amplifies the signal, and transmits the amplified signal.
In repeater 110, signals from base station 125 are amplified using forward link circuitry 135, while signals from mobile device 130 are amplified using reverse link circuitry 140. Many configurations may be used for forward link circuitry 135 and reverse link circuitry 140.
There are many types of repeaters. In some repeaters, both the network and mobile interfaces are wireless; while in others, a wired network interface is used. Some repeaters receive signals with a first carrier frequency and transmit amplified signals with a second different carrier frequency, while others receive and transmit signals using the same carrier frequency. For “same frequency” repeaters, one particular challenge is managing the feedback that occurs since some of the transmitted signal can leak back to the receive circuitry and be amplified and transmitted again.
Existing repeaters manage feedback using a number of techniques; for example, the repeater is configured to provide physical isolation between the two antennae, filters are used, or other techniques may be employed.
Systems, apparatuses, and methods disclosed herein allow for enhanced repeater capability. In one embodiment, a method in a wireless repeater deployed in an environment including at least one other wireless repeater and other wireless communication devices includes transmitting a transmit signal over a first antenna of the repeater; receiving an input signal at a second antenna of the repeater, the input signal being a sum of a remote signal to be repeated, a feedback signal resulting from a feedback channel between the first antenna and the second antenna, and any interference from neighboring repeaters; processing the input signal to generate an output signal to be transmitted; generating a predetermined signal sequence to be transmitted; transmitting a transmit signal which is either the output signal, the predetermined signal sequence, or a linear combination of both; performing channel estimation using the transmitted signal or signals as well as the receive signal to generate a feedback signal estimate; and when the channel estimate is determined using the predetermined signal sequence, determining whether the feedback channel estimate has channel taps greater than a predetermined time delay as an indication of the presence of a neighboring repeater.
In some implementations, a repeater may comprise transmit circuitry configured to generate signals to transmit on a first antenna and a second antenna (a donor antenna and a server antenna), and receive circuitry to receive input signals from the first antenna and the second antenna. The transmit and receive circuitry may be implemented in hardware, software, firmware, or a combination. For example, the transmit and receive circuitry may include amplifiers, filters, demodulation/modulation circuitry, as well as processing circuitry (either as dedicated or shared processing circuitry) and may include instructions stored on memory.
The repeater may include processor circuitry to estimate a channel between the first antenna and the second antenna. For example, the processor circuitry may identify and/or determine whether there is at least one channel tap corresponding to delay greater than the delay of the feedback channel of the repeater. If so, the processing circuitry may be configured to initiate one or more mitigation measures. The processor circuitry may be implemented in hardware, software, firmware, or some combination. For example, a microprocessor, digital signal processor, application specific integrated circuit, or other hardware can be used, as can instructions stored on memory. The instructions can be implemented as software or firmware (e.g., instructions stored on EEPROPM or Electrically Erasable Programmable Read-Only Memory).
The nature, objectives, and advantages of the disclosed method and apparatus will become more apparent to those skilled in the art after considering the following detailed description in connection with the accompanying drawings.
Prior art repeaters such as those described above may provide significant advantages for cellular telephone or similar networks. However, existing repeater configurations may not be suitable for some applications. For example, existing repeater configurations may not be suitable for indoor coverage applications (e.g., repeating signals for a residence or business environment) which may require substantially more isolation between the repeater's antennas. Moreover, in some traditional repeater implementations, the target is to achieve as high a gain as reasonable while maintaining a stable feedback loop (loop gain less than unity). However, increasing the repeater gain renders isolation more difficult due to the increased signal leaking back into the donor antenna. In general, loop stability demands require that the signal leaking back into the donor antenna from the coverage antenna be much lower than the remote signal (the signal to be repeated). The maximum achievable signal to interference/noise ratio (SINR) at the output of the repeater is then the same as the SINR at the input to the repeater. High gain and improved isolation form two contradicting demands required for modern day repeaters, especially those for indoor applications.
