DE202004021935U1 - System for channel adaptive antenna selection - Google Patents

Abstract

A communication system for selecting N antenna elements in an M antenna element transmitter or an M antenna element receiver, wherein N is smaller than M, comprising: M antenna elements in the M antenna element transmitter or the M antenna element receiver; N HF chains; and a switch coupled to the N RF chains.

Description

BACKGROUND OF THE INVENTION

Most current wireless communication systems are composed of nodes that are configured with a single transmit and receive antenna. However, for a wide range of wireless communication systems, it has been predicted that the performance, including capacity, can be significantly improved through the use of multiple transmit antennas and / or multiple receive antennas. Such configurations form the basis of so-called "smart antenna" techniques ("smart" techniques). "Smart Antenna" techniques, coupled with space-time signal processing, can be used to both combat the deleterious effects of multipath fading of a desired incoming signal and to suppress spurious signals. In this way, both the performance and capacity of existing or deployed digital wireless systems (eg, CDMA based systems, TDMA based systems, WLAN systems, and OFDM based systems such as IEEE 802.11a / g ) be improved.

At least some of the performance degradations of wireless systems of the type described above can be at least partially improved by using multi-element antenna systems designed to introduce diversity gain and suppress interference within the signal reception process. This is for example in "The Impact of Antenna Diversity on the Capacity of Wireless Communication Systems" by JH Winters et al., IEEE Transactions on Communications, Vol. 42, No. 2/3/4, pages 1740-1751, February 1994 , has been described. Such diversity gains improve system performance through the multipath suppression for more uniform area coverage by increasing a signal-to-noise ratio (SNR) for a wider range or a reduced required transmit power, and by providing more robustness to interference or by allowing greater frequency reuse for higher capacity.

Within communication systems incorporating multiple antenna receivers, a set of M receive antennas may be capable of zeroing up to M-1 interferers. Accordingly, N signals can be transmitted simultaneously in the same bandwidth using N transmit antennas, the transmitted signal then being separated into N respective signals by a set of N antennas used at the receiver. Systems of this type are commonly referred to as MIMO (Multiple Input Multiple Output) systems and have been extensively and extensively studied. See for example "Optimum Combination for Indoor Radio Systems with Multiple Users" by JH Winters, IEEE Transactions on Communications, Vol. COM-35, No. 11, November 1987 ; "Capacity of Multi-Antenna Array Systems in Indoor Wireless Environment" by C. Chuah et al., Proceedings of Globecom '98 Sydney, Australia, IEEE 1998, pages 1894-1899, November 1998 ; and "Fading Correlation and Its Effect on the Capacity of Multi-Element Antenna Systems" by D. Shiu et al., IEEE Transactions on Communications, Vol. 48, No. 3 , Pages 502-513, March 2000 ,

Some multi-element antenna arrays (eg, some MIMOs) provide system capacity improvements that can be achieved using the above-mentioned configurations. Assuming perfect estimates of the usable channel at the receiver, in a MIMO system the received signal is decomposed into M "spatially multiplexed" independent channels. This results in an M-fold increase in capacity compared to systems with a single antenna.

For a fixed total transmission power, the capacity offered by MIMOs scales linearly with the number of antenna elements. In particular, it has been found that with N transmit antennas and N receive antennas, an N-fold increase in data rate over a single-antenna system can be achieved without there being an increase in overall bandwidth or overall transmit power. See for example "On Limits of Wireless Communications in a Fading Environment When Using Multiple Antennas" by GJ Foschini et al., Wireless Personal Communications, Kluwer Academic Publishers, Volume 6, No 3, pages 311-355, March 1998 , In MIMO experimental systems based on N-times spatial multiplexing, more than N antennas are often used on a given transmitter or receiver. This is because each additional antenna adds diversity gain and antenna gain and increases the interference suppression that can be applied to all N spatially multiplexed signals. See for example GJ Foschini et al., IEEE Journal on Selected Areas in Communications (Simplified Processing for High Spectral Efficiency wireless communication employing multi-element arrays) (Simplified processing for wireless communication with high spectral efficiency using multi-element arrays) Volume 17, Issue 11, November 1999, pages 1841-1852 ,

Although increasing the number of transmit and / or receive antennas improves various aspects of the performance of MIMO systems, providing a separate RF chain for each transmit and receive antenna increases the cost. Each RF chain generally consists of a low-noise amplifier, a filter, a buck converter, and an analog-to-digital converter (A / D), the latter three typically accounting for most of the cost of the RF chain are. In certain existing wireless receivers with a single antenna, the only RF chain needed may account for more than 30% of the total receiver cost. It is thus apparent that as the number of transmit and receive antennas increases, total system cost and overall power consumption can increase dramatically.

Some attempts to address these disadvantages can be found, for example, in the U.S. Patent Publication No. 20020102950 entitled "Method and apparatus for selection and use of optimal antennas in wireless systems" (method and apparatus for selecting and using optimal antennas in wireless systems); in "Molecular capacity of MIMO systems with antenna selection" by A. Molisch et al., Proceedings of IEEE ICC, Helsinki, Finland, June 2001, Vol. 2, pp. 5701-574 ; and in "Optimum MIMO with antenna selection" by RS Blum et al., IEEE Communications Letters, Vol. 6, Issue 8, August 2002, pages 322-324 are found in which a subset of transmit / receive antennas is selected from a larger number of antennas. Since at least N RF chains must be used with N-times spatial multiplexing, typically N of a total of M antennas would be selected at the receiver and / or N of a total of n _T antennas would be selected at the transmitter, where M> N and n _T > N is.

The performance of a system with antenna selection, for example, depends on the criteria used in the selection process. Different criteria, even used under the same channel condition, can result in a different selected subset of antennas, resulting in different performances. Some of the above documents support the maximum capacity criterion to select the antenna subset. But the capacity is an idealized size, which can be an unattainable barrier because it may require perfect coding and / or equalization and / or continuous modulation. In practice, the equalizer is not ideal and limited coding (or no coding at all) and quantized modulation is used.

SUMMARY OF THE INVENTION

Some embodiments in accordance with some aspects of the present invention may relate to systems that provide channel adaptive antenna selection in multi-antenna element communication systems.

In one embodiment, in accordance with some aspects of the present invention, a system that selects N antenna elements in an M antenna element transmitter or an M antenna element receiver, where N is less than M, may include M antenna elements in the M antenna element Transmitter or in the M antenna element receiver, N RF chains and a switch coupled to the N RF chains. The M antenna element receiver may calculate an output bit error rate for each possible N antenna element subset of the M antenna elements. Each output bit error rate may be calculated based on at least one set of channel parameter statistics. The M antenna element receiver may select the particular N antenna element subset based on a criterion based on the calculated output bit error rates. In response to selecting the particular N antenna element subset based on the criterion, the switch may couple the N RF chains to the N antenna elements of the particular N antenna element subset.

In another embodiment, in accordance with some aspects of the present invention, a mechanism that selects a subset of receive antennas of a receiver for receiving a transmitted RF signal may include, for example: forming possible subsets of the receive antennas; Determine sets of channel parameter statistics corresponding to the possible subsets correspond to the receiving antennas; Calculating receiver output bit error rates, wherein each output bit error rate is calculated based on at least one set of channel parameter statistics; Selecting a particular possible subset of the receive antennas based on a criterion based on the calculated output bit error rates; and connecting one or more RF chains of the receiver to the receive antennas of the selected special subset.

In another embodiment, in accordance with some aspects of the present invention, a mechanism that selects a subset of transmit antennas of a transmitter for transmitting an RF input signal as a plurality of RF output signals subsequently received by a receiver may include, for example: Forming possible subsets of the transmit antennas; Determining sets of channel parameter statistics corresponding to the possible subsets of the transmit antennas; Selecting transmission modes corresponding respectively to the sets of channel parameter statistics; Calculating output bit error rates of the receiver, wherein each output bit error rate is calculated based on at least one set of channel parameter statistics and at least one selected transmit mode; Selecting a particular possible subset of the transmit antennas based on a criterion based on at least the calculated output bit error rates; and connecting one or more RF links of the transmitter to the transmit antennas of the selected special subset.

In yet another embodiment, in accordance with some aspects of the present invention, in a communication system having a transmitter and a receiver, the transmitter having transmit antennas configured to use a set of spatially multiplexed RF output signals through a channel of two or more transmit RF chains, and wherein the receiver comprises receive antennas configured to receive the set of spatially multiplexed RF output signals and configured to respond in response thereto a set of spatially multiplexed received ones To generate RF signals processed by two or more receive RF chains, an antenna selection mechanism, for example, comprises: forming possible subsets of the transmit antennas and possible subsets of the receive antennas; Determining sets of channel parameter statistics corresponding to combinations of the possible subsets of the transmit antennas and the possible subsets of the receive antennas; Selecting transmission modes corresponding respectively to the sets of channel parameter statistics; Calculating receiver output bit error rates, wherein each output bit error rate is calculated based on at least one set of channel parameter statistics and a corresponding selected transmit mode; Selecting a particular possible subset of the transmit antennas and a particular possible subset of the receive antennas based on a criterion based on at least the calculated output bit error rates; Connecting the two or more of the transmit RF chains to the selected special possible subset of the transmit antennas; and connecting the two or more receive RF chains to the selected particular possible subset of the receive antennas.

