Various embodiments of the invention may be better understood by reading the following detailed description with reference to the accompanying figures, in which like reference numerals refer to like elements throughout, and in which:
In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures, and/or techniques have not been shown in detail in order not to obscure an understanding of this description.
References to “one embodiment”, “an embodiment”, “example embodiment”, “various embodiments”, etc., indicate that the embodiment(s) of the invention so described may include a particular feature, structure, or characteristic, but not every embodiment necessarily includes the particular feature, structure, or characteristic. Further, repeated use of the phrase “in one embodiment” or “in an embodiment” does not necessarily refer to the same embodiment, although it may.
In the following description and claims, the term “coupled,” along with its derivatives, may be used. It should be understood that “coupled” may mean that two or more elements are in direct physical or electrical contact with each other or that the two or more elements are not in direct contact but still cooperate or interact with each other.
An algorithm is here, and generally, considered to be a self-consistent sequence of acts or operations leading to a desired result. These include physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers or the like. It should be understood, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities.
Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices.
In a similar manner, the term “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory. A “computing platform” may comprise one or more processors.
Embodiments of the present invention may include apparatuses for performing the operations herein. An apparatus may be specially constructed for the desired purposes, or it may comprise a general purpose device selectively activated or reconfigured by a program stored in the device.
Embodiments of the invention may be implemented in one or a combination of hardware, firmware, and software. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by a computing platform to perform the operations described herein. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium may include machine-readable storage media, such as read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, and others, as well as electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. A machine-readable storage medium may be located locally or remotely, with respect to other portions of embodiments of the invention (for example, but not limited to, a machine-readable medium accessed by means of a communication network).
A switched diversity scheme may work in several ways, which may, for example, depend upon the type and/or quantity of processing facilities. As noted above, in a switched diversity scheme, some quantity indicative of the quality of a signal being received by an antenna 11a-11c may be determined and used to determine which antenna to couple to a receiver chain 13. The determination of signal quality may be performed by appropriate apparatus associated with each antenna, or the signals from the various antennas may be switched among one or more such apparatuses. Furthermore, the determination of signal quality may be based on analog and/or digital methods.
In many communication systems, a preamble may be included as a first portion of a transmission. Such a preamble may be used to determine signal quality for purposes of diversity switching, prior to processing data content of a transmitted signal.
In one embodiment of the invention, as mentioned above, the receive apparatus 12 may have only a single apparatus, which may be part of or separate from receiver chain 13, for evaluating signal quality from the antennas 11a-11c. In that case, the single apparatus may be shared among all of the antennas 11a-11c.
One way to determine an antenna to use would be to compute a signal-to-noise ratio (SNR) for each antenna and to compare the SNRs for the different antennas. In general, SNR may be represented as:
where “X” represents signal energy, while “E” represents the total received energy (signal plus noise). The subscript “k” is used to denote the kth antenna. For the exemplary case discussed above, in which there is a single apparatus for determining the signal quality for all of the antennas, the various quantities may be computed, in general, as follows:
where {rk}k=0256−1 represents the data of the four 64-sample exemplary preamble portions shown in
It is further noted that, if there is more than one apparatus for evaluating signal quality, more than one antenna may be analyzed during a single interval. Therefore, a common block of samples may be used to evaluate the signal quality for more than one antenna.
In the case of a pair of antennas (k=1,2), one may decide to use antenna 1 if SNR1>SNR2 or antenna 2 if SNR2>SNR1. Given this, and cross-multiplying from the SNR equation above (and squaring both sides), results in the following alternative formulation of the problem:
QF1=(X1,re2+X1,im2)·E22, QF2=(X2,re2+X2,im2)·E12, where Xk,re is the real part of Xk and Xk,im is the real part of Xk for k=1, 2. QFk may be called the “quality factor” for the kth antenna. The first factor of the quality factor may be thought of as the square of a received signal strength indicator, while the second factor of the quality factor may be thought of as the square of total received energy. A flowchart of the case of two antennas, corresponding to this formulation is shown in
It is noted that if there are an arbitrary number of antennas, the formulation of the problem in terms of SNRs would involve pair-wise comparisons of the SNRs of the various antennas. Similarly, as may be shown by forming the corresponding inequalities and cross-multiplying and squaring, pair-wise determination and comparisons of quality factors may be used in the alternative formulation of the problem. For example, the flowchart of
In yet a further exemplary expansion of the flowchart of
It is noted that the above development may be further generalized. The QFk developed above is one example of what will be termed here a “comparative quality factor” (CQF). In general, a CQF may be defined as any quantity, based on signals received at two antennas, on which the relative signal qualities at those two antennas may be based. For example, SNR may be formulated in terms of signal power (Ps) and noise power (Pn) (i.e., as
where the subscript k is used to denote the kth antenna. Using this formulation, another CQF may be computed as Ps,i·Pn,j, for use in comparing the signals received by the ith and jth antennas (in other words, Ps,i·Pn,j may be compared to Ps,j·Pn,i to determine which signal has the better quality). This formulation of the CQF is reflected in the flowchart shown in
When apparatus is switched between or among antennas, physical switches may cause latency (delay) and/or ripple effects. To avoid these, which may improve the accuracy of the calculations above, a few samples may be skipped at the beginning and/or at the end of each portion of the preamble.
In some cases in which there may be large amounts of latency and/or ripple, the sum of x and z may be relatively large in comparison with the number of samples in a preamble portion that may be used to determine QF. For example, in the above example shown in
As noted above, various embodiments of the invention may include more than one receiver chain 13, say N receiver chains 13a-13b, as shown in the exemplary block diagram of
In some embodiments of the invention, filtered switched diversity statistics, over a number of frames or other time intervals, may be used to determine which antenna(s) to connect to the receiver chain(s). Such filtering may be, but is not limited to, a first-order moving average filter, such as:
y(n)=α·x(n)+(1−α)·y(n−1),
where x(n) may represent the quality factor, e.g., for the nth frame, and where α is a filter parameter, which may be predetermined, set by the user, or set by the system designer. As noted above, other filters may be used.
Some embodiments of the invention, as discussed above, may be embodied, at least in part, in the form of software instructions on a machine-accessible medium. Such an embodiment may be illustrated in
The embodiments illustrated and discussed in this specification are intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the present invention. The above-described embodiments of the invention may be modified or varied, and elements added or omitted, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described.