Diversity signal reception

A signal is received at a plurality of antennas of a wireless device, and a signal strength indicator is calculated for the signal received at each of the plurality of antennas. From the plurality of antennas, a subset of antennas associated with the highest signal strength indicators are selected, and maximum ratio combining is performed on the signals received by the selected subset of antennas.

TECHNICAL BACKGROUND

Wireless communication systems are subject to interference and fading phenomena which introduce noise and distortion into signals. One approach to overcoming the effects of fading and interference is the use of diversity reception where more than one antenna is employed at a receiver to increase the probability that a signal of relatively strong amplitude will be received. Signals received at multiple antennas may be combined to mitigate the effects of fading.

One method of combining a signal received at multiple antennas is maximum ratio combining, in which a signal received at each antenna is processed and summed. The use of multiple antennas at the receiver increases the gain of the received signal as well as the amount of data to be processed.

OVERVIEW

In an embodiment, a signal is received at a plurality of antennas of a wireless device, and a signal strength indicator is calculated for the signal received at each of the plurality of antennas. From the plurality of antennas, a subset of antennas associated with the highest signal strength indicators are selected, and maximum ratio combining is performed on the signals received by the selected subset of antennas.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary communication system100to process a call request comprising wireless device102, access node104, and communication network106. Examples of wireless device102can include a cell phone, a smart phone, a computing platform such as a laptop, palmtop, or tablet, a personal digital assistant, or an internet access device, including combinations thereof. Wireless device102is in communication with access node104over communication link108. Wireless device102can comprise a plurality of antennas which can receive a signal from access node104over communication link108.

Access node104is a network node capable of providing wireless communications to wireless device102, and can be, for example, a base transceiver station, a radio base station, an eNodeB device, or an enhanced eNodeB device. Access node104is in communication with communication network106through communication link110.

Communication links108and110can be wired or wireless communication links. Wired communication links can be, for example, twisted pair cable, coaxial cable or fiber optic cable, or combinations thereof. Wireless communication links can be a radio frequency, microwave, infrared, or other similar signal, and can use a suitable communication protocol, for example, Global System for Mobile telecommunications (GSM), Code Division Multiple Access (CDMA), Worldwide Interoperability for Microwave Access (WiMAX), or Long Term Evolution (LTE), or combinations thereof. Other wireless protocols can also be used.

Other network elements may be present in the communication system100to facilitate wireless communication but are omitted for clarity, such as base stations, base station controllers, gateways, mobile switching centers, dispatch application processors, and location registers such as a home location register or visitor location register. Furthermore, other network elements may be present to facilitate communication between access node104and communication network106which are omitted for clarity, including additional processing nodes, routers, gateways, and physical and/or wireless data links for carrying data among the various network elements.

In an embodiment, a signal is received at a plurality of antennas of wireless device102, and a signal strength indicator is calculated for the signal received at each of the plurality of antennas. A subset of antennas of the plurality of antennas which are associated with the highest signal strength indicators is selected. Maximum ratio combining is performed on the signals received by the selected subset of antennas.

FIG. 2illustrates an exemplary method of diversity signal reception. In operation202, a signal is received at a plurality of antennas of a wireless device. For example, wireless device102can comprise more than one antenna to receive a signal from, for example, access node104. One technique used to improve signal reception at a wireless device is to increase the number of antennas at the wireless device, as diversity gain improvement is directly related to the number of receiving antennas.

In operation204, a signal strength indicator is calculated for the signal received at each of the plurality of antennas. The signal strength indicator can be, for example, a received signal strength indicator (RSSI), a received channel power indicator (RCPI), a signal to interference-plus-noise ratio (SINR), or a carrier to interference-plus-noise ratio (CINR). Other indications of signal strength can also be used. As an example,FIG. 3Aillustrates a signal strength indicator calculated for four antennas A1-A4 of a wireless device (such as wireless device102). For illustration purposes only, two signal strength indicators are calculated for each antenna at two different times, t1 and t2. Greater or fewer signal strength indicators can be calculated.

Returning toFIG. 2, based on the calculated signal strength indicators, in operation206, a subset of antennas is selected from the plurality of antennas associated with the highest signal strength indicators. For example, at time t1 antennas A1 and A2 (FIG. 3A) can be selected since they are associated with the highest signal strength indicators (inFIG. 3A,10and7, respectively). As another example, at time t2 antennas A2 and A3 can be selected, since they are associated with the highest signal strength indicators (9and10, respectively, inFIG. 3A).

In operation208(FIG. 2), maximum ratio combining is performed on the signals received by the selected subset of antennas. Result column R1 (FIG. 3A) illustrates an exemplary result of performing maximum ratio combining on each signal from all antennas A1-A4, and result column R2 illustrates an exemplary result of performing maximum ratio combining on a signals received by the selected subset of antennas.

The results in column R2 at times t1 and t2 are higher than the results illustrated in column R1 at the same times, illustrating that the selection of a subset of antennas typically results in a greater received gain of the signal. In addition, performing maximum ratio combining on signals received by a subset of antennas of the wireless device reduces the amount of data to be processed, which reduces processor load and decreases drain on a battery or other power source of the wireless device. The results illustrated in column R1 are typical of a conventional approach to maximum ratio combining, which relies on both the addition of antennas to increase gain and the collection and processing of greater amounts of data. The results illustrated in column R2 illustrate that, contrary to the conventional approach, the selection of a subset of antennas typically results in a greater received gain of the signal while reducing a drain on a battery or other power source of the receiving wireless device. In an embodiment, a resultant four-fold decrease in signal processing can be achieved.