In practice, the gain of repeater 210 is limited by the isolation between donor antenna 215 and server antenna 220. If the gain is too large, the repeater can become unstable due to signal leakage. Signal leakage refers to the phenomenon where a portion of the signal that is transmitted from one antenna (in
In a same-frequency repeater, the incoming signal is retransmitted on the same frequency as which it is received. In cases where high gain is desired than there is isolation in the antennas, interference cancellation is often used to increase the stability of the repeater and increase the overall gain.
In embodiments of the present disclosure, a wireless repeater employs interference cancellation or echo cancellation to improve the isolation between the repeaters' donor antenna (“the receiving antenna” for forward link communications) and the coverage antenna (“the transmitting antenna” for forward link communications). Interference cancellation is accomplished by actively cancelling out the transmit signal received on the repeater's own receive signal, referred to as the “leakage signal” or the “feedback signal.” In some cases, interference cancellation is carried out in baseband that is in the digital domain. Baseband interference cancellation is accomplished by storing a digital reference of the signal to be transmitted and using this digital reference to estimate the feedback channel. The feedback channel estimate is then used to estimate the feedback signal so as to actively cancel the leakage signal.
More specifically, the echo cancellation process involves estimating the feedback channel using the transmit signal as a reference signal, convolving the feedback channel estimate with the transmit signal to generate a feedback signal estimate, and applying the feedback signal estimate to cancel the undesired feedback signal in the receive signal. Effective echo cancellation requires very accurate channel estimation of the leakage channel. In general, the more accurate the channel estimate, the higher the cancellation and hence the higher the effective isolation. Herein, “interference cancellation” or “echo cancellation” refers to techniques that cancel an estimated feedback signal to reduce or eliminate the amount of leakage signal between repeater antennas; that is, “interference cancellation” refers to partial or complete cancellation of the leakage signal.
A repeater is often installed in an environment where one or more other repeaters are present. Stability and interference of the repeater's operation in the presence of multiple RF repeaters are common concerns. A typical repeater receives a remote signal, amplifies the remote signal and then transmits the amplified remote signal as the output signal. Part of the transmitted signal leaks back into the receiver over a feedback channel. If the isolation between the donor and coverage antennas is large enough, the system remains stable. However, if there are other repeaters in the coverage zone, the transmitted signal from the output of one repeater will be received by another and vice versa. Signal leakage in a multiple repeater environment can cause problems in maintaining stability of the individual repeater. A repeater operating in a multi-repeater environment can lead to poor repeater performance. Such a scenario can arise in unplanned repeater deployments; for example, when one person unknowingly installs repeaters near currently operating repeaters.
According to one aspect of the present invention, systems and techniques herein provide for improving repeater performance in a multi-repeater environment. In embodiments of the present invention, a repeater in a multi-repeater environment operates to detect the presence of neighboring repeaters and to maintain repeater stability in the presence of a neighboring repeater. In some embodiments, the repeater transmits a known signal sequence to discover the presence of a neighboring repeater. When a neighboring repeater is detected, the repeater may apply mitigation measures to maintain operational stability at the repeater.
According to one embodiment of the present invention, one or more of repeaters 252, 254 and 256 implement a neighboring repeater detection method of the present invention to discover the presence of other repeaters in the repeater's own coverage area. When a neighboring repeater is detected, the repeater may implement one or more mitigation strategies to mitigate interference or other degradation due to the presences of multiple repeaters in the same coverage area.