In yet another embodiment, in accordance with some aspects of the present invention, in a communication system having a transmitter and a receiver, the transmitter having transmit antennas configured to transmit a set of RF output signals through a channel using one of a plurality of RF transmit signals or multiple transmit RF chains, and wherein the receiver has receive antennas configured to receive the set of RF output signals and configured to generate a set of received RF signals in response thereto is processed by one or more receive RF chains, an antenna selection mechanism include, for example: forming possible subsets of the transmit antennas and possible subsets of the receive antennas; Determining sets of channel parameter statistics corresponding to combinations of the possible subsets of the transmit antennas and the possible subsets of the receive antennas; Selecting transmission modes corresponding respectively to the sets of channel parameter statistics; Calculating receiver output bit error rates, wherein each output bit error rate is calculated based on at least one set of channel parameter statistics and a corresponding selected transmit mode; Selecting a particular possible subset of the transmit antennas and a particular possible subset of the receive antennas based on a criterion based on at least the calculated output bit error rates; Connecting the one or more of the transmit RF chains to the selected special possible subset of the transmit antennas; and connecting the one or more of the receive RF chains to the selected particular possible subset of the receive antennas.

These and other features and advantages of some embodiments in accordance with some aspects of the present invention may be appreciated and understood from a review of the following detailed description, taken in conjunction with the accompanying drawings in which like reference numbers refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

1A and 1B show an embodiment of a conventional MIMO communication system.

2A and 2 B show an embodiment of a MIMO system in accordance with some aspects of the present invention.

3 FIG. 12 shows one embodiment of an SM-MIMO-OFDM system in accordance with some aspects of the present invention. FIG.

4A and 4B 10 are flowcharts illustrating embodiments of an antenna selection mechanism in accordance with some aspects of the present invention.

5 FIG. 12 is a graph illustrating exemplary performance results in accordance with some aspects of the present invention. FIG.

6 FIG. 12 shows an embodiment of an SC-MIMO-OFDM system in accordance with some aspects of the present invention. FIG.

7 FIG. 12 shows an embodiment of a receiver in a DS-SS SIMO system in accordance with some aspects of the present invention. FIG.

DETAILED DESCRIPTION OF THE INVENTION

I. OVERVIEW OF SOME ASPECTS OF THE PRESENT INVENTION

Some embodiments in accordance with some aspects of the present invention may relate to communication systems that use a transmitter and / or a receiver having multiple antenna elements.

Some embodiments in accordance with some aspects of the present invention may relate to systems that provide channel adaptive antenna selection in multi-antenna element communication systems.

Some embodiments in accordance with some aspects of the present invention may be implemented to facilitate selection of a subset of antenna elements in one or more multi-antenna wireless communication devices based on a criterion based at least in part on calculated output bit error rates based.

Some embodiments in accordance with some aspects of the present invention may be implemented to facilitate the selection of a subset of antenna elements in one or more multi-antenna wireless communication devices such that, for example, a bit error rate (BER) is used. can be minimized or optimized.

Some embodiments in accordance with some aspects of the present invention may be implemented to facilitate channel-adaptive selection of a subset of antenna elements in one or more multi-antenna wireless communication devices based on a criterion that is based, at least in part, on computed output. Bit error rates based.

Some embodiments in accordance with some aspects of the present invention may enable the use of a larger number of antenna elements than the number of radio frequency (RF) chains. Some embodiments in accordance with some aspects of the present invention may improve system performance in a cost effective manner.

Some embodiments in accordance with some aspects of the present invention may be employed to select a subset of antenna elements of a multi-antenna transmitter for transmitting a signal, and / or to select a subset of antenna elements of a multi-antenna receiver to receive a signal ,

Some embodiments in accordance with some aspects of the present invention may provide that a selection of the subset of antenna elements is based, at least in part, on a criterion based at least in part on at least calculated output bit error rates.

Some embodiments in accordance with some aspects of the present invention may provide that the selection of the subset of antenna elements is based at least in part on minimizing a BER.

Some embodiments in accordance with some aspects of the present invention may be applied to communication systems that include code division multiple access (CDMA) signals, spread spectrum signals, single carrier signals, multicarrier signals, orthogonal frequency division multiplexed (orthogonal frequency division multiplexed) OFDM) signals, UWB signals, space-time diversity signals, and spatially multiplexed signals.

Some embodiments in accordance with some aspects of the present invention may provide that a selection of the subset of antenna elements is based, at least in part, on minimizing a BER based on, for example, parameters (eg, statistical parameters) related to one or more several communication channels. Some embodiments in accordance with some aspects of the present invention may provide that selection of a subset of antenna elements is based on minimizing a BER based, at least in part, on parameter statistics from one or more usable communication channels.

Some embodiments in accordance with some aspects of the present invention may be used for antenna selection in a MIMO (Multiple Input Multiple Output) communication system. For example, the MIMO communication system may provide a transmitter that transmits a plurality (N) of spatially multiplexed signals through N transmitting antenna elements selected from a set of n _T antenna elements, where n _T > N. For example, the MIMO communication system may provide a receiver in which N receive antenna elements selected from a total of M elements, where M> N, form a number of output signals equal to the number of spatially multiplexed signals. The output signals in turn are provided to corresponding RF chains for processing in baseband. Thus, in accordance with some aspects of the present invention, some embodiments may advantageously allow minimization of BER (eg, channel adaptive minimization of BER) and / or reduction of RF signal processing costs within multi-antenna systems.

Some embodiments in accordance with some aspects of the present invention may provide a transmitter having one or more RF chains and a particular plurality of transmit antennas, which may be all or less than all of the transmit antennas of the transmitter. Some embodiments in accordance with some aspects of the present invention may provide a system that selects, for example, a subset of a particular plurality of transmit antennas, wherein the subset transmits an RF input signal as, for example, a plurality of RF output signals be received by a recipient. A variety of possible subsets (eg, all or less than all of the possible subsets having a certain number of transmit antennas or other types of grouping characteristics) of the particular plurality of transmit antennas may be formed. Sets of channel parameter statistics or other parameters corresponding to the possible subsets of the particular plurality of transmit antennas may then be determined. Sending modes or other types of modes corresponding to respective sets of channel parameter statistics may be selected. Transmission modes may include, for example, a modulation level and / or a coding rate. For example, a plurality of BERs (bit error rates) (eg, output BERs) of the receiver may be calculated. For example, each of the plurality of output BERs may be computed, at least in part, based on, for example, a set of channel parameter statistics and / or corresponding selected transmit modes. For example, a possible subset of the particular plurality of transmit antennas may be selected based on criteria that are at least partially related to the source BERs and / or the selected transmission modes. One or more RF chains may then be connected to the transmit antenna (s) of the selected possible subset of the particular plurality of transmit antennas.

Some embodiments in accordance with some aspects of the present invention may provide channel parameter statistics, which may include, for example, first order statistics, second order statistics, or higher order statistics. Channel parameter statistics may include, for example, one or more of the following: an output signal-to-noise ratio, an output signal-to-interference-plus-noise ratio, a likelihood ratio (eg, a log-likelihood ratio), an Euclidean Distance in a signal constellation, for example, of a receiver. Channel parameter statistics can be calculated, for example, over a frequency range or a time range.

Some embodiments of an antenna selection mechanism in accordance with some aspects of the present invention may be used with various types of multi-antenna communication systems. In certain embodiments, some embodiments of an antenna selection mechanism in accordance with some aspects of the present invention may, for example, refer to a multi-antenna receiver within a "single channel" (SC) system (ie, a spatial Multiplexing), to a multi-antenna transmitter in a single-channel system or to the transmitter and / or receiver of a MIMO system using spatial multiplexing (SM) or a single channel.

For example, some embodiments in accordance with some aspects of the present invention may provide a number N of receive antenna elements selected from a set of M available antenna elements (where M> N) such that the selected subset of antenna elements comprise the BER minimized, for example when different channel parameter statistics are considered. This can be accomplished by forming possible subsets of a plurality of transmit antennas and possible subsets of the M receive antennas. The mechanism further comprises determining a plurality of sets of channel parameter statistics corresponding to combinations of subsets of the possible subsets of the plurality of transmit antennas and subsets of the possible subsets of the plurality of receive antennas. Multiple transmit modes, each corresponding to the multiple sets of channel parameter statistics, are then selected. In addition, multiple output bit error rates of the receiver are computed based at least in part on one of the multiple sets of channel parameter statistics and a corresponding transmit mode of the plurality of transmit modes. One of the possible subsets of the plurality of transmit antennas and one of the possible subsets of the plurality of receive antennas are then selected based on a criterion based at least in part on the multiple output bit error rates and the multiple transmit modes. The mechanism further comprises connecting one or more of the transmit RF chains to the one of the possible subsets of the plurality of transmit antennas and connecting the one or more receive RF chains to the one of the possible subsets of the plurality of receive antennas.

