Close proximity antenna measurement and tuning

A method and apparatus for providing close proximity antenna measurement and tuning, includes a first receive-only antenna, a second antenna operable in a transmit mode, a tuning circuit coupled to the first antenna, a transmitter coupled to the second antenna, a receiver coupled to the first antenna, the receiver operable to measure a power into the first antenna delivered by a signal from the second antenna driven by the transmitter, and a processor coupled to the tuning circuit, transmitter, and receiver, the processor operable to step changes in the tuning circuit until a substantially maximum power of the signal is measured by the receiver.

FIELD OF THE DISCLOSURE

The present invention relates generally to wireless communication systems, and in particular, to a mechanism for providing close proximity antenna measurement and tuning.

BACKGROUND

At present, there are wireless communication systems which demand the use of antenna diversity, such as in fourth generation Long Term Evolution (4G LTE) communication systems. These LTE systems can utilize different antenna configurations including multiple-input, multiple-output (MIMO) spatial-diversity antennas, multiple-input, single-output (MISO) transmit-diversity antenna, and single-input, multiple-output (SIMO) receive-diversity antennas, including beamforming variations. As a result, there is a need to properly tune these antennas. This can be problematic if a given antenna is a receive-only antenna, which is the case for some LTE systems, for example.

In order to tune an antenna, the antenna must first be measured and then that information can be used to determine the degree of tuning that is applied to the antenna. This measurement is normally achieved by measuring the ratio of energy applied to the antenna versus the energy measured reflecting from the antenna. In the case of most antennas, the antenna measurements can be done during manufacturing, and the results used to compensate the antenna while in use.

However, this approach can be problematic when dynamic variables affecting the antenna(s) while in use need to be compensated for. As an example; if the device that contains the antennas is of the handheld type, the presence of a user's hand holding the device may detune the antennas. Therefore, the antenna measurements made at the factory during manufacturing of the device may no longer be valid in the presence of hand-loading of the antenna(s).

One solution is to perform active antenna measurements while the device is in use to accurately determine the degree of hand-loading, and therefore the degree of compensation to apply to retune the antenna to the correct frequency, and to maximize power transfer into the antenna. However, this solution can be problematic if the antenna is a receive-only antenna, as in the case of a diversity LTE antenna which is receive only. If no power can be applied directly to the antenna, it is difficult to know the antenna performance.

The only way currently to assess the antenna performance is to measure the quality of the received data. This, however, is a measurement of the entire system, including the base station and the channel condition due to obstructions between the handheld unit and the signal source (the base station).

Accordingly, what is needed is a technique to measure antenna performance while a communication device is in use. It would also be of benefit to provide a technique that can measure a receive-only antenna, and to measure an antenna in close proximity to another antenna.

DETAILED DESCRIPTION

The present invention provides a technique to measure and tune antenna performance while a communication device is in use. It particular, the present invention provides a technique that can measure and tune a receive-only antenna while it is in close proximity to another antenna. As used in the example herein, a communication device is provided that uses two antennas, a first receive-only antenna, and a second antenna that can transmit and receive. When the device is transmitting a signal, it uses only the second antenna, and when the device is receiving a signal, it can use the first or both antennas. Alternatively, the communication device can operate in full duplex mode where it can transmit and receive simultaneously on a single antenna.

Specifically, the present invention provides the ability to measure and tune the performance of a receive-only antenna while in use by simply measuring the energy radiated by a transmit antenna of the device with the receive-only antenna while that transmit antenna is transmitting in the same band as the receive antenna. This measurement can then be analyzed to assess the degree of compensation applied to the receive-only antenna. Even if the transmit antenna reverts to a receive mode or switches frequency bands, the receive antenna can operate at improved efficiency by maintaining the correction coefficients in effect when the transmitter is turned off or switched bands. Normally both antennas are designed for maximum isolation between one another. However, some degree of coupling will always exist between them, due to their close proximity This coupling between the close proximity antennas is used by the present invention to measure and correct the effects of hand-loading and other environmental effects upon one or both of the antennas.

The wireless communication network as described herein can include not only an LTE communication network, but also WiMax networks, other IEEE 802.11 wireless communication systems, or local area networks such as Wi-Fi networks, modified to implement embodiments of the present invention.

FIG. 1is a block diagram depiction of a system in accordance with the present invention. A plurality of network entities are shown, which can support a 4G LTE wireless communication network for example, in accordance with the present invention. Those skilled in the art will recognize thatFIG. 1does not depict all of the equipment necessary for network to operate but only those network components and logical entities particularly relevant to the description of embodiments herein. Base stations and mobile devices can all include separate processors, communication interfaces, transceivers, memories, etc. In general, components such as processors, transceivers, memories, and interfaces are well-known. For example, processing units are known to comprise basic components such as, but not limited to, microprocessors, microcontrollers, memory, application-specific integrated circuits (ASICs), and/or logic circuitry. Such components are typically adapted to implement algorithms and/or protocols that have been expressed using high-level design languages or descriptions, expressed using computer instructions, expressed using messaging logic flow diagrams.