The neighboring repeater detection method of the present invention will be described with reference to
The repeater 252 then determines if the transmit signal sequence is received back on its second antenna after a given delay excluding the delay of its own feedback channel. More specifically, the repeater 252 receives input signals on a second antenna 272 (step 412). The input signal received on the second antenna 272 may be a feedback signal resulted from a feedback channel h between the first antenna 271 and the second antenna 272. A feedback signal received on the second antenna 272 will have a first delay from the transmit signal being transmitted from the first antenna 271 indicative of the delay of the feedback channel h. Accordingly, when the repeater 252 transmits the transmit signal sequence on the first antenna 271, the same signal sequence will be received by the second antenna 272 as a feedback signal after the delay of the feedback channel. However, the same transmit signal sequence may be received and transmitted by a neighboring repeater 254. In that case, the repeater 252 may receive on the second antenna 272 an input signal that is the transmit signal sequence being transmitted by the neighboring repeater 254 and referred to as the “received-back signal sequence”. The received-back signal sequence originated from the neighboring repeater 254 will have a different delay, typically longer, then the delay of the repeater 252's own feedback channel h.
Accordingly, method 400 proceeds with performing channel estimation based on the input signals (step 414). Because the feedback signal of the repeater and the received-back signal sequence contains the same transmit signal sequence, the repeater treats the received-back signal sequence as if it is a feedback signal but with a different channel tap, that is, a different time delay. The channel estimation process identifies the channel taps or the delay spread of each input signal. The repeater determines if an input signal has channel taps outside a given time range (step 416). If an input signal has channel taps outside a given time delay, then the repeater recognizes such longer channel taps as indicator of a neighboring repeater. That is, when the repeater 252 receives the same transmit signal sequence back on its second antenna 272 with a delay that is longer than the delay of its own feedback channel h, then the repeater 252 can conclude that there is a repeater 254 present in the neighborhood or within the same coverage area.
When the repeater 252 determines that there is a neighboring repeater, the repeater may then proceed with taking mitigation measures to maintain the stability of the repeater. On the other hand, if the repeater 252 determines that there is no neighboring repeater, that is, there is no channel tap outside of the given time delay, the repeater 252 may continue with normal repeater operations (step 418). Method 400 repeats at step 410 where the transmit signal sequence is periodically transmitted.
According to embodiments of the present invention, the repeater may undertake one or more mitigation measures once a neighboring repeater is detected using method 400 above. For instance, from the received-back signal sequence, the repeater 252 can determine information about the neighboring repeater, such as how far away it is, how much power it is transmitting, and other characteristics of the neighboring repeater. Accordingly, the repeater 252 may initiate mitigation measures to reduce inter-repeater interference and maintain stability of operation even in the presence of the neighboring repeater 254.
In one embodiment, after detecting channel taps outside of the given time delay to indicate the presence of a neighboring repeater, method 400 continues with computing a metric indicative of characteristics of the neighboring repeater (step 420). In one embodiment, the method computes a metric indicative of the received power from the neighboring repeater 254. Method 400 may then apply mitigation measures (step 422) to maintain stability of operation in the presence of neighboring repeaters. In one embodiment, the repeater 252 may reduce its gain to an acceptable level. In another embodiment, after adjusting the gain, the repeater 252 may change a controllable internal delay amount to mitigate interference from the neighboring repeater. That is, the repeater 252 may change its delay such that its channel estimate is not adversely affected by the other repeater. Finally, in yet another embodiment, the repeater may change its operation mode, such as to an insert pilot mode to allow the repeater to operate in the presence of other repeaters but with reduced SNR. In the present description, the “insert pilot mode” refers to a repeater which inserts a pilot signal to the transmit signal and uses the received-back pilot signal for channel estimation.