Some embodiments in accordance with some aspects of the present invention may provide a criterion based, for example, on one or more of the following: an output bit error rate; a transmission mode; a minimization of an output bit error rate; a maximization of a data rate; maximizing a data rate in a first stage of a receiver; and minimizing an output bit error rate in a second stage of the receiver.

In the case of a single-channel or spatially multiplexed MIMO system using multiple RF chains on a transmitting and / or receiving side, certain baseband weighting and combining mechanisms within the transmitter (e.g., precoding) and / or the Be integrated with the selection mechanism. For example, baseband weights and antenna selection may both be designed to help minimize BER. In another example, the baseband weights may be designed to have, for example, an output signal-to-noise ratio (SNR), an output signal-interference-plus ratio (SNR). SIRV) or to maximize a capacity, while the BER is minimized by an appropriate antenna selection.

Some embodiments in accordance with some aspects of the present invention are directed to a channel adaptive antenna selection system based on minimizing the BER for the antenna Used in multi-antenna systems, which include, for example, N-way spatially multiplexed multi-antenna systems. In order to enable some embodiments to be understood in accordance with some aspects of the present invention, an overview of exemplary architectures that can implement antenna selection within multi-antenna systems is provided. After review, further details related to systems for channel adaptive antenna selection based on, for example, minimizing BER may be presented.

II. ARCHITECTURE FOR THE ANTENNA SELECTION

Some embodiments in accordance with some aspects of the present invention may be implemented in wireless communication systems that use a smaller number of RF links within a transmitter and / or receiver than the number of transmit / receive antennas used. In some embodiments, in accordance with some aspects of the present invention, a number N of receive antenna elements is selected from a total number of elements M, where M> N. This forms N RF output signals, which are then passed through N RF chains. In an exemplary implementation, each RF chain includes, for example, a filter, a down converter and an analog-to-digital converter (A / D converter). The output signals produced by the A / D converter of each RF chain are then digitally processed to produce the N spatially multiplexed output signals. By performing the necessary selection of a subset of antennas in RF, an N-times spatially multiplexed system with more than N receive antennas, but only N RF chains, can be realized at a cost similar to that of a N-receive antenna system. Accordingly, the receiver performance can be improved by using additional antennas at a relatively low cost.

A similar technique may be used at a transmitter, the N RF chains and a number n _T of transmit antennas greater than N includes. In an exemplary implementation, the N RF chains are followed by a switch that connects each of these RF chains to a subset of N transmit antennas selected from n _T. As with the receiver, by performing such selection of a subset of antennas at RF, an N-times spatially multiplexed system with more than N transmit antennas but only N RF chains can be realized at a cost similar to that of a system N transmit antennas and N RF chains are similar. Accordingly, transmitter power can be improved through the use of additional antennas at a relatively low cost.

A. Spatial multiplexing

In accordance with some embodiments in accordance with some aspects of the present invention, spatial multiplexing (SM) provides a mode of signal transmission based on the use of multiple antennas at both a transmitter and a receiver in such a manner based on that the bit rate of a wireless radio link can be increased without the power consumption or bandwidth consumption increases accordingly. In the case where N antennas are used at both a transmitter and a receiver, an input stream of information symbols provided to the transmitter is split into N independent sub-streams. Spatial multiplexing considers that each of these sub-streams will occupy the same "channel" (eg, a time slot, frequency, or code / key sequence) of the useable multiple access protocol. Within the transmitter, each substream is applied separately to the N transmit antennas and routed to a receiver via an intervening multipath communication channel. The composite multipath signals are then received by a receive array of N receive antennas used at the receiver. At the receiver, a "spatial signature" defined by the N phases and N amplitudes arising at the receive antenna array for a given sub-stream is then estimated. Signal processing techniques are then used to separate the received signals, allowing the original substreams to be recovered and merged into the original input symbol stream. The principles of spatially multiplexed communication system implementations and exemplary system implementations are, for example, in the document "Optimum Combining for Indoor Radio Systems with Multiple Users" by JH Winters, IEEE Transactions on Communications, Vol. COM-35, No. 11, November 1987 which is hereby incorporated herein by reference in its entirety.

B. Conventional MIMO System

Some aspects of the present invention can be more fully explained by first considering a conventional MIMO communication system, which is illustrated by FIG 1 is shown. As shown, the MIMO system includes 100 from 1 a transmitter 110 who in 1A is illustrated, and a receiver 130 who in 1B is illustrated. The transmitter 110 and the receiver 130 each comprise a set of T transmit RF chains and a set of R receive RF chains configured to transmit and receive a set of N spatially multiplexed signals. Within the system 100 it is assumed that either (i) T is greater than N and R is N, (ii) T is N, and R is greater than N, or (iii) both T and R are greater than N.

With reference to 1A For example, an input signal S to be transmitted, which typically has a stream of digital symbols, is output from a demultiplexer 102 in N independent sub-streams S _{1, 2 ..., N} demultiplexed. The sub-streams S _{1, 2, ..., N} are then converted to a digital signal processor (DSP) 105 which produces a set of T output signals T _{1, 2 ..., T.} The T output signals T _{1, 2 ..., T} are typically obtained from the N sub-streams S _{1, 2 ..., N} by weighting (eg by multiplying by a complex number) each of the N sub-streams S _{1, 2. .., N} generated with T different weighting coefficients to form NT substreams. These N * T substreams are then combined to form the T output signals T _{1, 2..., T.} The T outputs T _{1, 2 ..., T} are then sampled using a set of T digital-to-analog (D / A) converters 108 in T analog signals A _{1, 2 ..., T} converted. Each of the T analog signals A _{1, 2 ..., T} is then switched to the usable transmit carrier RF frequency within a mixer 112 up-converted or mixed-up by mixing with a signal received from a local oscillator 114 provided. The resulting set of T RF signals (eg, HF _{1, 2, ..., T} ) is then passed through respective amplifiers 116 amplified and by respective antennas 118 Posted.

Now, reference is made 1B taken. The RF signals coming from the transmitter 110 are sent from a set of R receive antennas 131 received at the receiver 130 to be used. Each of the R signals from an antenna 131 is received by a respective low-noise amplifier 133 reinforced and through a filter 135 directed. The resulting filtered signals are then each using mixers 137 , each with a signal from a local oscillator 138 is down-converted or down-converted by HF to baseband. Although the recipient of 1B As a homodyne receiver, a heterodyne receiver characterized by an intermediate IF frequency could also be used. The respective R baseband signals coming from the mixers 137 are then generated using a corresponding set of R analog-to-digital (A / D) converters 140 converted into digital signals. The resulting R digital signals D _{1, 2 ..., R} are then processed using the digital signal processor 142 weighted and combined to form N spatially multiplexed output signals S ' _{1, 2 ..., N} , having estimated values of the transmitted signals S _{1, 2 ..., N.} The N output signals S ' _{1, 2 ..., N} are then multiplexed 155 multiplexed to an estimate 160 (S ') of the original input signal S to produce.

C. Antenna Selection in RF in Spatially Multiplexed Communication Systems

Now it will open 2 Reference is made in the a block diagram of a MIMO communication system 200 with a transmitter 210 and a receiver 250 which is configured to effect N-times spatial multiplexing using only N transmit / receive RF chains, although more than N transmit / receive antennas each at the transmitter 210 and the receiver 250 be used. In particular, the transmitter includes 210 a lot of MT transmit antennas 240 and the receiver comprises a set of MR receiving antennas 260 In some embodiments, in accordance with some aspects of the present invention, some embodiments may provide that MT and / or MR are greater than or equal to N. For example, (i) MT is greater than N and MR is N, (ii) MT is N and MR is greater than N, or are (iii) both MT and MR greater than N.

As in 2A is shown, an input signal S to be transmitted by the demultiplexer 202 in N independent sub-streams SS _{1, 2 ..., N} demultiplexed. The substreams SS _{1, 2 ..., N} are then using a corresponding set of D / A converters 206 in N analog partial currents AS _{1, 2 ..., N} converted. Next, the N analog sub-streams AS _{1, 2 ..., N are set} to the usable transmit carrier RF frequency using a set of mixers 212 up-converted or up-converted, which are provided with the signal from a local oscillator 214 is produced. The resulting N RF signals (ie, RF _{1, 2, ..., N} ) are then each switched with a selected subset of N transmit antenna elements by a switch 218 connected. The desk 218 connects N RF signals (eg HF _{1, 2 ..., N} ) with a set of N transmit antennas from the available MT transmit antennas 240 , which produces a set of N output signals. A corresponding set of N amplifiers 234 then amplifies these N output signals, the amplified output signals then using the N selected transmit antennas 240 be sent. In another example, the amplifiers may 234 in front of the counter 218 are located. In this configuration, all in all, only N amplifiers are needed instead of a total of MT amplifiers when an amplifier is placed on each of the MT antennas. The selection of the N antennas is generated so as to minimize the BER of the output signal at the receiver.