FIG. 4illustrates another exemplary method of diversity signal reception. In operation402, a signal is received at a plurality of antennas of a wireless device. For example, wireless device102can comprise more than one antenna to receive a signal, for example, from access node104.

In operation404, a correlation coefficient is calculated based on the signal received at each of the plurality of antennas. In an embodiment, a correlation coefficient (or several correlation coefficients) can be calculated based on a comparison of pairs of each of the antennas of the wireless device. For example, in a wireless device comprising four antennas A1-A4, a correlation coefficient can be calculated for comparisons of the signal received at antennas A1 and A2, A1 and A3, A1 and A4, A2 and A3, A2 and A4, and A3 and A4. In embodiment, the correlation coefficient can provide an indication of relative spatial diversity between two antennas. In general, a lower correlation corresponds to greater relative diversity. In an embodiment, a correlation coefficient can be calculated for two antennas by dividing a difference in received signal strength by an average signal strength. In an embodiment, a correlation coefficient can be calculated for two antennas by dividing a difference in received signal quality (such as a signal to interference-plus-noise ratio (SINR), or a carrier to interference-plus-noise ratio (CINR)) by an average signal quality. In an embodiment, two correlation coefficients can be calculated for two antennas based on each of the signal strength and the signal quality as described above.

In operation406, a signal strength indicator is calculated for the signal received at each of the plurality of antennas. The signal strength indicator can be, for example, based on a received signal strength indicator (RSSI), a received channel power indicator (RCPI), a signal to interference-plus-noise ratio (SINR), or a carrier to interference-plus-noise ratio (CINR). In an embodiment, a calculated correlation coefficient can be used to determine the signal strength indicator. The correlation coefficient can be based on signal strength, signal quality, or a combination thereof. IN an embodiment, the signal strength indicator can be based on a received signal strength indicator (RSSI), a received channel power indicator (RCPI), a signal to interference-plus-noise ratio (SINR), or a carrier to interference-plus-noise ratio (CINR), a correlation coefficient based on signal strength, a correlation coefficient based on signal quality, and combinations thereof.

Based on the calculated signal strength indicators, in operation408, a subset of antennas is selected from the plurality of antennas associated with the highest signal strength indicators. In an embodiment, the antennas associated with the two highest signal strength indicators can be selected.

In operation410, maximum ratio combining is performed on the signals received by the selected subset of antennas. The result of performing maximum ratio combining on the signals received by the selected subset of antennas will typically be higher than the result of maximum ratio combining on the signals received by all of the antennas of the wireless device.

In operation412, it can be determined whether the result of maximum ratio combining on the signals received by the selected subset of antennas meets a result threshold. For example, an application requirement of an application running on the wireless device can be determined, and meeting the result threshold may indicate that the resultant signal strength from the maximum ratio combining is insufficient to meet the application requirement. An application requirement can be, for example, a minimum data rate, or a maximum data delay, tolerable by the application. For example, wireless device102may be running a voice application (such as Voice over Internet Protocol) or a streaming video or audio application, which requires a minimum data rate (or can tolerate a maximum data delay) to provide a minimum threshold of performance. When the result of maximum ratio combining on the signals received by the selected subset of antennas does not meet a result threshold (operation412-NO), it can be determined that the application requirement is met, and maximum ratio combining will be performed on the selected subset of antennas.

When the result of maximum ratio combining on the signals received by the selected subset of antennas meets a result threshold (operation412-YES), it can be determined, for example, that the application requirement is not met. In operation414, an additional antenna can be selected. The antenna selected in operation414is an antenna not selected as part of the selected subset of antennas, and thus is an additional antenna. In operation416, maximum ratio combining is performed on the signals received by the selected subset of antennas together with the signal received by the additional antenna. In a situation where the addition of one additional antenna does not result in meeting the application requirement, a further additional antenna can be selected, and maximum ratio combining can be performed on the signals received by the selected subset of antennas together with the signals received by all of the additional antennas.

While the result threshold is met (operation418-YES), maximum ratio combining can be performed on the signals received by the selected subset of antennas together with the signal received by the additional antenna. When the result threshold is no longer met (operation418-NO), it can be determined that the additional antenna is not needed, and maximum ratio combining can be performed on the originally selected subset of antennas.

FIG. 5illustrates an exemplary wireless device500in a communication system. Wireless device500comprises communication interface502, user interface504, and processing system506in communication with communication interface502and user interface504. Wireless device500is capable of diversity signal reception. Processing system506includes storage508, which can comprise a disk drive, flash drive, memory circuitry, or other memory device. Storage508can store software510which is used in the operation of the wireless device500. Storage508may include a disk drive, flash drive, data storage circuitry, or some other memory apparatus. Software510may include computer programs, firmware, or some other form of machine-readable instructions, including an operating system, utilities, drivers, network interfaces, applications, or some other type of software. Processing system506may include a microprocessor and other circuitry to retrieve and execute software510from storage508. Wireless device500may further include other components such as a power storage unit, a control interface unit, etc., which are omitted for clarity. Communication interface502permits wireless device500to communicate with a communication system and to receive a signal, and can comprise a plurality of antennas to receive the signal. User interface504permits the configuration and control of the operation of wireless device500. Wireless device102is an example of wireless device500.