Thus, given an algorithm, a logic flow, a messaging/signaling flow, and/or a protocol specification, those skilled in the art are aware of the many design and development techniques available to implement a processor that performs the given logic. Therefore, the entities shown represent a known system that has been adapted, in accordance with the description herein, to implement various embodiments of the present invention. Furthermore, those skilled in the art will recognize that aspects of the present invention may be implemented in and across various physical components and none are necessarily limited to single platform implementations. For example, the memory and control aspects of the present invention may be implemented in any of the devices listed above or distributed across such components.

Referring back toFIG. 1, a base station (BS)130is operable to communicate with one or more subscriber modules (SM)100, such as an LTE system. For example, the communication system can utilize an Orthogonal Frequency Division Multiplexed (OFDM) or multicarrier based architecture. The architecture may also include the use of spreading techniques such as multi-carrier CDMA (MC-CDMA), multi-carrier direct sequence CDMA (MC-DS-CDMA), Orthogonal Frequency and Code Division Multiplexing (OFCDM) with one or two dimensional spreading, or may be based on simpler time and/or frequency division multiplexing/multiple access techniques, or a combination of these various techniques. In addition, in alternate embodiments the communication system may utilize other cellular communication system protocols such as, but not limited to, TDMA, direct sequence CDMA (DS-CDMA), and the like.

The BS130includes one or more transmit antennas communicating a data stream to an SM100. Any transmission122from the base station130has been modulated, coded, and multiplied by transmit weights before being fed to the BS transmit antenna(s), as is known in the art. The transmit weights are based on at least a partial channel response, to tailor spatial diversity of the transmission. The transmission122form the BS transmit antenna(s) propagates through a matrix channel H132.

The SM100in this example includes at least two receive-capable antennas. In particular, the SM includes at least a first antenna114that is a receive-only antenna, and at least a second antenna112that can operate as either a receive antenna or a transmit antenna. The transmission122from the BS is received by at least one of the receive antennas112,114of the SM100and is then demodulated by a receiver106and decoded by a processor102.

The SM100also includes a switch108that operates to switch the second antenna112between a receive functional mode or a transmit functional mode. The switch can be realized in many different configurations as are known in the art including a duplexer, diplexer, or any other type of switching apparatus that may or may not be under control of the processor102. During a transmit mode of the SM, the switch108must connect a transmitter104to the Tx/Rx second antenna112in order to send a signal120to the BS. During a receive mode of the SM, the switch108may connect the Tx/Rx second antenna112to the receiver106such that the SM has two receive antennas112,114for spatial diversity.

In accordance with the present invention, the SM100also includes a tuning circuit110for the receive-only antenna114. The SM can also include a tuning circuit116for the Tx/Rx antenna112. Optionally, the tuning circuit116can provide different tuning for the second antenna112depending on whether it is in receiver or transmit mode. During manufacture, tuning of the second antenna112is relatively straight forward since a signal can be injected into the antenna by the transmitter104and the tuning circuit116can be adjusted to minimize the reflection coefficient (i.e. S11) of the signal that is reflected back. However, the receive-only antenna114can not be directly tuned this way since there is no signal injector available to it.

The present invention solves this problem by using signals124received by the receive-only antenna114from second antenna112during transmit mode for tuning the receive-only antenna114. In particular, when the transmitter104is transmitting, the receiver106can use an envelope detector to detect a power level of the signal124emanating from the second antenna112. It can be reasonably assumed in this case that signal124will be much greater than any received signal122in the band from the BS, due to the close proximity of the transmit antenna, even where the antennas112,114have good isolation. The tuning circuit110can change tuning of the first antenna114in small steps (increments and/or decrements) until a maximum power of the signal124is measured by the envelope detector. For example, after an initial measurement by the envelop detector, the tuning circuit can be incremented, and another measurement can be made. If an increase power is detected, then it is determined that the tuning was in the right direction, and more increments are used for subsequent measurements until no further improvements are realized. If a decrease power is detected after the tuning circuit change, then it is determined that the tuning was in the wrong direction, and decrements are used for subsequent measurements until no further improvements are realized.

The above procedure is predicated on different factors. Firstly, the transmitter104and receiver106should be operating within the same frequency band when this occurs. The exact same frequency is not required as long as the operating frequencies of the transmitter and receiver are within this operational bandwidth of the envelop detector, which can be coordinated by the processor102. Secondly, the second antenna112should be in transmit mode, i.e. both antennas112,114are not receiving. Thirdly, the transmitter may be changing its output power during the receiver measurements of the signal124, due to base station commands for the transmitter to change its output power, which must be accommodated during the measurement, as will be detailed below with respect toFIG. 2.