With reference to 2 B be the N RF signals transmitted by the transmitter 210 have been sent from the set of MR receive antennas 260 received at the receiver 250 be used. Each of the MR received signals is received by a respective low noise amplifier (LNA). 264 amplified and then a subset N of these with a set of N RF chains through a switch 276 connected to form a set of N RF signals passing through a corresponding set of N filters 280 be directed. In another example, the low noise amplifier may be 264 after the switch 276 so that the total number of low-noise amplifiers used is N and not MR, as when a low-noise amplifier is placed on all MR receive antenna elements. The resulting N filtered signals are then used using a set of N mixers 282 each of which is provided with a carrier signal supplied by a local oscillator 284 is generated, baseband down-converted or down-mixed. Although the receiver 250 in the embodiment of 2 B As a homodyne receiver, it could also be implemented as a heterodyne receiver characterized by an intermediate IF frequency. (Indeed, in accordance with some aspects of the present invention, each of the embodiments may include, for example, homodyne configurations or heterodyne configurations). The N baseband signals coming from the mixers 282 are then generated via a corresponding set of NA / D converters 286 converted into digital signals. The N digital signals are then processed using a digital signal processor 288 is further processed to form the N spatially multiplexed output signals SS ' _{1, 2 ..., N} , which are the estimates of the N independent substreams SS _{1, 2 ..., N.} The N output signals SS ' _{1, 2 ..., N} are then by means of a multiplexer 292 multiplexed to produce the output signal S ', which is an estimate of the input signal S.

In some embodiments, in accordance with some aspects of the present invention, a baseband weighting and combining mechanism (e.g., a "precoding" mechanism) may be added to the transmitter for use in conjunction with the antenna selection mechanism discussed below. In this case, a DSP block is placed between the demultiplexer 202 and the D / A converters 206 is placed so that the N independent substreams SS _{1, 2 ..., N} are weighted and combined by complex coefficients to form a set of N output signals. These N outputs are then converted using the appropriate set of D / A converters 206 converted into analog signals AS _{1, 2 ..., N.}

In some embodiments, in accordance with some aspects of the present invention, space-time coding may be added on the transmitter side for use in conjunction with an exemplary antenna selection mechanism. In this case, the demultiplexer 202 is replaced by a DSP block that processes the input signal S over the space and time domain to form a set of N output signals. These N outputs are then converted using the appropriate set of D / A converters 206 converted into analog signals AS _{1, 2 ..., N.} The two most commonly used space-time techniques include 1) inserting a time delay (or equivalent of a phase jump) into one or more of the N output signals, and 2) using the transmit diversity technique described, for example, in the document "A Simple Transmit Diversity Technique for Wireless Communications" by SM Alamouti, IEEE Journal on Selected Areas in Communications, Volume 16, Issue 8, October 1998, pages 1451-1458 , which is incorporated herein by reference in its entirety.

Space-time coding techniques may be applicable, for example, to the SC-MIMO systems and / or systems designed to provide diversity gain. Precoding techniques may, for example, be applied to SC-based MIMO systems or to MIMO systems based on spatial multiplexing or to systems designed to yield both data rate increases and diversity gains.

III. CHANNEL ADAPTIVE ANTENNA SELECTION SYSTEM FOR HF BASED ON A MINIMUM BIT ERROR RATE

A. Overview

For example, some embodiments in accordance with some aspects of the present invention relate to a channel adaptive antenna selection system in a multi-antenna communication system based, for example, on minimizing a bit error rate. In some embodiments, in accordance with some aspects of the present invention, a subset of antenna elements are selected to transmit and / or receive the signals such that the bit error rate is minimized, for example, in a multi-antenna communication system. Some embodiments in accordance with some aspects of the present invention, in a multiple antenna communication system, may provide that a subset of antenna elements be selected to transmit and / or receive the signals such that, for example, over time Presence of a fluctuation in one or more usable communication channels is minimized. Some embodiments in accordance with some aspects of the present invention may be used for antenna selection at the transmitter when multiple antennas are used for transmission. Some embodiments in accordance with some aspects of the present invention may be used for antenna selection at the receiver when multiple antennas are used for reception.

For example, some embodiments in accordance with some aspects of the present invention may be applicable to (1) receivers using multiple antennas in systems referred to herein as single channel systems (eg, a system lacking spatial multiplexing); (ii) transmitters using multiple antennas in single channel systems; and (iii) systems in which a smaller number of RF chains are used at the transmitter and / or receiver than the number of transmit and / or receive antennas in a MIMO spatial multiplexing or single channel system.

Some embodiments in accordance with some aspects of the present invention are described below with reference to FIG 3 to 7 in the following exemplary contexts: 1) a spatial multiplexing MIMO system in which a smaller number of RF chains are used at the transmitter and receiver than the number of transmitter / receiver antennas; 2) a single-channel MIMO system without spatial multiplexing in which a smaller number of RF chains are used at the transmitter and receiver than the number of transmitter / receiver antennas; and 3) a single-channel (SC) single input multiple output (SIMO) system without spatial multiplexing that includes a receiver using multiple antenna elements. Some embodiments in accordance with some aspects of the present invention may also be used in the case of a single-channel (SC) "Multiple Input Single Output (MISO)" / non-spatial (multiple input, output) system Multiplexing can be used in which a transmitter uses multiple antenna elements.

For illustrative purposes, the following exemplary examples are described with reference to systems employing OFDM modulation (e.g. 802.1-1a WLAN standard follows) or with reference to systems based on a direct sequence spread spectrum (DS-SS) (eg, following the WCDMA standard). In certain embodiments, in accordance with some aspects of the present invention, the processing capabilities of the DS-SS receiver may be extended to cover the spatial area by using a space-time RAKE receiver that is operative to "multipath" branches "(Multipath" taps ") to combine, which correspond to both the temporal area and the spatial area, is integrated. This extension illustrates that the techniques described herein can be generalized to virtually any system that uses, for example, a temporal range and / or frequency range when processing in a frequency selective fading environment.

B. antenna selection in an SM-MIMO-OFDM system

3 Illustratively illustrates the transmitter and receiver structure of an SM-MIMO OFDM system 300 which uses antenna selection in accordance with an embodiment in accordance with some aspects of the present invention. As shown, two independent sub-streams 304 (eg, spatially multiplexed signals) are modulated onto _Nt frequency subcarriers according to Orthogonal Frequency Division Multiplexing (OFDM) and OFDM modulated and by two RF chains 308 to prepare them for sending. At this point, a switch block selects 312 two out of four transmitting antenna elements 316 off to those with the two RF chains 308 connect to. Because only two out of four elements 316 within the transmitter 302 are selected, the number of transmit RF chains is advantageously reduced to the number of spatially multiplexed signals.

In the embodiment of 3 contains the switching block 312 Information that the pair of antenna elements 316 identify which one to send at a given time. The block 312 This information (for example, in the case where the channel 318 reciprocal) according to an algorithm based on the minimum BER criterion. In another example, the block 312 the information from the receiver 330 received via a feedback path (not shown). This latter approach can be used in the case where the channel 318 is not reciprocal, for example in an interference limited environment.

In the receiver 330 selects a switch block 334 two out of four antenna elements 338 for receiving incoming signals from the transmitter 302 be sent out. The switching block 334 connects the two selected antennas 338 with two HF chains 342 which are operative to convert the two signals to the digital domain for baseband processing. Then a weight matrix 346 applied to the received signals at each tone to separate and recover each of the transmitted spatially multiplexed signals.

In typical implementations, the switch block becomes 334 be configured to self-calculate which pair of antenna elements 338 is to be selected for reception by executing an algorithm based on the minimum BER criterion. In the case when the channel is not reciprocal, the block may 334 further configured to calculate which pair of antenna elements 316 in the transmitter 302 should be used and that he provides this information. A description of two possible implementations of an antenna selection algorithm, that of the switching blocks 312 . 334 is executable with reference to 4A and 4B provided.

Now, reference is made 4A in which is a flowchart of an antenna selection algorithm 400 in which the coding / modulation mode (eg data rate or throughput) is fixed or adapted on a long-term basis (eg adapted to the large fluctuations of the SNR). The task of the selection algorithm is to select which pair of antenna elements with respect to each packet for the given mode 316 at the transmitter 302 should be used and which pair of antenna elements 338 at the receiver 330 should be used. For example, the selection process may assume that the channel 318 is quasi-stationary (eg, that the channel 318 is constant over the duration of the sent packet and is changed independently between two consecutive packets). Although the channel 318 may show some frequency selectivity, the antenna selection may be common to the entire frequency bandwidth.

