BACKGROUND

(1) Technical Field

The present disclosure is related to antenna arrays, and more particularly to methods and apparatus for element by element power tracking of antenna array.

(2) Background

In wireless communication systems using electrically or mechanically steerable phased array antennas, the antenna side-lobe interference may cause challenging design issues. By way of example, in the 5G New Radio (NR) standard where time division duplex (TDD) is used, a single frequency shares the channel between transmission and reception, spacing them apart by multiplexing the two signals on a time basis. In such a scenario, the interference of the neighboring antenna or sub-array may be a performance limiting factor. In order to illustrate this issue, reference is made toFIG. 1, wherein a 4×4 spatially multiplexed array of subarrays (10) is shown. User1is covered by beam (11) and user2is covered by beam (12) with different data at the same time. As shown inFIG. 1, the user1's interference level equals the side-lobe level, which is the same for each beam. Similar to time domain, and in the case of a rectangular pulse, when applying Fourier transform to spatial domain, it is known that the first side-lobe is only 13 dB down from the main lobe. However, for code rates such as 64 quadrature amplitude modulation (QAM) or higher, the required signal to interference plus noise ratio (SINR) at the digital modem may be 24 dB or higher. In other words, without any type of signal processing, the signal may already be 11 dB below the noise requirement, thus degrading drastically the system performance. In other words, in such a system, the side-lobe needs to be suppressed to allow the 64 QAM and/or greater communication rates to occur.

One of the commonly used methods for reducing the side-lobe levels of a uniform antenna array involves amplitude tapering, in which the excitation amplitudes of the array elements generally decrease with the distance from the center of the array. As a result of tapering, the total transmitted power is reduced. Moreover, in the systems where the maximum output power per element is limited, tapering may reduce the effective isotropic radiated power (EIRP). This is because tapering always comes with the additional cost of broadening of the main lobe and as result, a reduction in gain. A commonly used tapering method is to use the Taylor window which is known to provide a strong side-lobe suppression with a minimum broadening of the main lobe.

As described above, in antenna arrays where tapering is used, the elements closer to the edges often transmit less power compared to the elements closer to the center of the array. The existing designs based on such an approach are often not optimized in terms of power dissipation requirements. More in particular, in most such systems, the power amplifiers (PA) associated with each antenna may be operating as class B or class AB amplifiers where even without having an input signal, a non-negligible amount of power is dissipated, thus decreasing drastically the overall efficiency of the system. The main reason for the low efficiency of existing systems is that, as a result of tapering, the elements closer to the array edges transmit much less power than the maximum power they can effectively handle.

A well-known technique for wireless transmitter power savings is the average power tracking (APT). Such a technique consists of switching to a lower-dissipation bias condition during intervals with sufficient link margin that permit transmitting at a correspondingly lower power level. As an example, when the transmitter is close to the receiver, the link may be power reduced via signaled feedback. APT conventionally operates on the entire transmit signal (i.e. all array elements simultaneously); as a result, and for the reason evoked previously, it is not an efficient scheme. Moreover, APT, as conventionally done, is based on a mobile environment that is inherently slow in power level changes and therefore does not lend itself for implementations over shorter time intervals.

In general, the distortion is higher in an amplifier when the amplifier is driven closer to its saturation point. In other words, in antenna arrays using tapering without APT, the PAs associated with the elements in the middle of the array are near saturation while the PAs associated with antennas closer to the edges of the array transmit effectively much smaller signals. This represents a non-uniform distribution of non-linearity across the elements in the array, and may impose significant challenges when facing the linearization problems while designing wireless systems based on antenna arrays.

In view of the above, wireless systems using phased array antennas and providing better power efficiency over the existing designs are highly desired. Providing more uniform non-linear distortion differences across the power amplifier array is also needed for the sake of design simplicity. The disclosed methods and devices address such needs and provide solution to the above-mentioned problems. As will be described more in detail, the presented methods are adaptive, and inherently faster than existing solutions and can also be implemented over shorter time intervals.

SUMMARY

According to a first aspect of the present disclosure, a method of power tracking in a wireless transmission system with an antenna array is disclosed, comprising: for each array element of the antenna array, providing a corresponding power amplifier to feed the array element; adjusting transmitted power of the power amplifiers according to a one or more dimension spatial window applied across the antenna array, and for each power amplifier, biasing the power amplifier such that a maximum power handled by the power amplifier is substantially equal to or higher than the transmitted power of the power amplifier.

According to a second aspect of the present disclosure, a wireless transmission system is provided, comprising: an antenna array; and a plurality of power amplifiers, each power amplifier of the plurality of the power amplifiers feeding a corresponding antenna of the antenna array; wherein: the plurality of power amplifiers are configured to transmit power according to a one or more dimension spatial window applied across the antenna array; and for each power amplifier of the plurality of power amplifiers, the power amplifier is configured to handle a maximum power which is substantially equal to or larger than a transmitted power of the power amplifier.

Further aspects of the disclosure are provided in the description, drawings and claims of the present application.