Referring toFIG. 2, two curves are shown that demonstrate: the change of transmitter power with time200, and the change of measured power of the transmitter antenna by the receive-only antenna with time202, including changes by the receive-only antenna tuning circuit. In normal operation, the BS commands the SM to adjust its transmitter output power200to maintain a good signal level as received by the base station. This compensates for channel conditions, environmental variables, and spatial nulls and peaks caused by multipath, as is known in the art. As a result, transmitter power will exhibit short term changes in power over time204. As shown here, the transmitter power exhibits a long term trend for slowly lowering power output.

In one embodiment, to mitigate these short term power changes, the processor will direct the receiver envelope detector to make a series of brief sequential power measurements immediately before206and after208the receiver-only antenna tuning circuit change. Alternatively and additionally, since the processor knows when it directs the BS-commended transmitter power changes, it can direct the envelop detector to make the brief sequential power measurements before and after it directs the transmitter power changes. In this way, the longer term changes caused by the BS power control can be mitigated. In the example shown202, the sequential measurements206,208show an improvement with the tuning change, whereas if further-apart measurements were made206,210no improvement would be shown due to the lowering transmitter power.

As shown, the tuning circuit is making changes212that improve the received power, and therefore improves the receive antenna tuning, at each change. Tuning changes212keep being made until a change214that results in a worsening of received power. At this point, a maximum point in the tuning has just been passed. One option is to keep this one tuning point for a predetermined time period, since it is close to, or at, an optimum receive-only antenna tuning solution. Another option is to subsequently alternate incrementing and decrementing the antenna tuning as needed (216as shown) to always keep the receive-only antenna tuning near an optimum solution (i.e. a maximum power), in order to compensate for changing conditions such as a user moving their hands near the antennas on the SM.

In another embodiment, the processor knows the transmitter power setting and can detect a relative change between the transmit power and detected receive-only antenna power for each change in the receive-only antenna tuning. In this way, only a single receiver measurement needs to be made after each tuning change, which can result in a quicker optimization of the antenna tuning.

The present invention can also be used to measure and tune the transmit antenna as well. Any change in the transmitter tuning will cause a change in the transmit antenna output power, and resultantly in the receive power measured. Therefore, given a known transmitter power setting, and changing a tuning of the transmit antenna, will result in a change of received power measured, which can be fed back through the processor to adjust the transmit antenna tuning, similar to the tuning described above for the receive-only antenna.

FIG. 3illustrates a flowchart of a method for providing close proximity antenna measurement and tuning, in accordance with the present invention.

At the start, the present invention provides300a subscriber module with at least one receiver-only antenna and at least one antenna switchable between a transmit mode and a receive mode.

A next step includes determining302whether the antennas of the subscriber module are not all in receive mode and whether the transmit antenna and receive antenna are operating within the same frequency band. If both conditions are not met, the process keeps repeating this step.

A next step includes measuring304the power received into the receive-only antenna.

Another step includes storing306the measurement from step304.

Another step includes incrementing308a change in a tuning circuit for the receive-only antenna.

Another step includes measuring310the power received into the receive-only antenna.

Another step includes determining312if the power measured in step310is greater than the power stored in step306. If this condition is true, the process continues to, and repeats, steps306,308,310until the power measured in step310is no longer greater than the power stored in step306(i.e. the incremental tuning has passed maximum optimization), whereupon the process goes on to the next step.

A next step includes determining314whether the antennas of the subscriber module are not all in receive mode and whether the transmit antenna and receive antenna are operating within the same frequency band. If both conditions are not met, the process keeps repeating this step.

Another step includes storing316the measurement from step310.

Another step includes decrementing318a change in the tuning circuit.

Another step includes measuring320the power received into the receive-only antenna.

Another step includes determining322if the power measured in step320is greater than the power stored in step316. If this condition is true, the process continues to, and repeats, steps316,318,320until the power measured in step320is no longer greater than the power stored in step316(i.e. the decremental tuning has passed maximum optimization), whereupon the process can return to step306to keep hunting for optimal tuning, or end324for a predetermined amount of time before the process starts all over again.

Advantageously, the apparatus and method described herein provides a technique to tune a receive-only antenna of a subscriber module while in use. The same technique can be used to tune both the transmit mode and receive mode of a switchable Tx/Rx antenna.

It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or “processing devices”) such as microprocessors, digital signal processors, customized processors and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, at least some of the functions of the method and/or apparatus described herein. Alternatively, at least some of the functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which at least some function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used.