Now, reference is made 4A taken. If the transmitter 302 initially starts or is switched on (step 401 ) and the state of the channel 318 is still unknown, becomes a standard subset of two of the antenna elements 316 used to send the wireless signal. The recipient 330 similarly uses a standard subset of two of the receive antenna elements 338 to get a sync. Next, the channel state information (CSI) is acquired (step 402 ). In some embodiments, in accordance with some aspects of the present invention, operations for detecting the CSI at the receiver 330 executed. A training sequence composed of known symbols is sent by the transmitter 302 to the recipient 330 Posted. At the receiver 330 becomes the channel 318 estimated on the basis of the received signal and the known sequence of symbols. This operation is performed as often as the channel 318 changes, for example with every package realization. For the selection mechanism to be successful, the complete channel matrix should be estimated over the entire frequency bandwidth (eg, estimating the channel path gain from all antenna elements 316 the transmitter 302 to all antenna elements 338 the receiver across all tones). Channel estimation techniques based on training sequences that can be applied to MIMO systems are disclosed, for example, in the document of JJ Van de Beek et al., "On Channel Estimation in OFDM Systems", IEEE 45th Vehicular Technology Conference, Volume 2, 25-28. July 1995, pages 815-819 , and in the document of AN Mody and GL Stuber, "Synchronization for MIMO OFDM Systems", IEEE Globecom 2001, Vol. 1, pp. 509-513 , which are hereby incorporated herein by reference in their entirety.

Now reference is made again 4 taken. Mode information is obtained through the execution of a connection adaptation algorithm (step 404 ). In the embodiment, by 4A is illustrated, the change of the mode can take place slowly. This allows a link adaptation algorithm to be used to decide which of the possible mode candidates is best suited for use in terms of the average long-term SNR. The use of a link adaptation algorithm can ensure that, when given a mode selection criterion (eg, a maximum data rate and a minimum transmit power), the most efficient mode is always used with respect to varying long-term channel / SNR conditions. An example connection adaptation algorithm that may be used in MIMO frequency selective systems is, for example, in the document "Adaptive Modulation and MIMO Coding for Broadband Wireless Data Networks" by S. Catreux et al., IEEE Communications Magazine, Vol. 40, No. 6, June 2002, pages 108- 115 which is hereby incorporated herein by reference in its entirety. The mode selection may be generally independent of the mechanism for selecting transmitter / receiver antenna elements. The mode can be selected based on long-term SNR statistics only. Accordingly, it changes at a much slower speed than the speed at which the antennas are selected. In other words, the selection algorithm may select a new subset of antennas with respect to each packet realization, while the mode changes as a function of long term SNR variations.

The steps 406 . 408 and 410 are repeatedly executed in a loop until all possible combinations of subsets of transmit / receive antenna elements have been evaluated (step 411 ). For example, consider a MIMO-OFDM system of the kind that is described in US Pat 3 is shown (and that, for example, with 4 transmitting antenna elements 316 and 4 receiving antenna elements 338 equipped), the complete channel matrix in the frequency domain at the tone k may be represented by a 4 × 4 matrix, designated H _k . After selecting a subset of two antennas on each side, the subchannel matrix is reduced in size to a 2x2 matrix, which can be used with H ~ _k referred to as. There is (4/2) = 6 Options for selecting 2 elements from a total of 4 elements. Because the antenna selection both at the transmitter 302 as well as the transmitter 330 is applied, is the total number of combinations for H ~ _k is 36. In the general case of an MxM MIMO system that is reduced in size to an nxn MIMO system (where M> n), there is (M / n) = M! / n! (M - n)! Possibilities for selecting n antenna elements from M possible elements. If the selection takes place both at a transmitter and at a receiver, the total number of combinations for H ~ _k equal (M! / N! (M - n)!) ² . This corresponds to the number of iterations of the loop resulting from the steps 406 . 408 and 410 consists. These iterations may be performed sequentially (eg, reuse, shared processing resources) or in parallel (eg, at the expense of additional processing resources). In an exemplary example, all possible antenna combinations could be processed simultaneously, which may mean using a separate processing resource for each possible antenna combination.

• 
  berechnen, wobei
  
  ist, σ² und σ 2 / s jeweils für die Rausch- und Signalleistung stehen und k = 1, ..., N_t ist (Schritt 408-1).
• C_k = 1/diag(B –1 / k) berechnen. Dies ist ein N×1-Vektor für jeden k = 1, ..., N_t (Schritt 408-2).
• 
  berechnen. Dies ist ein N×1-Vektor für jeden k = 1, ..., N_t (Schritt 408-3).

Each iteration in the loop, resulting from the steps 406 . 408 and 410 the processing results from a single antenna subsystem. First, the 2 × 2 matrix H ~ _k across all tones (k = 1, ..., N _t ) for the subsystem of interest (step 406 ). The signal-to-interference-plus-to-noise ratio (SINR) after processing is then calculated at each tone k and for each transmitted spatially multiplexed signal (step 408 ). The SINR can most often be found by a closed solution depending on which signal processing method at the transmitter 302 and / or the recipient 330 (eg Maximum Ratio Combining (MRC), Minimum Mean Square Error (MMSE), Eigen Beamforming, and Maximum) -Likelihood - / (ML) -method (maximum probability method)). For example, if there is no spatial processing on the sender 302 is implemented and at the receiver 330 MMSE is applied, the SINR can be determined as follows:

• 
  calculate, where
  
  is, σ ² and σ 2 / s are each for the noise and signal power and k = 1, ..., N _t (step 408-1 ).
• C _k = 1 / diag (B -1 / k) to calculate. This is an N × 1 vector for each k = 1, ..., N _t (step 408-2 ).
• 
  to calculate. This is an N × 1 vector for each k = 1, ..., N _t (step 408-3 ).

In step 410 the SINR information is converted into BER information with respect to the current mode (see eg step 404 ). Since the BER is a complicated function of the channel 318 and the coding / modulation techniques and antenna combining techniques used, an approximation of the BER can be used. The approximation may also be a function of the channel 318 and the applicable coding / modulation techniques and antenna combining techniques. The BER through the packet (eg, at the output of the Viterbi decoder, if encoding is used) for a transmitted sub-stream i may be considered a nonlinear, unknown function f of the set of SINR _k , where k = 1, .. ., N _t , for example, are expressed as follows: BER _t = f ({SINR i / k), i = 1, ..., N; k = 1, ..., N _t

wobei BER i / k die Bitfehlerrate hinsichtlich eines gegebenen SINR beim Ton k für den räumlich gemultiplexten Teilstrom i ist. In einem anderen Beispiel kann BER_k auch die Bitfehlerrate hinsichtlich eines gegebenen Signal-Rausch-Verhältnisses beim Ton k sein. Der Mittelwert kann auch in dem Zeitbereich genommen werden, in dem BER_k die Bitfehlerrate hinsichtlich des gegebenen SINR bei dem Kanalzeitabtastwert k ist. BER_k kann die Bitfehlerrate im Hinblick auf eine gegebene Signalkomponente sein (z. B. ein Signalton oder eine Abzweigungsverzögerung (tap delay)).Next, the function f is approximated by a known function. In particular, the output BER is approximated by the average bit error rate over the channel, for example, as follows:

in which BER i / k is the bit error rate with respect to a given SINR in the sound k for the spatially multiplexed substream i. In another example, BER _{k may} also be the bit error rate with respect to a given signal-to-noise ratio in the sound k. The mean value can also be taken in the time range in which BER _{k is} the bit error rate with respect to the given SINR at the channel time sample k. BER _k may be the bit error rate with respect to a given signal component (eg, a beep or a tap delay).

Furthermore, BER _{k is} also approximated by a simple closed function. Through simulations, it has been found that for mode 1 of 802.1-1a (eg BPSK, R1 / 2) the behavior of the average bit error rate BER with respect to the SINR or SNR (in some instances the BER normalization factor may be 1 / N _t , since it does not affect the antenna selection), for example, can be modeled by:

The BER at the signal component k has been approximated by -tanh (SINR _k ).