In operation, signal leakage from the transmitting antenna 320 back to the receiving antenna 315 of the repeater 300 causes part of the output signal Y to be leaked back through a feedback channel h and added to the remote signal X before the signal is received by the repeater. Thus, the repeater 300 actually receives a composite receive signal being the sum of the remote signal X, the feedback signal where the feedback signal is basically an attenuated version of the output signal Y, and any additional interference from other repeaters. The repeater 300 includes an echo canceller 325 for performing echo cancellation to remove all or part of the feedback signal. The echo cancelled signal x′ is provided to a variable gain stage 330 to be amplified. The amplified signal is the transmit signal y which is provided to the transmitter circuit 338 to generate the repeater output signal Y to be transmitted on the transmitting antenna 320. A channel estimation block 340 receives the transmit signal y as a reference signal and performs channel estimation to generate a feedback channel estimate. The feedback channel estimate in turn is used to generate a feedback signal estimate for use by the echo canceller 325 to cancel the undesired feedback signal in the receive signal. Repeater 300 may include other functional blocks not shown in
In
In the present embodiment, repeater 300 includes a control circuit 337 to supply a supplemental signal sequence for transmission on the transmitting antenna 320 (either with or without a repeated signal). More specifically, the signal sequence is provided to the transmitter circuit 338 to be processed into the repeater output signal Y. The signal sequence may be transmitted periodically to enable detection of neighboring repeaters.
Many implementations for repeater 300 can be used to carry out the techniques disclosed herein. For example, each of receiver circuit 322, echo canceller 325, channel estimation block 340, variable gain stage 330, transmitter circuit 338 and control circuit 337 can be implemented in hardware, software, and/or firmware. Additionally, some of the circuitry shown as functional modules can be shared and/or included in modules different than those shown in
The communication system in which the repeater of the present invention can be deployed includes various wireless communication networks based on infrared, radio, and/or microwave technology. Such networks can include, for example, a wireless wide area network (WWAN), a wireless local area network (WLAN), a wireless personal area network (WPAN), and so on. A WWAN may be a Code Division Multiple Access (CDMA) network, a Time Division Multiple Access (TDMA) network, a Frequency Division Multiple Access (FDMA) network, an Orthogonal Frequency Division Multiple Access (OFDMA) network, a Single-Carrier Frequency Division Multiple Access (SC-FDMA) network, and so on. A CDMA network may implement one or more radio access technologies (RATs) such as CDMA2000, Wideband-CDMA (W-CDMA), and so on. CDMA2000 includes IS-95, IS-2000, and IS-856 standards. A TDMA network may implement Global System for Mobile Communications (GSM), Digital Advanced Mobile Phone System (D-AMPS), or some other RAT. GSM and W-CDMA are described in documents from a consortium named “3rd Generation Partnership Project” (3GPP). CDMA2000 is described in documents from a consortium named “3rd Generation Partnership Project 2” (3GPP2). 3GPP and 3GPP2 documents are publicly available. The current techniques may be implemented using 4G systems such as Long Term Evolution (LTE), as well as future technologies and protocols. A WLAN may be an IEEE 802.11x network, and a WPAN may be a Bluetooth network, an IEEE 802.15x, or some other type of network. The systems and techniques described herein may also be used for any combination of WWAN, WLAN and/or WPAN.
Those skilled in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example: data, information, signals, bits, symbols, chips, instructions, and commands may be referenced throughout the above description. These may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.
In one or more of the above-described embodiments, the functions and processes described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. The term “control logic” used herein applies to software (in which functionality is implemented by instructions stored on a machine-readable medium to be executed using a processor), hardware (in which functionality is implemented using circuitry (such as logic gates), where the circuitry is configured to provide particular output for particular input, and firmware (in which functionality is implemented using re-programmable circuitry), and also applies to combinations of one or more of software, hardware, and firmware.
For a firmware and/or software implementation, the methodologies may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. Any machine readable medium tangibly embodying instructions may be used in implementing the methodologies described herein. For example, software codes may be stored in a memory, for example the memory of mobile station or a repeater, and executed by a processor, for example the microprocessor of modem. Memory may be implemented within the processor or external to the processor. As used herein the term “memory” refers to any type of long term, short term, volatile, nonvolatile, or other memory and is not to be limited to any particular type of memory or number of memories, or type of media upon which memory is stored. The phrases “computer readable medium,” “storage medium,” and the like are used herein to refer to manufactures and not to refer to transitory propagating signals.
Moreover, the previous description of the disclosed implementations is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these implementations will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the features shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