• 1) Die BER einer uncodierten BPSK-Modulation in einem AWGN-Kanal (engl.: AWGN = Additive White Gaussian Noise; auf Deutsch: AWGR = additives weißes gaußsches Rauschen) ist (siehe z. B. J. G. Proakis, Digital Communications (Digitale Kommunikationen), 3. Auflage, McGraw-Hill Series, 1995 )
  
  Die Form der Funktion erfc wird durch die Funktion vernünftig approximiert (im Vergleich zu y = –tanh(x))
  
• 2) Die BER einer uncodierten QPSK-Modulation in einem AWGN-Kanal ist (siehe z. B. J. G. Proakis, Digital Communications, 3. Auflage, McGraw-Hill Series, 1995 )
  
  Die Form von erfc(√x/2) wird durch die Funktion:
  
  besser approximiert als durch y = –tanh(x).
• 3) Die BER einer uncodierten 16QAM-Modulation in einem AWGN-Kanal kann von der Symbolfehlerrate (SER; Symbol Error Rate), die zum Beispiel in J. G. Proakis, Digital Communications, 3. Auflage, McGraw-Hill Series, 1995 , gegeben ist, abgeleitet werden als
  
  Eine geeignete Anpassungsfunktion ist y = –(1 – e^–0,2x).
• 4) Die BER einer uncodierten 64QAM-Modulation in einem AWGN-Kanal kann von der Symbolfehlerrate (SER), die zum Beispiel in J. G. Proakis, Digital Communications, 3. Auflage, McGraw-Hill Series, 1995 , gegeben ist, abgeleitet werden als
  
  Eine geeignete Anpassungsfunktion ist
  

The tanh function may not always adequately approximate the BER, especially for different modulation techniques. Some of the following functions can generally provide better approximations when using certain techniques:

• 1) The BER of an uncoded BPSK modulation in an AWGN (AWGN = Additive White Gaussian Noise) channel (AWGR = additive white Gaussian noise) is (see eg. JG Proakis, Digital Communications, 3rd Edition, McGraw-Hill Series, 1995 )
  
  The form of the function erfc is reasonably approximated by the function (compared to y = -tanh (x))
  
• 2) The BER of an uncoded QPSK modulation in an AWGN channel is (see eg. JG Proakis, Digital Communications, 3rd Edition, McGraw-Hill Series, 1995 )
  
  The shape of erfc (√ x / 2 ) is by the function:
  
  better approximated than by y = -tanh (x).
• 3) The BER of an uncoded 16QAM modulation in an AWGN channel may be of the symbol error rate (SER), for example, in JG Proakis, Digital Communications, 3rd Edition, McGraw-Hill Series, 1995 , is given as derived
  
  An appropriate fit function is y = - (1-e ^-0.2x ).
• 4) The BER of an uncoded 64QAM modulation in an AWGN channel may be of the symbol error rate (SER), for example, in JG Proakis, Digital Communications, 3rd Edition, McGraw-Hill Series, 1995 , is given as derived
  
  A suitable adaptation function is
  

It should be understood that any fitting function that reasonably models the behavior of the BER over the SINR can be used in equation (2). The number of suitable fitting functions is not limited to the few examples given above.

As mentioned above, the steps become 406 to 410 performed iteratively until all possible combinations of subsets of antennas have been considered (step 411 ). At the conclusion of this iterative process, a set of N estimates of BER values (one for each spatially multiplexed signal) for all M! / n! (M - n)! (or (M! / N! (M - n)!) ² ) possible antenna combinations obtained. Then, all that remains is to select the subset of antennas that will minimize the mean over the set of BERs, the maximum over the set of BERs, or the minimum of the set of BERs (step 412 ).

4B is a flowchart of an antenna selection algorithm 500 in that the coding / modulation mode is repeated as many times as once per packet realization in response to corresponding changes in the channel 318 can be changed. In this example, the Encoding / Modulation mode is adapted to the same speed at which antenna selection is effected.

With reference to 4B are the steps 501 and 502 each similar to the steps 401 and 402 , As shown, the steps include 504 to 510 a loop that is iteratively executed until all possible combinations of subsets of antennas have been evaluated. It follows that the number of iterations of this loop is equivalent to M! / n! (M - n)! (eg selection at one end of the connection) or (M! / N! (M - n)!) ² (eg, selection at both ends of the connection). In this regard, the steps are 504 and 506 each of the steps 406 and 408 similar. Based on the knowledge of the instant SINR for all tones, a link adaptation block determines the most efficient mode for each spatially multiplexed signal when a mode selection criterion (e.g., a maximum data rate and a minimum transmit power) is specified (step 508 ). This step is similar to the step 404 with the exception that the mode decision is made on the basis of instantaneous SNR (or SINR) statistics and not on the long term SNR (or SINR) statistics. As a result, different combinations of subsets of antennas can produce different mode decisions. Finally, the step calculates or determines 510 with respect to the given instantaneous SINR and mode information, the corresponding BER in the same manner as described above with reference to the step 410 has been described.

Again, the steps become 504 to 510 until all possible combinations of subsets of antennas have been considered (step 511 ). When this is done, a set of N estimates of BER values (eg one for each spatially multiplexed signal) for all M! / n! (M - n)! (or (M! / N! (M - n)!) ² ) possible antenna combinations obtained. The selection algorithm 500 is different from the algorithm 400 in that the M! / n! (M - n)! (or (M! / N! (M - n)!) ² ) possible antenna combinations do not necessarily use the same coding / modulation mode. The decision as to which antenna subset to select depends not only on minimizing the BER, but also on the mode (eg, data rate or throughput). Several exemplary options will be made in view of the final decision to select a subset of antenna elements according to step 512 of the selection algorithm 500 provided:

Option 1

• 1) Group all combinations of subsets of antennas that use the same mode into a common pool.
• 2) Select the pool according to the highest mode (resulting in a maximum data rate).
• 3) Select the combination of subsets of antennas within this pool that minimizes the BER in a manner substantially similar to that described with reference to step 412 has been described.

Option 2

Selecting the combination of antenna subsets that minimizes the BER in a manner substantially similar to that described with reference to the step 412 without regard to the mode used by each combination.

Option 3

• 1) Alle Kombinationen von Untermengen von Antennen, die den gleichen Modus verwenden, in einen gemeinsamen Pool gruppieren.
• 2) Die X Pools auswählen, die den X höchsten Modi entsprechen (wodurch sich eine maximale Datenrate ergibt), wobei X eine ganze Zahl gleich 1 oder 2 oder 3, etc. ist.
• 3) Auswählen der Kombination von Untermengen von Antennen innerhalb dieser Pools, die die BER in einer Art und Weise minimiert, die im Wesentlichen ähnlich zu der unter Bezugnahme auf Schritt 412 beschriebenen Art und Weise ist.

Implement a hybrid version of option 1 and option 2, for example:

• 1) Group all combinations of subsets of antennas that use the same mode into a common pool.
• 2) Select the X pools that correspond to the X highest modes (giving a maximum data rate), where X is an integer equal to 1 or 2 or 3, and so on.
• 3) Selecting the combination of subsets of antennas within these pools which minimizes the BER in a manner substantially similar to that described with reference to step 412 way described is.

5 Illustratively illustrates the packet error rate (PER) as a function of SNR resulting from the use of an exemplary antenna selection technique within an SM-MIMO OFDM system that is operational in a noise limited environment. The results of 5 For example, they may be applicable to a system having four transmit and receive antennas in the and Way used as through 3 is shown by way of example. The results reflect, as merely exemplary examples, a packet size of 1000 bytes and a fixed encoding / modulation mode. The results also reflect that two exemplary RF chains are integrated into both the useable transmitter and the useable receiver. Also, use the results of 5 a BPSK modulation, a coding rate of 1/2 (e.g., a mode 1 of 802.11a), a channel model characterized as "channel A" (e.g., 50 ns rms delay spread, 0 , 5 antenna correlation) and an adaptation function of tanh.

The caption for the curves in 5 is as follows:
2 × 2 2SM-MIMO MMSE: This system corresponds to an SM-MIMO-OFDM system that uses 2 transmit antennas and 2 receive antennas along with 2 spatially-multiplexed (SM) signals. Since the number of antennas is equal to the number of SM signals, no antenna selection is applied. A baseband combining mechanism is used at the receiver to separate the two sub-streams, e.g. MMSE.

4 × 4 2 SM-MIMO sel mcap MMSE: This system corresponds to an SM-MIMO OFDM system that uses 4 transmit and 4 receive antenna elements along with 2 spatially multiplexed (SM) signals. A conventional selection mechanism is applied to both the transmitter and the receiver to select a subset of 2 antenna elements from the four antenna elements according to a maximum capacity criterion. After selection at the receiver, MMSE is applied to the baseband to separate the two sub-streams.

2 × 4 2 SM MIMO via MMSE (bound): This system corresponds to an SM-MIMO OFDM system using 2 transmit and 4 receive antenna elements along with 2 spatially multiplexed (SM) signals. A selection mechanism is applied only at the receiver end to select a subset of 2 antenna elements from the four antenna elements according to the minimum BER criterion. In this case, no fitting function is used to approximate the BER. Instead, it is assumed that the BER is perfectly known. This case may not be readily implemented, but rather provides a bound on performance that can be achieved through the use of some embodiments in accordance with some aspects of the present invention.

4 × 4 2 SM MIMO via MMSE (bound): This system corresponds to an SM-MIMO OFDM system using 4 transmit and 4 receive antenna elements along with 2 spatially multiplexed (SM) signals. A selection mechanism is applied to both the transmitting side and the receiving side to select a subset of 2 antenna elements from four antenna elements according to the minimum BER criterion. In this case, no fitting function is used to approximate the BER. Instead, it is assumed that the BER is perfectly known. This case may not be readily implemented, but rather provides a bound on performance that can be achieved through the use of some embodiments in accordance with some aspects of the present invention.

4 × 4 2SM MIMO via MMSE (implementation tanh): This system corresponds to an SM-MIMO OFDM system using 4 transmit and 4 receive antenna elements along with 2 spatially multiplexed (SM) signals. A selection mechanism in accordance with some embodiments in accordance with the present invention is applied to both the transmitting side and the receiving side to select a subset of 2 antenna elements from four antenna elements according to a minimum BER criterion. The fitting function for approximating the BER is tanh.

The results illustrative by 5 show that all systems using any type of antenna selection provide gains as compared to systems without selection, and that the antenna selection based on the minimum BER provides a considerably greater improvement than the selection based on the criterion provides the maximum capacity. In particular, at a PER level of 10e-2 and with an antenna selection in accordance with the present invention applied to both the transmitter and the receiver, a gain of 7.6 dB is achieved compared to a system with no selection and a gain of 4.2 dB is demonstrated compared to a system in which the selection is based on the maximum capacity. When the selection according to some embodiments in accordance with some aspects of the present invention is applied only to the receiver, it can be seen that the resulting performance between that achieved when no selection is used and that which occurs when a selection is used at both the sender and the receiver. Finally, the performance of the system in accordance with some embodiments in accordance with some aspects of the present invention comes very close to a theoretical performance limit imposed by 5 is illustrated.

C. Antenna selection in a SC-MIMO-OFDM system

6 illustrates an SC-MIMO-OFDM system 600 , which uses precoding techniques in addition to an exemplary antenna selection mechanism in accordance with some embodiments of the present invention. In the embodiment of 6 precoding refers to different baseband weighting and combining mechanisms used at a transmitter 602 be performed. With reference to 6 becomes a single stream of symbols 604 through a set of complex coefficients 608 weighted and combined to produce a set of N output signals, where N is the number of RF chains 612 refers to that in the transmitter 602 be used. These N output signals are then passed through the N RF chains 612 conducted to produce N RF signals. These N RF signals are then coupled to a corresponding set of N of M transmit antenna elements 616 via a switch 620 coupled and through a channel 624 Posted.

At a receiver 622 becomes a set of N of M receive antenna elements 626 via a switch 630 selected to receive incoming signals through a channel 624 be communicated. The N RF receive signals are then passed through N RF chains 634 processed and converted to the digital domain for baseband processing to recover the originally transmitted signal.

For example, some embodiments in accordance with some aspects of the present invention may provide baseband weights 608 and the antenna selection mechanism is designed to collectively contribute to the minimization of the BER. For example, some embodiments in accordance with some aspects of the present invention may provide baseband weights 608 can be chosen to maximize the output SNR (or -SINR) or capacitance while antenna selection is performed to minimize the BER. The right and left singular vectors of the subchannel matrix H ~ _k , which correspond to the largest singular value can be used to provide optimal subsets of transmit antenna elements 616 and receiving antenna elements 626 as well as the appropriate transmit baseband weights 608 and receive baseband weights 640 select. The determination of baseband weighting values in the context of MIMO systems that do not have antenna selection is, for example, in the document of JB Andersen, IEEE Antennas and Propagation Magazine, Vol. 42, No. 2, April 2000, pages 12-16 which is hereby incorporated herein by reference in its entirety.

The exemplary embodiment shown in FIG 6 can be illustrated by replacing the baseband weights 608 within the transmitter 602 be modified by a space-time coding block. In this case, an antenna selection mechanism may be used to select the subset of antennas in both the transmitter and the receiver according to some embodiments of the present invention. In addition, the space-time coding block processes the input stream of symbols, as for example in the document "A Simple Transmit Diversity Technique for Wireless Communications" by SM Alamouti, IEEE Journal on Selected Areas in Communications, Volume 16, Issue 8, October 1998, pages 1451-1458 which is hereby incorporated herein by reference in its entirety.

D. Antenna Selection in a DS-SS SIMO System

7 Represents a receiver 700 of a DS-SS SIMO system, the two receiving antenna elements 704 has (n _R = 2). The recipient 700 Integrates RAKE receiver functionality with an exemplary antenna selection process. As shown, the receiver is 700 with only a single RF chain 708 equipped so as to communicate with only one of the two receiving antenna elements 704 at a certain time via a switch 712 is connected. The choice of which of the two elements 704 with the HF chain 708 is to be connected is made on the basis of the criterion of minimum BER. Some embodiments in accordance with some aspects of the present invention may provide that the BER of the received signal corresponding to each receive antenna element 704 corresponds, is calculated, and the element 704 that yields the minimum value of BER, is selected. Since the BER may typically comprise a complicated function of the usable channel and coding / modulation and antenna combining techniques used, the BER is approximated for a given channel and antenna combining technique so that it varies as a function of the coding / modulation mechanism used.

If then the optimal element of the antenna elements 704 has been selected, the RAKE receiver behaves in the same way as if it were implemented in a SISO (Single-Input Single-Output) / (An Input, Output) system (e.g. Antenna at each end of the connection). The RAKE receiver uses a variety of J correlators 720 (eg J = 2 in 7 ), each of which corresponds to one of the first J separable multipath components. Each multipath component is associated with a time delay τ _j , where j = 1, ..., J. The output of each correlator 720 (eg a finger) is then weighted 730 and combined 740 to a single output received signal 750 forming an estimate of the transmitted signal.

wobei L_i die Anzahl an Abzweigungen (taps) in dem Kanal ist, der an dem i-ten Antennenelement 704 empfangen wird, h_i,l der komplexe Kanalgewinn an der Antenne i und der Abzweigung l ist, P die Signalsendeleistung ist, d die Datensequenz ist, die aus Symbolen des Zeitraums T besteht, und p die Spreizsequenz ist, die sich aus Chips des Zeitraums T_c = T/G zusammensetzt, wobei G der Spreizfaktor ist. Außerdem ist τ_i,l die Wegeverzögerung, die mit der Abzweigung l und der Antenne i assoziiert ist, entspricht w₀ der Trägerfrequenz w₀ = 2πf₀, und ist θ_i,t der Phasensprung, der der Abzweigung l und der Antenne i entspricht. Das Rauschen n_i, das an dem i-ten Antennenelement 704 gemessen wird, wird als ein AWGN-Prozess mit zweiseitiger spektraler Dichte N₀/2 modelliert. Aus Gründen der Einfachheit und der Klarheit des Ausdrucks nimmt die Gleichung (3) eine Einzelbenutzerumgebung an. Aber die vorliegende Erfindung muss nicht darauf beschränkt sein und zieht es auch in Betracht, dass sie in der Gegenwart von mehreren Benutzern angewendet werden kann.In an exemplary embodiment, the received signal corresponding to the ith antenna element 704 at the entrance of the RAKE receiver, expressed as:

where L _{i is} the number of taps in the channel that is at the ith antenna element 704 h _{i, l is} the complex channel gain at the antenna i and the branch l, P is the signal transmission power, d is the data sequence consisting of symbols of the period T, and p is the spreading sequence consisting of chips of the period T _c = T / G, where G is the spreading factor. In addition, τ _{i, l is} the path delay associated with the branch l and the antenna i, w ₀ corresponds to the carrier frequency w ₀ = 2πf ₀ , and θ _{i, t is} the phase jump corresponding to the branch l and the antenna i , The noise n _i , that at the ith antenna element 704 is measured is modeled as an AWGN process with two-sided spectral density _N0 / 2. For the sake of simplicity and clarity of expression, equation (3) assumes a single-user environment. However, the present invention need not be limited thereto, and also contemplates that it can be applied in the presence of multiple users.

wobei d₀ das gewünschte, zu demodulierende Symbol ist und n_i,j die AWGN-Rauschkomponente mit einem Mittelwert Null und mit einer zweiseitigen spektralen Dichte N₀/2 ist. Wieder wurde aus Gründen der Einfachheit und der Klarheit der Darstellung in Gleichung (4) angenommen, dass es keine Inter-Pfad-Interferenz (IPI) gibt. Aber die vorliegende Erfindung zieht es auch in Betracht, beim Vorhandensein einer IPI benutzt zu werden.At the output of the correlator 720 of the jth finger, the received signal can be represented as:

where d ₀ is the desired symbol to be demodulated and _{i, j} n is the AWGN noise component with a mean zero and with a two-sided spectral density _N0 / 2. Again, for the sake of simplicity and clarity of presentation in Equation (4), it has been assumed that there is no inter-path interference (IPI). But the present invention also contemplates being used in the presence of an IPI.

wobei J die Anzahl an RAKE-Fingern ist, und wobei die optimalen Kombinierungsgewichtungen allgemein so ausgewählt werden, dass sie zu dem Kanal passen, zum Beispiel: w_i,j = h * / i,j (6.) After diversity combining, the final output of the RAKE receiver is the i-th antenna element 704 corresponds, following:

where J is the number of RAKE fingers, and where the optimal combining weights are generally selected to match the channel, for example: w _{i, j} = h * / i, j (6.)

wobei γ_i,j das SNR nach der Kombinierung in dem j-ten Pfad bzw. Weg ist, der mit dem i-ten Antennenelement 704 assoziiert ist. Auf der Grundlage von (4) kann γ_i,j ausgedrückt werden durch:

wobei

die Rauschleistung ist.In this case, the RAKE performs maximum ratio combining and the SNR at the RAKE output that is the i th antenna element 704 is given by

where γ _{i, j is} the SNR after combining in the jth path that is associated with the ith antenna element 704 is associated. On the basis of (4), γ _{i, j} can be expressed by:

in which

the noise power is.

dargestellt ist, über die WDF von γ_i integriert wird, zum Beispiel:

The BER at the output of the RAKE receiver, the i-th antenna element 704 can be obtained by knowing the probability density function (WDF) of γ _i . For example, if no coding is used and BPSK modulation is applied to the data sequence according to the methodology described, for example, in US Pat "Digital Communications" by JG Proakis, 3rd Edition, McGraw-Hill Series, 1995 BER is found out by the error probability determined by

is integrated over the WDF of γ _i , for example:

wobei n_R die Gesamtanzahl an Empfängerantennenelementen darstellt.If the BER is then estimated for all receive antennas, the antenna element becomes 704 that produces the minimum BER selected:

where n _{R represents} the total number of receiver antenna elements.

As will be readily appreciated, since coding is added to the system (eg, turbo coding, convolutional coding) and other modulation levels are used, the modeling function used in (9) for estimating the BER will change have to. Some embodiments in accordance with some aspects of the present invention may provide that any fitting function that accurately models the BER behavior for a given system may be used by an exemplary antenna selection algorithm. The adaptation function will generally depend on parameters which include, for example, one or more of the following: the channel, the encoding and modulation used, the signal processing at the transmitter and / or receiver side, the receiver SNR and other parameters.

The exemplary embodiment shown in FIG 7 can be extended to a two-dimensional RAKE receiver in which the processing is performed in both the space area and the time area. In this context, an exemplary antenna selection algorithm may be integrated to select a subset of N antennas (N> 1) from a total of M antennas (M> N) that minimizes the BER at the output of the 2D RAKE.

Although the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from the scope thereof. Therefore, the present invention should not be limited to the particular embodiments disclosed, but the present invention will include all embodiments falling within the scope of the appended claims.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 20020102950 [0007]

Cited non-patent literature

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• "Molecular capacity of MIMO systems with antenna selection" by A. Molisch et al., Proceedings of IEEE ICC, Helsinki, Finland, June 2001, Vol. 2, pp. 5701-574 [0007]
• "Optimum MIMO with antenna selection" by RS Blum et al., IEEE Communications Letters, Vol. 6, Issue 8, August 2002, pages 322-324 [0007]
• "Optimum Combination for Indoor Radio Systems with Multiple Users" by JH Winters, IEEE Transactions on Communications, Vol. COM-35, No. 11, November 1987 [0044]
• "A Simple Transmit Diversity Technique for Wireless Communications" by SM Alamouti, IEEE Journal of Selected Areas in Communications, Volume 16, Issue 8, October 1998, pages 1451-1458 [0052]
• 802.1-1a WLAN standard [0057]
• JJ Van de Beek et al., "On Channel Estimation in OFDM Systems", IEEE 45th Vehicular Technology Conference, Volume 2, 25-28. July 1995, pages 815-819 [0063]
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• JG Proakis, Digital Communications, 3rd Edition, McGraw-Hill Series, 1995 [0071]
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• JG Proakis, Digital Communications, 3rd Edition, McGraw-Hill Series, 1995 [0071]
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• JB Andersen, IEEE Antennas and Propagation Magazine, Vol. 42, No. 2, April 2000, pages 12-16 [0088]
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• "Digital Communications" by JG Proakis, 3rd Edition, McGraw-Hill Series, 1995 [0096]

Claims (31)

A communication system for selecting N antenna elements in an M antenna element transmitter or an M antenna element receiver, where N is less than M, comprising: M antenna elements in the M antenna element transmitter or the M antenna element receiver; N HF chains; and a switch coupled to the N RF chains. The communication system of claim 1, wherein the M antenna element receiver is configured to calculate an output bit error rate for each possible N antenna element subset of the M antenna elements, each output bit error rate being calculated based on at least one set of channel parameter statistics, and wherein the M antenna element receiver is arranged to select the particular N antenna element subset based on a criterion based on the calculated output bit error rates. The communication system of claim 2, wherein the switch is configured to couple the N RF chains to the N antenna elements of the particular N antenna element subset in response to the selection of the particular N antenna element subset based on the criterion. A system for selecting a subset of receive antennas of a receiver for receiving a transmitted RF signal, comprising: Means for forming possible subsets of the receive antennas; Means for determining sets of channel parameter statistics corresponding to the possible subsets of the receive antennas; Means for calculating output bit error rates of the receiver, wherein each output bit error rate is calculated based on at least one set of channel parameter statistics; Means for selecting a particular possible subset of the receive antennas based on a criterion based on the calculated output bit error rates; and Means for connecting one or more RF chains of the receiver to the receive antennas of the selected special subset. The system of claim 4, further comprising: Means for selecting transmission modes, each transmission mode being selected based on at least one set of channel parameter statistics; and Means for basing the criterion on at least the selected transmission modes. The system of claim 4 or 5, wherein each set of channel parameter statistics has at least one of an output signal-to-noise ratio, an output signal-to-interference-plus-noise ratio, a log-likelihood ratio, and a Euclidean distance in a signal constellation of the recipient. The system of any one of claims 4 to 6, wherein each set of channel parameter statistics comprises at least one of a first-order statistic, a second-order statistic, and a higher-order statistic. The system of any one of claims 4 to 7, wherein each set of channel parameter statistics is calculated over a range of frequencies. The system of any one of claims 4 to 8, wherein each set of channel parameter statistics is calculated over a time range. The system of any of claims 5 to 9, wherein each selected transmit mode has a modulation level and a coding rate. The system of any one of claims 4 to 10, wherein the criterion is based on minimizing the output bit error rates. The system of any one of claims 4 to 11, wherein the criterion is based on at least one of maximizing a data rate in a first stage of the receiver and minimizing the output bit error rates in a second stage of the receiver. The system of any one of claims 4 to 12, wherein at least one of the output bit error rates is approximated by a closed expression. The system of claim 13, wherein each output bit error rate is approximated by a closed expression. The system of claim 13, wherein the closed expression is at least one of

includes. The system of claim 13, wherein the closed expression depends on at least one of encoding and modulation of the transmitted RF signal. The system of claim 13, wherein the closed expression is a function of an output signal-to-noise ratio or an output signal-to-interference-plus-noise ratio of the receiver. System according to one of claims 4 to 17, wherein the number of receiving antennas is greater than the number of RF chains, and wherein the number of receive antennas in each possible subset is equal to the number of RF chains. A system for selecting a subset of transmit antennas of a transmitter for transmitting an RF input signal as a plurality of RF output signals subsequently received by a receiver, the system comprising: Means for forming possible subsets of the transmit antennas; Means for determining sets of channel parameter statistics corresponding to the possible subsets of the transmit antennas; Means for selecting transmission modes corresponding respectively to the sets of channel parameter statistics; Means for calculating the output bit error rates of the receiver, each output bit error rate being calculated based on at least one set of channel parameter statistics and at least one selected transmit mode; Means for selecting a particular possible subset of the transmit antennas based on a criterion based on at least the calculated output bit error rates; and Means for connecting one or more RF links of the transmitter to the transmit antennas of the selected special subset. The system of claim 19, wherein each set of channel parameter statistics includes at least one of an output signal-to-noise ratio, an output signal-to-interference-plus-noise ratio, a log-likelihood ratio, and a Euclidean distance in a signal constellation of the receiver includes. The system of claim 19 or 20, wherein each set of channel parameter statistics comprises at least one of a first-order statistic, a second-order statistic, and a higher-order statistic. The system of any one of claims 19 to 21, wherein each set of channel parameter statistics is calculated over a range of frequencies. The system of any one of claims 19 to 22, wherein each set of channel parameter statistics is calculated over a time range. The system of any of claims 19 to 23, wherein each selected transmit mode has a modulation level and a coding rate. The system of any of claims 19 to 24, wherein the criterion minimizes the receiver's output bit error rates. The system of any one of claims 19 to 25, wherein the criterion is based on the calculated output bit error rates and the selected transmit modes. The system of any one of claims 19 to 26, wherein the criterion is based on at least one of maximizing a data rate in a first stage of the receiver and minimizing the output bit error rates in a second stage of the receiver. The system of any one of claims 19 to 27, wherein each output bit error rate is approximated by a closed expression. The system of claim 28, wherein the closed expression is at least one of

includes. The system of claim 28, wherein the closed expression of at least one of a coding and a modulation of the RF output signals is dependent. The system of claim 28, wherein the closed expression is a function of at least one of an output signal-to-noise ratio or an output signal-to-interference-plus-noise ratio of the receiver.

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